Browsing by Subject "Faults"
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Item 3-D seismic evaluation of fault control on quaternary subsidence patterns, rates, and related surface morphology in southeastern Louisiana(2008-08) George, Terra Jane; Mohrig, DavidThroughout the past century, the Louisiana coastline has been deteriorating at an alarming rate. Fault induced subsidence has been suggested to be one of the likely drivers of this land loss. I directly addressed the control of faulting on Quaternary delta subsidence using subsurface architectural data. I carried out a systematic process for evaluating fault movement on individual faults in the subsurface by using an industry grade 3-D seismic survey to evaluate the interaction of complex fault patterns and shallow substrate (< 1s or 1,000m). Using amplitude data, as well as a coherency algorithm, horizons and faults were mapped in ~1400km² of data in southeastern Louisiana. Measurements of fault displacement were obtained by determining time offset of synchronous horizons. Down-to-the-basin and counter-regional growth faulting was observed. Both styles of faulting are associated with movement of Jurassic-age salt deposits and display measurable offset at depths as shallow as ~.450s (roughly 380m). Fault displacements increase roughly linearly with burial depth. The displacement data together with well-log data provide a tentative Quaternary rate for the normal faulting of 0.1mm · yr⁻¹ to 1mm · yr⁻¹. I have assessed the possible control of subsurface faulting on surface topography using co-registered maps of fault traces and orthophoto quadrangles. This analysis has revealed a number of instances where faulting affects modern surface morphology. Often, the up-thrown sides of growth faults are capped by marshland, whereas the downthrown blocks are drowned by ~.7m of surface water (Snedden et al., 2007). Further, the influence of faulting extends to the modern planform of the lower Mississippi River, as data indicate that growth faults control the position of a major bend near the river's outlet.Item 3D seismic geomorphology and stratigraphy of the late Miocene to Pliocene Mississippi River Delta : fluvial systems and dynamics(2012-05) Armstrong, Christopher Paul; Steel, R. J.; Mohrig, David; Kim, WonsuckThis study uses a 1375 km2 3D seismic dataset located in the late Miocene to Pliocene Mississippi River Delta in order to investigate the external characteristics, lithology, and evolution of channelized deposits within the seismic survey. Fluvial thicknesses range from about 11 m to 90 m and widths range from about 100 m to 31 km. Channel fill can be generalized as sandy with low impedance and high porosity (~ 35%), though heterogeneity can be high. Three distinct fluvial styles were recognized: incised valleys, channel-belts, and distributive channel networks. Fluvial styles were interpreted as a result of changes in sea-level and a speculative late Miocene to Pliocene Mississippi River Delta sea-level curve constructed using these relationships. Additionally, a characteristic interval between the major changes in fluvial style was found. These fluvial systems interact with and are affected by other elements in the landscape. Growth faults in particular are common within the survey area; however, the dynamic between fluvial systems and growth fault related subsidence has been poorly understood and so was also a focus of this project. Previous work as well as this study found little evidence that growth faults are able to affect the course or geometry of the majority of small (with most < 500 m in width and < 20 m in depth) channels. However, the relationship between growth faults and larger scale channel-belt systems (between 1 km and 5 km in width and > 25 m in depth) has not been previously evaluated in this area. In contrast to the majority of small distributary channels found within the survey, channel-belts appear to be steered by growth faults. Fluvial response or insensitivity to fault induced subsidence is related to the relative timescales of avulsion and faulting. Channel-belts are longer lived features than more ephemeral small distributary channels. Channel-belts, due to their relatively low mobility compared to small channels, are more likely to experience punctuated faulting events which results in greater apparent sensitivity to faulting than seen in small channels.Item Chronostratigraphy, depositional rates, continental margin progradation, and growth-fault dynamics within the tertiary wedge, San Marcos arch, northwest Gulf of Mexico(1988) Travis, Deborah Sue, 1963-; Galloway, William E.Sedimentation, growth fault slip, and shelf-margin progradation rates were determined for a transect of Tertiary sediments along the axis of the San Marcos arch in the northwestern Gulf of Mexico basin. This low relief area was the site of shorezone depositional systems throughout most of the Tertiary and has not been affected by salt mobilization or the sedimentological overprint of large delta systems. Consequently, rates calculated in the area represent average rather than extreme values. Detailed correlation of 142 well logs and the utilization of paleontologic data from 17 wells made possible the construction of a chronostratigraphic cross section which divided the Tertiary section into 1 or 2 million year increments. A decompaction computer program, which utilizes published compaction curves and distinguishes between normally pressured shale, underconsolidated overpressured shale, and sandstone, calculated original sediment thickness and sedimentation rates for each of the chronostratigraphic layers. Regional sedimentation rates varied almost two orders of magnitude during the Tertiary. These findings seriously challenge the common assumption of relatively uniform sediment supply over geological time spans. Within individual chronostratigraphic layers, sedimentation rates ranged from 4 cm/1000 yrs in the fluvial and transgressive facies to 130 cm/1000 yrs in the lower Miocene outer shelf and slope facies. Decompaction of the section also allowed the calculation of growth fault slip rates and of the percent increase in accommodation on the downthrown side of the faults relative to their upthrown equivalents. Slip rates during times of maximum movement ranged from 250-600 m/my, agreeing with rates calculated for salt dome growth. Percent increase in accommodation on the downthrown side of the faults ranged from 20-83%. Shelf-margin progradation rates were calculated and ranged from -1.5 mi/my (2.4 km/my) during brief times of temporary retrogradation (Queen City and Yegua Formations) to 17.5 mi/my (28.2 km/my) during the Early MioceneItem Considering faults in CCS(Outreach Working Group (OWG) for the regional carbon sequestration partnerships, teleconference, 2007-06-14) Meckel, Timothy A.Item Edge-of-grid voltage control in distribution networks(2018-08) Padullaparti, Harsha Vardhana; Santoso, Surya; Baldick, Ross; Hallock, Gary; Korgel, Brian; Nikolova, EvdokiaAs the electric power supply systems are undergoing major changes with the integration of renewables, the issues related to voltage regulation and system protection are arising. In this scenario, advanced voltage regulation technologies that provide voltage control at the grid-edge, that is at the low-voltage secondary side of the distribution circuit, have emerged as a potential solution to address the shortcomings of traditional voltage control practices in distribution systems. In this work, these technologies are modeled and algorithms are developed to strategically deploy them, tune their control parameters, and evaluate their voltage regulation performance. A two-stage optimization framework is proposed for optimal placement and real-time control of the low-voltage static var compensators to minimize the energy losses while maintaining the voltage regulation. Integration of high levels of distributed generation such as photovoltaic (PV) systems impacts the voltage regulation by causing steady-state voltage variations and transient voltage fluctuations. This work further develops a procedure to tune the control parameters of PV smart inverters to mitigate these voltage issues. Furthermore, the PV penetration levels in a distribution network can be increased without creating voltage problems by dynamic controlled reactive power absorption at several strategic buses. This concept is modeled and demonstrated in this work. Furthermore, the high levels of PV generation can interfere with the overcurrent protection schemes prevalent in distribution networks. An analytical approach is proposed in this work to estimate the distribution feeder PV accommodation limits with respect to overcurrent protection issues as the impact criteria, without needing to simulate numerous PV screening scenarios to assess the impactItem Fault and fracture systems related to reactivation of pre-existing structural elements, Devils River Uplift and Maverick Basin, Texas(2013-12) Smith, Gordon Allen; Fisher, W. L. (William Lawrence), 1932-; Zahm, Christopher KentPre-existing structural elements can have substantial effects on fracture and fault development in younger strata, especially in areas that undergo significant changes in tectonic setting due to reactivation along older structures. This may affect reservoir permeability, yet remain difficult to detect in subsurface data. The focus of this study centers on two styles of pre-existing structures—Paleozoic thrust belts and Late Triassic rift faults in the Devils River Uplift and Maverick Basin, respectively—which affect the development of faults and fractures in Cretaceous strata. Fault and fracture data were characterized in both the outcrop and within a 3D seismic volume. Furthermore, the role of mechanical stratigraphy on fault and fracture style in both localities was examined. The Pecos River Canyon overlies the Paleozoic Ouachita fold-thrust belt with associated EW and SE-NW trending structures. At the surface, faults are expressed in two predominant orientations (N38E and N70E), which may be predictable angles if the pre-existing structures are reactivated by left lateral oblique slip. Detailed investigation of the fracture development related to these faults was conducted in a dry side canyon along the Pecos River. Mechanical layers were identified and mapped in outcrop to highlight fracture intensity variations between the different layers. The porosity and/or the degree of dolomitization are identified as controls on fracture development, with the lowest strength layer and least fractured being highly dolomitized with the largest porosity of any observed layer in outcrop. Southeast of Lewis Canyon, a 3D seismic of the Maverick Basin reveals linear discontinuities, interpreted as low-offset faults, within the Cretaceous Glen Rose through Austin Chalk that appear similar to those observed in outcrop along the Lower Pecos River. These faults are shown to have an increase in intensity within strata above older Late Triassic-age rift faults. It is proposed that the small faults form during reactivation of the rift faults and exhibit differential degrees of intensity and vertical terminations against six identified mechanical boundaries observed within the 3D seismic volume.Item Fracture sets, timing, and size distributions in the Cretaceous Frontier Formation, Greater Green River Basin, Wyoming(2015-05) Copley, Lauren Kupecz; Laubach, Stephen E. (Stephen Ernest), 1955-; Marrett, Randall; Behr, Whitney; Wilkins, ScottFractures influence permeability but sampling subsurface fractures is difficult in vertical wells. Horizontal cores are special cases allowing fracture abundance, distribution, and aperture size populations to be measured. Four horizontal cores (41.5 m) in Cretaceous Frontier Formation, eastern Greater Green River Basin, Wyoming, sample litharenites to sublitharenites (average 87.4% quartz, 2.1% feldspar, 10.6% lithics) deposited in upper and lower shoreface marine environments. Low porosity (3-10%) results from compaction and quartz, calcite, and kaolinite cement. Younger north-striking Set 2 fractures cross cut older east-striking Set 1 fractures, and both are likely regional fractures predating local folding. Both sets contain quartz, calcite, and kaolinite cement with local remnant porosity. Fluid inclusion assemblage temperatures were sequenced using quartz crack-seal cement textures compared to thermal history, and indicate Set 1 opened at 140-160°C during burial in Eocene time. Set 2 fractures opened at maximum burial, and continued to open during uplift from local basement-involved fold-fault. Subsequently some Set 1 fractures reactivated as faults. Fault-related kaolinite deposits locally occlude fracture porosity. Extensive SEM-CL micro-imaging demonstrates that transgranular microfracture populations are rare. Although only 48% of macrofracture aperture sizes could be measured accurately, aperture size ranges appear to be narrow, with apertures of 0.62-1.75 mm. Spacing ranges from 0.01 mm to meters with moderate clustering. Lower macrofracture abundance in the upper shore face (2.39 fractures/m) compared to the lower shore face (4.12 fractures/m) corresponds to lower subcritical crack index (SCI) and fracture toughness of the upper shoreface. Upper shoreface sandstones have lower average SCI (46) and fracture toughness (1.6 Mpa√m) than upper shoreface sandstones (54 and 2.2 Mpa√m, respectively). Presence of crack-seal quartz in both sets, together with extremely sparse microfractures, indicates thin, sparse, intermittently-bridging synkinematic quartz likely provided insufficient within-fracture bonding to partition deformation into microfracture populations during fracture development. High initial gas production in these wells correlate with observations of persistent fracture porosity in fractures through burial and uplift, locally-large apertures, and extremely long regional fracture lengths (>500 m) in Frontier Formation outcrops. Results suggest that for the Frontier Formation in this setting, productive fractures are not necessarily localized near folds and faults.Item Kinematic analysis of outcrop-scale structures, southern Big Sur segment of Highway 1, Monterey and San Luis Obispo Counties, California(2007) Trasko, Keith Patrick; Cloos, MarkThe Nacimiento Block is located in the Southern Coast Ranges of California, and consists mainly of Franciscan Complex accretionary prism rocks. It is cross-cut by the San Gregorio-Hosgri Fault Zone, a major right-lateral strand of the San Andreas Fault System. The Nacimiento Block is bounded on the east by the Nacimiento Fault, of debated timing and kinematics, which separates it from the Salinian Block. The Salinian Block is a piece of the Sierra Nevada Batholith, and both the Salinian and Nacimiento Blocks have been displaced from southern California by right-lateral slip on the San Andreas Fault System. To address the question of fault kinematics, a 48 kilometer long section of the Nacimiento Block was examined along California Highway 1 between Lopez Point and Ragged Point. Exposure occurs along approximately 20 kilometers of the transect, and landsliding obscures approximately half of the exposure. The remaining 10 kilometers of outcrop were mapped. Kinematic data were taken on 29 outcrops, totaling 542 minor faults, 406 with slickenlines and 258 with sense of slip indicators, along with 314 veins. Of the faults, 202 are dip-slip (60-90° rake), 113 are oblique-slip (31-59° rake), and only 91 are strike-slip (0-30° rake). The dominant mode of minor faulting is normal, with 111 faults observed, compared to 25 reverse, 24 left-lateral, and 28 right-lateral strike-slip. Two sets of vein and one set of dike orientations were measured. Stereographic analysis reveals the normal and reverse faults dip steeply to the southwest and strike northwest-southeast, subparallel to the coast and San Gregorio-Hosgri and Nacimiento Faults. There is no dominant orientation to the strike-slip faults. Faults of all types cut 17 slab-window related andesitic dikes, which are likely Early Miocene in age according to apatite and zircon fission track ages. The character of all fault planes is similar, indicating they are coeval. Three stages of deformation are recognized. Subduction generated mélange, the dominant lithology in this area, and "broken formations". A second stage of deformation is recorded in the emplacement of dikes and one set of veins. A third stage of deformation is recorded in the minor planar faults that were measured in this study. It is proposed that this latest phase of deformation is caused by the gravitational collapse of the western edge of the Santa Lucia Range. The normal faults parallel the coastline and local slope angles are up to 40°. Coeval strike-slip associated with the San Gregorio-Hosgri Fault Zone is superimposed on this deformation. Apatite fission track ages (n=3) indicate that the dikes mapped along Highway 1 cooled to 110°C at approximately 11 Ma. This indicates an unroofing rate on the order of 300 m/my. This anomalously fast unroofing is accomplished by side-inwards gravitational collapse and erosionItem Size distribution and spatial arrangement of normal faults in A-Bomb Canyon, Buckskin Mountains, Western Arizona(2017-04-20) Hundley, Thomas Harland; Marrett, Randall; Helper, Mark A; Cloos, MarkThe spatial arrangement of structural features, such as faults, can be randomly located, clustered together, or anti-clustered in space. The objective of this project is to understand the spatial arrangement of normal faults in A-Bomb Canyon, in the Buckskin Mountains of Arizona, as a function of fault offset, herein defined as displacement. The normalized correlation count (NCC) methodology is used in this study to quantify the spatial arrangement of faults. In the process of studying the arrangement of faults at A-Bomb Canyon, the displacement distribution, coefficient of variation as well as the NCC are examined to understand whether the faults cluster or are randomly spaced and if clustered, whether clusters show fractal scaling. Data analysis uses a traditional approach of size distribution analysis along with the correlation count technique. Results show that the frequency distribution of fault displacements follows a power law that spans ~four orders of magnitude. Faults with displacement thresholds of less than 1 meter display plateau patterns in NCC, indicate clustering at varying spacing, but clustering is not self-organized. Normal faults with > 1 meter displacement reflects faults with a dominant spacing of approximately twenty meters.Item Stratigratigraphic architecture and basin fill evolution of a plate margin basin, eastern offshore Trinidad and Venezuela(2006-05) Garciacaro, Emilio José; Mann, Paul, 1956-; Wood, Lesli J.Eastward migration of the Caribbean plate relative to the South American plate is recorded by a 1100-km-long foreland basin which is oldest in the west (Maracaibo basin, 65-55 Ma) and youngest in the east (Columbus basin, eastern offshore Trinidad, 15-0 Ma). Regional transpression has caused lithospheric loading and flexure along the northern margin of South America creating a large foreland basin area which propagated from west to east as the Caribbean plate moved eastward relative to the South American plate. I have integrated 775 km of deep-penetration 2D seismic lines acquired by the 2004 BOLIVAR survey, 325 km of 1975 GULFREX seismic data, 8,000 km2 of industry 3-D seismic data, and published industry well data from offshore eastern Trinidad. Interpretation of seismic sections tied to wells reveals the following fault chronology: 1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; 2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; 3) early Pliocene-Recent strike-slip faults parallel to the trend of the Darien ridge and accommodate present-day plate motions. Active mud diapirism in the Columbus basin is widespread and is related to overthrusting and loading of upper Miocene-lower Pliocene age mud. Analysis of the 3-D seismic data reveals the presence of extensive gravity-flow depositional elements on the Columbus basin deepwater area, characterized by mass-transport deposits at the base, turbidite frontal-splay deposits, leveed-channel deposits, and capped by fine-grained condensed-section deposits. Deep basin wells drilled in recent years have proven that turbidites were transported into the Columbus basin deepwater during the Plio-Pleistocene. Analysis of these well results suggest that a deeper oil charge is present within the Columbus basin deepwater area. The primary uncertainty for this variable hydrocarbon system is whether fault or diapiric pathways connect the petroleum charge at depth with shallower reservoir rocks.Item Sustained and incipient fault location for utility distribution system(2009-12) Chopra, Shivaz; Santoso, Surya; Grady, MackAutomated fault location systems use power quality monitoring and circuit data to provide with a distance or impedance estimate to the fault. This can be used to avoid manual patrolling of the entire feeder in case of a main feeder lockout. It can also be used for circuits with repeated momentary interruptions to pinpoint the section of the circuit causing such problems. Self clearing sub cycle faults have been identified as the precursors of a number of sustained faults (requiring the operation of protective device) in utility distribution networks. The frequency of such incipient faults increases considerably as they are about to evolve into a full blown fault. This report proposes a modified and improved fault location algorithm that can be used to accurately identify sustained as well as temporary faults. The algorithm is based in the time domain and takes into account the arc voltage during a fault event. The proposed algorithm is developed, validated and applied to known distribution field data. Time domain simulation models are also used for validation purposes. The developed algorithm was observed to be very accurate when compared to other impedance based fault location algorithms proposed in the literature. Finally, sub cycle event identification and fault pre-location is proposed that can be very useful for electric utility operations. Highly accurate results were observed during this application study. For instance, a current waveform containing three incipient and one full fault event is shown in the figure given below. The estimated reactance to an incipient fault location is approximately 1.1 Ω. The fault location results obtained from the first three sub-cycle faults can be used to avert the final sustained fault event.