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Equipment Repair and Replacement—Seismic/Geomagnetic Monitoring Assets in Puerto Rico

In FY 2018, the U.S. Geological Survey (USGS) Earthquake Hazards Program (EHP) received disaster supplement funds (P.L. 115-123) to help rebuild the Puerto Rico Seismic Network (PRSN) and the Puerto Rico Strong Motion Network (PRSMP) and to repair USGS Caribbean stations, because of damage inflicted by Hurricane Maria in 2017.

The potential for earthquakes combined with the large population in Puerto Rico and the presence of infrastructure susceptible to earthquake damage makes this region one of the highest areas of earthquake risk in the United States. Seismic monitoring in and around Puerto Rico is a coordinated activity involving the University of Puerto Rico at Mayagüez, the USGS, and the National Oceanic and Atmospheric Administration’s (NOAA) tsunami program. The upgrades facilitated by disaster supplement funding have made PRSN and PRSMP among the most modern and reliable networks across the USGS Advanced National Seismic System, robust to the risks posed by future hurricanes and other natural hazards, and able to serve as critical life safety systems for the people of Puerto Rico and the United States.

seismic site damage in Puerto Rico
Seismic site damage in Puerto Rico after Hurricane Maria.

Within Puerto Rico, the main entities involved in providing earthquake and tsunami response products (e.g., earthquake location, magnitude, strong ground motion parameters) are the PRSN and the PRSMP, both of which are facilities within UPRM that operate seismic stations in Puerto Rico and adjacent islands. Earthquake monitoring for Puerto Rico is conducted jointly by the PRSN and USGS National Earthquake Information Center (NEIC), and the PRSN is a participating network in the USGS ANSS. The USGS National Strong Motion Project also coordinates closely with the PRSMP. The engineering community relies heavily on easy access to high-quality strong motion data needed for evaluation of building designs. The general public routinely feels earthquakes in Puerto Rico and relies on timely and high-quality information on earthquake activity provided by the USGS and the PRSN.

The PRSN is a regional seismic network that focuses on operating broadband and short period seismic stations and that performs data analyses to characterize and catalog earthquakes around Puerto Rico and the Virgin Islands in real time. With P.L. 115-123funding, 22 seismic stations, 17 in Puerto Rico and 5 in US and British Virgin Islands were upgraded. The network was hardened to ensure future operations under adverse conditions by deploying new posthole broadband sensors that are impervious to flooding. Furthermore, ten of the Puerto Rico seismic stations were supplemented with VSAT communications and full solar backups, to ensure reliable data continuity to the USGS NEIC and the NOAA tsunami warning centers, thus providing continuous monitoring in the event of future outages to PRSN operations. The PRSN upgrades also included migration from its homegrown earthquake location processing software to the AQMS (ANSS Quake Monitoring System) system employed by the majority of US regional seismic networks of the ANSS.

installing new equipment
Installing new equipment in Puerto Rico.

The USGS has been cooperating with the PRSMP since the 1970s. PRSMP operates a dense network of strong motion stations. These special instruments are designed to record large amplitude motions near the epicenter of large earthquakes and are important for understanding the generation and propagation of damaging ground motions and the shaking performance of structures; these data are also critical for USGS ShakeMap and PAGER products. The PRSMP upgrades improved a total of 77 free-field (out of their network of 113) and 11 structural (out of their network of 14) sites. The PRSMP effort is also focused on improved real time communications, such that data collected can be utilized for earthquake monitoring and disaster response efforts. While this effort is not yet complete, today 85% of PRSMP free field sites have communications, compared to 70% in 2017.

The new networks facilitated a rapid and reliable response to the 2020 Southwest Puerto Rico earthquake sequence, allowing PRSN and the USGS to provide the information and products necessary to support response to this devastating sequence of earthquakes, which included a magnitude 6.4 event on January 7, 2020. For example, network data supported the generation of an Operational Aftershock Forecast for the earthquake sequence, which provides situational awareness of the expected number of aftershocks, as well as the probability of subsequent larger earthquakes, and a subsequent Sequence Duration report, estimating how long elevated probabilities of significant aftershocks may last. The valuable data recorded by the improved networks in this sequence will also be important for a planned update of the USGS seismic hazard model for Puerto Rico and the US Virgin Islands, which support earthquake hazard mitigation in the territories.

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