Migrations and Clusters of Shallow Very Low Frequency Earthquakes in the Regions Surrounding Shear Stress Accumulation Peaks Along the Nankai Trough

Takemura, Shunsuke; Noda, Akemi; Kubota, Tatsuya; Asano, Youichi; Matsuzawa, Takanori; Shiomi, Katsuhiko

doi:10.1029/2019gl084666

Cited by 28 publications

(52 citation statements)

References 71 publications

(122 reference statements)

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“…The results of previous studies (Saffer & Wallace, 2015; Takemura, Matsuzawa, et al, 2019; Takemura, Noda, et al, 2019) strongly suggested that the presence of pore fluid can control the slow earthquake activity. In Baba et al (2020), we clarified the difference in the VLFE activity inside and outside the largest coseismic slip area of the 2011 Tohoku earthquake.…”

Section: Discussionmentioning

confidence: 94%

Slow Earthquakes Illuminating Interplate Coupling Heterogeneities in Subduction Zones

Baba

Takemura

Obara

et al. 2020

Geophysical Research Letters

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Slow earthquakes are mainly distributed in the vicinity of seismogenic zones of megathrust earthquakes and relationships between both types of earthquakes are expected. We examined the activity of very low frequency earthquakes (VLFEs), classified as one type of slow earthquake, around Japan because they have the potential to clarify detailed spatiotemporal slip behaviors at the plate boundaries. The distribution of the shallow VLFE activity rate is heterogeneous along trench axes and exhibits an anticorrelation relationship with the spatial distribution of the interplate coupling ratio, whereas deep VLFEs are distributed only in weakly coupled areas, and the spatial variation of the activity rate is small. Furthermore, VLFEs are mainly hosted by low seismic velocity anomalies. Thus, slow earthquakes can be triggered by decreased effective stress due to the high pore fluid pressure within regions with weak interplate coupling, and their activity can be an indicator of interplate slip behavior.

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Section: Discussionmentioning

confidence: 94%

Slow Earthquakes Illuminating Interplate Coupling Heterogeneities in Subduction Zones

Baba

Takemura

Obara

et al. 2020

Geophysical Research Letters

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“…The source process of slow earthquakes is studied through the analysis of scaling relationships among the source characteristics: event duration, recurrence interval, size of the source fault, seismic moment release, radiated seismic energy, and so on (e.g., Ide et al., 2007; Ide & Yabe, 2014; Tan & Marsan, 2020; Yabe et al., 2019). Recent studies suggest that heterogeneities in the frictional properties on the fault control the distribution of events and their source characteristics (e.g., Baba et al., 2020; Nishikawa et al., 2019; Obara et al., 2010; Takemura et al., 2019; Tanaka et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Changes of Event Size Distribution During Episodes of Shallow Tectonic Tremor, Nankai Trough

Yabe

2021

Geophysical Research Letters

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Slow earthquakes follow a power‐law size distribution with an exponential taper for the largest events. We investigated changes in the size distribution of shallow tectonic tremor events during two prolonged tremor episodes (>1 month) along the Nankai trough and found that the slope of the size distributions increased while the cut‐off magnitudes decreased late during each episode, as tremor activity waned. Interpreting these changes with the two‐dimensional probabilistic cell automaton model of slow earthquakes, we found that a decrease in event ignition probability or an increase in energy dissipation during slip can qualitatively explain the observed changes. These changes imply that a decrease in accumulated stress or pore‐fluid pressure on the fault interface occurred during each tremor episode. Because the tremor source migrates during an episode, the changes in the size distribution parameters can be attributed to spatial variations or temporal changes in the source characteristics.

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“…and shallow VLFEs(Takemura et al 2019c) as indicators of shallow slow earthquake activity. The spatial distribution of slip-deficit rates from GNSS and GNSS-A observations byNoda et al (2018), is plotted using blue contour lines in Figure11.At deeper depths (30-40 km), deep slow earthquakes were active, especially in areas with high SSE slip rates, but no interplate regular earthquakes were found.…”

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confidence: 99%

Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: slip distributions on the plate boundary along the Nankai Trough

Takemura

Okuwaki

Kubota

et al. 2020

Geophysical Journal International

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SUMMARY Due to complex 3-D heterogeneous structures, conventional 1-D analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3-D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough between April 2004 and August 2019 to evaluate decade-scale seismicity. Green's functions for CMT inversions of earthquakes with moment magnitudes of 4.3–6.5 were evaluated using finite-difference method simulations of seismic wave propagation in the regional 3-D velocity structure model. Significant differences of focal mechanisms and centroid depths between previous 1-D and our 3-D catalogues were found in the solutions of offshore earthquakes. By introducing the 3-D structures of the low-velocity accretionary prism and the Philippine Sea Plate, dip angles and centroid depths for offshore earthquakes were well-constrained. Teleseismic CMT also provides robust solutions, but our regional 3-D CMT could provide better constraints of dip angles. Our 3-D CMT catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the Nankai Trough. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths along the Nankai Trough plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution, regions with strong coupling were clearly identified.

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Migrations and Clusters of Shallow Very Low Frequency Earthquakes in the Regions Surrounding Shear Stress Accumulation Peaks Along the Nankai Trough

Cited by 28 publications

References 71 publications

Slow Earthquakes Illuminating Interplate Coupling Heterogeneities in Subduction Zones

Slow Earthquakes Illuminating Interplate Coupling Heterogeneities in Subduction Zones

Changes of Event Size Distribution During Episodes of Shallow Tectonic Tremor, Nankai Trough

Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: slip distributions on the plate boundary along the Nankai Trough

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