Estimation of shallow S-wave velocity structure using microtremor array exploration at temporary strong motion observation stations for aftershocks of the 2016 Kumamoto earthquake

Abstract The earthquake rupture termination mechanism and size of the ruptured area are crucial parameters for earthquake magnitude estimations and seismic hazard assessments. The 2016 Mw 7.0 Kumamoto Earthquake, central Kyushu, Japan, ruptured a 34-km-long area along previously recognized active faults, eastern part of the Futagawa fault zone and northernmost part of the Hinagu fault zone. Many researchers have suggested that a magma chamber under Aso Volcano terminated the eastward rupture. However, the termination mechanism of the southward rupture has remained unclear. Here, we conduct a local seismic tomographic inversion using a dense temporary seismic network to detail the seismic velocity structure around the southern termination of the rupture. The compressional-wave velocity (Vp) results and compressional- to shear-wave velocity (Vp/Vs) structure indicate several E–W- and ENE–WSW-trending zonal anomalies in the upper to middle crust. These zonal anomalies may reflect regional geological structures that follow the same trends as the Oita–Kumamoto Tectonic Line and Usuki–Yatsushiro Tectonic Line. While the 2016 Kumamoto Earthquake rupture mainly propagated through a low-Vp/Vs area (1.62–1.74) along the Hinagu fault zone, the southern termination of the earthquake at the focal depth of the mainshock is adjacent to a 3-km-diameter high-Vp/Vs body. There is a rapid 5-km step in the depth of the seismogenic layer across the E–W-trending velocity boundary between the low- and high-Vp/Vs areas that corresponds well with the Rokkoku Tectonic Line; this geological boundary is the likely cause of the dislocation of the seismogenic layer because it is intruded by serpentinite veins. A possible factor in the southern rupture termination of the 2016 Kumamoto Earthquake is the existence of a high-Vp/Vs body in the direction of southern rupture propagation. The provided details of this inhomogeneous barrier, which are inferred from the seismic velocity structures, may improve future seismic hazard assessments for a complex fault system composed of multiple segments.

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Attenuation of Seismic Wave Energy with Strong Motion Records (KiK-net) of the 2016 Kumamoto Earthquake

Japanese Geotechnical Journal ◽

10.3208/jgs.15.81 ◽

2020 ◽

Vol 15 (1) ◽

pp. 81-89

Author(s):

Tomohiro ISHIZAWA ◽

Takaji KOKUSHO ◽

Hemanta HAZARIKA

Keyword(s):

Seismic Wave ◽

Wave Energy ◽

Strong Motion ◽

2016 Kumamoto Earthquake ◽

Strong Motion Records ◽

Kumamoto Earthquake ◽

The 2016 Kumamoto Earthquake

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Tuning S-Wave Velocity Structure of Deep Sedimentary Layers in the Shimousa Region of the Kanto Basin, Japan, Using Autocorrelation of Strong-Motion Records

Bulletin of the Seismological Society of America ◽

10.1785/0120200156 ◽

2020 ◽

Vol 110 (6) ◽

pp. 2882-2891

Author(s):

Kosuke Chimoto ◽

Hiroaki Yamanaka

Keyword(s):

Wave Velocity ◽

Velocity Structure ◽

Strong Motion ◽

S Wave ◽

Reflected Waves ◽

Arrival Times ◽

Strong Motion Records ◽

Kanto Basin ◽

Determination Of Parameters

ABSTRACT The autocorrelation of ambient noise is used to capture reflected waves for crustal and sedimentary structures. We applied autocorrelation to strong-motion records to capture the reflected waves from sedimentary layers and used them for tuning the S-wave velocity structure of these layers. Because a sedimentary-layered structure is complicated and generates many reflected waves, it is important to identify the boundary layer from which the waves reflected. We used spectral whitening during autocorrelation analysis to capture the reflected waves from the seismic bedrock with an appropriate smoothing band, which controls the wave arrival from the desired layer boundary. The effect of whitening was confirmed by the undulation frequency observed in the transfer function of the sedimentary layers. After careful determination of parameters for spectral whitening, we applied data processing to the strong-motion records observed at the stations in the Shimousa region of the Kanto Basin, Japan, to estimate the arrival times of the reflected waves. The arrival times of the reflected waves were found to be fast in the northern part of the Shimousa region and slow in the western and southern parts. These arrival times are consistent with those obtained using existing models. Because we observed a slight difference in the arrival times, the autocorrelation function at each station was used for tuning the S-wave velocity structure model of the sedimentary layers using the inversion technique. The tuned models perfectly match the autocorrelation functions in terms of the arrival time of the reflected waves from the seismic bedrock.

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Investigation of Damages in Immediate Vicinity of Co-Seismic Faults During the 2016 Kumamoto Earthquake

Journal of Disaster Research ◽

10.20965/jdr.2017.p0899 ◽

2017 ◽

Vol 12 (5) ◽

pp. 899-915 ◽

Cited By ~ 4

Author(s):

Shohei Naito ◽

Ken Xiansheng Hao ◽

Shigeki Senna ◽

Takuma Saeki ◽

Hiromitsu Nakamura ◽

...

Keyword(s):

Fault Zone ◽

Active Fault ◽

Strong Motion ◽

Site Amplification ◽

Building Damage ◽

2016 Kumamoto Earthquake ◽

Severe Damage ◽

Kumamoto Earthquake ◽

The 2016 Kumamoto Earthquake ◽

The Relationship

In the 2016 Kumamoto earthquake, the Futagawa fault zone and the Hinagu fault zone were active in some sections, causing severe damage in neighboring areas along the faults. We conducted a detailed investigation of the surface earthquake fault, building damage, and site amplification of shallow ground within about 1 km of the neighboring areas of the fault. The focus was mainly on Kawayou district, Minamiaso village and Miyazono district, Mashiki town, and locations that suffered particularly severe building damage. We explored the relationship between local strong motion and building damage caused in areas that were in the immediate vicinity of the active fault.

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Estimation of shallow S-wave velocity structure using microtremor exploration at strong motion stations observed the 2014 Aegean Sea earthquake

10.1190/segj2018-132.1 ◽

2019 ◽

Author(s):

Kosuke Chimoto ◽

Hiroaki Yamanaka ◽

Seckin Ozgur Citak ◽

Ozlem Karagoz ◽

Oguz Ozel ◽

...

Keyword(s):

Wave Velocity ◽

Velocity Structure ◽

Strong Motion ◽

Aegean Sea ◽

S Wave

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BROADBAND SOURCE CHARACTERISTICS OF THE 2016 KUMAMOTO EARTHQUAKE ESTIMATED FROM STRONG MOTION RECORDS

Journal of Structural and Construction Engineering (Transactions of AIJ) ◽

10.3130/aijs.82.1707 ◽

2017 ◽

Vol 82 (741) ◽

pp. 1707-1717 ◽

Cited By ~ 2

Author(s):

Toshimi SATOH

Keyword(s):

Strong Motion ◽

2016 Kumamoto Earthquake ◽

Strong Motion Records ◽

Kumamoto Earthquake ◽

Source Characteristics ◽

The 2016 Kumamoto Earthquake

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Estimation of Velocity Structures in the Grenoble Basin, France, Using Pseudo Earthquake Horizontal-to-Vertical Spectral Ratio from Microtremors

Bulletin of the Seismological Society of America ◽

10.1785/0120200211 ◽

2021 ◽

Vol 111 (2) ◽

pp. 627-653

Author(s):

Eri Ito ◽

Cécile Cornou ◽

Fumiaki Nagashima ◽

Hiroshi Kawase

Keyword(s):

Wave Velocity ◽

Velocity Structure ◽

Strong Motion ◽

Spectral Ratio ◽

Empirical Method ◽

S Wave ◽

Wave Velocities ◽

Strong Linear Correlation ◽

Large Velocity ◽

The Difference

ABSTRACT Based on the diffuse field concept for a horizontal-to-vertical spectral ratio of earthquakes (eHVSR), the effectiveness of eHVSRs to invert P- and S-wave velocity structures down to the seismological bedrock (with the S-wave velocity of 3 km/s or higher) has been shown in several published works. An empirical method to correct the difference between eHVSR and a horizontal-to-vertical ratio of microtremors (mHVSR), which is called earthquake-to-microtremor ratio (EMR), has also been proposed for strong-motion sites in Japan. However, the applicability of EMR outside of Japan may not be warranted. We test EMR applicability for the Grenoble basin in France with plentiful microtremor data together with observed weak-motion recordings at five sites. We thereby establish a systematic procedure to estimate the velocity structure from microtremors and delineate the fundamental characteristics of the velocity structures. We first calculate the EMR specific for the Grenoble basin (EMRG) and calculate pseudo eHVSR (pHVSR) from EMRG and mHVSR. We compare the pHVSRs with the eHVSRs at five sites and find sufficient similarity to each other. Then, we invert velocity structures from eHVSRs, pHVSRs, and mHVSRs. The velocity structures from eHVSRs are much closer to those from pHVSRs than those from mHVSRs. We need to introduce a number of layers with gradually increasing S-wave velocities below the geological basin boundary from a previous gravity study because the theoretical eHVSR of the model with a large velocity contrast has larger peak amplitudes than the observed. The depth of the S-wave velocity of 1.3 km/s (Z1.3) shows a strong, linear correlation with the geological boundary depth. Finally, we apply our validated methodology and invert velocity structures using pHVSRs at 14 sites where there are no observed earthquakes. The overall picture of Z1.3 at a cross section in the northeastern part of the basin corresponds to the geological boundary.

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