Paleoseismic Evidence of anMw7 Pre‐Hispanic Earthquake in the Peruvian Forearc

Carlos Benavente,Xavier Robert,Laurence Audin,Anderson Palomino,Sam Wimpenny,Briant García,Enoch Aguirre,Lorena Rosell

doi:10.1029/2020tc006479

Abstract

AbstractWe present the results of a paleoseismic survey of the Incapuquio Fault System, a prominent transpressional fault system cutting the forearc of South Perú. High‐resolution Digital Elevation Models, optical satellite imagery, radiocarbon dating, and paleoseismic trenching indicate that at least 2–3 m of net slip occurred on the Incapuquio Fault generating a complex, ∼100‐km long set of segmented fault scarps in the early 15th century (∼1400–1440 CE). We interpret the consistent along‐strike pattern of fault scarp heights, geometries and kinematics to reflect a surface rupture generated by a singleMw7.4–7.7 earthquake, suggesting that brittle failure of the forearc poses a significant, yet mostly overlooked, seismic hazard to the communities in coastal areas of Perú. The timing of this earthquake coincides with the collapse of the Chiribaya civilization in ∼1360–1400 CE, and we present evidence of damaged buildings along the fault trace that may be of Chiribayas age. Our surface faulting observations, when combined with observations of deformation in the forearc from geodesy and seismology, also demonstrate that the forearc in South Perú experiences a complex, time‐varying pattern of permanent strain, with evidence for trench‐parallel shortening, trench‐parallel extension, and trench‐perpendicular shortening all in close proximity but in different periods of the megathrust earthquake cycle. The kinematics of recent slip on the Incapuquio Fault are consistent with the sense of interseismic strain within the forearc measured by GPS, suggesting the fault is loaded toward failure between megathrust earthquakes.

Highlights

The major seismic hazard along the coast in South Perú is widely attributed to the Mw 8–9 earthquakes that occur every 150–300 years due to strain accumulation and release on the interface between the subducting Nazca plate and the overriding South American plate (Villegas-Lanza et al, 2016)
We present the results of a paleoseismic survey of the Incapuquio Fault System, a prominent transpressional fault system cutting the forearc of South Perú
We have presented evidence that 2–4 m high fault scarps were formed by a transpressional earthquake that ruptured 100 km of the southern segment of the Incapuquio Fault System in the early 15th century (∼1400–1440 CE)

Summary

Introduction

The major seismic hazard along the coast in South Perú is widely attributed to the Mw 8–9 earthquakes that occur every 150–300 years due to strain accumulation and release on the interface between the subducting Nazca plate and the overriding South American plate (Villegas-Lanza et al, 2016). The possibility of large earthquakes generated by faults rupturing the forearc is generally overlooked. Major earthquakes within the forearc may occur by linking a complex series of oblique faults during a single rupture (e.g., Hamling et al, 2017; Schermer et al, 2020), which could pose a significant, yet poorly constrained, seismic hazard in the region. There is tentative evidence that slip on forearc faults may change the stress state on highly strained sections of the megathrust, triggering large megathrust earthquakes (González et al, 2015). Understanding the magnitude, kinematics, and history of fault slip in the forearc is key to assessing the mechanics and the seismic hazard within subduction zones

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