All over the world, GPS/GNSS stations are used to track the motion of tectonic plates. GPS ground stations anchored into the Earth communicate with satellites in orbit to determine their precise position over time. For the Cocos Plate, a small plate off the western coast of Central America, this type of monitoring is especially challenging because the plate lies almost entirely underwater with the exception of one place: Cocos Island. This June, the ISCO station on Cocos Island was rebuilt, allowing for the first real-time geophysical data for the Cocos Plate since 2020.
What is NOTA and Where is Cocos Island?
The ISCO station is part of the Network of the Americas, a system of GNSS and borehole stations that span from the tip of the Aleutian Islands through to Central America and the Caribbean. NOTA is funded by the National Science Foundation and is part of the National Geophysical Facility. Maintenance and operation of this network are managed by EarthScope Consortium in collaboration with researchers across the network. The ISCO station is operated in close collaboration with El Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA). Located approximately 550 kilometers off the west coast of mainland Costa Rica, Cocos Island (not to be confused with Australia’s Cocos (Keeling) Islands nearly 13,000 miles away in the Indian Ocean) is the only point of the Cocos Plate that reaches above sea level.
The Cocos Plate is believed to have formed approximately 23 million years ago during the breakup of the Farallon Plate. The plate is bounded by the Pacific Plate to the west, and the Nazca Plate to the south and east. The Cocos Plate is being subducted beneath the North American, Caribbean, and Panama Plates along a boundary known as the Middle America Trench. This boundary has the potential to produce devastating earthquakes throughout Mexico and Central America, such as the 1985 Mexico City and 2012 Costa Rica earthquakes. The subduction zone also feeds the Central American Volcanic Arc. This arc is home to some of Earth’s most active, and most densely populated, volcanoes such as Volcán de Fuego in Guatemala and Poás in Costa Rica. Given how active this region is, it is important to keep a close eye on plate motion through time.
ISCO Station Illuminates Cocos Plate Motion
In 2020, the ISCO station went offline. This meant that the only permanent above-water station used to monitor the motion of the Cocos Plate went offline. In recent years, advances in seafloor geodesy have enabled scientists to monitor plate motion directly from the ocean floor. These techniques however, are limited in that deploying such instruments is typically very expensive and often temporary as they are deployed in short-term campaigns. Since the ocean floor cannot be studied with satellites as their signal is scattered by the ocean water itself, this small island serves as the most convenient window into the motion of this plate.
Preliminary measurements indicate that the station has subsided nearly 5 centimeters since the station was last operational in 2020. Since the station was originally installed in 2012, the island itself has also shifted about 1.3 meters, about 10 cm/yr. This type of data is used to help constrain plate convergence rates and add to the complete picture of complex and dynamic plate motion in this region of the world. In addition to a reinstall, NOTA field engineer Lia Lajoie and Christian Garita from partner OVSICORI also worked to upgrade the AC power system, added a six-battery back up power bank, incorporated Starlink, and added a seismometer to the existing GPS and meteorological system that were part of the original install. These new instruments should ensure uninterrupted data transmission from Cocos Island, but also will collect new datasets that had not previously been obtainable from the station.
Station Challenges
Cocos island is very difficult to access, being so remote. Cocos Island is a Costa Rican National Park. This distinction helps keep the unique land and marine ecosystems pristine, but also means that access to the island requires special permitting which can take time to secure. There are no residents of the island aside from park rangers, meaning not only does equipment need to be transported to the island, but so do the personnel needed to service the station. The boat ride from the city of Puntarenas takes 40 hours in each direction.
The island’s heat, humidity, and frequent rainfall make installation and maintenance efforts particularly challenging, even once engineers and researchers have reached the island. Because of its location on an otherwise submerged tectonic plate, the ISCO station highlights the importance of upkeep of even the most remote of these stations.