The Late Quaternary slip-rate of the Kichera Fault (North Baikal Rift) from morphotectonic, paleoseismological and cosmogenic 10Be analyses
Résumé
Late Quaternary slip rates characterize the seismic potential of an active fault in terms of estimating the average expected recurrence period for rupturing episodes. Along the Baikal Rift faults the slip rate distributions are poorly understood. This study provides morphotectonic and paleoseismological analyses of the Kichera Fault that stretches within the North Baikal Rift over a length of 100 km. Exposure ages of key displaced terraces of the Neruchanda River from in-situ produced cosmogenic Be-10 depth profiles show that the highest terrace T5 is older than 315 ka, intermediate terrace T3 was abandoned 100.0 +/- 30 ka ago and the lowest terrace T1 is as old as 48.3 +/- 19.9 ka. These exposure ages, coupled with terrace elevation from the actual Neruchanda River bed, allow us to estimate the incision rates for the corresponding time periods which are 0.1 (maximum), 0.16 +/- 0.05 and 0.19 +/- 0.08 mm yr(-1), respectively. Using the cumulated amplitudes of the terrace displacement, we estimate the vertical slip rates along the Kichera Fault are 0.42 +/- 0.13 and 0.19 +/- 0.08 mm yr(-1) over the last similar to 100 ka and similar to 48.3 ka, respectively. Paleoseismological studies including morphomertic analyses of the tectonic scarp and trenching across the fault allowed estimating the age (5.4 ka) and minimum magnitude (6.8) of the last Kichera Fault rupture. Using the estimates of short- and long-term slip rates, we propose mean recurrence intervals of 5.3 and 2.4 ka, respectively. The last interval is shorter than the time since the last earthquake, indicating that the future event could be of greater magnitude to maintain the long-term average slip rate.