Boletín de la Sociedad Geológica Mexicana Volumen 66, núm. 3, 2014, p. 441-457 http://dx.doi.org/10.18268/BSGM2014v66n3a3

Tomografía de Velocidad de Grupo de Ondas de Rayleigh para el Oriente de México y el Istmo de Tehuantepec

Francisco Córdoba Montiel¹, Arturo Iglesias Mendoza², Shri Krishna Singh², Zack Spica², Denis Legrand²

¹ Centro de Ciencias de la Tierra de la Universidad Veracruzana, Francisco J. Moreno # 207, Colonia Emiliano Zapata, C.P. 91000; Xalapa, Veracruz.
² Instituto de Geofísica de la UNAM, Circuito de la investigación Científica s/n, Ciudad Universitaria, Delegación Coyoacán, C.P. 04510, México D.F.
^* This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

In this study seismic noise records from the permanent broadband network of the Mexican National Seismological Service (Servicio Sismológico Nacional) and from the temporal broadband networks of MASE and VEOX have been used to compute the Green functions from vertical-vertical component of noise cross correlations between station pairs. MASE (Mesoamerican Seismic Experiment) consisted of one hundred stations deployed along a profile perpendicular to the trench from Acapulco, Guerrero, to Tempoal, Veracruz, Gulf of Mexico. This experiment was carried out from December 2004 to May 2007. Forty six of these stations were relocated along a N-S profile crossing the Tehuantepec Isthmus from the Gulf of Mexico to the Pacific coast. These stations operated from July 2007 to March 2009 and this stage of the experiment was called VEOX (Veracruz-Oaxaca). From the Green functions extracted from the correlation for each pair of stations, Rayleigh wave dispersion curves were computed which represent the average group velocity between station pairs. Furthermore, regional earthquakes recorded by the stations were used in order to compute Rayleigh wave dispersion curves, which represent the average group velocity between epicenter-station pair. This mixed set of group velocity measurements was inverted to obtain tomographic images at discrete periods between 5 and 50 s. Resolution tests show that the regions of best coverage surround both temporal experiments. A good velocity model was obtained in a large area between the two experiments. The images show good correlation at short periods (< 15 s) with the shallowest geological features. Low velocity anomalies are related with sedimentary basins and Cenozoic volcanic areas, whereas high velocity anomalies correlate with the forearc region. A low-velocity anomaly was clearly observed at the north of the Isthmus of Tehuantepec where an active volcanic field is located. At larger periods (> 25 s) a low velocity region coincides with the border of the Trans- Mexican Volcanic Belt, suggesting the presence of a mantle wedge. For these periods, high velocity anomalies are related with the shallow presence of the oceanic mantle in the forearc and the presence a shallower mantle in the backarc, where the continental crust becomes thin.

Keywords: Cross-correlations, tomography, dispersion curves, inversion, Green functions.