@article {RN183,
	title = {Precision Seismic Monitoring and Analysis at Axial Seamount Using a Real-Time Double-Difference System},
	journal = {Journal of Geophysical Research-Solid Earth},
	volume = {125},
	number = {5},
	year = {2020},
	type = {Journal Article},
	abstract = {Seven three-component ocean bottom seismometers (OBS) of the Ocean Observatories Initiative (OOI) Cabled Array on top of Axial Seamount are continuously streaming data in real time to the Incorporated Research Institutions for Seismology (IRIS). The OBS array records earthquakes from the submarine volcano which last erupted on 24 April 2015, about 4 months after the array came online. The OBS data have proven crucial in providing insight into the volcano structure and dynamics (Wilcock et al., 2016, https://doi.org/10.1126/science.aah5563). We implemented a real-time double-difference (RT-DD) monitoring system that automatically computes high-precision (tens of meters) locations of new earthquakes. The system{\textquoteright}s underlying double-difference base catalog includes nearly 100,000 earthquakes and was computed using kurtosis phase onset picks, cross-correlation phase delay times, and 3-D P and S velocity models to predict the data. The relocations reveal the fine-scale structures of long-lived, narrow (<200 m wide), outward dipping, convex faults on the east and west walls of the caldera that appear to form a figure 8-shaped ring fault system. These faults accommodate stresses caused by the inflation of magma prior to and deflation during eruptions. The east fault is segmented and pulled apart in east-west direction due to its interaction with the Juan de Fuca Ridge, which at this location forms an overlapping spreading center. The RT-DD system enables the monitoring and rapid analysis of variations in fine-scale seismic and fault properties and has the potential to improve prediction of timing and location of the next Axial eruption expected to occur in the 2022{\textendash}2023 time frame.

},
	issn = {2169-9313},
	doi = {10.1029/2019JB018796},
	author = {Waldhauser, F. and Wilcock, W. S. D. and Tolstoy, M. and Baillard, C. and Tan, Y. J. and Schaff, D. P.}
}
@article {RN125,
	title = {Optimizing Sensor Configurations for the Detection of Slow-Slip Earthquakes in Seafloor Pressure Records, Using the Cascadia Subduction Zone as a Case Study},
	journal = {Journal of Geophysical Research-Solid Earth},
	year = {2019},
	type = {Journal Article},
	abstract = {We present seafloor pressure records from the Cascadia Subduction Zone, alongside oceanographic and geophysical models, to evaluate the spatial uniformity of bottom pressure and optimize the geometry of sensor networks for resolving offshore slow-slip transients. Seafloor pressure records from 2011 to 2015 show that signal amplitudes are depth-dependent, with tidally filtered and detrended root-mean-squares of <2 cm on the abyssal plain and >6 cm on the continental shelf. This is consistent with bottom pressure predictions from circulation models and comparable to deformation amplitudes from offshore slow slip observed in other subduction zones. We show that the oceanographic component of seafloor pressure can be reduced to <=1-cm root-mean-square by differencing against a reference record from a similar depth, under restrictions that vary with depth. Instruments at 100{\textendash}250 m require depths matched within 10 m at separations of <100 km, while locations deeper than 1,400 m are broadly comparable over separations of at least 300 km. Despite the significant noise reduction from this method, no slow slip was identified in the dataset, possibly due to poor spatiotemporal instrument coverage, nonideal deployment geometry, and limited depth-matched instruments. We use forward predictions of deformation from elastic half-space models and hindcast pressure from circulation models to generate synthetic slow-slip observational records and show that a range of slip scenarios produce resolvable signals under depth-matched differencing. For future detection of offshore slow slip in Cascadia, we recommend a geometry in which instruments are deployed along isobaths to optimize corrections for oceanographic signals.},
	issn = {2169-9313},
	doi = {10.1029/2019JB018053},
	author = {Fredrickson, E. K. and Wilcock, W. S. D. and Schmidt, D. A. and MacCready, P. and Roland, E. and Kurapov, A. L. and Zumberge, M. A. and Sasagawa, G. S.}
}
@article {RN1,
	title = {Mechanics of fault reactivation before, during, and after the 2015 eruption of Axial Seamount},
	journal = {Geology},
	volume = {46},
	number = {5},
	year = {2018},
	pages = {447-450},
	type = {Journal Article},
	abstract = {Ocean-bottom seismic and seafloor pressure data from the Ocean Observatories Initiative{\textquoteright}s Cabled Array were used to study fault reactivation within Axial Seamount (offshore Oregon, USA). Microearthquakes that occurred during 2015{\textendash}2016 were located on portions of an outward-dipping ring fault system that was reactivated in response to the inflation and deflation of the underlying magma chamber. Prior to an eruption in April 2015, focal mechanisms showed a pattern of normal slip consistent with the differential vertical uplift of the caldera floor relative to the rim. During the eruption, seismic activity remained localized along these outward-dipping structures; however, the slip direction was reversed as the caldera floor subsided. After the eruption, as the volcano reinflated and the caldera floor uplifted, these faults exhibited sparser seismicity with a more heterogeneous pattern of slip. Monitoring the evolution of ring fault behavior through time may have utility as a metric in future eruption forecasts.},
	issn = {0091-7613},
	doi = {10.1130/G39978.1},
	url = {<Go to ISI>://WOS:000431359800019},
	author = {Levy, S. and Bohnenstiehl, D. R. and Sprinkle, P. and Boettcher, M. S. and Wilcock, W. S. D. and Tolstoy, M. and Waldhauser, F.}
}
@article {RN2,
	title = {THE RECENT VOLCANIC HISTORY OF AXIAL SEAMOUNT Geophysical Insights into Past Eruption Dynamics with an Eye Toward Enhanced Observations of Future Eruptions},
	journal = {Oceanography},
	volume = {31},
	number = {1},
	year = {2018},
	pages = {114-123},
	type = {Journal Article},
	abstract = {To understand the processes that form oceanic crust as well as the role of submarine volcanoes in exchanging heat and chemicals with the ocean and in supporting chemosynthetic biological communities, it is essential to study underwater eruptions. The world{\textquoteright}s most advanced underwater volcano observatory{\textemdash}the Ocean Observatories Initiative Cabled Array at Axial Seamount{\textemdash}builds upon ~30 years of sustained geophysical monitoring at this site with autonomous and remote systems. In April 2015, only months after the Cabled Array{\textquoteright}s installation, it recorded an eruption at Axial Seamount, adding to the records of two prior eruptions in 1998 and 2011. Between eruptions, magma recharge is focused beneath the southeast part of the summit caldera, leading to steady inflation and increasing rates of seismicity. During each eruption, the volcano deflates over days to weeks, coincident with high levels of seismicity as a dike is emplaced along one of the volcano{\textquoteright}s rifts and lava erupts on the seafloor. Cabled Array seismic data show that motions on an outward-dipping ring fault beneath the caldera accommodate the inflation and deflation. Eruptions appear to occur at a predictable level of inflation; hence, it should be possible to time deployments of additional cabled and autonomous instrumentation to further enhance observations of the next eruption.},
	issn = {1042-8275},
	doi = {10.5670/oceanog.2018.117},
	url = {<Go to ISI>://WOS:000427367300017},
	author = {Wilcock, W. S. D. and Dziak, R. P. and Tolstoy, M. and Chadwick, W. W. and Nooner, S. L. and Bohnenstiehl, D. R. and Caplan-Auerbach, J. and Waldhauser, F. and Arnulf, A. F. and Baillard, C. and Lau, T. K. and Haxel, J. H. and Tan, Y. J. and Garcia, C. and Levy, S. and Mann, M. E.}
}
@article {RN46,
	title = {The Role of the Ocean Observatories Initiative in Monitoring the Offshore Earthquake Activity of the Cascadia Subduction Zone},
	journal = {Oceanography},
	volume = {31},
	number = {1},
	year = {2018},
	pages = {104-113},
	type = {Journal Article},
	abstract = {Geological and historical data indicate that the Cascadia subduction zone last ruptured in a major earthquake in 1700. The timing of the next event is currently impossible to predict, but recent studies of several large subduction zone earthquakes provide tantalizing hints of precursory activity. The seismometers at the Ocean Observatories Initiative (OOI) Slope Base and Southern Hydrate Ridge nodes are well placed to provide new insights into interplate coupling because they are located over a segment of the subduction zone that is nominally locked but that has been relatively active for more than a decade. Since their installation in 2014, 18 earthquakes with magnitudes up to 3.8 have been located by the Pacific Northwest Seismic Network between 44{\textdegree}N and 45{\textdegree}N in the region of the plate boundary thought to be accumulating strain. The OOI seismometers have also detected events that were not reported by the onshore seismic network. Noting that OOI data are available in real time, which is a necessary criterion for routine earthquake monitoring, and that the OOI seismometers generally have lower noise levels than campaign-style ocean bottom seismometers, there would be significant benefit to adding seismometers to existing nodes that are not yet instrumented with seismometers.

},
	issn = {1042-8275},
	doi = {10.5670/oceanog.2018.116},
	url = {<Go to ISI>://WOS:000427367300016},
	author = {Trehu, A. M. and Wilcock, W. S. D. and Hilmo, R. and Bodin, P. and Connolly, J. and Roland, E. C. and Braunmiller, J.}
}
@article {RN8,
	title = {Structure, Seismicity, and Accretionary Processes at the Hot Spot-Influenced Axial Seamount on the Juan de Fuca Ridge},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {123},
	number = {6},
	year = {2018},
	pages = {4618-4646},
	type = {Journal Article},
	abstract = {Axial Seamount is the most volcanically active site of the northeast Pacific, and it has been monitored with a growing set of observations and sensors during the last two decades. Accurate imaging of the internal structure of volcanic systems is critical to better understand magma storage processes and to quantify mass and energy transport mechanisms in the crust. To improve the three-dimensional velocity structure of Axial Seamount, we combined 469,891 new traveltime arrivals, from 12 downward extrapolated seismic profiles, with 3,962 existing ocean-bottom-seismometers traveltime arrivals, into a joint tomographic inversion. Our approach reveals two elongated magma reservoirs, with melt fraction up to 65\%, representing an unusually large volume of melt (26{\textendash}60 km3), which is likely the result of enhanced magma supply from the juxtaposition of the Cobb hot spot plume (0.26{\textendash}0.53 m3/s) and the Axial spreading segment (0.79{\textendash}1.06 m3/s). The tomographic model also resolves a subsided caldera floor that provides an effective trap for ponding lava flows, via a {\textquotedblleft}trapdoor{\textquotedblright} mechanism. Our model also shows that Axial{\textquoteright}s extrusive section is thinnest beneath the elevated volcano, where anomalously thick (11 km) oceanic crust is present. We therefore suggest that focused and enhanced melt supply predominantly thickens the crust beneath Axial Seamount through diking accretion and gabbro crystallization. Lastly, we demonstrate that our three-dimensional velocity model provides a more realistic starting point for relocating the local seismicity, better resolving a network of conjugate outward and inward dipping faults beneath the caldera walls.},
	keywords = {axial seamount, hot spot, Juan de Fuca ridge, magmatic system, traveltime tomography, volcano},
	issn = {21699313},
	doi = {10.1029/2017jb015131},
	author = {Arnulf, A. F. and Harding, A. J. and Kent, G. M. and Wilcock, W. S. D.}
}
@article {RN219,
	title = {A Tale of Two Eruptions HOW DATA FROM AXIAL SEAMOUNT LED TO A DISCOVERY ON THE EAST PACIFIC RISE},
	journal = {Oceanography},
	volume = {31},
	number = {1},
	year = {2018},
	pages = {124-126},
	type = {Journal Article},
	issn = {1042-8275},
	doi = {10.5670/oceanog.2018.118},
	author = {Tolstoy, M. and Wilcock, W. S. D. and Tan, Y. J. and Waldhauser, F.}
}
@article {RN231,
	title = {THE CASCADIA INITIATIVE A Sea Change In Seismological Studies of Subduction Zones},
	journal = {Oceanography},
	volume = {27},
	number = {2},
	year = {2014},
	pages = {138-150},
	type = {Journal Article},
	abstract = {Increasing public awareness that the Cascadia subduction zone in the Pacific Northwest is capable of great earthquakes (magnitude 9 and greater) motivates the Cascadia Initiative, an ambitious onshore/offshore seismic and geodetic experiment that takes advantage of an amphibious array to study questions ranging from megathrust earthquakes, to volcanic arc structure, to the formation, deformation and hydration of the Juan De Fuca and Gorda Plates. Here, we provide an overview of the Cascadia Initiative, including its primary science objectives, its experimental design and implementation, and a preview of how the resulting data are being used by a diverse and growing scientific community. The Cascadia Initiative also exemplifies how new technology and community-based experiments are opening up frontiers for marine science. The new technology{\textemdash}shielded ocean bottom seismometers{\textemdash}is allowing more routine investigation of the source zone of megathrust earthquakes, which almost exclusively lies offshore and in shallow water. The Cascadia Initiative offers opportunities and accompanying challenges to a rapidly expanding community of those who use ocean bottom seismic data.},
	issn = {1042-8275},
	doi = {10.5670/oceanog.2014.49},
	author = {Toomey, D. R. and Allen, R. M. and Barclay, A. H. and Bell, S. W. and Bromirski, P. D. and Carlson, R. L. and Chen, X. W. and Collins, J. A. and Dziak, R. P. and Evers, B. and Forsyth, D. W. and Gerstoft, P. and Hooft, E. E. E. and Livelybrooks, D. and Lodewyk, J. A. and Luther, D. S. and McGuire, J. J. and Schwartz, S. Y. and Tolstoy, M. and Trehu, A. M. and Weirathmueller, M. and Wilcock, W. S. D.}
}
