Sunday, April 28, 2013

Shake, Rattle, and Roll: Lessons for Oregon

Distant view of Rikuzentakata, Iwate, Japan (photo by Mitsukuni Sato via Wikipedia)

2011’s devastating Tohoku earthquake and tsunami in Japan provided both a wakeup call and wealth of information for seismologists, hydrologists, and engineers here in the Pacific Northwest. At this month’s Willamette Valley Chapter CSI meeting, Oregon State University professors Harry Yeh(1) and Ben Mason(2) described how we need to become far better prepared by investing more in earthquake and tsunami-resistant infrastructure and preparedness. 

The disaster along Honshu’s northeastern shore provided us with a glimpse of what is likely to occur along the Oregon coast. Both Harry and Ben pointed to how Oregon's geography resembles northeastern Japan, with isolated coastal communities separated by a mountain range from a heavily populated valley. Like Japan, Oregon faces an undersea subduction zone, in which an oceanic plate pushes beneath a continental plate. A mega-thrust earthquake caused by a rupturing of the colliding plates off our shore along the Cascadia subduction zone is long overdue (the last occurring in 1700). The next one could happen tomorrow; are we prepared? 

The challenges we would face when the unthinkable happens include how to deliver timely rescue and relief to affected coastal communities, especially if vital roads and other conduits through the Coast Range are severed. The likely scope a Cascadia mega-quake (which could rival the 9.0 Mw magnitude of the great Japan earthquake) would extend well beyond our beaches to involve and impact lives and property in the Willamette Valley as well. It’s only prudent for us to take heed of Japan’s experience and prepare accordingly. 

Harry has thoroughly studied the physics of tsunamis; regardless, he and other researchers were astounded by what they learned when they visited Japan in the aftermath of the Tohoku event. They understood morphological variability influenced the effects and magnitude of the run-up of water a tsunami pushes onto the shore; however, they did not foresee how significantly these variations contributed to the force of the run-up. 

The funneling and reflecting effects in narrow gulfs parallel to the tsunami propagation vector combined with narrow valleys onshore to generate peak run-up elevations of as much as 40 meters. The run-up devastated virtually everything in its path. Even buildings many stories tall failed those who believed height provided a sanctuary. Regardless, Harry asserts “vertical evacuation” within a reinforced concrete building is a valid survival strategy when people don’t have time to otherwise escape a tsunami and the predicted run-up does not exceed the structure’s height. 

On the other hand, vertical evacuation provides no refuge for victims if the building cannot withstand the force of a tsunami. The power of the surging water toppled a multistory reinforced concrete structure in Onagawa. Harry was stunned such a building could be tipped over by water alone. He analyzed the dynamics of the tsunami/structure interaction and the scouring effects in the wake of the run-up. With the data collected from this analysis, Harry now plans to research how to prevent strong, structurally rigid buildings from tipping over. 

Cascadia Subduction Zone

Ben’s current research interests include the seismic response of Oregon's native soils, effects of longduration earthquake motions on the built environment, soil liquefaction, soil‐fluid-structure interactions, seismic resiliency on a city-scale, cumulative damage caused by successive hazards, and coastal geotechnical engineering. He explained how our Willamette Valley silt possesses distinct properties that contribute to increased risk and the potential for destructive effects. 

The valley traps and amplifies the motions of the deposited sediments. During a subduction event, the duration and peak ground accelerations would be much greater than those of a more common crustal fault earthquake. It is these factors that would lead to soil liquefaction, which can be extremely damaging. Buildings whose foundations bear directly on soil which liquefies will experience a sudden loss of support, resulting in drastic and irregular settlement. The bottom line is the built environment of our cities in the Willamette Valley is vulnerable to significant devastation. 

Ben and his colleagues are utilizing LIDAR (Light Detection and Ranging) technology to provide very precise, accurate, and high-resolution images of the surface of the earth, vegetation, and the built environment. Airborne LIDAR uses a laser range finder mounted in a precisely navigated aircraft to scan the earth's surface at very high rates and collect very dense clouds of X-Y-Z coordinates. He is using the collected data for landscape scarp modeling, which can identify and help predict zones of risk (i.e. for landslides) vulnerable to seismic activity. 

If we’re determined enough, the lessons learned from Tohoku and similar subduction mega-thrust earthquakes will lead to the implementation of specific seismic and tsunami resiliency plans. Prior to the disaster in Japan (and before it the 2010 Chile earthquake), state and regional governments paid little attention to the vulnerabilities of population centers in the Pacific Northwest. The Oregon legislature has since begun allocating money, a welcome development. The research Harry and Ben are engaged in today is broadening our knowledge about how our cities’ infrastructures will respond to the impending Cascadia earthquake and helping make Oregon a safer place. 

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This post is my first on the subject of the monthly programs produced by the Willamette Valley Chapter of the Construction Specifications Institute. Ever since I started this blog, I’ve reported on AIA-Southwestern Oregon’s chapter events. I’ll attempt now to do the same for WVC-CSI meetings. 

As I wrote previously, the accomplishments of CSI include continuous development of construction documentation standards and the education of professionals to improve project delivery processes; however, it is perhaps the organization’s diversity that is its greatest achievement. 

Unlike the AIA, which primarily exists to serve the good of the architectural profession, CSI membership is open to anyone interested in the advancement of construction communication standards. In addition to architects, the institute welcomes the participation of engineers, contractors, facility mangers, product representatives, manufacturers, owners, and of course construction specifiers. The only qualification is a common desire to contribute to the improvement of communication in the construction industry. If you’re not already a member, I strongly encourage you to join the Construction Specifications Institute.

(1)   Harry Yeh is the Miles Lowell and Margaret Watt Edwards Distinguished Chair in Engineering at Oregon State University. Yeh received an AB in Economics from Keio Gijuku University (Japan), BS and MS degrees in Agricultural Engineering from Washington State University, and a PhD in Civil Engineering from University of California. He worked for Bechtel Inc. in the late 1970s and early 1980s, primarily analyzing hydrodynamics problems involved in electric power plants. Yeh began his academic career in 1983 at the University of Washington, and joined the faculty of School of Civil and Construction Engineering at Oregon State University in 2003. Yeh's primary research interest is in the field of hydrodynamics of tsunamis, focusing on controlled laboratory experiments and theoretical development of nonlinear longwave theory.

(2)   Ben Mason is an assistant professor in the School of Civil and Construction Engineering at Oregon State University. His current research interests include the multi-disciplinary field of urban earthquake engineering. This field combines the expertise of geotechnical and structural earthquake engineering, engineering seismologists, public policy experts, and decision-makers to improve the seismic resiliency of urban areas. Dr. Mason uses physical modeling techniques such as centrifuges, shaking tables, laminar soil boxes, and cyclic laboratory equipment, as well as numerical modeling tools including FLAC, OpenSees and PLAXIS. Additionally, Dr. Mason is interested in the fields of sustainable geotechnical engineering and geotechnical engineering education.

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