Present-day Crustal Deformation and Neotectonics in Northern Hualien, Taiwan
Date Issued
2009
Date
2009
Author(s)
Chen, Chia-Yu
Abstract
Eastern Taiwan has long been well-known as sitting at the collision suture between the Eurasian and Philippine Sea plates which is characterized by numerous earthquakes and several active faults. The Hualien City is located at the transition point at the northern end of the Longitudinal Valley, whereas the Philippine Sea plate westward thrusts upon the Eurasian plate in the south, while dives under the Eurasian plate from the latitude of Hualien northwards. At least two major active faults have been documented in this relatively complex area of transition zone, in addition to the Coastal Range fault on the northwestern side of the Coastal Range. The Milun fault, on which it ruptured during the 1951 M=7.3 Hualien earthquake, has been mapped running through the city of Hualien, showing coseismic slips of 1.2 and 2 m for its vertical and sinistral slip respectively during the 1951 earthquake. The Beipu fault or lineament, by contrast, was only revealed by its geomorphic feature.n this study, we used 40m-DTM and several high-resolution topographic profiles obtained from GPS-RTK measurement to characterize the geomorphic features related to the aforementioned two structures. Besides, we deployed repeated campaign measurements of a dense network of GPS stations. We carried out measurements for five times during April 2007 to February 2009, in order to obtain the horizontal GPS velocity and subsequent strain analysis. Furthermore, we carried out D-InSAR analysis to observe and monitor the vertical crustal deformation. everal pieces of the geomorphic evidence show that the Milun fault extends southward and probably turns southeastward into the sea. Nevertheless, it remains problematic because GPS velocities show that the surface trace of the Milun fault might lie farther west to the geomorphic scarp, which seems to be modified by river erosion that made the scarp retrieve to the east. As for the Beipu structure, base on its geomorphic features, we tend to interpret it as a positive flower structure, presumably resulted from left-lateral strike slip on the Beipu fault, although the GPS horizontal velocities and InSAR analysis indicated little tectonic rate occurred along the Beipu structure. he GPS results show that Hualien area moves northwestward at a rate of 13-41 mm/yr relative to the stable reference of the station S01R at Penghu, and the orientation is 295-360 degree. On the other hand, the same results under ITRF2000 reference framework illustrate a much intriguing deformation pattern, with a likely eastward extrusion of the Meilun Tableland and the Beipu area, north of the Coastal Range. The Milun fault shows a small sinistral slip at the rate about 3-8 mm/yr; however, our D-InSAR results show there is no significant vertical offset across the Milun fault in the studied period, with a rate of about 1 mm/yr. We thus interpret that the Milun fault probably is now locked, so that the stress were accumulated during the interseismic period, and it would release to cause earthquake and surface movement in the future. he strain analysis from the GPS measurements demonstrate that the northern half of the Hualien area shows a strong clockwise rotation, whereas the southeast part shows a moderate counter-clockwise rotation. We suspect this phenomena is a result of collision-extrusion tectonics that is initiated by the northwest compression of the Coastal Range under the sea east off the Haulien area to push the Meilun Tableland and the Beipu area not only upward but also eastward. The Milun fault may probably developed from this mechanism to let the block more easily to move to free space in the up and east directions. In this case, the Milun fault is more likely a high-angle sinistral fault that is subparallel to the Coastal Range fault, and these two faults might not necessarily connect to each other.
Subjects
Hualien
Neotectonic
Tectonic geomorphology
Crustal deformation
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-R96224221-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):b135732dcdcb05b268fb24b3a60da9c9