[H-DS09] Seismic hazards on subduction earthquakes and active faults in the Central Japan

[HDS09-P08] How should we deliver seismic hazard information to the public?

*Takeshi Sagiya¹, Noa Mitsui¹, Hashitomi Shogo¹ (1.Disaster Mitigation Research Center, Nagoya University)

Keywords:seismic hazard, earthquake probability, seismic shaking forecast, outreach

Inland earthquakes occurring at active faults are smaller than those at subduction zones. But these earthquakes cause strong shakings and surface offsets due to their proximity to human habitation. Repeat times of inland earthquakes are several hundred years in the shortest cases, and more than 10,000 years are common. Such an extremely low frequency makes our mitigation countermeasures very difficult. In Japan, after the 1995 Kobe earthquake, the government has been conducting active fault investigations and ground motion predictions extensively. Outcomes of these activities have been published as long-term earthquake forecasts and nationwide seismic hazard maps. But it should be noted that such published information contains large uncertainties and the presentation becomes very difficult. As a part of the "Intensified Investigation and Observation of the Byubusan-Enasan Fault Zone and the Sanageyama Fault Zone" project, we conduct questionnaires to experts in both earthquake science and earthquake engineering, interviews with local authorities, and questionnaires to residents. We will argue the problems regarding the publication of earthquake hazards and discuss possible improvements.
Currently, the Headquarters for Earthquake Research Promotion provides seismic hazard information such as earthquake occurrence probabilities and predicted seismic intensities. However, it is advised to clearly distinguish original data and analysis results for experts from plainly explained information for the public. Earthquake probabilities for active faults are mostly less than a few % and such a low probability cannot make any sense to the public. If we present such a low probability, it is definitely important to provide a plain explanation about the existence of a risk to be prepared. For local authorities, supporting materials should be provided to facilitate the explanation for the public. For the public, it is advised to provide information about expected damages and their countermeasures in addition to seismic intensities.