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  • 1
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    Seismic-Wave Modeling in the Presence of Surface Topography in 2D General Anisotropic Media by a Curvilinear Grid Finite-Difference Method (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-06-10
    Description: In this article, the curvilinear grid finite-difference method is extended to simulate seismic-wave propagation in 2D general anisotropic media with surface topography. In order to better describe the surface topography, the geological model is discretized in curvilinear coordinates by body-conforming grids whose grid lines align with the surface topography. To implement the free-surface boundary condition, we derive the analytical relationship between derivatives of velocity components for anisotropic media and use the compact finite-difference scheme and traction-image method. We fully validate the proposed method using complex topographic surface models and compare the synthetic waveforms with the spectral-element method. The results show a good agreement between the two methods, confirming the validity of our method.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    On the Free-Surface Problem in Dynamic-Rupture Simulation of a Nonplanar Fault (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-06-10
    Description: Spontaneous dynamic-rupture simulation in 3D is a difficult task in seismology, especially for the rupture dynamics of a fault with complex geometry and a free surface. In this study, we model an irregular fault that reaches the free surface and investigate the rupture dynamics of the intersection between the earthquake-induced fault and the Earth’s surface. We use the recently proposed curved grid finite-difference method (CG-FDM) to simulate a spontaneous dynamic rupture. However, this involves solving the inversion of an ill-conditioned matrix that is required in finite-difference method modeling at the point of intersection, which must be addressed to achieve stable simulation conditions. We achieve stable conditions at the intersection between the fault plane and the free surface by considering the continuity of the fault’s normal displacement, ensuring that the point of intersection meets the conditions of both the fault and the free surface. To verify our method, we simulate the spontaneous dynamic rupture of a rough fault in half-space and compare the results with those from another method. The good agreement between two methods validates our mathematical strategy for modeling the intersection between an irregular fault plane and a free surface using CG-FDM.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 3
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    Rupture Dynamics and Ground Motion from Potential Earthquakes around Taiyuan, China (2017)
    Seismological Society of America (SSA)
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    Publication Date: 2017-05-31
    Description: Using the curved grid finite-difference method, we develop dynamic spontaneous rupture models of earthquakes on the Jiaocheng fault (JF) near Taiyuan, the capital and largest city of Shanxi Province in north China. We then model the wave propagation and strong ground motion generated by these scenario earthquakes. A map of the seismic-hazard distribution for a potential M  7.5 earthquake is created based on dynamic rupture and true 3D modeling. The tectonic initial stress fields derived from the inversion of focal mechanisms of historical earthquakes, a nonplanar fault, and a rough surface are considered in the dynamic rupture simulation. Based on the geological structure of the Taiyuan basin, normal faulting with a dipping angle of 60° is implemented for the scenario earthquake simulations. The largest uncertainty of a potential earthquake in the JF zone is the hypocenter. Four cases are used to nucleate the earthquake at different locations. Using these dynamic rupture sources for the JF, we further simulate and analyze both the seismic wave generated by the scenario earthquake and the strong ground motion. It is found that the low-velocity media of the Taiyuan basin redistribute the ground motion well. The effects of the regional stress fields on the dynamic rupture and hazard distribution are investigated and discussed further. Moreover, a scenario earthquake, which can cause great damage to the city of Taiyuan, is modeled and analyzed.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    Preface to the Focus Section on the 3 September 2016 Pawnee, Oklahoma, Earthquake (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-06-28
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 5
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    Coulomb Stress Interactions during the Mw 5.8 Pawnee Sequence (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-06-28
    Description: We investigate the stress interaction between the Watchorn, Labette, and Sooner Lake fault systems and the effect of precursory activities on the 3 September 2016 M w  5.8 Pawnee earthquake. We obtain fault-plane solutions for earthquakes with sufficient azimuthal coverage using the HASH algorithm, and then perform coulomb stress analysis on both seismogenic faults and individual nodal planes. Our results found that the three M w ≥3.0 foreshocks exerted a cumulative coulomb stress change increase of 0.68–1.98 bars at the mainshock hypocenter and also promoted failure for most aftershocks within 2 km of the mainshock. The coulomb stress change of 5 bars exerted by the mainshock also promoted failure for most aftershocks within the conjugate fault system. The results suggest that earthquake interaction should be fully considered in hazard assessment for induced seismicity.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 6
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    Mechanism of the Coseismic Change of Volumetric Strain in the Far Field of Earthquakes (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-02-03
    Description: Coseismic strain is important for understanding the crustal response to earthquakes. Several studies showed a large discrepancy between the measured coseismic change of volumetric strain in the far field and that which was predicted from the theoretical static strain, yet the underlying mechanism for this discrepancy is unknown. Here, we compare the tidal response of the volumetric strain with that of the groundwater level documented in a well located in northeastern China before and after three distant great earthquakes. The phase of water-level fluctuations increased after each earthquake and became the same as that of the volumetric strain. Furthermore, both the sign and the time history of the volumetric strain match that expected from the poroelastic response of aquifers to a localized coseismic increase in pore pressure. These observations imply that the coseismic change of volumetric strain in the far field of great earthquakes may primarily reflect the poroelastic response to coseismic pore-pressure change that, in turn, is caused by earthquake-enhanced permeability.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 7
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    Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California (2013)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2013-03-03
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 8
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    Identification of Pulse Periods in Near‐Fault Ground Motions Using the HHT Method (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Large‐amplitude and long‐period pulses are observed in velocity time histories of near‐fault ground‐motion records. The pulses in these records have significant damage effect on flexible structures due to their long‐period property; therefore, more attention should be paid to the frequency components in the ground motion. Based on the identification of frequency components in the original record, a new method based on the Hilbert–Huang transform (HHT) is proposed here. A ground‐motion record can be decomposed into several intrinsic mode functions (IMFs) that carry different frequency components by the HHT without contamination from any a prior function. Only two fixed parameters, the peak ground velocity (PGV)/peak ground acceleration (PGA) ratio and the energy change of every IMF, are used to classify pulse‐like ground‐motion records. The inherent pulses of these records can also be extracted, based on the selection of IMFs for which PGV/PGA ratios are larger than 0.12 and energy changes that are greater than 0.1. For multipulse cases, all the pulses can be captured after extracting once, and the time course of inherent pulses can also be obtained. Then, pulse periods are calculated based on the solutions of instantaneous frequency of the peak for the extracted pulses. All the periods obtained using the HHT method can be verified by the results obtained from Baker’s wavelet method. The 24 controversial records that are discussed in previous studies are examined here as well. The HHT method is a complete procedure that includes the classification of pulse‐like ground motions, the extraction of velocity pulses, and the solution of pulse periods. It works well for multipulse records, especially because it can provide the exact timing of all the inherent pulses.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 9
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    Identification of Pulse Periods in Near‐Fault Ground Motions Using the HHT Method (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Large‐amplitude and long‐period pulses are observed in velocity time histories of near‐fault ground‐motion records. The pulses in these records have significant damage effect on flexible structures due to their long‐period property; therefore, more attention should be paid to the frequency components in the ground motion. Based on the identification of frequency components in the original record, a new method based on the Hilbert–Huang transform (HHT) is proposed here. A ground‐motion record can be decomposed into several intrinsic mode functions (IMFs) that carry different frequency components by the HHT without contamination from any a prior function. Only two fixed parameters, the peak ground velocity (PGV)/peak ground acceleration (PGA) ratio and the energy change of every IMF, are used to classify pulse‐like ground‐motion records. The inherent pulses of these records can also be extracted, based on the selection of IMFs for which PGV/PGA ratios are larger than 0.12 and energy changes that are greater than 0.1. For multipulse cases, all the pulses can be captured after extracting once, and the time course of inherent pulses can also be obtained. Then, pulse periods are calculated based on the solutions of instantaneous frequency of the peak for the extracted pulses. All the periods obtained using the HHT method can be verified by the results obtained from Baker’s wavelet method. The 24 controversial records that are discussed in previous studies are examined here as well. The HHT method is a complete procedure that includes the classification of pulse‐like ground motions, the extraction of velocity pulses, and the solution of pulse periods. It works well for multipulse records, especially because it can provide the exact timing of all the inherent pulses.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
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    One-year record of organic and elemental carbon in fine particles in downtown Beijing and Shanghai (2005)
    Copernicus
    Details
    Publication Date: 2005-06-15
    Description: Weekly PM2.5 samples were collected for one year (1999-2000) in Beijing and Shanghai and the carbonaceous species analyzed to investigate and compare their time series patterns and possible sources in the two biggest cities of China. Weekly carbonaceous concentrations varied in wide ranges with 8.6-59µg m-3 for OC and 1.5-25.4µg m-3 for EC in Beijing, and with 5.1-38.4µg m-3 for OC and 2.3-13.0µg m-3 for EC in Shanghai. Similar weekly and seasonal variations of OC and EC concentrations were found in each city though major combustion sources presented source-dependent emission characteristics and seasonal differences in emission amount for carbonaceous species. Both OC and EC maintained much higher concentrations in late fall through winter, probably due to enhanced emissions coupled with unfavorable meteorological conditions. In Beijing, the 14C analysis of limited samples suggested there was a significant contribution (33-48%) of modern carbon to the total fine carbonaceous PM burden with higher fractions in the harvest seasons. The high mass ratios of excessive potassium to EC in both Beijing and Shanghai also indicated that biomass burning had important contribution to fine carbonaceous particles.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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