Specifying the extent and location of rifted, crystalline Precambrian crust in the eastern United States is important for seismic hazard evaluation and for models that relate upper‐mantle structure to ancient tectonic features and ongoing tectonism. As currently depicted in the National Seismic Hazard Maps (NSHM), the western limit of Iapetan rifted crust is beneath the Appalachian plateau physiographic province, west of the Valley and Ridge province. New estimates of crustal thickness using EarthScope Transportable Array and other data do not support the presence of rifted crust beneath the Blue Ridge, Valley and Ridge, and Appalachian plateau physiographic provinces. Crustal thicknesses exceed 45 km throughout most of this region. The crust thins to the southeast beneath the southeastern part of the Piedmont physiographic province and is only 36 km thick near the edge of the Atlantic coastal plain. We suggest that the western limit of Iapetan rift‐extended crust is east of the Blue Ridge province and is associated with the prominent Appalachian gravity gradient. This location coincides with palinspastic reconstructions based on geologic data for the Iapetan rifted margin. Recognition of thick crust beneath the Blue Ridge and Valley and Ridge provinces, unextended by Iapetan rifting, will support more robust modeling of the effects of mantle structure (such as delamination and abrupt changes in lithospheric thickness) on ongoing tectonism and earthquake activity in the eastern United States and will provide more accurate seismotectonic zonation in the NSHM.

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美国东部伊帕坦裂谷的西部界限：一项新的评估

确定美国东部裂谷前寒武纪地壳的范围和位置，对于地震危险性评估以及将上地幔结构与古代构造特征和正在进行的构造运动联系起来的模型而言都非常重要。正如目前在《美国国家地震危险性地图》（NSHM）中所描绘的那样，伊帕坦裂谷地壳的西界在阿巴拉契亚高原地貌学省以下，在山谷和里奇省以西。使用EarthScope可移动阵列和其他数据对地壳厚度进行的新估算不支持在蓝岭，山谷和山脊以及阿巴拉契亚高原地理学省以下存在裂谷地壳。在该地区大部分地区，地壳厚度超过45公里。地壳向皮埃蒙特地理学省东南部下方的东南方向变薄，在大西洋沿岸平原边缘附近仅36公里厚。我们建议，Iapetan裂谷扩展壳的西界在蓝岭省的东部，并且与阿巴拉契亚山脉引力梯度有关。该位置与基于Iapetan裂谷缘的地质数据的大地构造重建相吻合。识别Iapetan裂谷不会扩展蓝脊山脉，山谷和脊山脉各省下的厚壳，这将支持更可靠地模拟地幔结构对东部构造和地震活动的影响（例如分层和岩石圈厚度的突然变化）。美国，并将在NSHM中提供更准确的地震构造带。