Spatio-Temporal Changes of Microseismicity in Taiwan Around the 2009 Typhoon Morakot

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Typhoon Morakot brought up to 3 meters of rainfall within a few days in August 2009, leading to numerous landslides in Southern Taiwan. These landslides produced significant sediment debris to be removed by subsequent erosional processes, resulting in a reduction of normal load at depth. Previous studies have suggested that such transient stress change can trigger small to moderate-size earthquakes in Taiwan and elsewhere (e.g., Wdowinski, 2011). However, Taiwan is seismically active and many earthquakes would occur without such triggering effects. In addition, other types of stress perturbations such as seasonal variations of underground water storage are also capable of triggering microseismicity. Hence, a detailed study of microseismicity in southern Taiwan can help improve our understanding of the triggering relationship with Typhoon Morakot and other processes. Because many microearthquakes were missing from the standard earthquake catalogs (especially during and right after Typhoon Morakot), we apply our recently developed Matched Filter Technique (MFT) to systematically detect microearthquakes in Taiwan half a year before to one year after Typhoon Morakot. We use 71 short-period stations in the Central Weather Bureau (CWB) and 31508 CWB catalog events around Taiwan as the templates to scan through the ~ 1.5 years of continuous seismic data. So far we have detected about 16 times more than the standard CWB catalog. After relocation with the double-pair double-difference technique, about 3 times more seismic events than the CWB catalog can be relocated. The relocated seismicity shows many linear features, highlighting detailed subsurface fault structures. In addition, we find a clear increase in microseismicity during the time period with significant rainfalls brought by in Typhoon Morakot southern Taiwan. Our next step is to examine spatio-temporal evolution of microseismicity in this time period and compare statistical properties (e.g., b-values) to confirm and better understand the triggering behavior with Typhoon Morakot.

Presenting Author: Qiushi Zhai

Authors