The determination of rock friction at seismic slip rates (about 1 m s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip(1). Given the difficulty in determining friction by seismological methods(1), elucidating constraints are derived from experimental studies(2-9). Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built(4-6), quartz-built(3) and carbonate-built(7,8)) rocks and non-cohesive rocks (clay-rich(9), anhydrite, gypsum and dolomite(10) gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger(11,12) a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates(13,14) suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved

Although the mechanism responsible for cognitive deficits in stress-related neuropsychiatric disorders has been obscure, prefrontal cortical (PFC) dopaminergic dysfunction is thought to be involved. In animals, the mesoprefrontal dopaminergic system is particularly vulnerable to stress, and chronic stress induces working memory impairment. However, the relation between the working memory impairment and altered dopaminergic activity in chronically stressed rats is unclear. Furthermore, the change of dopaminergic activity in the PFC induced by stress is thought to express as a stress response, not as a disorder of organic function. We have previously reported that chronic stress administered by water immersion and restraint for 4 weeks induces a organic disorder such as hippocampal neuronal degeneration. We therefore examined whether chronically stressed (4 weeks) and recovered (10 d) rats show a working memory impairment caused by reduced dopamine (DA) transmission in the PFC, as suspected in the neuropsychiatric disorders. The stress impaired the spatial working memory evaluated by T-maze task and induced a marked reduction of DA transmission concomitant with an increase in DA D1 receptor density in the PFC. This memory impairment was sufficiently ameliorated by intra-PFC infusion of 10 ng SKF 81297, a D1 receptor-specific agonist. Pretreatment with intraperitoneal injection of 20 g/kg SCH 23390, a D1 receptor antagonist, reversed the SKF 81297 response. These results indicate that chronic stress induces working memory impairment through a D1 receptor-mediated hypodopaminergic mechanism in the PFC. These findings provide important information for understanding of the mechanisms underlying PFC dysfunction in stress-related neuropsychiatric disorders.Key words: chronic stress; working memory; prefrontal cortex; dopaminergic neuron; D1 receptor; cognitive deficit Exposure to stress is known to precipitate or exacerbate many neuropsychiatric disorders such as depression, Parkinson's disease, schizophrenia, and others (Schwab and Zieper, 1965;Mazure, 1995). All these disorders involve a working memory deficit caused by prefrontal cortical (PFC) dysfunction (Mattes, 1980;Weinberger et al., 1986;Deutch, 1993;Fibiger, 1995). Several antidepressants increase dopamine (DA) levels in the PFC (Tanda et al., 1994), and raising the DA level in patients with Parkinson's disease with L-3,4-dihydroxyphenylalanine improves their working memory deficit (Lange et al., 1992). These findings suggest that a reduced dopaminergic transmission in the PFC is responsible for the working memory deficits in the neuropsychiatric disorders.In animals, reduced PFC dopaminergic function or blockade of DA receptor in the PFC of monkeys and rats impairs working memory function (Brozoski et al., 1979;Simon et al., 1980;Bubser and Schmidt, 1990), which supports the observations in the neuropsychiatric disorders. In addition, an exposure to acute stress in monkeys or rats has been reported to produce working memory impairment, which can be blocked by...

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[1] High-velocity friction experiments on a fault gouge collected from the Nojima fault activated during the 1995 Kobe earthquake showed that the friction coefficient decreased from 0.63 to 0.18 over a slip weakening distance, D c , at high slip rates of $ 1 m/s. The dramatic drop in friction coefficient of more than 0.3 is consistent with that for the Kobe earthquake estimated from seismological observations. Experimentally determined D c becomes 5 m at a higher normal stress of 1.85 MPa, close to the order of magnitude of seismologically determined D c of 0.5 to 1 m. The difference in D c is not significant because the fracture energy consumed during frictional slip is the same order of 10 6 N/m for both cases. Here we show that frictional behavior of a fault during an earthquake can be predicted by conducting high-velocity friction experiments. Citation: Mizoguchi, K., T. Hirose, T. Shimamoto, and E. Fukuyama (2007), Reconstruction of seismic faulting by high-velocity friction experiments: An

The abnormal deposition of the amyloid ␤-protein (A␤) in the brain appears crucial to the pathogenesis of Alzheimer's disease (AD). Recent studies have suggested that highly amyloidogenic A␤ 1-42 is a cause of neuronal damage leading to AD pathogenesis and that monomeric A␤ 1-40 has less neurotoxicity than A␤ 1-42 . We found that mouse and human brain homogenates exhibit an enzyme activity converting A␤ 1-42 to A␤ 1-40 and that the major part of this converting activity is mediated by the angiotensin-converting enzyme (ACE).

[1] We examined two effects of the presence of clay in brittle deformations: the reduction in frictional strength and the impediment of across-fault fluid flow. Permeability was monitored during the sliding deformation of a gouge of various mixes of Na-montmorillonite powder and granular quartz along a 30°precut surface of Berea sandstone under 80 MPa of normal stress, 5 MPa of pore water pressure, and room temperature. The decrease in the friction coefficient of a gouge with increasing clay content was not simple, but showed a sharp drop at 50 vol.% clay content. The reduction in permeability due to deformation increased with increasing clay content from 0 to 24 vol.%, and a dramatic reduction of $2.5 orders of magnitude occurred at 18 and 24 vol.% clay content. However, in a gouge with more than 29 vol.% clay content, deformation reduced the permeability by only 0.5 orders of magnitude. Thus the transitional clay contents at which the clay dominated the properties of fault strength and fluid transport were 50 and 29 vol.%, respectively. These values almost agree well with values obtained using a model with an equal-sized clast (quartz) framework. The clay matrix can completely fill the pores sustained by a closest-packed quartz framework when the clay content reaches 29 vol.%, whereas the content required to fill the pores of a framework that can barely sustain quartz-quartz contact is 50 vol.%.

[1] To determine the processes responsible for slipweakening in clayey gouge zones, rotary-shear experiments were conducted at seismic slip rates (equivalent to 0.9 and 1.3 m/s) at 0.6 MPa normal stress on a natural clayey gouge for saturated and non-saturated initial conditions. The mechanical behavior of the simulated faults shows a reproducible slip-weakening behavior, whatever initial moisture conditions. Examination of gouge obtained at the residual friction stage in saturated and non-saturated initial conditions allows the definition of two types of microstructures: a foliated type reflecting strain localization, and a non-foliated type composed of spherical aggregates. Friction experiments demonstrate that liquid-vapor transition of water within gouge due to frictional heating has a high capacity to explain the formation of spherical aggregates in the first meters of displacement. This result suggests that the occurrence of spherical aggregates in natural clayey fault gouges can constitute a new textural evidence for shallow depth pore water phase transition at seismic slip velocity and consequently for past seismic fault sliding.

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