摘要
利用面波层析成像和远震接收函数方法对长白山地区的地壳上地幔速度结构进行了研究。结果表明:长白山火山区附近存在岩石圈减薄、上地幔软流圈增厚以及上地幔S波速度降低等与上地幔高温物质有关的现象,它表明长白山的岩浆系统一直延伸到上地幔软流圈范围。天池火山区地壳内部存在明显的S波低速层,在离天池火山口较近的WQD台附近,低速层顶部埋深约8km,厚度近20km,S波最小速度约2.2km/s。在距离天池火山北部50km的EDO台地壳中没有明显的低速层。火山区S波速度结构总体表现出距离天池越近,地壳的V_P/V_S越大,低速层的厚度和幅度增加的特征,表明天池火山口附近地壳内部存在高温物质或岩浆囊。CBS台站不同方位的接收函数及反演结果表明,地表低速层厚度以及莫霍面深度存在随方位的变化。地表低速层在南部方向明显较厚,莫霍面深度在南部天池火山口方向存在小幅度抬升。CBS台站附近特殊的近地表速度结构可能是该台站记录的火山地震波形主频较低的主要因素。天池火山口附近莫霍面的小幅度抬升意味着存在与火山作用有关的壳幔物质交换通道。
The crustal and upper mantle S-wave velocity structures in Changbaishan volcanic region were obtained from surface wave tomography and teleseismic receiver function modeling. In Changbaishan region, the S-wave velocity shows a thin lithosphere,thick asthenosphere with relatively low S-wave velocity in upper mantle,which indicates the high temperature volcano system at least extends to asthenosphere. There exist distinct low velocity layers in the crust of the volcano area. Beneath WQD station near to the caldera,the low velocity layer at 8kin depth is 20km thick with the lowest S-wave velocity about 2.2km/s. Beneath the EDO station located 50km north of Tianchi caldera,no obvious low velocity layer was detected in the crust. The average crustal Vp/Vs near the caldcra is higher than those obtained in surrounding area. In the volcanic region, the thickness of crustal low velocity layer is greater and the lowest velocity is more obvious with the distance shorter to the caldera. It indicates the existence of the high temperature material or magma reservoir in the crust near the Tianchi caldera. The receiver functions and inversion result from different back azimuths at CBS permanent seismic station shows that the thickness of near surface low velocity layer and Moho depth change with directions. The near surface low velocity layer is obviously thicker in south direction. The Moho depth shows slightly rising in the direction of the caldera located. We consider that the special near surface velocity structure is the main cause of relatively lower prominent frequency of volcanic earthquake waveform recorded by CBS station. The slightly rising of Moho depth beneath Tianchi caldera indicates there is a material exchanging channel between magma reservoir and upper mantle.
出处
《地震地质》
EI
CSCD
北大核心
2009年第4期584-597,共14页
Seismology and Geology
基金
地震行业专项(20070827)
"十一五"国家科技支撑计划项目(2006BAC01 B040101)
地震科学联合基金(106023)共同资助
关键词
长白山
火山
速度结构
接收函数
Changbaishan,volcano,seismic velocity structure,receiver function
