Inverting for slip on three-dimensional fault surfaces using angular dislocations" Bulletin Of The Seismological Society Of America 95.5 (2005): 1654-1665. 1654Bulletin of the Seismological Society of America, Vol. 95, No. 5, pp. 1654-1665, October 2005, doi: 10.1785 Most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries. These geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults, and they preclude a more complete understanding of the role of fault geometry in the earthquake process.We have developed a new three-dimensional slip-inversion method based on the analytical solution for an angular dislocation in a linear-elastic, homogeneous, isotropic, half-space. The approach uses the boundary element code Poly3D that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces. The use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three-dimensional surfaces bounded by curved tiplines: shapes that commonly are imaged by three-dimensional reflection seismic data and inferred from relocated aftershock data.We demonstrate the method's ability to model three-dimensional rupture geometries by inverting for slip associated with the 1999 Hector Mine earthquake. The resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models, improving the fit to the geodetic data by 32%, and honors the observed surface ruptures, thereby allowing more direct comparisons between geologic and geodetic data on slip distributions.

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Global Positioning System (GPS) measurements registered up to >5m of coseismic displacements during the 28 March 2005 Mw = 8.7 Nias earthquake, Indonesia. The vertical offsets put tight constraints on the northern and southern limit of the rupture. The inferred coseismic slip distribution indicates high slip patches near the epicenter and near the southern extent of the 26 December 2004 Aceh‐Andaman rupture, where aftershocks have been abundant. Six months of postseismic time‐series are better fit with a logarithmic instead of exponential function, suggesting that the postseismic deformation is likely controlled by afterslip. Our inversion model predicts afterslip to be concentrated both up‐ and down‐dip from patches of maximum coseismic slip where aftershocks are sparse. The shallow afterslip adds further evidence that the earthquake probably did not break the surface (with implications for tsunami generation) and instead caused aseismic deformation in shallow parts of the subduction zone after the event.

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