T7 Earth Surface Processes in Tectonically Active and Unstable Regions I

Sunday, 22 September 2024
8:00 AM - 12:00 PM
210B

ARCHAEOLOGY AND PALEAOSEISMOLOGY - EXPLORING LINKS BETWEEN ANCIENT CIVILIZATIONS AND PAST EARTHQUAKES, CHINCHA VALLEY, PERU

Paper number: T7-12
Program: Technical Sessions
Time: 10:50 AM – 11:05 AM

Authors

Abstract

The Chincha Valley (CV) is located ~200 km south of Lima, Peru. The coast is formed by the subduction zone between the Nazca and South American plates. An old geologic map shows a NNE-SSW and an E-W trending fault in the area of an archaeological site; while the most recent geologic map shows no faults in the area. Research on the archaeological site revealed a clay layer with evidence of liquefaction, suggesting past seismic activity has occurred in very close proximity. Electrical Resistivity Tomography (ERT) surveys conducted at the archaeology site suggest a fault bisecting the site.

The main objectives of this research were to map the location and geometry of faults and their damage zones using geophysical methods. Preliminary results suggest there is a fault system very close to the archaeological site. The fault was last active prior to settlement of the site and the faults are directly related to landscape changes. We study the fault system using geophysical methods: ERT and Ground Penetrating Radar (GPR). ERT uses resistivity to electric current to image the gross subsurface architecture. GPR uses radar waves to image, at high-resolution, subsurface structures. GPR and ERT were chosen as they allow rapid, multiscale approach, and noninvasive imaging of the subsurface. Integrating GPR with ERT results provides stratigraphic information for identifying fault locations and fault-associated damage. Both methods have been successfully utilized on the Peruvian coast.

ERT data were collected using an ABEM Terrameter LS2 with 81 pin arrays spaced between 0.5 and 5 m on lines perpendicular to the fault. Straight ERT lines were located on the roads surrounding the area (2.7 km approx.). A GPR grid (100m x 50m) with lines in E-W and N-S directions were collected using the MALA Ground Explorer, using a 450 MHz frequency antenna, with lines orientated parallel and perpendicular to fault locations identified on ERT lines.

ERT and GPR data reveals the stratigraphic relationship of fault activity and site settlement allowing for development of a rough temporal framework. Additionally, liquefaction events link fault activity to social development and landscape change. This information is essential to understand how the faults influenced the occupation of the surrounding population and influenced the archeology of CV. This research was funded by a 2023 GSA Graduate Student Research Grant.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405085

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