Are megaquakes clustered?

TL;DR

This study analyzes earthquake data over the past century and finds that, generally, large earthquakes occur randomly in time, with some clustering at lower magnitudes over longer intervals, mainly due to early 20th-century data uncertainties.

Contribution

It provides a comprehensive statistical analysis showing that large earthquakes are mostly random in time, with specific clustering observed only at lower magnitudes and longer intervals, influenced by historical data uncertainties.

Findings

Earthquake occurrences are generally consistent with a random process.

Significant clustering appears only at lower magnitudes (7-7.2) over 2-5 year intervals.

Clustering signals are affected by early 20th-century data uncertainties.

Abstract

We study statistical properties of the number of large earthquakes over the past century. We analyze the cumulative distribution of the number of earthquakes with magnitude larger than threshold M in time interval T, and quantify the statistical significance of these results by simulating a large number of synthetic random catalogs. We find that in general, the earthquake record cannot be distinguished from a process that is random in time. This conclusion holds whether aftershocks are removed or not, except at magnitudes below M = 7.3. At long time intervals (T = 2-5 years), we find that statistically significant clustering is present in the catalog for lower magnitude thresholds (M = 7-7.2). However, this clustering is due to a large number of earthquakes on record in the early part of the 20th century, when magnitudes are less certain.