A Method to Generate Initial Fault Stresses for Physics-Based Ground-Motion Prediction Consistent with Regional Seismicity

To better understand how normal stress heterogeneity affects earthquake rupture, we conducted laboratory experiments on a 760 mm poly (methyl‐mathacrylate) PMMA sample with a 25 mm “bump” of locally higher normal stress (∆σbt). We systematically varied the sample‐average normal stress () and bump prominence (). For bumps with lower prominence () the rupture simply propagated through the bump and produced regular sequences of periodic stick‐slip events. Bumps with higher prominence () produced complex rupture sequences with variable timing and ruptures sizes, and this complexity persisted for multiple stick‐slip supercycles. During some events, the bump remained locked and acted as a barrier that completely stopped rupture. In other events, a dynamic rupture front terminated at the locked bump, but rupture reinitiated on the other side of the bump after a brief pause of 0.3–1 ms. Only when stress on the bump was near critical did the bump slip and unload built up strain energy in one large event. Thus, a sufficiently prominent bump acted as a barrier (energy sink) when it was far from critically stressed and as an asperity (energy source) when it was near critically stressed. Similar to an earthquake gate, the bump never acted as a permanent barrier. In the experiments, we resolve the above rupture interactions with a bump as separate rupture phases; however, when observed through the lens of seismology, it may appear as one continuous rupture that speeds up and slows down. The complicated rupture‐bump interactions also produced enhanced high frequency seismic waves recorded with piezoelectric sensors.

Section: Effect Of the Bump On Earthquake Spectramentioning

confidence: 94%

Laboratory Earthquake Rupture Interactions With a High Normal Stress Bump

Cebry,

Sorhaindo,

McLaskey

2023

“…Introducing high-frequency radiation in dynamic rupture models to simulate broadband data (0-10 Hz) is a challenging problem. As also demonstrated here, simple elliptical models with constant or smooth dynamic parameters do not generally radiate an omega-square source spectrum, but instead generate depleted high-frequency strong ground motions (Kaneko & Shearer, 2015;Madariaga, 1976;Oral et al, 2022). Madariaga (1977) associated local omega-square radiation with abrupt changes in rupture velocity due to, for example, frictional or stress heterogeneity (Pulido & Dalguer, 2009).…”

mentioning

confidence: 55%

“…We prescribe a linearly increasing slip‐weakening distance from a small nucleation patch. Such a model generally allows an approximately constant rupture velocity (Aochi & Ide, 2004; Kaneko & Shearer, 2015; Oral et al., 2022) and a relatively small nucleation patch, preventing overly strong nucleation that would contaminate the rest of the spontaneously propagating rupture (Galis et al., 2015). We define an ad‐hoc model with

{D}_{\mathrm{c}}^{\mathrm{s}\mathrm{m}\mathrm{o}\mathrm{o}\mathrm{t}\mathrm{h}}(\rho )=0.05[\mathrm{m}]+0.08\rho [\mathrm{k}\mathrm{m}],

where ρ is the distance from the assumed nucleation, see Figure 2.…”

Section: Resultsmentioning

confidence: 99%

“…We prescribe constant normal stress We prescribe a linearly increasing slip-weakening distance from a small nucleation patch. Such a model generally allows an approximately constant rupture velocity (Aochi & Ide, 2004;Kaneko & Shearer, 2015;Oral et al, 2022) and a relatively small nucleation patch, preventing overly strong nucleation that would contaminate the rest of the spontaneously propagating rupture (Galis et al, 2015). We define an ad-hoc model with…”

Section: Elliptical Modelmentioning

confidence: 99%

“…Madariaga (1977) associated local omega-square radiation with abrupt changes in rupture velocity due to, for example, frictional or stress heterogeneity (Pulido & Dalguer, 2009). Numerical experiments with self-similar initial stress distributions along planar faults (keeping frictional parameters constant or smooth) improve the high-frequency radiation, but still not enough, mainly for frequencies above 1-2 Hz (e.g., Andrews & Ma, 2016;Baumann & Dalguer, 2014;Oral et al, 2022;Ripperger et al, 2007). Note that although Valentová et al (2021) considered all dynamic parameters to vary smoothly along the fault, they still underestimated spectral accelerations (SAs) above 1-2 Hz with respect to a ground motion model (GMM, Boore et al, 2014).…”

mentioning

confidence: 99%

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

Gallovič

Valentová

2023

Dynamic rupture modeling represents a promising physics‐based approach to strong ground motion simulations. However, its application in a broad frequency range (0–10 Hz), interesting for engineering studies, is challenging. The main reason is that widely used and relatively simple planar fault models with smooth distributions of initial stress and frictional parameters, or even self‐similar initial stress, result in ground motions depleted in high‐frequency content. Here we propose an efficient approach for the linear slip‐weakening friction model on a planar fault based on the Ide and Aochi (2005, https://doi.org/10.1029/2004jb003591) multiscale model with a small‐scale random fractal distribution of the slip‐weakening distance Dc. We propose a way to combine these variations with a large‐scale deterministic dynamic model. We illustrate the approach on an elliptical model and a smooth model of the 2016 Mw 6.2 Amatrice, Italy, earthquake from low‐frequency dynamic rupture inversion. To intensify the incoherence of the rupture propagation, we also include a variation of the strength and initial stress, both correlated with Dc. These additions result in sustained high‐frequency radiation during the whole rupture propagation and omega‐square source time functions. The new model of the Amatrice earthquake generates synthetics that agree with the local ground motion model up to 5 Hz in terms of spectral accelerations while preserving the average and integral dynamic rupture parameters (e.g., stress drop, fracture and radiated energy). The fractal dynamic model can be easily implemented in any dynamic rupture propagation code and is thus readily applicable in broadband physics‐based ground motion predictions for earthquake scenarios in seismic hazard assessment.

Dynamic Rupture Modeling of Large Earthquake Scenarios at the Hellenic Arc Toward Physics‐Based Seismic and Tsunami Hazard Assessment

Wirp,

Gabriel,

Ulrich

et al. 2024

The Mediterranean Hellenic Arc subduction zone (HASZ) has generated several 8 earthquakes and tsunamis. Seismic‐probabilistic tsunami hazard assessment typically utilizes uniform or stochastic earthquake models, which may not represent dynamic rupture and tsunami generation complexity. We present an ensemble of ten 3D dynamic rupture earthquake scenarios for the HASZ, utilizing a realistic slab geometry. Our simplest models use uniform along‐arc pre‐stresses or a single circular initial stress asperity. We then introduce progressively more complex models varying initial shear stress along‐arc, multiple asperities based on scale‐dependent critical slip weakening distance, and a most complex model blending all aforementioned heterogeneities. Thereby, regional initial conditions are constrained without relying on detailed geodetic locking models. Varying epicentral locations in the simplest, homogeneous model leads to different rupture speeds and moment magnitudes. We observe dynamic fault slip penetrating the shallow slip‐strengthening region and affecting seafloor uplift. Off‐fault plastic deformation can double vertical seafloor uplift. A single‐asperity model generates a 8 scenario resembling the 1303 Crete earthquake. Using along‐strike varying initial stresses results in 8.0–8.5 dynamic rupture scenarios with diverse slip rates and uplift patterns. The model with the most heterogeneous initial conditions yields a 7.5 scenario. Dynamic rupture complexity in prestress and fracture energy tends to lower earthquake magnitude but enhances tsunamigenic displacements. Our results offer insights into the dynamics of potential large Hellenic Arc megathrust earthquakes and may inform future physics‐based joint seismic and tsunami hazard assessments.