Tectonics and Structure Commons^™

Fold-Related Faults Track Progressive Fold Development From Layer-Parallel Shortening To Subsequent Orthogonal Extension Within An Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, Pa Usa, Arlo B. Weil, Mary Beth Gray, Kylie G. Cush, Mattathias D. Needle, Juliet G. Crider

Faculty Journal Articles

Outstanding three-dimensional exposures of adjacent folds in an abandoned coal mine within the Appalachian Valley-and-Ridge tectonic province permit a detailed analysis of macroscopic strain accommodation by minor faulting in the lead up to and during buckle folding. A kinematic analysis of more than 900 outcrop-scale faults coupled with clearly established relative age relationships allows delineation of distinctive fault sets and their roles in accommodating strain within a quartz-dominated sandstone and an overlying silty shale. Conjugate contractional faults are interpreted as evidence of layer-parallel shortening (LPS) prior to and during fold initiation, based on geometric relationships to primary bedding. A clearly …

Plate Boundary Trench Retreat And Dextral Shear Drive Intracontinental Fault-Slip Histories: Neogene Dextral Faulting Across The Gabbs Valley And Gillis Ranges, Central Walker Lane, Nevada, Jeffrey Lee, Andrew K. R. Hoxey, Andrew Calvert, Peter Dubyoski

All Faculty Scholarship for the College of the Sciences

The spatial-temporal evolution of intracontinental faults and the forces that drive their style, orientation, and timing are central to understanding tectonic processes. Intracontinental NW-striking dextral faults in the Gabbs Valley–Gillis Ranges (hereafter referred to as the GVGR), Nevada, define a structural domain known as the eastern Central Walker Lane located east of the western margin of the North American plate. To consider how changes in boundary type along the western margin of the North American plate influenced both the initiation and continued dextral fault slip to the present day in the GVGR, we combine our new detailed geologic mapping, structural …

An Analysis Of Fractures Around The Sevier Fault Zone Near Orderville, Utah, Charley H. Hankla

Senior Independent Study Theses

Structural discontinuities—such as opening mode joints, shear fractures, and faults— tend to occur in close geographic proximity to one another; however, the timing relationships between these structures is not always easy to discern in the field. In southwestern Utah, the Jurassic Navajo Sandstone is cut by large-scale normal faults associated with the Sevier Fault Zone, making it perfect for observing several fracture types. The aim of this study is to complete a dynamic and kinematic analyses of the fractures near a major fault and to determine the chronologic relationships between the fractures. Specifically, we observed a previously unnamed segment of …

New Borehole Breakout Derived Stress Constraints And Their Implications For Stress Heterogeneity Near High Risk Fault Systems In The Santa Barbara Channel, Southern California, Edward Harris Pritchard

LSU Master's Theses

The Santa Barbara Channel represents the offshore portion of the Ventura Basin in Southern California. Ongoing transpression related to a regional left step in the San Andreas Fault has led to the formation of E-W trending en-echelon fault systems, with both north and south dips, which accommodate varying rates of localized shortening across the basin. Recent studies have suggested that faults within the northern region of the channel could be capable of a multisegment rupture and producing a M_w 7.7–8.1 tsunamigenic earthquake. However, dynamic rupture models producing these results have not accounted for stress heterogeneity, which is …

Large Rotations Of Crustal Blocks In The Tjörnes Fracture Zone Of Northern Iceland, Andrew J. Horst, J. A. Carson, R. J. Varga

Natural Resources and Earth Sciences Faculty Research

The interpretation of uppermost crustal deformation near oceanic transform faults is based on bathymetric lineaments and earthquake focal mechanisms, and relatively little is known about the detailed kinematics within the transform tectonized zone. The Tjörnes Fracture Zone is a broad zone of deformation produced by right‐lateral transform shearing in north Iceland and is partly exposed on land providing the opportunity to study shallow‐level crustal structure of mid‐Miocene, thick, oceanic‐like crust formed by subaerial spreading. A pronounced structural curvature of lava and dike orientations near the Húsavík‐Flatey Fault within the transform zone is well documented, yet of controversial origin. In order …

Miocene-Quaternary Deformation Along The Central Maynard Lake Fault, Pahranagat Shear Zone, Nevada, Alexander Peck

UNLV Theses, Dissertations, Professional Papers, and Capstones

The left-lateral Pahranagat shear zone (PSZ) and Caliente-Enterprise zone (CEZ) exist at the boundary between two sub-provinces, the Northern (NBR) and Central Basin and Range (CBR). The PSZ contains three major ENE striking sinistral faults, including the Maynard Lake fault (MLF), which is the longest fault and marks the southern boundary of the zone. The PSZ has been suggested to be a transfer zone, but little is known about the structures along these major faults that are involved in strain transfer. These left-lateral systems exist within the Central Nevada seismic belt which has experienced significant earthquakes in recent history. Possible …

Basement And Cover Structural Analysis Along The Eagle River Gorge, Sawatch Range, Colorado, Kaitlin Lee Askelson

Electronic Theses and Dissertations

The Sawatch Range within the Rocky Mountains of central Colorado exposes Paleoproterozoic basement and overlying Paleozoic sedimentary rocks with a complex history of ductile and brittle deformation.

The goal of this study is to conduct analyses of brittle structures that occur in the basement and cover units to determine geometric relationships between the structures, provide a detailed description of structures and refine a geologic history for structures along the basement-cover contact in the northeastern Sawatch Range along the Eagle River canyon and U.S. Highway 24 from Red Cliff to Gilman, Colorado. Paleoproterozoic basement rocks include the Cross Creek granite, diorites, …

Hidden Intrabasin Extension: Evidence For Dike-Fault Interaction From Magnetic, Gravity, And Seismic Reflection Data In Surprise Valley, Northeastern California, Noah D. Athens, Jonathan M.G. Glen, Simon L. Klemperer, Anne E. Egger, Valentina C. Fontiveros

All Faculty Scholarship for the College of the Sciences

The relative contributions of tectonic and magmatic processes to continental rifting are highly variable. Magnetic, gravity, and seismic reflection data from Surprise Valley, California, in the northwest Basin and Range, reveal an intrabasin, fault-controlled, ~10-m-thick dike at a depth of ~150 m, providing an excellent example of the interplay between faulting and dike intrusion. The dike, likely a composite structure representing multiple successive intrusions, is inferred from modeling a positive magnetic anomaly that extends ~35 km and parallels the basin-bounding Surprise Valley normal fault on the west side of the valley. A two-dimensional high-resolution seismic reflection profile acquired across the …

Paleoseismologic Evidence For Holocene Activity On The Pinto Mountain Fault, Twentynine Palms, California, Ana Maria Cadena

All Master's Theses

Excavations across the Pinto Mountain fault in Twentynine Palms, California exposed faulted strata across a 32-m wide zone. Trench wall exposures revealed clear evidence for five ground-rupturing events during the Holocene, and two additional events in the late Pleistocene. Optically stimulated luminescence ages from alluvial sediments suggest that the most recent event occurred between 1.7-2.9 ka B.P. and the penultimate event between 2.7-4.2 ka B.P.. Prior to the penultimate event, there were five ground-rupturing earthquakes on the eastern Pinto Mountain fault between 3.5-13.6 ka B.P.. The average recurrence interval since 13.3-13.6 ka B.P. is 1510-1680 years, and 1200-1500 years in …

Interseismic Strain Accumulation Along The Western Boundary Of The Indian Subcontinent, Walter Szeliga, Roger Bilham, Din Mohammad Kakar, Sarosh H. Lodi

All Faculty Scholarship for the College of the Sciences

Despite an overall sinistral slip rate of ≈3 cm/yr, few major earthquakes have occurred in the past 200 years along the Chaman fault system, the western boundary of the India Plate with the Eurasia Plate. GPS and InSAR data reported here indicate sinistral shear velocities of 8–17 mm/yr across the westernmost branches of the fault system, suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east. At its southernmost on‐land segment (≈26°N), near the triple junction between the Arabia, Eurasia, and India Plates, we find the velocity across the …

Penrose Conference Report: Neotectonics Of Arc-Continent Collision, Paul Mann, Carlos Vargas, Caroline Whitehill

Geological Sciences Faculty Scholarship

Collisions of arcs with continents are some of the most significant tectonic processes on Earth, leading to crustal accretion, continental growth, formation of sedimentary basins, large areas of regional uplift and deformation, complex interactions between continuous and torn subducted slabs and the surrounding mantle, and large regions of large earthquakes and seismic, volcanic, and landslide hazards that can threaten the lives of millions.
The objective of this conference was to bring together an international group of scientists to discuss the neotectonics and seismic hazards of shallow slab subduction in areas of arc-continent collisions.

Miocene - Quaternary Tectonic Evolution Of The Northern Eastern California Shear Zone, Kurt L. Frankel, Jeffrey Lee, Kim Bishop, Nancye Dawers, Plamen Ganev, Jeff Unruh, Lewis A. Owen

All Faculty Scholarship for the College of the Sciences

The northern eastern California shear zone is an important component of the Pacific– North America plate boundary. This region of active transtensional deformation east of the San Andreas fault extends from the Garlock fault northward along the east side of the Sierra Nevada and into western Nevada. The eastern California shear zone is thought to accommodate nearly a quarter of relative plate motion between the Pacific and North America plates. Recent studies in the region, utilizing innovative methods such as cosmogenic nuclide geochronology, airborne lidar, structural mapping, and (U-Th)/He geochronology, are helping elucidate deformation histories for many of the major …

Moment Release Rate Of Cascadia Tremor Constrained By Gps, Ana C. Aguiar, Timothy I. Melbourne, Craig W. Scrivner

All Faculty Scholarship for the College of the Sciences

A comparison of GPS and seismic analyses of 23 distinct episodic tremor and slip events, located throughout the Cascadia subduction zone over an 11-year period, yields a highly linear relationship between moment release, as estimated from GPS, and total duration of nonvolcanic tremor, as summed from regional seismic arrays. The events last 1–5 weeks, typically produce ~5 mm of static forearc deformation, and show cumulative totals of tremor that range from 40 to 280 h. Moment released by each event is estimated by inverting GPS-measured deformation, which is sensitive to all rates of tremor-synchronous faulting, including aseismic creep, for total …

Basal Mechanics Of Ice Streams: Insights From The Stick-Slip Motion Of Whillans Ice Stream, West Antarctica, J. Paul Winberry, Sridhar Anandakrishnan, Richard B. Alley, Robert A. Bindschadler, Matt A. King

All Faculty Scholarship for the College of the Sciences

The downstream portion of Whillans Ice Stream, West Antarctica, moves primarily by stick-slip motion. The observation of stick-slip motion suggests that the bed is governed by velocity-weakening physics and that the basal physics is more unstable than suggested by laboratory studies. The stick-slip cycle of Whillans Ice Plain exhibits substantial variability in both the duration of sticky periods and in slip magnitude. To understand this variability, we modeled the forces acting on the ice stream during the stick phase of the stick-slip cycle. The ocean tides introduce changes in the rate at which stress is applied to the ice plain. …

Episodic Tremor And Slip In The Pacific Northwest, Kenneth C. Creager, Timothy I. Melbourne

Geological Sciences Faculty Scholarship

Every 14 months the Pacific Northwest experiences slow slip on a fault that is the equivalent of about a magnitude 6.5 earthquake. While a typical earthquake of this magnitude happens in less than 10 seconds, the duration of these slip events is two to several weeks. The most recent event occurred from January 14 through February 1, 2007.

Late Holocene Uplift Of The Chihshang Segment Of The Longitudinal Valley Fault At Fuli, Eastern Taiwan, Brian Thomas Gray

All Master's Theses

Uplifted Holocene strath terraces of the Bieh River drainage, eastern Taiwan, were analyzed in order to determine millennial-scale uplift and horizontal shortening rates of the Longitudinal Valley fault. Detrital charcoal fragments collected from three terraces within the Bieh River drainage yield ages between 1395 and 555 cal. yr B.P, suggesting an average uplift rate of 11.3 ± 3.6 mm yr^-1 for the last 1400 cal. yr B.P. The average horizontal shortening rate of 19.7 ± 9.5 mm yr^-1 was within error of present-day conventional geodetic measurements, but near the lower limit of the geodetic measurements. This suggests that …

Penrose Conference Report: Kinematics And Geodynamics Of Intraplate Dextral Shear In Eastern California And Western Nevada, Jeffrey Lee, Daniel Stockli, Christopher Henry, Timothy Dixon

Geological Sciences Faculty Scholarship

This conference provided a forum to discuss the range of geological and geophysical datasets from the eastern California shear zone (ECSZ) and Walker Lane belt (WLB) that bear on how intraplate deformation is accommodated and how to integrate the data into a comprehensive, spatially and kinematically coherent view of intraplate deformation through time.

Gps-Determination Of Along-Strike Variation In Cascadia Margin Kinematics: Implications For Relative Plate Motion, Subduction Zone Coupling, And Permanent Deformation, M. Meghan Miller, Daniel J. Johnson, Charles M. Rubin, Herb Dragert, Kelin Wang, Anthony Qamar, Chris Goldfinger

All Faculty Scholarship for the College of the Sciences

High‐precision GPS geodesy in the Pacific Northwest provides the first synoptic view of the along‐strike variation in Cascadia margin kinematics. These results constrain interfering deformation fields in a region where typical earthquake recurrence intervals are one or more orders of magnitude longer than the decades‐long history of seismic monitoring and where geologic studies are sparse. Interseismic strain accumulation contributes greatly to GPS station velocities along the coast. After correction for a simple elastic dislocation model, important residual motions remain, especially south of the international border. The magnitude of northward forearc motion increases southward from western Washington (3–7 mm/yr) to northern …

New Kinematic Models For Pacific‐North America Motion From 3 Ma To Present, Ii: Evidence For A “Baja California Shear Zone”, Timothy Dixon, Fred Farina, Charles Demets, Francisco Suarez-Vidal, John Fletcher, Bertha Marquez-Azua, M. Meghan Miller, Osvaldo Sanchez, Paul Umhoefer

All Faculty Scholarship for the College of the Sciences

We use new models for present‐day Pacific‐North America motion to evaluate the tectonics of offshore regions west of the Californias. Vandenburg in coastal Alta California moves at the Pacific plate velocity within uncertainties (∼1 mm/yr) after correcting for strain accumulation on the San Andreas and San Gregorio‐Hosgri faults with a model that includes a viscoelastic lower crust. Modeled and measured velocities at coastal sites in Baja California south of the Agua Blanca fault, a region that most previous models consider Pacific plate, differ by 3–8 mm/yr, with coastal sites moving slower that the Pacific plate. We interpret these discrepancies in …

Present‐Day Motion Of The Sierra Nevada Block And Some Tectonic Implications For The Basin And Range Province, North American Cordillera, Timothy H. Dixon, M. Meghan Miller, Frederic Farina, Hongzhi Wang, Daniel Johnson

All Faculty Scholarship for the College of the Sciences

Global Positioning System (GPS) data from five sites on the stable interior of the Sierra Nevada block are inverted to describe its angular velocity relative to stable North America. The velocity data for the five sites fit the rigid block model with rms misfits of 0.3 mm/yr (north) and 0.8 mm/yr (east), smaller than independently estimated data uncertainty, indicating that the rigid block model is appropriate. The new Euler vector, 17.0°N, 137.3°W, rotation rate 0.28 degrees per million years, predicts that the block is translating to the northwest, nearly parallel to the plate motion direction, at 13–14 mm/yr, faster than …

"A Geological Interpretation Of The Stanley Fault And Other Thrust Faults In Page County, Virginia", Michael James Sarros

OES Theses and Dissertations

Paleozoic carbonate rocks flooring Page Valley (within Page County) are overthrust by Precambrian to Cambrian elastic rocks of the Blue Ridge to the east of the study area. King (1950) recognized that the Cambrian carbonate sequence of Page Valley, near Stanley, Virginia, is broken by a large transverse fault which he named the Stanley fault. King (1950) interpreted the Stanley fault as a high-angle reverse fault with oblique-slip displacement. However, detailed mapping and structural data collected in this study indicate the Stanley fault is a low angle thrust fault which cuts all pre-Alleghanian and Early Alleghanian structures.

Two previously unrecognized …