Imaging Earthquakes from Optical Images and Seismic Waveforms Analysis

这个项目的目的是通过详细分析地表静态位移和确定良好约束的震源模型，更好地了解地震的力学，特别是地震断层的摩擦性质。数据集和震源模型被用来研究同震滑动分布如何与断层几何形状和大小有关，同震静态滑动分布有多大变化，以及是什么决定了这种变化。断层破裂和同震滑动的几何形状通常是通过野外调查和大地测量获得的。野外测量通常只能在有限数量的、不规则间隔的地点进行，精度通常不会好于几十厘米。滑动的走向垂直分量一般是不可测量的。此外，一些滞弹性变形可能分布在主断层道之外，如果只测量主断层道的偏移量，就会漏掉一些滞弹性变形。大地测量技术不受这些限制的影响。然而，大地测量数据往往过于稀疏，无法严格约束滑移分布，而在断层附近，差动InSAR通常会失效，因为那里的位移较大，导致图像相关性较差。另一种方法是通过地震前后获取的光学图像的相关性来测量变形。在本项目中，利用SPOT、ASTER和航空照片等相关光学图像测量了同震静态形变。这项新技术可以提供断层几何形状和同震滑动分布的详细测量，具有前所未有的亚像素精度，并可应用于发生在当地地球物理基础设施较少或难以现场访问的地区的地震。这些测量与地震波形的反演相结合，以产生良好的约束震源模型。一些重大事件被选为重点目标。它们包括走滑地震，具有复杂的分段断层几何结构(1992年的兰德斯地震)，或简单的断层几何结构(1999年的伊兹米特和赫克托矿地震)和逆冲事件(1999年的集集地震和2005年的克什米尔地震)。还将分析在项目过程中将发生的任何大型陆内事件。作为该项目的一部分，正在编制一个软件以供公开发布，该软件将允许自动进行精确的正射校正、联合配准和亚像素相关。该软件对于地震构造学领域之外的应用非常有意义，特别是用于冰流测量、滑坡监测或变化检测。

This project aims at a better understanding of the mechanics of earthquakes, in particular the frictional properties of seismic fault, by analyzing in detail static surface displacements and determining well constrained earthquake source models. The data set and the source models are used to investigate how co-seismic slip distribution relates to fault geometry and size, how variable is the co-seismic static slip distribution and what determines this variability. Geometry of fault ruptures and coseismic slip are generally obtained from field investigations and geodetic measurements. Field measurements are generally possible only at a limited number of sites, irregularly spaced, and the accuracy is generally no better than a few tens of cm. The strike perpendicular component of slip is generally not measurable. In addition some anelastic deformation could be distributed off the main fault trace and would be missed when only features offset at the main fault trace are measured. Geodetic techniques do not suffer from these limitations. However geodetic data are always too sparse to constrain tightly the slip distribution and differential inSAR generally fails in the near-fault zone where large displacements result in poorly correlated images. An alternative approach consists in measuring deformation from the correlation of optical images acquired before and after an earthquake. In this project co-seismic static deformation is measured from cross correlating optical images such as SPOT, ASTER and air photos. This new technique can provide detail measurements of fault geometry and co-seismic slip distribution with unprecedented sub-pixel accuracy, and can be applied to earthquakes occurring in areas with little local geophysical infrastructure, or difficult to access in the field. These measurements are combined with inversion of seismological waveforms to produce well constrained source models. A few major events were selected as key targets. They include strike-slip earthquakes with either a complex segmented fault geometry (the 1992 Landers earthquake), or a simpler fault geometry (the 1999 Izmit and Hector Mine earthquakes) and thrust events (the 1999 Chi-Chi and the 2005 Kashmir earthquakes). Any large intracontinental events which will occur over the course of the project will be analyzed as well. As part of the project, a software is being prepared for public release that will allow automatic precise orthorectification, co-registration and sub-pixel correlation. This software is of interest for applications outside the field of seismotectonics in particular for ice flow measurements, landslide monitoring or changes detection.