Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

abstract: Meter-resolution topography gathered by LiDAR (Light Detection and Ranging) has become an indispensable tool for better understanding of many surface processes including those sculpting landscapes that record information about earthquake hazards for example. For this reason, and because of the spectacular representation of the phenomena that these data provide, it is appropriate to integrate these data into Earth science educational materials. I seek to answer the following research question: "will using the LiDAR topography data instead of, or alongside, traditional visualizations and teaching methods enhance a student's ability to understand geologic concepts such as plate tectonics, the earthquake cycle, strike-slip faults, and geomorphology?" In order to answer this question, a ten-minute introductory video on LiDAR and its uses for the study of earthquakes entitled "LiDAR: Illuminating Earthquake Hazards" was produced. Additionally, LiDAR topography was integrated into the development of an undergraduate-level educational activity, the San Andreas fault (SAF) earthquake cycle activity, designed to teach introductory Earth science students about the earthquake cycle. Both the LiDAR video and the SAF activity were tested in undergraduate classrooms in order to determine their effectiveness. A pretest and posttest were administered to introductory geology lab students. The results of these tests show a notable increase in understanding LiDAR topography and its uses for studying earthquakes from pretest to posttest after watching the video on LiDAR, and a notable increase in understanding the earthquake cycle from pretest to posttest using the San Andreas Fault earthquake cycle exercise. These results suggest that the use of LiDAR topography within these educational tools is beneficial for students when learning about the earthquake cycle and earthquake hazards. / Dissertation/Thesis / M.S. Geological Sciences 2011

xv, 95 p. : ill. (some col.), maps (some col.) Plate 1. Geologic Map of the Sierra Bacha, Coastal Sonora, Mexico (1:30,000 scale) attached as a separate file. / The Gulf of California is an active rift basin formed by late Cenozoic dextral-oblique extension along the Pacific-North America plate boundary. Well exposed volcanic and sedimentary rocks in the Sierra Bacha, coastal Sonora, Mexico, preserve a history of proto-Gulf (late Miocene) deformation and offer insight into the structures and kinematics responsible for localization of the plate boundary and inception of the Gulf at about 6 Ma. Geologic mapping, fault kinematic analysis, and paleomagnetic data suggest that proto-Gulf deformation in the Sierra Bacha occurred primarily by ENE-WSW extension and that vertical-axis rotation related to dextral strain was minor. Lack of significant dextral shear supports an emerging model for proto-Gulf deformation in which dextral strain was not ubiquitous across Sonora but instead became localized during latest Miocene time in a narrow coastal shear zone that mechanically weakened the lithosphere and helped facilitate continental rupture. This thesis includes the "Geologic Map of the Sierra Bacha, Coastal Sonora, Mexico" as supplemental material. / Committee in charge: Dr. Rebecca J. Dorsey, Chairperson; Dr. Marli B. Miller, Member; Dr. Ray J. Weldon II, Member

abstract: There is a need to understand spatio-temporal variation of slip in active fault zones, both for the advancement of physics-based earthquake simulation and for improved probabilistic seismic hazard assessments. One challenge in the study of seismic hazards is producing a viable earthquake rupture forecast—a model that specifies the expected frequency and magnitude of events for a fault system. Time-independent earthquake forecasts can produce a mismatch among observed earthquake recurrence intervals, slip-per-event estimates, and implied slip rates. In this thesis, I developed an approach to refine several key geologic inputs to rupture forecasts by focusing on the San Andreas Fault in the Carrizo Plain, California. I use topographic forms, sub-surface excavations, and high-precision geochronology to understand the generation and preservation of slip markers at several spatial and temporal scales—from offset in a single earthquake to offset accumulated over thousands of years. This work results in a comparison of slip rate estimates in the Carrizo Plain for the last ~15 kyr that reduces ambiguity and enriches rupture forecast parameters. I analyzed a catalog of slip measurements and surveyed earth scientists with varying amounts of experience to validate high-resolution topography as a supplement to field-based active fault studies. The investigation revealed that (for both field and remote studies) epistemic uncertainties associated with measuring offset landforms can present greater limitations than the aleatoric limitations of the measurement process itself. I pursued the age and origin of small-scale fault-offset fluvial features at Van Matre Ranch, where topographic depressions were previously interpreted as single-event tectonic offsets. I provide new estimates of slip in the most recent earthquake, refine the centennial-scale fault slip rate, and formulate a new understanding of the formation of small-scale fault-offset fluvial channels from small catchments (<7,000 m2). At Phelan Creeks, I confirm the constancy of strain release for the ~15,000 years in the Carrizo Plain by reconstructing a multistage offset landform evolutionary history. I update and explicate a simplified model to interpret the geomorphic response of stream channels to strike-slip faulting. Lastly, I re-excavate and re-interpret paleoseismic catalogs along an intra-continental strike-slip fault (Altyn Tagh, China) to assess consistency of earthquake recurrence. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

abstract: Quantifying the temporal and spatial evolution of active continental rifts contributes to our understanding of fault system evolution and seismic hazards. Rift systems also preserve robust paleoenvironmental records and are often characterized by strong climatic gradients that can be used to examine feedbacks between climate and tectonics. In this thesis, I quantify the spatial and temporal history of rift flank uplift by analyzing bedrock river channel profiles along footwall escarpments in the Malawi segment of the East Africa Rift. This work addresses questions that are widely applicable to continental rift settings: (1) Is rift-flank uplift sufficiently described by theoretical elliptical along-fault displacement patterns? (2) Do orographic climate patterns induced by rift topography affect rift-flank uplift or morphology? (3) How do uplift patterns along rift flanks vary over geologic timescales? In Malawi, 100-km-long border faults of alternating polarity bound half-graben sedimentary basins containing up to 4km of basin fill and water depths up to 700m. Orographically driven precipitation produces climatic gradients along footwall escarpments resulting in mean annual rainfall that varies spatially from 800 to 2500 mm. Temporal oscillations in climate have also resulted in lake lowstands 500 m below the modern shoreline. I examine bedrock river profiles crossing the Livingstone and Usisya Border Faults in northern Malawi using the channel steepness index (Ksn) to assess importance of these conditions on rift flank evolution. River profiles reveal a consistent transient pattern that likely preserves a temporal record of slip and erosion along the entire border fault system. These profiles and other topographic observations, along with known modern and paleoenvironmental conditions, can be used to interpret a complete history of rift flank development from the onset of rifting to present. I interpret the morphology of the upland landscape to preserve the onset of extensional faulting across a relict erosion surface. The linkages of individual faults and acceleration of slip during the development of a continuous border fault is suggested by an analysis of knickpoint elevations and Ksn. Finally, these results suggest that the modern observed climate gradient only began to significantly affect denudation patterns once a high relief rift flank was established. / Dissertation/Thesis / M.S. Geological Sciences 2014

From Introduction: The Canadian Cordilleran Orogenic Belt forms part of the circum-Pacific orogenic zone. It underlies an area of about 1,54 million sq. kilometres, is over 2400 kilometres long and 800 kilometres wide. The region is characteristically mountainous, much of it glaciated and alpine, containing plateaux, trenches, valleys, and fjords. The mountains, in general, rise to elevations between 2100 m and 3600 m above sea level, although Mount Logan in the St. Elias Mountains attains an altitude of 6000 m. The Canadian Cordillera is divided into two dominant orogenic belts: the eastern Columbian Orogenic Belt comprising defonned miogeosynclinal rocks and the western Pacific Orogenic Belt comprising allochthonous eugeosynclinal rocks. The Cordillera is further subdivided into five longitudinal tectonic belts within which rocks are broadly similar in type, age, and history. These belts are, from east to west: the Rocky Mountain Belt, the Omineca Crystalline Belt, the Intermontane Belt, the Coast Plutonic Complex, and the Insular Belt (Wheeler et al., 1972a). The Canadian Cordillera is important in that it contains: one of the world's largest lead-zinc-silver mine, Sullivan; the second-largest molybdenum mine, Endako; one of the most important concentrations of porphyry copper deposits, Highland Valley; Canada's largest tungsten mines, Cantung and Mactung; and Canada's second-largest silver district, Keno Hill (Sutherland Brown et a1., 1971). In addition, it contains several large massive sulphide and lead-zinc deposits.

The northern Cascadia subduction zone involves convergence of the Explorer Plate and northern part of the Juan de Fuca Plate with the North American Plate along a margin lying west of Vancouver Island, Canada. A wide accretionary complex which underlies the continental slope and shelf has been formed. Two allochthonous terranes, the Crescent Terrane of Eocene oceanic crustal volcanics and the Pacific Rim Terrane of Mesozoic melange sedimentary rocks and volcanics, lie against the Wrangellia Terrane backstop beneath the west coast of Vancouver Island and outcrop on the southern tip of the island. The intrusive Coast Plutonic Complex underlies the westernmost part of the British Columbia mainland east of Vancouver Island and marks the location of the historic and modern volcanic arcs. An integrated interpretation of geophysical and geological data has been conducted for the northern Cascadia subduction zone. Regionally extensive gravity and magnetic anomaly data have formed the basis of the interpretation, while surface geology, physical properties, and seismic reflection, refraction, heat flow, borehole, magnetotelluric, and seismicity data have provided constraints on structure and composition. Horizontal gradient and vertical derivative maps of the potential field data were calculated to provide additional control on the locations of major faults and lithologic boundaries. Iterative forward modelling of the gravity and magnetic anomaly data was conducted along three offshore multichannel seismic reflection lines and their onshore extensions. The two-and-a-half-dimensional (2.5-D) models extended from the ocean basin across the accretionary complex and Vancouver Island to the mainland along lines perpendicular to the major structural trends of the margin and revealed lateral changes in the location of several structural components along the length of the margin. The interpretations were extended laterally by moving the original models to adjacent parallel positions and perturbing them to satisfy the new anomaly profile data and other constraints. The models thus formed were moved to the next position and the process repeated until a total of eleven models was developed across the margin. A twelfth line across a gravity anomaly high on southern Vancouver Island was independently modelled to examine the source of this feature. An average density model for the southern half of the convergent margin was constructed by averaging the models and profiles for seven lines at 10 km spacings. This process removed anomalies due to small source bodies and concentrated on the larger features. Finally, a regional density structural model was developed by linearly interpolating between all eleven cross-margin lines to construct a block model which could then be 'sliced' open to examine the internal structure of the margin at any location. The final models allow the Pacific Rim and Crescent Terrane positions to be extended along the offshore margin from their mapped locations. The Pacific Rim Terrane appears to be continuous and close to the coastline along the length of Vancouver Island, while the Crescent Terrane either terminates halfway along the margin or is buried at a depth great enough to suppress its magnetic signature. The location of the Westcoast Fault, separating the Pacific Rim and Wrangellia Terranes, has been interpreted to lie west of Barkley Sound at a position 15 km west of its previously interpreted position. Beneath southern Vancouver Island and Juan de Fuca Strait, the Crescent Terrane appears to have been uplifted into an anticlinal structure, bringing high density lower crustal or upper mantle material close to the surface and thereby causing the observed gravity anomaly high. The western part of the Coast Plutonic Complex has been interpreted as a thin lower density layer extending from its surface contact with Wrangellia to a position 20 to 30 km further east where the unit rapidly thickens and represents the main bulk of the batholith. The complexity of the thermal regime and its effects on density in this region allows for other interpretations. Finally, a comparison of the models along the length of the margin reveals that the crust of Vancouver Island appears to thin toward the north above the shallower Explorer Plate and the complex low - high density banding used in the southern Vancouver Island models is replaced with a single high density unit on the northernmost line. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Strong evidence suggests that the Cascadia subduction zone, off the west coast of Canada and the United States, is strongly seismically-coupled and that a possible megathrust earthquake might occur in that area in the near future. A study of tsunami hazards along the Canadian west coast associated with such a hypothetical earthquake is presented in this report. Numerical simulations of tsunami generation and propagation have been carried out using three models based on shallow water wave theory. Three cases of ground motion representing the ruptures of different crustal segments in the area have been examined. Computed results provide information on tsunami arrival times and a general view of the wave height distribution. The outer coast of Vancouver Island was found to be the most strongly affected area. At the head of Alberni Inlet, wave amplitudes reached up to three times the source magnitude. Inside the Strait of Georgia, the wave heights are significant enough to receive closer attention, especially in low-lying areas. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The 1980 Vancouver Island Seismic Project (VISP) was conducted to investigate lithospheric structure associated with the underthrusting oceanic Juan de Fuca plate and the overriding continental America plate. The principal components of the survey were: (l) an onshore-offshore refraction line, which was approximately perpendicular to the continental margin (line 1), and (2) a refraction line which ran along the length of Vancouver Island approximately parallel with the continental margin (line IV). Lines I and IV were originally interpreted by Spence el a.1. (1985) and McMechan and Spence (1983), respectively. However since the original interpretations of these lines, deep multichannel seismic reflection data have been obtained on southern Vancouver Island as part of the 1984 LITHOPROBE project and off the west coast of the island during a marine survey in 1985. This study was undertaken to resolve differences between the subsurface structures proposed in the original interpretations of lines I and IV and those suggested by the more recently acquired deep reflection data. The vertical two-way traveltimes to prominent reflectors, observed in the onshore-offshore deep reflection data, were used as a constraint in constructing velocity models which are consistent with both the reflection and refraction data. The traveltimes and amplitudes observed in the VISP refraction data were modeled using a two-dimensional raytracing and asymptotic ray theory synthetic seismogram routine. The principal difference between the model originally interpreted for line I and the revised model involves the introduction of a twice repeated sequence of a low velocity zone (≈ 6.4 km/s) above a thicker high velocity zone (≈ 7.1 km/s) for the underplated region directly above the subducting Juan de Fuca plate in place of the single high velocity block underlain by a thick low velocity zone. The revised model for line IV is significantly different from the originally interpreted model. The two low-high velocity zones of line 1 are continued along the length of the island at depths between 10 and 35 km. Below this, the structure of the subducted plate is included to maintain consistency with the revised model developed for line 1. Additional features of the revised onshore-offshore model corresponding to line 1 include an oceanic lithosphere that dips approximately 3° beneath the continental slope, then 14° to 16° beneath the continental shelf and Vancouver Island, and an average velocity for the upper oceanic mantle of 8.22 km/s. Two separate two-dimensional models were needed to explain the data collected along line IV as a result of considerable azimuthal coverage due to a 30° change in profile direction. The revised models developed for line IV are consistent with the revised model developed for line 1. The velocity in the upper 10 km ranges from 5.5 km/s to approximately 6.7 km/s. Below 10 km the velocity structure is consistent with that interpreted for line 1 and shows some variations along strike of the subduction zone. Several possible interpretations can be made for the origin of the sequence of layers directly above the subducting plate beneath Vancouver Island. The two favored interpretations are: (1) a. three stage tectonic process consisting of: stage 1 — offscraping of sediment from the top of the subducting plate forms the uppermost low velocity layer in the sequence; stage 2 — an imbricated package of mafic rocks derived by continuous accretion from the top of the subducting oceanic crust forms the first high velocity layer; and stage 3 — stages 1 and 2 repeat themselves with stage 2 currently occurring; or (2) remnant, pieces of oceanic lithosphere left stranded above the current subducting plate during two previous episodes of subduction in which the subduction thrust jumped further westward isolating the remnant. The revised model along line IV indicates that this process of subduction underplating could have been a pervasive feature of this convergent margin. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

D.Phil. / The tectonic history of the Kheis Terrane and its relationship with the Namaqua-Natal Metamorphic Province (NNMP) along the western margin of the Kaapvaal Craton were the focus of this study. Major issues addressed in this study are the origin and timing of formation of the Kheis Terrane and the recognition and definition of terrane boundaries in the area. Results of detailed measured sections across the Kheis Terrane, heavy mineral provenance studies, 40Ar/39Ar analyses of metamorphic muscovite, U-Pb SHRIMP dating of detrital zircon grains from 12 samples from the Kheis- and Kakamas Terranes and one igneous body from the Kakamas Terrane are presented. A new stratigraphic unit, the Keis Supergroup, comprising the Olifantshoek-, Groblershoop- and Wilgenhoutsdrif Groups, is defined. The base of the Keis Supergroup is taken at the basal conglomerate of the Neylan Formation. The Mapedi- and Lucknow Formations, previously considered part of the Olifantshoek Group, are now incorporated into the underlying Transvaal Supergroup. The Dabep Fault was found not to represent a terrane boundary. Rather, the Blackridge Thrust represents the boundary between the rocks of the Kheis Terrane and the Kaapvaal Craton. Provenance studies indicate that the rocks of the Keis Supergroup were deposited along a passive continental margin on the western side of the Kaapvaal-Zimbabwe Craton with the detritus derived from a cratonic interior. Detrital zircon grains from the rocks of the Keis Supergroup of the Kheis Terrane all gave similar detrital zircon age populations of ~1800Ma to ~2300Ma and ~2500Ma to ~2700Ma. The Kaapvaal Craton most probably never acted as a major source area for the rocks of the Keis Supergroup because of the lack of Paleo- to Mesoarchean zircon populations in the Keis Supergroup. Most of the detrital zircon grains incorporated into the Keis Supergroup were derived from the Magondi- and Limpopo Belts and the Zimbabwe Craton to the northeast of the Keis basin. The rock of the Kakamas Terrane was derived from a totally different source area with ages of ~1100Ma to ~1500Ma and ~1700Ma to ~1900Ma which were derived from the Richtersveld- and Bushmanland Terranes as well as the ~1166Ma old granitic gneisses ofthe Kakamas Terrane. Therefore the rocks of the Kheis- and Kakamas Terranes were separated from each other during their deposition. Detrital zircon populations from the Sprigg Formation indicate that it this unit was deposited after the amalgamation of the Kheis- and Kakamas Terranes and therefore does not belong to the Areachap Group. Results provide clear evidence for a tectonic model characterised by the presence of at least two Wilson cycles that affeected the western margin of the Kaapvaal Craton in the interval between the extrusion of the Hartley lavas at 1.93Ga and the collision with the Richtersveld tectonic domain at ~1.13Ga. According to the revised plate tectonic model for the western margin of the Kaapvaal- Zimbabwe Craton, the Neylan Formation represents the initiation of the first Wilson Cycle, with rifting at ~1927Ma ago, on the western margin of the Kaapvaal-Zimbabwe Craton. The metasedimentary rocks of the Olifantshoek Group were deposited in a braided river environment which gradually changed into a shallow marine environment towards the top of the Olifantshoek Group in the Top Dog Formation. The metasedimentary rocks of the Groblershoop Group were deposited in a shallow, passive or trailing continental margin on the western side of the Kaapvaal-Zimbabwe Craton. The rocks of the Wilgenhoutsdrif Group overlie the Groblershoop Group unconformably. This unconformity is related to crustal warping as a volcanic arc, represented by the metavolcanics of the Areachap Group, approached the Kaapvaal-Zimbabwe Craton from the west. The rocks of the Keis Supergroup were deformed into the Kheis Terrane during the collision of the Kaapvaal-Zimbabwe Craton, Areachap Arc and the Kgalagadi Terrane to form the Kaapvaal-Zimbabwe-Kgalagadi Craton. This event took place sometime between 1290Ma, the age of deformed granites in the Kheis Terrane and 1172Ma, the initiation of rifting represented by the Koras Group. This is supported by 40Ar/39Ar analyses of metamorphic muscovite from the Kheis Terrane that did not provide any evidence for a ~1.8Ga old Kheis orogeny (an age commonly suggested in the past for this orogeny). This collisional event resulted in the deformation of the rocks of the Keis Supergroup into the Kheis Terrane sometime between 1290Ma and 1172Ma.The second Wilson cycle was initiated during rifting along the Koras-Sinclair-Ghanzi rift on the Kaapvaal-Zimbabwe-Kgalagadi Craton at ~1172Ma. It was followed soon after by the initiation of subduction underneath the Richtersveld cratonic fragment at ~1166Ma after which the rocks of the Korannaland Group were deposited. The closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment occurred about 50Ma later (~1113Ma, the age of neomorphic muscovite in the metasedimentary rocks of the Kakamas Terrane) and resulted in the large open folds characterising the Kheis terrane and NNMP. Detrital zircon populations in the Sprigg Formation show that this formation does not belong to the Areachap Group and that it was deposited after the closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment at ~1113Ma. The Areachap Group can be extended towards the north and into Botswana along the Kalahari line where it forms the boundary between the Kaapvaal-Zimbabwe Craton to its east and the Kgalagadi Terrane to its west. The Areachap Terrane is thus related to the collision of the Kaapvaal-Zimbabwe Craton and Kgalagadi Terrane and was deformed a second time during the oblique collision of the Richtersveld cratonic fragment with the combined Kaapvaal-Zimbabwe-Kgalagadi Craton. The extension of the Areachap Group to the north along the Kalahari line opens up new exploration prospects for Coppertontype massive sulphide deposits underneath the Kalahari sand.