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  • A non-stationary random field model for earthquake slip
    J. Seismol. (IF 1.494) Pub Date : 2020-01-17
    J. Dhanya, S. T. G. Raghukanth

    The present work aims at building a non-stationary random field model for the slip distribution on the rupture plane. The estimates are arrived based on 230 slip fields available in the SRCMOD database. The evaluation is performed by segregating and quantifying the trend and fluctuation components of the field. Here, the trend portion of the slip is extracted by fitting a 2D elliptical Gaussian surface. The remaining fluctuation part is observed to be stationary following a normal distribution. Further, we propose scaling relations as a function of magnitude for all the unknowns in trend and fluctuation part of the field. Furthermore, an additive model to generate a slip field for a given magnitude combining the deterministic trend part and randomly generated fluctuation part is also developed in the study. Ground motion simulations performed with the components of the slip field showed that the trend portion controls the low frequency, and the fluctuation portion influences the high-frequency characteristics of ground motion. The model developed from the study can be used to generate an ensemble of slip fields for ground motion simulations.

    更新日期:2020-01-17
  • Monumental articulated ancient Greek and Roman columns and temples and earthquakes: archaeological, historical, and engineering approaches
    J. Seismol. (IF 1.494) Pub Date : 2020-01-13
    Stathis C. Stiros

    Structural analyses indicate that monumental articulated ancient Greek and Roman (MAGR) columns and temples have a very particular seismic response, differing from rigid structures (made with mortar); tall columns in particular, have an excellent seismic performance, favoring anthropogenic effects as causes of their destruction. Archeoseismological studies, on the other hand, provide evidence of seismic damage in MAGR structures. To investigate this apparent conflict, we analyzed the conditions and limitations of structural models, as well as historical and archeological evidence of response of such structures to natural and anthropogenic effects. In addition, we examined two groups of MAGR structures: first, structures damaged or destroyed by known causes, including earthquakes and wind; second, structures damaged by unknown causes, based on comparative damage analyses with emphasis on geotechnical (soil dynamics) effects. This analysis indicates that reports of deliberate destructions of MAGR structures are exaggerated, and in addition, (i) these structures seem safe against earthquakes only if structurally healthy, concerning both their superstructure and foundations; this condition is not always satisfied, and hence, no controversy exists between structural engineering and archeoseismological approaches; (ii) their seismic response is sensitive to small changes of the source- and site-specific parameters; and (iii) no deterministic evidence of absence or of occurrence of critical earthquakes can be derived from their survival or damage, because the latter reflects superimposition of natural and anthropogenic destructive effects, some with apparently similar outcomes, and rarely only single event destructions. These results are important for palaeoseismology (paleoseismology), seismic risk assessment, archaeology (archeology), and restoration of ancient monuments.

    更新日期:2020-01-13
  • A database of damaging small-to-medium magnitude earthquakes
    J. Seismol. (IF 1.494) Pub Date : 2020-01-09
    Cecilia I. Nievas, Julian J. Bommer, Helen Crowley, Jan van Elk, Michail Ntinalexis, Marialuigia Sangirardi

    Interest in small-to-medium magnitude earthquakes and their potential consequences has increased significantly in recent years, mostly due to the occurrence of some unusually damaging small events, the development of seismic risk assessment methodologies for existing building stock, and the recognition of the potential risk of induced seismicity. As part of a clear ongoing effort of the earthquake engineering community to develop knowledge on the risk posed by smaller events, a global database of earthquakes with moment magnitudes in the range from 4.0 to 5.5 for which damage and/or casualties have been reported has been compiled and is made publicly available. The two main purposes were to facilitate studies on the potential for earthquakes in this magnitude range to cause material damage and to carry out a statistical study to characterise the frequency with which earthquakes of this size cause damage and/or casualties (published separately). The present paper describes the data sources and process followed for the compilation of the database, while providing critical discussions on the challenges encountered and decisions made, which are of relevance for its interpretation and use. The geographic, temporal, and magnitude distributions of the 1958 earthquakes that make up the database are presented alongside the general statistics on damage and casualties, noting that these stem from a variety of sources of differing reliability. Despite its inherent limitations, we believe it is an important contribution to the understanding of the extent of the consequences that may arise from earthquakes in the magnitude range of study.

    更新日期:2020-01-09
  • Depth corrections to surface-wave magnitudes for intermediate and deep earthquakes in the regions of North Eurasia
    J. Seismol. (IF 1.494) Pub Date : 2020-01-04
    Nataliya V. Petrova, Irina P. Gabsatarova

    Abstract This paper reports a study of surface wave MS,MOS magnitudes from the seismological catalog derived from teleseismic stations of the Geophysical Survey of the Russian Academy of Sciences (GS RAS) with aim of determination of depth corrections to MS and subsequent standardization of the catalogs with regard to MS. Unlike the MS reported by major international centers, such as National Earthquake Information Center of United States Geological Survey (NEIC USGS) and the International Seismological Centre (ISC), for earthquakes occurring at shallow and crustal depths up to 50–60 km, MS,MOS is also determined for intermediate-depth and deep earthquakes. The analysis of depth corrections to MS was based on MS,MOS from the GS RAS Seismological Catalog and MW from the ISC-GEM (Global Earthquake Model) Catalogue for 736 earthquakes of North Eurasia with MW ≥ 5.5 for the period 1988 through 2014. It was found that the decrease in MS,MOS with increasing depth becomes noticeable for h > 40 km. For the earthquakes of h > 40 km, we found two increasing log linear relations for the correction of MS,MOS as function of depth: ΔMS,MOS(h) = 1.71·log(h) − 2.726 for h = 40–90 km and ΔMS,MOS(h) = 0.556·lg(h)− 0.508 for h > 90 km. We applied these corrections to MS,MOS and found a substantially better correlation and lower standard errors in the MS,MOS vs MW relation. Applying the corrections to MS,MOS of the Okhotsk Sea earthquake on May 24, 2013, h = 617 km showed a good agreement between the corrected MS,MOS = 8.4 and MW = 8.3.

    更新日期:2020-01-04
  • Investigation of cliff instability at Għajn Ħadid Tower (Selmun Promontory, Malta) by integrated passive seismic techniques
    J. Seismol. (IF 1.494) Pub Date : 2020-01-03
    Roberto Iannucci, Salvatore Martino, Antonella Paciello, Sebastiano D’Amico, Pauline Galea

    Abstract Għajn Ħadid Tower represents an important cultural heritage of Malta (Central Mediterranean Sea). This tower, built in 1658 on the Selmun Promontory on the northeast coast of the island, was severely damaged by the 1856 Crete earthquake (MW 7.7). The area where the tower ruins stand is involved in a significant landslide process of lateral spreading. During 2015 and 2016, engineering geological surveys and passive seismic measurements were carried out to evaluate the main resonance frequencies of the promontory and monitor the gravity-induced instability process. Seismic ambient noise measurements in the area of the tower show significant horizontal-to-vertical spectral ratio (HVSR) resonance peaks at 3.3–3.5 Hz characterized by linearity and polarization of the particle motion. These features are not present in the measurements carried out on the stable zone and can be related to the vibrational behaviour of the unstable rock block. Additionally, a shear wave velocity profile for the area was obtained by using a seismic array. At the same time, two different approaches were tested for monitoring the landslide process: (i) a Seismic Navigating System (SNS) array detected 20 natural microseismic events caused by the ongoing landslide process; (ii) few-days continuous seismic noise measurements on the unstable rock block were used to carry out a preliminary study of the variation of specific parameters over time.

    更新日期:2020-01-04
  • Application of monitoring guidelines to induced seismicity in Italy
    J. Seismol. (IF 1.494) Pub Date : 2020-01-02
    Thomas Braun, Stefania Danesi, Andrea Morelli

    Abstract Public concern about anthropogenic seismicity in Italy first arose in the aftermath of the deadly M ≈ 6 earthquakes that hit the Emilia-Romagna region (northern Italy) in May 2012. As these events occurred in a (tectonically active) region of oil and gas production and storage, the question was raised, whether stress perturbations due to underground industrial activities could have induced or triggered the shocks. Following expert recommendations, in 2014, the Italian Oil & Gas Safety Authority (DGS-UNMIG, Ministry of Economic Development) published guidelines (ILG - Indirizzi e linee guida per il monitoraggio della sismicità, delle deformazioni del suolo e delle pressioni di poro nell’ambito delle attività antropiche), describing regulations regarding hydrocarbon extraction, waste-water injection and gas storage that could also be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining. The ILG describe the framework for the different actors involved in monitoring activities, their relationship and responsibilities, the procedure to be followed in case of variations of monitored parameters, the need for in-depth scientific analyses, the definition of different alert levels, their meaning and the parameters to be used to activate such alerts. Four alert levels are defined, the transition among which follows a decision to be taken jointly by relevant authorities and industrial operator on the basis of evaluation of several monitored parameters (micro-seismicity, ground deformation, pore pressure) carried on by a scientific-technical agency. Only in the case of liquid reinjection, the alert levels are automatically activated on the basis of exceedance of thresholds for earthquake magnitude and ground shaking – in what is generally known as a Traffic Light System (TLS). Istituto Nazionale di Geofisica e Vulcanologia has been charged by the Italian oil and gas safety authority (DGS-UNMIG) to apply the ILG in three test cases (two oil extraction and one gas storage plants). The ILG indeed represent a very important and positive innovation, as they constitute official guidelines to coherently regulate monitoring activity on a national scale. While pilot studies are still mostly under way, we may point out merits of the whole framework, and a few possible critical issues, requiring special care in the implementation. Attention areas of adjacent reservoirs, possibly licenced to different operators, may overlap, hence making the point for joint monitoring, also in view of the possible interaction between stress changes related to the different reservoirs. The prescribed initial blank-level monitoring stage, aimed at assessing background seismicity, may lose significance in case of nearby active production. Magnitude – a critical parameter used to define a possible step-up in activation levels – has inherent uncertainty and can be evaluated using different scales. A final comment considers the fact that relevance of TLS, most frequently used in hydraulic fracturing operations, may not be high in case of triggered tectonic events.

    更新日期:2020-01-04
  • Hybrid modelling of multi-layered geological structure under seismic excitation
    J. Seismol. (IF 1.494) Pub Date : 2019-12-18
    Sonia Parvanova, Georgi Vasilev, Petia Dineva

    This paper deals with seismic response evaluation of a finite multilayered geological structure with non-parallel boundaries rested on semi-infinite elastic half-plane subjected to transient seismic wave. The hybrid modelling approach is applied. It is based on the decomposition of the whole domain under consideration into two subregions: a finite-sized near-field zone and the open semi-infinite far-field region. The near-field range is presented by a finite geological profile, which is heterogeneous due to non-parallel layering. The far-field region is semi-infinite elastic isotropic homogeneous medium where the finite layered structure is located. An efficient 2D hybrid computational tool based on the boundary element method (BEM) for the far-field zone and the finite element method (FEM) for the finite layered domain is developed and verified in frequency domain. The BEM model of the seismically active far-field zone is inserted as a macro-finite element (MFE) in the FEM commercial program ANSYS. The hybrid model is of the FEM hosted type, where the boundary element domain (BED) is converted into macro-finite element, the nodal forces along the interface between two zones are expressed through the BED nodal tractions and the entire BEM formulation is converted to FEM-like approach. This hybrid model is applied for modelling of a real geological profile of the main wall of the “Liulyakovitsa” tailing pond, near Panagyurishte town, Bulgaria. Simulation results are given in the form of free surface synthetic seismograms stemming from the real seismic signals recorded at bedrock so as to establish the tailing pond’s seismic response.

    更新日期:2020-01-04
  • Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study
    J. Seismol. (IF 1.494) Pub Date : 2019-12-16
    Kajetan Chrapkiewicz, Monika Wilde-Piórko, Marcin Polkowski, Marek Grad

    Non-linear inverse problems arising in seismology are usually addressed either by linearization or by Monte Carlo methods. Neither approach is flawless. The former needs an accurate starting model; the latter is computationally intensive. Both require careful tuning of inversion parameters. An additional challenge is posed by joint inversion of data of different sensitivities and noise levels such as receiver functions and surface wave dispersion curves. We propose a generic workflow that combines advantages of both methods by endowing the linearized approach with an ensemble of homogeneous starting models. It successfully addresses several fundamental issues inherent in a wide range of inverse problems, such as trapping by local minima, exploitation of a priori knowledge, choice of a model depth, proper weighting of data sets characterized by different uncertainties, and credibility of final models. Some of them are tackled with the aid of novel 1D checkerboard tests—an intuitive and feasible addition to the resolution matrix. We applied our workflow to study the south-western margin of the East European Craton. Rayleigh wave phase velocity dispersion and P-wave receiver function data were gathered in the passive seismic experiment “13 BB Star” (2013–2016) in the area of the crust recognized by previous borehole and refraction surveys. Final models of S-wave velocity down to 300 km depth beneath the array are characterized by proximity in the parameter space and very good data fit. The maximum value in the mantle is higher by 0.1–0.2 km/s than reported for other cratons.

    更新日期:2020-01-04
  • Microzonation map of the Abbottabad basin and immediate surroundings
    J. Seismol. (IF 1.494) Pub Date : 2019-12-06
    Sarfraz Khan, Muhammad Waseem, Muhammad Asif Khan, Zahid Hussain, Waqas Ahmed, Ahmad Hamad Khaliq, Nisar Bin Umair, Mian Luqman Hussain

    Abstract This study presents seismic hazard and seismic microzonation maps for the Abbottabad basin and surroundings, which are used in assessment and seismic design of buildings and bridges and other infrastructures. This research work determines microzonation parameters (shear wave velocity, fundamental frequency, and acceleration on ground surface) using geotechnical and geophysical testing procedures. Standard penetration test (SPT) and H/V methods are used to characterize the soils by estimating shear wave velocity at different locations. Microzonation maps for Abbottabad are developed in terms of acceleration parameter for 10% and 2% probability of exceedances in 50 years return period. These maps have been obtained based on the mean of average spectral acceleration values between 0.10 and 1.00 s following the Borcherdt (1994) recommendations. Based on H/V data (using Tromino Engy Plus instrument), it has been observed that the study area has average fundamental frequency range from 1 to 5 Hz, which represents the deposition of alluvial sediments (i.e., stiff and dense soil). Site characterization based on shear wave velocity indicated that soil in the study area consists of categories C and D. For the return period (Tr) of 475 years, the surface acceleration values ranges from 0.623 to 0.673 g, and for Tr = 2475 years, the area ranges from 1.007 to 1.107 g. These results show that soils in the Abbottabad basin will amplify 0.540 and 0.548 time respectively for Tr = 475 and 2475 against bed rock ground motions. Microzonation maps for Abbottabad basin do not exist; the maps produced in this study will be the basic input for carrying out the earthquake resistant design of the structures in Abbottabad.

    更新日期:2020-01-04
  • Effects of geometry and rheological parameters of large basin on the SH-wave response of sub-basin in the basin-sub-basin models
    J. Seismol. (IF 1.494) Pub Date : 2019-12-04
    J. P. Narayan, Garima Yadav

    The effects of impedance and shape-ratio of large basin on the nature of occurrence of 2D resonance, spectral amplifications, sub-basin-induced Love (SBIL)-waves and sub-basin-transduced Love (SBTL)-waves and associated differential ground motion (DGM) across the sub-basin of the basin-sub-basin models are documented in this paper. The analysis of SH-wave responses of the considered small basin, large basin, and various basin-sub-basin models reveals that the presence of large basin does not change the occurrence of 2D resonance phenomenon in the sub-basin. But, the presence of large basin reduces the fundamental frequency (\( {F}_{02D}^{SLB}\Big) \) of sub-basin and increases the spectral amplifications and amplitude of the SBIL-wave in the sub-basin. The cause of reduction of \( {F}_{02D}^{SLB} \) of sub-basin is the decrease of the lowest fundamental mode of vibration of basin-sub-basin model in the vertical direction. A considerable effect of location of sub-basin, impedance, and shape-ratio of the large basin on the amplitudes of both the SBIL- and SBTL-waves is observed. The amplification of SBTL-wave in the sub-basin is due to the drop of impedance and the decrease of wavelength of SBTL-wave in the vertical direction. A decrease of DGM with an increase of span and decrease of shape-ratio of the large basin is obtained. The obtained largest DGM of the order of 1.85 × 10−3 near the edge of sub-basin for 1 cm/s particle velocity at basement level calls for further study on the complex basin and sub-basin interaction effects on the ground motion characteristics for earthquake engineering purposes.

    更新日期:2020-01-04
  • Recent seismicity in northern European Russia
    J. Seismol. (IF 1.494) Pub Date : 2019-12-04
    Alexey N. Morozov, Natalya V. Vaganova, Yana V. Konechnaya, Irina A. Zueva, Vladimir E. Asming, Nataliya N. Noskova, Nikolay V. Sharov, Bela A. Assinovskaya, Natalyia M. Panas, Zinaida A. Evtyugina

    A revised comprehensive catalog has been made for earthquakes that occurred in northern European Russia for the period between 2005 and 2017. The earthquake parameters were determined to greater accuracy using the same velocity model (BARENTS), the same location method (based on generalized beamforming), combining data from catalogs, bulletins, and (in part) from waveform supplied by regional seismograph networks in Russia and the Scandinavian countries. The resulting unified catalog formed a basis to assess the recent seismicity in northern European Russia, which occurs as low magnitude earthquakes. The distribution of earthquake epicenters is not uniform. The Fennoscandian Shield shows the highest activity (by seismicity rate and epicenter density), the next to follow are the northeastern Russian plate and the northern Urals Fold-Thrust Region. All earthquakes typically occurred at crustal depths.

    更新日期:2020-01-04
  • Identifying archaeological evidence of past earthquakes in a contemporary disaster scenario: case studies of damage, resilience and risk reduction from the 2015 Gorkha Earthquake and past seismic events within the Kathmandu Valley UNESCO World Heritage Property (Nepal)
    J. Seismol. (IF 1.494) Pub Date : 2019-12-04
    Christopher Davis, Robin Coningham, Kosh Prasad Acharya, Ram Bahadur Kunwar, Paolo Forlin, Kai Weise, Prem Nath Maskey, Anie Joshi, Ian Simpson, David Toll, Sean Wilkinson, Paul Hughes, Vasilis Sarhosis, Ashutosh Kumar, Armin Schmidt

    Abstract The 2015 Gorkha Earthquake was a humanitarian disaster but also a cultural catastrophe that damaged and destroyed historic monuments across Nepal, including those within the Kathmandu Valley UNESCO World Heritage Property. In the rush to rebuild, traditionally constructed foundations are being removed and replaced with modern materials without assessments of whether these contributed to the collapse of a monument. Generally undertaken without scientific recording, these interventions have led to the irreversible destruction of earlier subsurface phases of cultural activity and the potential loss of evidence for successful traditional seismic adaptations and risk reduction strategies, with no research into whether modern materials, such as concrete and steel, would offer enhanced resilience. In response to this context, multidisciplinary post-disaster investigations were undertaken between 2015 and 2018, including archaeological excavation, geophysical survey, geoarchaeological analysis, linked to architectural and engineering studies, to begin to evaluate and assess the damage to, and seismic adaptations of, historic structures within Nepal’s Kathmandu Valley. Where possible, we draw on archaeoseismological approaches for the identification and classification of Earthquake Archaeological Effects (EAEs) at selected monuments damaged by the 2015 Gorkha Earthquake. Lessons learned from evidence of potential weaknesses, as well as historic ‘risk-sensitive tactics’ of hazard reduction within monuments, are now being incorporated into reconstruction and rehabilitation initiatives alongside the development of methods for the protection of heritage in the face of future earthquakes.

    更新日期:2020-01-04
  • Fast M W estimation of microearthquakes recorded around the underground gas storage in the Montello-Collalto area (Southeastern Alps, Italy)
    J. Seismol. (IF 1.494) Pub Date : 2019-11-26
    Alessandra Lanzoni, Luca Moratto, Enrico Priolo, Maria Adelaide Romano

    Abstract Underground fluid injection and extraction is able to change pore fluid pressure at depth and make faults unstable, due to friction-force reduction, with an increased possibility of triggering earthquakes. Studying the local seismicity, down to microearthquakes, and stress field in areas where such activities are developed are essential steps to discriminate between natural and induced events. In this context, the moment magnitude (MW) is a key-parameter to both evaluate the energy balance and the stress involved in earthquake rupture process and assess seismic hazard accurately. Here, we focus on the fast MW estimation of microearthquakes recorded around the underground gas storage of Collalto (Northeastern Italy) by a dedicated seismic monitoring network. The area of Montello-Collalto, where this industrial activity is carried out, is densely populated and characterized by relevant seismic hazard. We compute MW from the response spectra (SA) calculated at fixed periods (i.e., 1.0 and 0.3 s); we show that log (SA) and MW scale as 2/3 and extend our method to microseismicity by using response spectra at 0.1 s. We eventually estimate MW for 1659 events (0.4 ≤ MW ≤ 3.5) and find that ML and MW scale as 2/3 too. The discrepancy between these two magnitude scales affects both the Gutenberg-Richter parameters and completeness magnitude estimations; therefore, it has consequences when those quantities are used for physical interpretation. Our procedure shows to be efficient and suitable to be implemented within standard routine analyses of real-time monitoring and feed decision-making processes about plant management, such as the traffic light protocols.

    更新日期:2020-01-04
  • The initial high-energy phenomena of earthquake sources in fluid-saturated environments
    J. Seismol. (IF 1.494) Pub Date : 2019-11-22
    Sergii D. Kaim

    Abstract Experimental data pertaining to weak faults requires construction of microscopic models of the earthquake sources. This study proposes a new high-energy mechanism of transformation of potential energy of strata, saturated with free or bounded fluids, into a kinetic energy of motion of rocks. The proposed approach relies within the framework of classic statistical theory. The high-energy phenomena at a nanometer level are generated by self-consistent molecular fields acting on individual particles. The analysis is carried out using the Bogolyubov-Born-Green-Kirkwood-Yvon equations for the particle group distribution functions. We have investigated the number of high-energy phenomena: (1) the emission of atoms and molecules with high energies from the abruptly opened surface of a condensed system; (2) the implosion of convergent streams of high-energy particles, accompanied by a phenomena of their shock dissociation and ionization, with a subsequent formation of partially ionized plasma; and (3) the recombination processes inside a plasma leading to a formation of molecules with high kinetic energies. The initiation of an earthquake occurs due to an abrupt opening of a cavity in the fluid-saturated medium. At certain thermodynamic conditions, the work function of atoms and molecules from the surface of the system may take negative values. As a result, the emission of molecules of fluids from the cavity walls will generate the high-speed streams of molecules. The emitted flux of molecules leads to the phenomena of implosion, impact dissociation, and ionization of the molecules. This plasma state of the medium is sufficient for an explosion. The explosion initiates a self-supporting chain of consequent explosions in a plane of the tectonic fault. As an example, we have considered the Bridgman explosion of serpentinite.

    更新日期:2020-01-04
  • Nomogram to help explain probabilistic seismic hazard
    J. Seismol. (IF 1.494) Pub Date : 2019-11-22
    John Douglas, Laurentiu Danciu

    Abstract Nomograms are an easy to use and visually attractive graphical tool to solve for any of the variables within an often complex equation. In seismology, the most well-known nomogram is a three-parallel-scale graphic for the calculation of local magnitude given the epicentral distance and trace amplitude. Until the advent of computers, nomograms were often employed by engineers and scientists in many fields as they provide a means for rapid and accurate calculations as well as helping the user understand the sensitivity of the final results to the input parameters. It is this aid to understanding that remains a key attraction of these graphical tools, which are now rarely seen (although they remain common in some fields of medicine where they are used for rapid screening and estimating risks). In this research letter, we present a nomogram summarising the results of simple probabilistic seismic hazard assessments (PSHAs) for peak ground acceleration and elastic response spectral acceleration for a structural period of 1s and return periods from 100 to 2500 years, where the effects of the activity rate and the slope of the Gutenberg-Richter relation are captured. We believe that this nomogram has considerable educational benefit for engineering seismology students, decision makers and other non-expert users of results of PSHAs.

    更新日期:2020-01-04
  • 1-D velocity model for the North Korean Peninsula from Rayleigh wave dispersion of ambient noise cross-correlations
    J. Seismol. (IF 1.494) Pub Date : 2019-11-16
    Sang-Jun Lee, Junkee Rhie, Seongryong Kim, Tae-Seob Kang, Chang Soo Cho

    Abstract Monitoring seismic activity in the north Korean Peninsula (NKP) is important not only for understanding the characteristics of tectonic earthquakes but also for monitoring anthropogenic seismic events. To more effectively investigate seismic properties, reliable seismic velocity models are essential. However, the seismic velocity structures of the region have not been well constrained due to a lack of available seismic data. This study presents 1-D velocity models for both the inland and offshore (western East Sea) of the NKP. We constrained the models based on the results of a Bayesian inversion process using Rayleigh wave dispersion data, which were measured from ambient noise cross-correlations between stations in the southern Korean Peninsula and northeast China. The proposed models were evaluated by performing full moment tensor inversion for the 2013 Democratic People’s Republic of Korea (DPRK) nuclear test. Using the composite model consisting of both inland and offshore models resulted in consistently higher goodness of fit to observed waveforms than previous models. This indicates that seismic monitoring can be improved by using the proposed models, which resolve propagation effects along different paths in the NKP region.

    更新日期:2020-01-04
  • Numerical simulation of the 1940 Lima-Peru earthquake and tsunami (Mw 8.0)
    J. Seismol. (IF 1.494) Pub Date : 2019-11-16
    César Jiménez, Nabilt Moggiano

    In this research, we have conducted a numerical simulation to obtain the seismic source, coseismic deformation field, and the tsunami propagation of the great Lima-Peru 1940 earthquake and tsunami, based on macroseismic information and focal mechanism from the literature. The seismic dimensions of our preferred model were set at 162 km×71 km according to VIII isoseismal intensity. The slip distribution is homogeneous with a mean value of 2.7 m. The fault plane orientation was set at strike = 330∘, dip = 20∘, and rake = 90∘. The maximum simulated uplift was 1.27 m and the maximum subsidence was 0.36 m. Due to the proximity of the seismic source to the coast, the city of Huacho was uplifted around 11 cm. The fault plane of the 1940 earthquake was located in the updip near the coast. The maximum tsunami height simulated in Huacho was 1.80 m. We suggest that there is a high tsunamigenic potential near the trench to generate a shallow earthquake.

    更新日期:2020-01-04
  • Local site conditions modeling in stochastic simulation of ground motions generated by Vrancea (Romania) intermediate-depth seismic source
    J. Seismol. (IF 1.494) Pub Date : 2019-11-16
    Anabella Coțovanu, Radu Vacareanu

    Abstract Analyses of stochastic simulations methods for Vrancea (Romania) intermediate-depth earthquake recorded at seismic station INCERC Bucharest were made. The main research topic highlighted in this paper is the quest for the best model able to simulate the influence of the local site conditions considering to this aim different types of soil behavior. Two types of linear behavior and one type of nonlinear behavior of the soil layers were considered to investigate the site effects. Comparisons between the simulations and the recorded accelerograms and between the simulation methods were made in terms of amplitude parameters, frequency content, duration parameters, and energy release. A better approximation was found when the nonlinear behavior of the soil layers was employed.

    更新日期:2020-01-04
  • Capturing epistemic uncertainty in the Iranian strong-motion data on the basis of backbone ground motion models
    J. Seismol. (IF 1.494) Pub Date : 2019-11-16
    Milad Kowsari, Saeid Ghasemi, Zoya Farajpour, Mehdi Zare

    In the current practice of probabilistic seismic hazard analysis (PSHA), the different estimates of ground motions predicted by ground motion models (GMMs) are attributed to epistemic uncertainty. The epistemic uncertainties arise from the lack of knowledge which is reflected in imperfect models and can be handled by either logic tree or backbone approaches. The use of backbone approach for PSHA provides a more robust estimation of the GMM contribution to the epistemic uncertainty. In this study, we quantify the epistemic uncertainty in the Iranian strong-motion data by a scale factor that can be calibrated to the recorded strong-motions. The scale factor is then added and subtracted from the backbone GMM to fairly cover the spread in the predictions from other GMMs. For this purpose, we used the Iranian strong-motion database that includes 865 records from 167 events up to 2013, with the moment magnitude range of 5.0 ≤ M ≤ 7.4, and distances up to 120 km including a variety of fault mechanisms. On the other hand, several candidate GMMs were selected from local, regional, and worldwide data. Then, we applied a data-driven method based on the deviance information criterion to rank the candidate GMMs and select the best GMM as the backbone model. The results of this study show that the epistemic uncertainty varies approximately from 0.1 to 0.3 in base-10 logarithmic units. It generally has minima in the magnitude range of prevalent data (M 5.5–6.5) and increases for small (M 4.5–5.5) and large earthquake magnitudes (M 6.5–7.5). The results also show that the scale factors generally grow with distance. Moreover, notable site effects are seen in the Iranian strong-motions. We conclude therefore that the proposed backbone GMMs along with the estimated scales factors of this study are promising for use in future earthquake hazard estimation in Iran, as they capture the recorded data and provide information on the upper and lower bounds of ground motion estimates.

    更新日期:2020-01-04
  • Seismic networks layout optimization for a high-resolution monitoring of induced micro-seismicity
    J. Seismol. (IF 1.494) Pub Date : 2019-11-07
    Grazia De Landro, Matteo Picozzi, Guido Russo, Guido Maria Adinolfi, Aldo Zollo

    Abstract The continuous monitoring of the space-time-magnitude evolution of seismicity is a crucial task to assess the geo-mechanical conditions of hydrocarbon reservoirs. It is fundamental to design optimized high-sensitivity and cost-effective seismic networks able to detect and locate low magnitude events with high accuracy. In Italy, after the concern for the 2012 Emilia earthquake, the government released the guidelines for monitoring the seismicity in areas surrounding subsurface industrial activities. In this work, we propose an optimization study for seismic monitoring networks based on the guideline requirements. We evaluated the performance, in terms of detection/location thresholds and events location errors, of different network layouts constructed by varying the station density and geometry and considering also the integration of seismic arrays. We simulated sets of seismic sources at different depths by varying magnitude and stress drop values. We considered two different values of noise level at the stations. The results show that the station density and the noise level represent the crucial parameters for the seismic network performances. The performances of a standard network comply the guidelines requirements in terms of detection/location thresholds. Only the integration of seismic networks with arrays allows to decrease the location errors of several hundreds of meters and to reach the location accuracy required by the Italian guidelines. We foresee the integration of standard networks with seismic arrays to achieve high performance in terms of detection capability and location accuracy.

    更新日期:2020-01-04
  • Rayleigh wave group velocity dispersion tomography of West Africa using regional earthquakes and ambient seismic noise
    J. Seismol. (IF 1.494) Pub Date : 2019-11-08
    Yacouba Ouattara, Dimitri Zigone, Alessia Maggi

    Abstract West Africa could teach us much about the early tectonic history of Earth, but current seismic models of the regional crustal and lithospheric structure lack the resolution required to answer all but the most basic research questions. We have improved the resolution of group velocity maps of the West African Craton by complementing the uneven path distribution of earthquake-generated surface waves with surface waves reconstructed from ambient noise cross-correlations. Our joint dataset provides good spatial coverage of group velocity measurements from 20- to 100-s period, enabling us to reduce artifacts in our group velocity maps and improve their resolution. Our maps correlate well with regional geological features. At short periods, they highlight differences in crustal thickness, recent tectonic activity, and thick sediments. At long periods, we found lower velocities due to hot, thin lithosphere under the Pan-African mobile belt and faster velocities due to cold, thick lithosphere under the Man-Leo and Reguibat shields. Our higher resolution maps advance us a step towards revealing the detailed lithospheric structure and tectonic processes of West Africa.

    更新日期:2020-01-04
  • Microseismicity analysis in the geothermal area of Torre Alfina, Central Italy
    J. Seismol. (IF 1.494) Pub Date : 2019-10-11
    Arianna Lisi, Alessandro Marchetti, Alberto Frepoli, Nicola Mauro Pagliuca, Giuliana Mele, Maria Luisa Carapezza, Marco Caciagli, Daniela Famiani, Alessandro Gattuso, Thomas Braun

    Abstract The geothermal field of Torre Alfina is located in central Italy at the northern edge of the Vulsini Volcanic District, the northernmost area of the so-called Quaternary Roman Co-Magmatic Province. In the framework of a medium-enthalpy geothermal exploitation project, INGV installed a local seismic network close to the future geothermal production site for monitoring natural local seismicity. In this paper, we show the results of a study of the microseismicity recorded from June 2014 to May 2016 in a small area of about 10 km2 around Torre Alfina. Analyzing seismic signals recorded by a local temporary network of ten short-period stations and by four permanent stations of the INGV national seismic network, we detected 846 local earthquakes. Then, we accurately relocated 799 events using HypoDD code. Our results show that the region of Torre Alfina is characterized by intense microseismicity, with hypocentral depths between 3 and 7 km and with moderate magnitudes between Md = 0.1 and ML = 2.8. Moreover, more than half of the earthquakes are grouped into six main swarm-like clusters each lasting few days. Furthermore, we computed 36 well-constrained fault plane solutions, which show a clear transtensional deformation regime in the whole study area. Three main tectonic directions have been evidenced from the focal mechanisms analysis: E-W, WSW-ENE, and NW-SE. The understanding of the seismogenic structural setting of the Torre Alfina geothermal field, and the study of its background natural seismicity can be of great importance in recognizing any possible future seismicity induced by the exploitation of the field.

    更新日期:2020-01-04
  • A case study of seismograph self-noise test from Trillium 120QA seismometer and Reftek 130 data logger
    J. Seismol. (IF 1.494) Pub Date : 2019-11-06
    Weiwei Xu, Songyong Yuan

    Seismograph self-noise has become a de facto standard for instrument comparisons and their performance assessment and is considered as one of the most vital parameters for instrument comparison. For self-noise testing of modern force-balance feedback broadband seismometers, several factors have been thoroughly discussed and thought to be attributable to the self-noise estimate, including the data selection criteria, sensor alignment correction, timing error, correlation analysis method, and computational parameter selection during the computational process. This study focuses on some other factors, such as local site conditions, temperature insulating methods, and data logger self-noise interferences, with an aim to differentiate the self-noise contribution of these sources and their dependencies on time and frequency. A series of experiments were conducted at the Beijing National Earth Observatory using a Trillium 120QA seismometer and Reftek-130 data acquisition system at three different locations ranging from the ordinary equipment warehouse to global seismographic network level cave with a hard-rock base. Results show that noise-free site is necessary for the self-noise test in a frequency band greater than approximately 0.1 Hz. However, for a frequency band less than 0.1 Hz, the insulation method and installation procedures are far more important, although the influence of the site location cannot be neglected fully. A suitable preamp should be selected in the data logger configurations to ensure that the low-noise amplitude of the sensor signal is above the digitizer noise level.

    更新日期:2020-01-04
  • The 1895 Ljubljana earthquake: can the intensity data points discriminate which one of the nearby faults was the causative one?
    J. Seismol. (IF 1.494) Pub Date : 2018-10-30
    Lara Tiberi,Giovanni Costa,Petra Jamšek Rupnik,Ina Cecić,Peter Suhadolc

    The earthquake (Mw 6 from the SHEEC defined by the MDPs) that occurred in the central part of Slovenia on 14 April, 1895, affected a broad region, causing deaths, injuries, and destruction. This event was much studied but not fully explained; in particular, its causative source model is still debated. The aim of this work is to contribute to the identification of the seismogenic source of this destructive event, calculating peak ground velocity values through the use of different ground motion prediction equations (GMPEs) and computing a series of ground motion scenarios based on the result of an inversion work proposed by Jukić in 2009 and on various fault models in the surroundings of Ljubljana: Vič, Želimlje, Borovnica, Vodice, Ortnek, Mišjedolski, and Dobrepolje faults. The synthetic seismograms, at the basis of our computations, are calculated using the multi-modal summation technique and a kinematic approach for extended sources, with a maximum peak ground velocity value of 1 Hz. The qualitative and quantitative comparison of these simulations with the macroseismic intensity database allows us to discriminate between various sources and configurations. The quantitative validation of the seismic source is done using ad hoc ground motion to intensity conversion equations (GMICEs), expressly calculated for this study. This study allows us to identify the most probable causative source model of this event, contributing to the improvement of the seismotectonic knowledge of this region. The candidate fault that has the lowest values of average differences between observed and calculated intensities and chi-squared is a strike slip fault with a toward-north rupture as the Ortnek fault.

    更新日期:2019-11-01
  • Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet.
    J. Seismol. (IF 1.494) Pub Date : 2018-07-13
    Samar Amini,Roland Roberts,Mohammad Raeesi,Zaher Hossein Shomali,Bjorn Lund,Zoya Zarifi

    An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane.

    更新日期:2019-11-01
  • Characterisation of ground motion recording stations in the Groningen gas field.
    J. Seismol. (IF 1.494) Pub Date : 2018-05-15
    Rik Noorlandt,Pauline P Kruiver,Marco P E de Kleine,Marios Karaoulis,Ger de Lange,Antonio Di Matteo,Julius von Ketelhodt,Elmer Ruigrok,Benjamin Edwards,Adrian Rodriguez-Marek,Julian J Bommer,Jan van Elk,Dirk Doornhof

    The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity (VS). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ VS values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed VS profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent VS information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative VS profiles at the accelerograph station sites. The measured VS profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the VS profile and the observed amplification from vertical array stations is also excellent.

    更新日期:2019-11-01
  • Probabilistic seismic hazard assessment of southern part of Ghana.
    J. Seismol. (IF 1.494) Pub Date : 2018-05-15
    Sylvanus T Ahulu,Sylvester Kojo Danuor,Daniel K Asiedu

    This paper presents a seismic hazard map for the southern part of Ghana prepared using the probabilistic approach, and seismic hazard assessment results for six cities. The seismic hazard map was prepared for 10% probability of exceedance for peak ground acceleration in 50 years. The input parameters used for the computations of hazard were obtained using data from a catalogue that was compiled and homogenised to moment magnitude (Mw). The catalogue covered a period of over a century (1615-2009). The hazard assessment is based on the Poisson model for earthquake occurrence, and hence, dependent events were identified and removed from the catalogue. The following attenuation relations were adopted and used in this study-Allen (for south and eastern Australia), Silva et al. (for Central and eastern North America), Campbell and Bozorgnia (for worldwide active-shallow-crust regions) and Chiou and Youngs (for worldwide active-shallow-crust regions). Logic-tree formalism was used to account for possible uncertainties associated with the attenuation relationships. OpenQuake software package was used for the hazard calculation. The highest level of seismic hazard is found in the Accra and Tema seismic zones, with estimated peak ground acceleration close to 0.2 g. The level of the seismic hazard in the southern part of Ghana diminishes with distance away from the Accra/Tema region to a value of 0.05 g at a distance of about 140 km.

    更新日期:2019-11-01
  • Was the Mw 7.5 1952 Kern County, California, earthquake induced (or triggered)?
    J. Seismol. (IF 1.494) Pub Date : 2017-12-05
    Susan E Hough,Victor C Tsai,Robert Walker,Fred Aminzadeh

    Several recent studies have presented evidence that significant induced earthquakes occurred in a number of oil-producing regions during the early and mid-twentieth century related to either production or wastewater injection. We consider whether the 21 July 1952 Mw 7.5 Kern County earthquake might have been induced by production in the Wheeler Ridge oil field. The mainshock, which was not preceded by any significant foreshocks, occurred 98 days after the initial production of oil in Eocene strata at depths reaching 3 km, within ~1 km of the White Wolf fault (WWF). Based on this spatial and temporal proximity, we explore a potential causal relationship between the earthquake and oil production. While production would have normally be expected to have reduced pore pressure, inhibiting failure on the WWF, we present an analytical model based on industry stratigraphic data and best estimates of parameters whereby an impermeable splay fault adjacent to the main WWF could plausibly have blocked direct pore pressure effects, allowing the poroelastic stress change associated with production to destabilize the WWF, promoting initial failure. This proof-of-concept model can also account for the 98-day delay between the onset of production and the earthquake. While the earthquake clearly released stored tectonic stress, any initial perturbation on or near a major fault system can trigger a larger rupture. Our proposed mechanism provides an explanation for why significant earthquakes are not commonly induced by production in proximity to major faults.

    更新日期:2019-11-01
  • Estimating the upper limit of prehistoric peak ground acceleration using an in situ, intact and vulnerable stalagmite from Plavecká priepast cave (Detrekői-zsomboly), Little Carpathians, Slovakia-first results.
    J. Seismol. (IF 1.494) Pub Date : 2017-09-05
    K Gribovszki,K Kovács,P Mónus,G Bokelmann,P Konecny,M Lednická,G Moseley,C Spötl,R L Edwards,M Bednárik,L Brimich,L Tóth

    Earthquakes hit urban centres in Europe infrequently, but occasionally with disastrous effects. Obtaining an unbiased view of seismic hazard (and risk) is therefore very important. In principle, the best way to test probabilistic seismic hazard assessments (PSHAs) is to compare them with observations that are entirely independent of the procedure used to produce PSHA models. Arguably, the most valuable information in this context should be information on long-term hazard, namely maximum intensities (or magnitudes) occurring over time intervals that are at least as long as a seismic cycle. The new observations can provide information of maximum intensity (or magnitude) for long timescale as an input data for PSHA studies as well. Long-term information can be gained from intact stalagmites in natural caves. These formations survived all earthquakes that have occurred over thousands of years, depending on the age of the stalagmite. Their 'survival' requires that the horizontal ground acceleration (HGA) has never exceeded a certain critical value within that time period. Here, we present such a stalagmite-based case study from the Little Carpathians of Slovakia. A specially shaped, intact and vulnerable stalagmite in the Plavecká priepast cave was examined in 2013. This stalagmite is suitable for estimating the upper limit of horizontal peak ground acceleration generated by prehistoric earthquakes. The critical HGA values as a function of time going back into the past determined from the stalagmite that we investigated are presented. For example, at the time of Jókő event (1906), the critical HGA value cannot have been higher than 1 and 1.3 m/s2 at the time of the assumed Carnuntum event (∼340 AD), and 3000 years ago, it must have been lower than 1.7 m/s2. We claimed that the effect of Jókő earthquake (1906) on the location of the Plavecká priepast cave is consistent with the critical HGA value provided by the stalagmite we investigated. The approach used in this study yields significant new constraints on the seismic hazard, as tectonic structures close to Plavecká priepast cave did not generate strong earthquakes in the last few thousand years. The results of this study are highly relevant given that the two capitals, Vienna and Bratislava, are located within 40 and 70 km of the cave, respectively.

    更新日期:2019-11-01
  • Structural features and seismotectonic implications of coseismic surface ruptures produced by the 2016 Mw 7.1 Kumamoto earthquake.
    J. Seismol. (IF 1.494) Pub Date : 2017-09-05
    Aiming Lin

    Field investigations and analyses of satellite images and aerial photographs reveal that the 2016 Mw 7.1 (Mj 7.3) Kumamoto earthquake produced a ∼40-km surface rupture zone striking NE-SW on central Kyushu Island, Japan. Coseismic surface ruptures were characterized by shear faults, extensional cracks, and mole tracks, which mostly occurred along the pre-existing NE-SW-striking Hinagu-Futagawa fault zone in the southwest and central segments, and newly identified faults in the northeast segment. This study shows that (i) the Hinagu-Futagawa fault zone triggered the 2016 Kumamoto earthquake and controlled the spatial distribution of coseismic surface ruptures; (ii) the southwest and central segments were dominated by right-lateral strike-slip movement with a maximum in-site measured displacement of up to 2.5 m, accompanied by a minor vertical component. In contrast, the northeast segment was dominated by normal faulting with a maximum vertical offset of up to 1.75 m with a minor horizontal component that formed graben structures inside Aso caldera; (iii) coseismic rupturing initiated at the jog area between the Hinagu and Futagawa faults, then propagated northeastward into Aso caldera, where it terminated. The 2016 Mw 7.1 Kumamoto earthquake therefore offers a rare opportunity to study the relationships between coseismic rupture processes and pre-existing active faults, as well as the seismotectonics of Aso volcano.

    更新日期:2019-11-01
  • On the rotation of teleseismic seismograms based on the receiver function technique.
    J. Seismol. (IF 1.494) Pub Date : 2017-07-22
    M Wilde-Piórko,M Grycuk,M Polkowski,M Grad

    The receiver function (RF) technique is a well-established method to investigate the crustal and upper mantle structures based on three-component seismograms of teleseismic events. In the present study, we propose a modified automatic procedure to determine the back azimuth and polarization angles of a teleseismic event based on the RF technique. The method is tested for the recording of 3 permanent and 3 temporary broadband seismic stations located in the vicinity of Poland. Additionally, the analysis of Rayleigh wave polarization is conducted to show that the new procedure is not sensitive to incorrect seismometer orientation. The synthetic modelling of RF by a modified ray-tracing method for 2.5D models beneath each seismic station down to a depth of 60 km is performed to show the effectiveness of the proposed method in the calculation of RF for a complex structure with dipping layers.

    更新日期:2019-11-01
  • Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa-Shizuoka Tectonic Line, Japan.
    J. Seismol. (IF 1.494) Pub Date : 2017-07-22
    Aiming Lin,Mikako Sano,Maomao Wang,Bing Yan,Di Bian,Ryoji Fueta,Takashi Hosoya

    The Mw 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa-Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2-E8) prior to the 2014 Mw 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2-E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300-400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800-1400 and is associated with the 1791 Mw 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000-700, likely corresponding to the AD 841 Mw 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600-6000 years. The throw rate during the early Holocene is estimated to be 1.2-3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7-1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.

    更新日期:2019-11-01
  • Cross-correlation beamforming.
    J. Seismol. (IF 1.494) Pub Date : 2017-06-13
    Elmer Ruigrok,Steven Gibbons,Kees Wapenaar

    An areal distribution of sensors can be used for estimating the direction of incoming waves through beamforming. Beamforming may be implemented as a phase-shifting and stacking of data recorded on the different sensors (i.e., conventional beamforming). Alternatively, beamforming can be applied to cross-correlations between the waveforms on the different sensors. We derive a kernel for beamforming cross-correlated data and call it cross-correlation beamforming (CCBF). We point out that CCBF has slightly better resolution and aliasing characteristics than conventional beamforming. When auto-correlations are added to CCBF, the array response functions are the same as for conventional beamforming. We show numerically that CCBF is more resilient to non-coherent noise. Furthermore, we illustrate that with CCBF individual receiver-pairs can be removed to improve mapping to the slowness domain. An additional flexibility of CCBF is that cross-correlations can be time-windowed prior to beamforming, e.g., to remove the directionality of a scattered wavefield. The observations on synthetic data are confirmed with field data from the SPITS array (Svalbard). Both when beamforming an earthquake arrival and when beamforming ambient noise, CCBF focuses more of the energy to a central beam. Overall, the main advantage of CCBF is noise suppression and its flexibility to remove station pairs that deteriorate the signal-related beampower. ELECTRONIC SUPPLEMENTARY MATERIAL The online version of this article (doi:10.1007/s10950-016-9612-6) contains supplementary material, which is available to authorized users.

    更新日期:2019-11-01
  • Cohesive zone length of metagabbro at supershear rupture velocity.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    Eiichi Fukuyama,Shiqing Xu,Futoshi Yamashita,Kazuo Mizoguchi

    We investigated the shear strain field ahead of a supershear rupture. The strain array data along the sliding fault surfaces were obtained during the large-scale biaxial friction experiments at the National Research Institute for Earth Science and Disaster Resilience. These friction experiments were done using a pair of meter-scale metagabbro rock specimens whose simulated fault area was 1.5 m × 0.1 m. A 2.6-MPa normal stress was applied with loading velocity of 0.1 mm/s. Near-fault strain was measured by 32 two-component semiconductor strain gauges installed at an interval of 50 mm and 10 mm off the fault and recorded at an interval of 1 MHz. Many stick-slip events were observed in the experiments. We chose ten unilateral rupture events that propagated with supershear rupture velocity without preceding foreshocks. Focusing on the rupture front, stress concentration was observed and sharp stress drop occurred immediately inside the ruptured area. The temporal variation of strain array data is converted to the spatial variation of strain assuming a constant rupture velocity. We picked up the peak strain and zero-crossing strain locations to measure the cohesive zone length. By compiling the stick-slip event data, the cohesive zone length is about 50 mm although it scattered among the events. We could not see any systematic variation at the location but some dependence on the rupture velocity. The cohesive zone length decreases as the rupture velocity increases, especially larger than [Formula: see text] times the shear wave velocity. This feature is consistent with the theoretical prediction.

    更新日期:2019-11-01
  • G: Fracture energy, friction and dissipation in earthquakes.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    S Nielsen,E Spagnuolo,M Violay,S Smith,G Di Toro,A Bistacchi

    Recent estimates of fracture energy G' in earthquakes show a power-law dependence with slip u which can be summarized as G' ∝ ua where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to Gf : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G' and Gf should be comparable and show a similar scaling with slip. We test this hypothesis by analyzing experiments performed on various cohesive and non-cohesive rock types, under wet and dry conditions, with imposed deformation typical of seismic slip (normal stress of tens of MPa, target slip velocity > 1 m/s and fast accelerations ≈ 6.5 m/s2). The resulting fracture energy Gf is similar to the seismological estimates, with Gf and G' being comparable over most of the slip range. However, Gf appears to saturate after several meters of slip, while in most of the reported earthquake sequences, G' appears to increase further and surpasses Gf at large magnitudes. We analyze several possible causes of such discrepancy, in particular, additional off-fault damage in large natural earthquakes.

    更新日期:2019-11-01
  • Seismological asperities from the point of view of dynamic rupture modeling: the 2007 Mw6.6 Chuetsu-Oki, Japan, earthquake.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    Hideo Aochi,Masayuki Yoshimi

    We study the ground motion simulations based on three finite-source models for the 2007 Mw6.6 Niigata Chuetsu-oki, Japan, earthquake in order to discuss the performance of the input ground motion estimations for the near-field seismic hazard analysis. The three models include a kinematic source inverted from the regional accelerations, a dynamic source on a planar fault with three asperities inferred from the very-near-field ground motion particle motions, and another dynamic source model with conjugate fault segments. The ground motions are calculated for an available 3D geological model using a finite-difference method. For the comparison, we apply a goodness-of-fit score to the ground motion parameters at different stations, including the nearest one that is almost directly above the ruptured fault segments. The dynamic rupture models show good performance. We find that seismologically inferred earthquake asperities on a single fault plane can be expressed with two conjugate segments. The rupture transfer from one segment to another can generate a significant radiation; this could be interpreted as an asperity projected onto a single fault plane. This example illustrates the importance of the fault geometry that has to be taken into account when estimating the very-near-field ground motion.

    更新日期:2019-11-01
  • Spatial organization of seismicity and fracture pattern in NE Italy and W Slovenia.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    G Bressan,M Ponton,G Rossi,S Urban

    The study focuses on the spatial organization of seismicity and the relation between fracture pattern and earthquakes in the Friuli (north-eastern Italy) and western Slovenia seismic regions. The structural setting is characterized by a complex structure resulting from the superposition of several tectonic phases that generated NW-SE trending Dinaric faults and about E-W trending Alpine faults. The upper crust is characterized by lithological and mechanical heterogeneities. The fractal analysis shows that, in general, the seismicity only partially fills a plane. Only in a few cases, the earthquakes distribute on planar structures. The orientation of planes that fit through the hypocentres shows a different disposition at the two depth intervals analysed. The shallower interval (0-10 km) is characterized by planes with highly variable orientations. The spatial seismicity is investigated in the context of a general damage model, represented by the crack density distribution. The results evidence that the seismicity appears mostly located along sharp transition areas from low crack density to higher crack density, i.e., from zones of low damage to zones of intermediate damage. These zones are characterized by high heterogeneity due to the superposition of different tectonic phases and by the maximum interference between Dinaric and Alpine domains. The orientation of the planes fitting the seismicity at 10-20-km depth appears less dispersed, coinciding with the trend of Dinaric sub-vertical faults in the northern and eastern parts of the study area, and with Alpine low-angle faults in the western and southern parts.

    更新日期:2019-11-01
  • Ambient noise levels and detection threshold in Norway.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    Andrea Demuth,Lars Ottemöller,Henk Keers

    Ambient seismic noise is caused by a number of sources in specific frequency bands. The quantification of ambient noise makes it possible to evaluate station and network performance. We evaluate noise levels in Norway from the 2013 data set of the Norwegian National Seismic Network as well as two temporary deployments. Apart from the station performance, we studied the geographical and temporal variations, and developed a local noise model for Norway. The microseism peaks related to the ocean are significant in Norway. We, therefore, investigated the relationship between oceanic weather conditions and noise levels. We find a correlation of low-frequency noise (0.125-0.25 Hz) with wave heights up to 900 km offshore. High (2-10 Hz) and intermediate (0.5-5 Hz) frequency noise correlates only up to 450 km offshore with wave heights. From a geographic perspective, stations in southern Norway show lower noise levels for low frequencies due to a larger distance to the dominant noise sources in the North Atlantic. Finally, we studied the influence of high-frequency noise levels on earthquake detectability and found that a noise level increase of 10 dB decreases the detectability by 0.5 magnitude units. This method provides a practical way to consider noise variations in detection maps.

    更新日期:2019-11-01
  • Local seismic network for monitoring of a potential nuclear power plant area.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    Timo Tiira,Marja Uski,Jari Kortström,Outi Kaisko,Annakaisa Korja

    This study presents a plan for seismic monitoring of a region around a potential nuclear power plant. Seismic monitoring is needed to evaluate seismic risk. The International Atomic Energy Agency has set guidelines on seismic hazard evaluation and monitoring of such areas. According to these guidelines, we have made a plan for a local network of seismic stations to collect data for seismic source characterization and seismotectonic interpretations, as well as to monitor seismic activity and natural hazards. The detection and location capability of the network were simulated using different station configurations by computing spatial azimuthal coverages and detection threshold magnitudes. Background noise conditions around Pyhäjoki were analyzed by comparing data from different stations. The annual number of microearthquakes that should be detected with a dense local network centered around Pyhäjoki was estimated. The network should be dense enough to fulfill the requirements of azimuthal coverage better than 180° and automatic event location capability down to ML ∼ 0 within a distance of 25 km from the site. A network of 10 stations should be enough to reach these goals. With this setup, the detection threshold magnitudes are estimated to be ML = -0.1 and ML = 0.1 within a radius of 25 and 50 km from Pyhäjoki, respectively. The annual number of earthquakes detected by the network is estimated to be 2 (ML ≥ ∼ -0.1) within 25 km radius and 5 (ML ≥ ∼-0.1 to ∼0.1) within 50 km radius. The location accuracy within 25 km radius is estimated to be 1-2 and 4 km for horizontal coordinates and depth, respectively. Thus, the network is dense enough to map out capable faults with horizontal accuracy of 1-2 km within 25 km radius of the site. The estimation is based on the location accuracies of five existing networks in northern Europe. Local factors, such as seismic noise sources, geology and infrastructure might limit the station configuration and detection and location capability of the network.

    更新日期:2019-11-01
  • Characteristics of strong ground motions in the 2014 Ms 6.5 Ludian earthquake, Yunnan, China.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    J J Hu,Q Zhang,Z J Jiang,L L Xie,B F Zhou

    The 2014 Ms 6.5 (Mw6.1) Ludian earthquake occurred in the eastern Sichuan-Yunnan border region of western China. This earthquake caused much more severe engineering damage than the usual earthquakes with the same magnitude in China. The National Strong Motion Network obtained large set of ground motion recordings during the earthquake. To investigate the engineering interested characteristics of ground motion from Ludian earthquake and compare it with the Mw 7.9 Wenchuan and the Mw 6.6 Lushan earthquakes in western China, studies on the ground motion field, attenuation relationship, distance dependence of significant duration, and site amplification were carried out. Some conclusion is drawn. Specifically, the ground motion field reveals a directional feature, and the distribution characteristics of the two horizontal components are similar. The attenuation relationship for Ludian earthquake is basically consistent with the ground motion prediction equation (GMPE) for western China, except the slight smaller than the GMPE predicted at short periods. The distance dependences of ground motion duration are different in Sichuan and Yunnan regions due to the local physical dispersion and Q value. The site amplification factors are dominated by linear site response for lower reference ground motion, but the nonlinearity becomes notable for higher reference ground motion. This feature is basically consistent with the empirical model for western China. All the results indicate that the spatial distribution of ground motion, the attenuation characteristics, and the site amplification effect should be considered in characterization of near-field ground motion.

    更新日期:2019-11-01
  • A new significance on the vertical component ratio of the power spectra between two sites in the application of array methods.
    J. Seismol. (IF 1.494) Pub Date : 2017-02-14
    Xinrui Zhang,Hitoshi Morikawa

    Array methods like spatial auto-correlation (SPAC) method and the centerless circular array (CCA) method have provided a convenient means of inferring the phase velocity of surface waves. However, these methods are under the assumption of horizontally layered medium (lateral homogeneity) while the ground structure is actually likely to be inclined. Hence, it is expected to obtain more detailed information of ground structure such as inclination by making better use of the records. In recent years, the seismic interferometry theory has also been widely used to estimate ground structure. According to seismic interferometry theory, the cross correlation of motion between two sites is proportional to the imaginary part of the Green's function (IOG) between the two sites in diffuse wavefield. In this study, we can obtain the ratio of IOG between two sites by taking the ratio of power spectra between the same two sites. We propose this ratio as an indicator of the lateral heterogeneity between two sites. Through numerical simulation and a field test, we demonstrate that the significance of ratio of power spectra can be interpreted from the sight of ratio of IOG successfully.

    更新日期:2019-11-01
  • A risk-mitigation approach to the management of induced seismicity.
    J. Seismol. (IF 1.494) Pub Date : 2015-01-01
    Julian J Bommer,Helen Crowley,Rui Pinho

    Earthquakes may be induced by a wide range of anthropogenic activities such as mining, fluid injection and extraction, and hydraulic fracturing. In recent years, the increased occurrence of induced seismicity and the impact of some of these earthquakes on the built environment have heightened both public concern and regulatory scrutiny, motivating the need for a framework for the management of induced seismicity. Efforts to develop systems to enable control of seismicity have not yet resulted in solutions that can be applied with confidence in most cases. The more rational approach proposed herein is based on applying the same risk quantification and mitigation measures that are applied to the hazard from natural seismicity. This framework allows informed decision-making regarding the conduct of anthropogenic activities that may cause earthquakes. The consequent risk, if related to non-structural damage (when re-location is not an option), can be addressed by appropriate financial compensation. If the risk poses a threat to life and limb, then it may be reduced through the application of strengthening measures in the built environment-the cost of which can be balanced against the economic benefits of the activity in question-rather than attempting to ensure that some threshold on earthquake magnitude or ground-shaking amplitude is not exceeded. However, because of the specific characteristics of induced earthquakes-which may occur in regions with little or no natural seismicity-the procedures used in standard earthquake engineering need adaptation and modification for application to induced seismicity.

    更新日期:2019-11-01
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