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Community => Recreation Commons => Our researchers have made a breakthrough! => Topic started by: Buster's Uncle on August 25, 2014, 01:02:38 am

Title: Strongest Earthquake in 25 Years Hits Northern California
Post by: Buster's Uncle on August 25, 2014, 01:02:38 am

Questions and answers about California earthquake
Associated Press
By TERRY TANG  2 hours ago


(http://l3.yimg.com/bt/api/res/1.2/OMNKJQ9ntGu9_UXusLG3IA--/YXBwaWQ9eW5ld3M7Zmk9ZmlsbDtoPTU2NTtweW9mZj0wO3E9NzU7dz05NjA-/http://media.zenfs.com/en_us/News/ap_webfeeds/9be2f2c83ff8bc215d0f6a70670038dc.jpg)
A boy examines cars trapped beneath a collapsed carport at Charter Oaks apartments in Napa, Calif., following an earthquake Sunday, Aug. 24, 2014. More than fifteen vehicles were trapped or crushed as multiple carports collapsed at the complex during a large earthquake. (AP Photo/Noah Berger)



A magnitude-6.0 earthquake struck the San Francisco Bay Area early Sunday. Scientists say it was the largest earthquake to hit the region in 25 years. The quake struck at 3:20 a.m. about 6 miles from the city of Napa and reportedly lasted between 10 and 20 seconds. Here is a look at some of the basic questions about the science behind the quake that has shaken so many in California.
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Q: What caused Sunday's earthquake?

A: Kate Hutton, a seismologist at the Caltech Seismological Laboratory in Pasadena, California, says all earthquakes in the state are caused by motion between two tectonic plates — the North American plate and the Pacific plate. The plates move horizontally past each other about 2 inches a year. A deformation or strain develops over time in the Earth's crust. "Then something breaks and moves suddenly and that's an earthquake," Hutton said. "If it happens to be a big motion, it's a big earthquake."

Q: Was there any seismic activity in recent weeks that could have set the stage for this earthquake?

A: Most earthquakes happen at random without any precursory seismic activity or what are called "foreshocks." Brad Aagaard, a seismologist at the U.S. Geological Survey in Menlo Park, said there was a small seismic "event" recorded on Aug. 5 near the area of Sunday's quake. But it wasn't any kind of sign. "In the past three weeks, there's been no indication in that immediate area that this was going to happen," Aagaard said. "That's consistent with what happens most of the time."


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Bricks fallen from the upper floor rest atop a car in Napa, Calif., following an earthquake Sunday, Aug. 24, 2014. At left is the historic Napa County Courthouse which sustained major damage. A large earthquake caused significant damage in California's northern Bay Area early Sunday, igniting fires, knocking out power to tens of thousands and sending residents running out of their homes in the darkness. (AP Photo/Noah Berger)


Q: On what fault line did this earthquake occur?

A: A team of seismologists, engineers and other experts go out in the field after a major earthquake to determine the fault line it took place on. The USGS is still trying to figure out where this quake occurred. According to Aagaard, scientists will be looking for cracks at the surface. However, the earthquake appears to be near the West Napa Fault.

Q: How did this earthquake compare to the Loma Prieta earthquake in 1989?

A: The San Francisco Bay Area was shaken by a magnitude-6.9 earthquake on Sept. 17, 1989. A 0.9 difference may sound small on paper, but not on the seismic scale. Hutton, of Caltech, said if Sunday's quake had been one full point bigger, it would have had "30 times more energy." If the quake were a perfect circle, it would be 6 miles in diameter. A magnitude-7 quake would have three times that length, Aagaard said.

Q: How long can we expect aftershocks and how strong will they be?

A: There have already been more than 50 aftershocks since Sunday's earthquake. All have been greater than magnitude 1, with the largest — so far — at 3.6 at 5:45 a.m. Sunday. "We expect they will occur less frequently but they won't necessarily be smaller," Aagaard said. There is a 50 percent chance of a magnitude-5 aftershock happening in the next week, he said.


http://news.yahoo.com/questions-answers-california-earthquake-212327049.html (http://news.yahoo.com/questions-answers-california-earthquake-212327049.html)

Title: Map: How does the Napa earthquake compare to the big one in 1989?
Post by: Buster's Uncle on August 25, 2014, 01:07:50 am

Map: How does the Napa earthquake compare to the big one in 1989?
Vox
Updated by Brad Plumer on August 24, 2014, 7:10 p.m. ET @bradplumer brad@vox.com



The earthquake that rattled Napa Valley and other parts of northern California on Sunday measured 6.0 on the magnitude scale. That was strong enough to damage buildings, injure 87 people, and leave thousands without power.

It was also the biggest quake in the Bay Area since the Loma Prieta earthquake in 1989 that wreaked havoc in Santa Cruz, San Francisco, and Oakland. That one measured 6.9 on the magnitude scale and caused far more destruction — killing 63 people and injuring 3,757.

So how did the two earthquakes compare in terms of actual shaking on the ground? The map below, put together by UC Davis geologist Dawn Sumner, shows the difference. The 1989 earthquake (on the right) had much more violent shaking throughout the region:


The 2014 Napa quake (magnitude 6.0) vs the 1989 Loma Prieta quake (magnitude 6.9)
(http://cdn3.vox-cdn.com/uploads/chorus_asset/file/667464/2014_quake_vs_1989_quake.0.png)
Credit: Dawn Sumner, using data from the California Integrated Seismic Network


It's worth remembering that the scale that geologists use to measure the size of the energy released by an earthquake is logarithmic. That means that a magnitude 6.9 earthquake releases roughly 22 times as much energy as a magnitude 6.0 earthquake.

That said, the amount of ground shaking that actually occurs depends on a variety of additional factors besides magnitude — the depth at which the earthquake takes place, how far away the quake is, the type of rock and soil in the region, as well as how the seismic waves propagate through the Earth's crust.

Further reading:

David Perlman of the San Francisco Chronicle has a good rundown of what geologists know so far about the 2014 Napa earthquake. The quake appears to have occurred along the West Napa Fault, a right-lateral strike slip fault. (Strike slip faults are common in California — in an earthquake, the blocks on either side of the fault slip horizontally past each other.)

By contrast, the 1989 Loma Prieta quake occurred further south — likely on an offshoot of the San Andreas Fault. Here's a rundown from the US Geological Survey of that earthquake, which involved not just horizontal slipping along the fault but also some possible lifting and sinking.

The AP offers a helpful list of major earthquakes throughout California since 1989. And Roger Pielke Jr. of the University of Colorado ranks the most damaging quakes in the United States over the past century (when adjusted for inflation, population growth, etc., the 1906 earthquake in San Francisco tops the list).

Title: Strongest Earthquake in 25 Years Hits Northern California
Post by: Buster's Uncle on August 25, 2014, 01:16:09 am

Strongest Earthquake in 25 Years Hits Northern California
LiveScience.com
By Jeanna Bryner, Managing Editor  3 hours ago


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A 6.0-magnitude earthquake struck on Aug. 24, 2014, near Napa, California, with damage shown here south of Highway 12. Image taken on Aug. 24.



A 6.0-magnitude earthquake struck the Bay area near Napa, California, this morning (Aug. 24), the largest such event in the area since the magnitude-6.9 Loma Prieta earthquake in 1989, according to the U.S. Geological Survey (USGS).

Dozens of injuries and severe damage to homes, buildings and infrastructure have been reported, along with fires and power outages, according to news reports.

The earthquake — called the South Napa earthquake — struck at 3:20 a.m. PT (10:20 UTC), 4 miles (6 kilometers) northwest of American Canyon, California, and 6 miles (9 km) south-southwest of Napa. It occurred along a 44-mile-long (70 km) stretch of major faults of the San Andreas Fault system, where the Pacific and North American tectonic plates grind past each other in what is called a strike-slip movement rather than vertical motion. [Photos: The Great San Francisco Earthquake]

The last big quake in the area, the Loma Prieta earthquake, struck on Oct. 17, 1989, near Loma Prieta peak in the Santa Cruz Mountains, killing 63 people and causing $6 billion in damage.

Today's earthquake ruptured a segment of earth near the West Napa Fault and the Carneros-Franklin Faults, with USGS seismologist David Oppenheimer telling SF Gate that it seems to have occurred along the Browns Valley section of the West Napa Fault. 

The location of the aftershocks suggests the West Napa Fault is the culprit and is something seismologists are looking into at the moment, another seismologist told SF Gate.

The earthquake happened between two major fault systems: the Hayward-Rodgers Creek Fault system, on the west, and the Concord-Green Valley Fault system, on the east. A 1999 report from a panel of scientists had concluded the Hayward fault had a 32-percent chance of producing a large earthquake, of magnitude 6.7 to 7.4, by 2030; the same report suggested a 6-percent chance for such an earthquake being generated by the Concord fault in that same time period.

Gov. Edmund G. Brown Jr. issued a state of emergency for California due to the damage from the earthquake and its aftershocks.

This article will be updated as new information becomes available.


http://news.yahoo.com/strongest-earthquake-25-years-hits-northern-california-202422019.html (http://news.yahoo.com/strongest-earthquake-25-years-hits-northern-california-202422019.html)