SEISMIC MICROZONATION STUDY BY COMPARING MEASURED MICROTREMORS WITH OBSERVED EARTHQUAKE MOTIONS -A Case Study in the Damaged Area during the 2007 Noto Hanto Earthquake, Japan
Supervisor: Kazuoh SEO, and Kentaro MOTOKI
The influence of local geology and soil conditions on the intensity of ground shaking and earthquake damage has been known for many years. Therefore, a significant part of damage observed in destructive earthquakes around the world is associated with seismic wave amplification due to local site effects. Microtremor measurements were carried out for 55 sites in Monzen-machi, Wajima city, where the damage had been concentrated during the 2007 Noto Hanto Earthquake. The site response (transfer functions) had been calculated by using individual site to reference spectral ratio of microtremors as well as horizontal to vertical spectral ratio. These resulted transfer functions are then compared with the transfer functions obtained from aftershock records for 7 sites where we have aftershock observation points. Also, the dynamic characteristics of two public reinforced concrete buildings have been estimated by using microtremors and then compared with dynamic characteristics which were calculated from aftershock records inside these buildings. The results show high amplification factors in the heavily damaged area due to site effects which can be estimated by microtremors as well as by aftershock records. The comparison between microtremors and observed earthquake motions demonstrate that microtremors can be considered as a powerful tool for estimating the earthquake site response as well as for evaluating the dynamic characteristics of building.
|Citation: ||Bulletin of IISEE, 42, 109-114.|