Frictional experiments of dolerite at intermediate slip rates with controlled temperature: Rate weakening or temperature weakening?

A rotary shear apparatus has been newly set up in Chiba University which can control the temperature near a sliding surface, T_meas, up to 1000°C independently from slip rate, V. Frictional experiments at 0.010 m/s, 1 MPa normal stress, and variable T_meas for dolerite have revealed a remarkable effect of temperature on the friction coefficient, f. With increasing T_meas, f starts from 0.7 to 0.8 at room temperature (RT), decreases down to 0.5–0.6 at 400°C, increases until 800°C, and then decreases again. We have also conducted XRD analyses of the wear materials (mainly submicron particles) and investigated microstructures of the sliding surfaces developed at different temperatures T_meas, and we found that there is a negative correlation between f and the amount of amorphous material except at RT and 1000°C. The generation of the amorphous phase probably causes the weakening. There is no amorphous phase recognized for a sample at 1000°C which is an aggregate of rounded crystals. EBSD analyses show that the material on the sliding surface at 1000°C contains randomly oriented hematite grains, which together with the observed microstructural features suggests that granular flow was taking place. We have also demonstrated that f depends not only on the instantaneous value of temperature, but also on its history. By comparing with conventional rotary shear friction experiment for the same dolerite without temperature control, we conclude that strong “rate weakening” as recently observed in high-velocity frictional experiments without an active control of the temperature has a significant amount of contribution from the temperature effect

Three-dimensional stress state above and below the plate boundary fault after the 2011 Mw 9.0 Tohoku earthquake

東北地方太平洋沖地震を引き起こしたプレート境界断層より以深の応力状態を初めて決定 --海洋底掘削で採取されたコア試料の非弾性ひずみ解析からのアプローチ--. 京都大学プレスリリース. 2022-11-11.Finding faults deeply stressful: First investigation of stress state below plate boundary fault of Tohoku earthquake. 京都大学プレスリリース. 2022-12-09.The Integrated Ocean Drilling Program conducted Expedition 343 and 343T, named the Japan Trench Fast Drilling Project (JFAST), to drill through the plate boundary fault that ruptured during the 2011 Mw 9.0 Tohoku earthquake in the area with the largest fault slip displacement near the Japan trench. Analyses of breakouts observed from borehole C0019B produced postearthquake stress states above the plate boundary fault between the subducting Pacific plate and overriding North American plate. To supplement the lack of stress data below the rupture zone of the earthquake, we conducted core-based three-dimensional stress measurements by the anelastic strain recovery (ASR) method using four whole-round core samples of sediments, of which three samples were located above, but one sample was located below the plate boundary fault in borehole C0019E. As a result of the stress measurements, the postearthquake three-dimensional stress magnitudes at ∼802 and ∼828 meters below seafloor (mbsf) across the plate boundary fault at ∼820 mbsf reveal a normal faulting stress regime. The differences between the three-dimensional intermediate principal stress and the minimum principal stress at the two depths are less than 1 MPa, suggesting a complete release of horizontal tectonic stresses that accumulated before the earthquake. In addition, the maximum horizontal stress S[Hmax] azimuth N115°E at ∼828 mbsf below the plate boundary fault from ASR measurements shows consistency with the S[Hmax] azimuth N139 ± 23°E (mean ± standard deviation) at ∼550–810 mbsf from breakout analyses above the fault. Taken together with the similar stress magnitudes at ∼802 and ∼828 mbsf, we interpret that the postearthquake stress states are almost the same in the sediments above and below the plate boundary fault. In other words, the stress state in terms of both orientation and magnitude is continuous across the fault. At a shallower depth of ∼177 mbsf in the slope sediments, the ASR stress data reveal a “stress state at rest”, which is likely free from tectonic effects of plate subduction, suggesting that the stress state was reset by the great coseismic displacement of ∼50 m slipped during the Tohoku earthquake

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10^(−7) to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse

Fault rheology beyond frictional melting

During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or “pseudotachylytes.” It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics

A novel physicological index for Driver\u27s Activation State derived from simulated monotonous driving studies

金沢大学大学院自然科学研究科Automobile driving in monotonous situations such as driving for long periods and/or travelling a familiar route may cause the lowering of the driver\u27s awareness level or what we term here as a Driver\u27s Activation State (DAS), resulting in an increased risk of an accident. We propose here to develop means with which to create an in-car environment so as to allow active driving, hopefully thus avoiding potentially dangerous situations. In order ultimately to develop a validated activation method, we firstly set out to examine physiological variables, including cardiovascular parameters, during simulated monotonous driving. Subsequently, we investigated the derivation of a suitable DAS index. During the experiment, a momentary electrical test stimulus of 0.5 s duration was applied at a rate of approximately once per 10 min to the subject\u27s shoulder to evoke a physiological responses. In 11 healthy male volunteers we successfully monitored physiological variables during the experiment and found particular patterns in the beat-by-beat changes of blood pressure in response to the electrical test stimulus. This finding, explained by autonomic activity balance, suggests that the patterns may be used as an appropriate and practicable index relevant to the Driver\u27s Activation State. © 2008 Elsevier Ltd. All rights reserved

Physiological measurements and analyses in motor sports: A preliminary study in racing kart athletes

金沢大学自然科学研究科The aims of this study were to assess methods for performing physiological measurements in motor sports, and to carry out a preliminary study in athletes participating in kart racing. The measurement of physiological variables in motor sports is practically challenging, largely due to the restricted space available for sensors and instrumentation and to movement artefacts from driver\u27s operations and car vibration, hence the paucity of publications. We performed a preliminary study of amateur racing kart athletes to assess the performance of basic measurement apparatus and to collect preliminary data on the possible influences of gravity on cardiovascular activity. We measured the vector magnitude of acceleration (G), instantaneous heart rate using electrocardiography, blood pressure with a wrist sphygmomanometer, eardrum temperature (taken as a measure of core body temperature) with a radiation thermometer, and lap time. The instrumentation functioned satisfactorily during karting on a racing circuit. In all participants during driving, heart rate was maintained at approximately 150 beats min 1. Time-frequency analysis of all heart rate data was performed to evaluate cardiac control mechanisms and this suggested that the observed rise in heart rate could be due to sympathetic acceleration. Furthermore, while we do not have sufficient data to draw firm conclusions, it is suggested that the rise in heart rate could be related to the G stresses to which the drivers were subjected. Cross-correlation analysis of the G and heart rate signals was performed in one participant and this showed a statistically significant correlation. We also found a statistically significant decrease in blood pressure (P<0.01) and a rise in eardrum temperature (P<0.01) immediately after the driving period. We conclude that although current sensors and instrumentation can allow basic monitoring of physiological variables in motor sport athletes, further developments are needed to allow more detailed investigations to be performed. Cardiovascular activity in response to G stresses warrants particular detailed investigation. © 2010 European College of Sport Science

Relationship between salivary Chromogranin-A and stress induced by simulated monotonous driving

金沢大学大学院自然科学研究科The purpose of the present study was to evaluate the use of salivary Chromogranin-A (CgA), which is already used in general as a mental stress marker, for studying the stressful situation created by simulated monotonous driving. After informed consent, 25 healthy male and female subjects were studied under constant environment-controlled conditions. We measured the following physiological variables: blood pressure (BP), cardiac output, total peripheral resistance (TPR), normalized pulse volume (NPV) as an index of alpha-adrenergic sympathetic activity to the finger arteriolar vessels, levels of cortisol and CgA during monotonous driving. The induced stress led to the expected decreases in NPV and increases in TPR and BP caused by peripherally related sympathetic acceleration. However, CgA levels were found to fall gradually in accordance with the gradual increase of subjective rating of stress (SRS) and significantly (p < 0.01) decreased over the period of the simulated monotonous driving. Our hypothesis for the gradual decrease of CgA levels during the simulated monotonous driving is as follows. CgA, catestatin and catecholamines are co-released into the extra-cellular environment. Peripheral sympathetic activity was accelerated by stress resulting from the simulated monotonous driving. Upon peripheral vessel constriction, an increase in TPR then increased BP which, in turn, activated catestatin. Consequently, secretion of CgA was blocked by the co-secreted catestatin from chromaffin granules. The results obtained strongly indicate that, although CgA has been reported as a possible marker of stress, CgA levels are not increased in the stressful situation of simulated monotonous driving. © 2009 International Federation for Medical and Biological Engineering

A simplified PCR assay for fast and easy mycoplasma mastitis screening in dairy cattle

A simplified polymerase chain reaction (PCR) assay was developed for fast and easy screening of mycoplasma mastitis in dairy cattle. Species of major mycoplasma strains [Mycoplasma (M.) bovis, M. arginini, M. bovigenitalium, M. californicum, M. bovirhinis, M. alkalescens and M. canadense] in cultured milk samples were detected by this simplified PCR-based method as well as a standard PCR technique. The minimum concentration limit for detecting mycoplasma by the simplified PCR was estimated to be about 2.5 × 103 cfu/mL and was similar to that of the standard PCR. We compared the specificity and sensitivity of the simplified PCR to those of a culture method. Out of 1,685 milk samples cultured in mycoplasma broth, the simplified PCR detected Mycoplasma DNA in 152 that were also positive according to the culture assay. The sensitivity and specificity of the simplified PCR were 98.7% and 99.7%, respectively, for detecting mycoplasma in those cultures. The results obtained by the simplified PCR were consistent with ones from standard PCR. This newly developed simplified PCR, which does not require DNA purification, can analyze about 300 cultured samples within 3 h. The results from our study suggest that the simplified PCR can be used for mycoplasma mastitis screening in large-scale dairy farms