Rob Witter, Tom Brocher, Scott Bennett, Ginger Barth, Bruce Jaffe, Janet Watt, Jenna Hill, Maureen Walton, Brian Sherrod, Art Frankel, Erin Wirth, Jean Paul, Ruth Harris, Ray Wells, Corina Cerovski-Darriau, Seanpaul La selle, Alan Nelson, Kevin Schmidt, Jonathan Perkins, Joan Gomberg
Jonathan summarized the activities that have taken place since the last meeting. These included the following: 1) A Cascadia landslide workshop at the UofO, which was attended by both USGS, university and DOGAMI partners. The first day participants discussed current activities related to using landslide studies to constrain earthquake recurrence, and approaches that may be tried going forward. The group took a field trip the second day to the Oregon coast range, to the site of a landslide dam with potentially datable drowned trees. An outcome was the decision to write a white paper on the state of landslide studies relevant to this topic, and work on this is underway with Jonathan Perkins and Josh Roering taking the lead. Two key promising approaches identified include using landslide morphology to constrain earthquake chronologies and shaking strength, and using tree rings of trees in landslide-dammed lakes to date landslides. Both types of studies are underway, as collaborative efforts with university partners and DOGAMI. Jonathan and Kevin also summarized the presentations at the GSA session on coseismic subduction zone landslides and the Subduction Zone Town Hall where Cascadia landslide activities were featured.
Alan summarized the group's recent work on dating and modeling Oregon tsunami deposits. Motivated by successes in Japan Seanpaul described how he and others have used modeling to reveal where data gaps are, particularly that more information about thickness and lateral extent of tsunami deposits. Thus, in July they collected 100 cores and other samples. The group also has been working at a coastal lake in southern Oregon, where they have Collected more 1700 deposits to constrain modeling, including 20 vibracores. Alan and others have been working on dating samples collected last year at Cannon Beach, focusing on deposits from 1700 and previous two events, using carbon 14 and OSL methods; OSL dates just received show that the method worked very well and that previous inferences from sands deposited just 250 meters away attributed to pre-1700 events were likely from 1700. Ruth asks if deposits can be distinguished from storm surge and Alan and Bruce assured her that all evidence suggests that they are not, with a high degree of confidence.
Rob summarized the GSA session about Cascadia earthquakes, which had presentations on a broad array of topics, 17 of 19 which addressed subsidence and uplift issues. Some of the presentations highlighted 1) new transfer function Bayesian analysis results that suggest that in 1700 there was greater subsidence than previously thought in southern WA/norther OR, 2) another approach to date vertical displacements (need filling in!), 3) a marsh study in Bandon, OR of a tidal flooding experiment to test how quickly micro-organisms (diatoms and forams) recolonize after a flooding event, showing different organisms have different response times, 4) abHumboldt Bay study looking at variability of subsidence across the bay. Rob will send a summary of all the talks, as well as the discussion after the session.
Janet noted that Nathan Miller presented a briefing to CMG Program Council about the 5-year CMG subduction zone plan, which was very well received. Cascadia is the focus of the plan, and Nathan and Janet will lead the project. The CMG Program Council gave the green light to develop detailed implementation plans.
The group has assessed systematically morphological and structural variations along the margin using existing data, providing a framework for future studies. In FY18 and FY19 they will focus on end-member regions, Grays Harbor and Cape Mendocino, respectively. In each, new multibeam bathymetry and other data will be collected. Jenna Hill is working with NOAA to coordinate FY18 work. In response to Rob's question, Janet noted various ways in which their work would coordinate with onshore efforts and focus on coast-crossing structure and processes.
Art summarized the simulated ground motions from 50 Cascadia rupture that he and Erin have been completed and will make publicly available. He highlighted the importance of subevents in determining ground shaking and vertical deformation, and noted the large amplifications in sedimentary basins. Erin summarized work on the downdip limit of slip and how it affects predicted subsidence and shaking. Both note that paleoseismic evidence would be very helpful in constraining plausible slip models. Janet suggests comparing uplift/subsidence patterns from the simulations with geologic data. Ruth noted that future work might model uplift/subsidence patterns using finite-element or boundary-element models, which are much faster computationally than the ground motion simulations.
Joan mentioned her site-response study, which showed strong east-west and frequency-dependent variability in site-response, but little obvious change going along strike. However, more detailed analyses are needed to improve the resolution and may be undertaken.
Lydia summarized some new published work on the Gales Creek and Boundary Creek faults. Brian is working with Chris Goldfinger to get his offshore structural database published, and how to get it incorporated in the project database. Brian also is working on updating the Quaternary fault database in the PNW.
Scott summarized a paleoseismic trench study of the Canyon River fault (southern Olympic Mtns), which revealed evidence for 1-2 Holocene surface rupturing earthquakes, and was presented at the GSA 2017 meeting. Additional radiocarbon ages are needed to improve earthquake age models. This ~60-km-long fault system is likely kinematically linked at its eastern end to the Seattle fault, and may continue to the west, offshore Grays Harbor. They are hoping to add high-res aeromag in several areas (e.g. covering the Canyon River fault and elsewhere where faults may cross the coastline), tying into existing surveys towards the south that already cover the Doty fault. He noted that analyses of Seattle fault zone marine/lake geophysical data acquired in Feb 2017 are underway, with prelim results presented at the GSA 2017 meeting. The team hopes to follow up with some coring cruises to provide age control and rates of deformation, landslides, and sedimentation. The results of a paleoseismic trench study on the Leech River fault on southern Vancouver Island was presented at the GSA 2017 meeting, and shows the last major earthquake was 1600 years ago, possibly linked to a megathrust event. Lidar mapping of active faults, folds, and landslides continues in Yakima fold and thrust belt. Scott also summarized the GSA session he and academic colleagues organized, entitled "Decadal to Millennial Strain Accumulation at Subduction Zones".
Fred noted that ESC scientists are collaborating with Scripps to establish seafloor geodetic monuments using wavegliders (in Alaska). If positive, the experience will pave the way for needed offshore monitoring in Cascadia.
Lydia has been putting together a ArcGIS database with reflection and other seismic profiles, fault information, landslides inventories, and Lidar footprints with links to data. She plans to add gravity and magnetic profiles with links, offshore landslides, and site of various paleoseismic observations. She explored the database management approach GEM is using, and learned that licenses are an issue that we will need to address. The USGS may have tools to help make the database more accessible and enable others to contribute to it. Others suggested other potential data sources.
Brian said that our FY18 budget will start at the same level as last year, but we should plan on a 10-15% cut. He is putting together a package with Woods Hole for $10k of carbon dates and working on a second with $10-20k (with whom TBD). Brian noted that summary talks about the project to management have been very well received.
Joan encourage everyone to look at the new CDI Subduction Zone Focus Group, join the CDI (send an email to firstname.lastname@example.org), and contribute to the webpages and other features. The project website is part of this broader effort to exchange information.
The project will begin writing a short-form, broad summary of the project, which would serve as a planning doc and way to update management and promote the project. The first step will be for discipline leaders to come to next meeting with a ~2-page summary of where we're at, where we need to go, and how we may get there. We will invite partners outside the USGS to contribute.
The Powell Center proposal submitted last year will be resubmitted for at the end-of-January. Reviewers requested including a social science component in the proposed work, and to learn how to best address this Lydia and Jonathan met with Jeanne Hardebeck (Jeanne was involved in a project about Operational Earthquake Forecasting, which had such a component); Jeanne said they had 4 meetings at the Powell Center, each with differing participants, and only one was focused on the social science component. Lydia noted that we hope to request support for a Fellow who could work on the database; please provide suggestions of potential Fellows to any of the above people. Rob noted that the current Tsunami project may have useful elements to learn from.
To leverage the fact that WHOI project scientists will already be in Santa Cruz the days before, all agreed that a face-to-face project meeting at the PCMG Center in Santa Cruz Feb. 7-8 would be very useful. In addition to presenting results and integrating results and activities, another goal will be to work on a review paper. Non-USGS Colleagues on IPAs focused on Cascadia Recurrence will be invited to participate. Reserve the dates and send agenda ideas and topics to Brian or Joan.
After discussion about the focus and purpose we decided to table any decisions about this until the February project meeting in Santa Cruz. In the meanwhile, Lydia will send around a summary of the responses she got to the solicitation for the pre-GSA workshop.