3.5 Future tasks

We wish to raise issues involved in the "Seismic Hazard Map for Specified Seismic Source Faults" and in the evaluation of strong ground motion, and to describe future outlook.

(1) Reflecting more detailed information of the region

The "National Seismic Hazard Maps for Japan" are prepared in units of about 1 km mesh. It is necessary to prepare the map using finer meshes by reflecting characteristic of surface soil layers that varies locally inside the 1 km mesh to plan the detailed earthquake disaster migigation measures.

(2) Estimating uncertainties of scenarios

The available scenarios are limited, they do not always include the conditions that cause the greatest seismic ground motion. With the remarkable progress in computation performance, it is possible to use the probabilistic approach when the intensity and its fluctuations of many scenarios are evaluated.

(3) Adding new assumed earthquakes

Assumed earthquakes at this stage are limited mainly to subduction-zone earthquakes and earthquakes based on information on active faults. It is necessary to add assumed earthquakes such as earthquakes that may occur from the view points of seismology even without information and evidence of past earthquakes, the earthquakes excluding characteristics events, and aftershocks in order to evaluate strong ground motions and damages.

(4) Tasks with the evaluation method of seismic ground motion

• It is necessary to keep upgrading the evaluation methods of seismic ground motion and to improve the preparation technique of the seismic hazard map.
• Distribution of seismic ground motion greatly depends on the position of asperity, the rupture initiation point, and the direction of rupture propagation, but there is not enough knowledge and information required to constrain and set these conditions. Therefore, further research and studies are required.
• Mainly for big subduction-zone earthquakes, modeling of seismic sources and evaluation methods of seismic ground motion need to be devised and improved to apply a hybrid method while securing the evaluation precision of seismic ground motions around the overlapping period, connecting the short period range and the long period range.
• It is necessary to improve subsurface structure models by confirming its applicability mainly through comparisons for the calculated waveforms with the observed records.
• The detailed method currently only uses the site amplification factor to model surface soil layers, just as the conventional method does. It is necessary to develop a method to estimate the site amplification and seismic ground motion on ground surfaces, taking into consideration the detailed information of the site and nonlinear response characteristics.