Can Earthquake Locations Be Improved for Real-time Monitoring? Revisiting the 1995 seismicity at Soufri`ere Hills Volcano, Montserrat

Abstract

Volcanic earthquakes provide a wealth of information about the magmatic system. Monitoring volcanic seismicity is one of the primary methods used by volcano observatories globally, including at Soufri`ere Hills Volcano, Montserrat. Computed earthquake locations represent the optimal solution given the information available, and vary depending on the chosen location method and seismic velocity model, but rarely are these parameters tested for suitability in each region. We propose a new method that utilises synthetic earthquakes to evaluate whether the calculated hypocenters and their associated errors accurately represent the true source locations. We define this evaluation as a confidence parameter that highlights events we can 'trust'. By comparing several location methods and seismic velocity models for Montserrat we show the current setup is not optimal, and suggest an alternative location method. Analysis using new 'trusted' relocations focuses on four seismic clusters distal from Soufriere Hills in 1995. Our results highlight differences in hypocenters during this period, suggesting alternative interpretations of the distal seismicity. We propose a WNW dyke orientation supporting previous studies, and local fault complexes in the region. Overall, this paper highlights the importance of using a robust location method suitable for the region to ensure that calculated hypocenters are trustworthy and accurate. Use of sub-optimal methods can influence apparent spatial earthquake trends, impacting interpretations and our understanding of volcanic systems.