ONE OF THE SCENARIOS FOR SUPERSHEAR EARTHQUAKES

Abstract

This paper is a part of the study on rupture propagation and seismic wave emission during movement along the fault, the main displacement of which in different regions is made by geomaterials with different frictional properties. The slip surface of the fault is not frictionally homogeneous. It contains asperities, barriers and “background” regions that are almost neutral with respect to velocity and displacement. The scenario of a seismogenic rupture is determined precisely by the presence, number and size of such regions with different dynamics of frictional characteristics. The study deals with the mechanics of supershear earthquakes, in which the rupture propagates with an unusually high velocity exceeding the shear wave velocity of the medium. Numerical simulation results confirm the existence of two different mechanisms governing the transition of an earthquake to a supershear regime. A model of the so-called “weak” fault is considered, for which the rupture velocity continuously increases from the sub-Rayleigh velocity CR to the shear wave velocity Cs and quickly exceeds it without any jump. This scenario is typical for faults with the value of the measure of strength S not reaching 0.8. The solved problem is not only of fundamental importance for understanding the earthquake mechanics, but also can find application in engineering seismology and the study of earthquake-induced rupture processes, because unlike an ordinary earthquake, supershear or fast ruptures cause strong shaking at a much greater distance from the source of the event (from the fault). This is confirmed by direct data on near-field ground motion obtained in recent years by research groups from different countries.