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Physical properties of seafloor massive sulfides provide a basis for interpreting of sub-seafloor images obtained from geophysical surveys. They are useful for elucidating the evolution of seafloor mineral deposits. A few reports have described studies of the correlation between electrical conductivity and the volume of conductive minerals of rocks collected from seafloor massive sulfide deposits. More studies are performed on artificial samples than on natural rock samples, and the characteristics of natural samples are not well understood. For this study, complex conductivity measurements, elemental concentration analysis, and content mineral identification analysis were applied to rock samples collected from the hydrothermal active zones of the Okinawa Trough in Japan. The measured complex conductivity is characterized by a very high overall value, with a large imaginary component and a wide frequency band by induced polarization. Most of the rock samples have contained large amounts of conductive sulfide minerals, e.g., pyrite, chalcopyrite, and galena predominating. A rock physics model, the Cole–Cole model, was applied to the measured data. Our results indicate good correlation between rock chargeability and the volume fraction of conductive sulfide minerals. However, the correlation trend differs from those found from earlier studies. The intensity of the induced polarization is much larger than that predicted from earlier studies of artificial samples. The samples have less distinct quadrature conductivity peaks, and might continue to be polarized outside of the conventional measurement frequency bands. This discrepancy is probably attributable to the geometric characteristics of sulfide minerals.

Knowledge of the strength of sediments overlying sub-seafloor gas-hydrate deposits is crucial for predicting borehole and seafloor stability during hydrate extraction. Ideally, sediment strength should be determined along a continuous downhole profile from the seafloor to the hydrate reservoir, but few such profiles have been obtained. In this study we used cores retrieved at Site NGHP-02-23 in the Krishna–Godavari Basin in unconfined penetration tests on split cores and in triaxial deformation experiments on hydrate-free sediment samples. Although penetrometer tests identified relatively low strength (70–250 kPa) likely due to hydrate dissociation in the hydrate-bearing interval 90–300 m below seafloor (mbsf), sediment strength exceeded 350 kPa in the intervals 140–170 and 250–270 mbsf, each of which lies just above a zone of high gas-hydrate concentration. The average stress ratio of triaxial strength at 4% axial strain to effective mean stress (qe=4%/p’) of hydrate-free silts was about 0.67 throughout the Hole. An exception to this trend was in fine sands from 280 mbsf in the deeper gas-hydrate zone, where the stress ratios were greater than 1.0. The stress ratios of hydrate-bearing sediments in the deeper gas-hydrate zone that were reported from the pressure-core measurements were far greater than those of any hydrate-free sediments for a given effective mean stress. The high-strength intervals in silty sediments we identified by the penetration tests could be associated with zones of high hydrate concentration. Because high-strength layers in fine-grained silty sediments commonly exhibit lower permeability than sandy layers (potential hydrate-host), they may act as seals that assist the precipitation of hydrate below them.

The temperature response to stress changes of rocks is key to understanding temperature anomalies in geoscience phenomena such as earthquakes. We developed a new hydrostatic compression system in which the rock specimen center can achieve adiabatic conditions during the first ~10 s following rapid loading or unloading, and systematically measured several representative sedimentary, igneous and metamorphic rocks sampled from two seismogenic zones [the Longmenshan Fault Zone in Sichuan, and the Chelungpu Fault Zone (TCDP Hole-A) in Taiwan], and several quarries worldwide. We built a finite element model of heat conduction to confirm the measured results of temperature response to stress changes of rocks. The results show that: (1) the adiabatic pressure derivative of the temperature (β) for most crustal rocks is ~1.5 mK/MPa to 6.2 mK/MPa, (2) the temperature response to stress of sedimentary rocks (~3.5-6.2 mK/MPa) is larger than that of igneous and metamorphic rocks (~2.5-3.2 mK/MPa), and (3) there is good linear correlation between β (in mK/MPa) and the bulk modulus K (in GPa): β=(-0.068·K + 5.69) ± 0.4, R2 = 0.85. This empirical equation will be very useful for estimating the distribution of β in the crust, because K can be calculated when profiles of crustal density (ρ) and elastic wave velocities (Vp, Vs) are obtained from gravity surveys and seismic exploration

Heat transport properties are significant parameters that affect geothermal processes in deep sedimentary basins. We measured the thermal properties of deep sediment core samples to a depth of approximately 2500 m below sea floor (mbsf), whereas most previous studies have only presented data −1 K −1 , and calcite-cemented sandstone/siltstone exhibits the highest conductivity of approximately 3 Wm −1 K −1 . The other thermal properties are also influenced by the porosity and lithological contrast. The correlation between thermal conductivity and porosity is explained by the mixed-law model of the geometric mean. The one-dimensional temperature-depth profile at site C0020 estimated from measured thermal conductivity reveals a regression of the thermal gradient with depth, and the surface heat flow of 30 mWm −2 , which is consistent with the heat flow data near this site, was evaluated. The obtained results suggest that the linear geothermal gradient estimated from the average thermal conductivity value at shallow sediment materials could overestimate the temperature at greater depths and underestimate the heat flow.

The zooxanthellate dendrophylliid coral, Turbinaria peltata (Scleractinia), exhibit various growth forms that increase the photoreception area through the development of coenosteum skeletons. Because it is difficult to make detailed observations of the internal structures, we visualized inner skeletal structures using nondestructive microfocus X-ray computed tomography (CT) imaging. After removal of the coenosteum skeletons from the X-ray CT images, three-dimensional 3D-models were reconstructed for individual corallites. Regular budding was observed from the 3D-model and cross-sectional images as follows: 1) lateral corallites occurred only near the two primary septa on one side, apart from a directive primary septum with distinct polarity; 2) the budding occurred upward at acute angles; and 3) these regular structures and polarity were repeated throughout growth with every generation. Even in zooxanthellate dendrophylliids, the same budding modes as observed in azooxanthellate equivalents control the colonial growth. These characteristics provide clues for understanding the mechanisms that regulate the shapes of modular marine organisms. J. Morphol. 276:1100–1108, 2015. © 2015 Wiley Periodicals, Inc.

Friction experiments at high velocities (0.1 to 0.4 m/s) at room temperature under high pore fluid pressures (2 or 5 MPa) and trace element analyses of the run products were carried out on simulated fault gouge derived from the Chelungpu fault, Taiwan. The friction coefficient decreased to ~0.1 during sliding, and the slip surface temperature reached 300°C by 6 m of slip displacement. The slip caused a small, but distinct decrease of Li in the deformed gouge when the slip surface temperature exceeded 300°C. The observed Li depletion agreed with calculated results, indicating that it resulted from a hydrothermal reaction at a high temperature produced by short-duration (up to 40 s) frictional heating. The geochemical data suggest a small fluid/rock ratio and low reaction temperature in the simulated fault, which is explained by higher normal stress or repeated earthquakes which elevated fluid-rock ratios in the natural fault.

Thermal–hydrological–mechanical coupling processes suggest that fault permeability should undergo dynamic change as a result of seismic slip. In igneous rocks, a fault's slip surface may have much higher permeability than the surrounding rock matrix and therefore operate as a conduit for fluids. We conducted laboratory experiments to investigate changes in fracture permeability (or transmissivity) of a fault in granite due to shear slip and cyclic heating and cooling. Our experiments showed that high initial fracture transmissivity (>10−18 m3) was associated with a high friction coefficient and that transmissivity decreased during slip. We propose that this reduction in transmissivity reflects the presence of gouge in fracture voids, increasing the area of contact in the fault plane and reducing the hydraulic aperture. In contrast, when initial fracture transmissivity was low (

Human-made structures and shaped stones on the seafloor near coasts, possibly submerged by tsunami waves, coseismic subsidence, or flooding during typhoons, can often be linked to folk traditions of ancient natural disasters. Stone pillars that appear to have been artificially shaped are submerged in shallow waters inshore Tosashimizu city, southeast Japan, an area subject to repeated Nankai Trough earthquakes. We performed geophysical and geochemical analyses of samples from these pillars, building stones in use in villages in the Tsumajiro area, and nearby natural rock outcrops. In porosity and grain density, the pillars are similar to sandstone from the Tatsukushi Formation and to foundation stones used in the villages; this similarity was confirmed by a principal component analysis of chemical composition data. The shape and surface morphology of the pillars are also similar to those of the foundation stones and stone steps at nearby temples. Therefore, we inferred that the submerged stone pillars were made from Tatsukushi sandstone and had been utilized as building stones for structures such as steps and foundations in Tsumajiro village possibly >100 years ago. Because radiocarbon ages obtained on calcareous fragments adhering to the pillars were inconclusive, when, and by what process, the stone pillars were transported from the land and submerged in the sea is still uncertain.

Fluid transport properties such as permeability and porosity are significant parameters that affect earthquake generation. We measured the transport properties of shallow sediments sampled around the plate boundary near the Japan Trench during IODP Expedition 343 at confining pressures up to 40 MPa. The permeabilities of samples from the shallow plate boundary fault were very low at 10 − 20 m 2 , equivalent to a hydraulic diffusivity of 10 − 10 m 2 s − 1 . Permeability and porosity in the core of the fault zone at the plate boundary were lower than those in the immediately overlying sediments and the surrounding intact sediment, suggesting that the plate boundary fault can act as a barrier for fluid flow. Low permeability and high pore compressibility in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating, even when the initial shear stress is low. Our investigation supports the hypothesis that thermal pressurization on the fault plane helped facilitate the extremely large slip in the shallow part of the subduction zone during the Tohoku earthquake. As the fault zone has a lower permeability than the surrounding sediments and a higher clay content, pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust, which does not affect pore pressure at depth in the fault zone. Although there are many possible mechanisms of fault weakening, thermal pressurization can act relatively efficiently as slip begins, even at shallow depths. Therefore our results support the role of thermal pressurization in shallow slip during the Tohoku earthquake.

We used a rotary shear apparatus to investigate changes of fluid transport properties in a fault zone by real-time measurement of gas flow rates during and after shearing of hollow sandstone cylinders at various slip rates. Our apparatus measures permeability parallel to the slip plane in both the slip zone and wall rocks. In all cases, permeability decreased rapidly with increasing friction, but recovered soon after slip, reaching a steady state within several tens of minutes. The rate of reduction of permeability increased with increasing slip velocity. Permeability did not recover to pre-slip levels after low-velocity (ca. 0.0019 m/s) tests but recovered to exceed them after high-velocity (ca. 0.29 m/s) tests. Frictional heating of gases at the slip surface increased gas viscosity, which increased gas flow rate to produce an apparent permeability increase. The irreversible permeability changes of the low-velocity tests were caused by gouge formation due to wearing and smoothing of the slip surface. The increase of permeability after high-velocity tests was caused by mesoscale fracturing in response to rapid temperature rise. Changes of pore fluid viscosity contributed more to changes of flow rate than did permeability changes caused by shear deformation, although test results from different rocks and pore fluids might be different.

Strontium and Nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the Arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the Chukchi and Bering Seas over the past 100 years. Regional distributions of the Sr and Nd isotopes of the surface sediments show higher Sr isotope ratios and lower Nd isotope ratios in the Chukchi Sea ( 87 Sr/ 86 Sr=0.7106–0.7150; e Nd =–10.1 to –8.3), and lower Sr isotope ratios and higher Nd isotope ratios in the eastern Bering Sea (0.7045–0.7109; –8.6 to +3.0). In addition, the Rb and Sr contents and REE patterns (e.g., Eu/Eu⁎) changed noticeably across the Bering Strait. These variations mean that the sediments in the Bering and Chukchi Seas have clearly distinct sources. The terrigenous detritus in the Chukchi Sea is mainly derived from northeastern Siberia ( 87 Sr/ 86 Sr=0.711; e Nd =–9) and Bering Strait inflow (essentially from the Yukon River), and additionally from the Mackenzie River basin including the Canadian Shield (0.732–0.734; –14). The detritus in the eastern Bering Sea mainly consists of two components: the continental material from the Yukon River basin mainly underlain by Mesozoic and Paleozoic rocks in the Alaskan mainland (0.708–0.709; –9 to –8), and the Aleutian-arc volcanics (0.703; +6 to +10) transported northward by the Alaska Coastal and Bering Shelf Waters. The eastern Bering sediments over the past 100 years show slight variations of the Sr isotope ratio and relatively wide variations of the Nd isotope ratio, and the variations and trends of the time-series of the northeastern Bering Sea in the Sr–Nd isotope diagram are probably controlled by changes in the grain size of the detritus from the Yukon River basin. Some of the e Nd time-series show periodic fluctuations correlating with the annual mean surface air temperature (SAT) for the Arctic: the e Nd value is low in the high SAT period, and high in the low SAT period. In the warm period, the Yukon River was likely to supply a higher amount of the fine-grain material with a relatively low e Nd value such as surficial overburden, probably because partial melting of continental glaciers and permafrosts in the Alaskan mainland increased. More detailed analysis with high time resolution is needed to clearly understand the effects the SAT have on the Arctic continental and marine environments.

We used 210Pb and 137Cs concentrations in twelve cores from the continental shelf and slope of the Bering Sea to investigate recent mass accumulation rates in sediments and sedimentation processes. No decreases in exogenic 210Pb concentrations with depth were observed in sediments from the shallow shelf area, suggesting that there has been considerable mixing of the sediments there. However, we calculated mass accumulation rates from 210Pbex profiles for several cores collected from the outer shelf and the slope. Mass accumulation rates in the sediments from these cores ranged from 0.11 to 0.44 g cm−2 y−1. For the cores with a mixed surface layer, we showed that sediments that accumulated over the last 50–78 years were mixed. The 210Pbex inventories in the sediment cores suggested deposition of 210Pb particles was focused in the slope area. 137Cs was observed in the sediments collected from the northern to western shelf areas. The 137Cs inventories showed higher values in the shelf area, which suggests that fine-grained particles from the Yukon River have contributed to sedimentation there.

Generation and maintenance of overpressure can prevent sediments from compaction and weaken sedimentary rocks in deep basins. Excess fluid pressure is one of the key factors to explain the disastrous mud eruption that took place in Sidoarjo, East Java, on 29 May 2006, though the mechanism by which it developed is not well known. We measured permeability and specific storage at a confining pressure of 100 MPa in outcrop samples from the East Java Basin. Both permeability and specific storage in our samples showed large stratigraphic variations. The mudstone of the Upper Kalibeng Formation that is thought to be the source of mud at Lusi had the lowest permeability of our samples at around 10 − 19 –10 − 20 m 2 , and the permeability of the Upper Kujung Formation limestone was 10 − 16 m 2 , which is two orders of magnitude larger than that of the Lower Kujung Formation limestone. In addition, the permeability and porosity of cemented sedimentary rocks showed low sensitivity to effective pressure. From numerical basin analysis of the Lusi site together with laboratory data, we evaluated the evolution of pore pressure and porosity histories and their present distributions. Our results show that high overpressure was generated below the mudstone of the Upper Kalibeng Formation and almost reached lithostatic levels. The modeled fluid pressure variation is consistent with the observed data. The long-lived overpressure at depth is mainly caused by the existence of thick low-permeability sediments and a high sedimentation rate. Undercompaction of the Upper Kalibeng Formation because of overpressurization may have caused the mud to lose strength and cause liquefaction (and hydrofracturing) as a result of small stress fluctuations induced by the Yogyakarta earthquake, which may have ended up causing the mud eruption.

Chemical and isotopic variations in crushed material along the Chelungpu fault in Taiwan are suggestive of interactions at high temperatures with coseismically generated aqueous fluids. High fluid pressures along the fault zone during the magnitude 7.6 Chi-Chi earthquake in 1999 could have reduced friction and fault strength. Aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture. Fluid overpressure can affect earthquake nucleation1,2 and in a process termed thermal pressurization, pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface3,4,5. This may lead to a marked reduction in fault strength during slip. However, the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate. Here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine-grained deformed material from three active zones of the Chelungpu fault, Taiwan. Depth profiles across the most intensely sheared bands that range in thickness from 2–15 cm exhibit sharp compositional peaks of fluid-mobile elements and of strontium isotopes. We suggest that high-temperature fluids (>350 ∘C) derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements. The coseismic presence of high-temperature fluids under conditions of low hydraulic diffusivity6 within the fault zone is favourable for thermal pressurization. This effect may have caused a dynamic decrease of friction along the Chelungpu fault during the 1999 magnitude 7.6 Chi-Chi earthquake.

We presented the total and inorganic carbon contents of core samples recovered from the Taiwan Chelungpu fault system, which slipped at the 1999 Chi-Chi earthquake, and reported lower contents of inorganic carbon within the black gouge zone in FZB1136 (fault zone at depth 1136 m in Hole B) and in the black-material disks in FZB1194 and FZB1243.

The zooxanthellate dendrophylliid coral, Turbinaria peltata (Scleractinia), exhibit various growth forms that increase the photoreception area through the development of coenosteum skeletons. Because it is difficult to make detailed observations of the internal structures, we visualized inner skeletal structures using nondestructive microfocus X-ray computed tomography (CT) imaging. After removal of the coenosteum skeletons from the X-ray CT images, three-dimensional 3D-models were reconstructed for individual corallites. Regular budding was observed from the 3D-model and cross-sectional images as follows: 1) lateral corallites occurred only near the two primary septa on one side, apart from a directive primary septum with distinct polarity; 2) the budding occurred upward at acute angles; and 3) these regular structures and polarity were repeated throughout growth with every generation. Even in zooxanthellate dendrophylliids, the same budding modes as observed in azooxanthellate equivalents control the colonial growth. These characteristics provide clues for understanding the mechanisms that regulate the shapes of modular marine organisms.

We report thermal conductivities, thermal diffusivities, and volumetric heat capacities determined by a transient plane heat source method for four whole-round core samples obtained by the Japan Trench Fast Drilling Project/Integrated Ocean Drilling Program Expedition 343. These thermal properties are necessary for the interpretation of a temperature anomaly detected in the vicinity of the plate boundary fault that ruptured during the 2011 Tohoku-Oki earthquake and other thermal processes observed within the Japan Trench Fast Drilling Project temperature observatory. Results of measured thermal conductivities are consistent with those independently measured using a transient line source method and a divided bar technique. Our measurements indicate no significant anisotropy in either thermal conductivity or thermal diffusivity.

[1] Since 1997, ocean color satellite images have revealed large-scale blooms of the coccolithophorid Emiliania huxleyi in the eastern Bering Sea. The blooms are often sustained over several months and have caused ecosystem changes in the Arctic Ocean, as well as in the Bering Sea. We examined continental shelf sediment profiles of alkenone, a biomarker for E. huxleyi, covering the past ∼70 years. The alkenone records suggest that large E. huxleyi blooms are a novel feature in the Bering Sea as they have occurred only since the late 1970s. Recent changes in alkenone content were closely related to the 1976–77 climatic regime shift in the North Pacific, implying that warming and freshening of Bering Sea waters promoted E. huxleyi blooms. The production rate of diatoms (total valves in sediment samples), the dominant primary producers in the Bering Sea, also increased during the past several decades. However, the ratio of alkenone content to total diatom valves in the sediments increased as E. huxleyi production increased, suggesting that the increase in the E. huxleyi production rate frequently exceeded the increase in the diatom production rate. Overall, our results indicate a possible subarctic region ecosystem shift driven by climate change.

[1] We measured frictional properties and permeability of core materials from the megasplay fault zone (site C0004) and the frontal thrust (site C0007) in the shallow part of the Nankai subduction zone. Permeability was measured before and after 7.9 m slip displacement at high (1.05 m/s) and low velocities (0.013 m/s) under normal stresses of 1.5 MPa using the rotary-shear apparatus, from which we estimated the shear-induced permeability change in an experimental fault gouge prepared from core material. Gouge permeability (10−18 m2) decreased after sliding for wet gouge and increased for dry gouge. The high-velocity friction test under wet conditions yielded a smaller reduction in permeability than the low-velocity test, whereas the opposite trend was observed in dry conditions. We attribute the differences in permeability to the effects of thermal/mechanical pore pressurization upon shear-induced compaction. Symmetric boudin structures may represent evidence of hydrofracturing induced by pore fluid pressurization. The large friction coefficient of the megasplay fault material in the slow and wet friction tests is explained by homogeneous shear deformation and higher permeability that promotes faster shear-induced compaction. The similarity in post-shear permeability for the gouges from the both faults may account for the similar friction coefficients in high-velocity friction, assuming that the pore fluid pressurization process controls high-velocity frictional behavior. This velocity dependence on friction suggests that a large dynamic stress drop is expected for the megasplay fault, implying that large slip displacement followed by a giant tsunami is plausible when a rupture from depth propagates to the megasplay fault.

We examined the effects of high pressure on thermal conductivity in core samples from the slope–apron facies and the upper part of the accretionary prism at site C0001 of the NanTroSEIZE drilling program and in other samples of five terrestrial rock types. Thermal conductivity clearly increased with increasing pressure for both wet (water saturated) and dry samples. We determined the rate of thermal conductivity change of the NanTroSEIZE sediments to be 0.014 Wm−1K−1/MPa when pressure was increased, and 0.01 Wm−1K−1/MPa when pressure was decreased. Using the rate determined for decreasing pressure, we estimated that thermal conductivities measured at atmospheric pressure rather than at in situ pressure may be underestimated by 7% for a core sample from around 1 km depth and by 20% for a core sample from around 3 km depth. In general, the rate of thermal conductivity change with pressure showed a positive correlation with porosity. However, the relationship of the rate of thermal conductivity change to porosity is also dependent on the fabric, mineral composition, and pore structure of the sediments and rocks. Furthermore, for two sandstones we tested, the effect of pressure on thermal conductivity for dry samples was greater than that for wet samples.

[1] We measured permeability in sandstone and granite sheared at slip rates from 10 ―4 to 1.3 m/s under low-normal stress at confining pressures up to 120 MPa. As the slip rate increased, the permeability of Berea sandstone decreased by an order of magnitude, whereas that of Indian sandstone and Aji granite increased by 3 orders of magnitude at high slip rates. A fine-grained gouge layer of thickness developed during slip, and the wear rate was increased abruptly at high slip rates. Microcracks and mesoscale fractures formed at slip rates above 0.13 m/s. Numerical modeling showed that the slip surface temperature increased by several hundred degrees for slip velocities above 0.13 m/s and exceeded the α-β phase transition temperature of quartz at 1.3 m/s. Both the temperature rise and the temperature gradient at the slip surface were high at fast slip rates. We attributed reduced permeability after slip in porous sandstone to the low-permeability gouge layer. An abrupt permeability increase in low-permeability rocks at high slip rates was caused by heat-induced cracks. An increase in the rate of wear of gouge with increasing slip velocity was caused by frictional heating that reduced the rock strength. The host-rock permeability that separated reductions and increases in permeability was about 10 ―16 m 2 at 10 MPa effective pressure. Our results suggest that abrupt increases in shear stress during slip in a low-permeability fault zone caused by thermal cracking, which may decrease the total slip displacement. The abrupt permeability increase at high slip rates in low-permeability rocks agrees with hydrogeochemical phenomena observed after earthquakes.

[1] To understand the chemical reactions of clay minerals in a fault zone during an earthquake, we analyzed the clay minerals in the Chelungpu fault, which slipped during the 1999 Chi-Chi earthquake. X-ray diffraction spectroscopy showed that kaolinite and smectite contents were lower in the black gouge zone than in the surrounding gray gouge, breccia, or fracture-damaged zones. We applied a chemical kinetics approach to examine whether dehydroxylation of kaolinite and dehydration of interlayer water, dehydroxylation, and illitization of smectite occurred during coseismic frictional heating, and found that the first two reactions could complete under the temperature-time profile of the Chi-Chi earthquake, reconstructed by a previous study. Because dehydration of smectite interlayer water and dehydroxylation of kaolinite would have completed 3.6 and 8.2 s after the beginning of slip, the resulting release of water might have affected the frictional mechanism during the earthquake.

International audience; The iron content and the asymmetry of iron and magnesium ions in chlorites are examined for the Chelungpu Fault in Taiwan, which is a seismogenic fault. The samples are collected from the cores drilled for the Taiwan Chelungpu Fault Drilling Project (TCDP, borehole B). Three fault zones are recognized as candidates for the source of seismogenic materials. The fault zones are composed of fractured-damaged rocks, breccia, gray gouge, black gouge, and black material. Chlorite from each type of rock was analyzed by using X-ray diffraction (XRD). The iron content and asymmetry of the iron and magnesium ions in the chlorites were estimated from the XRD peak ratios. The hydroxide and silicate layers of chlorite in the black gouge and black material have low iron contents. Many studies have suggested that a temperature rise occurred at the fault zones. In addition, the temperature rise can result in the production of iron oxides such as magnetite or maghemite, as reported by other studies. However, the temperature rise cannot explain the low value of iron content in the chlorites. Another reason for the low value of iron content is the variation in the pH of the fluid, which can be controlled by radical reactions. Therefore, on the basis of chlorite characteristics, the reactions at the seismogenic fault are due not only to the thermal decomposition resulting from the temperature rise and but also to rock-fluid interactions.

掘削試料 (コアおよびカッティングス) の熱伝導率の測定手法を確立するために, 本研究ではインド産の砂岩とカオリン粉体試料を使用して, 非定常細線加熱法 (熱線法) に基づいたQTM (Quick Thermal conductivity Meter) よる熱伝導率の測定を行なった. 実験の結果, 掘削によって採取される多くの岩石や堆積物の熱伝導率測定に必要な試料サイズは, 熱線長が95mmのボックス型プローブの場合には, 長さ100mm, 幅40mm, 厚さ20mm以上であることがわかった. よって,掘削試料を測定する場合, 直径40mm以上の半割コア試料が必要になる. また, ニードル型プローブを用いたカオリン粉体試料の実験では, 圧密した試料の密度と熱伝導率の正の相関関係が認められ, 断層粘土やカッティングスなどの少量の掘削試料でも容器内に詰めて圧密させるなどの工夫を施すことで, 将来的に熱伝導率測定ができると思われる.