Eruptions

Earthquake near Nevado del Huila

Whether this is a coincidence or not, I thought I’d mention a report of an earthquake near the crater of Nevado del Huila in Colombia. The earthquake is reported as a magnitude 4.6 and at a depth of 20 km (although that is only a rough estimate), indicating that magma might be moving up the conduit system under the volcano – or that it might be just coincidental seismicity in a seismically active area. However, Huila had recently become active for the first time in 500 years, so this could be a sign of new activity to come.

Comments

  1. #1 Bruce
    September 4, 2008

    Hi Erik,
    glad you are back and even more glad I’ve discovered your blog..

    I am having real trouble trying to decipher seismic plots and now, thanks to you guys in the field, laymen like me can get access to real time seismic plots. Can you point me in any direction that would clarify the difference in hybrid, volcanic tremor, long-period quakes etc. and what the signals look like? I found a bit on the NZ geonet site, but I’m still pretty in the dark… also how can you distinguish between normal tectonic activity and volcanic activity? The Kasatochi quake was associated with a huge number of quakes in the surrounding vicinity but I still don’t know how, or even if, they were associated with the eruption. Hope I am not asking too much!!!

  2. #2 Erik Klemetti
    September 4, 2008

    Hi Bruce —

    I don’t know if this helps, but here are some explanations/resources:
    Volcanic Earthquakes
    USGS VHP Seismicity

    And here’s a nice website with seismicity at various volcanoes in the Cascades (run by the PNSN).

  3. #3 Bruce
    September 5, 2008

    Thanks Erik, that was a good start and got me off on a long internet search last night!!

    If I understand it correctly, a volcanic tectonic signal is indistinguishable from a normal tectonic signal apart from the fact that the P and S waves will be virtually on top of each other owing to the close proximity and volcanic tremor or long period signals will generally have a longer duration and relatively constant amplitude (it’s kind of hard to distinguish the difference in the frequency when the timeline is so squashed up). Where I have problems is distinguishing between noise (wind, rock falls etc.) and volcanic tremor. I presume volcanic tremor are those extended but solid patches that sometimes appear. And background noise is lower amplitude more intermittent and longer lasting. The last view days Ngauruhoe in New Zealand has had a pretty busy seismogram but there have been no reports by GNS.. I was wondering if I was interpreting the signals correctly, because it looks like a bit of volcanic tremor to me!

    Here’s the link, if you’re interested (and hoping the activity doesn’t die off in the meantime)
    http://www.geonet.org.nz/images/volcano/drums/ch/otvz/10/drum.png

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