GPS CONSTRAINTS ON PHILIPPINE FAULT SLIP RATE IN MASBATE ISLAND, CENTRAL PHILIPPINES
Teresito Bacolcol , Eric Barrierz , Thierry Duquesnoy, Agnes Aguilar, Robinson Jorgio', Ronald de la Cruz and Melchor Lasala
We use horizontal site velocity derived from Global Positioning System (GPS) to calculate the slip rates of the Philippine Fault and the Sibuyan Sea Fault in Masbate Island, Central Philippines. Data from GPS campaigns culled between February 1991 and February 2002 showed that the Philippine Fault in Masbate has a slip rate of 2.2 J; 0.2 cm/yr at an azimuth of about N323°. A similar slip rate of 2.3 j 0.2 cm/yr is calculated for the Sibuyan Sea Fault, projected parallel to the fault (N300°). The results also reveal the existence of a gradient of displacement along NE of the Philippine Fault in Masbate, with the northern part of the network showing a more significant movement than the southern part. This probably explains the geometry of Ticao island, as well as the presence of small groups of islands south of Ticao that extends towards the SE.
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