We use a Bayesian probabilistic framework to invert for the kinematic locking distribution on the Cascadia Subduction Zone, constrained by surface deformation data and a prior assumption of the locking pattern. Interseismic surface deformation observations include land and seafloor GNSS data, along with decades-averaged vertical rates from spirit leveling. Using a Bayesian inversion framework, we explore a range of priors, including different updip and downdip limits and along-strike heterogeneity in locking. Data corrections account for contemporary glacial isostatic adjustment and viscoelastic effects. The mean of the locking distributions suggests a highly coupled offshore zone, transitioning to creep at a depth that varies along strike, with sensitivity to the prior. The shape of the locking distributions varies along strike, with the highest means near the deformation front and in Central Oregon. Results suggest high probability of strong locking offshore and low locking deeper than 20 km depth, which can provide insight into associated hazards. This work also highlights the importance of tradeoffs among different deformation signals. We find that the combined influence of viscoelasticity and glacial isostatic adjustment is relatively small in Cascadia, on the order of a few mm/yr vertically, indicating that elastic strain accumulation dominates the contemporary crustal deformation.

Estimates of coseismic vertical displacements from past and potential future subduction zone earthquakes provide critical constraints on regional seismic and tsunami hazard. Many studies use elastic homogeneous half-space models to calculate vertical displacements from a specified earthquake slip distribution, neglecting complexities of 3D structure in subduction zone settings. Here, we use 3D ground motion simulations of potential Cascadia Subduction Zone earthquakes to investigate the impact of realistic 3D Earth structure on estimated vertical displacements. We show that offshore uplift increases when including 3D structure due to high fault slip in low-rigidity accretionary wedge sediments and coastal subsidence decreases due to higher rigidity material at depth. These larger offshore uplifts cause increased tsunami maximum wave heights, and coastal subsidence at paleoseismic sites decreases on average by similar to 17 cm, or similar to 60%, which can have important implications for the amplitude and extent of slip in earthquake scenarios developed based on paleoseismic data constraints.

We explore the evolution of slow slip on the Cascadia megathrust during two large episodic tremor and slip events and compare stress changes to the spatial evolution of tremor from Pacific Northwest Seismic Network tremor locations. We used displacement time series from similar to 72 GPS stations, along with the Extended Network Inversion Filter to solve for the time-dependent fault slip. The 2010 (Mw 6.8) and 2012 (Mw 6.8) events propagated northward and southward, respectively, allowing us to assess directional effects on slip behavior. We observed that tremor occurs on the leading edge of propagating slipping regions, well ahead of the highest slip rates, independent of the along-strike propagation direction. Resolution tests using the actual tremor distributions to generate synthetic data show that our result of peak tremor rates leading peak slip rates is not due to biases introduced by temporal smoothing. Calculated stress changes due to the time-dependent slip distributions imply that tremor is sensitive to kilopascals of stress, consistent with studies of tidally triggered tremor. Within the resolution of our model, our results are consistent with the hypothesis that significant tremor is triggered by stresses ahead of the highest slip rates. We also observe ongoing slip continuing several days after tremor has passed. Our observations are consistent with some numerical models of tremor patches that suggest that this behavior can be explained by densely packed asperities resulting in somewhat crack-like propagation rather than a slip pulse that is as concentrated as the tremor activity.

Abstract We measured displacement vectors from horizontal components of 80 Global Positioning System stations to analyze six major episodic tremor and slip (ETS) events from 2007 to 2016 in northern Cascadia and inverted for slip on a realistic plate interface. Our results indicate that slow slip of up to 2 cm extends updip of tremor by about 15 km beneath the Olympic Peninsula. In these ETSs, slow slip extends from the downdip portion of the tremorgenic region beyond the updip extent of tremor, although still downdip of the inferred locked megathrust. Slip updip of tremor is a persistent feature of all six ETS events. Inversions that restrict slip to occur only in regions that generated tremor produced slip distributions with unphysical characteristics, such as 8‐cm slip concentrated at the updip part of the tremor footprint. Updip slow slip without tremor may suggest that the gap between stress and strength widens updip above the observed limit of tremor. In these ETSs, the region updip of tremor may have undergone only limited ductile failure surrounding potentially tremorgenic patches. A widening gap between stress and strength in the updip direction is consistent with an observed along‐dip dependence of low‐frequency earthquake occurrence and numerical simulations of slow slip. Alternatively, rheological properties in the region updip of tremor may favor stable slip and not permit seismic slip (i.e., tremor). Additionally, we find that along‐strike variations in the amount of slow slip updip of tremor correspond to changes in lithology of the overlying crust.

Research Article| May 01, 2015 How to Recognize a "Beast Quake" and a "Dance Quake" Stephen Malone; Stephen Malone aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Search for other works by this author on: GSW Google Scholar Kelley Hall; Kelley Hall aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Search for other works by this author on: GSW Google Scholar Lynn Simmons; Lynn Simmons bU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98115 U.S.A.simmonsl@uw.edu Search for other works by this author on: GSW Google Scholar John Vidale John Vidale aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Search for other works by this author on: GSW Google Scholar Author and Article Information Stephen Malone aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Kelley Hall aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Lynn Simmons bU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98115 U.S.A.simmonsl@uw.edu John Vidale aPacific Northwest Seismic Network, University of Washington, Box 351310, Seattle, Washington 98195 U.S.A.smalone@uw.eduhallka01@uw.eduseismoguy@mac.com Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2015 by the Seismological Society of America Seismological Research Letters (2015) 86 (3): 1006–1008. https://doi.org/10.1785/0220150053 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Stephen Malone, Kelley Hall, Lynn Simmons, John Vidale; How to Recognize a "Beast Quake" and a "Dance Quake". Seismological Research Letters 2015;; 86 (3): 1006–1008. doi: https://doi.org/10.1785/0220150053 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Any good seismologist–carryball (i.e., American football) fan remembers the "beast quake" of 2011. Seahawks fans' exuberant reactions to a Marshawn Lynch (in beast mode) run caused the stadium to shake enough to be well recorded on a strong‐motion seismograph a block away (Vidale, 2011). With the Seahawks at home for the National Football Conference (NFC) Championship playoffs, both last year and this year, the Pacific Northwest Seismic Network (PNSN) received permission to install some seismometers in the stadium. Motivations for the experiment included testing the field and telemetry equipment, examining analysis and display techniques, and practicing quick reactions... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.