Modeling volcano and earthquake deformation from satellite radar interferometric observations

Volcanic eruptions and earthquakes remain significant natural hazards that threaten life and property. While driven by underground processes inaccessible to us directly, they may nonetheless be studied by observing ground surface deformation. Here we study volcanic and seismic processes using spaceborne synthetic aperture radar interferometry (InSAR) and develop deformation modeling strategies exploiting the spatially-dense data—InSAR provides meter-scale resolution displacement maps at centimeter-level accuracy. We begin by characterizing the statistics of InSAR observations to better understand the technique's limitations and potential in studying ground deformation. We derive the covariance matrix of interferograms, identify its form with that of the atmospheric turbulence that is the main error source in these data, and show how the large data volume of an interferogram may be reduced without much loss of integrity so that inverse methods may be used in analysis. InSAR reveals unsuspected widespread volcanic deformation in the Galapagos archipelago throughout the past decade. Summit inflation and deflation patterns indicate shallow magma chambers beneath each volcano at depths ranging from 2 to 5 km. In some cases, a simple point pressure source in an elastic medium reproduces the observed inflation, while in others more complicated models are required to image the expanding magma body. On Fernandina island, a dipping dike appears to have fed a flank eruption in 1995, while time-variable deformation patterns on Sierra Negra volcano on Isabela island suggest that trapdoor faulting occurred, triggered by strong inflation. We also study the 1999 magnitude 7.1 Hector Mine, California earthquake and find mainly right-lateral strike-slip motion on a near-vertical fault, with a small reverse faulting component accounting for less than 10% of the total moment. Similar analysis for two magnitude 6.5 earthquakes in south Iceland in 2000 shows two parallel and vertical right-lateral strike-slip faults, separated by 18 km. Here observed postseismic deformation follows from poro-elastic rebound in the 1–2 months after the earthquakes. Since the aftershock sequence decays on a 3–4 year time scale, pore-pressure changes play an insignificant role in controlling aftershock decay for these events.