Application of microtremors to seismic microzoning procedure

Mete MIRZAOGLU* and Ünal DÝKMEN*

* General Directorate of Disaster Affairs, Earthquake Research Department, Ankara, TURKEY

Abstract: Due to the close relation between the nature of microtremors and the fundamental dynamic behavior of the surface soil layer, these small vibrations are well-known and useful in the field of earthquake engineering. The technique of microtremors measurement and analysis has been successful for microzoning in many places around the world. This technique has the advantage of being a fast and easy way to estimate the effect of ground motion characteristics due to an earthquake. This paper presents an experimental study of microtremors for investigation ground characteristics. In this study, 114 microtremors data were obtained from Shin-Yokohama area in Japan. A map showing the distribution of the site predominant periods was developed for microzonation purposes. These periods showed good agreement with periods of earthquake ground motions recorded during the July 1997 Chiba earthquake (M=5.3), the February 2000 Yamanashi earthquake (M=4.6) and the May 1998 Izu Peninsula earthquake (M=5.1). In the result of this study, it should be noted that the characteristics of microtremors are dependent on the type of soil deposits. Site effect plays an important role in microtremors measurements.

Key words: Seismic microzonation, microtremor, H/V spectral ratio, Nakamura method