Written by Jim Normandeau
6 January 2020
From the NSF award abstract
The great earthquakes and tsunamis of 2004 (Sumatra) and 2011 (Japan) were wake-up calls that our forecasting skill for these catastrophic events remains poor. Measurement of the slow motions of the Earth's surface near active faults could help to forecast the location and the size of future earthquakes. This project tests the concept by operating a network of a high precision GPS/GNSS receivers in Costa Rica. This area is an active subduction zone that experiences frequent large earthquakes. The GPS/GNSS units will measure ground motion for a 3-year period with a precision of a few millimeters per day. This will continue a long history of geodetic observations here that now span both the late and early stages of the earthquake cycle. The data from this project will improve understanding of the earthquake process, and could lead to improvements in our ability to forecast these potentially deadly events. UNAVCO, the NSF-funded consortium for geodesy, will provide critical maintenance support for the network.
The existence of earthquake clusters in subduction interfaces suggests that not all accumulated strain is necessarily released in a single earthquake, and can be stored over a seismic cycle for release in a subsequent, larger than average event. With the discovery of slow slip events (SSEs: earthquake-like phenomenon within the interseismic phase that release energy slowly) it is now clear that determination of a full strain accumulation budget, and improved understanding of frictional conditions on the plate interface, also require study and understanding of these interseismic strain release mechanisms. Data from the M 7.6 September 5, 2012 Costa Rica earthquake suggests that a pre-event SSE changed Mohr Coulomb failure stress by a trivial amount, which may have pushed the fault to failure, although other failure mechanisms are also possible. SSEs are also important indicators of frictional conditions. Shallow SSEs are an important subset, and while generally difficult to observe, can be clearly seen in northern Costa Rica due to proximity to the trench. They may be critical for understanding tsunami potential in this difficult-to-observe region. More generally, SSEs may outline the region of subsequent seismic rupture; this pattern has now been documented in the active margins off Costa Rica, Ecuador and parts of Japan. This project deploys geodetic infrastructure to better observe and understand these slow slip events in the Nicoya Peninsula.
UNAVCO, in collaboration with El Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI), is tasked with providing operations and maintenance for the continuously operating GPS/GNSS (cGNSS) network located on the Nicoya Peninsula and the surrounding areas. Support also includes data downloading and archiving. This currently funded project’s goal is to upgrade the existing GPS stations to GNSS and to overhaul the cGNSS station’s infrastructure where needed. There are 19 stations in total. Some of these cGPS stations have been running since 2003, with the bulk of them installed in 2006.
Several stations in Costa Rica were absorbed into the Caribbean-wide COCONet network, which allowed for continued O&M support as funding at the time for the entire Costa Rican network was uncertain. One new station, VRAI, was installed as part of COCONet. These three stations (VERA, QSEC and IND1) and VRAI are now part of the Network of the Americas (NOTA), a core component of the National Science Foundation Geodetic Facility for the Advancement of Geoscience (GAGE), operated by UNAVCO.
For this preliminary trip, UNAVCO optimized support for stations in both networks. We visited three stations that are part of NOTA and most of the other stations in the Coast Rica network. Repairs, upgrades and assessment of the infrastructure were completed. A second trip is planned in early 2020 to complete the overhaul of stations in need and to relocate the HATI station.
All station data are available free and open access through the UNAVCO Geodetic Data Archive; the PIs encourage researchers to access and use it.
Last modified: 2020-02-05 17:18:58 America/Denver