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.
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