Detailed Analysis of Structures in the Foot Wall of the Champlain Thrust at Lone Rock Point, Burlington, Vermont

The objective of this project was to identify a strain gradient and relative chronology within the foot wall of the Champlain Thrust Fault at Lone Rock Point, Burlington, Vermont in order to determine how the unique fault-bounded ellipsoidal lozenge structures formed and why they are contained to one area within the foot wall. Previously researched models seemed to suggest the fault bounded lozenges were a horse thrust system that followed the strong pre-existing limestone/dolostone bedding layers of the Iberville Shale. However, this paper indicates that the lozenges are a horse thrust system formed by an S-C fabric between the 1st and 2nd generation cleavages, not by bedding, and as such are a gauge of moderate strain within the foot wall. Also, by identifying a relative chronology within the foot wall, this paper lays the groundwork to explain why two wells drilled near Lone Rock Point by McGill University in the summer of 2014 observed the Champlain Thrust Fault to have a thirty five meter depth difference over a ten meter distance. The original hypothesis to explain this observation was that normal faults were crosscutting the main thrust and causing the displacement. However, this paper failed to conclusively support that hypothesis since the normal faults identified within the foot wall were found to neither cross the main thrust nor displace rock more than one centimeter. Further research should be conducted within the hanging wall at Lone Rock Point to conclusively interpret this observation

On the growth of normal faults and the existence of flats and ramps along the El Asnam active fold and thrust system

The combination of detailed topographic leveling on the southwest segment of the El Asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps. The fault appears to be growing along strike toward the southwest end, where the main shock initiated in 1980. From a depth of about 10 km, the main thrust appears to ramp to the basement-Cenozoic cover interface on a plane striking N40°E and dipping 50°–55° to the northwest. Along the southwest segment where folding has not yet developed, the thrust continues steeply through the Cenozoic cover to the near surface where it flattens, causing normal faulting. Along the central and northeast segments, which display a more evolved fold structure, the deep thrust probably flattens at a depth of 5–6 km, into a decollement along the Cenozoic-Jurassic interface before ramping to the surface. The Sara El Marouf and Kef El Mes anticlines have thus formed as fault propagation folds. Normal faults at Beni Rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement. The greater separation (∼7 km) between the normal faults at Beni Rached and the thrust where it crosses Oued Cheliff than along the southwest segment (∼1 km) reflects the greater depth of the ramp to flat bend. We infer that the September 9, 1954, earthquake activated only the central deep segment of the main thrust together with the Beni Rached normal faults, while that of October 10, 1980, activated the whole system of flat decollements, ramp thrusts and compatibility normal faults. Further complexities of the faulting in map view are related to changes of strike of the thrust (in particular north of Oued Cheliff)

Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal

We analyze geomorphic evidence of recent crustal deformation in the sub-Himalaya of central Nepal, south of the Kathmandu Basin. The Main Frontal Thrust fault (MFT), which marks the southern edge of the sub-Himalayan fold belt, is the only active structure in that area. Active fault bend folding at the MFT is quantified from structural geology and fluvial terraces along the Bagmati and Bakeya Rivers. Two major and two minor strath terraces are recognized and dated to be 9.2, 2.2, and 6.2, 3.7 calibrated (cal) kyr old, respectively. Rock uplift of up to 1.5 cm/yr is derived from river incision, accounting for sedimentation in the Gangetic plain and channel geometry changes. Rock uplift profiles are found to correlate with bedding dip angles, as expected in fault bend folding. It implies that thrusting along the MFT has absorbed 21 ± 1.5 mm/yr of N-S shortening on average over the Holocene period. The ±1.5 mm/yr defines the 68% confidence interval and accounts for uncertainties in age, elevation measurements, initial geometry of the deformed terraces, and seismic cycle. At the longitude of Kathmandu, localized thrusting along the Main Frontal Thrust fault must absorb most of the shortening across the Himalaya. By contrast, microseismicity and geodetic monitoring over the last decade suggest that interseismic strain is accumulating beneath the High Himalaya, 50–100 km north of the active fold zone, where the Main Himalayan Thrust (MHT) fault roots into a ductile décollement beneath southern Tibet. In the interseismic period the MHT is locked, and elastic deformation accumulates until being released by large (M_w > 8) earthquakes. These earthquakes break the MHT up to the near surface at the front of the Himalayan foothills and result in incremental activation of the MFT

Georgetown Lake Seismic Survey

A near surface seismic survey was performed in order to locate the Georgetown Thrust Fault. The location of the thrust fault relative to Georgetown Lake has been previously proposed by field mapping methods (Lonn et al.,2004). A seismic survey could be useful to identify the thrust fault because of possible geologic discontinuities at the boundaries of the thrust fault that could give rise to diffraction energy indicative of the presence of those discontinuities. The Montana Tech summer field camp recorded a seismic survey along the southern edge of Georgetown Lake. This report focuses on the optimal processing methods for near surface seismic data with the goal of producing a coherent seismic section for this dataset. The area around the thrust fault did not have coherent reflections that could directly correlate to the presence of a thrust fault. Due to the lack of reflections in the vicinity of the thrust fault, no direct indication of the thrust fault on the seismic section was observed. Indirectly, the only evidence of the thrust fault was lateral discontinuities in the seismic section. On the other hand, reflections characteristic of a basins were clearly visible on the seismic profile

The width of fault zones in a brittle-viscous lithosphere: Strike-slip faults

A fault zone in an ideal brittle material overlying a very weak substrate could, in principle, consist of a single slip surface. Real fault zones have a finite width consisting of a number of nearly parallel slip surfaces on which deformation is distributed. The hypothesis that the finite width of fault zones reflects stresses due to quasistatic flow in the ductile substrate of a brittle surface layer is explored. Because of the simplicity of theory and observations, strike-slip faults are examined first, but the analysis can be extended to normal and thrust faulting

New active faults on Eurasian-Arabian collision zone : Tectonic activity of Özyurt and Gülsünler faults (eastern Anatolian Plateau, Van-Turkey)

The Eastern Anatolian Plateau emerges from the continental collision between Arabian and Eurasian plates where intense seismicity related to the ongoing convergence characterizes the southern part of the plateau. Active deformation in this zone is shared by mainly thrust and strike-slip faults. The Özyurt thrust fault and the Gülsünler sinistral strike-slip fault are newly determined fault zones, located to the north of Van city centre. Different types of faults such as thrust, normal and strike-slip faults are observed on the quarry wall excavated in Quaternary lacustrine deposits at the intersection zone of these two faults. Kinematic analysis of fault-slip data has revealed coeval activities of transtensional and compressional structures for the Lake Van Basin. Seismological and geomorphological characteristics of these faults demonstrate the capability of devastating earthquakes for the area

Fault Slip and Exhumation History of the Willard Thrust Sheet, Sevier Fold‐Thrust Belt, Utah: Relations to Wedge Propagation, Hinterland Uplift, and Foreland Basin Sedimentation

Zircon (U‐Th)/He (ZHe) and zircon fission track thermochronometric data for 47 samples spanning the areally extensive Willard thrust sheet within the western part of the Sevier fold‐thrust belt record enhanced cooling and exhumation during major thrust slip spanning approximately 125–90 Ma. ZHe and zircon fission track age‐paleodepth patterns along structural transects and age‐distance relations along stratigraphic‐parallel traverses, combined with thermo‐kinematic modeling, constrain the fault slip history, with estimated slip rates of ~1 km/Myr from 125 to 105 Ma, increasing to ~3 km/Myr from 105 to 92 Ma, and then decreasing as major slip was transferred onto eastern thrusts. Exhumation was concentrated during motion up thrust ramps with estimated erosion rates of ~0.1 to 0.3 km/Myr. Local cooling ages of approximately 160–150 Ma may record a period of regional erosion, or alternatively an early phase of limited... (see full abstract in article)

Identification and interpretation of tectonic features from ERTS-1 imagery

The author has identified the following significant results. ERTS-1 imagery shows that the southern segment of the San Gabriel fault which controls the west fork of the San Gabriel River is strikingly similar to the Mill Creek Fault in the San Bernardino Mountains. It has also been noted that there is a similarity between the Sierra Madre thrust zone of the San Gabriel Mountains to the Banning thrust of the San Bernardino Mountains. This suggests that the southern San Gabriel fault was once continuous with the Mill Creek fault. When the San Bernardino Mountain block is theoretically moved to the northwest along the San Jacinto fault so that the Mill Creek fault is aligned with the southern part of the San Gabriel fault, it was found that the four transverse fault segments become aligned with the Pinto Fault on the east and with the Raymond-Santa Monica Malibu Fault zone on the west. The reconstruction identifies a continuous zone of transverse faulting extending from the Colorado River Desert to the Pacific. It seems likely that the entire fault zone was once a continuous left-lateral shear. This Anacapa Shear has probably been subjected to a 50 km left lateral movement. This analysis strongly indicates that the tectonic history of the Transverse Range has been characterized by left lateral shear on transverse faults and right lateral shear on the San Andreas fault system

Bridge-Pier Caisson foundations subjected to normal and thrust faulting:physical experiments versus numerical analysis

Surface fault ruptures can inflict serious damage to engineering structures built on or near them. In the earthquakes of Kocaeli, Chi-chi, and Wenchuan a number of bridges were crossed by the emerging normal or thrust faults suffering various degrees of damage. While piles have proved incapable of tolerating large displacements, massive embedded caisson foundations can be advantageous thanks to their rigidity. The paper explores the key mechanisms affecting the response of such bridge foundations subjected to dip-slip (normal or thrust) faulting. A series of physical model experiments are conducted in the National Technical University of Athens, to gain a deeper insight in the mechanics of the problem. The position of the caisson relative to the fault rupture is parametrically investigated. High-resolution images of the deformed physical model is PIV-processed to compute caisson displacements and soil deformation. A novel laser scanning technique, applied after each dislocation increment, reveals the surface topography (the relief) of the deformed ground. 3D finite element analyses accounting for soil strain-softening give results in accord with the physical model tests. It is shown that the caisson offers a kinematic constraint, diverting the fault rupture towards one or both of its sides. Depending on the caisson's exact location relative to the rupture, various interesting interaction mechanisms develop, including bifurcation of the rupture path and diffusion of plastic deformation.</p

Kinematics of fault-related folding derived from a sandbox experiment

We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata