A re-assessment of the faulting in the 1967 Mogod earthquakes in Mongolia

The 1967 January 5 Mogod earthquake (M-s 7.5, M-w 7.1) in Mongolia produced spectacular surface faulting and has been the subject of several previous seismological and field reports. However, early field accounts were sketchy, and existing seismological analyses preceded the detailed field descriptions that are now available. In this paper we synthesize information on surface ruptures (both published and supplemented by our own observations), geomorphology and satellite imagery with a new seismological analysis of long-period P and SH waveforms and aftershock relocations to produce a description of the faulting in the Mogod earthquake sequence that is self-consistent and compatible with all this information. The main shock ruptured in three subevents occurring sequentially from north to south, all of them associated with segments of coseismic surface faulting. The first and second subevents involved predominantly N-S right-lateral strike slip, with the second, larger one occurring on a fault dipping steeply east with a significant reverse component of slip. The third subevent involved thrust faulting with a NW-SE strike at the southern end of the strike-slip faulting. A large (M-w 6.4) aftershock on January 20 was associated with a different thrust fault segment, which terminates the southern end of the strike-slip rupture in the first subevent. The association of the surface faulting and seismology with the geomorphology gives some insight into how the faulting in this region evolves with time.