Omori-like slow decay (p &lt; 1) of postseismic displacement rates following the 2011 Tohoku megathrust earthquake

Morikami, Shunsuke; Mitsui, Yuta

doi:10.1186/s40623-020-01162-w

Cited by 13 publications

(14 citation statements)

References 44 publications

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“…In Phase 1 before the 2011 off the Paci c coast of Tohoku earthquake, we nd that W t = 12 can reduce the overall IQR(σ). In Phase 2 immediately after the 2011 off the Paci c coast of Tohoku earthquake, W t = 4 is the optimum, which may re ect the in uence of the postseismic deformation of the 2011 off the Paci c coast of Tohoku earthquake (e.g.,Ozawa et al 2012;Suito 2017;Morikami and Mitsui 2020). In Phase 3, a few years later, the IQR(σ) are close to the minimum values at W t = 12, as in Phase 1, probably due to the decay of the postseismic deformation.Therefore, we propose that the optimal W t for the GEONET array in the Japanese Islands is 12 except immediately after the 2011 off the Paci c coast of Tohoku megathrust earthquake (as Phase 2).…”

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confidence: 63%

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

Kosugi

Mitsui

2022

Preprint

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Geodetic and seismological observations have shown discrepancies between azimuths of maximum contraction of strain rates and maximum compression of stress. These discrepancies can be the results of the superposition of localized or transient mechanical processes such as fault coupling during seismic cycles. Rich sets of recent geophysical data allow us to conduct spatiotemporal imaging of the discrepancies. Here, we estimate the spatiotemporal evolution in the strain-rate fields of the Japanese Islands with optimized smoothing distances from 1997 to 2021 using Global Navigation Satellite System (GNSS) data, and investigate how the maximum contraction axes of horizontal strain rates differ from those of horizontal stress based on earthquake focal mechanisms. Several characteristic results are observed for each region within the Japanese Islands. Both azimuths of the strain rates and stress differ by more than 60 degrees over hundreds of kilometers from the Kanto region to along the Nankai Trough, related to seismotectonics due to the dual subduction of the Philippine Sea plate and the Pacific plate beneath the Japanese Islands. The azimuthal differences tend to be small along tectonic zones with active inland earthquakes and high strain rates on the back-arc sides. We also find that the 2011 off the Pacific coast of Tohoku earthquake caused notable azimuthal differences in the strain rates and the stress in the Tohoku region. Our dataset has wide spatiotemporal coverage and can serve as a basis for further research, for example, to estimate the current fault conditions during seismic cycles.

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confidence: 63%

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

Kosugi

Mitsui

2022

Preprint

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“…All these studies reveal the importance of early postseismic deformation, and the fact that measurements made using daily GNSS solutions can lead to a significant overestimation of the coseimic offsets. Concerning the mechanisms involved at this early stage, Langbein (2006) and Morikami & Mitsui (2020) show that the GPS data starting from a few minutes after the mainshock are adequately fitted by an « Omori-like » evolution of the velocity, i.e. v ~ 1 / 𝑡 𝑝 and p<1.…”

Section: Introductionmentioning

confidence: 95%

Transient Brittle Creep mechanism explains early postseismic phase of the 2011 Tohoku-Oki megathrust earthquake: observations by high-rates GPS solutions

Periollat

Radiguet

Weiss

et al. 2022

Preprint

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The early stage of the postseismic phase is characterized by a large deformation rate. Its analysis is thus key to decipher the role played by different mechanisms (afterslip and viscoelasticity) at various time scales. Here, we process GPS data to obtain 30-seconds kinematic position time series recording the surface deformation following the Mw 9.0 Tohoku-Oki megathrust earthquake (2011), and combine them with static solutions over 9 years. We analyze the temporal evolution of the time series and use these observations to image the postseismic slip. We find that the first month of deformation following Tohoku-Oki can be explained by an afterslip mechanism, that exhibits an "Omori-like" decay, with a p-value around 0.75 almost everywhere with the exception of a small region around Ibaraki prefecture where p˜1 is observed. This p<1 indicates that the postseismic displacements do not increase logarithmically with time as predicted by rate-and-state rheology. Instead, we argue that early afterslip is associated to a transient brittle creep mechanism. We use numerical simulations to show that an exponent of p<1 can be explained by a combination of thermal activation of local slips and elastic interactions. Over longer time scales, an additional mechanism is required to explain the observed deformation signal, and the transient brittle creep mechanism is combined with viscoelastic relaxation modeled by a Newtonian flow. The spatial analysis reveals two distinct afterslip regions, a major one on the North, associated with a p-value around 0.75, and a smaller one close to the Ibaraki aftershock, associated to p˜1.

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“…In Phase 1 before the 2011 off the Pacific coast of Tohoku earthquake, we find that W t = 12 can reduce the overall IQR(σ ) . In Phase 2 immediately after the 2011 off the Pacific coast of Tohoku earthquake, W t = 4 is the optimum, which may reflect the influence of the postseismic deformation of the 2011 off the Pacific coast of Tohoku earthquake (e.g., Ozawa et al 2012;Suito 2017;Morikami and Mitsui 2020). In Phase 3, a few years later, the IQR(σ ) are close to the minimum values at W t = 12 , as in Phase 1, probably due to the decay of the postseismic deformation.…”

Section: Date (Jst) Longitude Latitude [°] Magnitudementioning

confidence: 99%

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

Kosugi

Mitsui

2022

Earth Planets Space

Self Cite

View full text Add to dashboard Cite

Geodetic and seismological observations have shown discrepancies between azimuths of maximum contraction (strain rate) and maximum compression (stress). These discrepancies can be the results of the superposition of localized or transient mechanical processes such as fault coupling during seismic cycles. Rich sets of recent geophysical data allow us to conduct spatiotemporal imaging of the discrepancies. Here, we estimate the spatiotemporal evolution in the strain-rate fields of the Japanese Islands with optimized smoothing distances from 1997 to 2021 using Global Navigation Satellite System (GNSS) data, and investigate how the maximum contraction axes of horizontal strain rates differ from those of horizontal stress based on earthquake focal mechanisms. Several characteristic results are observed for each region within the Japanese Islands. Both azimuths of the strain rates and stress differ by more than 60° over hundreds of kilometers from the Kanto region to along the Nankai Trough, related to seismotectonics due to the dual subduction of the Philippine Sea plate and the Pacific plate beneath the Japanese Islands. The differences in the azimuths imply the effect of the very long-term stable subduction of the Pacific plate. We find that the azimuthal differences tend to be small along tectonic zones with active inland earthquakes and high strain rates on the back-arc sides. We also find that the 2011 off the Pacific coast of Tohoku earthquake caused notable azimuthal differences in the strain rates and the stress in the Tohoku region. The strength of fault may cause lower response sensitivity of seismological stress to major earthquakes than geodetic strain rate. Our dataset has wide spatiotemporal coverage and can serve as a basis for further research, for example, to estimate the current fault conditions during seismic cycles. Graphical Abstract

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Omori-like slow decay (p < 1) of postseismic displacement rates following the 2011 Tohoku megathrust earthquake

Cited by 13 publications

References 44 publications

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

Transient Brittle Creep mechanism explains early postseismic phase of the 2011 Tohoku-Oki megathrust earthquake: observations by high-rates GPS solutions

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

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