Imaging Crustal Deformation Along the San Andreas Fault System with ALOS InSAR and GPS
David Sandwell(1), Bridget Smith-Konter(2) and Meng Wei(1)
(1) Scripps Institution of Oceanography, 1102 IGPP, La Jolla, CA 92093-0225, United States
(2) University of Texas at El Paso, Department of Geological Sciences, El Paso, Texas 79968-0555, United States
Earthquakes occur along the San Andreas Fault System 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 (Rosen, Hensley et al. 1996) and thus provide critical new information along the entire fault system.
In this paper we will report on the improvements in temporal correlation at L-band with respect to C-band. Over the past 2 years ALOS has collected enough small baseline data to begin to record interseismic deformation along the San Andreas Fault System. We are constructing L-band interferograms in three regions: Northern California with dense forests and moderate rainfall, Central California with moderate grasslands and brush, and the Imperial Valley section of Southern California with active agriculture. We will report on the strengths and limitations of using ALOS PALSAR data for measuring the strain rate along this active, and potentially destructive, fault system.