scholarly journals Evaluating and Improving the USGS 3D Seismic Velocity Model in the San Francisco East Bay by Integrating Earthquake Ground-Motion Simulations and Noise-Derived Empirical Green's Functions

2019 ◽  
Author(s):  
Taka'aki Taira ◽  
Arthur Rodgers
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Earthquake Ground Motion ◽  
3D Seismic ◽  
Empirical Green’S Functions ◽  
Ground Motion Simulations ◽  
East Bay ◽  
Empirical Green's Functions

Three-Dimensional Seismic-Wave Propagation Simulations in the Southern Korean Peninsula Using Pseudodynamic Rupture Models

2021 ◽  
Author(s):  
Jaeseok Lee ◽  
Jung-Hun Song ◽  
Seongryong Kim ◽  
Junkee Rhie ◽  
Seok Goo Song
Keyword(s):  
Wave Propagation ◽  
Ground Motion ◽  
Korean Peninsula ◽  
Seismic Velocity ◽  
Ground Motions ◽  
Velocity Model ◽  
Wave Radiation ◽  
3D Seismic ◽  
Earthquake Scenarios ◽  
Large Earthquakes

ABSTRACT Accurate and practical ground-motion predictions for potential large earthquakes are crucial for seismic hazard analysis of areas with insufficient instrumental data. Studies on historical earthquake records of the Korean Peninsula suggest that damaging earthquakes are possible in the southeastern region. Yet classical ground-motion prediction methods are limited in considering the physical rupture process and its effects on ground motion in complex velocity structures. In this study, we performed ground-motion simulations based on rigorous physics through pseudodynamic source modeling and wave propagation simulations in a 3D seismic velocity model. Ensembles of earthquake scenarios were generated by emulating the one- and two-point statistics of earthquake source parameters derived from a series of dynamic rupture models. The synthetic seismograms and the distributions of simulated peak ground velocities (PGVs) were compared with the observations of the 2016 Mw 5.4 Gyeongju earthquake in the Korean Peninsula. The effects of surface-wave radiation, rupture directivity, and both local and regional amplifications from the 3D wave propagation were reproduced accurately in the spatial distribution of simulated PGVs, in agreement with the observations from dense seismic networks by mean log residuals of −0.28 and standard deviations of 0.78. Amplifications in ground motions were found in regions having low crustal velocities and in regions of constructive interference from the crustal shear-wave phases associated with postcritical reflections from the Moho discontinuity. We extended the established approach to earthquake scenarios of Mw 6.0, 6.5, and 7.0, at the same location, to provide the distribution of ground motions from potential large earthquakes in the area. Although we demonstrate the value of these simulations, improvements in the accuracy of the 3D seismic velocity model and the scaling relationship of the source models would be necessary for a more accurate estimation of near-source ground motions.

Non‐Double‐Couple Moment Tensors of Earthquakes Calculated Using Empirical Green’s Functions

2019 ◽  
Vol 91 (1) ◽  
pp. 390-398
Author(s):  
Václav Vavryčuk ◽  
Petra Adamová
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Joint Inversion ◽  
Velocity Model ◽  
Moment Tensors ◽  
Empirical Green’S Functions ◽  
Fracturing Process ◽  
Double Couple ◽  
Focal Zone ◽  
Empirical Green's Functions

Abstract We present a joint inversion for empirical Green’s functions (EGFs) and high‐resolution non‐double‐couple (non‐DC) moment tensors. First, the EGFs are constructed using known moment tensors of earthquakes occurring in a small focal zone. Second, the estimated EGFs are applied to refine the original moment tensors used for constructing the EGFs. Because the EGFs describe the velocity model better than the standard GFs, the refined moment tensors are more accurate. The method is applied to real observations of earthquakes of the 2008 swarm in West Bohemia, Czech Republic, where tiny details in fracturing in the focal zone are revealed. Refined moment tensors indicate fault closing caused by compaction of fault gouge during fracturing process related to fault weakening by fluids in the focal zone. The application of the proposed inversion can improve moment tensors reported in existing local, regional, or global catalogs for areas with a concentrated seismicity.

scholarly journals The Effect of Fault Geometry and Minimum Shear Wavespeed on 3D Ground-Motion Simulations for an Mw 6.5 Hayward Fault Scenario Earthquake, San Francisco Bay Area, Northern California

2019 ◽  
Vol 109 (4) ◽  
pp. 1265-1281 ◽  
Author(s):  
Arthur J. Rodgers ◽  
Arben Pitarka ◽  
David B. McCallen
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Hanging Wall ◽  
3D Models ◽  
Peak Ground Velocity ◽  
Earth Model ◽  
Fault Geometry ◽  
Bay Area ◽  
Ground Motion Simulations ◽  
Vertical Fault

Abstract We investigated the effects of fault geometry and assumed minimum shear wavespeed (VSmin) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VSmin values of 500 and 250  m/s reveal that PGVs are on average 25% higher west of the HF when using the lower VSmin, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VSmin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VSmin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VSmin of 250  m/s. We conclude that assuming a VSmin of 500  m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth <10  km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

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