Azimuth Verification of the MeSO-net Seismographs

将行, 加納; 大道, 長尾; 慎一, 酒井; 茂樹, 中川; 覚信, 水迫; 宗朗, 堀; 直, 平田; 勝彦, 汐見; 亮, 本多

doi:10.4294/zisin.68.31

Cited by 13 publications

(8 citation statements)

References 5 publications

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“…Due to the location of the sensors in 20‐m deep boreholes, the horizontal components are not perfectly aligned to the north‐south and east‐west directions. We rotate the horizontal components to the true north‐south and east‐west directions using the estimated orientations determined by Kano et al ().…”

Section: On Monitoring the Soil Responsementioning

confidence: 99%

Complex Near‐Surface Rheology Inferred From the Response of Greater Tokyo to Strong Ground Motions

et al. 2018

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Strong ground motion can induce dynamic strains large enough for the Earth's subsurface to respond nonlinearly and to cause permanent, or plastic, damage. The 2011 Mw 9.0 Tohoku‐Oki earthquake, Japan, generated exceptional and well‐recorded ground motions in the greater Tokyo area. We use continuous records from 234 stations of the dense MeSO‐net seismic network to monitor the temporal evolution of the material properties of the shallow subsurface (upper ∼100 m). We apply the single‐station cross‐correlation method to reconstruct the near‐surface reflectivity response through time. We find that the strong ground motions from the mainshock caused large perturbations in the near‐surface structure, with significant drops in seismic velocities up to 11%. For most sites, we observe a logarithmic and complete recovery of the seismic wave speed, suggesting a relaxation process that can be explained by a viscoelastic rheology. Some sites exhibit an instantaneous and permanent change, which suggests a plastic rheology. Finally, dense seismic measurements allow for statistical inference between seismic velocity drops, recovery time scales, and permanent perturbations and ground motion strength and site conditions. This study highlights the potential for seismic interferometry to assess near‐surface rheology with dense seismic arrays.

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Section: On Monitoring the Soil Responsementioning

confidence: 99%

Complex Near‐Surface Rheology Inferred From the Response of Greater Tokyo to Strong Ground Motions

et al. 2018

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“…In the Kanto basin, the MeSO‐net accelerometers continuously record waveforms at a sampling rate of 200 Hz in boreholes at a depth of ~20 m. Figure shows the waveforms observed for a M w 5.5 earthquake that occurred on 16 September 2014, following a decimation of the sampling rate to 25 Hz and azimuth correction of each sensor based on the deviation from true north evaluated by Kano et al []. This earthquake produced the largest magnitude among all events that have occurred in or near the Kanto area since all MeSO‐net stations became operational in 2012, causing seismic intensities >4 on the Japan Meteorological Agency (JMA) scale in Tokyo.…”

Section: Meso‐net Datamentioning

confidence: 99%

Seismic wavefield imaging of long‐period ground motion in the Tokyo metropolitan area, Japan

et al. 2017

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Long‐period ground motions due to large earthquakes can cause devastating disasters, especially in urbanized areas located on sedimentary basins. To assess and mitigate such damage, it is essential to rapidly evaluate seismic hazards for infrastructures, which can be simulated by seismic response analyses that use waveforms at the base of each infrastructure as an input ground motion. The present study reconstructs the seismic wavefield in the Tokyo metropolitan area located on the Kanto sedimentary basin, Japan, from seismograms of the Metropolitan Seismic Observation network. The obtained wavefield fully explains the observed waveforms in the frequency band of 0.10–0.20 Hz. This is attributed to the seismic wavefield imaging technique proposed by Kano et al. (2017), which implements the replica exchange Monte Carlo method to simultaneously estimate model parameters related to the subsurface structure and source information. Further investigation shows that the reconstructed seismic wavefield lower than 0.30 Hz is of high quality in terms of variance reduction, which quantifies a misfit in waveforms but that the variance reduction rapidly worsens in higher frequencies. Meanwhile, the velocity response spectra show good agreement with observations up to 0.90 Hz in terms of the combined goodness of fit, which is a measure of misfit in the velocity response spectra. Inputting the reconstructed wavefield into seismic response analyses, we can rapidly assess the overall damage to infrastructures immediately after a large earthquake.

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“…The MeSO-net and K-NET/KiK-net sensors were aligned in horizontal and vertical directions, but the azimuths of the horizontal sensors were not aligned in the north-south and east-west directions for the MeSO-net. We used the azimuths of the MeSO-net sensors from Kano et al (2015) to compare the MeSO-net records with other networks. On the other hand, the three-component sensors at the S-net stations were not necessarily aligned in the horizontal and vertical directions.…”

Section: Data and Processingmentioning

confidence: 99%

An Evaluation of Strong-Motion Parameters at the S-net Ocean-Bottom Seismograph Sites Near the Kanto Basin for Earthquake Early Warning

Dhakal

Kunugi

2021

Front. Earth Sci.

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We analyzed strong-motion records at the ground and borehole in and around the Kanto Basin and the seafloor in the Japan Trench area from three nearby offshore earthquakes of similar magnitudes (Mw 5.8–5.9). The seafloor strong-motion records were obtained from S-net, which was established to enhance tsunami and earthquake early warnings after the 2011 great Tohoku-oki earthquake disaster. The borehole records were obtained from MeSO-net, a dense network of seismometers installed at a depth of 20 m in the Tokyo metropolitan area. The ground records were obtained from the K-NET and KiK-net networks, established after the 1995 great Hanshin-Awaji earthquake disaster. The MeSO-net and S-net stations record the shakings continuously, while the K-NET and KiK-net records are based on triggering thresholds. It is crucial to evaluate the properties of strong motions recorded by the S-net for earthquake early warning (EEW). This paper compared the peak ground accelerations (PGAs) and peak ground velocities (PGVs) between the S-net and K-NET/KiK-net stations. Because the MeSO-net records were from the borehole, we compared the PGAs and significant durations of the low-frequency motions (0.1–0.5 Hz) between the S-net and MeSO-net stations from identical record lengths. We found that the horizontal PGAs and PGVs at the S-net sites were similar to or larger than the K-NET/KiK-net sites for the S wave. In contrast, the vertical PGAs and PGVs at the S-net sites were similar to or smaller than those at the K-NET/KiK-net sites for the S wave. Particularly, the PGAs and PGVs for the P-wave parts on the vertical-component records of S-net were, on average, much smaller than those of K-NET/KiK-net records. The difference was more evident in the PGAs. The average ratios of S-wave horizontal to vertical PGAs were about 2.5 and 5 for the land and S-net sites, respectively. The low-frequency PGAs at the S-net sites were similar to or larger than those of the MeSO-net borehole records. The significant durations between the two-networks low-frequency records were generally comparable. Quantification of the results from a larger dataset may contribute to ground-motion prediction for EEW and the design of the offshore facilities.

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Azimuth Verification of the MeSO-net Seismographs

Cited by 13 publications

References 5 publications

Complex Near‐Surface Rheology Inferred From the Response of Greater Tokyo to Strong Ground Motions

Complex Near‐Surface Rheology Inferred From the Response of Greater Tokyo to Strong Ground Motions

Seismic wavefield imaging of long‐period ground motion in the Tokyo metropolitan area, Japan

An Evaluation of Strong-Motion Parameters at the S-net Ocean-Bottom Seismograph Sites Near the Kanto Basin for Earthquake Early Warning

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