Searching for signs of spectral depletion at repeated ruptures observed in repeating earthquakes in northern Chile

Abstract

The study of repeating earthquakes can provide critical insights into the dynamics of fault heal- ing and rupture processes, especially in seismically active regions like northern Chile. In this work the focus is on identifying spectral depletion in repeated ruptures, defined as the decrease in high-frequency radiation during a re-rupture of the same fault surface compared to the pre- vious earthquake. A deeper understanding of this process can be valuable for understanding fault behavior and improving earthquake hazard assessments. Using data from the IPOC seis- mic network, situated in northern Chile, advanced methods, such as template matching and cross-correlation analysis, are employed to detect repeating earthquake sequences. These are primary targets that have been postulated to exhibit spectral depletion. The key objective of this work is to evaluate the spectral characteristics of p-phase seismic waves, specifically their high- frequency content, across different recurrence intervals and then to compare the characteristics of events within a sequence. This is accomplished by applying a smoothing technique to the amplitude spectra of the events and measuring the gradient of the spectra using linear curve fitting. Good indications that spectral depletion is a function of fault healing can be found, if the slope of the fitted line can be correlated with the recurrence time of the repeaters. Despite thorough analysis, consistent signs of spectral depletion could not be observed. The results suggest three possible explanations: (I) either spectral depletion does not occur in the subduction zone, (II) fault healing in northern Chile might occur rapidly, completing within days and thus prohibiting the observation spectral depletion in the analyzed dataset, or (III) effects that modify the signal when propagated from the earthquake source need to be filtered out in a more sophisticated approach, as these remaining effects could significantly influence and potentially obscure the spectral depletion. These results underscore the complexity of fault processes and highlight the need for further research to fully elucidate the mechanisms driving spectral variations in repeating earthquakes. Understanding these processes is pivotal for enhancing predictive capabilities regarding earth- quake occurrences and their potential impacts in subductions zones.