Seismo-Watch, Your Source for Earthquake Information EARTHQUAKE EPICENTER MAP 
(Click on map to enlarge) TRACK GLOBAL AND REGIONAL SEISMIC ACTIVITY WITH SEISMO-WATCH EARTHQUAKE REPORTS 
NORTHERN CALIFORNIA 
GLOBAL 
WESTERN GREAT BASIN 
SOUTHERN CALIFORNIA
Other Seismo-Watch Special Earthquake Reports
- Notations:
- An earthquake registering a preliminary magnitude of ML 5.0 (NCSN), Mw 4.7 (UC Berkeley) was detected 01:06:18 UTC, August 18, (6:06 p.m. PDT) along the coast of Marin County of Northern California. The focal depth was placed at a depth of 6.9 km and and the fault plane solution suggested predominately reverse motion along a northwest trending fault plane, with a slight strike-slip component. (See fault plane solution)
- The quake was centered about 17 miles north-northwest of San Francisco at Bolinas Bay and the small coastal town of Bolinas. (Location Maps) It was centered either along the northern segment of the San Andreas Fault where it comes briefly back on shore north of San Francisco or a nearby fault splay. The northern segment of the San Andreas Fault is considered locked and has not produce a M5+ earthquake north of the Golden Gate since the powerful 1906 San Francisco ~M8 earthquake. In 1957, however, a M5.3 jolt occurred just west of Daly City but it occurred along the peninsula segment of the San Andreas Fault and not the locked northern segment. The Daly City quake caused over $1 million in damage and injured 40 people.
- Preliminary reports indicate the quake was strongly felt in the epicentral area and as far away as Gilroy, Vacaville, Livermore, and Santa Rosa. Items toppled from tables and shelves in homes, hanging objects swung, and pictures shook on walls. Commercial items, like bottles and other light objects, are said to have toppeled in one Safeway store and there is a report of a few windows being cracked or broken. Most people reported the shaking lasted about 5-10 seconds. There have been no reports of injuries at this time.
- One of the most common comments witin the hundreds of "Felt Earthquake Reports" received by Seismo-Watch was the noise that accompanied the quake. Most in the epicentral region heard a loud explosion-like sound, manying thinking it was a bomb or an accident of some sort. Sounds are common with moderate to large earthquakes, however, most sounds are commonly described as freight trains passing by or through the house, of course, depending on how close one is to the epicenter.
- While the fault motion is rather surprising, the 1957 Daly City earthquake also had reverse-slip motion. For the most part, the San Andreas Fault is a strike-slip type of fault.
- Curiously, there have been only a few aftershocks at this time. The largest was a M2.6 at 11:44 p.m., August 17, which was locally felt. As a precaution, the USGS have issued an aftershock warning which states the following probabilities: 10% chance of a M5.0 or larger quake in the next 7 days; 5-10% chance of a quake larger than the main quake; and there is a likelihood of between 3-12 M3+ aftershocks.
Update: 9:30 p.m. PDT, August 18, 1999.
- Other News Reports:
San
Francisco Chronical
KTVU
- TV News Channel 2
KRON
- TV NewsCenter4 - Video
(requires REAL Player)
Marin
Independant Journal
San Francisco
Examiner
CNN
Reuters
Did
you feel this tremor? Send
us a quick note on what you felt.
A
similar copy of this earthquake report was sent to subscribers
of the Seismo-Watch
Earthquake Fax Alert Bulletins within an hour of the event.
Feel
free to browse other Seismo-Watch
Special Earthquake Reports.
Stay
informed, Stay Safe. Subscribe to Seismo-Watch
Global and Regional Earthquake Reports. Six global and regional
earthquake reports to choose from, including two FREE Brief Regional Reports. Stay
informed with FREE e-mail updates to the Seismo-Watch
Online Earthquake Reports.
Don't forget our
FREE Brief
Central California Earthquake Report! Covering all the earthquake
activity for the Central California region, including the ever
active creeping segments of the San Andreas and Calaveras faults.
Updated
weekly. Subscribe to our FREE Update
e-mail messages NOW.
Have you seen our
FREE Brief
Western Great Basin Earthquake Report! Covering earthquake
activity for the California/Nevada border region, including detailed
activity of the Mammoth Lakes area.
Updated
weekly. Subscribe to our FREE Update
e-mail messages NOW.
You can't miss
our FREE Coachella
Valley Earthquake Report! Covering magnitude M1+ earthquake
activity in the Palm Springs area from the southern Landers aftershock
zone to the locked Coachella Valley segment of the San Andreas
fault.
Updated
weekly. Subscribe to our FREE Update
e-mail messages NOW.
