Update, Comparison, and Interpretation of the Ground‐Motion Prediction Equation for “The Geysers” Geothermal Area in the Light of New Data

Abstract

The reliability and accuracy of the ground-motion prediction equations(GMPEs) are of prime interest while evaluating seismic hazard for any region. Theregular updates and minimization of the uncertainties associated with the coefficientsof the GMPEs are important for improving ground-motion predictions and consequentperformance of seismic hazard maps.Thus, in the present study, we propose an update of the GMPEs estimated bySharmaet al.(2013)in The Geysers geothermal area. The update is done usingthe huge dataset available and by extending the magnitude range as well as distancerange. The previous dataset used bySharmaet al.(2013)was composed of 212 earth-quakes recorded at 29 stations with the magnitude range between1:3≤Mw≤3:3anddistance range between0:6≤Rhypo≤20km. The new dataset encloses 10,974induced earthquakes recorded at 29 stations with the magnitude range between0:7≤Mw≤3:3and distance range between0:1≤Rhypo≤73km. We computeupdated GMPEs for peak ground velocity (PGV), peak ground acceleration (PGA),and 5% damped spectral acceleration (SA) (T)atT0.05, 0.1, 0.2, 0.5, and 1.0 s.The mean ground-motion predictions of the updated model proposed in thepresent study and the associated uncertainties are compared with the previous modelproposed bySharmaet al.(2013)and with other models specifically developed forsmall-magnitude earthquakes. The GMPEs are derived using a nonlinear mixed-effectregression technique that accounts for both interevent and intraevent dependencies inthe data. We also demonstrate the dependency of aleatory (random) uncertainties andepistemic (informative) uncertainties on source, medium, and site properties. We alsoconcluded that the medium is behaving homogeneously in terms of peak ground-motion attenuation by analyzing uncertainties associated with different ground-motion periods.