Vargas, K., Villegas-Lanza, J. C., Battaglia, M., & Euillades, P. (2024b). Volcano-tectonic interaction in the Central Andes: seismic sequences and uplift in the Purupuruni-Casiri volcanic complex. Version 1.0 [Data].

Volcano-tectonic interaction in the Central Andes: seismic sequences and uplift 
in the Purupuruni-Casiri volcanic complex
by K. Vargas(1), J. C. Villegas-Lanza(1), M. Battaglia(2,3) and P. Euillades(4,5)

(1) Geophysical Institute of Peru, Lima 15012, Peru
(2) US Geological Survey, Volcano Disaster Assistance Program, NASA Ames Research Center, 
    Moffett Field, CA 94035, USA
(3) Department of Earth Sciences, Sapienza-University of Rome, 00185. Rome, Italy
(4) CONICET, National Research and Technical Council, Argentina
(5) Universidad Nacional de Cuyo, Facultad de Ingeniería, Instituto, CEDIAC, 
    Mendoza, Argentina

Purupuruni and Casiri are a group of lava domes located in the Vilacota Maure Conservation
Area, a remote, desertic area in southern Peru. Although no historical eruptions are known,
the volcanoes are considered potentially active, and present various hydrothermal features 
and hot springs. A significant unrest, characterized by deformation and seismic activity, 
was observed in the area between the April 2020 and January 2022. Because of the remote 
location, difficulty of access and desertic landscape, we used InSAR to monitor
the local tectonic and volcanic deformation. We were able to identify two different 
deformation processes. A large-scale uplift (see data in UPLIFT 1 to UPLIFT 3) that began 
shortly before the earthquake sequencesand ceased a few months after the end of the seismic
unrest, and co-seismic deformation associated with motion along the local system of normal 
faults. The co-seismic deformation occurred in four distinct fault segments and with 
different deformation rates (see data in ZONE 1 to ZONE 4). The possible origin of this 
large-scale uplift could be the intrusions of small batches of magma from a deep reservoir
feeding the local volcanoes, which would have caused the re-activation of the normal faults.

We used the open-source software dMODELS (Battaglia et al., 2013) to infer the location, 
geometry and slip of the fault segments that ruptured near Purupuruni and Casiri volcanoes. 
This software (available in the folder SOFTWARE) is based on analytical models of 
dislocation sources (Okada, 1985) to reproduce the surface deformation in an elastic, 
flat half space. The inverse models implement a weighted least-squares algorithm combined 
with a random search grid to infer the minimum of the penalty function, the chi-square 
per degree of freedom (Bergstra and Bengio, 2012). Using rectangular dislocations with a 
constant slip to model the  faults is a major simplification, although it may lead to 
reasonable first-order solutions (Lisowski, 2007). 

Two types of subsampling methods were applied to the final InSAR images to compare and 
assess the robustness of our modeling results. The first was a regular subsampling, and 
the second a quadtree subsampling. 

Corresponding author : Katherine Vargas (kvargas@igp.gob.pe) 
Contact for software : Maurizio Battaglia (mbattaglia@usgs.gov)