The slow earthquake spectrum in the Japan Trench illuminated by the S-net seafloor observatories

Abstract

Investigating slow earthquake activity in subduction zones provides insight into the slip behavior of megathrusts, which can provide important clues about the rupture extent of future great earthquakes. Using the S-net ocean-bottom seismograph network along the Japan Trench, we mapped a detailed distribution of tectonic tremors, which coincided with very-low-frequency earthquakes and a slow slip event. Compiling these and other related observations, including repeating earthquakes and earthquake swarms, we found that the slow earthquake distribution is complementary to the Tohoku-Oki earthquake rupture. We used our observations to divide the megathrust in the Japan Trench into three along-strike segments characterized by different slip behaviors. We found that the rupture of the Tohoku-Oki earthquake, which nucleated in the central segment, was terminated by the two adjacent segments.

Structural Heterogeneity in Source Zones of the 2018 Anchorage Intraslab Earthquake and the 1964 Alaska Megathrust Earthquake

“…Aside from the SSEs, an ~80‐km‐wide tectonic tremor zone begins near the southwestern edge of the SSEs in the Upper Cook Inlet and has a transition from periodic in the west to continuous in the east along the ~300‐km‐long strike (Figure b), which may be related to fluid‐rich sediments overlying the Yakutat slab (Wech, ). The spatial distribution from shallow to deep for the megathrust earthquake, long‐term SSEs, and deep tectonic tremors in south‐central Alaska is generally consistent with those in the Nankai (Nishikawa et al, ) and Mexico (Kostoglodov et al, ) subduction zones, reflecting trench‐normal variations of fault behaviors from a seismogenic zone to a transition zone (Audet et al, ; Obara & Kato, ; Peng & Gomberg, ). It is important to investigate the relationship between structural heterogeneity and these different earthquake phenomena (e.g., X. Liu & Zhao, ), but there is still no such a study in south‐central Alaska till today.…”

“…The blue closed line in (b) denotes a tectonic underplating area (Mankhemthong et al, 2013). spatial distribution from shallow to deep for the megathrust earthquake, long-term SSEs, and deep tectonic tremors in south-central Alaska is generally consistent with those in the Nankai (Nishikawa et al, 2019) and Mexico (Kostoglodov et al, 2010) subduction zones, reflecting trench-normal variations of fault behaviors from a seismogenic zone to a transition zone (Audet et al, 2009;Obara & Kato, 2016;Peng & Gomberg, 2010). It is important to investigate the relationship between structural heterogeneity and these different earthquake phenomena (e.g., X.…”

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

“…the Tohoku region (Nishikawa et al, 2019). Note that during the 2009 episode, a low-angle thrust earthquake with Mw 4.5 (the gray star and focal sphere in Figure 2a), estimated by our 3-D CMT inversion method, also occurred, but the activity of SVLFEs in 2009 seemed unchanged.…”

Characteristics of Shallow Low‐Frequency Earthquakes off the Kii Peninsula, Japan, in 2004 Revealed by Ocean Bottom Seismometers

“…In Hyuga-nada, shallow LFEs associated with VLFEs were observed in June 2013 by OBSs (Yamashita et al, 2015). And the S-net dense seafloor seismic observation network along the Japan trench has detected many shallow LFEs along the Japan trench off Tokachi, Sanriku, and Ibaraki (Nishikawa et al, 2019;Tanaka et al, 2019). Sugioka et al (2012) observed a VLFE swarm off the Kii Peninsula in March 2009 with a broadband OBS network near the source area and pointed out that their waveforms contained low-frequency components around 3 Hz, which correspond to LFEs, as well as very low frequency (< 0.1 Hz) components.…”