Prehistoric large earthquakes deduced from fault activities along the Atera Fault, central Japan.

Prehistoric fault activities along the Atera fault one of the most prominent active strike slip faults in central Japan, have been revealed from studies on faulted humic soil layers and river terraces. Many organic samples for radiocarbon dating were collected from the outcrop on the Atera fault at Ogo, Kashimo Village, Gifu Prefecture, in order to determine the periods of prehistoric earthquakes. Displacements of river terraces around Sakashita Town on the right bank of the Kiso river, have been measured in order to deduce the amounts of coseismic displacements. Prehistoric earthquakes deduced from fault activities have repeatedly taken place along the fault at the periods of before 10 300 y.B.P., 7 900 y.B.P., 5 500 y.B.P. and 1 850 y.B.P. Recurrence intervals between succeeding two earthquakes are not equal. The average vertical slip rate has been calculated as 0.71 m/10³ y. The average lateral slip rate is calculated as 3.55 m/10³ yrs. Along the Atura fault a great earthquake is expected to occur withon 1000 years.-Authors.