Near coastlines, harbors and rivers, earthquakes can make the wet, sandy soil jiggle, turning it temporarily from a solid to a liquid state, a process known as liquefaction. Heavy sand and rock sinks, while water and lighter sand bubble to the surface. The slurry spreads, often toward the water, and the surface shifts. Japan's liquefaction occurred over hundreds of miles, surprising even experienced engineers who are accustomed to seeing disaster sites, including from the recent earthquakes in Chile and New Zealand.
The study raises questions about whether existing building codes in other vulnerable locations can enable structures to withstand massive liquefaction, including in areas of Oregon, Washington and California. "We've seen localized examples of soil liquefaction as extreme as this before, but the distance and extent of damage in Japan were UNUSUALLY SEVERE. Entire structures were tilted and sinking into the sediments, even while they remained intact. The shifts in soil destroyed water, sewer and gas pipelines, crippling the utilities and infrastructure these communities need to function. We saw some places that sank as much as 4 feet," or 1.2 meters.
The duration of the Japanese earthquake, about five minutes, could be the key to the severity of the liquefaction and may force researchers to reconsider the extent of liquefaction damage possible. "With such a long-lasting earthquake, we saw how structures that might have been okay after 30 seconds just continued to sink and tilt as the shaking continued for several more minutes. And it was clear that younger sediments, and especially areas built on recently filled ground, are much more vulnerable."
An event almost exactly like Japan's is expected in the Pacific Northwest from the Cascadia Subduction Zone, and the new findings make it clear that liquefaction will be a critical issue in the young soils there. "Young" sediments, in geologic terms, are those deposited within the past 10,000 years or so. In Oregon, for instance, that describes much of downtown Portland, the Portland International Airport, nearby industrial facilities and other cities and parts of the Willamette Valley.
About 1,100 bridges in Oregon are at risk from an earthquake on the Cascadia Subduction Zone, according to the Oregon Department of Transportation. Fewer than 15 percent of them have been retrofitted to prevent collapse. Some damage may be reduced or prevented by different construction techniques or retrofitting. But another reasonable goal is to at least anticipate the damage - to know what will probably be destroyed, make contingency plans for what will be needed to implement repairs, and design ways to help protect and care for residents until services can be restored, the researchers say.
only dread one day at a time.**
Charlie Brown
LARGEST QUAKES -
This morning -
None 5.0 or higher.
Yesterday -
4/19/11 -
5.4 SOUTHERN MID-ATLANTIC RIDGE
5.1 NEAR EAST COAST OF HONSHU, JAPAN
5.0 GUAM REGION
5.1 XIZANG-QINGHAI BORDER REGION
5.0 FIJI REGION
5.1 EASTERN HONSHU, JAPAN
5.3 OFFSHORE VALPARAISO, CHILE
5.0 OFF EAST COAST OF HONSHU, JAPAN
5.4 SOUTH SANDWICH ISLANDS REGION
5.0 OFFSHORE VALPARAISO, CHILE
CALIFORNIA - Power temporarily knocked out after Pacifica quake. An earthquake rattled the San Francisco Bay area Monday afternoon on the 105th anniversary of the Great 1906 Earthquake. The quake, with a magnitude of 3.7, hit about two miles southeast of Pacifica, or about 12 miles south of San Francisco at 2:57 p.m. Monday. No structures were damaged and nobody was hurt. Electrical service to about 10,000 homes and businesses in Pacifica was knocked out around 3 p.m., but was restored a little before 4:30 p.m. Though the outage occurred at nearly the same time as the quake, its cause is still under investigation.
Dozens gathered in San Francisco early Monday morning to commemorate the 1906 quake and ensuing fire, which killed thousands and destroyed much of the city. There are only three known survivors left of that devastating quake, and only one of them - who was just a few months old at the time - was able to make this year's ceremony. The event included a moment of silence for the victims of Japan's earthquake and tsunami, and organizers collected American Red Cross donations for the relief effort. Historians say Japan stepped forward in 1906 to help San Francisco's victims and gave $250,000 - the most of any other country - toward the city's recovery.
VOLCANOES -
Earthquakes may spur eruptions - ABNORMAL volcanic activities and earthquakes observed this week have nothing to do with each other, the Philippine Institute of Volcanology and Seismology said yesterday, although it did not discount a very remote connection between the two events. "Volcanic activity in recent years has always been abnormal in Mayon and Taal. And Bulusan has been exploding, albeit mildly, from time to time. Earthquakes are not strong enough to cause volcanic eruptions," but they can facilitate the early eruption of a volcano.
The magnitude 7.8 quake that hit Luzon on July 16, 1990, preceded almost by a year the June 15, 2000, eruption of Mt. Pinatubo. "What happened was that the earthquake shook the volcano and facilitated the eruption. Because of the changes in the stress in Mt. Pinatubo, magma moved up faster and earlier, shaking the magma in Mt. Pinatubo fast enough for it to erupt earlier. It’s like a bottle of soda, you shake it and it pops. Soda has gas which separates from the liquid; magma also has gas." But they said there is no connection between earthquakes observed nationwide and the Alert Level 2, meaning an eruption is possible, raised over Taal in recent weeks.
While doomsayers, especially in the Internet, link earthquakes and volcanic eruptions among the natural disasters that will lead to the end of the world in 2012, volcanologists disagree. Earthquakes are not unusual considering the country lies between two of the world’s most active tectonic plates: the Philippine Trench on the east in the Pacific and, on the west, the Manila Trench in the South China Sea that continues to the Negros-Sulu trenches between Palawan and Western Visayas and western Mindanao.
Phivolcs said six volcanic earthquakes were recorded in Taal volcano during the past 24 hours, five volcanic tremors around Mayon Volcano and six volcanic earthquakes at Bulusan, Mayon’s neighboring volcano last Monday. Phivolcs said magma rising towards the surface in Taal is a sign of impending eruption, causing it to raise the alert level to 2. Other warning signs are increased volcanic quakes, especially 1 to 4 kilometers near the surface; rumbling sound; steaming from crater vents; significant increase in the carbon dioxide content of gas coming from the main crater lake, indicating it’s from magma; and ground deformation, also indicating magma movement below.
TROPICAL STORMS -
No current tropical storms.
EXTREME HEAT & DROUGHT / WILDFIRES / CLIMATE CHANGE -
TEXAS - Wildfires continue to rage across Texas. Firefighters continued to battle rampant wildfires that have burned 1.4 million acres, destroyed hundreds of homes and prompted the evacuation of communities across the state. The state's WORST DROUGHT IN NEARLY A CENTURY, UNUSUALLY HIGH temperatures and strong winds have fueled more than 20 uncontained fires, spreading firefighting resources thin. "We're seeing it from border to border. They're spanning the entire state right now."
Since January, 797 wildfires have broken out across Texas, destroying 285 structures. This week, four smaller fires converged into what is known as the PK Complex Fire. It grew significantly overnight and had charred more than 147,000 acres in Stephens and Pinto counties near Possum Kingdom Lake, about 100 miles west of Fort Worth, by Tuesday. Strawn, Bunger and other communities in the area were evacuated. The blaze destroyed at least 31 homes and threatened more than 600.
Firefighters north of San Angelo continued to struggle with a 150,000-acre blaze, known as the Wildcat Fire, which remained at 10% containment Tuesday. Firefighters were able to save 400 homes near the fire. On Saturday, Texas's governor requested federal emergency assistance, saying all but two of the state's 254 counties had been threatened or affected by the fires. Weather forecasts for Wednesday say there will be a break in the high winds that have whipped up flames, and possible showers. But critical fire conditions are expected to return in the following days. "We're looking at it as a marathon, not a sprint."
