Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes due to a low-angle dipping slab

Takemura, Shunsuke; Shiomi, Katsuhiko; Kimura, Takeshi; Saito, Tatsuhiko

doi:10.1186/s40623-016-0527-9

Cited by 17 publications

(15 citation statements)

References 41 publications

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“…Hereafter, shallow VLFE is referred to as SVLFE. Activity of SVLFEs may provide us with information on the frictional conditions around shallower parts of the plate boundaries (e.g., Saffer & Wallace, 2015 a conventional analysis using a one-dimensional (1-D) velocity structure is not expected to be accurate due to offshore lateral heterogeneities related to the subducting plate and accretionary prism (e.g., Takemura et al, 2016Takemura et al, , 2018, especially since the accretionary prism has a significant influence on seismic wave propagation for periods around predominant periods of SVLFE signals (e.g., Furumura et al, 2008;Shapiro et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Centroid Moment Tensor Inversion of Shallow Very Low Frequency Earthquakes Off the Kii Peninsula, Japan, Using a Three‐Dimensional Velocity Structure Model

Takemura

Matsuzawa

Kimura

et al. 2018

Geophysical Research Letters

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We conducted centroid moment tensor inversions of shallow very low frequency earthquakes (SVLFEs) that occurred around off the southeast Kii Peninsula, Japan. A set of Green's functions was evaluated using numerical simulations of seismic wave propagation in a three‐dimensional velocity structure model, including the subducting Philippine Sea slab and the accretionary prism. We used observed seismograms for periods of 20–50 s at an onshore broadband network, which enable us to investigate the long‐term activity of SVLFEs. Estimated centroid locations and focal mechanisms of SVLFEs, including SVLFEs that occurred prior to the deployment of seafloor observations, were very similar to those estimated using seafloor records. Low‐angle thrust faulting mechanisms were concentrated around the accretionary prism toe. SVLFE activity in April 2016 was concentrated further west in an area of previous activity. Our results imply seismic slip around the very shallow part of the Philippine Sea plate boundary.

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Section: Introductionmentioning

confidence: 99%

Centroid Moment Tensor Inversion of Shallow Very Low Frequency Earthquakes Off the Kii Peninsula, Japan, Using a Three‐Dimensional Velocity Structure Model

Takemura

Matsuzawa

Kimura

et al. 2018

Geophysical Research Letters

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“…However, strong horizontal heterogeneities of seismic wave velocities due to plate subduction could affect the precision of determining the hypocenter locations. Takemura et al (2016) showed that an accurate 3D velocity model reflecting the plate subduction is necessary to explain the spatial distributions of P-wave first motion polarities observed for this earthquake. Therefore, a velocity model reflecting the horizontal heterogeneities is crucial for precise determination of hypocenters.…”

Section: Introductionmentioning

confidence: 99%

The 2016 Mw 5.9 earthquake off the southeastern coast of Mie Prefecture as an indicator of preparatory processes of the next Nankai Trough megathrust earthquake

Hyodo

Nakanishi

Yamashita

et al. 2018

Prog Earth Planet Sci

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Megathrust earthquakes have occurred repeatedly at intervals of 100 to 150 years along the Nankai Trough, situated in the southwest of Japan. Given that it has been 70 years since the last event, the occurrence of the next devastating earthquake is anticipated in the near future. On April 1, 2016, a moderate earthquake (M w 5.9, M JMA 6.5) occurred off the southeastern coast of Mie Prefecture in the source region of the 1944 Tonankai earthquake (M w 8.2). In this study, we investigated the influence of the 2016 earthquake on future megathrust earthquakes. We first determined the hypocenter distributions using a precise velocity structure obtained from seismic surveys in the source region. Using data obtained from the DONET ocean-bottom observation network, we found that this earthquake occurred along the plate boundary fault, which is also believed to have slipped during past megathrust earthquakes. We then performed a preliminary numerical simulation to reproduce the occurrence of a moderate earthquake in the middle of a megathrust earthquake cycle. We used a hierarchical asperity model, in which smaller asperities causing moderate earthquakes are embedded in a hyper-asperity that serves as the source region of megathrust earthquakes. The simulation shows that moderate earthquakes, caused by ruptures of a smaller asperity, occur as a result of shrinkage of strongly coupled areas in the hyper-asperity. This result is consistent with the observation that the hypocenter of the 2016 earthquake was located at the edge of a strongly coupled region along the plate boundary. The simulation also reproduced postseismic slip (afterslip/slow slip) along the plate boundary updip of the hyper-asperity, which is consistent with the observations of slow slip events and very-low-frequency earthquakes after the 2016 earthquake. Thus, the occurrence of the moderate earthquake offshore southeastern Mie Prefecture in the middle of the megathrust earthquake cycle implies that the shrinkage of the strongly coupled area along the plate boundary is occurring as a preparatory process for the next megathrust earthquake in the region.

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“…due to 3-D velocity structure (e.g. Nakamura et al, 2016;Takemura et al, 2016). We therefore assume that a layer average provides meaningful information in lieu of more detailed depth analysis, comment on some depth-dependence below, and furthermore assume that any mislocation bias in the catalog will be temporally stationary.…”

Section: Catalog Analysismentioning

confidence: 99%

Stress change before and after the 2011 M9 Tohoku-oki earthquake

Becker

Hashima

Freed

et al. 2018

Earth and Planetary Science Letters

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Megathrust systems hold important clues for our understanding of longand short-term plate boundary dynamics, and the 2011 M9 Tohoku-oki earthquake provides a data-rich case in point. Here, we show that the F-net moment tensor catalog indicates systematic changes in crustal stress in the years leading up to the M9, due to the co-seismic effect, and for the last few years due to viscous relaxation. We explore the match between imaged stress change and the perturbations that are expected from 3-D, mechanical models of the visco-elastic relaxation and afterslip effects of the M9. While these models were constructed based on geodetic and structural seismology constraints alone, they match many characteristics of the seismicityinferred stress change. This provides additional confidence in the modeling approach, and new clues for our understanding of plate boundary dynamics for the Japan trench. The success of deterministic approaches for explor-*

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Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes due to a low-angle dipping slab

Cited by 17 publications

References 41 publications

Centroid Moment Tensor Inversion of Shallow Very Low Frequency Earthquakes Off the Kii Peninsula, Japan, Using a Three‐Dimensional Velocity Structure Model

Centroid Moment Tensor Inversion of Shallow Very Low Frequency Earthquakes Off the Kii Peninsula, Japan, Using a Three‐Dimensional Velocity Structure Model

The 2016 Mw 5.9 earthquake off the southeastern coast of Mie Prefecture as an indicator of preparatory processes of the next Nankai Trough megathrust earthquake

Stress change before and after the 2011 M9 Tohoku-oki earthquake

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