1872 North Cascades Earthquake

On December 14, 1872, Washington experienced one of its largest earthquakes in recorded history. There were no seismometers at the time, so the exact location and magnitude of the earthquake remain uncertain. But based on historical newspaper analyses as well as modern scientific research, geologists estimate that the earthquake’s magnitude was between 6.8 and 7.2. 

Contemporary newspaper coverage and eyewitness accounts show that the entire Pacific Northwest was impacted by shaking. The communities of Entiat and Wenatchee experienced severe shaking, rated VIII on the Modified Mercalli Intensity scale. Meanwhile, moderate shaking was felt in Oregon and the Puget Sound area, and light shaking impacted areas as far as Montana and Alberta.

Until recently, the precise location of the fault that caused this earthquake was unknown. Due to the slow speed of communications in 1872 and the variety of ways shaking was reported, the event's location was variously reported as being in southern British Columbia (by a Canadian seismologist) and the middle of the North Cascades in Washington (by a PNSN seismologist). In 2002, Bill Bakum and others from the USGS and the PNSN used more recent well known earthquakes to better understand the distribution of the shaking pattern from the 1872 event and determined a location near the southern end of Lake Chelan with a magnitude of about 6.8. See our original legacy web page for this study.

In 2014, scientists discovered a new fault that pinpointed the epicenter near the small Central Washington town of Entiat. A U.S. Geological Survey researcher, Brian Sherrod, used LiDAR imagery to intensively study the surrounding landscape. LiDAR is a remote sensing and mapping technology that can visually strip away vegetation in order to display subtle topographic features. Sherrod finally spotted a possible fault scarp in nearby Spencer Canyon. A fault scarp is the scar that is created when an earthquake cracks the Earth’s surface. By digging perpendicular trenches that cut through the scarp, Sherrod confirmed his hypothesis. Soil layers on either side were clearly offset by up to two meters, showing where they had shifted in past earthquakes.

Was this the fault that caused the 1872 North Cascades earthquake? Probably, yes. The scarp was partially buried by a small landscape that dammed nearby streams, creating small ponds. By dating the trees growing in the landslide as well as the dead ones that drowned in the ponds, Sherrod determined that the landslide occurred around 1872. While the depth of this earthquake can not be determined from seismic data (no such data existed in 1872), the fact that a surface fault can be found means that it was shallow as is would be expected for a crustal fault in this region.

The PNSN has been continuously monitoring the area around Lake Chelan and Entiat since 1975. There has been an ongoing sequence of earthquakes here that are possibly related to the 1872 event. It seems too long since then for these to be aftershocks, but certainly stress concentrations and/or weakened faults could allow for a low level of seismicity to be in the same area as the 1872 earthquake. The area encompassing these earthquakes is slightly elongated in an SW-NE direction and overlaps the Spencer Canyon fault. Other than a few small swarms of events in the mid-1980s, the rate of events has been fairly steady at a few events per month with a slight decreasing rate.

Additional research is needed to confirm that a rupture in the Spencer Canyon Fault caused the 1872 earthquake, as well as to determine how often earthquakes on this fault occur. The results will be of great interest to communities in Central and Eastern Washington, who may be less aware of earthquake risk than people west of the Cascades. While the North Cascades was remote wilderness in 1872, today it is home to hundreds of thousands of people and significant energy and road infrastructure. Dam operators in particular need to know where and how often the ground will shake. Understanding the 1872 earthquake has implications for region-wide earthquake preparedness.

Damage from the 1872 earthquake was fortunately limited. At the time, Washington was a sparsely populated territory. It was home to few besides soldiers, traders, trappers, and Native American communities. Some nearby log cabins suffered dislodged roofs and detached kitchens. Buildings across the northwest United States suffered minor damage as well. Chimneys cracked as far away as Olympia, windows shattered in Victoria, and people were knocked off their feet at Snoqualmie Pass. Strong aftershocks over the next year kept people on edge.

The 1872 earthquake also impacted the physical landscape of the Pacific Northwest. The earthquake caused numerous landslides. One landslide at Ribbon Cliff near Entiat even temporarily dammed the Columbia River. Near Chelan Falls, the shaking opened a large hole in the earth, through which a 27-foot geyser erupted. The geyser activity continued for many days and left permanent springs. Fissures split the ground as far away as Seattle. The geologic evidence of the 1872 earthquake can still be seen today.

The North Cascades 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. Individuals should ensure 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 the 1872 event 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.