So, what caused this earthquake???
Well, some scientists believe that it could be caused by the release of stress from a small thrust fault in the region. The impact of the earthquake was then increased by the fact that, because it occured far away from major plate boundaries, the continental rock is much older (bedrock beneath Virginia is believed to have formed when the continents collided to form a supercontinent about 500-300 million years ago) and denser, so more like a solid sheet of bedrock, and so the seismic waves were permitted to travel further.
Another suggestion is that fracking could have caused the earthquake. Now I don't personally know that much about fracking but I will try and explain why some believe that a recent rise in fracking could have provoked the earthquake. Correct me if I am wrong but I believe that fracking, or hydraulic fracturing, is the man-made splintering of underground rocks to speed up the exploitation of natural resources and, since its inception in 2004, has become increasing popular as it can allow for the recovery of oil and gas supplies. Due to the impact that fracking can have on the geological make-up of the Earth many are starting to insinuate that it could cause earthquakes. In locations were fracking occurs, the waste salt water produced is injected back into the earth (after the fractures have been created) and some estimate that, in each well, 3 million gallons of waste is injected. With reference to the East of USA, earthquakes, as previously mentioned are rare, but the surrounding area has experienced 8 minor tremors last year alone - an area that has also seen an increase in fracking operations over the past few years.
This is not the only earthquake that some are suggesting has been caused by fracking. The USGS have said that "Earthquakes induced by himan activity have been documented in a few locations in the United States, Japan and Canada" with "The cause the injection of fluids into deep wells for waste disposal and secondary recovery of oil and the use of reservoirs for water supplies". Geologists have more recently blamed fracking for the 20 tremors witnessed in the state of Arkansas in one day; also similar size earthquakes have been experienced in Texas, New York and Oklohoma, all of which are not normally likely locations for epicentres but have experienced a significant increase in fracking over the last few years. What is quite interesting is that the multi-stage fracking being held responsible (it drills several miles deep into the Earth), has only recently, over the past 2 years, become prevalent in the above mentioned areas, all of which have seen a rise in tremors, and have since banned fracking - an action that seems to have been followed by a reduction in size and frequency of tremors. Since this, more states are now reviewing their current legislation on fracking.
So, what do you think? Is it possible that these earthquakes are really being caused by fracking and if so, along with some of its other detrimental impacts, is this reason to prevent it from being utilised in the future? Do you actually think that we would ever place a global ban on it, due to our increasing hunger for energy and dwindling supplies of oil? On the other hand, do you feel that a release of stress from the thrust boundary is a more logical explanation? My knowledge on this is a bit limited so if anyone knows are more I would love to hear about it! Let me know what you think.........
Whilst on the topic of earthquakes, I read this other blog that is related to geography (kind of more human geography I suppose and is one that Millie suggested) written by this person from Sheffield University, and he produces these really interesting maps as a graphical way of presenting data (they are a bit different to maps I have ever seen before!). He wrote a post yesterday on the earthquake, although it focuses a bit more generally just on earthquakes as a whole and the impacts, which is definetly worth a read. Magnitude 5.9: Earthquakes revisited I do try and keep some sort of balance between my human and physical geography posts but if you are ever looking for something human related to read, his posts are often quite interesting - it is included on my (extremely short!) blogs I read list at the bottom of the blog so keep an eye out for it in the future! If you ever come across anyother earth science related blogs you think are worth reading just let me know - I am always looking for different things to read!