Great earthquakes in low strain rate continental interiors: An example from SE Kazakhstan

The Lepsy fault of the northern Tien Shan, SE Kazakhstan, extends E-W 120 km from the high mountains of the Dzhungarian Ala-tau, a sub-range of the northern Tien Shan, into the low-lying Kazakh platform. It is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region (SCR), and follows a known Palaeozoic structure. Field-based and satellite observations reveal a ~10 m vertical offset exceptionally preserved along the entire length of the fault. Geomorphic analysis and age control from radiocarbon and optically stimulated luminescence (OSL) dating methods indicate that the scarp formed in the Holocene and was generated by at least two substantial earthquakes. The most recent event, dated to some time after ~400 years BP, is likely to have ruptured the entire 120 km fault length in a Mw 7.5{8.2 earthquake. The Lepsy fault kinematics were characterised using digital elevation models and high-resolution satellite imagery, which indicate that the predominant sense of motion is reverse right-lateral with a fault strike, dip and slip vector azimuth of ~110°, 50°S and 317{343 respectively, which is consistent with predominant N-S shortening related to the India-Eurasia collision. In light of these observations, and because the activity of the Lepsy fault would have been hard to ascertain if it had not ruptured in the recent past, we note that the absence of known active faults within low-relief and low strain-rate continental interiors does not always imply an absence of seismic hazard.We thank NERC for a small grant (NE/G010978/1) awarded to RTW, the Royal Society International Travel Grant, Mike Coward Fund of the Geological Society of London, Percy Sladen Fund of the Linnean Society, The Gilchrist Educational Trust, and the Earth and Space Foundation for their support in funding the field component of this project. GEC's doctoral studentship is funded by the National Environmental Research Council (NERC). RTW is supported by a University Research Fellowship awarded by the Royal Society. We also thank the National Centre for Earth Observation (NCEO), the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET+), and the NERC-ESRC funded project, Earthquakes without Frontiers (EwF), all of which have contributed to the funding of this project. DigitalGlobe high resolution satellite imagery was obtained from Google Earth (earth.google.co.uk/). Shuttle Radar Topography Mission (SRTM) was obtained from CGIAR-CSI.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/2015JB01192