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 Ge´ophysique 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).