S016-07
Evidence for fluid control on faults in the Chilean Andes from seismicity and magnetotellurics

Tuesday, 8 December 2020: 17:56
Virtual
Almudena Sanchez De La Muela Garzon1, James Hammond1, Thomas M Mitchell2, Ashley Stanton-Yonge3, Jose M Cembrano4, Rebecca Pearce5, Max Moorkamp6, W. Ashley Griffith7, Jonathan Daniel Smith8 and Neill Marshall9, (1)Birkbeck, University of London, London, WC1E, United Kingdom, (2)University College London, Department of Earth Sciences, London, United Kingdom, (3)University College London, Earth Sciences, London, United Kingdom, (4)Pontifical Catholic University of Chile, Santiago, Chile, (5)University College London, London, United Kingdom, (6)University of Leicester, Leicester, LE1, United Kingdom, (7)The Ohio State University, School of Earth Sciences, Columbus, OH, United States, (8)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (9)University of Oxford, Earth Sciences, Oxford, United Kingdom
Recorded Presentation
Abstract:
Microseismicity is useful to identify and track the interaction of fluids and seismogenic structures. Variations in the spatial and temporal distribution of seismicity can show changes in the physical properties of the crust related to fluids migration such us: changes in pore fluid pressure, variations of water level, fluid diffusion, degassing, stress transfer and/or stress field rotations.

The Andes constitute a perfect natural laboratory to study how magmatic-related fluids and faults interact, with faults determining the emplacement of volcanoes and hot springs along the mountain chain, while hosting some of the largest ore deposits on Earth at the intersection of arc-parallel and arc-oblique structures.

To investigate tectono-magmatic relationships of the Andean volcanic arc we deployed a seismic network and conducted a magnetotelluric survey in the Southern Volcanic Zone of the Andes from March 2017 to December 2018. We relatively relocate earthquakes to produce a catalogue of 951 hypocentres with a magnitude of completeness of 0.9 ML. Hypocenters are focussed in two regions, clustered along the edges of an arc-related fluid reservoir highlighted in the magnetotelluric study. Seismicity shows periods of intense activity coinciding with periods of higher b-value and the presence of normal, reverse and strike slip fault ruptures. Periods of low seismicity coincide with low b-values and a reduction of normal faulting events. We interpret this to be caused by changes in differential stress and/or shear stress over time possibly caused by changes in the proximal fluid reservoir.

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