Temperature, Heat flow, Geoid height, Magnetic anomalies and Seismic depth in the Gulf of Cadiz and SW of Cape St. Vincent, Portugal

Abstract

The region on study, is known as the source region of historical and recorded high magnitude earthquakes and tsunamis affecting regions in the western and southern parts of the Iberian Peninsula and Morocco, causing damage and depths. Seismicity in the region has been studied and seismic profiles were made to obtain the structure of the crust and first mantle layers in the region. Heat flow density data and geoid height anomalies in the region were used in the present work to obtain information related with depth-temperature values trying to obtain information related to the transition from brittle to ductile deformation in the region. As earthquakes generally occur in regions of brittle deformation, these results may give information about the maximum depth of earthquake occurrence. Temperature-depth values were obtained from heat flow density data, considering heat flow by conduction on the vertical direction in a stratified medium, formed by horizontal layers with different thicknesses but with constant thermal conductivity and heat production values in each layer. Lithosphere thickness values were obtained in the region, considering the temperature value of 1350 oC as the temperature of the lower boundary of the lithosphere. Temperature values lower or about 600oC (maximum temperature considered for brittle deformation occurrence) were obtained in depth values close to the focal depth of many earthquakes in the region but deep earthquakes were registered in regions with higher temperature values.