俯冲带波速结构的数值模拟

NUMERICAL SIMULATION OF P-WAVE VELOCITY STRUCTURE OF SUBDUCTION ZONES

数值模拟结果显示 ,俯冲带在大部分深度都存在高速异常 ,并在 40 0km左右和550km左右的深度存在高速异常的极大值 ,这和地震层析成像得到的波速结构相一致 .说明虽然层析成像方法的分辨率较低 ,但它能给出俯冲板块上P波速度随深度变化的基本特征 .俯冲带既有正的波速异常 ,也有负的波速异常 ,幅度约在 - 1 0 %— 9%之间 ,这在区域台网的资料中可以得到反映 .俯冲带在约 70 0km深度存在低速异常 ,亚稳态橄榄石的存在也使俯冲带出现沿俯冲方向的倾斜低速区 .地震层析成像结果没有类似的波速结构 ,可能是其分辨率较低所致 .要研究俯冲带的细结构 ,应基于高精度的区域台网的资料 .

Numerical simulation shows that high velocity anomalies exist in most depths of subduction zones with the maximum velocity at the depth of about 400km and 550km,which is consistent with the wave velocity structure determined by seismic tomography. Though resolution is low,seismic tomography shows the basic properties of P wave speed variation in subduction zones. The data from regional stations indicate that P wave velocity anomalies can be positive or negative,in the range from -10% to 9%. Low velocity anomalies exist at the depth of about 700km,and metastable olivine causes low speed regions that decline along the dip direction of subduction zones. Low resolution of seismic tomography is an obstacle to show detailed P wave speed structure of subduction zones. To investigate fine structure of subduction zones,we should use high resolution data obtained from regional networks.