Research teams such as the University of Tokyo have revealed that the Genroku-type Kanto earthquakes, which the government has evaluated as having an average interval of about 2300 years, have occurred at least five times in the past 6300 years, at a minimum interval of 5 years. I made it.This is a result of urging a review of the probability of future earthquakes, and it is necessary to broaden the scope and elucidate the past occurrence patterns of large earthquakes that affect the metropolitan area in the future.
The Genroku-type Kanto earthquake is the same type of earthquake as the Genroku Kanto earthquake that occurred in 1703 from Kanagawa prefecture off the southeastern coast of the Boso Peninsula.The government's Headquarters for Earthquake Research Promotion has evaluated that Genroku-type Kanto earthquakes occur at intervals of about 2000 to 2700 years (average 2300 years).This is based on the result of estimating the formation age of the terraces by collecting shell fossils from the stepped topography (coastal terraces) formed by the ground uplift caused by the earthquake.However, the accuracy of the survey results was not well understood, as it may contain old shellfish that happened to be buried in the stratum.
Therefore, this research team conducted an unprecedented dense boring (excavation) survey and selected fossil shellfish in good condition.Furthermore, dating was performed with the latest accelerator mass spectrometer, and the age of terrace formation was determined with extremely high accuracy.
From the obtained dating values, it was found that the conventional seismic history was greatly updated, the interval between occurrences was shorter, and the variation was large.Future earthquake forecasts calculated by the national government based on the conventional terrace age values are the result of having to be reviewed.
The research team aims to further expand the scope of the survey and elucidate more detailed earthquake occurrence patterns.
Paper information: [Earth and Planetary Science Letters] History of the great Kanto earthquakes inferred from the ages of Holocene marine terraces revealed by a comprehensive drilling survey
