Focal parameters of strong earthquakes of Baikal area: The main regularities

Abstract

971 The structure of sampling containing the focal mechanisms of strong earthquakes of CisBaikalia is analyzed, and the average distributions of parameters are obtained on the entire sampling and depending on the slip type in a seismic source. The main regularities are formed by the quantitatively predominant quakes with normal faulting mechanisms. After the sam� pling's subdivision into normal faulting, strikeslip, and reverse faulting mechanisms, both significant dif� ferences and coincidences of focal mechanisms were found. The correspondence between average dipping angles , moduli of slipping angles SLIP, and strike azimuths STK indicates possible displacements on the zones of the same faults. The average dipping angles for slips of different types exceed 50°, indicating a steep sink of the fault zones. Focal parameters enable us to estimate the stressed state of a medium and the structure of ruptures in a fault zone in which an earthquake has occurred. This information is unique because there are no other methods of definition and parametric description of the geophysical state for rocks at great depths yet. Understanding of how important the solution of this problem is for the region of CisBaikalia has been reached long time ago (1), and the systematic defini� tion of focal mechanisms for strong earthquakes (energy class is KР ≥ 10) has been carried out in the region for more than half a century. Information about the focal mechanisms for strong earthquakes for the region of CisBaikalia has been presented in numerous publications, but unfortunately there is no united database yet. The sampling containing the focal mech� anisms of strong earthquakes of CisBaikalia, which is used in the present study, was compiled by the author on the basis of published sources in order to compare the focal mechanisms and the dynamical parameters of earthquake sources (2). The results of statistical aver DP processing of focal parameters for 335 strong (KР≥10) earthquake that occurred in the period since 1950 until 1998 in the region of CisBaikalia characterize the dis� tributions of the available solutions of focal mecha� nisms.