The hidden simplicity of subduction megathrust earthquakes

Meier, Men‐Andrin; Ampuero, Jean‐Paul; Heaton, Thomas H.

doi:10.1126/science.aan5643

Cited by 103 publications

(153 citation statements)

References 47 publications

(53 reference statements)

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“…Combining this moment‐rate equation with the rupture‐tip‐equation‐of‐motion, one can numerically solve for the rupture speed and stress drop distributions along strike based on the STF if an additional assumption is adopted, for instance, a relation between G c and final slip. This approach could be used to infer statistical properties of fault stress and strength from the statistical properties of large catalogs of STFs (Meier et al, ). If the slip (and thus stress drop) distribution has been well constrained for an event, for instance by geodetic or remote sensing data, the rupture speed distribution can be computed from equation and then the fracture energy distribution can be derived from the rupture‐tip‐equation‐of‐motion.…”

Section: Discussionmentioning

confidence: 99%

The Dynamics of Elongated Earthquake Ruptures

Weng

Ampuero

2019

JGR Solid Earth

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The largest earthquakes propagate laterally after saturating the fault's seismogenic width and reach large length‐to‐width ratios L/W. Smaller earthquakes can also develop elongated ruptures due to confinement by heterogeneities of initial stresses or material properties. The energetics of such elongated ruptures is radically different from that of conventional circular crack models: they feature width‐limited rather than length‐dependent energy release rate. However, a synoptic understanding of their dynamics is still missing. Here we combine computational and analytical modeling of long ruptures in three dimension (3D) and 2.5D (width‐averaged) to develop a theoretical relation between the evolution of rupture speed and the along‐strike distribution of fault stress, fracture energy, and rupture width. We find that the evolution of elongated ruptures in our simulations is well described by the following rupture‐tip‐equation‐of‐motion: Gc=G0()1−v̇rWvs2γAαsP where Gc is the fracture energy, G0 is the steady state energy release rate, vs is the S wave speed, vr is the rupture speed, v̇r=dvr/italicdt is the rupture acceleration, and γ/AαsP is a known function of rupture speed. The steady energy release rate is limited by rupture width as G0 = γ∆τ2W/μ, where γ is a geometric factor, ∆τ is the stress drop (spatially smoothed over a length scale smaller than W), and μ is the shear modulus. If Gc is a constant and exactly balanced by G0, the rupture can in principle propagate steadily at any speed. If Gc increases with rupture speed, steady ruptures have a well‐defined speed and are stable. When Gc ≠ G0, the rupture acquires an inertial effect: the rupture‐tip‐equation‐of‐motion depends explicitly on rupture acceleration. This inertial effect does not exist in the classical theory of dynamic rupture in 2‐D unbounded media and in unbounded faults in 3D, but emerges in 2‐D bounded media or, as shown here, as a consequence of the finite rupture width in 3D. These findings highlight the essential role of the seismogenic width on rupture dynamics. Based on the rupture‐tip‐equation‐of‐motion we define the rupture potential, a function that determines the size of next earthquake, and we propose a conceptual model that helps rationalize one type of “supercycles” observed on segmented faults. More generally, the theory developed here can yield relations between earthquake source properties (final magnitude, moment rate function, radiated energy) and the heterogeneities of stress and strength along the fault, which can then be used to extract statistical information on fault heterogeneity from source time functions of past earthquakes or as physics‐based constraints on finite‐fault source inversion and on seismic hazard assessment.

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Section: Discussionmentioning

confidence: 99%

The Dynamics of Elongated Earthquake Ruptures

Weng

Ampuero

2019

JGR Solid Earth

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“…Point source time functions are routinely determined by the SCARDEC method (e.g., Vallée and Douet, 2016). Efforts are under way to synthesize the accumulated data sets (e.g., Kanamori, 2014;Lay, 2015;Ye et al, 2016bYe et al, , 2016cDenolle and Shearer, 2016;Meier et al, 2017;Melgar and Hayes, 2017;Hayes, 2017), and we will not attempt to summarize the multitude of studies. Large shallow coseismic slip occurred in the 2015 Illapel (e.g., Li et al, 2016;Melgar et al, 2016), 2011 Tohoku (e.g., Lay et al, 2011b;Iinuma et al, 2012;Ozawa et al, 2012;Satake et al, 2013;Romano et al, 2014;Bletery et al, 2014;Melgar and Bock, 2015;Lay, 2017), 2010 Maule (e.g., Vigny et al, 2011;Yue et al, 2014b;Yoshimoto et al, 2016;Maksymowicz, et al, 2017), and 2004 Sumatra (e.g., Ammon et al, 2005;Rhie et al, 2007;Fujii and Satake, 2007) events, accompanying slip on the downdip portions of the megathrusts.…”

Section: Spatial Variations Of Slipmentioning

confidence: 99%

Subduction zone megathrust earthquakes

2018

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Subduction zone megathrust faults host Earth's largest earthquakes, along with multitudes of smaller events that contribute to plate convergence. An understanding of the faulting behavior of megathrusts is central to seismic and tsunami hazard assessment around subduction zone margins. Cumulative sliding displacement across each megathrust, which extends from the trench to the downdip transition to interplate ductile deformation, is accommodated by a combination of rapid stick-slip earthquakes, episodic slow-slip events, and quasi-static creep. Megathrust faults have heterogeneous frictional properties that contribute to earthquake diversity, which is considered here in terms of regional variations in maximum recorded magnitudes, Gutenberg-Richter b values, earthquake productivity, and cumulative seismic moment depth distributions for the major subduction zones. Great earthquakes on megathrusts occur in irregular cycles of interseismic strain accumulation, foreshock activity, main-shock rupture, postseismic slip, viscoelastic relaxation, and fault healing, with all stages now being captured by geophysical monitoring. Observations of depth-dependent radiation characteristics, large earthquake slip distributions, variations in rupture velocities, radiated energy and stress drop, and relationships to aftershock distributions and afterslip are discussed. Seismic sequences for very large events have some degree of regularity within subduction zone segments, but this can be complicated by supercycles of intermittent huge ruptures that traverse segment boundaries. Factors influencing variability of large megathrust ruptures, such as large-scale plate structure and kinematics, presence of sediments and fluids, lower-plate bathymetric roughness, and upper-plate structure, are discussed. The diversity of megathrust failure processes presents a suite of natural hazards, including earthquake shaking, submarine slumping, and tsunami generation. Improved monitoring of the offshore environment is needed to better quantify and mitigate the threats posed by megathrust earthquakes globally.

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“…The overall similarity among the functions shown in Figure suggests a common behavior of earthquakes. Most of the STFs in the SCARDEC database are relatively simple, with the greatest moment rate release between 30% and 60% of the rupture duration, and somewhat symmetric as discussed in Meier et al (). There is a slight difference between shallow and deeper events, whereby the development of radiation is faster for shallow events than for deeper events (i.e., smaller T M and T S , Figures a–c).…”

Section: Functional Formsmentioning

confidence: 98%

“…I stretch the three functions to normalize their duration and time integral (see Text S2). Similar normalizations for the moment rate function have been employed in time domain (Houston, 2001;Meier et al, 2017) and in frequency domain (Prieto et al, 2004;Allmann & Shearer, 2009).…”

Section: Functional Formsmentioning

confidence: 99%

Energetic Onset of Earthquakes

Denolle

2019

Geophysical Research Letters

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Earthquake radiation is broadband, and its temporal evolution carries the seismic signature of the rupture process. I use established and develop new observational metrics to quantify the temporal variation in radiated energy (seismic power) and in a time‐dependent scaled radiated energy. Universal functional forms of moment rate, seismic power, and scaled energy arise from a global database of source time functions. Earthquakes radiate mostly and most efficiently in the early stage of development of the rupture that is in the first 10–30% of the overall rupture duration. This result is independent of earthquake magnitude, depth, and focal mechanism. Beyond depth dependence in elastic properties with depth that explain variations in source duration and radiated energy, subtle differences in functional forms exist between shallow and deep earthquakes. Deep events have a slower development than shallow earthquakes, but they carry a higher peak in seismic power.

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The hidden simplicity of subduction megathrust earthquakes

Cited by 103 publications

References 47 publications

The Dynamics of Elongated Earthquake Ruptures

The Dynamics of Elongated Earthquake Ruptures

Subduction zone megathrust earthquakes

Energetic Onset of Earthquakes

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