西南日本火山区三维地震成像研究
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摘要
利用日本气象厅(JMA)以及日本国立大学联合地震观测台网(JUNEC)记录到的3218个地震事件的231918条P波到时资料,反演求得西南日本160km深度范围内的三维P波速度结构。研究表明,在九州地区,俯冲的菲律宾海板块以高速为主要特征,该海洋板块在30～60km深度处的脱水使得弧前地幔楔顶端的橄榄石蛇纹岩化,在120km深度处的脱水使得地幔楔中的岩石局部熔融,融体上升引起该区的火山活动。在本州西部地区大山火山之下,低速异常显著,并伴随低频地震活动,说明该火山可能是个潜在的活火山,将来有喷发的可能性。
We used 231918 P-wave arrival times from 3218 earthquakes recorded by the seismic networks operated by Japan Meteorological Agency and Japanese national universities to determine the three-dimensional P-wave velocity structure in the depth range of 0-160 km beneath Southwest Japan.In Kyushu,the subducting Philippine Sea slab was imaged clearly as a high-velocity zone.The forearc mantle wedge was serpentinized due to the dehydration of the subducting Philippine Sea slab in the depth range of 30-60 km.The further dehydration of the Philippine Sea slab at about 120 km depth caused partial melting in the mantle wedge,and the upwelling of melting materials finally led to active volcanoes on the surface.A pronounced low-velocity anomaly and high seismic activity exist beneath Daisen volcano in western Honshu,suggesting that Daisen is a potentially active volcano and so it has a danger to erupt in the future.
We used 231918 P-wave arrival times from 3218 earthquakes recorded by the seismic networks operated by Japan Meteorological Agency and Japanese national universities to determine the three-dimensional P-wave velocity structure in the depth range of 0-160 km beneath Southwest Japan.In Kyushu,the subducting Philippine Sea slab was imaged clearly as a high-velocity zone.The forearc mantle wedge was serpentinized due to the dehydration of the subducting Philippine Sea slab in the depth range of 30-60 km.The further dehydration of the Philippine Sea slab at about 120 km depth caused partial melting in the mantle wedge,and the upwelling of melting materials finally led to active volcanoes on the surface.A pronounced low-velocity anomaly and high seismic activity exist beneath Daisen volcano in western Honshu,suggesting that Daisen is a potentially active volcano and so it has a danger to erupt in the future.
引文
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[2]Zhao D,Asamori K,Iwamori H.Seismic structure and mag-matismof the young Kyushu subduction zone[J].Geophys Res Lett,2000,27(14):2057-2060.
[3]Wang Z,Zhao D.vpandvstomography of Kyushu,Japan:Newinsight into arc magmatism and forearc seismotectonics[J].Physics of the Earth and Planetary Interiors,2006,157(3/4):269-285.
[4]Xia S,Zhao D,Qiu X.Tomographic evidence for the subduc-ting oceanic crust and forearc mantle serpentinization under Kyushu,Japan[J].Tectonophysics,2008,449:85-96.
[5]Nakaji ma J,Hasegawa A.Subduction of the Philippine Sea plate beneath southwestern Japan:Slab geometry and its re-lationship to arc magmatism[J].J Geophys Res,2007,112:doi:10.1029/2006JB004770.
[6]Zhao D,Hasegawa A,Horiuchi S.Tomographic i maging of P and S wave velocity structure beneath Northeastern Japan[J].J Geophys Res,1992,97(B13):19909-19928.
[7]UmJ,Thurber C.Afast algorithmfor two-point seismic ray tracing[J].Bull Seismol Soc Amer,1987,70(3):972-986.
[8]Paige C C,Saunders M A.LSQR:An algorithmfor sparselinear equations and sparse least squares[J].ACM Trans Math Soft,1982,8:43-71.
[9]Humphreys E,Clayton R W.Adaptation of back projection tomography to seismic travel ti me problems[J].J Geophys Res,1988,93(B2):1073-1085.
[10]Sun A,Zhao D,Ikeda M,et al.3-D P and S wave velocity structure and its relationship to seismic and volcanic activity in Southwest Japan[J].Progress in Geophysics,2008,23(4):1013-1022(in Chinese).
[11]Shelly D R,Beroza G C,Ide S,et al.Low-frequency earth-quakes in Shikoku,Japan,and their relationship to episodic tremor and slip[J].Nature,2006,442:188-191.
[12]Oda H,Tanaka T,Seya K.Subducting oceanic crust on the Philippine Sea plate in Southwest Japan[J].Tectonophysics,1990,172:175-189.
[13]Ohkura T.Structure of the upper part of the Philippine Sea plate esti mated bylater phases of upper mantle earthquakesin and around Shikoku,Japan[J].Tectonophysics,2000,321:17-36.
[14]Kamiya S,Kobayashi Y.Seismological evidence for the exist-ence of serpentinized wedge mantle[J].Geophys Res Lett,2000,27(6):819-822.
[15]Christensen NI.Poisson s ratio and crustal seismology[J].J Geophys Res,1996,101(B2):3139-3156.
[16]Horen H,Zamora M,Dubuisson G.Seismic waves velocities and anisotropyin serpentinized peridotites from Xigaze ophio-lite:Abundance of serpentine in slow spreading ridge[J].Geophys Res Lett,1996,23:9-12.
[17]Hasegawa A,Yamamoto A.Deep,low-frequency microe-arthquakes in or around seismic low-velocity zones beneath active volcanoes in northeastern Japan[J].Tectonophysics,1994,233:233-252.
[10]孙安辉,赵大鹏,池田伦治,等.西南日本地区地壳P、S波速度结构与地震活动的关系[J].地球物理学进展,2008,23(4):1013-1022.
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