Observations with STS broadband seismographs on the Philippines and the deployment of a Western Pacific global seismograph network

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This project intends to install a three-component broad-band wide-dynamic-range seismometer (STS-2) at a station in the Philippines to study deep Earth's interiors and earthquake mechanisms in the Western Pacific region. The sensors and recording system were set up in the 1991 fiscal year and since then have been working at a good condition without any major trouble. The data from the station have been shipped first to Disaster prevention Research Institute (DPRI), Kyoto University, from Philippine Institute of Volcanology and Seismology (PHIVOLCS) for the purpose of edition and analysis at an approximately monthly rate. Then the data are edited and duplicated at DPRI, and the edited disks are shipped back to PHIVOLCS again for the use of research in the PHLIPPINES. The data are digitized and sampled at two rates, one for the continuous recording at 1 Hz and the other for the triggered recording at 41 Hz. About 15 events are detected per month and stored on magneto-optical disks. The most serious problems with the system are two folds : (1) a poor receiving condition of clock signals from OMEGA, and (2) frequent blackouts in the metropolitan area which seems to have started recently. For clarifying these problems people will be dispatches in May to PHIVOLCS.A seismic exploration survey was made in February and March in the Taal volcano area using artificial explosions in two 50-m deep drilling holes. Eight people from DPRI and ten from PHIVOLCS participated for the collaboration tasks for about 2 weeks. 32 EDRs (Event triggered Recorder) were used for the survey. The two shots were exploded at suitable conditions and recoded at all stations. The data are at this moment being analyzed and the results will be brought in three months. It is worthy noting that our exploration survey is the first attempt in the Philippines which used explosives for a geophysical scientific purpose. The experiment have stimulated and promoted our future collaboration.