1999 North Coast Seismicity
1999 was a relatively quiet year for north coast earthquakes. Only 14 earthquakes of magnitude 4 or larger were recorded, and none in the magnitude 5 range. The largest, a magnitude 4.8 on December 26, was located offshore of Cape Mendocino on the Mendocino fault about 7 miles west of Petrolia. Only 8 were reported felt and none were strong enough to cause damage. Most of the earthquakes were located offshore along the Mendocino fault or in the Gorda plate. This was the fourth lowest annual number of earthquakes in the past 25 years; the average number of earthquakes of this size per year is about 21.
1999 Northcoast California Earthquakes of magnitude 4 or larger
(Northern Mendocino, Humboldt, Del Norte Counties)
DATE TIME LAT LONG ML MW LOCATION, COMMENTS
24-Jan 7:35 AM 39.56 123.771 4.0 4.1 Near Fort Bragg, felt.
9-Feb 6:32 AM 40.70 124.96 4.1 4.1 Gorda plate, 38 miles WNW of Ferndale.
14-Feb 10:00 PM 40.28 124.39 3.7 4.7 Mendocino fault, 7 miles W of Petrolia, felt.
24-Feb 2:02 AM 40.75 124.47 3.9 4.2 Gorda plate, 16 miles NW of Ferndale, felt.
28-Feb 3:33 PM 40.25 127.26 4.5 Mendocino fault, 155 miles W of Petrolia.
13-Apr 5:48 PM 40.49 127.36 4.0 Mendocino fault, 160 miles W of Petrolia.
15-May 1:59 PM 40.36 125.130 4.0 4.0 Mendocino fault, 45 miles W of Petrolia, felt.
1-Jun 1:28 AM 41.72 126.96 4.6 Gorda plate, 143 miles W of Crescent City.
23-Jul 5:38 PM 40.39 125.13 4.4 4.5 Mendocino fault, 45 miles W of Petrolia. Felt Petrolia, Briceland, Ferndale, Fields Landing, Little Salmon.
7-Aug 9:45 PM 41.069 127.257 4.8 Gorda plate, 160 miles W of Trinidad.
28-Sept. 11:22 PM 41.36 123.42 4.0 4.0 Subducted Gorda plate, 3 miles ESE of Sommes Bar. Felt Orleans, hoopa, Willow Creek, Trinidad, Weott.
21-Nov. 9:38 PM 40.41 125.22 4.5 4.6 Mendocino fault, 50 miles W of Petrolia.
26-Dec. 11:41 AM 40.27 124.39 4.2 4.8 Mendocino fault, 7 miles W of Petrolia. Felt Petrolia, Honeydew, Weott, Hydesville, Ferndale, Fortuna, Stanton, Cutten, Eureka.
31-Dec. 12:46 AM 40.64 124.72 4.0 Gorda plate, 25 miles west of Ferndale. Felt.
Note: ML is the Local or Richter magnitude as determined by the U.S. Geological Survey; MW is the moment magnitude as determined by the Berkeley Seismological Laboratory. The Moment magnitude is calibrated to agree on average with the Richter magnitude. For large earthquakes, the moment magnitude is considered a better measure of energy released.
Compiled by Lori Dengler, Humboldt Earthquake Education Center, Department of Geology, Humboldt State University from data supplied by the U.S. Geological Survey and the Berkeley Seismological Laboratory. January 6, 2000