Vs30 Mapping of the Greater Montreal Region Using Multiple Data Sources

Abstract

The metropolitan community of Montreal (MMC) is located in Eastern Canada and included in the western Quebec seismic zone characterized by shallow crustal earthquakes and moderate seismicity. Most of the urbanized areas are settled close to the Saint-Lawrence River and its tributaries and within the region, delimiting the extension of the clay deposits from the Champlain Sea. The influence of these recent and soft deposits on seismic waves has been observed after the 1988 M5.8 Saguenay earthquake and has proven to be crucial in seismic hazard analysis. The shear-wave velocity Vs averaged over the 30 m of soil, abbreviated Vs30, is one of the most used parameters to characterize the site condition and its influence on seismic waves. Since 2000, a site condition model has been developed for the municipalities of Montreal and Laval, combining seismic and borehole data for risk mitigation purposes. The paper presents an extended version of the Vs30 mapping for the entire region of the MMC, which accounts for half of the population of Quebec, including additional ambient noise recordings, recently updated borehole datasets, geological vector map and unpublished seismic refraction data to derive Vs profiles. The estimated Vs30 values for thousands of sites are then interpolated on a regular grid of 0.01 degrees using the inverse distance weighted interpolation approach. Regions with the lowest estimated Vs30 values where site amplification could be expected on seismic waves are in the Northeastern part and in the Southwest of the MMC. The map expresses in terms of site classes is compared with intensity values derived from citizen observations after recent felt. In general, the highest reported intensity values are found in regions with the lowest Vs30 values on the map. Areas where this rule does not apply, should be investigated further. This site condition model can be used in seismic hazard and risk analysis.

Influence of the 2020 Seismic Hazard Update on Residential Losses in Greater Montreal, Canada

“…A detailed site condition model for the MMC based on V s30 mapping has been incrementally developed over the last 20 years (e.g., [25,26]) as illustrated in Figure 4. This map is derived from shear-wave velocity (Vs) data from non-invasive seismic methods, borehole profiles converted into vs. profiles, and geological data.…”

Seismic Microzonation of Urban Site Using the Target Spectral Ratio Method (HVSR): A Case Study of Algiers City.

“…Data collection and analysis highlighted several parameters related to seismic hazards, including shear wave (Vs) and compression wave (Vp) propagation velocities, which are crucial for this study. The average propagation velocity of shear waves, or 'Vs30,' within the first 30 meters is a common indicator for evaluating soil seismic classification (Pinzón et al, 2019;Thamarux et al, 2019;Mori et al, 2020;Raddatz et al, 2021;Rosset et al, 2023). However, geophysical testing can be expensive and complex in urban environments.…”