seismic monitoring

The installation and operation of a multi-parameter volcano monitoring network on the islands of Saba and St. Eustatius in the Caribbean Netherlands

In the Caribbean Netherlands, the islands of Saba and St. Eustatius host the active but quiescent volcanoes Mt. Scenery and The Quill. To mitigate volcanic risk to the islands, robust monitoring is essential. Therefore in the past five years the Royal Netherlands Meteorological Institute (KNMI) significantly expanded the volcano monitoring network on both islands.

The seismic monitoring network was expanded from seven to 11 broadband seismometers located across the islands. Seismic data are sent to and stored at KNMI and Observatories and Research Facilities for European Seismology (ORFEUS). Eight permanent continuous Global Navigation Satellite System (GNSS) stations were newly installed, where possible co-located with the broadband seismometers. GNSS data are sent to and stored at KNMI and UNAVCO. On a daily basis we run an automatic earthquake detection system and coincidence trigger to identify seismic events and create GNSS time series using both network and Precise Point Positioning (PPP) solutions.

The installation of new instruments was challenging due to the remoteness of the envisioned locations which were needed to monitor all sides of the volcanoes.  Local governmental and military assistance was key to the success of the mission. At the most remote locations instruments are operated on solar power and data are transmitted using  Very-Small-Aperture Terminal (VSAT) technology. Ensuring the operability of the monitoring network remains demanding due to the harsh tropical conditions (hurricanes, UV-radiation, sea spray, lightning) as well as network and power outages. 

Apart from seismic and GNSS instruments, we also deploy three temperature sensors and four cost-effective GNSS units to extend our monitoring network. Furthermore, in collaboration with Delft University of Technology (TU Delft) we test the feasibility of the use of Interferometric Synthetic Aperture Radar (InSAR) for the monitoring of these islands.

Date
2023
Data type
Research report
Theme
Research and monitoring
Report number
EGU General Assembly 2023, Abstract
Geographic location
Saba
St. Eustatius

Developments during 15 years of seismic monitoring in the Caribbean Netherlands

In the Caribbean Netherlands, on Saba, St. Eustatius and St. Maarten, the Royal Netherlands Meteorological Institute (KNMI) deploys the seismic network NA (Caribbean Netherlands Seismic Network) to monitor local tectonic earthquakes and volcanic seismicity. Saba and St. Eustatius are part of the Lesser Antilles volcanic arc and each host an active but quiescent volcano: Mt. Scenery on Saba and The Quill on St. Eustatius. The network comprises 11 broadband seismometers of which data are a) transmitted to KNMI by DSL, cellular connection and VSAT, b) processed in real-time at KNMI using SeisComP and a coincidence trigger, c) forwarded in real-time to the Pacific Tsunami Warning Center (PTWC) and d) openly available to research and monitoring communities through ORFEUS/EIDA and EPOS via standardized services. 

In the past six years we detected and located more than 350 earthquakes with magnitudes ranging from 0.4 to 6 within a 150 km radius from the center of the network. About 230 of these earthquakes were exclusively reported by KNMI as they were probably too small to be detected by, or too distant from, seismic networks operated by other agencies in the region. A previously unnoticed shallow (5-10 km depth) swarm of 22 tectonic earthquakes was detected and located through reanalysis of data from before 2017. This swarm took place in 2008, in the same area as the tectonic swarm of earthquakes in 1992, less than 15 km west of Saba, with magnitudes ranging between 2.3 and 4. One of the challenges for our network is building a reliable detection, identification and location system for volcanic earthquakes, which is hampered by the quiet state of both volcanoes. Another challenge is decreasing the hypocenter uncertainties, which are caused by the complex seismic velocity structure underneath the volcanoes, the large lateral velocity inhomogeneities in the subduction zone and the elongated set-up of the regional seismic networks.

Date
2023
Data type
Research report
Theme
Research and monitoring
Report number
EGU General Assembly 2023, Abstract
Geographic location
Saba
St. Eustatius
St. Maarten