Imaging Earthquakes from Optical Images and Seismic Waveforms Analysis

该项目旨在通过详细分析静态地表位移和确定良好约束的震源模型，更好地了解地震力学，特别是地震断层的摩擦特性。数据集和源模型被用来调查如何同震滑动分布与断层的几何形状和大小，如何可变的是同震静态滑动分布，是什么决定了这种变化。断层破裂和同震滑动的几何形状一般是从野外调查和大地测量中获得的。野外测量一般只能在有限的地点进行，而且不规则地间隔，精度一般不超过几十厘米。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迹线之外，并且当仅测量主断层迹线处的特征偏移时会被遗漏。大地测量技术不受这些限制。然而，大地测量数据总是太稀疏，不能严格限制滑动分布和差分干涉合成孔径雷达通常失败的近断层带，大位移导致相关性差的图像。另一种方法是根据地震前后获得的光学图像的相关性来测量变形。 本项目利用SPOT、ASTER和航空照片等互相关光学图像测量同震静态形变。这种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，并可应用于当地地球物理基础设施很少或难以在现场访问的地区发生的地震。这些测量结果与地震波形反演相结合，以产生良好的约束源模型。一些重大事件被选为关键目标。它们包括具有复杂分段断层几何形状（1992年兰德斯地震）或简单断层几何形状（1999年伊兹米特和赫克托矿山地震）的走滑地震和逆冲事件（1999年集集和2005年克什米尔地震）。任何大的陆内事件，将发生在该项目的过程中进行分析。作为该项目的一部分，正在准备公开发布一个软件，该软件将允许自动精确的正射校正、共配准和亚像素相关。该软件对于地震构造学领域以外的应用，特别是对于冰流测量、滑坡监测或变化探测，是有意义的。

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.