1980 Eureka earthquake
 Salem
Roseburg
Fallon
Palo Alto
Eureka
 |
|
| Date | November 8, 1980 |
|---|---|
| Origin time | 10:27:34 UTC |
| Magnitude | 7.3 Mw |
| Depth | 6.2 mi (10 km) |
| Epicenter | 41°08′N 124°26′W / 41.13°N 124.44°WCoordinates: 41°08′N 124°26′W / 41.13°N 124.44°W |
| Type | Strike-slip |
| Areas affected |
North Coast (California) United States |
| Total damage | $2–2.75 million |
| Max. intensity | VII (Very strong) |
| Peak acceleration | .15–.25g |
| Landslides | Yes |
| Casualties | Six injured |
The 1980 Eureka earthquake (also known as the Gorda Basin earthquake) occurred on November 8 at 02:27:34 local time along the northern coastal area of California in the United States. With a moment magnitude of 7.3 and a maximum Mercalli intensity of VII (Very strong), this strike-slip earthquake was the largest to occur in California in 28 years. Although damage was considered light, several loss estimates equaled or exceeded $2 million, and six injuries resulted when two vehicles came down with the partial collapse of a highway overpass on US 101 in Fields Landing. The north coast of California experiences frequent plate boundary earthquakes near the Mendocino Triple Junction and intraplate events also occur within the Gorda Plate.
Due to the regional seismic risk, the nuclear portion of the Humboldt Bay Nuclear Power Plant was shut down in the 1970s. No substantial damage occurred to the two fossil-fuel units that were still operational at the facility. Several types of sensors were installed at the site to capture strong motion data in this seismically-active area, but the majority of records from the event were considered unreliable due to faulty equipment or inadequate maintenance. Only one piece of equipment at the facility provided data by which an estimate of the peak ground acceleration could be made.
Near Cape Mendocino, the Mendocino Triple Junction is an area of active seismicity where three tectonic plates come together. The Mendocino Fracture Zone (also known as the Mendocino Fault east of the Gorda Ridge) is a transform fault that separates the Pacific and Gorda Plates. To the south, the relative motion between the Pacific Plate and North American Plate is accommodated by the San Andreas Fault, and to the north, the Gorda Plate is converging with the North American Plate at the Cascadia Subduction Zone. Earthquakes within the Gorda Plate are the result of north-south compression at the Mendocino Fault.
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