Risk assessment of anomalous induced seismicity

Abstract

Anomalous induced seismicity (AIS) is defined as the induced seismic events larger than moment magnitude (Mw) 0. Moderate-sized seismicity (that is, around Mw 4) has the potential to be felt by humans and damage infrastructure. Industrial operations such as hydraulic fracturing, have the potential of creating AIS. A risk assessment before such an operation is important. It helps us better understand, control and mitigate the risk of AIS. In this thesis, several practices applied to the risk assessment of AIS are examined. This thesis consists of three parts. First, refinements are made on the fault slip potential (FSP) analysis to utilize more information and provide a more comprehensive preliminary assessment of the risk. FSP analysis quantifies the likelihood of fault reactivation under the current knowledge. Second, guidance is given on choosing locations for additional samples because reducing the uncertainty in key parameters with more samples improves the accuracy of the risk assessment. Here the key parameter is the in situ stress. Simulations show that the optimal locations for adding samples are in the least-sampled areas. Third, practical tactics are applied to simplify the risk assessment process and make effective decisions to mitigate the risk. Because giving quantitative measurements of the risk of AIS is complex, the three-level risk evaluation system is implemented to assess the risk qualitatively. This approach is applied to an operation in Fox Creek, Alberta. The anticipated risk of AIS is transferred into an expected loss in the decision tree analysis. Using the decision tree, how the anticipated risk affects the decision-making process is demonstrated. The risk assessment of AIS becomes more complete by adopting these suggestions.