About the Klamath Falls Earthquake

Until September, 1993, the Scotts Mills earthquake in northwestern Oregon was the largest earthquake ever measured in Oregon. Two quick shocks on September 20, 1993, changed all that.

Klamath Falls is off the beaten path for West Coast earthquakes. Parts of the town of Klamath Falls sit on geologically active ground, as evidenced by its natural geothermal springs. The West Klamath Lake fault zone stretches roughly 50 miles through Crater Lake National Park, with the Annie Spring fault passing less than half a mile from Rim Village. Its long-term vertical displacement is about an inch per century.

Previous seismic events in the region are not well documented. Only 3 previous seismic events have been recorded in the Crater Lake region over magnitude 3, the lowest that can usually be felt. There might have been more, but there were no instruments to prove it.

At 8:28 pm on September 20, 1993, the first shock hit. It measured 6.0 magnitude. Just over 2 hours later at 10.45 pm, a second shock hit, nearly as strong as the first at 5.9 magnitude. The epicenter of both earthquakes was just west of Klamath Falls in the Mountain Lakes Wilderness Area, but they were felt as far south as Redding, California, and as far north as Eugene. The major earthquakes were followed by thousands of aftershocks which lasted all the way into December, including one on December 4 which measured 5.4 magnitude.

Together, the earthquakes damaged more than 1,000 homes and commercial buildings in Klamath Falls, with older brick buildings being the most vulnerable. The worst damage occurred downtown toward the north end of Klamath Falls. One person was killed when his car was caught under one of the many rock falls in the region. Another person died from a heart attack. Half of the highways leading to Klamath Falls were temporarily closed for fear of other rock falls or hidden damage to bridges. Not counting loss of tourism, the total damage was later figured at $7.5 million.

As a result of the 1993 Klamath Falls earthquakes, seismometers were brought into the area. While Klamath Falls region earthquakes died down after December, Crater Lake low-level seismic activity was found to be much higher than previously thought.

In 2002, Klamath Falls residents felt history repeat itself when another earthquake struck the area on May 15 at 10:54 am. At only 4.3 on the Richter scale and with an epicenter nearly 12 miles from the city, along the southwestern shore of Lower Klamath Lake in California, this trembler turned out to be much less damaging than the 1993 earthquake. This time, no injuries were reported. Even so, windows shivered, hanging plants swung, and at least one person reported that their Internet connection cut out. It was followed by a smaller 1.4 aftershock.

Although a magnitude 5.4 Coos Bay offshore earthquake occurred only 10 hours before the 2002 Klamath Falls earthquake, they were probably not linked. The Coos Bay earthquake occurred along the southern segment of the Blanco Fracture Zone, which to the best of current knowledge is not connected to the inland Klamath Basin and Range geologic province.

The West Klamath Lake fault zone is capable of stronger earthquakes, perhaps as much as magnitude 7.3. No one knows when the next large earthquake is due. It is not the only active fault zone in the region. The east side of Klamath valley is home to the East Klamath Lake fault zone, responsible for the 2002 earthquake. The region has not been studied enough to know how the fault zones interact. Crater Lake itself is still an active volcano. However, the greatest threat even to inland Klamath Falls is the offshore Cascadia subduction zone, which has the potential to generate magnitude 9 earthquakes, as well as tsunamis all along the West Coast.