Inelastic models of lithospheric stress-11. Implications for outer-rise seismicity and dynamics

Abstract

S U M M A R YOuter-rise seismicity and dynamics are examined using inelastic models of lithospheric deformation, which allow a more realistic characterization of stress distributions and failure behaviour. We conclude that thrust-and normal-faulting outer-rise earthquakes represent substantially different states of stress within the oceanic lithosphere. Specifically, the normal-faulting events occur in response to downward plate bending, which establishes the 'standard', bending-dominated state of outer-rise stress, and the thrust-faulting events occur in response to an elevated level of in-plane compression, which develops only in response to exceptional circumstances. This interpretation accounts for the observation that normal-faulting outer-rise earthquakes occur more frequently and are more widely distributed than their thrust-faulting counterparts, an observation for which the simple bending model offers no explanation. In addition, attributing both thrust-and normal-faulting outer-rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution, whereas, in reality, this is not observed. We propose that the tendency for thrust-faulting outer-rise earthquakes to exhibit greater source depths than their normal-faulting counterparts (an observation that is frequently cited in support of the bending interpretation of the former) is merely a consequence of the fact that bending-induced tension is confined to the upper lithosphere. Our model predicts that outer-rise in-plane-force variations may promote thrust-faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer-rise activity following such an earthquake, but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake. A corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer-rise earthquakes. Levels of in-plane compression necessary to generate thrust-faulting outer-rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate-driving forces. Resistance of this nature may result from either the attempted subduction of relatively buoyant (i.e. isostatically compensated) bathymetric features or the existence of strong interplate asperities.

Modeling the evolution of the Guadalquivir foreland basin (southern Spain)

“…Instead, in our modeling the inversion occurs over a maximum curvature point (Figure 10c). The reader is referred to the work by Mueller et al [1996a, 1996b] for further details on this subject.…”

The 2011 Northern Kermadec earthquake doublet and subduction zone faulting interactions

“…[4] The relationship between interplate stress cycles and intraslab earthquake activity has been of interest, because it reveals intuitive aspects of stress transfer, faulting interactions, and seismic hazard that may be quantitatively modeled [e.g., Isacks et al, 1968;Stauder, 1968;Abe, 1972;Ruff and Kanamori, 1980;Christensen and Ruff, 1988;Dmowska et al, 1988;Lay et al, 1989;Liu and McNally, 1993;Dmowska et al, 1996;Taylor et al, 1996;Mikumo et al, 1999;King, 2007;Ammon et al, 2008;Lay et al, 2009]. However, it has also been shown that viscoelastic deformation can complicate the behavior [e.g., Mueller et al, 1996aMueller et al, , 1996bLay et al, 2009].…”

Inelastic models of lithospheric stress-I. Theory and application to outer-rise plate deformation

“…However, the strain rate associated with a specified tectonic process is determined by the ratio of accumulated strain and the accumulation time. Estimates of the accumulated strain determined by Mueller, Spence & Choy (1996), combined with a recurrence interval of the order of one century, indicate that the strain rate associated with in-plane-force variations is comparable to that associated with outer-rise flexure.…”

“…Christensen & Ruff 1988). The manner in which either of these may lead to substantial levels of in-plane compression within the outer-rise complex is discussed in Mueller et al (1996). The loading sequence represented in Fig.…”

“…If it is assumed that outer-rise seismicity is exclusively associated with a brittle rheology (e.g. Sibson 1982Sibson , 1984Miller & Furlong 1988;Scholz 1990;Tullis 1994;Mueller et al 1996), the loading sequence represented in Fig. 6(a) would be exclusively associated with thrust-faulting earthquakes, whereas that in Fig.…”