The Ghost of an Earthquake

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Science  02 Dec 2005:
Vol. 310, Issue 5753, pp. 1440-1442
DOI: 10.1126/science.1121349

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Seismic activity can cause Earth's crust and upper mantle to deform and then relax slowly, and this relaxation can be detected decades after the original event. In his Perspective, Hammond discusses results reported in the same issue by Gourmelen and Amelung in which satellite-based radar (InSAR) was used to detect the surface deformation in the Basin and Range province of the western United States caused by earthquakes in the early to mid-20th century. The data indicate that disagreements between geodetic mapping (such as obtained by Global Positioning System measurements) and paleoseismic observations may be explained by postseismic relaxation. Moreover, the results suggest that magnitude information about past earthquakes might be retrieved by such postseismic analysis.