Thanks John! I should've realized that some of the types of NVT I speculated on WOULD be double-couple; thanks for clearing that up.

By "redder spectrum" I take it you mean lower frequency.

By NVT showing up "on lower edges of regions with normal quakes", I take it you mean at the lowest reaches of the fault. If so, you might have at least a small quibble with this statement from the article Michael T. posted: "Unlike earthquakes, tremors occur deeper below the surface . . .". (Obviously not _generally_ true, since subduction quakes have occurred at much greater depth than the tremor cited or even most other tremor I recall reading about. But even along the SAF, if it occurs at the lowest reaches of the fault, then SOME quakes might occur at that depth.)

Very interesting that the slip can migrate so far so fast.

Thanks again, John.

Mike W.