Earthquake-induced methane migration through the gas hydrate stability zone in the subduction regime offshore Pakistan

Although gas hydrates often occur in seismically active regions, the role of earthquakes as triggers of hydrocarbon seepage through gas hydrate-bearing sediments has been only super�cially addressed. The Makran continental margin o�shore Pakistan hosts hydrocarbon-laden sediments and gas hydrates and is prone to vigorous seismicity. The area was visited in the frame of RV METEOR expedition M 74/3 in 2007 (Bohrmann et al. 2008). Here we present geochemical evidence for a substantial increase in upward gas �ux inducing methane emission into the water column and gas hydrate formation in the sediment, a phenomenon which occurred within a few decades of the strongest earthquake ever reported for the entire Arabian Sea. We propose a causal relation and present re�ection seismic data supporting our hypothesis that co-seismic ground shaking induced mechanical fracturing of gas hydrate-bearing sediments creating pathways for free gas to migrate from a shallow reservoir within the gas hydrate stability zone into the water column. Our �ndings lead to conclude that hydrocarbon seepage triggered by earthquakes might play a role for carbon budgets at other seismically active continental margins. The newly identi�ed process presented here can help interpret data from similar sites