Sub-Moho seismic profile in the Mariana Basin — Ocean bottom seismograph long-range explosion experiment |
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| Authors: | S Nagumo T Ouchi J Kasahara S Koresawa Y Tomoda K Kobayashi AS Furumoto ME Odegard GH Sutton |
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| Institution: | Earthquake Research Institute, University of Tokyo, Tokyo Japan;Ocean Research Institute, University of Tokyo, Tokyo Japan;Hawaii Institute of Geophysics, University of Hawaii, Honolulu, HI U.S.A. |
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| Abstract: | Ocean bottom seismograph (OBS) long-range explosion experiments were carried out in the Mariana Basin in 1973 and 1976. Seven large shots (8.5–1.5 ton) as well as several tens of small shots were fired. The maximum range of observation was about 1900 km. As many as 25 OBS stations were deployed in an array of about 800 km. It is found that the sub-Moho P-wave velocity structure is of stratified nature, being composed of alternating high- and low-velocity layers. High-velocity layers with apparent velocities of 8.1, 8.2, 8.4, 8.6 and 8.7 km/s are identified. Low-velocity layers, sandwiched between the high-velocity layers of 8.4, 8.6 and 8.7 km/s, are very prominent. The sub-Moho high-velocity lid with an apparent velocity of 8.4 km/s is very thin. Thinning of this lid, thickening of the low-velocity layer, and the presence under it of another high-velocity layer (8.6 km/s) appear to characterize the uppermost mantle structure beneath the Mariana Basin. |
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