In this article, I present a Fortran package (XCORLOC) that improves relative earthquake location accuracy based on compressional and/or shear-wave seismic data. The program can perform phase arrival (e.g., single event, static station term, and source-specific station term [SSST]) and waveform crosscorrelation relocation sequentially or separately. It performs an iterative grid-search approach that allows application of more robust norms (L1 and hybrid L1-L2) than traditional least squares, which are less sensitive to gross timing errors. This package can be used for relocations in local, regional, and global scales. Specific topography information can be included to avoid artificial effects in the presence of significant topographic relief. In addition, the package can be used to compute station corrections in areas with strong velocity contrasts from a suite of wellconstrained earthquake locations and then achieve similar location accuracies for a different set of events. As an illustration, I show location improvements of the SSST and the waveform cross-correlation locations relative to the typical seismic network locations for three regions, the Vallecitos Valley region in southern California, Parkfield in central California, and the North Island of New Zealand. Comparison with other location techniques is also provided for a case study. The XCORLOC package is available for free download (see Data and Resources).
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