title: Ultra-thin clay layers facilitate seismic slip in carbonate faults.
abstract: Many earthquakes propagate up to the Earth's surface producing surface ruptures. Seismic slip propagation is facilitated by along-fault low dynamic frictional resistance, which is controlled by a number of physico-chemical lubrication mechanisms. In particular, rotary shear experiments conducted at seismic slip rates (1 ms-1) show that phyllosilicates can facilitate co-seismic slip along faults during earthquakes. This evidence is crucial for hazard assessment along oceanic subduction zones, where pelagic clays participate in seismic slip propagation. Conversely, the reason why, in continental domains, co-seismic slip along faults can propagate up to the Earth's surface is still poorly understood. We document the occurrence of micrometer-thick phyllosilicate-bearing layers along a carbonate-hosted seismogenic extensional fault in the central Apennines, Italy. Using friction experiments, we demonstrate that, at seismic slip rates (1 ms-1), similar calcite gouges with pre-existing phyllosilicate-bearing (clay content ≤3 wt.%) micro-layers weaken faster than calcite gouges or mixed calcite-phyllosilicate gouges. We thus propose that, within calcite gouge, ultra-low clay content (≤3 wt.%) localized along micrometer-thick layers can facilitate seismic slip propagation during earthquakes in continental domains, possibly enhancing surface displacement.
authors.affiliation: Dipartimento di Scienze della Terra, Sapienza University of Rome, Rome, Italy. luca.smeraglia@uniroma1.it.
authors.forename: Luca
authors.identifier: http://orcid.org/0000-0002-6136-2609
authors.initials: L
authors.lastname: Smeraglia
authors.affiliation: Consiglio delle Nazionale Ricerche, IGAG, Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Billi
authors.affiliation: Dipartimento di Scienze della Terra, Sapienza University of Rome, Rome, Italy.|Consiglio delle Nazionale Ricerche, IGAG, Rome, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Carminati
authors.affiliation: CERTEMA, Multidisciplinary technology laboratory, Cinigiano, Grosseto, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavallo
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester, UK.|INGV, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy.|Dipartimento di Geoscienze, Padova University, Padova, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Di Toro
authors.affiliation: INGV, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy.
authors.forename: Elena
authors.identifier: http://orcid.org/0000-0002-1377-5812
authors.initials: E
authors.lastname: Spagnuolo
authors.affiliation: Dipartimento di Geoscienze, Padova University, Padova, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Zorzi