Geophys. J. Int. (2007) 171, 478–494 doi: 10.1111/j.1365-246X.2007.03539.x Gravimetric determination of an intrusive complex under the Island of Faial (Azores): some methodological improvements Antonio G. Camacho,1 J. Carlos Nunes,2 Esther Ortiz,1 Zilda Fran¸ca2 and Ricardo Vieira1 1Instituto de Astronom´ıay Geodesia (CSIC-UCM), Fac. CC. Matem´aticas.Ciudad Universitaria, Madrid 28040, Spain. E-mail: antonio
[email protected] 2Universidade dos A¸cores – Departamento de Geociˆencias,Rua da M˜aede Deus, Apartado 1422, 9501-801 Ponta Delgada, Azores, Portugal Downloaded from https://academic.oup.com/gji/article-abstract/171/1/478/2126298 by guest on 12 October 2019 Accepted 2007 June 26. Received 2007 June 26; in original form 2006 September 6 SUMMARY We present some improvements of a gravity inversion method to determine the geometry of the anomalous bodies for priori density contrasts. The 3-D method is based on an exploratory process applied, not for the global model, but for the steps of a growth approach. The (positive and/or negative) anomalous structure is described by successive aggregation of cells, while its corresponding gravity field remains nearly proportional to the observed one. Moreover, a simple (e.g. linear) regional trend can be simultaneously adjusted. The corresponding program is applied to new gravity data on the volcanic island of Faial (Azores archipelago). The inver- sion approach shows a subsurface anomalous structure for the island, the main feature being an elongated high-density body. The body is interpreted as a compact sheeted dyke swarm, emplaced along Faial-Pico Fracture Zone, a leaky transform structure that forms the current boundary between Eurasian and African plates in the Azores area.