Seismic velocities of the uppermost igneous crust versus age

Grevemeyer, Ingo; Weigel, W.

doi:10.1111/j.1365-246x.1996.tb07041.x

Cited by 68 publications

(86 citation statements)

References 21 publications

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“…Grevemeyer and Weigel [1996] made such a compilation, and though they did not make a formal statistical analysis, the data do appear to support their conclusion that upper crustal velocities double within 5 million years and remain constant thereafter. These data further suggest that seismic velocities in old crust are appreciably lower than the average velocity in layer 2B.…”

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confidence: 96%

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Seismic velocities in the uppermost oceanic crust: Age dependence and the fate of layer 2A

Carlson¹

1998

J. Geophys. Res.

104

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mentioning

confidence: 96%

“…Consequently this study has several objectives. One is to expand the compilation of Grevemeyer and Weigel [1996] by scouring the literature for additional data and including more data from downhole logs and borehole experiments. A second is to make a rigorous test of the hypothesis that most of the increase in seismic velocities occurs in <10 million years.…”

mentioning

confidence: 99%

Seismic velocities in the uppermost oceanic crust: Age dependence and the fate of layer 2A

Carlson¹

1998

J. Geophys. Res.

104

122

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“…, NOBEL (~) [Christeson et al, 1994a], and this study (*). The best fitting curve from Grevemeyer and Weigel [1996] (thin) and this study (thick) are shown. Results older than a decade (i.e., ROSE, Capricorn and early 504B) were not used in the least squares inversion and are marked by an unfilled symbol.…”

Section: Aging Of Extrusive Crustmentioning

confidence: 99%

“…Recently, Grevemeyer and Weigel [1996] and Carlson [1998] compiled the most comprehensive set of compressional wave velocities for acoustic basement since Houtz and Ewing [1976]. Grevemeyer and Weigel [1996] approximate the relationship be-…”

Section: Aging Of Extrusive Crustmentioning

confidence: 99%

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Seismic and magnetic constraints on the structure of upper oceanic crust at fast and slow spreading ridges

Hussenoeder¹

1998

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The upper ocean crust contains a comprehensive record of the shallow geological processes active along the world's mid-ocean ridge system. This thesis examines the magnetic and seismic structure of the upper crust at two contrasting ridges-the fast spreading East Pacific Rise (EPR) and the slow spreading Mid-Atlantic Ridge (MAR)-to build a more complete understanding about the roles of volcanic emplacement, tectonic disruption and hydrothermal alteration in the near-ridge environment.A technique that inverts potential field measurements. directly from an uneven observation track is developed and applied to near-bottom magnetic data from the spreading segments north of the Kane transform on the MAR. It is concluded that the central anomaly magnetization high marks the locus of focused volcanic emplacement. A cyclic faulting model is proposed to explain the oscillatory magnetization pattern associated with discrete blocks of crust being transported out of the rift valley between intensely altered fault zones. Seismic waveform and amplitude analyses of the magma sill along the EPR reveal it to be a thin «100 m) body of partial melt. These characteristics have important implications for melt availability and transport within the cycle of eruption and replenishment. A genetic algorithm-based seismic waveform inversion technique is developed and applied to on-and near-axis multichannel data from 17°20 's on the EPR and the spreading segment south of the Oceanographer transform (MAR) to map and compare for the first time the detailed velocity structure of the upper crust at two different spreading rates. Combined with conventionally processed seismic profiles, our results show that, while final extrusive thickness is comparable at all spreading ridges (300-500 m), the style of thickening may vary. While a thin (:S100 m) extrusive carapace quadruples in thickness within 1-4 km of the EPR crest, the extrusive section at the MAR achieves its final thickness within the inner valley. Both show evidence for a narrow zone of volcanic emplacement. Vigorous hydrothermalism at the EPR may produce a more rapid increase in basement velocities relative to the MAR. Rapid modification of the extrusive/dike transition at both ridges indicates that hydrothermalism is enhanced in this interval. Along-axis transport of lavas may thicken the extrusive pile at slow spreading segment ends, strengthening the magnetic highs generated by lava chemistry. Biographical SketchIn order to wax only partially rhapsodic, let me start at my formative age as a marine geophysicist ... the age of six. The first hint that I wasn't going to grow up to be a successful businessman was dropped in Germany, where my best friend and I rejected the idea of opening a lemonade stand in favor of selling fossils and geodes on the street corner. We soon went bankrupt. Our village in southern Germany was not far from Solnhofen, home of the famed Archaeopteryx. The countryside was full of geological treasures exposed in streambeds or along roadsides. Our final m...

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The influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust

Carlson

2014

Geochem Geophys Geosyst

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[1] The purpose of this study is to explore the relationships between porosity, crack morphology, seismic velocity, and permeability in the upper oceanic crust. In a theoretical model, velocity is a quadratic function of porosity U, and the coefficients are functions of the fractional area of asperity contact A f across the cracks, a measure of crack morphology; thus, v 5 v(A f , U). Fits to data sets from the lava and dike sections in Holes 504B and 1256D yield A f 5 0.096(8) and 0.045(3), with rms errors of 1.7 and 0.3%, respectively. Lower values of A f account for the high porosities and low velocities observed in Layer 2A. After 0.2 Ma, the porosities of both Layer 2A and the deeper part of the lava pile remain in the range 8 6 4%. The observed increase of Layer 2A velocities after 0.2 Ma is caused largely by changing crack morphology as opposed to decreasing porosity; at 8% porosity, an increase of A f from 0.003 to 0.1 accounts for an increase of velocity from 3 to >5 km/s. An empirical log-linear relationship between permeability j and v suggests a relationship between j and A f as well. This relationship between j and v can be explained if the permeability coefficient j o is a closely constrained quadratic function of the area of asperity contact A f . A f is thus the primary variable affecting both seismic velocities and the permeability of the uppermost oceanic crust.

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Seismic velocities of the uppermost igneous crust versus age

Cited by 68 publications

References 21 publications

Seismic velocities in the uppermost oceanic crust: Age dependence and the fate of layer 2A

Seismic velocities in the uppermost oceanic crust: Age dependence and the fate of layer 2A

Seismic and magnetic constraints on the structure of upper oceanic crust at fast and slow spreading ridges

The influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust

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