Gravity Terrain Effect of the Seafloor Topography in Taiwan

Abstract

Gravity terrain correction is used to compensate for the gravitational effects of the topography residual to the Bouguer plate. The seafloor topography off the eastern offshore of Taiwan is extremely rugged, and the depth of the sea bottom could be greater than 5000 m. In order to evaluate the terrain effect caused by the seafloor topography, a modern computer algorithm is used to calculate the terrain correction based on the digital elevation model (DEM).Based on the results of this study, the terrain effect caused by the seafloor topography makes a significant contribution to the total terrain effect in every region of Taiwan. In the southern coastal area of Taiwan, the terrain effect caused by the seafloor topography is approximately six times that caused by land topography. Therefore, the terrain effect caused by the seafloor topography cannot be neglected in the reduction of gravity data measured on land. The terrain correction should be calculated from the DEM of both land topography and bathymetry. The optimum correction distance for different regions in Taiwan is different. In eastern and southern Taiwan, the proper correction distance is 300 km, while in western and central Taiwan, it is 100 and 200 km, respectively.The accuracy of terrain correction over the rugged topography of Taiwan can be improved by compensating for the gravitational effect caused by the seafloor topography. The complete Bouguer gravity map of eastern Taiwan is reproduced based on the total terrain correction introduced in Terr. Atmos. Ocean. Sci., Vol. 18, No. 4, October 2007 700 this paper. The lineation of the gravity anomaly coincides with the known fault traces and provides the possible position of extension in those areas that are difficult to trace on the surface. In this paper, the southern extension of the Chihshang fault is well delineated in the vicinity of Luye from the gravity anomaly map and confirmed by a ground resistivity survey.

Magma storage in a strike-slip caldera

“…2 ). This was based on the optimum correction distance determined for a Taiwan gravity survey in a location surrounded by seafloor topography of similar depth and ruggedness to that of offshore El Salvador 43 . With a correction distance this great, the uncertainties induced from nearby topographic undulations will exceed the uncertainties induced by more distant topographic features 42 .…”

“…When conducting a gravity survey near lakes and seabed features, it is not sufficient to carry out a standard terrestrial terrain correction. Where the seafloor is at great depth, such as the slope between coastal El Salvador and the Middle America Trench, it is also important to take the gravitational attraction of the water into account 42 43 . This is particularly important at Ilopango as the survey surrounds a large freshwater lake.…”

“…For this reason, and to increase computational efficiency, separate DEMs were built for the lake bed and seabed. In the terrestrial section, the distal elevation data creates the most computational expense 43 ; to reduce this, the terrestrial DEM was split into two parts, with a higher-resolution section for proximal data and a lower-resolution section for distal data (see Supplementary Fig. 2 ).…”

Insight into the Geothermal Structure in Chingshui, Ilan, Taiwan

“…This dataset has been reprocessed to 416 Tong et al (Fig. 5) is created after full terrain correction (Tong and Guo 2007). Figure 6 shows the residual gravity anomaly map after third-order trend removal.…”

Refinement and Quantification of Terrain-Induced Effects on Global Gravity Data

“…A refined Bouguer gravity anomaly contains a terrain correction that uses more complete representation of the local topography by taking care of the deviation of the topography from the plate. The importance of carrying out Residual Terrain Correction (that is, refinement) has been emphasized in many studies [12] [13] [14] International Journal of Geosciences [15] [16].…”