Torres Ortiz, Denny M.

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    Tomografía preliminar de Puerto Rico
    (2013) Torres Ortiz, Denny M.; Huérfano Moreno, Víctor A.; College of Engineering; Camacho Padrón, Beatriz I.; Suárez Colche, Luis E.; Department of Civil Engineering; Vásquez Urbano, Pedro
    Seismic Tomography has been used by researchers to obtain information about the internal structure of the Earth at different depths. This method is applied to identify and visualize the seismic wave velocity propagation through the Earth interior. In this research we use seismic wave data recorded in the stations operated by the Puerto Rico Seismic Network (PRSN) from local sources. PRSN locates seismic events using specialized systems like Earlybird (EB), EarthWorm (EW), and the Puerto Rico Data Analysis and Information System (PRDANIS) software. Arrival times of all seismic waves are recorded with these systems, but final location of the seismic event can only be obtained by using the P, S, and Coda phases in the PRDANIS software which uses a five horizontal layers velocity model in 1D. The 1D velocity model was used initially, along with the arrival times to the seismic stations and the location errors (Tobs – Tcal) to develop the 3D velocity model. The secondary phases of the primary wave (P) were identified with its theoretical and observed travel times using wave reflections on upper earth layers using the Puerto Rico velocity model in 1D. In order to obtain the 3D velocity model, the Fast Marching Tomography Software (FMTOMO) was used. In this thesis the tomography results for Puerto Rico were based on an estimation of the primary seismic wave’s velocities traveling in the upper layers of the Earth at depths less than 40 km. As a result, a better understanding of the upper crust geology structure and related velocity anomalies beneath Puerto Rico and Virgin Island (US and British) was obtained.
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    Análisis de la distribución de PGA de sismos de magnitud moderada y escenario de la respuesta del terreno ante un sismo de M7.4 para Puerto Rico usando funciones empíricas de Green
    (2022-12-14) Torres Ortiz, Denny M.; Huerta López, Carlos I.; College of Engineering; Martínez Cruzado, José A.; Suárez, Luis E.; Camacho Padrón, Beatriz I.; Department of Civil Engineering; Huérfano Moreno, Víctor A.
    Peak Ground Acceleration (PGA) and Pseudo Spectral Accelerations (PSA) distribution of two moderate magnitude earthquakes (M5.8, and M6.4) occurred in mainland and off-shore of Puerto Rico Island (PRI), recorded by the accelerometers of the Puerto Rico Strong Motion Program (PRSMP) were analyzed. Standard strong motion processing was applied to the data, obtaining uncorrected and, corrected acceleration records in physical units of acceleration, velocity and displacement, as well as the spectral representation of all above, respectively. Ground motions showed significant variation of PGA and PSA all around PRI, which is in disparity to the expected amplitude distance decay. The values of PGA distribution in PRI were compared with various Ground Motion Predictive Equations (GMPE) estimated for regions with apparent similarity tectonic environment of PR region as well as for PRI to clarify the contribution of local site response effect. The above, was the motive to conduct a ground motion scaling study in order to obtain a scenario of PGA distribution in PRI upon the probable occurrence of large magnitude (M≥ 7) earthquakes using moderate magnitude earthquake. Empirical Green’s Functions (EGF) was the processing method of the scaling a moderate magnitude earthquake into a large magnitude earthquake, which requires used to scale the source rupture process analysis as well. The variation of the PGA in terms of the instrumental intensity (MMI): (i) for the 13/01/2014 earthquake (M6.4) was V in the area of Arecibo Town (epicentral distance ~ 74.4 km), other areas within even shortest epicentral distances barely reached III; (ii) for the earthquake of 05/16/2010 (M5.8) was VII in Utuado Town area (epicentral distance ~ 42 km) and V in Añasco Town area (epicentral distance ~ 15 km), which corresponds to PGA values of 0.23g and 0.0651g, respectively. PSA peak values with the shortest period were at UTD3 (0.06-s, 75.2-PSA). Finally, a scenario of PGA and instrumental intensity distribution was generated within PRI upon the occurrence of large magnitude, M7.4 earthquake in the epicentral region of the M6.4 earthquake. The results showed an expected and reasonable behavior which is in agreement with the previous studies of earthquakes of moderate magnitude (5≤M≤6.4). Amplification effect due to local site conditions seems to be the dominant contribution on ground response. Empirical Green's function method can be successfully applied to generate scenarios of PGA (or instrumental MMI) distribution in regions where large earthquake has not been recently occurred or never been recorded instrumentally, which is the case for the mainland of PRI.