Cascadia Region Research Articles

Substantial Cold Bias During Wintertime Cold Extremes in the Southern Cascadia Region in Historical CMIP6 Simulations

AbstractGlobal climate models often simulate atmospheric conditions incorrectly due to their coarse grid resolution, flaws in their dynamics, and biases resulting from parameterization schemes. Here we document a bias in the magnitude and extent of minimum temperature extremes in the CMIP6 model ensemble, relative to ERA5. The bias is present in the southern Cascadia region (i.e., Pacific Northwestern United States and southwestern British Columbia, Canada, spanning from the coast to the Rocky Mountains), with some models showing a bias magnitude in excess of −10°C in the first percentile of daily winter minimum temperature. The sea level pressure pattern for these events is similar in CMIP6 models and ERA5, showing high anomalies in the Northeast Pacific that are indicative of an atmospheric blocking pattern and consequently more northerly flow. Though this atmospheric blocking pattern is typically concurrent with cold winter temperatures across much of North America, Rocky and Cascade mountain ranges prevent the cold air from reaching the southern Cascadia region as confirmed by the observations and reanalysis. Our results suggest that the bias in CMIP6 minimum temperatures is a result of unresolved topography in the Rockies and Cascade mountain ranges, such that the terrain does not adequately block cold air advection from reaching the southern Cascadia region.

The Cascadia Innovation Corridor: The role of social entrepreneurship in the making of a North American innovative cross-border region

There remains a dearth of literature dedicated to urban core-to-core cross-border regions, especially ones described as highly innovative. Hence, there is a growing need to advance the concept of a cross-border region, especially through the lens of clusters and smart system innovation policy by considering what might be the role of social entrepreneurship regarding its development. Thus, this article focuses on how an innovative cross-border region may be emerging between the bi-national Cascadia region, and analyzes the role of corporate driven social entrepreneurship in its advancement.

Detection and description of four Vespa mandarinia (Hymenoptera, Vespidae) nests in western North America

Vespa mandarinia Smith 1852 is a semi-specialized predator of other social Hymenoptera and one of the two largest species of Vespa. Several individuals of this predatory wasp were detected in Canada and the United States in 2019, including an entire nest that was located and destroyed on Vancouver Island, British Columbia. The Washington State Department of Agriculture and the United States Department of Agriculture’s Animal and Plant Health Inspection Service have collaborated to survey Washington State for V. mandarinia since 2020, using traps staffed by agency personnel, collaborators from local governments and nongovernmental organizations, and the general public. Trap data and public reports were used to select sites for live-trapping or net surveys, and live hornets captured in these efforts were subsequently collected and fitted with radio tags to locate nests. The survey ultimately led to the discovery of a V. mandarinia nest in October 2020, and three nests in August and September 2021. All of the nests were located within in red alder trees (Alnus rubra), with one just above the ground in a standing dead tree, and the other three in cavities ~2 to 5 meters above the ground in living trees. The number of combs in each nest varied between four and ten, cells between 418 and 1,329, and total hornets per nest between 449 and 1,474 (including immature and mature stages). Together, the four nests indicate an incipient population of V. mandarinia in the Cascadia region, and ongoing action by local, state, provincial, and federal governments, and residents of both countries is required to avoid the establishment of this exotic species in the region.

Cascadia: Subduction and People

The well-studied Cascadia subduction zone has enriched our general understanding of global subduction zones. This Elements issue explores the interconnected set of processes that link geodynamics, tectonics, and magmatism at depth and the surface expressions of these processes, which shape the landscape and give rise to natural hazards in the Cascadia region. This issue also addresses the impact of subduction zone processes on human populations using cultural records, and reviews the state of knowledge of Cascadia while highlighting some key outstanding research questions.

The Role of Subduction Zone Processes in the Cultural History of the Cascade Region

The Cascadia subduction zone continuously shapes the landscape of the Pacific Northwest of North America and the cultures of its inhabitants. The impacts of subduction processes on Pacific Northwest societies and cultures are varied, but Native Americans and European settler cultures alike have described geological processes through oral histories and have relied on resources provided by the subduction zone. Indigenous peoples focus many aspects of their religious practices and art around the geohazards of the Cascadia region, and our melded modern cultures continue to take part in storytelling related to subduction zone hazards through movies and other forms of narration.

How does strategic choice affect the performance of community forest enterprises? A study in the Cascadia region

Proponents of decentralized forest governance make a compelling case that community forest enterprises (CFEs) can aid in sustainable and equitable utilization of forest resources. The effectiveness of CFEs is thus dependent on their ability to balance social, environmental, and financial performance. In this paper, we examine the relationship between a commonly recommended differentiation strategy and CFE effectiveness. Using data obtained through a survey administered on 51 CFEs located in the Cascadia region (British Columbia province of Canada; and Oregon and Washington states of the United States), we find that CFEs pursuing a differentiation strategy are able to balance social, environmental, and financial objectives. Further, recognizing that all CFEs cannot pursue a differentiation strategy, and some may not even have a defined strategic orientation, the paper compares social, environmental, and financial performance of CFEs pursuing a differentiation strategy, a hybrid strategy (a combination of differentiation and cost leadership strategy), and no defined strategy. This analysis reveals that CFEs pursuing a hybrid strategy deliver better financial performance than those with no defined strategy but are similar to those pursuing a differentiation strategy.

Assessing Margin-Wide Rupture Behaviors Along the Cascadia Megathrust With 3-D Dynamic Rupture Simulations.

From California to British Columbia, the Pacific Northwest coast bears an omnipresent earthquake and tsunami hazard from the Cascadia subduction zone. Multiple lines of evidence suggests that magnitude eight and greater megathrust earthquakes have occurred ‐ the most recent being 321 years ago (i.e., 1700 A.D.). Outstanding questions for the next great megathrust event include where it will initiate, what conditions are favorable for rupture to span the convergent margin, and how much slip may be expected. We develop the first 3‐D fully dynamic rupture simulations for the Cascadia subduction zone that are driven by fault stress, strength and friction to address these questions. The initial dynamic stress drop distribution in our simulations is constrained by geodetic coupling models, with segment locations taken from geologic analyses. We document the sensitivity of nucleation location and stress drop to the final seismic moment and coseismic subsidence amplitudes. We find that the final earthquake size strongly depends on the amount of slip deficit in the central Cascadia region, which is inferred to be creeping interseismically, for a given initiation location in southern or northern Cascadia. Several simulations are also presented here that can closely approximate recorded coastal subsidence from the 1700 A.D. event without invoking localized high‐stress asperities along the down‐dip locked region of the megathrust. These results can be used to inform earthquake and tsunami hazards for not only Cascadia, but other subduction zones that have limited seismic observations but a wealth of geodetic inference.

A generic soil velocity model that accounts for near-surface conditions and deeper geologic structure

Near-surface soil conditions can significantly alter the amplitude and frequency content of incoming ground motions – often with profound consequences for the built environment – and are thus important inputs to any ground-motion prediction. Previous soil-velocity models (SVM) have predicted shear-wave velocity profiles based on the time-averaged shear-wave velocity in the upper 30 m (VS30). This article presents a generic soil-velocity model that accounts both for near-surface conditions (VS30) and deeper geologic structure, as represented to the depth at which the profile reaches a velocity of 1.0 km/s (Z1.0). To demonstrate the advantages of our new SVM, we apply it to the Cascadia Region of North America, where numerous geologic basins and glaciated landscapes give rise to a wide range of VS30 and Z1.0 combinations. This soil velocity model yields good estimates of site response across all site conditions, and significantly improves upon a model calibrated using only VS30 data. In conjunction with existing models that describe the deep velocity structure of the region (e.g., (Stephenson et al., 2017) [27]; the proposed model is particularly suited for use in regional-scale predictions of site response, liquefaction, landslides, infrastructure damage, and loss. The proposed methodology is broadly applicable to the development of SVMs elsewhere, and with improved understanding of near-surface and deep velocity structures, can facilitate more accurate ground-motion predictions globally.

The Proximity Puzzle in Cross-Border Regions

ABSTRACTThis paper studies cross-border cooperation at the US-Canadian Cascadia region by implementing an in-depth analysis to examine the role of cognitive proximity as a proxy for favourable conditions for cross-border economic interaction (measured as co-publications, co-patents and networking). The analysis deploys primary and secondary data sources analysed with qualitative and quantitative methods. Based on the results, the case study region demonstrates what is termed as a ‘proximity puzzle’: relatively low levels of economic interaction despite high cognitive proximity across the border. The paper concludes by discussing, based on survey data, the barriers that impede cross-border economic interaction.

Comparison of British Columbia and Washington State City Powers

This project focuses on two cities in British Columbia (Vancouver and Surrey) and two in Washington State (Seattle and Bellevue). . All four cities lie in the Cascadia Corridor (west of the Cascade Range, which stretches from lower mainland British Columbia to Oregon) and share common attributes, including strong technology sectors, a shortage of affordable housing, and unusually high levels of homelessness for cities in developed countries. Equally, these cities occupy the traditional, historic, and largely unceded territories of the local Indigenous peoples. The cities face common problems, including transportation, housing, and the opioid crisis. What legislative and policy tools are available to them? What can we learn by comparing the legal powers of cities in British Columbia and in Washington State, in two neighboring national federal systems? The paper lays the legal groundwork for thinking about how innovation in one city might influence and guide innovation in other cities across borders, particularly in those policy areas that challenge urban communities and governance This guide outlines the basic legal framework of these cities, providing a basic guide to municipal power in the two jurisdictions, as well as points of similarity and difference as the border between Canada and the United States is crossed. Thus, chapters engage with questions about the relationship between cities and other levels of government, the structure and sources of municipal authority, and the legislative and policy tools available to cities. The paper is the product of a cooperative venture of faculty and students from the University of British Columbia Peter A. Allard School of Law and the University of Washington School of Law. More broadly, this project is part of the Cascadia Urban Analytics Cooperative (CUAC), an “applied, interdisciplinary, regional venture that brings together academic researchers, students, and public stakeholder groups” to address issues affecting residents of the Cascadia region. A joint initiative between Microsoft, the University of Washington, and the University of British Columbia, CUAC seeks to use data science to inform and fuel social objectives in urban contexts. CUAC projects cover a broad range of topics but CUAC specifically endeavors to address issues related to “equitable transportation, housing stability, population health and responsible data science” throughout Cascadia.

The Most Recent Cascadia Earthquake and Native American Narratives

The Cascadia subduction zone fault lies just off the Pacific coast of the USA and Canada. Although this fault has been seismically inactive over the written history of the Cascadia region, it has the potential to produce catastrophic earthquakes and tsunamis. A variety of dating methods have been used to show that the most recent Cascadia earthquake occurred in 1700. Among these methods is an informal analysis of oral traditions handed down by Native American peoples that appear to refer to a major earthquake in this region. A central difficulty in analyzing these narratives quantitatively is their use of a generation and other qualitative measures of time that have no fixed lengths. Here, these narratives are analyzed under an explicit statistical model of the lengths of these measures. The results raise a question about the previous conclusion that these narratives all refer to the most recent Cascadia earthquake.

Functional emulation of high resolution tsunami modelling over Cascadia

The rarity of tsunamis impels the scientific community to rely on numerical simulation for planning and risk assessment purposes because of the low availability of actual data from historic events. Numerical models, also called simulators, typically produce time series of outputs. Due to the large computational cost of such simulators, statistical emulation is required to carry out uncertainty quantification tasks, as emulators efficiently approximate simulators. There is thus a need to create emulators that respect the nature of time series outputs. We introduce here a novel statistical emulation of the input-output dependence of these computer models. We employ the Outer Product Emulator with two enhancements. Functional registration and Functional Principal Components techniques improve the predictions of the emulator. Our phase registration method captures fine variations in amplitude. Smoothness in the time series of outputs is modelled, and we are thus able to select more representative, and more parsimonious, regression functions than a fixed basis method such as a Fourier basis. We apply this approach to the high resolution tsunami wave propagation and coastal inundation for the Cascadia region in the Pacific Northwest. The coseismic representation in this analysis is novel, and more realistic than in previous studies. With the help of the emulator, we can carry out sensitivity analysis of the maximum wave elevation with respect to the source characteristics, and we are able to propagate uncertainties from the source characteristics to wave heights in order to issue probabilistic statements about tsunami hazard for Cascadia.

Overview of Ground-Motion Issues for Cascadia Megathrust Events: Simulation of Ground-Motions and Earthquake Site Response

Ground motions for earthquakes of M7.5 to 9.0 on the Cascadia subduction interface are simulated based on a stochastic finite-fault model, and used to estimate average response spectra for reference firm soil conditions. The simulations are first validated by modeling the wealth of ground-motion data from the the 2011 M9.0 Tohoku earthquake of Japan. Adjustments to the calibrated model are then made to consider average source, attenuation and site parameters for the Cascadia region. This includes an evaluation of the likely variability in stress drop for large interface earthquakes, and an assessment of regional attenuation and site effects. We perform best-estimate simulations for a preferred set of input parameters. Typical results suggest mean values of 5%-damped pseudo-acceleration in the range from about 100 to 200 cm/s2, at frequencies from 1 to 4 Hz, for firm-ground conditions in Vancouver. Uncertainty in most-likely value of the parameter representing stress drop causes variability in simulated response spectra of about ±50%. Uncertainties in the attenuation model produce even larger variability in response spectral amplitudes – a factor of about two at a closest distance to the rupture plane (Rcd) of 100 km, becoming even larger at greater distances. It is thus important to establish the regional attenuation model for ground-motion simulations, and to bound the source properties controlling radiation of ground motion. We calculate theoretical 1D spectral amplification estimates for four selected Fraser River Delta sites to show how the presence of softer sediments in the region may alter the predicted ground motions. The amplification functions are largely consistent with observed spectral amplification at Fraser River delta sites, suggesting amplification by factors of 2.5 to 5 at the peak frequency of the site; we note that deep sites in the delta have a low peak frequency, ~0.3 Hz. This work will aid in seismic hazard assessment and mitigation efforts in the active Cascadia region of southwestern B.C. An important consideration is that the uncertainties are large and present a dominant unknown when assessing seismic risk. We find that variability in the expected motions exceeds a factor of two even on rock-like sites, with uncertainty

Accuracy enhancement of GPS time series using principal component analysis and block spatial filtering

This paper focuses on performance analysis and accuracy enhancement of long-term position time series of a regional network of GPS stations with two near sub-blocks, one block of 8 stations in Cascadia region and another block of 14 stations in Southern California. We have analyzed the seasonal variations of the 22 IGS site positions between 2004 and 2011. The Green’s function is used to calculate the station-site displacements induced by the environmental loading due to atmospheric pressure, soil moisture, snow depth and nontidal ocean. The analysis has revealed that these loading factors can result in position shift of centimeter level, the displacement time series exhibit a periodic pattern, which can explain about 12.70–21.78% of the seasonal amplitude on vertical GPS time series, and the loading effect is significantly different among the two nearby geographical regions. After the loading effect is corrected, the principal component analysis (PCA)-based block spatial filtering is proposed to filter out the remaining common mode error (CME) of the GPS time series. The results show that the PCA-based block spatial filtering can extract the CME more accurately and effectively than the conventional overall filtering method, reducing more of the uncertainty. With the loading correction and block spatial filtering, about 68.34–73.20% of the vertical GPS seasonal power can be separated and removed, improving the reliability of the GPS time series and hence enabling better deformation analysis and higher precision geodetic applications.

Detecting transient signals in geodetic time series using sparse estimation techniques

AbstractWe present a new method for automatically detecting transient deformation signals from geodetic time series. We cast the detection problem as a least squares procedure where the design matrix corresponds to a highly overcomplete, nonorthogonal dictionary of displacement functions in time that resemble transient signals of various timescales. The addition of a sparsity‐inducing regularization term to the cost function limits the total number of dictionary elements needed to reconstruct the signal. Sparsity‐inducing regularization enhances interpretability of the resultant time‐dependent model by localizing the dominant timescales and onset times of the transient signals. Transient detection can then be performed using convex optimization software where detection sensitivity is dependent on the strength of the applied sparsity‐inducing regularization. To assess uncertainties associated with estimation of the dictionary coefficients, we compare solutions with those found through a Bayesian inference approach to sample the full model space for each dictionary element. In addition to providing uncertainty bounds on the coefficients and confirming the optimization results, Bayesian sampling reveals trade‐offs between dictionary elements that have nearly equal probability in modeling a transient signal. Thus, we can rigorously assess the probabilities of the occurrence of transient signals and their characteristic temporal evolution. The detection algorithm is applied on several synthetic time series and real observed GPS time series for the Cascadia region. For the latter data set, we incorporate a spatial weighting scheme that self‐adjusts to the local network density and filters for spatially coherent signals. The weighting allows for the automatic detection of repeating slow slip events.

The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

Abstract The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic–Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE–SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

Episodic tremor triggers small earthquakes

It has been suggested that episodic tremor and slip (ETS), the weak shaking not associated with measurable earthquakes, could trigger nearby earthquakes. However, this had not been confirmed until recently. Vidale et al. monitored seismicity in the 4‐month period around a 16‐day episode of episodic tremor and slip in March 2010 in the Cascadia region. They observed five small earthquakes within the subducting slab during the ETS episode. They found that the timing and locations of earthquakes near the tremor suggest that the tremor and earthquakes are related. Furthermore, they observed that the rate of earthquakes across the area was several times higher within 2 days of tremor activity than at other times, adding to evidence of a connection between tremor and earthquakes. (Geochemistry, Geophysics, Geosystems, doi:10.1029/2011GC003559, 2011)

Modeling short‐ and long‐term slow slip events in the seismic cycles of large subduction earthquakes

Slow slip events (SSEs) occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones, such as the Nankai region of Japan and the Cascadia region of North America. In the Nankai region, SSEs are divided into long‐ and short‐term SSEs, depending on their duration and recurrence interval. We modeled and examined the occurrence of long‐ and short‐term SSEs and changes in their behavior during the seismic cycles of large interplate earthquakes. In these numerical simulations we adopted a rate‐ and state‐dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long‐ and short‐term SSEs. The recurrence intervals of reproduced short‐term SSEs decrease during a long‐term SSE, as observed in western Shikoku, in the Nankai region. The recurrence intervals of both types of SSEs become shorter in the later stages of interseismic periods. Large interplate earthquakes nucleate between the region where SSEs occur and the locked region of the large earthquakes, as suggested from observations of the 1944 Tonankai earthquake. Our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of SSEs.

Predicted Ground Motions for Great Interface Earthquakes in the Cascadia Subduction Zone

Ground motions for earthquakes of moment magnitude ( M ) 7.5–9.0 on the Cascadia subduction zone interface are simulated based on a stochastic finite-fault model and used to estimate average response spectra for firm-site conditions in Vancouver, Victoria, and Seattle. We also express the response spectra as ground-motion prediction equations (GMPEs) for Cascadia events. The simulations are calibrated by modeling the wealth of ground-motion data from the M 8.1 Tokachi-Oki earthquake sequence of Japan. Adjustments to the calibrated model are made to consider average source, attenuation, and site parameters for the Cascadia region. We perform best estimate simulations for a preferred set of input parameters. Typical results suggest mean values of 5%-damped pseudoacceleration in the range from about 100 to 200 cm/sec2, at frequencies from 1 to 4 Hz, for firm-ground conditions in Vancouver, Victoria, and Seattle. Uncertainty in stress drop causes uncertainty in simulated response spectra of about ±50%. Uncertainties in the attenuation model produce even larger uncertainties in response spectral amplitudes—a factor of about 2 at 100 km, becoming even larger at greater distances. It is thus important to establish the regional attenuation model for ground-motion simulations. Furthermore, combining data from regions with different attenuation characteristics—in particular Japan and Mexico—into a global subduction zone database for development of global empirical GMPEs may not be a sound practice. Time histories of acceleration for the stochastically simulated motions are provided for reference sites in Vancouver, Victoria, and Seattle. An alternative set of motions, based on lightly modifying real recordings from the Tokachi-Oki earthquake to match expected conditions for Cascadia cities, are also provided. These alternative records have similar spectral content to the simulated motions but contain additional complexity and more realistic phasing. The provision of alternative record sets allows users to conduct studies to determine the importance of these effects for structural response.

Learning from dynamic triggering of low-frequency tremor in subduction zones

Abstract Remote triggering of small low-frequency seismic tremor (non-volcanic tremor) near the seismic-aseismic transition zone of subduction zones, by surface waves from large distant earthquakes, has been reported in southwest Japan and the Cascadia region. Recent observed triggering in southwest Japan from three large earthquakes (2003 Tokachi-oki, 2007 Solomon, and 2008 Wenchuan) covering wide azimuthal information provides strong evidence for the influence of fluids in the source area. The Coulomb failure stress analyses suggest the effective friction coefficient is large for southwest Japan and small for the Cascadia region, which could be related to the amount of fluid in the source regions of the low-frequency tremor.