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Crustal structure near Explorer Ridge : ocean-bottom seismometer results parallel to Revere-Dellwood fracture zone Cheung, Henry P. Y.


An 80 km seismic refraction line was recorded on an array of three ocean bottom seismometers located 5 km west of the northern tip of Explorer ridge and parallel to Revere-Dellwood fracture zone on the Pacific plate. One reversed and two split-spread profiles have been obtained. The combined use of rotated SV component and polarization filtered record sections enabled identification and timing of the refracted S-wave on most sections. The travel time - distance relation for both P and S waves is interpreted in the intercept time (tau) and ray parameter domain using the technique introduced by Bessonova et al. (1974). This enables application of tau inversion to give extremal bounds for velocity-depth curves. A linearized inversion technique is applied to give the smoothest velocity-depth profiles consistent with the travel time data. Amplitude analysis using disk ray theory synthetic seismograms further refine the P-wave velocity-depth models. The final P- and S-wave velocity-depth profiles show a general increase of velocity with depth and no distinct structural discontinuities. A normal oceanic crustal thickness of approximately 6.5 km and an anomalously low Pn velocity of 7.3 km sec⁻¹ are interpreted. The existence of an abnormally thick crust (8-10 km}., on the opposite side of the ridge in Explorer plate, determined in other studies, contrasts markedly with the results of this research. Such a contrast lends support to the proposal that the complex structure and thick crust are the result of compressive interaction between the young, small Explorer plate and the older, larger North America plate. Values of Poisson's ratio in the range of 0.25 to 0.32 are determined for the crustal material but better resolution of the velocity-depth profiles is required before a meaningful geological interpretation can be made.

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