Taking the pulse of Patagonian Andes

Monday, 26 de September

A team led by José Cembrano is installing broadband and short period seismic stations at the extreme north Liquiñe-Ofqui Fault System, in order to decrypt its seismotectonic nature and its implications with geothermal resources and seismic hazard in the area.

How are seismicity, faults in the earth’s crust, hydrothermal fluid flow and distribution of volcanoes related? This question mobilizes the project that seeks to deepen the understanding of seismotectonic nature of the Patagonian Andes, through the collection of data provided by a network of 35 seismic stations installed this summer between the Alto Biobío and Liquiñe, 27 of them of short-period and 8 broadband instruments. The sensitivity of the equipment, along with the spatial distribution of the stations have been selected to be able to detect events up to 1 Mw magnitude (Richter scale) and locate events of magnitude 1.5 to 2Mw. Uo to date, 31 sensors have been installed.

José Cembrano, head of the initiative declares: “This project is the first in the history of Chilean geology that considers the installation of 35 seismometers in the volcanic chain of the southern Andes in order to learn about the nature of the interaction between a system of active faults (Liquiñe-Ofqui System) and volcanic and geothermal activities. This knowledge is crucial for more accurate assessment of potential seismogenic faults in the upper crust and its relationship to the distribution and activity of volcanoes and geothermal reservoirs”.

This project began as a partnership between the CEGA-PUC group and the GFZ (Germany), who facilitated the stations that will monitor the area for, at least, one year. “The density of stations will allow a very accurate resolution to monitor the area on a regional scale,” says Gerd Sielfeld PhD student (PUC) who coordinated the fieldwork during February, adding: “The instruments are installed approximately every 20 kilometers, in an area of 60 x 200 km, and we are prepared to create an even more dense network in the event that a volcanic eruption occurres. If that happens we can mobilize stations to record the increased flow of fluids”.

The dense distribution of active volcanism and hot springs, spatially associated with faults and fractures systems are the three key pillars that make the study area an area of interest to better understand both the nature of geothermal resources and the seismic risk. “This is a segment of the Andes where the crust delicately responds to tectonic forces – derived from the oblique convergence between the Nazca and South American plates – leading to the creation of space to promote the circulation of geothermal fluids and magmas”, says Gerd.

“Lo que buscamos es poder identificar zonas de alta permeabilidad. Las zonas de alta sismisidad nos indican zonas donde se están generando y/o reactivando fallas y fracturas. Estas redes de fallas y fracturas cuando se encuentran interconectadas favorecen el flujo de fluidos a través de la corteza, aumentando la permeabilidad”, señala Pamela Pérez, alumna de doctorado (UC) quien actualmente estudia el rol de la arquitectura de los sistemas de falla en el flujo de fluido hidrotermal. “Con este proyecto vamos a poder obtener datos en tiempo real,  quevan a complementar los estudios que estamos realizando de los sistemas de fallas y fracturas presentes en superficie” ”, acota Pamela.

El equipo espera poder monitorear los sensores cada tres meses y recolectar los primeros datos en julio de este año. “Vamos a obtener una gran cantidad de datos actuales sobre lo que está pasando abajo con una sensibilidad a la que no habíamos tenido acceso antes”, concluye Gerd.

El proyecto se ha desarrollado a la fecha gracias a las gestiones de José Cembrano, el respaldo y trabajo de Dietrich Lange (Geomar, Kiel, Alemania), Gerd Sielfeld, Pamela Pérez, y la cooperación de un grupo de alumnos de pregrado de la Udec, UC, UChile para la instalación de los sensores.