First Optical Seismometer at the Top of La Soufrière Volcano, Guadeloupe

Abstract

Abstract Accurate monitoring of volcanic activity demands expertise in fields including geophysics, geology, and geochemistry. Data obtained from the most recent technical advances are particularly vital in pre-eruptive phases. In particular, seismic monitoring in near real time is essential to locating and discriminating early signs among different sources of seismic waves, especially those related to movement and overpressure in underground fluids. Among the major indicators of volcanic restlessness are fumaroles, or gas and steam vents, often located near a volcanic summit. Their activity could be monitored by seismometers in their vicinity, but today’s standard instruments cannot last very long when exposed to the high temperatures and the billowing, sulfurous, acidic gases near a fumarole. Conventional gear may also not be accessible for emergency deployment, or repair, even in pre-eruptive phases. La Soufrière de Guadeloupe Volcano in the Caribbean typifies such challenges. Its last significant event was a phreatic (gas and steam) eruption in 1976 that prompted evacuation of the archipelago’s nearby capital. Since early 2018, the 1467-meter-high stratovolcano has shown signs of increased activity. To provide a hardy, high-resolution monitoring system, we installed a recently developed type of seismometer just 10 m from a vigorous summit fumarole. The sensor is a purely opto-mechanical geophone that is interrogated through a 1.5 km fiber-optic cable by a remote, and thus it is a much safer optic-electronic system down the volcano’s flank. The ESEO Group and the Institut de Physique du Globe de Paris (IPGP) started development of this novel seismometer in 2008. The 2019 Guadeloupe installation is part of the HIgh PERformance SeISmometer (HIPERSIS) project (French Agence Nationale de la Recherche [ANR]). It is, to our knowledge, the first high-resolution optical seismometer ever installed on an active volcano or other active, hazardous zone. We report here the details of this installation, the means we are using for measurements, and our implementation strategy, and we share some of the first results. Such an optical seismometer, as well as a variety of other geophysical sensors built on the same principle, can be installed in a wide variety of sites with fibers up to 50 km long.