[1] Twenty-six broadband seismic stations in an areal array spanning 500 Â 500 km across Ethiopia were used for shear-wave splitting studies. Our results show small-tomoderate delay times (0.5 -1.7s) with fast-polarization azimuths sub-parallel to the orientation of the East African Rift (NNE-SSW) and also to the Proterozoic tectonic fabric across the entire studied area. Our results imply Ethiopian upper-mantle anisotropy is controlled largely by the Proterozoic accretion of the Mozambique belt, with possible minor effects within the rift due to aligned cracks or melt pockets parallel to the rift axis. Our observations are not consistent with anisotropy created by asthenospheric flow parallel either to the Cenozoic extension direction (NW-SE) or to the modern absolute plate motion direction (NNW-SSE), or to asthenospheric radial flow from the ''Afar'' plume.

[1] We utilized teleseismic receiver function techniques complemented by active source refraction seismology to study the crustal structure and continental rift processes responsible for the development of the northwest corner of the Basin and Range province in northwest Nevada. Our passive seismic array of 28 short-period stations, spanning 70 km west to east, and 5 broadband USArray transportable array stations that extended our aperture to 230 km provided data on crustal properties independent of the results of our active source refraction experiment. Combining data from the two experiments provides better constraints on Moho depth, V p /V s ratio, and the structure and composition of the crust beneath the northwestern Basin and Range province than possible from either experiment alone. Our new data indicate Moho depths that vary from 29.5 on the east to 36.5 km in the west along the passive source array and V p /V s ratios that systematically span a wide range from 1.68 to 1.83. Velocity modeling of data collected from the 300 km, wide-angle refraction/reflection survey provides comparable Moho depths of 32-37 km under the same region. Decreasing V p /V s is correlated with decreasing crustal thickness, with V p /V s ratio > 1.80 in northeast California and V p /V s < 1.74 in the thinner crust of the Basin and Range province. We associate the high V p /V s of northeast California with mafic additions to the crust during formation of the Modoc Plateau in a region of accreted Paleozoic island arc terrans similar to those exposed in the eastern Klamaths and northwestern Sierra Nevada. Unusually low V p /V s in conjunction with low absolute V p and V s is observed beneath the central part of our array and may be due to the roots of the Sierra Nevada batholith, now dismembered by Basin and Range faults. Back azimuthal stacking of our receiver function data suggests a northwest oriented crustal anisotropy fast direction beneath this region, parallel to the northwest to southeast oriented Cenozoic extension experienced by the Basin and Range province and suggestive of a similar flow direction in the middle to lower crust.

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A combination of both shallow and deepwater, plus islands and coral reefs, are some of the main features contributing to the complexity of subsalt seismic exploration in the Red Sea transition zone. These features often result in degrading effects on seismic images. State-of-the-art ocean bottom acquisition technologies are therefore required to record seismic data with optimal fold and offset, as well as advanced processing and imaging techniques. Numerical simulations of such complex seismic data can help improve acquisition design and also help in customizing, validating and benchmarking the processing and imaging workflows that will be applied on the field data. Subsequently, realistic simulation of wave propagation is a computationally intensive process requiring a realistic model and an efficient 3D wave equation solver. Large-scale computing resources are also required to meet turnaround time compatible with a production time frame. In this work, we present the numerical simulation of an ocean bottom seismic survey to be acquired in the Red Sea transition zone starting in summer 2016. The survey's acquisition geometry comprises nearly 300,000 unique shot locations and 21,000 unique receiver locations, covering about 760 km2. Using well log measurements and legacy 2D seismic lines in this area, a 3D P-wave velocity model was built, with a maximum depth of 7 km. The model was sampled at 10 m in each direction, resulting in more than 5 billion cells. Wave propagation in this model was performed using a 3D finite difference solver in the time domain based on a staggered grid velocity-pressure formulation of acoustodynamics. To ensure that the resulting data could be generated sufficiently fast, the King Abdullah University of Science and Technology (KAUST) supercomputer Shaheen II Cray XC40 was used. A total of 21,000 three-component (pressure and vertical and horizontal velocity) common receiver gathers with a 50 Hz maximum frequency were computed in less than three days. After careful optimization of the finite difference kernel, each gather was computed at 184 gigaflops, on average. Up to 6,103 nodes could be used during the computation, resulting in a peak computation speed greater than 1.11 petaflops. The synthetic seismic data using the planned survey geometry was available one month before the actual acquisition, allowing for early real scale validation of our processing and imaging workflows. Moreover, the availability of a massive supercomputer such as Shaheen II enables fast reverse time migration (RTM) and full waveform inversion, and therefore, a more accurate velocity model estimation for future work.

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