Comparison of Hypocenter Catalogues Produced by the Kanto-Tokai Seismograph Network (KT-net) and the High-Sensitivity Seismograph Network (Hi-net)

Based on two earthquake catalogs for the Kanto-Tokai area - one produced by the Kanto-Tokai seismograph network (KT-net) and operating since mid 1979, and the other produced by the recently developed nationwide high-sensitivity seismograph network (Hi-net) - we compared differences in seismicity and hypocenter parameters between these catalogs. The KT-net catalog contains data on 49,421 earthquakes observed in the area of 33.6-37°N and 137-142°E, which covers KT-net, from January 1, 2001, through December 31, 2005, at depths 0.0. The Hi-net catalog contains data on 82,746 events detected in the same range. Over 90% of events were microearthquakes of M Mkt relationship holds for all Mhi >5.3 earthquakes. This magnitude shift varying with M is basically due to the difference in both number of station magnitude Mst and their spatial coverage used to calculate mean magnitude M, and to the different dynamic ranges of data transfer between Kt-net and Hi-net. To examine precisely the long-term seismicity change in the Kanto-Tokai area by combining these two catalogs, it is important to produce a uniform catalog taking these differences between the two catalogs into consideration.