A new high-resolution gravimetric geoid for South Spain and the Gibraltar Strait area: SOSGIS V. Corchete a, * , M. Chourak b,c , D. Khattach d , E.H. Benaı ¨m e a Higher Polytechnic School, University of Almeria, 04120 Almeria, Spain b Faculte ´ Polidisciplinaire d’Errachidia, University of Moulay Ismaı ¨l, B.P. 509 Boutalamine, Morocco c NASG (North Africa Seismological Group), Gelderland, The Netherlands d Faculte ´ des Sciences, University of Mohamed I, Oujda, Morocco e Institut Agronomique et Ve ´te ´rinaire Hassan, B.P. 6202 Rabat Instituts, Rabat, Morocco Received 5 July 2007; received in revised form 7 January 2008; accepted 10 January 2008 Available online 18 January 2008 Abstract A new gravimetric geoid is computed for South Spain and the Gibraltar Strait area. This geoid is located just in the junction between two tectonic plates (Euro-Asiatic and African plates) and in the junction of two gravimetric geoids: IGG2005 (the Iberian Gravimetric Geoid obtained in 2005) and MORGEO (the MORoccan GEOid). IGG2005 is the Iberian geoid and MORGEO is the Moroccan geoid, both geoids have been previously obtained. The new geoid is the gravimetric geoid solution that connects the two above-mentioned geoids, getting a more accurate and reliable picture of this area than the other previous geoids. The method used is the Stokes integral in convolution form, which shows to be an efficient method to reach the proposed objective. The terrain correction and the indirect effect have been taken into account. The new geoid is obtained as a regular grid (with a mesh size of 1.5 0  1.5 0 ) in the GRS80 reference system, covering the study area from 34° to 40° of latitude and from 8° to 0° of longitude. This gravimetric geoid and the previous geoids: IGG2005 and MORGEO; are compared to the geoid undulations derived at the validation points located on the study area (four GPS/levelling points measured on Morocco and five points of the European vertical reference network (EUVN) measured on Iberia). As it is expected, the new geoid is a more precise and reliable model, fitting the geoidal heights of these validation points with more accu- racy than the other previous geoids. This new model will be useful for orthometric height determination by GPS in the mountains and remote areas, where levelling has many logistic problems. Also, it can be interesting for other geophysical purposes different to the height measurements, because it can provide a constraint for the density distribution, the thermal state of Lithosphere and the viscosity in the mantle. Such details can be inferred from a geoid model and the seismic velocity structure. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Gravity; Geoid; GPS/Levelling; EUVN; Gibraltar strait; South Spain 1. Introduction In South Spain and the Gibraltar Strait area, two previ- ous studies have taken as objective the geoid computation (Corchete et al., 2005, 2007). IGG2005, calculated by Cor- chete et al. (2005), is provided as a data grid in the GRS80 reference system covering Iberia from 35° to 44° of latitude and 10° to 4° of longitude, in a 361  561 regular grid with a mesh size of 1.5 0  1.5 0 . MORGEO, calculated by Corchete et al. (2007), is provided as a data grid in the GRS80 reference system covering Morocco from 27° to 37° of latitude and 14° to 0° of longitude, in a 401  561 regular grid with a mesh size of 1.5 0  1.5 0 . Unfortunately, these previous geoids only cover partially the studied area (South Spain and Gibraltar Strait) that corresponds to the junction between two plates. Further- more, since the publication of IGG2005 and MORGEO, a new geopotential model (EIGEN-GL04C) is available. Logically, this new global model represents an improve- 1464-343X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2008.01.002 * Corresponding author. Fax: +34 950 015477. E-mail address: corchete@ual.es (V. Corchete). www.elsevier.com/locate/jafrearsci Available online at www.sciencedirect.com Journal of African Earth Sciences 51 (2008) 145–150