The Coulomb stress transfer and possible interactions between seismic and volcanic activity in the Colca Region (Central Andes)

The Coulomb stress transfer analysis is based on the hypothesis that failure on a fault plane occurs when the Coulomb stress exceeds a certain threshold. Positive Coulomb stress changes are thought to bring faults closer to failure, whereas negative ones inhibit failure. The Colca Region in Central Andes, southern Peru, is prone to small- to moderate-sized (Mw ≤ 6.0) shallow (< 20 km) earthquakes associated with normal and strike-slip crustal faults within the overriding plate in the Nazca-South American subduction zone. Along with the activity of the Sabancaya volcano, which in recent years comprised mainly of ash and fumarole emissions, this region offers an opportunity to investigate the complex relationship between seismic and volcanic activity, their potential interplay, and triggering factors.

To explore these dynamics, we carried out a Coulomb stress transfer analysis examining the interactions between source faults of 28 significant recent earthquakes (1991-2022), as well as the impact of magmatic inflation (2013-2022) on seismic events. The results confirm a tectonic origin for most earthquakes, while the magmatic source appears to play a secondary role, primarily amplifying the effects of prior seismic activity. However, the Coulomb stress transfer does not seem to be the main factor impacting the seismicity of the Colca Region, as most of the analyzed source faults were not brought closer to failure due to a positive stress change. Preceding seismic activity induced positive Coulomb stress changes on source faults in 43% of the events, while negative stress changes potentially inhibited 25%. Magmatic inflation contributed to positive stress changes in 22% of cases but also induced negative changes in a similar proportion. Notably, no direct connection was identified regarding the significant increase in seismic activity in 2013, which appeared to be potentially correlated with the start of the fumarolic emissions (late 2012) by the Sabancaya volcano.

While the coseismic static Coulomb stress change does not fully account for the complexity of seismic and volcanic activity and their interplay in the Colca Region, it provides valuable insights into active geological processes and highlights open questions warranting further investigation.

This research was funded by the National Science Centre (Poland), Grant Number 2020/39/B/ST10/00042.