On Friday afternoon in Japan, disaster struck as a massive 8.9 magnitude earthquake generated a wall of water that surged over the east coast of the island nation, sweeping many to their deaths.
- Here’s what you need to know about the quake and its aftermath:
* Where did the earthquake come from?
Japan is situated along the world’s most active earthquake belt, the Pacific Ring of Fire, where rigid plates in the Earth’s crust collide along the rim of the Pacific Ocean. This earthquake originated 231 miles (373 kilometers) northeast of Tokyo and 80 miles (130 km) east of Sendai, Honshu in the Pacific Ocean.
The earthquake occurred at a depth of about 15.2 miles (24.4 kilometers).In this area, the Pacific Plate, the plate beneath the Pacific Ocean, is moving almost due west and being pushed down into the Earth’s interior along a trench off Japan’s east coast. On average, the Pacific Plate is moving at 3.5 inches (8.9 centimeters) per year, but this process is not continuous, according to Keith Sverdrup, a professor of geophysics .
The process of one plate being pushed beneath another is called subduction, and it occurs all along the Ring of Fire, producing other earthquakes,
* How does this earthquake rank in global records?
While the magnitude estimate of this latest earthquake may later be revised, 8.9 is the largest Japanese quake on record and the fifth-largest quake worldwide since 1900, according to the U.S. Geological Survey (USGS).
*How did the earthquake generate a tsunami?
The earthquake caused the seafloor at the fault to suddenly shift vertically and this motion, in turn, shifted the water column above it. This motion then spawned a series of massive waves known as a tsunami. .
The waves simultaneously spread toward the east coast of Japan and toward the west, on a much longer path to the west coast of North America.The highest of the waves are believed to have reached 30 feet (9.1 meters).
*How well can we predict events like this?
“Earthquake prediction is something we haven’t really been able to master yet,” “With earthquakes, the best we can say is these are areas where earthquakes are likely to occur and this is our best estimate of the statistical probability of an earthquake of a certain size happening within a certain period of time.”
Once an earthquake like this one has occurred, it’s possible to assess whether or not it will generate a tsunami by determining whether a vertical shift occurred at the fault and by looking at measurements of water height recorded around the Pacific Ocean basin by the Tsunami Warning Network.
In Japan, the tsunami warning went out about five minutes after the earthquake and included an estimated height for the waves, .
* Why do some earthquakes cause tsunamis while others don’t?
A few factors come into play: the strength of the quake, the direction of the temblor’s motion and the topography of the seafloor.
First, the magnitude of the quake — which is a measure of the amplitude of the largest seismic wave recorded for the earthquake — must exceed a certain threshold. The 8.9-magnitude of Japan’s earthquake was enough to trigger a tsunami, but the magnitude-7.7 earthquake that struck Indonesia in October 2010 just surpassed the threshold for causing a tsunami.
“Earthquakes below 7.5 or 7.0 usually do not trigger tsunamis,” said geophysicist Don Blakeman of the U.S. Geological Survey’s National Earthquake Information Center.
Earthquakes trigger tsunamis when the seismic activity causes the land along fault lines to move up or down. When parts of the seafloor shift vertically, either becoming raised or lowered, entire water columns become displaced. This creates a “wave” of energy, which propels the water .
The height of a tsunami wave is influenced by the ground’s vertical movement, so changes in the seafloor’s topography can either amplify or dampen a wave as it travels along.
*Why is there a danger of radiation leaks at two Japanese nuclear reactors?
The cooling systems have failed at the two facilities as a result of power loss in the region. Even though the reactors have been shut down, a small, base level of nuclear decay is still happening, and that means a small amount of residual heat is still coming off the nuclear fuel rods.
Under normal conditions, the cooling systems use water to surround the nuclear fuel rods and dissipate that heat, but power loss means the plants aren’t able to pump water around the rods. If the fuel rods get exposed, they could melt, and in that case their containers may not be able to contain the radiation emitted from them. Dangerous leaks could occur.
* Aftershock alert
The Japanese earthquake ruptured near the boundary between the Pacific and North American tectonic plates — huge, moving slabs of the Earth’s crust.
The quake was a megathrust earthquake, where the Pacific plate dove underneath Japan at the Japan Trench. The seafloor was pushed away from Japan sending waves roaring toward Hawaii and the West Coast of the United States.
* What about the tsunamis now moving east?
They travel at the speed of a jet airliner and propagate at low amplitude deep in the ocean. As they approach land, the tsunami slows down but the amplitude increases, generating waves with huge energy. So you still get large waves several metres high many hours after the original quake. They can still cause extreme amounts of damage many kilometres away.
* Was Japan ready?
Japan is a country with a long history of earthquakes, but this one is unprecedented in Japanese history. The previous largest was Great Kanto in 1923, south of Tokyo, which resulted in 140,000 deaths, and that was 7.9 magnitude. That puts this latest one in perspective. It’s easily the largest Japan has ever experienced.
Japan has well-regulated building codes, and large buildings are constructed not to collapse. Also, people are well prepared both for quakes and tsunamis, with regular evacuation drills. All those will have saved life this time.
* How Japan’s Earthquake and Tsunami Warning Systems Work ?
The earthquake warning system, which has never been triggered before, automatically issued alerts via television and cell phones shortly after the first, less harmful, shock wave was detected, providing time for many people to prepare for the more powerful shock wave that followed. It also caused many energy and industrial facilities, and transportation services to shut down automatically. A string of detection buoys in the Pacific Ocean detected the tsunami that resulted from the earthquake, sending warnings of possible catastrophe to many different nations.
** Here are some good resources that will help you learn more about both warning systems.
** If you have any reletive or friend in Japan check this link to get information about them & please reshare this link
(Google Person Finder: 2011 Japan Earthquake)