Fukui Akihiro

Earthquake estimation using H / V spectrum ratio

Miyaki Yasuyuki

We have suffered earthquake damages many times. That makes an opportunity to increase earthquake wave observation points. But there points are not enough.It is necessary to grasp the ground structure and the vibration characteristics used by geophysical exploration for earthquake damage reduction. Microtremor observation is one of those geophysical explorations, and that is low cost and expedient.It has been studied to evaluate the ground structure by calculating the ratio of horizontal spectrum and vertical spectrum of microtremor, H/V spectrum. It is very usefully to convert earthquake wave record at other spot by use of the H/V spectrum and estimate the earthquake vibration of non-observation spot.Therefore, in this study, I aimed the validity of estimating method of using microtremor record and earthquake record in two spots, with the goal of the establishment the technique of estimating the earthquake vibration of non-observation spot by using microtremor data.In this study, when the ground as a linear elastic body is regarded, earthquake wave is estimated by the characteristics of source of earthquake, propagation characteristics and site characteristics. Hence, the site characteristic is substituted by using H/V spectrum. Method of that hypothesis corroboration is to measure a micro tremor at two spots of an earthquake observation point, and then estimate and study many earthquakes. This confirms the accuracy of the estimation and clarifies the source of the error. Distance attenuation was confirmed for different distance estimations. We also found that the observation time was different for each observation point. However, it is small between nearby observation points and large between distant observation points. To eliminate these errors, we used Si and Midorikawa's distance attenuation formula. Then, we used the data, paying attention to the observation start time.As a result, the accuracy of estimation was improved in many cases, and the accuracy of estimation was confirmed to some extent even for large-scale ground motions. The advantage of the estimation method proposed in this study is that the estimation can be performed quickly. In other words, it could be a guide for a detailed estimation that will be made after that. We have proposed a simple and inexpensive estimation method, which is the purpose of this study, and we would like many people to use it.