Dave, Regarding the 6 second microseisms: Nothing special should be needed to observe the microseisms in the data from a long period instrument that is properly damped, has sufficient protection from noise, and sufficient gain to record moderate quakes. The Ms 5.7 in Mexico on Dec. 04 had P-wave amplitudes about 10x the (unfiltered) 6-second microseisms at the time (at St. Louis). They are very clear and monochromatic in period, so much so that I have used passive twin-T notch filters for years to remove them from analog monitor records at the observatory. An analysis of the average period at St. Louis showed 6.2 seconds to be the optimum period to design the filter for. The notch filter reduces the microseisms by over 40 db (factor of 100) to improve the readability of the record. A notch here between the VBB-STM and the analog drum makes them disappear for most of the time. They are very clear sine waves on a long period record: simply count the peaks or number of sine waves between minute marks: sometimes there are 9, mostly 10, or sometimes 11. A FFT of the LP data should show the microseism peak an average of about 40 db above the noise level at 20 seconds or so. Regards, Sean-Thomas ps: Jeff, BIGQUAKE is working; just received the report on the Mw 7.2 this AM in Turkmenistan. A very nicely dispersed surface wave train arrived here, starting at about 90 seconds period and rising to 20 seconds over about 15 minutes. You might have to re-subscribe. __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>