Coseismic Velocity Reduction Correlated with Volumetric Strain Change Induced by Recent Large Earthquakes in the Central Range of Taiwan
Date Issued
2014
Date
2014
Author(s)
Wu, Sin-Mei
Abstract
Coseismic velocity reduction has been considered to be mediated by perturbations of stress and strain conditions in the crust and/or increased permeability/porosity of fractured rocks within the quake-damaged zones. To investigate potential changes and causes in crustal strains and rock properties of areas impacted by the earthquake ruptures of the two recent large events, Jiasian and Nantou, (Mw > 6 and focal depth > 20 km) occurring in the south Central Range of Taiwan, we construct empirical Green’s functions (EGFs) from cross-correlation functions (CCFs) of continuous ambient noise between available station pairs near the epicenters from the short-period Central Weather Bureau Seismic Network (CWBSN) and the Broadband Array in Taiwan for Seismology (BATS). The temporal variations in seismic velocity perturbations are estimated by measuring the relative time shifts of late-arriving coda waves between short-term and long-term stacked EGFs.
The resulting EGFs at 0.1-0.9 Hz show the statistically significant coseismic velocity reduction immediately after both the events. The velocity drop is detected most pronouncedly from the pairs with the interstation paths traversing through the hanging-wall block of the ruptured fault. The sensitivity of surface wave coda arrivals to shear wave speed in the dominant period range of 3-5 s is confined within the depth of 10 km, where the crust mostly experienced the coseismic dilatational strain change induced by the slip distribution from the finite-fault models. Compared with the coseismic slip distribution from GPS data and finite-fault inversion, peak ground velocity, and slip-induced volumetric strain, we suggest the coseismic velocity reduction associated with these two events is plausibly caused by the induced dilatational strain in the shallow part of the crust above the blind thrust ruptures.
Subjects
經驗格林函數
交互相關函數
同震速度下降
靜態體積應變
Type
thesis
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