SCEC INSTANeT News
	Big Bear Awakened, "Dry Spell" Broken by Minor Earthquake

By John Marquis Just 28 minutes past midnight on Saturday, December 2, 2000, a magnitude 4.1 earthquake struck the San Bernardino Mountains of southern California. Located just 8 miles (13 kilometers) east-northeast of the town of Big Bear Lake, it was felt throughout the many camps and small resort towns of the area, in the communities of the high desert and the Inland Empire, and even as far away as San Clemente, Los Angeles, and the western Antelope Valley. Some of these places seem to lie beyond the limits suggested by instrumental records of ground motion, though the TriNet ShakeMap does show a few small "pockets" of higher intensity outside of the primary zone of shaking; seismic waves are sometimes magnified locally in areas small enough to slip through the instrumental network unnoticed. The strongest shaking reported was in the Big Bear area, where ground motion of intensity V (five) on the Modified Mercalli Intensity Scale was reported. This means that practically all those awake in Big Bear at the time of Above: A map shows the earthquakes of magnitude 4 or greater that occurred in the six months prior to this weekend's earthquake near Big Bear. Move the mouse over the image to see the previous six months' magnitude 4+ activity. the earthquake felt the tremor, and many of those who were asleep were awakened by it. What little damage might have occurred was very minor, probably mostly in the form of broken glassware and other fragile, unstable objects that were knocked over during the shaking. What makes this earthquake especially notable, however, is its status as the first earthquake greater than magnitude 4 to occur in southern California since June 26, 2000. That period of 23 weeks without an earthquake of this size or larger is one of the longest seismic "dry spells" in recorded history. Instrumental records have been kept since 1932, and in all that time, the longest period without an earthquake greater than or equal to magnitude 4 was a span of 30 weeks in 1977. The most recent comparable period of quiescence was snapped dramatically on June 28, 1991, by the Mw 5.8 Sierra Madre earthquake which caused moderate amounts of damage across the northern San Gabriel Valley and in the foothills of the San Gabriel Mountains. Though the ending of this year's "dry spell" was not such a rude awakening, it was definitely an unwanted, weekend "wake-up call" for sleepers near Big Bear!

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