Journal of Geophysics
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Long range propagation of seismic energy in the lower lithosphere
Get PDFObservations of seismic arrivals from the lower lithosphere in France revealed a low mean velocity of observed first arrivals of about 8.1 km/s between 150 and more than 1,000 km distance and several high velocity phases with apparent velocities between about 8.2 and 8.6 km/s. Each one of these high velocity phases is only observed over a range of about 100 or 200 km. The possibility of interpreting these phenomena in terms of fine structure of the lower lithosphere is investigated. The resulting model consists of alternating high and low velocity layers. No first order discontinuities seem to exist between these layers. A reliable quantitative estimate of the thickness of these high and low velocity zones can only be obtained by a joint travel time and amplitude study.
ARK: https://n2t.net/ark:/88439/y070109
Permalink: https://geophysicsjournal.com/article/177
 
Oceanic basalt magnetic properties and the Vine and Matthews Hypothesis
Get PDFKonigsberger ratios of DSDP basalts were rather low (mean value around 7) but were usually high enough to justify interpreting oceanic anomalies with a remanent magnetization model. Natural remanent magnetizations were considerably lower than in dredged basalts but were strong enough to account for amplitudes of oceanic magnetic anomalies. Both stable and unstable remanent types were encountered. The observed stable inclinations showed a large scatter when compared to expected inclinations, largely due to non-cancellation of secular variation. All the basalts were categorized in deuteric oxidation Class I by opaque petrology observations. Extensive maghemitization, inferred from thermomagnetic analyses, may explain the low NRM intensities. Unstable specimens easily acquired large viscous remanent magnetizations, in some cases as large as the NRM. The basalt magnetic properties were in general accord with the expectations of the Vine and Matthews hypothesis.
ARK: https://n2t.net/ark:/88439/y075179
Permalink: https://geophysicsjournal.com/article/103