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Crustal Structures Of Diebold Knoll And Adjacent Juan De Fuca Oceanic Crust From Integration Of Seismic Gravity And Magnetic Data
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Book Synopsis Crustal Structures of Diebold Knoll and Adjacent Juan de Fuca Oceanic Crust from Integration of Seismic, Gravity and Magnetic Data by : Md Ariful Islam
Download or read book Crustal Structures of Diebold Knoll and Adjacent Juan de Fuca Oceanic Crust from Integration of Seismic, Gravity and Magnetic Data written by Md Ariful Islam and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cascadia Subduction Zone (CSZ) has a long history of devastating earthquakes as the Juan de Fuca plate subducts beneath North America, where an imminent megathrust earthquake is expected. Compared to other subduction zones, CSZ exhibits unusually low seismic activity, particularly in the central region with respect to relatively high seismicity zones to the north and south. Some researchers attribute this behavior to subducted seamounts, although their impact on seismicity remains poorly understood and highly debated in the literature. Examining subducted seamounts is challenging due to complexity of the overburden strata. That is why this study focuses on an isolated notyet-subducted intraplate seamount known as the Diebold Knoll, located approximately 60 km west of the deformation front. Seismic reflection, gravity, and magnetic data were acquired over that seamount during the cruise RR1718. The first objective of this research was to determine heterogeneities in physical properties of oceanic crust resulted from addition of the seamount by integrated geophysical analysis along two intersecting profiles. The second objective was to reveal the tectonic history of the Diebold Knoll by combining magnetic polarity reversals with cross-cutting relationship analysis of seismic structures and constrained by the nearby ocean drilling sites. These models revealed that Diebold Knoll does not require complete isostatic compensation. Instead, a flat Moho or a less than 1 km thick root is sufficient to satisfy gravity data; both of these Moho geometries are observed in the study area. To achieve a better fit with observed gravity and magnetic anomalies, lower density and magnetic susceptibility values within the top portion of the seamount are required, which are attributed to faulting and hydration. This finding is also in agreement with a recent study that analyzed seismic velocity variations within seamounts. Furthermore, the negative magnetic anomaly of the seamount and the cross-cutting relationships between sedimentary layers and the seamount body indicated that Diebold Knoll is a very young feature formed approximately 0.8-1.8 Ma.
Book Synopsis The Structure of the Earth's Crust by : Stephan Mueller
Download or read book The Structure of the Earth's Crust written by Stephan Mueller and published by Elsevier Science & Technology. This book was released on 1974 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Crustal Structure in Western Lake Superior from the Integration of Seismic and Gravity Data by : Rodolfo Anzoleaga
Download or read book Crustal Structure in Western Lake Superior from the Integration of Seismic and Gravity Data written by Rodolfo Anzoleaga and published by . This book was released on 1971 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Earth's Crust and Upper Mantle by : Pembroke J. Hart
Download or read book The Earth's Crust and Upper Mantle written by Pembroke J. Hart and published by American Geophysical Union. This book was released on 1969 with total page 801 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Crustal Structure of Carnegie Ridge Inferred from Gravity and Seismic Data by :
Download or read book The Crustal Structure of Carnegie Ridge Inferred from Gravity and Seismic Data written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Carnegie Ridge is a prominent bathymetric feature of the Galápagos Volcanic Province originated from the interaction of the Galápagos Hot Spot and the Cocos-Nazca Spreading Center. Our present knowledge regarding its crustal structure is limited to ridge transects along which wide-angle refraction seismic experiments have been conducted. In this study, the long-wavelength crustal structure of Carnegie Ridge between [equivalent]81° W and 89° W was determined by employing 2-D forward gravity modeling as the primary analytical technique. Model structures were built by assuming Airy isostasy and crustal layers of constant density. The geometry and density structure of the thickened oceanic crust beneath the ridge was constrained based on available seismic velocity models. Except for regions near the Ecuador Trench, the gravity modeling solution along the different transects examined in this study accounted adequately for the observed gravity anomaly field over the ridge. Crustal overthickening mainly accommodated in oceanic layer 3 and the asymmetry of the crustal root geometry characterize the estimated long-wavelength crustal structure. The asymmetry on eastern Carnegie Ridge is thought to be related to a ridge-related rifting whereas the origin and nature of that estimated on western Carnegie Ridge remain uncertain. Crustal volume fluxes were calculated at Carnegie Ridge and the Galápagos Archipelago, and at Cocos Ridge in order to explain the along-axis variations of the estimated crustal thickness. Along-axis crustal thickness variations on eastern Carnegie Ridge, and the formation of its bathymetric saddle were found to be related to the decline in the total volume output of the Galápagos Hot Spot. According to my results, this decay started soon after the spreading center shifted to the south of the hotspot (i.e., [equivalent]15 Ma) and continued for [equibvalent]4.5m.y. Since [equivalent]10 Ma the volume output of the GHS started to increase again, giving rise to the formation of western Carnegie Ridge and the Galápagos Archipelago. This increase continued until [equivalent]2 Ma, when the hotspot intensity started a new decrease that continues until the present time.
Author :Frank Steve Schilt Publisher :Ann Arbor, Mich. : University Microfilms International ISBN 13 : Total Pages :422 pages Book Rating :4.E/5 ( download)
Book Synopsis Studies of Continental and Oceanic Crust from Seismic, Geodetic, and Magnetic Observations by : Frank Steve Schilt
Download or read book Studies of Continental and Oceanic Crust from Seismic, Geodetic, and Magnetic Observations written by Frank Steve Schilt and published by Ann Arbor, Mich. : University Microfilms International. This book was released on 1981 with total page 422 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Structure of the Oceanic Crust and Upper Mantle by : John Orcutt
Download or read book Structure of the Oceanic Crust and Upper Mantle written by John Orcutt and published by . This book was released on 1976 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Seismic and Magnetic Constraints on the Structure of Upper Oceanic Crust at Fast and Slow Spreading Ridges by :
Download or read book Seismic and Magnetic Constraints on the Structure of Upper Oceanic Crust at Fast and Slow Spreading Ridges written by and published by . This book was released on 1998 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Imaging the Oceanic Crust with Broadband Seismic and Pressure Data by : Adrian K. Doran
Download or read book Imaging the Oceanic Crust with Broadband Seismic and Pressure Data written by Adrian K. Doran and published by . This book was released on 2019 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: The oceanic crust, the uppermost layer of the rigid oceanic lithosphere, has a well defined general architecture, but the magnitude and wavelength of heterogeneities in crustal structure remain poorly observed in detail. In this thesis, I have characterized the seismic structure of the marine sediments and crust surrounding the Hawaiian islands. I primarily analyzed seafloor compliance data, the deformation of the seafloor in response to infragravity wave loading. These long-period (50+ seconds) measurements are estimated from broadband ocean-bottom seismic data and are sensitive to the elastic structure of oceanic sediments and crust, particularly shear-velocity structure. I produced a map of sediment thickness and shear velocity, which includes high-velocity volcanic sediments and low-velocity pelagic sediments. I then used surface wave dispersion data to constrain the structure of the lower crust and the uppermost mantle beneath the Hawaiian Islands. Initial results indicate that the uppermost mantle may exhibit variations in shear velocity on the order of several percent. These variations could be explained through a combination of thermal anomalies and partial melting. Another focus of this thesis is the analysis of seafloor compliance data as a function of time to investigate melt content in the lower crust before and after the submarine eruption of 2015 at Axial Volcano. I found that Vs dropped dramatically following the eruption and took several years to recover to pre-eruption levels. The changes can be explained by variations in the geometry of melt. The station distribution also allowed me to constrain the lateral extent of the variations to within several hundred meters of the center of the caldera. In the course of these studies, I developed tools and theory to improve OBS data quality. I wrote automated software to determine the orientation of horizontal seismometer components using surface wave arrival angles, and spent considerable time characterizing the long-period response of differential pressure gauges. Finally, I demonstrated the viability of measuring horizontal seafloor compliance, although I was limited in my geologic interpretations due to instrument response issues and data quantity. The techniques and results developed in this thesis should provide insight into the dynamics of the oceanic lithosphere, including the mechanics of intraplate plumes and crustal accretion. These results will become more valuable as OBS instrumentation progresses and expands data coverage into the furthest reaches of the world's oceans.
Book Synopsis A Global Crustal Thickness Map by : David R. Soller
Download or read book A Global Crustal Thickness Map written by David R. Soller and published by . This book was released on 1981 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Structural and Thermal Evolution of Upper Oceanic Crust in the Western South Atlantic by : Dominik A. Kardell
Download or read book The Structural and Thermal Evolution of Upper Oceanic Crust in the Western South Atlantic written by Dominik A. Kardell and published by . This book was released on 2020 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: The evolution of oceanic crust plays an integral role in global heat flow, geochemical cycles, and in shaping the environmental conditions harboring the crustal biosphere. Because oceanic crust is normally buried beneath several kilometers of water and encompasses a vast area of the Earth's rigid surface, spatially extensive and coherent geophysical data are difficult to acquire in the oceanic domain. Consequently, our current understanding of the evolution of oceanic crust is based on partially conflicting compilations of data that are acquired at different scales and using different methods. Here I present geophysical constraints from an extensive seismic dataset that continuously covers 0-70 Ma crust in the western South Atlantic. Analysis of regional seismic velocity trends in the upper crust shows a continuous increase in basement velocity to crustal ages of at least 58 Ma. This trend indicates an evolution of upper crustal velocities that lasts significantly longer than measured or predicted by previous studies. The results provide evidence for ongoing hydrothermal circulation in relatively old upper crust, which is consistent with heat flow studies. To further test this concept, I used high-resolution seismic velocity models to estimate detailed porosity and permeability distributions that constrain models of hydrothermal fluid flow at five different crustal ages. The resulting advective and conductive surface heat fluxes are consistent with both predictions of heat flux by lithospheric cooling models and measured conductive heat flux at the seafloor. Additionally, computed hydrothermal volume fluxes largely agree with global estimates for the modeled crustal ages. The models are therefore consistent with a "sealing age" of ~65 Ma, which is also inferred from a compilation of global heat flow measurements at the seafloor. Close to the Rio Grande Rise, an oceanic plateau west of the study area, a fine-scale seismic velocity model reveals multiple large fault zones penetrating at least ~1.5 km into the crust. These faults likely accommodate differential subsidence between thickened, warm oceanic plateau crust and cold oceanic crust. Modeled fluid fluxes are elevated along the interpreted fault zones and across the seafloor. Crust adjacent to oceanic plateaus may exhibit elevated levels of tectonic activity and fluid flow globally. The estimated global volume of fluid entering the ocean in this type of setting amounts to 43 km3, which is ~2% of the hydrothermal flux in the axial region. This potentially has implications for global chemical cycles, the hydration of mature oceanic crust, and the oceanic crustal biosphere
Book Synopsis A Search for Layering in the Oceanic Crust by : John Anthony Collins
Download or read book A Search for Layering in the Oceanic Crust written by John Anthony Collins and published by . This book was released on 1988 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of numerous seismic refraction and reflection experiments have shown that the seismic structure of the oceanic crust can be usefully parameterized by a small number of locally horizontal layers within which the rates of change of velocity and impedance as a function of depth are approximately constant. Layer boundaries are defined by changes in velocity and/or impedance gradient. This dissertation discusses the structure of seismic layer boundaries within the oceanic crust, and investigates the relationships between the seismic characteristics of these boundaries and the geological structure of the crust. The seismic signature of the crust/mantle boundary (Moho) is a prominent event on multichannel seismic (MCS) reflection data. In the Western North Atlantic, the character of the Moho reflection event varies from a single well-defined phase to a more complex event consisting of two or more overlapping phases of up to 1.0 s total duration. In Chapter 1 of this dissertation, the geological structures generating Moho reflections are investigated by calculating synthetic reflection profiles for three laterally varying velocity models totaling 64 km in length. These velocity models were derived from the observed distribution of lithologies that comprise the inferred fossil crust/mantle transition found in the Bay of Islands Ophiolite. Along the synthetic profiles, the Moho reflection is characterized by both single-phase and multi-phase events, the geometry and durations of the latter being similar to those observed on MCS data from the Western North Atlantic. In addition, the lateral variation in Moho travel time, up to 0.25 s over distances of less than 10 km, is similar to that observed on MCS data. The similarities between the observed and synthetic data suggest that the complicated interlayered sequences of mafic and ultramafic rocks that comprise the inferred crust/mantle transition in ophiolites might also be characteristic of the oceanic crust. Although ophiolites provide a useful model of the lithological structure of the oceanic crust, the unambiguous correlation of geologic and seismic structures can only be achieved by conducting seismic experiments in the vicinity of deep crustal drillholes. Chapters 2 and 3 of this dissertation present analyses of the velocity and reflectivity structure of the crust in the immediate vicinity of Deep Sea Drilling Project Hole 504B in the Panama Basin, currently the deepest drillhole (1.288 km) into oceanic igneous crust. Reflectivity synthetic seismogram modeling of amplitude features common to four sonobuoy profiles collected in the immediate vicinity of Site 504B shows that crustal thickness at the drillsite is only 5 km. A critical constraint on this interpretation is the observation, on four MCS profiles passing through the drillsite, of a near-normal-incidence reflection event with a crustal travel time of 1.4-1.5 s. This event is assumed to correlate with a wide-angle reflection/refraction event observed at ranges of 16-28 km on the sonobuoy profiles. Seismic modeling demonstrates that both of these events are generated at the Moho. The crustal velocity-depth profile at Site 504B is unusual in comparison to typical oceanic profiles in having high velocity gradients (up to 0.6 km s- 1 km- 1) in the middle crust and a 1.8 km thick low-velocity zone (Vp=7.1-6.7 km s- 1) immediately above Moho. A simple explanation for this unusual profile is that the velocity of the middle crust has been increased by the addition of a high-velocity mineral component such as olivine. The olivine concentration of the middle crust need be no greater than 34-37%. Hole 504B is the only site where the volcanics/sheeted-dike boundary, predicted by the ophiolite model to Qe a fundamental feature of oceanic crust, has been drilled. The downward change in rock type coincides with changes in a variety of logged physical properties. The normal-incidence travel time to this boundary is similar to the travel times of shallow reflection events observed in other areas. Accordingly, Site 504B is an ideal location to test the hypothesis that shallow reflection events correlate with the extrusives/dike boundary. Despite extensive processing, MCS data collected 'in the immediate vicinity of Hole 504B show no conclusive evidence for a laterally coherent reflection event generated within the upper crust. The lack of a detectable reflection event from the upper crust is consistent with the results of synthetic seismogram modeling of velocity-depth profiles constructed from the logged downhole variation in physical properties. On these normal-incidence synthetic seismograms, low-amplitude reflections from the volcanic/dike contact are obscured by the high-amplitude basement reflection and by sediment-column multiples. In contrast to the synthetic reflection data, the seismic signature of the volcanics/dike boundary is readily recognizable on a synthetic wide-angle reflection/refraction profile. The change in velocity across this boundary causes focusing of refracted arrivals in the range window 6-7 km. High-amplitude arrivals are observed at similar ranges on the sonobuoy profiles collected near the drillsite, suggesting that at Site 504B, variations in depth to this layer boundary are more easily mapped with the wide-angle reflection/refraction method.
Book Synopsis The Structure of Mature Oceanic Crust by : Eric Hallenborg
Download or read book The Structure of Mature Oceanic Crust written by Eric Hallenborg and published by . This book was released on 2003 with total page 478 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Crustal Structure and Tectonic Framework of the Gulf of Panama by : Luis Alberto Briceno-Guarupe
Download or read book The Crustal Structure and Tectonic Framework of the Gulf of Panama written by Luis Alberto Briceno-Guarupe and published by . This book was released on 1978 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gravity and magnetic data from cruises by the R/V Yaquina in 1973 and the R/V Wecoma in 1975 provide new data that make possible the construction of a map of the free-air gravity anomalies at sea and simple Bouguer anomalies on lano in Panama, western Colombia, and the eastern Panama Basin. The gravity measurements and a wide angle reflection line provide data to construct a crustal and subcrustal cross section that starts at 6°N latitude, 80°22.7'W longitude in the Panama Basin and extends 800 km along a line which strikes N19°E across the Gulf of Panama and the Isthmus of Panama to the Colombia Basin. Two important features in the gravity map are the -90 and -100 mgal lows, oriented approximately east-west at 7°N and at 1O°N 1atitude. It is postulated that the southern low reflects a downwarp of the oceanic crust and the northern low reflects a shallow subductjon zone. Filtered magnetic anomalies and seismic refraction measurements support the conclusion that a piece of the oceanic crust which originated at the Nazca-Cocos Rift, forms the upper part of the continental shelf in the Gulf of Panama. The northernmost magnetic anomaly, approximately 50 km south of Panama City, is identified as anomaly number 9 in the geomagnetic scale and indicates 30 million years in age for these rocks which form part of the continental shelf of Panama. The model crustal cross section indicates a maximum thickness for the crust of 25 km for the Isthmus of Panama and a thickness of 17 km for the crust of the Gulf of Panama. The data and the model suggest that both a collision and subduction mechanism may be necessary to explain the tectonics and geology of the area.
Book Synopsis Crustal Structure of the Mid-Ocean Ridges by : Manik Talwani
Download or read book Crustal Structure of the Mid-Ocean Ridges written by Manik Talwani and published by . This book was released on 1965 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Crustal Structure and Tectonic Evolution of Oceanic Crust Off Morocco by : James Steven Holik
Download or read book The Crustal Structure and Tectonic Evolution of Oceanic Crust Off Morocco written by James Steven Holik and published by . This book was released on 1990 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Regional Investigation of Crustal Structure Using Integration of Seismic and Potential Field Data, Northern Rockies/Great Plains Region by : Bryce Evan Jensen
Download or read book Regional Investigation of Crustal Structure Using Integration of Seismic and Potential Field Data, Northern Rockies/Great Plains Region written by Bryce Evan Jensen and published by . This book was released on 2010 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt:
