Estimation of the Recurrence Period of Strong Earthquakes in Zones of the Main Sayan and Tunka Faults according to the Data of Radiocarbon Dating and Statistical Analysis

Abstract

The conventional radiocarbon ages of soil horizons limiting the timing of six fault-generating dis- placements within the East Sayan structure of the Main Sayan Fault and four displacements within the Tora structure of the Tunka Fault (M > 7) have been calibrated according to the IntCal04 calibration curve. It was revealed that between time periods of 12 Ka and 5.4 Ka years ago, the recurrence of earthquakes associated with movements along the faults in the East Sayan structure occurred once every 3000 years. After seismic quiescence, since 1100 years, one earthquake has occurred every 440 years. Using the Monte Carlo method, the possibility of the recurrence of strong earthquakes at different probability levels was considered. At a fre- quency probability of 95% the Main Sayan fault may be hazardous, dating from about 2120 AD. When low- ering the threshold probability to 72%, the beginning of the period of potential hazard is reduced to about 2030 AD. In both cases the maximum possibility of the occurrence of the next strong earthquake is not earlier than in the 22nd century. For the Tora structure, the periodicity of the recurrence of the earthquakes was esti- mated as 2800 yearsfor the past 11Ka with a probability of over 95% of the recurrence of earthquakes. This allows us to assume that currently the Tora structure is within the time interval of the potential risk of the recurrence of a strong earthquake.