Fig. 7

Gravity field of the Philippines (Bouguer gravity onshore, free-air gravity offshore) computed from a combination of conventional and airborne gravity onshore and satellite altimetry offshore (Gatchalian et al., 2017). White arrows show motion vectors relative to the West Philippine Basin derived from the GEODYSSEA GPS programme (Rangin et al., 1999). The three unlabelled vectors record motions close to major fault zones and are considered to be heavily influenced by local tectonics. Subsequent GPS studies reported by Hsu et al. (2016) have confirmed the effective locking of North and Central Luzon to the Philippine Sea Plate but did not extend far enough south to define their relative motion with respect to the rest of the archipelago. The heavy black line shows the location of the Philippine Fault System as proposed by Barrier et al. (1991) and is generally similar to the locations suggested by most other authors. The NW–SE segment marked A.F. that separates North from Central Luzon is the Aurora Fault. In the south, between 120 and 128^oE, the area covered by this figure adjoins the area covered by Fig. 10