Correlation between the Bouguer gravity anomaly and the TAIGER tomography of the Taiwan region

The Bouguer gravity anomaly derived from observed gravity data and calculated from a 3-D P-wave velocity model were used to investigate the compatibility between the two to understand the crust structure of the Taiwan region. The seismic velocity model determined by Kuo-Chen et al. (2012) was used for our study. We converted the velocity model to a density model using the relationship between P-wave velocity and rock density proposed by Brocher (2005), and then calculated the corresponding gravity anomaly. The differences between observed gravity anomaly and calculated gravity anomaly in vicinity of the dense TAIGER seismic stations are in general small. To discuss the anomaly discrepancy between shallow and deep structure, we used the upward and downward continuation method to separate the gravitational signal into shallow and deep effects for the comparison of gravitational effect of the 3-D velocity model. A conspicuous gravity low which is lower than the observed Bouguer gravity anomaly occurred beneath the main edge of the Central Range, as shown in the calculated deep-structure gravitational map. This indicates that the Moho depth estimated by the seismic tomography is deeper than that estimated by the gravity data. The negative anomaly location differences resulted from deep-structure effects suggest that the locations of crustal thickening estimated by gravity and seismic tomography are different.