Global Catalog of Calibrated Earthquake Locations

We produced a globally distributed catalog of earthquakes and nuclear explosions with calibrated hypocenters, referred to as the Global Catalog of Calibrated Earthquake Locations or GCCEL. This dataset currently contains more than 18,000 events in about 250 clusters distributed around the world. Also included are more than 2.7M arrival times observed at more than 18,000 stations. The term “calibrated” refers to the property that the hypocenters are minimally biased by unknown Earth structure and that the uncertainties are meaningful. We calculate uncertainties using empirically determined variability of the arrival time data itself, specific to each calibrated cluster of hypocenters. We carefully process the arrival-time dataset to remove outliers defined by the variability of the data. In each cluster, we estimate the empirically determined uncertainty for each set of station-phase arrival times. We use a version of the Hypocentroidal Decomposition multiple event relocation algorithm specifically adapted for calibrated relocations of clusters of seismic events. Most clusters are calibrated by fitting the subset of direct crustal first arrivals (Pg and Sg) with a locally appropriate travel-time model to estimate the cluster hypocentroid. A few clusters are calibrated by aligning the pattern of relative locations in space and time with one or more events for which a ground-truth hypocenter is available from an independent source with known uncertainty, such as a nuclear explosion. Epicentral uncertainties in GCCEL typically range from 1-5 km with a 90% confidence interval. Most events have depth constraint from one or more sources, usually with an uncertainty of 5 km or less. GCCEL is a significant resource for research at local, regional, and global scales because it provides minimally biased absolute hypocenters, meaningful associated error estimates, and curated arrival times as a reference dataset that can be used as prior constraints in the development of new regional, national, and global earthquake catalogs, validation of new location techniques, and the generation of advanced Earth models.