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The geomagnetic total intensity data recorded by a geomagnetic network in Taiwan comprised of 11 permanent proton magnetometers was used to compute diurnal variation ranges to examine if any discrepancies were present. Diurnal variations with similar ranges were obtained from all stations except for the HC station. The ranges at the HC station are often two times greater than those recorded at the other stations. This is an interesting phenomenon that requires considerable attention. Eight temporary stations were set up between the Taitung (TT) and Hengchun (HC) stations, distributed evenly over the Hengchum peninsula during 13 September 2012 to 25 January 2013 to clarify the phenomenon. The local stations in Taiwan are compared with 2 international stations to explain the diurnal ranges resulting from the interaction between solar activities and the Earth's main geomagnetic field and/or local effects. Analytical results show that the unusually large diurnal ranges were observed mainly on the Hengchun peninsula. The surrounding the sea water produces the magnetic coast effect.

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 Pwave 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.

We constructed a new free-air gravity anomaly map of the Philippine Sea Plate (PSP) using ship-tracked gravity data from the National Geophysical Data Center (NGDC). Our results show that the isogals trend correlates well with the tectonic structures in the PSP. After removing the gravity induced by sea water from the free-air gravity data, we obtained the regional Bouguer gravity anomaly, which is later used to compute the Moho geometry in the PSP by applying the Parker-Oldenburg iterative method. Our results indicate that in the southern part of the West Philippine Basin (WPB) the crustal thickness is nearly homogeneous with a value of about 5 km, which implies that the WPB is quite stable. The low-amplitude and near-zero free-air gravity anomalies clearly indicate that the whole WPB, except at trenches and island arcs, is nearly in a state of isostatic equilibrium. The average crustal thickness of the Palau Kyushu Ridge (PKR) is more than 10 km. In the eastern PSP the crustal thickness gradually increases eastward. Our results also imply that a relatively thin and low density mantle exists beneath the Parece Vela Basin (PVB) as a consequence of back-arc spreading and serpentinized upwells of the thin crustal thickness.