Seismo-Watch
Earthquake Alert Bulletin No: 98-281

Preliminary data indicates a significant earthquake has occurred:

Regional Location:

Preliminary Magnitude:

Moment Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Latitude:
Longitude:
Focal Depth (km):
Analysis Quality (A-D):

NORTHERN CALIFORNIA

5.2 ML (NCSN)

5.1 Mw (UCBSL)

98/11/26
19:49:53 (11:49 a.m. PST)
40.63N
122.42W
25.9 km
A

Notations:

An earthquake registering a preliminary magnitude of Ml 5.2 (NCSN), Mw 5.1 (UCB) occurred at 19:49:53 UTC (11:49 a.m. PST), November 26, Thanksgiving Day, in the northern Sacramento Valley of Northern California. The focal point was placed at a depth of 26 km beneath the surface and the Moment magnitude analysis from the University of California, Berkeley, Geophysical Laboratory indicated a fault plane solution with strike-slip motion along an either north-northeast or west-northwest trending fault plane with a slight dip-slip component. The quake was centered about 3-4 miles northwest of Redding near the town of Keswick.

The quake was widely felt in the region, knocking light items from tables and shelves, causing hanging plants to swing wildly, and windows and walls to shake vigorously. The jolt was felt as far away as Sacramento and Eureka. There was no reports of significant damage, however, some windows broke, including those at the downtown Safeway Store in Redding. Many people were frightened by the shaking and some heard sounds and noises accompanying the shaking.

There have been dozens of aftershocks since the main jolt, the largest of which measured M4.4 at 2:58 p.m., Nov. 26 and M4.2 at 8:41 p.m. Nov. 27. The USGS Northern California office has issued and aftershock warning which indicates there is a 5-10% chance of a quake of equal or larger magnitude to occur within the next 7 days. Please consult the USGS in Menlo Park, California or at Seismo-Watch before using this information.

The initial M5.2 earthquake was the largest quake ever recorded in the Redding area and the Northern Sacramento Valley as a whole. The largest quake prior to this quake was a M4.7 recorded in 1968. Interestingly, a M4.6 temblor on July 21st earlier this year occurred in the same location and depth. The focal depths suggests the activity is occurring well above the subduction zone contact between the Gorda and North American tectonic plates and within a broad belt of seismic activity recorded in the northern Sacramento Valley. This latest series of quakes highlights that this region of California is susceptible to large, damaging earthquakes and increased seismic monitoring of the region is warranted to better understand its seismic potential.

 

 

 

 


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Subtract 8 hours from Greenwich Mean Time to obtain PST or 5 hours for EDT
Location Quality: A (good), B (fair), C (poor), D (bad)
Magnitude: Ml (local or Richter magnitude), Lg (mblg), Md (duration), Mb (body wave), Ms (surface wave), Mw (moment)

Standard Sources Include:
U.S. Geological Survey, National Earthquake Information Center, Golden, CO (NEIC)
Harvard Geophysical Observatory, Harvard University, Cambridge, MA (HRV)
U.S. Geological Survey, Northern California Seismic Network (NCSN)
University of California, Berkeley, Seismological Laboratory (UCBSL)
California Institute of Technology, Pasadena, California (Caltech)
various wire reports and/or personal communications

All data are preliminary and subject to change.
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