“Lucky” may not be the first word that comes to mind after an earthquake that injured more than 200 and caused more than $1 billion damage, but it fits.
“Because this earthquake was centered more than 35 miles underground, much of the ener-gy radiated out, instead of up. Because much of the energy was absorbed throughout the west in places like Baker City, Spokane, and even Salt Lake City, there was less damage than we would expect in a magnitude (M) 6.8 earthquake,” explains Oregon’s State
Geologist, Dr. John D. Beaulieu.
Geologists call this an intraplate quake, a type that is only found in places like the
Northwest where one plate is subducting, or sliding under another plate (see figure above. People evacuated buildings throughout the Willamette Valley, as well as places along the north Oregon coast. Although there was no danger of a tsunami, many residents on the coast acted responsibly in heading for high ground when they felt the earth shake.
(continued next page)
Contact us
800 NE Oregon Street #28, Portland 97232 (503) 731-4100 http://www.OregonGeology.com
Field offices
1510 Campbell Street, Baker City 97814 (541) 523-3133 5375 Monument Drive, Grants Pass 97526 (541) 476-2496 Coastal Program 313 SW 2nd, Suite D, Newport 97365 (541) 574-6632 Mined Land Reclamation Program, 1536 Queen Avenue SE, Albany 97321
(541) 967-2039
Nature of the Northwest Information Center
800 NE Oregon Street #5, Portland 97232 (503) 872-2750 This picture shows how much deeper an intraplate earthquake is than other types of quakes. The February 28 “Ash Wednesday” earthquake was located about 33 miles deep, approximately 11 miles northeast of Olympia. It was felt as far north as British Columbia, east to Idaho, and south to Salt Lake City. Damage from this type of earthquake is usu -ally less than from other types of earthquakes of similar size.
Though their van was destroyed, finding a purse from inside was still reason to cele -brate. (Photo from Seattle Times)
February 28 Earthquake:
“We got off easy”
State Geologist John Beaulieu
This map shows three faults going through downtown Portland and areas at most risk if a large quake hit
directly under downtown; most other communities in Oregon also have faults nearby. These are crustal, or shal -low, faults, where the energy is directed upward, and would probably produce extensive damage throughout the region. A M6.9 quake in Kobe, Japan resulted in 5,000 deaths and more than $100 billion in damages.
How bad will it be here?
A 1993 study estimated damages in a 60-block area in downtown Portland after a 6.5 earthquake, assuming about 12,500 people were present. In that area, an estimated 46% of the building stock (worth $20 million) would be seriously dam-aged, more than 100 people would be injured and there would be more than 30 fatalities in that area alone.
The devastating numbers in this study reflect the importance of upgrading old, unreinforced, brick buildings. Most downtown areas have an aggregation of older, more dangerous buildings that could create serious problems for earth-quake safety, response and recovery. Upgrading building codes means that these buildings will be phased out and replaced with stronger building stock over time.
Of particular concern are essential facilities like hospitals and police/fire stations. Many communities are upgrading these buildings to make sure that aid is available when it is needed. Besides these, we need to have a transportation net-work that is usable: roads, airports, railroads and river ports.
Does Oregon really have earthquakes?
YES!
The map below shows the quakes throughout Oregon since 1997. Blue circles are events from up to M2 (these would not normally be felt); Orange diamonds are M2–3 (generally felt only close to the epicenter, under special conditions); Red stars are M3–4 (felt more widely). Because magnitude scales are exponential, each number represents a release of 30 times more energy than the lower number. The Ash Wednesday quake released about 25,000 times more energy than the largest earthquake shown below.
Because of our risk of a M9 Cascadia subduction zone earthquake, some people think of earthquakes as a problem only for western Oregon. As you can see from the map, there is a great deal of activity on the eastern side of the Cascades. The last earthquake deaths in Oregon were the two people who died in the 1993 Klamath Falls quake. Earthquake safety is a statewide issue.
Earthquake dangers
Building damage is the major source of injury in earthquakes, but there are many other problems after an earthquake. In Oregon, earthquake-induced landslides and rockfalls are always a threat. One death in the Klamath Falls quake was from rock crushing a truck.
Transportation lines are often built in some of the places that do most poorly in an earthquake. The Ash Wednesday quake showed how vulnerable we are. After a large event, it may be necessary to bring in food, water, and other supplies from out of the area; if roads, airports and railroads aren’t operational, the problems grow exponentially.
Utilities are critical in earthquake response and recovery. Electricity, phones, gas, water, and sewers are all needed in increased amounts after a quake. Many of these systems did much better in Seattle than in other earthquakes.
Loss of life
The best part of the Olympia earthquake was the low number of serious injuries and absence
of fatalities. Here are the number dead from other events with similar magnitudes (from the
United States Geological Survey). The last entry is an estimate of fatalities in Oregon alone
from a magnitude 9 subduction zone earthquake.
Year
Location
Magnitude
Deaths
1949
Olympia
7.0
8
1965
Seattle
6.5
7
1971
San Fernando
6.2
65
1989
Loma Prieta
7.1
63
1994
Northridge
6.8
60
2001
Olympia
6.8
0
????
(Oregon) subduction zone
M9 5,000+
Property damage
We won’t know the extent of damages for several days or weeks to come, but there was less
destruction than there could have been. Here is a comparison from other events (from the
United States Geological Survey—the first three events are in 1979 dollars). The last entry is
an estimate of damage in Oregon alone from a M9 subduction zone earthquake.
Year
Location Magnitude
Damages
1949
Olympia
7.0
$80,000,000
1965
Seattle
6.5
$28,000,000
1971
San Fernando
6.2
$550,000,000
1987
Whittier
6.3
$358,000,000
1989
Loma Prieta
7.1
$5,000,000,000
1994
Northridge
6.8
$20,000,000,000
2001
Olympia
6.8
$1,000,000,000
????
Oregon Cascadia subduction
$13,000,000,000+
zone earthquake M9
Sea-Tac is running at about 60% because
of damage to the control tower.
Many businesses
suffered damage to
inventory and facilities,
and some will be
unable to reopen for
business soon. Small
businesses are
particularly hard hit in
most earthquakes,
reducing the long term
economic vitality of a
community.
S i g n i f i c a n t h i s t o r i c a l e a r t h q u a k e s a f f e c t i n g O r e g o n
The written history of Oregon covers a short time, particularly in the context of geologic processes. Because of that short time frame, we do not have a complete earthquake record of the area.
For most of our information about Oregon’s earthquakes, we rely on geologists to interpret the land around us. For example, mountains can be made by earthquakes, volcanoes, or several other natural processes. Geologists use a variety of methods, including field observation, geochemistry, and geophysics to discover what natural processes have occurred in the past, and which are likely to occur again.
In addition, much of Oregon has been sparsely populated, so that some earthquakes have been felt by only a few people, which makes it difficult to get an accurate reading on the strength and epicenter of the quakes.
Even today, we do not have complete seismograph coverage of Oregon. This means we do not have a complete record of the very small earthquakes that are important in understanding the earthquake potential of an area.
We do have information on some previous earthquakes, however. There have been several in the last hundred years that were strongly felt or caused damage in Oregon. Note that the quakes are not just a western Oregon problem. Milton-Freewater and Klamath Falls have had magnitude 6 or above events.
From Earthquake damage in Oregon: Preliminary estimates of future earthquake losses (Oregon Department of Geology and Mineral Industries Special Paper 29).
This report, along with earthquake hazards maps and other information is available from the Nature of the Northwest, 800 NE Oregon St., Portland, OR 97232, 503-872-2750, www.naturenw.org.
The Nature of the Northwest is a joint project of the Oregon Department of Geology and the United State Forest Service. It has information about Oregon’s outdoors, including natural hazards, natural resources, and recreation.
