Constraints on the Near‐Distance Saturation of Ground‐Motion Amplitudes for Small‐to‐Moderate Induced Earthquakes

Abstract

The accurate modeling of ground motion for induced-seismicity hazard estimation is critically dependent on how amplitudes scale with distance near the hypocenter. A rich database of ground motions from small events recorded at close distances in the Geysers region of California has been used to constrain the near-distance saturation effects that control the maximum observed ground motions and intensities for shallow-induced events. The results of this study support the modeling of these effects using an equivalent point-source concept, in which the effective source depth increases from a value near 1 km at moment magnitude (M) of 2 to a value near 3 km at M 4. This near-distance saturation behavior can be applied to the development of ground-motion models for induced seismicity in any region. BSSA Early Edition / 1

Are Ground‐Motion Models Derived from Natural Events Applicable to the Estimation of Expected Motions for Induced Earthquakes?

“…Pointsource scaling concepts suggest that events of M 3.5 should not have significant near-distance saturation. This has recently been confirmed by analysis of empirical data from induced events in the Geysers, California, region (Atkinson et al, 2016) and in Oklahoma (Yenier et al, 2017); these recent analyses support the alternative-h saturation shape in A15.…”

“…Empirical data in both CENA and California show that steep attenuation (R −1:3 in the first 50 km in the Fourier domain) is required to match the observed decay rate for small events, whereas for larger events there is a trade-off between the attenuation rate and the near-source saturation term (e.g., Yenier and Atkinson, 2014). The median value of the near-distance saturation term is constrained empirically (e.g., Atkinson et al, 2016), but it also shows much variability, which maps into aleatory variability in amplitudes at close distances.…”

“…The A15 model originally considered two alternatives for the term in the functional form that controls near-distance saturation scaling. It has since been determined, using additional data, that of the two considered saturation models, the one called the alternative-h model is more appropriate (Atkinson et al, 2016). This model features a saturation distance (h) that increases from a value of 2.4 km at M 3.5 to a value of 7.2 km at M 6.…”

Source Spectral Properties of Small to Moderate Earthquakes in Southern Kansas

“…In addition to their utility in understanding source dynamics, source parameter estimates may also provide observational constraints for seismic hazard assessment. Because ground motion intensities at high frequencies are controlled primarily by stress drop (Baltay et al, , ; Boore, ; Douglas & Edwards, ; Yenier & Atkinson, ), its characterization is of fundamental interest to studies that aim to develop ground motion prediction equations for induced events (Atkinson & Assatourians, ; Atkinson et al, ; Yenier et al, ). In this study, we observe quantifiable time‐dependent and depth‐dependent variations in stress drop, both of which are in accord with the conclusions of Yenier et al () and Atkinson and Assatourians () for ground motions of recent seismicity in Oklahoma.…”

“…Scientific consensus has attributed much of the elevated seismicity rate to anthropogenic activity and in particular to the injection of wastewater from the oil production process into the Arbuckle Group that is stratigraphically above the granitic basement (e.g., Buchanan, 2015;Ellsworth, 2013;Ellsworth et al, 2015;Rubinstein & Mahani, 2015;Walsh & Zoback, 2015;Yeck et al, 2017). The abrupt increase in seismic hazard within this region (Petersen et al, 2016(Petersen et al, , 2017 has spurred numerous observational studies focused on connections between fluid injection and seismicity rates (Barbour et al, 2017;Choy et al, 2016;Goebel, 2015;Keranen et al, 2013Keranen et al, , 2014Weingarten et al, 2015), the source properties of a subset of the larger events (Boyd et al, 2017;Choy et al, 2016;Cramer, 2017;Sumy et al, 2017;Walter et al, 2017), and observed ground motion amplitudes (Atkinson & Assatourians, 2017;Atkinson et al, 2016;Hough, 2014;Yenier et al, 2017). Although these studies have rapidly advanced scientific understanding of these earthquakes, there is still much that remains unanswered, and the nonstationary nature of the seismicity warrants continued monitoring.…”