Very Fast Characterization of Focal Mechanism Parameters Through W-Phase Centroid Inversion in the Context of Tsunami Warning

Most of the tsunami potential seismic sources in the NEAM region are in a magnitude range of 6.5 ≤ M_w≤ 7.5 (e.g. the tsunami triggered by the Boumerdes earthquake of 2003 with M_w=6.9 ). The CENtre d’ALerte aux Tsunamis (CENALT), in operation since 2012 as the French National Tsunami Warning Centre (NTWC) and Candidate Tsunami Service Provider (CTSP), has to issue warning messages within 15 min of earthquake origin time. These warnings are based on the seismic source parameters ( M_w magnitude, focal depth and type of fault), which are computed by focal mechanisms and centroid inversion methods. The W-phase method, developed by Kanamori and Rivera, allows quick computation of seismic source parameters due to the early arrival time between P-waves and surface waves, and is therefore particularly useful for monitoring. We assess the W-phase method with 29 events of magnitude M_w ≥ 5.8 for the period 2010–2015 in the NEAM region. Results with 10 min of signal length are in good agreement compared to the Global Centroid Moment Tensor (GCMT) catalog.