With an average of one magnitude 7-8 earthquake occurring per decade, Japan experiences some of the highest rates of seismic activity in the world, around 20% of recorded earthquakes worldwide. As a result, Japan is arguably the world leader in disaster preparedness.
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| Every > 7.4 magnitude earthquake along the Okhotsk/Pacific subduction zone from 1896-2010 which set precedent for earthquake and tsunami warnings across the country's coastlines. |
One of Japan's subduction zones, where the oceanic Pacific Plate dives below the continental Okhotsk plate (I previously named this the North American Plate), earthquakes are concentrated up to 70 km deep, meaning that the many "Megathrust" earthquakes occur and often also create Tsunamis. The 2011 Tohoku Earthquake and subsequent tsunami was one of these occurrences.
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| 2011 Tohoku Earthquake |
This "Megathrust" quake was caused by convergent tension building up for centuries until the Okhotsk plate sprang eastward up to 40m, the largest fault displacement documented in history. This displacement also occurred vertically, where parts of the seafloor rose 7m while slightly closer inland, the seafloor dropped 2m. This instant change caused
the tsunami 20 minutes after the initial earthquake.
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| Elastic tension built up over centuries |
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| Elastic tension released in a matter of minutes |
Unfortunately, Japan's progress in preparing for earthquakes comes from experiencing the damage first hand. TIME reports that, since 1960, the country holds Disaster Prevention Day on September 1st. They have set the example that maintaining awareness of the region's susceptibility to quakes is the first step to reinforcing infrastructure and creating more strict building codes. Japan updated building codes and reevaluated the country's damage prevention in 1981. Following the 1995 Kobe Earthquake, Japan buildings constructed after those codes were enforced swayed like palm trees rather than topple over. Unfortunately, many buildings were still poorly constructed and were built atop artificial land with large amounts of water-saturated sediment. These types of damages forced Japan to look for more ways to prevent and prepare for future earthquakes. These code updates, enacted in 2000, as well as updated warnings to prepared citizens, allowed for 96% of citizens to successfully evacuate the Tohoku earthquake and tsunami. Despite nearly 20,000 dead from the earthquake and tsunami, the damage would have been far worse had Japan laid out cities like the left "before" image below. Though damage from this disaster has been estimated up to $250 billion, without the disaster preparations, the cost would have been exponentially higher.
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No protection, Extremely susceptible to damage
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| Thoughtful disaster city planning. Note elevated construction and protective levees. Though the levees were not nearly high enough to block the 2011 tsunami, they were able to deflect the waves for a few precious minutes allowing some time for evacuations. |
Sources:
1. https://www.iris.edu/hq/inclass/animation/japans_earthquakes__tectonic_setting
- Information and Images - Used the embedded video (I highly recommend watching this in its entirety!!)
2. https://www.npr.org/2011/03/11/134468071/japanese-preparedness-likely-saved-thousands
3. http://content.time.com/time/world/article/0,8599,2058390,00.html
Japan is one country with first hand experience with both earthquakes and Tsunamis, and the damage both of these natural disasters cause. The tsunami that hit Fukushima and the incident at it's Nuclear Plant is something I remember watching on the news with horror and sadness.
ReplyDeleteI wish other countries took precautions as seriously as Japan with it's city planning, taking into consideration layout and architectural design is super important in disaster prevention. I know California tries it's hardest with Earthquake prevention, and a lot of homes in the southern united states try to make their homes able to withstand heavy winds from tornadoes, but citywide planning isn't something we have been able to do due to how old most of our cities actually are, so a major earthquake would be horrible if it ever occurred in something like San Francisco. Lets hope we eventually do invent ways to help with disaster prevention, even in our older more established cities!
- Alex W. - Wales
Great post and images this week-as you say, Japan is definitely ready for these hazards...it reminds me a bit of New Zealand [I just commented that on Tyler's blog]....yes, iris videos and information is great....
ReplyDelete