Using a genetic algorithm to estimate the details of earthquake slip distributions from point surface displacements

摘要

Examining fault activity over several earthquake cycles is necessary for long-term modeling of the fault strain budget and stress state. While this requires knowledge of coseismic slip distributions for successive earthquakes along the fault, these exist only for the most recent events. However, overlying the Sunda Trench, sparsely distributed coral microatolls are sensitive to tectonically induced changes in relative sea levels and provide a century-spanning paleogeodetic and paleoseismic record. Here we present a new technique called the Genetic Algorithm Slip Estimator to constrain slip distributions from observed surface deformations of corals. We identify a suite of models consistent with the observations, and from them we compute an ensemble estimate of the causative slip. We systematically test our technique using synthetic data. Applying the technique to observed coral displacements for the 2005 Nias-Simeulue earthquake and 2007 Mentawai sequence, we reproduce key features of slip present in previously published inversions such as the magnitude and location of slip asperities. From the displacement data available for the 1797 and 1833 Mentawai earthquakes, we present slip estimates reproducing observed displacements. The areas of highest modeled slip in the paleoearthquake are nonoverlapping, and our solutions appear to tile the plate interface, complementing one another. This observation is supported by the complex rupture pattern of the 2007 Mentawai sequence, underlining the need to examine earthquake occurrence through long-term strain budget and stress modeling. Although developed to estimate earthquake slip, the technique is readily adaptable for a wider range of applications.