miocene pliocene boundary magnetostratigraphy at capo sopartivento calabria itlay a magnetostratigraphic study at capo spartivento calabria southern italy indicates that the miocene pliocene boundary lies in the lowest reversed interval chron 3r of the gilbert chron the magnetostratigraphic time frame gives an estimate close to 19 ka for the duration of individual limestone marl couplets that characterize the lithology the eight couplets within chron 3r indicate that the age of the miocene pliocene boundary is about 154 ka older than the age of the reversal at the top of chron 3r 4 78 ma we therefore estimate the age of this boundary as 4 93 ma which is 420 ka younger than that given by berggren et al and 100 ka older than that given by zijderveld et al the first appearance datums of globorotalia margaritae and globorotalia puncticulata are similarly estimated to have ages of 4 66 and 4 15 ma respectively the former being considerably younger than its first appearance in the open ocean

stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

lower pliocene polarity transitions from the suva marl fiji we present a paleomagnetic record of the lower cochiti polarity transition and new results from the lower and upper nunivak transitions obtained from the lower pliocene suva marl fiji 18 s 178 e this formation has yielded a well defined magnetostratigraphy that combined with 40ar 39ar ages from interbedded tuff beds provides excellent chronostratigraphic control clement et al 1997 we previously presented the upper cochiti and the upper and lower nunivak polarity transition records from this unit clement et al 1995 1996 new results were obtained from oriented block samples spanning these reversals each of these reversals was sampled at duplicate sections separated by 4 to 8 km the agreement between the records obtained from different sections suggests that the paleomagnetic records are not artifacts of local sedimentary disturbances or random degrees of incompletely removed overprints instead the similarities in these and other records of these same reversals from different types of paleomagnetic recorders suggest that they provide information about the behavior of the geomagnetic field as it reverses

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

frictional properties of natural gouges from longmenshan fault zone ruptured during the wenchuan mw7 9 earthquake abstract we investigated the properties of frictional sliding of natural gouges collected from longmenshan fault zone which ruptured during the wenchuan mw7 9 earthquake based on xrd analysis five gouge samples of different mineralogical assemblies and mineral contents are chosen for frictional sliding experiments with initial confining pressure of 50 mpa and at different temperatures from 25 c to 150 c to obtain the rate dependence of friction shearing rates are stepped up and down in the range of 0 0488 to 6 1 m s while the friction coefficient of most gouge samples decreases with the clay content following a general trend consistent with previous studies the organic matter bearing sample px 3 shows a much lower value than the prediction by the general trend indicating further strength reduction due to the 9 organic matter included we also found a significant effect of temperature on the sliding behavior of organic matter bearing and carbonate rich gouges when temperature increases to 150 c the px 3 sample with organic matter exhibits unstable oscillation that indicates velocity weakening frictional sliding behavior in contrast to the velocity strengthening behavior at lower temperatures the velocity dependence of carbonate rich samples px 1 px 2 with more than 50 wt carbonates is also sensitive to temperature and shearing rates and both samples have smaller velocity dependence of friction a b at higher temperatures the a b value of the px 2 sample with 80 carbonates even decreases to the velocity neutral point at 150 c and slow shearing rates based on the rate and state friction framework fast slip nucleation is possible for faults associated with the organic matter bearing gouge at 150 c whereas triggered seismic slips are possible in faults that include the carbonate rich samples which have a small a b value at 150 c the temperature dependent sliding behavior of carbonate dominant and organic matter bearing gouges probably provides a new clue to the problem of transition from shallow aseismic zone to seismic zone in subduction interfaces of the oceanic plate

thermo mechanical pressurization of experimental faults in cohesive rocks during seismic slip earthquakes occur because fault friction weakens with increasing slip and slip rates since the slipping zones of faults are often fluid saturated thermo mechanical pressurization of pore fluids has been invoked as a mechanism responsible for frictional dynamic weakening but experimental evidence is lacking we performed friction experiments normal stress 25 mpa maximal slip rate 3 ms 1 on cohesive basalt and marble under 1 room humidity and 2 immersed in liquid water drained and undrained conditions in both rock types and independently of the presence of fluids up to 80 of frictional weakening was measured in the first 5 cm of slip modest pressurization related weakening appears only at later stages of slip thermo mechanical pressurization weakening of cohesive rocks can be negligible during earthquakes due to the triggering of more efficient fault lubrication mechanisms flash heating frictional melting etc

structures and high velocity frictional properties of the pingxi fault zone in the longmenshan fault system sichuan china activated during the 2008 wenchuan earthquake abstract this paper reports on the internal structures of the pingxi fault zone near the northeastern end of the coseismic surface ruptures associated with the 2008 wenchuan earthquake the fault zone consists of a 50 80 cm wide fault core and several meter wide fault breccia zones the fault core contains yellowish gouge yg gray blackish gouge gbg black gouge bg and gray blackish fault breccia a coseismic slip during the wenchuan earthquake occurred within gbg in a slip zone of 24 9 mm in width high velocity friction experiments were conducted at normal stresses n of 0 45 2 50 mpa and slip rates v of 0 0014 2 09 m s yg and gbg exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient p to steady state friction coefficient ss over a slip weakening distance dc specific fracture energy eg for yg and gbg was 0 37 2 02 mj m2 of the same order of magnitude as the fracture energy estimated for natural earthquakes empirical equations describing the changes in p ss and dc in terms of n and v indicate that eg decreases with increasing n so that higher normal stress experiments will lead to eg lower than seismic values thus our experiments probably reproduced deeper seismic fault motion under dry conditions with respect to eg frictional behavior of bg is characterized by a sharp initial weakening subsequent strengthening to the second peak friction and slip weakening towards the steady state friction the initial weakening and strengthening seem to be caused by the formation of a very sharp slip zone 5 m in width and subsequent formation of a widely deformed zone a comparison of our data with reported results for other outcrops indicates that the high velocity frictional properties of the longmenshan fault system may be quite uniform the observed dramatic high velocity weakening must have promoted dynamic rupture propagation during the wenchuan earthquake

the upper and lower thvera sedimentary geomagnetic reversal records from southern sicily detailed paleomagnetic records of the upper and lower thvera polarity transitions have been determined from pliocenc marine marls in southern sicily the dominant magnetic mineral is fine grained magnetite the two transitions have vgp paths following a great circle passing south america and the west coast of north america there are strong indications that the vgp paths result from smoothing of the non antipodal stable directions before and after the transitions the upper thvera transitional record is preceded by two excursions and followed by a third one the first excursion is a sedimentary artefact caused by post depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment the upper thvera transition from sicily is compared with the record from calabria about 250 km away the two records show similarities as well as differences both transitions have identical vgp paths but in calabria the transition is recorded lower in the sediment the first and third excursions have different characters and the second one is not present apparently the registration of transitions of the earth s magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition

water vaporization promotes coseismic fluid pressurization and buffers temperature rise we investigated the frictional properties of carbonate rich gouge layers at a slip rate of 1 3 m s under dry and water saturated conditions while monitoring temperature at different locations on one of the gouge host rock interfaces all experiments showed a peak frictional strength of 0 4 0 7 followed by strong slip weakening to steady state values of 0 1 0 3 experiments which used a pore fluid with a constant drainage path to the atmosphere showed the development of a temperature plateau beyond 100 c contemporaneous with the dynamic slip weakening and consistent with thermodynamic considerations of ongoing vaporization of pore water upon pore fluid vaporization the pore pressure increases while the temperature is buffered endothermically such that the pore water moves along the liquid vapor transition curve in a pressure temperature phase diagram pore fluid phase transitions of this kind are expected to occur in natural earthquakes at relatively shallow crustal levels enhancing fluid pressurization while impeding the achievement of high temperatures therefore the operation of vaporization may help explain the low downhole temperature anomalies obtained shortly after large earthquakes

evidence of thermal pressurization in high velocity friction experiments on smectite rich gouges terra nova 22 347 353 2010 abstract thermal pressurization of pore fluid is one of the possible mechanisms responsible for dynamic weakening in landslides and earthquakes but to date has not been reproduced in the laboratory here we report high velocity experiments performed in a rotary shear friction apparatus on smectite rich gouges from the 1963 vaiont landslide italy the gouges were slid under 1 mpa normal stress for displacements up to 30 m and a slip rate of 1 31 m s 1 under room humidity and water saturated conditions sample dilatancy was observed in room humidity runs after 3 4 m of slip concomitant with an increase in normal stress and a decrease in shear stress mineralogical and microstructural investigations suggest that dilatancy resulted from expansion of the h2o released by the collapse of the smectite structure due to frictional heating of the slipping zone at t 200 c we conclude that sample dilatancy is due to thermal pressurization of the clay rich gouge

holocene paleoearthquake history on the qingchuan fault in the northeastern segment of the longmenshan thrust zone and its implications abstract although much work has been performed for faults with high slip rates little attention has been paid to low slip rate faults such as the longmenshan thrust zone ltz on which the wenchuan earthquake occurred the ltz is a long and matured fault that evolved during the mesozoic as a structural boundary but its quaternary activity had been considered insignificant the wenchuan earthquake on the central segment of the ltz and the following lushan earthquake on the southwestern segment illustrate the necessity of assessing the regional seismic potential around the northeastern extension of the ltz however little is known about its activity and paleoearthquake history to solve these problems we conducted paleoseismological trench excavations at two sites on the qingchuan fault to establish its paleoearthquake history only one and the latest event that occurred in the holocene is identified based on the radiocarbon dating the faulting event is constrained to occur between 4115 and 3820 b c and a long recurrence interval of greater than 6000 years is thus estimated judging from the matured fault structure of the qingchuan fault the latest event was likely to have ruptured the full length of the fault according to the empirical scaling laws between magnitude and rupture length the magnitude of the event is estimated to be mw 7 6 7 9 on the basis of the slip rate from gps measurements and the elapsed time since the last event it is estimated that a seismic moment equivalent to mw 7 5 has been accumulated on the qingchuan fault considering the increased coulomb failure stress and the shortened time of earthquake recurrence triggered by the wenchuan earthquake it is suggested a high seismic risk along the qingchuan fault and its neighboring area furthermore the slow strain buildup unadapted geometry and matured fault structure of the ltz may be the reason why it produces rare but large intraplate earthquakes

rainy periods and bottom water stagnation initiating brine accumulation and metal concentrations 1 the late quaternary a working hypothesis is proposed to account for the present accumulation of brines in isolated pockets of the ocean floor and for the formation of the underlying organic and metal rich sediments these are the tyro and bannock basins in the east mediterranean the red sea deeps and the orca basin in the northern gulf of mexico initiation of brine derived deposition in the red sea deeps and orca basin occurred between 12 000 and 8000 years b p this time bracket also encompasses the formation of the latest east mediterranean sapropel and the wettest global climate since the last glacial maximum this wet period first appeared in the tropics around 12 000 years b p then in the subtropical and middle latitudes during the same period the 23 000 year precession cycle brought the summer insolation of the northern hemisphere to its peak at 11 000 years b p with retreating northern hemisphere ice sheets the red sea deeps and the orca basin became anoxic during this humid period and metal rich sapropel deposition then began in contrast the tyro and bannock basins began accumulating a brine long before and persisted beyond this climatic stage the hypothesis involves two propositions 1 as in the eastern mediterranean sea marine anoxia was mainly the consequence of the large influx of continental runoff and local precipitation longer residence time of bottom waters so called stagnation in silled rimmed basins would have resulted from lower salinity at the sea surface in areas of deep water formation in the eastern mediterranean the red sea and the gulf of mexico and 2 miocene or older evaporites underlie these basins or outcrop on their flanks leaching from these evaporites was an ongoing process before the quasi stagnation phase but the initial leachate much less saline than the present brines was continuously flushed by bottom circulation the climate induced quiescence of bottom waters in these basins enabled the leachate to accumulate the feedback of stagnation by increased density progressively raised the salinity of entrapped bottom waters to the present brine concentration the high density has resisted brine removal by bottom circulation until present time long after cessation of the initiating wet period the brines therefore are stagnant fossil waters

high velocity frictional properties of alpine fault rocks mechanical data microstructural analysis and implications for rupture propagation abstract the alpine fault in new zealand is a major plate bounding structure that typically slips in m8 earthquakes every c 330 years to investigate the near surface high velocity frictional behavior of surface and borehole derived alpine fault gouges and cataclasites twenty one rotary shear experiments were conducted at 1 mpa normal stress and 1 m s equivalent slip velocity under both room dry and water saturated wet conditions in the room dry experiments the peak friction coefficient p p n of alpine fault cataclasites and fault gouges was consistently high mean p 0 67 0 07 in the wet experiments the fault gouge peak friction coefficients were lower mean p 0 20 0 12 than the cataclasite peak friction coefficients mean p 0 64 0 04 all fault rocks exhibited very low steady state friction coefficients ss room dry experiments mean ss 0 16 0 05 wet experiments mean ss 0 09 0 04 of all the experiments performed six experiments conducted on wet smectite bearing principal slip zone psz fault gouges yielded the lowest peak friction coefficients p 0 10 0 20 the lowest steady state friction coefficients ss 0 03 0 09 and commonly the lowest specific fracture energy values e g 0 01 0 69 mj m 2 microstructures produced during room dry and wet experiments on a smectite bearing psz fault gouge were compared with microstructures in the same material recovered from the deep fault drilling project dfdp 1 drill cores the near absence of localized shear bands with a strong crystallographic preferred orientation in the natural samples most resembles microstructures formed during wet experiments mechanical data and microstructural observations suggest that alpine fault ruptures propagate preferentially through water saturated smectite bearing fault gouges that exhibit low peak and steady state friction coefficients

high velocity frictional strength of longmenshan fault gouge and its comparison with an estimate of friction from the temperature anomaly in wfsd 1 drill hole this paper addresses the issue of whether high velocity friction experiments yield frictional strengths of fault materials that are consistent with the level of friction estimated from the postseismic temperature anomaly measured across a coseismic fault zone experiments were conducted on gouge composed of quartz dolomite illite albite and other clay minerals collected from a large outcrop of the yingxiu beichuan fault zone and from wenchuan earthquake fault scientific drilling project hole 1 drill cores in hongkou sichuan province china this fault is a major fault of the longmenshan fault system that caused the 2008 mw7 9 wenchuan earthquake all experiments revealed dramatic weakening at high velocities with peak friction coefficient p of 0 07 0 35 and steady state friction coefficient ss of 0 02 0 15 for wet gouge as compared with p 0 49 0 86 and ss 0 12 0 21 for dry gouge the average friction coefficients over a displacement of 5 5 m coseismic displacement extrapolated to the normal stress in the fault zones are 0 1 0 05 and 0 06 0 03 for dry and wet gouges respectively the average friction coefficients of dry and wet gouges are within the upper and lower bounds of friction coefficients estimated from the temperature profiles and there are overall agreements between the two sets of data that are completely independent dry and wet gouges are characterized by highly sheared slip zones often forming overlapping slip zone structures and by broad shear zones respectively wet gouge textures are perhaps closer to those of natural fault zone but repeated slip experiments are needed to determine the textural evolution of wet gouge

the age of the tortonian messinian boundary the tortonian messinian boundary is marked by the first occurrence datum fod of globorotalia conomiozea which is found all over crete in open marine marls with good palaeomagnetic properties within the framework of the miomar project the previously studied sections of langereis et al 1 have been extended and partly resampled here we present new magnetostratigraphic and biostratigraphic results from sections on eastern crete faneromeni central crete kastelli and western crete potamida and skouloudhiana supplemented by cyclostratigraphic data the recently developed geomagnetic polarity time scale ck92 of cande and kent 2 allows an unambiguous correlation of the polarity sequences on crete the fod of g conomiozea occurs in the reversed interval of anomaly c3bn lr this leads to a new age determination of 6 92 ma for the tortonian messinian boundary and a duration of 1 76 myr for the messinian a slightly modified version of ck92 if we use more recent age estimates provides an age of 7 10 ma and a duration of 1 78 myr respectively bipartite sedimentary cycles are distinctly present in the cretan sections studied assuming that these cycles are precession induced and using an average periodicity of 21 7 kyr enables us to independently estimate the duration of the successive individual polarity zones the astronomically derived durations of the cretan polarity zones are in good agreement with ck92 but are approximately 10 shorter

east pacific rise 18 19 s asymmetric spreading and ridge reorientation by ultrafast migration of axial discontinuities a detailed bathymetric side scan and magnetic survey of the east pacific rise out to a seafloor age of 1 ma has been carried out between 18 and 19 s it reveals that some left stepping axial discontinuities have been migrating southward at rates an order of magnitude faster than the spreading rates 1000 mm a or higher these rapid migration events have left on the nazca plate discordant features striking nearly parallel to the ridge axis a discontinuity with an offset of several kilometers has migrated in two stages at around 0 45 and 0 3 ma and has left two large discordant zones consisting of a series of unfaulted hummocky basins bounded to the east by short ridges oriented about n s oblique to the ambient 013 fabric the morphology and reflectivity characteristics of these discordant zones are akin to the overlap basins and abandoned ridge tips which make up the migration trails of large slowly migrating overlapping spreading centers between 18 35 and 19 03 s the ridge axis is flanked a few kilometers to the east by a prominent sedimented ridge previously recognized as a recently abandoned ridge axis the present ridge segment steadily deepens and narrows southward which suggests the abandoned ridge has been rafted onto the nazca plate during the ultrafast southward propagation of the ridge segment rather than by one discrete ridge jump by transferring pacific lithosphere to the nazca plate these migration events account for most of the asymmetric accretion observed faster to the east this process is consistent with the features common to asymmetric spreading namely the sudden onset or demise of asymmetric spreading and the ridge segment to ridge segment variability because the discordant zones left by these rapid migration events are near parallel to the ambient seafloor fabric they are unlikely to be detected by conventional bathymetry or magnetic surveys and so called ridge jumps may actually often represent ultrafast propagation of a ridge segment variations in fault azimuth with age show there has not been any significant change in spreading direction over the past 0 8 m y instead the counterclockwise trend of the east pacific rise relative to the brunhes matuyama reversal 0 78 ma mostly reflects that ultrafast propagation of ridge segments has transferred a larger amount of the pacific lithosphere to the nazca plate at 18 s than at 19 s in keeping with the regional features of the magnetic anomalies we propose that an 8 to 10 km left stepping discontinuity which was located between 17 and 17 30 s at 0 78 ma has been recently redistributed into the present staircase of small left stepping discontinuities between 16 and 19 s this smoothing of the ridge geometry probably occurred through repeated small lateral steps of the ridge segments inside of the discontinuities during ultra fast propagation episodes and may be the consequence of a significant replenishment of the magma reservoir between 17 and 17 30 s during the past 1 m y

the influence of ambient fault temperature on flash heating phenomena 1 recent high velocity friction experiments on room temperature rocks reveal a dramatic weakening caused by extreme frictional heating and thermal degradation of the strength of microscopic asperity contacts on a slip surface i e flash heating here we explore the effects of elevated ambient fault temperature up to that at the base of the earth s seismogenic zone on the flash heating behavior of quartzite westerly granite and india gabbro the experiments demonstrate that elevated ambient fault temperature causes 1 an increase in the characteristic weakening velocity for flash heating and 2 an increase in the friction coefficient at a given velocity above this characteristic weakening velocity these unexpected results are reconciled with flash heating theory when temperature specific values of various material parameters are incorporated in existing constitutive descriptions of flash heating our results suggest that constitutive equations for flash heating can be extrapolated with confidence to the elevated ambient temperatures of the seismogenic zone

co seismic ruptures of the 12 may 2008 ms 8 0 wenchuan earthquake sichuan east west crustal shortening on oblique parallel thrusts along the eastern edge of tibet abstract the m s 8 0 wenchuan earthquake which devastated the mountainous western rim of the sichuan basin in central china produced a surface rupture over 200 km long with oblique thrust dextral slip and maximum scarp heights of 10 m it thus ranks as one of the world s largest continental mega thrust events in the last 150 yrs field investigation shows clear surface breaks along two of the main branches of the ne trending longmen shan thrust fault system the principal rupture on the nw dipping beichuan fault displays nearly equal amounts of thrust and right lateral slip basin ward of this rupture another continuous surface break is observed for over 70 km on the parallel more shallowly nw dipping pengguan fault slip on this latter fault was pure thrusting with a maximum scarp height of 3 5 m this is one of the very few reported instances of crustal scale co seismic slip partitioning on parallel thrusts this out of sequence event with distributed surface breaks on crustal mega thrusts highlights regional ew directed present day crustal shortening oblique to the longmen shan margin of tibet the long rupture and large offsets with strong horizontal shortening that characterize the wenchuan earthquake herald a re evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau and require a re assessment of seismic hazard along potentially under rated active faults across the densely populated western sichuan basin and mountains

late gauss to early matuyama invasions of neogloboquadrina atlantica in the mediterranean and associated record of climatic change a well dated high resolution record of climatic change is presented for the late pliocene mediterranean principal component analysis on abundances of 14 planktonic foraminiferal species reveals a series of late gauss to early matuyama surface water cooling events which can be correlated with north atlantic glacial isotope stages 108 to 94 the abundance record of the benthic foraminifer trifarina angulosa suggests lowered bottom water temperatures at times of surface water cooling the record of surface water oxygen and carbon isotopes shows an inverse pattern with 18o maxima and 13c minima at times of cool sea surface temperature conditions concomitant decrease in p b value and increased admixtures of clastic material suggest that late gauss to early matuyama surface water cooling events in the mediterranean are accompanied with glacioeustatic sea level low stands major surface water cooling events are associated with invasions of neogloboquadrina atlantica this north atlantic mid to high latitude species is at 2 55 ma close to the gibraltar portal whereafter it could invade the mediterranean repeatedly during periods of climatic cooling until it disappears from all over the north atlantic and mediterranean at the end of glacial stage 96

paleomagnetic constraints on the initiation of uplift on the santa susana fault western transverse ranges california the plio pleistocene nonmarine saugus formation is widely exposed in the east ventura basin and the northern san fernando valley north and south of the santa susana fault in the east ventura basin the saugus is overlain by the pacoima formation magnetostratigraphy of the fine grained saugus and pacoima strata and the presence of the 0 76 ma bishop ash are used to calculate their average sedimentation rates 0 9 km m y in the east ventura basin and 1 1 km m y in the northern san fernando valley extrapolation of the saugus and pacoima sedimentation rates shows that they were deposited from about 2 3 to 0 5 ma both north and south of the santa susana fault the shift from remote to locally derived clasts marks the initiation of uplift of the santa susana mountains the extrapolated age of this boundary is about 0 7 0 6 ma

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

vaporization of fault water during seismic slip laboratory and numerical studies as well as field observations indicate that phase transitions of pore water might be an important process in large earthquakes we present a model of the thermo hydro chemo mechanical processes including a two phase mixture model to incorporate the phase transitions of pore water occurring during fast slip i e a natural earthquake in order to investigate the effects of vaporization on the coseismic slip using parameters from typical natural faults our modeling shows that vaporization can indeed occur at the shallow depths of an earthquake irrespective of the wide variability of the parameters involved sliding velocity friction coefficient gouge permeability and porosity and shear induced dilatancy due to the fast kinetics water vaporization can cause a rapid slip weakening even when the hydrological conditions of the fault zone are not favorable for thermal pressurization e g when permeability is high at the same time the latent heat associated with the phase transition causes the temperature rise in the slip zone to be buffered our parametric analyses reveal that the amount of frictional work is the principal factor controlling the onset and activity of vaporization and that it can easily be achieved in earthquakes our study shows that coseismic pore fluid vaporization might have played important roles at shallow depths of large earthquakes by enhancing slip weakening and buffering the temperature rise the combined effects may provide an alternative explanation for the fact that low temperature anomalies were measured in the slip zones at shallow depths of large earthquakes

sonic and gamma ray astrochronology cycle to cycle calibration of atlantic climatic records to mediterranean sapropels and astronomical oscillations a high resolution analysis of cyclical patterns in gamma ray and sonic logs of the lower pliocene sediments from the gulf of cadiz southern spain was carried out results suggest that these cycles can be successfully used for a bed to bed correlation with the global reference section for the astronomical time scale in capo rossello sicily cycle patterns were used to tune the logs to the astronomical solutions of j laskar the gamma ray and sonic cyclicity was interpreted in terms of precession induced oscillations of annual rainfall in southern spain that were in part responsible for the increasing input of freshwater into the mediterranean at times of sapropel formation we demonstrate that gamma ray and sonic astrochronology can be successfully used for interregional correlation and astronomical dating with errors not higher than 20 k y

shear induced graphitization of carbonaceous materials during seismic fault motion experiments and possible implications for fault mechanics abstract carbonaceous materials often concentrate in fault zones developed in pelitic rocks among carbonaceous minerals graphite is known as a lubricant and possibly plays a key role in frictional properties of the fault graphite reported from slip localized zones suggests that graphitization can occur during seismogenic fault motion thus we performed friction experiments on amorphous carbon and graphite to investigate how graphite forms in association with fault motion and how these carbonaceous minerals affect frictional properties of faults experiments were done at normal stresses of 0 5 2 8 mpa and slip rates of 50 m s to 1 3 m s in atmospheres of air and n 2 gas using rotary shear apparatuses xrd and tem analyses revealed that graphitization can indeed occur during seismogenic fault motion perhaps due to large shear strain short lived flash heating and stress concentration at asperity contacts even at low temperatures and pressures under anoxic environments we found large differences in steady state friction coefficient ss between graphite ss 0 1 and amorphous carbon ss 0 54 at low slip rate but amorphous carbon exhibits marked velocity weakening at slip rate above 10 mm s and its steady state friction reduces to the same level as that of graphite at a slip rate of 1 3 m s faults with amorphous carbon are not weak at low slip rates but they can become dynamically weak to foster fault motion during the generation of large earthquakes enriched graphite in fault zones can lubricate at all slip rates even at great depths and should receive more attention

global to regional nested grid climate simulations in the gfdl high resolution atmospheric model abstracta two way nested grid version of the geophysical fluid dynamics laboratory high resolution atmosphere model hiram has been developed that uses simple methods for providing nested grid boundary conditions and mass conserving nested to global communication nested grid simulations over the maritime continent and over north america were performed each at two different resolutions a 110 km mean grid cell width refined by a factor of 3 and a 50 km mean grid cell width refined by a factor of 2 nested grid simulations were compared against uniform resolution simulations and against reanalyses to determine the effect of grid nesting on both the modeled global climate and the simulation of small scale features orographically forced precipitation was robustly found to be simulated with more detail and greater realism in a nested grid simulation compared with when only the coarse grids were simulated alone tropical precipitation biases were reduced in the maritime continent region when a nested grid

high velocity frictional properties of clay rich fault gouge in a megasplay fault zone nankai subduction zone 1 we conducted high velocity friction experiments on clay rich fault gouge taken from the megasplay fault zone in the nankai subduction zone under dry and wet conditions in the dry tests dehydration of clay minerals occurred by frictional heating and slip weakening is related to thermal pressurization associated with water vaporization resulting in a random distribution of clay clast aggregates in the gouge matrix in the wet tests slip weakening is caused by pore fluid pressurization via shear enhanced compaction and frictional heating and there is a very weak dependence of the steady state shear stress on the normal stress the resulting microstructure reflects the grain size segregation in a granular fluid shear flow at high shear rates these results suggest that earthquake rupture propagates easily through clay rich fault gouge by high velocity weakening potentially leaving the microstructures resulting from the frictional heating or the flow sorting at high slip rates

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

experimental investigation of flash weakening in limestone abstract flash heating and weakening could operate during earthquake nucleation and propagation we performed 27 friction experiments in a compression torsion apparatus on ring shaped limestone samples at sub seismic to seismic slip rates 340 mm s centimetric displacements and normal stresses of 8 mpa friction decreases dramatically at slip rates of 50 150 mm s flash weakening was contemporaneous with a peripheral temperature rise of 90 c measured with an infrared camera the peripheral temperature yields a lower limit to the slipping zone temperature the decrease in friction may result from weakening of the asperity contacts due to decarbonation of calcite induced by 1 flash heating or 2 mechanically activated reactions however x ray powder diffraction and raman spectroscopy analyses do not reveal the presence of decarbonation products in the slipping zone instead white light interferometry and field emission scanning electron microscope observations reveal the presence of a smooth sliding surface made of nanometric particles the mechanical data can be fit by the rate and state dependent friction model or by a quadratic model the latter proposed for powder lubrication we conclude that flash heating and weakening and powder lubrication may operate together to decrease dynamic friction in limestone in experiments and for the conditions investigated here in nature

long eccentricity cycle in pliocene oceanic carbon reservoir a comparison between the mediterranean and the south china sea abstract as quantitative paleoclimate time series extend deeper into the geological past growing evidence indicates the extensive occurrence of the 400 kyr long eccentricity cycle in geological records the long cycles are best manifested in the marine carbon isotope as a series of 13 cmax which correspond to the long eccentricity s minima however it remains unclear how eccentricity affects the oceanic carbon reservoir to determine what processes are involved in generating the 400 kyr cycles one long eccentricity cycle in the late pliocene from 3 2 myr to 2 8 myr was examined in two sections respectively from the mediterranean and the south china sea the results indicate that the mediterranean section displays distinct precession cycles in all of the studied proxy time series and their amplitudes are modulated by eccentricity whereas the precession cycles and the eccentricity modulation are much weaker in the proxy sequences from the south china sea the difference is attributed to the fact that african monsoon was overwhelmingly dominated by precessional forcing and the mediterranean basin was isolated from glacial induced reorganizations of the global ocean whereas totally different conditions existed in the south china sea it may be inferred from the comparison that the 13 cmax originated largely from the global ocean and was unlikely caused by local basin factors at the long eccentricity maximum summer insolation reached a maximum at low latitudes and the intensified global monsoon changed the ocean carbon reservoir and the 13 c value because of the long residence time of carbon in the ocean 13 c changes in the global oceanic reservoir primarily occur on a 10 5 yr time scale with a smoothing effect in the lower frequencies the 400 kyr long eccentricity was pervasive at least in the cenozoic ocean but its expression was subject to spatio temporal variations particularly under the influence of the ice sheet development

impact of lateral boundary errors on the simulation of clouds with a nonhydrostatic regional climate model abstracta nonhydrostatic regional climate limited area model lam was used to analyze lateral boundary condition lbc errors and their influence on the uncertainties of regional models simulations using the fully compressible nonhydrostatic lam d nicam were compared against the corresponding global quasi uniform grid nonhydrostatic icosahedral atmospheric model nicam and a stretched grid counterpart s nicam by this approach of sharing the same dynamical core and physical schemes possible causes of model bias and lbc errors are isolated the simulations were performed for a 395 day period from march 2011 through march 2012 with horizontal grid intervals of 14 28 and 56 km in the region of interest the resulting temporal mean statistics of the temperatures at 500 hpa were generally well correlated between the global and regional simulations indicating that lbc errors had a minor impact on the large scale flows however the time varying statistics of the surface precipitation showed that the

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

extension and compression related basins in central italy during the messinian lago mare event abstract during the messinian lago mare event in the central mediterranean area compression and extension related basins developed as a consequence of the post tortonian evolution of the tyrrhenian apennines system all these syn tectonic sedimentary basins were characterized by different subsidence rates and sedimentary processes several sections located in different tectonic domains from the tyrrhenian to the adriatic margin of the apennine chain have been investigated s valentino in abruzzo citeriore roccamorice penscosansonesco roccacaramanico and le vicenne sections are located in compression related basins foreland basin system while the tolfa blera sections and the sedimentary succession of mondragone 1 well drilled in the garigliano coastal plain are located in extension related basins hinterland or back arc basins the recognition of ostracod assemblages with paratethyan affinities allows them to be referred to the messinian lago mare event loxoconcha djaffarovi zone this result allows us to consider the tyrrhenian rifting the accretion of the apennine thrust belt and the increase in subsidence rate during the flexuration of the foreland domain as synchronous processes due to the same geodynamical process taking into account the thicknesses of the analysed sedimentary basins different total subsidence rates have been computed for both the compression and extension related basins the syn rift basins that developed on the eastern margin of the northern tyrrhenian basin volterra val di fine and tolfa blera basins recorded a mean total subsidence rate of 1 25 mm a whereas higher subsidence rates affected the eastern margin of the central tyrrhenian basin 5 mm a garigliano coastal plain the differences in horizontal stretching and total subsidence rates that affected the tyrrhenian extensional area correspond to different migration rates of the apennine orogenic system in the northern 10 mm a and central apennines 40 mm a this difference in the total syn rift subsidence rate fits in well with the segmentation model of the tyrrhenian apennines system along a nne ssw lithosphere discontinuity which crosses the system from ancona northern apennines to the r selli lineament in the tyrrhenian basin

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

dynamic weakening of gouge layers in high speed shear experiments assessment of temperature dependent friction thermal pressurization and flash heating 1 the rotary shear of gouge demonstrates dramatic weakening at coseismic slip rates but the inherent variation in shear rate with radius of the rotary shear configuration prohibits determining friction constitutive properties from measures of whole sample response here representative results of rotary shear high speed experiments including both constant velocity tests 0 1 1 3 m s and constant acceleration tests 0 1 3 m s 0 05 and 0 1 m s2 are analyzed using a thermal mechanical and hydrologic finite element method fem model to constrain friction constitutive properties and test hypotheses of dynamic weakening by thermal pressurization and flash heating the observed frictional behavior of room dry gouge can be explained by using a state variable friction constitutive relation in which the friction coefficient is inversely proportional to temperature and by employing a two mechanism constitutive formulation in which the friction coefficient increases with temperature temperature strengthening at low temperatures and decreases with temperature temperature weakening at higher temperatures water dampened gouge displays a transient weakening during the early stages of constant acceleration tests fem analysis indicates the weakening could reflect thermal pressurization of pore water provided both the permeability of the gouge layer and the sealing capacity of the teflon sleeve used to contain the gouge during shear contribute to restricting fluid flow microstructural observations indicate that the dynamic weakening coincides with slip localization and temperature increase by frictional heating which are conditions that favor weakening by flash heating at steady state the relationship between slip rate and coefficient of friction by the fem model analysis is consistent with predictions of micromechanical models for weakening by flash heating

thermal pressurization and slip weakening distance of a fault an example of the hanaore fault southwest japan a controversy over the last decade is the large difference in the slip weakening distance d c between laboratory measured and seismically estimated values our numerical analyses of the thermal pressurization process based on measured transport properties of the hanaore fault zone in japan reveal that the process is effective for this fault and that d c becomes of the order of several decimeters to about 1 m when the width of the deformation zone is less than 10 20 mm this d c value is of exactly the same order as that determined seismically so thermal pressurization can be a mechanism for solving the d c paradox the thermal pressurization process effectively reduces the heat production rate and the temperature rise expected for this fault zone is at most about 600 c which is not high enough a temperature to melt rocks

early late pliocene biochronology and surface water temperature variations in the mediterranean a high resolution magnetobiostratigraphy is presented for the early late pliocene in sicily paleomagnetic measurements on samples from 100 stratigraphic levels provide an unprecedented high quality polarity sequence which extends from the upper reversed gilbert to the upper normal gauss subchron the resultant chronology for the early late pliocene provides ages for the following principal mediterranean bioevents 1 fodgloborotalia crassaformis at 3 40 ma 2 prolonged absence ofgloborotalia puncticulata between 3 38 and 3 16 ma 3 loduvigerina rutila at 3 16 ma 4 lodsphaeroidinellopsis seminulina at 3 07 ma 5 lodgloboquadrina altispira at 3 04 ma 6 lodcibicides italicus at 2 96 ma summer and winter surface water temperature estimates for the period 3 50 to 2 92 ma are based on the abundances ofglobigerinoides sacculifer andgloborotalia puncticulata in 111 samples with an average resolution of some 5000 years short term variations in temperature of the surface water and in colour and carbonate content of the sediment are primarily controlled by the equinoxal precession a higher seasonality during deposition of the grey coloured carbonate poor facies suggests that at that time the summer solstice occurred near perihelion whereas an inverse alignment occurred at the time of deposition of white coloured carbonate rich layers this phase relationship between the precession cycle and grey coloured layers is also valid for the sapropels which began to intercalate in the grey coloured layers at 2 94 ma long term changes in surface water temperatures include a warming between 3 38 and 3 18 ma followed by a cooling from 3 18 to 3 03 ma the warming of mediterranean surface waters at 3 38 ma is believed to be associated with the final closure of the isthmus of panama consequent strengthening of the gulf stream injected larger volumes of warm surface water into the north atlantic drift and eastern boundary current and this caused surface water temperatures in the mid to high latitude northeast atlantic and mediterranean to rise the subsequent climatic cooling at 3 18 ma is linked to a first stage of northern hemisphere continental ice growth

strain localization and the onset of dynamic weakening in calcite fault gouge abstract to determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates single slide and slide hold slide experiments were conducted on 2 3 mm thick layers of calcite gouge at normal stresses up to 26 mpa and slip rates up to 1 m s 1 microstructures were analyzed from short displacement 35 cm experiments stopped prior to and during the transition to dynamic weakening in fresh calcite gouge layers dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness strain is initially distributed across the full thickness of the gouge layer but within a few millimeters displacement the strain becomes localized to a boundary parallel high strain shear band c 20 m wide during the strengthening phase which lasts between 3 and 30 cm under the investigated conditions the shear band broadens to become c 100 m wide at peak stress the transition to dynamic weakening in calcite gouges is associated with the nucleation of micro slip surfaces dispersed throughout the c 100 m wide shear band each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite interpreted to result from grain welding driven by local frictional heating in the shear band by the end of dynamic weakening strain is localized to a single 2 3 m wide principal slip surface flanked by layers of recrystallized gouge calcite gouge layers re sheared following a hold period weaken nearly instantaneously much like solid cylinders of calcite marble deformed under the same experimental conditions this is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide reducing the effective gouge layer thickness to a few microns our results suggest that formation of a high strain shear band is a critical precursor to dynamic weakening in calcite gouges microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate the delayed onset of dynamic weakening in fresh calcite gouge layers particularly at low normal stresses may inhibit large coseismic slip at shallow crustal levels in calcite bearing fault zones

the origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

the crucial role of temperature in high velocity weakening of faults experiments on gouge using host blocks with different thermal conductivities we study the important role of temperature rise in the dynamic weakening of fault gouge at seismic slip rates by using host blocks composed of brass stainless steel titanium alloy and gabbro with thermal conductivities h of 123 15 5 8 and 3 25 w m k respectively our experiments are performed mostly on fault gouge collected from the longmenshan fault sichuan china consisting primarily of illite and quartz high velocity weakening of gouge becomes more pronounced as h decreases because the temperature in the gouge increases microstructure observations reveal welded slip zone material and more compact slip surfaces for the gouge deformed with low h host blocks which is probably caused by a sintering process indicative of higher temperatures these conclusions are supported by temperature calculation performed using the finite element method the observed differences in frictional behaviors deformation microstructures and calculated temperature demonstrate that temperature rise driven by frictional heating is essential in causing dynamic weakening of gouge at seismic velocities we show that our data are in good agreement with the flash heating model though thermochemical pressurization may also be important some of our experiments where nanoparticles are present but show negligible weakening demonstrate that the presence of nanoparticles alone is not sufficient to cause dynamic weakening of faults

neogene sapropels in the mediterranean a review for 50 years the existence of sapropels organic carbon rich sediments deposited within plio pleistocene sediments of the mediterranean sea has been known initially research concentrated on material recovered in relatively short gravity piston cores taken from the eastern basins where sequences were found to be well developed preserved and had extensive spatial coverage in the main previous studies concentrated upon establishing a workable stratigraphy spatial correlation of individual layers and determining the probable depositional mechanisms however despite a plethora of research papers some issues still remain unresolved this is in part due to a lack of agreement between investigators sampling and analytical short comings restricted sample size and the fact that in many instances like was not being compared with like recently the limit of sapropels in the western basin has been further extended as a result the palaeoceanographic palaeoclimate models which had previously been developed for deposition of sapropels in the eastern basin have been modified most recently strong links have been established between astronomical cyclicity and sapropel formation this review paper provides a summary of sapropel research to date and ongoing sapropel research in the mediterranean some of which appears in this thematic issue of marine geology it is fitting that this thematic issue of marine geology be dedicated to the memory of colette vergnaud grazzini and rob kidd who in many ways helped to initiate the resurgence in sapropel studies in the 1970s in the mediterranean perhaps in 50 more years we will know all of the answers 1999 elsevier science b v all rights reserved

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

dynamic weakening of smectite bearing faults at intermediate velocities implications for subduction zone earthquakes the hydrous clay mineral smectite which is pervasive in sediments on subducting oceanic plates is thought to weaken and stabilize subduction thrust faults however these frictional properties of smectite alone cannot explain the large coseismic slip in the vicinity of a trench here we performed friction experiments to demonstrate the rate dependence of friction at slip rates from 30 m s to 1 3 m s for water saturated smectite quartz mixtures with various smectite contents so as to shed light on the frictional response of smectite bearing faults at intermediate to high slip rates at slip rates of 30 to 150 m s the friction coefficients decreased gradually from 0 5 0 6 to 0 1 with an increase in smectite content from 20 to 50 wt in contrast at slip rates higher than 1 3 mm s friction exhibited marked slip weakening resulting in low friction coefficients of 0 1 0 05 even for low smectite contents roughly 30 wt drastic slip weakening occurred at smectite contents of 10 30 wt at slip rates of 10 mm s which is 1 to 2 orders of magnitude lower than the slip rate at which slip weakening was observed in previous experiments on various rock types the intermediate velocity weakening could be attributed to a rise in pore pressure caused by both shear enhanced compaction and microscopic thermal pressurization of pore fluids this process could weaken the fault even below seismic slip rates leading to an acceleration of fault motion and potentially facilitating large coseismic slip and a stress drop in the vicinity of a trench

the age of the miocene pliocene boundary in the capo rossello area sicily detailed correlations of magnetostratigraphy biostratigraphy and lithostratigraphy reveal that the basal pliocene is equally complete in the eraclea minoa and capo rossello sections sicily and the singa section calabria and that in accordance with the model of the pliocene flooding event in the mediterranean the deposition of the pelagic marls of the trubi formation started synchronously on sicily and in adjacent calabria in addition the data obtained from the trubi in the eraclea minoa section allows the age of the miocene pliocene boundary to be adjusted slightly from 4 83 4 84 1 to 4 86 ma because downward extrapolation of both sedimentation rate and average duration of small scale sedimentary cycles in the trubi yields this age for the boundary in this section linearly interpolated ages for the top of the sphaeroidinellopsis acme and the first substantial increase in globorotalia margaritae the fod of this species is non existent in the mediterranean pliocene at eraclea minoa arrive at 4 74 and 4 63 ma respectively because of the detailed magnetostratigraphy and the very accurate dating of the miocene pliocene boundary it is preferable to select the eraclea minoa section as the boundary stratotype rather than the capo rossello section finally this age of 4 86 ma for the miocene pliocene boundary suggests that the beginning of the pliocene is connected with the termination of a series of latest miocene glaciations and that the re establishment of open marine conditions in the mediterranean might be of glacio eustatic origin

importance of thermochemical pressurization in the dynamic weakening of the longmenshan fault during the 2008 wenchuan earthquake inferences from experiments and modeling 1 we determined the internal structure and mineral composition of the yingxiu beichuan fault zone at the zhaojiagou exposure and measured frictional and transport properties of the fault rocks collected to gain a better understanding of dynamic weakening mechanisms during seismic fault motion this fault is a major fault in the longmenshan fault system that caused the 2008 wenchuan earthquake the exposure studied is located midway along the surface rupture close to where the largest coseismic displacement occurred high velocity friction experiments reveal exponential slip weakening from a peak friction toward a steady state value slip weakening is more pronounced for water dampened gouge than dry gouge suggesting thermal pressurization the fault gouge has a very low permeability 10 21 m2 at 165 mpa effective pressure and is surrounded by fault breccia with a permeability of 10 19 to 10 17 m2 grading into less permeable fractured country rocks the fault zone thus exhibits a conduit barrier structure allowing fluid flow only in the breccia zone we numerically modeled coseismic slip weakening including thermal pressurization and mineral dehydration decarbonation basing our calculation on measured frictional and transport properties and on the slip history inferred for the wenchuan earthquake the results indicate that 1 thermochemical pressurization played an important role in causing dynamic slip weakening 2 the slip weakening distance is similar to the seismologically determined values and 3 pore pressures might have exceeded the normal stress thus maintaining temperatures below 600 c interestingly enough heat was generated to fully remove and thermally pressurize the interlayer water from smectite contributing an excess pore pressure of 6 mpa in addition we found that the incorporation of state dependent fluid properties predicts much more efficient fluid pressurization than using constant properties the dramatic weakening predicted probably offers a compelling explanation for the large coseismic displacement and slip acceleration observed near beichuan city

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

moisture related weakening and strengthening of a fault activated at seismic slip rates 1 from high velocity friction experiments on gabbro rock at a rate of 85 mm s we found that a fault with a thin gouge layer experienced slip weakening with a drop of about 80 in the friction coefficient at room humidity conditions the fault subsequently recovered its complete strength over an interval of several minutes after the slip terminated the strength recovery did not occur under dry n2 gas saturated condition this result can be interpreted as the interaction of moisture with gouge particles moisture drained weakening due to frictional heating and moisture absorbed strengthening due to cooling this new mechanism can cause dynamic weakening of faults which controls earthquake rupture propagation

role of the atmospheric mean state on the initiation of the madden julian oscillation in a tropical channel model tropical channel models defined as models that are global in the zonal direction but bounded in the meridional direction are particularly useful for simulating the madden julian oscillation mjo and understanding its physical and dynamical basis influences from the extratropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain mjo events this led to a hypothesis that multi year simulations using a tropical channel model would reproduce reasonable mjo statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses interestingly the mjo statistics in such a multi year simulation by a high resolution tropical channel model are not better than those from global climate models the error in the atmospheric mean state is found to be a possible reason for the poor mjo statistics in the simulation nevertheless even with a large error in the mean state the multi year simulation captures two mjo events previously found to be initiated by extratropical influences however the model does not reproduce a third event whose initiation is not directly influenced by the extratropics this implies that in the absence of dynamical interactions between the mjo and the lateral boundary conditions the error in the mean state could be sufficient to prevent the mjo initiation to explore this third mjo event further a series of sensitivity tests are conducted these tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed nor the initial conditions when the model is integrated 2 weeks prior to the mjo initiation the model captures this event when the mjo signal is already present in the initial conditions the use of high resolution sea surface temperature does not improve the simulation of the third mjo event a higher resolution nested domain covering the indo pacific warm pool region and including a cloud system resolving domain over the indonesian maritime continent has little effect on the mjo initiation over the indian ocean in 2 weeks the error in the simulation is comparable to the climate error the role of the simulated mjo on the mean state is also explored implications and limitations of these results are discussed

mineralogy porosity and fluid control on thermal conductivity of sedimentary rocks summary estimates of thermal conductivity of the main non clay and clay sedimentary minerals are presented especially for the case of argillaceous ones these estimates are averaged estimates based on the interpretation of laboratory conductivity porosity and mineralogy measurements performed on small volumes of the order of 100cm3 of water saturated moist and air saturated samples the sampling is representative of the main sedimentary rocks sandstones carbonates evaporites and shales and it is composed of samples considered as structurally isotropic material first we experimentally verify the first order control of mineralogy porosity and fluid content on bulk conductivity and we demonstrate that such influences may be predicted accurately using a geometric mean model as long as isotropic samples are used then we interpret the data using an inverse method in order to estimate the average mineral conductivities of the main non clay and clay minerals which give the best fit to the individual laboratory measurements through the geometric mean model the analysis is based on measurements on 82 non clay samples and 29 clay samples taken on oil well cores or cuttings on outcrops and on artificially recompacted samples estimates of average mineral conductivities returned by the inversion process for the main non clay minerals are similar to generally admitted values 7 7 w m k for quartz 3 3 w m i k for calcite 5 3 w m l k for dolomite and 6 3 w m k for anhydrite values obtained for the clay minerals are systematically lower than those obtained for non clay ones they are of the order of 1 9 w m k for illite and smectite 2 6 w m k for kaolinite and 3 3 w m l k for chlorite these estimates combined with porosity and mineralogy data are used with the geometric mean model in order to verify its first order validity for predicting thermal conductivity of small volumes of porous isotropic sedimentary rocks the bulk conductivity is predicted with an accuracy of the order of f10 per cent for moist or water saturated samples and of the order of f20 per cent for air saturated samples

convectively coupled kelvin and easterly waves in a regional climate simulation of the tropics this study evaluates the performance of a regional climate model in simulating two types of synoptic tropical weather disturbances convectively coupled kelvin and easterly waves interest in these two wave modes stems from their potential predictability out to several weeks in advance as well as a strong observed linkage between easterly waves and tropical cyclogenesis the model is a recent version of the weather research and forecast wrf system with 36 km horizontal grid spacing and convection parameterized using a scheme that accounts for key convective triggering and inhibition processes the domain spans the entire tropical belt between 45 s and 45 n with periodic boundary conditions in the east west direction and conditions at the meridional lower boundaries specified based on observations the simulation covers 6 years from 2000 to 2005 which is long enough to establish a statistical depiction of the waves through space time spectral filtering of rainfall data together with simple lagged linear regression results show that both the horizontal phase speeds and three dimensional structures of the waves are qualitatively well captured by the model in comparison to observations however significant biases in wave activity are seen with generally overactive easterly waves and underactive kelvin waves evidence is presented to suggest that these biases in wave activity which are also correlated with biases in time mean rainfall as well as biases in the model s tropical cyclone climatology stem in part from convection in the model coupling too strongly to rotational circulation anomalies nevertheless the model is seen to do a reasonable job at capturing the genesis of tropical cyclones from easterly waves with evidence for both wave accumulation and critical layer processes being importantly involved

long term temperature records following the mw 7 9 wenchuan china earthquake are consistent with low friction this is the publisher s final pdf the published article is copyrighted by the geological society of america and can be found at http geology gsapubs org

tropical cyclone activity in nested regional and global grid refined simulations the capacity of two different grid refinement methods two way limited area nesting and variable mesh refinement to capture northwest pacific tropical cyclone tc activity is compared in a suite of single year continuous simulations simulations are conducted with and without regional grid refinement from approximately 100 20 km grid spacing over the northwest pacific the capacity to capture smooth transitions between the two resolutions varies by grid refinement method nesting shows adverse influence of the nest boundary with the boundary evident in seasonal average cloud patterns and precipitation and contortions of the seasonal mean mid latitude jet variable mesh on the other hand reduces many of these effects and produced smoother cloud patterns and mid latitude jet structure both refinement methods lead to increased tc frequency in the region of refinement compared to simulations without grid refinement although nesting adversely affects tc tracks through the contorted mid latitude jet the variable mesh approach leads to enhanced tc activity over the southern indian and southwest pacific basins compared to a uniform mesh simulation nesting on the other hand does not appear to influence basins outside the region of grid refinement this study provides evidence that variable mesh may bring benefits to seasonal tc simulation over traditional nesting and demonstrates capacity of variable mesh refinement for regional climate simulation

the rossello composite a mediterranean and global reference section for the early to early late pliocene a high resolution magnetostratigraphy planktonic foraminiferal biostratigraphy and cyclostratigraphy is presented for the pliocene trubi marls in the punta di maiata section on sicily the integrated stratigraphy of the rossello composite section of hilgen 1 newslett stratigr 17 1987 is thereby completed this composite section provides an unprecedented high quality reference section for the early to early late pliocene containing a continuous sequence ranging from below the thvera subchron into the matuyama chron 4 86 2 45 ma the punta di maiata section extends from the sidufjall subchron of the gilbert into the gauss chron 4 50 3 30 ma linear interpolation between paleomagnetic datum planes in this section yields first order age estimates of 3 72 0 01 and 3 59 0 01 ma for the last common occurrence lco and the actual last occurrence lo of globorotalia margaritae in addition this age of 3 59 ma provides an accurate age for the zanclean piacenzian z p boundary provided the lo of g margaritae is maintained as a criterion to define this boundary in the mediterranean irrespective however of the criterion used the punta di maiata and punta piccola subsections of the rossello composite are at present the most suitable sections to be designated as stratotypes for the z p boundary the global significance of the rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the trubi sedimentary cycles with the astronomical record

calcareous plankton biostratigraphy and biochronology of the pliocene lower pleistocene succession of the capo rossello area sicily abstract in the first part of this paper we present the calcareous nannofossil biostratigraphy of the capo rossello section sicily which suggests that a sedimentary gap exists at the contact between the trubi and the overlying monte narbone formation close to the top of the proposed zanclean stratotype this suggestion is supported by the planktonic foraminiferal results and field observations in contrast the transition from the trubi to the monte narbone formation is well exposed gradational and biostratigraphically continuous in the nearby section of punta piccola a composite of the capo rossello and punta piccola sections serves as a good biostratigraphic reference for the pliocene of the mediterranean in a second part of this paper we have attempted to update the mediterranean pliocene time framework by integrating all of the available biostratigraphic biochronologic chronostratigraphic paleomagnetic and radiometric data

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

new data from hadar ethiopia support orbitally tuned time scale to 3 3 ma support for the astronomically calibrated geomagnetic polarity time scale is provided by new 40ar 39ar dating and magnetostratigraphic data from the hadar formation ethiopia three tuffs and a basalt flow at hadar span the mammoth subchron of the gauss chron and range in age from 3 18 0 01 to 3 40 0 03 ma interpolation of sediment accumulation rates in two magnetostratigraphic sections yields an estimated age range of 3 30 0 02 to 3 21 0 01 ma for the mammoth subchron closely coinciding with orbitally based predictions of 3 33 to 3 22 ma rather than with previous estimates of 3 15 to 3 05 ma

magnetostratigraphy and paleontology of ait kandoula basin high atlas morocco and the african european late miocene terrestrial fauna exchanges abstract a magnetostratigraphic study has been carried out on a middle miocene to upper pliocene lacustrine sedimentary deposit in the central part of the ait kandoula basin which contains micromammal faunas and is situated in the southern high atlas morocco in total 113 samples were subjected to paleomagnetic analysis 60 out of the 113 studied samples representing 52 different stratigraphic levels yielded a paleomagnetic direction and at least the polarity could be recognized in 42 specimens eleven specimens were submitted to af demagnetization the mean direction for normal polarity samples was d 349 4 i 50 7 n 36 95 4 5 k 27 and for reversed polarity samples d 191 2 i 53 4 n 16 95 12 32 k 9 these results yielded a polarity sequence which we interpret as spanning from chron c5n 2n to the beginning of chron c3n 4n this interpretation relies on biostratigraphic data previously proposed for a part of the continental fauna found in the basin this result is in agreement with the 40ar 39ar dating previously carried out on a volcanic ash layer which provided an age of 5 9 0 5 ma 1 and which is shown here to be reversely magnetized this layer is correlated here with the reverse polarity zone corresponding to chron c3r biostratigraphic studies on the same section have shown that the micromammal levels extend here only from middle vallesian to upper turolian upper miocene four localities have yielded western european species of micromammals indicating trans mediterranean terrestrial faunal exchanges between these two continents during the late miocene the european murid rodent occitanomys is recorded for the first time in north africa in level 8 of the afoud section an age younger than 5 32 ma being assigned to this level by the present study level 1 of the same section yields the lagomorph prolagus cf michauxi with an age of 6 1 ma the magnetostratigraphic data suggest therefore that the beginning of terrestrial faunal exchanges between north africa and western europe took place in subchron c3an 1n at about 6 1 ma some 0 4 myr before the beginning of the messinian salinity crisis

mediterranean neogene stratigraphy development and evolution through the centuries the mediterranean area in general and italy in particular played an important role in developing the principles of stratigraphy since the early days of geological thinking in the middle of the 19th century there was a rush to name all the intervals of the stratigraphic column at that time when invertebrate palaeontology was the principal source of information on the relative age of the rock units dozens of stage names were created for the neogene only a few of these stage names survive and are accepted worldwide as langhian serravallian tortonian messinian zanclean and piacenzian in the later part of the 19th century and in the first decades of the 20th century a wealth of new data was made available by extensive palaeontological studies but the correlation potential of the fossil faunas was constrained poorly and understood less leading to the development of a floating stratigraphy the situation improved after world war ii when micropalaeontology underwent a fast development the creation of common stratigraphic guidelines the introduction of the stratotype concept followed by the golden spike concept global stratotype section and point combined with the application of multiple stratigraphic methodologies especially palaeomagnetic stratigraphy or magnetic polarity time scale astrocyclostratigraphy or astronomical time scale resulted in new scenarios a turning point may be located around 1970 soon after the beginning of the deep sea drilling project which greatly contributed to the development of a new approach to neogene stratigraphy now all the global stratotype sections and points for the neogene stages are being defined by multiple criteria with precise definitions in terms of magnetic polarity time scale and astronomical time scale the rossello composite section in southern sicily is the template for the late neogene stratigraphy with the best time resolution provided by astronomical forcing to complete the planned study the same criteria have to be applied downwards and upwards

flash weakening of serpentinite at near seismic slip rates 1 to investigate the processes responsible for dynamic frictional weakening in antigorite serpentinite we conducted single velocity and velocity stepping friction experiments at slip rates v from 0 01 to 0 4 m s 1 sliding displacements up to 40 mm and a normal stress of 5 mpa single velocity experiments demonstrate an approximately 1 v dependence of friction on velocity above a characteristic weakening velocity vw 0 1 m s 1 consistent with theoretical predictions for flash heating and subsequent weakening of asperities velocity stepping experiments impose stepwise increases in slip rate show stepwise weakening at slip rates above vw scanning electron microscopy of experimental fault surfaces reveals nanoparticle gouge textures at raised sites 10 m in diameter in tests that exhibit dramatic weakening furthermore x ray diffraction analyses of fault gouge from the sliding surface document the formation of significant talc in these tests indicating that weakening temperatures reached 500 c 700 c in contrast no talc is observed in samples for which v remained significantly below vw the observed value for vw is consistent with published microphysical models for flash weakening when independent constraints on the thermal stability and contact strength of antigorite are considered finally while serpentinite displays velocity strengthening behavior at plate tectonic slip rates our results indicate that seismic ruptures propagating into serpentinized regions in the shallow lithosphere may trigger seismicity or slow earthquakes after limited amounts of displacement

paleomagnetic evidence for a pleistocene clockwise rotation of the calabro peloritan block southern italy abstract a paleomagnetic study of marine marls of early pliocene age and clays of late pliocene to middle pleistocene age from sites along the ionian coast spartivento basin and catanzaro depression of calabria and from sites along the tyrrhenian coast of both calabria and sicily was carried out to determine the amount and timing of tectonic rotation of the underlying calabro peloritan block the magnetisations of the lower pliocene trubi marls have maximum blocking temperatures indicating the presence of magnetite these lower pliocene sediments as well as the younger upper pliocene lower pleistocene clays of this area reveal consistent clockwise rotations of 10 20 there is evidence for a uniform 15 clockwise rotation of the entire calabro peloritan block during the middle pleistocene this is opposite in sense of rotation to the earlier established 23 counterclockwise rotations for the southern apennines but the timing is the same between 0 7 and 0 2 ma the tectonic rotations occur 1 myr after the major phases of extension in the southeastern part of the tyrrhenian basin but simultaneously with the onset of major uplift of the block

flash heating and local fluid pressurization lead to rapid weakening in water saturated fault gouges coseismic fault displacement is quite large at shallow depths in some earthquakes and it implies that fault gouges and sediments have extremely low dynamic friction during seismic slip however the dynamic weakening mechanisms of gouges under wet conditions are still not well constrained here we present direct evidence for the occurrence of flash heating and local fluid pressurization in water saturated gouges by performing low to high velocity v 10 m s to 1 m s friction experiments in a pressure vessel under conditions specially designed to suppress weakening effects of bulk thermal and compaction induced pressurization the tested gouges exhibit transition from velocity strengthening to drastic velocity weakening as slip rates increase strong dynamic weakening starts to occur at v 0 04 m s at the initiation of sliding 0 1 m which is much more efficient than previously reported in terms of the weakening velocity and distance furthermore the onset of weakening is always accompanied by an instantaneous dilatancy 10 25 m which is much larger than that observed in dry tests and in contrast with gradual changes displayed in the wet tests without dynamic weakening numerical modeling integrated with microstructural observation reveals that bulk thermal pressurization cannot explain the experimental results while flash weakening triggered by vaporization of water layers on around asperity contacts and the resultant local fluid pressurization may be responsible for the observed rapid weakening concomitant with instantaneous dilatancy given high efficiency of such weakening process fluid infiltrated faults could be weakened more rapidly than previously recognized during seismic slip

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

plate motions crustal and lithospheric mobility and paleomagnetism prospective viewpoint the shift in viewpoint from a static to a mobilistic solid earth as brought about by paleomagnetism opened many new directions of research that continue to be exciting today and hold prospects for an exciting future here five topics of current research on earth s mobilistic surface are reviewed and their future directions discussed first dividing earth s solid surface into two domains 1 nearly rigid plate interiors and 2 plate boundaries some of them very wide leads to a review and discussion of the kinematics of wide plate boundaries many more adjustable parameters will be needed to describe the complex kinematics of plate boundaries which cover 15 of earth surface than the few dozen parameters needed to describe the kinematics of plate interiors which cover 85 of earth s surface second the question of the degree of rigidity of plate interiors is discussed the integral of the velocity gradient across plates interiors is at least a few hundredths or tenths of millimeters per year and in several well determined cases less than 2 or 3 mm yr future investigations will no doubt be aimed at narrowing these limits and to expanding the area of earth s surface over which limits are known third space geodetic data mainly from very long baseline inter ferometry satellite laser ranging and the global positioning system have demonstrated a remarkable similarity of velocities of stable plate interiors averaged over a few to a dozen years with plate velocities averaged over a few million years already however significant differences of a few millimeters per year are emerging and the tectonic and dynamic significance of these differences need to be evaluated fourth despite more than two decades of investigation the question of how fast hotspots move relative to one another is still a contentious issue one group of researchers maintains that maximum speeds are 3 mm yr whereas another maintains that speeds are 10 20 mm yr or more the differences cannot be reconciled until the uncertainties in plate reconstructions relative to hotspots are systematically and properly incorporated into analyses of hotspot motion fifth paleomagnetists have estimated true polar wander over the past 200 myr by equating it with the apparent polar wander of hotspots however the possible motion among hotspots and the neglect of the uncertainties in reconstructions relative to the hotspots have left these analyses unconvincing further progress requires the incorporation of these uncertainties a possible exception is the apparent polar wander of the hotspots over the past 10 20 myr or less which requires only small adjustments for plate motion and has presumably smaller uncertainties due to plate reconstructions the cause of this apparently significant geologically recent shift of the pole is poorly understood compared with the rate and direction of the secular shift of the pole observed this century from the international latitude service and for 1976 to 1994 from space geodetic data the paleomagnetically observed shift is unlikely to be due to the removal of northern hemisphere midlatitude ice sheets which is the commonly accepted explanation for the shift observed over the past century i speculate instead that the apparently rapid uplift of the tibetan plateau sometime during the past 10 20 myr is at least partly responsible for the geologically recent shift of the pole finally i conclude that the theory of plate tectonics has provided a framework that leads naturally to further quantification of the kinematics and deformation of earth s solid surface chiefly because of the key assumption of the rigidity of plate interiors which permits specific predictions to be made this revolution in quantification still has far to go and holds exciting prospects for future tectonic studies

geophysical study of the east pacific rise 15 n 17 n an unusually robust segment bathymetric side scan sonar magnetic and gravity data from the east pacific rise epr between 15 and 17 n are used to establish the spreading history and examine melt delivery to an unusually robust spreading segment the axial ridge between the orozco transform fault 15 30 n and the 16 20 n overlapping spreading center osc has an average elevation of 2300 m which is 300 m shallower than typical epr depths and its cross sectional area is double the average value for the northern epr the total opening rate is 86 km myr but the inflated segment appears to have spread faster to the east by more than 20 since 0 78 ma the orientation of magnetic isochrons and lineaments in the side scan sonar indicates a 3 counterclockwise rotation of the spreading direction since 1 8 ma c2 and reflects a change in the pacific cocos plate motion the side scan lineaments also show that the percentage of inward facing faults 83 and the spacing between faults 1 5 km are consistent with the spreading rate dependence shown by carbotte and macdonald 1994 however the mean fault length 4 8 km is 1 5 km shorter than expected for the spreading rate and suggests that extensive off axis volcanism has draped the faults gravity analysis shows that the inflated segment has a 12 mgal bull s eye shaped low in residual mantle bouguer anomaly we offer several possible end member models for the anomaly including a prism of 10 partial melt in the mantle and lower crust or a crustal thickness anomaly of 2 25 km kinematic modeling that is based on structure and magnetic data suggests that two large magmatic pulses occurred at approximately 0 8 ma and 0 3 ma and have reshaped the plate boundary geometry and inflated the segment

thermal decomposition of serpentine during coseismic faulting nanostructures and mineral reactions abstract this paper reports a detailed characterization of an antigorite bearing serpentinite deformed at seismic slip rate 1 1 m s in a high velocity friction apparatus micro nanostructural investigation of the slip zone 200 m thick revealed a zonal arrangement with a close juxtaposition of horizons with significantly different strength respectively consisting of amorphous to poorly crystalline phases with bulk anhydrous composition close to starting antigorite and of highly crystalline assemblages of forsterite and disordered enstatite 200 nm in size and in polygonal like nanotextures the slip zone also hosts micro nanometre sized cr magnetite grains aligned at low angle with respect to the slipping surface and inherited from the host serpentinite overall observations suggest that frictional heating at asperities on the slipping surface induced a temperature increase up to 820 1200 c in agreement with flash temperature theory responsible for serpentine complete dehydration and amorphization followed by crystallization of forsterite and enstatite under post deformation static conditions the results of this study may provide important keys for the full comprehension of the mechanical behaviour and of the possible geodynamical role of serpentinite hosted faults through the seismic cycle

confirmation of the astronomical calibration of the magnetic polarity timescale from sea floor spreading rates the dating of the history of reversals of the earth s magnetic field since the jurassic period has been based primarily on radiometric dating of a small number of reversals with most ages of individual reversals interpolated or extrapolated on the basis of the widths of marine magnetic anomalies recently however pliocene and pleistocene reversals have been dated by an entirely independent method which relies on correlating climate proxies such as oxygen isotope ratios in sediments with calculated variations of the earth s orbit and inclination1 4 the dates obtained from this astronomical calibration are 3 8 older than radiometrically calibrated ages published between 1979 and 1989 see for example refs 5 and 6 although recent dating by the 40ar 39ar method tends to confirm the astronomical calibration7 10 at least for the past 3 3 myr here i use sea floor spreading rates determined from high precision plate rotation solutions for five plate pairs to test the astronomically calibrated timescale over the past 5 32 myr the results suggest that the errors in the astronomical calibration are no greater than 0 02 myr and also show that spreading rate can remain constant for several million years even for fast moving plates

the role of the mediterranean region in the development of sedimentary geology a historical overview the mediterranean region source of so much knowledge in the world is the site of major advances in sedimentary geology in addition to its economic and cultural richness the geological and geographic diversity of the region plus its active geological processes have long stimulated indigenous scholars along with attracting talented outsiders such as steno lyell walther kuenen and bagnold since classical hellenic times debates about the origin of fossils and the changing positions of sea level served as catalysts for studies of sediments sedimentary rocks and ancient life the presence of geologically young and easily interpreted marine shell beds in many mediterranean coastal areas adjacent to their modern analogues was a particular stimulus for progress in sedimentary geology for example the very advanced stratigraphic ideas of leonardo da vinci expressed solely in his unpublished notebooks impeding progress was the geological complexity of facies faunas and structure in the circum mediterranean alpine belts once the secrets of these were unlocked however the mediterranean region became the source of major discoveries about syn sedimentary tectonics carbonate platforms pelagic and anoxic sediments turbidites evaporites aeolian processes cyclostratigraphy magnetic stratigraphy and impact events in many of these mediterranean discoveries the critical element is the occurrence of extensive mesozoic cenozoic pelagic successions whose precise age dating was made possible by pioneering biostratgraphic studies using microfossils

friction properties and deformation mechanisms of halite mica gouges from low to high sliding velocities the evolution of friction as a function of slip rate is important in understanding earthquake nucleation and propagation many laboratory experiments investigating friction of fault rocks are either conducted in the low velocity regime 10 8 10 4 ms 1 or in the high velocity regime 0 01 1 m s 1 here we report on the evolution of friction and corresponding operating deformation mechanisms in analog gouges deformed from low to high slip rates bridging the gap between these low and high velocity regimes we used halite and halite muscovite gouges to simulate processes governing friction active in upper crustal quartzitic fault rocks at conditions accessible in the laboratory the gouges were deformed over a 7 orders of magnitude range of slip rate 10 7 1 m s 1 using a low to high velocity rotary shear apparatus using a normal stress of 5 mpa and room dry humidity microstructural analysis was conducted to study the deformation mechanisms four frictional regimes as a function of slip rate could be recognized from the mechanical data showing a transitional regime and stable sliding 10 7 10 6 m s 1 unstable sliding and weakening 10 6 10 3 m s 1 hardening 10 2 10 1 m s 1 and strong weakening 10 1 1 m s 1 each of the four regimes can be associated with a distinct microstructure reflecting a transition from mainly brittle deformation accompanied by pressure solution healing to temperature activated deformation mechanisms additionally the frictional response of a sliding gouge to a sudden acceleration of slip rate to seismic velocities was investigated these showed an initial strengthening the amount of which depended on the friction level at which the step was made followed by strong slip weakening 2016 elsevier b v

integrated stratigraphy and astronomical tuning of the serravallian and lower tortonian at monte dei corvi middle upper miocene northern italy an integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy and cyclostratigraphy is presented for the serravallian and lower tortonian part middle upper miocene of the monte dei corvi section located in northern italy the detailed biostratigraphic analysis showed that both the discoaster kugleri acme and the first influx of neogloboquadrina acostaensis are recorded at monte dei corvi these events which passed unobserved in previous studies play an important role in delineating the serravallian tortonian boundary thermal and alternating field demagnetization revealed a characteristic low temperature component marked by dual polarities the resultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the gpts ranging from c5n 2n up to c4r 2r unfortunately the lower part of the section including the serravallian tortonian boundary interval did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervals and a single normal interval are recorded using sedimentary cycle patterns in combination with the calcareous plankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping and previously tuned section of monte gibliscemi on sicily the monte dei corvi section is dated astronomically by calibrating the basic small scale sedimentary cycles to the precession and 65 n lat summer insolation time series of the la93 solution following an initial tuning of larger scale cycles to eccentricity an almost perfect fit is found between the cycle patterns and intricate details especially precession obliquity interference in the insolation target between 8 5 and 10 ma the tuning to precession remains robust for most intervals back to the base of the section dated at 13 4 ma and shows that the section is continuous apart from a possible short hiatus in the tortonian it provides accurate astronomical ages for all sedimentary cycles calcareous plankton events polarity reversals and ash layers and marks a significant improvement of the recently proposed astronomical calibrations of the monte dei corvi section and of parallel sections in the mediterranean astronomical ages for the ancona and respighi ashbeds are significantly older than previously reported 40 ar 39 ar biotite ages even if the revised older age for the fct san dating standard of 28 02 ma is applied the astronomical dating of the magnetic reversals in the monte dei corvi section results in the completion of the astronomical polarity time scale for the last 13 myr the monte dei corvi section has recently been proposed as the stratotype section for the serravallian tortonian boundary despite the moderate to

thermochemical pressurization of faults during coseismic slip 1 during earthquakes frictional heating on the fault plane induces a temperature rise and thus a pore pressure rise which is known as thermal pressurization tp coseismic mineral dehydrations may occur because of this temperature increase and are included within the tp framework dehydrations are modeled as a source term for pore pressure because of the total volume change and as a sink term for temperature because they are endothermic the reaction occurs within the slipping zone when a threshold temperature ts is reached dehydration reaction kinetic is modeled using a first order reaction rate using energy and fluid mass conservation we derive analytically the equations of evolution of pore pressure temperature and reaction extent in the undrained adiabatic case using a constant reaction rate we investigate the values of the kinetic rate constant required to produce a significant effect which are much higher than laboratory data reported in the literature on clay serpentine and phyllosilicate dehydration we show however that such high values can be reached if the temperature dependency of the rate constant is taken into account next we include fluid and heat transport and use an arrhenius law to calculate the rate constant as a function of temperature the subsequent set of differential equations is then solved numerically the main effect of dehydration reactions is an increase of pore pressure and a stabilization of the temperature during slip we explore a wide range of parameters in order to determine in which cases dehydration can be considered as a nonnegligible process for high permeability rocks 10 18 m2 and when the amount of water that can be released is of the order of 10 dehydration is an important mechanism as it delays the onset of melting which would normally occur even within the tp framework if the onset temperature is low compared to the initial temperature t0 ts t0 150 c overpressure can occur if the reactions are highly endothermic and if their kinetic is fast enough frictional melting would not occur unless the dehydration reactions are completed within the slipping zone

astronomical dating of a tectonic rotation on sicily and consequences for the timing and extent of a middle pliocene deformation phase a detailed palaeomagnetic study of long and continuous middle pliocene sections from the caltanisetta basin on sicily reveals a differential clockwise rotation occurring around 3 21 ma the rotation appears to be a rapid event 80 000 100 000 years which suggests that the responsible tectonic processes also occur rapidly its timing corresponds closely to the transition from the trubi to the narbone formation at 3 19 ma this transition marks a major change in sedimentary environment on sicily and in calabria and it is coeval for instance with the onset of sapropel formation in the eastern mediterranean apparently it marks a synchronous and central eastern mediterranean wide event data from the oldest sediments overlying the tyrrhenian basement odp leg 107 suggest an acceleration in opening of the tyrrhenian sea during the middle pliocene we speculate that this acceleration is related to a transpressional event in the sicilian fold and thrust belt and extension which formed troughs in the foreland the strait of sicily thrust imbrication accompanying the transpressional event on sicily induced the middle pliocene clockwise rotation and resulted in shallowing of the caltanisetta basin causing the change in sedimentation regime characterised by the trubi narbone transition following this middle pliocene tectonic phase no rotation took place in the southern apennines calabria and sicily until the middle pleistocene 1 0 0 7 ma 1998 elsevier science b v all rights reserved

dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates to investigate differences in the frictional behavior between initially bare rock surfaces of serpentinite and powdered serpentinite gouge at subseismic to seismic slip rates we conducted single velocity step and multiple velocity step friction experiments on an antigorite rich and lizardite rich serpentinite at slip rates v from 0 003 m s to 6 5 m s sliding displacements up to 1 6 m and normal stresses n up to 22 mpa for gouge and 97 mpa for bare surfaces nominal steady state friction values nss in gouge at v 1 m s are larger than in bare surfaces for all n tested and demonstrate a strong n dependence nss decreased from 0 51 at 4 0 mpa to 0 39 at 22 4 mpa conversely nss values for bare surfaces remained 0 1 with increasing n and v additionally the velocity at the onset of frictional weakening and the amount of slip prior to weakening were orders of magnitude larger in gouge than in bare surfaces extrapolation of the normal stress dependence for nss suggests that the behavior of antigorite gouge approaches that of bare surfaces at n 60 mpa x ray diffraction revealed dehydration reaction products in samples that frictionally weakened microstructural analysis revealed highly localized slip zones with melt like textures in some cases gouge experiments and in all bare surfaces experiments for v 1 m s one dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge friction values for gouge decrease at higher velocities and after longer displacements than bare surfaces because strain is more distributed

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr