Collaborative Research: Postseismic deformation for the Izmit-Duzce, Turkey earthquakes: Implications for the mechanics of the earthquake cycle and rheology of the continent

1999年土耳其伊兹米特地震序列（8月Gulcuk地震为M=7.5, 11月Duzce地震为M=7.1）发生在一个预先存在的GPS网络中，使其成为在大陆主要走滑断层上测量最准确的地震事件之一。明确的震前应变积累、同震运动（可达~2米）、震后短期（天-月）余震和较长期（年- 10年）震后弛豫都可以通过大地测量观测得到很好的图像。此外，地震似乎以意想不到的方式改变了地震间运动的特征（即，不容易归因于标准的震后过程），距离同震断层200 - 300公里。因此，这一事件为地震变形周期（地震间、地震前、地震同震和地震后）提供了基本的约束，对预测该断层系统上未来的地震有直接的影响，并通过类比来理解类似的走滑断层的动力学，包括加州的圣安德烈亚斯断层。1999年的地震序列发生在伊斯坦布尔以南横跨马尔马拉海的地震间隙的东段，这引起了人们对马尔马拉西部地区未来地震的严重担忧，这可能会对这个脆弱的特大城市（2000万人口）造成毁灭性的影响。关于马尔马拉海未来可能发生地震的震级，以及应变如何从伊兹米特段转移到海中的马尔马拉主断层（MMF）（即，连接断层的几何形状、锁定程度、滑移率），仍然存在不确定性。王子群岛位于伊斯坦布尔南部的马尔马拉，距离伊兹米特-马尔马拉连接断层段不到5公里。位于连接段附近的两个岛屿（Sivriada和b<s:1> y<e:1> kada）已被选为ICDP钻孔点（GFZ，德国领导这项ICDP计划）。为了配合这项工作，我们最初的工作重点是在两个钻孔地点安装GPS站。这些台站的数据将由我们在马尔马拉研究中心的土耳其伙伴和联安援助团下载。在三年多的时间里，这些GPS观测将提供更好的倾角、锁定深度和当前断层段应变积累率的约束条件。这些预期结果与整个马尔马拉地区的震后变形分析一起，有望提供对地震变形周期的更好理解，并相应地估计马尔马拉海未来地震的时间和震级。本项目由美国国家科学基金会地球物理学和构造学项目资助。

The 1999 Izmit, Turkey earthquake sequence (M=7.5, August, Gulcuk and M=7.1, November, Duzce earthquakes) occurred within a pre-existing GPS network making it one of the most geodetically well observed seismic events on a major continental strike slip fault. Well-defined pre-earthquake strain accumulation, coseismic motions (reaching ~2 m), short-term (days - months) postseismic afterslip, and longer-term (years - 10 years) postseismic relaxation are all well imaged by geodetic observations. In addition, the earthquake appears to have altered the character of interseismic motions in unexpected ways (i.e., not easily ascribed to standard postseismic processes) as far as 200 - 300 km from the coseismic fault. As such, this event is providing fundamental constraints on the earthquake deformation cycle (inter-, pre-, co-, and postseismic) with direct implications for forecasting future earthquakes on this fault system, and by analogy for understanding the dynamics of similar strike slip faults, including the San Andreas Fault in California.The 1999 sequence occurred along the eastern segment of a seismic gap that extends south of Istanbul across the Sea of Marmara, raising serious concerns about a future earthquake on the western Marmara segment that could have devastating effects on this vulnerable mega-city ( 20 million people). Uncertainty persists about the possible magnitude of future earthquakes in the Marmara Sea, as well as how strain is transferred from the Izmit segment to the Main Marmara Fault (MMF) within the Sea (i.e., the geometry, degree of locking, slip rate on the connecting fault). The Princes Islands are located within the Marmara south of Istanbul and approach within less than 5 km of the Izmit-Marmara connecting fault segment. Two islands (Sivriada and Büyükada) located very near the connecting segment have been selected for ICDP borehole sites (GFZ, Germany are leading this ICDP initiative). In cooperation with this work, we are focusing our initial efforts on installing GPS stations at both borehole sites. Data from these stations will be downloaded by our Turkish partners at the Marmara Research Center and by UNAVCO. Over three years, these GPS observations will provide improved constraints on the dip, locking depth, and present-day rate of strain accumulation on this fault segment. These anticipated results together with analyses of postseismic deformation throughout the Marmara region, promise to provide improved understanding of the earthquake deformation cycle, and accordingly, estimates of the timing and magnitude of future earthquakes in the Sea of Marmara.This project is funded by the Geophysics and Tectonics Programs of NSF.