Capstone reports of the Masters in Earth & Space Sciences - Applied Geosciences

Permanent URI for this collectionhttps://digital.lib.washington.edu/handle/1773/34973

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Establishing Baseline Monitoring for Retreat of the North and South Beach Bluffs of Discovery Park, Seattle, Washington, USA
(2021-03) Sarieddine, Nicole
Surficial Geology and Hydrologic Features of the Port Gamble S’Klallam Tribal Lands, Kitsap County, Washington
(2020-12) Lambert, Crystal
Quaternary Deformation of the Hog Ranch-Naneum Anticline Region, Northeast Kittitas Valley, Washington
(2020-03) Sherrod, Joseph
Geomorphic evaluation of the northeastern Kittitas Valley and Hog Ranch-Naneum Anticline (HRNA) region provides new insight into the recent deformation and uplift by Quaternary faults along the northern range front of Kittitas Valley. I conducted LiDAR and landform mapping as well as a suite of geomorphic analyses to assess recent faulting in northeastern Kittitas Valley potentially linked to Quaternary deformation of the HRNA area. Upon generation of normalized channel steepness (Ksn) maps, the northeastern basin front was identified as a starting point for additional geomorphic analyses, LiDAR mapping and focused field truthing/mapping. I identified a flight of six strath river terraces near the entrance of Coleman Creek into Kittitas Valley. I also identified knickpoints and knickzones along the southern basin front which I was able to correlate to the knickpoint groupings along Coleman Creek. Based on geomorphic evidence and LiDAR mapping two fault scarps were identified; the Facet fault located at the base of the range front and the Dead Coyote fault located ~2 km south of the range front. Regional geologic mapping and aeromagnetic data suggests that initial tectonic uplift along the HRNA predates the Yakima folds. Exact ages of newly identified faults are unknown. The presence of uplifted strath surfaces within Kittitas Valley suggests a more recent deformation history based on the premise that the landscape within the fold province and HRNA was reset to relatively level relief ~15.6 Ma following the emplacement of the Grand Ronde Basalt member of the CRBG; deformation seems to have continued into the Quaternary (Kelsey et al., 2017 and Reidel, 1989).
Optimizing Arsenic Removal in a Groundwater Treatment Cell
(2020-03) Russell, Luke
The goal of this research is to investigate geochemical factors on arsenic removal from groundwater in a groundwater treatment cell. The treatment cell is near Metaline Falls, WA, and is operated by Geosyntec Consultants. Using PHREEQ-C, a program developed by the USGS for chemical modeling, I determined which adsorptive media will remove the most arsenic under site conditions, which ions inhibit or encourage arsenic adsorption, and which ions have the potential to remove arsenic through co-precipitation. The groundwater samples collected from the site were taken to the UW SEFS Analytical Lab for inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentrations of each ion present in the groundwater. These lab results were used for the model validation initial conditions. Historical data collected at the site by Geosyntec was compiled into a database for statistical analysis, which identified conductivity, a proxy for ionic strength, and manganese in solution as two main factors influencing arsenic removal. These factors were further studied using PHREEQ-C. From the modeling results I found that titanium oxide media, particularly MetasorbG manufactured by Graver Technologies, to be the most efficient media at removing arsenic via adsorption. I found that phosphate in the groundwater plays the largest role in inhibiting arsenic adsorption by directly competing with arsenate for surface sites. Conductivity, or ionic strength, will reduce adsorption rates upgradient of the treatment cell and lead to higher arsenic concentrations being delivered to the cell. And, finally, I determined that arsenic is oxidized by manganese oxides and will readily precipitate with manganese ions in high pH conditions, which are typically found upgradient of the treatment cell. For further study, I recommend monitoring phosphate levels in the treatment cell, determining residence time of the water in the treatment cell, performing XRD or FTIR analysis on gravel inside the treatment cell to determine what minerals are precipitating, and starting two batch-scale trials with titanium oxide and manganese oxide media.
Modeled tsunami in Lake Washington from hypothetical ruptures on the Seattle Fault
(2020-03) Richwine, Kathryn
Tsunami deposits from an earthquake on the Seattle fault have been found around the Puget Sound area. Tsunami modeling has been conducted in Puget Sound with the Seattle fault as the initiating event, however published modeling efforts have not investigated the effects of an event from the Seattle fault on the Lake Washington area. The Seattle fault crosses Lake Washington extending east towards Lake Sammamish, and a tsunami generated from this fault could create hazardous conditions along the lake’s shorelines. The parameters of the Lake Washington section of the Seattle fault are applied to create deformation files modeling potential tsunami waves generated from a fault rupture. Four simulations are run with the modern-day lake level and again with the pre-ship canal lake level using the open source software GeoClaw. These eight simulations are analyzed to determine which fault parameters produce a wave that inundates the shoreline. A scenario modeling a 10-meter slip at a depth of 1-km that uses the pre-ship canal lake level and a four-hour runtime determines the extent of inundation and locates potential areas for tsunami deposits. These results show that the shoreline is inundated four times over the first four hours after the earthquake, with maximum tsunami wave heights of 2 m to nearly 4 m arriving within minutes to tens of minutes of the fault rupture. I identify seven low-lying areas susceptible to inundation and suggest three sites for paleotsunami investigation as a test for these models. More extensive modeling of different scenarios and fault parameters is needed to understand the range of possible or likely inundation from a tsunami wave in Lake Washington triggered from the Seattle fault.
Variations in Atterberg Limits for the Lawton Clay with Acidic Pore Fluids
(2020-03) King, Esten
The physical mechanisms that cause slope failure involving the Lawton Clay in the Puget Lowland have been well studied; however, the physio-chemical mechanisms, specifically acidic pore fluid are poorly understood. This study attempts to quantify the effect of pore fluid acidity on the Lawton Clay’s plasticity through Atterberg Limit tests. I conducted multiple runs of the liquid limit and plastic limit tests on rehydrated, homogenized samples of Lawton Clay with acidic solutions mimicking the composition of acid rain in the Seattle area at a pH range of 3.5 to 7. My results show a trend of increasing and then decreasing liquid limit with increasing acidity. This trend is best explained by changes in the thickness of the double diffuse layer and clay minerals’ ability to attract water to its surface. The changes in Atterberg Limits can be used as a proxy for changes in strength. The liquid limit results suggest that variations in pore fluid pH could affect the strength of the Lawton Clay and hence be an important variable in slope stability.
The Lost Lake Landslide: Evidence for an Earthquake-Triggered Landslide Vashon Island, Washington
(2020-03) Jensen, Cole
I address the large-scale stability and potential past and future triggers of the Lost Lake Landslide on Vashon Island, one of the largest mapped landslides in the Puget Lowland. I focus on three landslide triggers; groundwater fluctuation, the Seattle Fault Zone and the Tacoma Fault Zone and identify the most likely trigger. No previous work has analyzed the trigger, age, or stability of the slope. Using an end member approach, I calculate the factor of safety and seismic critical acceleration using a two-dimensional limit equilibrium model for three different Lost Lake Landslide scenarios. Two scenarios are a reconstruction of potential past failure and one scenario is a future failure of the modern slope. Using USGS ShakeMaps I compare modeled Seattle Fault Zone and Tacoma Fault Zone peak ground accelerations with calculated critical accelerations from this study. I find that significant groundwater fluctuations have a surprisingly low influence on large-scale slope stability. Additionally, shaking from either a Seattle Fault Zone or Tacoma Fault Zone earthquake could have triggered the Lost Lake landslide. A Tacoma Fault Zone earthquake is a more likely trigger due to its greater exceedance of the required critical acceleration to cause a slope failure. My results indicate that large magnitude crustal earthquakes can potentially trigger extremely large landslides in the Puget Lowland. As a first order assessment, factor of safety and critical acceleration analysis can potentially identify other large co-seismic landslides in the Puget Lowland.
Port Gamble SíKlallam Tribe Coastal Analysis: Shoreline Change and Extreme Water Levels
(2020-03) Hatfield, Mitchell
The Port Gamble SíKlallam Tribe (PGST) relies on coastal resources for recreation, cultural enrichment, spiritual enhancement, and food. Shoreline change and extreme water levels associated with climate change will impact the future of the PGST. As part of their effort to create a coastal management plan, PGST contracted with our project team to assess geologic aspects of coastal risk and provide recommendations for future monitoring. There is limited information on coastal geomorphology, sediment transportation, and accurate water levels for the PGST coast (Ladd et al., 2016; McCollum et al., 2016). This report addresses shoreline changes, extreme water levels, and coastal hazards associated with climate change along the PGST coastline. I designed a sediment transport monitoring system and conducted water level measurement and analyses. For the first Phase of this project, I assessed historical coastal bluff and shoreline changes using aerial photographs, historical maps and photographs, shoreline topographic surveys, LiDAR analysis, and time-lapse photography. I established shoreline transects for future monitoring of the PGST shoreline and collected baseline data. Using historical T-sheet survey data with modern LiDAR, I found the PGST bluff erosion rates to be less than 3.7 ± 2.8 in/yr over a 162-yr period from 1856 to 2018, with the highest rate along the Tribal Center bluff. Overall, the beach face appears to be relatively stable with little evidence of change from our GNSS beach transect surveys. To evaluate extreme water levels, I collected water level data along the PGST coast and compared our local water level measurements to long-term water level records at Port Townsend and Seattle. Water level data at PGST suggest that using longer water level records from Seattle and Port Townsend would reliably predict flood magnitude and frequency at PGST. Our data show bluffs currently undergo frequent interaction with sea water. During our study, time-lapse photography showed small (< 1 ft) waves with limited wave run-up. However, while not entirely common along the PGST coastline, the combination of larger storm events with high tides may cause flooding of Point Julia and increase bluff erosion rates. Lastly, I assessed the response of coastal flooding to climate change along the PGST coastline. Extreme water levels will flood most of Point Julia under different climate change scenarios. We created a series of inundation maps at Point Julia based on recent sea level rise projections for the area (Miller et al., 2018). Climate change and sea level rise will impact the coastline and how the tribe interacts with it. The development of detailed sediment budgets and shoreline change models requires long-term, high-resolution datasets. While our data provide a baseline, continued study and additional data are recommended to make informed coastal management decisions. I recommend performing frequent (2-3 years, seasonally, or event-aligned) repeat surveys of the established shoreline transects. I recommend yearly surveying for transects in areas of highest erosion (i.e. near the Tribal Center). Flooding and bluff erosion may be mitigated by projects which support large woody debris and increased sediment on beaches. Coastal inundation maps may be helpful for planning and management strategies, considering the time frame and likelihood of each scenario.
Paleowind Direction and the Regional Pattern of Grain Size and Atterberg Limits of Loess in Adams and Lincoln Counties, WA
(2020-03) Chou, Charlie
Loess is a fine-grained floury material carried by wind. The properties of loess are important for infrastructure, agriculture, and construction planning in areas where it is abundant. Eastern Washington is one such location where loess hills dominate the landscape. Past studies have established the geologic origins of loess in Eastern Washington on a broad regional scale. These studies established that paleowinds carried the loess Northeast and that gran size decreases downwind. Naturally, I set out to ask if the paleowind direction and subsequent decrease in grain size can be detected over a smaller two county area. To answer this, I collected 27 samples of loess in Adams and Lincoln counties to determine its index properties and look for regional patterns in grain size. I analyzed grain size, moisture content, and Atterberg limits. Then I evaluated the results in a geographic information system. I found that paleowind influence can be found in the grain size and properties of the loess within Adams and Lincoln counties. The results of my study provide insight into the general characteristics of loess index properties in parts of Eastern Washington and confirm the results from previous work.
Landslide Ages and Implications for a Marine Terrace at Rialto Beach, WA
(2020-03) Bush, Chelsea
Holocene landslides and marine terraces at Rialto Beach, on the Olympic coast of Washington state, may provide clues about the response of the Pacific coastline and adjacent hillslopes to Cascadia subduction zone (CSZ) earthquake activity. This study uses seven 14C samples from four distinct locations within a low-elevation marine terrace at Rialto Beach, WA to date landslides and constrain age of formation of the terrace. Two distinct landslides have been explored in detail: landslide 1 that occurred 800 years cal BP, and landslide 3, that occurred 150-300 years cal BP. The causes and triggers of these slope failure events were explored with new detailed field mapping and timing constraints. Observed landslide evidence includes hillslope geomorphology, soil composition of hillslopes, low-elevation marine terrace composition, and presence of slickenside bedrock-colluvium contacts within a drainage system. On landslide 1 I found a buttress unconformity on the hillslope containing interglacial peat and organic soil layer dated >48-27.5 cal ka, causing extensive zones of perching water that increases pore pressure and lowers slope stability. These geological layers are assumed to span the Rialto hillslope region. Dendrochronology to determine the age of trees on landslide 1 suggests that this slope was partially denuded during an intense winter storm in 1921 AD, potentially causing slope instability. Landslide 3, 150-300 yrs cal BP sits atop the potentially uplifted marine terrace which contains beach deposits older than 500-600 years cal BP. Dating suggests that the slide and uplift may be coseismic with the 1700 AD (270 BP) Cascadia subduction zone rupture. This study adds constraining dates of two distinct landslides that sit on top of the low elevation marine terrace, contributing to studies of coseismic uplift and landsliding on the Olympic coast.
Characterizing the style, composition, and timing of Cedar River Landslide Complex
(2017-03) Polster, Sarah
The Cedar River Landslide Complex (CRLC) is a series of debris flowslides about 3 km down river from the Masonry Dam at Chester Morse Reservoir in the Cedar River Municipal Watershed, the source of drinking water for 1.4 million people in Seattle, WA. These hillslope failures all originated from the terminal moraine deposits of the Puget lobe of the Vashon glacier. The CRLC was discovered in 2009 by new geologic mapping and LiDAR imagery. This study created a landslide inventory, including dimensions, composition and dating all units of the CRLC. Fieldwork involved digging test pits at sites on three different units of the CRLC. Soil samples of all units, including both landslide and undisturbed material were collected. Sieve analysis tests, water content, and mineralogy data were collected. Volumes of each unit of the CRLC were calculated to determine mobility indices for each landslide to compare the CRLC to other large landslides in the region. To estimate the ages of the CRLC slides, radiocarbon samples were collected and surface roughness of the landscape was calculated using GIS. The underlying material in the Cedar River valley is well-graded gravel and the CRLC is composed mostly of well-graded gravel and sand. The landslide material has lower water content than the underlying material. Five absolute dates on three landslides were calculated using radiocarbon dating. The dated CRLC slides range in age from 170 Yr B.P. to younger than 6,850 Yr B.P. Standard deviation of slope (SDS) was used as a measure of surface roughness, the roughness of the CRLC has a small range in values (4.15 to 4.51). No correlation between surface roughness and landslide age was found. Several reasons for this are discussed. No correlation suggests the surface roughness measure used in this study (standard deviation of slope) is not a good measure of landslide age in this watershed. Absolute ages are calculated using organic samples found in soil horizons below the landslide material. As such, these dates represent only the maximum age and may not accurately date the events. A series of landslide triggers are considered, including coseismic, glacial retreat, and precipitation events, however our data set does not allow definitive conclusions or elimination of any particular trigger. Future work, including gathering more samples for landslide ages, is needed to consider the full landslide history of this complex.
A comparative Analysis of Grain Size distributions and Cross Sections using an Oblique Photoset on the Nisqually Riverbed Adjacent to Longmire In Mount Rainier National Park
(2019-03) Rains, Austin
Collecting cobble counts and gathering cross sections out in the field can be a tedious and time consuming process. An attempt was made at expediting this process using structure from motion technology to create an orthophoto and a digital surface model of the Nisqually riverbed adjacent to Longmire in Mount Rainier National Park. An oblique photoset was gathered of the Nisqually riverbed using a telescoping pole with a digital camera and high-precision GPS mounted at the end of it. This photoset was then used to create a point cloud, an orthophoto, and a digital surface model using Pix4D. Automated cobble counts were gathered using two different Matlab scripts; DigitalGrainSize, and BASEGRAIN. DigitalGrainSize proved to be fairly accurate and may act as a replacement if grain sizes 11 mm and below are not relevant to a study. An automated grain size distribution may be even more accurate if a higher resolution digital surface model is produced or if a single photo is used instead of an orthophoto. BASEGRAIN did not perform as well and did not detect both smaller and larger grain sizes. Cross sections were derived from the digital surface model and have a high resolution when compared to 1 m resolution lidar in the same area. Channels that are only active at higher flows can be seen clearly in the digital surface model cross sections as well. The only drawbacks are that vegetation, and water are included in the digital surface model, so it cannot measure beneath the water’s surface as opposed to a total station, and the elevation was approximately 60 feet lower than actual elevation. This was likely due to a GPS error. I believe that these two applications show promise, especially if these techniques are refined.
Geomorphic Reconstruction of Alki Point in West Seattle Based on Chronostratigraphic Relationships of Mid-Late Holocene-Aged Intertidal Deposits
(2019-12) Dunham, Eric
A tombolo may have tied a bedrock knoll at the western tip of Alki Point to the mainland before a large magnitude 7 or greater earthquake ruptured within the Seattle fault zone, resulting in ~23 ft of uplift at Alki Point and exposing shallow beach/intertidal deposits. The purpose of this study was to (1) reconstruct the geomorphology of Alki Point during the mid-late Holocene in order to understand the conditions under which marsh deposits at Alki Point were formed, and (2) partially characterize the spatial variability of marsh deposits at Alki Point. The motivation behind this work was to provide future paleoseismic studies a basis as to where reliable paleoenvironmental data within marsh deposits can be found. This data can be used by paleoseismologists to reconstruct the abrupt or gradual nature of environmental changes that may be related to coseismic uplift or other environmental factors. Data from three sites at Alki Point and one at a marsh near Restoration Point on Bainbridge Island include; (1) stratigraphic observations from borings and trench observations, (2) radiocarbon ages, and (3) elevation data from microfossil assemblages. Two-foot contours constructed over LiDAR data for Alki Point show low topographic relief trending northwest-southeast where a tombolo may have connected a bedrock knoll near the western tip of Alki Point to the mainland, with beach ridges shoreward of and parallel to a suspected tombolo. The direction of the shore-drift at Alki Point is from the south, driving the propagation of waves towards the southern shore of Alki Point. These factors would be the most important control on sediment transport, and would have assisted in shaping a tombolo along the southern margin of Alki Point. A sample taken 6 ft above MLLW from a tree log in the middle of a peat layer shoreward of the current beach ridges had a radiocarbon age of 6264 to 6529 cal yr B.P. This would have required that one or more beach ridge(s) were further offshore from where this peat would have deposited in a quiescent intertidal environment. As sea levels rose to near to the present level ~5500-6000 cal yr B.P., the beach ridge(s) would have transgressed to the current position. The formation of a tombolo with shoreward beach ridges may have allowed for one or more marshes to form on Alki Point since shore-drift derived from the south. Ages on beach deposits below the middle peat layer at Alki Playground are between 3078 to 4826 cal yr B.P., and the age on the upper peat layer at Alki Playground is modern (after 1950 AD) to 297 cal yr B.P. This suggests that the middle peat layer encountered at two of the Alki Point sites, was deposited sometime between 297 to 3078 cal yr B.P., after a tombolo would have formed.
Using the Rockfall Activity Index to assess the impact of scaling on rock fall activity at Glitter Gulch, Alaska
(2019-06) Marohl, Kristen
This research examines terrestrial-laser scan data on a road cut in the Glitter Gulch area of Alaska, immediately preceding and following a slope stabilization project, noting changes in rock fall and comparing the work done during excavation to the hazardous areas identified through the "Rockfall Activity Index (RAI) model (Dunham et al., 2017). Using the RAI for the study we may also determine its efficacy by noting if the model identified the same high hazard areas as engineers. In this report, I compare RAI predictions of future failure with on-the-ground assessments of hazard as indicated by scaling activity.
Predicting the Position of Fault Strands through Borehole Correlation of the Top of Tertiary Bedrock in the Seattle Fault Zone, Seattle, Washington
(2019-12) Maloney, Devin A.
Only a few strands of the Seattle Fault Zone have been identified on land in Seattle, Washington due to heavy manipulation of the landscape by repeat glaciations, geomorphic reworking, and the interference of the growing metropolitan community concealing potentially dangerous active faults below the surface. Previous difficulty locating faults on the ground surface led to the idea of using geotechnical boring logs to ìsee intoî the subsurface structure. Can the depth to the contact between Quaternary deposits and Tertiary bedrock, obtained from existing geotechnical boring logs, be used to predict the locations of fault strands in the Seattle Fault Zone in Seattle? The University of Washington Pacific Northwest Center for Geologic Mapping Studies (GeoMapNW) database contains thousands of geotechnical boring logs readily available. Over 18,000 boring logs were processed using the computer programming language Python to select boring logs containing bedrock-related terms describing Blakely Harbor Formation, Blakeley Formation, Tukwila Formation, and any other bedrock in Seattle. This process isolated 1700 boreholes that potentially intersected bedrock. Each of the 1700 boring logs were individually categorized to determine if the Python code was valid. This process reduced the queried boring logs to 809 boreholes containing bedrock within the Seattle Fault Zone. The boreholes containing bedrock were used to construct preliminary contours of the bedrock surface in AutoCAD Civil 3D. Both boreholes containing bedrock and boreholes not containing bedrock were used to generate 108 geologic cross sections using the geographic information system (GIS) Geologic Cross Section Toolbox developed in 2018. The variation in depth to the contact between Quaternary deposits and Tertiary bedrock was evaluated in the cross sections highlighting 66 anomalies in southeast Seattle. The anomalies were checked against the triangular irregular network (TIN) surface and contours generated in AutoCAD Civil 3D to better visualize the Seattle Fault Zone structure. The anomalies ranged from potential faults and geomorphic alterations to possible human alterations such as hillslope grading along Interstate 5. Fifty percent of the anomalies were identified as potential faults based on the continuation of offset patterns in neighboring cross section. Published fault locations from multiple reliable sources supplied by the U.S. Geological Survey (USGS) and Washington State Department of Natural Resources (DNR) were checked to assess the connection of anomalies to mapped faults. Some of the anomalies found through borehole correlation suggest revisions and continuations of existing published fault locations through the City of Seattle. Identifying potential fault anomalies by correlating detailed boring logs proved successful and could be applied to complex fault zones worldwide. The next step is to investigate the anomalies identified as potential faults to determine if they are representations of faults strands within the Seattle Fault Zone.
Evaluating River Profile Geometries to Identify Evidence of Active Deformation Associated with the Doty Fault Zone in Southwest Washington
(2019-06) Tavangar, Varqa
In 1996, 2007, and 2009, flooding of the Chehalis River near the Town of Chehalis in southwest Washington severely impacted infrastructure and property. Damage was such that Interstate 5, the major transportation throughway in this region, was closed for several days. In 2012, the Washington State Geological Survey and United States Geological Survey began an assessment of the seismic hazards posed by the regional and local geologic systems on proposed construction of a dam near the Town of Pe Ell, Washington. Of these structural systems, the Doty Fault Zone is of interest as; (1) its level of activity is not well known, (2) its geometry is not described in detail, (3) it extends along a portion of the Chehalis River, and (4) would pose a hazard to the construction of the dam if it were active. The Doty Uplift (DU) is one of several basement uplifts in southwest Washington, and the western extent of the Doty Fault Zone bounds the southern boundary of the DU. In this report, the morphology of streams draining the DU are studied and characterized to identify topographic evidence of active deformation associated with the Doty Fault Zone. I performed a digital analysis of the morphology of twenty-two streams, including the description of channel steepness and longitudinal-profile geometry and the identification of knickpoints, or locations of sharp changes in the channel slope along each river. The influence of lithology and the discrimination between discrete (fault-related) and persistent (anticlinal and lithologic) forcings were considered in the analysis. Patterns in the normalized channel steepness index (ksn) across the study site show increasing ksn values moving upstream along drainages within the DU. These range from less than ~150m on the outer margins of the DU to ~400m within it. Anomalous high ksn values that rise to up to 800m point to areas on long profiles that may be identified as knickpoints. Ten knickpoints found within the DU are identified, located between elevations of 137 and 320 meters. They range in size from ~4-meter-deep steps to 36 meter near-vertical drops over distances that range between 6 and 45 meters. Nine of the knickpoints are located at higher elevations that the Doty Fault, yet they do not form similar geometries at similar elevations. In addition, the location of the knickpoints in relation to lithologic boundaries and mass wasting deposits introduces complicating factors that make tying these features to fault-related formation tenuous. Six knickpoints are located within the Crescent Formation, three are located within sedimentary units, and one at a lithologic boundary where streams cross over rocks of variable resistances. The lack of spatial continuity and differences in knickpoint form does not point to the influence of an active Doty Fault. The spatial patterns of normalized channel steepness indices and knickpoints within and around the DU do not point to discrete, fault-offset related causes. Instead, they are likely the product of the structural signature of the Crescent Formation, accented by the influence of lithologic boundaries and mass-wasting deposits. Further investigations of the adjustment of streams of the Doty Hills, thorough in-channel surveys and wider-scale basin instability analyses would help elucidate the topographic evolution of this area.
Evaluation of Subsurface Impacts on Occurrence of Sand Boils from the 2001 Nisqually Earthquake in the SoDo Neighborhood of Seattle, Washington
(2019-06) Simon, Morgan
The 6.8 magnitude Nisqually earthquake occurred on February 28th, 2001 causing liquefaction in multiple areas of Seattle, mostly in the SoDo neighborhood. Following the earthquake, scientists recorded field observations of the liquefaction in Seattle, which was compiled into a database. While the SoDo neighborhood is mapped as having the same liquefaction potential throughout, large areas did not show above-ground signs of liquefaction, such as sand boils. I looked at the subsurface in areas where sand boils were reported and in areas where no sand boils were reported to determine if significant geologic differences occur in the subsurface that could explain why liquefaction occurred in some areas and not others. The study area has undergone multiple glaciations, and is part of the former Duwamish River delta, occupying a former subglacial trough. In the last century, humans have modified the delta and associated tide flats to expand buildable land by adding variable thicknesses of fill, primarily sourced from nearby glacial deposits. To examine the subsurface, I used the GeoMapNW subsurface database to find borings adjacent to sand boils and borings at sites where sand boils were not reported. I identified target locations, where sand boils did and did not occur, and where good subsurface data are available. I compared the subsurface stratigraphy to depths of 40 feet from selected borings in the target areas and looked at density, sand content and clay content. I also compared the ratio of the thickness of fine-grained sediment to coarse-grained sediment. To compare the densities of the subsurface, I performed clean sand corrections and performed modeling to generate a Liquefaction Potential Index (LPI) at the target locations. I found that areas with capping clay layers at/near the surface of greater than 3ft in thickness or significant amounts of clay within the upper 40 feet were more common in areas where no sand boils were reported. I also found that areas where no sand boils were reported typically had higher ratios of fine-grained thickness to total thickness, and that these ratios were higher in the eastern portion of the site area. The LPIs at borings adjacent to sand boils were calculated to be high risk or very high risk. The LPIs for the borings chosen in areas where there were no sand boils ranged from low risk to very high risk. Some of the high or very high risk boring locations had caps of clay or near surface layers had undergone construction-related compaction, which may have resulted in liquefaction not reaching the surface and instead potentially spreading laterally. For the Nisqually earthquake the LPI alone does not adequately predict whether or not liquefaction will occur at the ground surface in the SoDo area due to geologic or human-influenced variability. LPI will over predict liquefaction at the ground surface for the SoDo area.
Analysis of the Timing of Building Displacement during Intense Seismic Shaking for three Earthquakes, 2001 Mw 6.8 Nisqually (Washington State), 2017 Mw 7.1 Puebla (Mexico), 2018 Mw 7.1 2018 Anchorage (Alaska)
(2019-06) Sackman, Nancy A
Localized intense ground shaking from strong earthquakes pose significant hazards to humans including building damage that may lead to structural failure and possible collapse. Building failure can cause harm or loss of life and also result in economic loss. For example, in the 2017 Mw 7.1 Puebla Earthquake in Mexico, more than 300 people died with the majority of those deaths in Mexico City. More than 3000 buildings were damaged and 44 buildings collapsed (Grillo, 2017). Structural engineers and designers study rigorously whether or not a building may experience damage and/or structural failure. However, little emphasis has been placed on the timing of displacement and/or failure during strong shaking. For example if a building were to fail late in a long-duration earthquake while the interstory drift rose to destructive levels, the advice to its occupants might be to attempt to evacuate. Therefore, I undertook an analysis to explore factors that might impact and constrain the variability in timing to maximum building displacement. To provide a range of estimates of building response timing to shaking, I explored the buildings’ temporal responses to different ground motions from seismic inputs recorded at different seismic stations. I modeled the building responses as a simple single degree of freedom oscillator, programmed in the Python programming language. I used ground motion recordings from three deep “intraslab” subduction zone earthquakes characterized by normal faulting, the 2001 Nisqually (Washington), the 2017 Puebla Earthquake, and the 2018 Anchorage Earthquake ( Figures 1-3). Using computer simulations, I tested the responses of a range of concrete building heights from 1 to 30 stories tall. Results show that the time to maximum building displacement changes with the height of a building and varies with distance to rupture as well as local site responses. While perhaps not an accurate indication of the absolute time when a building would fail, the time between the onset of an earthquake and the maximum displacement observed in the modeled building response can be interpreted as a proxy for time to failure and perhaps its relative sensitivity to seismic shaking. Earthquake Early Warning (EEW) is a newly emerging technology that uses real-time seismic data, rapid telecommunications, and new real-time processing algorithms to provide several seconds to up to 3 minutes of advanced warning of strong shaking to an at risk population. The actual warning time depends on factors like the latency of the system and the distance the earthquake source is from the targeted at-risk population. Prior to EEW, the most efficient life saving action that disaster prevention officials could offer was, “when you feel shaking, drop, cover and hold on”. With EEW, there is now the possibility of an additional response. Namely, if the timing of maximum building displacement from strong shaking were known for different storied buildings, it might be possible that warnings could be issued with sufficient lead time to allow people to exit the structure rather than shelter in place in a collapsing building. An EEW-mediated evacuation strategy would depend on the range of timing between an earthquake and a building collapse. The single degree of freedom oscillator shows it can be a first step in quantifying the timing of building displacement during strong shaking. Understanding the tectonic setting, the distance of the rupture to an at-risk population, earthquake recurrence intervals, aftershock sequencing, earthquake directivity and seismic amplification should also be put into context when modeling earthquakes.
Sediment accumulation in a manipulated bay of Puget Sound, Bellingham, WA.
(2019-06) Benson, Mary Alice
Mud Bay, located in Bellingham, Washington at the north end of Chuckanut Bay, is filling with sediment at a rate greater than projected sea-level rise. This is worrisome as the bay is an important habitat for eelgrass meadows, shellfish beds, and birds. Also, Chuckanut Creek, the primary fluvial input into the bay, has historically been a salmon-spawning ground. In 2013 the City of Bellingham identified this bay and pocket estuary as a top-ranked 10-year restoration priority due to degradation of wildlife habitat from sediment accumulation. Anthropogenic stressors that could increase sediment accumulation include logging, mining and quarrying in proximal areas during the late 1800s to early 1900s. In the 1920s a rip-rap railroad causeway was constructed across the mouth of the bay, limiting tidal and storm wave energy. During the construction of Interstate 5 in the early 1960s, additional sediment could have been transported to the bay by Chuckanut Creek. To determine if the bay is filling, I collected cores from 4 sites in the intertidal zone of the study area, near where Chuckanut Creek enters the bay. Using 210Pb, I calculated the accumulation rates to range from 0.20 to 1.07 cm yr-1, with spatial variations attributed to differences in tidal and fluvial energy at each coring location. This accumulation rate was corroborated using 137 Cs at one coring site, and depth-of-penetration values for both radiochemical analyses agree. All 210Pb profiles indicated constant accumulation rates, and a link between increased accumulation and construction of the causeway was not found. Grain size analyses and X-radiography images were used to interpret sedimentation patterns in the bay. Grain-size distributions indicate that the east side of the bay is finer grained. There is potentially a sediment signature that can be linked to the construction of Interstate 5. Sea level has risen by 0.12 cm yr-1 since 1934 and relative sea-level projections range from ~0.38 to 0.71 cm yr-1 by 2100 so accommodation space has, and continues to, fill faster than sea-level rise in the bay.
Rockfall Reconnaissance and Stability Assessment: Frenchman Coulee, WA
(2019-03) Guzek, Ethan
The Sunshine Wall, a 30-meter tall outcrop of Columbia River Flood Basalt, is a popular climbing wall within Frenchman Coulee, located in central Washington. This study investigates the stability of the columnar basalt that makes up the wall, to educate climbers on how this slope fails and provide qualitative estimates of how close portions of the wall are to failure. Because the wall predominantly consists of columnar basalt, the most probable mode of large-scale slope failure is toppling. Some portions of the wall are “entablature,” a highly fractured basalt which presents a significant risk with regard to rockfall. The stability of the Sunshine Wall was assessed using geomechanical rock mass classification systems, geometric measurements, and kinematic analyses. Data were collected using traditional field methods along with digital photogrammetry, from which I produced a high-density 3D point cloud and digital model of the wall. By combining traditional field methods and modern technology, a thorough and organized investigation was conducted. Data obtained by implementing these methods includes rock strength, rock mass ratings (quality), and kinematic analyses, which indicate that the columns are most likely to fail in direct toppling. Further, a simple qualitative center-of-mass analysis was applied to determine how close these columns may be to failure. Although many of the columns are stable, some are precariously balanced and may be unstable. In summary, the high strength of the intact rock, rough fracture surfaces, and lack of steeply dipping daylighting joints add to the stability of the slope. Low quality rock zones, areas with high densities of randomly oriented fractures, and the presence of potentially weak underlying material add to the instability of the slope. Climbers should use caution while belaying under zones of entablature, which are delineated in this study. They should also be aware of the conditions that lead to elevated risks of toppling failure. These conditions include columns that lean significantly away from the slope creating a large gap at the top of the colonnade, columns that are narrow and tall, and the presence of lower quality rock coinciding with the point at which a column might rotate away from the slope. To monitor the toppling hazard, the movement of key columns could be evaluated by repeatedly measuring the gaps at the top of the colonnade over time. These measurements will help to evaluate the significance of this hazard and whether or not these failures are slow and continuous or unpredictable and sporadic.

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