Cascadia ETS Events Seen in Tidal Records (1980–2011)

Sequoia Alba; Ray J. Weldon; Dean Livelybrooks; David A. Schmidt

doi:10.1785/0120180218

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Research Article| February 12, 2019

Cascadia ETS Events Seen in Tidal Records (1980–2011)

Sequoia Alba;

Sequoia Alba

^a

Department of Earth Sciences, University of Oregon, 100 Cascade Hall, 1272 University of Oregon, Eugene, Oregon 97403‐1272, sequoiaa@uoregon.edu, ray@uoregon.edu

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Ray J. Weldon, II;

Ray J. Weldon, II

^a

Department of Earth Sciences, University of Oregon, 100 Cascade Hall, 1272 University of Oregon, Eugene, Oregon 97403‐1272, sequoiaa@uoregon.edu, ray@uoregon.edu

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Dean Livelybrooks;

Dean Livelybrooks

^b

Department of Physics, University of Oregon, 120 Willamette Hall, 1371 East 13th Avenue, Eugene, Oregon 97403, dlivelyb@uoregon.edu

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David A. Schmidt

^c

Department of Earth and Space Sciences, University of Washington, Johnson Hall Room‐070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195‐1310, dasc@uw.edu

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Author and Article Information

Sequoia Alba

^a

Department of Earth Sciences, University of Oregon, 100 Cascade Hall, 1272 University of Oregon, Eugene, Oregon 97403‐1272, sequoiaa@uoregon.edu, ray@uoregon.edu

Ray J. Weldon, II

^a

Department of Earth Sciences, University of Oregon, 100 Cascade Hall, 1272 University of Oregon, Eugene, Oregon 97403‐1272, sequoiaa@uoregon.edu, ray@uoregon.edu

Dean Livelybrooks

^b

Department of Physics, University of Oregon, 120 Willamette Hall, 1371 East 13th Avenue, Eugene, Oregon 97403, dlivelyb@uoregon.edu

David A. Schmidt

^c

Department of Earth and Space Sciences, University of Washington, Johnson Hall Room‐070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195‐1310, dasc@uw.edu

Publisher: Seismological Society of America

First Online: 12 Feb 2019

Online ISSN: 1943-3573

Print ISSN: 0037-1106

Bulletin of the Seismological Society of America (2019) 109 (2): 812–821.

https://doi.org/10.1785/0120180218

Abstract

Coseismic vertical displacements and interevent uplift rates associated with 12 episodic tremor and slip events on the Cascadia subduction zone occurring between 1996 and 2011 have been determined from hourly water level records from four National Oceanic and Atmospheric Administration (NOAA) tide gauges (Neah Bay, Port Angeles, Port Townsend, and Seattle). Whereas vertical displacements during individual events are on the order of millimeters with centimeter uncertainties, 12‐event average displacements by site are resolved to a few millimeters (⁠ $- 1.35 \pm 1.50 mm$ at Neah Bay, $3.86 \pm 1.29 mm$ at Port Angeles, $- 2.38 \pm 1.22 mm$ at Port Townsend, and $- 0.13 \pm 1.78 mm$ at Seattle), which agree with displacements inferred from modeling Global Positioning System (GPS) data. Examination of water levels between events shows an interseismic deformation rate approximately equal in magnitude but opposite sign (but with higher uncertainties) with episodic tremor and slip events, on average, releasing strain accumulated between events. Analysis of pre‐GPS (1980–1995) water levels suggests that the time interval or average displacement pattern has changed between 1980 and 2011.