Seismic stations installed on Shishaldin the summer of 1997 registered a series of earthquakes. One of the six stations was not working, so Tytgat couldnt identify the source of the quakes. Once the station was repaired, the quakes stopped, abruptly, and Shishaldin resumed its quiet vigil on the Pacific. Tytgat, who has been monitoring volcanoes at the observatory since it opened, said it takes time to get to know a volcanos individual seismic signature. Even when a volcano is dormant, the seismic stations installed around it register the violent storms that bash the Aleutians, the grinding of glaciers and other phenomena that are not volcanic.
Every volcano is different.
Keeping a close eye. Tremor is a continuous signal that can last for hours, days, weeks. It can be loud and unmistakable, and it can also be so subtle it's hard to identify. For the longest time we looked at the thing and we really didn't decide anything. You look at it so much, you become accustomed to it.