Imaging Magma Under St. Helens

A service run means a lot of driving between stations and about 15-30 minutes at each station to check that all parts are working properly and are secure and to down-load data recorded since installation or the previous service run.  Typically these may be several month apart; however with the active experiment starting at the end of next week we want to make sure all stations are functioning properly so we are doing service runs now and two stations have already been serviced (MP04, MO03).  The data collected have been down-loaded to a computer at the UW and are provided on a "wave-server" so that researchers can examine it for quality and completenes.  We provide below some plots of seismic waveforms from these two stations for a few selected events.

Here are plots of about an hour showing the seismograms from a magnitude 6.9 earthquake that occurred off the coast of southern Mexico on July 7.  There are three channels of broad-band data (BH?) and three channels of long-period filtered data (LH?).  The three channels are for ground motion in the vertical direction (?HZ), the east-west direction (?HE) and the north-south direction (?HN).  For this event the broad-band and the long-period look very similar because the waves from a distant earthquake (teleseism)  are naturally filtered by the earth to be mostly long-period signals.

The following seismograms are from the broad-band channels of the two stations for a small (Mag=0.5) earthquake located at 15 km depth below the west end of Yale Lake SSW of Mount St. Helens. Note the fairly weak P-waves at 09:22:50 and the stronger S-waves about three seconds later.