  Wenatchee Ross Lake Olympia Chilliwack Astoria Fort Lapwai Portland Entiat  Proposed epicenter at Lake Chelan | |
| UTC time | 1872-12-15 05:40 |
|---|---|
| USGS-ANSS | ComCat |
| Local date | December 14, 1872 |
| Local time | 21:40[1] |
| Magnitude | 6.5–7.0 Mw[2] |
| Epicenter | 47°54′N 120°18′W / 47.9°N 120.3°W[1] |
| Type | Unknown |
| Areas affected | Pacific Northwest |
| Max. intensity | MMI VIII (Severe)[3] |
| Casualties | None |
The 1872 North Cascades earthquake occurred at 9:40 p.m. local time on December 14 in central Washington Territory (now Washington state). A maximum Mercalli intensity of VIII (Severe) was assessed for several locations, though less intense shaking was observed at many other locations in Washington, Oregon, and British Columbia. Some of these intermediate outlying areas reported V (Moderate) to VII (Very strong) shaking, but intensities as high as IV (Light) were reported as far distant as Idaho and Montana. Due to the remote location of the mainshock and a series of strong aftershocks, damage to structures was limited to a few cabins close to the areas of the highest intensity.
Because the earthquake occurred before seismometers were operating in the region, the magnitude of the shock and its location were never precisely determined, but the intensity reports that are available for the event were studied, and various epicenters for the event were proposed based on these limited data. One study presented an estimated Mw of 6.5–7.0, with a proposed location on the east side of the Cascade Range near Lake Chelan. The results of a separate study indicated that it may have been a larger event, placing the shock in the North Cascades, just south of the Canada–United States border at Ross Lake.