Bridging the Seismic Monitoring Gap around Saba, St. Eustatius, and St. Maarten in the Caribbean Netherlands: The NA Network

The seismic network NA (Caribbean Netherlands Seismic Network) in the Caribbean Netherlands is deployed by the Royal Netherlands Meteorological Institute (KNMI) to monitor local seismicity around Saba, St. Eustatius, and St. Maarten, and to contribute data to regional earthquake and tsunami warning monitoring systems. The network currently comprises 11 broadband seismometers that record data processed in real time at KNMI, using SeisComP and a coincidence trigger. Between January 2017 and April 2022, we detected and located 241 earthquakes within 150 km distance from the center of the network with magnitudes from 0.4 to 6. Reanalysis of data before 2017 revealed a swarm of 22 tectonic earthquakes in 2008, within 15 km distance west of Saba with magnitudes between 2.3 and 4 at shallow (5–10 km) depths. The complex seismic velocity structure, the large lateral velocity inhomogeneities in the subduction zone, and the elongated setup of the regional seismic network are challenges for the earthquake location process. We compare our results with the U.S. Geological Survey catalog and find differences that fall within the uncertainty ellipses for 85% of the earthquakes. The NA network is an important contribution to the regional earthquake and tsunami warning monitoring systems, and for studying subduction and volcanic processes in the Lesser Antilles arc.