Fluid migration before and during slow earthquakes in the shallow Nankai subduction zone

Tonegawa, Takashi; Takemura, Shunsuke; Yabe, Suguru; Yomogida, Kiyoshi

doi:10.1002/essoar.10508646.1

Cited by 6 publications

(14 citation statements)

References 35 publications

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“…Tonegawa et al. (2021) also illustrated various heterogeneous change patterns associated with shallow slow earthquakes. According to their heterogeneous change and our shallow VLFEs in the episode from December 2020, pore fluid and/or rupture front of shallow SSE might propagate from the paleo‐Zenisu Ridge to the west.…”

Section: Discussionmentioning

confidence: 98%

“…Then, we estimate the moment rate functions of detected shallow VLFEs using Green's functions of the local three-dimensional (3-D) model in order to determine their source characteristics. Detailed tectonic environments, such as velocity structures and slip-deficit rate estimations, have been studied southeast off the Kii Peninsula (e.g., Agata, 2020;Akuhara et al, 2020;Noda et al, 2018;Park et al, 2002Park et al, , 2004Tonegawa et al, 2021). Thus, a high-resolution moment-rate-function catalog of long-term shallow VLFE activity allows us to discuss characteristics of the spatial pattern of slips due to shallow slow earthquakes southeast off the Kii Peninsula.…”

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confidence: 99%

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Spatiotemporal Variations of Shallow Very Low Frequency Earthquake Activity Southeast Off the Kii Peninsula, Along the Nankai Trough, Japan

et al. 2022

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Cross‐correlation analysis was applied to long‐term onshore broadband records from April 2004 to March 2021 to detect and relocate shallow very low frequency earthquakes (VLFEs) southeast off the Kii Peninsula, along the Nankai Trough, Japan. We then determined the moment rate functions of detected shallow VLFEs using the Monte Carlo‐based simulated annealing method. According to this new comprehensive catalog, shallow VLFEs are widespread beneath the accretionary prism toe, but shallow VLFEs with large cumulative moments are localized around the western edge of the paleo‐Zenisu Ridge, which is subducted beneath southeast off the Kii Peninsula. Our results from the long‐term shallow VLFE catalog are well consistent with previous studies in this region, suggesting that heterogeneous structures and stress conditions due to the subducted paleo‐Zenisu Ridge promote the occurrence of shallow slow earthquakes. The relocated shallow VLFE epicenters illustrated three major episodes characterized by a similar activity area and five minor episodes characterized by different areas. The three major episodes exhibited slow frontal migration with different initiation locations, directions, and speeds, as well as several rapid reverse migrations. Episodes of minor activity were distributed in different locations within part of the area of major activity. Different patterns of shallow VLFE migration could reflect temporal changes in the pore‐fluid distribution or stress conditions of the plate boundary.

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Section: Discussionmentioning

confidence: 98%

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confidence: 99%

Spatiotemporal Variations of Shallow Very Low Frequency Earthquake Activity Southeast Off the Kii Peninsula, Along the Nankai Trough, Japan

et al. 2022

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“…Tonegawa et al. (2017, 2022) suggested that pore fluid pressure around the plate boundary in region C is expected to be higher than that in region A. Observed differences in the migration velocity may also be caused by such fluid distribution.…”

Section: Discussionmentioning

confidence: 99%

Source Characteristics and Along‐Strike Variations of Shallow Very Low Frequency Earthquake Swarms on the Nankai Trough Shallow Plate Boundary

Takemura

Baba

Yabe

et al. 2022

Geophysical Research Letters

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We detected shallow very low frequency earthquakes (VLFEs) off the Cape Muroto and Kii Channel in the Nankai subduction zone and estimated their moment rate functions. Combining the new and previously estimated catalogs, we obtained the comprehensive catalog of shallow VLFE moment rate functions along the Nankai Trough. We defined the shallow VLFE swarms and investigated the scaling relationships of their cumulative moments, activity area, and durations in each region. Detected swarms were considered candidates for shallow slow slip events. A similar scaling relationship was observed between the cumulative moments and activity areas, irrespective of regions. It indicates similar stress drops in each region. However, the relationship between the cumulative moments and durations varied. This difference was explained by the along‐strike variations in the faulting conditions of shallow slow earthquakes, such as material or hydrological properties.

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“…Recently, Tonegawa et al. (2022) succeeded in detecting waveform decorrelations in seismic ambient noise CCFs before and during slow earthquakes in the Nankai accretionary prism, Japan. They interpreted that those decorrelations were caused by fluid migrations.…”

Section: Discussionmentioning

confidence: 99%

Seismic Scattering Property Changes Correlate With Ground Deformation at Suwanosejima Volcano, Japan

2022

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Continuous estimation of changes in seismic velocity and seismic scattering property by passive interferometry using seismic ambient noise is a promising tool for monitoring volcanoes. To improve the usefulness of this method, it is necessary not only to detect subsurface structural changes but also to quantitatively compare the estimated changes in seismic wave velocity and seismic wave scattering property with other observations, such as ground deformation. We applied passive interferometry to continuous seismic records from the Suwanosejima volcano, Japan, recorded between April 2017 and December 2021. We detected repeated significant waveform decorrelations in seismic ambient noise cross‐correlation functions (CCFs), indicating changes in seismic scattering property in the shallow areas of the volcano. These decorrelations were observed from 2 weeks to a few days before the increase in the number of explosions, suggesting that seismic scattering properties changed significantly during that period. We found that the timing of the decorrelation in seismic ambient noise CCFs and tilt changes related to magma accumulation and injection beneath Suwanosejima were well synchronized. The high correlation between the amounts of decorrelation and the tilt change during the magma accumulation period possibly suggests that a large volume of accumulated magma caused great changes in the scattering property. These results provide a significant first step toward a quantitative comparison of the amount of changes in the scattering property with the amount of magma accumulation beneath volcanoes.

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Fluid migration before and during slow earthquakes in the shallow Nankai subduction zone

Cited by 6 publications

References 35 publications

Spatiotemporal Variations of Shallow Very Low Frequency Earthquake Activity Southeast Off the Kii Peninsula, Along the Nankai Trough, Japan

Spatiotemporal Variations of Shallow Very Low Frequency Earthquake Activity Southeast Off the Kii Peninsula, Along the Nankai Trough, Japan

Source Characteristics and Along‐Strike Variations of Shallow Very Low Frequency Earthquake Swarms on the Nankai Trough Shallow Plate Boundary

Seismic Scattering Property Changes Correlate With Ground Deformation at Suwanosejima Volcano, Japan

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