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1. A quantitative comparison and validation of finite-fault models: The 2011 Tohoku-Oki earthquake

   https://doi.org/10.22541/essoar.169203075.50034612/v1  

   Wong, Jeremy_Wing Ching; Fan, Wenyuan; Gabriel, Alice-Agnes (August 2023, Authorea, Inc.)

   Large earthquakes rupture faults over hundreds of kilometers withinminutes. Finite-fault models elucidate these processes and provideobservational constraints for understanding earthquake physics. However,finite-fault inversions are subject to non-uniqueness and substantialuncertainties. The diverse range of published models for thewell-recorded 2011 M_w 9.0 Tohoku-Oki earthquake aptly illustrates thisissue, and details of its rupture process remain under debate. Here, wecomprehensively compare 32 finite-fault models of the Tohoku-Okiearthquake and analyze the sensitivity of three commonly-usedobservational data types (geodetic, seismic, and tsunami) to the slipfeatures identified. We first project all models to a realisticmegathrust geometry and a 1-km subfault size. At this scale, we observepoor correlation among the models, irrespective of the data type.However, model agreement improves significantly when subfault sizes areincreased, implying that their differences primarily stem fromsmall-scale features. We then forward-compute geodetic and teleseismicsynthetics and compare them with observations. We find that seismicobservations are sensitive to rupture propagation, such as thepeak-slip-rise time. However, neither teleseismic nor geodeticobservations are sensitive to spatial slip features smaller than 64 km.In distinction, the synthesized seafloor deformation of all modelsexhibits poor correlation, indicating sensitivity to small-scale slipfeatures. Our findings suggest that fine-scale slip features cannot beunambiguously resolved by remote or sparse observations, such as thethree data types tested in this study. However, better resolution maybecome achievable from uniformly gridded dense offshore instrumentation. 

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2. A Decade of Lessons Learned from the 2011 Tohoku‐Oki Earthquake

   https://doi.org/10.1029/2020RG000713  

   Uchida, N.; Bürgmann, R. (May 2021, Reviews of Geophysics)

   Abstract The 2011 Mw 9.0 Tohoku‐oki earthquake is one of the world's best‐recorded ruptures. In the aftermath of this devastating event, it is important to learn from the complete record. We describe the state of knowledge of the megathrust earthquake generation process before the earthquake, and what has been learned in the decade since the historic event. Prior to 2011, there were a number of studies suggesting the potential of a great megathrust earthquake in NE Japan from geodesy, geology, seismology, geomorphology, and paleoseismology, but results from each field were not enough to enable a consensus assessment of the hazard. A transient unfastening of interplate coupling and increased seismicity were recognized before the earthquake, but did not lead to alerts. Since the mainshock, follow‐up studies have (1) documented that the rupture occurred in an area with a large interplate slip deficit, (2) established large near‐trench coseismic slip, (3) examined structural anomalies and fault‐zone materials correlated with the coseismic slip, (4) clarified the historical and paleoseismic recurrence of M∼9 earthquakes, and (5) identified various kinds of possible precursors. The studies have also illuminated the heterogeneous distribution of coseismic rupture, aftershocks, slow earthquakes and aseismic afterslip, and the enduring viscoelastic response, which together make up the complex megathrust earthquake cycle. Given these scientific advances, the enhanced seismic hazard of an impending great earthquake can now be more accurately established, although we do not believe such an event could be predicted with confidence. 

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3. Linking 3D Long‐Term Slow‐Slip Cycle Models With Rupture Dynamics: The Nucleation of the 2014 M _w 7.3 Guerrero, Mexico Earthquake

   https://doi.org/10.1029/2023AV000979  

   Li, Duo; Gabriel, Alice‐Agnes (March 2024, AGU Advances)

   Abstract Slow slip events (SSEs) have been observed in spatial and temporal proximity to megathrust earthquakes in various subduction zones, including the 2014M_w7.3 Guerrero, Mexico earthquake which was preceded by aM_w7.6 SSE. However, the underlying physics connecting SSEs to earthquakes remains elusive. Here, we link 3D slow‐slip cycle models with dynamic rupture simulations across the geometrically complex flat‐slab Cocos plate boundary. Our physics‐based models reproduce key regional geodetic and teleseismic fault slip observations on timescales from decades to seconds. We find that accelerating SSE fronts transiently increase shear stress at the down‐dip end of the seismogenic zone, modulated by the complex geometry beneath the Guerrero segment. The shear stresses cast by the migrating fronts of the 2014M_w7.6 SSE are significantly larger than those during the three previous episodic SSEs that occurred along the same portion of the megathrust. We show that the SSE transient stresses are large enough to nucleate earthquake dynamic rupture and affect rupture dynamics. However, additional frictional asperities in the seismogenic part of the megathrust are required to explain the observed complexities in the coseismic energy release and static surface displacements of the Guerrero earthquake. We conclude that it is crucial to jointly analyze the long‐ and short‐term interactions and complexities of SSEs and megathrust earthquakes across several (a)seismic cycles accounting for megathrust geometry. Our study has important implications for identifying earthquake precursors and understanding the link between transient and sudden megathrust faulting processes. 

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4. 3D Dynamic Rupture Modeling of the 6 February 2023, Kahramanmaraş, Turkey Mw 7.8 and 7.7 Earthquake Doublet Using Early Observations

   https://doi.org/10.1785/0320230028  

   Gabriel, Alice-Agnes; Ulrich, Thomas; Marchandon, Mathilde; Biemiller, James; Rekoske, John (October 2023, The Seismic Record)

   Abstract The 2023 Turkey earthquake sequence involved unexpected ruptures across numerous fault segments. We present 3D dynamic rupture simulations to illuminate the complex dynamics of the earthquake doublet. Our models are constrained by observations available within days of the sequence and deliver timely, mechanically consistent explanations of the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, heterogeneous fault offsets, locally strong shaking, and fault system interactions. Our simulations link both earthquakes, matching geodetic and seismic observations and reconciling regional seismotectonics, rupture dynamics, and ground motions of a fault system represented by 10 curved dipping segments and embedded in a heterogeneous stress field. The Mw 7.8 earthquake features delayed backward branching from a steeply branching splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral Mw 7.7 earthquake are explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous earthquake. Our models explain the northward deviation of its eastern rupture and the minimal slip observed on the Sürgü fault. 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multifault systems. 

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5. Optimizing a Model of Coseismic Rupture for the 22 July 2020 M _W 7.8 Simeonof Earthquake by Exploiting Acute Sensitivity of Tsunami Excitation Across the Shelf Break

   https://doi.org/10.1029/2022JB024484  

   Bai, Yefei; Liu, Chengli; Lay, Thorne; Cheung, Kwok Fai; Ye, Lingling (July 2022, Journal of Geophysical Research: Solid Earth)

   Abstract The Shumagin seismic gap along the Alaska Peninsula experienced a major,M_W7.8, interplate thrust earthquake on 22 July 2020. Several available finite‐fault inversions indicate patchy slip of up to 4 m at 8–48 km depth. There are differences among the models in peak slip and absolute placement of slip on the plate boundary, resulting from differences in data distributions, model parameterizations, and inversion algorithms. Two representative slip models obtained from inversions of large seismic and geodetic data sets produce very different tsunami predictions at tide gauges and deep‐water pressure sensors (DART stations), despite having only secondary differences in slip distribution. This is found to be the result of the acute sensitivity of the tsunami excitation for rupture below the continental shelf in proximity to an abrupt shelf break. Iteratively perturbing seismic and geodetic inversions by constraining fault model extent along dip and strike, we obtain an optimal rupture model compatible with teleseismicPandSHwaves, regional three‐component broadband and strong‐motion seismic recordings, hr‐GNSS time series and static offsets, as well as tsunami recordings at DART stations and regional and remote tide gauges. Slip is tightly bounded between 25 and 40 km depth, the up‐dip limit of slip in the earthquake is resolved to be well‐inland of the shelf break, and the rupture extent along strike is well‐constrained. The coseismic slip increased Coulomb stress on the shallow plate boundary extending to the trench, but the frictional behavior of the megathrust below the continental slope remains uncertain. 

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