Finally, step 4 involves estimating the probability that structures and people are affected (cell 4A). Analytical methods for seismic risk analysis (cell 4B) are well established for tectonic earthquakes, and these should be applicable to induced earthquakes. The methods will not depend on technology (cell 4C), because a structure’s response does not depend on how the shaking was generated. However, the methods do depend on region (cell 4D); structures outside of California and Alaska are generally not designed to withstand high levels of ground shaking, and people in aseismic regions may be less tolerant of low-level shaking than those who have previously felt natural earthquakes. Deeper earthquakes will have an influence on the numbers of structures and people affected (cell 4E) if the associated earthquake shaking covers a wide region and affects more structures and people.
Table 5.2 summarizes steps that can be taken to estimate hazard and risk for individual energy projects. The specific statistical data that need to be collected, and analytical methods that need to be modified from other fields, are summarized in column B. Each of the statistical or analytical methods in column B will calculate the probability indicated in the corresponding cell in column A, and these calculations will depend on the corresponding cells in columns C, D, and E. For instance, statistical data on M ≥ 2 earthquake generation (cell 1B) need to be collected and analyzed by energy technology, volume of fluid, injection pressure, rate of injection, etc. An unstated assumption in Table 5.2 is that data are to be collected for new energy projects in areas that are known to have a history of induced seismicity, as well as existing projects. The reason is that, going forward, we presumably are interested in estimating hazard and risk from induced seismicity caused by further expansion of energy production, not by existing energy production. However, data from existing projects will allow forecasts of induced seismicity for industries as a whole. The distinction is important: seismicity induced by a new injection or disposal well will differ from seismicity induced by a well that has been in production for years, where crustal stresses may have equilibrated.
Note that steps 1 through 3 apply regardless of whether the potential induced seismicity will occur in areas of high population or sparse population. Step 4 determines the effect on structures and people, and this effect of course depends on the location with respect to structures at risk and people. Induced seismicity could be caused in a region of sparse population, affecting few people, but could affect dams, bridges, or power plants, with large concurrent costs.
These steps, if developed, can be used in three important ways:
First, by compiling statistics on earthquake generation by technology and characteristics (cell 1C), insight can be gained on what combinations of volumes, pressures, rates of injection/extraction, and so on lead to higher probabilities of induced seismicity. This insight can be used to create well-documented, data-based input to best practices protocols (see also Chapter 6).
Second, energy technology development, whether through public or private efforts, will have data with which to make decisions to minimize induced seismicity effects on