A new European satellite has given us a new way to monitor the impact of earthquakes. Sentinel measure the small changes in the position of parts of the Earth's crust by comparing 'before' and 'after' images of an area that has experienced an earthquake. Analysis of these results can show where stresses in the crust are being concentrated which may allow for predictions to be made about the location of subsequent tremors.
In the search to find a method of effectively predicting seismic events, any new tool that can contribute has to be welcomed.
Over the last few weeks you may have noticed that one of Iceland's many volcanoes has been getting more active, generating hundreds of volcanoes in a day. Bárðarbunga is one of the volcanoes underneath the huge ice sheet of Vatnajökull and though it is a mafic eruption it does have the potential to create similar aviation problems that Eyjafjallajökull caused in 2010 because of its similar sub-glacial setting. So far there has been a little ash and a fissure eruption as a dyke reached the surface. The aviation warnings have fluctuated from yellow to orange and then back again. Perhaps the bigger hazard is from a jökulhlaup that can be triggered by the melting of the glacial ice from the volcano's heat. It will be worth keeping an eye on what's happening with this.
For the latest updates, check out the website of the Icelandic Meteorological Office.
The earthquake hazard map of the USA has a major seismic puzzle. It's not the high hazard in California (CA) caused by the San Andreas Fault or in Washington (WA) and Alaska (AK) easily explained by the occurrence of subduction zones around the Pacific Ring of Fire. There is another high hazard zone along the Mississippi River further east.
Harri P in Year 12 drew my attention to this odd occurrence of earthquakes thousands of kilometres from a plate boundary. There have been some major seismic events in this region, in particular the magnitude 7 New Madrid earthquakes of 1811-12. The cause of these 'quakes was a puzzle until a few years ago when a team of geologists from the University of Quebec discovered a slab of crust that is descending into the mantle, disrupting the flow of the mantle and the crust in this area. It is similar in some ways to a subduction zone but without the fold mountains, trench and volcanoes. It does pose a continuing danger of creating major earthquakes.
It is a very strange phenomenon and goes to show just how much we still have to discover about how the crust and the mantle work.
Los Angeles will be struck by a devastating earthquake.... soon. We don't know when but we do know that it will happen. By recording the earthquakes along the San Andreas Fault for nealry the last 200 years it is very apparent that through the 20th century the fault hasn't moved much comapred to the frequent earthquakes along the fault during the 19th Century. Contrary to what many people would think, geologists know that this is a "bad thing" because if the fault is locked, energy is being built up in the fault so that when it moves it will move a lot.
At the American Geophysical Union conference in San Fransisco, geoscientists from the US Geological Survey have been posing the question "is LA ready for a megaquake?"
Read through the article, do you think that they can cope with a shock on the scale predicted?
A Griffith Crack is a mechanism to explain how rocks, which can be very strong materials, are fractured by stress in the crust. Microscopic cracks in the rock, which can be the result of a flaw or inclusion in a mineral, will concentrate the tensile stress in a rock. This can lead to the expansion (or propagation) of the crack and even to failure of the rock resulting in a fault.
A big earthquake has struck southern Pakistan. A magnitude 7.7 seismic event has killed at least 30 people in Balochistan Province and been felt around much of the region.
This is a big earthquake but the death toll may not rise too high (though any deaths are a tragedy for the people involved). This area is sparsely populated and poor; many of the houses are low-rise and made of mud so when they collapse in the shaking, they are less likely to kill than stone structures. There is a real danger though of more people dieing in the aftermath of the event from food, shelter and water shortages than died in the earthquake itself.
UPDATE: 25/9/13
The death toll has , unsurprisingly, risen to over 200 at the latest count. More surprising has been the appearance of a new island off the coast of Pakistan. As the stress has changed in the plate, it has deformed to push the sea bed above sea level to make new land.
A slideshow of photographs from the area affected.
In 2010 and 2011 the city of Christchurch on New Zealand's South Island was heavily affected by a series of large earthquakes. The worst of these was the 22nd February earthquake that as well as causing some 185 deaths also severely damaged many buildings including the city's Victorian cathedral. Much of the damage was caused, not by the power of the earthquake which wasn't that large, but by the liquefaction of the ground that the city is built on.
Video explanation of liquefaction
Footage of liquefaction
To replace the cathedral that was built from stone, a new one has been constructed using cardboard as a light and cheap material to quickly give Christchurch an important step to recovery after such a devastating event.
BBC News story
We have known since the 1960s that humans can cause earthquakes by pumping water into rocks. The technique has even been used to release the stress on faults by triggering small earthquakes (though with litle real success). An attempt to generate geothermal energy in Switzerland in 2009 by injecting water deep under the Alps resulted in a prison sentence for the owner of the company when earthquakes were triggered under the city of Basel.
Earthquakes under Basel
Recent research has shown that distant earthquakes combined with injection of waste water into the ground can set off relatively large earthquakes, even a 5.7 magnitude event in Oklahoma. Why then is this relevant to us? With our increasing need to find reliable sources of energy from geothermal sources or by fracking shale for gas, we are injecting a lot of water into the ground, particularly in the US so events like these may become more common. A lot of fuss was made about some very small earthquakes near Blackpool because of fracking activity.
Fracking Earthquakes - BGS report
The question is whether our need for energy is worth the inconvenience of increased seismic activity?
Predicting earthquakes is difficult, really difficult. Geologists in America have been working on ways to collect data from a wide area to enable predictions and possibly warnings to be made. Small seismometers plugged into internet routers have been used, with some success. The latest developments are to use smart phones to record and report data as they have positional data (from their built-in GPS) and shaking data (from their accelerometer). There are some problems with the system, such as telling the difference between someone bumping into a table and an earthquake and with the sensitiy of the accelerometer. These may create too many problems with false alarms in the US but there is huge potential for trying to make predictions in the developing world where they may lack infrastructure, but the use of mobile phones is very common.
Can you suggest any other ways that you think a smart phone could be used to help to manage the effects of hazards?
BBC News story
Red Cross Earthquake App
