Thesis (Geophysical Engineer)--California Institute of Technology, 1950. / Title from home page (viewed 04/27/2010). Includes bibliographical references.

Thesis (Ph.D.(Exploration Geophysics))--University of Pretoria, 2007. / Abstract in English. Includes bibliographical references (leaves 72-76).

This article provides a comprehensive reference list to the extensive studies of marine natural gas hydrate surveys and studies on the northern Cascadian margin of Western Canada. The references are divided into each of the major study methods, surveys, analyses and conclusions. A number of MSc and PhD theses are included. We first refer to the articles that address the local tectonics and sedimentary accretionary prism in which the hydrate forms, then those that describe the numerous geophysical and geological surveys and studies, and finally the articles that address the most important conclusions that have resulted from this work on the distribution , concentrations, and amounts of hydrates, and on the processes of hydrate formation and dissociation.

This paper presents new interpretations of two normal-slip, low-angle faults near Smithfield and Richmond, Utah. The faults have previously been interpreted as landslides, gravity slides, slide blocks, and depositional contacts. Recent work in the Basin and Range province allows new interpretations concerning the origins of the low­-angle faults. Working hypotheses used to interpret origins of the faults are classified as folded thrust fault, rotated high-angle normal fault, gravity slide, listric normal fault, and low-­angle normal fault Among these general categories are several subhypotheses. The evaluation of each hypothesis includes a description of the geologic requirements of the hypothesis, a comparison of field data to the requirements, and a conclusion regarding the hypothesis. Field maps, computer analyses of fault orientations, geophysical surveys, well logs, and published discussions of low-angle-fault origins provide the data base from which to derive conclusions. The data best fit a low-angle-normal-fault hypothesis which states that low-angle normal faults in the study area represent a pre-Basin and Range style of extensional tectonism in which principal stress axes were in a transitional state between compressional tectonism and modern Basin and Range extensional tectonism. The northern low-angle normal fault formed as early as the late Eocene, followed by the southern low-angle normal fault in the early to middle Miocene(?). Episodes of high­-angle normal faulting followed formation of the southern low-angle normal fault. The faulting history indicates that two distinct stress states existed resulting in two different styles of normal faults. Schematic cross-sectional reconstructions based on two other low-angle-normal­fault subhypotheses and the gravity-slide subhypothesis 2 indicated that these subhypotheses could be valid However, the two low-angle-normal-fault subhypotheses cannot account for transitional stress states, and the gravity-slide subhypothesis explains only the southern low-angle normal fault. On the basis of geologic simplicity, the best hypothesis should explain both low-angle faults because of their similarities in deformation, orientation, and age. The applicability of the low-angle-normal-fault model to the rest of the Basin and Range province is somewhat limited. Too many local variables are involved to allow one model to be regionally applied. (112 pages)

Thesis (M.A.)--University of Tennessee, Knoxville, 2009. / Title from title page screen (viewed on Oct. 22, 2009). Thesis advisor: Gerald F. Schroedl. Vita. Includes bibliographical references.

Abstract Impact cratering is a fundamental geomorphic process on planetary surfaces. More than 60% of known hypervelocity impact craters on Earth are either partially or completely buried beneath post-impact sediments and one-third have been discovered with geophysical methods. In this thesis, geophysical surveys (gravity, magnetics, seismic, bathymetric mapping) were conducted at the deeply buried (>400 m) Holleford impact crater (~2.35 km) and two probable impact structures (Charity Shoal, Skeleton Lake) in southern Ontario, Canada. 3-D potential field models were constructed to determine the subsurface geology and buried crater morphology, and to evaluate evidence for possible impact versus endogenic origins. Holleford Crater is a deeply buried, Late Proterozoic-Early Cambrian (ca. 550 ±100 Ma) simple impact crater (~2.4 km) in southeastern Ontario, Canada. Land-based magnetic and gravity surveys and modelling were conducted in this study, recorded a ~ -3 mGal Bouguer anomaly and small (~30 nT) magnetic anomaly over the crater basin. 3-D gravity modelling revealed a deeply buried simple impact basin in Mesoproterozoic basement with an estimated rim-to-rim diameter (D) of 1.8-2 km, a residual rim height of ~20-30 m and true depth (dt) >400 m. The southeast crater rim is dissected by a 150 m deep, 400 m wide erosional channel produced by fluvial rim dissection. The outflow is infilled by >50 m of Late Cambrian clastic sediments, indicating a probable Late Proterozoic to Early Paleozoic impact event. Charity Shoal is a 1.2-km-diameter, 20 m deep, circular bedrock shoal in eastern Lake Ontario. Marine seismic profiling and total field magnetic surveys (140-line km) were conducted over a 9-km2 area and combined with available multi-beam bathymetric data to evaluate the subsurface geology and structure origin. Seismic surveys revealed ~30 m of Quaternary sediments overlying Middle Ordovician (Trenton Group) carbonates in the central basin and evidence for folding and faulting of the structure rim. Magnetic surveys recorded an annular magnetic high (> 600 nT) and a central magnetic low (~500-600 nT) coincident with a ~-1.7 mGal Bouguer gravity anomaly. The continuity of Middle Ordovician bedrock below the structure rules out a post-Paleozoic intrusion and a pre-Paleozoic intrusion is ruled out with the gravity anomaly. A deeply-buried (> 450 m) impact crater is the only scenario consistent with geophysical evidence. The crater has a rim-to-rim diameter of ~1.2 km, and rim height of ~15-20 m. A 100-m wide breach in the southwestern rim records a possible outflow channel. Skeleton Lake is a suspected (~4.0 km) Paleozoic-age impact structure in Muskoka, Ontario. The lakebed morphology, subsurface structure and possible impact origin were investigated with high-resolution geophysical surveys (magnetics, bathymetry; ~140 line-km) and 3-D magnetic modelling. Bathymetric data reveal a deep (>65 m) central basin with arcuate (Paleozoic?) bedrock ridges that rise >30 m above the southwestern lakebed. Magnetic surveys recorded a >700 nT magnetic low, which truncates northwest-southeast regional magnetic trends. Low-amplitude, northwest-trending magnetic lineaments delineate basement shear zones below the basin centre. Through-going magnetic lineaments and lack of thermal alteration (e.g., dikes, fenitization) in Mesoproterozoic rocks indicate a volcanic origin is unlikely. A 1.2 km diameter volcanic plug with an Early Cambrian remanence (D = 82.2°, I = 82.7°) can reproduce some aspects of the magnetic anomaly but is at odds with the Bouguer gravity anomaly (~ -3 mGal). Forward modelling of a crater-form basin with induction and remanence magnetization yielded an estimated structure depth of ~1200 m. The basement surface model shows a complex basement topography with no apparent rim structure and elevated ‘pinnacles’ that may represent eroded remnants of a central uplift or a highly-dissected basement topography. The structure apparent diameter (> 4.2 km) and complex basement topography suggest a heavily-modified transitional crater, similar with the Gow (Saskatchewan, Canada) and Kärdla (Estonia) impact structures. This thesis demonstrates the subsurface exploration of confirmed and suspected impact structures, integrating seismic, potential field (magnetics, gravity) and digital elevation data within a 3-D geophysical modelling workflow. The approach provides important new insights into the surface and subsurface geology, morphology, and post-emplacement modification of the Holleford impact crater, and new geophysical constraints for evaluating two suspected impact structures. Geophysical data confirm that Charity Shoal and Skeleton Lake are deep-seated, crater-form depressions in Mesoproterozoic basement rocks. The weight of geophysical and geological evidence points to impact cratering processes as opposed to an endogenic (volcanic) origin for both structures. / Thesis / Doctor of Science (PhD)

The need for accurate reference bases for any gravimetric work can hardly be overemphasized. During the months of March, April, and May, 1964, about 130 gravity observations were made in Arizona, with LaCoste Romberg Gravity Meter DL-1 and Worden Gravity Meter (Educator) No. 461. The purpose of this program was to establish 1) a 1st order control airport gravity base network, 2) a standard calibration range for the State of Arizona, and 3) to gain a structural interpretation of the Tucson Basin. Gravity data were analyzed as to their accuracies and reliabilities, taking into consideration errors involved in tidal corrections, drift corrections, reference datum, and nonlinearity of scale factor of the meters. It is concluded that the reliability of these data is .1 milligal or better. While correcting for the tidal variation of gravity, it was noticed that there was a discrepancy between the theoretical and observed tidal correction values. For any additional precise work, it is desirable to correct for tidal variations from actual records, if available, in conjunction with the theoretical tables. Causes for this discrepancy in tidal gravity variation need further study. Programs were written for a digital computer to calculate 1) the theoretical gravity values from the International Gravity Formula, and 2) Free-Air Anomalies, Bouguer Anomalies and Special Bouguer Anomalies from field data for various stations. Free-Air and Bouguer Anomaly values for different stations were analyzed as to their implications in terms of isostasy, crustal structures and local geological structures. Results from Simple Bouguer Anomaly values indicate a crustal thickness of 49 km to 33 km for Arizona with broad isostatic compensation for regional surface irregularities. An analysis of residual Bouguer gravity anomalies of the Tucson Basin in terms of local geological structures, indicates a basin and range structure for this region. The thickness of sediments ranges from more than 700 feet on the north to more than 8000 feet towards the south of the basin with faults indicated in it. Application of a limiting -depth interpretation method implies that the tops of the disturbing bodies can be no deeper than 2 miles below sea level. A total mass deficiency corresponding to the residual gravity low in this basin comes out to be 1.8 x 10¹⁷ grams according to two – dimensional form of Gauss' Theorem. This corresponds to a 135 cubic mile volume of material with a density .3 grams per cubic centimeter less than the enclosing rocks. From porosity and volume considerations of the sediments in the Tucson Basin, it is estimated that the total water holding capacity may be of the order of 4.6 x 10⁷ acre feet.

no / No Abstract

yes / This document reviews Legacy Data generated from 10 years’ worth of road scheme activity in Ireland to determine how archaeological geophysical surveys could be carried out on national roads in the future. The geophysical surveys were carried out by several different contractors across a range of challenging field conditions, geologies, weather and seasons. The research is based upon the results of linear schemes but also has validity for wider approaches. The findings of this research are based upon the compilation of all terrestrial archaeological geophysical surveys carried out on behalf of the National Roads Authority (NRA), a review of the success or otherwise of those surveys in comparison with ground-observed excavations and in combination with experimental surveys that tested previously held assumptions or knowledge to determine best practice methods for the future. The use and success of geophysical surveys in Ireland differ quite significantly from those in the UK, from where many of the methods of assessment were derived or adapted. Many of these differences can be attributed to geology. Ireland has a very high percentage of Carboniferous limestone geology, overlain mostly by tills and frequent occurrences of peat. These soils can reduce, to some extent, the effectiveness of magnetometer surveys; the most frequently used geophysical technique in Ireland. However, magnetometer data can be maximised in these cases by increasing the spatial resolution to produce effective results. An increase in spatial resolution is also effective generally, for enhancing the chances of identifying archaeological features by discriminating between archaeological and geological anomalies as well as increasing anomaly definition and visualisation of small and subtle archaeological features. Seasonal tests have determined that Irish soils are generally suitable for year round earth resistance assessments although some counties in the southeast of the country may experience very dry soils at the surface during some periods of the year. A variety of sampling strategies were used in the past, however it is now apparent that detailed assessments across the full length and width of a proposed road corridor are the most appropriate form of geophysical investigation. Magnetometer surveys are generally suitable for most Irish soils and geologies, although exceptions apply in areas of near-surface igneous deposits, deep peat and alluvial soils; however magnetometer surveys are not capable of identifying all types of archaeological features and other methods will be required for a full evaluation. Analysis of the Legacy Data has determined that in general the NRA archaeological geophysical surveys were historically used in a very positive way on road schemes. The range of features assessed or identified account for most types of archaeological sites in Ireland. These have provided a significant archive of case studies that will be of benefit to future archaeological geophysical research and will help to protect the globally dwindling archaeological resource that is threatened by development-led or commercially driven projects.

Η παρούσα διπλωματική εργασία περιγράφει την έρευνα της θαλάσσιας γεωφυσικής διασκόπησης η οποία εκτελέστηκε στον Πατραϊκό κόλπο και παρουσιάζει τα αποτελέσματα της ερμηνείας των γεωφυσικών στοιχείων που συλλέχθηκαν με την βοήθεια του τομογράφου υποδομής πυθμένα. Τα στοιχεία συλλέχθηκαν από το Εργαστήριο Θαλάσσιας Γεωλογίας και Φυσικής Ωκεανογραφίας του τμήματος Γεωλογίας του Πανεπιστημίου Πατρών. Η συλλογή, επεξεργασία και ερμηνεία του συνόλου των σεισμικών γραμμών επέτρεψε την χαρτογράφηση των υποθαλάσσιων ρηγμάτων του Πατραϊκού κόλπου. Ο χάρτης με τα υποθαλάσσια ρήγματα αποτελεί έναν τροποποιημένο χάρτη από τον ήδη διαθέσιμο χάρτη ρηγμάτων του Πατραϊκού κόλπου του 1985 από τους Ferentinos et al., 1985. / The present study describes the submarine geophysical survey which was carried out in the Gulf of Patras and presents the results of the geophysical data analysis using a subbottom profiler system. The data were collected by the Laboratory of Marine Geology & Physical Oceanography, department of Geology, University of Patras. A detailed fault map was produced by the data analysis of the collected seismic profiles of the Gulf of Patras. The present fault map is a modified map from a former map that has been produced in a 1985 survey by Ferentinos et al., 1985.