Causes of induced seismicity

A variety of human activities can induce earthquake sequences. A breakdown of the causes and proportions documented in HiQuake is shown below.

Maximum magnitude per human activity

What is the largest earthquake a specific human activity can induce? We do not know. In theory, earthquakes of any magnitude could be induced by human activity, since nearly all of the energy released by large earthquakes is natural in origin. Indeed, large earthquakes occur naturally with no human intervention. The graph below shows the maximum observed magnitudes to date for various human activities proposed to induced seismicity.

Number of cases per magnitude range

The graph below shows the number of cases in HiQuake per magnitude range. The different lines represent the different human activities as defined by the key. The most commonly reported induced earthquakes have magnitudes 2 ≤ M < 4. These cases are dominated by mining, surface water reservoir and fracking projects. The most commonly reported fracking-induced earthquakes have magnitudes 2 ≤ M < 3.

Injection volumes and maximum magnitudes

One of the most successful theories for determining the maximum magnitude earthquake an injection activity may cause is that of McGarr (2014), who proposed that the maximum magnitude earthquake for fluid injection activities may be limited by the injected fluid volume. This theoretical limit holds for most cases, but there are exceptions and it does not explain why some projects do not achieve their predicted maximum magnitude.