Abstract. Four multichannel-seismic reflection profiles, collected as part of the Mendocino triple junction seismic experiment, image the toe of the southern Cascadia accretionary prism. Today, 250-600 m of sediment is subducting with the Gorda plate, and 1500-3200 m is accreting to the northern California margin. Faults imaged west and east of the deformation front show mixed structural vergence. A north-south trending, 20 km long portion of the central margin is landward vergent for the outer 6-8 km of the toe of the prism. This region of landward vergence exhibits no frontal thrust, is unusually steep and narrow, and is likely caused by a seaward-dipping backstop close to the deformation front. The lack of margin-wide preferred seaward vergence and wedgetaper analysis suggests the prism has low basal shear stress. The three southern lines image wedge-shaped fragments of oceanic crust 1.1-7.3 km in width and 250-700 m thick near the deformation front. These wedges suggest shortening and thickening of the upper oceanic crust. Discontinuities in the seafloor west of the prism provide evidence for mass wasting in the form of slump blocks and debris fans. The southernmost profile extends 75 km west of the prism imaging numerous faults that offset both the Gorda basin oceanic crust and overlying sediments. These high-angle faults, bounding basement highs, are interpreted as strike-slip faults reactivating structures originally formed at the spreading ridge. Northeast or northwest trending strike-slip faults within the basin are consistent with published focal mechanism solutions and are likely caused by north-south Gorda-Pacific plate convergence.

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One dimensional (1D) velocity models are still widely used for computing earthquake locations at seismological centers. The location accuracy of an earthquake strongly depends on the velocity model used to compute the location. In the past, the local velocity model developed for the Hangay region was lacking precision due to insufficient data. Within the framework of the “Intracontinental Deformation and Surface Uplift- Geodynamic Evolution of the Hangay Dome, Mongolia, Central Asia” project [15], 72 seismic Broadband stations network were deployed in the Hangay Dome. This gives us an opportunity to estimate the crustal velocity structure of the South Hangay region using recorded local earthquake data. For this purpose, available velocity models for the South Hangay region have been re-evaluated.  By simultaneous invertion P- and S-wave arrival times using VELEST algorithm, we estimated minimum 1D velocity models, station corrections, hypocentre locations, and origin times for the south Hangay region. Consequently, 1D crustal velocity model is proposed for the South Hangay region. This new model is expected to improve the accuracy of the routine hypocenter determination and as initial reference models for seismic tomography study.

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Southeastern Tibet hosts the termination of the Himalayan orogen in the Eastern Himalayan Syntaxis and a transition between the geodynamic setting of the main Plateau, its eastern margin, and the lithosphere of southeast Asia. The Eastern Himalayan Syntaxis occupies a substantial portion of the diffuse India-Asia collision zone, and because it serves as the watershed for the largest rivers in Asia, its highly active tectonic and surface processes have a direct impact on over one billion people. The syntaxis is a crustal manifestation of the complex lithospheric dynamics associated with the Indian "indentor corner." Steep lateral surface velocity gradients and a laterally heterogeneous lithospheric structure mark the northeastern margin of the Indian plate. Such corners are also sites of significant accommodation of crustal convergence by erosion and fluvial evacuation. Within the core of the syntaxis, the Yarlung-Tsangpo River exits the Tibetan Plateau dropping ~2 km in elevation along an ~100 km section of the river cross cutting the Namche BarwaGyala Peri massif. This metamorphic massif is the site of high relief, high topography, and rapid recent ongoing exhumation exposing mid to lower crustal rocks of the Indian plate at the surface. Analysis of data recorded by a temporary seismic array document substantial lateral heterogeneity in lithospheric structure and rheology across southeastern Tibet. To first order, observed heterogeneity correlates to surface topography indicating that tectonic and surficial processes interact to shape the evolution of the orogen.In southeastern Tibet, the fast directions of seismic anisotropy in the lithospheric mantle correlate with surficial geology including major sutures and shear zones, extensional rifts, and with the surface strain derived from the GPS velocity field. These observations are consistent with a clockwise rotation of material around the eastern Himalayan syntaxis and suggest coherent and distributed lithospheric deformation beneath much of southeastern Tibet. The presence of small-scale and regional lateral variations in seismic anisotropy is observed within individual tectonic domains such as the Lhasa terrane and across major sutures and tectonic blocks. In the Lhasa terrane, we observe a change in the orientation of the fast axis of shear-wave polarization suggesting a change in the mode of deformation from orogen perpendicular extension in central Tibet to orogen parallel strike-slip in the eastern syntaxis. Shear-wave splitting measurements also show lateral variations in seismic anisotropy across the Tsangpo and the Bangong sutures indicating that these sutures separate lithospheric domains with distinct rheological properties or deformation regimes.Detailed 3-d receiver function analysis documents a dramatic change in crustal thickness, Poisson's ratio, and lower crustal reflectivity across the transition from the central Tibetan plateau to the eastern syntaxis. Crustal thickness beneath the southeastern Tibetan plateau varies between 65 to 75 km but t...