Three-dimensional Q structure in Jiashi earthquake region of Xinjiang

Introduction It is well known that the occurrence of moderate and strong earthquakes and the distribution of seismically active belts are most directly related to deep crustal faults. Therefore, studying geometrical spreading and physical state of medium of deep crustal faults has always been a major subject in earthquake science. It is not only of great significance to the understanding of deep structural background and seismogenic mechanism of strong earthquakes, but also of great help to se…

Three-dimensional Q structure in Jiashi earthquake region of Xinjiang

D S-wave Q structure in Jiashi earthquake region is inverted based on the attenuation of seismic waves recorded from earthquakes in this region in 1998 by the Research Center of Exploration Geophysics (RCEG), CSB, and a rough configuration of deep crustal faults in the earthquake region is presented. First, amplitude spectra of S-waves are extracted from 450 carefully-chosen earthquake records, called observed amplitude spectra. Then, after instru-mental and site effect correction, theoretical amplitude spectra are made to fit observed amplitude spectra with nonlinear damped least-squares method to get the observed travel time over Q, provided that earthquake sources conform to Brunes disk dislocation model. Finally, by 3-D ray tracing method, theoretical travel time over Q is made to fit observed travel time over Q with nonlinear damped least-squares method. In the course of fitting, the velocity model, which is obtained by 3-D travel time tomography, remains unchanged, while only Q model is modified. When fitting came to the given accuracy, the ultimate Q model is obtained. The result shows that an NE-trending low Q zone exists at the depths of 10~18 km, and an NW-trending low Q zone exists at the depths of 12~18 km. These roughly coincide with the NE-trending and the NW-trending low velocity zones revealed by other scientists. The difference is that the low Q zones have a wider range than the low velocity zones.