Abstract

The seismicity in the vicinity of the Song Tranh 2 reservoir that commenced in late 2010 is an example of reservoir‐induced seismicity. Moment tensor (MT) solutions are mostly normal‐faulting mechanisms with shearing as the main component of full MT, which suggest reservoir exploitation stress field changes as a triggering origin of this seismicity. However, the local tectonic stress field plays a role in the seismogenic process, which is accelerated by the reservoir exploitation. Two main orientations of discontinuities reactivated by reservoir exploitation are identified, with clustering of events located in two main areas: northern and southern. In addition to the northern cluster (NC) and southern cluster (SC), further smaller clusters are distinguishable, assuming both clustering of epicenters and similarity of focal mechanisms as the clustering criteria. Maximum seismic activities in clusters appear in different periods, with high seismicity in the SC preceding that in the NC. The results indicate significant differences between the NC and SC. It is shown that the SC is an example of rapid triggering, whereas the NC is a delayed triggering type. Also, magnitude distribution differs between the NC (b1.1) and SC (b1.3).

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