I appreciate the comments by Forsyth et al., which clarify the nature of seismicity at 18°S, and I agree that the link between seismicity and El Niños is unclear. I also believe that off-axis seismicity by itself is an unlikely direct link to El Niños and that many of the earthquakes recorded teleseismically from distant ridge systems are off-axis events with no volcanic or hydrothermal component at their epicenters. Nonetheless, the times of occurrence of these teleseismically recorded episodes of unusual seismicity appear to be somewhat contemporaneous with El Niños. How can this be? It is well-known to T-phase researchers that unusually high levels of reported seismic activity along ridge systems are often accompanied by unusual swarms of T-phases. (For some ridge segments, unusual activity may be only a couple of teleseismically recorded earthquakes per month.) In such swarms, the T-phases of unreported events occurring in roughly similar regions and during the same hours or days as the reported earthquake activity are often stronger than the T-phases from the reported earthquakes. It is reasonable to presume that such T-phases are from sources with shallower focal depths than the reported earthquakes.
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