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°N and 45°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.
Tréhu, A.M., W.S.D. Wilcock, R. Hilmo, P. Bodin, J. Connolly, E.C. Roland, and J. Braunmiller. 2018. The role of the Ocean Observatories Initiative in monitoring the offshore earthquake activity of the Cascadia subduction zone. Oceanography 31(1):104–113, https://doi.org/10.5670/oceanog.2018.116.
Atwater, B.F., S. Musumi-Rokkaku, K. Satake, Y. Tsuji, K. Ueda, and D.K. Yamaguchi. 2015. The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America, 2nd ed. US Geological Survey Professional Paper 1707, Seattle, University of Washington Press, 135 pp, https://pubs.er.usgs.gov/publication/pp1707.
Bouchon, M., V. Durand, D. Marsan, H. Karabulut, and J. Schmittbuhl. 2013. The long precursory phase of most large interplate earthquakes. Nature Geoscience 6:299–302, https://doi.org/10.1038/ngeo1770.
Burgmann, R. 2014. Warning signs of the Iquique earthquake. Nature 512:258–259, https://doi.org/10.1038/nature13655.
Collins, J.A., F.L. Vernon, J.A. Orcutt, R.A. Stephen, K.R. Peal, F.B. Wooding, F.N. Speiss, and J.A. Hilderbrand. 2001. Broadband seismology in the oceans: Lessons from the Ocean Seismic Network Pilot Experiment. Geophysical Research Letters 28(1):49–52, https://doi.org/10.1029/2000GL011638.
Crawford, W.C., and S.C. Webb. 2000. Identifying and removing tilt noise from low-frequency (<0.1 Hz) seafloor vertical seismic data. Bulletin of the Seismological Society of America 90:952–963, https://doi.org/10.1785/0119990121.
Cozzens, B.D., and G.A. Spinelli. 2012. A wider seismogenic zone at Cascadia due to fluid circulation in subducting oceanic crust. Geology 40(10):899–902, https://doi.org/10.1130/G33019.1.
deMets, C., R.G. Gordon, and D.F. Argus. 2010. Geologically current plate motions. Geophysical Journal International 181(1):1–80, https://doi.org/10.1111/j.1365-246X.2009.04491.x.
Dziak, R. 2001. Empirical relationship of T-wave energy and fault parameters of Northeast Pacific ocean earthquakes. Geophysical Research Letters 28:2,537–2,540, https://doi.org/10.1029/2001GL012939.
Gerdom, M., A.M. Tréhu, E.R. Flueh, and D. Klaeschen. 2000. The continental margin off Oregon from seismic investigations. Tectonophysics 329:79–97, https://doi.org/10.1016/S0040-1951(00)00190-6.
Goldfinger, C., C.H. Nelson, A. Morey, J.E. Johnson, J. Gutierrez-Pastor, A.T. Eriksson, E. Karabanov, J. Patton, E. Gracia, R. Enkin, and others. 2012. Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone. US Geological Survey Professional Paper 1661-F, Reston, VA, 332 pp, https://pubs.usgs.gov/pp/pp1661f/pp1661f_text.pdf.
Hyndman, R.D. 2013. Downdip landward limit of Cascadia great earthquake rupture. Journal of Geophysical Research 118(10):5,530–5,549, https://doi.org/10.1002/jgrb.50390.
Hyndman, R., and K. Wang. 1993. Thermal constraints on the zone of major thrust earthquake failure: The Cascadia subduction zone. Journal of Geophysical Research 98(B2):2,039–2,060, https://doi.org/10.1029/92JB02279.
Ito, Y., R. Hino, M. Kido, H. Fujimoto, Y. Osada, D. Inazu, Y. Ohta, T. Ilinuma, M. Ohzono, S. Miura, and others. 2013. Episodic slow slip events in the Japan subduction zone before the 2011 Tohoku-Oki earthquake. Tectonophysics 600:14–26, https://doi.org/10.1016/j.tecto.2012.08.022.
McCaffrey, R., A.I. Qamar, R.W. King, R. Wells, G. Khazaradze, C.A. Williams, C.W. Stevens, J.J. Vollick, and P.C. Zwick. 2007. Fault locking, block rotation and crustal deformation in the Pacific Northwest. Geophysical Journal International 169(3):1,315–1,340, https://doi.org/10.1111/j.1365-246X.2007.03371.x.
McNamara, D.E., C. von Hillebrandt-Andrade, J.-M. Saurel, V.R. Huerfano, and L. Lynch. 2016. Quantifying 10 years of improved earthquake-monitoring performance in the Caribbean region. Seismological Research Letters 87:26–36, https://doi.org/10.1785/0220150095.
Montagner, J.-P., J.-F.O. Karczewski, B. Romanowicz, S. Bouaricha, P. Lognonné, G. Roult, E.O. Stutzmann, J.-L. Thirot, J. Brion, B. Dole, and others. 1994. The French Pilot Experiment OFM-SISMOBS: First scientific results on noise level and event detection (1994). Physics of the Earth and Planetary Interiors 84(1):321–336, https://doi.org/10.1016/0031-9201(94)90050-7.
Morton, E.A., and S.L. Bilek. 2015. Preliminary event detection of earthquakes using the Cascadia Initiative data. Seismological Research Letters 86(5):1,270–1,277, https://doi.org/10.1785/0220150098.
Rogers, G., and H. Dragert. 2003. Episodic tremor and slip on the Cascadia subduction zone: The chatter of silent slip. Science 300:1,942–1,943, https://doi.org/10.1126/science.1084783.
Romanowicz, B., D. Stakes, R. Uhrhammer, P. McGill, D. Neuhauser, T. Ramirez, and D. Dolenc. 2003. The MOBB experiment: A prototype permanent off-shore ocean bottom broadband station. Eos, Transactions American Geophysical Union 84(34):325–332, https://doi.org/10.1029/2003EO340002.
Spence, W. 1989. Stress origins and earthquake potentials in Cascadia. Journal of Geophysical Research 94(B3):3,076–3,088, https://doi.org/10.1029/JB094iB03p03076.
Toomey, D.R., R.M. Allen, A.H. Barclay, S.W. Bell, P.D. Bromirski, R.L. Carlson, X. Chen, J.A. Collins, R.P. Dziak, B. Evers, and others. 2014. The Cascadia Initiative: A sea change in seismological studies of subduction zones. Oceanography 27(2):138–150, https://doi.org/10.5670/oceanog.2014.49.
Tréhu, A.M. 2016. Source parameter scaling and the Cascadia paleoseismic record. Bulletin of the Seismological Society America 106:904–911, https://doi.org/10.1785/0120150272.
Tréhu, A.M., J. Braunmiller, and E. Davis. 2015. Seismicity of the central Cascadia continental margin near 44.5°N: A decadal view. Seismological Research Letters 86:819–829, https://doi.org/10.1785/0220140207.
Tréhu, A.M., J. Braunmiller, and J.L. Nabelek. 2008. Probable low-angle thrust earthquakes on the Juan de Fuca-North America plate boundary. Geology 36:127–130, https://doi.org/10.1130/G24145A.1.
Wang, K., and S.L. Bilek. 2011. Do subducting seamounts generate or stop large earthquakes? Geology 39:819–822, https://doi.org/10.1130/G31856.1.
Wang, K., and A.M. Tréhu. 2016. Invited review paper: Some outstanding issues in the study of great megathrust earthquakes—The Cascadia example. Geodynamics 98:1–18, https://doi.org/10.1016/j.jog.2016.03.010.
Webb, S.C. 1998. Broadband seismology and noise under the ocean. Reviews of Geophysics 36(1):105–142, https://doi.org/10.1029/97RG02287.
Wilcock, W.S.D., R.P. Dziak, M. Tolstoy, W.W. Chadwick Jr., S.L. Nooner, D.R. Bohnenstiehl, J. Caplan-Auerbach, F. Waldhauser, A.F. Arnulf, C. Baillard, and others. 2018. The recent volcanic history of Axial Seamount: Geophysical insights into past eruption dynamics with an eye toward enhanced observations of future eruptions. Oceanography 31(1):114–123, https://doi.org/10.5670/oceanog.2018.117.
Williams, M.C., A.M. Tréhu, and J. Braunmiller. 2010. Local earthquake detection in marine environments using seismic signal parameters. Eos, Transactions American Geophysical Union 91, Abstract S53A-1965.
This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.