1996 Duvall Earthquake

On the night of May 2, 1996, at 9:04 pm PDT (May 3, 4:04 am UTC), the residents of the Puget Sound region were shaken by the most powerful earthquake to strike the region in 30 years. With a local magnitude of ML 5.3 (Mw 5.1), the earthquake resulted in a few minor injuries, interrupted electrical power and telephone service, cracked a few walls, and broke up a baseball game between Seattle and Cleveland at the Kingdome.

The quake hit during the seventh inning of the baseball game. While some fans made their way to the exit, some chanted, "Let's play ball!" Despite the willingness of some fans to remain in the bleachers, the remainder of the game was postponed due to safety concerns. 

The Duvall earthquake originated about 25 miles northeast of Seattle and 6 miles east-northeast of Duvall at a depth of about 7 km (~5 miles). Such a shallow event means the shaking will be strongest near the epicenter and die off rapidly with distance. It was felt most strongly in the Duvall-Monroe area where residents reported items knocked from shelves and broken china and glassware. The earthquake was felt moderately by many residents throughout the Puget Sound area. Communities as far as Portland, Oregon, Vancouver, B.C., and Coeur d'Alene, Idaho also experienced minor shaking from this event. This earthquake occurred on a crustal fault, perhaps an extension of the Southern Whidbey Island Fault Zone.

In 1996, the PNSN had a very different website but provided information on this event including maps, seismicity rates, examples of seismograms and a very early version of the "Did-You-Feel-It" reporting system that allowed for producing maps of felt reports. This original information is available from our original legacy web pages.

The process of determining this earthquake's magnitude demonstrates how seismologists study and measure earthquakes. Ten minutes after the earthquake, the PNSN released an initial magnitude estimate of 4.8 that was based on the duration of shaking as automatically processed by a computer recording system. An hour after the earthquake, the U.S. Geological Survey issued a magnitude estimate of 5.4, which was based on the amplitude or height of the initial signal on a seismogram. This initial signal reflects the earthquake’s P-wave, or primary seismic wave, and is used to produce the body wave magnitude, or Mb. At about the same time, manual analysis of the local seismograms at the University of Washington determined a local magnitude, or ML, of 5.3. A few hours later, Oregon State University determined a magnitude of 5.2 by analyzing the complete wave forms of the earthquake as recorded by broadband seismographs. This measurement is known as the moment magnitude and is considered by seismologists the best type of magnitude to measure the relative amount of energy released by the earthquake. The next day, a similar analysis on a subset of data used by Oregon State was conducted at the University of Washington which determined a moment magnitude of 5.1.

After an earthquake of this size, aftershocks are likely to continue for months, although at a diminishing rate. Although most will be too small to be felt, occasional aftershocks in the magnitude 3 to 4 range may occur. In the first three days following the Duvall event, more than 45 aftershocks of magnitude 2 or larger were recorded. Among the notable aftershocks were a magnitude 3.0 at 9:21 pm on Thursday May 2, a magnitude 3.1 at 9:02 am on Friday May 3, a magnitude 3.6 on Saturday May 4 at 7:38 am, and a magnitude 3.1 on Sunday May 5 at 4:06 am.

As a result of the Duvall earthquake, as many as 16,000 people in the Monroe, Clearview, Sultan, and Everett areas were left without power, and some buildings suffered minor damage. Among the injuries reported were bruises from falling, getting hit by falling objects inside a house, and attacks by frightened animals. 

The epicentral region was sparsely populated, and only one residence was located within 2 km of the mainshock. Structural damage appeared to be restricted to a single facility, a Bonneville Power Administration (BPA) power station located near Monroe, Washington. Repairing this BPA substation cost over 1 million dollars and resulted in blackouts. The damage to this substation led to renewed urgency to retrofit substations in the Pacific Northwest.

Earthquake-related road failure occurred on two unpaved roads east of the epicentral area and evidence for several earthquake-induced rock failures was observed on a hill south-southeast of Cedar Ponds Lake. Ralph Haugerud, a USGS geologist, estimated the largest failure to have a volume between 200 and 2,000 cubic meters. He noted no evidence of liquefaction during an aerial reconnaissance.

The earthquake left about eight floor-to-ceiling cracks in the walls of the detention center at King County Department of Youth Services in Seattle. The cracks, deemed superficial by a county building inspector, ran along the mortar in the masonry joints of the gym and corridor walls. Masonry joints are designed to help the building flex and homeowners should inspect the masonry joints on their home at least once a year, and repair the joints where required because these joints are meant to improve the overall security of a structure.

Despite this earthquake being the most powerful to shake the region in 30 years, it ultimately resulted in minor damage, few injuries, and no fatalities. There is evidence that seismically retrofitted buildings and newer buildings built to higher standards performed better and faced less damage. This earthquake serves as a reminder that being properly prepared for a damaging earthquake can save lives and reduce damage. Retrofitting older buildings and performing non-structural hazard mitigation can greatly reduce hazards to human life and property during an earthquake. Make sure you know what to do during and after an earthquake – if you feel shaking, Drop, Cover, and Hold On. Have an emergency kit prepared and accessible. Simple preparation steps can greatly reduce injuries, loss of life, and damage.

For more information about how to prepare for an earthquake, visit this page: Preparedness.