LOCAL EARTHQUAKES SEISMIC TOMOGRAPHY IN THE BETIC CORDILLERA (SOUTHERN SPAIN)

A crustal tomographic image, from the surface down to 35 km depth bene ath the Betic Cordillera (southern Spain), is obtained using data on l ocal earthquakes recorded at stations from the National and Andalusian Seismic Networks. The velocity structure and the hypocentre locations are derived from the inversion of P first arrival times, using an ite rative simultaneous inversion method. The reliability of the results i s assessed using different control parameters. The inverted velocity f ield in the uppermost layers shows a significant lateral variability w hich reflects most of the large-scale geological features of the Betic Cordillera. Well determined local surface anomalies allow to constrai n the location and geometry of the most prominent Neogene sedimentary basins. The upper crust is well resolved throughout the whole region, and is characterized by relatively high velocities in the Internal Bet ics and in the South Iberian Massif and lower velocities within the Ex ternal Betics. A relatively well constrained event cluster displays a NNE-SSW trend, and outlines the contact zone between the Internal and the External domains. The middle and lower crustal levels show reliabl e results beneath the central part of the Betic Cordillera. High avera ged velocities are obtained within the South Iberian and the Alboran d omains, in contrast to a relatively low velocity anomaly which charact erizes the boundary between them. These findings support the hypothesi s of the lack of well differentiated crustal levels below the contact zone, while crustal layering is better defined beneath the Alboran and the Iberian domains. (C) 1998 Elsevier Science B.V. All rights reserv ed.