Evaluation of Site Periods in the Metro Vancouver Region Using Microtremor Testing

Abstract

Metro Vancouver, located in British Columbia, Canada, comprises the city of Vancouver and twenty more municipalities of its metropolitan area. The Metro Vancouver region has a population of about 2.25 million people and it is located in an area of high seismicity. A future earthquake close to Metro Vancouver would cause tens of billions of dollars damage and would seriously impact the economy of both British Columbia and Canada. Therefore, some of the municipalities in the region have initiated a program to evaluate the level of seismic hazard potential and identify the most vulnerable areas. In this regard, the identification of soil conditions plays a very important role in the evaluation of the seismic hazard potential. A cost effective technique to identify the dynamic characteristics of soil deposits is through microtremor testing. Between 2009 and 2010 a series of microtremor tests were performed over the region of Metro Vancouver. Data obtained from these tests was analysed using both the horizontal to vertical ratio (H/V) and the frequency domain decomposition techniques of the recorded motions to find the predominant periods of vibration of the ground in the horizontal direction. For each test, in addition to the predominant period, values of peak ground velocity, PGV, root mean square ground velocity (RMS), and amplitude were recorded. Combining the results from a series of tests, maps of site periods were created for the regions investigated. This paper discusses the details of the testing campaign and the site period maps developed for Metro Vancouver.