In SEP-60, the results of some initial processing of the data were presented. The results were not very encouraging, but since then processing tools have evolved and I have made some significant gains. In this report, I will discuss three topics I've been working on. First, the USGS set off several blasts varying in size in a quarry about 15 km away from our experiment, timed so that we could record them. Two of the three blasts were so small that they are not observable on single geophone records at our site. But beam steering or slant-stacking of the data sees these blasts quite well. There is evidence in the coda of at least one blast of multipath effects, which deserve closer study.
Second, we have observed a large number (one every few seconds during nighttime recording) of weak, near-vertically incident events. While we cannot explain their origin, it will be shown here that while they are nearly vertically incident (as electrical interference might be) they have a distinct, non-vertical incidence angle that rules out the possibility that they are electrical noise.
Finally, the goal of this work is to use ambient noise recording to image subsurface structure. One hypothesis is that we can ``see'' ambient energy diffract off near-surface structure and thereby learn about the near-surface. I have applied a simple hyperbola-summation method to data from the quarry blasts as well as ambient noise data in attempt to do this. At first glance the results are quite consistent. But a closer look shows that they are dominated by artifacts introduced by plane-wave energy which stacks in even when hyperbolic paths are used.