Crustal velocity model along the southern Cuban margin: implications for the tectonic regime at an active plate boundary

Abstract

Summary A new 1‐D velocity model along the southern Cuban margin has been determined using local earthquake data, which are the result of the merged Cuban and Jamaican catalogues. Simultaneous inversion using joint‐hypocentre determination was applied to solve the coupled hypocentre–velocity model problem. We obtained a seven‐layer model with an average Moho interface at 20 km. The average velocity was found to be 7.6 km s−1 on the top of the crust–mantle transition zone and 6.9 km s−1 in the basaltic layer of the crust. The improvement in the earthquake locations allowed us for the first time to use local seismicity to characterize the activity on local faults and the stress regime in the area. For this purpose, 34 earthquake focal mechanisms were determined along the eastern segments of the Oriente Fault. These solutions are consistent with the known left‐lateral strike‐slip motion along this major structure as well as with the stress regime of two local structures: (1) the Cabo Cruz Basin and (2) the Santiago deformed belt. The first structure is dominated by normal faults with minor strike‐slip components and the second by reverse faults. The shallow seismicity in the Cabo Cruz Basin is associated with fault planes trending N55°–58°E and dipping 38°–45° to the north. The Santiago deformed belt, on the other hand, exhibits diverse fault plane orientations. These local structures account for most of the earthquake activity along the southern Cuban margin. Deep seismicity observed in the Santiago deformed belt, supported by focal mechanisms, suggests underthrusting of the Gonave Microplate beneath the Cuban Block in this area. The principal stress orientations obtained from stress inversion of earthquake focal mechanisms suggest a thrust faulting regime along the Southern Cuban margin. We obtained a nearly horizontal σ1 and nearly vertical σ3, which indicates active compressional deformation along the major Oriente transcurrent fault in agreement with the dominant structural trend associated with the Santiago deformed belt.

Modelo de velocidades sísmicas de Cuba Oriental

“…La solución del problema inverso depende fuertemente del modelo inicial e hipocentros iniciales. Como modelo inicial se seleccionó el obtenido por Moreno et al (2002) (Figura 4). Solo un 50% de los eventos sísmicos seleccionados tenía inicialmente un RMS menor que 0,5, por lo que se hicieron varias corridas de VELEST usando cada vez, más terremotos y un modelo inicial diferente.…”

“…4). La figura 4 muestra además el modelo de velocidades de onda P obtenido por Moreno et al (2002). Ambos modelos son similares, con algunas diferencias en el número de capas superficiales, pero en general las velocidades de cada una de las capas son similares.…”

“…Según Bush & Shcherbakova (1986) la corteza de Cuba Oriental se puede dividir en tres capas: (1) Una capa sedimentaria-volcánica con velocidad de la onda P de 4,0 a 4,8 km/s; (2) una capa superior de corteza consolidada (5,8-6,4 km/s); y (3) una capa inferior de corteza consolidada (6,3-6,7 km/s). Moreno et al (2002) determinaron un modelo de velocidades para la zona del mar Caribe entre Cuba y Jamaica, por lo que el presente estudio se enmarca en el interior de la isla de Cuba, particularmente en la zona oriental. El objetivo principal del trabajo era determinar un modelo de velocidades tridimensional, pero la cantidad de eventos sísmicos disponible no permitió una densidad adecuada de rayos sísmicos para este tipo de cálculos.…”

Seismic microzoning from synthetic ground motion parameters: case study, Santiago de Cuba

“…The regional structural model (until 110 Km of depth) has been constructed, using geophysical studies [28,29], and tomographic inversions [30,31] (Fig. 2) and it has been used to calculate the bedrock P-SV and SH waves seismograms by modal summation until a maximum frequency of 10…”

Crust and Upper Mantle Structure in the Caribbean Region by Group Velocity Tomography and Regionalization

“…The availability of data about the crust structure, summarized and generalized by several authors e.g. [4,10], the most recent regional studies [3,[11][12][13][14][15] and global studies [16][17][18] allow us now to make a refined study of the region. For this purpose we perform Rayleigh waves group velocity tomography, considering relatively short paths (regional trajectories), we regionalize the dispersion curves locally obtained by the tomography and we invert them, into average regionalized structural models, with a non-linear inversion scheme.…”