Seismological Indicators of Geologically Inferred Fault Maturity

Abstract

Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.

Fault Orientation Trumps Fault Maturity in Controlling Coseismic Rupture Characteristics of the 2021 Maduo Earthquake

“…Previous studies have argued that faster rupture speeds, to even super‐shear speeds, should occur along smoother and structurally more mature faults rather than geometrically rough and immature faults (Bruhat et al., 2016; Guo et al., 2023; Perrin, Manighetti, Ampuero, et al., 2016). By contrast, our observations from the Maduo earthquake suggest that the structurally less mature fault, if more stress‐optimally oriented, promoted a faster and more energetic rupture, more localized deformation, and larger coseismic slip.…”

“…The process affects the fault organization at all scales and might influence the source properties of earthquakes. For example, it has been proposed that immature faults, compared to more mature faults, often have a more complex geometry (Manighetti et al., 2021; Stirling et al., 1996; Wesnousky, 1988), produce slower rupture speed and smaller coseismic slip (Guo et al., 2023; Perrin, Manighetti, Ampuero, et al., 2016), higher percentage of off‐fault deformation (Dolan & Haravitch, 2014; Milliner et al., 2021), and a wider deformation zone (Perrin et al., 2021). However, evolving faults intrinsically have spatially varying maturity and geologic inheritance along strike, for instance with more immature sections toward the fault propagation direction (Perrin, Manighetti, & Gaudemer, 2016).…”

Revisiting the San Andreas Heat Flow Paradox From the Perspective of Seismic Efficiency and Elastic Power in Southern California

“…However, in a recent study Guo et al. (2023) find that the scaled energy may depend non‐monotonously on the geological maturity of the fault, with peak scaled energy at intermediate maturity and lower scaled energy at low and high maturity. They propose increased energy dissipation in fracture growth for the very immature, and lack of high‐frequency radiation in mature faults as mechanisms for this dependency.…”

“…The study of Guo et al. (2023) might, in conjunction with a detailed study of the seismic moment rate distribution across the Southern Californian fault system, be a promising starting point for future tests of this hypothesis 4.…”

“…The significance of the surface energy E S within the overall energy budget of earthquakes on a fault can vary on a fault‐to‐fault basis, and is presumably related to the structural maturity of the fault (a measure of the slip history; Guo et al., 2023). For instance, on one end of the maturity scale Zang et al.…”