As previously discussed, microseismic events are generated when pore pressure reaches a pre-existing fracture plane and induces slip. This process is described in more detail in Chapter 10 as well as how microseismic data can be used to better understand the stimulation process.

To use the microseismic data properly, it is important to understand what can be determined and the limitations of such information. To this end, the topics considered in this chapter briefly consider how microseismic monitoring is carried out, how we know the events reflect shear slip on pre-existing faults, how accurately we know the locations of the seismic events, what can be determined about the seismic sources in terms of the size of the faults that slip (and the distribution of fault sizes) and the geometry of slip as defined by focal plane mechanisms (first introduced in Chapter 7).