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Cascade mountains earthquake of December 1872

When
1872
Where
central Washington Territory; Idaho and southern British Columbia
Episodes
2

The 1872 North Cascades earthquake occurred on December 14 in central Washington Territory. Due to the lack of seismometers, magnitude and location remain uncertain, with estimates ranging from 6.5 to 7.0. Intensity reports indicate severe shaking locally, while aftershocks were felt across a broad region including Idaho and British Columbia.

Episodes

  1. 1872-12-14 · central Washington Territory1872 North Cascades Earthquake

    A magnitude 6.5–7.0 earthquake struck central Washington Territory on December 14, 1872, with uncertain precise location.

  2. from 1872-12-14 · Idaho and southern British ColumbiaAftershock Activity

    Aftershocks followed the mainshock, felt over a broad area including Idaho and southern British Columbia.

Background and detail

Background. The event occurred in central Washington Territory, now Washington state, on December 14. Because seismometers were not operating in the region at the time, the magnitude and precise location were never determined. Scientists rely on intensity reports and field work, such as trenching studies, to estimate the shock's characteristics and propose epicenters.

Intensity and Estimates. A maximum Mercalli intensity of VIII was assessed for several locations, though shaking was less intense elsewhere. One study estimated a magnitude of 6.5–7.0 with a location near Lake Chelan. Analysis of intensity patterns compared to instrumentally recorded earthquakes helps resolve the location, accounting for local geological conditions that affect seismic wave propagation.

Geological Evidence. Field work identified a fault scarp likely resulting from the 1872 earthquake. Trenching revealed a northwest-dipping thrust fault at least 75 km long, active between 1856 and 1873. The event is not well understood due to limited instrumental records, but calibration using 20th-century earthquake intensities aids in interpreting the available data.

Sources

  1. 1872 North Cascades earthquake Wikipedia, revision of 2026-07-26

Machine-drafted from the cited Wikipedia passages and checked by a reviewing model, not by a human editor. Every passage cites the revision it was written from; dates and places follow those passages.