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  • Peak Ground Motions and Site Response at Anza and Imperial Valley, California
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Jon B. Fletcher, John Boatwright

    Abstract Power spectra of shear-waves for eighteen earthquakes from the Anza-Imperial Valley region were inverted for source, mid-path Q, site attenuation and site response. The motivation was whether differences in site attenuation (parameterized as t*, r/cQ, where r is distance along ray path near the site, c is shear velocity and Q is the quality factor that parameterizes attenuation) and site response could be correlated with residuals in peak values of velocity or acceleration after removing the affect of distance-dependent attenuation. We decomposed spectra of S-waves from horizontal components of 18 earthquakes from 2010 to 2018 into a common source for each event with ω−2 spectral fall-off at high frequencies and then projected the residuals onto path and site terms following the methodology of Boatwright et al. (Bull Seismol Soc Am 81:1754–1782, 1991). The site terms were constrained to have an amplification at a particular frequency governed by VS30 at two of the sites which had downhole shear-wave logs. The 18 events, 3 < M < 4, had moments between approximately 1020 and 1022 dyne-cm, and stress drops between 1 and 100 bars. Average mid-crust attenuation had a Q of 844 reflecting the average path through the crystalline rock of the San Jacinto Mountains. t* for each station corresponded to the geologic environment such that stations on hard rock had low t* (e.g. stations KNW, PFO and RDM) a station in the San Jacinto fault zone (station SND) had a moderate t* of 0.035 s and stations in the Imperial Valley usually had higher t*s. Generally t* correlated with average amplification suggesting that sites characterized by low surface velocities and higher attenuation also have more amplification in the 1–6 Hz band. Residuals of peak values were determined by subtracting the prediction of Boore and Atkinson (2008). There is a correlation between average amplification and peak velocity, but not peak acceleration. Interestingly, there is less scatter at high values of amplification although there is also less data. Scatter in values of peak velocity and peak acceleration are higher at shorter compared to longer durations. When using a frequency-dependent form for Q, variances are higher, sometimes much higher; the dataset does not support frequency-dependent Q, which is not similar to results from the Imperial Valley and northeastern North America.

    更新日期:2020-01-15
  • Study of the PGV, Strong Motion and Intensity Distribution of the February 1969 (Ms 8.0) Offshore Cape St. Vincent (Portugal) Earthquake Using Synthetic Ground Velocities
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    C. Pro, E. Buforn, A. Udías, J. Borges, C. S. Oliveira

    The 28 February 1969 (Ms 8.0) Cape St. Vincent earthquake is the largest shock to have occurred in the region after the Lisbon earthquake of 1755. However, the study of the rupture process has been limited due to the characteristics of the available seismic data which were analogue records that were generally saturated at both regional and teleseismic distances. Indeed, these data consist of just one accelerograph record at the 25th April Bridge in Lisbon (Portugal) and the observed intensities in the Iberian Peninsula and northern part of Morocco. We have used these data to simulate the distribution of PGV (Peak Ground Velocity) for the 1969 event at regional distances (less than 600 km) by using a 3D velocity model. The PGV values are very important in seismic hazard studies. The velocity model and the methodological approach were tested by comparing synthetic and observed ground velocities at regional distances for two recent, well-studied earthquakes that occurred in this region, namely, the 2007 (Mw = 5.9) and the 2009 (Mw = 5.5) earthquakes. By comparing the synthetic and observed PGA (Peak Ground Acceleration) at Lisbon, the focal depth was estimated equal to 25 km and the seismic moment equal to 6.4 × 1020 N m (Mw = 7.8) for 1969 earthquake. With these parameters, PGV values were obtained for 159 sites located in the Iberian Peninsula and northern region of Morocco where we have felt intensity values. Using different empirical relations, the instrumental intensity values were calculated and compared with the felt intensities. As a result, the synthetic PGV values obtained in this study for the 1969 earthquake could be used as reference values, and the methodological approach would allow the PGV and intensity to be simulated for other events in the region.

    更新日期:2020-01-15
  • Present-day Tectonic Stress Field and GPS Observations in Hubei Province, Central China
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Yanjun Dong, Fanxi Liao, Dongzhen Wang, Chengchen Du, Kai He

    Here, we show the present-day tectonic stress field and regional GPS velocity and strain rate fields in Hubei Province, central China. Our results are calculated based on the digital observation data from 01 January 2010, to 31 December 2017, by using the seis-CAP, P-wave first motion, and grid search methods and the software GAMIT/GLOBK10.4. The results show that the P axis azimuths of focal mechanism solutions, the principal compressional stress field, and the regional velocity and strain rate fields are conformably compressional in a NW–SE direction. The regional stress shape ratio R values are relatively low, and the faults are dominantly compressive-shear or compresso-shear faults. The average velocity modulus value for the GPS observation stations in western Hubei is 6.1 mm/a, which is higher than that in eastern Hubei (5.4 mm/a). The average velocity modulus value in the Jianghan Basin interior is relatively low (4.4 mm/a), while that in the northwestern Jianghan Basin is higher (7.6 mm/a). The strain rate field is characterized by NW–SE compression accompanied by NE–SW tension. The results suggest that the present-day crustal movement in Hubei Province is mainly controlled by collisions with the Indian Plate in the west and the Philippine Plate in the east and the consequent crustal shortening induced by western Hubei wedging into the Jianghan Basin. Further, the resistance by the thrust-and-fold belt in eastern Hubei contributes to the principal compressional movement in the study area. The T axis azimuth of focal mechanism solutions is consistent with the principal extensional stress field direction. In the central and northern Jianghan Basin, the R values are relatively high, the faults are mainly transtensional, and the crustal deformation is mainly extensional, which may be affected by the denudation, thinning and rapid rebound of the Dabie Orogen, resulting in tectonic extrusion and flow in the Jianghan Basin to both the NE and SW sides.

    更新日期:2020-01-15
  • New Updated World Maps of Sea-Surface Salinity
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Aleksandar Valjarević, Dejan Filipović, Miško Milanović, Dragana Valjarević

    Sea surface salinity presents one of the most important chemical elements in the water. Climatic variables, included in new view of salinity distribution at a global scale, were used in this research. For the purpose of this research newly updated climate parameters for the period until 2100 were used along with (CMIP5) climatological model. The new distribution of surface salinity may show water desalination and energy potential. This map can be useful in the determination of new littoral areas or for fishermen’s routes. These data are presented in geo-tiff raster extension with the resolution of 0.1. This map could be updated with climatological parameters with obtained medium climate change effects. Some places in the world sea have low, some have high salinity. Salinity increases in accordance with the increase of precipitation and decreases with the decrease of it. The paper presents following maps; salinity world map when there is no climate change; the moderate one, if the temperature increases for 2.0 °C until 2100, and high if the increase of temperature was between 2.0 °C and 5.0 °C. The three scenarios were taken to show updated maps of world salinity in comparison with climate change effects.

    更新日期:2020-01-15
  • Statistical Method of Forecasting of Seasonal Precipitation over the Northwest Himalayas: North Atlantic Oscillation as Precursor
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Usha Devi, M. S. Shekhar, G. P. Singh, S. K. Dash

    Abstract Dynamical and Statistical models are operationally used by Snow and Avalanche Study Establishment (SASE) for winter precipitation forecasting over the Northwest Himalayas (NWH). In this paper, a statistical regression model developed for seasonal (December–April) precipitation forecast over Northwest Himalaya is discussed. After carrying out the analysis of various atmospheric parameters that affect the winter precipitation over the NWH two parameters are selected such as North Atlantic Oscillation (NAO) and Outgoing Long wave Radiation (OLR) over specific areas of North Atlantic Ocean for the development of statistical regression model. A set of 27 years (1990–1991 to 2016–2017) of observed precipitation data and parameters (NAO and OLR) are utilized. Out of 27 years of data, first 20 years (1990–1991 to 2009–2010) are used for the development of regression model and remaining 7 years (2010–2011 to 2016–2017) are used for the validation purpose. Precipitation over NWH mainly associated with Western Disturbances (WDs) and the results of the present study reveal that NAO during SON has negative relationship with WDs and also with the winter precipitation over same region. Quantitative validation of the multiple regression model, result shows good Skill Score and RMSE-observations standard deviation ratio (RSR) which is 0.79 and 0.45 respectively and BIAS − 0.92.

    更新日期:2020-01-15
  • Improvement of the Efficiency of Time-Domain Electromagnetic Measurement
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Chong Liu, LiZhen Cheng, Xueping Dai, Mamadou Cherif Diallo

    The long-term sustainable development of mineral exploration under covers require effective deep detection techniques and methods. Start from enhancing the surface-borehole time-domain electromagnetic (TEM) technique, the present study established a new relationship between the pulse width (Δ), the target time constant (τ) and the measurement time (t). Under certain conditions, the new formula has been extended to all TEM systems that use square or trapezoidal waveforms. A series of numerical simulations illustrate the consistent behaviors of the surface-borehole, ground and airborne TEM fields. The new relationship allows us to evaluate optimal pulse widths for different off-times and to help TEM survey design.

    更新日期:2020-01-15
  • Utilizing the Geophysical and Hydrogeological Data for the Assessment of the Groundwater Occurrences in Gallaba Plain, Western Desert, Egypt
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Sayed Mosaad, Alhussein Adham Basheer

    Abstract The investigated region is located in the western desert fringes of the Nile Valley which requires studies of groundwater related to the many projects of land reclamation. The key objective of this paper is to estimate the qualitative and geometrical features of the investigated aquifer. Using 60 vertical electrical sounding and time-domain electromagnetic soundings allows us to suggest one possible model of the geometrical features of the local aquifer. A hydrogeological monitoring has been undertaken to investigate the current groundwater situation at the Gallaba plain. Such hydrological monitoring has not been undertaken before in detail. The results show that the investigated region has high groundwater potentialities in two main aquifers which belong to Pleistocene: shallow fresh water and deep brackish water. The lithological and structural elements contribute mainly to recharge and store the groundwater in the western part of the River Nile in Kom Ombo graben. The geochemical properties of the groundwater of the studied aquifers reflect meteoric water, which is a fresh to slightly brackish water. The small amount of groundwater salinity arises from silicate weathering and evaporation processes occurring in the aquifer matrix. Moreover, most of the studied groundwater samples are unfit for human consumption. Such samples are very satisfactory for livestock and poultry purposes and they can be used for irrigation using modern and improved irrigation methods e.g. sprinkler and drip methods. Furthermore, the hydrogeological monitoring of the concerned area indicates that it has high groundwater potentialities which will support its sustainable development.

    更新日期:2020-01-15
  • The Subsurface Structure on the CE-3 Landing Site: LPR CH-1 Data Processing by Shearlet Transform
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Ling Zhang, Bin Hu, Zhuo Jia, Yi Xu

    Abstract The Lunar penetrating radar (LPR) carried by Chang’E-3 (CE-3) mission is an important application of radar in lunar exploration. An opportunity of significance to detect the information of regolith and the subsurface structure on the landing site is offered by LPR aboard the Yutu rover. On the basis of a data processing flow, a low-frequency radar image has been available for mapping subsurface structure. The noise interfered data give a huge challenge for geological stratification and interpretation. To solve the limitation imposed by noise, we adopt the shearlet transform as a promising tool for data analysis and noise attenuation. The different distributions of the noise and signal in the shearlet domain decrease the difficulty of noise attenuation. To optimize the denosing strategy, we replace a local adaptive thresholding function with the conventional hard threshold. The quality of the processed data is improved, which is helpful for geological stratification and interpretation. Finally, by combining these data with the regional geology and previous research, especially the LPR data, we can provide an interpretation of the LPR CH-1.

    更新日期:2020-01-15
  • Machine Learning Using U-Net Convolutional Neural Networks for the Imaging of Sparse Seismic Data
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-15
    Jiayuan Huang, Robert L. Nowack

    Machine learning using convolutional neural networks (CNNs) is investigated for the imaging of sparsely sampled seismic reflection data. A limitation of traditional imaging methods is that they often require seismic data with sufficient spatial sampling. Using CNNs for imaging, even if the spatial sampling of the data is sparse, good imaging results can still be obtained. Therefore, CNNs applied to seismic imaging have the potential of producing improved imaging results when spatial sampling of the data is sparse. The imaged model can then be used to generate more densely sampled data and in this way be used to interpolate either regularly or irregularly sampled data. Although there are many approaches for the interpolation of seismic data, here seismic imaging is performed directly with sparse seismic data once the CNN model has been trained. The CNN model is found to be relatively robust to small variations from the training dataset. For greater deviations, a larger training dataset would likely be required. If the CNN is trained with a sufficient amount of data, it has the potential of imaging more complex seismic profiles.

    更新日期:2020-01-15
  • The Role of Atmospheric Processes Associated with a Flash-Flood Event Over Northwestern Turkey
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Hakki Baltaci

    This study investigates the atmospheric mechanisms triggering flash-flood event in Thrace Basin of Turkey on November 27, 2018. Underestimation of this extreme precipitation amounts by NWP global and regional models (i.e. ECMWF, ALARO, WRF) and other meteorological difficulties (i.e. complex topography, land-sea interactions) in weather forecasting disabled disaster risk reduction before the event occurred. Detailed synoptic, thermodynamic, in-situ, and remote sensing analyzing results showed that significant amount of moisture during the afternoon times of the day was transferred to the atmosphere (from ground to 300-hPa) as a consequence of the excessive heating of sea surface temperatures (SSTs) of the Aegean Sea (16.5 °C in Ayvacik-Gulpinar place, 0.9 °C above its long-term normals). Strong southwesterly wind speeds associated with slow meridional movement of mid-latitude cyclone from its origin to the Eastern Mediterranean (EM) enabled transferring of relatively warm moist air to the land areas of Thrace Region (> 300 km fetch distance). Strong updraft and instability conditions under developed a supercell resulted with lightning (totally 63 cloud-to-ground and 59 intra cloud) and heavy rainfall especially Suloglu, Kofcaz, and Edirne settlements with the 12-hour total amounts 160.0, 123.0, and 97.4 mm (rainfall return period ~ 100 years), respectively. Flash-flood event caused numerous injuries and the death of a person and damaged, automobiles, houses, crops, and infrastructure of the Edirne and its neighboring settlements. From Showalter, K, Total of Totals, SWEAT, and CAPE instability indices; SWEAT is most appropriate to represent high possibility of occurrence of severe thunderstorms over the Edirne province owing to low-level moisture, warm air advection and low and mid-level wind speed terms in its equation.

    更新日期:2020-01-08
  • Closed-Form Expressions of Plane-Wave Reflection and Transmission Coefficients at a Planar Interface of Porous Media with a Normal Incident Fast P-Wave
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Dongyong Zhou, Xingyao Yin, Zhaoyun Zong

    Abstract A porous medium is composed of a rock skeleton and pore fluids, and seismic wave propagation in it will produce complex and diverse variations influenced by pores and fluids filling. It is very important to carry out the study of closed-form expressions of the plane-wave reflection and transmission coefficients at a planar interface between porous media for analyzing the properties of pores and its fluids and eventually revealing underground oil-bearing reservoirs. In this paper, based on the relationships among seismic wave functions, displacements and stresses in porous media, an exact equation of plane-wave reflection and transmission coefficients with a normal incident fast P-wave is first derived. Considering the characteristics of the parameters in a coefficient matrix of an exact equation, the closed-form expressions with clear geophysical meaning are further derived, which include three parts, the rock skeleton term, the fluid–solid coupling term and the pore fluid term. Through the establishment of two porous media models, the influence of each term in the approximate expression on the reflection characteristics of a fast P-wave is analyzed. Different approximate expressions of the reflection coefficient of a fast P-wave can be selected for oil and gas prediction of different reservoirs, which lays a foundation for the identification of gas, oil and brine.

    更新日期:2020-01-08
  • Frequency-Domain Finite-Difference Elastic Wave Modeling in the Presence of Surface Topography
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Zhencong Zhao, Jingyi Chen, Xiaobo Liu

    Seismic numerical modeling in the presence of surface topography has become a valuable tool to characterize seismic wave propagation in basin or mountain areas. Regarding advantages of frequency-domain seismic wavefield simulations (e.g., easy implementation of multiple sources and straightforward extension of adding attenuation factors), we propose a frequency-domain finite-difference seismic wavefield simulation in 2D elastic media with an irregular free surface. In the frequency domain, we first transform second-order elastic wave equations and first-order free surface boundary conditions from the Cartesian coordinate system to the curvilinear coordinate system. Then we apply complex frequency-shifted perfectly matched layer (CFS-PML) absorbing boundary condition to second-order elastic wave equations in the curvilinear coordinate. To better couple free surface boundary conditions and CFS-PML absorbing boundary condition, we also apply the complex coordinate stretching method used in CFS-PML to free surface boundary conditions in the curvilinear coordinate. In the first numerical test, the comparison of the seismograms calculated by our algorithm with an analytical solution indicates that our algorithm can accurately simulate seismic wavefield in the frequency domain. Finally, we choose three more elastic models with different types of surface topographies to further characterize seismic wave propagation.

    更新日期:2020-01-08
  • Spatio-temporal Analysis of Precipitation and Temperature: A Case Study Over the Beijing–Tianjin–Hebei Region, China
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Baohui Men, Zhijian Wu, Huanlong Liu, Wei Tian, Yong Zhao

    Climate change have a profound impact on the production and life of the people in the Beijing–Tianjin–Hebei region. Precipitation and temperature are regarded as two basic components of climate. This study investigated the spatial and temporal characteristics of precipitation and temperature over the region from 1960 to 2013. Different methods were used to analyze temporal variation and the results are mutually verified. Wavelet analysis was adopted to analyze the abrupt changes of precipitation and temperature. Empirical orthogonal function decomposition method was utilized to analyze the spatial distribution of temperature and precipitation. The study yielded three major findings: First, the inter-annual decrease and increase of precipitation appeared alternately in the region. Temperature was rising significantly in the last 50 years, apart from a slow reduction in the late 1970s. Second, the spatial distribution characteristics of precipitation vary due to the distance from the ocean. The increasing trend of temperature in Beijing-centered region was more obvious than that in areas away from the sea. Third, precipitation and temperature show strong correlations in change. When temperature increased, the rainfall decreased. What is more, when the temperature mutated, the precipitation also changed rapidly. The results can guide local agriculture production and provide reference for the further study of climate change.

    更新日期:2020-01-08
  • Radiological Impact and Environmental Monitoring of Gamma Radiations Along the Public Beach of Port Said, Egypt
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Akram Aziz, Tamer Attia, Mahmoud Hanafi

    Abstract Port Said is an Egyptian coastal city, laying on Mediterranean Sea. The city is a world-renowned international harbor and a free-trade zone. Therefore, it is one of the most popular shopping destinations in Egypt, where people can buy duty-free goods and enjoy the city’s free public beaches in summer vacations. Recent radiological hazards studies had located several high radioactive lenses along the Nile Delta coastline, resulted from accumulations of black sand deposits. Concerns had been raised regarding the safety of individuals who might be exposed to high doses of radiations due to the presence of black sand deposits along Port Said beach, especially when the beach is characterized by positive accretion rates. Detailed ground radioactivity surveys were conducted at the beach aiming to measure the activity concentrations of the naturally occurring radioelements (238U, 232Th and 40K). Spatial distributions of the three elements were mapped. Dose Rate (DR) and Annual Effective Dose Rates (AEDR) were calculated. Although the results of AEDR revealed that the radiations levels are fallen within the allowed limits, the Excess Lifetime Cancer Risk (ELCR) factor exceeded the world’s average of 0.25. For public awareness, high-risk areas were delineated on a risk map, showing the locations where gamma radiation emissions exceeded the allowed exposure limits for humans. It is recommended to apply the same surveying procedures at all of the public beaches along Sinai coasts, where larger quantities of Black Sands had been detected along its shoreline.

    更新日期:2020-01-08
  • Correlation of a 410-km Discontinuity Low Velocity Layer with Velocity Tomograms Beneath the Colorado Plateau Using the RISTRA Array
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Zhu Zhang, Kenneth G. Dueker

    The transition zone water filter model (Nature 425(6953), 39–44; 2003) predicts that a hydrous partial melt layer is only actively produced in a region of upwelling mantle. We test the transition zone water filter model via stacking of P-to-S converted receiver functions by using the IRIS-PASSCAL RISTRA (Colorado Plateau/Rio Grande Rift Seismic Transect Experiment) array. Assuming the high velocity regions found at the northwest and southeast ends of the array at 350–440 km by teleseismic velocity tomograms e.g. Schmandt and Humphreys (Earth and Planetary Science Letters 297(3–4): 435–445; 2010) are cold and sinking vertically, the 410-km low velocity layer should be absent in these regions. The receiver function stacking profiles find the mean depths of the two primary discontinuities at 417 ± 7.1 km for the 410-km discontinuity and 667 ± 8.2 km for the 660-km discontinuity. The average arrival amplitudes with respect to Z component are 3.0% for the 410-km discontinuity, 2.8% for the 660-km discontinuity, and − 1.8% for the 410-km low velocity layer. The stacked Pds image show the 410-km low cabsent at ~ 350 to 390 km in the high velocity regions, but present in low velocity region. A correlation plot of sum of the 410-km low velocity arrival amplitudes and P-wave perturbation finds a positive linear relationship. Therefore, our findings provide seismic evidence for the transition zone water filter model at a small scale.

    更新日期:2020-01-08
  • Megathrust Locking and Viscous Mantle Flow Induce Continental Shortening in Central Andes
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-08
    Fuqiang Shi, Shaoyang Li, Marcos Moreno

    Abstract Crustal faults at subduction zones show evidence of activity over geological time, but at the scale of earthquake cycle the mechanical behavior of these faults is not fully understood. Here we construct 2-D viscoelastic models constrained by both horizontal and vertical GPS-derived interseismic velocities to investigate the contribution and interrelation between subduction zone locking, viscous mantle flow, and upper plate faulting on surface deformation in Central Andes. Main pattern of horizontal velocities can be explained by a combination of locking degree and viscous flow, whereas vertical signal is found essential for estimating the locking depth. A sharp deformation gradient near the major back-arc fault suggests an active interseismic shorting across this structure. We further conduct mechanical viscoelastic models with a frictional back-arc fault to analyze its displacement and activation conditions. Our results suggest that the back-arc fault is creeping at ~ 3 mm/year and its motion is mainly driven by the interseismic viscous mantle flow, which spreads plate tectonic stresses broadly across the continent. Moreover, the frictional strength of the back-arc fault must be remarkably weak and its mechanics re-distributes the interseismic deformation and shortens the continental plate in Central Andes. Geological estimates suggest that the long-term shortening rate at the back-arc fault is ~ 10 mm/year, suggesting that this structure can accumulate ~ 7 mm/year of slip deficit, confirming the seismic potential of this structure.

    更新日期:2020-01-08
  • Using GPR Data as Constraints in RMT Data Inversion for Water Content Estimation: A Case Study in Heby, Sweden
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2020-01-03
    Mehdi Mohammadi Vizheh, Behrooz Oskooi, Mehrdad Bastani, Thomas Kalscheuer

    This study uses ground penetrating radar (GPR) data as constraints in the inversion of radio-magnetotelluric (RMT) data, to provide an improved model at shallow depth. We show that modification of the model regularization matrix using all GPR common-offset (CO) reflections can mislead the constrained inversion of RMT data. To avoid such problems, common mid-point (CMP) GPR data are translated to a resistivity model by introducing a new petrophysical relationship based on a combination of Topp’s and Archie’s equations. This model is updated through a semi-iterative method and is employed as an initial and prior model in the subsequent inversion of RMT data. Finally, a water content model that fits the GPR CMP and RMT data is derived from the resistivity model computed by the constrained inversion of RMT data. To assess the proposed scheme, it is applied to a synthetic data set. Then, real RMT data collected along an 870 m-long profile across a known aquifer situated in the north of Heby, central Sweden, are inverted. By removing the smoothness constraints across GPR CO interfaces or using CMP-based inversion, thick (> 10 m) vadose and saturated zones are resolved and shown to correlate with logs from nearby boreholes. Nevertheless, the application of our CMP-based inversion was the only efficient scheme to retrieve thin (~ 3 m) saturated zones and the water table at a depth of 7–15 m in the RMT models. The estimated models of water content are in good agreement with the available hydrogeological information in the study area.

    更新日期:2020-01-04
  • Enhancement and Sharpening the Migration Images of the Gravity Field and Its Gradients
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-23
    Xiaolei Tu, Michael S. Zhdanov

    Potential field migration represents a rapid technique for imaging the subsurface based on gravity data. However, migration transformation usually produces a smooth and unfocused image of the targets due to the diffusive nature of the potential fields. In this paper, we introduce a method of the migration image enhancement and sharpening based on the application of the hybrid focusing stabilizer, which combines the edge-preserving smoothing filter with the minimum support functional. The method is based on the model resolution matrix of the migration operator. We also improve the migration image with a novel target-oriented migration method. The developed method of migration image enhancement and sharpening is illustrated by synthetic model studies and case studies. The case study involves imaging the full tensor gravity gradient data collected in the Nordkapp Basin of the Barents Sea.

    更新日期:2020-01-04
  • Comment on the Paper “Seismic Hazard Analysis of Surface Level, Using Topographic Condition in the Northeast of Algeria” by Mouloud Hamidatou, Mohammedi Yahia, Abdelkrim Yelles-Chaouche, Itharam Thallak, Dietrich Stromeyer, Saad Lebdioui, Fabrice Cotton, Nassim Hallal and Omar Khemici
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-20
    Mohamed Hamdache, José A. Peláez

    Abstract We would like to make some comments on the paper by Hamidatou et al. (2019). Initially, these comments are motivated to reveal that, previous results on probabilistic seismic hazard analyses, some of them computed and published by our research group, are wrongly quoted in the paper by these authors. In our opinion, some other points are worthy of debate, mainly, but not only, the used seismic source zone model, the used logic-tree, and also the comparison of estimated values of peak ground horizontal acceleration (PGA) with previous results.

    更新日期:2020-01-04
  • The December 22, 2018 Anak Krakatau, Indonesia, Landslide and Tsunami: Preliminary Modeling Results
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-20
    Alexandre Paris, Philippe Heinrich, Raphaël Paris, Stéphane Abadie

    On the evening of December 22, 2018, the coasts of the Sunda Strait, Indonesia, were hit by a tsunami generated by the collapse of a part of the Anak Krakatau volcano. Hundreds of people were killed, thousands were injured and displaced. This paper presents a preliminary modeling of the volcano flank collapse and the tsunami generated based on the results of a 2D depth-averaged coupled model involving a granular rheology and a Coulomb friction for the slide description and dispersive effects for the water flow part. With a reconstructed total volume (subaerial and submarine) of the landslide of 150 million \(\hbox {m}^{3}\) inferred from pre and post-collapse satellite and aerial images, the comparison of the simulated water waves with the observations (tide gauges located all around the strait, photographs and field surveys) is satisfactory. Due to the lack of information for the submarine part of the landslide, the reconstructed submarine slope is assumed to be approximately constant. A significant time delay on the results and particularly in the Bandar Lampung Bay could be attributed to imprecisions of bathymetric data. The sensitivity to the basal friction and to dispersive effects is analyzed through numerical tests. Results show that the influence of the basal friction angle on the simulated wave heights decreases with distance and that a value of \(2^{\circ }\) gives consistent results with the observations. The dispersive effects are assessed by comparing water waves simulated by a shallow water model and a Boussinesq model. Simulations with frequency dispersion produce longer wave periods and smaller wave amplitudes in the Sunda Strait and particularly in deep waters.

    更新日期:2020-01-04
  • A Major Hydrothermal Reservoir Underneath the Tatun Volcano Group of Taiwan: Clues from a Dense Linear Geophone Array
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-20
    C. H. Lin, Y. C. Lai, M. H. Shih, C. J. Lin, J. S. Ku, Y. C. Huang

    A dense linear geophone array is deployed across the Tatun volcano group (TVG) at the northern tip of Taiwan, where more than 7 million residents live in the Taipei metropolis. The array is composed of 50 geophones with a station spacing of ~ 200 m in average, and it is designed for striking in the NW–SE direction to record the many earthquakes in eastern Taiwan, where the Philippine Sea plate subducted beneath the Eurasia plate. The detailed examination of felt earthquakes shows consistent P-wave delays are recorded at particular stations of the array. The further forward modeling indicates there is a low-velocity zone (LVZ) at depths between ~ 0.5 and ~ 2.5 km beneath the major fumarole sites. Combining this preliminary result with previous studies including clustering seismicity, volcanic earthquakes, low-resistivity zone, strong degassing processes and shallow velocity structures, we suggest that the LVZ might be associated with the major hydrothermal reservoir at the TVG. The identification of the hydrothermal reservoir by the LVZ not only implies a potential volcanic threat, such as phreatic eruptions, in the future, but also provides the possibility of sustainable geothermal resources for replacing traditional nuclear and fossil fuel power plants. Detailed images of the LVZ and other volcanic structures will be obtained soon when dense geophone arrays with more than 600 geophones are deployed from 2020 to 2022.

    更新日期:2020-01-04
  • Fractal Analysis of Data from Seismometer Array Monitoring Virgo Interferometer
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-18
    Alessandro Longo, Stefano Bianchi, Wolfango Plastino, Bartosz Idźkowski, Maciej Suchiński, Tomasz Bulik

    Abstract The local Hurst exponent H(t) has been computed for an array of 38 seismometers, deployed at the Virgo West End Building for Newtonian Noise characterisation purposes. The analysed period is from January 31st, 2018 to February 5th, 2018. The Hurst exponent H is a fractal index quantifying the persistent behaviour of a time series, higher H corresponding to higher persistency. The adopted methodology makes use of the local Hurst exponent computed using small sliding windows, in order to characterise the properties of the seismometers. Hourly averages and averages of H(t) have been computed over the whole analysed period. Results show that seismometers placed on a concrete slab closer to the centre of the room systematically exhibit higher persistency than the ones that are not placed on it. Seismometers placed next to the outer walls also exhibit higher persistency. The seismometer placed on a thin metal plate exhibits instead very low values of persistency during the analysed period, compared to the rest of the array.

    更新日期:2020-01-04
  • Towards Improved Probabilistic Seismic Hazard Assessment for Bangladesh
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-18
    Dewan Mohammad Enamul Haque, Nawar Wadud Khan, Md. Selim, A. S. M. Maksud Kamal, Sara Hanan Chowdhury

    Abstract This study aims to build on the existing knowledge and improve the overall PSHA results by modifying source, path and site characteristics for Bangladesh. Firstly, six potential seismotectonic zones have been re-defined based on the recent study of Wang et al. (J Geophys Res Solid Earth 119:3576–3822, 2014) and Nath and Thingbaijam (J Seismol 15(2):295–315, 2011), and the updated earthquake catalogue has been declustered using two methods. Important source parameters, such as recurrence b-values and maximum magnitudes, have been determined using the Maximum Likelihood and cumulative moment methods, respectively, and their uncertainties have been addressed using a logic-tree approach. Secondly, based on literature review and studies in neighboring countries, suitable GMPEs have been selected for the seismic zones and the uncertainties have been addressed using a logic tree approach. A significant novelty of the study lies in the consideration of the site effects by integrating Vs30 values throughout the country. The ground motions—PGA and SA (at 0.2, 1.0 and 2.0 s) are computed using GEM’s OpenQuake and presented in form of hazard maps for 2% and 10% probabilities of exceedance in 50 years as well as mean hazard curves and uniform hazard spectra. Disaggregation for capital city Dhaka has also been carried out to show the hazard contributions of magnitude–distance pairs. The spatial distribution of PGA and SA are found remarkably higher than previous findings, likely due to differences in parameters and uncertainties. The results show a marked increase (by almost 20%) in the observed ground motions with respect to those carried out previously by uniformly characterizing the whole country as a firm rock.

    更新日期:2020-01-04
  • The 1674 Ambon Tsunami: Extreme Run-Up Caused by an Earthquake-Triggered Landslide
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-17
    Ignatius Ryan Pranantyo, Phil R. Cummins

    We present an analysis of the oldest detailed account of tsunami run-up in Indonesia, that of the 1674 Ambon tsunami (Rumphius in Waerachtigh Verhael van de Schuckelijcke Aerdbebinge, BATAVIA, Dutch East Indies, 1675). At 100 m this is the largest run-up height ever documented in Indonesia, and with over 2300 fatalities even in 1674, it ranks as one of Indonesia’s most deadly tsunami disasters. We consider the plausible sources of earthquakes near Ambon that could generate a large, destructive tsunami, including the Seram Megathrust, the South Seram Thrust, and faults local to Ambon. We conclude that the only explanation for the extreme run-up observed on the north coast of Amon is a tsunami generated by an earthquake-triggered coastal landslide. We use a two-layer tsunami model to show that a submarine landslide, with an approximate volume of 1 km3, offshore the area on Ambon’s northern coast, between Seith and Hila, where dramatic changes in coastal landscape were observed can explain the observed tsunami run-up along the coast. Thus, the 1674 Ambon tsunami adds weight to the evidence from recent tsunamis, including the 1992 Flores, 2018 Palu and Sunda Strait tsunamis, that landslides are an important source of tsunami hazard in Indonesia.

    更新日期:2020-01-04
  • Precursory Behavior of Groundwater Radon in Southeastern Taiwan: Effect of Tectonic Setting in the Subduction Zone
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-17
    T. Kuo, W. Chen, C. Lewis, C. Ho, H. Kuochen

    Abstract Monitoring precursory decline in groundwater radon at the Antung hot spring is a useful means of forecasting the magnitude and precursor time of local disastrous earthquakes. With the help of a case study in southeastern Taiwan, this paper demonstrates the effect of tectonic setting in the subduction zone on the correlation between radon decline, precursory time and earthquake magnitude. Given a radon-monitoring site located near the plate boundary in the tectonic setting of advanced arc-continental collision, the observed radon decline and precursory time prior to the earthquakes in the tectonic setting of initial arc-continental collision are smaller than those observed prior to the earthquakes occurring on the plate boundary in the tectonic setting of advanced arc-continental collision. In the advanced arc-continental collision state, the coupling between the plates is strong and the stress transfer is efficient, whereas in the incipient collision state, the coupling and stress transfer are not as good. It also takes additional time lag and attenuation for the stress transfer from one tectonic setting to the other. This paper presents the difference in the precursory behavior of groundwater radon between earthquakes which occurred in two different tectonic settings: advanced and initial arc-continental collision.

    更新日期:2020-01-04
  • Continental Earthquakes: Physics, Simulation, and Data Science—Introduction
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-17
    Zhongliang Wu, Yongxian Zhang, Thomas H. W. Goebel, Qinghua Huang, Charles A. Williams, Huilin Xing, John B. Rundle

    During May 12–14, 2018, the International Conference for the Decade Memory of the Wenchuan Earthquake, in connection to the 4th International Conference on Continental Earthquakes (4th ICCE) and the 12th General Assembly of the Asian Seismological Commission (ASC), was held in Chengdu, China. There have been several outcomes of the Conference (for example, the book published jointly by Higher Education Press and Springer) as well as the present special issue. Among the 58 submissions, 34 have been accepted after peer review. Some of the papers came from the presentations during the Conference, but with additional submissions, the scope of this special issue is far beyond that of the proceedings of the meeting.

    更新日期:2020-01-04
  • A Reappraisal of Seismicity Recorded During the 1996 Gjálp Eruption, Iceland, in Light of the 2014–2015 Bárðarbunga–Holuhraun Lateral Dike Intrusion
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-16
    K. I. Konstantinou, I. Wahyu Utami, D. Giannopoulos, E. Sokos

    Abstract This study performs a reanalysis of the seismicity recorded during the 1996 Gjálp eruption that occurred at NW Vatnajökull, Iceland. The seismicity was recorded by the temporary HOTSPOT network consisting of 30 three-component broadband stations. In total 301 events were identified between 29 September and 12 October and their phases were manually picked. A velocity model was estimated from P-phase travel times by using VELEST. Events were first located using the algorithm NONLINLOC in order to obtain absolute locations. Precise relative locations were obtained with HYPODD by utilizing catalog and cross-correlation differential travel times. Results show that events clustered first along the SW rim of the Bárðarbunga caldera and later along the Gjálp fissure, with most hypocentral depths located between 3 and 8 km. Waveforms of the 10 largest events that followed the Bárðarbunga earthquake were inverted in order to obtain moment tensors. For all events we found that the deviatoric moment tensor fits the data better than pure double-couple or full moment tensor solutions. Events along the Bárðarbunga caldera exhibited reverse focal mechanisms, while those at the Gjálp fissure exhibited mostly strike-slip faulting. Seismic velocity variations calculated using ambient noise interferometry, point to the possibility that a small subglacial eruption occurred at Bárðarbunga before the main earthquake. This removed melt from the magma chamber causing its roof to collapse, and also resulted in the lateral migration of magma towards the Gjálp fissure. The 2014–2015 Bárðarbunga–Holuhraun eruption shares common characteristics with the 1996 Gjálp eruption, although the size of the latter was much smaller.

    更新日期:2020-01-04
  • Estimation of Hypocentral Parameters of Regional Earthquakes Using a Fuzzy Logic Approach
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-16
    Hüseyin Gökalp

    Abstract This study presents improvements on the hypocentral location method using the fuzzy logic approach proposed by Lin and Sanford (Bulletin of the Seismological Society of America 91:82–93, 2001) in resolving regional earthquakes location. In addition to trying to determine epicentral parameters of the earthquake, focal depths are also attempted utilizing this method in a three-dimensional (3D) space. In this study, instead of P- and S- wave models, a trapezoidal membership function constructed by the direct use of travel time difference between the two stations for P- and S- arrival times was utilized. In this procedure, it is not necessary to precisely know the velocity structure of the studied area in order to map the uncertainties in arrival-times into the fuzzy logic space. The location determination process was performed with the defuzzification of only the grid points having the membership value of 1 obtained by normalizing all the maximum fuzzy output values of the highest values which gives more reliable epicentral locations for both real and synthetic earthquakes. The results show that this method for epicentral estimation works well if the depth of the earthquake is sufficiently shallow and according to the distance between the event and seismic network. In this method of hypocenter determination, firstly, epicenter coordinates are determined, then the hypocenter location is found by considering only the epicentral area in 3D. In the case of very shallow events (e.g., h < 10 km), the estimation of the focal depth using this method seems to fail, causing faulty results in the hypocenter coordinates; however, the estimation of epicentral coordinates is successful in giving a more reasonable epicentral location. Otherwise, the obtained results would be reversed. Consequently, the deeper the focal depth, the better the hypocenter location, but a worse epicenter determination. This method is only valid in the hypocentral location of the earthquake occurring in the upper crust because only primarily the arrivals of Pg and Sg on the seismograms and a half-space velocity model are used. The hypocenter locations of some selected shallow earthquakes that occurred in the south east of the Aegean Sea have been determined by this method with results that are highly comparable with those obtained by other seismic agencies.

    更新日期:2020-01-04
  • Gutenberg–Richter’s b Value and Earthquake Asperity Models
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-16
    Piotr Senatorski

    The Gutenberg–Richter (G–R) relationship can be derived as the Gibbs distribution. For a given earthquake set (all earthquakes in a given region, time period, magnitude range, tectonic settings) the Gibbs probability density function for magnitudes, with a given b value in its exponent, is the most uniform distribution under the constraints of the magnitude range and mean value. Therefore, it represents our limited knowledge about the system output: the only pieces of information are the mean value and the magnitude range. Honest earthquake forecasts can be based on such a distribution, since it represents all and only available information about the seismic system. The b value can change among different earthquake sets (in time, space, magnitude ranges, or tectonic settings), since it is related to earthquake rupture dynamics, or seismic source characteristics. The relationship between the b value and the exponent \(\beta\) in the rupture area vs. maximum slip scaling, \(A\propto D^{\beta }\), results from viewing earthquake recurrence time in connection with the slip budget. This makes a link between earthquake statistics (the G–R law) and physics (fault characteristics). Specifically, the relationship enables us to explain different ranges of b values at megathrust faults, in dependence on interplate asperity and coupling distributions, as well as on amounts of sediments and fluids in subduction channels. The approach differs from common interpretations of the G–R law in that the b value becomes a field variable, not a constant. It is always the Gibbs distribution for a given magnitude range that we use due to our ignorance about the system outcome, and it is the b value that variates, depending on our knowledge about the system physics. This is important for seismic forecasts, which are mostly based on the G–R relationship. First, because the physical processes leading to the largest earthquakes can be revealed by observing the b value variations. Second, because earthquake generation process can be thought of as sampling with constraints, where the b value and the magnitude range are the constraints.

    更新日期:2020-01-04
  • The Tsunami Inundation Hazard of the Maltese Islands (Central Mediterranean Sea): A Submarine Landslide and Earthquake Tsunami Scenario Study
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-16
    Christof Mueller, Aaron Micallef, Daniele Spatola, Xiaoming Wang

    The tsunami hazard for the Maltese Islands is poorly defined, and historic records are available for only two recent events. Most of the population and touristic infrastructure of the archipelago is concentrated along the eastern low-lying coastline, which is exposed to tsunamis from near-field and far-field sources. In this study we present a scenario-based tsunami inundation study to assess the impact of potential significant cases. We simulated four scenarios—two submarine landslide sources (outer Malta Plateau slide and Gela Basin slide) and two earthquake sources mimicking events comparable to the 365 A.D. western Hellenic Arc event and the 1693 south-east of Sicily event. We find that all scenarios cause inundation in densely populated low-lying bays or rias of Mellieha Bay, Xemxija, Salini, Gzira, Msida, Marsaskala, St Thomas Bay, Marsaxlokk and Birzebbuga. The largest inundation extents and flow depths (> 10 m) are produced by the two landslide sources and the western Hellenic Arc earthquake. Of interest is the role of the Malta Escarpment and Sicily in amplifying and reflecting tsunami waves, and in generating consistent hot spots along the eastern coastline of Malta.

    更新日期:2020-01-04
  • Effect of Wave Radiation Stress in Storm Surge-Induced Inundation: A Case Study for the East Coast of India
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-13
    P. L. N. Murty, A. D. Rao, K. Siva Srinivas, E. Pattabhi Rama Rao, Prasad K. Bhaskaran

    Tropical cyclone-induced coastal inundation is a potential hazard for the east coast of India. In the present study, two case studies are presented to examine the significance and importance of wave radiation stress in storm surge modeling during two extreme weather events associated with the Phailin and Hudhud cyclones. Model computations were performed using the advanced circulation (ADCIRC) model and the coupled ADCIRC + SWAN (Simulating Waves Nearshore) model for these two events. Meteorological and astronomical forcing were used to simulate the hydrodynamic fields using the ADCIRC model run in a stand-alone mode, whereas the coupled ADCIRC + SWAN model also incorporated the wave radiation stress attributed from wave breaking effects. Cyclonic wind fields were generated using the revised Holland model. Results clearly indicate an increase in the peak surge of almost 20–30% by incorporating the wave radiation stress and resulting inundation scenario in the coupled model simulation. The validation exercise showed that the coupled ADCIRC + SWAN model performed better than the ADCIRC model in stand-alone mode. Key findings from the study indicate the importance of wave-induced setup due to radiation stress gradients and also the role of the coupled model in accurately simulating storm surge and associated coastal inundation, especially along flat-bottom topography.

    更新日期:2020-01-04
  • Two Geoscience Applications by Optimal Neural Network Architecture
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-13
    Juliana Aparecida Anochi, Reynier Hernández Torres, Haroldo Fraga de Campos Velho

    Nowadays, artificial neural networks have been successfully applied on several research and application fields. An appropriate configuration for a neural network is a complex task, and it often requires the knowledge of an expert on the application. A technique for automatic configuration for a neural network is formulated as an optimization problem. Two strategies are considered: a mono-objective minimization problem, using multi-particle collision algorithm (MPCA); and a multi-objective minimization problem addressed by the non-dominated sorting genetic algorithm (NSGA-II). The proposed optimization approaches were tested for two application in geosciences: data assimilation for wave evolution equation, and the mesoscale seasonal climate prediction for precipitation. Better results with automatic configuration were obtained for data assimilation than those obtained by network defined by an expert. For climate seasonal precipitation, automatic configuration presented better predictions were presented than ones carried out by an expert. For the worked examples, the NSGA-II presented a superior result for the worked experiments.

    更新日期:2020-01-04
  • Tsunami Inundation and Maritime Hazard Modelling for a Maximum Credible Tsunami Scenario in Southeast Tasmania, Australia
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-13
    Claire L. Kain, Barrie Lewarn, Edward H. Rigby, Colin Mazengarb

    The east coast of Tasmania is directly exposed to tsunamis originating from the Puysegur subduction zone, off New Zealand’s southwest coast. However, the potential impacts of tsunami inundation for coastal communities and Hobart Airport, and risks to maritime operations in Hobart Port, are poorly understood. The purpose of this project is to simulate a maximum credible earthquake/tsunami/high tide scenario (a Mw 8.7 rupture of the Puysegur subduction zone) across a 17,000 km2 model area and provide outputs that can inform local hazard management plans. Modelling was performed using the ANUGA hydrodynamic library, along with a detailed elevation model constructed from LiDAR, photogrammetric contours and bathymetric datasets. The modelling strategy comprised three primary scenarios: a 13 h simulation of tsunami activity focusing on maritime hazard from waves and currents, with two further 4 h simulations focusing on coastal inundation for 71 coastal communities and Hobart Airport. The models were run on a variable triangulated mesh with a detailed Manning’s n surface roughness model. Tsunami erosion of sand dunes was accounted for through the development of an erosion operator. Results predict severe inundation (> 4 m flow depth) in exposed east-facing areas and the maritime hazard assessment advises that water disturbance would pose a significant threat to marine craft. The assessment suggests that the feasibility of shipping evacuation from Hobart port is questionable, given the timeframes involved and the nature of simulated water disturbance. Modelling results suggest that the dune line in front of Hobart Airport would not be breached in this instance and so inundation would not occur.

    更新日期:2020-01-04
  • A Multiple-Parameter Methodology for Placement of Tsunami Sensor Networks
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-06
    Joaquín Meza, Patricio A. Catalán, Hiroaki Tsushima

    A methodology to optimize the design of an offshore tsunami network array is presented, allowing determination of the placement of sensors to be used in a tsunami early warning system framework. The method improves on previous sensor location methods by integrating three commonly used tsunami forecast performance indicators as a measure of the predictive accuracy through a single cost function. The joint use of different tsunami parameters allows for a network that is less subject to bias found when using a single parameter. The resulting network performance was tested using a set of synthetic target scenarios and also verified against a model of the 2014 Pisagua event, suggesting that having such a network in place could have provided meaningful information for the hazard assessment. The small number of sensors required (three spanning nearly 700 km of the Northern Chile coast) may be useful in implementing such networks in places where funding of denser arrays is difficult.

    更新日期:2020-01-04
  • Modelling the Dynamic Relationship Between Mining Induced Seismic Activity and Production Rates, Depth and Size: A Mine-Wide Hierarchical Model
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-04
    J. Martinsson, W. Törnman

    Abstract The dynamic properties of mining induced seismic activity with respect to production rate, depth and size are studied in seven orebodies in the same underground iron ore mine. The objective is to understand the relationship between the measured seismic activity and the: seismic decay time, planned production rate, production size and mining depth. This relationship is the first step to individually customise the production rate for each orebody in the mine, make short-term predictions of future seismicity given planned productions, and to find out in what way the available predictors affect the seismicity. The seismic response with respect to the dependent variables is parametrised and the estimated decay times for each orebody, which are of particular interest here, are compared. An autoregressive model is proposed to capture the dynamic relationship between the induced seismic activity, the current production rate and the past seismic activity. Bayesian estimation of the parameters is considered and parameter constraints are incorporated in the prior distributions. The models for all orebodies are tied together and modelled hierarchically to capture the underlying joint structure of the problem, where the mine-wide parameters are learnt together with the individual orebody parameters from the observed data. Comparisons between the parameters from the hierarchical model and independent models are given. Group-level regressions reveal dependencies on size and mining depth. Model validation with posterior predictive checking using several discrepancy measures could not detect any model deficiencies or flaws. Posterior predictive intervals are evaluated and inference of model parameters are presented.

    更新日期:2020-01-04
  • Eurasia–Africa Plate Boundary Affected by a South Atlantic Asthenospheric Channel in the Gulf of Cadiz Region?
    Pure Appl. Geophys. (IF 1.466) Pub Date : 2019-12-04
    M. Catalán, Y. M. Martos, J. Martín-Davila

    Abstract The Gulf of Cadiz has been affected by a long and complex geodynamic evolution. The lithospheric structure is poorly understood in this region, and it also shows a diffuse seismicity, spanning over a broad area. The Canary Archipelago has been extensively studied. Nevertheless, there are fundamental topics that are still under debate. No studies have addressed or suggested the possibility of a plausible geodynamic connection between both remarkable locations. In this study we integrate total tectonic subsidence (TTS), Curie point depth (CPD), Bouguer gravity anomaly, and seismic information. TTS shows the existence of a basement bulge in the area of the Canary Archipelago that extends to the north, and in the area of Madeira Island, which extends in a more subtle way to the north, too. Likewise, the CPD reaches the shallowest values in the same location at the Canary Archipelago. These two aspects suggest a cause-effect relationship between TTS and CPD at this specific area. Gravity data and CPD show a linear feature, which links the NW of the Canary Archipelago and the Gulf of Cadiz. The data we manage in this work show remarkable clues as: (a) the absence of a similar signal in the TTS, (b) the fact that CPD it is rather constant along this track, (c) CPD amplitude also almost doubles the values obtained on Canary Archipelago, and (d) the existence of a clear correlation between seismogenic depths and CPD, which points to the existence of a correlation between seismicity and the thermal architecture of the lithosphere. All of these evidences support the presence of a lithospheric thinning between Canary Islands and Gulf of Cádiz area, and in turn, the presence of an asthenospheric channel which feeds and alter locally the Eurasia–Africa Plate Boundary.

    更新日期:2020-01-04
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