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[1] GPS measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the Kamchatka subduction zone from about 51°to 57°N latitude. Inversions for the distribution of aseismic slip rate along the $15°NW dipping underthrust suggest a nonslipping plate interface in southern Kamchatka above $50 km depth, along the segment that ruptured in the M w = 9, 1952 earthquake. North of $53°N, the subduction interface experiences significant aseismic slip, consistent with the lower seismic moment release in M 8.5 earthquakes along this portion of the subduction zone. The GPS velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities, surrounded by a zero shear stress subduction interface loaded by plate convergence. Models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling. Reducing the area of the locked model asperities to the central 25% area of historic rupture zones fits the data well, suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface. Areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins, while less coupled portions of the Kamchatka subduction zone coincide with high-gravity anomalies offshore of two peninsulas, possibly related to the subduction of the Emperor-Meji seamount chain and the Kruzenstern fracture zone.Citation: Bürgmann, R., M. G. Kogan, G. M. Steblov, G. Hilley, V. E. Levin, and E. Apel (2005), Interseismic coupling and asperity distribution along the Kamchatka subduction zone,

[1] The Ganges, Brahmaputra, and Meghna rivers converge in Bangladesh with an annual discharge second to the Amazon. Most of the flow occurs during the summer monsoon causing widespread flooding. The impounded water represents a large surface load whose effects can be observed in Gravity Recovery and Climate Experiment (GRACE) and GPS data. Bangladesh is at the center of the second largest seasonal anomaly in the GRACE gravity field, reflecting water storage in Southeast Asia. Eighteen continuous GPS stations in Bangladesh record seasonal vertical motions up to 6 cm that inversely correlate to river level. We use 304 river gages to compute water height surfaces with a digital elevation model to separate surface water from groundwater. Porosity of 20% was used to estimate groundwater mass and calculate the water load. Results show ∼100 GT of water are stored in Bangladesh (7.5% of annual discharge) but can reach 150 GT during extreme events. The calculated water mass agrees with monthly GRACE water mass equivalents from Bangladesh within statistical limits. We compute the deformation due to this water load on an elastic half-space, and we vary Young's modulus to fit GPS data from our two most continuous records. The water loading can account for >50% of the variance in the GPS data. The best fitting Young's modulus is 117-124 GPa for DHAK and 133-135 GPa for SUST, although the upper bound is not well constrained. These estimates lie between sediment (30-75 GPa) and mantle (190 GPa) values, indicating that response to loading is sensitive to structure throughout the lithosphere and is not absorbed by the weak sediments.

This note constructs the flat toric degeneration of the manifold F ℓ n of flags in C n from [GL96] as an explicit GIT quotient of the Gröbner degeneration in [KM03]. This implies that Schubert varieties degenerate to reduced unions of toric varieties, associated to faces indexed by rc-graphs (reduced pipe dreams) in the Gel ′ fand-Cetlin polytope. Our explicit description of the toric degeneration of F ℓ n provides a simple explanation of how Gel ′ fand-Cetlin decompositions for irreducible polynomial representations of GL n arise via geometric quantization.

GPS observations in east Siberia combined with global observations, collected 1995–2002, place constraints on the geometry and motions of the Eurasian, North American, and Pacific plates in east Asia. By comparing velocities relative to Eurasia and to North America, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate, hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity. Smaller plates in east Asia, such as Okhotsk and Amurian, can neither be resolved nor excluded by the GPS velocities.

[1] We present the vectors of rotation of 10 major lithospheric plates, estimated from continuous GPS observations at 192 globally distributed stations; 71 stations were selected as representing stable plate regions. All days for the period 1995.0-2007.0 were included in the analysis. In contrast to previous GPS plate models, our model is independent of international terrestrial reference frames (ITRF). The origin of our plate-consistent reference frame is the center of plate rotation (CP) rather than the center of mass of the entire Earth's system (CM) as in recent versions of ITRF. We estimate plate rotations and CP by minimizing the misfit between the horizontal velocities predicted by the plate model and the observed GPS velocities. If any version of ITRF is used as the reference frame, the drift of the ITRF origin relative to CP cannot be neglected in estimation of plate rotation vectors and plate-residual station velocities. The model of the plate kinematics presented here addresses the problem debated since the beginning of the space geodesy: how big are disagreements between the current plate motions and the motions averaged over several million years? We compare the vectors of relative plate rotations estimated here with the published vectors from GPS and geologic models. We also discuss the integrity of individual plates as exhibited by plate-residual station velocities. For seven largest plates, the RMS value of plate-residual station velocities in stable plate interiors is 0.5-0.9 mm/a; this value is an upper bound on deviation of real plates from infinite stiffness.

In the summer of 1991 we installed 27 seismic stations about lake Baikal, Siberia, aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the Baikal rift zone and adjacent regions. Sixty‐six teleseismic events with high signal‐to‐noise ratio were recorded. Travel time and Q analysis of teleseisms characterize an upwarp of the lithosphere‐asthenosphere boundary under Baikal. Theoretical arrival times were calculated by using the International Association of Seismology and Physics of the Earth's interior 1991 Earth model, and travel time residuals were found by subtracting computed arrival times from observed ones. A three‐dimensional downward projection inversion method is used to invert the P wave velocity structure with constraints from deep seismic sounding data. Our results suggest that (1) the lithosphere‐asthenosphere transition upwarps beneath the rift zone, (2) the upwarp has an asymmetric shape, (3) the velocity contrast is −4.9% in the asthenosphere, (4) the density contrast is −0.6%, and (5) the P wave attenuation contrast t* is 0.1 s.

Abstract.Model (Fig. 1A). Historically, the Kamchatka subduc-