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Guangyu Xu Research Scientist/Engineer - Senior guangyux@apl.uw.edu Phone 206-543-6860 |
Research Interests
Guangyu Xu's research combines underwater acoustic and numerical modeling techniques to study fluid flows within both the seafloor and the ocean. Xu's scientific questions focus on: dynamics associated with seafloor hydrothermal discharge and its dispersal near a mid-ocean ridge, deep ocean flows and their interconnections with surface processes, sub-seafloor hydrothermal circulation, and acoustic seafloor characterization.
Education
B.S. Ocean Technology, Ocean University of China (Qingdao, Shandong Province, China), 2008
M.S. Marine Sciences, University of Georgia, 2010
Ph.D. Marine Sciences, Rutgers University, 2015
Publications |
2000-present and while at APL-UW |
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A physics-based inversion of multibeam sonar data for seafloor characterization Xu, G., B.T. Hefner, D.R. Jackson, A.N. Ivakin, and G. Wendelboe, "A physics-based inversion of multibeam sonar data for seafloor characterization," IEEE J. Ocean. Eng., EOR, doi:10.1109/JOE.2024.3467308, 2024. |
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9 Dec 2024 ![]() |
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A physics-based algorithm has been developed for the inversion of multibeam sonar survey data for sediment properties. The algorithm relies on high-frequency acoustical models of seafloor scattering to estimate sediment properties, taking as input the calibrated backscatter intensity time series data for multiple incidence angles. The inversion proceeds in three stages to produce estimates for a suite of geoacoustic and physical parameters of the seafloor, which include sediment attenuation and strengths of interface and volume scattering in the first stage, surface roughness and reflectivity in the second stage, and porosity, density, and sound-speed ratios and mean grain size in the third and final stage. The algorithm uses a Monte-Carlo approach to determine the uncertainties in inversion-derived sediment properties based on the measured statistics of seafloor backscatter. This assessment also takes into account the uncertainties associated with the empirical relations utilized in the final stage of inversion to determine sediment properties from reflectivity. The performance and accuracy of the algorithm have been evaluated through implementation in the processing of field data recorded from Sequim Bay, WA, USA, in 2019. Comparison of inversion output with ground-truth measurements demonstrates the effectiveness and robustness of the algorithm in seafloor characterization with multibeam sonars. |
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Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses Barkat, A., Y.J. Tan, G. Xu, F. Waldhauser, M. Tolstoy, and W.S.D. Wilcock, "Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses," Earth Planet. Sci. Lett., 632, doi:10.1016/j.epsl.2024.118625, 2024. |
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15 Apr 2024 ![]() |
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Transient stresses from the passage of seismic waves are known to trigger earthquakes and cause crustal permeability changes. However, whether permeability change is a main driver of dynamic earthquake triggering remains debated. Our understanding of the characteristics of dynamic triggering in submarine volcanic environments is also limited due to the lack of offshore observations. Here, we utilize a high-resolution micro-seismicity catalog from July 2015 to July 2022 to evaluate the triggering response of Axial Seamount, an inflating and seismically active submarine volcano located in the northeast Pacific Ocean. We report statistically significant episodes of dynamic earthquake triggering for ∼18 % of the teleseismic events investigated, which is comparable with subaerial tectonic and volcanic environments. We do not observe any obvious dependence of triggering rate on the amplitude of peak ground velocity. However, a comparison of the triggering rate and the cumulative magma volume shows that the triggering susceptibility might increase as the volcano becomes more critically stressed. Using data recorded by a temperature sensor in a black smoker, we compute the phase lag between hydrothermal vent-fluid temperature and tidal loading amplitude before and after the arrival of teleseismic waves to probe the relationship between permeability change and dynamic triggering. While the energy density thresholds for dynamic earthquake triggering and permeability change are comparable, both triggering and non-triggering observations show similar proportions of permeability changes. Our results suggest that permeability change induced by transient stresses might not be a necessary or primary mechanism that drives dynamic earthquake triggering. |
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Subsurface acoustic ducts in the Northern California current system Xu, G., R.R. Harcourt, D. Tang, B.T. Hefner, E.I. Thorsos, and J.B. Mickett, "Subsurface acoustic ducts in the Northern California current system," J. Acoust. Soc. Am., 155, 1881-1894, doi:10.1121/10.0024146, 2024. |
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7 Mar 2024 ![]() |
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This study investigates the subsurface sound channel or acoustic duct that appears seasonally along the U.S. Pacific Northwest coast below the surface mixed layer. The duct has a significant impact on sound propagation at mid-frequencies by trapping sound energy and reducing transmission loss within the channel. A survey of the sound-speed profiles obtained from archived mooring and glider observations reveals that the duct is more prevalent in summer to fall than in winter to spring and offshore of the shelf break than over the shelf. The occurrence of the subsurface duct is typically associated with the presence of a strong halocline and a reduced thermocline or temperature inversion. Furthermore, the duct observed over the shelf slope corresponds to a vertically sheared along-slope velocity profile, characterized by equatorward near-surface flow overlaying poleward subsurface flow. Two potential duct formation mechanisms are examined in this study, which are seasonal surface heat exchange and baroclinic advection of distinct water masses. The former mechanism regulates the formation of a downward-refracting sound-speed gradient that caps the duct near the sea surface, while the latter contributes to the formation of an upward-refracting sound-speed gradient that defines the duct's lower boundary. |