Real-time earthquake source parameter monitoring by using grid-based moment tensor inversion technique: an example of offshore northeast Taiwan

 

Hui-Wen Cheng1, Shiann-Jong Lee2, Kuo-Fong Ma1

 

1Department of Earth Science, National Central University, Taoyuan, Taiwan
2Institude of Earth Sciences, Academia Sinica, Taipei, Taiwan

Abstract

We use a grid-based moment tensor inversion technique and broadband continuous recordings to real-time monitoring the earthquakes offshore northeast Taiwan. The moment tensor inversion technique and a grid search scheme are applied to obtain the information of source parameters, including the hypocenter, moment magnitude, and focal mechanism. In Taiwan, the routine moment tensor solutions are reported by CWB(Central Weather Bureau) and BATS(Broadband Array in Taiwan for Seismology) which both require some lag time for the information on event time and location before doing CMT(Centroid Moment Tensor) analysis. By using the Grid-based moment tensor inversion technique, the event location and focal mechanism could be obtained simultaneously within about two minutes after the occurrence of the earthquake. This inversion procedure is based on a 1-D Green's functions database calculated by frequency-wavenumber(fk) method. The northeast offshore of Taiwan has been taken into account as our first test area which covers the region of 121.5E to 123E, 23.5N to 25N, and the depth to 136 km(figure 1). A 3D grid system is set in this study area with average grid size of 10 x 10 x 10 km3. We compare our results with the past earthquakes from 2006 to 2010 which had analyzed by BATS CMT. We also compare the event time detected by GridMT with the CWB earthquake reports. The results indicate that the grid-based moment tensor inversion system is efficient and realizable to be applied real-time on monitoring the local seismic activity. Our long-term goal is to use the GridMT technique with fully 3-D Green's functions for the whole Taiwan in the future.

Key words: real-time monitoring, CMT inversion, source parameter

 

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