Surface Ruptures Associated with the 1937 M 7.5 Tuosuo Lake and the 1963 M 7.0 Alake Lake Earthquakes and the Paleoseismicity along the Tuosuo Lake Segment of the Kunlun Fault, Northern Tibet

Abstract

Examination of aerial photos taken in the late 1960s and field mapping allowed us to re-evaluate the surface ruptures associated with the 1937 M 7.5 Tuosuo Lake and 1963 M 7.0 Alake Lake earthquakes along the Tuosuo Lake and Alake Lake segments, central part of the Kunlun fault. Individual ruptures can be distinguished by their freshness of surface expression, slip distributions, and surficial geometry; they are separated by the geometrical bend that probably acts as an effective barrier to rupture propagation of these earthquakes. The rupture (∼40 km long with 1–2 m left-lateral slip) of the 1963 Alake Lake earthquake occurred on the west of the bend, whereas that of the 1937 Tuosuo Lake earthquake (about 150 km long with 4.1 m mean left-lateral offset) occurred on the east of the bend. The change of dip- slip sense reflects the characteristics of jogs and bends along the segment boundaries. Systematically and progressively displaced terrace risers and gullies indicate repeated activity of the fault during the late Quaternary. Five trenches excavated across the surface ruptures along the Tuosuo Lake segment reveal distinct indicators of paleoseismic events. At least nine earthquakes are constrained in the Holocene deposits, and a 630 ± 130 yr, upper-bound recurrence interval of large earthquakes in the past 2000 years is determined.