E. Karasozen1 , E. Bergman2 , E. Nissen3
1Colorado School of Mines, Golden, CO, USA
2Global Seismological Services, Golden, CO, USA
3University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada
Uncertainties in standardized earthquake locations, which run into tens-of kilometers in many regions of the world, are a serious limitation to seismotectonic studies. We have developed a new two-tiered multiple-event relocation approach that seeks to improve upon these catalog locations, and have applied it to Iran, a country with abundant seismicity (> 40,000 ISC Bulletin events since 1960), a recent surge in station coverage, but with known shortcomings in location accuracy. In the first stage, locations of small clusters of well-recorded earthquakes at local spatial scales are calibrated either with near-source arrival times or with independent location constraints such as from InSAR or short-duration aftershock deployments. This stage uses MLOC, an implementation of the Hypocentroidal Decomposition relocation technique, that specifically minimizes systematic bias and fully calibrates the location uncertainty, usually to better than 5 km (GT5). Secondly, these calibrated locations with their uncertainties are used as a backbone of "ground truth" events in BayesLoc, a Bayesian relocation algorithm that can handle larger datasets, to yield region-wide earthquake catalogs that are less vulnerable to systematic bias and have realistic estimates of the location uncertainty. We illustrate the improved locations by re-interpreting a selection of early instrumental and modern mainshock-aftershock sequences.