Interpretation is the science of finding meaning in data. The primary purpose of microseismic monitoring is to develop insights into the nature and extent of brittle deformation processes in the subsurface. Passive-seismic monitoring has many applications, including monitoring of fluid stimulation for enhanced geothermal systems and mine-safety protocols. The main focus of this chapter is passive seismic monitoring of MW < 0 induced microseismicity associated with hydraulic fracturing, although the interpretation workflow is more broadly applicable and could be used, for example, in passive seismic monitoring of geothermal stimulation programs. Interpretation of passive-seismic data for induced seismicity, considered here as events with MW ≥ 0, is the subject of the next chapter. In the case of hydraulic-fracture monitoring, microseismic data are generally acquired for the following purposes:

There is considerable research potential for development of more advanced microseismic interpretation methods, such as quantifying the state of stress, imaging discrete fracture networks, time-lapse studies, understanding possible slow-slip processes and reservoir characterization, including facies analysis.

In this chapter, a systematic approach to microseismic interpretation is introduced. This approach is guided by an underlying philosophy that the interpretation of any experimental data should be repeatable, observation-driven and, to the greatest extent possible, quantitative. As part of this approach, applicable uncertainties in measured quantities should be reported, along with metadata describing how reported uncertainties were obtained. The proposed interpretation procedure is built upon four key concepts: