Three Problems in Aftershock Physics
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e Problems in Aftershock Physics A. D. Zavyalova, *, A. V. Guglielmia, and O. D. Zotova aInstitute
of Physics of the Earth, Russian Academy of Sciences, B. Gruzinskaya, 10, str. 1, Moscow, 123242 Russia *e-mail: [email protected] Received March 30, 2020; revised May 20, 2020; accepted June 1, 2020
Abstract—In recent years three new problems emerged in aftershock physics. We shall refer to these problems in a preliminary way as the dynamic, the inverse, and the morphological problem. They have been distinctly stated, partially solved, and have a fundamental character. The dynamic problem consists in searching for the effect of a circumnavigating seismic echo that occurs after the main shock of an earthquake. According to theory, the convergent seismic surface wave due to a main shock returns to the epicenter about 3 h later and initiates the occurrence of a large aftershock. The results of our study corroborate this theory. The second problem consists in an adequate description of the average evolution of the aftershock process. We introduce a new quantity, a deactivation coefficient for an earthquake source. It describes the “cooling” of the source after the main shock, and we proposed an equation to describe aftershock evolution. We used the evolutionary equation to formulate and solve the inverse problem in earthquake source physics, resulting in an Atlas of Aftershocks, which demonstrates the diversity of ways for the evolution of the deactivation coefficient. The third fundamental problem consists in modeling the spatial and space–time distribution of aftershocks. The solution enhances our understanding of the structure and dynamics of an earthquake source. We also discuss in great detail some other interesting problems in aftershock physics. Keywords: circumnavigating seismic echo, deactivation coefficient, evolutionary equation, inverse problem, space–time distribution of aftershocks DOI: 10.1134/S0742046320050073
1. INTRODUCTION The numerous aftershocks that follow large earthquakes have been under careful scrutiny of seismologists since the very inception of modern seismology (Davison, 1924, 1930). It is sufficient to recall that the first empirical law in earthquake physics was discovered by Fusakichi Omori, who studied aftershocks following several large earthquakes at the end of the last but one century (Omori, 1894). At present, there is a growing interest in the morphology, in the space– time organization of aftershocks, and in the physics of the aftershock process. This is no surprise, seeing that the observation and analysis of aftershocks provide valuable information on the evolution of the source of a large earthquake that is “cooling” down after the main shock. It is aftershocks which are responsible for the release of tectonic stresses stored in the source zone. The present study focuses on three separate problems in aftershock physics. We shall refer to these, in a preliminary way, as the dynamic, the inverse, and the morphologic problem. They are treated in Sections 2, 3, and 4, respectively. We
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