4.5 Future tasks

We wish to raise issues involved in the "Probabilistic Seismic Hazard Maps" and evaluation method of seismic hazard, and to described future outlook.

(1) Modeling earthquake activities

The modeling of earthquake activities aims to estimate future earthquake activities with high precision. In the current model, characteristic earthquakes occurring in the 98 major active fault zones, as well as subduction-zone earthquakes, are based on the results of long-term evaluation, and it is possible to model an individual earthquake with a relatively concrete image. However, most other earthquakes are modeled as "earthquakes without specified source faults" by describing the characteristics of a group of earthquakes that occur in an extended area.
For models of seismic activities to be easily understood, it is important to increase the evaluation cases to be individual earthquakes, along with our knowledge about seismic activities. The following are future tasks.

1. The modeling of earthquakes occurring in the active fault, excluding the characteristics events
2. The modeling of earthquakes occurring together with adjacent regions considering interactions
3. Considering changes of seismic events on land occurring before and after activities of an subduction-zone earthquake
4. Developing proper elimination of foreshocks and aftershocks, or modeling of seismic activities considering are series of foreshocks and aftershocks

(2) The evaluation of seismic ground motions

Improvement of the evaluation model of seismic ground motions aims to show the probability distribution at the target point as accurately as possible when a specified earthquake occurs. The following are future tasks to achieve improvement.

1. To study what type of distribution follows the dispersion of peak values of strong ground motion, and how to fix a limit interval of the distribution
2. Studying fluctuation parameters (including amplitude, scale, and distance dependency)
3. Increasing the precision of the evaluation of seismic ground motions in the vicinity of the seismic source with the help of the detailed method
4. Increasing the precision of the evaluation of site amplification factors and the consideration of nonlinear soil response
5. Reflecting the influence of deep sedimentary layers

At the same time, there is a growing demand for seismic hazard maps with maximum acceleration and a response spectrum as an index other than peak velocity and seismic intensity. It is necessary to meet the demand as a short-term issue.

(3) The integration of the "Probabilistic Seismic Hazard Maps" with detailed prediction method for strong ground motions

The following two forms are representative examples that integrate the "Probabilistic Seismic Hazard Maps" with the "Seismic Hazard Maps for Specified Seismic Source Faults".

1. Degree of influence
2. Reflecting results of prediction of strong ground motions using the detailed method in the "Probabilistic Seismic Hazard Maps"

At present, the former has already been implemented. Discussions have already started on integration according to various forms of utilization. Further discussion and study are needed to realize the integration.

(4) Handling uncertainties

Constructing a model for preparing the "Probabilistic Seismic Hazard Maps" involves various uncertainties due to a shortage of knowledge and data. At present, these uncertainties are handled by applying the most probable case, but it is necessary to review how to handle and how to quantify them, and how to represent results from now on.