Motivation: The island of Madagascar occupied a key role in both the assembly and the multi-stage breakup of Gondwanaland itself part of the super-continent Pangaea. Madagascar consists of an amalgamation of continental fragments and contains a major shear zone system. During the Neogene moderate volcanism has occurred in the central and northern part of the island. Located within the interior of the African plate and far away from major plate boundaries (>1000 km), Madagascar shows seismic activity, an indicator that some deformation is taking place. Present-day kinematic models based on geodetic data and earthquake moment tensors identify a diffuse N-S-oriented minor boundary, apparently passing through Madagascar and separating two micro-plates. Global lithospheric studies indicate a thin lithosphere (<120 km) throughout Madagascar, but these are based on sparse data and cannot resolve possible differences between the eastern and the western island.
Seismic network: We have operated a SW NE oriented linear array of 25 broadband stations in southern Madagascar, extending from coast to coast and crossing surface geological boundaries at high angle: the sedimentary basin in the west, the Proterozoic and Archean metamorphic rocks in the east, as well as the major shear zones (e.g., the prominent Bongolava-Ranotsara). The array recorded a local M 5.3 earthquake in January 2013, which motivated us to deploy an additional 25 short period sensors in the eastern part of southern Madagascar, to record the so-far poorly characterized seismicity.
Studies: We applied multiple techniques to image the seismic structure of the crust and mantle lithosphere in southern Madagascar: Receiver function analysis, ambient noise correlation and tomography, shear wave splitting, computation of radial anisotropy and local seismicity analyses.