May 2, 2012
February 21, 2012 By Sandi Doughton
Scientists are still unraveling last year's giant Tohoku earthquake and tsunami in Japan, and some of what they're finding doesn't bode well for the Pacific Northwest.
Detailed analyses of the way the Earth warped along the Japanese coast suggest that shaking from a Cascadia megaquake could be stronger than expected along the coasts of Washington, Oregon and British Columbia, researchers reported Sunday at the annual meeting of the American Association for the Advancement of Science.
"The Cascadia subduction zone can be seen as a mirror image of the Tohoku area," said John Anderson, of the University of Nevada.
Anderson compiled ground-motion data from the Japan quake and overlaid it on a map of the Pacific Northwest, which has a similar fault - called a subduction zone - lying offshore.
In Japan, the biggest jolts occurred underwater. The seafloor was displaced by 150 feet or more in some places, triggering the massive tsunami. But in the Northwest, it's the land that will be rocked hardest - because the Pacific coast here lies so close to the subduction zone.
Cities like Seattle, Portland and Vancouver, B.C., are far enough from the coast that they might dodge the most violent hammering. But all of the urban areas sit on geologic basins that can amplify ground motion like waves in a bathtub.
"Basins shake more than hard rock," Anderson said. "Local site conditions can have an enormous effect on the nature of strong ground motions."
The U.S. Geological Survey (USGS) is already at work on a new analysis of how hard the ground is likely to shake and how close the rupture zone might come to urban areas the next time the Cascadia subduction zone really lets loose. The last time was in 1700, and the resulting quake was a magnitude-9 - just like the monster that struck Japan on March 11, 2010.
Japan's extensive network of seismometers, satellites, strain meters and GPS sensors logged a wealth of data that scientists continue to mine for insights.
"It's the best-recorded megaquake ever, and it's very relevant for the hazard in Cascadia," Anderson said.
Japanese scientists are struggling to answer several haunting questions: Why was the quake so big? How did the tsunami swell to such giant proportions? And why was it such a surprise to the world's most earthquake-savvy nation?
"It was very disheartening for people doing earthquake research and hazard mitigation in Japan," said Jim Mori, of Kyoto University's Disaster Prevention Research Institute.
Seismologists were fooled by a series of small quakes that rocked the area every 35 years or so, said Kenji Satake, of the University of Tokyo.
They believed each small quake relieved the pressure on the subduction zone - the boundary where two geologic plates slip past each other as the ocean floor shoves under the continent.
Now they realize strain continues to build until the series of small quakes is punctuated by a giant one about every 700 years. Similar quakes and tsunamis struck in the years 869 and 1896, but Japanese scientists failed to look far enough into their own history, Satake said. "We needed longer time records."
The longest record for a subduction zone is from Cascadia, where scientists have linked buried marshes and submarine landslides with a series of about 22 megaquake quakes going back 10,000 years. The time between quakes ranges from 200 to 1,000 years, with an average of about 500 years.
There's no obvious "supercyle" of supergiant quakes, as Satake suggests, in Japan. But it is clear that quakes on Cascadia have varied in size, said USGS scientist Brian Atwater. Some geologists argue the magnitude-9 quake 300 years ago was simply average and that the Northwest has been slammed by quakes twice as big in the distant past.
Most earthquake scenarios for the Northwest coast project tsunamis of about 30 feet, and scientists still don't know how much that needs to be ratcheted up post-Tohoku. Walls of water up to 120 feet high washed away entire communities on the Japanese coast.
"Does Cascadia also have a 40-meter tsunami coming onshore?" Mori asked.
Several of the yardsticks used to gauge the risk on subduction zones were proved questionable in Japan, he added.
Foremost among them is the measurement of strain buildup, as reflected by bulging and sinking land masses. Scientists had hoped they could identify fault segments that are about to snap - but the tension on the Japan subduction zone was not remarkable, Mori said.
Scientists are rethinking which subduction zones are most dangerous, said Kelin Wang, of the Geological Survey of Canada.
One emerging theory suggests seafloor topography might be key. Oceanic plates dotted with mountains seem to hang up and slip more frequently as they scrape under continental plates, he explained.
The result is a series of smaller quakes that occur when segments of the fault break. Giant quakes seem to occur most frequently where the seafloor is smooth and featureless - as off the Northwest coast, Wang said. With no surface bumps and hills to interfere, the two plates can stick together over vast distances, he said. When they slip, the whole fault breaks at once.
The nuclear-power industry around the world is still dealing with fallout from the meltdowns at Japan's Fukushima nuclear complex, said Stuart Nishenko, of Pacific Gas and Electric, which operates the Diablo Canyon nuclear plant on the California coast.
Seven nations, including Switzerland, Germany and Mexico, opted to either phase out nuclear power or halt construction of new plants. The U.S. Nuclear Regulatory Commission is preparing to issue orders to all of the nation's 104 nuclear reactors, requiring new seismic safety analyses, Nishenko said.
Operators also will be required to walk through their plants with inspectors, looking for any parts or systems vulnerable to earthquakes or floods, and to upgrade plans for coping with a complete loss of power, as happened when the Japanese tsunami knocked out electrical lines and flooded backup generators.
The Northwest's only nuclear power plant is the Columbia Generating Station, located on the Hanford Nuclear Reservation. In recent years, geologists have discovered several new faults running through the area, capable of generating earthquakes as big as magnitude 7.5. Plant operators recently applied for a license extension to operate the 28-year-old reactor though 2023.
Mary Ellen and I are both extremely pleased with the work that your crew did. Please pass on my personal "thank you" to each of them.
We were pleased with the amount of clean-up that was done at the end of each day.
Even with your discovery of unforeseen conditions that necessitated additional framing, it was still done within a very reasonable time-frame. My overall experience with Sound Seismic has been very positive and we will recommend your services to our circle of friends and family.
Again, thank you for a very "enjoyable" experience!
Mark and Mary Ellen Whitesell, Ballard, Seattle
I wish to praise SOUND SEISMIC for the earthquake retrofit they completed on my home. From the estimate to the finished job, Leif and his crew were professional, hard working, pleasant and exceptionally CLEAN. They handled the permit and inspections seamlessly. Office support from Elizabeth was equally professional, reliable and fast. I can't describe everything so I'll just say the whole experience was great.
Kristin Hill, Wallingford, Seattle
We recently had Sound Seismic do our earthquake retrofit. I cannot compliment enough the very professional job they did. Leif Jackson, the owner, sat with us for two hours answering questions and explaining how earthquakes work. He was completely above board, not promising more than he could deliver. He left interesting reading material so that we could evaluate and decide for ourselves. The most compelling was from FEMA warning people in the Puget Sound area to do everything they could to protect their homes because of our earthquake risk.
Once we were in contract, Leif sent our information to a structural engineer who drew up the plans. The bid was fair and complete. The crew showed up on the date the job started and completely it quickly. It looks great. Our new pony walls are gorgeous and the bolts and clamps very reassuring. City inspections were completed for the bolting and then for the finished job. This company is certified and high quality. Our house will be sticking around on the foundation. I encourage you to get over gambling about retrofitting and hire these guys. They are great.
Emily Elliott, Queen Anne
The crew kept me informed of their progress and plans all the time. They told me what their plans were, and delivered every time. Very satisfying knowing I could count on them doing what they promised - when they promised it!
Martin Muller, Olympic Manor, Seattle
Sound Seismic was the most professional group of contractors/employees I have ever dealt with. They were knowledgable, dependable, and skilled. The project lead was obviously well trained and knew what he was doing, was able to effectively manage and direct his crew and subcontractors. A quality job. Discovered an area behind my walls were my house was not up to code. Worked well will me to correct the problem and professional and reasonable about the change order.
Andrew Austin, Phinney Ridge
The Sound Seismic crew arrived on time and got started on this structurally engineered and contracted job. It was estimated to take approximately one week to complete this work. The job was completed in 4 days with great professionalism and dedication to the work completed. The work passed a city inspection with no additional work required. The quality of work is excellent with great attention to detail.
Based in Ballard, the 2 man crew of Sound Seismic did a very clean, professional job of installing the earthquake retrofit. I was very happy with quality of the work and the way the crew kept the site clean and organized every day. They stick to a firm 8-hour work day for their employees and offer health benefits, a rarity in the contract world, it would seem. So their bid was not the lowest, however was comparable to a number of other firms, within 5-10%. Very punctual and professional in all coordination and in handling the 2 inspections reqd. by the city. No surprises or additional costs. I would recommend this contractor overall.
Jennifer Dovey, Broadview, Seattle
Sound Seismic did such a thorough job. Looking at their work lets me sleep better at night knowing my house is now very unlikely to shift off its foundations in an earthquake.
P. Kiraly, Madrona, Seattle
We thank you for the very professional work done by all of your people that we have had contact with. The crew working here were outstanding, and we were charmed by your lead carpenter, Matt.
Our basement has not been this clean in 70 years (the house is 70 years old)!
Bryant neighborhood, Seattle
We had a wonderful experience with Sound Seismic. After the devastating earthquake in Japan my husband and I were quite worried about our 3 story brick home and decided to retrofit our basement as a way to ease our anxiety and protect our family.
Sound Seismic's estimate was more reasonable than any of the others we got and we felt very confident knowing that Leif and his team have done many retrofits, including our friend's basement. Leif was able to explain the process to me, answer my questions, and gave me the estimate within an hour of coming to the house.
The hardest part of the process was moving our furniture and boxes out of the way to prepare the basement - after that things just moved along smoothly. I had been expecting huge holes in the walls and dust everywhere but the work was really tidy and not nearly as disruptive as I had feared. My kids and I were able to stay in the house the whole time, only playing out in the backyard a couple times when the banging was loud. The baby was even able to take naps in the midst of the demolition!
Matt was very professional and friendly, he always arrived on time and he communicated well, checking in with us at the end of each day to show us the progress of the work. He was able to finish the work a half-day sooner than planned and there were no hidden costs or extra changes when the invoice arrived.
I would highly recommend Sound Seismic to anyone -- they were fantastic!
Rachel Opel, Ballard, Seattle
Thanks for the great work on the house - you've done an outstanding job of prompt, low-impact work - and leaving the job site in excellent shape. Appreciate the attention to detail."
Wayne Dodge, Ravenna, Seattle
"I wanted to follow up and thank you for your good communication, strong planning and flexibility.
Your foreman was great. Very professional, low key, friendly and efficient."
Urs Koenig, Madrona, Seattle
Sound Seismic gave a very competitive bid, clearly explained everything they were going to do, accomodated my schedule, and produced a very high quality outcome. I highly recommend them.
Gary Johnson, Wallingford, Seattle
Your crew did a great job! It was a pleasure to meet them. And as soon as I met your lead carpenter, I knew that everything would be done 'right.'
They took extra care at every level: and left everything better than ever. They were able to remove the siding without cutting it, which is great, too.
I am glad that I got to see how substantial the anchors, fasteners, etc. are - and how robustly the plywood panels are nailed in. ( It was hard for me to tell from the blueprints alone.)
I am very happy with all aspects of the plan and the work, Leif.
David Rosenbaum, Sand Point, Seattle
All in all, we felt the project went extremely well. Given the number of earthquakes worldwide of late, we are pleased to have had the work done. We’d rather not have it tested, but we know we are in as good a position as possible if the ground starts shaking!
I wanted to let you know what a great job that your crew did on our earthquake retrofit. They were very knowledgeable about the whole process and answered any questions we had without hesitation. Their work was excellent and they finished the job quickly. I have done my share of remodeling in the past and I can say that they cleaned up after each day’s work more thoroughly than anyone I’ve ever encountered. They took obvious pride in the retrofit work they did but also in the cleanup. They saw that as an integral part of the Sound Seismic service. All in all, it was a fast and painless experience.
Thanks for assigning those fine young men to our job.
Paul Gustie, Fremont
Sound Seismic performed an engineered retrofit on our house built in 1928. I've never had a better experience working with a contractor - thoroughly professional (truly experienced and knowledgeable in their craft), they were also excellent communicators throughout the engagement. And the cleanup afterwards was amazing. I would recommend them without reservation!
George Murphy, Northgate, Seattle
I wanted to thank you for the wonderful job you did retrofitting my home in South Seattle. I was aware that it would be a challenge and it proved to offer more problems than we expected. You met them all and did a great job correcting the rot and damage that happened over the years since 1927, when the house was built.
When I arrived home yesterday the basement was clean and organized. It was the first time I did not have to spend hours cleaning up after a contractor. Your lead carpenter and his assistant were a great team. Thanks for all your efforts.
Patrick Murphy, Mount Baker
I can't think of a single way you could improve the service of your company. Yours is one of the VERY best companies I've worked with on this home.
Jeannie Macri, West Seattle
Sound Seismic completed a earthquake retrofit on our house. Their explanation about what to expect and what we'd get was clear and straightforward; the work was completed as described, as scheduled and exactly on time; clean-up: spotless.
Harriet B., Ballard
"The experience with Sound Seismic was possibly the finest I have had in my dealings with any of my trade contractors. Your crew was knowledgable, well informed, hard working, tidy, as well as a pleasure to have on my job."
Thank you very much for your excellent work on retrofitting our house. We appreciated your careful oversight of the project, ongoing contact with the engineering firm, attention to detail, and clean and timely work. You really rose to the challenges presented by "this old house."
Sound Seismic exhibited a great combination of skill, hard work, and professionalism. You treated our home and our project as though you were doing it on your own house.
Everything looks good. Thanks for the all the work your guys did, very professional.
Stuart Jamieson, Montlake
Sound Seismic did an excellent job of the seismic retrofit on my two-story house, which entailed quite a lot of siding work as I don't have a basement. The workmen were punctual, neat and meticulous. I feel safer because of their work.
Pippa Kiraly., Madrona
Just wanted to send you a note to express how pleased we are with the work your firm recently completed. You did exactly what you said you would and the quality of the work is first rate. Also, please tell Matt how much we enjoyed him. Thanks,
Gary Johnson, Wallingford