SIMULTANEOUS INVERSION OF HYPOCENTRAL PARAMETERS AND STRUCTURE VELOCITY OF THE CENTRAL REGION OF MADAGASCAR AS A PREMISE FOR THE MITIGATIONOF SEISMIC HAZARD IN ANTANANARIVO

A layered velocity is obtained using arrival-time data of P and S wave s from local earthquakes for the Central Region of Madagascar. A dampe d least-squares method is applied in the inversion of the data. The da ta used are 770 P-wave arrival times for 154 events which have epicent ers 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- an d S-wave velocity models. S waves are not used in the first step of th e inversion, since their use leads to large location errors. If the er ror 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).