Phivolcs explains issuance of alert bulletins

By Alice V. Sicat

Monday 24th of September 2012

QUEZON CITY, Sept 24 (PIA) -- Philippine Institute of Volcanology and Seismology (Phivolcs) explained to members of media about the earthquake and tsunami alerts issued by the agency.

Ma. Antonio V. Bornas, chief senior research specialist, Volcano Monitoring and Eruption Prediction Division, Phivolcs, said “tsunami alert cancellation” are often misinterpreted or understood to mean that the agency committed a mistake issuing an earlier warning.

Bornas said the issuance of a tsunami alert cancellation simply means that the “Tsunami Alert” issued earlier is already lifted and is no longer needed.

The alert cancellation must be done always after the threat of tsunami is already gone.

The tsunami bulletins, issued by Phivolcs, contain the full details of the height of the waves that was generated and the place and time they were observed as recorded by the tide gauges, Bornas added.

During the August 31 Eastern Samar earthquake, the United States Geological Survey (USGS) said it was a magnitude 7.9. The Phivolcs, however, later stated it is only a magnitude 7.6.

Charmaine Villamil, senior research specialist, Geologic Disaster Awareness and Preparedness Division, Phivolcs, explained that there was no mistake in their report, only that the information released by Phivolcs has become more precise because more data from other seismic stations were added.

Villamil said the data in alert bulletins of Phivolcs take some time to gather and are recalculated before these are released.

On the other hand, Henremagne Peñarubia, science research specialist, Seismological Observation and Earthquake Prediction Division, said the difference of magnitude readings depends on the station location.

USGS is using a global station, while Phivolcs uses a local station.

The closer the station is to the epicenter of the earthquake, the more accurate the reading it produces, Peñarubia added.

Bornas, Villamil and Peñarubia were guest speakers in the National Disaster Risk Reduction and Management Council Resilience Project workshop held in Taal Vista Hotel in Tagaytay City from September 18-21. (RJB/AVS-PIA NCR)