33 Do ” double SS precursors ” mean double discontinuities ?

SS precursors are the underside reflections from the upper mantle discontinuities such as those at 410 and 660 km. They are important tools for studying the existence and characteristics of mantle discontinuities both on the global and regional scales (see Deuss, 2009 for a review). Due to their sensitivity at the midpoint between source and receiver, coverage for oceanic regions is achieved where other methods such as receiver functions and triplications are not feasible. Their amplitudes are generally small (5-10% of the main phase), at or below noise level. Stacking is therefore necessary. Midpoint stacking over geographical bins with radius of 10◦ has been common. Recently, the deployment of the US Transportable Array (TA) allows unprecedented density of ray coverage and brings new opportunities to try and resolve finer scale discontinuity characteristics for much broader regions.