Triggering of volcanic degassing by large earthquakes

Statistical analysis of temporal relationships between large earthquakes (M w ≥ 7) andvolcanic eruptions suggests that seismic waves may trigger eruptions over great (>1000 km)distances from the epicenter, but a robust relationship between volcanic and teleseismic activityremains elusive. Here we investigate the relationship between dynamic stresses propagatedby surface waves and a volcanic response, manifested by changes in sulfur dioxide (SO 2 )emissions measured by the spaceborne Ozone Monitoring Instrument (OMI). Surface waveamplitudes for a catalog of 69 earthquakes in A.D. 2004–2010 are modeled at 12 persistentlydegassing volcanoes detected by the OMI. The volcanic response is assessed by examiningdaily OMI SO 2 measurements in 28 day windows centered on earthquakes meeting a variablepeak dynamic stress threshold. A positive volcanic response is identified if the averagepost-earthquake SO 2 mass was at least 20% larger than the pre-earthquake SO 2 mass. Wefind two distinct volcanic responses, correlating strongly with eruption style. Open-vent,basaltic volcanoes exhibit a positive response to earthquake-generated dynamic stress (i.e.,the earthquake triggers increased SO 2 discharge), and andesitic volcanoes exhibit a negativeresponse. We suggest that the former is consistent with disruption or mobilization of bubbles,or magma sloshing, in low-viscosity magmas, whereas the latter observation may reflect moredominant controls on degassing in viscous magmas or a post-earthquake reduction in permeability.Overall this analysis suggests that the potential effects of large earthquakes shouldbe taken into account when interpreting trends in volcanic gas emissions.