Earth Planets Space, Vol. 56 (No. 2), pp. 179-192, 2004
Md. Mahmudul Alam and Masaaki Kimura
Department of Physics and Earth Sciences, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan
(Received May 12, 2003; Revised March 1, 2004; Accepted March 3, 2004)
Volcanic eruptions preceded by seismicity, and great earthquakes (magnitude, M 7.6) within 100 km depth during a period of 123 years from 1880 to 2003 along the Pacific and Philippine Sea Plate in Japan are investigated. Correlation coefficients show that the relationship between earthquakes and eruptions (r = 0.99), and time and distance (r = -0.89) are highly correlated with 1% level of significance. The time-distance relationship between major eruptions and great earthquakes are shown by the model,Y = 40.15-14.53log(X), where Y and X indicate time (time interval from the starting time of a major eruption to the occurrence of the earthquake) and distance (distance from the volcano to the epicenter of the shock), respectively. Statistical analysis based on the relation shows that the eruptions occurred earlier prior to the concerned shock if the epicenter of the earthquake is nearer to the respective volcanic activity. This relation is recognized by various statistical testing procedures. Based on this relation, the crustal strain accumulation time in the estimated epicenter should be known. This suggests that eruptions may be a precursor for enough strain accumulation in the epicentral region where the increased accumulated regional strain may squeeze up magmas before breaking the crust. If this is true then the occurrence time of the shock may be predicted by a major eruption.
Key words: Least squares method, correlation, regression, regional strain, eruptions, earthquakes.