Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Thermal models of flat subduction and the rupture zone of great subduction earthquakes

Abstract: [1] In subduction zones, the size of the seismogenic zone that ruptures during a great thrust earthquake may be thermally controlled. We have constructed finite element thermal models of six transects across three different subduction zones in order to determine the temperature distribution along the plate interface and to predict the size of the seismogenic zone. These models incorporate the complex plate geometries (variable dip downsection) necessary to model a flat slab subduction style. We focus on the rupture zones of the great earthquakes of Nankai (SW Japan) 1946 M8.3 and Alaska 1964 M9.2 as well as on the Cascadia margin. Subduction zone segments with moderate to steep dips exhibit rupture zones of 100–150 km downdip width, consistent with earlier elastic dislocation models and thermal models. For shallow dipping flat slab segments, our models predict larger locked zones, of 150–250 km width, in good agreement with aftershock and geodetic studies. The wider seismogenic zone predicted for flat slab segments results from an uncommonly wide, cold, forearc region, as corroborated by surface heat flow observations. A global analysis of great M > 8 interplate earthquakes of the 20th century reveals that more than a third of these events occurred in flat slab segments, whereas these segments represent only 10% of modern convergent margins. This implies substantially higher interplate coupling for flat slab segments, likely due to the increased downdip extent of the seismogenic zone, and suggests that the seismic risk near such regions may be higher than previously thought.

Green's functions for planar soft and hard surfaces derived by asymptotic boundary conditions

Abstract: The Green's functions for different realisations of planar soft and hard surfaces are developed by using the asymptotic boundary conditions and the spectral-domain approach. The geometries considered are the ideal perfect electric conductor/perfect magnetic conductor (PEC/PMC) strip surface, the strip-loaded grounded dielectric slab and the corrugated surface. In all cases the strips and corrugations are straight. The asymptotic boundary conditions are valid in the limiting sense, when the period of the strips or corrugations approaches zero. The Green's functions developed have poles corresponding to surface waves. These are of three types: an ordinary surface wave in the grounded dielectric slab propagating radially out from the source; a strip wave propagating along the strips of the strip-loaded dielectric slab and also along the strips of the PEC/PMC strip surface; and surface waves occurring due to the corrugated surface. Fulfilment of both the soft and hard boundary conditions is discussed in both the near- and far-field regions. The strip wave of the strip-loaded dielectric slab prevents the boundary conditions in the near-field from being fulfilled, and is thus undesired. The other two surface waves are needed to realise the hard boundary condition.

Seismic constraints on the morphology of deep slabs

Abstract: Residual sphere images from deep earthquakes not only detect the presence of slab-associated velocity anomalies but also lend insight into the flow and deformation of lithosphere subducted into the lower mantle. We have compared travel times from deep events in the Kuril and Mariana arcs with the seismic velocity anomalies implied by kinematical models that thicken the slab perpendicular to its plane by reducing the vertical velocity of the flow with depth. We assume that the details of the deformation (whether the slab buckles, imbricates, fragments, etc.) are averaged out along the ray paths, and hence our models constrain the scale, not the mode, of slab thickening. The deep event travel times are best fit by undeformed models, but the ability of the residual sphere method to resolve slab thickness is limited by ray bending effects. Although the Mariana times are consistent with advective thickening factors of 5 or more, factors larger than 3 are ruled out by the Kuril data. For all models examined, the data require that slab material extends to depths of 900–1000 km. Global tomographic models and regional studies which delineate high-velocity anomalies in the lower mantle beneath zones of Cenozoic subduction are consistent with our results, as is recent work on pulse distortion by slab gradients. Comparison of observed and predicted rates of seismic moment release suggests that if substantial advective thickening does occur, it is largely aseismic.