由背景噪声多阶面波反演阿拉斯加地壳三维横波速度结构

The 3D vs structure of Alaska’s crust from multimodal ambient noise tomography

阿拉斯加由若干具有不同构造演变历史的地块构成,其南部边缘受太平洋板块向北美板块俯冲影响,整体构造运动活跃,具有很大的研究价值。本研究从美国阿拉斯加及加拿大西北部地区的310个台站共6年的背景噪声数据中提取出瑞利多阶频散曲线,最终得到研究区域地壳的三维横波速度结构。我们在阿拉斯加地下约10 km~20 km深度范围发现一广泛分布的中地壳低速层。该低速层位于阿拉斯加内陆区域,包括Seward半岛,Yukon-Koyukuk地块,Yukon-Tanana地块及阿拉斯加东南部部分区域。低速层与阿拉斯加四大地热区域中的两个(CAHSB和SEP温泉分布区)高度重合。中地壳低速层与当地地热资源的对应性一定程度上证实了我们所得速度模型的可靠性,同时对该低速层的进一步研究或许有助于阿拉斯加温泉带起源的探索。

Alaska consists of several terranes with different evolution histories and is subducted by the Pacific plate at the southern edge.It is tectonically active,which makes a detailed study of the subsurface velocity structures necessary.In this paper,Rayleigh wave multimodal dispersion curves are extracted from ambient noise recorded at 310 stations in Alaska and northwestern Canada over six years,and a 3-D Vs model of Alaska and northwestern Canada’s crust is obtained.We find a widespread mid-crust low-velocity layer(LVL)in about 10-20 km depth.The LVL covers part of interior Alaska between the Brooks Range and the Denali faults,including the Seward Peninsula,the Yukon-Koyukuk terrane,the Yukon-Tanana terrane,and part of the southeastern Alaska,which largely coincide with the Central Alaskan Hot Spring Belt(CAHSB)and the Southeastern Panhandle(SEP).The correspondence between the LVL and geothermal regions indicates that the involvement of higher-mode dispersion curves in the inversion processes could provide additional information and make our final velocity model more accurate.Besides,the mid-crust LVL may shed light on exploring Alaskan geothermal resources.