Short wave gravity anomaly is correlated to sea floor topography in the gravity field of ×Taiwan and its adjacent seas. Gravity values of 20010-5ms-2 at Yushang and -×16010-5ms-2 at Liuqiu sea trench are respectively the maximum and minimum gravity values in this area. Bouguer gravity anomaly reflects not only Moho interface undulation, but also fault distribution. The inflexion of gradient belt of Bouguer gravity anomaly is a spot liable to earthquakes . Middle-long wave geoid is the best data to invert crustal thickness. We calculate crustal thickness by using geoid data, and the maximum value is 38km; the minimum value is 12km in Taiwan and its adjacent seas.
On the basis of the reality of recent tectonic movement and discarding such a viewpoint that the isostatic adjust-ment only results from excessive or insufficient compensation, we have discussed the tectonic stress causing ine-quality and regarded the isostatic anomaly as a load on the earths interior, thus the earths inner stress can be cal-culated. The research results show that in the East China Sea and its eastern marginal seas the change of the verti-cal stress derived from the isostatic gravity anomaly is more marked than that of the horizontal stress. Along the Ryukyu trench there is an enhancement of vertical stress by 5 MPa, which evidently reflects the effect of plate subduction. On contrary, along the island arc to the northwest of the trench the vertical stress weakens by about 5 MPa. The horizontal stresses in eastern and western parts are obviously different, the east westward stress on the oceanic crust sx is negative (while the pressure is positive) but on the continental crust is positive. These facts indicate the effect of compression between plates.
