Distribution of Earthquake Generating Stresses Obtained by Smoothing the First Motion Patterns

• Published in: Journal of Physics of the Earth Vol. 19; no. 3; pp. 181 - 198
• Main Author: OIKE, Kazuo
• Format: Journal Article
• Language: English
• Published: The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan 1971
• ISSN: 0022-3743; 1884-2305
• DOI: 10.4294/jpe1952.19.181

The world wide distribution of the earthquake generating stress of intermediate and deep earthquakes has been obtained from the smoothed radiation patterns of P waves of groups of earthquakes in fifty-one seismically active regions. Data used in this study were taken from the Bulletins of the International Seismological Center, 1964 and 1965 for the very active regions; and for the regions where a few inter-mediate and deep earthquakes occurred data from the Earthquake Data Reports of the U.S. Coast and Geodetic Survey, 1966-1969, were added. The smoothed radiation patterns of the Kuril-Japan, the Izu-Marianas and the Tonga-Kermadec regions determined from only two years' data showed satisfactory agreement with the patterns obtained for larger earthquakes by many seismologists. In almost all regions the axes of maximum pressure align themselves with the dip of the seismic plane. The direction of the horizontal component of the axis of maximum pressure in each region was compared with the direction of differential movement between two blocks computed by Le Pichon, and they agreed well with each other except in the following regions. In the South America region, the horizontal components of the axes of maximum pressure lie in the east-west direction. The patterns of intermediate earthquakes of the Chile-Peru border region, the Honshu of Japan and the New Hebrides region show that the axes of maximum tension align themselves with the dip of the seismic plane.