Abstract

The Chilean Andes, as a characteristic tectonic and geomorphological region, is a perfect location to unravel the geologic nature of seismic hazards. The Chilean segment of the Nazca-South American subduction zone has experienced mega-earthquakes with Moment Magnitudes (Mw) >8.5 (e.g., Mw 9.5 Valdivia, 1960; Mw 8.8 Maule, 2010) and many large earthquakes with Mw >7.5, both with recurrence times of tens to hundreds of years. By contrast, crustal faults within the overriding South American plate commonly have longer recurrence times (thousands of years) and are known to produce earthquakes with maximum Mw of 7.0 to 7.5. Subduction-type earthquakes are considered the principal seismic hazard in Chile, with the potential to cause significant damage to its population and economy. However crustal (non-subduction) earthquakes can also cause great destruction at a local scale, because of their shallower hypocentral depth. Nevertheless, the nature, timing and slip rates of crustal seismic sources in the Chilean Andes remain poorly constrained. This work aims to address the seismic potential of the crustal faults in Chile, contributing to the estimation of key fault parameters for the seismic hazard assessment. We have examined the main parameters involved in the magnitude of an earthquake, including length, width and mean displacement of some case studies crustal faults and their morphotectonic settings, exposing the parametrical similarities in longitudinal domains (N-S stripes) and disparity from W to E, across latitudinal domains. The maximum hypocentral depths for crustal earthquakes vary across margin parallel tectonic domains aligned parallel, from 25-30 km in the outer forearc to 8-12 km in the volcanic arc, thus allowing for a first-order approach for seismic potential assessment. Current structural, paleoseismological and geodetic data, although sparse and limited, suggest that slip rates of Chilean crustal faults range from 0.2 mm/yr (in the forearc region) to up to 7.0 mm/yr (in the intra-arc region). The different tectonic modes for crustal fault reactivation and their wide range of slip rates complicates the estimation of seismic hazard. A rigorous seismic hazard assessment must therefore consider the different tectonic settings, timing and slip rates of Andean crustal faults. Understanding the nature of these faults will allow a better evaluation of the associated seismic hazard, and better constraints to be placed on their relationship with the subduction seismic cycle.

Highlights

  • The maximum hypocentral depths for crustal earthquakes vary across margin parallel tectonic domains aligned parallel, from 25-30 km in the outer forearc to 8-12 km in the volcanic arc, allowing for a first-order approach for seismic potential assessment

  • The different tectonic modes for crustal fault reactivation and their wide range of slip rates complicates the estimation of seismic hazard

  • Chile is located in an outstanding physical laboratory to investigate the nature of earthquakes and related seismic hazard: The Chilean Andes is a distinctive tectonic and geomorphological orogenic region formed, in the north, by the ocean-continent convergence between the South American and Nazca plates, and in the south by the convergence between the Antarctic and Scotia plates

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Summary

Introduction

Chile is located in an outstanding physical laboratory to investigate the nature of earthquakes and related seismic hazard: The Chilean Andes is a distinctive tectonic and geomorphological orogenic region formed, in the north, by the ocean-continent convergence between the South American and Nazca plates, and in the south by the convergence between the Antarctic and Scotia plates. Continental Chile is affected by three main types of earthquakes: subduction, or thrust-type events, due to the Nazca-South America interplate motion, which typically have a hypocentral depth up to 60 km (e.g., Tichelaar and Ruff, 1993; Suárez and Comte, 1993; Allmendinger and González, 2010; Scholz and Campos, 2012); intraplate earthquakes, which occur within the subducting Nazca plate, and typically have hypocentral depths of 60-200 km (e.g., Barrientos, 1980; Campos and Kausel, 1990); and crustal intraplate earthquakes, which occur within the overriding South American plate, and generally have hypocentral depths of less than 30 km (e.g., Barrientos et al, 2004; Leyton et al, 2010). “megathrust” subduction type earthquakes are considered the principal seismic hazard in Chile, with the potential to cause significant damage to its population and economy

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