New (And Fast) Geologic Slip Rates Along Patagonia's Major and Oftentimes Concealed Crustal Strike-Slip Faults

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems
Type: Oral
Date: 4/28/2020
Time: 05:30 PM
Room: 240
Description: 

Strike-slip faults play a major role in Patagonia (Chile and Argentina) and are first-order elements within the neotectonic framework of Southern South America. The Liquiñe-Ofqui fault zone (LOFZ) is dextral strike slip structure than is ~1,200 km long, whereas the Magallanes Fault System (MFS) is a Plate Boundary sinistral structure (Scotia and Southern American Plates). Although they are proven seismogenic structures (e.g. LOFZ Mw 6.2 in 2007; MFS Mw 7.5 and 7.8 in 1949), geologic slip rates are unknown. This is partially due to dense vegetation, major Quaternary glaciations, extensive submarine portions and recent volcanism. We conducted both onshore and offshore field investigations and used remote mapping including structure from motion (SfM) models and light detection and ranging (lidar)-derived and multibeam elevation data combined with field observations. Clear LOFZ Quaternary offset streams and a novel offset glacial valley and separation of bedrock units provide dextral slip rates of 3.6–18.9 mm/yr (Late-Cenozoic geologic) and 11.6–24.6 mm/yr (Quaternary geomorphic). Recent fieldwork allowed us to better constrain the vertical component along the LOFZ as well (up to the east) with a significant signature in the landscape suggesting rapid uplift directly above the subducted Chile Triple Junction coincident with some of the highest peaks including the >4 km San Valentine. Along the MFS, long-term Late-Cenozoic slip rates along the main MFS fault is 5.4 ± 3.3 mm/yr (2.1 to 8.7 mm/yr) based on geological separations along with two other MFS faults with ≥1 mm/yr slip rates (Deseado and Hope faults). By combining displacements observed in SfM models with regional Late-Quaternary glacial deposit ages, we obtain MFS sinistral slip-rates of 10.5 ± 1.5 mm/yr and 7.8 ± 1.3 in Chile and Argentina respectively. These fit well with previously modelled rates. Our Chilean Government (Fondecyt/CONA) supported study provides new slip rates and a first order understanding of the neotectonics and seismic hazard in Patagonia along these fast slipping and oftentimes concealed faults.

Presenting Author: Gregory P. De Pascale

Authors