Earthquake activity has increased recently in parts of the U.S. midcontinent. Some of that increase has been associated with human activity, rather than occurring naturally. Earthquakes associated with human activities are referred to as induced or triggered (as opposed to natural) seismicity. They include both small events that cannot be felt, but are measureable by sensitive instruments, and larger events that may be felt and that can cause damage1. Disposal of fluids from oil and gas production, geothermal energy production, mining, construction, disposal of waste fluids, and impoundment of large reservoirs can cause induced seismicity. Determining whether a single earthquake is natural or induced can be extremely difficult, in part because fluids may be injected in areas where earthquakes occur naturally. In some situations, however, it is possible to correlate fluid injection with an increase in the frequency and/or magnitude of earthquakes. Efforts are underway to understand and prevent human-caused earthquakes that are strong enough to be felt or cause damage; this includes voluntary efforts by industry and by more comprehensive regulatory arrangements. Both are supported by more thorough information collected and managed on a coordinated basis by industry and both state and federal agencies, including state geological surveys. The following statement discusses seismicity, induced seismicity, causes of induced earthquakes, means to prevent such occurrences, and expresses the position of the Association of American State Geologists (AASG).
- Position Statement