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The central Betic Cordillera, southern Spain, is affected by an uplift related to the NNW–SSE Eurasia-Nubia convergence and shallow ENE–WSW orthogonal extension accommodated by the extensional system of the Granada Basin. The combination of geophysical, geodetic, and geological data reveals that the southwestern boundary of this extensional system is a seismically active compressional front extending from the W to the SW of the Granada Basin. The near-field Global Navigation Satellite System data determine NNE–SSW shortening of up to 2 mm/yr of the compressional front in the Zafarraya Polje. In this setting, the normal Ventas de Zafarraya Fault developed as a result of the bending-moment extension of the Sierra de Alhama antiform and was last reactivated during the 1884 Andalusian earthquake (Mw 6.5). The uplift in the central Betic Cordillera together with the subsidence in the Western Alborán Basin may facilitate a westward to southwestward gravitational collapse through the extensional detachment of the Granada Basin. The heterogeneous crust of the Betic Cordillera would generate the compressional front, which is divided into two sectors: thrusting to the west, and folding associated with buttressing to the south. Our results evidence that basal detachments, linking extensional fault activity with compressional fronts, may determine the activity of local surface structures and the geological hazard in densely populated regions., A combination of geological, geophysical, and geodetic methods is used to understand the evolution in the frontal area of the extensional system of Granada Basin, near the Zafarraya Polje. In particular, this approach improves our knowledge of the Ventas de Zafarraya Fault (VZF) that hosted the 1884 Andalusian earthquake. Seismic data provide information on the distribution of stress and deformation in the region and made it possible to identify a compressional front linked to the extensional system of the Granada Basin. Global Navigation Satellite System (GNSS) data accurately locate the sites of the Zafarraya GNSS network surrounding the VZF, and repeated measurements provide deformation rates of the area that suggests shortening. Thus, we locate the VZF within the former compressional setting. Meanwhile, electrical-resistivity tomography images sub-surface structures given its electrical properties and, together with the field geological observations, suggests the extensional behavior of the fault. Therefore, it is considered to be a fold-related fault formed due to the extension of the outer arc of the Sierra de Alhama antiform. As in the research presented here, a joint interpretation of data from different methods makes it possible to propose active seismic tectonic extensional models in a compressional setting applicable to other regions., Junta de Andalucía/FEDER, Universidad de Jaén, Universidad de Granada / CBUA, Depto. de Geodinámica, Estratigrafía y Paleontología, Fac. de Ciencias Geológicas, TRUE, pub

The Granada basin, located in the central sector of the Betic Cordillera, is one of the most seismically active zones of the Iberian Peninsula. For the first time, a geodetic network along the Padul fault and two levelling profiles (Genil and Viznar) crossing the Granada fault were operated to detect crust micro-deformations in this area. Three years of terrestrial geodetic measurements are analysed to characterize the behaviour of these faults in a low to moderate strain rate environment. After the comparison of these three campaigns, we can conclude that there is no significant short-term movement of the Padul fault. Granada fault measurements show significant differences between 1999 and 2001 campaigns in Viznar profile. However, more data are needed to correlate this displacement to the tectonic activity., Leica Geosystems, S.L., Forward Modelling Network Deformation Analysis Software, Direccion General de Enseñanza Superior e Investigacion Cientıfica, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

To estimate ionospheric delays from the Global Positioning System (GPS) measurements, satellite and receiver equipment biases have to be modeled. This paper presents a procedure based on the least squares (LS) approach, which implicitly takes into account these equipment biases in the estimation of the ionospheric effect. The second part of this work deals with the interpolation of the ionospheric correction from a permanent GPS network to a single frequency GPS user. The results obtained show that for 10-cm position accuracy the ionospheric delay can be successfully interpolated when the GPS user is within 40 km of the GPS permanent network., Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

The Granada Basin (Central Betic Cordillera), one of the most seismically active areas of the Iberian Peninsula, is currently subjected to NW-SE compression and NE-SW extension. The present day extension is accommodated by normal faults with various orientations but particularly with a NW-SE strike. At the surface, these active NW-SE normal faults are mainly concentrated on the NE part of the Basin. In this part we have selected a 15-km long segment where several active normal faults crop out. Using the marine Tortonian rocks as a reference, we have calculated a minimum extensional rate of 0.15-0.30 mm/year. The observed block rotation, the listric geometry of faults at depth and the distribution of seismicity over the whole Basin, indicate that this rate is a minimum value. In the framework of an interdisciplinary research project a non-permanent GPS-network has been established in the central sector of Betic Cordillera to monitor the crustal deformations. The first two observation campaigns were done in 1999 and 2000., Dirección General de Enseñanza Superior e Investigación Científica, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

In the 1991 the first determination of a gravimetric geoid in a test area in central Spain was computed by using least square collocation. In 1995 a gravimetric geoid in the Iberian Peninsula, Ibergeo95, was calculated by FFT. Nowadays an improved geoid of Andalusia, ANDALUSGeoid2002, has been computed by fast collocation procedure and remove-restore technique in the GRS80 Reference System. The computations have been done from 16562 free-air gravity anomaly data set, obtained from IGN (Instituto Geografico Nacional) and BGI (International Gravity Bureau), the Earth Gravity Model EGM96 and detailed (100 m x 100 m), coarse (5 km x 5 km) and reference (20 km x 20 km) digital terrain models. Relative carrier-phase GPS measurements at 69 benchmarks of the Spanish Levelling Network in Andalusia have been done. The standard deviations of differences between +/-11 cm, +/-39 cm and +/-38 cm in western, eastern and whole Andalusia, respectively. The ANDALUSGeoid2002 shows an improvement of Ibergeo95 in this territory., Servicio Geográfico del Ejército, Instituto Geográfico Nacional, International Gravity Bureau have provided the Digital Terrain Model and gravity data, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

In precise point positioning (PPP), the ionospheric delay is corrected in a first-order approximation from GPS dual-frequency observations, which should eliminate almost completely the ionosphere as a source of error. However, sudden plasma density variations can adversely affect the GPS signal, degrading accuracy and reliability of positioning techniques. The occurrence of plasma density irregularities is frequent at equatorial latitudes and is reflected in large total electron content (TEC) variations. We study the relation between large changes in the rate of TEC (ROT) and positioning errors in single-epoch PPP. At equatorial latitudes and during post-sunset hours, the estimated altitudes contain errors of several meters for a single-epoch position determination, and latitude and longitude estimates are also degraded. These results have been corroborated by the online CSRS-PPP (NRCan) program. Moreover, abrupt changes in the satellite geometry have been discarded as possible cause of such errors, suggesting an apparent relation between the occurrence of large ROT and degraded position estimates., GNSS, Universidad Complutense Comunidad de Madrid, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

Two new GPS surveys have been carried out to check the accuracy of an existing gravimetric geoid in a test area located in northern Andalusia (Spain). The fast collocation method and the remove-restore procedure have been used for the computation of the quasigeoid model. The Spanish height system is based on orthometric heights, so the gravimetrically determined quasigeoid has been transformed to a geoid model and then compared to geoid undulations provided by GPS and levelling at benchmarks belonging to the Spanish first-order levelling network. The discrepancies between the gravimetric solution and GPS/levelling undulations amount to +/-2 cm for one survey and FS cm for another after fitting a plane to the geoid model., Servicio Geografico del Ejeicito, Instituto Geogrifico Nacional for the gravimetry data, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

The Campo de Dalias is an area with relevant seismicity associated to the active tectonic deformations of the southern boundary of the Betic Cordillera. A non-permanent GPS network was installed to monitor, for the first time, the fault- and fold-related activity. In addition, two high precision levelling profiles were measured twice over a one-year period across the Balanegra Fault, one of the most active faults recognized in the area. The absence of significant movement of the main fault surface suggests seismogenic behaviour. The possible recurrence interval may be between 100 and 300 y. The repetitive GPS and high precision levelling monitoring of the fault surface during a long time period may help us to determine future fault behaviour with regard to the existence (or not) of a creep component, the accumulation of elastic deformation before faulting, and implications of the fold-fault relationship, Topo-Iberia, Ministry of Science and Innovation, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

This work focuses on the comparison between satellite-only and combined Global Geopotential Models (GGMs) derived from the CHAMP and GRACE satellite missions with land gravity anomalies, geoid undulations provided by the gravimetric geoid ANDALUSGeoid2002 and GPS/levelling geoid undulations in Andalusia in order to find the GGM that best fits this area in order to be used in a further geoid computation. The results show that the EIGEN-CG01C model or the combined models GGM02C/EIGEN-CG01C and ITG-CHAMP01E/EIGEN-CG01C should be used., Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub

We present the new MAP3 algorithms to perform static precise point positioning (PPP) from multifrequency and multisystem GNSS observations. MAP3 represents a two-step strategy in which the least squares theory is applied twice to estimate smoothed pseudo-distances, initial phase ambiguities, and slant ionospheric delay first, and the absolute receiver position and its clock offset in a second adjustment. Unlike the classic PPP technique, in our new approach, the ionospheric-free linear combination is not used. The combination of signals from different satellite systems is accomplished by taking into account the receiver inter-system bias. MAP3 has been implemented in MATLAB and integrated within a complete PPP software developed on site and named PCube. We test the MAP3 performance numerically and contrast it with other external PPP programs. In general, MAP3 positioning accuracy with low-noise GPS dual-frequency observations is about 2.5 cm in 2-h observation periods, 1 cm in 10 h, and 7 mm after 1 day. This means an improvement in the accuracy in short observation periods of at least 7 mm with respect to the other PPP programs. The MAP3 convergence time is also analyzed and some results obtained from real triple-frequency GPS and GIOVE observations are presented., Spanish government, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, TRUE, pub

The Betic Cordillera, located in the south of the Iberian Peninsula, is currently subjected to NW-SE compression and NE-SW extension. Until a few years ago, there were hardly any geodetic studies to quantify the tectonic deformation taking place in the Betic Cordillera. In 1999, in the framework of an interdisciplinary research project to monitor the deformation, several geodetic studies were initiated by the Universities of Jaén, Granada and Alicante. These studies were centred on the basins of Granada and the Bajo Segura (Alicante), sectors in which the last two destructive earthquakes in the Iberian Peninsula took place. This paper describes the geodynamic context of these study areas and the main features of the geodetic studies, focusing on the deformation analysis of the three observation surveys carried out in 1999, 2000 and 2001 over a non-permanent GPS network established in the Granada Basin. The results agree with the low rates of deformation previously calculated from geological data. To detect such small rates, observation over a longer time span will be needed.

The problem of phase ambiguity resolution in: global positioning system (GPS) theory is considered. The Bayesian approach is applied to this problem and, using Monte Carlo simulation to search over the integer candidates, a practical expression for, the Bayesian estimator is. obtained. The analysis of the integer grid points inside, the search ellipsoid and their evolution with time, while measurements are accumulated, leads to the development of a Bayesian theory based on, a mathematical mixture model for the ambiguity., Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, Instituto de Matemática Interdisciplinar (IMI), TRUE, pub