Macroscopic Fault Structure of the 1911 Mw8.1 Chon Kemin Earthquake (Tien Shan, Kyrgyzstan) from Combined Seismic Imaging, Palaeo-Seismological Investigations and Historial Seismicity

Tuesday, 16 December 2014
Tim Sonnemann1, Christian A Haberland2, Angela Landgraf3, Trond Ryberg2, Galina Kulikova4, Frank Krueger3, Atyrgul Dzhumabaeva5, Kanatbek Abdrakhmatov5, Ulan Abdybachaev6, Sagynbek Orunbaev6, Swenja Rosenwinkel3 and Azamat Sharshebaev6, (1)Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, (2)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (3)University of Potsdam, Potsdam, Germany, (4)University of Potsdam, Potsdam - Golm, Germany, (5)Institute of Seismology, Bishkek, Kyrgyz, (6)CAIAG, Bishkek, Kyrgyz
Earthquakes in low-strain regions and their driving forces are still sparsely studied and understood, and constitute serious first-order research questions. Data acquisition concerning paleo-earthquakes, related hazards, and tectonic activity beyond historical records plays an important role. Such information can be obtained with tools from tectonic geomorphology, geophysics, historic seismicity, and paleo-seismology that should span a variety of time and length scales.
The Chon-Kemin Valley in the northern Tien Shan (Kyrgyzstan) is a small, intermontane basin of unknown origin framed by a network of active faults. In the year 1911, the Chon-Kemin earthquake (Mw=8.1) activated fault structures of about 200 km length which also ruptured the surface along the Chon-Kemin Valley and caused numerous landslides and rock avalanches of up to several tens of millions of cubic meters in volume. The Chon-Kemin earthquake was one of a series of strong seismic events that affected the northern Tien Shan between 1885 and 1938.
A seismic survey across the Chon-Kemin Valley was conducted to investigate the subsurface velocity structure of the valley and its surrounding faults. Tomographic inversion techniques were applied to first-arrival traveltimes of refracted P waves, and the seismic data were screened for reflection signatures. Additionally, the region was analyzed through paleo-seismological trenching.
Tomographic and reflection images identified a shallow basin structure bounded by a set of thrust faults in the south only which - in part – correlate with the surface trace of the rupture. The deformation seems to be distributed in time and space across several sub-parallel fault strands. Synthesis of historical (analog) recordings of this earthquake provide new insights into the source mechanisms and processes.