13. Ocean-Bottom Seismograph Study of the Western Margin of the Pacific

  1. George H. Sutton,
  2. Murli H. Manghnani,
  3. Ralph Moberly and
  4. Ethel U. Mcafee
  1. Shozaburo Nagumo and
  2. Junzo Kasahara

Published Online: 17 MAR 2013

DOI: 10.1029/GM019p0155

The Geophysics of the Pacific Ocean Basin and Its Margin

The Geophysics of the Pacific Ocean Basin and Its Margin

How to Cite

Nagumo, S. and Kasahara, J. (1976) Ocean-Bottom Seismograph Study of the Western Margin of the Pacific, in The Geophysics of the Pacific Ocean Basin and Its Margin (eds G. H. Sutton, M. H. Manghnani, R. Moberly and E. U. Mcafee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM019p0155

Author Information

  1. Earthquake Research Institute, University of Tokyo, Tokyo 113, Japan

Publication History

  1. Published Online: 17 MAR 2013
  2. Published Print: 1 JAN 1976

ISBN Information

Print ISBN: 9780875900193

Online ISBN: 9781118663592

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Keywords:

  • Geophysics—Pacific area—Congresses;
  • Woollard, George Prior, 1908

Summary

The locations at which OBS observations have been made since 1966 by the Earthquake Research Institute, University of Tokyo, extend from the Japan trench to the Mariana basin, and to the Fiji plateau along the western margin of the Pacific. The method of observation is the anchored-buoy system, using an OBS containing fully automatic tape recording apparatus. In the Japan trench, we find that very high micro-earthquake activity is taking place both at the marginal escarpment of the Japan trench and in the adjacent ocean basin. This suggests that the oceanic lithosphere is capable of generating earthquakes, and that the marginal escarpment of the Japan trench is an active tectonic element. Micro-earthquake activity is very high in the south Mariana trench. A high concentration of micro-earthquakes is observed along both the midslope basement-high of the trench and the southern terminus of the Mariana ridge. Epicentral distribution suggests uplifting of the Mariana ridge. No micro-earthquakes were observed in the central region of the Mariana basin during a 16-day period. At present the Mariana basin seems to be tectonically very quiet. The ocean floor in the central region of the Fiji plateau is unusually active, with very high micro-earthquake activity including several swarms. The Fiji plateau seems to be tectonically very active. From these observations, it is inferred that mantle diapirism beneath the volcanic islands or ridge is the main cause of the dynamics of the island arc-trench system.