A Community Seismic Network for the Early Detection of Seismic Activity Close to Active Volcanoes in Western El Salvador

Abstract Seismic monitoring can provide key constraints on volcanic processes, magma migration, and preparatory processes before volcanic eruptions. Nevertheless, the high cost of broadband networks limits the number of volcanoes that are actively monitored. Here, we test the capability of a network of raspberry shake (RS) seismographs to monitor volcanoes in El Salvador and characterize associated seismicity sequences in real time. We deployed seven three-component, short-period RS velocity seismometers around Santa Ana volcano, which has a long history of phreatomagmatic eruptions as recently as 2007. The new network primarily supports training, research, and outreach activities but also has the potential to provide early alerts before volcanic unrest. The seismometers were installed at schools, a university campus, and hotels within 20 km of Santa Ana volcano. We recorded an accelerating seismicity sequence within ∼15 km distance from the volcano between 28 December 2023 and 1 February 2024. Both magnitudes and seismicity rates increased systematically, culminating in two events above ML 4 on 28 January 2024 without causing detectable changes in temperature or gas emissions at the summit of Santa Ana. Detailed space–time clustering analyses reveal dominant mainshock–aftershock triggering at local to regional distances, similar to tectonic earthquake sequences. The new RS network around Santa Ana volcano demonstrates the ability of low-cost seismometers to improve seismic event detection, location, and classification. The observations suggest that dense volcano monitoring networks facilitate an early detection of unfolding seismicity sequences and improve tectonic versus volcanic event classifications—a key component of reliable eruption alerts.