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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

DIAS, N.A., MORAIS, I., VALES, D., MATIAS, L., GASPAR, J.L., CARRILHO, F., SENOS, L. (2004) - Reanálise da sequência sísmica do Faial de Julho de 1998. 4ª Assembleia Luso Espanhola de Geodesia e Geofísica, Figueira da Foz, Fevereiro 2004 (Comunicação Oral).


In July 1998, a set of portable digital seismic stations were deployed in the islands of Faial, Pico and São Jorge, Azores, adding to the permanent network of SIVISA that was monitoring the seismic swarm that followed the July 9th Faial earthquake. Due to the human capability of response, only part of the dataset of events recorded was then analysed and used in several geophysical studies. The existence of data not analysed, together with the detection of mispickings of some seismic phases (mainly S waves) and the presence of some instrumental problems in some stations, strongly affected the results obtained.
Recently the lacking information was analysed and integrated into the dataset, the instrumental problems were corrected or minimised and a global reanalysis was performed, allowing a revision of previous results. Here we present the results of such revision, using a broad and better-constrained dataset. The preliminary results show a minimum 1-D model with a heterogeneous upper crust (due to the different stations site effects), and a homogeneous middle crust from 2,5-3 to 8 km depth. The Moho appears to be present at 12-13 km depth. The vp/vs ratio that minimizes the global RMS is found to be around 1,78. The spatial distribution of events is more organized, mainly concentrated in the middle-lower crust. The focal mechanisms were also revised.