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

Tamaribuchi, Koji; Kobayashi, Akio; Nishimiya, Takahito; Hirose, Fuyuki; Annoura, Satoshi

doi:10.1029/2019gl085158

Cited by 14 publications

(24 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Because we did not introduce a small-scale velocity heterogeneity into the reference model in this simulation, we confirmed that the 10 shallower heterogeneities, such as seawater and the thick low-velocity accretionary prism, also distorted the maximum amplitude distribution. Thus, the assumption of isotropic radiation for energy estimations of small offshore seismic events in many studies could be suitable (e.g., Tamaribuchi et al, 2019;Yabe et al, 2019). Because our simulations did not include site amplifications caused by structures with VS < 0.5 km/s, the observed maximum amplitude distribution could be more complicated because of site amplification factors at DONET stations for high-frequency seismic waves (e.g., Kubo et al, 2018;Yabe et al, 2019).…”

Section: Simulation Resultsmentioning

confidence: 99%

“…Around the Japanese Islands, permanent OBS networks of DONET and S-net (National Research Institute for Earth Science and Disaster Resilience, 2019c, 2019a) have been recently deployed. Several studies have used temporal OBS data or such permanent networks to estimate the source characteristics of small earthquakes and shallow low-frequency tremors (LFTs) (e.g., Nakano et al, 2015Nakano et al, , 2019Nishikawa et al, 2019;Tamaribuchi et al, 2019;Tanaka et al, 2019;Yabe et al, 2019). Offshore 3D heterogeneities, seawater, and bathymetry significantly affect seismic wave propagation even for low-frequency ground motions (e.g., Gomberg 2018;Guo et al 2016;Nakamura et al 2015;Shapiro et al 1998Volk et al 2017), complicated seismic waves such as T phase, Scholte, acoustic-coupled, and ocean-mode Rayleigh waves, as has been observed in previous studies (e.g., Haney & Tsai, 2017;Muyzert, 2007;Noguchi et al, 2016;Okal, 2008;Takeo et al, 2014;.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

Takemura

Yabe

Emoto

2020

Geophysical Journal International

View full text Add to dashboard Cite

Summary The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their source physics and frictional conditions at the plate boundary. Due to strong three-dimensional heterogeneities in offshore regions, such as those relating to seawater, accretionary prism, and small-scale velocity heterogeneity, conventional methods using a one-dimensional Earth model may misestimate source parameters such as the duration and radiation energy. Estimations could become severe inaccuracies for small offshore seismic events because high-frequency (> 1 Hz) seismograms, which are strongly affected by three-dimensional heterogeneities, are only available for analysis because of their signal-to-noise ratio. To investigate the effects of offshore heterogeneities on source parameter estimation for small seismic events, we analysed both observed and simulated high-frequency seismograms southeast off the Kii Peninsula, Japan, in the Nankai subduction zone. Numerical simulations of seismic wave propagation using a three-dimensional velocity structure model clarified the effects of each heterogeneity. Comparisons between observations and model simulations demonstrated that the thick low-velocity accretionary prism has significant effects on high-frequency seismic wave propagation. Especially for shallow low-frequency tremors occurring at depths just below the accretionary prism toe, seismogram durations are significantly broader than an assumed source duration, even for stations with epicentral distances of approximately 10 km. Spindle-shape seismogram envelopes were observed even at such close stations. Our results suggest that incorporating three-dimensional heterogeneities is necessary for practical estimation of source parameters for small offshore events.

show abstract

Section: Simulation Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

Takemura

Yabe

Emoto

2020

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…It is difficult to locate tremors in the offshore region by using an onshore network because sources of tremors are distant from the network and signals of tremors attenuate strongly compared to VLFE (0.02–0.05 Hz) signals. Based on the spatiotemporal correlation between VLFEs and tremors reported in other regions (e.g., Ghosh et al., 2015; Maeda & Obara, 2009; Tamaribuchi et al., 2019) and the interpretation that VLFEs and tremors are components of broadband slow earthquake phenomena (Gomberg et al., 2016; Hawthorne & Bartlow, 2018; Ide & Maury, 2018), we estimated the energy rate functions of tremors accompanied by VLFEs by assuming that a tremor occurs at the same location as the VLFE, that is, the VLFE source grid with the highest CC as written in Section 2.1.3 (e.g., Yabe et al., 2021). We simulated the waveforms at the location of a VLFE using the same model which is described in Section 2.1.2 but discretized by a finer grid interval (0.04 km).…”

Section: Methodsmentioning

confidence: 99%

Shallow Slow Earthquake Episodes Near the Trench Axis off Costa Rica

et al. 2021

View full text Add to dashboard Cite

Slow earthquakes are mainly distributed in regions surrounding seismogenic zones along the plate boundaries of subduction zones. In the Central American subduction zone, large regular interplate earthquakes with magnitudes of 7–8 occur repeatedly around the Nicoya Peninsula, in Costa Rica, and a tsunami earthquake occurred off Nicaragua, just north of Costa Rica, in 1992. To clarify the spatial distribution of various slip behaviors at the plate boundary, we detected and located very low frequency earthquakes (VLFEs) around the Nicoya Peninsula using a grid‐search matched‐filter technique with synthetic templates based on a regional three‐dimensional model. VLFEs were active in September 2004 and August 2005, mainly near the trench axis, updip of the seismogenic zone. The distribution of VLFEs overlapped with large slip areas of slow slip events. Low frequency tremor signals were also found in high‐frequency seismogram envelopes within the same time windows as detected VLFEs; thus, we also investigated the energy rates of tremors accompanied by VLFEs. The range of scaled energy, which is the ratio of the seismic energy rate of a tremor to the seismic moment rate of accompanying VLFE and related to the rupture process of seismic phenomena, was 10−9–10−8. The along‐dip separation of shallow slow and large earthquakes and the range of the scaled energy off Costa Rica are similar to those in shallow slow earthquakes in Nankai, which shares a similar thermal structure along the shallow plate boundary.

show abstract

“…Observations using self-pop-up-type ocean bottom seismometers (OBSs) detected low-frequency tremors and earthquakes in Kumano-nada (Obana and Kodaira 2006;Tamaribuchi et al 2019) and Hyuga-nada (Yamashita et al 2015). Using broadband OBSs, Sugioka et al (2012) detected sVLFEs that occurred along the plate boundary fault.…”

Section: Introductionmentioning

confidence: 99%

Spatio-Temporal Distribution of Shallow Very-Low-Frequency Earthquakes between December 2020 and January 2021 in Kumano-Nada, Nankai Subduction Zone, Detected by A Permanent Seafloor Seismic Network

Yamamoto

Ariyoshi

Yada

et al. 2021

Preprint

View full text Add to dashboard Cite

We estimate the hypocenter locations and the centroid moment tensor solutions of the shallow very-low-frequency earthquake (sVLFE) activity that occurred in the Kumano-nada region of the Nankai Trough megathrust zone in central Japan from December 2020 to January 2021. Using seafloor observation data, we examined the detailed spatio-temporal distribution of the sVLFE activity. During this episode, the activity area was within the vicinity in which the sVLFE activity has been observed in the past and can be divided into two major parts. The sVLFE activity started from the eastern side and remained there for the first 5 days and then migrated to the western side via secondary expansion. The eastern active area is located just below the outer ridge and coincides with the location where the paleo-Zenith Ridge is subducted. The western activity area is centered between the outer wedge and the outer ridge with the primary active area being at the outer wedge. Comparing the activity in the eastern and western areas, the eastern side is more active, but the individual moment releases on this side are smaller than those on the western side. This may indicate a difference in the fluid pressure along the plate boundary between the eastern and western areas. After the second expansion of the active area, we observed several migration patterns within the expanded area with a faster velocity than those of the initial and second expansions. The direction of these migrations is opposite to that of the first and second expansions. This indicates that the fluid pressure and/or stress level in the sVLFE generation region changed with time within this episode. Furthermore, many waveforms with sVLFE characteristics were observed at only one or a few observation points near the trough axis in the middle to latter half of January 2021. This indicates the occurrence of small-scale sVLFEs in the vicinity of the trough axis at the end of this sVLFE episode.

show abstract

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

Cited by 14 publications

References 39 publications

Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

Shallow Slow Earthquake Episodes Near the Trench Axis off Costa Rica

Spatio-Temporal Distribution of Shallow Very-Low-Frequency Earthquakes between December 2020 and January 2021 in Kumano-Nada, Nankai Subduction Zone, Detected by A Permanent Seafloor Seismic Network

Contact Info

Product

Resources

About