NEIC listings this morning give Mb 5.2 to the largest of the Coso Junction
earthquakes that occurred yesterday. This is the largest non-mid-ocean-ridge
earthquake to occur in the world since a Mb 6.0 in New Britain on July 8, the
day after the Mw 7.6 aftershock in Peru. It appears that the final readjustment
of stresses after that aftershock pretty much shut down global seismicity for a
short time. Of course, 10 days without a subduction zone event of Mb>=5.2
is a very long time.
The longest period ever recorded in the NEIS/NGDC catalogs between events
with M>5.2 occurred between May 26, 2000 and June 2, 2000 (7 days). A Ml 6.5
ocurred off the coast of Oregon on June 2, followed by earthquakes in the M 6+
range in Kamchatka, Honshu, Japan, and the Pacific-Antarctic Ridge on
June 3 and Mw 8.3, Sumatera earthquake on June 4, 2000, so this 10-day
period seems quite long (even though there have been some mid-ocean
ridge events of Mb>5.2 in this time).
This also appears to be the largest event within the states of California and
Nevada since the Hector Mine earthquake of Oct 16, 1999 (Mw 7.6). The last
comparably sized earthquake within California occurred at the Geysers with Ml 5.2
on September 3, 2000. Two larger events have occurred off the coast of Northern
California during the last two years - on Jan. 13, 2001 (Ml 5.6) and on March 16, 2000
(Ml 5.9). The last event in the general area which was larger occurred on August 1, 1999
about 100 km north of Coso with Ml 5.7.