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Crustal Extension and Graben Formation by Fault Slip-Associated Pore Opening, Kyushu, Japan
Wang, Zhi; Fukao, Yoshio1; Miyakawa, Ayumu2; Hasegawa, Akira3; Takei, Yasuko4
AbstractCrustal extension in graben takes place by normal (+strike-slip) faulting, yet the physical processes involved are poorly understood. A series of shallow large earthquakes struck the Kumamoto area of Kyushu, Japan, in 2016. The M(w)7.0 main shock was a slip along the southern boundary of the Beppu-Shimabara Graben, where NS-extensional crustal deformation is now taking place. We conducted a tomographic inversion for crustal P and S velocities and Poisson's ratio (V-p, V-s, and sigma) in Kyushu. The most outstanding feature in this region is a Beppu-Shimabara Graben-parallel belt of low V-p and V-s anomalies at depths of the upper crust. We find that within the belt dV(s)/V-s approximate to dV(p)/V-p (<0) in marked contrast to relations in other low-velocity regions where |dV(s)/V-s|>|dV(p)/V-p|. This observation can be interpreted as due to water-saturated, oblate-spheroid pores with either of two very different geometries: one almost round pore and the other very flat pore. We calculate 3-D density anomaly distributions and 2-D gravity anomaly profiles for these two pore models. The gravity anomaly map calculated for spherical pores shows a significant negative anomaly belt that spatially agrees with observed Bouguer anomaly map. The spatial agreement is very poor if pores are modeled as flat. This and extensive seismicity within Beppu-Shimabara Graben imply significance of fault-associated round pore formation in the process of graben opening. Seismic tomography combined with gravity and poroeasticty analyses can constrain the crack/pore state of extensionally deforming crust.
Keywordcrustal extension graben poroelasticity Bouguer anomaly seismic tomography
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Document Type期刊论文
Affiliation1.Chinese Acad Sci, South China Sea Inst Oceanol, CAS Key Lab Ocean & Marginal Sea Geol, Guangzhou, Guangdong, Peoples R China
2.Japan Agcy Marine Earth Sci & Technol, CEAT, Yokohama, Kanagawa, Japan
3.Geol Survey Japan, AIST, Tsukuba, Ibaraki, Japan
4.Tohoku Univ, Dept Geophys, Sendai, Miyagi, Japan
5.Univ Tokyo, Earthquake Res Inst, Tokyo, Japan
Recommended Citation
GB/T 7714
Wang, Zhi,Fukao, Yoshio,Miyakawa, Ayumu,et al. Crustal Extension and Graben Formation by Fault Slip-Associated Pore Opening, Kyushu, Japan[J]. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH,2019,124(5):4879, 4894.
APA Wang, Zhi,Fukao, Yoshio,Miyakawa, Ayumu,Hasegawa, Akira,&Takei, Yasuko.(2019).Crustal Extension and Graben Formation by Fault Slip-Associated Pore Opening, Kyushu, Japan.JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH,124(5),4879.
MLA Wang, Zhi,et al."Crustal Extension and Graben Formation by Fault Slip-Associated Pore Opening, Kyushu, Japan".JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 124.5(2019):4879.
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