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The Significance of Tomographic Edge Zones for Large Earthquakes in Taiwan
Author(s) -
Wang Z.,
Kao H.
Publication year - 2019
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb017875
Subject(s) - geology , seismology , tectonics , seismic tomography , seismotectonics , fault (geology) , crust , geophysics , mantle (geology)
Abstract Seismogenesis of large earthquakes in Taiwan are often controlled by regional tectonics. Despite decades of efforts, the detailed relationship between seismogenesis of disastrous earthquakes and the geophysical properties of the earth materials remains unclear. In this study, we conduct high‐resolution tomography inversion of seismic velocities ( V p and V s ) and the Poisson's ratio (σ), and the results are used to infer the three‐dimensional (3‐D) distributions of crack density (ε) and saturation rate (ζ). We find that more than 70% of large (moment or local magnitudes ≥6, M6+) earthquakes occurred along tomographic edge zones (TEZ) within the crust where the spatial gradient exceeds 0.1, including all three disastrous events in the past two decades: the 1999 M7.6 Chi‐Chi, 2016 M6.5 Meinung, and the 2018 M6.4 Hualien earthquakes. We attribute the preference of large crustal earthquakes along TEZ as the consequence of fluid migration from the more saturated side to the opposite, leading to the build‐up of high pore pressure along TEZ. Locations of historical M6+ earthquakes are consistent with the inference of excessive fluids from either the extensive dehydration of hydrous minerals within the subducting Philippine Sea plate or the sedimentary compaction of alluvium and clastic deposits in the foreland basin west of the orogenic belt. Positive correlation between M6+ earthquakes and TEZ is not unique to Taiwan. Several famous earthquakes in regions with different tectonic settings appear to be associated with local TEZ. Our study could provide insights to long‐term mitigation of regional seismic hazards in Taiwan and probably elsewhere.