Author Topic: 5.4 earthquake hits Southern California  (Read 868 times)

0 Members and 1 Guest are viewing this topic.

Offline wouldntyouliketoknow

  • Member
  • *****
  • Posts: 922
5.4 earthquake hits Southern California
« on: July 07, 2010, 08:50:09 pm »
Where are the PP Earthquake experts? Want you to weigh in please!

 Scientists say a magnitude 5.4 earthquake erupted 13 miles north-northwest of Borrego Springs at 4:53 p.m., shaking all of San Diego  County hard and rattling windows as far away as northern Los Angeles  County. The quake began 7.3 miles deep and follows a series of smaller quakes in that area in recent weeks, including a 4.9 near Coyote Creek on June 13. Seismologists initially listed today's quake at 5.9 but quickly downgraded it to 5.4.

USGS said that today's earthquake was not an aftershock to to 7.2 Easter Sunday quake. Instead, today's quake occurred on the Coyote Creek strand of the larger San Jacinto fault, the most active system -- and possibly most dangerous -- in Southern California . The 130 mile system snakes through parts of Imperial, San Diego, Riverside and San Bernardino counties, and is considered potentially very dangerous because much of the fault is located near heavily populated are

The northern Coyote Creek strand could likely produce a quake up to 6.9 in magnitude, says Tom Rockwell, a seismologist at San Diego State who studies the San Jacinto system.

Today's quake "felt like a bomb had exploded," said Bud Perez, a maintenance worker at the Borrego Water District in Borrego Springs.

But that didn't create any immediate problems for the agency, said general manager Richard Williamson.

"We are looking at all the tanks and facilities and everything seems to have rode through it pretty well," he said.

The earthquake produced minor ground motion at the San Onofre Nuclear Generating Station site. The motion was not sufficient to trigger the seismic alarms or lead to a plant shut-down. Plant personnel are conducting routine equipment inspections that follow an incident of this type. No damage has been reported. Both generating units continue to operate normally and safely.

“The building seemed to continue moving, even after the person I was on the phone with stopped feeling the shaking,” said Rachel Laing, a spokeswoman for the mayor who works on the 11th floor of San Diego City Hall. A few magazines even fell off a shelf, she said. “It was a pretty serious shake.”

At Center Market in Borrego Springs, Mary Jane Laws said the shaking was violent.

"I have been here 30 years and never felt one that strong," Laws said. "Quite a lot of items fell off the shelves -- quite a few breakages. Salad dressings, soap products, even fluor products and cake mixes."

Laws said her colleagues bolted for the front door but she stayed put. "We know the drills, but when it happened, I froze," she said.

The quake has been followed by seven aftershocks in the 3.0 to 3.6 range, including one at Lake Henshaw. There's a five percent possibility of a 5.0 aftershock within the next 24 hours.

"It looks like it is on the San Jacinto fault system in Borrego Springs, or a splinter of it," said Bob Dollar, a seismologist at the USGS. "A lot of scientists are working on this fault because it is the most active fault in Southern California. We've had more 6s there than any other fault in Southern California in the last century."

The fault produced a 6.5 earthquake on Dec. 25, 1899 that was felt throughout Southern California. The fault also produced a 6.8 quake on April 21, 1918.

Tom Rockwell, a seismologist at San Diego State, said, "Today's quake was on the Clark strand of the San Jacinto, near the Anza seismicity gap. When the San Jacinto has quakes that rupture the surface, they tend to be in the 7.2. to 7.3 range. But the system also gets a lot of quakes in the 5.0 to 6.0 range that don't break the surface."

Rockwell, who has been doing trench work on the San Jacinto, said a massive quake hit the fault on Nov. 22, 1800, and that the "return time" for an event of that scale is estimated at 210 years. However, scientists cannot reliably forecast quakes. So there is no way of knowing whether today's event was a foreshock to a much larger event.