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月古尔库克7.5级地震和11月杜兹斯7.1级地震)发生在现有的GPS网内，使其成为大陆主要走滑断层上观测最充分的地震事件之一。明确的震前应变积累、同震运动(达到~2m)、震后短期(天-月)、震后较长期(年-10年)松弛都得到了大地测量的很好的成像。此外，地震似乎以意想不到的方式改变了距离同震断层200-300公里的地震间运动的性质(即不容易归因于标准的震后过程)。因此，这次地震对地震形变周期(震间、震前、同震和震后)提供了基本约束，直接影响到对该断层系统未来地震的预测，并通过类比了解类似走滑断层的动力学，包括加利福尼亚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南部穿过马尔马拉海的地震空隙的东段，引起了人们对马尔马拉西部未来可能发生的地震的严重担忧，这可能会对这个脆弱的特大城市(2000万人)造成毁灭性影响。关于马尔马拉海未来可能发生的地震的震级以及应变如何从伊兹米特段转移到海内的马尔马拉主断层(MMF)(即连接断层上的几何形状、锁定程度和滑动速率)仍存在不确定性。王子群岛位于伊斯坦布尔以南的马尔马拉，靠近连接断裂带的伊兹米特-马尔马拉不到5公里。位于连接段非常近的两个岛屿(Sivriada和Büyükada)被选为ICDP钻孔选址(德国GFZ是ICDP倡议的领先者)。配合这项工作，我们最初的工作重点是在这两个井点安装GPS站。马尔马拉研究中心的土耳其合作伙伴和联合国志愿人员组织将下载来自这些站点的数据。在三年的时间里，这些GPS观测将改善这一断层段的倾角、锁定深度和现今应变累积速度的约束条件。这些预期结果加上对马尔马拉地区震后形变的分析，有望更好地了解地震形变周期，并相应地估计未来马尔马拉海地震的时间和震级。该项目由美国国家科学基金会的地球物理和构造计划资助。

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.