Comment on “Deformation of compliant fault zones induced by nearby earthquakes: Theoretical investigations

[1] Duan et al. [2011] recently presented analysis of deformation caused by dynamic and static stress changes on fault zones that have reduced strength and effective elastic moduli relative to the ambient rocks. Low-rigidity fault zones were previously proposed to explain anomalous geodetic signals around major crustal faults in the vicinity of large earthquakes [e.g., Fialko et al., 2002; Fialko, 2004; Hamiel and Fialko, 2007; Barbot et al., 2009]. Duan et al. [2011] claimed that “some deficiencies may exist” in the previously published results (in particular, those presented by Fialko et al. [2002]), and called for a reexamination of existing observations. Unfortunately, claims made by Duan et al. [2011] appear to stem from their misunderstanding of the published data and theory. Here I refute claims made by Duan et al. [2011], and explain why their arguments are flawed. [2] Inferences of low-rigidity zones surrounding major crustal faults have been made based on a number of seismic [e.g., Li et al., 1994; Ben-Zion et al., 2003; Spudich and Olsen, 2001; Cochran et al., 2009], and geodetic [e.g., Lisowski et al., 1991; Chen and Freymueller, 2002; Fialko et al., 2002] observations. Such zones most likely result from extensive damage associated with slip on faults, in agreement with geologic evidence [Faulkner et al., 2003; Oskin and Iriondo, 2004; Chester et al., 2005; Dor et al., 2006]. [3] Compliant fault zones are of considerable interest as they encapsulate a long-term record of time-dependent damage and healing associated with the earthquake cycle, likely affect the earthquake rupture dynamics, bear on the issue of strain localization in the brittle upper crust, and may even hold clues about the magnitude of stress at seismogenic depths [e.g., Hearn and Fialko, 2009]. Thus more studies of compliant fault zones are certainly warranted, from both the observational and theoretical perspectives. [4] Duan et al. [2011] (hereafter, DKL11) explored the effects of plastic yielding of fault zones due to dynamic stress changes from passing seismic waves, and compared predictions of their elastoplastic simulations to those of the elastic inhomogeneity model like that previously invoked to explain InSAR observations of small-scale strain anomalies on a number of faults in the Eastern California Shear Zone [Fialko et al., 2002; Fialko, 2004]. In the framework of the elastic inhomogeneity model, the observed strain anomalies represent elastic response of massive compliant fault zones to static stress changes from a nearby earthquake.