San Andreas fault giving off mysterious tremors

[vivfox]

Findings suggest underground stress is building up faster than expected

LOS ANGELES - Scientists have detected a spike in underground rumblings on a section of California's San Andreas Fault that produced a magnitude-7.8 earthquake in 1857.

What these mysterious vibrations say about future earthquakes is far from certain. But some think the deep tremors suggest underground stress may be building up faster than expected and may indicate an increased risk of a major temblor.

Researchers at the University of California, Berkeley, monitored seismic activity on the fault's central section between July 2001 and February 2009 and recorded more than 2,000 tremors. The tremors lasted mere minutes to nearly half an hour.

Unlike earthquakes, tremors occur deeper below the surface and the shaking lasts longer.

During the study period, two strong earthquakes hit — a magnitude-6.5 in 2003 and a magnitude-6.0 a year later. Scientists noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004.

Tremor episodes persist today. Though the frequency of tremors have declined since 2004, scientists are still concerned because they are still at a level that is twice as high as before the 2003 quake.

The team also recorded unusually strong rumblings days before the 2004 temblor.

Results of the research appear in Friday's issue of the journal Science. The work was funded by the U.S. Geological Survey and National Science Foundation.

"The fact that the tremors haven't gone down means the time to the next earthquake may come sooner," said Berkeley seismologist and lead researcher Robert Nadeau.

Nadeau first discovered tremors deep in the San Andreas Fault in 2005. Before that, the phenomenon was thought only to occur in Earth's subduction zones, where one tectonic plate dives beneath another.

USGS seismologist Susan Hough found the latest observations intriguing, but said it's too soon to know what they mean.

"We don't have enough data to know what the fault is doing in the long term," said Hough, who had no part in the research.
http://www.msnbc.msn.com/id/31836274...ience-science/

[Villavic]

unfortunately earthquakes are still unpredictable. Hope nothing serious happens to California people, though they have to be always prepared, as we peruvians do near the pacific shore.
some people say are afraid to live in a quakes zone, but could be safer than other places. Actually no zone is completely out of risks. If there are no earthquakes, there are tornados, or hurricanes, or floods, or snow storms.

I once read that in a period of 10 years, more people die in the USA east coast because of strong hard winters, than people in the west coast because of earthquakes. So you see, we can do nothing when mother nature is upset

[David]

Originally Posted by vivfox

LOS ANGELES - Scientists have detected a spike in underground rumblings on a section of California's San Andreas Fault that produced a magnitude-7.8 earthquake in 1857.

I wonder why the article (or the Berkeley researcher) says the 1857 Fort Tejon quake was a mag 7.8. The USGS for many years has listed the quake as a mag 7.9 -- the largest ever recorded in California.

USGS seismologist Susan Hough found the latest observations intriguing, but said it's too soon to know what they mean.

Susan Hough wrote a good lay reader book on California quakes called Earthshaking Science: What We Know & Don't Know About Earthquakes, for those who may be interested. She sometimes even posts to Usenet. She's very friendly, very approachable.

[David]

Originally Posted by Villavic

I once read that in a period of 10 years, more people die in the USA east coast because of strong hard winters, than people in the west coast because of earthquakes.

I believe it. The death count in California from earthquakes is very low, all things considered. Our two biggest earthquakes -- Ft. Tejon in 1857 & San Francisco in 1906 -- were so long ago, too. Only one person died in the Ft. Tejon quake.

Of course, another quake of those magnitudes (7.8 to 7.9) in California nowadays -- when our population has grown astronomically -- would be a major disaster, & the loss of life would be high. The question is, Which section of the fault zone would rupture (there are three major segments interspersed with a nonlocked zone): the north, the central, or the south. One of the other more recently discovered faults could also rupture big (though potentially not as big as the S.A. zone), & that would be a disaster too, if it's in a populated, developed area like Hayward or Long Beach.

Another disaster waiting to happen is the full or near-full rupture of the Cascadia subduction zone, offshore. It runs from Mendocino CA to British Columbia. It's roughly the size of the fault that unzipped near Sumatra in 2003. A fault that size has the potential to create a magnitude 9 earthquake, & the vertical movement will undoubtedly generate a tsunami throughout the Pacific basin.

As they always say, It's a question of when, not if. Active faults rupture, sooner or later. The longer the rupture, the higher the magnitude (give or take).

[chiliD]

Originally Posted by David

As they always say, It's a question of when, not if. Active faults rupture, sooner or later. The longer the rupture, the higher the magnitude (give or take).

A 5.1 hit yesterday 300+ miles off the coast of Oregon at 3:30pm PDT.

[vivfox]

July 13,2009

A giant squid has washed up on the shores of La Jolla after a powerful earthquake in San Diego. According to reports, around 7 a.m. on Saturday residents felt a 4.0 magnitude earthquake a few miles from the shore in La Jolla. This shook up the sea creatures apparently.

According to NBC News, "A spokesman for Scripps Institution of Oceanography said at this point they do not see a connection between the squid and the earthquake, but plan to look into it. Dozens of squid washing up at the same time is unusual but it has happened before, according to Sgt. Rains. But Mary Skeen said it is a first for her."

Some of the residents reportedly have never seen a squid in that area their entire life-spans. For one to wash up now after an earthquake is a mystery to some of them. The Squid apparently landed on shores around 8:30 a.m. on Saturday after the quake.

Scientists are currently looking into if it is possible the quake sent the squid to the shores. (c) tPC

From Wikipedia Northridge earthquake, 1994. Magnitude 6.7. Equal to 5.6 megatons Sichuan earthquake, 2008. Magnitude 7.9. Equal to 600 megatons The Richter Scale is logarithmic. Thus, an 8.0 can be hugely more destructive than a 7.0. I was in L.A. during... Read More »

Small Earthquake Hits Los Angeles
by The Inquisitr .A 4.5 magnitude earthquake shook Los Angeles and surrounding areas at 7:50pm local time Thursday. The quake was centered about a mile south of San Bernardino, and was felt across Los Angeles, San Pedro and Orange County. There were no reports of damage... Read More »

LA Quake 4.7 Mag. On Sunday Night - Experts Say More Aftershocks On The Way
by PostChronicle.com .Sunday night people in LA and the surrounding area were struck with a 4.7 magnitude earthquake. According to reports this is the strongest quake since last July and there are plenty more on the way. According to NBC, "The initial quake, which the U.S...
http://www.postchronicle.com/news/st...12243743.shtml

[daniellaaarisen]

As a born and raised Californian, let me tell you that earthquakes are NOTHING. They happen around once a year in my area and usually, the furniture and chandeliers shake for 10-15 seconds before everything is still again. Keep in mind that the intensity of an earthquake varies depending on how far you are from the source-- an 8.5 earthquake may be totally terrifying for someone 5-10 miles from the source while only half the people in surrounding areas feel as much as a slight vibration. That being said, I was not alive for the 1989 earthquake, the most recent "big" one. I can't REALLY talk until something huge has happened around here, but no one around here gives a second thought to earthquakes. We all think you midwesterners and coastal people are insane for knowingly living somewhere where you must somehow survive through tornadoes and hurricanes

[JWS]

Originally Posted by daniellaaarisen

As a born and raised Californian, let me tell you that earthquakes are NOTHING. They happen around once a year in my area and usually, the furniture and chandeliers shake for 10-15 seconds before everything is still again. Keep in mind that the intensity of an earthquake varies depending on how far you are from the source-- an 8.5 earthquake may be totally terrifying for someone 5-10 miles from the source while only half the people in surrounding areas feel as much as a slight vibration. That being said, I was not alive for the 1989 earthquake, the most recent "big" one. I can't REALLY talk until something huge has happened around here, but no one around here gives a second thought to earthquakes. We all think you midwesterners and coastal people are insane for knowingly living somewhere where you must somehow survive through tornadoes and hurricanes

That's what I say. If it weren't for the mudslides, brush fires and occassional riots we wouldn't have any fun at all.

[David]

Originally Posted by vivfox

A giant squid has washed up on the shores of La Jolla after a powerful earthquake in San Diego. According to reports, around 7 a.m. on Saturday residents felt a 4.0 magnitude earthquake a few miles from the shore in La Jolla.

They call a mag 4 a "powerful quake"?

Hell, that's a step or two above microquake.

[David]

I don't think any quake in California will ever be larger than magnitude 7.9. What do you guys think?

[JWS]

Originally Posted by David

I don't think any quake in California will ever be larger than magnitude 7.9. What do you guys think?

What was Northridge? 7.1. As I understand it, each .1 is 10 times the previous level.

[iamnotafraid]

Leave while you can!

[Villavic]

Originally Posted by David

Our two biggest earthquakes -- Ft. Tejon in 1857 & San Francisco in 1906 -- were so long ago, too. Only one person died in the Ft. Tejon quake.

Of course, another quake of those magnitudes (7.8 to 7.9) in California nowadays -- when our population has grown astronomically -- would be a major disaster, & the loss of life would be high.

There was an earthquake in SF circa 1988, right? How strong was it?

[David]

Originally Posted by JWS

What was Northridge? 7.1. As I understand it, each .1 is 10 times the previous level.

No, the moment magnitude was 6.7, according to the USGS:
http://earthquake.usgs.gov/regional/...1994_01_17.php

The magnitude scales are logarithmic, as you noted. But the difference in energy release is about 32 times from one magnitude to the next highest. In other words, a magnitude 7.0 quake releases about 32 times the energy of a magnitude 6.0 quake. A magnitude 8.0 quake releases more than 1,000 times the energy of a magnitude 6.0 quake (32 x 32).

[David]

Originally Posted by Villavic

There was an earthquake in SF circa 1988, right? How strong was it?

1989
Moment magnitude 6.9

Stevie Nicks & her band were getting ready to perform at Concord Pavilion. Show was canceled, obviously. But she played the following night in Sacramento, about 75 miles to the east.