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Japan Marine Science and Technology Center Institute for Frontier Research on Earth Evolution (IFREE) the first time that the stress distribution is heterogeneous around the subducted seamounts off Cape Muroto. This heterogeneous stress field is similar to that expected for seamount subduction (Fig.). 50˚N 40˚N (a) 50˚N 40˚N (b) () Numerical Simulation of Long-term Crustal Deformation in and around Japan Through collaborative research with the Graduate School of Science, the University of Tokyo, a D numerical model of plate interfaces in and around Japan was constructed and a numerical simulation was conducted for long-term crustal deformation in and around Japan caused by steady plate subduction with the modeled D plate geometry. From this result, the rate of free-air gravity anomaly change was calculated and is fairly consistent with the free-air gravity anomaly estimated from satellite altimatery data (Fig.). () Development of Simulation Codes on the Earth Simulator A numerical simulation code for D box type mantle convection was developed and optimized for the 30˚N 20˚N Hashimoto & Matsu'ura (2003) ES, in order to investigate the dynamics and evolution of subduction zones on a geological time scale. Large scale numerical simulation code for the earthquake cycle was also developed for an integrated earthquake generation model in the Nankai trough region including the results of structure surveys, source process 30˚N 20˚N 130˚E 140˚E 150˚E 130˚E 140˚E 150˚E Fig.26 Comparison of free-air gravity anomaly pattern between observation and calculated results in and around Japan: (a) free-air gravity anomaly estimated from satellite altimatery data (Sandwell & Smith, 1997), (b) Computed rate of freeair gravity anomaly change in and around Japan by steady plate subduction. White and black indicate positive and negative anomaly, respectively. 900 800 700 600 500 400 300 200 100 900 176 0.250369E+03 800 232 0.293494E+03 (1) 700 (4) 5.0 600 4.0 3.0 500 2.0 400 1.0 Kii 0.5 300 -0.5 -1.0 -2.0 200 -3.0 100 -4.0 -5.0 400 600 800 1000 1200 1400 1600 400 600 800 1000 1200 1400 1600 5.0 4.0 3.0 2.0 1.0 0.5 -0.5 -1.0 -2.0 -3.0 -4.0 -5.0 900 800 700 600 500 400 300 200 100 187 0.287985E+03 (2) 400 600 800 1000 1200 1400 1600 5.0 4.0 3.0 2.0 1.0 0.5 -0.5 -1.0 -2.0 -3.0 -4.0 -5.0 900 800 700 600 500 400 300 200 100 250 0.324856E+03 (5) 400 600 800 1000 1200 1400 1600 5.0 4.0 3.0 2.0 1.0 0.5 -0.5 -1.0 -2.0 -3.0 -4.0 -5.0 900 800 700 600 500 400 300 200 100 202 0.292293E+03 (3) 400 600 800 1000 1200 1400 1600 5.0 4.0 3.0 2.0 1.0 0.5 -0.5 -1.0 -2.0 -3.0 -4.0 -5.0 log (V/V ) 10 pl Fig.27 Normalized velocity distribution calulated by numerical simulation of earthquake cycle in the Nankai trough region: Red and blue indicate unstable sliding and locked regions, respectively. The unstable regions appear in the east and west of the Kii peninsula. 105
JAMSTEC 2002 Annual Report Institute for Frontier Research on Earth Evolution (IFREE) analyses, and rock experiments. A result using this code on the ES indicates that segmentation of the source region is caused by a complex slab geometry. Furthermore, optimization on the ES of the crustal activity simulation code for transcurrent plate boundaries and the development of the poro-viscoelastic FEM code for investigation of fluid around fault zones were also promoted (Fig.). Thickness (mm) 1200 1000 800 600 400 Research Program for Paleoenvironment 1. Research Overview The ultimate goal of our group's research is the establishment of a new view on the link between the Earth and the biosphere over the history of the Earth. We are focusing on the last million years when the geological record is preserved in deep sea sediments. Currently, our research focuses on the following three specific fields: a) Climatic change in the Cretaceous Greenhouse and Late Cenozoic Icehouse Earth b) Sedimentation and degradation processes of organic matter on the continental margin c) Database for paleoclimatology and paleogeography of continents and oceans Here, we briefly summarize the results of each topic to present an overview of the progress of our research in FY. 2. Cretaceous Greenhouse Earth 2.1. Investigation of Cretaceous black shales It has been known that several organic-rich "black shales" were widely deposited on Earth during the Cretaceous Period. They are believed to be the result of periods of reduced degradation rates of sedimentary organic matter, which have been referred to as Oceanic Anoxic Events (OAEs). The black shales are one of the major source rocks for petroleum on which modern civilization heavily relies. To understand the cause and bigeochemical processes of the OAEs, we have investigated black shales from central Italy and southern France. In FY we 200 0 -40 -35 -30 -25 -20 δ 13 C (per mil) Fig.28 Isotopic composition of organic carbon in the OAE2 black shales from Central Italy (Kuroda et al., submitted). Arrows indicate the clay layers that are substantially depleted in 13 C relative to adjacent layers. obtained a high-resolution record of stable isotopic compositions of total organic carbon through the Livello Bonarelli black shale (OAE, Ma) and found that thin (~cm) clay layers intercalate the black shale and are depleted in C by as much as relative to the adjacent layers (Fig.). This suggests that a portion of the organic matter in the clay layer originates from methane oxidizing bacteria. We are currently analyzing biomarkers, pigments, and carbon isotopic compositions of these molecules to further investigate the paleoenvironment when the clay layers formed. We have also investigated OAEb ( Ma) black shales distributed in the Vocontian Basin, southern France. In FY we performed stratigraphic descriptions of the sequence and measured the carbon isotope ratio of organic carbon in the black shale. Analyses of major element compositions using the newly established core-logger "Tatscan F" are currently underway to achieve high-resolution mapping of major elements in the black shale. 2.2. Model Ocean for Cretaceous OAEs To estimate the Cretaceous OAE environments, we are studying modern anoxic environments similar to 106
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