Re: Is oil and gas extraction one of the reasons for Earthqu
Earthquakes happen because of stresses and strains in the sub-surface.
These can be released slowly - over days - or rapidly - in a few seconds. The "slow earthquakes" have only recently been identified by having fixed GPS markers and monitoring accurately how things move; we tend to feel the "fast" ones, especially when the magnitude pushes above 2.5-3.0
The additional stresses and strains caused by drilling, oil and gas extraction and hydraulic fracturing are usually much smaller than those that already exist in the earth, so in that sense these activities alone do not "cause" earthquakes.
However, some activities associated with oil and gas production can make critical changes to the stress/strain underground, and can "trigger" a quake under certain circumstances; where this happens the chances are that a slow or fast earthquake was going to happen sooner or later anyway, the exploration activities just brought the timeline forward.
When oil or gas is produced water - which at those depths is heavily contaminated with salt and other minerals, not drinking water - replaces the oil or gas in the rock pores; in the short term this makes no difference, but over many years the overall pressure can drop. The pressure in the fluids - oil, gas or water - is one of the things that help to support the weight of the rocks, so when this drops, you get subsidence and associated earth tremors. The Groningen "super giant" gas field has been in production for more than 25 years, and the subsidence was known and being monitored as far back as the mid 1990s.
Hydraulic fracturing has been shown to lead to an increased earthquake risk in several studies, however only as a result of the disposal of the water-waste in deep bore holes. This practice is banned in some states and in Europe. The deep disposal of waste water (many km below the drinkable water table) is not just used in hydraulic fracturing, but other industries too. Disposal of the waste water is a big problem for hydraulic fracturing - there's a huge R+D effort into using less water, as well as better ways of "cleaning" the water. Its a big issue for farming too - hydraulic fracturing of a single well needs about the same amount of water as 70 dairy cows need in a year, with similar effluent disposal problems.
- oil and gas production does not "create" earthquakes
- in some geological settings it can be a contributing factor to the timing of an earthquake
- disposal of waste water in deep bore holes can be a significant factor in this triggering
- some places allow the disposal of waste water from hydraulic fracturing in deep bore holes
How the stress and strain released in one earthquake event modifies the probability of other events is very complex; the longer the interval between events the more catastrophic the earthquake is likely to be.