Aeromagnetic Interpretations of the Crittenden County Fault Zone

2020 ◽  
Vol 92 (1) ◽  
pp. 494-507
Author(s):  
Christopher Marlow ◽  
Christine Powell ◽  
Randel Cox
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Reverse Fault ◽  
Maximum Magnitude ◽  
Fault Systems ◽  
Basement Faults ◽  
Seismic Reflection Profiles

Abstract The Crittenden County fault zone (CCFZ) is a potentially active fault zone located within 25 km of Memphis, Tennessee, and poses a significant seismic hazard to the region. Previous research has associated the fault zone with basement faults of the eastern Reelfoot rift margin (ERRM) and described it as a northeast-striking, northwest-dipping reverse fault. However, we suggest that there is an incomplete understanding of the fault geometry of the CCFZ and the ERRM in this region due to significant gaps in seismic reflection profiles used to interpret the fault systems. To improve our understanding of the structure of both fault systems in this region, we apply two processing techniques to gridded aeromagnetic data. We use the horizontal gradient method on reduction-to-pole magnetic data to detect magnetic contacts associated with faults as this technique produces shaper gradients at magnetic contacts than other edge detection methods. For depth to basement estimations, we use the analytic signal as the method does not require knowledge of the remnant magnetization of the source body. We suggest that the CCFZ extends approximately 16 km farther to the southwest than previously mapped and may be composed of three independent faults as opposed to a continuous structure. To the northeast, we interpreted two possible faults associated with the ERRM that intersect the CCFZ, one of which has been previously mapped as the Meeman–Shelby fault. If the CCFZ and the eastern rift margin are composed of isolated fault segments, the maximum magnitude earthquake that each fault segment may generate is reduced, thereby, lowering the existing seismic hazard both fault systems pose to Memphis, Tennessee.

scholarly journals Estimating Effectiveness of Some Methods for Detecting Edge of Potential Field Sources

2020 ◽  
Vol 36 (4) ◽  
Author(s):  
Pham Thanh Luan ◽  
Le Thi Sang ◽  
Vu Duc Minh ◽  
Ngo Thi To Nhu ◽  
Do Duc Thanh ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Tilt Angle ◽  
Northeast China ◽  
Signal Amplitude ◽  
Analytic Signal ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
North Vietnam ◽  
Gradient Amplitude

This paper presents a comparative study of effectiveness of edge detection methods such as total horizontal gradient, analytic signal amplitude, tilt angle, gradient amplitude of tilt angle, theta map, horizontal tilt angle, tilt angle of total horizontal gradient, tilt angle of analytic signal, improved theta map, and total horizontal gradient of improved tilt angle. The effectiveness of each method was estimated on synthetic magnetic data and synthetic gravity anomaly data with and without noise. The obtained results show that the tilt angle of gradient amplitude can detect all the edges more clearly and precisely. The applicability of each method is demonstrated on the aeromagnetic anomaly data from the Zhurihe region of Northeast China, and Bouguer gravity anomaly data from a region of North Vietnam. The results computed by the tilt angle of horizontal gradient were also in accord with the geologic structures of the areas.

Limitations of determining density or magnetic boundaries from the horizontal gradient of gravity or pseudogravity data

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 118-121 ◽  
Author(s):  
V. J. S. Grauch ◽  
Lindrith Cordell
Keyword(s):  
Gradient Method ◽  
Gravity Data ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Maximum Magnitude ◽  
Gridded Data ◽  
Fourier Techniques ◽  
Gradient Magnitude ◽  
Vertical Fault ◽  
Over The Top

The horizontal‐gradient method has been used since 1982 to locate density or magnetic boundaries from gravity data (Cordell, 1979) or pseudogravity data (Cordell and Grauch, 1985). The method is based on the principle that a near‐vertical, fault‐like boundary produces a gravity anomaly whose horizontal gradient is largest directly over the top edge of the boundary. Magnetic data can be transformed to pseudogravity data using Fourier techniques (e.g., Hildenbrand, 1983) so that they behave like gravity data; thus the horizontal gradient of pseudogravity also has maximum magnitude directly over the boundary. The method normally is applied to gridded data rather than to profiles. The horizontal‐gradient magnitude is contoured and lines are drawn or calculated (Blakely and Simpson, 1986) along the contour ridges. These lines presumably mark the top edges of magnetic or density boundaries. However, horizontal‐gradient magnitude maxima (gradient maxima) can be offset from a position directly over the boundary for several reasons. Offsets occur when boundaries are not near‐vertical, or when several boundaries are close together. This note predicts these offsets. Many other factors also cause offsets, but they are less straightforward and usually are only significant in local studies; we discuss these factors only briefly.

Enhancement of the total horizontal gradient of magnetic anomalies using the tilt angle

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. J33-J41 ◽  
Author(s):  
Francisco J. F. Ferreira ◽  
Jeferson de Souza ◽  
Alessandra de B. e S. Bongiolo ◽  
Luís G. de Castro
Keyword(s):  
Tilt Angle ◽  
Real Data ◽  
Magnetic Anomalies ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Geometrical Properties ◽  
Different Depths ◽  
Deep Sources ◽  
Derivatives Of

Magnetic anomaly maps reflect the spatial distribution of magnetic sources, which may be located at different depths and have significantly different physical and geometrical properties, complicating the identification of the corresponding geologic structures. Filtering techniques are frequently used to balance anomalies from shallow and deep sources, and to enhance certain features of interest, such as the edges of the causative bodies. Most methods used for enhancing magnetic data are based on vertical or horizontal derivatives of the magnetic anomalies or combinations of them, and the edges or centers of the sources are identified by maxima, minima, or null values in the transformed data. Normalized derivatives methods are used to equalize signals from sources buried at different depths. We present an edge detector method for the enhancement of magnetic anomalies, which is based on the tilt angle of the total horizontal gradient. The notable features of this method are that it produces amplitude maxima over the source edges and that it equalizes signals from shallow and deep sources. The method is applied to synthetic and real data. The effectiveness of the method is evaluated by comparing it with other edge detection methods that have been previously reported in the literature and that make use of derivatives. The results show that our method is less sensitive to variations in the depth of the sources and that it indicates the position of the edges of causative bodies in a more accurate fashion, when compared with previous methods, even for anomalies due to multiple interfering sources. These results demonstrate that the proposed method is a useful tool for the qualitative interpretation of magnetic data.

Magma-rich transform margins: example from the Limpopo transform fault zone between Mozambique and Antarctica

2020 ◽  
Author(s):  
Sylvie Leroy ◽  
Vincent Roche ◽  
François Guillocheau ◽  
Pierre Dietrich ◽  
Sidonie Revillon ◽  
...  
Keyword(s):  
Fault Zone ◽  
Magnetic Data ◽  
Transform Fault ◽  
Passive Margins ◽  
The North ◽  
Oceanic Spreading ◽  
Transform Margin ◽  
Seismic Reflection Profiles ◽  
Uplift And Erosion ◽  
Transform Fault Zone

<p>Transform continental margins known across the Earth represent 31% of passive margins. Resulting from first-order plate tectonic processes, transform margins record a diachronous evolution mainly defined by three successive stages, including intra-continental transform faulting, active and passive transform margin. Due to their high complexity and a lack of large hydrocarbon discoveries (i.e. not a target for oil industry), they have only been sparsely studied, especially when compared with other margin types (i.e. divergent or convergent).</p><p>                  We present the structure and evolution of the NS-trending Limpopo Transform Fault Zone (LTFZ), corresponding to the main fracture zone from western part of the Africa-Antarctica Corridor (AAC). Here, we combine published and unpublished dataset (seismic reflection profiles, wells, multibeam bathymetry, gravity, magnetic data) in order to propose an interpretation of the LTFZ structure and adjoining segments and their evolution through time, from rifting to spreading.</p><p>The LTFZ is composed of two main segments: the East Limpopo segment and the Astrid conjugate one and the North and South Natal segment including the Dana-Galathea Plateau (Mozambique side) and the Maud rise/east of Grunehogna craton (Antarctica margin). The LTFZ offsets the segments of divergent conjugate margins (Southern Natal-off Grunehogna craton in the west and Beira High Angoche-Riiser Larsen Sea in the east) since 155 Ma (chron M25). We focus on the evolution of the transform fault zone from its initiation at chron M25 up to chron M0 (~126 Ma, Barremian). Oceanic spreading onset at chron M25 in the south of Beira High segment and Dana-Galathea Plateau triggered the uplift and erosion of the proximal parts of the margin and the formation of several seaward dipping reflectors wedges. Plate kinematic implies an NNW-SSE opening of the LTFZ. The oblique component of opening promotes the setting up of several volcanic wedges. These wedges rejuvenate southward trough time, which is consistent with the sliding of Antarctica with respect to Africa and thus confirm the diachronous evolution of the transform fault zone.</p>

Practical considerations in the use of edge detectors for geologic mapping using magnetic data

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. J1-J8 ◽  
Author(s):  
Mark Pilkington ◽  
Victoria Tschirhart
Keyword(s):  
Magnetic Field ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Recent Effort ◽  
Aeromagnetic Data ◽  
Geologic Mapping ◽  
Magnetization Direction ◽  
Model Studies ◽  
Edge Detectors

Locating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data. Much recent effort has been expended on developing improvements to existing edge-detection methods, resulting in purported increases in accuracy and continuity along edges, reduction of noise effects, and limiting the influences of variable depth to source, magnetization direction, and source dip. These endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data. Nevertheless, survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved. Using model studies, we quantify the effects that source size, depth, and interference between sources have on calculated edge locations. Based on the known behavior of established edge detectors, we found that many of the newer approaches offer limited advantages over older methods. Consequently, we studied an example of field mapping of geologic contacts in the Canadian Shield, supported by aeromagnetic data, using calculation of a standard edge detector: the horizontal gradient magnitude of the total magnetic field or TF-hgm. Calculated edge locations estimated from this method appear sufficiently accurate and continuous to provide a solid basis on which the mapping campaign was based and executed successfully.

Segmentation of the Eastern Reelfoot Rift Margin: Reinterpretation of the Northeastern Reelfoot Rift Fault Geometry and Seismic Potential

2020 ◽  
Author(s):  
Christopher Marlow ◽  
Randel Cox ◽  
Christine Powell
Keyword(s):  
Seismic Hazard ◽  
Moment Magnitude ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Basement Rocks ◽  
Magnetic Signature ◽  
Magnetic Gradients ◽  
The Moment ◽  
The City ◽  
Fault Length

Abstract The eastern Reelfoot rift margin (ERRM) poses a significant seismic hazard to the city of Memphis, Tennessee, and may be capable of generating moment magnitude 7 earthquakes. The goal of this study is to refine the fault structure and geometry of the ERRM, to improve understanding of the associated seismic hazard. We apply multiple filters (e.g., reduction-to-pole and horizontal-gradient) to aeromagnetic intensity data, to visualize the magnetic signature of ERRM basement rocks. To remove ambiguity in our fault interpretations from the magnetic data, we restrict our interpretations to magnetic gradients that correspond to geologic and geophysical evidence of faulting and rank faults on a confidence scheme. From near Covington, Tennessee, to Dyersburg, Tennessee, we interpret the ERRM to be segmented into nine intersecting faults that trend northeast, north-northeast, and north-northwest (two high confidence, four intermediate confidence, and three low confidence). We calculate the moment magnitude potential of each fault based on the estimated fault length. The minimum moment magnitude potential is 6.0, and the maximum is 7.0.

scholarly journals Mapping of Deep Tectonic Structures of Central and Southern Cameroon by an Interpretation of Surface and Satellite Magnetic Data

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Constantin Mathieu Som Mbang ◽  
Charles Antoine Basseka ◽  
Joseph Kamguia ◽  
Jacques Etamè ◽  
Cyrille Donald Njiteu Tchoukeu ◽  
...  
Keyword(s):  
Magnetic Data ◽  
Horizontal Gradient ◽  
Maximum Magnitude ◽  
Tectonic Structures ◽  
Structural Domains ◽  
3D Euler Deconvolution ◽  
Intensity Field ◽  
Southern Cameroon ◽  
Types Of Faults

The aim of this study is to determine the depth of deep tectonic structures observed in the Adamawa-Yadé zone (central part of Cameroon) and propose a new structural map of this area. The horizontal gradient associated with upward continuation and the 3D Euler deconvolution methods have been applied to the Earth Magnetic Anomaly Grid 2 (EMAG2) data from the study area. The determination of the maximum magnitude of the horizontal gradient of the total magnetic intensity field reduced to the equator, in addition to the main contacts deducted by Euler solution, allowed the production of a structural map to show the fault systems for the survey area. This result reveals the existence of two structural domains which is thus confirmed by the contrast of magnetic susceptibility in the Central Cameroon Zone. The suggested depths are in the range of 3.34 km to 4.63 km. The structural map shows two types of faults (minors and majors) with W-E, N-S, NW-SE, NE-SW, ENE-WSW, WNW-ESE, NNE-SSW, and NNW-SSE trending. The major faults which are deepest (3.81 km to 4.63 km) with NE-SW, W-E, and N-S direction are very represented in the second domain which includes the Pangar-Djerem zone. This domain which recovers many localities (Ngaoundéré, Tibati, Ngaoundal, Yoko Bétaré-Oya, and Yaoundé) is associated with the Pan-African orogeny and the Cameroon Volcanic Line.

High-Resolution Seismic-Reflection and Marine Magnetic Data Along the Hosgri Fault Zone, Central California

2009 ◽  
Author(s):  
Ray W. Sliter ◽  
Peter J. Triezenberg ◽  
Patrick E. Hart ◽  
Janet T. Watt ◽  
Samuel Y. Johnson ◽  
...  
Keyword(s):  
High Resolution ◽  
Fault Zone ◽  
Seismic Reflection ◽  
Magnetic Data ◽  
Central California

scholarly journals Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 117
Author(s):  
Maria Filomena Loreto ◽  
Camilla Palmiotto ◽  
Filippo Muccini ◽  
Valentina Ferrante ◽  
Nevio Zitellini
Keyword(s):  
Seismic Reflection ◽  
Magnetic Data ◽  
Normal Faults ◽  
Sedimentary Sequence ◽  
Initiation Zone ◽  
Arc Setting ◽  
Seismic Reflection Profiles ◽  
Back Arc ◽  
Flower Structures ◽  
Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

Influence of Boundary Conditions on Response of Pipelines Crossing Reverse Fault Zone

2021 ◽  
Author(s):  
Hamid Rostami ◽  
Abdolreza Osouli ◽  
Brent Vaughn ◽  
Hamed Gholizadeh Touchaei
Keyword(s):  
Boundary Conditions ◽  
Fault Zone ◽  
Reverse Fault
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