| dc.description.abstract | Earthquakes and tsunami events pose significant threats to human life and property. Accordingly, the scientific community is developing an understanding of what controls fault strength and failure mechanics in order to develop physics-based models for predicting earthquake-related phenomena. Subduction zones, such as the Nankai Trough offshore South Japan, are particularly susceptible to damaging earthquakes and tsunamis, e.g., the events of 1944 Tonankai (M8.1) and 1946 Nankaido (M8.3) earthquakes. A series of scientific boreholes was drilled through marine sediments across the Nankai Trough Seismogenic Zone by the International Ocean Discovery Program (NanTroSEIZE transect, IODP) to acquire geologic and geophysical data that may be used to characterize the geomechanical properties relevant to fault strength and failure mechanics. To better define the mechanical behavior of marine sediments in subduction zones, NanTroSEIZE drilling data are analyzed and modeled to characterize sediment mechanical response and strength as a function of depth, lithology and tectonic loading history. New methods are developed herein based on previous work in the mining and petroleum industry that relate drilling performance parameters to rock strength, and on geotechnical and geophysical understanding of marine sediment properties.
The methodology is applied to drilling data from two sites of the NanTroSEIZE transect, IODP Sites C0006 and C0011, to evaluate the differences between the tectonically deformed sediments within the frontal portion of the accretionary prism and the less deformed sediments at the outer rise of the incoming plate. Using the data analysis and modeling methods, and employing a novel Relative Drillability relationship, both the overall change in strength of sediment with depth due to burial consolidation, and the second-order deviations in strength due to lithology, in situ stress, and sediment burial history, can be characterized from drilling data for both IODP Sites. The findings are consistent with the hypothesis that the incoming sediments are relatively weaker than those accreted at the frontal thrust of the accretionary prism, and demonstrate the potential for utilizing the drilling data commonly acquired during IODP operations to quantify profiles of sediment strength versus depth. | en |
