If Puget Sound is Falling Down
Posted: 18 November 2003
Word Count: 2991
Summary: This article is about earthquake hazards in the Puget Sound region of Washington State. It was utilized by the University of Washington Geophysics Department in March of 2003.
If Puget Sound is Falling Down
by Karen Peralta
Published by the University of Washington, Seattle Campus, and utilized by students in the UW’s Geophysics Program, March of 2003
William Steele, the Seismology Lab Coordinator at the University of Washington Geophysics Program, has a son, Chris, who goes to elementary school. “He comes in sometimes and he loves to do stuff.” It seems he’d recently put a sticker on one of the lab’s monitors, and his father had some trouble accessing the equipment. “What an excuse!” Steele never did get into the program he’d wanted to show me.
December 4th of last year there was a magnitude 5.1 quake in Klamath Falls, Oregon. Aftershocks were felt in Washington State. I had headed out to the UW in search of information on recent earthquake activity in the Puget Sound region.
“Oregon is relatively quiet next to Washington. But this year, we’ve had an enormous amount of activity in Oregon, counter to past patterns.” Klamath Falls couldn’t be noisier, said Steele, ticking off the numbers: September 4th, 5.9; Sept. 20th, 5.9, 5.0, 4.3; Dec. 4th, 5.1; and Christmas Day, 4.0, 3.4.
Most of our local activity in the Puget Sound region is recorded by the UW’s lab equipment. They have an emergency preparation computer program called “Beat the Quake,” hailing from the land of quakes, California, which has suffered through quite a lot of severe earthquake damage lately. That’s the program Steele had trouble running on his computer. Fortunately, the UW’s Seismology Lab has far more emergency preparedness information “so we don’t have to begin from ground zero” in the likely event of an earthquake. Steele is also the Public Information Officer covering quakes through the UW. “We have 135 seismic stations throughout Washington and Oregon, currently operating, and we’re expanding. We really cover a tremendously broad area.”
They locate quakes precisely, then determine the magnitude (quantity of total energy released by the quake), location (area affected by the quake), and epicenter (location on the surface directly above the focus, or place where an earthquake originates.)
They collect data about the geology of the region as well. “It’s critical data. This lab is an educational center for graduate students in geophysics.” They also educate citizens. School groups bring in students, and Steele speaks at civic organizations, encouraging people to take action and make themselves safer from earthquakes.
Of course, the big question everyone asks is, “When?”
“We’re not able to put down a date. It’s more complicated because three types of quakes occur in the Puget Sound region. The most common are deep earthquakes.
“Signals travel through the planet’s crust, sometimes all the way from the other side.” Events from anywhere show up on their helicorder sheets, making an analog, a 24-hour record, of every quake. For example, the Klamath Falls quakes, which are very near California on the Oregon coast.
“We cover the Cascade Range, and have multiple stations on every volcano. We have a good station at Mt. Baker, adequate to cover the region.” Earthquakes around volcanoes are very common.
The lab shares data with California for quakes occurring on the border of California and Oregon. “We’re part of the Washington Regional Seismic Network.” Steele showed me a map of Pacific Northwest Seismicity, 1969-1991. There were huge blue clusters in Puget Sound. What are those, I asked. “Moderate, shallow, and deep quakes. The deep clusters are in the Puget Basin.”
Deep earthquakes, the ones you really tend to write home about, are the largest in magnitude as measured on the Modified Mercalli Intensity Scale. The values usually range from 1.0 (not felt) to 7.0 (extreme damage to buildings and land surfaces). They can go even higher, as they have in recent deep quakes in Alaska.
Here’s what’s happening in Puget Sound: about 300 kilometers or more out from the coast is where the deep quakes are generated. There’s a ridge 500 to 700 kilometers out called the Juan de Fuca Ridge, and new material, new sea floor, is being deposited all the time along it. It pushes the Juan de Fuca plate toward the North American plate underneath the Seattle area. The Juan de Fuca plate moves an average of two inches a year, towards us, lifting the other plate.
A border zone locks it up, an interface between the two plates that stops the oceanic plate, making it subduct beneath us, forcing the ocean plate down into the mantle of the Earth. This boundary is called the Cascadia Subduction Zone, and extends from the middle of Vancouver Island in British Columbia down to Northern California.
The Earth’s mantle lies beneath its brittle crust. It’s semi-solid, due to tremendous heat and pressure. “Our Cascade volcanoes are probably there because of plate subduction beneath us. The push deforms the crust and builds up tremendous stresses. Right now, the coast of Washington is rising. It’s bulging up.” The oceanic plate is “cold rock” and the shock of the two forces meeting leads to deep earthquakes. Washington has recently experienced two large ones, in 1949 and 1965.
A flyer from the lab states that roughly 1,000 earthquakes per year are recorded in Washington and Oregon. “Between one and two dozen of these cause enough ground shaking to be felt by residents. Most are in the Puget Sound region, and few cause any real damage. However, based on the history of past damaging earthquakes and our understanding of the geologic history of the Pacific Northwest, we are certain that damaging earthquakes (magnitude 6.0 or greater) will recur in our area, although we have no way to predict whether this is more likely to be today, or years from now.” Steele thinks it will be soon.
“In 1949, there was a severe earthquake in Olympia, 7.1. Eight people were killed and there was millions of dollars worth of property damage. The quake was located 70 kilometers deep.
“In 1965, there was a magnitude 6.5 quake between Seattle and Tacoma.” Both earthquakes were felt as far away as Montana. But there were no aftershocks, as is usual during a deep quake. The infamous aftershocks, known to catch people in the middle of recovering from a bad earthquake, happen during land-based shallow earthquakes. The ocean-based shocks occurred once, causing ground tremors that lasted several minutes. “The 1965 quake killed about five people, and again there was millions of dollars of property damage.” Other deep events, difficult to calculate from records of the times, occurred in 1882, 1909, and 1939. “Every 35 years or so a 6.0+ magnitude quake occurs beneath Puget Basin. The whole region along the coast will shift at once. When it finally builds up enough pressure to kick up, it’ll be a big one.”
Eighty percent of the quakes on the planet happen along the Pacific North West Rim, which is referred to as “The Ring of Fire” because of all our volcanic activity. In 1964, one year before this area’s last big event, south-central Alaska generated a monster 9.3 quake, shaking the ground for twenty minutes, generating tidal waves that decimated Seward’s coast, affected 34,000 square miles, and killed 143 people. And there’s been recent large quakes in Cape Mendecino, California, and Parkfield, California, infamous for ground shaking, in 1992.
Brian Atwater of the USGS (United States Geological Service) and the UW geology department has done studies along the coasts of Washington and Oregon. He’s found a kind of layered soil…”what he found…ghost forests killed by the last big quakes. Subduction zone material covered by coarse black sand.” A layer gradually turned into forest floor and then the sand layer. “As bulging continues, coastline rises, and low-lying areas are flushed clean by salt water. Stress released during the quake makes the coastline subside by seven or eight feet. It ‘drops.’ If you’re living at five feet above sea level, it’s not a very comfortable thing.”
Earthquakes also generate large tsunamis, or tidal waves; the biggest ones, generated by larger quakes, can rip up an entire coastline for miles, wiping out bridges, roads, and buildings. The really great subduction zone quakes, 9.0 or more, only occur about once a century on the face of the planet. Strangely, a big quake may result in only about three-and-a-half minutes worth of strong ground shaking, which doesn’t sound like much. “One recent California quake was only seventeen seconds of strong ground motion, a 7.1 quake. A 7.0 quake releases the equivalent of 199,000 tons of TNT in energy; a 9.0 releases 200 million tons, or 17,000 atomic bombs’ worth of force.
“The difference between an 8 and a 9 is greater than the difference between a 2 and an 8, because of the logarithmic scale. The force increases exponentially. It gets 30 times greater each time.” I wondered if it ever goes up to 10.0.
By carbon-14 dating organic matter in ground and sea levels, “scientists can determine approximate dates for events going back 10,000 years.” Finding clues about these earthquakes involves both painstaking research and educated guesswork.
Research has recently identified a Seattle fault which generated a large quake between 1,000 to 1,100 years ago. “There were landslides, and a huge seiche-when something big falls in the water, creating waves like tsunamis. Large block landslides occurred in forests. Restoration Point on Bainbridge Island rose twenty feet from Puget Sound in seconds during that event.”
Buildup from glacial ice sheets once covering the continent makes it difficult to analyze shallow crust faults. But geologists are pretty sure there are two major Seattle faults. The biggest one runs from the north tip of Mercer Island through Eastgate to the Kingdome, just north of West Seattle. The other fault runs through White Center, parallel to the bigger one. In 1872, an estimated 7.3 shallow quake caused what seismologists call “felt reports” from observers, the only evidence of some older quakes. Native Americans tell legends about what must have been some very sizeable earthquakes and tsunamis.
Nowadays, all the real-time telemetry (automatic transmission of data from a distant source to a receiving station) comes through in the back of the lab, where Steele poured me a cup of Starbucks coffee at their metal sink in a very equipment-crowded space. “Relays ‘zap’ activity energy in nanoseconds to the lab. Before people in a region know what’s going to hit them, we do.” The helicorders monitor 23 stations on analog. “We focus on volcanoes. All stations, including the ones on helicorders, go onto the computer system in the next room. The discriminator in the back takes FM carrier signals and separates them from seismic signals, leaving an amplified seismic signal. It goes to the front room, changing into digital information the computer can read.
“If it picks up a ‘jump’ (a skip in the needle on the helicorder) on a station, it checks other stations and records all data, whether there’s a signal or not. If it’s a big quake, it does estimates of the magnitude etc. via programs, beeps the people (like Steele), and sends information to seismologists around the region.” Steele might hear a “beep” anytime.
As I drank my coffee, Steele told me he’s a grad student, his life’s partner works, and together they support their family, renting a house in Wallingford and raising two kids. “It’s a rewarding job, but…the rewards are not monetary.” Nonetheless, he feels treated as a colleague by everyone, and has a good working relationship with all his “fellows at the lab.”
About earthquake preparedness, Steele is adamant. “The secret is not fear and loathing in Seattle, and that we have to hide under our beds. Let’s get ready. Our schools need to get to the point where we can withstand a 7.4 earthquake. How many little bodies do we need under bricks before we start spending some money?” Right now, there are no definite laws enforcing earthquake building codes, “if the building code years ago said you could pile bricks without mortar on top of each other.”
Unreinforced masonry creates structures that fall during even moderate earthquakes. “The entire wall of a school can fall down and kill students. A brick that falls three stories doesn’t slow down,” he said, referring to the death of a boy during the 1965 earthquake. Steele is certain such deaths are preventable.
At least six schools in Oregon have unreinforced structures, bricks that can fall and fill a doorway, blocking the exit. “Retrofit them, or tear them down and build another school. If a school has been considered unsafe for a quake lately, they can sell it, and it becomes a senior center. No laws stop that. These buildings need to be brought up to code or taken down. Deaths will happen unless we act. India just had a 6.8 quake…tens of thousands dead. There needs to be water and food stored away to last 72 hours. You need to get under a table and ride it out; get down on the ground, under something; check to see if you smell gas, and turn it off; electricity, too.”
You should get to know your community resources, Steele said. And in case of severe aftershocks, if you’re in a building “you should wait until the shaking stops, and then get out.” Lots of people are killed by falling debris while evacuating buildings.
The number of FEMA (the Federal Emergency Management Agency) in Woodinville, headed by Chris Trisler, is (206) 487-4645. It’s their job to assist people with earthquake preparedness.
What does Steele see for 2003? “I expect more of the same. Probably some quakes greater than 4.0 in the Puget Sound area. While we’ve been talking, there’ve been events in Klamath Falls,.” As I write this, there are aftershocks east of the Dec. 4 “sequence” starting in Klamath Falls. “The question is, are we going to recognize the danger and do something about it, or are we going to wait until we have an adequate death toll? I’d like to see a dedicated plan and some leadership from the state. It’ll be a lot of money.”
Steele said a colleague of his said it best: “The next great disaster will happen as soon as we forget about the last one.”
(Some of the information in this article is from “Washington State Earthquake Hazards,” by Lawrance, Qamar, and Thorsen, 1988.)
by Ted Centerwall, a local community college teacher
Every step I take
Creates a little earthquake
Somewhere in the world.
WHAT TO DO OTHER THAN SCREAM YOUR LUNGS OUT…FALL DOWN!!!
Apparently, you may hear a very loud, building sound before the frenzy begins. The below is from “How to Survive in Earthquake Country,” a FEMA pamphlet. Find out about your risks, at home, and in your workplace. Get more specifics from the American Red Cross, or FEMA Learn what causes injuries: parts falling off building exteriors and interiors; flying pieces of broken glass; overturning bookcases; unanchored water heaters; storage facilities; anything made of glass; fires from damaged gas lines; electric lines; wood stoves; chimneys; toxic fumes. Create emergency preparedness plans: find safe spots in your home; identify escape routes; plan two ways out of each room; pick two places to meet, outside your house and outside the neighborhood if you can’t return home; show everyone how to shut off water, gas and electricity; practice your plans, now; read “Your Family Disaster Plan,” and “Emergency Preparedness Checklist,” which you can get from FEMA. Reduce earthquake hazards: evaluate your home; strap water heaters and gas appliances down; remember, stiff items snap; place heavy objects on lower shelves; anchor everything heavy; anchor hanging objects; support community earthquake preparedness. Businesses, schools, daycares, neighborhoods, churches, and clubs: hold workshops. Assemble a disaster preparedness kit: store food, water, clothes, a first aid kit, a radio, flashlights, and batteries, good for 72 hours of use, in your car trunk, home, and office. For more details, consult the FEMA brochure, “Your Family Disaster Supplies Kit.”
During/after an earthquake: stay calm; don’t panic or run. Earthquakes are usually preceded by loud sounds, so take quick action. You actually have about two seconds, so get ready for that earthquake now to protect yourself and others. Stay where you are: drop, cover and hold something solid, or take immediate cover under a heavy desk or table, in a doorway, hallway, or against inside walls. Turn away from glass. Keep away from chimneys, windows, tall bookcases, and objects that might fall. Evacuate only after the shaking stops. Use the stairs, not the elevator. Remember, aftershocks may occur at any time. Listen to a radio or TV for instructions. Outdoors: move away from buildings, trees, and utility wires. Sit on the ground until the shaking stops. Flee inland immediately when near a coastline. Check for injuries. Do not move seriously injured people unless they’re in danger. Indoors: evacuate damaged buildings, as aftershocks could cause additional damage, or buildings can collapse. Do not re-enter a building until it’s declared safe by responsible authorities. Don’t use the telephone except for emergencies; stay off the phone. Check for fires. Have a fire extinguisher, and know how to use it. Check utilities: gas, electric, and water lines may be broken. Gas: do not use matches, candles, open flames or electric switches indoors, because of possible gas leaks. If you smell gas, open windows, leave, and shut off the main gas valve, which is usually outside. Electricity: if wiring is broken, shut off electricity at the main switch. Don’t touch anything near downed or damaged lines. Water: if water pipes are broken, shut off the supply at the main valve outside. Use water from ice cubes, water heaters, toilet tanks (if they don’t contain chemical cleaners). Clean up spills. Attend carefully to spills of potentially harmful materials such as medicines, drugs, and household cleaners. Provide adequate ventilation, as chemicals may combine to produce toxic gas. Remember to assist others in need. And also remember: it’s not your fault. (Sorry about that, I couldn’t resist the joke.)
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