Seismic Trenching for the Pulse of the Earthquake Engine

EAR-0207372：EARTHQUAKEENGINERONARD L.Bruhn和Gerard Schuster地质与地球物理系的地震沟槽犹他州盐湖城大学地质和地球物理系，UT 84112-01 11项目摘要这项研究项目的目的是研究地震是如何在正常断层上发生的。地震在空间和时间上的重复模式为地震引擎提供了“脉搏”。对这些模式的研究正在揭示地球内部相互作用产生地震的复杂过程。成功地了解过去心跳的性质是预测大断层未来发震行为的关键。到目前为止，跨越断层陡峭的沟槽一直是揭示过去地震历史的主要工具。通过仔细记录海沟中的沉积沉积，地质学家已经成功地推断出过去地震的大小和复发间隔。然而，挖沟方法有三个缺点：它昂贵且对环境造成干扰，深度不超过约30英尺，只产生断层的垂直横截面。这些限制意味着，地震心跳在空间和时间上的采样都很差，这可能导致对地震性质的错误结论。为了克服这些问题，并回答有关正常断层活动心跳的基本问题，犹他大学的地球科学家正在奥奎尔、斯坦斯伯里和瓦萨奇断层的断层陡坎上进行20多个浅层地震实验。这是位于犹他州瓦萨奇前线的三个大型正断层带。记录到的地震波的第一次到达时间会产生速度断层图或图像，这些图像描绘了过去地震期间因地表偏移而形成的沉积堆积楔形的浅部和深层模式。当发现时，大约50米深的堆积楔形岩心由强大的Odex钻头取心，楔形凹陷周围和内部的沉积物样本通过各种测年方法进行测年。通过这一程序，科学团队正在将我们对地震行为的知识扩展到10万年以上，并显著延长沿瓦萨奇断层和东部盆地和山脉省其他断层的地震历史。这种地震层析成像、钻井和测年方法的结合被称为地震挖槽。在本次研究中确定的扩展地震历史为预测该地区未来的地震历史和建立新一代断裂过程的力学模型提供了新的信息。该研究对地震灾害的应用领域和地震力学基础科学都具有重要的影响。

EAR-0207372: SEISMIC TRENCHING FOR THE PULSE OF THE EARTHQUAKEENGINERonald L. Bruhn and Gerard SchusterDepartment of Geology and GeophysicsUniversity of UtahSalt Lake City, UT 84112-01 11PROJECT ABSTRACTThe purpose of this research project is to study how earthquakes occur on normal faults. The patterns of earthquake recurrence in space and time provide the 'pulse' of the earthquake engine. Investigating these patterns is revealing the complex processes that interact to generate earthquakes within the earth. Successfully understanding the nature of past heartbeats is the key to predicting the future behavior of large faults that generate earthquakes.Until now, trenching across fault scarps has been the primary tool for revealing the past history of earthquakes. By carefully logging the sedimentary deposits in trenches, geologists have been successful in deducing the sizes and recurrence intervals of past earthquakes. However, there are three shortcomings with the trenching method: it is expensive and environmentally intrusive, it is limited to depths no deeper than about 30 feet, and yields only a vei7tical cross-section of the fault. These limitations mean that the earthquake heartbeat is poorly sampled in both space and time, which can lead to erroneous conclusions about the nature of earthquakes. To overcome these problems, and to answer fundamental questions about the heartbeat of normal faulting, University of Utah earth scientists are conducting more than two dozen shallow seismic experiments over fault scarps in the Oquirrh, Stansbury and Wasatch faults. These are three large normal fault zones located in the Wasatch Front of Utah. The first arrival times of the recorded seismic waves yield velocity tomograms, or images, that delineate both the shallow and deep patterns of sedimentary 'colluvial' wedges that formed in response to the offset of the earth's surface during past earthquakes. When identified, the colluvial wedges to a depth of 50 m or so are cored by a powerful Odex drill, and samples of the deposits surrounding and within the wedges are dated by a variety of dating methods. By this procedure the science team is extending our knowledge of earthquake behavior beyond 100,000 years, and significantly extending the history of earthquakes along the Wasatch Fault and other faults in the eastern Basin and Range Province. This combined use of seismic tomography, drilling and dating methods is referred to as seismic trenching.The extended earthquake history being determined during this study provides new information for predicting the future history of earthquakes in the region, and for creating a new generation of mechanical models of processes of faulting. The research has significant impact on the applied field of earthquake hazards and the basic science of earthquake mechanics.