Hi Steve - I'm not sure exactly which lines you're referring to - but very thin, vertical lines are usually not a seismic signal, but rather electrical noise. When seismologists interpret seismic data to determine if earthquakes are indicative of magma movement, they need the data from several stations, and often use parts of the data (frequency) that are not able to be shown on the traditional helicorder/webicorder. Here are some more webicorder information links you might be interested in: https://www.usgs.gov/media/videos/illustrated-guide-reading-a-seismogram ; http://www.mbmg.mtech.edu/quakes/quake-seismograms.html Thank you, cheryl -------- steve bradshaw wrote: Question on webicorder for Westdahl volcano. I used type WESE EHZ AV. At utc 0530 and 0600 on 8-26 there are 2 vertical lines which can be seen fairly clearly. Are these movement inside the volcano or outer noise? The lines seem thin and vertical and do not look like earthquakes which seem to have horizontal thickness like you say in your FAQs showing s and p waves. Trying to figure out what internal volcanic movement looks like and would appreciate your response. Sincerely, Steve Bradshaw -- Cheryl Cameron Geologist, Alaska Volcano Observatory Alaska Division of Geological & Geophysical Surveys voice: 907-451-5012 fax: 907-451-5050