Seismology of Outer Rise Earthquakes

外隆地震的地震学

• 批准号: 0125182
• 负责人: Hiroo Kanamori
• 金额: $ 6.39万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2004-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125182&HistoricalAwards=false
• 关键词: Seismology; Outer; Rise; Earthquakes

The world's largest and most destructive earthquakes occur on the interface between subducting and overriding plates, with interplate coupling playing an important role in their seismogenesis. Updip from this interface, the outer-rise comprises a broad and gentle upwarping of the oceanic lithosphere just before it descends into the trench. Almost 20 years ago, researchers, showed a correlation between the occurrence of outer-rise earthquakes and interplate thrust events. The improved seismological data and tools currently available enable us to develop an updated and enhanced catalog of outer-rise seismicity, including mechanisms, depths and spectral characteristics, which can be subsequently used to review models and hypotheses concerning these outer-rise events and the deformation of subducting plates.A large number of events have occurred since the earlier catalogs were compiled and, the seismic data quality, coverage and availability have improved significantly. This enables us to better constrain depth, location and focal mechanism through detailed waveform modeling. Using our new catalog, our understanding of the stress evolution within the trench and outer-rise and the relationship between seismic coupling and outer-rise earthquakes can be refined. This work is also a first step towards the development of a new generation of geodynamic models, improving the constraints on the mechanical properties of the lithosphere and the dynamics of the slab where it bends into the subduction zone. Additionally, it examines the relationship of these earthquakes to the structure of the subducting plates, as evidenced by bathymetric and reflection/refraction profiles.Of particular interest is the spatio-temporal behavior of outer-rise seismicity. Although most outer-rise events are tensional, a small number of deeper events are compressional. These compressional earthquakes have been speculated to either precede an interplate thrust, occur in regions which have not experienced an interplate thrust event during the preceding few decades, or occur adjacent to an area which has had interplate slip. The bending stresses and the pull of the subducting slab are probably large relative to regional tectonic stresses or the cyclic stresses associated with seismic coupling. However, these stress perturbations may still trigger events in the outer-rise and may cause the neutral surface (the zero stress boundary between tensional upper plate and compressional lower plate) to shoal significantly. The stress changes following interplate events can thus be viewed as perturbations of the overall dynamics. From these temporal and spatial relationships, it is clear that the state of stress in the outer-rise may change in both time and space in response to interplate coupling. The record of seismicity should reflect these changes and can therefore shed light on the physical processes at work. Of greatest importance is the enhancement of our understanding of the physics of outer-rise deformation. The results will have further implications for several other disciplines. Improved knowledge of the temporal and spatial character of outer-rise seismicity is an important first step towards the development of a new generation of models of subduction zone dynamics. Since some large interplate earthquakes occur close to populated areas or generate tsunamis, compressional outer-rise events as stress build-up indicators may be important for intermediate term earthquake hazard assessment.

世界上最大和最具破坏性的地震发生在俯冲和上覆板块之间的界面上，板块间耦合在它们的地震发生中起着重要作用。从这个界面向上倾斜，外隆起包括海洋岩石圈在下降到海沟之前的一个广泛而温和的上升。大约20年前，研究人员发现了外隆起地震与板块间逆冲事件之间的相关性。现有的地震数据和工具的改进使我们能够编制更新和增强的外升地震活动目录，包括机制、深度和频谱特征，这些目录可随后用于审查有关这些外升事件和俯冲板块变形的模型和假设。自编制早期目录以来，已经发生了大量地震事件，地震数据的质量、覆盖范围和可用性都有了显著提高。这使我们能够通过详细的波形建模来更好地约束深度、位置和震源机制。利用我们的新目录，我们对海沟和外隆起内部的应力演化以及地震耦合与外隆起地震之间的关系的理解可以得到改进。这项工作也是发展新一代地球动力学模型的第一步，改善了对岩石圈力学特性的限制，以及板块在俯冲带弯曲处的动力学。此外，它还研究了这些地震与俯冲板块结构的关系，这是由水深和反射/折射剖面所证明的。特别令人感兴趣的是外震活动的时空行为。虽然大多数外隆起事件是张性的，但少数深层事件是挤压性的。据推测，这些挤压地震要么发生在板块间逆冲之前，要么发生在过去几十年没有经历过板块间逆冲事件的地区，要么发生在板块间滑动的地区附近。相对于区域构造应力或与地震耦合有关的旋回应力，俯冲板的弯曲应力和拉力可能较大。然而，这些应力扰动仍可能触发外隆起的事件，并可能导致中性面（张性上板块与压性下板块之间的零应力边界）显着浅滩。因此，板间事件后的应力变化可以看作是整体动力学的扰动。从这些时间和空间关系来看，很明显，由于板间耦合，外隆起的应力状态可能在时间和空间上发生变化。地震活动性的记录应该反映出这些变化，因此可以阐明工作中的物理过程。最重要的是加强我们对外隆起变形的物理认识。研究结果将对其他几个学科产生进一步的影响。提高对外隆起地震活动时空特征的认识是开发新一代俯冲带动力学模型的重要的第一步。由于一些大型板块间地震发生在人口稠密地区附近或产生海啸，挤压外升事件作为应力积累指标可能对中期地震危险性评估很重要。