Abstract
The multi-channel analysis of surface waves (MASWs) method was used to obtain the shear wave velocity variations through near surface (depth < 30 m) and semi-deep (30 m < depth < 100 m) soil layers in the city of Ottawa, Canada. Sixteen sites were examined to evaluate the capability of the active and passive MASW methods for cases where the shear wave velocity(Vs)contrast between very loose soil (Vs< 200 m/s) and very firm bedrock (Vs> 2,300 m/s) is very large. The MASW velocity results compared with those of other geophysical approaches, such as seismic reflection/refraction methods and borehole data, where available, mostly confirming the capability of the MASW method to distinguish the high shear wave velocity contrast in the study area. We have found that, of the inversion procedures of MASW data, the random search inversion technique provides better results than the analytical generalized inversion method.
Highlights
The city of Ottawa is located in the active Western Quebec seismic zone (Adams and Halchuck [1]), which extends fromMontreal, Quebec to Ottawa, Ontario, Canada
In order to carry out the seismic microzonation measurements, a working group on seismic hazard microzonation in the Ottawa area was established based on a collaboration of Carleton University and the Geological Survey of Canada (GSC)
In order to provide a reliable shear wave velocitydepth function unique to the study area, several methods including seismic refraction/reflection, multi-channel analysis of surface waves (MASWs), spectral ratio methods, and borehole measurements have been applied in the microzonation measurements
Summary
The city of Ottawa is located in the active Western Quebec seismic zone (Adams and Halchuck [1]), which extends fromMontreal, Quebec to Ottawa, Ontario, Canada. With the new requirements in the National Building Code of Canada (NBC, 2005 [2]), seismic soil classifications have become an important issue for major Canadian cities, including Ottawa. This research group aims to obtain shear velocitydepth (S-wave or Vs ) functions and the thickness weighted average shear wave velocity for the top 30 meters, following the U.S National Earthquake Hazards Reduction Program (NEHRP) site classification as recommended by National. In order to provide a reliable shear wave velocitydepth function unique to the study area, several methods including seismic refraction/reflection, multi-channel analysis of surface waves (MASWs), spectral ratio methods, and borehole measurements have been applied in the microzonation measurements. The refraction/reflection method (black solid circles) has been applied to more than half of the study area while other methods have been applied in smaller portions of the city
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