Systematic Determination of Focal Mechanisms over a Wide Magnitude Range: Insights from the Real‐Time FMNEAR Implementation in Chile from 2015 to 2017

The FMNEAR method (for determination of Focal Mechanism using NEAR-source records) has already proved its efficiency for continental earthquakes recorded by a large number of well-distributed stations. Installed in January 2015, it has been running in real time in Chile, in the specific tectonic conditions of the active convergent margin of the Nazca plate, where most of the earthquakes occur offshore. About 3 yr of data were collected, containing thousands of earthquakes, for which 80% have low-to-moderate moment magnitudes (M-w < 4.6). Here, we show results of the FMNEAR inversion, processed in real time at the National Seismological Center of Chile. We compare our solutions with the solutions provided by the U.S. Geological Survey and the Global Centroid Moment Tensor. Our results tested on all the inverted earthquakes common to the three methods show that the main characteristics of the source are well retrieved by the FMNEAR inversion. With the present-day seismic network installed in Chile, FMNEAR was able to provide more than 6200 automatic event solutions, from which about 1000 were considered as reliable. All the inversions were conducted a few minutes after the earthquake origin time, with a calculation time varying from a few seconds for the smallest events to half an hour for the biggest and most complicated earthquakes. The FMNEAR approach showed its efficiency in inverting even small earthquakes in Chile (M-w < 4.5), if the azimuthal station coverage and the number of near stations are sufficient. By implementing FMNEAR in other tectonic settings and continuing to probe its results in the active seismic context of Chile, we expect to improve its capacity to provide viable and meaningful information in real time on the local seismic activity.