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A Novel Framework for Magma Supply Rate and Depth Controls on Volcanic Earthquake Magnitudes

Diana C. Roman1 , Terry A. Plank2

  • Affiliations: 1Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA  2Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA 

  • Presentation type: Talk

  • Presentation time: Friday 16:15 - 16:30, Room S160

  • Programme No: 2.1.14

  • Theme 2 > Session 1

Abstract

Many active, high threat volcanoes are monitored seismically; some volcanoes display escalating unrest that leads to timely forecasts, while others erupt with little seismic expression. Such has been the state of affairs for decades, and progress will come from integrating geophysical data with petrological data to elucidate the state, location and movement of magma in the sub-volcanic system. Here we focus on the depth evolution of seismic unrest and the relationships to magma storage, crustal rheology and recharge rate. Some volcanic systems display only shallow seismicity in the run-up to eruption, with earthquakes then deepening during the on-set and continuation of eruption ("Top-Down" behavior,). Other eruptions are presaged by deep seismicity that is typically interpreted as magma and/or vapor ascent ("Bottom-Up" behavior). We present a novel framework, based on experimental rock mechanics studies, for the influence of magma supply rate (proxied by strain rate) and temperature and confining pressure (proxies for increasing depth), which illustrates how higher magma flux leads to more abundant seismicity at a given depth/temperature. Critically, this framework demonstrates a relationship between depth and expected earthquake magnitude at a given strain rate (i.e., deeper earthquakes should have lower magnitudes at a given strain rate). Thus we predict that deep earthquakes at volcanoes with high magma flux should have larger magnitudes relative to those at low-flux systems, and test this prediction through assessment of key case studies for which independent constraints on magma flux exist.