Brunat, Preiser

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    Rumshake: Amplification of earthquake ground motion in Mayagüez, Puerto Rico
    (2020-05-29) Brunat, Preiser; Martínez-Cruzado, José A.; College of Engineering; Vanacore, Elizabeth A.; Suárez, Luis E.; Department of Civil Engineering; Cáceres, Luis F.
    Puerto Rico is a seismically active region with a history of destructive earthquakes such as the 1918 M7.3 Mona Passage event, and more recently, the 2020 Southwest Puerto Rico Earthquake sequence. In the years 2018 and 2019, The Puerto Rico Seismic Network detected over 4,000 and 6,000 earthquakes, respectively. Given the seismic hazard presented by this earthquake activity, it is imperative to assess the seismic wave amplification at specific frequencies caused by local unconsolidated sediments. As part of understanding the hazards, a site response study was conducted in the city of Mayagüez, western Puerto Rico, by the Puerto Rico Seismic Network and the Puerto Rico Strong Motion Program, in collaboration with the United States Geological Survey, to investigate the potential for seismic amplification by soils in Mayagüez. During a period of six months, from April to October 2019, twelve L-22 sensor stations were deployed in different sites in the city to record local, regional earthquakes, and teleseism data to determine site-amplification factors. Fifteen real, local earthquakes, in addition to five regional earthquakes and teleseisms, were used for analysis. Data were analyzed using spectral ratios of sediment 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 motion during earthquakes.