REGULARITIES OF INITIATING DYNAMIC MOVEMENTS ALONG FAULTS CONTAINING CONTACT PATCHES. LABORATORY EXPERIMENT

Abstract

This paper considers regularities of shearing model faults containing contact patches of different composition. Samples of quartzites and amphibolites collected at the Primorsky Fault of the Baikal Rift Zone, in its seismogenic and aseismic segments exhumed to the day surface, were pounded and used to fill the contact patches. It is shown that the material composing the patches does not affect on regularities of accumulating deformation. During the increase of shear force, a «locked» region emerges nearby the contact patch, where a deficit of deformation is observed. The material composition has a critical effect on the release of the accumulated deformations along the model fault. Dynamic ruptures are realized on quartz-containing contact patches with velocity-weakening behaviour. They are accompanied by the emission of oscillations in the frequency range of 1 Hz to 80 kHz. Ruptures in amphibole-containing contact patches with velocity-strengthening behaviour produce oscillations in the frequency range of 20– 80 kHz, oscillations with frequencies less than 10 kHz were not detected. It is shown that dynamic movements lead to microstructural changes in the geomaterial composing the contact patch. Minerals are abraded unevenly in the slip plane, the abrasion is accompanied by secondary mineral formation. High- temperature phase transformations of quartz into tridymite are detected at a temperature of ~ 700°C as a result of fast dynamic movements along quartz-containing contact patches.