S41D-08
Systematic Detections of Early Aftershocks and Remotely Triggered Seismicity in China Following the 2015 Mw7.8 Gorkha, Nepal earthquake
Thursday, 17 December 2015: 09:45
305 (Moscone South)
Zhigang Peng1, Jing Wu2, Dongdong Yao1, LU LI3, Xiaofeng Meng1, Baoshan Wang4, Weijun Wang5 and Chenyu Li1, (1)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (2)Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, (3)Institute of Geophysics, China Eathquake Administration, Beijing, China, (4)IGP Institute of Geophysics, China Earthquake Administration, Beijing, China, (5)IES Institute of Earthquake Science, China Earthquake Administration, Beijing, China
Abstract:
The 2015/04/25 Mw7.8 Gorkha, Nepal earthquake occurred beneath the central portion of the Himalayan Frontal Thrust Fault. The mainshock was followed by numerous aftershocks near its epicentral region, as well as many earthquakes at various distances in China. Small to moderate-size earthquakes in Chongqing (~2500 km) and around Fangshan Pluton near Beijing (~3500 km) coincided with the arrivals of surface wave train, suggesting that they were likely triggered by dynamic stresses from the passing surface waves. 3 hours later, a M5.8 normal-faulting earthquake in Southern Tibet. Because of their close distances (within two fault-rupture lengths), it is not clear whether the M5.8 Tibetan event is triggered by static or dynamic stresses. Here we conduct a systematic detection of microseismicity in Nepal and Southern Tibet around the Nepal mainshock. We use earthquakes listed in the Advance National Seismic Network (ANSS) and China Earthquake Network Center (CENC) catalogs as templates, and scan through continuous waveform data within 700 km of the Nepal mainshock to detect additional smaller events that were not listed in these catalogs. As was done before, we apply a 0.5 to 8 Hz band-pass filter to both the template and continuous waveform data, and detect events with mean cross-correlation (CC) values that are at least 12 times larger than the daily median absolute deviation (MAD) values. Overall we have detected 5 times more aftershocks, as well as more than 80 uncatalogued events in Southern Tibet near the epicentral region of the M5.8 event. We also compute the dynamic and static stress changes on the two nodal planes of the M5.8 event. While we cannot completely rule out the influence of static stress change (because the M5.8 event is in the positive Coulomb stress change region), the amplitude of the dynamic stress change is several times larger than the static stress change, suggesting that this event is possibly triggered by dynamic stress changes (albeit with some time delays). The early aftershocks show systematic along-strike migrations, similar to other recently studied aftershock sequences. Our next step is to extend the same analysis to longer time period before and after the mainshock to detect potential foreshocks and investigate longer-time evolutions of seismicity in Nepal.
