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Subducting oceanic plates at convergent plate boundaries generate devastating earthquakes and tsunamis through slips propagated in the accretionary wedge. The transient faulting decomposes sedimentary structures and produces frictional heat and chemical constituents. We demonstrate here that subseafloor sedimentary microbial communities have been affected by environmental changes associated with episodic fault activities in the Nankai Trough seismogenic zone. Cell abundances were one to two orders of magnitude higher above and below the megasplay fault zone. Analyses of the extracted DNA, lipid biomarkers, and hydrogenase activities consistently showed that microbial community compositions, structures, and metabolic activities near the fault zone were distinct from those in the overlying stratified sediment. Marked anomalies of temperature-sensitive biomarker proxies also were observed near the fault zone. Our results indicate that deep sedimentary microbial habitats on tectonically active continental margins have been affected by large fault activities: surviving subseafloor life presumably is adapted to these drastic environmental changes. |