Shallow Creep Along the Southern Longitudinal Valley Fault in Eastern Taiwan Using PSInSAR and Geodetic Approaches

Abstract

I integrate the near-fault geodetic measurements from 10 campaign-mode GPS stations total station measurements and 22 far-field continuous GPS stations with PSInSAR data for recognizing the spatiotemporal variation of the kinematics on the shallow part of the southern segment of the Longitudinal Valley Fault (LVF) which is also known as the Chihshang fault in SE Taiwan that has been considered as interseismic creep near the surface The GPS coordinate daily solutions were calculated using the software Bernese v 5 0 under the ITRF2008 The horizontal velocities estimated from coordinate time series using least squares method are relative to the station S01R in the Chinese continental margin The continuous GPS horizontal velocity pattern reflects the fault kinematics at deep part of the fault is stably moving between 84 4 mm/yr and 45 3 mm/yr The PSInSAR line-of-sight velocities from 2007 to 2010 evaluated by StaMPS show a localized shortening rate of up to ～25 mm/yr across the LVF consistent with the shallow creep reaching to the surface My results demonstrate the along strike cross-fault velocity offset and the width of the shear zone showing the along strike variation with both surface creep zone and shallow creep zone These variations indicate that the creeping behavior is certainly not uniform in the southern segment of the LVF However from the 2012-2016 near-fault campaign-mode GPS velocity (～30-meter station spacing) at Dianguang region almost no velocity difference (1-2 mm/yr) is observed across this segment of the Chihshang fault The cross-fault velocities (1-3 mm/yr) derived from the total station survey (～30-centimeter point spacing) in the same region during 2012-2016 are also compatible with the campaign-mode GPS velocity In other words the shallow part of this Chihshang fault segment at Dianguang region was creeping during 2007-2010 and is locked or creeping in a very slow rate between 2012 and 2016 Because this locked behavior is continued over four years and is not a seasonal signal a transient locked event at the creeping fault is therefore proposed in this study and it may be triggered to release energy aseismically by other earthquake However the mechanism of this behavior is still unclear so far In addition a slow-down creeping rate has been ever detected at the northern Chihshang fault before the 2003 Mw 6 8 Chengkung earthquake The transient locked event proposed in this study might also be a precursor of the future seismic hazard at the southern Chihshang fault in Taiwan

Date of Award	2017 Sept 27
Original language	English
Supervisor	Kuo-En Ching (Supervisor)