The research team used two broadband seismometers located over 750 kilometers from the volcano. They applied advanced signal processing techniques to extract and analyze Rayleigh waves, focusing on a specific frequency range between 0.03 and 0.1 Hz. By examining cross-correlation coefficients and spectral densities, they could identify and characterize the precursor seismic signal.

The study identified a significant seismic wave originating from the volcano's direction around 03:45 UTC, approximately 15 minutes before the main eruption. This wave had characteristics similar to those of an earthquake with a magnitude of 4.9 but occurred without any visible surface activity, as confirmed by satellite imagery.

The researchers acknowledged several limitations, including the lack of direct observation equipment near the volcano and the inability to definitively confirm the precise source mechanism of the precursor signal. The study relies on indirect evidence and theoretical modeling.

The research suggests that subtle seismic signals could potentially provide early warnings for catastrophic volcanic events. By demonstrating that distant seismic stations can capture critical precursor information, the study offers a promising approach to monitoring challenging volcanic systems.

This research was supported by the Science and Technology Research Partnership for Sustainable Development (SATREPS), funded jointly by the Japan International Cooperation Agency (JICA) and Japan Science and Technology Agency (JST).