GEOLOGICAL SOCIETY OF THE PHILIPPINES
Results of PHIVOLCS’ 15-year Ground Deformation Studies Along the Philippine Fault and other Active Crustal Structures Using Global Positioning System (GPS)
The Philippine Institute of Volcanology and Seismology (PHIVOLCS), in collaboration with various foreign research institutions, embarked on a program to derive new velocity fields for the Philippine Mobile Belt using Global Positioning System (GPS). The program also aims to characterize the deformational patterns along the different segments of the Philippine Fault and in other active crustal structures in the country. The program started with a few campaign points in 1991 in the central part of the Philippines. At present, there are more than 100 GPS campaign stations distributed across the Philippine archipelago, with more than 90 of these stations having been occupied more than once.
Calculations of GPS data relative to the Chinese continental margin showed that Luzon is moving between 57 mm/yr to around 81 mm/yr at azimuths ranging from N273° to N306°. Simple dislocation modeling puts the long-term slip rate of the Philippine Fault in Luzon at around 34 mm/yr. In Masbate, prior to the Ms=6.2 15 February 2003 earthquake, GPS data showed that this part of Philippine Mobile Belt is moving at around 19 mm/yr to around 75 mm/yr at azimuths ranging from N312° to N340°. GPS data derived in Southern Leyte showed that the island is moving at velocities ranging from 20 to 70 mm/yr. Estimates from a simple dislocation modeling puts the long-term slip rate of the Philippine Fault in Southern Leyte at around 28 mm/yr.
Results from past and future GPS campaigns will be eventually be integrated in the development of a more comprehensive program for evaluating seismic hazards and risks, an essential component of earthquake disaster risk mitigation.
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