G31C-06
Stress controlled magma-earthquake interaction during unrest at Chiles-Cerro Negro Volcanoes (Ecuador-Colombian border)

Wednesday, 16 December 2015: 09:15
2002 (Moscone West)
Susanna K Ebmeier1, John R Elliott2, Jean-Mathieu Nocquet3, Juliet Biggs1, Patricia A Mothes4, Paul Lundgren5 and Sergey V Samsonov6, (1)University of Bristol, Bristol, United Kingdom, (2)University of Oxford, COMET, Department of Earth Sciences, Oxford, United Kingdom, (3)Géoazur - Université Nice Sophia Antipolis, Valbonne, France, (4)Instituto Geofisico, Quito, Ecuador, (5)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (6)Canada Center for Remote Sensing, Ottawa, ON, Canada
Abstract:
The movement of fluids beneath a volcano can cause deformation, and therefore changes to the subsurface stress field that manifest in swarms of low magnitude (<M4) volcano-tectonic (VT) earthquakes. Moderate VT earthquakes (M 5-6) are unusual, but have the potential to alter the local stress field, affecting the propagation of magmatic fluids and resulting in magma- earthquake feedback.

Here, we present InSAR and GPS measurements of deformation during the height of an episode of unrest in October 2014 at Chiles-Cerro Negro volcanoes on the Ecuador-Colombian border. These volcanoes were previously considered to be historically inactive, but between 2013 and early 2015 there were three episodes of unrest characterised by VT swarms of increasing energy and duration.

GPS measurements at two stations near Volcán Chiles show inflation over a time period of approximately twenty days prior to the 20th October, consistent with the intrusion of magma at half space depths >13 km. This inflation took place during a swarm of VT seismicity with thousands of low magnitude events per day and culminated in a M 5.6 earthquake on the 20th October, when inflation abruptly ceased.

We measure coseismic displacements from the M 5.6 earthquake with data from three independent InSAR platforms and find that they are consistent with shallow slip of 1.2 m on an oblique reverse fault. This fault plane would have experienced positive Coulomb stress changes from some of the range of potential sources consistent with the inflation. Magmatic intrusion could therefore have contributed to the loading on the fault directly through stress changes caused by pressurisation, and indirectly through the decrease in effective friction coefficient due to elevated pore fluid pressure.

The cessation of inflation immediately after the moderate earthquake suggests a link between the two events. We expect slip on the fault plane identified from the InSAR data to have resulted in compression in the shallow crust south of Volcán Chiles, above the source that had previously been inflating. This would have inhibited further ascent of magma.

The Chiles-Cerro Nego unrest provides rare observations of interaction between magmatic intrusion and a moderate earthquake during volcanic unrest.

<< Previous Abstract | Next Abstract >>