Onshore Seismic Monitoring of Submarine Kavachi Volcano Reveals Vigorous Eruptive Activity

Submarine volcanoes pose considerable challenges in monitoring their activity. Kavachi, situated in the Western Province of the Solomon Islands, is a highly active submarine volcano that presents potential risks to nearby communities, as well as to air and marine traffic in the region. In this study, we employ onshore seismic stations to observe Kavachi's eruptive activity by analyzing volcano-seismic signals. Based on recordings from seismic array stations installed on Nggatokae Island, approximately 27 km and 36 km away from the volcanic edifice, we detected and quantified the eruptive activity of Kavachi between February and November 2023.

We first employed a dual-station approach, using recordings from stations separated by 9 km, to identify and quantify characteristic seismo-volcanic signals. This method is based on station-specific band-limited spectral-amplitude ratios, inspired by techniques originally developed in bioacoustics for detecting whale sounds in seismograms. Using this approach, we detected significant variability in volcanic activity, ranging from quiescent periods with no detected events to phases of intense activity with more than 2,500 seismo-volcanic events per day, associated with episodic volcanic tremors and short-duration explosive signals.

Additionally, array analysis was conducted using data from four closely spaced seismic stations (average spacing of 190 m) on the southern coast of Nggatokae. Cross-correlation techniques were applied to determine the back-azimuth and apparent velocity of the seismic wavefield associated with volcanic activity. Results indicated a consistent mean back-azimuth of 222.6°, closely aligning with the theoretical value of 225° for Kavachi.

Interpretation of these signals was further supported by waveform modeling to provide insights into the source mechanisms and path effects. The findings show that onshore seismic arrays can effectively monitor submarine volcanic eruptions. This methodology not only offers insights into the eruptive activity of Kavachi volcano but presents potential applications for monitoring other submarine volcanoes globally.