Thursday, November 10, 2016 - 2:00pm
Imaging the pre-, co- and post-seismic process of the 2015 Mw 7.8 Nepal-Gorkha earthquake.
Over the last decade, development of large-scale dense seismic networks has enabled rapid progresses in a broad spectrum of seismological sciences. In this talk, I will present our applications of array seismology in imaging the 2015 Gorhka earthquake sequence. High-frequency seismic waveforms from the large arrays have enabled back-projections, an emerging tool to probe earthquake dynamics. However, the exact locations of seismic radiations imaged by different arrays do not always align, indicating significant spatial biases. Recently, we proposed a new approach to effectively mitigate the back-projection uncertainties of large earthquakes based on their aftershocks. A slowness error term calibrated by aftershocks needs to be introduced to achieve consistency between BPs of different arrays. In the 2015 Mw 7.8 Gorkha earthquake, our refined source imaging reveals a narrow unilateral eastward rupture unzipping the lower bottom of the locked portion of the Main Himalaya Thrust. Such limited rupture extent indicates that the Gorkha earthquake is possibly an intermediate event during the inter-seismic period of larger earthquakes. Data sets from regional arrays in Tibet and Nepal also enables the combinations of matched-filter detections and repeater analysis that probe the aseismic slip processes preceding or after the mainshock. We find extensive foreshocks and aftershocks undocumented in the regular earthquake catalog. We observe a significant increase in seismicity rate a few days prior to the mainshock, initiating ~6 h after a local M 5.2 earthquake. The increase of seismic activities occurs in a wide region around the Gorkha principal slip zone, indicating that the effect of delayed dynamic triggering may contribute to the large-scale unloading process prior to the Gorkha mainshock.
October 19, 2016 - 4:25pm