Using the World's Fastest Slipping Normal Fault to Understand the Mechanics of Low-angle Normal Faults

利用世界上滑动最快的正断层来了解低角度正断层的机制

• 批准号: 1524729
• 负责人: Laura Wallace
• 金额: $ 52.33万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524729&HistoricalAwards=false
• 关键词: Using; World; Fastest; Slipping; Normal

Normal faults play a major role in stretching the earth?s crust and generating earthquakes, yet their mechanics are poorly understood. Determining their strength, seismogenic potential, and why some may slip rapidly or accumulate large displacements are key to understanding not only rifted plate margins - with their associated mineral resources and earthquake hazard - but also basic fault mechanics. Rock deformation experiments predict that normal faults should initiate at steep dips of about 60-70º and that they should frictionally lock up at dips less than 30-45º. However, geologists have long observed major low-angle normal faults in the rock record. This observation and the lack of normal fault earthquakes with dips less than 30-45º suggest that natural faults may be weaker than experiments indicate. Resolving this apparent mechanical paradox remains at the center of a debate about the strength of mature faults. To address the mysteries of slip on low-angle normal faults, this multi-disciplinary study of the best-exposed and fastest slipping of the few active examples known on Earth, the Mai'iu Fault in the Woodlark Rift of Papua New Guinea, uses GPS, thermochronometric, structural geologic and geomorphic observations, and modeling to test current ideas of low-angle fault mechanics. The project would advance desired societal outcomes through: (1) full participation of women in STEM; (2) increased public scientific literacy and public engagement with science and technology through outreach to Papua New Guinea native populations; (3) development of a globally competitive STEM workforce through the training of graduate students; and (4) increased partnerships through international collaboration with New Zealand scientists. The project is supported by the Tectonics Program and NSF's International Science and Engineering program.As the world's fastest slipping active low-angle normal fault, the Mai'iu fault represents a world class opportunity to resolve controversies regarding the mechanics and evolution of low-angle normal faults. The Mai'iu Fault slips at 6-10 mm/year, and its smooth, domal surface is exposed in the landscape for more than 20 km, yielding a rare natural laboratory of an active and rapidly slipping low-angle normal fault in a continental rift. Through multidisciplinary data acquisition and modeling efforts, the University of Texas team in collaboration with New Zealand scientists will address the following hypotheses: (1) slip on low-angle normal faults can occur at cm/year rates on intrinsically weak planes; (2) slip on low-angle normal faults can occur by aseismic creep; (3) low-angle normal faults undergo temporal variations in slip rate; and (4) normal faults on the continents can acquire large displacements through the rolling hinge process. The research team employs: (1) campaign GPS to determine contemporary slip rates and whether or not the fault is creeping or locked; (2) geochronology and thermochronology ((U-Th)/He, fission track, multi-diffusion domain K-feldspar 40Ar/39Ar) to evaluate the evolution of low-angle normal faults, and variations in exhumation/slip rates through time; (3) cosmogenic radionuclide studies to evaluate Quaternary slip rates of the Mai'iu Fault; (4) structural geology to identify slip mechanisms on the fault and structural evolution of the dome; and (5) geodynamical modeling to integrate and interpret the various data sets.

正断层在拉伸地球方面起着主要作用？地球的地壳和产生地震，但他们的机制知之甚少。确定它们的强度、孕震潜力以及为什么有些可能快速滑动或积累大位移，不仅是理解断裂板块边缘及其相关矿产资源和地震危险的关键，也是理解基本断层力学的关键。岩石变形实验预测，正断层应在约60-70º的陡倾角处开始，并应在小于30-45º的倾角处闭锁。然而，地质学家长期以来在岩石记录中观察到主要的低角度正断层。这一观测结果以及缺乏倾角小于30-45º的正断层地震表明，天然断层可能比实验表明的要弱。解决这个明显的力学悖论仍然是关于成熟断层强度的争论的中心。为了解决低角度正断层滑动的奥秘，这个多学科研究地球上已知的几个活动实例中最好的暴露和最快的滑动，巴布亚新几内亚Woodlark裂谷的Mai'iu断层，使用GPS，热计时，结构地质和地貌观测，以及建模来测试低角度断层力学的当前想法。该项目将通过以下方式推动取得预期的社会成果：（1）妇女充分参与科学、技术、工程和数学;（2）通过与巴布亚新几内亚土著人口的外联活动，提高公众的科学素养和公众对科学技术的参与;（3）通过培训研究生，培养具有全球竞争力的科学、技术、工程和数学工作队伍;（4）通过与新西兰科学家的国际合作，加强伙伴关系。该项目得到了构造学计划和美国国家科学基金会国际科学与工程计划的支持。作为世界上滑动速度最快的活动低角度正断层，Mai'iu断层代表了解决低角度正断层力学和演化争议的世界级机会。Mai'iu断层以每年6-10毫米的速度滑动，其光滑的圆顶表面暴露在景观中超过20公里，产生了大陆裂谷中活动和快速滑动的低角度正断层的罕见天然实验室。通过多学科的数据采集和建模工作，德克萨斯大学的团队与新西兰科学家合作，将解决以下假设：（1）低角度正断层的滑动可以以厘米/年的速度发生在固有的弱平面上;（2）低角度正断层的滑动可以通过无源蠕变发生;（3）低角度正断层的滑动速率随时间变化;（4）低角度正断层的滑动速率随时间变化。（4）大陆上的正断层可以通过滚动枢纽过程获得大的位移。研究团队雇用：（2）地质年代学和热年代学（（U-Th）/He、裂变径迹、多扩散域钾长石~（40）Ar/~（39）Ar），评价低角度正断层的演化和折返/滑动速率随时间的变化;（3）宇宙成因放射性核素研究，以评估迈尤断层第四纪滑动速率;（4）构造地质学，以确定断层的滑动机制和穹隆的构造演化;（5）地球动力学建模，以整合和解释各种数据集。