title: Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes.
abstract: Rupture fronts can cause fault displacement, reaching speeds up to several ms(-1) within a few milliseconds, at any distance away from the earthquake nucleation area. In the case of silicate-bearing rocks the abrupt slip acceleration results in melting at asperity contacts causing a large reduction in fault frictional strength (i.e., flash weakening). Flash weakening is also observed in experiments performed in carbonate-bearing rocks but evidence for melting is lacking. To unravel the micro-physical mechanisms associated with flash weakening in carbonates, experiments were conducted on pre-cut Carrara marble cylinders using a rotary shear apparatus at conditions relevant to earthquakes propagation. In the first 5 mm of slip the shear stress was reduced up to 30% and CO2 was released. Focused ion beam, scanning and transmission electron microscopy investigations of the slipping zones reveal the presence of calcite nanograins and amorphous carbon. We interpret the CO2 release, the formation of nanograins and amorphous carbon to be the result of a shock-like stress release associated with the migration of fast-moving dislocations. Amorphous carbon, given its low friction coefficient, is responsible for flash weakening and promotes the propagation of the seismic rupture in carbonate-bearing fault patches.
authors.affiliation: Sezione di Sismologia e Tettonofisica, Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Spagnuolo
authors.affiliation: Department of Earth Sciences, Utrecht University, Budapestlaan, 4 P.O. Box 80.021, 3584 CD Utrecht, the Netherlands.
authors.forename: Oliver
authors.initials: O
authors.lastname: Plümper
authors.affiliation: EPFL, LEMR, Station 18, 1015, Lausanne, Switzerland.
authors.forename: Marie
authors.initials: M
authors.lastname: Violay
authors.affiliation: Sezione di Sismologia e Tettonofisica, Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavallo
authors.affiliation: Dipartimento di Geoscienze, Università di Padova, Via G. Gradenigo 6, 35131 Padova, Italy.|School of Earth, Atmospheric and Environmental Sciences, Manchester University, Oxford Street, M13 9PL Manchester, United Kingdom.
authors.forename: Giulio
authors.initials: G
authors.lastname: Di Toro