Amplification effects of thin soft surface layers: A study for NBCC 2015

Abstract

The seismic response of shallow soft surface layers is of concern in developing the seismic section of the National Building Code of Canada for 2015. The response of such layers is studied using recorded data from the 2011 Tohoku earthquake. Fourteen sites have been studied in detail so far that had soft, shallow surface layers. At each site two records were available, one at the bottom of the borehole at a depth of the order of 100–500 m and one on the surface. Site response analyses were conducted to determine the ground motion at the top of the rock underlying the surface layer, so that the amplification of the soil layer itself relative to the rock surface could be determined. These analyses were conducted using the program SHAKE. The properties in SHAKE were calibrated to get a good match between the measured and computed surface motions for the recorded input at the bottom of the rock.