Friday, January 13, 2012

Really, Really Big Earthquakes

Perhaps we can get into some of the details of earthquakes by considering the largest one (so far) of this Century:

I have a question. Is it true that the Japan earthquake from this week moved the earth's axis 10 cm, moved Japan 8 feet and sped up the rotation of the earth? 
Laura P.


You are both informed and astute. Northern Japan DID shift roughly westward nearly 3 meters, and the Earth's axis DID shift 10 centimeters. To be fair, the Earth's axis is slowly shifting all the time, but not by this much, nor this fast.

To add another element to your perspective, a magnitude 9 earthquake event means that the crust east of Sendai Japan ripped at least 300 kilometers laterally, and probably at least another 200+ kilometers down-dip --> in the direction of the thrust fault.  In the direction of the northeastern Japanese coastline. While geologists have found bisected mountain ranges crossing the San Andreas Fault that have been shifted ~120 kilometers between what once were contiguous points, that sort of movement doesn't happen overnight - or the Coast WOULD be Toast, to quote a deservedly-maligned and utterly forgettable movie. The San Francisco earthquake of 1906 had a right-lateral tear nearly 6 meters in one place south of the city - but not over such a large distance.

Perhaps more astounding is the fact that by May 2011 there had been over 150 aftershocks (and a few close-in foreshocks) with magnitudes from 5 to 8 associated with the Great Tohoku Earthquake. Keep in mind that a magnitude 7 earthquake releases about 10 times more energy than a magnitude 6 event - the magnitude scale is logarithmic. Nevertheless, there was still a HUGE amount of energy released AFTER this event, now called the greatest crisis in Japan's history since WWII. If all those aftershocks had dumped their energy at the same time, I hesitate to think of how much worse it could have been.  This event was also pretty shallow - aftershocks continued (looking at an earthquake app on my Droid keyed to the USGS database) in a depth-range from 5 km to 60 km deep. The shallower the event, the less crustal dampening occurs. That means more of the "bang" you will actually feel.

The only event I can think of that is comparable in magnitude is the 1960 Chile earthquake... which caused truly cataclysmic damage at the time. It also destroyed downtown Hilo, Hawaii. I've seen Tsunami run-up markers 15 meter above sea-level in what is now a city park; a geologist friend calls it "unplanned urban renewal". That destruction was caused by the tsunami that followed the subduction event far away in Chile. Crustal dampening minimizes the shaking/rolling damage from the earthquake itself, but the tsunami effects will reach hundreds of times farther.

Some people have been questioning why the Fukushima nuclear reactors failed. Any engineer tries to design their creation to survive a certain level of event, but you could never plan for everything. What architect would have realistically anticipated someone flying 767 aircraft into their high-rise buildings? Fundamentally, it comes down to this: you could never afford to build ANYTHING if you planned for EVERYTHING. The death toll in Japan had reached beyond 18,000 people the last time I checked, and whole regions have been evacuated due to the radiation exposure risks.

Most worrisome of all, however, is the fact that the Fukushima Daiichi reactors No. 2, No. 4, and perhaps at least one other may have been so fatally damaged that, even with all the fail-safes built into these things, their cores have gone supercritical: overheated, and melted down through their containment structures.

Remember Chernobyl in 1986?  The heat and pressure of this fatally-compromised old-style reactor blew out upwards - and dusted most of Europe with radioactive iodine and strontium. Epidemiologists estimate that this contributed perhaps ~7,000 additional thyroid cancer deaths in Europe since then. There is a (currently failing) protective concrete structure above (and at enormous risk and expense also below) the Chernobyl reactor. As far as the Russians have told us, the radionuclides never got into the groundwater. A core meltdown at Fukushima, however, is something else: it could melt its way down to the water table and gain access to the sea. Huge steam explosion would be one of the minor consequences.

In volcanology, we call water-touching-magma events Phreatic Explosions - they blast huge tonnages of rock and ash to great altitudes and (under prevailing winds) lateral distances. Of all the dangerous radionuclides in a reactor core, however, plutonium is the most toxic - microgram for microgram, it is more toxic than botulin.  Imagine large quantities of plutonium getting into the coastal waters off NE Japan... a seafood-consuming nation. Think of the food-chain accumulation process. Now think of the downrange consequences of plutonium getting into the Humboldt current and crossing the north Pacific.

It's too late to ask the engineers and planners "what could you possibly have been thinking?" to build a nuclear reactor so close to a major subduction fault. However, Japan didn't have all that much land to build one on in the first place - nor had the Japanese ever experienced an earthquake of this magnitude in all their recorded history. The general rule of thumb for geologists and volcanologists is that history is the key to the future: map the deposits and calculate the explosive force of previous eruptions, and you'll have a good idea of what to plan for in the future.

That doesn't work always, of course. It sure didn't work for Japan.

Nor do I have much patience with the emotional, knee-jerk screamers out there. There are no other energy solutions out there free of "sin" - reasons driving antagonists for coal, tidal energy, solar energy, and especially windmills are legion. I once saw a bumper sticker in Tucson, around the time that a mining company wanted to develop a property, and a lot of environmentalists (for some, that's an alternative religion) fiercely objected.  The bumper sticker said in large block letters "BAN MINING", and in smaller letters below that "Let the Bastards Freeze in the Dark." There are people who object to clear-cutting old-growth forest. I suspect that they ALL live in wooden houses, and I would be willing to bet that they don't bike everywhere they have to go. Bikes are made using mining, metals, and chemical energy, anyway.

I suppose I'm saying that we have to balance all things, and a measured dialog between interested parties will always work out some sort of optimal solution. Note that I didn't say perfect solution.

The coast from Vancouver Island to California has its own mirror image of the Tohoku Subduction Fault.  Cores of Bouma sequences (laminated mud) off the Oregon and Washington coastline tell us that huge M ~ 8 subduction events (that is, earthquakes caused by continental crust riding up and over a down-going slab of denser oceanic crust) have occurred at least 7 times in the past 3,500 years. The last one happened in January of 1700 AD, and sank whole forests near Seattle below sea level in Puget Sound. That event caused something called the "Orphan Tsunami" in Japan - a wave that came out of a clear blue sky without the earthquake warning, ergo, the name. The Japanese already knew to run to high ground if the earth shook. The resulting tsunami obliterated a number of villages on this same northeastern Japanese coastline.

Scientist know that earthquakes on major faults do NOT follow a clock-like regularity, so we could say that we are "due" for a big event in the Pacific Northwest sometime. However, that means it could happen tomorrow or in 2300 AD. We still bought our house on a hill (for the view). We could spend our lives living in fear and trying to find some safe place to build our homes in this country... but there just ain't a place safe from all possible natural disasters. There are other ways to prepare, however, and these we do.

My Dad lived for many years near the top of a 25-story apartment building in San Francisco. As a young geoscientist, I asked him how he could live only 10 kilometers from the San Andreas Fault in such a building? His answer taught me yet another lesson: Jeff, I could worry about that and fan my ulcer problem. Or I could take what precautions are reasonable, and just enjoy this amazing view of the San Francisco Bay every day. He survived the Loma Prieta earthquake of 1989, and admitted to some sleepless nights for months afterwards.

However, my Dad died of lung cancer. A biopsy found asbestos in his lungs, which he traced to the insulation on the pipes in the basement of his building where he stored his bike. When 80 years old he would bike 80 kilometers in a day over the hills of San Francisco, cross the Golden Gate Bridge, and take a ferry back from Sausalito. He was in better shape than I was, 33 years his junior.

So I will continue to savor my view each evening before I go to bed. I will also be contributing money to help my brothers and sisters in Japan, something that I expect they may very well do for me or my children in the future.

We all live on the same planet. We're all part of the same family.


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