Estructura cortical en el Istmo de Tehuantepec, México, usando ondas convertidas

S U M M A R YWe used arrival time differences between direct S waves and converted Sp waves to determine the crustal thickness and the mean shear wave velocities of the crust and upper mantle beneath Chiapas, México. For this purpose, we used four seismological stations that operated in the region from 1994 to 1998. The data set consists of 35 digital records from moderate magnitude earthquakes (3.6 < Mb < 5.3) with focal depths between 50 and 300 km. To identify the seismic phases more accurately, the records were rotated in the longitudinal and vertical directions of motion. The results show differences, in both thickness of the crust and upper mantle velocity, between stations located near the trench and those located inland. Beneath Tapachula (Ta) and Arriaga (Ar), the nearest stations to the Middle American trench, we found the crustal thickness to be 17 km and 28 km, respectively. Under Tuxtla (Tu) and Comitán (Co), the thickness is 49 km and 53 km, respectively. Similarly, we estimated that the upper mantle S-wave velocity under Ar and Ta is 4.1 km s −1 , while under Tu and Co, 5.7 km s −1 and 5.6 km s −1 , respectively. The crustal S-wave velocity also varies from zone to zone: under Tu and Co it is 3.5 km s −1 and 3.7 km s −1 , respectively, and beneath Ar it is 3.8 km s −1 . It is likely that the presence of the Chiapas granitic massif may influence the velocity estimates. Under Ta, located near the Tacaná volcano and close to North American and Caribbean plate border, a crustal velocity of 3.3 km s −1 was calculated. In general, the thickness of the crust in Chiapas increases towards the northeast. This increment is probably related to the subduction zone process, since we observe similarities between the depth of the Moho and the geometry of the Benioff-Wadati zone that had been made for the Cocos plate.

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Determination of crustal thickness beneath Chiapas, Mexico usingSandSpwaves

Narcía-López

Castro

Rebollar

2004

Geophysical Journal International

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Crustal velocity structure of southern Guatemala using refracted and Sp converted waves

Ligorría

Molina

1997

GeoInt

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La distribución de velocidades en la estructura cortical del Sur de Guatemala es estimada utilizando los métodos de Velocidad Aparente Minima y Ondas Convertidas, aplicados a datos sísmicos locales. Los resultados son evaluados relocalizando una muestra aleatoria de eventos y por medio de modelado sintético de sismogramas. El modelo de velocidad obtenido posee un gradiente aproximadamente constante en la corteza, que sobrayace una capa intermedia de- 15 km de espesor. Las velocidades del Manto son aproximadamente 8.0 km/sec. Este es un modelo promedio para Guatemala con las limitantes impuestas por la compleja tectónica regional.doi: sin doi

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Distributions of stresses and geometry of the Wadati-Benioff zone under Chiapas, Mexico

Rebollar¹,

Espíndola

Mendoza³

et al. 1999

GeofInt

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La sismicidad registrada desde junio de 1994 a mayo de 1995, en una red portátil de estaciones sismológicas analógicas y digitales, definieron la geometría de la zona Wadati-Benioff bajo Chiapas, así como la distribución de los esfuerzos principales en la placa subducida. La sismicidad localizada en el antearco no fue bien localizada. Un módulo de Poisson de 0.24 fue calculado para la corteza de Chiapas. 321 sismos fueron localizados en el rango de magnitudes entre 3.3 y 5.6. Los hipocentros definieron la zona Wadati-Benioff de 39Â±4 km de grueso buzando 40°Â±3° hacia N45°E. La profundidad de los sismos varió entre 10 a 300 km. La placa de Cocos buza aproximadamente 25° en Oaxaca, 30° bajo el Golfo de Tehuantepec y 40° hacia el sudeste. Un fuerte cambio en el buzamiento de la placa de Cocos ocurre en la intersección de la cordillera de Tehuantepec y la Trinchera de Centro América. La sismicidad en esta zona es difusa hasta profundidades de 200 km. Nuestros datos sugieren un incremento gradual del buzamiento de la placa de Cocos de Oaxaca a Chiapas. Los mecanismos focales de eventos con profundidades menores de 50 km indican que la placa subducida está bajo tensión, mientras que a profundidades entre 50 y 200 km la placa experimenta un régimen mixto de esfuerzos. A profundidades entre 200 y 300 km la litosfera subducida está bajo un régimen comprensivo en la dirección del buzamiento.

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Estructura cortical en el Istmo de Tehuantepec, México, usando ondas convertidas

Cited by 3 publications

References 14 publications

Determination of crustal thickness beneath Chiapas, Mexico usingSandSpwaves

Determination of crustal thickness beneath Chiapas, Mexico usingSandSpwaves

Crustal velocity structure of southern Guatemala using refracted and Sp converted waves

Distributions of stresses and geometry of the Wadati-Benioff zone under Chiapas, Mexico

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