For effective earthquake and tsunami early-warning it is crucial that key earthquake parameters are determined as rapidly and reliably as possible. This requirement entails that initial estimates of earthquake locations will be based on a minimal data set, with the risk of large errors and bias in epicentre and hypocenter depth, or detection of a false event. The use of station travel-time corrections is a basic and important tool to avoid these problems.
At the INGV CAT* tsunami alert center, Early-est** is the module for rapid determination of the location, depth, magnitude, mechanism and tsunami potential of an earthquake. Early-est produces fully automatic results and their uncertainties using as few as 3 to 5 P onset observations.
Here we use the ISC bulletin arrival database to develop empirical, station travel-time corrections for the ak135 velocity model to improve routine, real-time location in Early-est. We use the R statistical computing and graphics language to explore, exploit and visualize the ISC arrival database and to map the obtained station corrections. We analyze and discuss the station corrections with regards to epicentral distance, source depth, tectonic setting and crustal structure, and their effect on location accuracy.
* CAT, “Centro di Allerta Tsunami”, part of the Italian, candidate Tsunami Service Provider ** Early-est (EArthquake Rapid Location sYstem with EStimation of Tsunamigenesis)