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EARTHQUAKE ›› 2010, Vol. 30 ›› Issue (1): 10-19.

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

XUE Yan1,2, ZHOU Long-quan2, MA Hong-sheng3, LIU Jie2   

  1. 1. Institute of Geophysics, CEA, Beijing 100081, China;
    2. China Earthquake Networks Center, Beijing 100045,China;
    3. Institute of Earthquake Science, CEA, Beijing 100036, China
  • Received:2009-05-11 Revised:2009-08-21 Online:2010-01-31 Published:2021-10-15

Abstract: 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 ML≥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 ML≥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).

Key words: Wen'an earthquake, Small earthquake relocation, Seismic gap, Focal depth

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