Eikonal equation-based earthquake location with irregular surfaces

Earthquake location is a basic seismological problem and has a key role in many quantitative seismic analyses. The significant anomaly of traveltimes observed in mountainous areas with irregular surfaces has made earthquake location a challenge. To cope with this problem, we develop an effective eikonal equation-based earthquake location method based on unstructured mesh for 2-D/3-D isotropic and anisotropic media with irregular surfaces. First, the location misfit function is established by the reciprocity principle. Then, we use a global search algorithm to find the optimal origin times and hypocentres. Afterward, we apply eikonal equation-based master-event relocation method to relocate earthquakes on lateral boundaries of the region where the location results may be biased. To accurately compute the traveltime in 3-D vertically transversely isotropic and tilted transversely isotropic models with irregular surfaces or interfaces, we also propose a 3-D iterative fast sweeping method for eikonal equation on the unstructured tetrahedral mesh. Finally, we verify the proposed method by performing numerical experiments in 2-D/3-D irregular isotropic and anisotropic models. The numerical tests indicate that the proposed eikonal equation-based earthquake location method provides an effective way to find accurate hypocentre and origin time in 2-D/3-D isotropic and anisotropic media with irregular surfaces, even for inhomogeneous complex structures. In addition, the eikonal equation-based master-event location method has also yielded promising relocation results.