Quality Factor to classify Earthquake Locations

In order to define the quality of a seismic location, we investigate a suite of ‘classical’ uncertainty estimators, i.e., the root mean square, the number of phases, the azimuthal gap, the errors on the hypocentral coordinates. Their mutual correlation makes difficult to estimate the complete hypocenter uncertainty in an objective and simple way. For this reason, we proposed to define a location ‘quality factor’ through an empirical formula, consisting of the combination of different uncertainty estimators, properly normalized. Thus, the formula provides a value, ranging from 0 to 1, through which a simple classification of the location’s quality can be obtained. Our scheme is to divide the quality factor range in 4 intervals, in order to define four quality classes, from A (best class) to D (worst class). We tested how this approach works in different case studies, e.g., different stations network density, sequence and no-sequence seismicity, different location method (linearized and global). We found a reasonable correspondence between our quality classification and the statistical distribution of estimators, related to the different quality classes. In addition, the defined best classes are able to clearly highlight the active seismic structures. We present the application of the method to different-type and -scale earthquake Italian catalogs, characterized by different spanned time periods, obtaining promising results. This approach can give important insights, especially for routinely monitoring location computation. We present the usefulness, the feasibility and the flexibility of this innovative method.