The Relationship Between Post-Little-Ice-Age Isostatic Rebound and Active Tectonics in Southern Alaska

这项研究正在确定阿拉斯加南部冰川反弹和构造应变之间的关系。据报道，在夏洛特皇后-费尔韦瑟断层系统结束的地区，隆升率非常高（基于GPS的25-30毫米/年）。高水平速度与这种转换系统有关，该地区自小冰期以来经历了快速的冰川消融。数值等静力回弹模型被用于生成三维变形预测，这将受到已经获得的大量数据集的限制。现有的数据集是跨学科努力的产物，旨在确定阿拉斯加东南部隆起和冰负荷变化的时间、幅度和历史。该观测包括76个站点的区域全球定位系统（GPS）地壳变形阵列、18个潮汐测量站点的海平面速率、凸起海岸线的总隆起测量以及27个站点的隆起开始。这些数据在百年、年代际和年尺度上刻画了区域隆升格局，描绘了当前区域三维地壳变形格局。研究小组正在：1)利用改进的GPS和提高的海岸线数据库改进当前的冰川均衡回弹模型；2)建立数值回弹模型，生成三维变形预测；3)利用三维变形模型预测，从水平速度观测中剔除均衡诱发运动的水平分量，得到该地区的构造变形；4)从区域地壳动力学和过程的角度评价构造速度场和应变场，特别强调对Fairweather和St. Elias山脉的形成、Denali断层的成因和Yakutat地块碰撞动力学的影响；(5)卸荷诱发地震电位的评价，以及卸荷对构造地震电位的影响。利用数值模型量化冰川均衡回弹，利用垂直形变信号解析地壳和地幔的粘弹性性质，从而为分离水平形变场中的构造和均衡信号提供了一种手段。

This study is determining the relationships between glacial rebound and tectonic strain in southern Alaska. Very high uplift rates (25-30 mm/yr based on GPS) are reported in the region where the Queen Charlotte-Fairweather fault system ends. High horizontal velocities are associated with this transform system and the area has experienced rapid deglaciation since the Little Ice Age. Numerical isostatic rebound models are being used to generate three-dimensional predictions of deformation, which will be constrained by the extensive data set that has already been acquired. This existing data set is the product of an interdisciplinary effort to determine the timing, magnitude and history of uplift and ice load changes in southeast Alaska. The observations consist of a regional Global Positioning System (GPS) crustal deformation array of 76 sites, sea level rates at 18 tide gauge sites, raised shoreline measurements of total uplift, and onset of uplift at 27 sites. These data characterize the regional pattern of uplift on centennial, decadal, and annual time scales, and portray the current regional pattern of three-dimensional crustal deformation. The research team is: 1) refining current glacial isostatic rebound models using an improved GPS and raised shoreline database; 2) developing numerical rebound models that generate three-dimensional predictions of deformation; 3) using model predictions of three-dimensional deformation to remove the horizontal component of isostatically induced motion from horizontal velocity observations to obtain the tectonic deformation of the region; 4) evaluating the resulting tectonic velocity and strain fields in terms of regional crustal dynamics and processes with specific emphasis on the implications for formation of the Fairweather and St. Elias Ranges, genesis of the Denali fault, and dynamics of the Yakutat Block collision; 5) evaluating seismic potential specifically induced by unloading, as well as effects of unloading on tectonic seismic potential. Using numerical models to quantify glacial isostatic rebound, crustal and mantle viscoelastic properties will be resolved using the vertical deformation signal, and thereby provide a means to separate tectonic and isostatic signals in the horizontal deformation field.