Please sir answer this question in 24 hours or... ASK YOUR OWN SOUL!

This is a question that I actually answered in some detail three months ago, so when it came in I thought I would just point the individual at my earlier response. However, I was struck by HOW I was asked this time. To give readers a sense of what we sometimes encounter in our email in-boxes, I share this, but I'm disguising the name and identity of the questioner. You can't make this stuff up, to paraphrase Dave Barry.

Q: Hello sir

In the defination of earthquake

Eathquake is the sudden terror or shaking of earths crust which lasts for the short time. But  in 2015 the earthquake in nepal not lasted for a short time . So why we use that sentance , " which last for the short time".But Generaly in most cases it not lasted for shot time. Sir please answer this question in 24 hrs please sir i sent this question you not answered please answer . Please tel me if you want to hep ,me  or not. I f you want to help, if you want to make a bright student please help me . aSK YOUR OWN SOUL AND HELP.

tHANKYOU

A: 

I cannot answer questions about your soul, nor about mine. This is not something you would ever address to a scientist.

Volunteer geoscientists in the US Geological Survey do not see questions that arrive during western hemisphere weekends. Please do not blame us for not instantly replying to your questions from <Asia>.

I have no idea what definition you are referencing, since you did not provide that information. The simple answer is the larger the moment magnitude (Mm) of an earthquake, the longer the coda. In other words, the greater the energy released, the longer the apparent shaking will last. In fact, you can get a rough idea of how big a regional earthquake is by timing the shaking.

Epigenetic or Syngenetic Deposits: Which is Easier to Find?

The following is a rather esoteric question – definitely not an elementary school question – but it provides a neat teaching moment or opportunity. 

Q: Between epigenetic and syngenetic deposits, which deposit would be easier to find?

- Rayon P.

A: Let's review the definitions of the two types of deposit first:

Syngenetic Deposit:

            This is a mineral deposit that was formed at the same time as its parent rock – and is always enclosed by it. There are two types of syngenetic deposits: igneous and sedimentary. Some examples of these kinds of mineral deposits include paleo-placer diamonds found in southern Venezuela. These diamonds are called “paleo-placer” diamonds because they weathered out of the ancient Tepuis, eerie platform-like mountains that are the inspiration for Aracnophobia and Avatar. There is also stratabound potash (e.g., pinkish salts found in the prairie provinces of Canada and in Central Asia, that are made of potassium, a critical element for agriculture and the “secret” of the “Green Revolution” of the past century. Other examples include the huge nickel deposits found around the huge, ancient asteroid impact crater near Sudbury, Ontario, Canada. There are many other examples, of course.

Epigenetic Deposit:

            This is a mineral deposit that formed following the development or emplacement of the enclosing or host rocks. These kinds of deposits might be found on top of the host rocks, or more commonly IN the host rocks. Some examples of these kinds of deposits include placer platinum group elements (e.g., palladium, rhodium, etc.), and Comstock-style placer gold deposits (think of what triggered the Gold Rush in 1849 in California). Another example are the huge porphyry copper deposits and sedimentary copper deposits found all over the world. Note: the latter example are secondary concentrations of copper in sedimentary rocks… the copper seeped in after the sediments were formed.

            For syngenetic deposits, especially those formed during sedimentary deposition, it makes sense that if you can find one economic outcrop of the mineral you’re looking for, then you could follow the strata it is found in to find more of that mineral of interest. 

            Epigenetic deposits, on the other hand, tend to be easier to see: by the definition above they disrupt the environment (the host rocks) that they are found in. Examples that come to mind are the low-sulfide gold-quartz deposits I found while working in the jungle in southern Venezuela. The gold there is found in thick mostly-quartz veins that fill faults and fractures in the geologic units that host them. Porphyry copper deposits on the other hand are huge things that I visited and occasionally worked in while living in the southwestern USA. These are the source of much of the wiring in your house that let you read this on a computer screen – and then walk out of the room later without stumbling in the dark.  Porphyry coppers, as they are often termed, form huge bulls-eye halos in the host rock. These haloes can usually be seen from the air, and can be detected with specialized instruments like a radiometric imaging system in an aircraft, or specialized electrical geophysical methods like induced polarization.

            In both cases, there are wide variabilities is how easy these deposits are to find, depending on the particular resource being sought. In virtually ALL cases, the “easy” deposits have already been found, and modern geoscientists must search beneath younger sediments or lava that have buried these deposits after they were formed. 

            In other words, the hard-to-find ones are what we are looking for now.

Terraforming Mars

Here's a Q&A that has nothing to do with earthly geology, but may have some instructive content for future geologists. There is usually at least SOME science in SciFi novels!

Q: What would happen to the Martian atmosphere, over the course of the next 100 years, if we could build a machine on Mars that could output the equivalent quantity and composition of greenhouse gasses as are released on earth (approximately) every year?  Thanks for your time, hopefully this has not already been answered!  

- Kyle R

A: That's a rather unique question, but it begs several critical assumptions.

According to a recent Science article, Mars lost its original atmosphere billions of years ago because the planet lost (if it ever had) its magnetic field. As a result the solar wind (high energy charged particles blasted out from the Sun) stripped most of Mars' atmosphere away. So one assumption is that the planetary magnetic field is somehow restored.

Another assumption is a bit more obvious: where would the carbon and oxygen come from? Certainly not the planet's crust, as it has been degassing for billions of years and is a depleted desert now. Hundreds of trillions of tons of material would have to be brought to Mars' surface. This is actually not as unreasonable as it may sound: comets can do (and have done) this in the past... but it would require a number of pretty large comets. A colliding planetary body from the Oort Cloud on the scale of Sedna could bring the mass as well as restart the magnetic dynamo, however. A collision like that is thought to be the reason why we still have a magnetic field here on Earth... and a Moon as big as the one we have.

A final assumption is also necessary: a weaker planetary gravity field would make it easier for gases to escape the planet. So another assumption would be that somehow the planet became much more dense. A comet impact couldn't solve this one. A collision with something like Sedna would only marginally increase the gravity field of the planet. Weak gravity -> easier for atmospheric gases to escape.

I'm not a specialist in atmospheric dynamics, so I don't want to speculate what would happen if all three of these conditions were somehow met. I suspect that Mars' currently pink sky might end up a different color, however.

Q: Thanks for the thoughtful reply Jeff, I appreciate you taking the time.  The thrust behind my question was basically to get an understanding of the scale of the terraforming humans have engineered on Earth and what the impact would be if that same process was applied to another planet of similar size.  I guess looking back I should have simply asked what the impact might be of 'magically' pumping 7,000 million metric tons of  carbon dioxide into the Martian atmosphere every year (7000 million metric tons being an approximate average volume created by human factors on Earth).  Thanks again and enjoy your weekend!

 -Kyle

A: Yes, I was fascinated by the book Dune and the movie Total Recall, but the physicist in me kept slapping me on the back of the head: There's no evidence of sequestered carbon on Mars except frozen CO2 at the poles. There is only rare (indirect) evidence of water - it's a desert world. Water being low density, it would be hard to hide it on a planet like Mars or Arrakis. THAT said, I participated in several expeditions across the Empty Quarter of Saudi Arabia. Ambient humidity there is about 2% (in an Arizona summer it is around 20%). It is so dry that you have to "snuff" a handful of water every hour all night long because your mucous membranes are on fire - and cracking from the desiccation. However, I did some geo-electrical soundings along our two routes to the Wabar Impact site and found evidence of conductors - probably above-bedrock water - in several locations at about 60 - 100 meter depths.

How To NOT Go Off-The-Wall Freakin' CRAZY...

...when a Cascadia Earthquake hits.

From personal experience, when a really big earthquake hits, it is extremely unnerving. In fact, my first earthquake was a magnitude 7.3 event in Southern California, and the serious shaking lasted not much more than 3 minutes.

However, it seemed like a lifetime to me then. If asked a week later, I probably would have said that it lasted at least a half an hour.

Look at the following diagram, taken from Wikipedia:

The P is what woke me up. It hit with a bang.
The S is what rattled and then broke the windows, and stutter-walked my bed 30 cm.
The R is what finally flipped me out of my bed and onto the floor.

It took several days for the information on this event to filter down through the scientists to the government entities, to the news media, to my parents, and then to me as a 6-yr-old child. By then we were back in our house, the power was restored, and we had water pressure again.

A Cascadia subduction earthquake might reach a moment magnitude 9+ when it next occurs. That will be at least 100 times more energy than the piddly 7.3 event that launched a sleepy 6-yr-old out of his bed in Bakersfield, California long ago. If I found a M=7.3 to be that terrifying, imagine how bad a M=9+ event will be.

There are two ways to deal with the terror:

#1. Understand immediately what is happening and what will come next.
#2. Be prepared for it. Know that you have your bases covered.

#2 is something that many people more or less do (some do OK, some do better, and some do extremely well at this):
A. Have a family plan in place. Where do we meet? What channels on the battery-powered, $40 hand-held walkie-talkies will we be using to find each other?
B. Have supplies at hand, including
    i. Food. And don't count your refrigerator contents here.
    ii. Water. A LOT more water than you might think.
    iii. A battery-or-crank-powered Radio
    iv. Batteries. Flashlights. LOTS of batteries.
    v. Blankets and sleeping bags, and/or a heat source to keep warm.
C. Start checking up on your neighbors, and offer to share your stuff with them. People you may hardly know will become life-long friends really quickly.

However, the purpose of THIS blog entry or chapter is to help you deal with #1: understand what in the world is going on, so you don't go crazy. 

Next, look at the following diagram:

This will help you to understand the TIMING difference between the several kinds of seismic waves. The P wave arrives with a bang, like someone with a large hammer just whacked one side of your house. The S wave will feel different: slewing everything back and forth, perpendicular to a line between you and the epicenter of the earthquake. The R (which stands for Raleigh, or surface) waves will feel to you like you are in a small skiff after a large boat roars past, careless of his wake. You will feel like you are rolling around, up and down, and sideways . You always end up pretty much in the same place with each complete roll. 

All these things are important clues for you. This is what you do:

FIRST: as soon as the P-wave hits, look at your watch... which we both hope includes a second hand.

Second: as soon as the S-wave hits, think about what direction is PERPENDICULAR to that sickening side-to-side motion: this gives you the important clue as to where this thing is coming from. If the slewing motion is north-south, then the earthquake epicenter is either east or (more likely in this case) west of you.

Third: as soon as the S-wave hits, look at your watch again. Subtract the P-wave arrival time in seconds from the S-wave arrival time. That difference tells you how far away the hypocenter (the actual sub-seafloor rock rupture) is from you.

Use the following diagram to convert that P-S time difference into a distance::

Fourth: KEEP TRACK OF THE TIME even after you have this number. If the event is a M=9+ event, the ground will keep shaking and heaving for a full 5 - 6 minutes. THIS will give you a sense of how bad things will be in the following several weeks. If it was just a segment of the Cascadia Subduction Fault breaking, then the time could be as little as 3 - 4 minutes. This is GOOD. If the heaving and shaking runs up to 6 minutes... well, you already have #2 above in place, right? So you are prepared.

This will help: If you live in Portland or Seattle, and the P-S time difference is 20 - 45 seconds, then the event is far enough away (or close enough, depending on your point of view) to be The Big One: A Cascadia Subduction Event. 

But YOU WILL ALREADY UNDERSTAND WHAT IS GOING ON even before the first news reports start coming in (assuming you have a flashlight close and a battery-powered radio on hand). 

AND YOU HAVE YOUR PREPARATIONS IN PLACE. 

And no, you are not crazy: you are informed and prepared. 

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.

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. 

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.

~~~~~