| Summary: | 碩士 === 國立臺北大學 === 不動產與城鄉環境學系 === 107 === Taiwan is located at the boundary of plates, and the relative movement of plates causes the changes of surface points with time. In the past, the geodetic datum adopted the method of static datum, and comprehensive inspection of control points was adopted in the update and maintenance, which not only consumed a lot of time and labor costs, but also caused the inconvenience in cadastral survey by different datum. At present, Japan, the United States and New Zealand adopt the semi-dynamic datum of the static datum and the surface deformation model (including velocity model and coseismic model), and apply the model to modify the coordinates to the reference time to consider the surface deformation and improve the accuracy of the geodetic datum. Most of the past studies on the semi-dynamic datum in Taiwan only used one horizontal velocity field, and did not consider that the velocity field might change with the occurrence of seismic events or the passage of time. So how to find the timing and frequency of velocity field updating is an important task to improve the accuracy of deformation model.
This study through the time series of GPS continuous station fitting, with major earthquake event time points as the reference, piecewise fitting for velocity, found that the time of velocity change point in the time of the major seismic event, and consistent with seismic event, mobile station fitting in the same way, getting the 12 periods of velocity field in Taiwan. Based on the velocity results of the coordinate time series fitting, it is not suitable to select the test stations to be included in the model establishment. It can be known that too short accumulation of the data of the test stations will lead to a large standard deviation of the velocity fitting. Therefore, the stability of the velocity fitting is tested in different data periods in this study. In the future establishment of velocity field model, the overall accumulation of long-term stable station coordinate data should be more than 3 years, and the station coordinate data less than 1 year should pay attention to the instability of velocity value estimation.
Then, using the horizontal velocity field of 376 continuous stations and 782 mobile stations for 12 periods, the horizontal velocity grid model was established by using the Kriging method, and the difference between the actual observation and model estimation values was compared by using 19 checking stations. Taking 20 mm as the threshold value of velocity field updating, which is the most rigorous in the practical application of Taiwan’s current geodetic datum. The average service life of the horizontal velocity grid model established in Taiwan is 27 years, 18 years in the southwest, 5 years in the east, and 2 years in the past static datum.
Therefore, in the future, the grid of horizontal velocity can be updated according to different frequencies and regions, and the time point of velocity change is consistent with the occurrence period of major earthquake events, so the updating of horizontal velocity field can be tracked back to the time of major earthquake.
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