Hi All. After Petra and I left the AGU conference I got to thinking about some of the things I saw and some of the things I learned from some very knowledgeable people.

The one thing that stuck in my mind was Long Valley Caldera. I wondered just what are the odds of it erupting in the very near future as opposed to erupting a thousand years from now. One of the very first speakers talked about long period earthquakes. I had seen those quakes, but at the time did not recognize their importance. I told Petra I had some work to do and she agreed. Anything that gets me to work she agrees with.

I got started on it as soon as I arrived back home and found quite a bit of information and in that information I found one thing that stood out. I’m sure there is more then this one paragraph, but for right now this is utmost in my mind. The following has been edited from a report by Randall A. White
“Long-Period (LP) earthquakes and LP tremor have been observed at many volcanoes (for example, Koyanagi and others, 1987). The vast majority of LP events reported in the literature originated at depths of less than 3 km. Such shallow LP events have preceded eruptions at many volcanoes (for example, Chouet and others, 1994). LP events deeper than 10 km are less commonly observed. Such earthquakes have been noted in California beneath Long Valley caldera (Hill and Pitt, 1992) and the nearby Mono cones (Mitch Pitt, USGS, oral commun., 1994), Mt. Lassen and Medicine Lake volcanoes (Steve Walter, 1988, 1991), and the Clear Lake volcanic complex (Steve Walter, USGS, oral commun., 1994). Other deep LP earthquakes occur regularly under Kilauea volcano, Hawaii (Koyanagi and others, 1987), many have been observed under Mount Spurr, Alaska (Power and Jolly, 1994), one at Izu-Ooshima, Japan (Ukawa and Ohtake, 1987), and at several other active volcanoes and low-velocity in Japan (Hasegawa and others, 1991)”.
“About 600 deep long-period (DLP) earthquakes occurred beneath Mount Pinatubo in late May and early June 1991. This number is higher than the combined total number of such earthquakes previously reported at all convergent-margin volcanoes worldwide. The DLP earthquakes occurred in two episodes of roughly similar total energy release, from 1700 May 26 to 1210 May 28 and from 2114 May 31 to 1510 June 8. During these same periods, at least 25 hours of very low amplitude DLP tremor also occurred, in 1- to 10-hour-long episodes. The DLP earthquakes exhibit clear P- and S-phases on three-component records. A P-S converted phase, which apparently converts at the base of the dacite pluton at about 14 kilometers in depth, is also observed. DLP earthquake spectra are dominated by very narrow-bandwidth signals with a quality factor of 20 to 50. The dominant frequency for the vast majority of the events, including the 10 largest, is at 2.0 hertz. A few events with dominant frequencies of 3.2-3.3 or 3.6-3.9 hertz were also observed, usually at the beginning of swarms which contain large-amplitude 2.0 hertz events. The Reduced Displacement for the largest event is about 3,100 square centimeters (magnitude ~3.7), making it the largest DLP earthquake ever reported. The events locate from 28 to 35 (possibly 40) kilometers below, and about 6 kilometers northwest of, the summit and apparently shallow with time”.
There have been three such DLP at Long Valley Caldera. In view of the eruption at Mount Pinatubo, Long Valley Caldera could very well start its birth towards a new eruputuion much the same way. At least that is my way of thinking. Take Care…Don in creepy town.