On Shaky Ground
As our understanding of underground events has increased, we have included seismic safety standards in our building and bridge codes to ensure the longevity of crucial structures upon which millions of Canadians rely every day. Determining how and where to build, however, depends on a detailed understanding of the ground beneath our feet and how it changes during an earthquake. To add further complication, different types of soils respond in different ways. Improving geotechnical engineering practices requires a high-resolution image of the subsurface – a costly and impractical affair using current methods.
Sheri Molnar and her research group in the Department of Earth Sciences at Western University are developing new methods to survey the ground. Traditionally, 30-metre deep boreholes have been used to gather information about the ground upon which future building projects are planned. Each borehole costs about $3000 and only gives a profile for a tiny radius of a few centimeters. The Molnar group’s new non-invasive method uses on-ground sensors rather than boreholes and, for the same price, can give detailed information for an entire city block.
Video: Three-dimensional wave propagation simulation of a magnitude 4.7 earthquake at 50 km depth in southwest British Columbia. Grey line highlights the base of the Georgia sedimentary basin. The predicted earthquake shaking (waveforms) at selected surface locations are shown above
Recently, the Molnar group was awarded a $3.5 million grant from Emergency Management British Columbia (EMBC) to provide seismic hazard mapping for the metro Vancouver area. The six-year project, ending in 2023, will give EMBC crucial information on shaking amplification factors, landslides, and liquefaction. This data is precisely what informs land-use planning, building codes, and safety retrofits for the millions of inhabitants in hazardous areas. The cheaper, more scalable, and less invasive technique that the Molnar lab has developed can be applied to cities around Canada, ensuring a higher degree of safety for building integrity than ever before possible.
The research group is currently leading an effort to create international guidelines for noninvasive geotechnical engineering methods to bring this critical improvement to countries across the globe that experience high levels of seismic activity.