Previously-published tomographic images show low-velocity anomalies (shear velocity up to 5% slow relative to the AK135 Earth model) in the asthenosphere beneath the southeastern margin of North America, including the Northern Appalachian (New England), the Central Appalachian (Virginia), and the Northern Gulf (Texas-Louisiana coast) Anomalies. Travel time anomaly ratios and attenuation indicate that they are thermal anomalies associated with mantle upwelling. We use teleseismic P and S wave differential travel times, as determined by cross-correlation of USArray data, and ratios of compressional-to-shear wave travel time fluctuations to characterize the South Coastal Anomaly (SCA), a fourth, weaker anomaly (about half as strong as these others) that stretches from Georgia to Virginia. P-wave tomography indicates that the SCA is about 800 km long in its north-south dimension and at least 300 km wide in its east-west dimension (its eastern edge is not imaged) and it is strongest (∆V_P ≈ − 0.1 km/s) in the 100–250 km depth range. Its western edge strikes north-south, parallel to the edge of the Laurentian Craton (LC). The maximum P and S wave travel time anomalies of the SCA are 1.09 ± 0.05 (95%) s and 4.20 ± 0.10 (95%) s, respectively, relative to the LC. The ratio of P-to-S wave differential travel time anomalies is 3.84 ± 0.10 (95%), a value close to the value of ~3.3 predicted for a thermal anomaly and very different from the value of ~1.8 predicted for a compositional anomaly. The compressional velocity is up to 0.41 km/s slower than the LC, which corresponds to a maximum temperature difference of about 700 °C, using a sensitivity of 1713 K-s/km. In the shallow asthenosphere, the SCA appears distinct from the Central Appalachian Anomaly, being weaker in magnitude and more tabular in shape, but the two anomalies may merge below ~250 km depth. Our findings support the notion of the vigorous edge convection along much of the eastern continental margin.

先前发布的断层图像显示了北美洲东南边缘以下的软流圈的低速异常（相对于AK135地球模型，剪切速度慢达5％），包括北阿巴拉契亚（新英格兰），中阿巴拉契亚（弗吉尼亚） ）和北湾（得克萨斯州-路易斯安那州海岸）异常。传播时间异常率和衰减表明它们是与地幔上升有关的热异常。我们使用由USArray数据的互相关确定的远震P波和S波差分传播时间，以及压缩波与剪切波传播时间波动的比率来表征南海岸异常（SCA），这是第四个较弱的异常（大约从佐治亚州延伸到弗吉尼亚州，强度只有其他同类产品的一半）。V _P  ≈ - 0.1公里/小号）在100-250公里深度范围内。它的西边沿南北走向，与Laurentian Craton（LC）的边平行。相对于LC，SCA的最大P和S波传播时间异常分别为1.09±0.05（95％）s和4.20±0.10（95％）s。P对S波差分传播时间异常的比率为3.84±0.10（95％），该值接近热异常预测的〜3.3的值，与成分异常预测的〜1.8的值非常不同。压缩速度比LC慢0.41 km / s，这对应于1713 Ks / km的灵敏度，最大温度差约为700°C。在浅流的软流圈中，SCA看起来不同于阿巴拉契亚中部异常，其大小较弱，且呈表格形式，但是这两个异常可能在〜250 km深度以下合并。我们的发现支持了沿东部大陆边缘大部分地区剧烈对流的观点。