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

138 PATA Days 2024 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 (1) Departamento de Geología, Universidad Nacional de San Luis, Argentina *Email: costa@email.unsl.edu.ar K E Y W O R D S Quaternary thrusts, fault scarps, hanging wall collapse, wedge thrusting. Carlos Costa (1) SOME COMMENTS ON THE MORPHO-STRATIGRAPHIC SIGNATURE OF QUATERNARY THRUSTING A B S T R A C T Active reverse faults exhibit a complex array of geomorphic expressions. The thrust surface may or may not rupture at the surface, resulting in hanging wall collapse or surface warping for emergent and blind thrusts respectively. Regardless of the resulting monocline- like scarp profile, the emergent or blind character of thrusting should be considered at a trench scale to better understand the type of scarp related to paleoseismic deformation. This also may help to discuss the coseismic or interseismic origin of scarp-derived deposits. A complementary classification of thrust-related scarps is presented. I N T R O D U C T I O N Morphologies coined by Quaternary-active thrusting have deserved much less attention than those related to normal and strike- slip types of faulting. Thrust- related landform assemblages are poorly organized in space and usually discontinuous. The scarp-free face is rarely preserved, and if so, fracture surfaces might represent secondary faulting, being the thrust trace buried by scarp colluvium in most cases. Thrust deformation at the surface usually results in monocline-like scarps, although similar shapes may express different thrust geometries at the deformation zone, which may be relevant to the paleoseismological analysis of these structures. When a reverse or thrust fault breaks to the surface, it results in an overhanging scarp (Fig. 1), leading to a suite of different thrust- related landforms according to the type and evolution of hanging wall collapse. These assemblages have been sketched by Phillip et al. (1992, Fig. 4) and also reported in several contributions (Gordon& Lewis, 1980; Weber &Cotton, 1980; Machette et al., 1993; Kelson et al., 2001; Yu et al., 2010; Rimando et al., 2019, among others). The preservation of the pristine scarp (simple thrust scarp sensu Phillip et al., 1992) (Fig. 1a) is rare in unconsolidated deposits and the hanging wall collapses at the base of the scarp, during or soon after a rupture event (hanging wall collapse scarp sensu USGS,