Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

216 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 K E Y W O R D S Fault reactivation, Frictional properties, Deformation mechanisms, Active tectonics, Subduction earthquake (1) Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile. (2) National Research Center for Integrated Natural Disaster Management, Universidad Católica del Norte, Antofagasta, Chile. *Email: ygc005@alumnos.ucn.cl Yerko González (1, 2) Gabriel González (1, 2) Erik Jensen (1, 2) FRICTIONAL PROPERTIES AND DEFORMATION MECHANISMS OF UPPER-PLATE FAULTS REACTIVATION TRIGGERED BY SUBDUCTION EARTHQUAKES: INSIGHTS FROM THE ATACAMA FAULT SYSTEM A B S T R A C T The Maule 2010 and Tohoku-Oki 2011 earthquakes triggered shallow reactivation in dormant upper plate faults. The seismo- mechanical behavior involved in these reactivations is still poorly explored. We investigated this phenomenon by examining the frictional properties and deformation mechanisms at different stress and sliding conditions on natural phyllosilicate-bearing/ rich gouges from the Atacama Fault System in northern Chile. We selected them due to tectonic setting and active tectonic characteristics, resembling fault reactivations following massive subduction earthquakes. Our mechanical results indicate that during the interseismic phase of the subduction seismic cycle, phyllosilicate-bearing/rich upper plate faults are prone to easily experience stable sliding due to low frictional strength and velocity-strengthening behavior. During the post-seismic phase of the subduction seismic cycle, the faults experience a slow-to- fast transition in creep and eventually might become unstable as the normal stress decreases due to post-seismic relaxation. I N T R O D U C T I O N Most destructive subduction earthquakes in the 21st century have drawn researchers' attention to a cascading process associated with this type of earthquake: shallow reactivation of upper-plate faults. These reactivations occur along high-angle faults located above seismogenic zones of subduction interface, during the post-seismic phase of the subduction seismic cycle. They are characterized by the nucleation of earthquakes (Mw ~7)