3-DIMENSIONAL NUMERICAL MODELING OF DETACHMENT OF SUBDUCTED LITHOSPHERE

Recent seismological studies suggest that slab detachment has occurred in the Mediterranean and the New Hebrides subduction zones. Subducted slabs in these regions are recognized to be torn at depths ranging fr om 100 to 300 km, presumably caused by the lateral migration of the te ar along the strike of the slab. To investigate the physical mechanism of the slab detachment and in particular its migration, we constructe d a viscoelastic three-dimensional finite element model and introduced a small initial tear from one side of the slab. We investigated spati o-temporal variations in the state of stress within the slab, as a fun ction of tear length, theology, and a variety of force distribution. O ur results show that an area of high shear stress concentration of the order of several hundred megapascals forms near the tip of the tear i nside the slab, which is probably sufficient to cause further lateral migration of the tear. The stress concentration increases with the len gth of the tear and lower viscosity values of the surrounding mantle a nd increases with downsnip tension. From our modeling, we conclude tha t favorable conditions for slab detachment are characterized by a high interplate frictional force at a subduction zone and a low convergenc e rate, forming in-plate tensional stress at intermediate depths. Such a condition is indeed observed in the Dinarides/Hellenic and the New Hebrides subduction zone.