Station Travel-Time Calibration Method Improves Location Accuracy on a Global Scale

Abstract

Online Material: Earthquake catalog and tables of station and data parameters. Earthquake location has been an outstanding issue for seismologists for over more than a century, and it is still an important subject of study. In fact, accurate locations of earthquakes are a requisite for investigations on the dynamics of the Earth and seismogenic processes. Another possible use of seismic locations is, for example, monitoring underground explosions in the context of the International Monitoring System (IMS) for verifying compliance to the Comprehensive Test Ban Treaty (CTBT). In fact, the CTBT makes provisions for On‐Site Inspections (OSI) requested by a member State that detects a suspicious event in the territory of another member State. As the CTBT states that the OSI area should not exceed a size of 1000 km2, it is crucial that the seismic event triggering the OSI be known with an uncertainty not exceeding a few km. Earthquake location accuracy is related to the degree of knowledge about the 3D structure of seismic‐wave velocity in the Earth. In fact, the location process is essentially the solution of an inverse problem in which observed arrival times of seismic waves are compared with theoretical arrival times computed from a given velocity model. Assuming such a velocity model is known, the unknown parameters of this problem are the origin time and the three spatial coordinates of the earthquake source. It is generally recognized that, and independently of the location algorithm, uncertainties in earthquake locations are dominated by two main factors (Husen and Hardebeck, 2010): 1. Measurement errors of seismic arrival times, and 2. Modeling errors of calculated travel times. Among numerous location methods developed by seismologists, the group of algorithms is very popular that is based on linearization of the inherently non‐linear inverse problem, and solution of the over‐determined problem by a …