RUMShake: A Pilot Amplification Study in Western Puerto Rico

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Puerto Rico is a seismically active region, with the Puerto Rico Seismic Network (PRSN) detecting over 6,000 earthquakes within and around Puerto Rico, the Virgin Islands and the Eastern Dominican Republic in 2019. More recently, the 2019-2020 sequence of earthquakes near the south coast of Puerto Rico has included several damaging earthquakes. Given the seismic hazard presented by this earthquake activity, it is important to assess the seismic wave amplification at specific frequencies caused by local unconsolidated sediments.

The PRSN at the University of Puerto Rico, Mayaguez (Recinto Universitario de Mayagüez [RUM]) and the Puerto Rico Strong Motion Program (PRSMP), in collaboration with the United States Geological Survey (USGS) conducted a passive-source seismic experiment to investigate seismic amplification by soils typical of Puerto Rico and other Caribbean Islands. The 2019 pilot project was conducted in Mayagüez, Puerto Rico, which had substantial damage in the 1918 M~7.3 earthquake despite being about 75 km from the inferred epicenter. Local soil and bedrock conditions in Mayagüez are similar to other areas of the Caribbean, so results will have implications throughout the region.

For this study, L-22 sensors with Reftek RT130 recorders were installed at 12 sites in April 2019 to continuously record data for six months. During this period, there were sixty-three M3.5 or greater earthquakes in the region. Fourteen of them in addition to six M6.5 teleseisms have been used for analysis. Data were analyzed using spectral ratios of soil sites relative to three bedrock sites. Results show strong amplifications, with peaks reaching values of 10 at some sites in the 0.5 to 5 Hz frequency range. The frequency and amplitude of the resonance peaks are consistent with soft soils over bedrock, which is a common situation on the island of Puerto Rico. Results indicate that Mayagüez, and likely other coastal cities in Puerto Rico, may be subjected to strongly amplified ground motions in earthquakes.

Presenting Author: Preiser Brunat

Authors