Oklahoma Earthquake - I felt it!

Those of us in Oklahoma this morning had quite a nice surprise when at about 9:06 AM local time the ground shook and many experienced an earthquake centered just outside of Norman, OK.  I live on the bottom floor of a 2-story apartment building and was standing when the quake hit.  I head a loud noise like a vehicle roll over, then felt the shake.  My blinds shook and a few plates rattled together.  After immediately realizing what it was I estimated the duration as about 15 seconds, but some of that could have been remnant swinging of objects in my house.  

The initial rating was 4.5 from the USGS (United States Geological Survey), and 5.1 from the OGS (Oklahoma Geological Survey).  These estimates have been revised many times over the day, as well as the location and depth of the quake.  The estimates seem to be settling around a 4.3-4.5 magnitude with a center just west of lake Thunderbird in Norman, OK.  Below is a google map (image: J. Leeman) plotting the OGS estimate of the center with the error as the shaded region.  This uncertainty is about 1.24mi in N/S and 1.12mi in E/W.  The USGS estimate is currently much less constrained, but subject to revision.  

 The earthquake was widely felt with reports from surrounding states.  If you felt the quake you should fill out the 'Did you Feel it?' question form available on the USGS website.  Many thousand reports have been submitted so far and data gathered from over 40 stations. The next image is courtesy of Bill Wilburn, planetarium director at the Science Museum of Oklahoma.  Following that is the plot of arrival times at different stations from Steve Piltz, Tulsa NWS.

 We are also fortunate to currently have the earthscope array stationed in Oklahoma.  The next figure shows current seismic stations on the OGS page.  The yellow stations are earthscope.  Those stations appear to have been saturated, but it could be a plotting issue.  I will not know until I can get ahold of the data.

The final two images are the Carlsbad, NM East Tower seismogram and a focal mechanism plot.  The Carlsbad plot just shows that the earthquake was still very detectable in NM and makes it easy to see why it was recorded by so many stations!  The focal mechanism plot (or moment tensor solution) plots the first movement (up/down) of the ground at the stations to determine the type of earthquake/fault.  Here we see evidence for a strike-slip fault along a SW-NE or SE-NW line.  Simply put this means the ground sheared on a horizontal plane, not shearing along a slanted/vertical face as in normal or transverse faults.  

I'll post more in a future post if we learn anything else significant from/about this quake.  Maybe also some neat arrival plots and a discussion of wave types.  As a note the largest earthquake recorded that originated in Oklahoma was in the El Reno area on April 9, 1952 with a magnitude of 5.5.  The USGS has the following to describe that quake:

This earthquake caused moderate damage at El Reno, Oklahoma City, and Ponca City, including toppled chimneys and smokestacks, cracked and loosened bricks on buildings, and broken windows and dishes. One crack in the State Capitol at Oklahoma City was 15 meters long. Slight damage was reported from many other towns in Oklahoma and from some towns in Kansas and Texas. The earthquake was caused by slippage along the Nemaha fault. Felt over most of Oklahoma and in Arkansas, Iowa, Kansas, Missouri, Nebraska, and Texas.

The iPad: How it is Revolutionizing Field Work

It's not even been one year since the iPad hit the market and it is well on it's way to becoming an essential for many people around the world.  According to CNN, the iPad has the fastest adoption rate of any consumer advice (read the full article here).  I know that the iPad is difficult to put down, after standing in line all afternoon the day of the 3G release I was entertained the entire weekend.

But, what else can you do with the iPad.  We've all seen the movies, games, and flashy organization apps in the adds, but what about more difficult work?  The productivity category was initially slow to start, but now is full of options.

The numbers/pages/keynote set is $30 ($10 each) and has saved me several times.  When I needed to make a promotion slide last minute at a conference keynote came to my rescue.  I simply took images I needed from various emails and online, added some text, and in 10 minutes had a decent looking slide to submit.  Numbers has allowed me to use some handy computational workbooks in the field to make very simple models of data that is coming in.  Last, pages is very handy for quick edits on the road, or when out somewhere on campus.  There are a few glitches, but they have continually be improving, especially in the area of importing Microsoft Office documents.  So far, no track changes exists, but hopefully that will be coming soon.

For quick remote server administration I use iSSH.  This is really a fantastic app with the exception that the arrow keys/command keys on the bluetooth keyboard don't work forcing you to use onscreen keys.  This is the only limitation that prevents me from doing some full scale programming while connected to another machine back at home.

It's always important to know the weather while in the field and I use a combination of Storm Spotter and Radar Scope.  The developer of Storm Spotter is another OU meteorology student and I highly recommend his app.  Radar Scope does have a few things like spotter network, but it does not have any form of surface street map.  Storm Spotter uses google maps which makes exact location or storm chasing much easier.

Another field essential is taking notes.  There are many note apps out there and most do about the same things with different degrees of reliability.  For quick sketches I use Penultimate and for class notes I use Note Taker HD, which has a 'zoom box' that lets me write large with my stylus (the Pogo Sketch) and it is normal sized writing on the page.  Sundry notes is also around, but has not received any use by me for some time.

File sync is also an essential and can be done with Dropbox.  I already loved this service and the mobile app made life easier! Now I can save notes from the field and they instantly sync to my computer at home, my phone, and my laptop.

For field math there is Wolfram alpha (cloud service), Quick Graph, and many apps like MathTasks that do simple calculations on the fly.

Sometimes I'll use a GPS utility to mark out rough locations on a map or even the iPad ArcGIS to get an approximate distance/area.

Finally, we all need files and file editing in the field.  I use Papers to keep my scientific paper library with me at all times.  In the field or at a conference it's easy to find that paper you need a snippet from and email it directly to the interested party/conference goer.  Annotating PDF files is easy with iAnnotate PDF and viewing large files is nice with GoodReader (though Books now does this also).

While all these apps are productivity, you can bet all iPad owners have their favorite music service loaded, Netflix, and other entertainment too.  While I do love using my iPad it does have overheating issues when working out in direct sun on a hot day.  The screen is great at letting solar radiation in, and trapping the re-emitted IR inside the device,  shutting it off in ~10 minutes.  What can you do? Use a case with an open back and keep the screen shaded.  I'm not quite ready to quit carrying paper notes all together, but it's getting close and my daily/travel backpack is getting lighter every year.  Read about other great apps for large scale studies used in Pompeii here.

Images are property Apple.

The Vuvuzela: An Annoying Horn but a Fun Filter Project!

As we've watched the world cup matches over the past weeks everyone has been annoyed by the droning hum of the vuvuzela.  Everyone in the crowd blowing on one of these pipes makes life for our ears unpleasant.  What can you do though?

While at SciPy 2010 this week we saw a tutorial about signals with Python.  Another student and I talked about filtering out the drone and after several late nights of hacking it worked! The principle is simple, block the frequency of the horn and it's harmonics.  To do this we use a notch filter that rejects the signal from a certain frequency range.

The code (waves.py) is available and is a short script to read in, filter, display, and write out the files.  Below I show an example of the signal and power spectral density before filtering (left) and after filtering (right).  There are also links to the audio files.  I found three example files and filtered them with three different filter widths (5,10,25 Hz). All runs are available at http://leemanwebb.org/vuvu/ , but that link will disappear and I'll then post a more permanent page after some tweaking with the project.  Be sure to listen to example 3 before and after the 5Hz width filter.

Earthquakes in NW Arkansas? Yep!

Those of you who live in the northwest Arkansas area were recently 'rocked' by two earthquakes.  These were both small being under 3.0 in magnitude.  I hesitate to give out exact magnitudes because these are determined by looking at at data from several seismic stations (as is the location and depth).  You can imagine that there are relatively few earthquakes in this part of the state, so the seismic network is lacking.

So, why did these earthquakes occur? Have they happened before? Well, in short we don't know and not in recorded history.  Yes there have been movements on faults that have been felt in Benton county before, but these two events are the only earthquakes originating in the county we know of.  The first map shows recorded earthquakes since 1974 to the present (not including these two).  You will observe almost none within 200km of the county.

The initial hypothesis by a University of Arkansas professor, given the shallow depths initially calculated, was that these were the results of cave collapses.  Karst topography (what we have in NWA) consists of layers of caves carved into the subsurface.  It is not uncommon for these to collapse and the UofA professor cited the loud noises heard as support for the collapse theory.  Though the theory is nice, but my initial thoughts were 'where are the sinkholes'?  None have been discovered, not that they would be like the recent sinkhole in Guatemala (picture from Guatemalan Govt.).  I had settled on the personal hypothesis of these being slips of old faults.  There are many of these faults throughout the area, but they have been inactive for a very long time (even in geologic time).  This slipping can be stress built up over long periods of time, introduction of fluids, or loading of the land.  I even thought about a fault running under the railroad bridge in Decatur which does not break, but creeps slowly.  That bridge has been rebuilt several times due to  fault movement.

I heard that people were rushing to buy earthquake insurance and couldn't help but to (almost literally) fall out of my chair laughing.  These are not indications of further earthquakes.  We don't know what exactly is happening, but that is mostly because the area is poorly mapped and we have little geophysical data available about it.  Could more earthquakes happen? Absolutely.  Will they? We can't say.

Next we must discuss how earthquakes are rated.  We use the Richter scale, which is a logarithmic scale.  This means that each step is an order of magnitude more energy.  A 3.0 is ten times larger than a 2.0, so a 4.0 is 100 times larger than a 2.0.  News media commonly misses this and says it was 'twice' as large which is simple ignorance.  We also know it takes a 4.0+ to start breaking glass and doing serious damage.  I have only head reports of a few cracked driveways and see no reason to expect anymore.  Finally there is no 'trend' with only two data points to support earthquakes getting stronger.

Physics of a Beer Head- It's All About Tension Gradients

Who doesn't like a good beer? Geologists/geophysicists are always appreciate a nice cold glass of their favorite beverage poured by a skilled bartender that produces a nice frothy head that persists for the entire experience.  The question is why does the head not disappear quickly like soap bubbles?  Douglas Durian and Srinivasa Raghavan wrote up a 'quick study' in the May 2010 issue of Physics Today.  This article is based on that article with some additional information.  Durian and Raghavan also discuss soap bubbles and present high magnification photos of foam structures, but those will be ignored here as their method of persistence is quite different than that of beer foam.

When beer is produced proteins are present in the mix.  If you enjoy the cloudy wheat beers you are seeing proteins precipitate out! Actually something called the isoelectric point determines what happens to the proteins.  If the pH of the beer is too close to the IEP the proteins precipitate out.  The further the pH gets from the IEP the more soluble the proteins are.  Why does it matter?

Remember from high school biology that proteins have hydrophilic and hydrophobic parts to them.  This means that one part of the protein 'likes' water and will immerse itself, but the other end does not like water and tries to stay away from it.  When we look at a foam magnified there are small fluid sections in-between the air bubbles.  Proteins orient themselves in the bubble walls.  Say that a bubble begins to stretch thin and is in danger of bursting.  The stretching of the wall means there are fewer proteins in the middle where the wall is thin and more on the edges.  Proteins can change the surface tension and this gradient is surface tension causes liquid to flow to the thin section, restoring the stability of the bubble.  This effect is known as the Gibbs-Marangoni effect, and is in fact a strong example of the phenomena.

This Gibbs-Marangoni effect was in fact first observed in glasses of wine (pictured) and discussed by Lord Kelvin's brother James back in the mid 1800's.  Carlo Marangoni studied the idea for this dissertation and the solutions of the problem were formalized by Williard Gibbs.  (Yep, that the same guy that independently developed vector analysis, Gibbs free energy, etc)

So is there anything other than pH that can change the persistence of head? Absolutely! Due to gravity the fluid drains to the bottom over time which destabilizes the foam.  There isn't much to do about that, but we can combat Ostwald ripening.  Basically this mean that gas diffuses from smaller bubbles to larger ones.  Laplace described this knowing that the large bubbles have a smaller curvature and therefore lower pressure than small bubbles.  According to the article brewers can add about 20ppm of nitrogen to the beer to slow this process.

The items discussed in this article apply across many scientific items.  There is an everyday example that scientists would call Benard-Marangoni convection, but you probably call it boiling water.

Once again these pictures are from the interweb and not my property.  

Deepwater Horizon and Hydrates

By now all are well aware of the well blowout in the gulf at the 'Deepwater Horizon' site.  Thus far several attempts have been made to curb the flow of crude into the gulf, but none have worked.  One of the first attempts was to use a dome structure to cover the rupture and direct the oil to a waiting barge.  This dome quickly filled with gas hydrate and was made much more buoyant by the hydrate (density of hydrate is less than that of water, especially sea water).  Attached is a picture of the 4-story dome courtesy telegraph.co.uk.  I feel it is important to point out a few things about hydrate the media has either left out or stated incorrectly.

First, what is gas hydrate? The most common buzz word I've seen is 'crystalline gas' or 'solid gas'.  These are contradictions.  We know there are three basic states of matter: solids, liquids, and gasses. (There are also plasmas, Bose-Einstein condensates, string-net liquids, and so on.) You can see that a 'solid gas' is simply incorrect! Gas hydrates are cages of water molecules with a guest molecule of gas trapped inside.  There are different types of cages for different sizes of guest molecules.  Though the material can look like ice it is fundamentally different.

Under the ocean there is quite a lot of methane hydrate.  We have known about hydrate for some time and it's important for past climate change, possible energy production, and as a potential hazard for sea slopes and drilling operations.  Dr. Robert Bea of UC Berkeley has suggested that Halliburton cementing the well only 20 hours before the explosion on the rig is important.  When cement is hardening is releases heat. This heat of crystallization could have heated the hydrate up.  The hydrate weakened the concrete and as it was melting released its gas, causing a surge of pressure to the rig.

Hydrates have been a problem to the industry before, clogging pipelines and apparatus.  Hydrates only form under certain pressure and temperature conditions, so the areas can simply be kept out of P-T ranges where hydrate would be stable.  This is easier said than done, and sometimes inhibitors are injected.  Chemicals such as methanol decrease the stability of hydrate.

So what is the plan now? Currently an attempt to place a new, capped section of pipe on is underway.  The difficulty with any plugging operation is the pressure at which the fluid is shooting out.  If this fails a smaller dome has been built in hopes that it will remain warmer and hydrate will not be stable. There are also measures in place to inject hydrate inhibitors, though this could have unknown environmental impacts.  Currently oil continues to gush out at about 210, 000 gallons/day.  Below is an image from NOAA (May 11) showing the spread of oil then some links to follow.  Numerical modeling of the spread has done surprisingly well as has put rapid mathematical modeling in the spotlight also.

Afterthought:
I received a question about why the flow rate estimates were so widely varied.  In the video of the flow you can see both oil and gas phases coming out of the pipe. If it were just one phase, knowing the scale and frame rate of the pipe would be sufficient to get an accurate estimate. It could be that as oil is releasing pressure more hydrate is dissociating and causing the bursts of mixed gas making the flow hard to figure.


LINKS:
Video of Oil Leak
NOAA Page on the Accident (Updated Daily)
LA Times Article on Dr.Bea's Idea

Chernobyl

Chernobyl nuclear unit number four blew up 24 years ago today.  Officially the disaster killed about 31 people, but we all know that the death toll is much higher.  Today I'd like to briefly discuss the very basic premise of the accident, what actions the Soviets took, and what we can learn from this accident.
The accident occurred during a test that really should have already been preformed.  In the event of the plant losing external power it would take backup generators about a minute to get up to speed and start coolant circulating again.  This was dangerous and the engineers believed that they could use the inertia of the already spinning turbines to generate enough power to run the plant for about 45 seconds.  The details are well documented, but in the end the power spiked, control rods jammed, and the reactor went out of control.  
These RMBK reactors are inherently unstable at low power levels, and the operators did not understand reactor physics well enough to understand what the instrumentation was telling them.  The control rods only reached just over 2m into the reactor before they seized.  The reactor was 7m deep.  
There were two explosions, a steam explosion, followed closely by an explosion from nuclear excursion.  All of this is well explained elsewhere, but at the time the causes were unclear.  In fact, several of the operators thought a tank of hydrogen had exploded, even though they could see chunks of graphite on the ground outside.  
Almost immediately radioactive dust was showering from vents in the plant and many crew received lethal doses and a 'nuclear tan' very quickly.  They were simply replaced with workers from the other reactors.  Some were sent i to lower the control rods manually, only to find that none of that existed anymore.  They instead saw fire hoses dangling unmanned, the firefighters had already fallen after standing right above the core of the unit.   
The government lied in many cases to the workers and public.  One community was given masks and iodine but didn't distribute them to prevent a panic.  The supplies went to waste.  After that liquidation crews were brought in.  The robots were unreliable and failed quickly.  The government sent soldiers onto the reactor with little protection, they were called 'bio-robots'.  The human side of the story is excellently captured in the book Voices from Chernobyl: The Oral History of a Nuclear Disaster, available here.  The book is also available in many libraries and I highly recommend it, though some of the stories are graphic. Pictured above is the reactor after the explosion, it was enclosed in a hastily built sarcophagus, which is now unstable and must be rebuilt.  The condition of the tunnels dug under the plant by 'bio-robots' is also unknown.  The next picture is of a robot bulldozer being tested.  These were used to bury the cities, but failed to work well and were often replaced by humans.  Some photos from the zone also show spots, recording the massive radiation release.  
So what can be learned from this accident? The obvious results are more training, containment domes, and better reactor design.  The other lessons are about government and public education.  Let's focus on the less controversial public education issue.  Many people refused to leave the zone because nothing was wrong.  They couldn't understand the power of the atoms, the sky was blue, and there was a fire in the distance; why should it mean anything to them? This is why the public needs a basic science education, but now I fear the US has gone too far and induced a fear of the atom.  Nuclear power is a technology to be respected, not feared.  With proper construction, safety measures, and current technology there is no reason to fear an accident in the US.  Waste products are another issue entirely.  
In closing I encourage you to do some research and learn about this disaster.  Also remember all the brave 'bio-robots' that were sent to the station to die while attempting to contain the situation.  You can watch this short video for some photographs from the area.  A documentary about the accident is also available on youtube. 
(None of the photographs are mine, all sourced from Wikipedia)