Velocity fields in deforming Asia from the inversion of earthquake‐released strains

Abstract

Average strain rates in sectors of deforming Asia are matched by a fifth‐order polynomial function, and that function integrated, to obtain the relative velocities and rotations occurring within east Tibet, western Sichuan, Yunnan, and south China. The method was applied to strain rates obtained from moment tensor summation of both modern and historic earthquakes but can be applied as well to strains obtained from Quaternary slip rates on major faults. If south China has negligible motion relative to Siberia, then the velocity results indicate that nearly all of the expected motion between India and the south China portion of Eurasia has, in the last 85 years, been accommodated by distributed intraplate deformation in east Burma, Yunnan, western Sichuan, and east Tibet. Calculations indicate that these regions constitute a zone of distributed right‐lateral shear that accommodates an overall north‐south sense of relative motion between east Tibet and south China and India and south China. Line elements parallel to both right‐lateral and left‐lateral faults in east Burma and western Yunnan are rotating clockwise relative to south China, with the line elements parallel to left‐lateral faults rotating most rapidly (2.0 ± 0.5°/m.y.). In eastern Tibet and the Gansu‐Ningxia, NW‐SE trending left‐lateral faults give rotation clockwise relative to south China (1–2.5°/m.y.). In central Tibet and western Sichuan, right‐lateral faults give slight counterclockwise rotation rates relative to south China (0.5–0.75°/m.y.) Instantaneous rotation rates within the deforming region, extrapolated over a 20–40 m.y. time period, are in rough agreement with the paleomagnetic rotations measured in Cretaceous‐aged rocks.