4.4 Utilization of the map

The following are major examples of how to utilize probabilistic seismic hazard maps and various related information and data. However, as these are merely basic examples, it is desirable to revise them according to specific purposes.

(1) Probabilistic Seismic Hazard Maps (distribution of probability of exceedance and intensity)

The map shows clearly that earthquake hazard varies with region. The map, which shows a probability of ground motions by region, is helpful for prioritizing regions in earthquake disaster mitigation measures and reviewing sites for construction. It also used to set the engineering load, since the distribution map of intensity with a fixed probability shows the maximum quake in a certain probability. However, measures for events with a lower probability also need to be reviewed. (From examples of Chuetsu and Fukuoka earthquakes)

(2) Hazard curve

The peak velocity on the engineering bedrock is an index of earthquake risk in the focused site when designing and evaluating structures in earthquake resistance. The peak velocity on the ground surface and seismic intensity are basic information for earthquake disaster mitigation and risk evaluations.
A probabilistic seismic hazard map represents cross sections of hazard curves calculated 1km square when probability or intensity is fixed. Seeing the entire hazard curve gives understanding of the characteristics of an earthquake hazard at the target point. Therefore, earthquake risk can be evaluated in details.

(3) Degree of influence

Knowing the degree of influence is useful in specifying earthquakes to be assumed for earthquake resistance design and earthquake resistance evaluation, and in earthquake disaster mitigation measures and risk evaluations.

(4) Improving evaluations of specified sites

Improving evaluations at specified sites is possible by applying independently-evaluated and detailed site amplification factors.

(5) Site amplification factor

The map of site amplification factors shows clearly the region's relative susceptibility to vibrations. However, for regions that need more detailed information on vibrations, more detailed modeling of subsurface structures is necessary.

(6) Fault model

For earthquakes with specified seismic source faults, seismic source faults are characterized in parameters, such as length and width. Therefore, the seismic source fault models can be changed easily when it is necessary in earthquake resistance design and earthquake resistance evaluation, and in earthquake disaster mitigation measures and risk evaluations.

(7) Adding detailed information of the site

It is possible to design structure with higher precision by detailing models for surface soil layers based on the detailed information of targeted sites.

(8) The advanced evaluation method of seismic hazard and risk

The evaluation method for the "National Seismic Hazard Maps for Japan" is currently not yet been completed; it is reviewed according to the progress of earthquake research and in the light of new knowledge. It is, therefore, vital to improve the evaluation methods of seismic hazard and risk based on an understanding of earthquake and seismic ground motion. The evaluation method used to prepare the "Probabilistic Seismic Hazard Maps" is expected to be the starting point of the discussion.