<p> A 3D seismic volume across the campus of California State University, Long Beach images the Alamitos Heights fault, a splay of the Newport-Inglewood fault zone (NIFZ). The Alamitos Heights fault is a zone that strikes approximately N55&deg;W, dips on average 80&deg;SW, and bounds the northeast extent of the Seal Beach oil field structure. It plays a role in the complex evolution of the Newport-Inglewood fault zone within the Los Angeles sedimentary basin, which is closely related to timing and trapping mechanisms of nearby oil fields. Its origin and development may be related to fault steps or discontinuities along the main NIFZ. Seismic evidence suggests the Alamitos Heights fault may have originated as a transtensional feature during the Miocene before transitioning to its current transpressional stress regime.</p>

First, paleomagnetic data were obtained from Tertiary red beds at two localities separated by several hundred kilometers within the Qaidam Basin. When compared with equivalent-age expected directions for Eurasia, the mean paleomagnetic directions indicate no Neogene vertical-axis rotation of the Qaidam Basin or the Altyn Tagh fault. The Qaidam Basin may act as an indentor translating without rotation toward the Sino-Korean craton. Second, the observed paleomagnetic direction from Miocene red beds in the central Tarim Basin indicates 30.8° ± 5.5° flattening of inclination and 15.3° ± 6.7° clockwise vertical-axis rotation. Anisotropy of magnetic susceptibility measurements indicate a rock-magnetic (depositional or compaction shallowed) origin for the inclination flattening. Local deformation is the preferred interpretation for the vertical-axis rotation. Third, paleomagnetic data were obtained along the arcuate Tula syncline to test whether its strike curvature is due to oroclinal bending. The observed 13.3° ± 8.8° declination difference between the two halves of the Tula syncline is far less than the ∼40° difference predicted by oroclinal bending. Instead the arc shape of the syncline is an original configuration produced by transport above an arcuate thrust ramp. Along with paleomagnetic data from the Qaidam Basin, this result indicates that crustal displacement between the Tarim Basin and the Tibetan Plateau is accommodated by strike-slip motion on the Altyn Tagh fault rather than distributed shear within the northern Tibetan Plateau. Finally, we present results from red beds in the Altun Shan, the Qilian Shan/Nan Shan fold-thrust-belt and the Hexi corridor. In the Altun Shan, results from Miocene beds indicate no significant vertical-axis rotation confirming that the Altyn Tagh fault has not rotated and that sinistral shear strain is concentrated on the fault. Paleomagnetic results from Nan Shan/Qilian Shan fold-thrust-belt indicate no rotation since 30 Ma contrasting with prediction from previous kinematic models. This result indicates that there is no transrotation of the belt associated with motion on the Altyn Tagh fault. In the Hexi corridor, the observed mean paleomagnetic direction is concordant with the expected direction at 110 Ma providing a new local paleomagnetic reference for the Sino-Korean craton in agreement with published reference paleomagnetic poles for Eurasia.

<p> This thesis examines different methods of communicating volcanic hazards to the population of Flagstaff, Arizona using the results of a recent lava flow hazard assessment of the nearby San Francisco Volcanic Field (SFVF). Harburger (2014) determined that given a lava flow originating in the SFVF, there is a statistical probability that it will inundate the city of Flagstaff or even originate from a vent within the city limits. Based on the recurrence rates for the most recent eruptions (3 x 10-4/year), the probability of lava flow inundation in Flagstaff is 1.1 x 10-5 per year. </p><p> This study considers the effects of three different communication methods on participants&rsquo; perceived risk. The methods were administered through a questionnaire and included a statement of probability of lava flow inundation per year, a statement of probability over a 100 year period, and an interactive lava flow map derived from the results of the lava flow hazard assessment. Each method was followed by questions gauging level of concern. Questionnaires were administered to 213 Flagstaff residents over a two week period in February 2015. </p><p> Results showed that levels of concern, rated from 1 (not concerned) to 5 (very concerned), varied based on each method of communication. The method with the greatest effect on perceived risk was the simulated lava flow map, while the first method with a one year odds resulted in a statistically lower mean rating of concern. It is suggested that the best way to change levels of perceived risk when communicating lava flow hazards includes a combination of comprehensible odds and visual aids. Further studies could also include visualization of the entire eruption scenario, including time scales and other volcanic hazards, which may have more effect on concern than a simplified visualization of lava flows.</p>

The question of how curved geologic structures form, from arcuate faults to curvilinear orogenic belts, is one that transcends scale as well as rock properties. Many scale-independent lines of evidence suggest that material within fold-thrust belts is transported in three dimensions. Paleomagnetic analysis is the primary method for determining distribution and magnitude of vertical-axis rotations in arcuate regions. Thus paleomagnetic information is essential to deciphering the three-dimensional kinematic evolution of a curved orogen. In addition, most studies of foreland fold-and-thrust belts focus on geometries and timing relationships, but do not identify the deformations internal to the thrust-bounded rock packages. The Southern Pyrenean and Sevier orogenic systems both provide an outstanding opportunity to investigate thrust-belt curvature by integrating paleomagnetic and structural studies. This dissertation addresses the interplay between three-dimensional motions and the structures they cause. In the Pyrenees, the Oliana anticline is a foreland structure related to the South Central Salient, a major curve in the thrust belt. Paleomagnetic data from the Oliana anticline document counter clockwise rotations about a vertical axis. The average rotation is R ± Δ R = -19.6° ± 10.5°. Based on the stratigraphic horizons that record the rotation, as well as the structural evolution of the Oliana anticline, the age of rotation is ≥ 35 Ma. This rotation is attributed to continued motion along the Serres Marginals thrust, causing rotation along the blind thrusts that underlie the Oliana anticline. Mode I fracture data from this region highlights the progressive development of joints in growing structures. Measurements were taken from four regions around the anticline, and from four sequential synorogenic conglomerates. A consistent NW-SW orientation for the development of joints was determined by performing sequential restorations of the Oliana anticline and incrementally analyzing joint orientations. Reanalysis of previously published data from the Wyoming salient of the western United States demonstrates the relationship between irregular fault traces and the three-dimensional motions that caused them to form. Interaction between rotation, strain and net translation is a global phenomenon and suggests that geologic shortening estimates can be improved by incorporating the effects of tectonic rotations.

Seismic studies in the area of the Ruby Mountains metamorphic core complex and adjacent basins of northeast Nevada provide new evidence for Cenozoic tectonic evolution of the Ruby Mountains. Results from interpretation of industry seismic data show that (1) asymmetric basins flanking the Ruby Mountains were created by normal faults beginning in the late Eocene-early Oligocene; (2) the metamorphic core complex detachment fault system was cut by the normal fault system; and (3) total subsidences of Huntington and Lamoille basins, and Ruby basins are ∼4.5 and ∼5.0 km. Analysis of crustal-scale 3-component normal-incidence to wide-angle seismic data shows that (1) the crust along the eastern flank of the Ruby Mountains can be divided into three layers corresponding to the upper, middle and lower crust; (2) upper crustal rocks likely consist of metaquartzite, schist, granite gneiss, and granite-granodiorite with P-wave velocities (Vp) of 5.80-6.25 km/s, S-wave velocities (Vs) of 3.20-3.72 km/s, Poisson's ratios (sigma) of 0.22-0.25, and anisotropy of 0.6-2.5%; (3) possible middle crustal rocks are paragranulite, felsic granulite, felsic amphibolite gneiss, granite-granodiorite, and mica-quartz schist with Vp of 6.35-6.45 km/s, Vs of 3.70-3.75 km/s, and σ of 0.24; (4) lower crustal rocks most likely consist of granulite- rather than amphibolite-facies rocks with Vp of 6.60-6.80 km/s, Vs of 3.85-3.92 km/s, σ of 0.24-0.25, and anisotropy of less than 3%; (4) depth to the Moho varies irregularly between 30.5 and 33.5. Interpretation of these results suggests that (1) Cenozoic extension of the Ruby Mountains and adjacent basins began by late Eocene-early Oligocene; (2) depth to Moho does not reflect local surface relief on the eastern flank of the Ruby Mountains and adjacent basin; (3) fluid-filled fractures and mafic large-scale underplating are unlikely in the lower crust; (4) the present seismic velocities of highly extended core complex crust and normally extended Basin and Range crust are similar; and (5) orientations of fast shear waves near the surface and in the upper crust are parallel to sub-parallel to the regional maximum horizontal compressive stress in the Nevada part of the Basin and Range province.

Following cessation of contractional deformation, the Sevier orogenic belt collapsed and spread west during a middle Eocene to middle Miocene (∼48-20 Ma) episode of crustal extension coeval with formation of metamorphic core complexes and regional magmatism. The sedimentary and structural record of this event is a network of half-grabens that extends from southern Canada to at least central Utah. Extensional structures superposed on this fold-thrust belt are rooted in the physical stratigraphy, structural relief and sole faults of preexisting thrust-fold structures. Commonly, the same detachment surfaces were used to accommodate both contractional and extensional deformation. Foreland and hinterland extensional elements of the Cordillera that are normally widely separated are uniquely collocated in central Utah where the thrust belt straddles the Archean-Proterozoic Cheyenne belt crustal suture. Here, the Charleston-Nebo allochthon, an immense leading-edge structural element of the Sevier belt collapsed during late Eocene-middle Miocene time when the sole thrust was extensionally reactivated by faults of the Deer Creek detachment fault system and the allochthon was transported at least 5-7 km back to the west. Concurrently, the north margin of the allochthon was warped by flexural-isostatic rise of a Cheyenne belt crustal welt and its footwall was intruded by crustal melts of the Wasatch igneous belt. Collectively, these elements comprise the Cottonwood metamorphic core complex. Extensional processes were also important in the formation of the Jurassic-Cretaceous Great Valley forearc basin. Advocates of a thrust-wedge hypothesis argued that this forearc experienced prolonged Jurassic-Cretaceous contraction and proposed that northwest-southeast-striking fault systems were evidence of a west-dipping blind Great Valley-Franciscan sole thrust and related backthrusts. Based on interpretation of seismic reflection, borehole, map and stratographic data, I propose that these faults and associated bedding geometries are folded synsedimentary normal faults and half-grabens. Thus, late-stage diastrophic mechanisms are not required to interpret a forearc that owes much of its present-day bedding architecture to extensional processes coeval with deposition.

We use broadband regional waveform modeling of earthquakes in the central Andes to determine seismic properties of the Altiplano crust. Properties of the shear-coupled P-wavetrain (SPL ) from intermediate-depth events provide particularly important information about the structure of the crust. We utilize broadband seismic data recorded at the BANJO and SEDA stations, and synthetic seismograms computed with a reflectivity technique to study the sensitivity of SPL to crustal and upper mantle parameters at regional distances. We find that the long-period SPL-wavetrain is most sensitive to crustal and mantle Poisson's ratios, average crustal velocity, and crustal thickness. A comprehensive grid search method developed to investigate these four parameters suggests that although trade-offs exist between model parameters, models of the Altiplano which provide the best fit between the data and synthetic seismograms are characterized by low Poisson's ratios, low average crustal velocity and thick crust. We apply our grid search technique and sensitivity analysis results to model the full waveforms from 6 intermediate-depth and 2 shallow-focus earthquakes recorded at regional distances by BANJO and SEDA stations. Results suggest that the Altiplano crust is much thicker (55-65 km) and slower (5.75-6.25 km/s) than global average values. Low crustal and mantle Poisson's ratios together with the lack of evidence for a high-velocity lower crust suggests a bulk felsic crustal composition, resulting in an overall weak crust. Our results favor a model of crustal thickening involving large-scale tectonic shortening of a predominantly felsic crust. To better understand the mechanics of earthquake rupture along the South American subduction zone, we have analyzed broadband teleseismic P-waves and utilize single- and multi-station inversion techniques to constrain source characteristics for the 12 November 1996 Peru subduction zone earthquake. Aftershock locations, intensity reports, directivity, and spatial locations of seismic moment pulses indicate that the 1996 Peru event ruptured primarily southeast. This earthquake re-ruptured a portion of the 1942 Peru event. We find no indication that the 1996 Peru earthquake ruptured to the northwest, suggesting a sizable gap along the Peru trench corresponding to the position of the northwest flank of the subducting Nazca Ridge.

Geologic endeavor is a continual search for windows into the past. Our ability to characterize ancient geological processes is only as good as the techniques we have at our disposal; often the desire to uncover new information drives the development of new geologic methods or the modification of old techniques. This dissertation is composed of a series of projects focused on gaining new insights into the history of orogenic systems through the application of existing techniques or the development of new methods. Three primary projects were undertaken, the first a paleoelevation study aimed at determining the elevation of the Colorado Rockies 28 million years ago (Ma). This study was an attempt to both constrain the paleoelevational geometry of North America and test a new paleoaltimetry technique. This "one-isotope" technique relies on the relationship between cosmogenic isotope production rates and elevation; while a paleoelevation for the Colorado Rockies was not derived, the technique should prove useful in other geologic situations. From this initial technique, a two-isotope technique was derived which bypasses some of the difficulties inherent to the one-isotope method. A complete theoretical development of this two-isotope technique is included. Finally, a project documenting the wide-spread remagnetization of a suite of pre-Cenozoic Bolivian red sedimentary rocks reflects the impact orogenesis can have on an entire region. Taken as a whole, these projects focus on both the effects of mountain-building events and the techniques we can use to better understand them.

A new stochastic inverse algorithm for the inversion of three-dimensional (3-D) electrical resistivity tomography (ERT) data has been developed and tested using both synthetic and field data. My stochastic inverse algorithm produced satisfactory inverse solutions that were very similar to those of the commonly used Occam's inversion. The ill-posed 3-D stochastic inverse problems were stabilized by incorporating a-priori information in the algorithm in the form of an a-priori model, and data and model covariance matrices. There were several novel features in my algorithm. First, a very fast successive over-relaxation (SSOR) preconditioner was implemented in the conjugate-gradient forward solver. Second, a trade-off factor adapted from the Occam's inversion was employed in the algorithm for better control of convergence. Third, the QMRCGSTAB inverse solver, a quasi-minimal residual (QMR) variant of the stabilized bi-conjugate gradient method (Bi-CGSTAB), was used to solve an asymmetric linearized iterative system, so the inversion of a large model covariance matrix was sidestepped. Therefore my algorithm can handle a variable scale of model correlation. Fourth, much better convergence was achieved by using the data standard deviation instead of the data variance as the entries of data covariance matrix. Fifth, a model covariance weighting scheme using the diagonal of the transposed sensitivity matrix times the sensitivity matrix improved the model resolution greatly in the region where is usually poorly resolved. The run-time of stochastic inversion with a biconjugate-gradient inverse solver doubled that of the Occam's inversion with a conjugate-gradient solver. To speed up the stochastic inversion in in-situ monitoring applications, I developed an efficient difference inversion algorithm to invert the difference between the background and subsequent data sets. The new difference inversion can be two to three times faster than the stochastic inversion. I also developed a unique cokriging approach to estimate a 3-D moisture content distribution quantitatively from 3-D ERT data and a limited number of neutron-derived moisture content data for an infiltration experiment in Socorro, New Mexico. I found that one neutron well in the center of ERT mesh, where model parameters are usually poorly resolved in ERT inversion, played an indispensable role in cokriging.

The Ingenika Range forms part of a large zone of structural divergence that roughly coincides with the boundary between North America and Superterrane I. Contrasting tectonic histories from the Intermontane, Omineca and Foreland Belts at the latitude of the thesis area are consistent with a collisional model involving tectonic wedging, delamination and large-scale backthrusting. / The Upper Proterozoic Ingenika Group in the Ingenika Range has undergone a progressive deformational history involving pre-, syn-, and post-metamorpic structures. During the Middle Jurassic regional structural vergence changed from northeast- to southwest-directed folds and faults. Regional metamorphism reached amphibolite grade and was synchronous with west-vergent deformation. Minor structures in the study area suggest that the Swannell fault was an east-dipping thrust fault that emplaced North American strata over allochthonous rocks of Quesnellia. The Swannell fault was probably also active during the Middle Jurassic and may have acted as the structural discontinuity between a backthrusted crustal flake and an underlying, eastward moving wedge.