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Abstract:
Precursor signals are a powerful tool for mapping topography of mantle discontinuities, which are sensitive to the thermal and compositional structure of the mantle. The depth of mantle discontinuities is usually estimated by using the measured differential traveltime between the main arrival and its precursor. However, this method ignores potential travel path deviations which influence the traveltime of precursor signals. Here, we use a different approach that considers directivity information as well as traveltime measurements to infer depth and location of mantle reflectors. We analyze events occurred in Indonesia and recorded at the broadband stations in Germany and in Morocco. Applying seismic array techniques, we measure slowness, backazimuth and traveltime of the signals and use this information to back-project to the point of reflection. We observe SS and PP reflections located beneath southern Asia and in the depth range between 100 and 1600 km in the Earth’s mantle. SS reflections show a clear trend from shallower depths (< 500 km) in the south-eastern part of the studied area to lower depths (> 500 km) in the north-western part. The location of most of deeper reflectors seems to correlate with a high velocity anomaly located beneath south Asia. Instead, shallower reflectors correlate with a prominent low velocity anomaly beneath south-east Asia. We compare the observed data with synthetic seismograms using 3D waveform modelling and test which structures in the Earth’s mantle (i.e., plume and slab) can potentially generate the strong topography observed in the data.
