Abstract The Castle Mountain Fault (CMF) lies less than 50 km from Alaska's most populous city of Anchorage and represents an important seismic hazard to the Anchorage-Matanuska-Susitna Valley region in southcentral Alaska. The character of seismicity varies along the CMF. Although the western CMF (between 149.5° and 151° W) shows evidence for Late Pleistocene or Holocene reverse and dextral movement, it has been seismically quiet over the past ~50 years of local seismic network operation. In contrast, the CMF east of 149.5° W is associated with considerable background seismicity, including the Mw 5.81984 strike-slip Sutton earthquake. We have used gravity and magnetic data, constrained with results of previous seismic reflection and seismic tomography studies, to model subsurface structure of the CMF in an effort to determine what may control the variation in its seismic behavior. Our models are consistent with a component of high angle reverse faulting (northwest side up, dip~85°to 87°) that appears to have vertically offset Late Mesozoic rocks 2000 to 2500 m. Lack of data coverage precludes an estimate of its total strike-slip motion. Holocene movement on the CMF appears to be associated with a region where both sides of the fault consist of sedimentary rocks as defined by a gravity and magnetic low. If most of the vertical offset has occurred since the Miocene in response to collision of the Yakutat microplate with North America, then our results are comparable to recent thermochronological and paleoseismic estimates of vertical slip rates. Subduction of the edge of the Yakutat microplate appears to spatially influence seismic behavior along the CMF while the occurrence of the 1964 Great Alaska earthquake has also temporally affected local seismicity.

中文翻译：

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阿拉斯加中南部城堡山断层的地球物理研究

摘要 城堡山断层 (CMF) 距阿拉斯加人口最多的城市安克雷奇不到 50 公里，是阿拉斯加中南部安克雷奇-马塔努斯卡-苏西特纳山谷地区的重要地震灾害。地震活动的特征沿 CMF 变化。尽管西部 CMF（在 149.5° 和 151° W 之间）显示出晚更新世或全新世逆向和右向运动的证据，但在过去约 50 年的本地地震网络运行中，它在地震上一直很平静。相比之下，149.5° W 以东的 CMF 与相当大的背景地震活动有关，包括 Mw 5.81984 走滑萨顿地震。我们使用了重力和磁性数据，受先前地震反射和地震层析成像研究结果的限制，模拟 CMF 的地下结构，以确定什么可以控制其地震行为的变化。我们的模型与大角度逆断层（西北侧向上，倾角~85°至 87°）的成分一致，该成分似乎垂直偏移晚中生代岩石 2000 至 2500 m。由于缺乏数据覆盖，无法估计其总走滑运动。CMF 上的全新世运动似乎与断层两侧由重力和磁低定义的沉积岩组成的区域有关。如果自中新世以来大部分垂直偏移发生在雅库塔特微板块与北美的碰撞响应中，那么我们的结果与最近的垂直滑动速率的热年代学和古地震估计相当。