@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 {cook_calibrated_2023,
	title = {Calibrated Absolute Seafloor Pressure Measurements for Geodesy in Cascadia},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {128},
	number = {6},
	year = {2023},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2023JB026413},
	pages = {e2023JB026413},
	abstract = {The boundary between the overriding and subducting plates is locked along some portions of the Cascadia subduction zone. The extent and location of locking affects the potential size and frequency of great earthquakes in the region. Because much of the boundary is offshore, measurements on land are incapable of completely defining a locked zone in the up-dip region. Deformation models indicate that a record of seafloor height changes on the accretionary prism can reveal the extent of locking. To detect such changes, we have initiated a series of calibrated pressure measurements using an absolute self-calibrating pressure recorder. A piston-gauge calibrator under careful metrological considerations produces an absolutely known reference pressure to correct seafloor pressure observations to an absolute value. We report an accuracy of about 25 ppm of the water depth, or 0.02 kPa (0.2 cm equivalent) at 100 m to 0.8 kPa (8 cm equivalent) at 3,000 m. These campaign survey-style absolute pressure measurements on seven offshore benchmarks in a line extending 100 km westward from Newport, Oregon from 2014 to 2017 establish a long-term, sensor-independent time series that can, over decades, reveal the extent of vertical deformation and thus the extent of plate locking and place initial limits on rates of subsidence or uplift. Continued surveys spanning years could serve as calibration values for co-located or nearby continuous pressure records and provide useful information on possible crustal deformation rates, while epoch measurements spanning decades would provide further limits and additional insights on deformation.},
	keywords = {absolute pressure, calibrated pressure, Cascadia subduction zone, marine geophysics, piston gauge calibrator, seafloor geodesy},
	issn = {2169-9356},
	doi = {10.1029/2023JB026413},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2023JB026413},
	author = {Cook, Matthew J. and Fredrickson, Erik K. and Roland, Emily C. and Sasagawa, Glenn S. and Schmidt, David A. and Wilcock, William S. D. and Zumberge, Mark A.}
}
@article {wilcock_distributed_2023,
	title = {Distributed acoustic sensing recordings of low-frequency whale calls and ship noise offshore Central Oregon},
	journal = {JASA Express Letters},
	volume = {3},
	number = {2},
	year = {2023},
	note = {Publisher: Acoustical Society of America},
	month = {feb},
	pages = {026002},
	abstract = {Distributed acoustic sensing (DAS) is a technique that measures strain changes along an optical fiber to distances of \~{}100 km with a spatial sensitivity of tens of meters. In November 2021, 4 days of DAS data were collected on two cables of the Ocean Observatories Initiative Regional Cabled Array extending offshore central Oregon. Numerous 20 Hz fin whale calls, northeast Pacific blue whale A and B calls, and ship noises were recorded, highlighting the potential of DAS for monitoring the ocean. The data are publicly available to support studies to understand the sensitivity of submarine DAS for low-frequency acoustic monitoring.},
	doi = {10.1121/10.0017104},
	url = {https://asa.scitation.org/doi/full/10.1121/10.0017104},
	author = {Wilcock, William S. D. and Abadi, Shima and Lipovsky, Bradley P.}
}
@article {chadwick_geodetic_2022,
	title = {Geodetic Monitoring at Axial Seamount Since Its 2015 Eruption Reveals a Waning Magma Supply and Tightly Linked Rates of Deformation and Seismicity},
	journal = {Geochemistry Geophysics Geosystems},
	volume = {23},
	number = {1},
	year = {2022},
	note = {Place: Washington Publisher: Amer Geophysical Union WOS:000751308100015},
	pages = {e2021GC010153},
	abstract = {Axial Seamount is a basaltic hot spot volcano with a summit caldera at a depth of similar to 1,500 m below sea level, superimposed on the Juan de Fuca spreading ridge, giving it a robust and continuous magma supply. Axial erupted in 1998, 2011, and 2015, and is monitored by a cabled network of instruments including bottom pressure recorders and seismometers. Since its last eruption, Axial has re-inflated to 85\%-90\% of its pre-eruption level. During that time, we have identified eight discrete, short-term deflation events of 1-4 cm over 1-3 weeks that occurred quasi-periodically, about every 4-6 months between August 2016 and May 2019. During each short-term deflation event, the rate of earthquakes dropped abruptly to low levels, and then did not return to higher levels until reinflation had resumed and returned near its previous high. The long-term geodetic monitoring record suggests that the rate of magma supply has varied by an order of magnitude over decadal time scales. There was a surge in magma supply between 2011 and 2015, causing those two eruptions to be closely spaced in time and the supply rate has been waning since then. This waning supply has implications for eruption forecasting and the next eruption at Axial still appears to be 4-9 years away. We also show that the number of earthquakes per unit of uplift has increased exponentially with total uplift since the 2015 eruption, a pattern consistent with a mechanical model of cumulative rock damage leading to bulk failure during magma accumulation between eruptions.},
	keywords = {bottom pressure recorders, de-fuca ridge, eruption forecasting, galapagos, ground deformation, high-resolution, inflation, kilauea volcano, lava flows, midocean ridge, ocean bottom seismometers, OOI cabled observatory, precursors, seafloor geodesy, sierra-negra-volcano, submarine volcano monitoring},
	doi = {10.1029/2021GC010153},
	url = {https://www.webofscience.com/api/gateway?GWVersion=2\&SrcAuth=DOISource\&SrcApp=WOS\&KeyAID=10.1029\%2F2021gc010153\&DestApp=DOI\&SrcAppSID=USW2EC0AF0FhQ3gq3aJ9tUIgn6Kiy\&SrcJTitle=GEOCHEMISTRY+GEOPHYSICS+GEOSYSTEMS\&DestDOIRegistrantName=American+Geophysical+Uni},
	author = {Chadwick, William W. and Wilcock, William S. D. and Nooner, Scott L. and Beeson, Jeffrey W. and Sawyer, Audra M. and Lau, T.-k}
}
@article {RN273,
	title = {Geodetic Monitoring at Axial Seamount Since its 2015 Eruption Reveals a Waning Magma Supply and Tightly Linked Rates of Deformation and Seismicity},
	journal = {Geochemistry Geophysics Geosystems},
	year = {2021},
	type = {Journal Article},
	doi = {10.1029/2021gc010153},
	url = {https://app.dimensions.ai/details/publication/pub.1144167182},
	author = {Chadwick, William W. and Wilcock, William S. D. and Nooner, Scott L. and Beeson, Jeff W. and Sawyer, Audra M. and Lau, T. -K}
}
@article {RN185,
	title = {Physical Sources of High-Frequency Seismic Noise on Cascadia Initiative Ocean Bottom Seismometers},
	journal = {Geochemistry Geophysics Geosystems},
	year = {2020},
	type = {Journal Article},
	abstract = {Physical sources of high-frequency seismic noise in the ocean are investigated using data from the Cascadia Initiative (CI) ocean bottom seismometer (OBS) network, hindcasts of wind speed, waves, and the bottom currents predicted by a regional ocean circulation model and observed at sites on cabled observatories. Seismic data in the 5{\textendash}12 Hz band are considered because it is best for detecting regional earthquakes and lies between the frequencies of local microseisms and the seasonal whale calls. Median noise levels in this range vary by ~20 dB between sites at a given depth but on average decrease with increasing depth. On the continental shelf, the orbital motions of ocean waves are a major source of noise while at the quietest sites in the deep ocean, noise increases when wind speeds exceed ~10 m/s. On the continental slope and abyssal plain within about 100 km of the slope, seismic noise is not predicted at specific sites by the bottom currents in the ocean circulation model. In these regions, ocean currents are inferred to be the primary source of noise, because noise varies on tidal periods, is low on buried seismometers, and has spatial variations broadly consistent with those of median absolute currents. Comparisons between OBSs suggest that high-frequency noise is reduced by low-profile hydrodynamic designs but not by shielding. Many OBSs also record numerous short duration events on and near the continental shelf that have been attributed elsewhere to animals bumping into the sensor or gas bubbles moving through sediments.},
	doi = {10.1029/2020gc009085},
	url = {https://app.dimensions.ai/details/publication/pub.1131195022},
	author = {Hilmo, Rose and Wilcock, William S. D.}
}
@article {RN66,
	title = {Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)},
	journal = {Earth and Planetary Science Letters},
	volume = {512},
	year = {2019},
	pages = {39-45},
	type = {Journal Article},
	abstract = {Earthquake size-frequency distributions commonly follow a power law, with the b value often used to quantify the relative proportion of small and large events. Laboratory experi13 ments have found that the b value of microfractures decreases with increasing stress. Stud14 ies have inferred that this relationship also holds for earthquakes based on observations of earthquake b values varying systematically with faulting style, depth, and for subduction zone earthquakes, plate age. However, these studies are limited by small sample sizes de17 spite aggregating events over large regions, which precludes the ability to control for other variables that might also affect earthquake b values such as rock heterogeneity and fault roughness. Our natural experiment in a unique seafloor laboratory on Axial Seamount involves analyzing the size-frequency distribution of \~{}60,000 microearthquakes which
delineate a ring-fault system in a 25 km3 21 block of crust that experiences periodic tidal loading of {\textpm}20 kPa. We find that above a threshold stress amplitude, b value is inversely correlated with tidal stress. The earthquake b value varies by \~{}0.09 per kPa change in Coulomb stress. Our results support the potential use of b values to estimate small stress variations in the Earth{\textquoteright}s crust.},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2019.01.047},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X19300731},
	author = {Tan, Yen Joe and Waldhauser, Felix and Tolstoy, Maya and Wilcock, William S. D.}
}
@article {RN122,
	title = {A Joint Inversion for Three-dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {n/a},
	number = {n/a},
	year = {2019},
	type = {Journal Article},
	abstract = {Axial Seamount is a prominent volcano located at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg hot spot in the northeast Pacific Ocean that has erupted in 1998, 2011, and 2015. The 2015 eruption was recorded by a seven-station seismic network in the southern part of the summit caldera that forms part of the Ocean Observatories Initiative Cabled Array. We utilize a data set of ~3,900 well-recorded earthquakes from January 2015 to February 2017 and a three-dimensional P wave velocity model obtained previously from active source data to conduct a joint inversion for three-dimensional P and S wave velocities and hypocentral parameters. The resulting velocity models are used to relocate >76,000 earthquakes with >=10 arrival times. The velocity models reveal a low-velocity anomaly in the center of the southern caldera at depths less than ~2 km, which corresponds to the top of the magma chamber and is interpreted as a region that is intensely fractured by the cyclical deformation of the caldera. High velocities around the caldera rim are likely due to consolidated undeformed lava flows. Low VP/VS in the southern caldera is consistent with the presence of hydrothermal vapor. Low S wave velocities and high VP/VS in the northern caldera may indicate a region dominated by thin cracks caused by dike injection. The relocated earthquakes delineate outward-dipping ring faults more clearly than previous studies and image a subvertical inward-dipping fault within the network that connects to the east caldera wall and eruptive fissures.},
	keywords = {axial seamount, Earthquakes location, Hydrothermal systems, Joint inversion, Tomography, volcano},
	issn = {2169-9313},
	doi = {10.1029/2019JB017970},
	author = {Baillard, Christian and Wilcock, William S. D. and Arnulf, Adrien F. and Tolstoy, Maya and Waldhauser, Felix}
}
@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}
}
