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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

LOPES, C., IBÁÑEZ, J., WALLENSTEIN, N., SILVEIRA, D. (2008) - Application of cross - correlation to the 2006 seismic array data in the Fogo-Congro region, São Miguel, Azores. IAVCEI 2008 General Assembly, Reykjavik, 17 - 25 Agosto (Poster).


São Miguel is the biggest island of the Azores archipelago, which is located in the intersection of the North - American, Eurasian and African lithospheric plates. In the last decades, the region of Fogo and Congro volcanoes is the main seismogenic area of the island. It is, located in the central part of S. Miguel, where structures with a general NW-SE and NNW-SSE directions dominate the tectonics of the area.


From November 2002 to 2006, an increase in the seismic activity occurred in the region. It was characterized by the occurrence of seismic swarms clustered in this area. These events had typically low magnitudes (Md<3) and few LP and Hybrids events were also recorded.   


In order to response to the increasing activity, at the end of 2005, a 12 channel permanent seismic array was deployed. Unlike the traditional techniques, the arrays are, originally, designed to capture more complex signals, such as volcanic tremor and LP events. Since then the seismic array is operating on a regular basis and many events have been recorded.


To detect and quantify the presence of low energy and low frequency signals that might be associated to magmatic or hydrothermal fluids dynamics, we analysed the 2006 seismic array data, to determine the apparent slowness and wave rays backazimuth, using the cross-correlation method. With this approach, we checked for the maximum consistency of the signal in the time domain, in a tentative to find coherent low frequency signals. This methodology was applied to 4 hours of data per day in two different frequency ranges: 1-2 Hz and 2-4 Hz. These values were chosen to detect the possible presence of two distinct types of tremors, as preliminary results indicate, which could be related with different kinds of sources.