Induced Seismicity

As most of us know, humans are creating a huge impact on the natural processes of the earth.  CO2 levels have risen dramatically, oil spills have created substantial problems for the environment and ecosystems, and glaciers are melting which have more then one problem that can be associated with their departure. These are very well known issues which need to be fixed.  An issue that is not well known but has a an extremely large impact on the earth and how humans live is induced seismicity.

Scientists describe this issue as earthquake activity that humans have caused.  Just like how CO2 has certain historical levels that changed dramatically after humans came into existence the same has happened with seismic activity.  Seismic activity has stayed at certain levels throughout history and have recently changed with increased human activities.   There are several reasons why this can be caused but some background information is necessary in order to help understand the causes.

There are fluids in the earth that create pressure.  The fluid resides in pores and cracks in the rocks.  This pressure is called pore pressure.  If the pore pressure is low then only natural imbalances may cause slight earthquakes.  If the pore pressure is high then less of an imbalance is necessary to create an earthquake accelerating earthquake activity in the process. By knowing this information, we can understand how by injecting water into the subsurface of the earth or by extracting water this can cause an imbalance in the pressures of the earth.  We can see these events occurring at injection wells and production wells.  Another type of induced seismic activity associated with what was just discussed is called hydrofracturing.  This activity is done by injecting fluid into the ground to create a distinct fracture which links to another fracture in order to create permeability in the ground.  The name hydrofracturing can only be applied if the the forces create a tensile fracture, also known as a “driven” fracture.  The main purpose of hydrofracturing is to extract oil and gas easier.  It is to be noted, though, that due to the short duration of the extraction period and other factors hydrofracturing is not a major cause of induced seismic activity.  One other possible cause of increased seismic activity is due to thermal changes and/or chemical changes with the fluid movement or injections.  In regards to human activities, this includes geothermal reservoirs, waste injections, oil and gas operations, and underground injections for waste disposal.

This is certainly an issue that not many people realize is happening.  It is also crazy to think that we could be the cause of something as big as an earthquake.

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