Earthquakes and volcanic activity are interconnected in a complex manner: There is evidence that large earthquakes can trigger volcanic activity but there are also examples for the opposite effect, i.e. an earthquake dampening down volcanic activity. For example, the 2011 magnitude 9 Tohoku earthquake, which had led to a devastating tsunami and the Fukushima nuclear meltdown, triggered activity at some volcanoes but also caused subsidence at some other volcanic areas, unexpected considering that such an earthquake would increase magma pressure.

What physical mechanism could explain simultaneously the positive and negative volcanic responses to earthquakes? A team of scientists from Japan, Germany, Italy and the USA, funded by Japan-Germany exchange scheme, has focused on the role played by the resonance of volcanic edifices to seismic waves: volcanoes often portray prominent topography that oscillates similarly to a skyscraper during earthquake shaking. The scientists simulated shaking of volcanic edifices under controlled conditions in a GFZ laboratory. They realized a scaled miniature volcano made of gelatin, injected it with a mix of water and air in varying proportions and shook it on a shaking table.

Shaking resulted in part of the gelatin volcano undergoing oscillatory compressions and dilatations, visualized by means of polarizer sheets (see movie). The compressions and dilatations squeezed the fluids in all directions depending on their buoyancy and depth: bubbly fluids stored at shallow depth ascended, while low-buoyancy fluids descended or migrated laterally. Such fluid migration occurred around one hundred times faster than without shaking.

These experiments may explain positive as well as negative effects, with fluids migrating up or down depending on their properties. The fluid migration is most efficient when the oscillation frequency is close to the resonance frequency of the edifice. The fundamental resonance frequency for a 30-km-wide volcanic range, such as those where subsidence was observed, is ~0.07 Hz. Only large earthquakes, where rupture occurs along ~100s km long faults, are able to cause oscillation at such low frequencies. This matches with the observation that large earthquakes are most effective in triggering unrest, with effects of magnitude 8 sometimes seen around the Earth. Resonance at volcanic edifices may reinforce other processes and triggering mechanism thus accelerating their effect.

Original study: Namiki, A., Rivalta, E., Woith, H., Willey, T., Parolai, S., Walter, T.R., 2018. Volcanic activities triggered or inhibited by resonance of volcanic edifices to large earthquakes. Geology. DOI: 10.1130/G45323.1

Scientific contact:
Dr. Eleonora Rivalta
Section Physics of Earthquakes and Volcanoes
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Telegrafenberg
14473 Potsdam
Phone: +49 331 288-28659
Email: eleonora.rivalta@gfz-potsdam.de

Media contact:
Dipl.-Geogr. Josef Zens
Head of Public and Media Relations
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Telegrafenberg
14473 Potsdam
Phone: +49 331 288-1049
Email: josef.zens@gfz-potsdam.de
Twitter: @gfz_potsdam