Seismic Trenching for the Pulse of the Earthquake Engine

地震工程师Ronald L.犹他大学地质与地球物理系，犹他州盐湖城湖城，犹他州84112-01 11项目摘要本研究项目的目的是研究地震是如何发生在正断层上的。 地震在空间和时间上的重现模式提供了地震引擎的“脉冲”。 对这些模式的研究揭示了地球内部相互作用产生地震的复杂过程。 成功地理解过去心跳的性质是预测产生地震的大断层未来行为的关键。到目前为止，在断层崖上挖沟一直是揭示地震过去历史的主要工具。 通过仔细记录海沟中的沉积物，地质学家已经成功地推断出过去地震的规模和复发间隔。 然而，挖沟法有三个缺点：费用昂贵，对环境有干扰，深度不超过30英尺，只能得到断层的垂直横截面。 这些限制意味着地震心跳在空间和时间上都很难采样，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心跳的基本问题，犹他州大学的地球科学家们正在奥奎赫、斯坦斯伯里和瓦萨奇断层的断层陡坎上进行二十多项浅层地震实验。 这是位于犹他州瓦萨奇前缘的三个大型正断层带。 记录的地震波的第一次到达时间产生速度断层扫描图或图像，描绘了沉积的“崩积”楔形物的浅部和深部模式，这些楔形物是在过去地震期间地球表面偏移的反应中形成的。 在确定崩积楔后，用强力Odex钻取50米左右深度的岩芯，用各种测年方法测定楔周围和楔内沉积物样品的年代。 通过这一程序，科学小组将我们对地震行为的认识扩展到10万年以上，并显著延长了东部盆地和山脉省沿着瓦萨奇断层和其他断层的地震历史。 这种地震层析成像、钻探和测年方法的综合使用被称为地震槽探。在这项研究中确定的延长的地震历史为预测该地区未来的地震历史提供了新的信息，并为建立新一代的断层作用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具有重要意义。

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.