Lowering earthquake construction costs
A Victoria University of Wellington visiting research associate has been involved in a project that identified earthquake shaking potential in Las Vegas to help developers build in safer and less expensive ways.
Seismologist Dr Aasha Pancha from Victoria’s School of Geography, Environment and Earth Sciences, was part of the project team which mapped and classified the earthquake shaking potential across most of the Las Vegas metropolitan area.
The "Parcel Map" is described as the most extensive effort to date in the United States to map and classify soils based on their effects on earthquake shaking across an entire urban area with systematic, closely spaced measurements. These "site classifications" are a key part of the building codes that structural engineers use to design new buildings—or to retrofit older buildings—to withstand earthquake damage.
One of the most important findings of the Parcel Map study is that much of the ground in the Las Vegas area is actually stiffer (stronger) and with potentially a reduction in risk for building than the current default site classifications for the region indicate.
As a result, the new Parcel Map offers a more definitive understanding of the ground response to seismic events, identifying areas which may be prone to shaking in an earthquake. The map will be used by local authorities, engineers, developers, builders and property owners to avoid over-strengthening buildings on stiffer sites, and properly assess the higher costs of developing softer sites.
"City officials can then plan retrofit campaigns and ensure buildings meet requisite safety standard on the basis of knowledge, rather than guesswork," says Dr Pancha.
The Parcel Map was drawn from more than 10,000 seismic-array measurements taken about every 300 metres, to cover most of urban Las Vegas.
The paper, recently published in the Bulletin of the Seismological Society of America, is particularly relevant to improving earthquake resilience in New Zealand—especially in light of recent earthquake events, says Dr Pancha.
“Besides direct measurements from expensive boreholes, this methodology is one of the most accurate ways of assessing material properties beneath the ground surface down to bedrock in the New Zealand Building Code.
“The site class values derived using this method enable structural engineers to efficiently design and build structures in line with the predicted earthquake loadings due to earthquake shaking.”
Victoria students are already using this new approach in their research—PhD student Francesco Civilini from the School of Geography, Environment and Earth Sciences has used the method to identify the location of a fault in the central North Island.
Dr Pancha is working with Victoria’s Professor Tim Stern on a joint proposal with the Ministry of Business, Innovation and Employment to apply these new mapping techniques here in New Zealand.
Dr Pancha also works as a Geophysical Ground Investigation Manager at engineering consultancy company Aurecon.