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Enhanced Seismicity at a Geothermal Spot in Southern Tibet Following 2004 Mw 9.1 Sumatra and 2005 Mw 8.6 Nias Earthquakes and Its Implication for Rifting Process

Description: 

There are several north-south trending rifts in southern Tibet, indicating the extensional stress perpendicular to the convergence direction between the Indian and Eurasia plates. However, the rifting geodynamic process is under debate. Strong geothermal and seismic activities are observed all over southern Tibet. In particular, there is a geothermal spot west of Pumqu-Xianza Rift in the Lhasa Terrane, where there are nearly continuous seismic activity with magnitude 3-5 based on the global and regional catalogues. With such high seismicity rates, it is expected to observe dynamic triggering around the geothermal spot. Here we conduct a systematic search for dynamically triggered microearthquakes in southern Tibet following the 2004 December 26 Mw 9.1 Sumatra and 2005 March 28 Mw 8.6 Nias earthquakes. We find clear increase of high-frequency signals during the surface waves of the Sumatra mainshock, a clear hallmark for instantaneous dynamic triggering. To better quantify seismicity rate changes, we apply a Network Waveform Matched Filter Technique (NWMFT) to continuous seismic data recorded by the Hi-CLIMB 2D array to obtain more complete earthquake catalogues in southern Tibet. Using 213 hand-picked events as templates, we detect ~36 times more events 90 days before and after both mainshocks. The detected catalogs show that local seismicity in the geothermal spot west of Pumqu-Xianza Rift was enhanced after the Sumatra earthquake, but no significant change after the Nias earthquake. The enhanced seismicity lasted about 20 days following the Sumatra mainshock. The difference in triggering response following these two distant earthquakes could be related with the fact that the Sumatra mainshock excited long-duration surface waves with cumulative energy density 15 times more than that of the Nias mainshock or due to potential recharge time since relative short time interval between these two mainshocks. We will examine spatio-temporal evolutions of seismicity to better constrain the physical processes of dynamic triggering at geothermal regions and its implication for rifting process in southern Tibet.

Session: Advances in Operational and Research Analysis of Earthquake Swarms -II

Type: Oral

Date: 5/3/2024

Presentation Time: 05:30 PM (local time)

Presenting Author: Xiaofeng

Student Presenter: No

Invited Presentation: 

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