Pet peeves vis-a-vis geology students & math

A bit of a continuation of yesterday's post.  Pretty self explanatory.

Example 1

Student is told that to convert 12 kilometers to meters, all they need to do is multiply by 1,000 since there are 1,000 meters in a kilometer (something I thought they would have learned in 4^th grade, but oh well).  Instead of just adding three zeros to 12 to obtain 12,000 meters, student whips out their $120+ TI-84 graphing calculator and enters 12 x 1,000!

Example 2

Student measures the mass of a mineral on a triple balance beam and gets a value of 203.5 grams.  The mineral displaces 29 ml of water and therefore has a volume of 29 cm³.  The density of the mineral is (mass/volume) or (203.5 g / 29 cm³) or 7.0172413793 g/cm³ as reported by the student.  Anyone see a problem with this answer?  The student's initial measurements, at best, have one decimal place precision while the answer is given to 10 decimal places (because that's what the calculator reported back).  The density should simply be reported as 7 g/cm³ (it was a hunk of galena - PbS).  The ten decimal place answer is nonsensical and was marked incorrect to the student's amazement.

Example 3

Student is trying to solve a problem.  A groundwater contaminant is slowly moving in the subsurface at an average rate of 1 in/day.  How many years will it take to move a mile (5,280 ft)?  Student makes a mistake and divides 5,280 by 12 to get 440 in.  Believes it will take a little over a year.  I ask student why they divided by 12.  Said it was because there are 12 inches in a foot.  I said you divided 5,280 ft by 12 in/ft and got 440 ft²/in. The units are nonsensical. If, however, they paid attention to the way I taught them to do unit conversions (a method they should have learned 10 years ago in middle school), they would have multiplied 5,280 ft by 12 in/ft to obtain 63,360 in which is a much better unit than ft²/in and the contaminant will take over 173 years to travel that distance (big difference!). Student looks at me blankly.

Example 4

In a similar type of conversion problem, student is off on their answer by several orders of magnitude because they multiplied instead of divided (e.g. answer is 4.3 km and student reports 430,000 km). No work is shown, I take off full credit. Student complains and wants partial credit.  My rule is no work shown, no partial credit.  I also ask them how a boss would respond to an error like this.  Would you like your doctor to be off by orders of magnitude when calculating a dosage?  An engineer when designing an aircraft?  A CPA doing your taxes?  Student hates me.

Example 5

When having to do a lab that contains nothing more complex than 8^th grade math, student complains "I hate math!" and, despite my attempts at providing one-on-one extra help, declines and clearly copies the work from someone else. Fails lab final when forced to do the problems on their own without assistance.

These are all true examples from science majors in my Physical Geology laboratory course.  Sigh.

Teaching math

I was in the doctor's office the other day, getting blood drawn, and the phlebotomist asked me what I was reading since I was carrying a book (I'd rather read when sitting in an examination room waiting for the doctor than stare at those charts of nasty medical illustrations on the walls and wondering which disease is eventually going to kill me).

I told him it was a book about math (which I'll review in a couple of days when I finish reading it).  He then asked if I taught math and I told him I was a geologist we talked for a bit.  He told me he was never very good at math (as most people will tell you if they see you reading a book about math for fun), and one his memories from a high school math class was his teacher yelling at the class - "You know why you kids do so badly on the test?  It's because you can't follow directions and that's what math is - following directions!"

He was done drawing my blood, so I didn't continue the conversation, but I was horrified that a math teacher would yell at his class like that.  Not because he yelled at the students - good for him, they probably deserved it and never followed instructions - but because he told them something I think is totally false.  Math, real math, is not simply "following directions".  I would contend just the opposite - that teaching math this way is the worst possible way to do it (to be fair, of course, I'm just going by some one's memory of a long-ago math class, reality may have differed).

Also keep in mind, in what follows, is that I'm not a math teacher.  I'm a geologist that likes math and think it's terribly interesting (I also find myself teaching elementary algebra to college students in my geology lab when they can't solve certain problems).  Take what I say with a grain of salt (perhaps a math teacher could chime in if they're reading this).

To be fair, a large part of math is "following directions" in that math has rules.  The plus sign + has a specific meaning in mathematics as an operation.  When doing something to one side of an equals sign, you also have to do the exact same thing to the other side.

The problem is when students reach college and think of math as simply a system of mysterious rules and formulas with zero understanding of how it all works.  That's why people always complain about "word problems" in math - if you don't understand the concepts, you can't apply them to solve a problem.

A concrete example.  Most people are aware that the Earth's rigid outer shell (called the lithosphere by geologists) is split into plates which drift around over geologic time.  This process is called plate tectonics and is central to modern science of geology.  The Pacific Ocean is mostly underlain by a plate called, not surprisingly, the Pacific Plate.

The Hawaiian Islands are in the middle of the Pacific Plate and formed from volcanic activity.  This is because that part of the plate is moving over a hot spot - a place where hot material is rising up through the mantle (a mantle plume) and generating magma at the base of the oceanic lithosphere (the "plate").  This magma erupts onto the seafloor and eventually builds up the volcanic islands we know as the tropical paradise of Hawaii.

The diagram below illustrates this.  The hot spot is currently under the Big Island and Hawaii and that's why volcanoes like Kilauea are still erupting there.  One million years ago, the Big Island didn't exist and Maui was over the hot spot.  From 1.1 to 1.8 million years ago, Molokai was over the hot spot.  From 2.2 to 3.3 million years ago, Oahu was over the hot spot.  You get the idea.  That's why old volcanoes on Oahu are extinct, they don't erupt anymore.  Oahu moved off the hot spot over two million years ago - there's no more heat and magma to initiate volcanic eruptions.

So, after students have had lectures on plate tectonics, volcanism, etc., we have a lab where students are given a diagram similar to that below (red numbers are ages of volcanic features in millions of years) and asked to calculate the approximate rate of plate movement, in cm/yr (plate movements are almost always reported in centimeters per year) for the Pacific Plate over the past 5 million years.

The first thing many students ask is "What formula do I use?"  This is like a word problem in math where all of the information is given, but some students have no idea what to do with that information because they don't really understand what they're doing.  Then I explain that they need to calculate the velocity of the plate and ask them how velocity is defined.  We finally get to the fact that it's distance divided by time (cm/yr in our plate movement example).

Then some students will proceed to measure the distance from Hawaii to Kauai using the scale bar shown on the map and get a distance of about 550 km or so.   Then they'll divide that by 5,000,000 years and get an answer of 0.00011 cm/yr.  Other students will divide 550 km by 5 million years and get an answer of 110 cm/yr.  Nope, sorry to both, you completely ignored your units and got incorrect answers.  Very common.

The answer, of course, requires you to convert 550 km into centimeters (55,000,000 cm) and 5 million years into 5,000,000 years and then divide to get 11 cm/yr.  If I had simply posed the problem as "Find the distance in centimeters and the time in years and use the formula Rate = Distance / Time, they'd have no problem.  But, when the problem is left more vague, and relies on the understanding that rate is distance over time and that you have to pay attention to your units, many supposedly college-level freshman science majors fall apart.

Why?  Where's the disconnect?  I don't know.  I also get students who multiply instead of divide when working with map scales on topographic maps and tell me that the distance between features within Ulster County is millions of kilometers!  No number sense at all.

Another advantage of home schooling compared to public schooling (my wife and I homeschool our kids).  If they tell us "I don't understand word problems" we'll just concentrate on giving them word problem after word problem until they get it.  In public schools, once you're lost it's likely you'll remain lost.

Auroras

In this final post in my series on sunspots, I want to say a few words about auroras.

Coronal mass ejections (CMEs) from the Sun send out charged particles which interact with the Earth's magnetic field and atmosphere.  When these charged particles come into the Earth's outer atmosphere - the ionosphere - they interact with molecules there to create light. Since the easiest ways for the particles to enter the Earth's atmosphere is near the magnetic north and south poles, those are the areas that most often experience auroras (auora borealis near the North Pole and aurora australis near the South Pole).

The Earth's atmosphere is 78% nitrogen gas (N₂) and 21% oxygen gas (O₂) with 1% everything else.  It's in the ionosphere, also called the thermosphere, where the charged particles (ions) from the Sun first start coming into contact with these atmospheric gases.

As these charged particles come into the outer atmosphere some of them collide with electrons orbiting the oxygen or nitrogen atoms and knock them up to a higher orbital (energy state).  This excitation of the electrons is temporary and the electrons quickly pop back down to a lower orbital giving off energy in the form of photons of visible light as they do so.  The resultant glow from a myriad of these interactions is what forms the aurora.

The color depends on whether or not the molecule being excited in oxygen or nitrogen and it depends on the orbitals an electron is jumping between (from orbital 2 back to 1, from 3 to 2, from 3 to 1, etc.).  Each of these jumps gives off a photon with a characteristic wavelength of visible light energy.  Oxygen emissions tend to be green or brownish-red while nitrogen emissions tend to be blue or red (if both are occuring, a purple color can be seen).  Below is a nice aurora picture showing green, red, and purple light.

Green, however, is the most common color seen in an aurora.  Here's an amazing time-lapse view from National Geographic of mostly-green northern lights over Norway.  Their curtain-like, shimmering shape is due to the charged particles moving along the lines of force of the Earth's magnetic field.

Below is an image of the aurora borealis from the International Space Station (ISS) on September 29 as it orbited over the midwestern U.S. at night. Note the prominant lights of Chicago and St. Louis near the center of the image (from NASA's Earth Observatory web site).

Under favorable conditions, auroras can be seen here in the Hudson Valley (I saw a red one during the last sunspot cycle).  So, hw can you know if a CME erupts during this sunspot cycle and there's a chance to view auroras here in the Hudson Valley (or wherever you live)?  I use SpaceWeather.com which has handy email elerts you can sign up for (in addition to having lots of other neat information).

Sunspots & the Earth

In previous posts, I introduced sunspots, discussed sunspot cycles, and tried to explain why the Sun has sunspots.  As a professor, I'm used to getting the "Why should we care?" argument from students.  My stock answer, expressed a bit more eloquently, is that it's fucking interesting.  But, in the case of sunspots, there are valid reasons why we, as a society, should be interested in them.  Check out this video.




This is a coronal mass ejection (CME) - a massive release of electromagnetic energy and ionized (charged) particles, mostly electrons and protons.  If the event occurs on the side of the Sun facing the Earth, electromagnetic energy from across the spectrum, long-wavelength radio waves to short-wavelength gamma rays, travel to Earth at the speed of light taking only 8.5 minutes or so to get here.  The stream of charged particles takes a bit longer to reach the Earth traveling, on average, about 500 km/s although sometimes reaching speeds of 2000 km/s.  Since the Sun is 150 million km away, it will take the charged particles anywhere from 1-4 days to arrive (depending on their speed).

These eruptions of energy on the Sun are associated with active regions - in other words sunspots.  They're not well understood but are thought to occur when lines of magnetic force break and reconnect releasing stored energy.  As much energy as a billion hydrogen bombs!

What are the consequences of this here on Earth?

Fortunately, here on Earth, we're shielded from much of the dangerous electromagnetic radiation (gamma rays and x-rays) and high-energy charged particles by the Earth's atmosphere and magnetic field.  Future astronauts on the surface of the Moon, or traveling on a ship to Mars, could get radiation poisoning or even be killed by such events (astronauts aboard the International Space Station are in a low-Earth orbit and still somewhat shielded from such events).

OK, you're thinking, I'm not planning a trip to Mars anytime soon so what's the worry?  The problem is that with a large enough CME, our atmosphere and magnetic field become a bit overwhelmed and there are effects here on Earth - some harmless and some more serious.

Our Earth has a magnetic field generated by the rotation of liquid iron in the outer core.  This field normally deflects away the constant stream of charged particles from the Sun (the solar wind).  This solar wind compresses the Earth's magnetic field on the side facing the Sun and stretches it out on the far side into a tail.

During a CME, so many charged particles (ions) interact with the magnetic field that some are able to leak down toward the Earth in the vicinity of the north and south magnetic poles.  Some get trapped in a doughnut-shaped ring called the Van Allen radiation belt and others spiral into the upper atmosphere (called the ionosphere).  These results in auroras.

More on auroras in a bit while we first take a short digression and talk about satellites and power grids...

Satellites are greatly affected by the charged particles released during a CME.  Most satellites don't orbit in the vicinity of the Van Allen belt, but those that do need to have their electronic components radiation hardened to survive.  Satellites in higher orbits are susceptible to damage from the high-energy particles from CMEs.  High energy electrons can physically damage the electronics and solar cells of satellites and even scramble the data stored in computer chips.

Large CME events can also compress the magnetosphere (the magnetic field "bubble" around the Earth) leaving the satellite outside of the protection of the magnetic field and more vulnerable to damage.  In addition, since satellites often use the Earth's magnetic field for guidance, this can disrupt their attitude control systems.  In 1997 and 1998, during the last sunspot cycle, a number of satellites were damaged from CMEs including the AT&T Telstar 401, PanAmSat Galaxy IV, and several Motorola Iridium satellites.  Almost a billion dollars in insurance claims were paid out in 1998 for satellite failures in orbit.

Low-Earth orbit satellites can also suffer from CMEs.  During a CME, the added energy into the Earth's atmosphere causes it to expand.  This creates increased frictional drag on these satellites reducing their orbital life-span.

There is another effect CMEs can have as well.  Large CMEs can induce currents in electrical lines here on Earth.  In March of 1989, two solar cycles ago, a large CME caused the power grid in Quebec to go down resulting in six million people losing power.  Are we still vulnerable 20+ years later?  More so than ever - check out these images from a recent study of this issue (click on the images to enlarge and read the captions).

It's theoretically possible for a large CME to knock out half of the U.S. power grid for weeks to years!  Think about that when wondering if it's worthwhile funding scientific research of the Sun.

Next time I'll post about auroras but for now I'll leave you with some information about the solar "superstorm" or 1859 (thought to be a once in every 500 years event).

On September 1, British astronomer Richard Carrington observed a large CME erupt from the Sun which took only 18 hours to reach the Earth (a velocity for the particles of over 2,000 km/s).  This triggered a massive geomagnetic storm on Earth resulting in auroras seen around the world (most notably down in the Caribbean!).  There were reports of people here in the Northeast being able to read newspapers by the light of the auroras at night.  Telegraph systems throughout the world failed.  Sparks flew from wires, operators received electrical shocks, and telegraph paper even caught fire.

Such an event today, in our electrified, wired world, would be literally catastrophic.

Why do we have sunspots?

In my last post, I talked about solar cycles and sunspots but I didn't explain what exactly sunspots were and how they formed.

First, to recap, we know that there is a roughly 11 year sunspot cycle where we go from essentially no sunspots on the surface of the Sun to a period of high sunspot activity and then back to essentially no sunspots again.

Large version here

It also turns out that sunspot position on the Sun is not random.  Graphing where sunspots appear during the sunspot cycle yields the famous "Butterfly Diagram" showing that, at the start of the sunspot cycle, sunspots initially appear near ±30° of latitude and then, as the cycle progresses, sunspots appear closer and closer to the equator.

Large version here

Keep in mind that the sunspots themselves don't move (although they appear to from Earth during the rotation of the Sun) but form, typically exist for a couple of weeks or more, and then dissipate.  Where they pop up on the surface of the Sun, however, is what changes during the sunspot cycle and is reflected on the butterfly diagram above.

What else have we learned about sunspots?

Well, a sunspot can be over 50,000 km across (for reference, the diameter of the Earth is about 12,750 km) and consists of two visible parts - the darker central umbra (Latin for shadow) and the lighter surrounding penumbra (the Latin prefix means almost or nearly).  The image below shows a large sunspot group (AR 1339 from November 4) with a filtered telescope.  Note the clearly visible umbra and penumbra for each sunspot.

Sunspots are darker than the surrounding Sun because they're cooler.  The surface of the Sun is around 6000 K (over 10,000° F) and sunspots are 1500 K (~2250°) or more cooler.  So, while they appear dark compared to the rest of the Sun, if you could somehow take a sunspot off the Sun and place it by itself in space, it would glow brightly in the sky!

The next image shows a sunspot a bit more dramatically.  This image was taken in August of 2010 at the Big Bear Solar Observatory in the San Bernadino Mountains of California.  This image was taken with a special filter called a hydrogen alpha (Ha) filter. It's a filter that only passes a narrow bandwidth of visible light at a wavelength of 656 nm (6.56 x 10^-7 m). This is the energy given off by electrons in a hydrogen atom falling from the 3^rd to the 2^nd orbital. The Sun, being a big ball of mostly hydrogen gas, gives off a lot of energy at this wavelength and these filters bring out a lot of detail on the "surface" (photosphere) of the Sun.

This image shows a granulation around the sunspot.  Those are the tops of convection cells where hot gases are "bubbling" up from deeper in the Sun.  Here's a neat animation of solar activity.

Click for image source

This convection of hot, ionized gas (plasma) generates the Sun's magnetic field.  Because the Sun is a big ball of gas, it doesn't rotate at the same speed everywhere - it takes about a 9 days less to rotate at the equator (~25 days) than it does near the poles (~34 days).  This differential rotation leads to magnetic flux tubes in the convection zone of the Sun getting twisted up (they actually behave much like rubber bands).  This inhibits convection and leads to the development of a cooler sunspot (don't ask me to explain this any better since I'm not a solar physicist).

Magnetic lines of force also pop up above the photosphere often leading to the formation of two sunspots of opposite magnetic polarity (one where the magnetic field emerges from the photosphere, the other where it reenters the Sun).  Sunspots have about 1000 times more magnetic energy than surrounding areas of the Sun.

Below is a magnetogram image of the Sun for today (November 13).  Black indicates areas where the Sun's magnetic lines of force are coming toward us and white indicates areas where the Sun's magnetic lines of force are moving away from us.  Compare this to the visible image of the Sun for today and you can see that major black and white areas correlate with the positions of sunspots.

Another interesting thing about the magnetic field of the Sun is that it has a 22-year cycle.  Every 11 years it reverses its polarity (i.e. the north and south magnetic poles flip).  Obviously closely tied into the 11-year sunspot cycle!

Anyway, models to explain this 22-year cycle are all based on the differential rotation of the Sun affecting the internal convection and thus changing the magnetic field over time.  If the Sun rotated faster or slower, or the convection zone was thicker or thinner, or convection was faster or slower, this cycle would be different.  The details are messy and I don't understand them myself (phrases like "...regeneration of the poloidal field by lifting and twisting a toroidal flux tube by helical turbulence..." follow by a page of equations are typical in the literature.

So, you may be thinking, sunspots are cool looking features on the surface of the Sun that we don't fully understand but do they have any significance for us here on Earth?  Yes, as a matter of fact they do.  That will be the topic of the next post.

Sunspot cycles

In a previous post, I had discussed how Galileo had begun making systematic observations of sunspots with a telescope starting in 1610.  Science has been observing sunspots ever since.  This led to the discovery of a sunspot cycle in 1843 by German astronomy Samuel Heinrich Schwabe (1789-1875).  This cycle averages 11 years (rounded off) but can range from 9 to 14 years in length.

Solar maximum                                                             Solar minimum

Each 11-year cycle goes from a solar minimum to a solar maximum and then back to a solar minimum again.  At a solar maximum, there are a lot of sunspots on the surface of the Sun. At a solar minimum, there are few to no sunspots.

The numbering scheme for solar cycles was developed by Swiss astronomer Rudolph Wolf (1816-1893) who began with the cycle starting in March of 1755.  The last solar cycle, number 23, peaked around April 2000 and we're currently in cycle 24, which began on January 8, 2008, and is expected to peak in May of 2013.  The current solar cycle seemed to be slow getting started and has exhibited about 50% less sunspot activity than expected.

One of the interesting things about the sunspot cycle is that its intensity varies cycle to cycle - at least over the past few hundred years of observation.  Keep in mind that the Sun has been around for four-and-a-half billion years.  If sunspot cycles have always averaged 11-years (highly improbable), then there would have been over 400 million sunspot cycles (and we've only observed a couple of dozen!).  Astronomers have been carefully observing, with satellites, only for the past couple of cycles.

Shortly after the earliest scientific studies of sunspots by Galileo, the Sun went quiet.  From about 1645 to 1715, sunspots practically disappeared from the Sun (that's a span of six or so sunspot cycles).  It's been named after English astronomy Edward Maunder (1851-1928).  Other minimums include the Dalton Minimum (1790-1830) and the Spörer Minimum (1460-1550) named for an event identified by the radiocarbon (¹⁴C) concentration in tree rings (¹⁴C is produced in the atmosphere strongly correlates with solar activity).

In more modern times we seem to be in a period of increased solar activity (except for the current sunspot cycle).  One of the most intense cycles was number 19 which peaked around 1960.  Why the variations?

I'll save that for the next post...

11/11

Wow, it's 11:11:11 on 11/11/11.  Cool.  Waiting for something wonderous to occur...  Anything...  No???  Just another banal moment on a Friday morning???  How disappointing.

Anyway, even though the magic of numerology didn't work for me today, I did want to say thanks to all those veterans and active duty military out there!

"We sleep soundly in our beds because rough men stand ready in the night to visit violence on those who would do us harm."

[Attributed to Winston Churchill]

While I don't always agree with what out government does with our military, there are a lot of people out there who wish us harm simply because we don't believe the way they do, and I certainly support the men and women in uniform who stand ready to risk their lives in our defense.

Sunspots & the Sun's Rotation

As my previous post mentioned, I had a sunspot observation on campus Tuesday afternoon.  It went well.  Most of the students seemed to enjoy seeing the sunspots, some were blase about it, and others walked by with no interest whatsoever even when asked if they'd like to see the Sun through a telescope.

The right image is from today at 2100 UTC (4:00 pm EST) and the left image is 4 days earlier.  Note how the sunspots move because the Sun is rotating on its axis.  It takes about 25 days for a rotation (at the equator, it takes longer as you move toward the poles due to the fact that the Sun is a big ball of gas, not a rigid body).  One can observe sunspots and easily work out this rotational period.

While there are scattered references to sunspot observations with the naked eye from ancient Chinese and Greek observers, Galileo was one of the first to observe them with a telescope starting in 1610 and he was able to show that they were actual features on the surface of the Sun and moved as the Sun rotated.

In the Aristotelian cosmology which still ruled in the early 1600s, and which was backed by the Roman Catholic Church, the Sun was a perfect and unblemished celestial body.  In was inconceivable to some that it had darks spots on it.  Christoph Scheiner (1573-1650), a Jesuit priest/astronomer, was one and he argued that these dark spots represented small satellites orbiting the Sun.

Careful observations by Galileo, however, showed that the sunspots moved more slowly when they were near the limb of the Sun and more quickly when they were in the center of the Sun.  This was due to foreshortening as shown in the diagram below.  A sunspot moving from A to D would travel the same distance as from D to C.  From the Earth, however, the A-D distance looks shorter than the D-C distance.  That makes it appear as if the sunspot was moving faster between D and C.

The idea that heavenly objects like the Sun were perfect and unblemished held sway for over 1,500 years because people philosophically liked the idea and it conformed to their religious beliefs.  A few simple observations, however, was all that was needed to topple this incorrect view.  No wonder the religious authorities of the day (and even some today) hated science.

Big Sunspots

Tomorrow afternoon, I'll be looking at the Sun with my observational astronomy students.

We have a solar filter (it basically looks like the one at right) for our telescope which passes only a small fraction of the visible light and cuts the harmful infrared and ultraviolet radiation.  Without it, looking at the Sun with a telescope will result in instant damage to your eyes.

The reason we're going to take a look at the Sun (other than the fact that it's interesting), is to observe a large group of sunspots that have been rotating into view.  It's called Active Region (AR) 1339.

Below is a solar image from 2345 UTC (7:45 pm EDT) on November 5 showing the large active region around the 10 o'clock position on the face of the Sun.

Check out this image of AR 1339 from Mexican amateur astronomer César Cantú (click here for a higher resolution image on his website).

When looking at this sunspot group, keep in mind that each of those darker dots is about the size of the Earth!  They're incredibly beautiful close up - almost looking like abstract art.

Sunspots often flare up, causing coronal mass ejections (CMEs) that send billions of tons of ionized gas screaming out into space.  If the sunpot is facing toward the Earth, this ionized gas interacts with the Earth's magnetic field and outer atmosphere resulting in a geomagnetic storm and strong auroral activity.

Keep an eye on SpaceWeather.com which will issue alerts if there are any CMEs in the next few days and the possibility of seeing an aurora.

Sunspots are fascinating phenomenon, I think I'll write more about them later this week.

Oklahoma Earthquake

On Saturday, November 5, at 2:12 am CDT, a 4.7 magnitude earthquake hit central Oklahoma (about 45 miles east of Oklahoma City between the towns of Prague and Sparks).  It was a foreshock followed by 7 others ranging from magnitude 2.7 to 3.6 and then culminating in a 5.6 magnitude quake at 10:53 pm CDT.  As of 8:00 am CST, there have been a dozen aftershocks ranging from 2.7 to 4.0 on this fault according the the National Earthquake Information Center (only quakes above magnitude 2.5 are reported).

From Oklahoma Geological Survey Observatory

On February 27, 2010, there was a magnitude 4.3 earthquake near this location as well.  The largest earthquake in Oklahoma, previous to Saturday's, was a 5.5 magnitude quake near El Reno just west of Oklahoma City back in 1952.  Moderate earthquakes, while not common, do occasionally occur in Oklahoma (as they do in other places in the continental interior - remember the 5.8 magnitude Virginia earthquake in August?).

 

From Oklahoma Geological Survey Observatory

All of these recent earthquakes were relatively shallow at 5 km (3 miles) or so of depth.  According to the Oklahoma Geological Survey, these earthquakes appear to have occurred on the Wilzetta Fault (line with red squares in the above map).  For those of you who know something about geology, the focal mechanism seems to indicate dextral strike-slip movement.

Not much information online regarding the Wilzetta Fault and associated Seminole Uplift (it's an area that's been studied, however, since there's oil and gas there).  Looks to me like strike-slip reactivation of an older basement thrust fault associated with the Pennsylvanian/Permian Alleghanian-Ouachita Orogeny.

Professor or Hobo?

Professor or Hobo?  Take the quiz!

I dedicate this to the late Dr. Russell Waines of SUNY New Paltz, a former professor of mine who would have fit right into this quiz.

Never judge a book by its cover or a man by his clothes (or scraggly beard).