利用小震重新定位结果研究河北文安地震前地震活动三维空间特征

利用首都圈地区小震重新定位结果,研究了2006年7月4日河北文安5.1级地震前地震活动特征,结果表明:①文安地震前5年,河北平原带中段ML≥3.0地震活动出现明显的增强(持续43个月)—平静(持续17个月)特点,蠕变曲线表现为加速—转平;②震前4年,在15~20 km深处存在一个纬向长约70 km、经向长约90 km的三维空区,文安地震的起始破裂点位于该三维空区的下部边缘;③2003年4月~2004年10月,平原带中段ML≥2.0地震震源深度从10 km的浅处逐渐增加到30 km左右的深处,在此过程中,中下地壳(20~30 km深度范围内)地震活动显著增强。

Characteristics of Seismic Activity in 3-D Space before Wen'an earthquake, Hebei Province by Small Earthquake Relocation in the Capital Area of China

Characteristics of seismic activity before the July 4, 2006 earthquake of M5.1 in Wen'an, Hebei province were analyzed by relocation of small earthquakes in China's capital area. Some results are obtained as below: ① The seismic activity of M_L≥3.0 in the middle part of the Hebei plain seismic belt displayed a feature of strengthening (lasting 43 months)-quiescence (lasting 17 months ) 5 years before the Wen'an earthquake. Simultaneously, the strain release curve showed a variation process of accelerating-flatting. ② A seismogenic gap in three-dimensional space, located in the depth of 15～20 km, with 70 km long in latitude direction and 90 km long in longitude orientation, was formed by M≥2.0 earthquakes 4 years prior to the Wen'an earthquake. The initial rupture point of the Wen'an earthquake situated at the bottom of the gap. ③ The focal depths of M_L≥2.0 earthquakes in the middle part of the Hebei plain seismic belt gradually deepened from 10 km to 30 km from April, 2003 to October, 2004. Meanwhile the seismic activity obviously strengthened in the middle and lower crust (from 20 km to 30 km in depth).