Study on the Recent Tectonic Stress Field in the “Huoshan Seismic Window” Region

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the"Huoshan seismic window"region are calculated with the method developed recently by Snoke,combining the use of the first motion of P,SV and SH waves with their amplitude ratios.Based on these abundant focal mechanisms,the mean tectonic stress field in the"Huoshan seismic window"region is inverted with the average stress tensor method,and the result shows that the"Huoshan seismic window"region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction,which is in accord with statistical results of focal mechanism parameters.We estimate the difference(also referred to as consistency parameterθ)between the force axis direction of the focal mechanism solution and the mean stress tensor,then further analyze the variation characteristics ofθversus time,and the relationship with moderately strong earthquakes in the east China region.The result indicates thatθin the"Huoshan seismic window"region is in good correspondence with moderately strong earthquakes in the East China region.Whenθis lower than the mean value,corresponding moderately strong earthquakes may occur in the East China region.

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the ＂ Huoshan seismic window＂ region are calculated with the method developed recently by Snoke, combining the use of the first motion of P, SV and SH waves with their amplitude ratios. Based on these abundant focal mechanisms, the mean tectonic stress field in the ＂Huoshan seismic window＂ region is inverted with the average stress tensor method, and the result shows that the ＂Huoshan seismic window＂ region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction, which is in accord with statistical results of focal mechanism parameters. We estimate the difference （also referred to as consistency parameter 0） between the force axis direction of the focal mechanism solution and the mean stress tensor, then further analyze the variation characteristics of 0 versus time, and the relationship with moderately strong earthquakes in the east China region. The result indicates that 0 in the ＂ Huoshan seismic window＂ region is in good correspondence with moderately strong earthquakes in the East China region. When 0 is lower than the mean value, corresponding moderately strong earthquakes may occur in the East China region.