Geodetic Imaging of Large-Scale Continental Deformation with ALOS InSAR and GPS

Earthquakes occur along the faults of the North American-Pacific plate boundary when the stress that has accumulated on a fault segment exceeds some threshold value. We use space geodetic tools to measure the present-day strain accumulation rate and to convert this measurement to stress accumulation rate using a physical model. When combined with historical and paleoseismic information, the stress rate grids provide critical information for earthquake hazard assessment. High accuracy point GPS measurements are used to estimate the 3-D strain field at length scales greater than the typical GPS spacing of 15 km. Radar interferograms are used to estimate the strain field at shorter length scales (0.5 km to 15 km). These two types of measurements are combined using a physical model as the interpolating function. This approach has already been successful using C-band data along the sparsely vegetated southern San Andreas Fault System but is far less successful along the more vegetated northern sections of the fault. L-Band interferometry should retain phase correlation over longer time periods in moderately vegetated areas and thus provide critical new information along the entire fault system.