Magnitude of completeness, b-value, and spatial correlation dimension of earthquakes in the South Baikal Basin, Baikal Rift System

Abstract

Magnitude of completeness, b-value, and correlation dimension of spatial epicenter distribution were estimated for the South Baikal basin using earthquake catalogue for the period of digital observations. All estimated parameters were mapped with a one-for-all approach that allowed revealing their spatial variability. The value of the completeness magnitude, which was evaluated on the frequency-magnitude distribution, was found to range from Mc 1.0 to 1.6 over the basin depending on network configuration change, with the average value of 1.1 ± 0.1. Then, b-value in the Gutenberg-Richter relation was estimated by maximum likelihood method based on the catalogue with M ≥ 1.1 earthquakes. The lower b-value (0.81 ± 0.03) was revealed for the southern part of the basin which is under transtension stress regime in contrast to pure extension characteristic for the rest of the territory. The higher b-value (1.01 ± 0.01) was obtained for the area to the north-east of the Selenga delta, where two of the largest Baikal earthquakes occurred in the last 150 years, and which is characterized by more heterogeneous crust structure. Correlation dimension in the southern part of the basin was found to be closed to 1 that is interpreted as a tendency of epicenters to be distributed along a line; whereas the central part is characterized by a higher value that corresponds to a tendency of epicenters to be distributed over a plane rather than along lineaments. A comparison of the Southern and Central basins, which make up the tectonically single South Baikal basin, shows that seismicity of the Central basin is characterized by higher b-values and correlation dimension that may imply different stress level and/or faulting type.