Testing the Hypothesis that Detachment Faults are Active and Generate Microearthquakes

检验滑脱断层活跃并产生微地震的假设

• 批准号: 1143693
• 负责人: Darrel Cowan
• 金额: $ 5.8万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-15 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1143693&HistoricalAwards=false
• 关键词: Testing; Hypothesis; Detachment; Faults; Active

Since low-angle normal, or detachment, faults and their role in accommodating large-scale extension were recognized in the 1970's, these enigmatic structures have captured the attention of a wide community of structural and tectonic geologists. Outstanding questions concerning detachment faulting include the putative mechanical impossibility of slip on gently dipping normal faults at and near the Earth's surface and if some detachment faults are active, why has not seismicity been observed? Are the faults slipping aseismically, or are recurrence intervals of large earthquakes longer than historic records? To address these questions, University of Washington researchers will install a ten-station, portable temporary network of seismometers in Death Valley for a period of six to nine months. Data recorded in the field will be analyzed to yield the locations of earthquake hypocenters. The seismometers will be situated on alluvial fans on the west side of Death Valley about 8 km above the projected positions of detachment faults at depth. West-dipping, geologically and possibly seismically active detachment faults are well exposed on the east side of Death Valley along the foot of the Black Mountains, as are range-front scarps of normal faults that formed due to slip during late Quaternary or Holocene earthquakes. The experiment will test the hypotheses that: (1) the gently dipping detachment faults are seismogenic, and (2) that rupture and slip nucleating at seismogenic depths produces microearthquakes. A positive result would challenge the hypothesis that slip on detachments is either mechanically impossible or aseismic.Low-angle normal, or detachment, faults are important tectonic elements in that they accommodate large-scale stretching in extensional regimes, such as the Basin and Range in western United States. However, these faults are paradoxical because mechanical analysis suggests movement should not occur at such low angles and earthquakes are rarely observed even though geological evidence suggests the detachments are active. This experiment, the first of its kind directed toward detachment faults in western North America, will explore these paradoxes. Observation of microearthquakes would challenge the widely-held idea that fault movement on detachments is either mechanically impossible or aseismic.

由于在1970年代认识到低角度的正常或分离，因此缺陷及其在适应大规模扩展方面的作用，这些神秘的结构引起了广泛的结构和构造地质学家的关注。关于支队断层的杰出问题包括在地球表面和附近轻轻浸入正常断层的假定机械不可能的问题，如果某些分离断层有效，为什么没有观察到地震性？断层在无性障碍上滑倒，还是大地震的复发间隔比历史记录更长？为了解决这些问题，华盛顿大学的研究人员将在死亡山谷中安装十个站点的临时临时网络网络，为期六到九个月。将分析记录在现场中的数据，以产生地震低中心的位置。地震仪将位于死亡谷西侧的冲积球迷上，高于预期的分离断层位置约8公里。西部倾斜，地质和可能具有地震活性的脱离断层沿着黑山脚下的死亡谷的东侧很好地暴露了，正常断层的范围前刺是由于在季季晚期或全新世地震期间滑倒而形成的正常断层。该实验将检验以下假设：（1）轻轻浸入的脱落断层是地震生成的，（2）在地震深度下破裂和滑移成核会产生微量。一个积极的结果将挑战以下假设：脱离是机械上不可能的，要么是无性的。低角度正常或脱离是重要的构造元素，因为它们可以适应美国西部盆地和范围的延伸方案中的大规模拉伸。但是，这些断层是自相矛盾的，因为机械分析表明，即使地质证据表明脱离活动是活跃的，也很少观察到这种运动的运动不应以如此低的角度进行。该实验是针对北美西部分离断层的第一个实验，将探索这些悖论。观察微夸克将挑战以机械上不可能的断层运动是不可能的，要么是无性抗病的观念。