2005 Interior of the Earth Gordon Conference

人们从来没有直接观察到地震的实际物理过程--传播中的裂缝打破了将断层两侧连接在一起的摩擦，使它们相互滑动。它必须通过对弹性波和地震引起的变形的分析来推断。2004年9月28日帕克菲尔德6.0兆瓦地震的数据提供了一个前所未有的机会来推断震源的动力学。在断层周围20公里范围内，有56台三分量强震加速度计，一个密集的13单元阵列(UPSAR)，13个连续的GPS站点，10个或更多的GPS运动站点和4个井眼膨胀仪。通过对这些数据的反演，可以得到震源的运动学描述。这种运动学描述为描述地震动力学的非线性过程奠定了基础。数据倒置的机制已经成为常规，但帕克菲尔德的数据可以回答的科学问题不仅仅是找到一个运动学断层模型。将所有数据倒置以找到断层过程的“最佳”模型将会完成，但这个数据集提供了一个更大的机会。数据的丰富性允许采用多方面的方法来反转数据。最重要的是，数据的密度和质量提供了一个难得的机会来探索运动学模型的哪些特征是健壮的和很好地解决的。坚固的运动学特征将定义地震的特征，这些特征对于建立模拟裂缝扩展的动力学模型的最佳初始应力条件至关重要。有许多根本性的问题将得到解决。为什么与1934年和1966年的地震相反，2004年的地震是从东南向西北方向移动的？在初始应力条件稍有扰动的情况下，破裂是否可能在中山附近成核并向东南方向传播？尽管破裂主要发生在西北方向，但是什么原因导致了向东南方向的大地震？它们是由破裂前锋的动力学引起的吗？有人提出，断层上的b值图与断层上的高应力和低应力区相关。2004年的主震震源位于高应力区。动态破裂会遵循一条模仿b值地图的路径吗？对于断层不同部位的应力变化，动力学模型会给出什么结果？这种变化会不会像以往地震活动研究中发现的那样大？答案取决于破裂的动力学。通过反演丰富的Parkfield数据，推导出一个运动学模型，该模型将为动态模拟提供初始条件，这反过来将允许对地震动力学进行最详细的检查之一。

The actual physical process of an earthquake-the propagating fracture that breaks the friction holding two sides of the fault together allowing them to slip past one another-is never directly observed. It must be inferred by analysis of the elastic waves and the deformation that the earthquake caused. The data from the MW 6.0 Parkfield earthquake of September 28, 2004, provide an unprecedented opportunity to infer the dynamics of an earthquake source. Within 20 km of the fault, there are 56 three-component strong motion accelerographs, a dense 13-element array (UPSAR), 13 continuous GPS sites with 10 or more GPS campaign sites and four borehole dilatometers. These data can be inverted to find the kinematic description of the earthquake source. The kinematic description lays the foundation for describing the nonlinear process of earthquake dynamics. The mechanics of inverting data have become routine, but the scientific questions that the Parkfield data can answer go beyond simply finding a kinematic faulting model. Inverting all of the data to find a "best" model of the faulting process will be done, but this data set provides a much greater opportunity. The richness of the data allows a multifaceted approach to inverting the data. Most importantly, the density and quality of the data allow a rare opportunity to explore what features of the kinematic models are robust and well resolved. The kinematic features that are robust will define features of the earthquake that will be vital for establishing the best initial stress conditions for developing dynamical models that will simulate the propagating fracture. There are many fundamental questions that will be addressed. Why did the 2004 rupture go from southeast to northwest, opposite to that of the 1934 and 1966 earthquakes? With minor perturbations to the initial stress conditions could the rupture have nucleated near Middle Mountain and propagated to the southeast? Even though the rupture is primarily northwest, what caused the large ground motions to the southeast? Do they arise from dynamics of the rupture front? It has been proposed that maps of b-values on the fault correlate with regions of high and low stress on the fault. The 2004 mainshock hypocenter is within a region of high stress. Will the dynamic rupture follow a path that mimics the b-value maps? What will dynamic models give for stress changes on different parts of the fault? Will the variation be as large as that found in studies of prior seismicity. The answers depend on dynamics of the rupture. By inverting the abundant Parkfield data, a kinematic model is deduced that will provide the initial conditions for dynamic simulations, which in turn will allow one of the most detailed examinations of the dynamics of an earthquake.