Leveraging spurious Omori-Utsu relation in the nearest-neighbor declustering method

TL;DR

This paper reveals that the nearest-neighbor declustering method can produce false Omori-Utsu relations in earthquake catalogs without actual triggering, but the method's parameters can help distinguish true aftershock sequences from spurious correlations.

Contribution

It analytically and numerically demonstrates the origin of spurious relations in declustering and proposes parameter robustness as a criterion to identify genuine aftershocks.

Findings

Spurious Omori-Utsu relations can arise without triggering.

Parameter robustness helps distinguish true aftershocks.

Natural swarm catalog is dominated by aftershocks.

Abstract

Static and dynamic stress changes in the Earth's crust induced by an earthquake typically trigger other earthquakes. Identifying such aftershocks is an important step in seismic hazard assessment but has remained challenging, especially in cases involving natural fluid migration or anthropogenic fluid injections, which can occur with varying time scales and/or episodically, leading to strong temporal variations in earthquake occurrences. Here, we demonstrate analytically and numerically that earthquake catalogs without triggering can lead to spurious Omori-Utsu and productivity relations for the commonly used nearest-neighbor declustering method. However, we show that the robustness of the Omori-Utsu exponent on newly introduced parameters of the method allows one to determine whether indeed aftershocks are present. For a natural swarm catalog, which lacks a clear distinction between triggered and background events, we find that the catalog is dominated by aftershocks.