Rg scattering has often been suggested as the source of the regional Lg phase generated by explosions (e.g., Patton and Taylor, 1995; Gupta and Wagner, 1998). The main point of our paper (Stevens et al. , 2009) was that it is very difficult to get enough energy out of Rg to generate the observed Lg and that direct generation of S by the source or pS conversion are likely to be stronger sources of Lg than Rg scattering. To compare the contributions of each mechanism, we derived an upper bound on the possible size of Rg -to- Lg scattering by assuming that 100% of Rg is scattered very quickly into Lg with no energy loss or conversion to other phases. This is almost certainly much more Rg -to- Lg scattering than actually occurs, and we showed that even this upper bound is only comparable to or less than direct generation of Lg or of Lg generated by P -to- S conversion at the free surface. Patton and Gupta (2009) disagreed with this analysis and made five specific points, which we subsequently address. We have summarized each of their points, followed by our response. 1. Stevens et al. ’s (2009) equations (19) and (21) for the spectrum of converted higher modes can be expressed as a convolution between Rg source excitation and higher-mode response for a surface load, mediated by an energy transfer function (ETF) for plane-layered velocity models. Yes, it can. Patton and Gupta’s (2009) equation 5 is identical to Stevens et al. ’s (2009) equation 19 for a step function explosion source (Patton and Gupta [2009] also include a Mueller–Murphy source spectral shape, so results will differ slightly for larger events). It should be remembered, however, that this is an upper bound based on 100% energy conversion, not a prediction for the actual …
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