Observations on Structural Damage

October 27, 2009 by  
Filed under Structural Observations

With funding from the U.S. National Science Foundation (NSF), EERI member and structural engineer Steven Baldridge, president of Baldridge and Associates in Honolulu, Hawaii, visited Pago Pago, American Samoa, to investigate structural damage associated with the M8 earthquake and the resulting tsunami of September 29, 2009.

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Figure 1: Within the inundation zone, most of the wood-framed residences were leveled down to the foundation.

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Figure 2: Many of the low-lying villages have churches near and facing the ocean. The typical construction is a combination of concrete frames and concrete masonry unit (CMU) infill. In several cases, the tsunami entered the churches through the front door and flowed out the windows along the sides of the church. While doors, windows, and interior furniture were damaged, the structures did not appear to have any distress from the hydrostatic loading. This picture shows the pews having been ripped from the slab as the tsunami flow rushed through the church.

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Figure 3: In addition to damage from the tsunami, floating debris such as vehicles and empty shipping containers caused large localized damage to buildings.

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Figure 4: While most CMU buildings withstood the tsunami, those that were poorly constructed did not fare well. The house in this picture was leveled to its foundation, while other nearby masonry buildings survived. Many of the block cells in the walls of this were not grouted, including many that had reinforcing steel in them.

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Figure 5: This CMU residence withstood most of the force of the tsunami except for an area at the back. It appears that some scouring of the foundation may have weakened the connection of the CMU walls at their base. The water passing through the house and trying to exit through small window openings would have created large forces on this wall.

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Figure 6: The seismic event did not appear to cause much, if any, damage. However, this school, located out of the inundation zone, exhibited some odd horizontal cracking along the top reinforcing steel in concrete frame members. This may be due to some pre-existing corrosion or construction issue that had been aggravated by the ground motion of the earthquake.

The tsunami alert

October 27, 2009 by  
Filed under General Info

From Lori Dengler, Humboldt State University

The layover in Honolulu has had some positive outcomes. I was able to visit with Chip McCreery, the geophysicist in charge of Pacific Tsunami Warning Center (PTWC) and Brian Yanagi of ITIC. I first met Chip in 1997 when I was in Hawaii working on the strategic plan for the National Tsunami Hazard Mitigation Program (NTHMP). He was the director of ITIC at that time – it was a tiny office, just Chip and a part time staff person. Since then Chip moved toPTWC, the 2004 tsunami happened and both PTWC and ITIC have expanded. I had an informal discussion with Chip about what worked and what didn’t work quite so well during the Samoa tsunami alerts. A fortuitous factor was that Vasily Titov, NOAA’s top tsunami modeler and other members of the NOAA’s Pacific Marine Environmental Laboratory’s modeling program happened to be at PTWC doing a training on how to run the new SIFT (Short-term Inundation Forecasting for Tsunamis) tsunami forecasting tool. Note – there are a lot of acronyms in the tsunami world. So they were able to assist in both the forecasts and in the discussions as the event ran its course. This was the first time SIFT was used in a fully operational manner at both tsunami warning centers. While it’s a great tool – it could use a little refining to make it easier to use in an operational sense. Unlike the other forecast tools, its output doesn’t automatically insert into messaging, and folks spent a lot of time writing things down on scraps of paper to later insert into messages. SIFT also creates simulations at a number of sites, producing a number of different screens and window all overlain on the same computer, making it sometimes hard to find the screen you want. But it’s a huge step forward and these are minor bugs that shouldn’t be too difficult to work out. When I first started working on tsunami issues, the idea of using modeling as a forecast tool dueing an actual event was unheard of. One other lesson had to do with the importance of a good PR person. Delores Clark, NOAA’s long term expert Public Affairs person, was on another assignment during the tsunami event and her replacement wasn’t nearly as skilled at managing the media, inadvertently letting them all into the operations core ofPTWC – not a good idea have cameras and news folks intermixed with the forecasters trying to work the event. This is an important lesson – make sure the rules for back up public relations people are well spelled out.

I’ve known Brian Yanagi for a long time too. He was the State of Hawaii emergency services representative to the NTHMP from 1996 until 2005, lasting about 2 years longer as an NTHMP rep than I did. After the 2004 tsunami ITIC was able to expand and Brian joined ITIC director Laura Kong in international tsunami trainings and outreach efforts. I missed Laura on this trip – she is in Vanuatu at the moment. Brian took me to a viewing a the movie “The Third Wave”, a documentary about a volunteer relief effort in the aftermath of the 2004 tsunami in Sri Lanka. This was the only showing at the Hawaiian International Film festival. It is the closest thing I’ve ever seen to putting you into the post tsunami aftermath and the volunteers who cobble together a long term relief-recovery program are inspiring. More about the movie athttp://www.thethirdwavemovie.com/Third_Wave/Welcome.html

And check out an interesting way of using Google for photos and eyewitness accounts at:
http://www.stuff.co.nz/world/2917454/Map-Tsunami-strikes-Samoa

Eye-witness Account from Boat

October 27, 2009 by  
Filed under Emergency Management & Response

From Lori Dengler, Humboldt State University

The most interesting piece of information I’ve gotten in the past day is an account from a family who were in a boat in Pago Pago harbor during the tsunami – courtesy of HSUalum Orion George. The most jarring part of this account to me is the failure to adequately educate people about what to do when they feel a strong earthquake near the coast. These folks should have immediately evacuated as soon as the shaking diminished enough for them to move. Instead they took the time to go on the internet! They were very fortunate – if the tsunami had been larger, they would not have survived.

“This morning (six hrs ago) we were shaken awake by an earthquake which seemed to have no end! We were aboard Gallivanter and tied side-to a big concrete dock in the heart of Pago Pago, American Samoa. And after living up & down the California coast, I knew this was no minor tremor.

After the rude awakening, Cath & I walked across the dock and chatted with a few of our fellow sailors, one of whom said that he’s just done a Google search on “recent earthquakes” and said that it measured-in at 8.1 and the epicenter was only 120 miles distant.

We returned to Gallivanter and I turned on our laptop and searched the same website. Sure enough there it was… “8.1 earthquake – American Samoa – 20 minutes ago”. I clicked on the “Show Map” option and noticed the epicenter was located south west of Pago Pago… which is located on the southern side of the island.

Just as I was considering the ramifications of that little fact… all hell started breaking loose! Our boat was on the move! My first reaction was to start the engine and dash up on deck to see what was going on. I witnessed the water around us was rapidly dropping! Rapidly! In a blink of an eye, we were on the bottom and the boat was falling away from the dock! Three of our big dock lines popped and we fell right over into the mud – the entire basin we had been floating in only moments ago had completely drained! People were screaming!

Next – the water came flooding back in at an even more alarming rate and the next thing I knew we were floating directly above the dock! Over the concrete slab and drifting toward a young lady we knew (from another boat) who was desperately hugging a power pole and up to her chin in swirling water! I told Cath to cut the two remaining dock lines with our serrated bread knife and to be quick about it!

Right as I put the boat into gear, we were somehow washed back off the dock and into the basin as I advance to full throttle and we accelerated through a floating debris field of floating docks, fuel drums, sinking boats, a shipping container and a barnicle encrusted wreck all of which were spinning in the torrent of rapidly dropping sea level. It was absolute mayhem! As we steered out toward the deep water in the center of the harbor I looked over my shouder and saw what appeared to be a waterfall pouring off the dock and shore beyond. Not one of the dozen vessels remained at the dock. All were underway in a matter of seconds… with or without crews aboard.

We motored around in the middle of the harbor watching the waves of floods & ebbs while wondering about after-shocks and our fellow cruising sailors. As we passed one of our neighbors she shouted to us that her husband had been washed off the dock as they were trying to get away. She was alone and seriously concerned. Other boats broke free from their moorings and anchors in the initial seismic waves and many were driven ashore, or driven under by loose tuna boats.

After about three hours, we felt it was finally safe enough to return to the dock. All we had were lengths of old line and we were short a couple fenders. We were the first to go in and we started un-tangling lines and helping others get back along side the concrete dock. All of the store-fronts along the water are destroyed, roving mobs of kids can be seen looting, the fence around the dock is gone, every boat on stands in a nearby boatyard were washed away. Big fishing boats are now in parking lots across the street. Absolute destruction is seen everywhere along the shore.

Phones and power are down but we got back online right away and I immediately went back to the recent earthquakes website to see if things have been calming down in the center of the earth. A number of aftershocks as strong as 6.0 have been recorded over the past few hours – but thankfully no more wave action has been noticed. We’ve been making Skype calls to our families and letting others use the computer as well to phone home.

Online news reports say that the earthquake lasted three minutes and the highest flood rose 25 ft above normal! There are 20 confirmed deaths… including our neighbor who was swept off the dock. Most fatalities occured in and around the harbor where we live. Boats are battered and nerves are fried. One friend wound-up on his boat nearly 1000 feet away from the water after breaking from his anchor and sailing right down Main St. taking power & telephone wires down with his mast! Some people lost everything… including their lives. We came through remarkably well with only minor dammage sustained to our toe rail when the dock lines parted and to our fender basket which was the only point of contact with that drifting wreck. I never felt any jarring loads while we were hurtling around above & below the concrete dock, so I believe our hull, keel & rudder suffered no dammage from the wildest boat ride I’ve ever been on. “

Leading a Post-Tsunami Field Study Team

October 27, 2009 by  
Filed under Tsunami Surveys

By Lori Dengler, Humboldt State University

I’m leading an interdisciplinary group under the auspices of the Earthquake Engineering Research Institute (EERI) of that includes an environmental scientist, an anthropologist and an emergency manger that will be working in American Samoa and Samoa over the next two weeks. We will be coordinating our efforts with a group of engineers sponsored by the American Society of Civil Engineers who will be examining the performance of port and coastal structures over the same time period as our visit.

Post tsunami field studies are important for a number of reasons. Usually the first teams to visit a tsunami-struck area are the water height specialists who measure tsunami runup (the elevation of the tsunami at the inland extent of inundation) and other water height indicators. Records of water heights such as debris lines, water marks on buildings, and debris in trees are ephemeral and these measurements are critical to calibrating numerical models of tsunami flooding such as those used to estimate California tsunami hazards. Almost as quick on the scene are scientists who study tsunami deposits – the cobbles, sands, silts and debris transported by tsunamis. The characteristics of deposits of recent tsunamis can be used to help interpret paleotsunami deposits such as those found in Crescent City and the southern parts of Humboldt Bay.

Our group is focusing on a different aspect of tsunamis – how people responded to the natural warning signs of the tsunami and how coastal structures, planning and management affected exposure. We are also going to be looking at how people responded to the natural warning of September 29 – the strong ground shaking of a magnitude 8 earthquake, and the official warning that was issued on October 7 when a large earthquake occurred in the Vanuatu Islands about 1500 miles away from Samoa.