(Survival Manual/1. Disaster/Earthquake)
What Does the Richter Scale Really Mean?
Earthquakes are measured using the Richter Scale. Here’s a breakdown of what the numbers really
Less than 2.0: Micro: Micro earthquakes, not felt. About 8,000 per day.
2.0-2.9: Very minor: Generally not felt, but recorded. About 1,000 per day.
3.0-3.9: Minor: Often felt, but rarely causes damage. 49,000 per year (est.).
4.0-4.9: Light: Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9: Moderate: Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings, 800 per year.
6.0-6.9: Strong: Can be destructive in areas up to about 100 miles across in populated areas. 120 per year.
7.0-7.9: Major: Can cause serious damage over larger areas. 18 per year.
8.0-8.9: Great: Can cause serious damage in areas several hundred miles across. 1 per year.
9.0 or greater: Rare, Very Great: Devastating in areas several thousand miles across. 1 per 20 years.
12.0: Would be strong enough to split the earth in half.
1. California overdue for major quake, study says
Scientists say tremblors along San Andreas Fault happening more often previously thought.
21 Aug 2010, Our Amazing Planet
“Earthquakes strike along California’s San Andreas Fault more often than scientists previously thought, a new study suggests.
Researchers at the University of California, Irvine and Arizona State charted tremblors that occurred there stretching back 700 years. They found that large ruptures have occurred on the Carrizo Plain portion of the San Andreas Fault — about 100 miles northwest of Los Angeles — as often as every 45 to 144 years. But the last big quake was in 1857, more than 150 years ago.
The researchers said that while it’s possible the fault is experiencing a natural lull, they think it’s more likely a major quake could happen soon. “If you’re waiting for somebody to tell you when we’re close to the next San Andreas earthquake, just look at the data,” said UCI seismologist and study leader
Lisa Grant Ludwig. “What we know is for the last 700 years, earthquakes on the southern San Andreas fault have been much more frequent than everyone thought,” Akciz said…
For individuals, that means having ample water and other supplies on hand, safeguarding possessions
in advance, and establishing family emergency plans. For regulators, Ludwig advocates new policies requiring earthquake risk signs on unsafe buildings and forcing inspectors in home-sale transactions to disclose degrees of risk.”
2. Comparable earthquakes in the New Madrid
The New Madrid Fault System spans a 120-mile stretch from Charleston, Missouri and Cairo, Illinois,
down Interstate 55 to end up in Marked Tree, Arkansas. The massive zone crosses five state lines and cuts across the Mississippi River in three places and the Ohio River in two.
It’s true that the greatest risk of earthquakes in the United States is definitely along the West Coast but, although the tremors may not be as frequent, when they do occur along the New Madrid Fault Line, the damage covers more than 20 times the area.
How about another event like the series of quakes felt in 1811-1812?
Researchers predict that these types of events occur only once every 500-600 years, which means they don’t expect another for 100 years or more. However, experts including emergency planners, engineers and seismologists have given the event a 3 percent chance of occurring by the year 2040.
According to the U.S. Geological Survey (USGS) and the Center for Earthquake Research and
Information of the University of Memphis, it’s estimated that in the next 50 years along the New Madrid Fault Zone:
- There’s a 7 percent to 10 percent chance of a magnitude 7.5-8.0 earthquake occurring in this region.
- There’s a 25 percent to 40 percent chance of a magnitude 6.0 or larger earthquake occurring.
The EMD has given it an even greater chance, saying there’s a 90 percent chance that a 6.0 earthquake will be felt in this region by the year 2040. They say it’s events of this size (6.0-7.6) that concern them the most, since they are the ones most likely to occur within the lifetimes of our children, and have
the potential to cause great damage.
If an Earthquake Hits the Midwest … Are They Prepared?
According to an investigation by the St. Louis Post-Dispatch, “Repeated recommendations from all levels of government in an eight-state region of the central United States have been largely ignored on how to best brace for an event that scientists expect will kill thousands and cause widespread chaos.”
“We are entirely unprepared,” said Amr Elnashai, who runs the Mid-America Earthquake Center at the University of Illinois. “It is really amazing –really amazing. How can a country as rich and prosperous as the U.S. leave itself in peril this way?”
The Post-Dispatch investigation, in a review of studies and reports and interviews with more than 150 government officials, researchers and preparedness advocates, found:
- Many government agencies haven’t estimated what kind of damage a major earthquake
will cause to their emergency facilities, which could cripple response efforts.
- No plan is in place to renovate older schools to more up-to-date, stricter building codes or even to use low-cost fixes to strengthen them.
- Utilities are not required to report on hazardous material spills and other problems that could occur during an earthquake, nor their plans to remedy them.
- Key bridges are vulnerable to earthquake damage, and some states have no programs in place to fix them.
- Over 80 percent of counties across the region are late to file required plans on how they will prepare for earthquakes and other natural disasters.
- Some communities haven’t held earthquake drills in more than a decade.
3. The Cascadia Subduction Zone (with earthquake & tsunami and/ or volcano)
The biggest earthquakes in the country are not in California. A much greater hazard, at least in terms of sheer magnitude, exists to the north of the San Andreas Fault where the ocean crust is being forced beneath the North American continent.
Known as the Cascadia Subduction Zone, this 680-mile long stretch of colliding land mass 50 miles offshore of Oregon, Washington state and southern British Columbia is capable of generating magnitude 9 earthquakes 30 times more powerful than the worst the San Andreas can dish out.
“There are lots of other earthquakes that may happen first, but they won’t be as big,” said marine geologist Chris Goldfinger of Oregon State University in Corvallis.
In less than 50 years, a number of great Cascadia-like earthquakes have occurred around the Pacific Rim, including Chile (1960), Alaska, (1964), Mexico (1985) and Japan (2011). A unique aspect of a great Cascadia earthquake is the strong likelihood that the three greater metropolitan areas of Portland, Seattle, and Vancouver will simultaneously feel the effects of strong and sustained ground shaking. This wide-spread earthquake, combined with accompanying elevation changes, and the likely generation of a tsunami along the Pacific coast, will cause loss of life, property damage, and business
interruption in vulnerable locations throughout southwestern British Columbia, Washington, Oregon, and northwestern California. The broad geographic distribution of damaging impacts will generate special challenges and severely stress the response and recovery resources of the three Pacific states and British Columbia.
An earthquake of this size would completely devastate the region, which includes Portland, Seattle and Vancouver. There could be thousands of deaths and unprecedented damage for a quake in this country. Major travel routes will be impassable. The shaking could last a full four minutes, which would damage or bring down structures that could have survived a shorter duration.
On top of the danger from shaking, within minutes, a tsunami would likely inundate the low-lying coastal areas. Cascadia is the same type of fault that caused the 2004 Sumatra quake and tsunami.
Fortunately, these mega quakes only come around once every few hundred years. Unfortunately, the fault may be due for another big one any day now.
The last monster quake that ruptured the entire length of the Cascadia fault occurred in 1700 and was around a magnitude 9. It created a tsunami that crossed the entire Pacific Ocean and caused damage along parts of the Japanese coast.
Recent findings concluded the Cascadia subduction zone is more hazardous than previously suggested.
It was previously calculated that the average time between these major quakes was around 530 years. But Goldfinger’s recent research on marine landslides caused by earthquakes over the last 12,000
years has revealed many magnitude 8 earthquakes on the southern portion of the fault in the intervening years, bringing the average down to 270 years.
“It’s been 308 years since the last one so the probability is much higher,” Goldfinger said. The feared next major earthquake has some geologists predicting a 10% to 14% probability that the Cascadia Subduction Zone will produce an event of magnitude 9 or higher in the next 50 years, however the most recent studies suggest that this risk could be as high as 37% for earthquakes of magnitude 8 or higher. Geologists have also determined the Pacific Northwest is not prepared for such a colossal
earthquake. In 1700 the subduction zone spawned an earthquake of roughly the same size as the Sendai event, unleashing a tsunami that may have reached 100 feet high (30 meters). “Portland has a lot of unreinforced masonry buildings that are likely to collapse in a major quake”, Goldfinger said.
“The retrofitting has barely begun. It’s going to be a mess.”
A subduction fault is deep and in this case, 680 miles long, it can release a lot more energy than a slip fault like the San Andreas Fault in California. “One of the signatures of a subduction fault,” says Mike
Blanpied, associate director of the US Geological Survey’s Earthquake Hazards Program, “is that they sit quietly– until they create a giant quake.” And by giant, he means a monster. The Sendai event contained more than 30 times the energy of the San Francisco Earthquake of 1906.
The Cascadia Subduction zone is the only subduction zone within the Lower 48 states and it lies off the coast of Oregon and Washington. Today, the Northwest seems seismically calm, but in reality the
fault could let go again at any moment.
To figure out what would happen if a Sendai-scale event struck today, a consortium called the Cascadia Region Earthquake Workgroup (CREW) drew up a detailed scenario of how the quake and its ensuing
tsunami would affect buildings, transportation, utilities, and emergency services. The report, entitled, Cascadia subduction zone earthquakes: A magnitude 9.0 earthquake scenario, painted a picture so grim that it read like a horror story. It was pretty hard to believe—until the Sendai quake brought all its horror vividly to life. It can happen.
When it does, it may well run something like this:
Somewhere, a dog starts barking. A hanging lamp begins to sway. The next thing you know, you’re in mid-air and your living room furniture is sliding across the room. You hit the ground and scramble underneath a coffee table as a cabinet tumbles, spilling broken china and shards of glass. The refrigerator topples over and the stove shuffles across the kitchen floor. Across town, bridges and high-rise buildings shudder, buckle, and collapse. The power goes out, and fires break out all across the city. Two minutes later, when the shaking stops, hundreds of buildings have collapsed and thousands are dead.
But the disaster isn’t over. Outside your window, the ocean is draining away from the beach. For a moment a strange silence hangs over the exposed seabed. Then, with a roar, the sea comes galloping in, a wall of frothy whitewater that surges over seaside towns, sweeping away roads and bridges and drowning thousands more. Landslides bury houses and sever mountain roads. In the aftermath, more lives wink out, as victims trapped beneath rubble suffocate or succumb to their injuries. With roads cut and power out, rescue services are all but helpless. Many victims in the quake zone could go days without help from the outside world.
If its imagined scenes of devastation sound a lot like what happened in reality in Japan, that’s no coincidence. Both catastrophes result from the same time of fault rupturing with the same intensity. They have one well-known precedent in the United States. On Good Friday, 1964, Alaska was hit by an epic five-minute-long quake that registered 9.2, making it the most massive ever recorded in North America. On Kodiak Island, land was raised up 30 feet. Elsewhere, whole villages were destroyed as the ground beneath liquefied and sank. Anchorage suffered devastating landslides, and 30 city blocks were
damaged or destroyed.
The magnitude of a quake alone tells you little about its effect on a population. The suffering that results is really a function of two things: the intensity of the shaking and the quality of the preparations
that have been made. Japan is by far most earthquake-savvy country on the planet. It lavishes millions on research, its building codes are tough, and its people are psychologically ready. Yet despite Japan’s preparations the 9.0 earthquake wreaked havoc on a scale not seen since World War II.
Americans, on the other hand, spend little time thinking about earthquakes, and even less money. We’re just starting to explore technologies that the Japanese have been implementing for decades. One step toward protecting the public, for instance, would be to establish an Earthquake Early Warning (EEW) system. The idea is to detect tremors as a fault begins to slip, and then transmit an alarm signal to population centers on the periphery of the quake zone.
Since motion of the quake travels at the speed of sound, and the signal can travel near the speed of light, an efficient system could provide a minute or two of warning—enough time to stop elevators and let passengers off, or for a teacher to shepherd her students under their desks.
Pressure building along the Cascadian subduction zone could be released either as an earthquake, as a volcanic eruption, or both. (see: survival manual/disaster/volcanic winter)
4. Cascade Volcanic Arc
The Cascade Volcanic Arc is a continental volcanic arc that extends from northern California to the coastal mountains of British Columbia, a distance of well over 700 mi (1,100 km). The arc consists of a series of stratovolcanoes.
Subduction-zone stratovolcanoes, like Mount St. Helen’s and Mount Pinatubo, typically erupt with explosive force: the magma is too stiff to allow easy escape of volcanic gases. As a consequence the tremendous internal pressures of the trapped volcanic gases remain in the pasty magma. Following the breaching of the magma chamber, the magma degasses explosively. Such an explosive process can be likened to shaking a bottle of carbonated water vigorously, and then quickly removing the cap. The shaking action nucleates the dissolution of CO2 from the liquid as bubbles, increasing the internal volume. The gases and water gush out with speed and force.
The Cascade Volcanic arc is located approximately 100 km inland from the coast, and forms a north-to-south chain of peaks that average over 3,000 m (10,000 ft) in elevation. The major peaks from south to north include:
- Lassen Peak and Mt. Shasta (California)
- Crater Lake (Mazama), Three Sisters, Mt. Jefferson, Mt. Hood (Oregon)
- Mt. Adams, Mt. St. Helens, Mt. Rainier, Glacier Peak, Mt. Baker (Washington)
- Mt. Garibaldi and Mt. Meager (British Columbia)
The arc has formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper.
Some of the major cities along the length of the arc include Portland, Seattle, and Vancouver, and the population in the region exceeds 10,000,000. All could be potentially affected by volcanic activity and
great subduction-zone earthquakes along the arc. Because the population of the Pacific Northwest is rapidly increasing, the Cascade volcanoes are some of the most dangerous, due to their past eruptive history, potential eruptions and because they are underlain by weak, hydrothermally altered volcanic rocks that are susceptible to failure. Many large, long-runout landslides originating on Cascade volcanoes have inundated valleys tens of kilometers from their sources, and some of the inundated areas now support large populations.
 Note: The highest tsunami on record was caused by a landslide in Lituya Bay in Alaska in 1958. The landslide itself was triggered by an earthquake, but the tsunami was caused by the earth that slid off a mountain and fell into the bay.” The resulting wave of displaced water was 1720 feet high (1/3 mile)- depending on how you measured it.
The 1720 feet was actually how high it ran [splashed] up on the mountain on the other side of the bay. The wall of water itself, as it crossed the bay, was anywhere from 150 to 500 feet high. No one knows for sure. We have eyewitness accounts from two of the three fishing boats that were in the bay at the time.”
Pasted from http://www.backwoodshome.com/articles2/silveira94.html
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