Faulting associated with large earthquakes and the average rate of deformation in central and eastern Asia

Abstract

We determine approximate average rates of deformation in portions of eastern and central Asia for the last 80 years. These rates are based on estimates of source dimensions, average displacements, seismic moments, and orientations of faults of all large earthquakes (M>7.5) and as many other major earthquakes (M≥7.0) as possible in Asia since 1900. A major part of this study is the compilation of these data. For separate parts of Asia we combine seismic moment tensors to estimate the average rotational strain (or deformation) tensors for these regions for the last 80 years. We estimate that shortening across the Tien Shan has occurred at 11 mm/yr (between 5 and 19 mm/yr). Left‐lateral shear on easterly trending planes in Mongolia, in northwestern Tibet, Gansu, and Ningxia, and on the Xianshuihe fault in western Sichuan has been very rapid, more than 10 mm/yr in each region, and apparently as rapid as 40 mm/yr in northwestern Tibet, Gansu, and Ningxia. Slower rates of a few to 10 mm/yr appear to characterize east‐west extension and conjugate north‐south shortening of Tibet. The earthquake history of the Himalaya is consistent with rates of underthrusting of more than 10 mm/yr but is probably less than the convergence rate of India with Eurasia of about 50 mm/yr. The overall strain field is consistent with a large part of India's penetration into Eurasia being absorbed by the extrusion of material out of India's way. As a result, southeast China moved at about 21 mm/yr east‐southeast with respect to Eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate.