A study for the mechanism of M(S) 6.4 earthquake on May 3, 1996, at west Bao Tou, Nei Mongol

The mechanism of M(S) 6.4 earthquake on May 3, 1996, at west Bao Tou, Nei Mongol, is estimated with a joint inversion method using mantle waveform fitting and P wave first motion signs. Nodal plane 1(40°, 70°, -174°), nodal plane 2(308°, 84°, - 20°); principal compressive axis P(- 13.95 x 10¹⁷Nm, 262°, 19°), principal extensional axis T(15.66 x 10¹⁷Nm, 356°, 10°), neutral axis N(B) (1.52 x 10¹⁷Nm, 112°, 69°) are obtained. The earthquake formed a left-lateral strike-slip and weak displip fault, and the fault plane is steep. That nodal plane 2 may be near the actual fault plane is inferred by the distribution of aftershocks with M(L)≥3.0 and the distribution of earthquake intensity with degree VIII, as well as the relative position of macroscopic epicenter to the microcosmic one. That the source depth is about 21km was estimated by the time differences between sP and P arrival time on BHZ channel.