Abstract
AbstractHere we focus on a basic statistical measure of earthquake catalogs that has not been studied before, the asymmetry of interevent time series (e.g., reflecting the tendency to have more aftershocks than spontaneous earthquakes). We define the asymmetry metric as the ratio between the number of positive interevent time increments minus negative increments and the total (positive plus negative) number of increments. Such asymmetry commonly exists in time series data for nonlinear geophysical systems like river flow which decays slowly and increases rapidly. We find that earthquake interevent time series are significantly asymmetric, where the asymmetry function exhibits a significant crossover to weak asymmetry at large lag index. We suggest that the Omori law can be associated with the large asymmetry at short time intervals below the crossover whereas overlapping aftershock sequences and the spontaneous events can be associated with a fast decay of asymmetry above the crossover. We show that the asymmetry is better reproduced by a recently modified Epidemic‐Type Aftershock Sequence (ETAS) model with two triggering processes in comparison to the standard ETAS model which only has one.
Highlights
Earthquakes are a major threat to society in many countries around the world
We study the asymmetry of synthetic catalogs based on the Epidemic–Type Aftershock Sequence (ETAS) model in comparison to the asymmetry observed in the time series of real records
We further study the dependence of the interevent time increments ∆τik on the mag(k) nitude increment ∆mi = mi+k −mi, to understand in more details the role of Omori law on the asymmetry
Summary
Earthquakes are a major threat to society in many countries around the world. A skillful and trustworthy earthquake forecasting approach for both short and long time scales is missing. Seismologists are not yet able to predict individual large earthquakes even very close to the event (Jordan et al, 2011; de Arcangelis et al, 2016). Earthquake catalogs are usually restricted to specific regions and include the magnitude, location, and time of earthquakes. Several seismic laws have been discovered based on earthquake records. According to the Gutenberg-Richter law, the number of earthquakes N (above a magnitude M ) drops exponentially with the magnitude such that, log N = a − bM , where b ≈ 1 and a is related to the earthquake rate
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