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，更好地理解地震力学，特别是地震断层的摩擦特性。数据集和源模型用于研究同震滑动分布与断层几何形状和大小的关系，同震静态滑动分布的可变性以及决定这种可变性的因素。断层破裂和同震滑动的几何形状通常是通过实地调查和大地测量获得的。现场测量通常只能在有限的几个地点进行，而且间距不规则，精度通常不超过几十厘米。滑动的走向垂直分量通常无法测量。此外，一些非弹性变形可能分布在主断层走线之外，如果只测量主断层走线处的特征偏移，则会遗漏这些变形。大地测量技术不受这些限制。然而，大地测量数据总是过于稀疏，无法严格约束滑动分布，而在近断裂带，由于大位移导致图像相关性差，差分inSAR通常失效。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。在这个项目中，同震静态变形是通过交叉相关的光学图像，如SPOT、ASTER和航空照片来测量的。这项新技术可以以前所未有的亚像素精度提供断层几何形状和同震滑动分布的详细测量，并且可以应用于当地地球物理基础设施很少或难以进入的地区发生的地震。这些测量与地震波形的反演相结合，产生约束良好的震源模型。一些重大事件被选为重点目标。它们包括走滑地震，或具有复杂的分段断层几何形状（1992年兰德斯地震），或具有简单断层几何形状（1999年伊兹米特地震和赫克托雷地震）和逆冲事件（1999年奇奇地震和2005年克什米尔地震）。在项目过程中发生的任何大型大陆内事件也将进行分析。作为该项目的一部分，一个软件正在准备公开发布，该软件将允许自动精确的正校正、共同配准和亚像素相关。该软件对地震构造学领域以外的应用很有兴趣，特别是对冰流测量、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.