Origin of the Co‐Seismic Variations of Elastic Properties in the Crust: Insight From the Laboratory. Issue 12 (22nd June 2021)

• Record Type: Journal Article
• Authors: Paglialunga, F.; Passelègue, F. X.; Acosta, M.; Violay, M.
• Is Part Of: Geophysical research letters. Volume 48:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-22
• Subjects: damage zone -- dynamic rupture -- faulting -- friction -- seismic properties; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL093619
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Seismological observations highlighted that earthquakes are often followed by changes in elastic properties around the fault zone. Here, we studied the origin of these variations using stick‐slip experiments on saw‐cut granite samples presenting different degrees of bulk damage (i.e., microcracks). Stick‐slip events were induced under triaxial compression configuration with continuous active ultrasonic measurements at confining pressures representative of upper crustal conditions (15–120 MPa). Both the P‐wave velocity ( V P ) and amplitude ( A P ) showed drops, concurrently with stress drops, and had a non‐monotonic dependence toward the fault's stress state. Our experimental results suggest that co‐seismic changes in V P were mostly controlled by the elastic re‐opening of microcracks in the bulk, rather than by co‐seismic damage or the formation of fault gouge. Co‐seismic changes in A P were controlled by a combination of elastic re‐opening of microcracks in the bulk and inelastic processes (i.e., co‐seismic damage and gouge formation and dilation). Plain Language Summary: Seismological studies have shown that the elastic properties of fault cores can be drastically affected by earthquakes. Despite the large number of studies, the origin of these variations is still debated. It is well known that in the upper crust, faults are surrounded by a zone of damage which could, as well, influence co‐seismic changes in elastic properties. We experimentally investigated the influence of a zone of damage surrounding the fault, on the evolution of elastic wave velocity and amplitude during stick‐slip experiments (proxies for earthquakes) on thermally treated granite samples. Our results indicate that the presence of a damage zone strongly contributes to the observed changes in elastic properties during earthquakes. Key Points: Laboratory earthquakes are associated with seismic velocity and amplitude drops in crustal rocks Velocity drops are controlled by the stress acting on the fault and degree of damage in the fault wall Amplitude drops are partly controlled by the state of stress and partly affected by dissipative (inelastic) phenomena occurring on‐fault