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

208 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 Atacama Fault System, northern Chile, Paleoseismology, upper plate earthquake, subduction zone (1) Departamento de Ciencias Geológicas Universidad Católica del Norte, Chile. (2) Departamento de Geodinámica, Universidad de Granada, España *Email: ggonzale@ucn.cl Gabriel Gonzalez (1) Luis Astudillo (2) Ian del Rio (1) PALEOSEISMOLOGY OF THE ATACAMA FAULT SYSTEM: TRACING THE RELATIONSHIP BETWEEN SUBDUCTION EARTHQUAKE AND UPPER PLATE FAULTING A B S T R A C T Inlandnormal faulting is recognizedas relevant process following large subduction earthquake; however, the lack of data limits the understanding how normal faulting relates to the subduction earthquakes cycle. We characterized the paleoseismology of the Atacama Fault System in northern Chile. Our results showed that M 7.0 upper plate normal faulting earthquakes have recurrences two magnitude longer than the recurrence of Mw>8.0 subduction earthquakes showing that both types of earthquakes are not synchronized. I N T R O D U C T I O N The 2010 Maule and 2011 Tohoku-Oki earthquakes reactivated dormant faults by postseismic relaxation of the upper plate (Kimura & Tsutsumi, 2023 and Farias et al., 2011). However, beside this clear observation, a substantial gap exists in understanding the temporal relationship between the recurrence time of large upper plate earthquakes and great subduction earthquakes. In northern Chile, Quaternary normal faults occur in the overriding plate including the largest recognized Atacama Fault System (AFS, Arabasz, 1971). These normal faults could represent examples of upper plate faults that have been reactivated close after great subduction earthquakes. In this contribution, we provide the results of a paleoseismological study aimed to estimate the mechanism of fault reactivation that formed conspicuous fault scarps in the AFS. An important task is to provide a slip rate constrain and recurrence interval of large upper plate earthquakes. We use the Salar del Carmen Fault (SCF) and the Naguayan Fault (NGF) as study cases. Our work is based on trench logging and optically stimulated luminescence (OSL) dating of quartz to constrain the age of colluvial wedges flooring the fault scarps.