Paleoseismological Investigations in the Chikoy Fault Zone (Southern Transbaikalia)

Abstract Active faults in Southern Transbaikalia, some of which are elements of the Mongolian–Okhotsk lineament, are still poorly studied seismically. The Chikoy fault has been characterized by weak earthquakes over a 100-year period of instrumental observations, which yields no knowledge of the seismic potential of the fault. However, distinct manifestation of a fault scarp in the modern relief suggests high rates of tectonic movements along it. This is also confirmed by the seismotectonic deformations discovered during our field studies. Field works in the Chikoy fault zone revealed signs of a seismogenic feature of the fault in segments with a total length of at least 32 km. Analysis of the morphology of the scarps and sections indicates that the dislocations were formed as a result of at least two to three paleoearthquakes with magnitudes of 7.0–7.2. According to absolute (radiocarbon) and relative (based on the slope of the scarps) dating data, the age of paleoearthquakes range from 5–8 ka, 2373–2832 years ago, and later than 760 years ago. The high seismic potential of the fault revealed by seismogeological data is confirmed by historical evidence of an earthquake with M = 6.0 that occurred here in 1830.