What controls gravity anomalies in subduction zones? The relationship with plate motion and slab geometry

Abstract Subduction zones have characteristic patterns of free-air gravity anomalies: high in the arc, low in the trench, and gently high in the outer rise. In order to understand which parameters control the formation of the gravity anomalies, we investigate the relationship between the free-air gravity anomalies and other parameters related to plate subduction (plate motion, slab age, and slab geometry) for the selected 20 subduction zones with relatively uniform gravity anomalies along the strike. The correlation analyses show that the gravity anomalies in the arc are well correlated with the gravity anomalies in the trench and the outer rise, which suggests that they share a common origin. We also find that the correlations of the convergence velocities with the gravity anomalies are basically weak, but the correlation with the arc gravity anomalies is significantly improved by taking the product with the sine of the shallow slab dip. This means that a faster descending rate of a slab results in larger gravity anomalies in the arc. We also review relationships between the parameters related to plate subduction. For example, we find a clear positive correlation between the slab age and the shallow slab dip, although this relationship has been denied after initial advocacy. We confirm this positive relationship is revived if we take longer (> 200 km) subduction zones with relatively good two-dimensional features.