New perspectives on seismicity: a bridge between seismic swarms, slow slides and underground fluids
Research
Published on January 16, 2025–Updated on January 16, 2025
Dates
on the December 12, 2024
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A study by researchers at GEOAZUR and INGV Bologna has opened up new perspectives on seismic swarms and induced seismicity by linking them to the mechanisms of slow landslides. Their work sheds further light on the mechanisms that trigger seismicity, provides a better understanding of the role of asismic deformation, and opens up new avenues for constraining the physical processes underlying seismic sequences that are still poorly understood.
Global seismicity is organized into several types of sequences. In "main shock - aftershock" sequences, a major earthquake is followed by numerous smaller aftershocks, the number of which diminishes over time. In contrast, seismic swarms are characterized by continuous seismic activity, lasting from a few hours to several days. These swarms occur in various tectonic contexts (subduction zones, rifts, transform faults, etc.), but also in environments linked to human activity, such as the injection of fluids into the subsoil (e.g. deep geothermal energy). In subduction zones, slow landslides are also observed, marked by so-called asismic displacement that can be accompanied by tremors and low-frequency earthquakes.
schema geoazur
Seismicity migration speed as a function of duration for different types of fluid-induced (FI) and slow slip (SSD) sequences worldwide. The results highlight that both sequences may involve similar dynamics, but differ in their underlying causes.
Migration of seismic foci was frequently observed during these phenomena, propagating along faults over time. This migration may offer valuable insights into the hydromechanical processes at work at depth, but it remains poorly understood. The study by Philippe Danré (carried out during his PhD thesis) and his collaborators is based on a global comparison of seismic migration phenomena, across more than a hundred sequences from a variety of tectonic contexts. The authors identify a certain regularity in migration speed as a function of sequence duration, enabling them to define two distinct domains: one associated with well-documented episodes of slow sliding, and the other with episodes induced by deep-seated fluid circulation. This dichotomy provides a valuable tool for identifying the mechanisms behind precursor swarms or seismic sequences.
Furthermore, the moment released during fluid-induced swarms shows similar behavior to that of slow slides, when the asismic contribution to deformation is taken into account. The authors thus introduce a third deformation behavior, in addition to conventional earthquakes and slow earthquakes: that of fluid-induced seismic swarms.
Philippe Danré, who carried out this work during his thesis and post-doctoral contract (ANR INSeis, Coordinator: Louis De Barros) at Géoazur, will now continue his post-doctorate in Strasbourg (ITES laboratory).
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