Should the whole of this stretch break in a single event the magnitude could be similar to the December 2004 earthquake. P wave tomographic imaging of the crust down to a depth of 90 km is performed beneath the region encompassing Sumatra, Java, Malacca Strait, peninsular Malaysia and Singapore. It has a deep red coloration and many people consider these Indonesian plume agates to be some of the finest in the world. It was collected from Karang Jaya in Northern Sumatra. AMR similar to that before the December 2004 and March 2005 events is found for a 750 km stretch of the southeastern Sumatra and western Java subduction system suggesting that it is close to failure. 75 5.4' Red, Indonesian Plume Agate Slab - North Sumatra, Indonesia This is a gorgeous, 5.4' wide, polished slab of red, Indonesian plume agate/jasper. No AMR is found for the region of the 1833 Sumatran earthquake suggesting that an event in this region in the near future is unlikely. Less clear AMR is associated with the regions north of Sumatra around the Nicobar and Andaman islands where rupture in the December 2004 earthquake was less vigorous. The effect is clearest for the epicentral regions with less than a 2% probability that it could occur in a random catalogue. AMR can be identified in the regions around the Sumatra Subduction system that must have been stressed before the 26 December 2004 and 28 March 2005 earthquakes. In contrast, recent work has suggested that Accelerated Moment Release (AMR) can help to identify when a stretch of fault is approaching failure without any knowledge of the seismic history of the region. However, in practice the large uncertainties in the seismic histories of most tectonically active regions limit this approach since a stress increase is only important when a fault is already close to failure. We also propose a model for the geodynamic evolution of slab detachment. A promising approach to assessing seismic hazards has been to combine the concept of seismic gaps with Coulomb-stress change modeling to refine short-term earthquake probability estimates. It strongly reects on trench migration, and causes along-strike variations in vertical motion and geochemically distinct subduction-related arc magmatism.
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