Abstract
The Bouguer anomaly of Taiwan has been revised in this study based on more accurate terrain data provided by the Taiwanese Digital Terrain Model compiled by the Taiwan Forestry Bureau. Three seismic velocity models, those determined by Rau and Wu (1995), Kim et al. (2005), and Wu et al. (2007) respectively, were selected for our study. We converted their velocity models to density models using the relationship between P-wave velocity and rock density proposed by Ludwig et al. (1970) and Barton (1986), and then calculated their corresponding gravity anomalies. According to the correlation coefficient between the Bouguer anomalies calculated from the velocity models and the revised Bouguer anomalies, the Kim et al. model was more compatible with gravity data than the other two velocity models. The differences between the revised gravity anomaly and the calculated gravity anomalies trend toward positive values at elevations higher than 2000 m. This indicates that the velocities at the shallower depths beneath the mountainous area of the three models are overdetermined, i.e., higher than the real velocities. This ratiocination implies that the crustal thickness beneath the Central Range is less than 55 km which was obtained from the velocity models.
Highlights
Taiwan is located at a complex juncture between the Eurasian and Philippine Sea plates as shown on the simplified geological map (Fig. 1)
The digital terrain data of Taiwan compiled by the Taiwan Forestry Bureau became available in 1998
We recalculated the terrain corrections using digital terrain data of Taiwan retrieved from topographic maps by the Taiwan Forestry Bureau with a 1 : 5000 scale, grid spacing of 40 m and average elevation accuracy of 1 m to obtain a revised Bouguer anomaly map (Fig. 2b)
Summary
Taiwan is located at a complex juncture between the Eurasian and Philippine Sea plates as shown on the simplified geological map (Fig. 1). 603 gravity stations were surveyed wherein 308 of these stations are located at elevations of 500 m or higher This survey had notably improved the observed coverage and collected gravity data to construct a Bouguer anomaly map (Fig. 2a) after applying latitude, Free-air, Bouguer, and terrain corrections. It is well-known that terrain correction, especially in areas of steep, rugged and erratic slope topography, is the most important factor in calculating the Bouguer anomaly. The terrain corrections of all gravity stations were jointly calculated using two methods in Taiwan (Yen et al 1995). Bouguer anomalies over mountainous areas, are commonly smaller than in the previous one
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