Abstract: The Longitudinal Valley Fault is one of the faults with the most active dynamic action and crustal movement deformation in Taiwan, China. Its fault movement characteristic and strong seismic risk have been concerned by scholars. Using constraints from coseismic surface displacement and interseismic deformation observations between 1992 and 1999, this paper inverted the coseismic slip distribution of the 2003 Chengkung Earthquake (MW 6.8) and the interseismic slip characteristic of the Longitudinal Valley Fault. The results show that the northern Longitudinal Valley Fault was almost fully locked (locking fraction up to 0.9) to the depth of 27 km; the southern fault was partially locked (locking fraction ~0.5) with shallower locking depth (~12 km); and the locking fraction and locking depth in the central fault was between north and south. The epicenter of the 2003 Chengkung earthquake was near the transition zone between the creeping zone and the locked zone. Based on the coseismic slip distribution and interseismic slip characteristic results, and combined with the characteristics of historical earthquake fault rupture distribution, one can see that there was a difference in the form of fault movement between southern and northern Longitudinal Valley fault: the northern is mainly in the form of seismic slip, and the southern the form of seismic and aseismic slips. Since the 1951 HualianTaitung ML 7.3 earthquake sequence, the southern, central and northern faults have become capable of releasing the stored strain in a future MW 6.4, 7.0 and 7.4 earthquakes, respectively. In case of a cascading rupture, however, the accumulated strain under the entire Longitudinal Valley Fault can engender a MW 7.5 earthquake.

Key words:  Longitudinal Valley Fault, GPS observation, coseismic slip distribution, interseismic fault movement