Three-dimensional P- and S-wave attenuation structures around the source region of the 2016 Kumamoto earthquakes

Komatsu, Masanao; Takenaka, Hiroshi; Oda, Hitoshi

doi:10.1186/s40623-017-0683-6

Cited by 11 publications

(13 citation statements)

References 36 publications

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“…5 ). The low-V and high- σ anomalies revealed by our velocity tomography correspond very well to the low-Q zones revealed by seismic attenuation tomography 18 , 19 and high-conductivity anomalies detected by electromagnetic imaging 32 .…”

Section: Discussionsupporting

confidence: 79%

“…The low-V, low-Q and high-σ zones reflect the forearc mantle serpentinization due to the presence of abundant fluids from the dehydration of the young and warm PHS slab (Fig. 2 ), as pointed out by several previous studies of seismic velocity 2 , 24 , 35 and attenuation 18 , 19 , 36 in Kyushu. Serpentinization is a common feature in the forearc mantle wedge when abundant fluids are released from a young and warm slab 37 – 39 .…”

Section: Discussionsupporting

confidence: 55%

“…Using a similar approach, Komatsu et al . 19 obtained Qp and Qs tomographic images down to ~40 km depth beneath central-north Kyushu using local events that occurred during 2002 to 2012, i.e., their data set does not include the 2016 Kumamoto aftershocks. Shito et al .…”

Section: Introductionmentioning

confidence: 99%

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Tomography of the 2016 Kumamoto earthquake area and the Beppu-Shimabara graben

Zhao

Yamashita

Toyokuni

2018

Sci Rep

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Detailed three-dimensional images of P and S wave velocity and Poisson’s ratio (σ) of the crust and upper mantle beneath Kyushu in SW Japan are determined, with a focus on the source area of the 2016 Kumamoto earthquake (M 7.3) that occurred in the Beppu-Shimabara graben (BSG) where four active volcanoes and many active faults exist. The 2016 Kumamoto earthquake took place in a high-velocity and low-σ zone in the upper crust, which is surrounded and underlain by low-velocity and high-σ anomalies in the upper mantle. This result suggests that, in and around the source zone of the 2016 Kumamoto earthquake, strong structural heterogeneities relating to active volcanoes and magmatic fluids exist, which may affect the seismogenesis. Along the BSG, low-velocity and high-σ anomalies do not exist everywhere in the upper mantle but mainly beneath the active volcanoes, suggesting that hot mantle upwelling is not the only cause of the graben. The BSG was most likely formed by joint effects of northward extension of the Okinawa Trough, westward extension of the Median Tectonic Line, and hot upwelling flow in the mantle wedge beneath the active volcanoes.

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Section: Discussionsupporting

confidence: 79%

Section: Discussionsupporting

confidence: 55%

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Tomography of the 2016 Kumamoto earthquake area and the Beppu-Shimabara graben

Zhao

Yamashita

Toyokuni

2018

Sci Rep

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“…Their results indicated that high‐attenuation zones were broadly distributed throughout the upper crust in and around volcanic regions and active faults, with most of the large inland crustal earthquakes located in or around the high‐attenuation zones. Komatsu et al (2017) and Wang et al (2017) estimated the 3‐D

Q_{i}^{- 1}

structures from the P ‐ and S ‐waves propagating in the source region of the 2016 Kumamoto earthquakes and identified high‐attenuation zones throughout the entire crust beneath the active volcanoes and throughout the lower crust beneath the source region. The authors concluded that the 2016 Kumamoto earthquakes occurred in a low‐attenuation zone in the upper crust that was underlain by a high‐attenuation zone in the lower crust.…”

Section: Resultsmentioning

confidence: 99%

3‐D Intrinsic and Scattering Seismic Attenuation Structures Beneath Kyushu, Japan

et al. 2020

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The attenuation of seismic wave energy is caused by intrinsic absorption and scattering. The former involves the conversion of seismic wave energy to heat energy via internal friction due to the anelasticity of the medium, whereas the latter involves the scattering of seismic wave energy due to random elastic heterogeneities in the medium. Quantifying both intrinsic ( Qi−1) and scattering ( Qs−1) attenuation is therefore important for understanding the physical properties of the Earth's interior and predicting seismic wave propagation. Here we develop a new procedure to separately map three‐dimensional (3‐D) Qi−1 and Qs−1 structures. The path‐averaged Qi−1 and Qs−1 values are obtained via an envelope‐fitting approach that employs a multiple‐scattering model. The path‐averaged Qi−1 and Qs−1 structures are then mapped into 3‐D space using a tomographic inversion technique based on sensitivity kernels, which are calculated from a Monte Carlo simulation of the radiative transfer equations. We apply this method to map the crustal structure beneath Kyushu, Japan, and obtain 3‐D Qi−1 and Qs−1 structures for the 1–2, 2–4, and 4–8 Hz frequency bands. The spatial attenuation patterns are similar for each of the analyzed frequency bands, with the spatial variability in Qs−1 being more pronounced than that in Qi−1. The high‐ Qi−1 and Qs−1 regions correspond to the locations of active volcanoes. Conversely, the northern Kyushu area possesses low‐ Qi−1 and Qs−1 zones that correspond to low heat flow and Cretaceous granite, respectively. The overall Qi−1 and Qs−1 distributions correlate with thermal and geological structures, respectively.

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“…This phenomenon is explained by that the monitoring wells were greatly subjected by tectonic setting more than local hydrogeological response. In fact, the lower crust of the Japanese island arc is the low Q subduction zone while the Korean peninsula is composed of the Precambrian massif of high Q (Komatsu et al 2017;Wang et al 2017). Since earthquake energy is highly attenuated in low Q region, the energy of the Kumamoto earthquake could not effectively transmit to Jeju Island.…”

Section: Discussionmentioning

confidence: 99%

Groundwater level changes on Jeju Island associated with the Kumamoto and Gyeongju earthquakes

Lee

Cheong²,

Park³

et al. 2017

Geomatics, Natural Hazards and Risk

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Groundwater levels on the monitoring wells on Jeju Island were monitored, which were caused by the M 5.4 earthquake in Gyeongju City area, South Korea, at 11:32:54 on 12 September 2016 (UTC time) and the Kumamoto earthquake, Kyushu, Japan, at 16:25:06 on 16 April 2016 (UTC time). The groundwater levels changed after 2-3 min by the generation of the Gyeongju and Kumamoto earthquakes and exhibited spikes or oscillations depending on the magnitude of the earthquakes. The groundwater level change caused by the Gyeongju earthquake (M 5.4) was mostly larger than that caused by the Kumamoto earthquake (M 5.4). The reason is explained by that the energy of the Kumamoto earthquake with high attenuation could not be effectively transmitted to Jeju Island since the earthquake took place in low Q region whereas a higher energy of the Gyeongju earthquake with low attenuation arrived on Jeju Island because the earthquake occurred in the south-eastern part of the Korean peninsula belonging to the high Q crust. Besides the seismic energy from the Kumamoto earthquake was scattered and reflected on the Tsushima-Goto fault zone between Kyushu and the Korean peninsula, with a strike in the ENE-WSW direction that elongates to the east of Jeju Island.

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Three-dimensional P- and S-wave attenuation structures around the source region of the 2016 Kumamoto earthquakes

Cited by 11 publications

References 36 publications

Tomography of the 2016 Kumamoto earthquake area and the Beppu-Shimabara graben

Tomography of the 2016 Kumamoto earthquake area and the Beppu-Shimabara graben

3‐D Intrinsic and Scattering Seismic Attenuation Structures Beneath Kyushu, Japan

Groundwater level changes on Jeju Island associated with the Kumamoto and Gyeongju earthquakes

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