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Published March 21, 2006 | Published
Journal Article Open

Coseismic surface deformation from air photos: The Kickapoo step over in the 1992 Landers rupture

Abstract

Coseismic deformation of the ground can be measured from aerial views taken before and after an earthquake. We chose the area of the Kickapoo-Landers step over along the 1992 Landers earthquake zone, using air photos (scale 1:40,000) scanned at 0.4 m resolution. Two photos acquired after the earthquake are used to assess the accuracy and to evaluate various sources of noise. Optical distortions, film deformation, scanning errors, or errors in viewing parameters can yield metric bias at wavelength larger than 1 km. Offset field at shorter wavelength is more reliable and mainly affected by temporal decorrelation of the images induced by changes in radiometry with time. Temporal decorrelation and resulting uncertainty on offsets are estimated locally from the correlation degree between the images. Relative surface displacements are measured independently every about 15 m and with uncertainty typically below 10 cm (RMS). The offset field reveals most of the surface ruptures mapped in the field. The fault slip is accurate to about 7 cm (RMS) and measured independently every 200 m from stacked profiles. Slip distribution compares well with field measurements at the kilometric scale but reveals local discrepancies suggesting that deformation is generally, although not systematically, localized on the major fault zone located in the field. This type of data can provide useful insight into the fault zone's mechanical properties. Our measurements indicate that elastic coseismic strain near the fault zone can be as large as 0.5 × 10^(−3), while anelastic yielding was attained for strain in excess of about 1–2 × 10^(−3).

Additional Information

© 2006 American Geophysical Union. Received 11 April 2005; revised 13 September 2005; accepted 16 November 2005; published 21 March 2006. This paper has benefited greatly from reviews by two anonymous reviewers and the AE Sandy Steacy. This study was supported by the Action Concertée Incitative "Catastrophes Naturelles" of INSU. We thank NSF for partial support through grant EAR- 0409652. This is Tectonics Observatory contribution 14.

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August 22, 2023
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