Southwestern Alaska encompasses a group of fault-bounded tectonostratigraphic terranes that were accreted to North America during the Mesozoic and Paleogene. To characterize the offshore extension of these terranes and several significant faults identified onshore, we reprocessed three intersecting multichannel deep seismic reflection profiles totaling ∼750 line-km that were shot by the R/V Ewing across part of the inner Bering continental shelf in 1994. Since the uppermost seismic section is often contaminated by high amplitude water layer multiples from the hard and shallow seafloor, the migrated reflection images are supplemented with high-resolution P wave velocity models derived by traveltime tomography of the recorded first-arrivals to depths of up to 2000 m. Additionally, other geophysical datasets such as seismicity, well logs, high resolution satellite-altimetry gravity, air-borne magnetics, ship-board gravity and magnetics, are also incorporated into an integrated regional interpretation. We delineate the offshore extension of the major mapped geological elements, including the Togiak fault (TGF), East Kulukak fault (EKF), Chilchitna fault (CF), Lake Clark fault (LCF), Togiak terrane (TT), Goodnews terrane (GT), Peninsular terrane (PT), Northern Kahiltna flysch (NKF) and Southern Kahiltna flysch (SKF) deposits, and the regional suture zone. The geophysical evidence from this study suggest that the major faults and terrane boundaries of southwestern Alaska, excluding the LCF, not only extend beneath the Bering shelf offshore but also appear to rotate, forming a trend parallel to the inactive Beringian margin. The LCF extends offshore but likely terminates in the northeastern part of the Bristol Bay basin. Additionally, the constraints from seismicity data indicates that while the major faults in southwestern Alaska exihibit some activity onshore, they remain dormant in the offshore region. These new findings will contribute to a better understanding of terrane accretion processes and existing fault models of southwestern Alaska.

中文翻译：

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阿拉斯加西南部近海内白令陆架上地壳结构的地震和位场约束


阿拉斯加西南部包含一组受断层限制的构造地层，这些地层在中生代和古近纪期间增生到北美。为了描述这些地体的海上延伸和陆上发现的几个重要断层，我们重新处理了 1994 年由 R/V Ewing 跨越白令内大陆架部分区域拍摄的 3 个相交的多道深地震反射剖面，总长约 750 线公里。由于最上面的地震剖面经常受到来自坚硬和浅海底的高振幅水层多次波的污染，因此偏移的反射图像由高分辨率 P 波速度模型进行补充，该模型是通过记录的初至深度的走时层析成像得出的2000 米。此外，其他地球物理数据集，如地震活动、测井曲线、高分辨率卫星测高重力、机载磁力、船载重力和磁力，也被纳入综合区域解释中。我们描绘了主要测绘地质要素的海上延伸，包括托贾克断层 (TGF)、东库鲁卡克断层 (EKF)、奇尔奇特纳断层 (CF)、克拉克湖断层 (LCF)、托贾克地体 (TT)、好新闻地体 (GT) ）、半岛地体（PT）、北卡希尔特纳复理石（NKF）和南卡希尔特纳复理石（SKF）矿床以及区域缝合带。这项研究的地球物理证据表明，阿拉斯加西南部的主要断层和地体边界（不包括LCF）不仅延伸到近海白令陆架下方，而且似乎发生旋转，形成与不活动的白令陆缘平行的趋势。 LCF 延伸至近海，但可能终止于布里斯托尔湾盆地的东北部。 此外，地震活动数据的限制表明，虽然阿拉斯加西南部的主要断层在陆上表现出一些活动，但它们在近海地区仍然处于休眠状态。这些新发现将有助于更好地了解阿拉斯加西南部的地体增生过程和现有断层模型。