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  • Crustal seismic attenuation parameters in the western region of the North Anatolian Fault Zone
    J. Geodyn. (IF 2.813) Pub Date : 2020-01-28
    Izgi Gizem; Eken Tuna; Gaebler Peter; Eulenfeld Tom; Taymaz Tuncay

    Detailed knowledge of the crustal structure along the North Anatolian Fault Zone can help in understanding past and present tectonic processes in relation to the deformation history. To estimate the frequency-dependent crustal attenuation parameters beneath the western part of the North Anatolian Fault Zone we apply acoustic radiative transfer theory under the assumption of multiple isotropic scattering to generate synthetic seismogram envelopes. The inversion depends on finding an optimal fit between observed and synthetically computed coda wave envelopes in five frequency bands. 2-D lateral variation of intrinsic and scattering attenuation at various frequencies tends to three crustal blocks (i.e., Armutlu-Almacık, Istanbul-Zonguldak and Sakarya Zones) separated by the southern and northern branches of the western part of the North Anatolian Fault Zone. Overall, scattering attenuation appears to be dominant over intrinsic attenuation in the study area at lower frequencies. Relatively low attenuation properties are observed beneath the older Istanbul Zone whereas higher attenuation properties are found for the younger Sakarya Zone. The Armutlu–Almacık Zone exhibits more complex lateral variations. Very high attenuation values towards the west characterize the area of the Kuzuluk Basin, a pull-apart basin formed under west-east extension. Our coda-derived moment magnitudes are similar to the local magnitude estimates that were previously calculated for the same earthquakes. For smaller earthquakes (ML < 2.5), however, the relation between local and moment magnitudes appears to lose its coherency. This may stem from various reasons including the use of seismic data recorded in finite sampling interval, possible biases in local magnitude estimates of earthquake catalogues as well as biases due to wrong assumptions to consider anelastic attenuation terms.

    更新日期:2020-01-29
  • A Multiple 1D Earth Approach (M1DEA) to account for lateral viscosity variations in solutions of the sea level equation: An application for glacial isostatic adjustment by Antarctic deglaciation
    J. Geodyn. (IF 2.813) Pub Date : 2020-01-24
    R. Hartmann; J. Ebbing; C.P. Conrad

    The pseudo-spectral form of the sea level equation (SLE) requires the approximation of a radially-symmetric visco-elastic Earth. Thus, the resulting predictions of sea level change (SLC) and glacial isostatic adjustment (GIA) often ignore lateral variations in the Earth structure. Here, we assess the capabilities of a Multiple 1D Earth Approach (M1DEA) applied to large-scale ice load components with different Earth structures to account for these variations. In this approach the total SLC and GIA responses result from the superposition of individual responses from each load component, each computed globally assuming locally-appropriate 1D Earth structures. We apply the M1DEA to three separate regions (East Antarctica, West Antarctica, and outside Antarctica) to analyze uplift rates for a range of Earth structures and different ice loads at various distances. We find that the uplift response is mostly sensitive to the local Earth structure, which supports the usefulness of the M1DEA. However, stresses transmitted across rheological boundaries (e.g., producing peripheral bulges) present challenges for the M1DEA, but can be minimized under two conditions: (1) If the considered time period of ice loading for each component is consistent with the relaxation time of the local Earth structure. (2) If the load components can be subdivided according to the scale of the lateral variations in Earth structure. Overall, our results indicate that M1DEA could be a computationally much cheaper alternative to 3D finite element models, but further work is needed to quantify the relative accuracy of both methods for different resolutions, loads, and Earth structure variations.

    更新日期:2020-01-24
  • Kinematic Evolution of the West Burma Block during and after India-Asia Collision Revealed by Paleomagnetism
    J. Geodyn. (IF 2.813) Pub Date : 2020-01-23
    Zhenyu Li; Lin Ding; Than Zaw; Houqi Wang; Fulong Cai; Wei Yao; Zhongyu Xiong; Kyaing Sein; Yahui Yue

    The magnitude and timing of deformation in the form of vertical-axis rotation in the eastern Tibetan Plateau and Southeast Asia during the Cenozoic period are the key to understanding the India-Asia collision and subsequent geological processes. Our new paleomagnetic and geochronological data from Myanmar show that the characteristic remanent magnetization (ChRM) mean directions of sedimentary tuffaceous layers (31 effective specimens) and rhyolites (11 paleomagnetic site-mean directions), which formed at ∼64.4 Ma and ∼26.6 Ma, were D±ΔD/I±ΔI = 50.8°±11.0°/33.1°±9.2° with α95 = 9.2° and D±ΔD/I±ΔI = 356.8°±6.5°/16.9°±6.2° with α95 = 6.2°, respectively. These data indicate that the West Burma Block (WBB) has experienced a significant clockwise rotation of 38.3°±6.9° since ∼64.4 Ma and a later counterclockwise rotation of 14.6 ± 4.2° since ∼26.6 Ma with respect to stable Asia. The clockwise rotation of ∼40° of the WBB since 64.4 Ma (early Paleocene) with respect to stable Asia is attributable to the India-Asia collision, and the later counterclockwise rotation of 14.6°±4.2° since 26.6 Ma (late Oligocene) is attributable to the dextral-slip faulting activity of the Sagaing Fault. These paleomagnetic analyses, combined with previously published geological research in SE Asia, are substantially consistent with the predictions of the extrusion model for the SE Asia realm.

    更新日期:2020-01-23
  • Accounting for spatiotemporal correlations of GNSS coordinate time series to estimate station velocities
    J. Geodyn. (IF 2.813) Pub Date : 2020-01-13
    C. Benoist; X. Collilieux; P. Rebischung; Z. Altamimi; O. Jamet; L. Métivier; K. Chanard; L. Bel

    It is well known that GNSS permanent station coordinate time series exhibit time-correlated noise. Spatial correlations between coordinate time series of nearby stations are also long-established and generally handled by means of spatial filtering techniques. Accounting for both the temporal and spatial correlations of the noise via a spatiotemporal covariance model is however not yet a common practice. We demonstrate in this paper the interest of using such a spatiotemporal covariance model of the stochastic variations in GNSS time series in order to estimate long-term station coordinates and especially velocities. We provide a methodology to rigorously assess the covariances between horizontal coordinate variations and use it to derive a simple exponential spatiotemporal covariance model for the stochastic variations in the IGS repro2 station coordinate time series. We then use this model to estimate station velocities for two selected datasets of 10 time series in Europe and 11 time series in the USA. We show that coordinate prediction as well as velocity determination from short time series are improved when using this spatiotemporal model, as compared with the case where spatiotemporal correlations are ignored.

    更新日期:2020-01-13
  • Discrete-element numerical modeling of sub-salt structures in the Central Kelasu fold-thrust belt, Kuqa Depression, northwestern China
    J. Geodyn. (IF 2.813) Pub Date : 2019-12-03
    Chunfang Zheng; Xiongwei Sun; Guiting Hou

    Knowledge of the deformation history and dominant factors influencing the formation of sub-salt structures is necessary to understand the formation of sub-salt traps. In this study, the discrete-element method (DEM) is used to assess the deformation mechanism of sub-salt structures in the Central Kelasu fold-thrust belt of the Kuqa Depression. A series of DEM models of the Central Kelasu fold-thrust belt are constructed, the final deformation styles of the models are compared with the real structures in order to determine the fitting degree of each models, and the dominant factors influencing the formation of sub-salt structures are determined. A thin salt layer promotes the deformation in the sub-salt sequence. Salt sub-sags, basal uplifts, and pre-existing faults can also promote the deformation in the sub-salt sequence in the northern part of the models. Large deformations accumulate in pre-existing structures in the northern part of the models, and then subsequent deformations are also transmitted to the salt layer and supra-salt sequence; however, these deformations are hardly transmitted to the sub-salt sequence in the middle and southern parts of the models. Among the eight DEM models constructed in our research, the horizontal-stratum model without any initial structures showed the best fit to actual phenomena. Earlier simple structures of Mesozoic layers can be deformed into the current complex structures under compression effects in the late Himalayan period. By comparing with other regions and analyzing the deformation progress of the DEM model, the sub-salt structures in the Kuqa Depression are considered to be fold-accommodation fault structures.

    更新日期:2020-01-04
  • Lithospheric structure of the xuefengshan belt, South China: Evidence from a seismic reflection profile
    J. Geodyn. (IF 2.813) Pub Date : 2019-12-03
    Xiaosan Zhu; Hongwei Zheng; Minjie Lu; Yinghui Zhang

    In this study, we analyse and interpret a new seismic reflection profile across the Xuefengshan Belt (XFSB), South China, to determine the deep structure of this belt and provide insights into collisional orogenic architecture. We identify a deep regional fault located beneath the XFSB, which cuts through the reflection Moho below the belt and is interpreted as representing the collisional boundary between the Yangtze and Cathaysia blocks along the southeastern margin of the belt. We identify structural evidence for collision between the two blocks, including two groups of layered narrow slip belts (∼30 km) in the middle crust, one distributed in the Yangtze Block and the other in the Cathaysia Block. A narrow velocity-gradient belt in the upper mantle at a depth of ∼90 km is revealed by numerous strong seismic reflectors, some of which are layered. The study provides important new information on the lithospheric structure of the South China Block at the interface between the Yangtze and Cathaysia blocks.

    更新日期:2020-01-04
  • Magnetic fabrics of the neoproterozoic piquiri syenite massif (Southernmost Brazil): Implications for 3D geometry and emplacement
    J. Geodyn. (IF 2.813) Pub Date : 2019-12-13
    Samuel Sbaraini; M. Irene B. Raposo; Maria de Fátima Bitencourt; Camila Rocha Tomé

    The study of magnetic fabrics and rock magnetic properties, together with geological and structural mapping, was carried out in a syenite pluton to investigate its shape and emplacement history. The Piquiri Syenite Massif (PSM) is an alkaline pluton which exhibits S >> L magmatic fabric and is interpreted to be part of the last Neoproterozoic post-collisional magmatic episodes in southernmost Brazil. Thermomagnetic curves, hysteresis data and coercivity spectra obtained from representative samples of different facies in the massif reveal that magnetic susceptibility is dominated by ferromagnetic minerals, especially magnetite. Magnetic fabric data were determined by using Anisotropy of Magnetic Susceptibility (AMS) and Anisotropy of Anhysteretic Remanence (AARM). Both fabrics are coaxial, and the parallelism of AMS and AARM tensors in more than 84 % of the sampled sites rules out the possibility of significant effects of Single Domain (SD) crystals. The magnetic foliation is concordant with the magmatic foliation field measurements, both parallel to pluton contacts, with high, inward dip angles. The magnetic lineation shows distinct but related behaviour from one facies to another. It is dominantly subvertical in the marginal facies rocks and plunges at moderate to shallow angles in the main facies. It is sub-horizontal in the quartz-syenites and plunges at shallow angles in the granitic rocks. Oxidizing conditions determined from the study of magnetic mineralogy leads to challenge former interpretation of in situ differentiation and crystallization and points to the multi-intrusive character of the pluton. Field relations such as fragments of marginal facies rocks found within the main facies rocks, which are in turn intruded by quartz-syenites, together with the general absence of contact metamorphism except near the marginal facies, lead to interpret that a sequence of magmatic pulses have built up the pluton. Thus, a first magmatic pulse may have heated the host rocks and resulted in the marginal facies which was followed by the next pulses to form the main facies and the quartz-rich varieties, therefore constructing the pluton from outside inwards.

    更新日期:2020-01-04
  • A study of the solid Earth tides, ocean and atmospheric loadings using an 8-year record (2010-2018) from superconducting gravimeter OSG-060 at Djougou (Benin, West Africa)
    J. Geodyn. (IF 2.813) Pub Date : 2019-12-03
    Jacques Hinderer; U. Riccardi; S. Rosat; J.-P. Boy; B. Hector; M. Calvo; F. Little; J.-D. Bernard

    We investigate a nearly 8-year record (2010-2018) of the superconducting gravimeter OSG-060 located at Djougou (Benin, West Africa). We first perform a tidal analysis with ET34-ANA v7.1 software that leads to the gravimetric amplitude and phase factors for all separable waves according to the available time duration. We test nine different ocean tide models for the main eleven tidal constituents (Ssa, Mm, Mf, Q1, O1, P1, K1, N2, M2, S2, K2). After correction for ocean tidal loading we obtain the real and imaginary parts of the residual vector. We also investigate atmospheric loading which is dominated in this equatorial location by the thermal waves S1 and S2 that are modulated in amplitude by annual and semi-annual components. After correction for ocean loading, we test different air pressure corrections on the tidal gravimetric factors for the waves Sa, Ssa, S1 and S2. We show the rather large discrepancy that exists between the classical single admittance pressure reduction and a hybrid model using global atmospheric models everywhere except in the local zone where the model pressure is replaced by the observed pressure.

    更新日期:2020-01-04
  • Lithological control on multiple surface ruptures during the 2016-2017 Amatrice-Norcia seismic sequence
    J. Geodyn. (IF 2.813) Pub Date : 2019-11-09
    Eugenio Carminati; Cristian Bignami; Carlo Doglioni; Luca Smeraglia
    更新日期:2020-01-04
  • Seismic signature of the Alpine indentation, evidence from the Eastern Alps.
    J. Geodyn. (IF 2.813) Pub Date : 2015-11-04
    I Bianchi,G Bokelmann

    The type of collision between the European and the Adriatic plates in the easternmost Alps is one of the most interesting questions regarding the Alpine evolution. Tectonic processes such as compression, escape and uplift are interconnected and shape this area. We can understand these ongoing processes better, if we look for signs of the deformation within the Earth's deep crust of the region. By collecting records from permanent and temporary seismic networks, we assemble a receiver function dataset, and analyze it with the aim of giving new insights on the structure of the lower crust and of the shallow portion of the upper mantle, which are inaccessible to direct observation. Imaging is accomplished by performing common conversion depth stacks along three profiles that crosscut the Eastern Alpine orogen, and allow isolating features consistently persistent in the area. The study shows a moderately flat Moho underlying a seismically anisotropic middle-lower crust from the Southern Alps to the Austroalpine nappes. The spatial progression of anisotropic axes reflects the orientation of the relative motion and of the stress field detected at the surface. These observations suggest that distributed deformation is due to the effect of the Alpine indentation. In the shallow upper mantle right below the Moho interface, a further anisotropic layer is recognized, extended from the Bohemian Massif to the Northern Calcareous Alps.

    更新日期:2019-11-01
  • Tidal Love and Shida numbers estimated by geodetic VLBI.
    J. Geodyn. (IF 2.813) Pub Date : 2013-10-01
    Hana Krásná,Johannes Böhm,Harald Schuh

    Frequency-dependent Love and Shida numbers, which characterize the Earth response to the tidal forces, were estimated in a global adjustment of all suitable geodetic Very Long Baseline Interferometry (VLBI) sessions from 1984.0 to 2011.0. Several solutions were carried out to determine the Love and Shida numbers for the tidal constituents at periods in the diurnal band and in the long-period band in addition to values of the Love and Shida numbers common for all tides of degree two. Adding up all twelve diurnal tidal waves that were estimated, the total differences in displacement with respect to the theoretical conventional values of the Love and Shida numbers calculated from an Earth model reach 1.73 ± 0.29 mm in radial direction and 1.15 ± 0.15 mm in the transverse plane. The difference in the radial deformation following from the estimates of the zonal Love numbers is largest for the semi-annual tide Ssa with 1.07 ± 0.19 mm.

    更新日期:2019-11-01
Contents have been reproduced by permission of the publishers.
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