Summary Interactive 3D potential field modelling has become feasible in the last years and has been used on a number of projects in the oil industry and academic research. It does not replace conventional inversion methods but is advantageous in cases where we quickly want to test scenarios based on our geological and geophysical understanding of the area. Integration with other methods becomes much easier when the modelling is done interactively. Based on experience with the current implementation of interactive 3D modelling in IGMAS+, some practical improvements have been implemented and will be presented.

M.R. Alvers, H.J. Götze, L. Barrio-Alvers, C. Plonka, S. Schmidt and B. Lahmeyer present a technique whereby triangulated facets and voxel-cubes are treated in parallel, allowing integrated models for seismic, magnetic and EM data. It is a commonly accepted truth in the oil industry that 'the easy oil has been found'. Finding the remaining hydrocarbons requires better technologies. Examples are exploration projects below salt and basalt, which are difficult to image with seismic. The main exploration method is still seismic but it has become more important to integrate seismic with other methods in order to improve imaging. In areas of strong lateral velocity and density changes, gravity modelling can help to improve velocity models used for seismic imaging. Efforts of joint interpretation of e.g., seismic, gravity and EM methods lead to more and more realistic and therefore more complex models.

ABSTRACTModern geophysical interpretation requires an interdisciplinary approach and software capable of handling multiple geophysical data types such as seismic, full tensor gravity gradiometry, magnetics and magnetotellurics. We use the IGMAS+ (Interactive Gravity and Magnetic Application System) geo‐modelling software that is designed for 3D gravity, gravity gradient and magnetic modelling. This paper deals with a special aspect of potential field modelling, combining conventional triangulated model geometries (building polyhedrons) with voxel cubes.The hybrid modelling combines the advantages of both the vector and raster modelling system: both may be used alone (polyhedrons without voxels, voxels without polyhedrons) or simultaneously by superposition of both effects, which provides flexibility towards full interoperability. The key idea of our approach is, on the one hand to use two different, completely independent geometries (vector and raster) and give on the other hand the possibility to link both on demand for either editing the voxel model or to combine a large number of voxel cells under a common physical parameter function – which results in more reliable parameter inversion results.

Modern geophysical interpretation requires an interdisciplinary approach and software capable of handling multiple data like seismic, FTG gravity, magnetic and magnetotelluric. We introduce the new IGMAS+ ("Interactive Geophysical Modeling Application System") geo-modeling software for realistic 3D FTG and magnetic modeling. The software is grid capable and allows extreme fast distributed calculations on normal hardware such as a network of PCs. An outlook is given towards semantic constraints generated by ontology based search technologies. A show case for CCS (carbon capture storage) will be presented. Finally the interlink between data modeling and text mining will be discussed.

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left‐lateral transform motion between the African and Arabian plates since early Miocene (∼20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the μ m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer‐size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100–300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull‐aparts along them. The damage zones of the individual faults are only 5–20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20–40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere.

In order to be successful in challenging depth imaging projects the integration of all available data is important. We present the interactive 3D gravity and magnetic modeling tool IGMAS+, its integration in the depth imaging workflow in Statoil and case histories from different geological settings.

In our study we show that the locations of largest coseismic slip (asperities) on the fault plane of the M(w) = 8.0 1995 Antofagasta earthquake in Northern Chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake. These areas of high seismic moment release and concurrent high-b values are congruent with anomalies of the gravity isostatic residual (IR) field in the Antofagasta region. They are superimposed on the seismogenic part of the north Chilean subduction zone where the strongest coupling of the upper and lower plate is expected. The IR anomalies are interpreted to be caused by large Jurassic-Early Cretaceous batholiths which intruded into the upper crust. The observed positive correlations between high seismic b values, IR anomalies, and geologic structures enable us to propose a mechanical model for the generation of the asperities in the Antofagasta region. We suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the Nazca plate are responsible for locking the interface where the asperities are located. This implies long-term conditions for the existence of the asperity generating tectonic situation. Concequently, the asperities around Antofagasta could be stationary features, at least for several seismic cycles. Hence we propose that the IR anomalies along the north Chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes.

Three-dimensional (3D) interactive modeling with the IGMAS software provides means for integrated processing and interpretation of geoid, gravity and magnetic fields and their gradients (full tensor), yielding improved geological interpretation. IGMAS fully three-dimensional models are constructed using triangulated polyhedra and/or triangulated grids, to which constant density and/or induced and remanent susceptibility are assigned. Interactive modifications of model parameters (geometry, density, susceptibility, magnetization), access to the numerical modeling process, and direct visualization of both calculated and measured fields of gravity and magnetics, enable the interpreter to design the model as realistically as possible. IGMAS allows easy integration of constraining data into interactive modeling processes, visualization and combination of geodata with density/susceptibility models. These visual overlays of different 2D and 3D datasets enables quantitative comparison and adjustment and results in models that are constrained by as much independently derived information as possible.

From 1993 to 1998 approximately 3.927 gravity stations were taken in the Central Southen Andes, comprising the southern central zone of Chile and the central western part of Argentina, between latitudes 37.50ºS to 42.5ºS and 69ºW as far as the coast of the Pacific Ocean. To this information, 9.123 old stations were included, which were reprocessed and when in some doubt, were remeasured. Now the the database contains 13.050 gravity stations available which can be used along with other geophysical and geological information for an interdisciplinary interpretation to be able to understand some structural aspects and evolution of the Southern Central Andes. In this paper, we present the new data base by means of maps of Bouguer anomaly and isistatic anomaly, together with a very preliminary interpretation.

From 1982 to 1986, more than 2500 gravity data were taken in an Andean Geotraverse covering northern Chile and northwestern Argentina between 64° and 71°W and 20° and 26°S. Including 2100 reprocessed older data, there is now a data base of about 4600 gravity values available, which can be used together with other geophysical and geologicalin formation for an interdisciplinary interpretation to solve some problems of the structure and development of the Central Andes. The new gravimetric data base, which includes the Bouguer‐, free‐air‐ and isostatic residual anomaly, is presented together with a preliminary interpretation.