Spatial Correlations of Global Seismic Noise Properties

Abstract

A study of global seismic noise during 1997–2022 was carried out. A property of waveforms known as the Donoho–Johnston (DJ) index was used, which separates the values of the wavelet coefficients into “small” and “large”. For each reference point in an auxiliary network of 50 points, a time series was calculated with a time step of one day for the median of the values at the five nearest stations. In a moving time window of 365 days, correlations between the index values at the reference points were calculated. A decrease in the average values of the DJ-index and an increase in correlations were interpreted as a sign of an increase in global seismic danger. After 2011, there was a sharp increase in the maximum distances between reference points with large correlations. The high amplitude of the response of the DJ-index to the length of the day for 2020–2022 could predict a strong earthquake in the second half of 2023. The purpose of this study was to improve the mathematical apparatus for assessing the current seismic hazard according to the properties of seismic noise.

Keywords

• seismic noise
• wavelet-based entropy
• wavelet-based Donoho–Johnston index
• correlations
• day length