SOURCE PARAMETERS OF MODERATE-SIZED EARTHQUAKES IN THE TIEN-SHAN, CENTRAL-ASIA FROM REGIONAL MOMENT TENSOR INVERSION

We estimate faulting geometry, depth, and seismic moment of 32 moderat e-sized earthquakes in the Tien Shan by matching observed and syntheti c seismograms recorded at regional distances. The moment-tenser compre ssion axes are oriented in the direction 170 degrees-350 degrees, cons istent with the orientation of India-Eurasia convergence. This compres sion is manifested in reverse faulting on roughly east-west trending f ault planes. Faults within the mountain system have moderate-to-steep dips, but range-bounding faults appear to dip more gently. Earthquake source depths are in the range 5-25 km, consistent with those determin ed from local earthquake studies. The distribution and mechanism of ea rthquakes in the Tien Shan suggests that a significant proportion of t he active deformation in the Tien Shan is absorbed by shortening acros s intramontane basins. The absence of strike-slip earthquake mechanism s associated with the Talas-Ferghana Fault suggests that the fault is presently locked, with deformation accommodated on neighboring compres sional structures.