Possibility of Estimating the Maximum Earthquake Magnitude Based on a Modified G-R Model for Magnitude-Frequency Distribution

Spatial Distribution of M_c East off Northeast Japan

Abstract

We investigated the spatial distribution of M_c value of the magnitude-frequency distribution proposed by Utsu (1971) for the region of east off northeast Japan. M_c is a model parameter that defines the upper limit of earthquake magnitude. We further examined the possibility of estimating the maximum earthquake magnitude based on M_c for a given region. The data we used are taken from the earthquake catalog of the Research Center for Prediction of Earthquakes and Volcanic Eruptions of Tohoku University for last 21 years. The magnitudes of M≥5 earthquakes in the catalog are replaced with those of the Japan Metrological Agency catalog to keep the continuity of magnitude scale. By using a moving window of 0.5°×0.5° for the analysis, we found a systematic pattern of the M_c distribution: the area of M_c>7 distributes off Aomori Prefecture, far off Iwate Prefecture, and off Miyagi and Fukushima Prefectures, while anomalously small value (M_c<6) prevails in a roughly 1°×1° area within 100km off the coast of Iwate Prefecture. M_c we estimated shows positive but weak correlation to M_cat, the maximum magnitude for last 115 years. By dividing the whole region into four zones based on the above result, we found excellent agreement between M_c and M_cat for each zone. This suggests that M_c may be used for predicting the maximum size of future earthquakes if appropriate zoning is done. Epicenters of past large earthquakes (M≥7) tend to locate in and near the high M_c areas, suggesting that the parameter M_c may reflect physical characteristics of earthquake generating field.