2005 Interior of the Earth Gordon Conference

地震的实际物理过程——不断扩展的裂缝打破了维系断层两侧的摩擦，使它们能够相互滑动——从未被直接观察到。必须通过对地震引起的弹性波和变形的分析来推断。2004年9月28日帕克菲尔德6.0级地震的数据为推断震源的动态提供了前所未有的机会。在断层20公里范围内，有56个三分量强震加速度仪，一个密集的13元阵列（UPSAR）， 13个连续GPS站点（10个或更多GPS活动站点）和4个钻孔膨胀仪。这些数据可以倒转，以找到震源的运动学描述。运动学描述是描述地震动力学非线性过程的基础。反演数据的机制已经成为常规，但帕克菲尔德数据可以回答的科学问题不仅仅是找到一个运动断层模型。将所有数据进行反转，以找到断层过程的“最佳”模型，但该数据集提供了更大的机会。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模型的哪些特征是鲁棒的和很好地解决了。强健的运动学特征将定义地震的特征，这些特征对于建立最佳的初始应力条件至关重要，从而开发模拟断裂传播的动力学模型。有许多基本问题需要解决。为什么2004年的地震从东南走向西北，与1934年和1966年的地震相反？在初始应力条件有轻微扰动的情况下，破裂是否会在中山附近成核并向东南方向传播？即使断裂主要是在西北方向，是什么导致了东南方向的大的地面运动？它们是由断裂前缘的动力学引起的吗？有人提出，断层上的b值图与断层上的高应力和低应力区域有关。2004年的主震震源位于高应力区域内。动态破裂是否会遵循类似b值图的路径？对于断层不同部分的应力变化，动态模型会给出什么结果？这种变化会像以前地震活动研究中发现的那样大吗？答案取决于破裂的动力学。通过反转丰富的帕克菲尔德数据，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，从而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.