Friday, October 30, 2015

The Coast is Toast...

When I was a child the White Wolf Fault, a splay-fault of the great San Andreas, ruptured about 60 km (40 miles) from my home. I recall hearing a bang, then hearing the windows rattling hard - and finally breaking. Shortly afterwards, I was thrown out of bed onto the floor. I didn't fall out of bed, I was thrown from my bed to the middle of my bedroom floor. When my mother called to me from her bedroom to come to her (she was trying to hold onto her own bed at the time), she told me that I replied "I can't. The walls keep hitting me." On our hands and knees we finally made it as a small family out to our back yard (my Mom was fearful of the gas line rupturing and suffocating or burning us all). This earthquake had a moment magnitude of about 7.3

The movie "Volcano" made the expression "The Coast Is Toast" famous. "Volcano" postulated a volcano somehow under the San Andreas Fault. When the film came out, my volcanologist colleagues cringed. While volcanoes ARE associated with faults, they are associated with deep subduction faults, where ocean floor is over-run by a continent in what is called a thrust fault. Think of the Cascades range, far inboard from the Cascadia subduction fault 50 - 100 kilometers offshore. The volcanoes themselves are found far inland from where the huge subduction fault reaches the ocean floor.



However, the expression "The Coast IS Toast" is not that far off the mark in the sense of massive destruction that could visit the Pacific Northwest coast if and when a Cascadia subduction event occurs. It could be a magnitude of 9.0 or higher - this would represent over 100 times more energy released that what woke me up years ago.



The Cascadia Subduction Zone (CSZ) is just that: a plate-subduction thrust fault spread over 1,000 kilometer length, extending from offshore Vancouver Island in Canada to offshore northern California. It's width depends on what you count, but earthquake imaging of the down-going oceanic slab extends well into central Washington and Oregon. Three major oceanic floor plates, the largest being the Juan de Fuca, are being over-ridden by a westward-moving North American continent. Part of the thrust fault is lubricated by the ocean-floor sediments atop the Juan de Fuca plate, and part of the down-going slab is partially melting in the upper Mantle, giving rise to that almost linear string of Cascades volcanoes. These volcanoes extend from Mt Garibaldi in British Columbia to Mount Shasta and Mount Lassen in Northern California.

But in between these parts is a segment, extending the entire length of the fault zone, that is stuck. The lubricating fluids have been squeezed out by pressure with increasing depth, and the stuck part is like a dry patch in the center of your hands as you try to slide one past the other. THIS is where the the rub lies, so to speak. In 2004 a similar subduction fault near Aceh in western Indonesia ruptured, creating a magnitude 9.3 earthquake. The tsunami alone killed over 250,000 people around the Indian Ocean as far away as Mozambique. When a similar subduction fault offshore of northern Japan ruptured in 2011, the surface area of the fault that was displaced or ripped was enormous: 300 kilometers long by 200 kilometers down-dip. This is important, because the surface area ruptured correlates closely with the energy released. "Down-dip" on the San Andreas Fault is only about 10 kilometers - because this fault is more or less vertical, and the rock becomes plastic at about 10 kilometers depth.

There is a security camera video of a 15-meter (50') wave breaching the 5-meter (16 ft) tsunami-protection walls of the Fukushima Dai-Ichi nuclear power plant on the coast. If you've been trying to body-board in the ocean, you know how hard a 2 meter (6 foot) wave can slam you. To state the obvious, you don't just stand your ground with even this small a wave: water is nearly as dense as your body. The estimated cost of this disaster to Japan as a nation is now in excess of $300 billion.

That sounds unimaginable. However, a Cascadia Subduction event is a very real, in fact inevitable, likelihood for the Pacific Northwest.

What will happen when this inexorable event occurs?

The coast will lurch westward 20 meters (60 feet)... and remain there permanently.

The coast will drop down on average 2 meters (6 feet)... and the low-lying parts will remain sunken permanently.

A tsunami up to 40 meters (130 feet) tall will strike coastal communities in as little as 15 minutes from the onset of the first shaking.

There will be fires that are unstoppable - because gas mains and water mains will both be ruptured. The 1906 earthquake in San Francisco was over in probably less than 3 minutes... but the fires that destroyed nearly ALL of San Francisco raged for four days afterwards. The fire department at the time was helpless. 

In the Pacific Northwest, emergency planners have estimated that 10,000 people will die, and another 30,000 people will be seriously injured.

The closer to the epicenter - a broad north-south line just off and beneath the coast - the greater the damage. The farther east you live, the greater the attenuation of the energy released by a CSZ event. Attenuation means the Earth's crust in between the fault and, say, Yakima, Washington, will absorb most of the radiating seismic energy. 

But first, the ground will first jerk westward, then begin going up and down and sideways, then begin rolling. This will go on for 4 - 6 minutes...

It will definitely wake you up. From experience, I can tell you that it seems to go on forever.

How often does Cascadia's fault rupture? An early study of bouma sequences (mud layering in deep-ocean coring) suggested 7 events in the past 3,500 years, but a recent report by Oregon State University suggests that the average time between major earthquake events may be as little as every 240 years. When was the last one?

January 1700 AD.

This event gave rise to the Orphan Tsunami in Japan, so-called because there was no felt earthquake nor approaching typhoon to provide warning before enormous waves suddenly appeared and obliterated or damaged many fishing villages along the Sendai coast. That's over 300 years ago. This is somewhat simplified, of course, because the CSZ cannot really be treated as a single entity that always behaves along its entire length the same way. Detailed geologic mapping, in fact, suggests that there are sometimes separate ruptures along the "northern zone" and the "southern zone"... 'mere' magnitude 8.5 events.

But make no mistake: while a magnitude 8+ event may feel different from a magnitude 9.0 full-rip event (lasting "only" 4-5 minutes instead of 6), there will still be widespread damage.

The event spacing (the average of 240 years vs. the current hiatus of 315 years) suggests we are then "overdue", doesn't it? Not necessarily, because the spacing between previous events has been as much as 500 years. Earthquakes do not click along like clocks. In fact, we cannot predict earthquakes unless we are injecting water into wells in a tectonic region like the area north of Denver, CO. For all large earthquakes, despite upwards of $100 billion spent on research over the past century, the best minds I personally know unequivocally say that current science cannot predict when an earthquake will happen.

But scientists can forecast major earthquakes. That's a very different thing than a prediction. This means that scientists can say, based on existing data, that there is a 40% chance of another Cascadia event in the next 50 years. So... less than a 1% chance in the next year. Buy earthquake insurance or not?

What can that plausibly mean to you - realistically, practically? What can you possibly do with this information?

First, scientists CAN make reasonable estimates of what will happen during and after a Cascadia event, and you and I CAN prepare for those. This is going on right now in local and state organizations in the Pacific Northwest. Infrastructure is being examined with an eye towards what can be reinforced. Building codes have already been upgraded - then upgraded again - to help us create new roads, bridges, and buildings that will better survive such an event. There are estimates in Oregon, for instance, that a majority of bridges will be compromised or fail on coastal US Highway 101, and at least five bridges on inland interstate I-5 will fail in Oregon alone. The damage will be worse the closer one is to the coast, but in both instances it takes just one bridge in a strategic location to shut down interstate commerce. Don't count on being able to find food on the shelves of your local supermarket for awhile... or even count on being able to GET to your supermarket. Repairs to powerlines, gas lines, roads, bridges, etc. will take time. They will happen sooner inland, and take longer in the coastal communities.

This means you should have at least 2 - 4 weeks worth of non-perishable food for each adult in your household. You should have at least two gallons of water, per day, per adult, enough to last you that whole time. A majority of people planning for a disaster forget about the water part - it's raining all the time in the "Pacific NorthWet", isn't it? You should also have batteries - LOTS of batteries. A hand-crank radio will be very helpful, perhaps a lifeline.

Most important of all, you need to have a family plan for dealing with this - or any other catastrophe. In the short term, only you can help your family and your neighbors. It will take awhile for the country as a whole to martial the necessary resources to even partially help.

If the example of Hurricane Katrina can be used, yes, we will recover. However, the recovery effort will consume much of the region's GDP, and it may be more than a decade before everything is running as smoothly as before the event. New Orleans and Memphis, TN, had similar economic output in 2005. Today New Orleans still has not caught up with Memphis.

We will survive. We will rebuild. We will be toast only if we refuse to do anything.



Friday, October 23, 2015

Why do I Need a Geologist to Build my Deck?

Most of what the geoscience community does is profoundly practical. As you cross any bridge, enter any building, you have a professional geologist or engineering geologist  to thank for the fact that you are safe there. 

Q: I would like to extend (cantilever) my deck over my back slope. I am told by construction contractor that I will need a geologist to determine type of bedrock and/or soil and determine the depth required for installment of support piers (caissons) to support deck structure.


    Do I need to hire only a geologist for determining whether hillside slope will support a deck?
- Walter H


A: Laws and codes are different for different cities and in different states, and are different for flat or hilly ground, hurricane-, tornado-, or earthquake-prone terrains,  so I cannot directly answer this question. Some states require assessments by someone who has passed qualifying tests, and can designate "PG" (for professional geologist) after their name. Some states require an engineering geologist to do this sort of job. These people basically provide crucial experience and data to ensure conformance with local building codes. 

    I can indirectly answer your question by sharing my own experience, which may or may not be relevant. I chose a home with a great territorial view. The price I must pay for this view is that the home is built on a slope, of course. Any slope - especially something graded within the past 20-50 years and not already covered with semi-mature trees, is inherently unstable. For instance, after just ten years I had to pay for a rock retaining wall to be built at the bottom of my back yard/slope - because the soil was slowly creeping downward and had already buried my neighbor's fence 20 cm deep. In this area there are known/mapped slow or creeping landslides, also. On one public trail that I often walk, you can see hundreds of trees that are bent almost horizontal at the base, and then curve to vertical as they go up - a sure sign of a slow or creeping landslide.

    As part of the negotiation for my new house, the company selling it agreed to build a deck in the back. The distance from my bedroom door to the ground at that time was about 15 meters. That's a long first step if you are sleep-walking, so local building code had required the outside of the door to be boarded. I had no idea what the real costs of the final deck were, but an engineer came twice to my door and apologized. First, that he would have to make it wider than my realtor had suggested - to meet code. Second, he would have to connect each of three decks by stairs - to meet code. It had to serve as a fire escape suitable for children. Then an excavator came in and dug a 2-meter-deep trench, a meter wide and the width of my house, behind the house. They set up molds and brought in a monster machine that looked like a Snuffelupagus, and poured 5 concrete cylinders a meter wide and 2 meters tall each. These were even more deeper anchored with some kind of rebar to about 3 meters below ground surface. They brought in a small grader that covered/filled in the trench. To the imposing concrete pylons they bolt-anchored five pressure-treated beams (several of them 15 meters long!). THEN they began building the deck. When I asked the builder why so much precaution (it seemed like massive over-kill to me), he said that building ANY deck on ANY slope was fraught with problems, and from experience this was the MINIMUM precautions they must take. These precautions were built right into the building code.

    “Precautions against what?" I asked.

    "Against your deck joining your neighbor's party," was the reply.

     In the 12 years since the deck was built (it remains stable) I have seen several things including the bent trees and my own sliding lower backyard slope that convince me he was correct. 

     So much for my theory that I could get away with a couple of cinder blocks with some posts standing on them and do it myself. 

Saturday, October 3, 2015

Gold and Lava

This ask-a-Geologist query began as a science fiction writer trying to make his novel more realistic. His original question was framed around a scene where gold is mixed in a lava flow. Barring the obvious difficulties of how you would (a) concentrate and refine the gold and (b) why would you want to play with gold in a lava flow in the first place...

           Q: Does the gold just melt completely away? Would It sink? Would it meld into the Lava and you couldn't tell the different between the two? Would it rest on top and be visibly different? I'm writing a story and I want to be as scientifically accurate as possible. And considering I don't know what happens when Molten Lava touches a refined Precious metal. I thought i would ask.

– Jeremy A

A: To start with, your hypothesis is a long way removed from any possible reality. This is because gold is rarely found in nature in a form larger than tiny flakes. The rare nugget found in Alaska is just that: extremely rare, and secondary at that (i.e., the nugget is not the original form).

            If you want to modify your story to deal with a refined gold artifact, the following may be helpful:

            The melting temperature of pure, refined gold is 1064 °C. By comparison, the melting point of magma is in the range 700 °C to 1300 °C - depending on its silica content. Gold is also extremely conductive, both electrically and thermally. Gold will thus tend to conduct heat through it very efficiently. 

            The density of pure refined gold is quite high: 19.3 g/cc. A typical magma might range in density from 2.4 g/cc to 3.35 g/cc - again depending on silica content. 

            From these, I can suggest two possible scenarios:

1. If a refined gold object is set on an active flow down-range from Kilauea/Pu'u O'o (on the Big Island, Hawai'i), it will initially start to sink into the magma. Experience has shown (including my personal experience) that magma exposed to air quickly forms a crust and hardens inward - rapidly - from that crust. I've personally walked over active toes of magma flows there, because it was already crusting over. And yes, it was still rough on my boot-soles, but mainly because the crust is really mostly glass. Under these very specific circumstances, the gold object would end up being locked, partially sunk, in the cooling magma crust. 

2. In another possible scenario, the refined gold object might be thrown into an active lava tube (look at the photo in the upper right of this link: https://profile.usgs.gov/jwynn for an example of a skylight broken into a lava tube). In this case, the magma temperature is in the 1200 - 1300 °C range, and the gold object would first sink, then slowly turn liquid and begin to disperse in the magma as it continues down the lava tube. 

Hope this helps your book be a bit more realistic.
~~~~~