Browsing by Author "Yu, SB"

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Impact of a large earthquake on a GPS network: The case of the 1999 Chi-Chi, Taiwan earthquake
(2002-04-01)
Kuo, LC
;
Yu, SB
;
Hsu, VJ
;
Hou, CS
;
Lee, YH
On 20 September 1999, Taiwan was hit by the largest inland earthquake (M-w = 7.6) in the last century resulting in an 80-kilometre thrust rupture almost directly along the existing Chelungpu fault. Here, we estimated the coordinates of the GPS stations by using the annual epoch-observed and permanent continuously-recorded GPS data covering the 1992-1999 period Taking into account the effects of secular motion and post-deformation, we calculated the corrected coseismic displacements. Relatively large coseismic displacements of 8-9 in in the horizontal and vertical components were found in the northern part of the fault. Stations on the hanging wall shifted horizonatly 2-9 in in the NW direction and decreased in magnitude from west to east. On the other hand, displacements on the footwall were less than 2 in in the SE direction hid increased from west to east. The size of the zone overlapping the hanging wall and the foowall showed a decrease of 796 ppm in 494 km(2). This is in direct contrast to areas near the fault which increased in size from 13 to 23 7 ppm. Significant postseismic deformations were also observed in data from the existing 44 permanent stations and 7 temporary stations. Additionally, large postseismic deformations of 10-20 cm were found at stations SUAM, 100 7 and YUSN within 10 months.
Single- and multiepoch analyses of global positioning system baseline network: Application to coordinate and velocity determinations in Central Taiwan
(2004-05-01)
Hwang, CW
;
Lee, LH
;
Yu, SB
;
Chen, HY
;
土木工程學系
Theories and computer programs are developed for single- and multiepoch analyses of a global positioning system (GPS) baseline network using the datum-free and weighted constraint solutions. Single-epoch analysis is for evaluating data quality, removing outliers, examining network precision, and estimating coordinates. Multiepoch analysis is for simultaneously determining epoch coordinates and station velocities. The datum-free solution yields estimable data residuals and relative coordinates and is suitable for adjusting data only and for detecting changes of relative coordinates. The weighted constraint solution allows a lower-order network to be attached to an existing, higher-order network. The analysis methods are applied to a multiepoch GPS baseline network in central Taiwan, which was hit by the 1999 Chi-Chi earthquake measuring 7.3 on the Richter scale. The velocities computed by the methods developed in this study are consistent with those from the Bernese GPS software. The result of the multiepoch analysis indicates that, in the first year after the Chi-Chi earthquake, the crust east of the Chelungpu Fault moved northwestwards at a mean rate of about 10 cm/year, while the crust west of the Chelungpu Fault moved in the opposite direction at a much lower speed.