TSUNAMI HAZARD ASSESSMENT ALONG THE WEST COAST OF CENTRAL LUZON, PHILIPPINES
Supervisor: Bunichiro SHIBAZAKI, Yushiro FUJII
This study assesses the tsunami hazard along the west coast of Central Luzon, the Philippines. The Manila Trench being the most potential source, four single fault case scenarios were simulated from the two segments along the west coast of Central Luzon and a multi-segment case from the three segments of the Manila Trench. Using TUNAMI N2 (Tohoku University Analysis Model for Investigation of Tsunami), tsunami generation and propagation were simulated for the five earthquake sources. The first segment extended from the southwest to the northwest of Subic Bay along the west coast of Central Luzon. Earthquakes with magnitudes of M7.6 and M8.3 were simulated from this segment. The second segment was from the south-southwest of Manila Bay to the southwest of Subic Bay. Magnitudes M6.6 and M8.1 earthquakes were simulated from this segment. These single fault cases generated tsunami with maximum amplitudes of less than 1m up to 4m along the west coast of Central Luzon and which arrived between 2 and 30 minutes after tsunami generation. Since the 1560s, there have been no earthquakes greater than M7.8 recorded from the Manila Trench, and it has been reported that it is slowly accumulating strain at a convergence rate of 87mm/yr. A very large event is posited as having a recurrence interval of more than 450 years, and the trench would have accumulated a strain which is relevant to approximately 39m slip deficit along the subduction zone. Hence, the multi-segment case scenario was a simultaneous event from three segments of the Manila Trench that extend from the south-southwest of Manila Bay to the north-northwest of Central Luzon and was generated by a Mw9.1 earthquake which yielded a maximum tsunami height of 29m measured at Iba. The earliest positive wave from the multi-segment case arrived at Palauig within 3 minutes after tsunami generation and reached the inner part of Subic Bay within 30 minutes. Using the results of the tsunami propagation of the multi-segment case, tsunami inundation modelling was performed for six coastal areas using GEBCO 30-arc seconds bathymetry data and SRTM 3-arc seconds topography data. As a tsunami early warning system is currently in operation for the Subic Bay coast, tsunami hazard for this area was assessed. The City of Olongapo which is situated at the innermost part of the Subic Bay, was inundated with a maximum depth of 19m.