Oil refineries aflame. Train tracks twisted like string. Buildings ripped from their foundations. Japan’s 8.9-magnitude earthquake has left its mark, especially in the expected death toll of over 1,000 people. This video roundup shows the science behind what happened today in Japan.
Why (Most) Buildings Didn’t Crumble
The death toll is estimated around 1,000, which is bad enough, but it would have been much higher without good engineering, mandated by strict building codes. But these codes haven’t been strict for long. In the 7.3-magnitude Kobe earthquake in 1995, 6,500 Japanese people died, and engineers looked on in horror as many buildings came crashing down; the most deadly ones were built before 1981, when building standards were still lower.
The Kobe tragedy, says The Telegraph‘s Peter Foster, compelled Japanese officials to tighten building regulations for residential offices and transportation infrastructure. Engineers made buildings “earthquake proof” by outfitting them with “deep foundation and massive shock absorbers that dampen seismic energy,” and by enabling the bases of buildings to move “semi-independently to its superstructure, reducing the shaking caused by a quake.” Skyscrapers now sway during an earthquake but don’t collapse, Foster says, and that helps explain why damage to buildings in Tokyo was kept to a minimum this time around. [The Atlantic Wire]
Why Couldn’t Geologists Predict It?
Some people may be asking themselves why geologists couldn’t predict today’s earthquake: Didn’t the smaller shocks earlier in the week give some inkling of Friday’s crusher?
There was no way to predict that Japan’s biggest-recorded earthquake was looming, said Paul Caruso, a geophysicist with the U.S. Geological Survey (USGS) in Golden, Colo. “We have big quakes there all the time,” Caruso told OurAmazingPlanet. For all scientists knew at the time, the 6.3-magnitude quake that struck yesterday was the main shock, Caruso said. “Not every big earthquake has a foreshock but they all have aftershocks.” [Science]
The only thing geologists can do is measure risk—the likelihood that an earthquake will happen—and as far as predicting is concerned, Japan’s earthquake broke the mold:
Japan’s latest national seismic risk map gave a 99% chance of a magnitude-7.5 or greater quake occurring in that area in the next 30 years, Geller says. Although today’s quake technically satisfies that prediction, the logarithmic scale used for measuring the power of earthquakes means that a magnitude-8.9 earthquake releases well over 100 times more energy than does a magnitude-7.5 quake. “I don’t think those hazard assessments are meaningful,” Geller says. [Science]
How the Tsunami Formed
The video footage of water and debris enveloping the Japanese landscape and towns is devastating just to watch:
And it didn’t stop at the town: It plowed right through airports as well.
So how did it come to this? “Generally we don’t get a tsunami unless we have a shallow quake,” Caruso told Live Science, and at 15.2 miles deep, this earthquake was close enough to the surface to disturb the water and generate a wave. Today’s earthquake is technically called a megathrust earthquake, and it formed when the Pacific plate slid under the Japan Trench, pushing the seafloor up, and in turn, pushing the water up as well. To put the energy involved in context, as Ken Hudnut, a USGS geologist in Pasadena, Calif. adds, “The tsunami wave speed in … open ocean, is about the same as a commercial jet’s ground speed.”
One alarming thing is that the story isn’t over: Japan may very well sustain more aftershocks:
The rule of thumb for seismologists is that an earthquake’s largest aftershock will be one magnitude smaller than the main shock, Caruso said. That means a 7.9-magnitude earthquake could hit the region even a year from now. Yet aftershocks are already hitting northern Japan now — 35 larger than magnitude 5.0 and 14 larger than magnitude 6 — according to the UGSS. [Live Science]
DISCOVER: Exactly What Happens to the Ground at a Fault Line?
DISCOVER: Is the West Coast Ready for a Tsunami?
DISCOVER: Waves of Destruction
DISCOVER: The Next Big Quake