| dc.description.abstract | For the purpose of understanding the crustal deformation in the Luzon region, the Institute of Earth Sciences, Academia Sinica cooperated with the Philippine Institute of Volcanology and Seismology to conduct 7 GPS surveys from 1996 to 2006. Summing up the 10-year survey-mode GPS data in the Luzon region and continuous GPS data in Taiwan, along with other 14 IGS sites in the Asian Pacific region, we use the GAMIT/GLOBK software to calculate the coordinates of each site and obtain the GPS time series. Then the intersesmic velocity field in the Luzon region is derived by utilizing GPS time series data with QOCA software. The velocity field in the Luzon region gradually increases from south to north with respect to the Eurasia plate. The velocity vectors to the west of the Philippine fault range from 44 to 59 mm/yr; while that to the east of the fault are from 59 to 79 mm/yr; The azimuths of velocity vectors range from 285o to 314 o. This indicates that there’s significant intend deformation in the Luzon Arc.
Based on the GPS observed 1996 ~ 2006 velocity field in the Luzon region and using the intersesmeic crustal deformation model suggested by Matsu’ura et al.（1986）, 2D and 3D dislocation models are utilized to invert for the fault geometry parameters and fault slip rates of the Philippine fault. In the two dimensional dislocation model, two profiles(azimuth 55o) perpendicular to the Philippines fault are studied. The fault dip (89o) is determined from the geological data. By utilizing grid search and bootstrap methods, optimal values of fault parameters and their confidence intervals are estimated. In the northern profile, the block motion is 37 (95% confidence interval, 35.3 ~ 40.9) mm/yr; fault width is 22 (8.5 ~ 28) km; and slip rate of the fault is 36 (30.9 ~ 44.3) mm/yr. In the southern profile, the block motion is 32 (29.7 ~ 37.2) mm/yr; fault width is 35 (27.2 ~ 58.9) km; and slip rate of the fault is 25 (15.7 ~ 41.2) mm/yr. In the three dimensional model, the surface location of the model fault is more or less consistent with the fault trace of the Philippine fault. Since the Philippians fault is a left-lateral strike slip fault, we constrain the fault slip with only strike-slip component in the model calculation. The fault width is fixed to be 30 km. The invented results indicate that the average slip rate of southern segment is 20.6 mm/yr, and northern segment is 32 mm/yr; the block motion is 31 (23 ~ 35) mm/yr; the azimuth of the block motion is 332 o (323 o ~ 341o). Our estimates of the fault slip rates from either two dimensional or three dimensional dislocation models are generally consistent with the previous studies. Recurrence interval of major earthquakes is roughly estimated to be from 128 to 183 years in the northern segment, and from 83 to 217 years in the southern segment. Because the density and aperture of the current GPS array are insufficient, it is not able to successfully detect the deformation of the entire fault system and the branch faults. The fault width can not be well determined from GPS observations through modeling, it can only be estimated for geological and earthquake data. | en_US |