The plate boundary between Iberia and Africa has been studied using data on seismicity and focal mechanisms. The region has been divided into three areas: A; the Gulf of Cadiz; B, the Betics, Alboran Sea and northern Morocco; and C, Algeria. Seismicity shows a complex behavior, large shallow earthquakes (h < 30 km) occur in areas A and C and moderate shocks in area B; intermediate-depth activity (30 < h < 150 km) is located in area B; the depth earthquakes (h » 650 km) are located to the south of Granada. Moment rate, slip velocity and b values have been estimated for shallow shocks, and show similar characteristics for the Gulf of Cadiz and Algeria, and quite different ones for the central region. Focal mechanisms of 80 selected shallow earthquakes (8 ‡ m b ‡ 4) show thrust faulting in the Gulf of Cadiz and Algeria with horizontal NNW-SSE compression, and normal faulting in the Alboran Sea with E-W extension. Focal mechanisms of 26 intermediate-depth earthquakes in the Alboran Sea display vertical motions, with a predominant plane trending E-W. Solutions for very deep shocks correspond to vertical dip-slip along N-S trends. Frohlich diagrams and seismic moment tensors show different behavior in the Gulf of Cadiz, Betic-Alboran Sea and northern Morocco, and northern Algeria for shallow events. The stress pattern of intermediate-depth and very deep earthquakes has different directions: vertical extension in the NW-SE direction for intermediate depth earthquakes, and tension and pressure axes dipping about 45°for very deep earthquakes. Regional stress pattern may result from the collision between the African plate and Iberia, with extension and subduction of lithospheric material in the Alboran Sea at intermediate depth. The very deep seismicity may be correlated with older subduction processes.

The Azores-Tunisia region is formed by the western part of the plate boundary between Eurasia and Africa. This plate boundary presents a complex nature due to its proximity to the pole of rotation of the African plate. This situation produces crustal extensions and normal faulting at the Azores archipelago, transcurrent motion with strike-slip faulting at the center part of the Azores-Gibraltar fault and at the eastern end, from the Gulf of Cadiz to Tunisia, plate convergence with reverse faulting. In this last part, the collision of Iberia with northern Morocco produces complex phenomena with intermediate depth and deep earthquakes and an extensional regime at the Alboran Sea. Recently, new evidence has been gathered in this region, based on observations from geology, geodesy, mainly through GPS measurements, seismology, especially with the installation of broad-band stations, and other fields of geophysics, such as paleomagnetism and gravimetry. The synthesis of these new observations is contributing to a new understanding of the complex geodynamics of this region.On May 31 to June 2, 2001, a Workshop was held in San Fernando (Cadiz, Spain) organized by the Real Instituto y Observatorio de la Armada (San Fernando) and the Universidad Complutense (Madrid) with the title ''Geodynamics of the Western Part of the Eurasia-Africa Plate Boundary (Azores-Tunisia)''. Five invited lectures and 77 papers were presented at the workshop covering many aspects of the geology, seismology, geodesy, paleomagnetism and other geophysical observations of the region. Attendance brought together 105 participants from Europe, Northern Africa and America. New observations in the different fields were presented and new models of the geodynamics of the region were proposed. The present volume is a selection of the papers presented at the workshop. The 12 papers of the volume include 5 papers pertaining to geological and tectonic structure of the regions and parts thereof, 4 papers focus on seismology and seismotectonics, 2 address geodetic observation and one paleomagnetism. These papers are representative of those presented at the workshop.