Use of Microtremors For Site Response Characterization.

The primary objective of this project was to investigate the feasibility of using microtremors to obtain information on the local site conditions for site specific ground motion analysis. Microtremors and microseisms have been used by many investigators for site response investigation. One of the old and rather neglected techniques is Akis 1957 Circular Array method. It uses microtremor data on a small scale circular array to infer information on the wave propagation properties of the local site materials. Aki successfully used this technique at a site in the University of Tokyo to obtain the information on the shear wave velocity profile for the site. The most attractive feature of this technique is its simplicity in data requirement and field operation. Theoretical, numerical, and field investigations of the Circular Array technique were conducted to evaluate its potential for site investigation. The results of this study clearly indicate that the Circular Array technique can provide general information on the seismic wave propagation properties of the local site materials. The data requirements i.e., microtremors and the field instrumentation are fairly simple. The data processing and interpretation can be simple or sophisticated depending upon the detail of the velocity model that is desired for a particular application. However, it is possible to automate different aspects of the data processing in order to make the interpretation the least time consuming.