The seismogenic deformation and Qp temporal variation before the M6.2 Mingjen earthquake, Taiwan

Detecting anomalies before an earthquake has become an important task in seismic hazard prevention. The purpose of this research is to use the intrinsic attenuative dispersion of the P-wave, Qp, to serve as an anomaly before an earthquake. On November 5, 2009, an earthquake (ML = 6.2; depth = 24 km) occurred in Ming-Jen, Nantou county, Taiwan. The vertical-component of the first-cycle of P-wave data recorded from the Central Weather Bureau Seismic Network from 2009/01 to 2010/01 was calculated to obtain the Qp parameter. Meanwhile, this study also utilizes global positioning system stations to examine changes in surface displacements that occurred during the Mingjen earthquake. Analysis results indicate that 2-months before the mainshock occurred; the Qp began to decrease for all stations, which implies that the crustal area became more fractured owing to a high stress accumulation. Such a lead time of ∼2 months is equal to the average lead time of Seismic Electric Signals (SES) activities being also compatible with a physical model suggested long ago for the SES generation. With stress accumulating a few days before the earthquake, an impeded region can be clearly identified by relatively-large difference values when the mainshock is going to occur. We conclude that the analysis of the Qp parameter and GPS index are very sensitive to changes in the stress state and may serve as a useful index in early warning of earthquake.