Source characteristics and along-strike variations of shallow very low frequency earthquake swarms on the Nankai Trough shallow plate boundary

Takemura, Shunsuke; Baba, Satoru; Yabe, Suguru; Emoto, Kentaro; Shiomi, Katsuhiko; Matsuzawa, Takanori

doi:10.1002/essoar.10510250.3

Cited by 1 publication

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“…Our results indicate that pore pressure levels are temporally changed at a fixed position in the eastern and central regions, and high pore pressure exists in the western region (i.e., red and black arrows in Figure 4 can be interpreted as high and low pore pressure conditions, respectively). A good example of the temporally changing pore pressure level at a fixed position in the eastern region is the slow earthquake event starting from the end of 2020 (e.g., Takemura et al., 2021, 2022). The SCC for Event 5 prior to the event became large at the margin of the source region, and then the SCC for Event 6 during the event extends in the source region.…”

Section: Discussionmentioning

confidence: 99%

Fluid Migration Before and During Slow Earthquakes in the Shallow Nankai Subduction Zone

et al. 2022

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Fluid migration in subduction zones is a key controlling factor of slow and megathrust earthquakes at plate boundaries. During the migration, seismic velocity and heterogeneous structures in its pathways may be temporarily perturbed, preferably triggering slow earthquakes. Here, we show that transient changes of seismic heterogeneity occurred 0–9 months before shallow slow earthquakes in the Nankai subduction zone, Japan, using very long‐term (6–10 years) records of ambient seafloor noise. The heterogeneity changes preceding to shallow slow earthquakes were observed near the margin of the source region, while concurrent changes primarily occurred in the source region. We propose that the heterogeneity changes are attributed to dynamic fluid migration, and the difference in timings reflects the pore pressure level in the corresponding source region. When fluids are supplied to a source region under relatively low pressure, fluids are leaked out from its downdip or updip side, and slow earthquakes occur not immediately but with a time delay of at most 9 months. In the high pore pressure case, slow earthquakes occur immediately with fluid migration from the source region. This study suggests that the heterogeneous seismic structure is possibly changed by fluid migration before slow earthquakes in the Nankai subduction zone.

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Section: Discussionmentioning

confidence: 99%