@article {barkat_permeability_2024,
	title = {Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses},
	journal = {Earth and Planetary Science Letters},
	volume = {632},
	year = {2024},
	pages = {118625},
	abstract = {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.},
	keywords = {Dynamic earthquake triggering, Permeability changes, Transient stresses, Volcanic inflation},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2024.118625},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X2400058X},
	author = {Barkat, Adnan and Tan, Yen Joe and Xu, Guangyu and Waldhauser, Felix and Tolstoy, Maya and Wilcock, William S. D.}
}
@article {xu_subsurface_2024,
	title = {Subsurface acoustic ducts in the Northern California current system},
	journal = {The Journal of the Acoustical Society of America},
	volume = {155},
	number = {3},
	year = {2024},
	month = {mar},
	pages = {1881{\textendash}1894},
	abstract = {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{\textquoteright}s lower boundary.},
	issn = {0001-4966},
	doi = {10.1121/10.0024146},
	url = {https://doi.org/10.1121/10.0024146},
	author = {Xu, Guangyu and Harcourt, Ramsey R. and Tang, Dajun and Hefner, Brian T. and Thorsos, Eric I. and Mickett, John B.}
}
@article {jackson_sonar_2022,
	title = {Sonar Observation of Heat Flux of Diffuse Hydrothermal Flows},
	journal = {Earth and Space Science},
	volume = {9},
	number = {n/a},
	year = {2022},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2021EA001974},
	pages = {e2021EA001974},
	abstract = {Previous work using multibeam sonar to map diffuse hydrothermal flows is extended to estimate the heat output of diffuse flows. In the first step toward inversion, temperature statistics are obtained from sonar data and compared to thermistor data in order to set the value of an empirical constant. Finally, a simple model is used to obtain heat-flux density from sonar-derived temperature statistics. The method is applied to data from the Cabled Observatory Vent Imaging Sonar (COVIS) deployed on the Ocean Observatories Initiative{\textquoteright}s Regional Cabled Array at the ASHES vent field on Axial Seamount. Inversion results are presented as maps of heat-flux density in MW/m2 and as time series of heat-flux density averaged over COVIS{\textquoteright} field of view.},
	keywords = {Deep-Sea Hydrothermal, Heat flux, sonar},
	issn = {2333-5084},
	doi = {10.1029/2021EA001974},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021EA001974},
	author = {Jackson, Darrell and Bemis, Karen and Xu, Guangyu and Ivakin, Anatoliy}
}
@article {xu_acoustic_2021,
	title = {Acoustic and In-Situ Observations of Deep Seafloor Hydrothermal Discharge: An OOI Cabled Array ASHES Vent Field Case Study},
	journal = {Earth and Space Science},
	volume = {8},
	number = {3},
	year = {2021},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2020EA001269},
	pages = {e2020EA001269},
	abstract = {The Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative{\textquoteright}s Regional Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. The acoustic backscatter data recorded by COVIS in August{\textendash}September 2018, in conjunction with in situ temperature measurements, are used to showcase and verify the use of COVIS for long-term, quantitative monitoring of hydrothermal discharge. Specifically, sonar data processing generates three-dimensional backscatter images of the buoyant plumes above major sulfide structures and two-dimensional maps of diffuse flows within COVIS{\textquoteright}s field-of-view. The backscatter images show substantial changes of plume appearance and orientation that mostly reflect plume bending in the presence of ambient currents and potentially the variations of outflow fluxes. The intensity of acoustic backscatter decreases significantly for highly bent plumes as compared to nearly vertical plumes, reflecting enhanced mixing of plume fluids with seawater driven by ambient currents. A forward model of acoustic backscatter from a buoyancy-driven plume developed in this study yields a reasonable match with the observation, which paves the way for inversely estimating the source heat flux of a hydrothermal plume from acoustic backscatter measurements. The acoustic observations of diffuse flows show large temporal variations on time scales of hours to days, especially at tidal frequencies, but no apparent long-term trend. These findings demonstrate COVIS{\textquoteright}s ability to quantitatively monitor hydrothermal discharge from both focused and diffuse sources to provide the research community with key observational data for studying the linkage of hydrothermal activity with oceanic and geological processes.},
	keywords = {acoustic, axial seamount, hydrothermal, imaging, observatory, sonar},
	issn = {2333-5084},
	doi = {10.1029/2020EA001269},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2020EA001269},
	author = {Xu, Guangyu and Bemis, Karen and Jackson, Darrell and Ivakin, Anatoliy}
}
@article {RN264,
	title = {The cabled observatory vent imaging sonar deployed on the Ocean Observatories initiative{\textquoteright}s cabled array},
	journal = {The Journal of the Acoustical Society of America},
	volume = {150},
	number = {4},
	year = {2021},
	pages = {a122-a122},
	type = {Journal Article},
	doi = {10.1121/10.0007839},
	url = {https://app.dimensions.ai/details/publication/pub.1142688757},
	author = {Xu, Guangyu and Jackson, Darrell R. and Bemis, Karen and Ivakin, Anatoliy N.}
}
@article {RN192,
	title = {Acoustic and In-situ Observations of Deep Seafloor Hydrothermal Discharge: an OOI Cabled Array ASHES Vent Field Case Study},
	journal = {Earth and Space Science},
	year = {2020},
	type = {Journal Article},
	abstract = {The Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative{\textquoteright}s Regional Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. The acoustic backscatter data recorded by COVIS in August{\textendash}September 2018, in conjunction with in situ temperature measurements, are used to showcase and verify the use of COVIS for long-term, quantitative monitoring of hydrothermal discharge. Specifically, sonar data processing generates three-dimensional backscatter images of the buoyant plumes above major sulfide structures and two-dimensional maps of diffuse flows within COVIS{\textquoteright}s field-of-view. The backscatter images show substantial changes of plume appearance and orientation that mostly reflect plume bending in the presence of ambient currents and potentially the variations of outflow fluxes. The intensity of acoustic backscatter decreases significantly for highly bent plumes as compared to nearly vertical plumes, reflecting enhanced mixing of plume fluids with seawater driven by ambient currents. A forward model of acoustic backscatter from a buoyancy-driven plume developed in this study yields a reasonable match with the observation, which paves the way for inversely estimating the source heat flux of a hydrothermal plume from acoustic backscatter measurements. The acoustic observations of diffuse flows show large temporal variations on time scales of hours to days, especially at tidal frequencies, but no apparent long-term trend. These findings demonstrate COVIS{\textquoteright}s ability to quantitatively monitor hydrothermal discharge from both focused and diffuse sources to provide the research community with key observational data for studying the linkage of hydrothermal activity with oceanic and geological processes.},
	keywords = {acoustic, axial seamount, hydrothermal, imaging, observatory, sonar},
	doi = {10.1029/2020ea001269},
	url = {https://app.dimensions.ai/details/publication/pub.1133310442},
	author = {Xu, Guangyu and Bemis, Karen and Jackson, Darrell and Ivakin, Anatoliy}
}
@article {RN10,
	title = {Observation and Modeling of Hydrothermal Response to the 2015 Eruption at Axial Seamount, Northeast Pacific},
	journal = {Geochemistry, Geophysics, Geosystems},
	number = {ja},
	year = {2018},
	type = {Journal Article},
	abstract = {The 2015 eruption at Axial Seamount, an active volcano at a depth of 1500 m in the Northeast Pacific, marked the first time a seafloor eruption was detected and monitored by an in situ cabled observatory{\textemdash}the Cabled Array, which is part of the Ocean Observatories Initiative. After the onset of the eruption, eight cabled and noncabled instruments on the seafloor recorded unusual, nearly synchronous and spatially uniform temperature increases of 0.6{\textendash}0.7{\textdegree}C across the southern half of the caldera and neighboring areas. These temperature signals were substantially different from those observed after the 2011 and 1998 eruptions at Axial and hence cannot be explained by emplacement of the 2015 lava flows on the seafloor. In this study, we investigate several possible explanations for the 2015 temperature anomalies and use a numerical model to test our preferred hypothesis that the temperature increases were caused by the release of a warm, dense brine that had previously been stored in the crust. If our interpretation is correct, this is the first time that the release of a hydrothermal brine has been observed due to a submarine eruption. This observation would have important implications for the salt balance of hydrothermal systems and the fate of brines stored in the subsurface. The observation of the 2015 temperature anomalies and the modeling presented in this study also demonstrate the importance of contemporaneous water column observations to better understand hydrothermal impacts of submarine eruptions.},
	issn = {15252027},
	doi = {10.1029/2018gc007607},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GC007607},
	author = {Xu, Guangyu and Chadwick, William W. and Wilcock, William S. D. and Bemis, Karen G. and Delaney, John}
}
