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This project contributes to an international effort to strategically place temporary arrays of instruments across the Pacific Ocean basin that record the energy from earthquakes. Recent community advances in ocean bottom seismographs will be used to record unique datasets in locations where large gaps in coverage exist today. These data will allow us to infer deformation and variations in mantle temperature related to small-scale convection. As part of the international collaboration, all data will be openly available to scientists worldwide. The project supports the training of graduate and undergraduate students. This project will collect 12-15 months of broadband ocean bottom seismograph (OBS) data in two 30-station arrays in the central and southern Pacific. These arrays, deployed at two distinct plate ages (~30 Ma and ~120 Ma), will address specific critical questions on the dynamics of the oceanic asthenosphere, including its underlying state (temperature, presence of melt, water or other volatiles, and deformation mechanism). The arrays are designed to image the anisotropic velocity signature of small-scale convection, which has been invoked to explain the flattening of the age versus depth curve in old ocean plates, 140-200 km wavelength gravity lineations, and ubiquitous off-axis, non-plume volcanism observed at a variety of scales. Anisotropic surface wave and body wave tomographic models will be supplemented by shear wave splitting and attenuation measurements to obtain a multi-faceted understanding of the asthenosphere and base of the plates. Finally, the order-of-magnitude increases in path coverage for surface and body waves in the south-central Pacific will enable new advances in global tomography. 

The seismology component of this experiment will consist of a 2.5 dimensional transect that will cross from Bangladesh into Myanmar. We will install as many stations as possible on hard rock sites to minimize noise, although this will not be possible in low-lying deltaic areas. The array will consist of three lines. The middle line will be closely spaced in order to image shallow crustal features. It will have a station spacing of 5-10 km in Bangladesh expanding to 15 km in eastern Myanmar. To image the detachment megathrust at 10-20 km depth in the accretionary prism, a 100-km-long section spanning the Bangladesh and India border will have station spacing of 5 km or less. Two flanking lines located ~40 km on either side will have ~40 km spacing. This 80 km wide swath is critical for earthquake locations and body- and surface-wave tomography. The stations will operate for ~2 years, providing ample recordings from a wide backazimuth distribution of local, regional, and teleseismic events, and ambient noise for analysis