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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

ESCUER, M. (2006) - Improving seismic vp and vs models of the Azores archipelago. Dissertação​ de Mestrado em Vulcanologia e Riscos Geológicos, Universidade dos Açores, 99p.


​The Azorean archipelago is situated in a triple tectonic junction in the North Atlantic. This geographical and geodynamic situation is marked by a high seismicity and by a tectonic controlled volcanism.
Since the settlement the Azorean archipelago has suffered high seismic activity with several destructive earthquakes and some volcanic activity, it attracted the scientists at the second half of the 21st century to the importance of studying the phenomena. Thus, the first seismic station on all Portuguese national territory was installed in the Azores at the beginning of the 20th century. Since then the maintenance and development of the Azorean seismic network has grown in parallel to the development of new seismic instruments and was adapted to the pattern of seismic activity.

Seismicity on the islands is mainly characterized by swarm seismicity, however at odd times, typical tectonic shock-aftershock sequences occur.

Locating events within both kinds of sequences is strongly depending on the crustal velocity models used for this task. The velocity models in the Azores that we use in our routine processes are the result several seismic surveys during the seventies.

With the development of the seismic instrumentation, the automation of some seismic processes and the archiving of the seismic data in digital databases the need to improve the routine velocity model is very important. There are a lot of scientific works with new geodynamic models based on modern surveys and the research works following the January 1st of 1980 Angra de Heroísmo crisis and the July 9th of 1998 Horta crisis . The main goal of this work is to evaluate these new models, compare them and select the best model for routine purposes.

For this work several selections of the local earthquakes of the SIVISA seismic data base were made, for different seismogenic areas, in order to do several inversion processes. In this work I am trying to determine if specific models are needed for different areas, or if we can generalize a model for the whole archipelago. This first step uses the Kissling inversion method. With the results for the Central Group as input, another method was used to validate the resultant velocity model. With the JHD and HypoDD relocation routines we try to relocate the SIVISA catalogue to constrain the close association of seismicity with the volcanic and tectonic structures cropping out in the Azores plateau.​