Strong quake hits Alaska islands
Agence France-Presse
First Posted 12:31:00 05/02/2008
WASHINGTON -- A strong 6.6-magnitude (USGS) or 7.0-magnituede (EMSC) earthquake struck Thursday near the Aleutian Islands in southwestern Alaska, the US Geological Survey reported.
The quake's epicenter was located at a depth of 10 kilometers (6.2 miles), 65 kilometers (40 miles) west of Adak, Alaska, the westernmost municipality in the United States with a population of some 300 people.
The earthquake occurred at 0133 GMT in the Andreanof Islands, one section of the earthquake-prone volcanic island chain, the survey said.
The reading was based on the open-ended moment magnitude scale, now used by US seismologists, which measures the area of the fault that ruptured and the total energy released.
A measurement of five indicates
a moderate earthquake, six or higher a strong quake, seven a major quake and
eight a great quake
Reno
Urged To Prepare For Worse As Earthquakes Continue
By Martin Griffith , Associated Press Published on 4/27/2008
Reno, Nev. - Scientists urged residents of northern Nevada's largest city to prepare for a bigger event as the area continued rumbling Saturday after the largest earthquake in a two-month-long series of temblors.
More than 100 aftershocks were recorded on the western edge of the city after a magnitude 4.7 quake hit Friday night, the strongest quake around Reno since one measuring 5.2 in 1953, said researchers at the seismological laboratory at the University of Nevada, Reno.
The latest quake swept store shelves clean, cracked walls in homes and dislodged rocks on hillsides, but there were no reports of injuries or widespread major damage.
Seismologists said the recent activity is unusual because the quakes started out small and continue to build in strength. The normal pattern is for a main quake followed by smaller aftershocks.
”A magnitude 6 quake wouldn't be a scientific surprise,” John Anderson, director of the seismological lab, said Saturday.“We certainly hope residents are taking the threat seriously after last night.”
But Anderson stressed there was no way to predict what would happen, and said the sequence of quakes also could end without a major one.
Reno's last major quake measured 6.1 on April 24, 1914, and was felt as far away as Berkeley, Calif., said Craig dePolo, research geologist with the Nevada Bureau of Mines and Geology.
A rockslide triggered by Friday night's quake was blamed for causing a 125-foot breach in a wooden flume that carries water to one of two water treatment plants in Reno, a city of about 210,000.
A backup pump was used to divert water to the plant, and the breach was not expected to cause any water shortages, said Aaron Kenneston, Washoe County emergency management officer.
The U.S. Geological Survey said Friday night's quake was centered around Mogul, just west of Reno. The area of upscale homes along the eastern Sierra was rattled by more than 100 quakes the day before, the strongest a magnitude 4.2 that caused high-rise casinos to sway in downtown Reno.
The strongest aftershock measured 3.7 and was recorded early Saturday.
Mike Lentini of Reno said Friday night's quake felt“like a big truck hit the building” and awakened his family.
”It's the unknown. It's shaking, and when's it going to stop?” he said Saturday.“And when stuff starts falling off the shelves it's a whole other ballgame.”
Jars of mayonnaise and bottles of ketchup and shampoo fell from shelves at a Wal-Mart store in northwest Reno. Overhead televisions swayed at a sports bar in neighboring Sparks, 11 miles east, where bartender Shawn Jones said the rumble was significantly stronger than Thursday's event.
”The bottles were shaking, so I sent everybody outside,” he said.
Hundreds of mostly minor quakes have occurred along one or possibly more faults since the sequence began Feb. 28, said Ken Smith, a seismologist at the Reno laboratory. The quakes have occurred along an area about 2 miles long and a half-mile wide.
”We can't put a number on it, but the probability of a major earthquake has increased with this sequence,” Smith said Saturday.“People need to prepare for ground shaking because there's no way to say how this will play out.”
Among other things, scientists urged residents to stock up on water and food, to learn how to turn off water and gas, and to strap down bookshelves, televisions and computers.
”It's getting a little bit frightening,” Daryl DiBitonto of Reno told the Reno Gazette-Journal.“I'm very concerned about this increase in not only activity, but also in magnitude.”
The quakes around Reno began a week after a magnitude 6 temblor in the northern Nevada town of Wells, near the Utah border. The Feb. 21 quake caused an estimated $778,000 in damage to homes, schools and historic downtown buildings, dePolo said.
Scientists said they're unsure whether the seismic activity at opposite sides of Nevada is related.
Nevada is the third most seismically active state in the U.S. behind California and Alaska. The Wells quake was the 15th of at least magnitude 6 in the state's 143-year history.
A magnitude-7.4 quake south of Winnemucca in 1915 is the most powerful in state history.
Associated Press writer Scott Sonner contributed to this report.
Recent Earthquakes in California and Nevada
California
Has More Than 99% Chance Of A Big Earthquake
WIthin 30 Years,
Report
Shows
ScienceDaily (Apr. 15, 2008) — California has more than a 99% chance of
having a magnitude 6.7 or larger earthquake within the next 30 years, according
scientists using a new model to determine the probability of big quakes.
The likelihood of a major quake of magnitude 7.5 or greater in the next 30 years is 46%-and such a quake is most likely to occur in the southern half of the state.
The new study determined the probabilities that different parts of California will experience earthquake ruptures of various magnitudes. The new statewide probabilities are the result of a model that comprehensively combines information from seismology, earthquake geology, and geodesy (measuring precise locations on the Earth's surface). For the first time, probabilities for California having a large earthquake in the next 30 years can be forecast statewide.
"This new, comprehensive forecast advances our understanding of earthquakes and pulls together existing research with new techniques and data," explained USGS geophysicist and lead scientist Ned Field. "Planners, decision makers and California residents can use this information to improve public safety and mitigate damage before the next destructive earthquake occurs."
The new information is being provided to decision makers who establish local building codes, earthquake insurance rates, and emergency planning and will assist in more accurate planning for inevitable future large earthquakes.
The official earthquake forecasts, known as the "Uniform California Earthquake Rupture Forecast (UCERF)," were developed by a multidisciplinary group of scientists and engineers, known as the Working Group on California Earthquake Probabilities. Building on previous studies, the Working Group updated and developed the first-ever statewide, comprehensive model of California.
The organizations sponsoring the Working Group include the U.S. Geological Survey, the California Geological Survey and the Southern California Earthquake Center. An independent scientific review panel, as well as the California and National Earthquake Prediction Evaluation Councils, have evaluated the new UCERF study.
The consensus of the scientific community on forecasting California earthquakes allows for meaningful comparisons of earthquake probabilities in Los Angeles and the San Francisco Bay Area, as well as comparisons among several large faults.
The probability of a magnitude 6.7 or larger earthquake over the next 30 years striking the greater Los Angeles area is 67%, and in the San Francisco Bay Area it is 63%, similar to previous Bay Area estimates. For the entire California region, the fault with the highest probability of generating at least one magnitude 6.7 quake or larger is the southern San Andreas (59% in the next 30 years).
For northern California, the most likely source of such earthquakes is the Hayward-Rodgers Creek Fault (31% in the next 30 years). Such quakes can be deadly, as shown by the 1989 magnitude 6.9 Loma Prieta and the 1994 magnitude 6.7 Northridge earthquakes.
Earthquake probabilities for many parts of the state are similar to those in previous studies, but the new probabilities calculated for the Elsinore and San Jacinto Faults in southern California are about half those previously determined. For the far northwestern part of the State, a major source of earthquakes is the offshore 750-mile-long Cascadia Subduction Zone, the southern part of which extends about 150 miles into California. For the next 30 years there is a 10% probability of a magnitude 8 to 9 quake somewhere along that zone. Such quakes occur about once every 500 years on average.
The new model does not estimate the likelihood of shaking (seismic hazard) that would be caused by quakes. Even areas in the state with a low probability of fault rupture could experience shaking and damage from distant, powerful quakes. The U.S. Geological Survey (USGS) is incorporating the UCERF into its official estimate of California's seismic hazard, which in turn will be used to update building codes. Other subsequent studies will add information on the vulnerability of manmade structures to estimate expected losses, which is called "seismic risk." In these ways, the UCERF will help to increase public safety and community resilience to earthquake hazards.
The results of the UCERF study serve as a reminder that all Californians live in earthquake country and should be prepared. Although earthquakes cannot be prevented, the damage they do can be greatly reduced through prudent planning and preparedness. The ongoing work of the Southern California Earthquake Center, USGS, California Geological Survey, and other scientists in evaluating earthquake probabilities is part of the National Earthquake Hazard Reduction Program's efforts to safeguard lives and property from the future quakes that are certain to strike in California and elsewhere in the United States.
Adapted from materials
provided by U.S. Geological Survey
24-Hour Aftershock Forecast Map
The Next Great California Earthquake
Why Where And When It Will Happen by George Pararas-Carayannis, Ph.D.
Uniform California Earthquake Rupture Forecast (UCERF)