Variations in Structural, Physical and Mechanical Properties of a Tectonic Fault in the Near-Surface Zone

Abstract—Tectonic faults are characterized by a heterogeneous structure, which determines the spatial variation of their deformation modes from aseismic creep and slow-slip events to dynamic ruptures, which are the sources of earthquakes of varying magnitudes. Based on a comprehensive analysis of geological and geophysical information, the authors investigated the features of localization of the deformations and slip modes along a 160-km section of the collision suture between the Siberian Craton and the Olkhon Terrane from the settlement of Buguldeyka to the village of Kurma. The width of the zone of the most intense deformations within the suture varies from 100 to 500 m in its different segments, while estimates of its width based on electric resistivity tomographic measurements and petrographic studies of rock samples taken from exhumed sections of the suture are comparable. Analysis of the material composition and frictional behavior of the collected samples showed that the fault segments with the narrowest width comprise rocks with the property of velocity weakening and are nucleation zones of strong earthquake foci. The typical length of such segments is about 10 km, and the distance between them is about 60 km. Segments hundreds of meters wide are also distinguished along the fault, comprising rocks with the property of velocity strengthening, where accumulated stresses relax through slow slip and aseismic creep.