5-4.  Paleoearthquake Studies

 

    Understanding of recurrence behavior of large earthquakes is essential for long-term earthquake forecast and also important for studies on earthquake generating mechanism, especially on its steady-state nature and various disturbances affecting it. Repeat time of large earthquakes ranges from hundred years to several thousand years or more and cooperative researches among university researchers on active faults, paleotsunamis, and historical earthquakes are carried out. Our findings are also helpful to estimate properties of a seismic fault such as static and dynamic parameters, mode of rupture propagation, and spatial distribution of asperities.

 

Geomorphological, Geological, and Geophysical Survey of Active Faults

    Not only occurrence time of paleoearthquake, but also co-seismic slip and its spatial variation will be estimated for examination of recurrence models and constructing seismic fault models for strong motion prediction.

 

Geological Paleotsunami Studies

    Historical and prehistoric Tokai and Nankai earthquakes and Tokachi-Oki earthquakes are studied by examining geological paleotsunami evidence for better understanding of the recurrence of interplate great earthquakes.

 

Fault Model of Historical Earthquakes Estimated from Historical Documents

    Exact location of each reported feature is identified and database is constructed for the 1804 Kisagata, 1847 Zenkoji, 1854 Iga-Ueno and the 1858 Hietsu earthquakes. Comparison of the data with surface geology improves our understanding of faulting mechanism.

 

Figure 1.  Right-latteral offest of road (by Hiroyuki Tsusumi, Kyoto Univ).

Figure 2.  Vibro-coring survey of tsunami deposit at Lake Hamana (by Hiromi Matsuoka, Kochi Univ).