Friday, January 6, 2017

Relative Hazard Threat – Where do YOU live?



More questions from an interested, but untitled, scientist. He may not have a college degree in science, but he IS a scientist. 


Q: I've often thought of why people live in high risk areas (say, tornado alley or places increasingly susceptible to climate change and hurricanes). But that's weather. How serious are our risks on the more western side of the country for geologic catastrophe like a massive quake or a volcanic eruption? To minimize my risk, should I just go live in a deep underground science research facility in Antarctica?? Kidding of course, but what kind of odds am I playing with living where i do versus somewhere with dangerous weather? As a geophysicist, I'd have to assume you have considered the smartest locations to live, concerning dangerous geologically active locations (and assuming the zombie apocalypse doesn't kill us first, of course.)
- Joe A.

A: I know something about volcanoes (published scientific papers in the field), and realized I would be safe in the Pacific Northwest if I accepted the job as volcano hazards chief scientist for five years. With the exception of the west side of Mount Rainier, the historical volcano debris footprints are generally localized. The real threat from Rainier is a lahar; one just 500 years ago went all the way to Puget Sound near Tacoma. Think of something like ~1,000,000+ people exposed to a 15+ meter high wall of mud and rock roaring down at 70 kph (45 mph).
     However, moving here got me out of the hyper-competitive and hyper-congested Right Coast. One small tornado, spun off of a hurricane, actually touched down in the forest ~50 meters from my former house in northern Virginia, leaving a 20-meter hole in the forest. However, the true character and history of the Juan de Fuca subduction fault (stretching offshore from Vancouver Island to northern California) was not fully appreciated when we first arrived. My home insurance had a 15% surcharge for earthquake damage in 2002; now the earthquake component is about 40% of the cost.
    When the Big One hits here, the coast really WILL be toast, mainly from tsunami damage. In our inland area there will be massive disruptions, so food and especially water storage are the keys. Most houses and buildings will probably remain occupiable, but the road and pipeline infrastructure will be severely compromised, meaning no water, no power, and empty shelves in grocery stores for weeks. In Bakersfield you can expect occasional earthquakes up to about M=7.5 because the faults are vertical or sub-vertical. Moment magnitude correlates with the surface area ripped (length x depth), and the rock is plastic below about 10-15 km, limiting the depth part of the tear. With a subduction earthquake, however, the thrust fault plane is closer to horizontal. When the Tohoku earthquake hit Japan in 2011, the down-dip part of the fault tear extended something like 200 km. So the rip surface was something like 200 km x 300 km. THAT's why the PacNw and Japan are facing events as high as magnitude M=9. In this area, these monster events average about 240 years between them. The last one was in January 1700 AD. The math isn't good here, folks.
     Bakersfield ain't so bad. If I were you, however, I would store sufficient food and a gallon of water per person for 2 - 4 weeks. It's cheap insurance by comparison. 

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