Liquefaction

Liquefaction

"When sediments liquefy, they lose their structure and strength. During earthquake shaking, the individual grains of sand within a deposit collapse on each other. Anything built on them can sink or collapse. Picture a container of balls of slightly different sizes–baseballs, golfballs, marbles. If they were transported by water into the container and then deposited, they would settle with spaces between them. Some of the spaces would be filled with water, some with air. When you shake the container, the balls settle against each other, and the water and air are forced to the surface. That is exactly what happens in a sediment-filled valley. The valley is a large ‘container’ holding gazillions of ‘balls’ or grains of sand. Shaking the container simulates an earthquake" (Science Views).

Source: Science Views

This video shows how and why houses get damaged or collapse during an earthquake in a seemingly stable geologic environment.
The following observations were made:

• The water works its way to the surface, flooding the area around the houses,
• The "houses" start leaning over and sinking into the sand, and
• The volume of the sand decreases by a small amount.

Another Aftershock for Japan

Areas are still flooded from the tsunami near Sendai, Japan and yet another aftershock it the east coast of Japan, 40 miles from Sendai, knocking out the power in the northern part of the country on Thursday morning.  It was orginally measured to be a magnitude 7.4 but was downgraded by the U.S. Geological Survey in Golden to be a magnitude 7.1 aftershock of the 8.9 earthquake.  It is the strongest aftershock since several were recorded on March 11.  Another two were killed as a result of the aftershock and over a 100 injuries were reported.  A tsunami warning was issued following the quake, but was then taken off and announced that there was no tsunami threat to Hawaii.

The operator of the Fukushima nuclear power plant said there was no sign that any more damage was done.  The plants spent fuel pools lost cooling capacity briefly when the power went down, but resumed shortly after just the way it was supposed to work.  There is no evidence of any radiation to have leaked so far.  It is constantly being monitored right now.  Japan cannot afforded to have more destruction to its nuclear power plant.

I-70 High Maintenance

Close to home, I-70 near Georgetown was closed this last Tuesday due to mitigation of rockfall hazard.  Rock scalers were working for seven hours prying unstable boulders from the rock outcropping 300 feet above the highway near Georgetown.  To loosen the rock, the Colorado Department of Transportation (CDOT) used high-pressure airbags as well as other devices.  The boulders were caught in netting that was strung across the slope of the Georgetown Grade.  Georgetown Grade gets a significant amount of attention because of the heavy traffic volumes on I-70 below and it has an especially high slope that can send rocks down a long distance, building energy and momentum as it goes.

Source:Denver Post

For a short video that shows rocks being scaled click here

Scaling is done periodically to help reduce the risk of rockfall coming onto the highway.  By closing the highway and prying these boulders out, they will no longer be taunting I-70 commuters below.  About 30,000 motorists drive along I-70 at Georgetown Hill every day.  In 2003, a commuter was killed when a boulder crashed into his windshield.

After working on the site, CDOT announced that another rockfall mitigation technique may need to be done in the coming weeks.  Anchoring boulders may be done, if a solid section of the slope can be found.  This would mean another lengthly closure of I-70.

CDOT has placed netting along the slope face.  The goal of these nets is to progressively slow down falling rocks by letting them slip through the netting and roll to the next fence.  The rocks will loose energy this way each time they hit the netting.

The full article can be find here: I-70 reopens near Georgetown; intermittent closures planned Wednesday

China Maps Active Faults

The Chinese government has announced it launched a campaign to map its country's active faults as a result of the strong earthquakes in Japan and Myanmar.

The reason for this being that earthquakes mostly occur on or near active faults.  China has faults that run tens to thousands of kilometers in length.

The CEA Institute of Geophysics has said that China is working on a new seismic map which would mark the different regions by the risk of a quake.  They have said the map will be finished this year.  Based on this new map, the government will have specific requirements for buildings and other facilities across the country.

You may be wondering if Japan was pursuing mapping their active faults within their own country?  Japan has already mapped the seismic risk of different regions. They are considered to be very well prepared for earthquake activity with codes for buildings and other infrastructure already in place.  However, I still find it quite scary that if an earthquake happens at the country's capital of Tokyo, it will hit one of the most densely populated city in the world.

It is encouraging that China is taking action to be better prepared for earthquakes in their country.