2:00 PM - 2:15 PM
[SCG56-13] Relationship Between Free-air Gravity Anomalies in Island Arcs and Various Parameters in Subduction Zones
Keywords:Free-air gravity anomalies, Subduction zone, Island-arc, Correlation analysis
Subduction zones have characteristic topography and free-air gravity anomalies: high in the island arc, low in the trench, and gently high in the outer-rise. There is variability in its height; for example, high in the Kuril and Tonga, but low in the Ryukyu and Cascadia. In order to understand what kind of parameters are important for the formation of island arcs, we investigate the relationship between the free-air gravity anomalies and other parameters (e.g., trench normal velocity, slab age, dip angle, curvature) in subduction zones all over the world.
The gravity anomaly peak in island arc has a good correlation with the gravity anomaly peak in the outerrise or the outerrise cross-sectional area (R=0.54, R=0.56). The gravity anomaly peak in island arc is correlated with dip angle (R=0.52). The trench normal velocity is negatively correlated with the curvature (R=-0.66). The gravity anomaly peak in island arc has only weakly to moderately positively correlation with the trench normal velocity and dip angle respectively (R=0.26, 0.52), but the most significant correlation with the product of the two (R=0.73). This suggests that the downward movement of an oceanic plate results in the formation of island arcs. Similar results were obtained by using curvature instead of slab dip (only curvature: R=0.33, a product with trench normal velocity: R=0.58).Our results are consistent with dislocation model in subduction zone (Matsuu'ra & Sato, 1989). In this model, the "dislocation" caused by plate subduction acts in the gravity field to explain the deformation of island arcs and outerrise. According to the model, the uplift rate in island arc is proportional to the plate convergence rate and positively correlated with the dip angle and curvature. Therefore, dislocation model in subduction zone is consistent with the free-air gravity anomaly in island arc and various parameters in subduction zone revealed from the observation data in this study.
The gravity anomaly peak in island arc has a good correlation with the gravity anomaly peak in the outerrise or the outerrise cross-sectional area (R=0.54, R=0.56). The gravity anomaly peak in island arc is correlated with dip angle (R=0.52). The trench normal velocity is negatively correlated with the curvature (R=-0.66). The gravity anomaly peak in island arc has only weakly to moderately positively correlation with the trench normal velocity and dip angle respectively (R=0.26, 0.52), but the most significant correlation with the product of the two (R=0.73). This suggests that the downward movement of an oceanic plate results in the formation of island arcs. Similar results were obtained by using curvature instead of slab dip (only curvature: R=0.33, a product with trench normal velocity: R=0.58).Our results are consistent with dislocation model in subduction zone (Matsuu'ra & Sato, 1989). In this model, the "dislocation" caused by plate subduction acts in the gravity field to explain the deformation of island arcs and outerrise. According to the model, the uplift rate in island arc is proportional to the plate convergence rate and positively correlated with the dip angle and curvature. Therefore, dislocation model in subduction zone is consistent with the free-air gravity anomaly in island arc and various parameters in subduction zone revealed from the observation data in this study.