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Abstract Repeated earthquake cycles produce topography, fault damage zones, and other geologic structures along faults. These geomorphic and structural features indicate the presence of co‐seismic permanent (inelastic) surface deformation, yet a long‐standing question in earthquake research is how much of the co‐seismic deformation field is elastic versus inelastic. These questions arise in part because it is unclear what measurable co‐seismic characteristics, such as off‐fault or distributed surface deformation and cracking, represent true unrecoverable deformation. One emerging descriptor of permanent co‐seismic deformation is surface strain magnitudes inferred from imaging geodesy observations. In this study, we present the surface strain field of the 2013 Mw7.7 Baluchistan strike‐slip earthquake in southern Pakistan. We invert co‐seismic displacement fields generated from pixel‐tracking of SPOT‐5 and WorldView optical imagery for co‐seismic surface horizontal strain tensors. We observe that co‐seismic strain field is dominated by negative dilatation strains, indicating that the co‐seismic fault zone contracted during the earthquake. We show that co‐seismic inelastic failure exhibits a relatively consistent width along the rupture that is localized to a zone 100–200 m wide on the hanging wall side. The width of co‐seismic permanent deformation does not correlate with variations in off‐fault deformation or surface geology. Based on comparisons to other recent earthquakes, we posit that the permanent surface strains reflect inelastic deformation of the faults inner damage zone, and that the width of this zone reflects fault maturity.
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Relating Slip Behavior to Off‐Fault Deformation Using Physical Models
Abstract Deformation in transform systems is accommodated by discrete fault slip and distributed off‐fault deformation. Here, we consider how a change in slip behavior along a fault can influence the distribution between on‐ and off‐fault deformation. We use a physical experiment to simplify the geometry, material properties, boundary conditions, and slip history along a strike‐slip fault to directly observe patterns of off‐fault deformation. We document deformation of a silicone slab on a simple shear apparatus using particle image velocimetry (2D) and photogrammetry (3D). The experimental results show regions of topographic highs and lows on either side of the slip transition that grow, evolve, and are displaced with progressive strain. The experimental dilatation field shares similarities with strain fields in central California along the San Andreas fault, which suggests that a change in slip behavior may explain some of the real‐world patterns in short‐ and long‐term deformation.
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- PAR ID:
- 10371804
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 11
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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