Tomography, Dynamical Modeling and the Geologic History of the Subduction Zone Around the Japanese Islands
Wednesday, 17 December 2014
Since the subduction zone is one of the most geologically active regions in the world, it has attracted much attention from the various fields of the earth science. In this presentation, we try to combine the results and knowledge of seismic tomography, geodynamic modeling and the geologic history of the subduction zone around the Japanese Islands to constrain the nature of the subduction zone there. For this purpose, first, we estimate the cold temperature anomaly by converting the fast velocity anomaly of GAP_P4 model [Fukao & Obayashi, 2013] to the cold temperature anomaly using the recent estimate of d(ln Vp)/dT by Karato . The magnitude of the anomaly is constrained by the work on the relation between the theoretical estimate of temperature and the seismicity in the subducting slab [Emmerson & McKenzie, 2007]. We find that, although the velocity anomaly itself does not show a significant high velocity anomaly just below the stagnated slab, the estimated temperature shows rather continuous cold anomaly from the upper to the lower mantle. This continuous feature is consistent with the recent results of geodynamic modeling of the subduction zone. However, we still see a significant thinning or an absence of the slab just below the stagnated slab in the transition zone. This is more evident in other tomographic models. Geodynamical modeling of subduction, especially, the stagnation of the slab in the transition zone shows that the slab behavior strongly depends on the geological settings of subduction zone such as the rollback of trench. To understand the present feature of the slab revealed by the seismic tomography, we construct a simple half-kinematic model of subduction zone by taking into account the geological settings, that is, the opening of the Japan Sea. We find that the slab similar to the present image is obtained in terms of disruption of the slab suggesting that it occurred during the opening of the Japan Sea.