Scientists Link Deep Wells To Deadly Spanish Quake 118
Meshach writes "Research has suggested that human activity triggered an earthquake in Spain that killed nine and injured over three hundred. Drilling deeper and deeper wells to water crops over the past 50 years were identified as the culprit by scientist who examined satellite images of the area. It was noted that even without the strain caused by water extraction, a quake would likely have occurred at some point in the area but the extra stress of pumping vast amounts of water from a nearby aquifer may have been enough to trigger a quake at that particular time and place."
Comment removed (Score:4, Informative)
Re:It's too complicated for me to understand ... (Score:4, Informative)
Most quake prone areas have a frequency in single digit years, not hundreds of years.
Hell the bad areas can have quakes on a monthly or weekly basis.
Humans don't cause quakes, we can only trigger them.
The stress was there with or without the pumping, and that stress must be relieved.
Usually caused by adding water (Score:5, Informative)
Human-induced earthquakes are usually caused by water injection, or more precisely by increasing pore fluid pressure which in turn has the effect of decreasing the rock's confining pressure. Basically, the water inside the rock pushes out in all directions with a (typically very high) pressure related to the height of the water column in hydrostatic communication with it above. The rock above is also pushing down, but other considerations aside, this confining pressure from the weight of the rocks tends to lock faults together preventing them from moving. The effective confining pressure is reduced by the pore fluid pressure pushing the rock apart. If you add to the water column the extra weight of the water may be minuscule compared to the increase in pressure caused by the greater height of the water column. That extra pore water pressure can then allow other forces, previously held in check by the rock's confining pressure, to break the fault causing an earthquake.
The most common place for this to occur is in filling new reservoirs and in deep waste injection wells used for disposal of fluids from oil and gas production. Suck quakes are usually very small, but I think they've been observed in rare cases above magnitude 5.
Removing water is a much less common cause of earthquakes. Pumping, for both water and oil, can ground subsidence, but rarely earthquakes. It will, however, subtly affect the balance of forces on a fault, so it's not inconceivable that it could cause a fault already near the breaking point to slip. I'd be curious to see the fault geometry and movement on the fault that caused the earthquake in Span.
Re:It's too complicated for me to understand ... (Score:5, Informative)
In this one they removed large quantities of water from the aquifer. While technically no energy was added to the system, the water's removal lowered the potential energy floor, essentially adding the potential energy of the now-too-high ground to any stress energy which had already been built up (if any).
An analogue to this case would be sinkholes caused by extracting or receding water from underground aquifers/caves. The removal of the water itself directly causes the sinkhole, or in this case the quake. Depending on the quantity of water removed (and thus the distance the ground above had to "settle"), there might not even have been any natural fault slippage involved, and this quake could have been entirely manmade.