1993 Klamath Falls Earthquake

On September 20, 1993, the quiet town of Klamath Falls, Oregon was rocked by two powerful earthquakes. A Mw 5.9 earthquake struck the town at 8:28 p.m. It was followed by a Mw 6.0 earthquake at 10:45 p.m., as well as over 3,000 aftershocks in the months that followed. Both earthquakes originated around 16 miles northwest of Klamath Falls in the Mountain Lakes Wilderness. The resulting seismic waves were felt over 50,000 square miles of southwestern Oregon and northern California, and as far away as Eugene and Redding. The Klamath Falls earthquakes were Oregon’s largest earthquakes since 1936. 

Overall, the earthquakes caused an estimated $10 million in damage, but the location of damaged buildings within Klamath Falls was highly uneven. While most of the town’s buildings escaped unharmed, around 1,000 were damaged. The greatest impacts were to the city’s downtown, where several brick masonry facades collapsed. Tragically, the earthquakes also caused two fatalities. A man was killed by an earthquake-induced landslide which caused a boulder to smash into his car, and a woman died from a heart attack.

In 1993, the PNSN had a very crude version of a website, yet even then provided some basic information about this earthquake sequence. For this historical document see our legacy web page.

The shaking caused by the Klamath Falls earthquake measured at a maximum of VII on the Modified Mercalli Intensity (MMI) scale. This level of shaking is considered very strong, can be felt by everyone who experiences it, and is usually frightening. It usually causes negligible damage to well-constructed buildings, but can cause considerable damage to poorly built or badly designed buildings.

Indeed, the Klamath Falls earthquakes caused extensive damage to the city’s unreinforced masonry buildings. Unreinforced masonry buildings are older brick buildings that were generally constructed before the 1950s. Due to their age, the mortar and bricks are often weak and deteriorating, and the floors and ceilings often lack a strong connection to the walls. During an earthquake, the buildings can collapse, causing bricks and parapets to rain on people below. 

In the town of Klamath Falls, the Klamath County Courthouse was severely damaged and required complete reconstruction in 1999. The Stevens Hotel Building also had to be demolished. At least eight brick facades collapsed, and bricks fell out and walls were damaged in many other buildings. While damage was concentrated in Klamath Falls, nearby towns also suffered. The town of Tulelake had to replace its city hall, and several other municipal buildings were also severely damaged.

By contrast, well-built wood homes that were bolted to their foundation fared relatively well. This shows the risk posed to life and property by old unreinforced masonry buildings in earthquakes. 

The earthquake serves as a reminder that being properly prepared for a damaging earthquake can save lives and reduce damage. Retrofitting older buildings, particularly unreinforced masonry buildings, and performing non-structural hazard mitigation can greatly reduce hazards to human life and property during an earthquake. Additionally, individuals should make sure they 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. Earthquakes like Klamath Falls don’t have to be devastating; 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.

Klamath Falls lies at the edge of the Basin and Range province, a vast geologic region covering much of the inland western United States. This region is defined by broad low valleys and parallel north-south mountain ranges, each of which are bounded by faults.

This distinct geomorphology is caused by the slow stretching of the Earth’s crust. The Basin and Range region is slowly being pulled apart like taffy. As the underlying tectonic plate stretches, the hot inner mantle beneath it begins to rise. This causes the overlying plate to rise, thin, and fracture into faults. A fault is a fracture or zone of fractures between two blocks of rock. Along these fault lines, basins are slowly sinking and mountain ranges are slowly rising.

The combined forces of crustal stretching and rising mantle has broken the Basin and Range region into hundreds of downdropped valleys and parallel upraised mountain ranges over the last 30 million years. Klamath Falls sits in one of those valleys near the West Klamath Lake Fault Zone. As the valley sinks and the surrounding ridges rise, pressure and friction slowly build along the fault that separates these blocks of rock. Eventually, when the compressive stresses on these faults become strong enough, the blocks of rock slip past each other. This movement unleashes the waves of energy that we call earthquakes. 

While Basin and Range faulting typically causes earthquakes of moderate magnitude, these earthquakes can be quite damaging because they occur at a relatively shallow depth. The Klamath Falls earthquakes occurred at a depth of 6 miles beneath the Earth’s surface. Fortunately, during this event, slip occurred on a relatively remote segment of the West Klamath Lake Fault Zone, as opposed to another fault segment that runs directly through the town. If the 1993 earthquake had occurred on the latter, the impacts on the community would have been far more devastating.