Seismic localization and observation of tectonic tremor in the northern Cascadia subduction zone

Convergent tectonic boundaries release accumulated stress on a spectrum of slip modes including large megathrust earthquakes with high societal impact, and slow slip events (SSEs), which are not felt by humans. In N. Cascadia, SSEs are regularly accompanied by seismic signals of tectonic tremor, such that the combined phenomena are referred to as episodic tremor and slip (ETS). This dissertation presents three related studies that characterize and localize tremor to better understand its generative processes and geophysical sources. I use a continuous 17-year record of tremor events to define episodes containing different numbers of events. This catalogue of episodes is used to demonstrate that major episodes (considered to represent ETS) and minor episodes exhibit distinct spatial distributions. Specifically, I provide the first observational evidence that the location of the forearc mantle corner controls whether major and minor episodes are segmented or colocated along dip. Minor episodes, which have been previously understudied, are ubiquitous along the margin but exhibit location-specific tendencies for episode sizes and recurrence intervals. To improve tremor localization, I developed the differential traveltime Bayesian inversion (DTBI) method, which prioritizes well-constrained localizations over comprehensive detection. DTBI localizes sources as 3D posterior probability distributions from which rigorous quantitative uncertainties (95% credibility intervals) are estimated. A test performed on small earthquakes supports the effectiveness of the method by relocating events within 4 km horizontally (100% of events) and 10 km vertically (90% of events) of their original locations. In addition, tremor localization exhibits less scatter than previous catalogues, indicating improved accuracy. I use the DTBI method to localize tremor sources during 20 episodes in N. Cascadia. This catalogue contains average horizontal and depth uncertainties of 4 km and 8 km, respectively. These uncertainties, which are computed for every tremor source, represent a significant improvement over previously-existing regional tremor catalogues. The enhanced constraints in the DTBI catalogue support detailed depth information that facilitates exploration of the tremor source region, which is often assumed to be the megathrust fault. I find that tremor is vertically-distributed within the deep accretionary complex up to 10 km shallower than the top of the oceanic crust (usually inferred to represent the megathrust fault). The compositional heterogeneity and structural complexity of the deep accretionary complex, as inferred from paleo-geologic studies, suggest that tremor may be generated by multiple mechanisms driven by high fluid pressures and elevated strain from subduction at deeper depths.Graduat

UVic Convocation November 14, 2023 – 2:30 pm

Students from the Faculties of Graduate Studies, Humanities, Fine Arts and Social Sciences. Dr. Linda Catlin Smith received an honorary degree.UndergraduateUnreviewe

Drivers of Coastal Morphodynamics on a Deltaic Barrier in the Colombian Caribbean

This research presents results from a series of analyses focussed on the overarching goal of identifying and understanding drivers of coastal morphodynamics on a deltaic barrier in the Colombian Caribbean coast, eastward from the Magdalena River mouth. Forcing mechanisms operating at different temporal scales were considered, including the influence of vertical land motion (VLM), storms, river discharge, trade winds, and wave conditions. These forcing mechanisms were related to geomorphic changes determined from satellite imagery taken before and after specific events. Satellite imagery and synthetic aperture radar acquisitions were used to assess decadal-scale coastline changes and VLM for the period 2007–2021. The findings revealed that VLM rates are highly variable alongshore, and that subsidence occurs mainly landward of highly erosive stretches of coastline associated with former mangrove forest. Drivers of coastal morphodynamics operating on time spans from days to seasons were assessed by focusing on four lagoons located along the back-barrier to better understand the interplay between extreme events and the breaching and healing of inlets that are temporarily formed between the lagoons and the ocean. Satellite data in conjunction with hourly readings from weather stations spanning the past 50 years helped to determine the conditions that enabled the breaching and healing processes to transpire in the lagoons. Aligned with the predominantly erosive regime along the study area, the findings indicated that the cumulative effect of the breaching and healing of the lagoons resulted in a deltaic barrier that has rolled over the lagoons, modifying their size over time. The occurrence of meteotsunamis and their role in coastal morphodynamics was investigated using a wavelet analysis applied to water-level readings in three tide gauges for the period 2013–2022. After the discovery of one event with meteotsunami-like characteristics, the atmospheric conditions and total water levels associated with this event were analyzed. The results indicated that total water levels related to the meteotsunami are similar to those produced by moderate storms and both phenomena can induce breaching of lagoons. To date, the barrier has responded to external forcers through a landward displacement of the coastline driven by cycles of lagoon breaching and healing as well as overwashes on lagoons, wetlands, and beaches. Seasonal storms have been critical in forcing these processes and have substantially influenced the barrier evolution during the last 50 years. Taken as a whole, this body of work provides knowledge about the response of deltaic barriers to geomorphologic forcers based on a study area in an understudied region of the Caribbean. At a regional level, the findings are relevant for science-based coastal planning and managing policies. Moreover, this research used a variety of methodological approaches to track causality on coastal landscapes in a manner that can be replicated in other areas with limited pre-existing information and without ongoing monitoring programs.Graduate2025-01-1

Comparing visualizations and text on smart watches while running in realistic environment

In today’s digital age, smartwatches have become popular tools for millions of runners, providing metrics like pace, heart rate, and distance. Despite the widespread use of text-based displays on these devices, research suggests that visualizations could offer a more effective alternative. However, little is known about how visualizations perform in real-world running scenarios. This study addresses this gap by investigating how visualizations compare to text is aiding runners’ performance and experience. Through a study involving 20 runners completing running tasks on an outdoor track, we found that visualizations significantly outperformed text, with runners completing tasks 1.5 to 8 times faster. Moreover, participants expressed a strong preference for visualizations and indicated a willingness to use them during their runs if available on their smartwatch. These findings highlight the potential of visualizations to enhance the usability and effectiveness of smartwatches for runners.Graduat

An Attempt to Erase: Colonial Histories and Contemporary Indigenous Identities in Cuba

This study seeks to investigate the complex history of Indigenous peoples in Cuba, exploring how this legacy influences modern perceptions of Indigenous identity. Since the 1970s there has been a growing movement among Taíno peoples, particularly among the Puerto Rican, Dominican, and Cuban diaspora in North America, to reclaim their Indigenous heritage and assert their existence, challenging the long held myth of a post-Columbus Indigenous extinction in the Caribbean. Within Cuba, this movement has taken shape, but its manifestation is multifaceted and influenced by unique socio-political dynamics and concepts of identity. Despite the presence of Taíno ancestry in Cuba's population and culture, the acknowledgment of Indigenous identity has faced challenges amidst a narrative of extinction and ideals of the Revolution, which prioritize Cuban identity over other racial or ethnic distinctions. Drawing from my experiences during the 2023 Cuba Ethnographic Field School and a review of the available literature, I aim to elucidate the intricate interplay between colonial historical production and contemporary Indigenous identities in Cuba. In addition, this research aims to think critically about the complex dynamics of Indigenous tourism occurring alongside cultural revitalization in the Cuban context.Jamie Cassels Undergraduate Research Awards (JCURA)UndergraduateReviewe

Safer alternatives to prevent biofouling in reverse osmosis polyamide membrane systems

Biofouling is the main technical barrier to the widespread application of reverse osmosis (RO) technology in addressing worldwide water scarcity. Biofouling reduces permeate production, escalates energy demands, and exacerbates the environmental impacts associated with RO technology. To overcome these challenges, this PhD project proposed a platform to select and test safe and green anti-biofouling agents to prevent biofouling in drinking water RO system applications. The platform consisted of a screening protocol followed by a validation protocol. The proposed platform was applied to assess the applicability of nine chemicals (MIT: 2-methyl-4-isothiazolin-3-one; DBNPA: 2,2-dibromo-3-nitrilopropionamide; SBS: sodium bisulfite; SB: sodium benzoate, PE: phenoxyethanol; LAE: ethyl lauroyl arginate, PHMGH: Polyhexamethylene guanidine hydrochloride; BDMDAC: Benzyldimethyldodecyl ammonium chloride; SNP: Sodium nitroprusside) for preventing membrane biofouling in RO potable water applications. The screening protocol involved three phases: a comprehensive review, antibiofouling testing, and polyamide membrane compatibility testing. The comprehensive review investigated the applicability of the selected biocides in preventing and controlling biofouling in RO systems. It evaluated their antimicrobial efficiency, hazard levels, membrane compatibility, and suitability for drinking water treatment. Antibiofouling testing involved biofouling experiments on a Center for Disease Control (CDC; the United States) biofilm reactor with the minimum concentrations determined in microtiter plates. Confocal Scanning Laser Microscopy (CLSM) and Scanning Electron Microscopy (SEM) were used to analyze the biocides' anti-biofilm efficacies under dynamic conditions relative to the minimum biofilm inhibitory and eradication concentrations. Polyamide membrane compatibility testing assessed membrane compatibility via rapid membrane degradation tests. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Microscopy (AFM), and SEM were used to assess the polyamide membrane damage due to exposure to biocides. The screening protocol revealed that DBNPA and MIT pose hazards to both human health and the environment, making them unsuitable as a full-scale solution to prevent biofouling in RO potable water applications. SBS was also considered to be unsuitable due to its low antibiofilm efficacy and pH dependency. PE and SB were deemed unsuitable due to their moderate antibiofilm efficacy and incompatibility with polyamide membranes. BDMDAC was considered unsuitable for biofouling control in RO potable water applications due to its inefficacy against biofilms and common biofilm-forming microorganisms in RO systems. Further research beyond this PhD is required to assess the suitability of PHMGH and SNP for use in RO potable water applications, given their early stage of development and limited available information in the literature. Among the examined chemicals, LAE was the only biocide to successfully pass all phases of the proposed screening protocol, emerging as a promising safe chemical alternative to prevent biofouling in RO systems. LAE showed the highest efficacy against P. aeruginosa biofilms among the tested biocides, successfully preventing biofilm formation by over 98% and removing existing biofilms by more than 99% from RO membranes. Additionally, rapid membrane degradation tests indicated that LAE did not cause morphological or chemical damage to the membranes. Consequently, LAE was the only biocide recommended to advance to further experiments in a RO benchtop system outlined in the validation protocol. Therefore, considering the current need for greener alternatives to prevent biofouling in RO polyamide membrane systems in potable water applications, this PhD project has the potential to contribute to the use of RO technology for the provision of reliable, secure, and safe water supply to municipalities, industries, marginalized groups, remote work sites, and Indigenous communities. This was accomplished by establishing a platform to screen anti-biofouling agents for preventing biofouling in RO drinking water applications, alongside the identification of a promising biocide (LAE) to address membrane biofouling in RO drinking water applications.Graduate2025-01-1

Is Cannabis Changing Our Relations? An Evaluation of British Columbia's Attempts at Economic Reconciliation

Prior to Canadian cannabis legalization, Indigenous nations had started to participate within the unregulated cannabis industry, turning it into a vehicle for cultural assertion. With the enactment of a federally regulated market, Indigenous cannabis businesses began to be displaced by regulated storefronts. With the increasing grievances from First Nation voices it was apparent that federal cannabis legalization actively excluded them from participating in a regulated economy (Crosby, 2019). In response to the increasing call for change, British Columbia enacted a unique amendment that aimed to create new government-to-government agreements between Indigenous communities involved in cannabis economies and the provincial government (BC Government News, 2022). Due to the recency of this amendment a large gap in evaluating its efficacy was apparent. Through the application of a historiographical analysis this research aims to establish the effectiveness of these newly formed agreements in the context of rebuilding Indigenous-Crown relations. This paper suggests that there is a growing amount of self-determination for those who participate within this new cannabis framework. However, based on the response by Indigenous voices and perspectives there is still a high degree of rigidity that excludes many from participating (Clarke, 2023). The overarching message is that this policy moves in the right direction but still lacks the ability to allow nations to assert an adequate degree of sovereignty.UndergraduateReviewe

Finger fluting in prehistoric caves: A critical analysis of the evidence for children, sexing and tracing of individuals

Finger flutings are channels drawn in soft sediments covering walls, floors and ceilings of some limestone caves in Europe and Australia and in some cases date as far back as 50,000 years ago. Initial research focused on why they were made, but more recently, as part of a growing interest in the individual in the past, researchers began asking questions about who made them. This shift in direction has led to claims that by measuring the width of flutings made with the three middle fingers of either hand, archaeologists can infer the ordinal age, sex and individuality of the ‘fluter’. These claims rest on a single dataset created in 2006. In this paper, we undertake the first critical analysis of that dataset and its concomitant methodologies. We argue that sample size, uneven distribution of sex and age within the sample, non-standardised medium, human variability, the lack of comparability between an experimental context and real cave environments and assumptions about demographic modelling effectively negate all previous claims. To sum, we find no substantial evidence for the claims that an age, sex and individual tracing can be revealed by measuring finger flutings as described by Sharpe and Van Gelder (Antiquity 80: 937-947, 2006a; Cambridge Archaeological Journal 16: 281–95, 2006b; Rock Art Research 23: 179–98, 2006c). As a case study, we discuss Koonalda Cave in southern Australia. Koonalda has the largest and most intact display of finger flutings in the world and is also part of a cultural landscape maintained and curated by Mirning people.FacultyReviewe

Laguerre-type Bernoulli and Euler numbers and related fractional polynomials

We extended the classical Bernoulli and Euler numbers and polynomials to introduce the Laguerre-type Bernoulli and Euler numbers and related fractional polynomials. The case of fractional Bernoulli and Euler polynomials and numbers has already been considered in a previous paper of which this article is a further generalization. Furthermore, we exploited the Laguerre-type fractional exponentials to define a generalized form of the classical Laplace transform. We show some examples of these generalized mathematical entities, which were derived using the computer algebra system Mathematica© (latest v. 14.0).FacultyReviewe

Orbital stability and secular dynamics of the Proxima Centauri planetary system

The authors thank Gongjie Li, Hanno Rein, and Juliette Becker for valuable insights and discussion, and thank the anonymous referee whose thoughtful recommendations substantially improved this manuscript. This work was facilitated through the use of advanced computational, storage, and networking infrastructure provided by the Hyak supercomputer system and funded by the Student Technology Fund at the University of Washington.The two innermost planets of the Proxima Centauri system are separated by just 0.02 au, inducing strong gravitational interactions between them. We assess this interaction by leveraging fast orbital stability indicators and find that orbital stability is very likely if the initial eccentricities of planets b and d are less than ∼0.2, but cannot confirm stability at larger values. We find that stability is not strongly affected by the true masses of the planets or by the distant planet c. However, mutual inclinations between 95° and 142° often result in unstable motion. We further explore the long-term evolution of the orbits in these stable regions of parameter space and find that circularization can take over 5 Gyr. This tidal evolution could support surface energy fluxes in excess of 1 W m−2 for over 1 Gyr, possibly affecting planet b's habitability.J.R.L. gratefully acknowledges partial support from a Mary Gates Research Scholarship. R.B. acknowledges support from NASA grant No. 80NSSC20K0229 and the NASA Virtual Planetary Laboratory under grant No. 80NSSC18K0829.FacultyReviewe