Collaborative Research: Tests of Postseismic Deformation Models with Continued Absolute Gravity and GPS Measurements in Alaska, Phase 1

ZumbergeEAR-0208164这个项目正在阿拉斯加测量重力绝对值，与GPS测量同步进行。对大地震后的瞬时变形提出了粘弹性反应、非地震蠕变以及两者结合的解释。不同的震后粘弹性松弛模型预测了1000公里尺度上的可观测重力变化，具有复杂的空间格局。到目前为止，粘度曲线最好的确定方法是冰后反弹研究。重力和GPS测量提供了获得阿拉斯加板块边界粘性剖面估计的机会。这一地区尤其有趣，因为俯冲带物质的粘度可能与大陆和海洋板块中心以下的粘度非常不同。无震蠕变预计将产生比粘弹性松弛更有限且明显不同的空间特征的变形。确定无震蠕变在震后变形中的贡献对于估计大地震的复发间隔很重要。这个项目正在建立一个由阿拉斯加15个台站组成的基线重力网络。该网络的大部分形成了一条垂直于远场最大重力变化预测等高线的横断面。附加的点位于形变近场内。重力测量与现有的GPS站并置。这些初始测量形成了测试不同震后变形模型的基础。其他活动包括收集辅助数据，以纠正重力数据中的信号，如地下水位变化。为了确定基奈半岛自地震以来的总重力变化，1964-1965年的部分相对重力调查也在重复进行。数据通过传统方式和互联网网站分发。

ZumbergeEAR-0208164This project is measuring the absolute value of gravity, co-located with GPS measurements, in Alaska. Proposed explanations for the transient deformation after great earthquakes include viscoelastic response, aseismic creep and combinations of the two. Different models of postseismic viscoelastic relaxation predict observable gravity changes over 1000 km length scales, with a complex spatial pattern. To date, the viscosity profile is best determined by postglacial rebound studies. Gravity and GPS measurements offer the opportunity to obtain viscosity profile estimates for the Alaskan plate boundary. The area is especially interesting, as the viscosity of subduction zone materials may be very different from that beneath the centers of continental and oceanic plates. Aseismic creep is predicted to produce deformation of a more limited and markedly different spatial character than that of viscoelastic relaxation. Determining the contribution of aseismic creep in postseismic deformation is important in estimating recurrence intervals for great earthquakes.This project is establishing a baseline gravity network of fifteen stations in Alaska. The bulk of the network forms a transect perpendicular to the predicted contours of maximum gravity change in the far field. Additional points are located within the deformation near field. Gravity measurements are collocated with existing GPS stations. These initial measurements form the basis for testing different postseismic deformation models. Additional activities include collecting auxiliary data to correct the gravity data for signals such as water table variations. A portion of a 1964-1965 relative gravity survey is being repeated as well, in order to determine the total gravity change over the Kenai Peninsula since the earthquake. Data are distributed through traditional means and an Internet website.