@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 {sasagawa_drift_2023,
	title = {Drift Corrected Seafloor Pressure Observations of Vertical Deformation at Axial Seamount 2018{\textendash}2021},
	journal = {Earth and Space Science},
	volume = {10},
	number = {2},
	year = {2023},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022EA002434},
	pages = {e2022EA002434},
	abstract = {Axial Seamount is a seafloor volcano with frequent eruptions and periodic cycles of inflation and deflation. Seafloor pressure gauges monitor vertical deformation with time, but inherent instrumental drift complicates and biases geodetic interpretation. A drift corrected pressure recorder was deployed on Axial Seamount on 6 July 2018, at coordinates 45{\textdegree} 57.29' North latitude, -130{\textdegree} 0.56' East longitude, depth 1,535 m. This system includes two independent quartz-resonant pressure gauges, which nearly continuously observe the seafloor pressure. At regular intervals, the gauges are calibrated in situ with a modified deadweight tester at a pressure within 98\% of the nominal seafloor pressure. Using the calibration data, the drift of each gauge has been modeled as a simple linear plus decaying exponential function of time. The two estimated linear sensor drift rates are 0.45 {\textpm} 0.12 and 0.36 {\textpm} 0.08 kPa/year; the modeled sensor drift represents a significant error if uncorrected. The standard deviations of the drift model residuals are of order 0.06 kPa or 6 mm depth equivalent. Once calibrated, the difference between the two seafloor pressure timeseries exhibits a RMS deviation of {\textpm}6 mm at the 90\% confidence limit and a linear trend less than 1 mm/year. A time series from July 2018 to December 2021 tracks the inflation of Axial Seamount with differing inflation rates over different time intervals.},
	keywords = {instruments and technique, ocean observatories and experiments, standards and absolute measurements, submarine tectonics and volcanism, volcano monitoring},
	issn = {2333-5084},
	doi = {10.1029/2022EA002434},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022EA002434},
	author = {Sasagawa, Glenn S. and Zumberge, Mark A. and Cook, Matthew J.}
}
