Importance of USING MICROTREMOR OBSERVATIONS IN Seismic Microzoning StudIES FOR Understanding Soil Condition in Seismic Risk Reduction Procedures
By Takahaisa Enomoto
Emeritus Professor, Kanagawa University
In 6th of January 2023, Turkey and Syria Earthquake Mw7.8 was occurred along to the East Anatolian Fault. The damages were so huge, more than 50,000 people was killed and more than 160,000 buildings were damaged. The information of this earthquake is not sufficient at this moment, but this earthquake disaster will be investigated in detail in the future, it will be very important for seismic risk reduction. Recently, many countries which are earthquake prone countries prepared PGA and PGV distribution and earthquake damage estimation map for scenario earthquakes.
In this keynote lecture, I would like to introduce the basic concept of seismic microzoning as the earthquake disaster risk reduction and its validity. At the first step, we introduce the originally recognized concept for the earthquake damage mitigation measures as the beginning of considering the risk management for the big cities like Tokyo Metropolis in Japan, it was started in 1960s. Recently, according to the development of computer technology, huge digital data of geological and geographical information and many kinds of implementation settlement are summarized and useful for such kind of simulated seismic risk assessment works and the contents are very visible and very complex. Anyway, the basic important procedure is to understand the soil conditions in the area, especially the surface soil condition. If we want to get more accuracy for seismic disaster risk, we must understand the differences of surface soil condition. In general, for detailed understanding of the surface soil condition, we use the geotechnical data, but it’s very difficult to use such kind of data densely in the area. So that, we try to use the microtremor observation densely for getting the possible information of surface soil condition and identify the differences depending on the natural period of soil conditions by using H/V spectral ratio.
In this lecture, the case study of such kind of research works were done at Sagami Plane, Yokohama City, Kobe City, Japan, Adra Town, Almeria City, Granada City, Lorca City, Spain, Caracas, Venezuela, Manila, Philippines and Colima City, Mexico etc. We would like to introduce and show the examples at several area and explain the validity of the results.