Three-dimensional velocity structure of Siletzia and other accreted terranes in the Cascadia forearc of Washington
Three-dimensional velocity structure of Siletzia and other accreted terranes in the Cascadia forearc of Washington
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华盛顿卡斯卡迪亚弧前 Siletzia 和其他增生地体的三维速度结构
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
U. Brink
中科院分区：
文献类型：
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作者：
T. Parsons;R. Wells;M. Fisher;E. Flueh;U. Brink
始新世镁铁质地壳具有较高的地震速度，位于俄勒冈州和华盛顿大部分前弧之下，并作为斜向俯冲的胡安德富卡板片的海洋沉积岩增生的支撑。这片被称为Siletzia的相对较强的板块的弧形平行迁移集中了沿沿着块体边界的上地壳变形，这些块体是潜在的地震源。在沿海华盛顿的三维速度模型中，我们结合了地表地质、钻井数据和地震和可控源地震实验的走时，以解决锡莱茨火山岩与相邻的增生沉积棱柱体和火山弧的主要边界。在华盛顿南部和北方俄勒冈州，锡莱茨岩似乎是一个厚块（约20 km），延伸到海岸线以西，与近海增生沉积棱柱体形成高角度接触。在其东侧，高速锡莱茨边界与弧形地震活动的雁行带相吻合。在北方华盛顿，西列茨亚的西部边缘与增生棱柱形成一个低角度的断层边界接触。此外，交替，东西走向的隆起和下沉的锡莱茨的反正规奥林匹克山脉为中心的西莱茨可能反映了集中在北方的锡莱茨西莱茨的北南压缩。这种挤压应变可能是由于锡莱茨山脉向北迁移和顺时针旋转进入相对固定的加拿大海岸山脉，限制了海岸的弯曲。
Eocene mafic crust with high seismic velocities underlies much of the Oregon and Washington forearc and acts as a backstop for accretion of marine sedimentary rocks from the obliquely subducting Juan de Fuca slab. Arc-parallel migration of relatively strong blocks of this terrane, known as Siletzia, focuses upper crustal deformation along block boundaries, which are potential sources of earthquakes. In a three-dimensional velocity model of coastal Washington, we have combined surface geology, well data, and travel times from earthquakes and controlled source seismic experiments to resolve the major boundaries of the Siletz terrane with the adjacent accreted sedimentary prism and volcanic arc. In southern Washington and northern Oregon the Siletz terrane appears to be a thick block (∼20 km) that extends west of the coastline and makes a high-angle contact with the offshore accreted sedimentary prism. On its east flank the high-velocity Siletz terrane boundary coincides with an en echelon zone of seismicity in the arc. In northern Washington the western edge of Siletzia makes a lower-angled, fault-bound contact with the accretionary prism. In addition, alternating, east-west trending uplifts and downwarps of the Siletz terrane centered on the antiformal Olympic Mountains may reflect focusing of north-south compression in the northern part of the Siletz terrane. This compressional strain may result from northward transport and clockwise rotation of the Siletz terrane into the relatively fixed Canadian Coast Mountains restraining bend along the coast.