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I was recently and for the first time caught in an earthquake. This being my first time, I freaked out and had no idea whether the building was going to collapse or not. I was later told that this earthquake was nothing to worry about because it was due to the volcanic activity of a nearby volcano (4.9 on the Richter, 1km depth). It caused minor damages near to the volcano, but nothing measurable in our location about 30 km away.

This got me thinking - if volcanic activity is less dangerous than plate activity (because it's closer to the surface, perhaps?), is there some upper limit to the scale of such earthquakes? I suppose that earthquakes and volcanic activity are correlated in some way, but I'm not considering the volcanic activity due to plate movement, rather the "normal" activity of active volcanos.

Or rather:

What is the largest magnitude measured of an earthquake attributable solely to volcanic activity?

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    $\begingroup$ when you say largest measured earthquake do you mean in the last 100 years or so,or the largest estimated quake in historic time.lahars and pyroclastic flows are a lot more dangerous than the shaking can be. $\endgroup$
    – trond hansen
    Jan 2, 2019 at 12:25
  • $\begingroup$ I mean it literally. Ie, not through inference, but directly measured with seismo-detectors (sorry! I'm a nuclear physicist, I'm not sure what you guys call the instruments). My question is purely related to the seismic effects, to keep it a "good" question in the SO-verse, but thanks, now I have another thing to worry about :) $\endgroup$
    – Bruce Becker
    Jan 3, 2019 at 18:33
  • $\begingroup$ Do you know what the Richter scale measurement was? I think your colleagues meant to say that this was a run-of-mill 3 or less on the scale. Certainly volcanic activity could cause a worse one. $\endgroup$
    – mkennedy
    Jan 3, 2019 at 19:20
  • $\begingroup$ I've updated the question with the relevant data (4.9 on the Richter, 1km depth, measured by the INGV) $\endgroup$
    – Bruce Becker
    Jan 4, 2019 at 9:13

1 Answer 1

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Earthquakes associated with volcanism or volcanic rifting are typically small. They are caused by over-pressurized magma as it moves around and intrudes into brittle rocks.

Sometimes, e.g., in Hawaii, you get earthquakes due to the gravitational sliding (e.g., the M6.9 earthquake in 2018 beneath Kilauea) as new eruption causes the volcano to grow in size (adding mass) which in turn cause it to slide over the older volcanic rocks underneath.

I don't think there's an exact upper bound for such an event but it is unlikely to exceed ~7.5. Another thing to keep in mind is that rocks near active volcanoes tend to be relatively hotter which in theory should cause less shaking during the earthquake (due to lower stress drop).

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  • $\begingroup$ thank you very much. This is a good answer - could you provide some reference or citations so that I can accept it please? $\endgroup$
    – Bruce Becker
    Jan 24, 2019 at 10:32

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