Ground motions characterized by a multi-scale heterogeneous earthquake model

Abstract

We have carried out numerical simulations of seismic ground motion radiating from a mega-earthquake whose rupture process is governed by a multi-scale heterogeneous distribution of fracture energy. The observed complexity of the Mw 9.0 2011 Tohoku-Oki earthquake can be explained by such heterogeneities with fractal patches (size and number), even without introducing any heterogeneity in the stress state. In our model, scale dependency in fracture energy (i.e., the slip-weakening distance D c ) on patch size is essential. Our results indicate that wave radiation is generally governed by the largest patch at each moment and that the contribution from small patches is minor. We then conducted parametric studies on the frictional parameters of peak (τ p ) and residual (τ r ) friction to produce the case where the effect of the small patches is evident during the progress of the main rupture. We found that heterogeneity in τ r has a greater influence on the ground motions than does heterogeneity in τ p . As such, local heterogeneity in the static stress drop (Δτ) influences the rupture process more than that in the stress excess (Δτ excess ). The effect of small patches is particularly evident when these are almost geometrically isolated and not simultaneously involved in the rupture of larger patches. In other cases, the wave radiation from small patches is probably hidden by the major contributions from large patches. Small patches may play a role in strong motion generation areas with low τ r (high Δτ), particularly during slow average rupture propagation. This effect can be identified from the differences in the spatial distributions of peak ground velocities for different frequency ranges.

Role of multiscale heterogeneity in fault slip from quasi-static numerical simulations

“…Comparing these results with the coseismic process, it is expected that small patches may keep a high slip rate if rupture onset on them is delayed. Note that the small patches are mostly hidden when a surrounding patch is sliding, if the phase of the peak friction is simultaneous among the patches (e.g., Aochi and Ide 2014).…”

Broadband Strong Ground Motion Modeling Using Planar Dynamic Rupture With Fractal Parameters

“…The original model of Ide and Aochi (2005) was defined as fractal and random at all scales without any deterministic component. In practical applications, it will be helpful to preserve the large‐scale properties of the model imposed in a deterministic way using, for example, low‐frequency dynamic source inversions (Aochi & Twardzik, 2020; Fukuyama & Mikumo, 1993; Gallovič et al., 2020; Herrera et al., 2017; Peyrat & Olsen, 2004; Ruiz & Madariaga, 2013) or a generator of low‐frequency dynamic scenarios (Aochi & Ide, 2014; Aochi & Ulrich, 2015; Harris et al., 2021; Valentová et al., 2021). Therefore, here we aim to introduce random small‐scale perturbations to large‐scale (low‐frequency) dynamic rupture models, requiring: the high‐frequency radiation is produced throughout the whole rupture propagation, the moment rates and the apparent moment rates have omega‐square Fourier spectra, for different random realizations of the small‐scale perturbations, the large‐scale rupture propagation and low‐frequency radiation are affected as little as possible. …”

“…The original model of Ide and Aochi (2005) was defined as fractal and random at all scales without any deterministic component. In practical applications, it will be helpful to preserve the large-scale properties of the model imposed in a deterministic way using, for example, low-frequency dynamic source inversions (Aochi & Twardzik, 2020;Fukuyama & Mikumo, 1993;Herrera et al, 2017;Peyrat & Olsen, 2004;Ruiz & Madariaga, 2013) or a generator of low-frequency dynamic scenarios (Aochi & Ide, 2014;Aochi & Ulrich, 2015;Harris et al, 2021;Valentová et al, 2021). Therefore, here we aim to introduce random small-scale perturbations to large-scale (low-frequency) dynamic rupture models, requiring:…”

Preface for the special issue of “New Perspective of Subduction Zone Earthquakes”

“…(1)The Nankai trough (14 papers; Sugihara et al 2014, Tsuji et al 2014, Idehara et al 2014, Akuhara and Mochizuki 2014, Hyodo et al 2014, Takahashi et al 2014, Yamada and Shibanuma 2015, Takeshita et al 2014, Hino et al 2015, and Toki et al 2014) (2)The Japan trench (6 papers; Aochi and Ide 2014, Koge et al 2014, Sawai et al 2014, and Boston et al 2014) (3)Other trenches and fault zones (4 papers; Maekawa et al 2014, Namiki et al 2014) and ancient accretionary complexes and faults on land (7 papers; Schumann et al 2014, Hamahashi et al 2015, Kogure et al 2014, and Hashimoto and Yamano 2014) (4)Theoretical treatments of fracture and earthquake (2 papers; Kame et al 2014 andNishiyama et al 2014) The papers are also categorized into three scientific issues, focusing on different regions within each topic:…”