InSAR Monitoring Of Inter-seismic Deformation And Analysis Of Fault Movement Characteristics On Leyte Island, Philippines

The Philippine fault zone is one of the largest strike-slip faults in the world and one of the main structural features in the Philippine region.It is a sinistral strike-slip fault which stretches 1200 km across the Philippine archipelago.On July 6,2017,an Mw 6.5 earthquake occurred in Ormoc area,north of Leyte Island,which is located in the central Philippines.Before the Ormoc earthquake,there had been no major earthquake in Leyte Island since the 17 th century,but only minor earthquakes.The researches based on Geodesy show that the average creep rate of the northern segment of Leyte fault near the Ormoc seismic belt is about 35 mm/yr,which indicates that there were both aseismic creep segments and locking segments in this area.In this paper,with Leyte Island as the research object,we use the PS-InSAR technology to detect the inter-seismic surface deformation on Leyte Island,analyzing its surface movement characteristics and the activity of the fault to investigate the characteristics of inter-seismic fault movement.The geological and tectonic background of the Philippine fault zone,the present geodetic researches on the structural activity of the Philippine fault and the historical earthquakes in the central Philippines are described in this paper.Based on these information,the tectonic movement and the activity of the Leyte fault are preliminarily inferred.In order to investigate the characteristics of inter-seismic fault movement in Leyte Island,first we use the PS-InSAR technology to acquire the the inter-seismic deformation field along the LOS direction with 25 ALOS satellite images covering the study area which spanning from 2006 to 2011.The result shows that the annual average deformation velocity along the LOS direction in Leyte Island changes from-44 mm/yr to 37 mm/yr.The result shows a distinct boundary between the upper and lower wall of the fault,and the lower plate is mainly moved away from the satellite,the upper plate is mainly moved close to the satellite.The surface trace of the Leyte fault is extracted based on the obtained inter-seismic deformation velocity along LOS direction,and the characteristics of surface movement in different regions are analyzed by using the uniformly selected deformation velocity profiles of PS points along the Leyte fault.The results show that Leyte fault can be divided into eight segments,of which five segments have obvious fluctuation of PS point deformation rate on the two sides of the fault,and there are significant differences in deformation between the upper and lower walls.The other three segments have small fluctuation of PS point deformation rate on the two sides of the fault,and there is only a slight difference of PS point deformation between the upper and lower plates.In order to analyze the activity of different segments of the Leyte fault,we project the inter-seismic deformation velocity along LOS direction to the component along the fault strike direction.Based on the difference of slip rate along the strike direction of PS points on the two sides of the fault,the activity of each segment of the Leyte fault is analyzed,and the locking depth range of each segment of the fault is inferred.The results show that three of the segments are creeping and three segments are locking.The deformation caused by tectonic movement of the other two segments is concealed by the influence of other factors,leading to the failsure of analysis for the fault activity.