Orange County Register

A couple of hours after a magnitude 5.4 earthquake erupted beneath the Chino Hills on July 29, renowned seismologist Lucy Jones said the temblor might represent the end of a seismic lull in Southern California. That still could happen. So far, it hasn’t.

The quake — which originated 5 miles north-northeast of Yorba Linda –produced a handful of 3.0 or larger aftershocks in the days following the mainshock. But through Saturday night, there hasn’t been a 3.0 anywhere in Los Angeles, Riverside or Orange counties since August 2. And most of the “background” seismicity in the region lately has been 2.5 or lower.

“I don’t think seismicity has been all that low in  (Southern California) the  — we’ve had M3ish quakes near the border and … near Taft.,” says Susan Hough, chief of the Pasadena office of the U.S. Geological Survey.

“But the aftershock sequence from the M5.4 itself turns out to be wimpy, about 75 percent less energetic than the average California aftershock sequence for a M5.4 mainshock.  There’s some indication that relatively deeper quakes have relatively fewer aftershocks.  Chino Hills wasn’t hugely deep, but at 14km it was deeper than some.”

Hough’s USGS colleague Karen Felzer adds that, “Because the Chino Hills aftershock sequence is weak, becuase the mainshock magnitude wasn’t really that large in the scheme of things, and because the rate of aftershocks dcays quickly with time, we are only expecting the sequence to produce 1.0 to 2 (or slightly larger) aftershocks this week.”

“Wimpy” aftershocks follow Chino Hills earthquakes

Public asked for help reconstructing Chino Hills quake

97,000 O.C. students to join “biggest” earthquake drill

Famed seismologist says seismic lull may be over

Real-time SoCal earthquake monitor

Images Apollo astronaut shot of O.C. now online

Blue whale videotaped diving off Dana Point

You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.