Collaborative Research: Seismic Imaging of Aseismic Transients

该项目使用机载激光测绘（ALSM）技术，也称为激光雷达，对南加州的圣安德烈亚斯断层（SAF）和其他选定的断层段进行非常高分辨率的地形调查。在这次调查中获得的航空摄影将覆盖在地形数据集上，以在断层的近场产生非常详细的地球表面特征。目的是在下一次大地震（即“大地震”）之前对断层系统进行非常详细的成像，这样当地震发生时，就有可能以前所未有的精度绘制近场位移和变形场。断层系统的事后勘测将确定滑动和余震的非均质性，从而有助于解决震源物理学中几个长期存在的争论。它还可以描述与SAF从连续爬行到完全锁定部分的沿走向过渡相关的近场变形。该项目广泛使用新的国家机载激光测绘中心（NCALM）设施，以及UNAVCO公司设施（借用全球定位系统（GPS）接收器来支持飞机定位）。NCALM设施将使用佛罗里达大学的飞机、激光雷达和数码相机获取调查数据。飞机将在低空（~600米）操作以确保出色的水平分辨率和垂直精度。它将沿着一组平行轨道飞行，大致以断层为中心，从而获得一组重叠的条带：这种地面覆盖的冗余将使系统的质量控制成为可能，并提供一种避免在陡峭地形中出现阴影问题的手段。飞机将使用惯性制导和全球定位系统的组合进行定位。飞机的动态GPS定位将利用沿飞行路径每30公里建立的众多GPS基站。ALSM数据将首先由NCALM使用其标准数据处理技术进行分析。点云（X，Y， Z和强度）观测结果将提供给OSU， OSU将与地面真值数据进行比较，从而提供外部验证。一旦经过验证，原始数据和初始“裸地”数字高程模型（DEM）将通过加州大学伯克利分校的NCALM数据档案发布给一般科学界。这大概需要6个月。这些数据将在俄勒冈州立大学以更悠闲的节奏重新分析，看看是否可以做出额外的改进。俄勒冈州立大学团队成员还负责将ALSM调查期间获得的数码照片覆盖到初步和最终的dem上。一旦这个注册过程完成，合并后的产品将绑定到广泛的现有图像和地形数据集，包括：1) NASA-USGS合作提供的ASTER、MODIS和Landsat高光谱图像数据，2)NASA和JPL提供的SRTM地形数据，3)美国地质勘探局国家高程数据集提供的USGS地形数据，3)EarthData International利用GeoSAR于2002年底获取的NOAA海岸服务中心地形数据，4)航空照片，例如为USGS飞行的低太阳角度、高分辨率集，以及摄影测量公司飞行的原始照片。5)美国地质勘探局绘制的显示断裂带地貌和偏移的详细地图（例如，Brown, 1970; Clark, 1984; Wallace, 1990）。

Airborne Laser Swath Mapping of the Southern San Andreas Fault This project is using Airborne Laser Swath Mapping (ALSM) technology, also known as LIDAR, to perform a very high resolution topographic survey of the San Andreas fault (SAF) and other selected fault segments in southern California. Aerial photography obtained during this survey will be draped over the topographic dataset to produce a highly detailed characterization of the earth's surface in the near field of the fault. The intent is to image the fault system in great detail prior to the next great earthquake, i.e. the 'Big One', so that when this event occurs it will be possible to map the near-field displacement and deformation field with unprecedented accuracy. Post-event resurveys of the fault system will determine slip and afterslip heterogeneity, and so help resolve several long-standing debates in earthquake source physics. It will also be possible to characterize near-field deformation associated with the along-strike transition from continuously-creeping to fully-locked sections of the SAF. The project makes extensive use of the new National Center for Airborne Laser Swath Mapping (NCALM) facility, as well as the UNAVCO Inc. facility (to borrow Global Positioning System (GPS) receivers to support aircraft positioning). The NCALM facility will acquire the survey data using the University of Florida's aircraft, LIDAR and digital camera. The aircraft will operate at low altitude (~600 m) to ensure excellent horizontal resolution and vertical accuracy. It will fly along sets of parallel tracks, roughly centered on the fault, so as to obtain sets of overlapping swaths: this redundancy in ground coverage will enable systematic quality control, and provide a means to avoid shadowing problems in steep terrain. The aircraft will be positioned using a combination of inertial guidance and GPS. Kinematic GPS positioning of the aircraft will make use of numerous GPS base stations established every 30 km along the flight path. The ALSM data will at first be analyzed by NCALM using their standard data processing techniques. The point cloud (X,Y, Z and intensity) observations will be provided to OSU, who will then compare them with ground truth data so as to provide external validation. Once validated the raw data and the initial 'bare earth' digital elevation model (DEM) will be released to the general scientific community via the NCALM data archive in UC Berkeley. Probably, this will take about 6 months. The data will be reanalyzed at a more leisurely pace at OSU to see if additional improvements can be made. The OSU team members are also be responsible for draping the digital photography obtained during the ALSM survey onto the preliminary and final DEMs. Once this registration process is complete, the combined product will be tied to a wide range of existing imagery and topographic datasets, including: 1) ASTER, MODIS and Landsat hyperspectral imagery data available through NASA-USGS cooperative efforts, 2) SRTM topographic data from NASA and JPL, 3) USGS topographic data from the National Elevation Dataset, 3) NOAA Coastal Services Center topographic data acquired in late 2002 by EarthData International using GeoSAR, 4) air photos, e.g., low sun-angle, high resolution sets that were flown for the USGS as well as stock photography flown by photogrammetry companies, 5) detailed maps by USGS showing fault zone geomorphology and offsets (e.g., Brown, 1970; Clark, 1984; Wallace, 1990).