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Evidence for seismogenic fracture of silicic magma


It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of 600 °C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle–ductile fault textures in silicic lavas2,3,4 has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines5,6, leading to models of seismogenic stick-slip along shallow shear zones in the magma7. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting.

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Figure 1: Experimental results from high-temperature fracture of rhyolitic obsidian.
Figure 2: Experimental results from high-temperature fracture of Mt Shasta andesite.
Figure 3: Schematic diagrams comparing faulting in silicic magma to tectonic faulting and showing where fault zones may develop during a lava dome eruption.


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We are grateful to J. Bowles, S. Boon and N. Hughes for technical assistance with the experiments, C. Kilburn and H. Pinkerton for discussions and W. Hirt for help during fieldwork on Mt Shasta. This research was supported by the UK Natural Environment Research Council and the Leverhulme Trust (H.T.).

Author Contributions H.T. provided the initial idea, carried out deformation experiments on obsidian, analysed data and co-wrote the paper. R.S. carried out deformation experiments on andesite, analysed data and co-wrote the paper. P.R.S. co-wrote the paper and assisted with the experimental programme.

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Correspondence to Hugh Tuffen.

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The file contains Supplementary Data, Supplementary Tables 1-6 and Supplementary Figures 1-9 with Legends. (PDF 304 kb)

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Tuffen, H., Smith, R. & Sammonds, P. Evidence for seismogenic fracture of silicic magma. Nature 453, 511–514 (2008).

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