Arkansas Earthquakes

Location of M4.7 earthquake, Feb. 28, 2011
From here.

A reader inquired about the Arkansas earthquakes and so, while I have little expertise in this area, I thought that I'd feature them today.  Some of this material is taken from the WWW site of the Arkansas Geological Survey (AGS).

Earthquakes have been noticed in Arkansas as far back as 1699 (by missionaries traveling down the Mississippi River). This region was affected by the 1811-1812 New Madrid earthquakes, and intermittent earthquakes have been felt since then. Current earthquake activity (available on the Arkansas site), which is not on the New Madrid fault zone, generally consists of several M2 - M2.5 earthquakes on most days, although on April 8, a pair of M3.9 earthquakes hit central Arkansas, about 35 miles north of Little Rock. About 1000 quakes have hit the region since September, 2010. The largest was a M4.7 on Feb. 27, the biggest quake to hit the state in 35 years.

Concerns have been raised that injections of wastewater from natural-gas production were related to the seismicity. The wells are owned by Chesapeake Energy and Clarita Operating.  The region is underlain by an "organically rich rock formation", a major source of natural gas.  To extract the gas, pressurized water, containing a slew of chemicals, is injected to create fractures deep in the ground, a process known as 'fracking.' When the fracking water is no longer useable, it is disposed of by injecting it into the ground. At the request of the Arkansas Gas and Oil Commission, the owners ceased operations of the injection wells on March 4, well before these April 8 M3.9 earthquakes. Scott Ausbrooks, a geo-hazards supervisor for the AGS says that it may be too early to rule out a cause-and-effect with the injection process.

Is the seismicity related to fracking? It seems like there is not a definitive experiment. Will fracking cause permanent changes in the shallow crust? Likely--once you've fracked a rock, you can't unfrack it.  It takes energy to fracture rocks (this energy comes from the motors of the engines that drive the fluids into the rocks), and you can't un-frack the rocks easily.  There are many questions and concerns raised about fracking, including not only the stability of the rocks and seismicity, but water quality as large volumes of water filled with chemicals are injected into the rocks. Fracking has been going on for a long time, and so the energy extraction industries have a lot of experience with this technique, but public awareness and concern has increased dramatically the past couple of years because of the increased emphasis on extraction of natural gas reserves.

Dust storms in Arizona

With apologies for not having time to interpret and research, I think that the Arizona dust storms will be of inerest.http://ireport.cnn.com/blogs/ireport-blog/2011/07/19/haboob-ii-return-of-the-dust?&hpt=hp_c2a

Happy New Year, Neptune!!

Neptune. It's blue appearance is due to traces
of methane in its atmosphere. The spots, like
the spots in Jupiter's atmosphere, indicate active
weather patterns.
 NASA Hubble Space Telescope photo.

Amidst all of the dismal stories on CNN.com regarding the national debt ceiling, bombings in Mombai, scandal in the British news media, there's a bit of joy in the Happy Birthday, Neptune, story!

Neptune is the farthest planet from the Sun, the fourth-largest planet by diameter, and has 17 times the mass of the Earth. It is about 30 times the distance from the sun as the earth.  It was discovered on September 23, 1846 and was the first planet found because of a mathematical prediction. Alexis Bouvard, a French astronomer could not predict the orbit of Uranus accurately without invoking a gravitational perturbation by an unknown planet.  It was subsequently observed by Johann Galle, and shortly after, it's largest moon, Triton, was discovered as well.  (When Voyager 2 flew by Triton in 1989, its instruments detected erupting geysers on the surface, see reference below.) It has the strongest sustained winds of any planet in the solar system, a record of 2100 km/hour (583 m/s).

Why "Happy Birthday?"  Neptune's "year" is 164.8 Earth years, so only now has Neptune returned to the same spot in its orbit as it had when it was discovered in September, 1846. Neptune has four seasons, like earth, but each season lasts about 41 Earth years.

References on Triton's geysers:

Soderblom, L.A., Becker, T.L., Brown, R.H., Cook II, A.F., Hansen, C.J., Kirk, R.L., Kieffer, S.W., Shoemaker, E.M. and Johnson, T., Triton's geyser-like plumes: discovery and basic characterization, Science, v. 250, pp.410-415, 1990. PDF

Kirk, R.L., Soderblom, L.A., Brown, R.H., Kieffer, Susan W., and Kargel, J.S., Triton's eruptive plumes: discovery, characteristics, and models, in Neptune and Triton, ed. D. Cruikshank, University of Arizona Press, 949-989, 1995.