Quake activity along the San Andreas fault is picking up

Moderate Subsea Earthquake Strikes Near Oregon Coastline

A strong earthquake struck off the coast of Oregon on early Wednesday evening, seismologists said, but there were no reports of damage or casualties and no tsunami warning was issued.

The 5.3-magnitude earthquake at 8.13 p.m. local time (0413 GMT Thursday) was centered about 144 miles (233 kilometers) west of Coos Bay, a city located in Coos County on the Pacific coast. It struck about 6.2 miles (10 kilometers) deep, making it a shallow earthquake, according to the United States Geological Survey (USGS).

The USGS said it did not expect to see damage or casualties due to the earthquake’s distance from the coast, and there were no immediate reports of tremors being felt anywhere along the coast.

Wednesday’s earthquake was one of the strongest earthquakes to hit off the coast of Oregon in recent years, but no tsunami warning was issued by the West Coast and Alaska Tsunami Warning Center (WCATWC).

'Monster' earthquake may hit off California coast within 50 years.
By David Perlman
San Francisco Chronicle
Mon, 10/10/2011 - 2:44pm

SAN FRANCISCO -- The ocean floor off the coast of Northern California and southern Oregon reveals a record of massive earthquakes that have hit the region over the past 10,000 years -- and there's a 1-in-3 chance that another could strike again within the next 50 years, scientists say.

Submarine landslides triggered by major quakes on land have sent layers of sediments onto the seabed, and by dating those sediments researchers led by Chris Goldfinger, a marine geologist at Oregon State University, have calculated that the temblors rupture the ground roughly every 240 years on what is called the Cascadia Subduction Zone.

That 600-mile zone runs approximately from the northern end of Vancouver Island in Canada along the coast of Oregon, and into California for 100 miles past Crescent City and Eureka to Cape Mendocino.

Goldfinger and his colleagues have found evidence in those sediment layers that 19 monster quakes with magnitudes of 9 or more have struck along the northern Cascadia zone within the past 10,000 years. Quakes that size would have been as violent as the undersea temblor off Japan that triggered the devastating tsunami there in March, and the great Sumatra quake and tsunami of 2004.

Goldfinger's sediment records show that 22 quakes have struck along the southern segment of the Cascadia zone during the same period. Their magnitudes were lower, Goldfinger found -- between 8 and 8.3 -- but even those were larger than San Francisco's 1906 Big One with its magnitude of 7.9.

The thin sediment layers, known as turbidites, show up in some 170 core samples that Goldfinger and his colleagues have collected by drilling into the ocean floor of the Cascadia zone.

Turbidites also mark the seafloor off the San Andreas fault, and core samples drilled by Goldfinger's team at more than 30 sites as far south as Monterey Bay revealed evidence of ancient onshore quakes there.

Their findings add information for the earthquake hazard teams that produce probability estimates of future quakes on the San Andreas and the Bay Area's many other faults, according to David Schwartz of the U.S. Geological Survey in Menlo Park.

Goldfinger heads the Active Tectonics and Sea Floor Mapping Laboratory at Oregon State, and most of his lab's studies have focused on the Cascadia Subduction Zone. That region beneath the Pacific Ocean is where a giant slab of Earth's crust called the Juan de Fuca Plate dives down beneath the North American plate, pushing up the Cascade mountains and causing dangerous upward-thrusting earthquakes.

The northern end of the 800-mile-long San Andreas fault runs into the sea near Cape Mendocino and turns west to become the Mendocino Transform Fault that marks the southern edge of the Cascadia zone.

Goldfinger's studies of turbidites and past earthquakes have been published in many recent scientific reports, and are more completely detailed now in a full-length report to the U.S. Geologic Survey.

Gary B. Griggs, an oceanographer and Director of the Institute of Marine Sciences at the University of California, Santa Cruz, has studied turbidite layers in the ocean off Oregon as evidence of Crater Lake's formation in Oregon some 7,700 years ago when a cluster of huge volcanoes now called Mt. Mazama erupted again and again.

Griggs, who has followed Goldfinger's work, said "his work is solid, and it has created a big picture of the seismic past along the Cascadia Subduction Zone."

More than 8 million Californians are expected to participate in a statewide earthquake drill at 10:20 a.m. Thursday.

From classrooms to offices to a Target store in Northridge, people will be asked to drop, cover and hold on as the minute strikes. Participants can register at www.shakeout.org.

"Across the state, we're asking folks to drill to practice," said John Bwarie, a spokesman for the U.S. Geological Survey. "Every time you practice, that'll give you more time to prepare when the shaking actually does start to occur."

In Northridge, a recording will be broadcast over the loudspeaker at a Target store asking customers to drop to the ground, take cover by getting underneath a sturdy desk or table and holding on to it until the shaking stops.

At Caltech in Pasadena, the college will send text messages to students and professors and ask them to participate.
The earthquake drills have grown steadily since they began in Southern California in 2008. Thursday's drill also will be held in British Columbia, Guam, Idaho, Nevada and Oregon. Officials from Chile, China, Japan and Mexico will be visiting a ShakeOut drill site in Northridge to learn from the event.

"People that are not prepared for disaster are inviting disaster," said Kenneth Hudnut, a geophysicist for the U.S. Geological Survey.

Hudnut also advised the public to take a couple more steps: "Make sure that things in your office or your home are not going to fly and hit" people during a quake, he said.

He also urged people to make sure they have plenty of water, have comfortable walking shoes under beds and in cars, and have emergency supplies both at home and in their cars.

Hudnut also urged that when an earthquake happens, "If you're inside, stay inside. If you're outside, stay outside. A lot of our fatalities in earthquakes are when people run outside from a building, and the building may collapse out onto the sidewalk."

Officials say groups can schedule drills for a later time. Some college dorms, for example, are holding their drill at 10:20 p.m. when students will be in their rooms. And on Saturday, an entire neighborhood in the Hermon area of northeast Los Angeles will undergo a community-wide drill.

A record-breaking earthquake rattled windows in Atascosa County and could be felt across Central and South Texas early Thursday.

The magnitude 4.8 quake was the largest since the U.S. Geological Survey first began keeping track of them in this area in 1973, said Julie Dutton, a USGS geophysicist.

It beat the 4.3 magnitude earthquake that hit on April 9, 1993, the previous record holder.

Earthquakes are rare here, but not unheard of. Thirteen quakes have struck the region since the agency began recording them.Thursday's quake struck at 7:24 a.m. , its epicenter about 47 miles southeast of San Antonio near the rural community of Campbellton, the USGS reported on its website.

The strongest tremors were felt just southeast of San Antonio, but people felt the quake as far south as Kingsville and as far north as Georgetown, according to USGS. No significant damage was reported.

A resident at the Cadillac Lofts in downtown San Antonio said he felt the apartment building swaying.

...


But Alan Dutton, who chairs the Department of Geological Sciences at the University of Texas at San Antonio, said Thursday's earthquake was not uncommon. The region gets a tremor about every 2 to 4 years more or less, he said.

“We have the usual suspects, but it's scientifically hard to determine if this earthquake was caused by such and such,” Dutton said. “There is sometimes some adjustment to the earth's crust because of the continued evolution of the Gulf of Mexico.”

Dutton said the quake was probably not caused by a recent increase in hydraulic fracturing and oil pumping in the Eagle Ford shale formation, which cuts across the region. The quake occurred deeper within the earth's crust than rock layers where that activity occurs.

Earthquakes have been associated not with fracking itself, but with the disposal of fracking fluids in deep wells, according to numerous studies. Last month, the Arkansas Oil and Gas Commission banned the use of disposal wells for fracking fluids after the commission traced a series of mini-quakes to four disposal wells on an existing fault line.

A study by Southern Methodist University and the University of Texas at Austin found links between the practice and small earthquakes in the Barnett shale region, and scientists with the British Geological Survey linked nearby fluid injection to two small quakes in the Blackpool area.

Earthquakes also can be induced by pumping groundwater, but the depth of Thursday's quake was so great that the possibility is unlikely, Dutton said.

“Earthquakes of this magnitude have been going on decades before fracking in Eagle Ford,” Dutton said. “They could be caused by many other things.”

The largest quake recorded in Texas history happened Aug. 16, 1931. It had a 5.8 magnitude and its epicenter was near Valentine.

Hi George,

Did you participate in any earthquake drills today?

Ask an Expert: What to Make of the Recent Hayward Fault Jiggles?

Seismic expert Dr. Robert Uhrhammer sheds some light on last week’s cluster of earthquakes on the Hayward Fault.

Every time there’s an earthquake, let alone a bunch in a row, seismic legends and lore fly. This means the Big One will hit soon. This means the Big One won’t hit soon. Highly unusual. No biggie – enjoy the ride.

We phoned retired UC Berkeley seismologist Robert Uhrhammer to help put last week’s local quakes in context. Uhrhammer, a seismic researcher and instrumentalist, still works in Cal’s Seismology Lab.

How many earthquakes were recorded in the Berkeley area last week? There have been 10 events since Oct. 20, all on the Hayward Fault. The first quake, of magnitude 4.0, occurred at 2:41 p.m., epicentered just southeast of the UC campus between the Clark Kerr campus and the Claremont Hotel. It had a depth of eight kilometers, or five miles.

The rest were all aftershocks. All of these events occurred in a 2.6-kilometer radius of the first quake — Berkeley’s own cluster.

How do you distinguish aftershocks? Basically, the timing. In California, two thirds of the time, when we look at a grouping of earthquakes, the biggest is the first. About one third of the time, we see one or more earthquakes preceding the main one, those are foreshocks.

Where are foreshocks most common? In volcanic regions, such as along the Pacific Rim.

When do people start feeling quakes? At a threshold of magnitude 2. That’s when people start reporting them.

Was the recent Hayward Fault quake sequence rare? No. Since 1970, there have been about 1,200 earthquakes in a 10-kilometer radius of last week’s 4.0 quake. Most of them are quite small; much smaller than what people would feel.

If you look at the seismic patterns, the cluster we’ve had in the past week doesn’t look anomalous or unusual when compared to other clusters that occur along the Hayward Fault.

The Hayward Fault behaves quite differently than other fault systems in the Bay Area. On the Hayward, earthquakes all occur in clusters or pockets, not along a continuum, which is more common. These little patches cover only 2 to 5 percent of the whole Fault.

Locally, there are pockets in Berkeley, Oakland, El Cerrito, Richmond and Pinole. They tend to occur where the Fault has bends or steps on it. The Fault isn’t a nice straight line.

Does the recent sequence give a read on the future? Not really. Whenever there is a cluster of little earthquakes like this on this section of Hayward Fault, statistically and mathematically the probability of getting a big earthquake within a few days increases a little, by about 1 to 2 percent. More probable minutes to hours after the first shock.

Every day that passes, this drops off. The most likely scenario is that a big quake would occur soon, within a few days of the biggest quake. (This is on the rare foreshock occasion.)

What about further in the future - The Big One? I can never say that we’re due; I can only say what the probability is. Using our best evidence at this time, in the next 30 years, there’s a 65 percent chance that we’ll get a magnitude-6.7 or larger on one or more of the seven Bay Area fault systems capable of producing quakes of this size.

If we go specifically to the Hayward, there’s a 28 percent chance of getting a magnitude-6.7 or larger in the next 30 years. This is the greatest “hazard probability” of all the seven fault systems.

The Hayward also has a great risk probability. There are 3.5 million people living in the Hayward Fault zone, extending out 15 miles.

Every year, there’s approximately a 1 percent chance of a magnitude-7 earthquake or greater occurring along this section of the Hayward Fault. That means a 99 percent chance it won’t.

I’ve heard that small quakes relieve stress, lessening the chance of future major earthquakes? That is wrong. There just aren’t enough small quakes to significantly impact the “strain release,” or to mitigate the possibility of a large earthquake occurring.

The Hayward Fault zone is accumulating what’s called elastic strain energy at the rate of about four-tenths of an inch a year. This is from the collision of the Pacific Plate and the North American Plate. The Farallon Islands are moving northwest about two inches a year. Those two inches are distorting the earth’s crust or creating strain energy. The crust will break where the strain is the weakest, namely the preexisting fault zones.

It’s like pulling a rubber sheet tighter and tighter. As time goes on, you’re storing more and more strained energy.

Earthquakes do release this energy, but only very slightly. The largest, and usually the first quake in a sequence, releases the most energy. Smaller aftershocks release much less as they drop in magnitude. (For every magnitude increase in a quake, the strain energy release goes up by a factor of 32.)

In fact, if a series of small quakes occurs in a stress pocket (asperity) on a fault, it can redistribute the pressure, increasing the chance of a larger quake.

The third-largest earthquake in state history rattled central Oklahoma early Saturday and could be felt as far as Kansas, Missouri and Arkansas.

"We have reports of it being felt very widely, as far south as Plano, Texas, and up into Fort Leavenworth, Kan.," said Paul Caruso, a geophysicist with the U.S. Geological Survey in Golden, Colo.

Heather Spicer of Sapulpa, Okla., told The Oklahoman the quake woke her whole household, including the dog.

"At first I thought an airplane had crashed nearby," Spicer said. "But now I believe it was an earthquake because the whole house just kept vibrating with what sounded like distant thunder outside."

The 4.7 magnitude quake was reported at 2:12 a.m. with an epicenter about six miles north of Prague, Okla., about 50 miles east of Oklahoma City, according to the USGS. The quake was the third-largest in state history, Caruso said, following a temblor that shook Noble, Okla., on Oct. 13, 2010, and a 5.5 quake reported in El Reno, Okla., about 30 miles west of the capital, on April 9, 1952.

The quake was followed by nine aftershocks in the same area, Caruso said.

He said it was difficult to say what caused the quake, but that it originated from rocks moving sideways on a "strike slip" fault similar to the San Andreas Fault. The Oklahoma fault is known as the Wilzetta Fault, also the Seminole uplift, according to the Oklahoma Geological Survey, which reported more than 30 aftershocks associated with Saturday's quake.

No injuries have been reported, but there have been reports of minor damage from items falling off walls, according to staff of the Lincoln County sheriff's office who spoke with The Times.

Oklahoma City police told The Times they have received several 911 calls but no reports of injuries or damage.