Analysis of Seismic Activity in the Crust from Earthquake Relocation in the Central Tien Shan

Abstract

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 Tien Shan and adjacent areas during 1997~1998, based on one-dimensional and three-dimensional velocity models. Seismic activity within crust was analyzed according to the source parameters of these relocated earthquakes. Earthquake distribution indicates that most range-bounding faults within the mountain belt are active and they have played a significant role in tectonic activity of the crust of the Tien Shan. However, seismic activity along the Talas-Fergana fault shows different features: the activity on its southeast segment and other faults in the southwest Tien Shan is less active, while its northwest segment, probably activated by adjacent faults, is more active. In addition, seismic activity seems to penetrate from the margins of the mountain belt into foreland basins on the north and south. The earthquakes at 30~40km depths indicate that brittle failure can take place in the mid-lower crust beneath the central Tien Shan and they are probably related to thermal perturbation near the crust-mantle boundary. This means that dynamic processes such as small-scale mantle convection and asthenosphere upwelling are still ongoing beneath the central Tien Shan.