Abstract
Abstract. The effects of the spatiotemporal evolution of failure threshold heterogeneity on the dynamics of fault criticality, and thus on regional seismogenesis, have attracted strong interest in the field of regional seismotectonics. The heterogeneity might be a manifestation of the macroscopic distribution and multiscale strength variation of asperities, the distinct regional stress level, and (microscopically) heterogeneous fault surface roughness or friction regimes. In this study, rather than attempting to mimic the complex microscale slipping physics on a fault surface, sandpile cellular automata were implemented with a straightforward toppling rule. The objective is to examine the influence of distinct configurations of the embedded heterogeneous toppling threshold field on the global system avalanche event statistics. The examination results revealed that increasing the coverage extent and decreasing the compactness of the heterogeneous failure threshold, rather than the magnitude, range of contrast, diversity, or the geometric configuration of the threshold heterogeneity, leads to a systematic increase in the scaling exponent of the avalanche event power law statistics, implying the importance of mutual interaction among toppling sites with distinct thresholds. For tectonic provinces with differing stress regimes evolving spatio temporally, it is postulated that the distinct extent and compactness of the heterogeneous failure threshold are critical factors that manifest in the reported dynamic variations of seismicity scaling.
Highlights
Rate- and state-dependent friction regimes lead to the manifestation of dynamic failure heterogeneity along a fault surface (Skarbek et al, 2012), whereas Prieto et al (2013) discussed thermal runaways that are controlled by temperature, pressure, and the degree of partial melting as another potential heterogeneous mechanism
They showed that the frequency–size scaling associated with these heterogeneous failure threshold fields behaves differently from that associated with a uniform threshold field. They postulated that when the dispersion in the failure threshold decreases, the critical system with the existence of a spinodal line crosses over to the self-organized criticality (SOC) regime and that pronounced heterogeneous failure threshold enforces the dependence of the critical behavior on the velocity of the loader plate. This loader plate velocity is a crucial parameter in the slider-block model, and it is sometimes envisioned to be analogous to the plate convergence rate that acts as the slow external drive for plate boundary seismogenesis
It is concluded that the systematic variation of the scaling exponent is controlled by the coverage extent of the embedded heterogeneity rather than the intensity level or the contrast range of the threshold (Fig. 2)
Summary
Recent studies of repeating earthquakes (e.g., Uchida et al, 2012; Yu, 2013) and mega-earthquakes such as the 11 March 2011 Tohoku-oki earthquake (Lay and Kanamori, 2011; Hashimoto et al, 2012; Tajima and Kennett, 2012) have indicated that heterogeneous slipping thresholds, which refer to the spatiotemporally distinct limits of failure stress that must be overcome to initiate slipping such as that manifested because of variations in the plate coupling strength (e.g., Yu, 2013), introduce dynamic complications in the plate boundary seismogenesis (Chlieh et al, 2011). Brodsky and Kanamori (2001) showed that hydrodynamic lubrication can help in reducing fault friction and that earthquakes can increase the effective permeability of distant aquifers. This loader plate velocity is a crucial parameter in the slider-block model, and it is sometimes envisioned to be analogous to the plate convergence rate that acts as the slow external drive for plate boundary seismogenesis These findings are intriguing because a heterogeneous failure threshold, as a plausible manifestation of varying roughness and friction regimes on the fault surface, is consistent with field observations and general geological understanding. We have briefly reviewed the observational evidence supporting heterogeneous failure threshold fields on realistic faults and the noticeable variation of the G–R scaling exponent, the b value. We have reviewed both the cellular automata and the physical modeling approaches that typically invoke homogeneous failure threshold fields with different loader plate velocity or implanted fractal heterogeneity to account for the variation of the scaling exponent of the frequency–size power law distribution. Dynamic evolution can be induced through invoking the annealed updating while fixing a particular proportion of the heterogeneity
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