Surface rupture of the 1933 M 7.5 Diexi earthquake in eastern Tibet: Implications for seismogenic tectonics

Abstract

The 1933M7.5 Diexi earthquake is another catastrophic event with the loss of over 10 000 lives in eastern Tibet comparable to the 2008Mw 7.9Wenchuan earthquake. Because of its unknown surface rupture, the seismogenic tectonics of the 1933 earthquake remains controversial. We collected unpublished reports, literatures and old photos associated with the 1933 earthquake and conducted field investigations based on high-resolution Google Earth imagery. Combined with palaeoseismological analysis, radiocarbon dating and relocated earthquakes, our results demonstrate that the source of the 1933 earthquake is the northwest-trending Songpinggou fault. This quake produced a > 30 km long normal-faulting surface rupture with the coseismic offset of 0.9-1.7 m. Its moment magnitude (Mw) is ~6.8. The Songpinggou fault undergoes an average vertical slip rate of ~0.25 mm yr-1 and has a recurrence interval of ~6700 yr of large earthquakes. The normal-faulting surface rupture of this quake is probably the reactivation of the Mesozoic Jiaochang tectonic belt in gravitational adjustment of eastern Tibet. Besides the major boundary faults, minor structures within continental blocks may take a role in strain partitioning of eastern Tibet and have the potential of producing large earthquake. This study contributes to a full understanding of seismotectonics of large earthquakes and strain partitioning in eastern Tibet.