A24 ネバド・デル・ルイス火山における火山性群発地震の震源およびスペクトル解析
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概要
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Several swarms of high frequency volcanic earthquakes were recorded during August and October 1990 in Nevado del Ruiz Volcano (NRV) using a digital portable network of 5 stations with three components. Three swarms were recorded during this time (August 28,Sept. 11 and Sept. 17) and each one showed a well defined epicentral zone, different from each other and located around active crater. In swarm of August 28th two sources were acting alternately, located at different places. Spectral analysis and waveform observation in a same station, showed that many of the events inside a swarm have very similar shapes (almost the same) in both spectra and wave forms and are very different from those in other swarms. It can be related to similar source time function and similar path effect during a swarm of volcanic earthquakes. The non-similarity between different swarms in a same station, could mean no similar source and/ or path effect. Several isolated events not belonging to swarms occurring in an almost same spatial region but in different times, were analyzed in order to compare with swarms. The spectrum shapes and waveforms in these events are pretty similar not only in a same station but also in different stations; this could mean that at least the path effect is not so important in these events and paths of them are located in a region of distinct character from those for the earthquake swarms. From this analysis it is possible to say that in NRV sources of high frequency swarms are very well defined and each one has characteristic spectrum shapes and waveforms. The mechanisms of generation of swarms and isolated events are different.
- 1993-10-04