Earthquakes and errors: Methods for industrial applications

Abstract

The high accuracies and realistic confidence assessments demanded for seismic monitoring of hydraulic fracturing work require specialist experimental approaches. These include seismic network design based on quantitative modeling, high-quality instrument deployments, and accurate and detailed crustal models. Confidence estimates must take into account uncertainties about crustal structure, which may dominate error budgets. Earthquake size should be expressed in terms of scalar seismic moment or the associated moment magnitude [Formula: see text], which is related to fundamental physical source processes, and not as traditional earthquake magnitudes. Representing earthquake mechanisms in terms of seismic moment tensors allows for processes such as volume changes and complex types of shearing that are important in hydrocarbon and geothermal reservoirs. Traditional fault-plane solutions are based on simplifying assumptions such as shear slip on a planar faults, and isotropic crustal structures, which may introduce large uncertainties. Quantitative assessment of confidence regions for moment-tensor source mechanisms, a newly emerging field, is important for distinguishing computational artifacts from real physical phenomena. We review methods currently available for realistic error estimation for earthquake locations and moment tensors, with particular emphasis on surface sensor arrays in geothermal areas.