天山中部的地震定位和地壳活动性分析

Analysis of seismic activity in the crust from earthquake relocation in the Central Tian Shan

利用宽频带流动台网记录的地震P波和S波到时,根据一维和三维地壳速度模型,对天山中部及其邻近地区1997～1998年的地震进行了重新定位,以重新确定的震源参数为依据分析了地壳的活动性.震源分布表明,造山带边缘和内部的大部分断裂都显示出活动的迹象,它们对天山的地壳构造变动起到明显的作用;塔拉斯-费尔干纳断裂的活动具有分段特征:其东南段以及西南天山的部分断裂目前活动比较弱,西北段受周边断裂的影响活动较强;另外造山带边缘的构造活动有向山前盆地渗透(Penetration)的趋势.30～40km深度的地震活动表明,天山中部的地壳中下层仍然具有一定的破裂条件,它们与壳幔边界附近热扰动的驱动有关,暗示小尺度地幔对流或软流层上涌等动力作用仍在持续进行.

Using P and S wave arrivals from local and regional earthquakes recorded by a temporary broadband seismic network, we relocated the earthquakes occurring in the central Tian Shan and adjacent areas during 1997 - 1998, based on one-dimensional and three-dimensional velocity models. Seismic activity in the crust was analyzed according to the source parameters of these relocated earthquakes. Earthquake distribution indicates that most range-bounding faults within the orogenic belt are active and they have played a significant role in the tectonic activity of the crust of the Tian Shan. However, the seismic activity along the Talas-Fergana fault reveals a different feature： the activity of its southeast segment and some faults in the southwestern Tian Shan is weak at present, while its northwestern segment, probably activated by adjacent faults, is more active. Tectonic activity seems to penetrate from the margin of the Tian Shan into foreland basins on the north and south. The earthquakes at 30 - 40km depths indicate that brittle ruptures exist in the mid-lower crust of the central Tian Shan and they are probably induced by thermal perturbation near the crust-mantle boundary. This means that dynamic processes roles like small-scale mantle convection and asthenosphere upwelling are still ongoing in the central Tian Shan.