Dynamic triggering and criticality: earthquake interactions during unrest at Sierra Negra volcano, Galapagos Islands

Observations across many earthquake fault systems and volcanoes tell us that the small changes in stress due to large earthquakes can trigger other large earthquakes or volcanic eruptions. In a recent example, these interactions underpinned the sequence of large destructive earthquakes in central Italy in 2016. The lack of current understanding of the susceptibility of certain faults and volcanoes to small stress changes and the nature of these interactions are some of the key unknowns hampering our ability to forecast future large earthquakes and eruptions. Opportunities to study these interactions, with high quality data over many repeated triggering events, are valuable, but extremely rare.

Sierra Negra volcano in the Galapagos Islands is currently showing considerable signs of unrest, due to the arrival of new magma at shallow levels. New observations in January 2018 show that the unrest has made the volcano particularly and unusually susceptible to remote earthquake triggering. The tiny low frequency shaking associated with large earthquakes many 1000s of kilometres away is triggering small high frequency earthquakes in the volcano. The high rate of large earthquakes along the Pacific coast of the Americas provides frequent triggering events, and preliminary analysis suggests that rapid deployment of a high resolution seismic network might expect to record many tens of triggering episodes in the next year. Sierra Negra is presenting a superb, but short-term, 'natural laboratory' to study earthquake-earthquake and earthquake-volcano critical triggering.

This project will deploy a high-density network of seismometers at Sierra Negra for 12 months for record the seismic activity taking place at the volcano. These data will allow us to determine when, where, and how earthquake triggering is taking place, and provide important new information about the factors that control the response of 'critically-stressed' geological systems. In addition, the data will allow us to follow the evolution of volcanic unrest, and the seismic signals associated with any eruptive activity that occurs during deployment.

The research will benefit volcanologists and seismologists working on questions of earthquake and volcano physics, earthquake-earthquake and earthquake-volcano interactions, and hazard forecasting models. These scientists will have access to a unique new dataset, both primary waveform data and derived catalogues, to provide a benchmark to test models and compare with less complete observations elsewhere. The empirical statistics of triggering, and new understanding of fundamental processes, will allow the development of a new generation of forecasting models where local susceptibility is a key control on hazard.
The work will also benefit volcano monitoring agencies, particularly the local IGEPN. Through their role as project partners and co-design of the work, our new findings will immediately be incorporated into the hazard analysis, and monitoring and management strategy, of Sierra Negra and other Galapagos volcanoes. We will have regular meetings with the staff of the Galapagos national park,
As part of the project, we will film and document the instrument deployment and activities in the field. This will form material for an online course in volcanic hazards currently in development, and we will also produce a short documentary film explaining the reason for the work, and volcanic processes and hazards in the Galapagos, for public engagement activities.