Two Memorable Dates in Seismology

TL;DR

This paper reviews the historical development of aftershock laws in seismology, compares Omori's and Hirano's laws, and discusses modern phenomenological theories revealing new geophysical phenomena.

Contribution

It provides a comprehensive overview of the evolution of aftershock modeling and introduces recent phenomenological approaches uncovering previously unknown seismic phenomena.

Findings

Comparison of Omori and Hirano laws

Discovery of new geophysical phenomena in aftershock evolution

Development of modern phenomenological seismology theories

Abstract

130 years ago, Omori formulated the first law of earthquake physics. The essence of the law is that the frequency of aftershocks decreases hyperbolically over time. 100 years ago, Hirano doubted the universality of Omori law and proposed a power law for the evolution of aftershocks. Our paper is devoted to these two outstanding events, which played a significant role in the development of seismology. The paper also contains a brief summary of the modern approach to the construction of a phenomenological theory of aftershocks. Within the framework of the phenomenological approach, the epoch of harmonic evolution of the source, cooling down after the main shock, the bifurcation of the source, the cumulative effect of a round-the-world echo, the modulation of global seismicity by spheroidal oscillations of the Earth, mirror triads, migration of aftershocks, and a number of other previously unknown geophysical phenomena were discovered. It is emphasized that the phenomenological theory has been formed in recent years on the basis of a thorough analysis of the fundamental research of the pioneers who laid the foundations of modern seismology. Keywords: earthquake, aftershock, Omori law, Hirano-Utsu law, source deactivation, proper time, evolution equation.