长白山火山区壳幔S波速度结构研究

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

S-WAVE VELOCITY STRUCTURE BENEATH CHANGBAISHAN TIANCHI VOLCANO INFERRED FROM RECEIVER FUNCTION

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 8km 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 V_p/V_s near the caldera 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