From Fault Creep to slow and fast Earthquakes in Carbonates

TL;DR

This study reproduces the full spectrum of faulting behaviors in carbonate rocks under conditions mimicking deep crustal environments, revealing how temperature and pressure influence transitions from fault creep to slow and fast earthquakes.

Contribution

It provides the first laboratory evidence of how increasing temperature and pressure induce transitions from fault creep to slow and fast seismic ruptures in carbonate rocks.

Findings

Transitions from fault creep to slow and fast ruptures are achieved by increasing P and T.

Temperature increase enhances elastic loading stiffness, promoting fast rupture propagation.

Fast ruptures radiate high frequency seismic waves, consistent with natural earthquakes.

Abstract

A major part of the seismicity striking the Mediterranean area and other regions worldwide is hosted in carbonate rocks. Recent examples are the destructive earthquakes of L'Aquila Mw 6.1 2009 and Norcia Mw 6.5 2016 in Central Italy. Surprisingly, within this region, fast (\approx 3km/s) and destructive seismic ruptures coexist with slow (maximum 10 m/s) and non-destructive rupture phenomena. Despite of its relevance for seismic hazard studies, the transitions from fault creep to slow and fast seismic rupture propagation are still poorly constrained by seismological and laboratory observations. Here, we reproduced in the laboratory the complete spectrum of natural faulting on samples of dolostones representative of the seismogenic layer in the region. The transitions from fault creep to slow ruptures and from slow to fast ruptures, are obtained by increasing both confining pressure (P) and temperature (T) up to conditions encountered at 3-5 km depth (i.e., P = 100 MPa and T = 100 $^{o}$C), which corresponds to the hypocentral location of slow earthquake swarms and the onset of regular seismicity in Central Italy. The transition from slow to fast rupture is explained by the increase of the ambient temperature, which enhances the elastic loading stiffness of the fault and consequently the slip velocity during the nucleation stage, allowing flash weakening. The activation of such weakening induces the propagation of fast ruptures radiating intense high frequency seismic waves.