Controlled-Source Seismic Experiment at Hole 581C

Frederick, K. Duennebier; Lienert, Barry R.; Robert, Kolos; Anderson, Paul D.; Mallick, Subhashis

doi:10.2973/dsdp.proc.88.108.1987

Cited by 17 publications

(11 citation statements)

References 13 publications

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“…Low-velocity zones in the lower oceanic crust have been proposed by many workers (e.g. Lewis, 1978;Lewis and Snydsman (1979);Duennebier et al, 1987), and are often interpreted in terms of the alteration of olivinerich mafic and ultramafic rocks to serpentine (e.g. Lewis, 1978).…”

Section: Implications For Crustal Structurementioning

confidence: 99%

A search for layering in the oceanic crust

Collins¹

1988

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Section: Implications For Crustal Structurementioning

confidence: 99%

A search for layering in the oceanic crust

Collins¹

1988

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“…Since Houtz and Ewing [1976] first documented an age-dependent increase in the velocity of the uppermost crust, several studies have confirmed this relationship. In the Pacific alone, these studies include conventional refraction [Spudich and Orcutt, 1980;Purdy, 1982;Bratt and Purdy, 1984;Bratt and Solomon, 1984;McClain and Atallah, 1985;Bee and Bibee, 1989;, borehole [Stephen and Harding, 1983;Little and Stephen, 1985;Duennebier et al, 1987;Whitmarsh et al, 1987;Collins et al, 1989], single-ship Tolstoy et al, 1997] and two-ship multichannel [Harding et ai., 1989;Vera et ai., 1990], and on-bottom seismics [Christeson et ai., 1994a]. Sensitivity to velocities immediately beneath the seafloor varies between methods.…”

Section: Aging Of Extrusive Crustmentioning

confidence: 99%

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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“…Our objective was to model the PolSo signal recorded from an earthquake during the OSSIV seismic experiment. The details of this seismic experiment have been reported elsewhere (see Duennebier et al 1987; but are briefly summarized here for completeness.…”

Section: Modelling Of P O L S O D a T A Recorded At O S S I Vmentioning

confidence: 99%

“…Recently, Mallick & Frazer (1986 showed how reflectivity codes can be made to vectorize even when the seismic velocities are frequency dependent. Applications of their method to the modelling of marine seismic refraction data were given in Duennebier & Mallick (1985), Duennebier et al (1987), andSen et al (1988). In this paper their method is used to synthesize Polso seismograms for a variety of oceanic models for comparison with PolSo data recorded during the OSS IV experiment .…”

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confidence: 99%

Po/So Synthetics For A Variety of Oceanic Models and Their Implications For the Structure of the Oceanic Lithosphere

Mallick¹,

Frazer²

1990

Geophysical Journal International

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S U M M A R Y Polso synthetic seismograms were computed for a variety of oceanic structures in order to model data from an t?zb = 5.7 earthquake, recorded during the OSS IV seismic experiment. Satisfactory modelling of Polso waveshapes and frequency content was achieved with no lateral heterogeneity, but with a small random vertical heterogeneity in the mantle, superimposed on a mean velocity structure which is consistent with seismic refraction data. The random heterogeneity in the P and S velocities appears to be about 2 per cent with a scale length of 5 km. This kind of heterogeneity is easily achieved by varying slightly the major mineral components in either the peridotite or eclogite mantle mineralogy and can be another cause of observed upper mantle anisotropy.Using a step-function source time behaviour, our numerical modelling also indicates that in the upper mantle Q p is roughly proportional to rising from about 450 at f = 1 Hz to about 800 at f = 15 Hz, and that Q, is roughly proportional to rising from about 900 at f = 1 H z to about 1800 at f = 15Hz. A slight decrease in Q, from these values in any small zone of the upper mantle reduces So amplitudes drastically and we believe this is why So is sometimes missing from observed seismograms.The computed synthetic record sections were also used to examine the relation between intrinsic Q and the apparent Q inferred from data in earlier studies. Apparent Q was found to be lower than intrinsic Q below about 5 H z and higher than intrinsic Q above 5 Hz. When these differences are accounted for, the mantle Q's of this study agree with the mantle Q's of Butler et al. (1987) to within 10 per cent. There can no longer be any doubt that oceanic upper mantle Q's are very large, above 5 Hz, and that Q, is about twice as large as Qp.

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Controlled-Source Seismic Experiment at Hole 581C

Cited by 17 publications

References 13 publications

A search for layering in the oceanic crust

A search for layering in the oceanic crust

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

Po/So Synthetics For A Variety of Oceanic Models and Their Implications For the Structure of the Oceanic Lithosphere

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