Abstract:

Abstract:  Satellite gravity field data recovered by digital global models with 2180 to 2360 order are mainly originated from the density variation in the depth of 1836 km, at which epicenters of most major structure earthquakes were located. Therefore, satellite gravity data can make great contribution to earthquake research.  The author has made a detailed analysis of the satellite gravity data over Wenchuan, Motuo, Zhongba, Jiashi  and Taiwan Areas in China, where earthquakes more than magnitude of 6 took place in recent several decades. It is surprising that the gravity field patterns over these areas are extremely similar, which is characterized by the following features: (1)Paired positive and negative anomaly.  (2)Epicenters usually were located between the pairs where the gradient of gravity field was the steepest.  (3)The value of positive peak increased and its width decreased at higher order field.  (4)The distance between positive and negative peaks varies in different tectonic background. (5)Different styles of crustmantle material diapirism in different stress fields. Geologically, rheological diapirism of high density crustmantle material could be a reasonable explanation to this unique pattern. The proposed high density growth index is a measurement of increase in density from deep to shallow. The passageways of diapirism for high density crustmantle plastic material may be formed by the crust faults or giant fault zones and detached strata.  The heterogeneity of crustmantle material reflects the complexity of dynamic processes in continental plate tectonics.

Key words: Key words: satellite gravity data; Wenchuan earthquake; Taiwan earthquake; deep structures; rheological diapirism; continental plate tectonic dynamics