Comparison of Coseismic Near-field and Off-fault Surface Deformation Patterns of the 1992 M_w 7.3 Landers and 1999 M_w 7.1 Hector Mine Earthquakes: Implications for Controls on the Distribution of Surface Strain

Abstract

Sub-pixel correlation of pre- and post-event air photos reveal the complete near-field, horizontal surface deformation patterns of the 1992 M_w 7.3 Landers and 1999 M_w 7.1 Hector Mine ruptures. Total surface displacement values for both earthquakes are systematically larger than 'on-fault' displacements from geologic field surveys, indicating significant distributed, inelastic deformation occurred along these ruptures. Comparison of these two datasets show 46 ± 10% and 39 ± 22% of the total surface deformation was distributed over fault zones averaging 154 m and 121 m in width for the Landers and Hector Mine events, respectively. Spatial variations of distributed deformation along both ruptures show correlations with the type of near-surface lithology and degree of fault complexity; larger amounts of distributed shear occur where the rupture propagated through loose unconsolidated sediments, and areas of more complex fault structure. These results have basic implications for geologic-geodetic rate comparisons, and probabilistic seismic hazard analysis.

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