Simultaneous inversion of hypocentral parameters and structure velocity of the Central Region of Madagascar as a premise for the mitigation of seismic hazard in Antananarivo

A layered velocity is obtained using arrival-time data of P and S waves from local earthquakes for the Central Region of Madagascar. A damped least-squares method is applied in the inversion of the data. The data used are 770 P-wave arrival times for 154 events which have epicenters in the region inside the Malagasy network operated by the Institut et Observatoire de Geophysique d'Antananarivo (IOGA). These data are jointly used in the inversion for the earthquake hypocenters and P- and S-wave velocity models. S waves are not used in the first step of the inversion, since their use leads to large location errors. If the error on the phase reading for the P wave is about 0.1 s, for the S wave it is considerably bigger. The reference average model used here is a variant of the model given by RAKOTONDRAINIBE (1977).