Dynamic subduction process of local plate revealed by Ibaraki earthquake sequence of 1982 in Japan

IntroductionIt has been brought forward in the plate tectonic theory that the global lithosphere consists of a number of active blocks floating above the asthenosphere since 1960s. And from then on, the kinematics and dynamics of lithosphere have been the frontal subjects in the contemporary geoscientific study. The Pacific Plate is the biggest one covering one fourth of the earth surface. Situated in the Eurasia Plate, our country is affected directly by the compression from the Pacific Pl…

Dynamic subduction process of local plate revealed by Ibaraki earthquake sequence of 1982 in Japan

The kinematics and dynamics of plate tectonics are frontal subjects in geosciences and the strong earthquake occurred along the plate boundary result directly from plate movement. By analyzing Ibaraki earthquake sequence, it has been found that the focal fault plane shows a special image of grading expansion along the direction of strike and adjustment along the dip direction respectively. With the consideration of strike, dip and slip directions of focal mechanism, we have confirmed that Ibaraki earthquake belongs to a thrust fault earthquake occurred under the Japan Trench. The cause of the earthquake sequence is discussed in the paper. The study on the temporal-spatial distribution of the earthquake sequence with a time-scale between the year-scale spatial geodetic data and the second-scale moment tensor of the strong earthquake has indicated the dynamic process of Pacific Plate subduction under the Eurasia Plate. According to the average slip distance of earthquake and the velocity of plate movement, it is predicted that a strong earthquake might occur in recent years.