The strongest earthquake in California today was a Ml 3.7 in the
Vacaville/Rio Vista area east of San Francisco. This was the largest
earthquake within 35 km of this epicenter since a Ml 4.3 on June
22, 1989, although comparably sized earthquakes (Ml 3.6-3.7) have
occurred more recently in the area on March 27, 1997 and on July 15, 2000.
It is the third largest earthquake in this area in the past 30 years -
the other having occurred as a Ml 3.9 on June 4, 1977, so it is quite
a rare event indeed. Any forecast (including on posted on this board)
pinpointing such an earthquake should be given the utmost consideration.
About 1.5 hours after the Rio Vista/Vacaville earthquake a Ml 3.0
occurred near Coalinga.This was followed later in the afternoon
by a Ml 2.0 at Parkfield. The Ml 3.0 was the largest event within
35 km of this location in nearly half a year, the last on Dec. 24, 2001
of Ml 3.1.
Since May 1 there have been 24 earthquakes of Ml>=3 in the region
of Northern and Central California (none in Southern California yet -
that drought extended to it's 35th day south of 35N today). This is
by far the most active week in this area at this magnitude level in the
past 4 years, and probably longer (this is all that was checked).