Collaborative Research: Seismic Imaging of Aseismic Transients

南圣安德烈亚斯断层的机载激光条带测绘该项目使用机载激光条带测绘(ALSM)技术，也称为LIDAR，对圣安德烈亚斯断层(SAF)和加利福尼亚州南部其他选定的断层段进行非常高分辨率的地形测量。在这次调查中获得的航空摄影将覆盖在地形数据集上，以产生断层近场中地球表面的高度详细的特征。其目的是在下一次大地震之前对断层系统进行非常详细的成像，这样当这次地震发生时，就有可能以前所未有的精度绘制近场位移和形变场。断层系统的震后复查将确定滑动和余滑的非均质性，从而有助于解决震源物理中几个长期存在的争论。它也将有可能表征与SAF的沿走向从连续爬行到完全锁定部分的过渡有关的近场变形。该项目广泛利用了新的国家机载激光条带测绘中心(NCALM)设施以及UNAVCO公司的设施(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)运行，以确保出色的水平分辨率和垂直精度。它将沿着几组大致以断层为中心的平行轨道飞行，以获得几组重叠的条带：地面覆盖的这种冗余将实现系统的质量控制，并提供一种手段，以避免陡峭地形中的阴影问题。这架飞机将使用惯性制导和GPS相结合的方式进行定位。飞机的动态GPS定位将利用沿飞行路线每30公里建立的多个GPS基站。ALSM数据将首先由NCALM使用他们的标准数据处理技术进行分析。点云(X、Y、Z和强度)观测将被提供给OSU，然后OSU将它们与地面真实数据进行比较，以便提供外部验证。一旦得到验证，原始数据和初始的“裸露地球”数字高程模型(DEM)将通过加州大学伯克利分校的NCALM数据档案馆发布给普通科学界。可能，这将需要大约6个月的时间。俄亥俄州立大学将以更从容的速度重新分析数据，看看是否可以做出进一步的改进。OSU团队成员还负责将在ALSM调查期间获得的数字照片覆盖到初步和最终的DEM上。一旦注册过程完成，合并后的产品将与各种现有的图像和地形数据集捆绑在一起，包括：1)通过NASA-USGS合作努力获得的ASTER、MODIS和Landsat高光谱图像数据，2)来自NASA和JPL的SRTM地形数据，3)来自国家海拔数据集的USGS地形数据，3)由EarthData International在2002年底使用GeoSAR获得的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、高分辨率组以及摄影测量公司飞行的库存摄影，5)美国地质勘探局绘制的显示断裂带地貌和偏移量的详细地图(例如，Brown，1970；克拉克，1984年；华莱士，1990年)。

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).