Seismicity in a Transpressional Volcanic Arc: The Liquiñe‐Ofqui Fault System in the Puyuhuapi Area, Southern Andes, Chile (44°S)

Abstract

Understanding the relationship between crustal faults and volcanic activity in transpressional environments is a main goal in geosciences and could help to understand geothermal resources and evaluate geological hazards. In the Andean Southern Volcanic Zone (SVZ), Chile, recorded seismicity is scarce, and few studies have evaluated the relationship between volcanic activity and crustal faults from seismic observations. Thus, in this study, we deployed a seismic network for almost 1 year to understand the brittle deformation of the upper crust within the Puyuhuapi area, located at~44°S in the SVZ. We analyzed the location and kinematics of seismicity together with previously published field structural geological data. Considering these results, we developed an integrative tectonic model for the area and discussed which faults facilitate magma transport through the crust. Our results indicate the existence of two NNE-oriented seismogenic dextral to dextral-reverse regional faults that generate a duplex in a continental-scale fault setting. Inside the duplex, we observed normal to strike-slip normal focal mechanisms which recurrently have NE trending nodal planes. At a regional scale, a strike-slip tectonic environment has a N60°E/18°shortening direction and a N151°E/03°extension direction. We conclude that stratovolcanoes are located inside the duplex in a local transtensional environment where NE oriented normal faulting may occur. These faults facilitate magma transport since they represent the preferential orientation for dilatational fractures. Conversely, in local transpressional environments such as the Puyuhuapi fault (NNE oriented dextral to dextral-reverse kinematics), only minor eruptive centers of small volume are emplaced, suggesting a less productive magma transportation process.

Fault‐Driven Differential Exhumation in a Transpressional Tectonic Setting: A Combined Microstructural and Thermochronologic Approach From the Liquiñe‐Ofqui Fault System, Southern Andes (39°S)

“…Major faults of this system strike N-S to NNE-SSW and record dextral and dextral-reverse kinematics (e.g., Cembrano et al, 2002;Göllner et al, 2021;Thomson, 2002), whereas subsidiary faults strike NE-SW to ENE-WSW and record dextral and dextral-normal kinematics (e.g., Pérez-Estay et al, 2020;Pérez-Flores et al, 2016;Sielfeld et al, 2017). Previous studies combined geochronological and microstructural analyses to document onset of ductile deformation at ∼10 Ma switching to brittle deformation after 4-5 Ma (41°-46°S, Arancibia et al, 1999;Cembrano et al, 1999Cembrano et al, , 2000Cembrano et al, , 2002Melnick et al, 2006).…”

Fast Holocene slip and localized strain along the Liquiñe-Ofqui strike-slip fault system, Chile

“…The LOFS is associated with clusters of shallow microseismicity that reach down to 15 km depth 10 , 24 , 25 , and with up to M w 6 strike-slip earthquakes recorded during the 1965 Hudson and 1989 Lonquimay volcanic eruptions 26 , 27 (Fig. 1 ).…”

Seismic evidence of the active regional tectonic faults and the Copahue volcano, at Caviahue Caldera, Argentina

“…As an example, circulation of crustal fluids at shallow depths in the brittle highly fractured crust has been imaged using magnetotellurics at the LOFS, near the Osorno volcano (Díaz et al 2020). When fluids migrate until the surface through crustal faults (Cox 2005;Gudmundsson 2011;Pérez-Estay et al 2020), they can generate a very specific seismicity, different from the more classical tectonic seismicity located at the interplate contact in a subduction zone. Studying this seismicity allows following the dynamics of these faults as well as monitor active volcanoes, especially to detect a possible volcanic unrest using volcano-tectonic earthquakes (VTs) as an early warning alert system (White and McCausland 2019).…”

“…Even if VTs have been located at many volcanoes, only a few studies have determined their focal mechanism, allowing discriminating when VTs are related to local faults or to the hydrothermal and/or volcanic activity. Seismic studies realized along the LOFS are rare, mainly for logistic reasons in these remote regions (Ibáñez et al 2008;Lange et al 2008;Mora-Stock et al 2010;Legrand et al 2011;Russo et al 2011;Agurto et al 2012;Vargas et al 2013;Kanamori and Rivera 2017;Sielfeld et al 2019;Pérez-Estay et al 2020).…”