"For very stiff soils, current building codes don't include amplification of ground motion," said lead author Sheri Molnar, a researcher at the University of British Columbia. "While the building codes say there should not be any increase or decrease in ground motion, our results show that there could be an average amplification of up to a factor of three or four in Greater Vancouver."
The research provides the first detailed studies of 3D earthquake ground motion for a sedimentary basin in Canada. Since no large crustal earthquakes have occurred in the area since the installation of a local seismic network, these studies offer refined predictions of ground motion from large crustal earthquakes likely to occur.
Southwestern British Columbia is situated above the seismically active Cascadia subduction zone. A complex tectonic region, earthquakes occur in three zones: the thrust fault interface between the Juan de Fuca plate, which is sliding beneath the North America plate; within the over-riding North America plate; and within the subducting Juan de Fuca plate.
Molnar and her colleagues investigate the effect the three dimensional (3D) deep basin beneath Greater Vancouver has on the earthquake-generated waves that pass through it. The Georgia basin is one in a series of basins spanning form California to southern Alaska along the Pacific margin of the North America and is relatively wide and shallow. The basin is filled with sedimentary layers of silts, sands and glacial deposits.
While previous research suggested how approximately 100 meters of material near the surface would affect ground shaking, no studies had looked at the effect of the 3D basin structure on long period seismic waves.
To fill in that gap in knowledge, Molnar and colleagues performed numerical modeling of wave propagation, using various scenarios for both shallow quakes (5 km in depth) within the North America plate and deep quakes (40 – 55 km in depth) within the Juan de Fuca subducting plate, the latter being the most common type of earthquake. The authors did not focus on earthquakes generated by a megathrust rupture of the Cascadia subduction zone, a scenario studied previously by co-author Kim Olsen of San Diego State University.
For these two studies, the authors modeled 10 scenario earthquakes for the subducting plate and 8 shallow crustal earthquakes within the North America plate, assuming rupture sites based on known seismicity. The computational analyses suggest the basin distorts the seismic radiation pattern – how the energy moves through the basin – and produces a larger area of higher ground motions. Steep basin edges excite the seismic waves, amplifying the ground motion.
The largest surface waves generated across Greater Vancouver are associated with earthquakes located approximately 80 km or more, south-southwest of the city, suggest the authors.
"The results were an eye opener," said Molnar. "Because of the 3D basin structure, there's greater hazard since it will amplify ground shaking. Now we have a grasp of how much the basin increases ground shaking for the most likely future large earthquakes."
In Greater Vancouver, there are more than 700 12-story and taller commercial and residential buildings, and large structures – high-rise buildings, bridges and pipelines – that are more affected by long period seismic waves, or long wavelength shaking. "That's where these results have impact," said Molnar.
The papers -- "Earthquake Ground Motion and 3D Georgia Basin Amplication in SW British Columbia: Deep Jan de Fuca Plate Scenario Earthquakes" and "Earthquake Ground Motion and 3D Georgia Basin Amplification in SW British Columbia: Shallow Blind-Thrust Scenario Earthquakes" -- by Molnar; John F. Cassidy, Natural Resources Canada; Kim B. Olsen, San Diego State University; Stan E. Dosso, University of Victoria; and Jiangheng He, National Resources Canada; will appear in the February print issue of BSSA and be published online Jan. 21, 2014.
Nan Broadbent | EurekAlert!
A new 3D viewer for improved digital geoscience mapping
20.09.2016 | Uni Research
The significance of seaweed
16.09.2016 | King Abdullah University of Science and Technology
The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.
“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...
With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.
Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...
For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.
Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...
At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.
In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...
Every three years, the plastics industry gathers at K, the international trade fair for plastics and rubber in Düsseldorf. The Fraunhofer Institute for Laser Technology ILT will also be attending again and presenting many innovative technologies, such as for joining plastics and metals using ultrashort pulse lasers. From October 19 to 26, you can find the Fraunhofer ILT at the joint Fraunhofer booth SC01 in Hall 7.
K is the world’s largest trade fair for the plastics and rubber industry. As in previous years, the organizers are expecting 3,000 exhibitors and more than...
23.09.2016 | Event News
20.09.2016 | Event News
16.09.2016 | Event News
23.09.2016 | Life Sciences
23.09.2016 | Health and Medicine
23.09.2016 | Life Sciences