Location and focal mechanism of the 1933 Diexi earthquake and its associated regional tectonics

The 1933 M7.5 Diexi, Sichuan, earthquake in western China caused tremendous loss of human lives and property damage. Because of data shortage,the seismogenic structure and focal mechanism of this earthquake are still not well constrained. Having collected worldwide seismic records of this earthquake, among which some polarities of the first arrival phases were picked, we relocated this earthquake and obtained the fault plane solution through grid search. The relocated epicenter of this earthquake is at (31.9deg;N, 103.6deg;E) and one of the nodal planes trends NNW, with the azimuth ranging N5deg;mdash;30deg;W. Taking this as the rupture plane of the Diexi earthquake, we conclude that the seismogenic structure is the southern segment of the Minjiang fault, which was dominated mainly by sinistral slip with a minor thrust component. GPS velocity profile across the Minshan mountains indicates that the Huya fault absorbs about 2 mm/a crustal shortening, which is associated with the rapid uplift process of the Minshan mountains since Quaternary. A discrepancy between the focal mechanism of the 1933 Diexi earthquake and the GPS determined present sense of motion across the Minjiang fault may be attributed to the interaction of crustal deformation processes of the Longmenshan and Minjiang fault systems and their earthquake cycles, particularly the role of Longmenshan fault system in modifying the regional deformation field at the late stage of preparing the 2008 Wenchuan earthquake.