Use of Microseismics to Predict Seismic Ground Amplification

One of the important and yet frustrating problems in engineering seismology is the determination of the characteristic site response to earthquake ground motions. The state-of-the-practice is to use the results of one dimensional SH-wave propagation in a layered medium to model the site response. Sophisticated numerical tech- ques are available to model the site response of 3-D structures. However, these models require information of subsurface soil material properties that is often difficult to obtain. Further- more, most techniques and models have not yet been rigourously tested against observed data. Methods that use earthquake data for site characterization are attractive since such data include the most realiastic information on the site response to earthquake ground motions. The difficulty, however, is to isolate the site effects from the source and path effects. Recent studies on site response have indicated that spectral ratio of ground motions at soil to adjacent rock sites, the spectral ratios of the horizontal to vertical components at the soil site, and coda waves method could have practical application in site characterization. The horizontal to vertical spectral ratio method has been applied to both microseismic and mecrotremor data with encouraging results. This method is specially attractive, since it requires seismic recording only at the site of interest. The objective of the Phase I study is to evaluate the most promising techniques for site response characterization using strong motion, weak motion, and microtremor data. The advantages and the shortcomings of each technique, for site characterization will be investigated and discussed. Based on such evaluation, the most practical and re- liable method that could have a broad application and commercial value in the practice of engineering seismology will be identified.