Volcano-tectonic interactions at Sabancaya volcano, Peru: eruptions,
magmatic inflation, moderate earthquakes, and fault creep
Abstract
We present evidence of volcano-tectonic interactions at Sabancaya
volcano that we relate to episodic magma injection and high regional
fluid pore pressures. We present a surface deformation time series at
Sabancaya including observations from ERS-1/2, Envisat, Sentinel-1,
COSMO-SkyMed, and TerraSAR-X that spans June 1992 - February 2019. These
data show deep seated inflation northwest of Sabancaya from 1992-1997
and 2013-2019, as well as creep and rupture on multiple faults.
Afterslip on the Mojopampa fault following a 2013 Mw 5.9 earthquake is
anomalously long-lived, continuing for at least six years. The best fit
fault plane for the afterslip is right-lateral motion on an EW striking
fault at 1 km depth. We also model surface deformation from two 2017
earthquakes (Mw 4.4 and Mw 5.2) on unnamed faults, for which the best
fit models are NW striking normal faults at 1-2 km depth. Our best fit
model for a magmatic inflation source (13 km depth, volume change of
0.04 to 0.05 km^3 yr^-1), induces positive Coulomb static stress
changes on these modeled fault planes. Comparing these deformation
results with evidence from satellite thermal and degassing data, field
observations, and seismic records, we interpret strong pre-eruptive
seismicity at Sabancaya as a consequence of magmatic intrusions
destabilizing tectonic faults critically stressed by regionally high
fluid pressures. High fluid pressure likely also promotes fault creep
driven by static stress transfer from the inflation source. We speculate
that strong seismicity near volcanoes will be most likely with high pore
fluid pressures and significant, offset magmatic inflation.