geophysical signatures for low porosity can mimic natural gas hydrate an example from alaminos canyon gulf of mexico natural gas hydrate in sand sediments can increase both the measured compressional velocity and resistivity the same geophysical signatures occur however in low porosity sand we investigate the possible occurrence of natural gas hydrate in a sand interval in alaminos canyon block 21 ac 21 in the gulf of mexico drilled by the u s gas hydrate joint industry project the sand interval has an increase in resistivity 2 2 m and a strong peak and trough at the top and bottom of the sand on exploration seismic which has been interpreted as natural gas hydrate we reexamine the logging data and construct a new reservoir model that matches the measured resistivity the high density sublayers in the sand and the surface seismic trace our model shows that the sand interval in ac 21 is most likely water saturated and the slight increase in resistivity higher measured density and the seismic amplitudes are caused by a reduction in porosity to 30 in the sand interval relative to a porosity of 42 in the surrounding marine muds more broadly we show that the average depth where the porosity of marine muds becomes lower than sand sediment is 900 mbsf though it could be as shallow as 600 mbsf for high porosity sands in any case the similar geophysical signatures for water saturated sand and low saturations of natural gas hydrate in sand probably occur throughout the gas hydrate stability zone at most sites worldwide

experiments on non channelized turbidity currents and their deposits abstract large scale experiments on non channelized turbidity currents show that a wide flow opening angle forms and a rapid dilution of the current with distance takes place the thickness of the deposit decreases radially away from the source resulting in tongue shaped isopachs the mean grain diameter also decreases with distance while the sorting improves with increasing distance the following succession of bedforms was observed non deposition parallel lamination ripples parallel lamination this corresponds to the b c and d division of the bouma sequence for turbidites the experiments are in good agreement with the models presented by bouma mutti and ricci lucchi and walker for classical turbidites in the depositional lobes of submarine fans

some comparisons between mining induced and laboratory earthquakes although laboratory stick slip friction experiments have long been regarded as analogs to natural crustal earthquakes the potential use of laboratory results for understanding the earthquake source mechanism has not been fully exploited because of essential difficulties in relating seismographic data to measurements made in the controlled laboratory environment mining induced earthquakes however provide a means of calibrating the seismic data in terms of laboratory results because in contrast to natural earthquakes the causative forces as well as the hypocentral conditions are known a comparison of stick slip friction events in a large granite sample with mining induced earthquakes in south africa and canada indicates both similarities and differences between the two phenomena the physics of unstable fault slip appears to be largely the same for both types of events for example both laboratory and mining induced earthquakes have very low seismic efficiencies eta tau a bar tau where a is the apparent stress and bar tau is the average stress acting on the fault plane to cause slip nearly all of the energy released by faulting is consumed in overcoming friction in more detail the mining induced earthquakes differ from the laboratory events in the behavior of as a function of seismic momentm0 whereas for the laboratory events 0 06 independent ofm0 depends quite strongly onm0 for each set of induced earthquakes with 0 06 serving apparently as an upper bound it seems most likely that this observed scaling difference is due to variations in slip distribution over the fault plane in the laboratory a stick slip event entails homogeneous slip over a fault of fixed area for each set of induced earthquakes the fault area appears to be approximately fixed but the slip is inhomogeneous due presumably to barriers zones of no slip distributed over the fault plane at constant bar tau larger events correspond to larger a as a consequence of fewer barriers to slip if the inequality a bar tau 0 06 has general validity then measurements of a ea m0 where is the modulus of rigidity andea is the seismically radiated energy can be used to infer the absolute level of deviatoric stress at the hypocenter

stability of giant sand waves in eastern long island sound u s a abstract a combination of a highly accurate bathymetric surveying technique and in situ submersible observations and measurements were used to assess the migrational trends and morphological changes of large sand waves ht 17 m in eastern long island sound although residing in a high energy tidal environment characterized by a net westward sediment flux the large bedforms are relatively stable over the short term over a 7 month period 55 1 of a total 2942 m of sand wave crestline lengths migrated less than the horizontal accuracy limits of navigation 2 m approximately 35 of the remaining sand wave crests migrated less than 4 m net migration of the sand wave crests in the study area was 0 2 m in addition the bulk form center of area in profile view or the base of the sand waves showed little if any movement these data in conjunction with flow data within the sand wave field suggest that net migration rates are greater than the time span of this study and or the sand waves move in response to large residual flows created by high energy aperiodic storm events the latter scenerio suggests that day to day processes only serve to rework and modify the sand waves

the effects of grain density variation on turbidity currents and some implications for the deposition of carbonate turbidites abstract sediment grains in carbonate turbidity currents vary greatly in size shape surface texture and density depending on the evolution of the source carbonate platform in time and space facies character and distribution may vary from traditional siliciclastic turbidite models not only because of the difference in composition but also because variation in grain properties influences flow and depositional behavior experimental gravity flows were generated to investigate one control on this variation the experiments used silicon carbide 3214 kg m 3 and glass ballotini 2650 kg m 3 with a similar grain size distribution in varying proportions to assess the influence of particle density on flow and sedimentation processes mixed particle density flows were more efficient than single particle density flows flow propagation was faster in flows with greater initial bulk density determined by grain density and suspended sediment concentration with mixed particle suspensions flow propagation velocity was maintained for longer due to the presence of low settling velocity particles as a result mixed particle density flows transported more sediment downstream compared to single particle density flows of similar initial suspended sediment volume concentration because of the wider range of grain types in carbonate turbidity currents they may more effectively transport coarse sand grade sediment to more distal sites in a marine basin compared to siliciclastic counterparts of equivalent initial volume this results in differences in bed and facies geometry and distribution

zircon fission track thermochronology and applications to fault studies zircon is one of the most useful minerals used to unravel the earth s history recorded in rocks after the success of etching fission tracks in zircon fleischer et al 1964 naeser 1969 krishnaswami et al 1974 early studies focused primarily on dating young volcanic horizons for stratigraphic purposes e g naeser et al 1973 hurford et al 1976 seward 1979 gleadow 1980 kowallis et al 1986 kohn et al 1992 subsequently fission track analysis of zircon has been extensively employed along with other radiometric dating methods such as u pb and u th he techniques e g davis et al 2003 reiners 2005 to understand the thermochronology of rocks in a variety of geological settings i e thermal history analysis of basement rocks for orogenic studies e g zeilter et al 1982 hurford 1986 kamp et al 1989 sorkhabi 1993 seward and mancktelow 1994 hasebe and tagami 2001 spikings et al 2001 thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults which will be highlighted below in this present chapter the thermal sensitivity of the zircon fission track thermochronometry is reviewed in the context of laboratory and field studies then laboratory procedures of the zircon fission track analysis using the external detector method are outlined as practiced in the fission track laboratory of kyoto university for basic fundamentals of these fission track analyses including data analysis and graphical displays see the chapter by tagami and o sullivan 2005 finally as an example of recent geological applications of the technique the results of zircon fission track analysis of the nojima fault zone japan are presented these rocks were the target of systematic drilling of an active fault system using five boreholes and a trench applications to other geological settings and the

tectonics and denudation adjacent to the xianshuihe fault eastern tibetan plateau constraints from fission track thermochronology the xianshuihe xiaojiang fault system extending from eastern tibet to central yunnan china is a major left shear structural boundary accommodating the clockwise rotation of crustal rocks between the eastern himalayan syntaxis and the south china block zircon and apatite fission track ft data are reported for 111 samples of basement collected from both sides of the northern part of this fault and spanning 300 km across the eastern margin of the tibetan plateau where its mean elevation drops from 3500 to 1500 m above sea level the zircon ft ages define two fossil partial annealing zones at different elevations one fossilised at circa 130 ma and the other at circa 21 ma as a result of cooling probably via regional denudation the apatite ft ages are mostly less than 25 ma but a few granitoids higher up on the plateau retain late cretaceous apparent ages within the apatite ft data with neogene ages there may be several partial annealing zones with mixture modeling identifying age components suggestive of discrete cooling phases at circa 22 7 and 2 ma the first order pattern of the minimum amount of neogene denudation for a section across the plateau margin immediately northeast of xianshuihe fault suggests that a relatively uniform 4 6 km has been eroded from the inner part of the plateau margin increasing to 7 10 km at kangding where the oldest rocks precambrian are exposed and then decreasing markedly into sichuan basin these new ft data combined with published ft data suggest that the present extent of the tibetan plateau was defined during the early miocene

uplift and denudation history of the akaishi range a thrust block formed by arc arc collision in central japan insights from low temperature thermochronometry and thermokinematic modeling fission track ft u th he he and u pb data were used to identify the denudation history of the akaishi range central japan the northern akaishi range is bounded on the east by the itoigawa shizuoka tectonic line fault zone istl fz the thermochronometric ages progressively decreases with the decreasing distance to the istl fz thermo kinematic calculations suggest that the age pattern observed can be explained by a 5 7 5 mm yr reverse slip on the istl fz that dips 34 45 west and soles onto detachment at a20 22 5 km depth by assuming the same geometry and slip rate of the fault thebedrock uplift rates and denudation rates are estimated at 4 mm yr thus the uplift and denudation style of the northern akaishi range is well explained asa simple tilted thrust block that has been exhumed along the listric istl fz on the other hand considering both the difference in apatite ft age and the active fault distribution the southern akaishi range might be different in uplift origin and timing although the difference in apatite ft ages between them may be attributable to the chlorine content variation in apatite the inferred total denudation is larger than several kilometers and likely exceeds 10 km since the beginning of the northern akaishi range uplift suggesting that the low relief surfaces on the ridges and the relatively constant elevations of the summits reflect post uplift denudation rather than pre existing low relief landforms

dating of fault zone activity by apatite fission track and apatite u th he thermochronometry a case study from the lavanttal fault system eastern alps introductionfaulting in the upper crust may leadto thermal anomalies caused by fric tional heating e g maddock 1983 dalessio et al 2003 and or in ltra tion of hydrothermal uids yamadaet al 2007 heating e ects are ex pected to be localised along faultzones and restricted to zones a fewcentimetres adjacent to the main faultsurface dalessio et al 2003 in this study we attempted to datethermal anomalies within fault zonesby comparison of cooling ages at thetransition from fault related rocks tothe undeformed host rocks for thispurpose we chose the lavanttal faultsystem due to underground excava tion and cored drillings related togeological site investigations for amajor railway project in austria it isone of the best exposed fault zones inthe eastern alps we used a combi nation of ssion track aft and u th he analysis on apatites thesensitivity intervals of these thermo chronometers are often referred to aspartial annealing and retention zones apaz heprz and range from 120to 60 c and 80 to 40 c respectively green et al 1986 wolf et al 1996 assuming holding times over geo logical time scales wagner 1979 ketcham et al 1999 the low temperature sensitivity of these ther mochronometers allows thermalanomalies along surfaces of fault slipor uid pathways to be detected forsuch applications however annealingand retention depend not only onheating temperature but also on heat ing duration laslett et al 1987 murakami et al 2006 a combina tion of forward and inverse modellingon apatite age track length and hedata allows quantitative analysis ofthe cooling behaviour of the hostrocks our new results underline theimportance of using multiple low temperature thermochronometersin elucidating details of the thermalhistory of a fault zone geological outlinethe nnw trending lavanttal faultsystem one of the major strike slipfaults in the eastern alps fig 1 separates the basement complexes ofthe kor and saualm by dextral o setof approximately 10 km reinecker 2000 it is assumed to have beenactive since early miocene times withpeaks in activity between 18 16 and14 12 ma reinecker 2000 as indi cated by the evolution of adjacentsedimentary basins and the regionalstructural framework e g pischingeret al 2008 near its southern termi nation the lavanttal fault o sets theperiadriatic fault by about 20 km despite some models at the scale ofthe eastern alps describing the gen eral evolution of con ning fault zonesduring miocene times e g peressonand decker 1997 frisch et al 1998 2000 neubauer et al 2000 littleremains known about the evolutionof the lavanttal fault system how ever these models include a relation ship between the lavanttal faultsystem and the uplift of the koralmcomplex neubauer and genser 1990 previous thermochronologicalstudies documented that the koralmcomplex was already near the surfaceduring the whole cenozoic period hejl 1997 the timing of its naluplift however is less constrained sample descriptionparts of the lavanttal fault system arecharacterised by cataclasites and faultgouges up to several tens of metresthick thermochronological analyseswere carried out on drill core samples diameter 10 cm taken during thegeological investigations for thekoralm railway tunnel drillingabstract

stress release in exhumed intermediate and deep earthquakes determined from ultramafic pseudotachylyte stresses released by coseismic faults during subduction toward lawsonite eclogite facies conditions in the alpine subduction complex of corsica can be estimated based on the energy required to form pseudotachylyte fault veins where shear strain can be measured congruent peridotite melting at ambient conditions of 1 5 gpa and 470 c requires a temperature increase of 1280 c to 1750 c we assume that more than 95 of the work is converted to heat during faulting hence that the stress drop is nearly proportional to the amount of melting and inversely proportional to shear strain minimum estimates of released stress are typically greater than 220 mpa and as high as 580 mpa the abundance of pseudotachylyte on small faults in the studied peridotite suggests that melting is very common on intermediate and deep earthquakes and that shear heating is important for seismic faulting at depth

thermal considerations in inferring frictional heating from vitrinite reflectance and implications for shallow coseismic slip within the nankai subduction zone abstract frictional properties within the upper few kilometers of subduction zones are generally thought to inhibit rupture propagation understanding whether large rapid slip propagates to the surface during megathrust earthquakes is important for characterizing tsunami hazard recent vitrinite reflectance analysis by sakaguchi et al 2011 on cores from the nantroseize drilling transect at the nankai trough japan has been interpreted to suggest that these faults reached temperatures 380 c considerably larger than background temperature values implying they hosted coseismic slip at shallow depths analysis of other temperature proxies on the megasplay by hirono et al 2009 however suggests temperatures have not exceeded 300 c and is inconclusive as to whether the fault slipped at high velocity we evaluate the effects of frictional heat generation on the spatial distribution of vitrinite reflectance its sensitivity to slip zone thickness and slip duration and the cumulative effects of numerous events we build on the analysis of sakaguchi et al 2011 by estimating frictional heating scenarios that are consistent with both the peak and spatial extent of anomalous vitrinite reflectance data our results imply coseismic slip magnitudes of several 10s of meters peak temperature estimates from the vitrinite reflectance data can be reconciled with the other geochemical constraints only by assuming the vitrinite reflectance results from the cumulative effects of multiple earthquakes however this results in unrealistically large estimates of total displacement our results imply that current understanding of how vitrinite reflectance is affected by fault slip is incomplete

mining induced microseismicity monitoring and applications of imaging and source mechanism techniques the study of microseismicity in mines provides an ideal method for remote volumetric sampling of rock masses the nature and uniqueness of microseismic monitoring is outlined in the context of acquisition hardware and software requirements several topics are used to highlight the potential for novel applications of microseismicity and to outline areas where further study is required these topics reflect some of the current interest areas in seismology namelyb values and source parameters fault plane solutions modes of failure and moment tensor inversion imaging and seismicityvelocity correlations these studies suggest potential correlations between zones of high seismic velocity high microseismic activity and maximal stress drops which can be interpreted spatially to be the locations of highly stressed ground with a potential for rock bursting fault plane solutions are shown to be useful in determining the slip potential of various joint sets in a rock mass source parameter studies and moment tensor analysis clearly show the importance of non shear components of failure andb values for microseismicity appear to be magnitude limited and related to spatial rather than temporal variations in effective stress levels

influence of source region properties on scaling relations for m 0 events excavation induced seismic events with moment magnitudesm 0 are examined in an attempt to determine the role geology excavation geometry and stress have on scaling relations correlations are established based on accurate measurements of excavation geometry and methodology stress regime rock mass structure local tectonics and seismic locations scaling relations incorporated seismic moments and source radii obtained by spectral analysis accounting for source propagation and site effects and using madariaga s dynamic circular fault model observations suggest that the interaction of stresses with pre existing fractures fracture complexity and depth of events are the main factors influencing source characteristics and scaling behaviour self similar relationships were found for events at similar depths or for weakly structured rock masses with reduced clamping stresses whereas a non similar behaviour was found for events with increasing depth or for heavily fractured zones under stress confinement additionally the scaling behaviour for combined data sets tended to mask the non similar trends overall depth and fracture complexity initially thought as second order effects appear to significantly influence source characteristics of seismic events withm 0 and consequently favour a non similar earthquake generation process

thermal effects of linked lithospheric and upper crustal scale processes insights from numerical modeling of the cenozoic central catalan coastal ranges ne spain processes influencing the thermal state of the continental crust such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion deposition and fault tectonic transport operate at different scales and their effects overlap in this paper we use lithospheric as well as crustal scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field establishing their relative relevance we apply the models to address the thermal evolution of the catalan coastal ranges ne spain during the cenozoic a period that is characterized by a change in tectonic style from pyrenean compression to extension related to the western mediterranean rifting results of the lithospheric scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11 c km in the catalan coastal ranges during the neogene related to extensional thinning of the lithosphere in the valencia trough western mediterranean predictions of the upper crustal scale thermal model incorporating fault motions and surface mass redistribution erosion and sedimentation point to little changes in the isotherms due to fault block movements in the paleogene and neogene in contrast erosion appears to have a significant effect on the then nal history of basement rocks sited in the shallowest crust comparison of the integrated lithospheric and upper crustal scale modeling results with apatite fission track and apatite u th he thermochronology data reveals larger amounts of neogene to present cooling than predicted by the models on the basis of this unresolvable mismatch we suggest that similar to present forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the neogene stage of rifting copyright 2007 by the american geophysical union

apatite and zircon fission track dating from the hirabayashi nied borehole nojima fault japan evidence for anomalous heating in fracture zones abstract fission track ft analysis using apatite and zircon was performed on samples from two fracture zones fz at the depths of 1140 and 1310 m within the 1838 m borehole core penetrating the ryoke granitic rocks in the nojima fault at nojima hirabayashi awaji island japan drilled just after the 1995 hyogo ken nanbu earthquake clear discordance in apatite and zircon ft age was found for two samples located at 2 m below the central part of each fzs where the presence of pseudotachylyte and or fault gouge would predict the largest amount of slip asymmetric distribution was identified by discordant ages with respect to the central part of fzs these very local discordant ages in the fault reflect thermal anomalies caused by secondary heating with an inferred maximum temperature in the region between apatite and zircon closure temperatures at a time post 48 ma as a source of the secondary heating heat transfer or dispersion via geothermal fluids caused presumably the observed similarity in asymmetric distribution of discordant ft ages at two different fzs other samples yield concordant ft zircon and apatite ages and these indicate rapid cooling within the bounds of two closure temperatures of these minerals at 60 ma of the ryoke granitic rocks

fission track dating of faulting events accommodating plastic deformation of biotites we performed fission track ft analyses to constrain the timing of fault slip events associated with plastic deformation of biotite grains formed at high temperature higher than 200 300 c apatite ft ages of 49 6 16 7 ma were obtained from late cretaceous granites near the fault with younger ages near a basaltic dike that intruded at 19 ma by comparing the distribution of apatite ft ages using forward thermal and ft annealing calculations we interpreted the younger ages as being explained by basaltic intrusion we concluded that the plastic deformation of the biotite grains could have occurred associated with the following events 1 primal cooling of the granitic body at 68 50 ma and or 2 basaltic intrusion at 19 ma a combination of detailed observation of microscale deformation structures and dense ft measurements successfully constrained timing of fault events distributed in bedrock without covering layers

depth dependent stress field in and around the atotsugawa fault central japan deduced from microearthquake focal mechanisms evidence for localized aseismic deformation in the downward extension of the fault 1 focal mechanisms have been determined from p wave polarity data as well as body wave amplitudes for 154 microearthquakes that occurred around the atotsugawa fault in central japan between 2002 and 2004 while we found many microearthquakes with a pure strike slip mechanism that is similar to the faulting style of the atotsugawa fault a considerable number of microearthquakes with reverse faulting components are also occurring most of the p axes are horizontal and oriented in the wnw ese direction which conforms to the general tectonic trend in this area in contrast the t axes have a wide range of plunge suggesting that reverse faulting type earthquakes as well as strike slip ones are occurring the most conspicuous feature in the focal mechanism distribution is the depth dependence where shallow earthquakes are primarily reverse faulting and strike slip earthquakes become predominant with depth a stress tensor inversion reveals that the shallower part is characterized by a mixture of reverse and strike slip faulting regimes and that a pure strike slip faulting regime appears only around the bottom of the seismogenic zone together with other geophysical observational evidence for the fault we suggest that the existence of a localized aseismic deformation below the atotsugawa fault is the simplest scenario that can explain the observed stress fields this scenario provides a stress accumulation mechanism of disastrous shallow inland earthquakes in which the localized aseismic deformation accumulates stress onto the fault plane in the seismogenic zone during an earthquake cycle and the main shock would occur when the failure stress is reached on the fault

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

cataclastic rocks of the san gabriel fault an expression of deformation at deeper crustal levels in the san andreas fault zone the san gabriel fault a deeply eroded late oligocene to middle pliocene precursor to the san andreas was chosen for petrologic study to provide information regarding intrafault material representative of deeper crustal levels cataclastic rocks exposed along the present trace of the san andreas in this area are exclusively a variety of fault gouge that is essentially a rock flour with a quartz feldspar biotite chlorite amphibole epidote and fe ti oxide mineralogy representing the milled down equivalent of the original rock anderson and osborne 1979 anderson et al 1980 likewise fault gouge and associated breccia are common along the san gabriel fault but only where the zone of cataclasis is several tens of meters wide at several localities the zone is extremely narrow several centimeters and the cataclastic rock type is cataclasite a dark aphanitic and highly comminuted and indurated rock the cataclastic rocks along the san gabriel fault exhibit more comminution than that observed for gouge along the san andreas the average grain diameter for the san andreas gouge ranges from 0 01 to 0 06 mm for the san gabriel cataclastic rocks it ranges from 0 0001 to 0 007 mm whereas the san andreas gouge remains particulate to the smallest grain size the ultra fine grain matrix of the san gabriel cataclasite is composed of a mosaic of equidimensional interlocking grains the cataclastic rocks along the san gabriel fault also show more mineralogiec changes compared to gouge from the san andreas fault at the expense of biotite amphibole and feldspar there is some growth of new albite chlorite sericite laumontite analcime mordenite and calcite the highest grade of metamorphism is laumontite chlorite zone zeolite facies mineral assemblages and constrained uplift rates allow temperature and depth estimates of 200 30 c and 2 5 km thus suggesting an approximate geothermal gradient of 50 c km such elevated temperatures imply a moderate to high stress regime for the san andreas which is consistent with experimental rock failure studies moreover these results suggest that the previously observed lack of heat flow coaxial with the fault zone may be the result of dissipation rather than low stress much of the mineralogy of the cataclastic rocks is still relict from the earlier igneous or metamorphic history of the protolith porphyroclasts even in the most deformed rocks consist of relict plagioclase oligoclase to andesine alkali feldspar quartz biotite amphibole epidote allanite and fe ti oxides ilmenite and magnetite we have found no significant development of any clay minerals illite kaolinite or montmorillonite for many sites the compositions of these minerals directly correspond to the mineral compositions in rock types on one or both sides of the fault whole rock major and trace element chemistry coupled with mineral compositions show that mixing within the zone of cataclasis is not uniform and that originally micaceous foliated or physically more heterogeneous rock units may contribute a disproportionally large amount to the resultant intrafault material as previously found for the gouge along the san andreas chemical mobility is not a major factor in the formation of cataclastic rocks of the san gabriel fault we see only minor changes for si and alkalies however there is a marked mobility of li which is a probable result of the alteration and formation of new mica minerals the gouge of the san andreas and san gabriel faults probably formed by cataclastic flow there is some indication presently not well constrained that the fine grained matrix of the cataclasite of from the san gabriel fault formed in response to superplastic flow

seismic heating signatures in the japan trench subduction plate boundary fault zone evidence from a preliminary rock magnetic geothermometer frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation the amount of annealing varies widely and is as yet poorly constrained here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced the case study comprises sheared clay cored from the japan trench subduction plate boundary fault zone decollement which accommodated the large slip of the 2011 mw 9 0 tohoku oki earthquake the decollement was cored during the integrated ocean drilling program iodp expedition 343 the japan trench fast drilling project jfast heating signatures with estimated maximum temperatures ranging from 300 to over 500 c are determined close to the multiple slip surfaces within the decollement since it is impossible to tie a specific slip surface to a certain earthquake thermal evidence for the cumulative effect of several earthquakes is unveiled this as yet preliminary rock magnetic geothermometer would be a useful tool to detect seismic heating along faults that experienced medium temperature rise a range which is difficult to assess with other approaches

implications of an elastic analysis of in situ stress measurements near the san andreas fault twenty nine measurements of in situ stress obtained with the hydraulic fracturing technique near palmdale california are the basis of an elastic analysis of the state of stress in the mojave desert adjacent to the san andreas fault the measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km the elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7 9 mpa km extrapolation yields an average shear stress in the upper 14 km of the crust of about 56 mpa a result that is higher than estimates of the average shear stress on the san andreas fault based on the analysis of heat flow data this finding is consistent however with estimates of fault strength based on laboratory determinations of the coefficient of friction for samples of san andreas fault gouge if the regional state of deviatoric stress is limited by the strength of the fault zone if so then the coefficient of friction of the san andreas fault zone inferred from the stress field results is about 0 45 the state of stress does not appear to vary systematically with distance from the san andreas fault although considerable localized variation is observed the observations suggest an upper bound of about 0 1 mpa km for the horizontal gradient of the maximum shear stress in the direction perpendicular to the san andreas fault a result that implies a corresponding limit of about 1 4 mpa on the shear traction applied to the base of the seismogenic layer finally we demonstrate the potential application of in situ stress data to the direct assessment of accumulated slip which could be released in a large earthquake we show that on the basis of a model involving a locked fault extending to about 22 km the total fault slip below the locked portion is less than 13 m a more comprehensive set of stress data could permit the estimation of an even lower bound

seafloor environments in the long island sound estuarine system abstract four categories of modern seafloor sedimentary environments have been identified and mapped across the large glaciated topographically complex long island sound estuary by means of an extensive regional set of sidescan sonographs bottom samples and video camera observations and supplemental marine geologic and modeled physical oceanographic data 1 environments of erosion or nondeposition contain sediments which range from boulder fields to gravelly coarse to medium sands and appear on the sonographs either as patterns with isolated reflections caused by outcrops of glacial drift and bedrock or as patterns of strong backscatter caused by coarse lag deposits areas of erosion or nondeposition were found across the rugged seafloor at the eastern entrance of the sound and atop bathymetric highs and within constricted depressions in other parts of the basin 2 environments of bedload transport contain mostly coarse to fine sand with only small amounts of mud and are depicted by sonograph patterns of sand ribbons and sand waves areas of bedload transport were found primarily in the eastern sound where bottom currents have sculptured the surface of a holocene marine delta and are moving these sediments toward the wsw into the estuary 3 environments of sediment sorting and reworking comprise variable amounts of fine sand and mud and are characterized either by patterns of moderate backscatter or by patterns with patches of moderate to weak backscatter that reflect a combination of erosion and deposition areas of sediment sorting and reworking were found around the periphery of the zone of bedload transport in the eastern sound and along the southern nearshore margin they also are located atop low knolls on the flanks of shoal complexes and within segments of the axial depression in the western sound 4 environments of deposition are blanketed by muds and muddy fine sands that produce patterns of uniformly weak backscatter depositional areas occupy broad areas of the basin floor in the western part of the sound the regional distribution of seafloor environments reflects fundamental differences in marine geologic conditions between the eastern and western parts of the sound in the funnel shaped eastern part a gradient of strong tidal currents coupled with the net nontidal estuarine bottom drift produce a westward progression of environments ranging from erosion or nondeposition at the narrow entrance to the sound through an extensive area of bedload transport to a peripheral zone of sediment sorting in the generally broader western part of the sound a weak tidal current regime combined with the production of particle aggregates by biologic or chemical processes cause large areas of deposition that are locally interrupted by a patchy distribution of various other environments where the bottom currents are enhanced by and interact with the seafloor topography

moment tensors of ten witwatersrand mine tremors ground motions recorded both underground and on the surface in two of the south african gold mining districts were inverted to determine complete moment tensors for 10 mining induced tremors in the magnitude range 1 9 to 3 3 the resulting moment tensors fall into two separate categories seven of the events involve substantial coseismic volumetric reduction v together with normal faulting entailing shear deformation ad where the summation is over fault planes of areaa and average slipd for these events the ratio v ad ranges from 0 58 to 0 92 with an average value of 0 71 for the remaining three events v is not significantly different from zero these events are largely double couple sources involving normal faulting surprisingly the two types of source mechanism appear to be very distinct in that there is not a continuous distribution of the source mix from v 0 to v ad presumably the coseismic closure indicates substantial interaction between a mine stope and adjacent shear failure in the surrounding rock under the influence of an ambient stress for which the maximum principal stress is oriented vertically

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

reaction kinetics of alkenone and n alkane thermal alteration at seismic timescales recent experiments and field observations have indicated that biomarker molecules can react over short timescales relevant to seismic slip thereby making these compounds a useful tool in studying temperature rise in fault zones however short timescale biomarker reaction kinetics studies have previously focused on compounds that have already experienced burial heating here we present a set of hydrous pyrolysis experiments on pleistocene aged shallow marine sediment to develop the reaction kinetics of long chain alkenone destruction change in the alkenone unsaturation ratio uk 37 and change in the n alkane chain length distribution our results show that biomarker thermal maturity provides a useful method for detecting temperature rise in the shallow reaches of faults such as subduction zone trench environments through the course of our work we also noted the alteration of total alkenone concentrations and uk 37 values in crushed sediments stored dry at room temperature for durations of months to years but not in the solvent extracts of these materials this result though parenthetical for our work in fault zones has important implications for proper storage of sedimentary samples to be used for alkenone paleotemperature and productivity analysis this article is protected by copyright all rights reserved

deep sea terrigenous organic carbon transfer and accumulation impact of sea level variations and sedimentation processes off the ogooue river gabon abstract sedimentary isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the ogooue turbidite system around 4000 m depth were used to develop a conceptual model to describe the accumulation of terrigenous organic matter om during the last 200 000 yrs bp in the eastern part of the gulf of guinea this model takes into account the influence of the different depositional processes turbiditic vs hemipelagic sedimentation geomorphological features and sea level variations total organic carbon toc and the stable organic carbon isotopes of the om 13 c variability follow the highstand lowstand interglacial glacial cyclicity with a very low accumulation rate of terrigenous om during periods of high sea level and higher accumulation rate during period of low sea level a sea level of 80 120 m below present day seems to favor the transfer of terrigenous sediments to the deep offshore environment through the turbidite system and thanks to the connection of the canyons heads with the river system presently located at the shelf edge at 120 m water depth in this system terrigenous om matter delivered by the river accumulate in the sediments via two main processes indeed a part of the terrigenous om settles in combination with the finest particles forming hemipelagites while another part formed of very well preserved land plant debris is transported and deposited far offshore with turbidity currents the proportion of terrigenous om accumulated due to turbidity currents is important as it can represent more than 70 of the carbon accumulated during sea level lowstand moreover terrigenous om seems to preferentially accumulate in the levees and the lobes of the system notably due to the higher frequency of organic rich turbidites this study demonstrates that gravity flows influenced by the sea level variations can significantly affect the terrigenous om budget of the deep offshore atlantic margins and that channel levee complexes as well as turbidite lobes can be regarded as good sink for terrestrial organic carbon these processes should be taken into consideration in the context of source rocks exploration but also for the estimation of the general carbon accumulation in ocean sediment

three dimensional earthquake sequence simulations with evolving temperature and pore pressure due to shear heating effect of heterogeneous hydraulic diffusivity 1 a new methodology for three dimensional 3 d simulations of earthquake sequences is presented that accounts not only for inertial effects during seismic events but also for shear induced temperature variations on the fault and the associated evolution of pore fluid pressure in particular the methodology allows to capture thermal pressurization tp due to frictional heating in a shear zone one dimensional 1 d diffusion of heat and pore fluids in the fault normal direction is incorporated using a spectral method which is unconditionally stable accurate with affordable computational resources and highly suitable to earthquake sequence calculations that use variable time steps the approach is used to investigate the effect of heterogeneous hydraulic properties by considering a fault model with two regions of different hydraulic diffusivities and hence different potential for tp we find that the region of more efficient tp produces larger slip in model spanning events the slip deficit in the other region is filled with more frequent smaller events creating spatiotemporal complexity of large events on the fault interestingly the area of maximum slip in model spanning events is not associated with the maximum temperature increase because of stronger dynamic weakening in that area the region of more efficient tp has lower interseismic shear stress which discourages rupture nucleation there contrary to what was concluded in prior studies seismic events nucleate in the region of less efficient tp where interseismic shear stress is higher in our model hypocenters of large events do not occur in areas of large slip or large stress drop

an implosive component in the seismic moment tensor of a mining induced tremor in early 1988 a special study in one of the major south african gold fields yielded seismograms that indicate seismic moment tensors having substantial implosive components the moment tensor resulting from the inversion of the ground motion data from the best recorded event was decomposed into isotropic and deviatoric components from which both the coseismic volumetric closure v and the total shear deformation ad where a is fault area and d is average slip could be estimated the finding here that v ad is consistent with earlier analyses of how the tabular mine stopes interact with the surrounding rock mass to produce seismic deformation

mechanical anisotropy in the woodford shale permian basin origin magnitude and scale the rock mechanical properties of shales are critical to how they perform as reservoirs determining both their tendency to develop natural fractures and their response to hydraulic stimulation these mechanical properties are in turn manifestations of composition fabric and porosity and fluid saturations such properties also dictate the seismic response of shales as well as their signature on many well logs it has long been recognized or perhaps assumed that shales are relatively homogeneous in the plane parallel to bedding and relatively heterogeneous in the direction perpendicular to bedding

extractable organic material in fault zones as a tool to investigate frictional stress abstract the detection of a frictional heating signature is an attractive but elusive way to measure frictional stress on exhumed faults with no evidence of melting we present a new paleothermometer for fault zones that utilizes the thermal maturity of extractable organic material to determine the maximum frictional heating experienced by the fault because there are no retrograde reactions in these organic systems maximum heating is preserved we investigate the punchbowl fault an ancient strand of the san andreas fault in southern california according to the methylphenanthrene index for thermal maturity there is no differential heating between the fault and off fault samples indicating that the fault did not get hotter than the surrounding rock during slip additionally the thermal maturity of the rocks falls within the range of heating expected from the bounds on burial depth and time and adds some constraint to the burial depth range simple heating models indicate that the fault must have had either 1 an extremely low shear stress during slip 2 an active slipping zone thicker than 1 mm or 3 earthquakes smaller than m6 to lack a differential heating signature after 44 km slip

thermochronological dating of brittle structures in basement rocks a case study from the onshore passive margin of sw sri lanka 1 the brittle structural inventory of southern and southwestern sri lanka has been studied by kinematic mineralogical and thermochronological techniques thermochronological analyses of faults comprise apatite and zircon fission track ft data and apatite u th sm he ages from fault planes and undisturbed host rocks and range between 65 and 230 ma the ages of both settings are undistinguishable for topographic altitudes below 100 m while fault planes from higher elevations are significantly younger than the corresponding host rocks thermal history modeling and qualitative interpretation of the thermochronological data identify at least five episodes of thermal overprint associated with faulting activity occurring at 159 18 144 14 120 10 94 8 and 70 10 ma the kinematic mineralogical and thermochronological data collectively show that sri lanka was subjected to major n s oriented extension subsequent to the gondwana breakup the resulting brittle structures exert primary control on the island s geomorphology especially on the southern escarpment of the sri lankan highlands

dating shallow thrusts with zircon u th he thermochronometry the shear heating connection new zircon u th he zhe ages from a shallow 6 7 km thrust fault zone and surrounding wall rocks in the helminthoid flysch of the ligurian alps were measured to test the applicability of the thermochronometer for dating brittle or brittle ductile faults the ages are integrated with x ray diffraction analysis of clay minerals and fluid inclusion microthermometry on vein filling minerals to constrain the temperature conditions of the damage zone and the wall rocks during thrusting the wall rocks yield pre depositional inherited zhe ages 125 3 15 to 312 3 37 ma while ages from the fault core are reset 28 8 3 4 to 33 8 4 0 ma this is consistent with independent geological and thermochronometric evidence for early oligocene motion of the thrust this implies that the fault zone exceeded 200 c during faulting and confirms the illite crystallinity and fluid inclusion constraints which indicate temperatures of 220 300 c in the fault zone while in those the wall rocks were 180 200 c thermal modeling of the fault zone suggests that the shear heating associated with the fault motion is an efficient mechanism for generating temperature increases of 50 70 c during a displacement of 10 25 km in 2 10 m y our results underscore the validity of the zhe technique for dating brittle or brittle ductile faults characterized by relatively high strain rate

thermal evolution of a sheared continental margin insights from the ballenas transform in baja california mexico abstract the ballenas transform margin in central baja california offers an unparalleled opportunity to study the thermal behaviour of a sheared continental margin during various stages of its evolution apatite fission track and u th he results from two transects perpendicular to the coast reveal a pronounced latest pliocene to pleistocene 1 8 ma heating event related to the neogene opening of the gulf of california proximity to a regional pre rift unconformity indicates that samples remained at near surface levels since paleogene unroofing despite having experienced reheating to maximum paleotemperatures within or above the fission track partial annealing zone in general maximum paleotemperatures during overprinting decrease from 100 120 c near the coast to below 60 c ca 5 8 km further inland suggesting lateral heat flow from a source within the gulf of california heat sources related to the structural development of the ballenas transform fault located approximately 1 5 4 5 km offshore from the two sample transects most likely controlled the observed reheating overprinting patterns do not support conductive reheating due to reburial magmatism or frictional shear instead a pronounced thermal spike in between much less overprinted neighbouring samples strongly favours convective heating by hydrothermal fluids as the dominant overprinting process hydrothermal activity may be caused by either deep fluid circulation along newly formed shear zones of the transform fault or more likely magmatic leaking along the transform fault latest pliocene to pleistocene 1 8 ma activity on the ballenas transform fault is closely linked to extension in the lower and upper delfin basins and provides a minimum age for the structural reorganisation and the relocation of extension in the northern gulf of california this study shows that hydrothermal activity can cause significant thermal events in a transform margin before the passage of the spreading centre paleotemperatures from the ballenas transform are similar to those of other transform margins after passage of a spreading centre which suggests that hydrothermal fluids may have an important thermal buffering effect moderating the maximum temperatures of the ridge segments near their intersection with a continental transform margin

particle dynamics of the surface intermediate and benthic nepheloid layers under contrasting conditions of summer monsoon and typhoon winds on the boundary between the taiwan strait and east china sea abstract two shipboard surveys of hydrographics and sediment dynamics were conducted off the mouth of minjiang the min river in july 2012 under contrasting summer monsoon and typhoon wind conditions observations included profiles of conductivity temperature depth fluorescence and suspended particle volume concentration and current velocity in addition water samples were taken for the analyses of mass concentration poc and chlorophyll of suspended sediment seafloor sediment samples were also taken for grain size analysis nepheloid layers nls were observed at surface intermediate and benthic depths snl inl bnl respectively the nl dynamics under the two wind conditions were mainly controlled by 1 the presence of the minjiang river plume and terrigenous material it carries 2 water column stability affected by wind current and waves 3 current induced resuspension of seafloor sediment and 4 physically coupled biological activities the wind field was the major forcing controlling the observed flow field and the upper water column stability in the typical summer condition southerly winds induced offshore directed currents enhancing the seaward dispersal of the minjiang river plume facilitating water column stratification thereby forming 3 nls in the water column phytoplankton growth was enhanced by terrigenous material and sunlight the suspension of the seafloor sediment was the one of the major sources for suspended particles in these nls furthermore the c n ratio of poc in the three nls is 5 72 almost identical to the redfield ratio indicating their predominant marine origin conversely under typhoon related northerly winds the offshore spread of the river plume was restricted the reduced riverine input and enhanced mixing resulted in the disappearance of the snl elevated turbidity in the inl was largely due to the presence of phytoplankton while the bnl was comprised of sediment resuspended off the seafloor and from horizontal advection our results suggest that the presence of the river plume from the minjiang at the study site sets the condition for the snl dynamics the dynamics of inl and bnl were dominated by the wind field and to a lesser degree the wave field and tidal current

magnetic evidence revealing frictional heating from fault rocks in granites abstract fault rocks share certain characteristics of melt origin pseudotachylyte due to elevated temperature caused by coseismic frictional heating however there is no broadly accepted quantitative evidence to identify signatures of coseismic frictional heating in fault rocks we report systematic magnetic studies on a brown ultracataclasite layer in the rocks from longmen shan thrust belt at the eastern margin of the tibetan plateau in sichuan province china the brown ultracataclasite has 1 the highest magnetic susceptibility 2 significant characteristics of magnetite neoformation and 3 similar demagnetization behavior of natural remanent magnetization and anhysteretic remanent magnetization the principal mechanism responsible for the high magnetic susceptibility of the brown ultracataclasite is most likely caused by the production of new magnetites from iron bearing paramagnetic minerals these new magnetites can be formed by frictional heating on slip planes along a seismic fault the study shows that magnetic analysis can help to recognize frictional heating events in specific fault rocks

shear heating during distributed fracturing and pulverization of rocks we provide estimates of temperature changes produced in fault damage zones during brittle deformation associated with distributed cracking and pulverization in contrast to localized faulting accompanied by significant frictional weakening the relatively high friction coefficient on the multitudinous small cracks generated in the fracturing process can lead to significant shear heating simple calculations with parameter values constrained by laboratory experiments and simulations indicate that the temperature can increase during the generation of rock damage and pulverization by 100 c or more the results can help explain signatures of elevated temperature observed in geometrically complex fault zone sections with significant rock damage and regions with broad distributed deformation

spatial variability in depositional reservoir quality of deep water channel fill and lobe deposits abstract initial porosity and permeability in deep water systems are controlled by primary sedimentary texture and mineralogy therefore understanding the sedimentary processes that control changes in primary texture is critical for improved reservoir quality predictions a well constrained exhumed submarine lobe in the jaca basin and a submarine channel fill element in the ainsa basin northern spain were studied to characterize the depositional reservoir quality in axial to marginal fringe positions construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties and their relationship to reservoir quality distribution samples were analyzed in thin section to establish how depositional processes inferred from outcrop observations affect textural properties results show that high density turbidites are concentrated in lobe and channel axis positions and exhibit good depositional reservoir quality lobe off axis deposits contain high and low density turbidites and have moderate depositional reservoir quality conversely low density turbidites dominate lobe fringe and channel margin positions and have relatively poor depositional reservoir quality there is a sharp decrease in depositional reservoir quality between the lobe off axis and lobe fringe due to 1 an abrupt increase in matrix content 2 an abrupt decrease in sandstone amalgamation and 3 a decrease in grain size there is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to 1 an increase in total sandstone thickness and amalgamation 2 an increase in grain size 3 a decrease in matrix content rates of change of key properties are up to two orders of magnitude greater between channel fill sub environments compared to lobe sub environments spatial variability in properties of discrete architectural elements and rates of changes provides input to reservoir models during exploration appraisal and development phases of hydrocarbon fields

moment tensor inversion of induced microseisnmic events evidence of non shear failures in the 4 m 2 moment magnitude range to assess objectively the source mechanism of mining induced seismic events we developed an algorithm to invert for the moment tensor components from this inversion the ratio of isotropic deviatoric component in the source is obtained we are applying this method to microseismic events 4 m 2 recorded at the underground research laboratory url in pinawa manitoba where a tunnel is being excavated at 420 m depth to monitor the seismic activity induced by this opening an array of 16 triaxial accelerometers was installed around the planned tunnel results from the moment tensor inversion on a fist data set provide evidence of non shear failure mechanisms furthermore the location of events displaying a tensile component corresponds to a breakout observed underground in the roof of the tunnel

no frictional heat along the san gabriel fault california evidence from fission track thermochronology large earthquakes generate frictional heat and the magnitude of heating is related to the slip magnitude the applied effective normal stress and the frictional strength of the fault we looked for evidence of this heating in apatite fission track age and track length distributions of samples from adjacent to and within the san gabriel fault zone in southern california the fault is thought to be an abandoned major trace of the san andreas fault system active from 13 to 4 ma and has since been exhumed from depths of 2 5 km at our sample locality as much as 40 km of total slip is thought to have accumulated along a localized ultracataclasite layer just 1 8 cm thick we see no evidence of a localized thermal anomaly in either fission track ages or track lengths even in samples within just 2 cm of the ultracataclasite because of the absence of any measurable impact on fission tracks we have been able to use forward modeling of heat generation heat transport and fission track annealing to constrain the frictional properties of the fault we find that either there has never been an earthquake with 4 m of slip at this locality or the average apparent coefficient of friction must have been 0 4

potential for geophysical experiments in large scale tests potential research applications for large specimen geophysical experiments include measurements of scale dependence of physical parameters and examination of interactions with heterogeneities especially flaws such as cracks in addition increased specimen size provides opportunities for improved recording resolution and greater control of experimental variables large scale experiments using a special purpose low stress 100 mpa

remote sensing of coastal sea surface features off northern british columbia this article presents an overview of surface oceanographic features identified by avhrr imagery in hecate strait and adjacent waters surrounding the queen charlotte islands canada an area still poor in in situ observations the observed features and their temporal variability are interpreted in terms of meteorological and hydrological forcing the effects of tidal mixing are discussed through the application of a finite element numerical model

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

a simple universal equation for grain settling velocity abstract a new equation is presented for sediment fall velocity as a function of grain diameter for given values of fluid viscosity and fluid and solid density sediment fall velocity is a fundamental parameter in the modeling and interpretation of fluviatile and coastal deposition the equation applies to the entire range of viscous to turbulent conditions and its simple explicit form makes it easy to use in computer models and other applications in sedimentology geomorphology and engineering the equation is derived from dimensional analysis and converges on stokes law for small grains and a constant drag coefficient for large grains its two physically interpretable parameters are easily adjusted for shape effects or for the use of sieve diameter rather than nominal grain diameter it gives a close fit to published and new experimental data for both quartz sand and low density materials with no more error than previous equations of more complicated form

seasonal variation of a coastal jet in the long island sound outflow region based on hf radar and doppler current observations 1 surface current hf radar and velocity profile observations obtained as part of the front resolving observational network with telemetry front project over an approximately 2 year period are used to describe the seasonal variability of a coastal jet in the long island sound outflow region the jet is observed in an area of the continental shelf where surface thermal fronts are frequently detected during both summer and winter the current jet is coincident with a band of high summer frontal probability and apparently arises from the interaction between long island sound outflow and larger scale alongshore currents on the shelf the jet reaches peak strength in summer transport of 0 07 sv and is weak or non existent in winter flow is strongest near the surface and weakens with depth with only moderate seasonal variations in the vertical shear the relatively long data set of currents combined with historical hydrographic measurements and buoy wind observations is analyzed to examine the seasonal variability of the terms in the depth averaged momentum balance the depth averaged pressure gradient is partitioned into a steric component evaluated from the hydrography and a non steric component that is estimated as the residual of the computed terms in the momentum equation the depth averaged momentum balance is found to be approximately geostrophic in the across shore direction the seasonal variability in the jet arises due to the shifting balance between buoyancy driven flow that is always downshelf but intensifies somewhat in summer and wind driven flow which dominates in winter when wind stress becomes strongly upwelling favorable

thermal history of the central gotthard and aar massifs european alps evidence for steady state long term exhumation 1 quantifying long term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces here we reconstruct the exhumation history of the central aar and gotthard external crystalline massifs in the european alps using apatite and zircon fission track and apatite u th he data age elevation relationships and time temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of 0 5 km ma since 14 ma a slightly accelerated rate 0 7 km ma occurred from 16 to 14 ma and again from 10 to 7 ma faster exhumation between 16 and 14 ma is most likely linked to indentation of the adriatic wedge and related thrusting along the alpine sole thrust which in turn caused uplift and exhumation in the external crystalline massifs the data suggest nearly steady moderate exhumation rates since 14 ma regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 ma or orogen perpendicular extension initiated in pliocene times recent uplift and denudation rates interpreted to be the result of climate fluctuations and associated increase in erosional efficiency are nearly twice this 0 5 km ma paleoexhumation rate

spring summer frontogenesis at the mouth of block island sound 1 a numerical investigation into tidal and buoyancy forced motion 1 the generation and underlying dynamics of late spring temperature and salinity fronts at the mouth of block island sound in the mid atlantic bight are examined using a three dimensional general circulation model the model is forced by tidal velocities at its outer boundaries an estuary shelf salinity gradient and surface warming runs representing the period from 18 april to 23 may 2000 are investigated through direct examination of the model results and diagnostic calculations that isolate individual processes three mechanisms are identified as significantly contributing to the location and structure fronts observed in this region vertical mixing produces the necessary horizontal temperature structure within and near block island sound but the southern frontal boundary is further affected by the subtidal circulation which is divided into two components defined using a momentum budget analysis tidal currents over the complex bathymetry leads to nonlinearly rectified flows including a headland eddy south of montauk point circumscribing this feature is a baroclinically adjusted buoyant outflow from the long island sound estuary while modifications to the buoyancy forcing can modify the frontal position it necessarily remains offshore of the tidally driven circulation analysis of the salinity anomaly fluxes indicates that both tidal and mean advection are responsible for the overall transport of buoyancy

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

circular plumes in lake pontchartrain estuary under wind straining circular shaped density plumes of low turbidity low fecal indicator escherichia coli and enterococci concentrations and high salinity have been observed near the industrial canal in lake pontchartrain north of the city of new orleans a conceptual model in polar coordinates and a numerical model are developed together with data analysis to illustrate the dense plume it is demonstrated that the northward expansion of the plume occurs under northerly winds the northward expansion of the plume occurs under northerly winds that drive downwind flow at the surface and upwind radial flow at the bottom northerly wind induced straining similar to tidal straining promotes vertical stratification as a result the water becomes stratified near a thin bottom layer 1 m within which density currents are facilitated the stability of the stratified plume suppresses wind induced turbulent mixing inside the plume the bottom water outside of the plume is more effectively stirred by the wind the result being that the suspended sediment concentration outside of the plume area is much higher than inside this contrast in mixing makes the plume visible from the surface by satellites even though the stratification is at the bottom laterally wind stress produces a torque vorticity in areas of non uniform depth such that upwind flow is developed in deep water and downwind flow in shallow water the continuity requirement produces an upwind flow along the axis of the industrial canal ic the upwind flow is balanced by the downwind flow over the shallower peripheral areas along the coast

analogue study of particle segregation in pyroclastic density currents with implications for the emplacement mechanisms of large ignimbrites analogue flume experiments were conducted to investigate the transport and sedimentation behaviour of turbulent pyroclastic density currents the experimental currents were scaled approximately to the natural environment in three ways 1 they were fully turbulent 2 they had a very wide range of particle sizes and associated rouse numbers the ratio of particle settling velocity to effective turbulent eddy velocity in the current and 3 they contained particles of two different densities two sets of surge type experiments were conducted in a 5 m long water filled lock exchange flume at five different volumetric particle concentrations from 0 6 to 23 in one set one component experiments the currents contained just dense particles in the other set two component experiments they contained both light and dense particles in equal volume proportions in both sets of experiments the population of each component had a log normal size distribution in the two component experiments the size range of the light particle population was selected in order to be in hydrodynamic equivalence with that of the dense particles dense particles were normally graded both vertically and downstream in the deposits from both sets of experiments the mass loading normalized to the initial mass of the suspension and grain size of the dense component in the deposits decreased with distance from the reservoir and were insensitive to initial total particle concentration in the currents on the other hand in the two component experiments the light particles were extremely sensitive to concentration they were deposited in hydrodynamic equivalence with the dense particles from dilute currents but were segregated efficiently at concentrations higher than a few per cent with increasing particle concentration the large light particles were carried progressively further down the flume because of buoyancy effects deposits from the high concentration currents exhibited reverse vertical grading of the large light particles efficient segregation of the light component was observed even if the bulk density of the current was less than that of the light particles in both sets of experiments marked inflexions in the rate of downstream decline in mass loading and maximum grain size of the dense component can be attributed to the presence of two different particle settling regimes in the flow 1 particles with rouse numbers 2 5 which did not respond to the turbulence and settled rapidly and 2 particles with rouse numbers 2 5 which followed the turbulent eddies and settled slowly the results are applied to the transport and sedimentation dynamics of pyroclastic density currents that generate large widespread ignimbrites field data fail to reveal significant departures from aerodynamic equivalence between pumice and lithic clasts in three such ignimbrites the particulate loads of some large ignimbrites are transported principally in turbulent suspensions of low concentration in some ignimbrites the well developed inflexions in curves of maximum lithic ml size vs distance can be attributed to the existence of distinct high and low rouse number particle settling regimes that mark the transition from an overcharged state to one in which the residual particulate load is transported more effectively by turbulence

fronts stratification and mixing in long island and block island sounds spatial patterns of bulk stratification in long island and western block island sounds observed near the fall equinox of 1978 show a strong correlation r 0 79 with contours of the h u3 stratification index derived from tidal stream and depth charts the index delineates stratified transitional and mixed regions with apparent good accuracy with the marginally stratified frontal zones being characterized by log10 h u3 1 5 m 2 s3 these results and theoretical considerations suggest that the index may be a useful parameter in corroborating and predicting frontal boundaries in other moderately stratified estuaries where local buoyancy fluxes are derived from fresh water sources

spatial variations in the composition of turbidites due to hydrodynamic fractionation 1 this study uses measurements from physical experiments to document turbidity currents which are density currents composed of suspended sediment and water to be effective at hydrodynamically fractionating minerals on the basis of grain density and grain shape alone resulting in large scale spatial variations in the composition of their deposits while grain composition varies spatially the population sampled at any one location is hydrodynamically equivalent spatial variations in composition of the deposits are modeled using exponential decay functions which are based on initial concentration of grain types and their respective differences in settling velocity we further discuss implications of this process for addressing practical geophysical problems in which mineralogical distributions are important such as provenance and geochronology studies subsurface imaging and predicting bulk properties of subsurface reservoirs

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

fossil earthquakes recorded by pseudotachylytes in mantle peridotite from the alpine subduction complex of corsica paleo earthquakes recorded by pseudotachylytes have recently been discovered in the blueschist facies subduction complex of alpine corsica pseudotachylytes occur in ophiolite gabbro and mantle peridotite belonging to the schistes lustres of cape corse ultramafic pseudotachylyte fault and injection veins are found within well preserved peridotite lenses and are progressively hydrated together with the host rock along the margins of the lenses numerous pseudotachylytes ranging in thickness from less than 1 to 380 mm have been identified veins thicker than 3 mm may show flow banded chilled glassy margins and cores with dendritic to spherulitic quench textures the newly formed minerals are zoned olivine fo93 89 clino and ortho pyroxene with compositions indicative of high crystallization temperatures 1300 1400 8c zoned cr spinel and a glassy to micro vesicular hydrous matrix showing that frictional melts contained up to 4 water frictional heating on co seismic faults raised the temperature from ambient blueschist facies conditions 450 8c and 1 1 5 gpa to more than 1700 8c which is required for 75 disequilibrium melting of spinel peridotite at 1 5 gpa the characteristic fault vein thicknesses observed are 1 to 3 cm but several fault veins are thicker than 10 cm co seismic displacement of 1 m a stress of 300 mpa and seismic efficiency of 5 may melt ca 60 kg peridotite pr m 2 fault surface corresponding to 20 mm thick layer of ultramafic pseudotachylyte the ultramafic pseudotachylytes described here formed by disequilibrium melting of peridotite in the upper part of the alpine subduction zone if the interpretations of typical displacements of approximately 1 m are correct the most common pseudotachylyte fault veins are related to magnitude ca 7 or larger subduction earthquakes d 2005 elsevier b v all rights reserved

a comparison of broadband source spectra seismic energies and stress drops of the 1989 loma prieta and 1988 armenian earthquakes broadband source spectra of the 1989 loma prieta mw 6 9 and 1988 armenian mw 6 7 earthquakes are computed at periods from 1 to 50 sec using digitally recorded teleseismic p body waves the effects of attenuation geometrical spreading and radiation pattern are removed from the spectra of individual stations which are then averaged the source spectra of the loma prieta and armenian earthquakes are higher for their seismic moments than the spectra of 11 intraplate earthquakes studied by zhuo and kanamori 1987 which in turn are 2 to 4 times larger than average spectra of interplate subduction zone earthquakes the seismically radiated energy can be computed from the source spectrum using haskell s 1964 formulation assuming a point source with no directivity an orowan stress drop can be obtained from the seismic energy and moment the orowan stress drops for the loma prieta and armenian earthquakes are both about 20 bars significantly higher than orowan stress drops of recent large interplate earthquakes there is a positive correlation between the orowan stress drops and the estimated repeat times consistent with the notion that mechanical fault strength increases with increasing interseismic period

paleo stress estimates on ancient seismogenic faults based on frictional heating of coal 1 faulted coals from eastern kentucky and montana usa and the south wales coalfield uk show fault related vitrinite reflectance anomalies interpreted as due to frictional heating during seismic slip the vitrinite reflectance anomalies are converted to temperature using kinetic based software easy r for post seismic cooling rates shear stresses are calculated using lachenbruch s 1986 piezometer which depends only on the area under the thermal anomaly and fault displacement for maximum displacements of 1 3 meters the minimum shear stresses are 13 64 mpa and overlap with seismological estimates of stress drops during modern earthquakes the calculated local mean normal stress is 100 mpa resulting in coefficients of friction of 0 1 0 6 thrust and 0 2 0 4 normal faults which are lower than laboratory based values

subtidal exchange in eastern long island sound abstractlong island sound lis is a large and wide macrotidal estuary with distributed river inputs including the connecticut river the largest freshwater source that flows into the eastern lis near the mouth in 2010 shipboard surveys of salinity temperature and currents were collected along an across estuary transect in eastern lis numerical model results are compared to these observations and used to study the spatial and temporal variability of salinity velocity and freshwater and salt fluxes over a 4 yr period for all low wind conditions observations and model results indicate an outward flowing low salinity wedge on the south side with an inward flowing higher salinity area underneath and to the north observations and model results during the low wind surveys indicate that stratification substantially decreases with increased tidal amplitude and decreased river discharge the velocity field is less variable among surveys model analysis indicates strong sensitivities to both tides and

sandstone petrology and geochemistry of the oligocene early miocene panjgur formation makran accretionary wedge southwest pakistan implications for provenance weathering and tectonic setting abstract the oligocene early miocene panjgur formation is comprised of submarine fan and abyssal plain turbidites deposited within the makran subduction complex sandstones of the formation are litharenite to feldspathic litharenite petrographic data indicates a quartzose recycled provenance dominated by plutonic and metamorphic fragments major elements concentrations reveal a moderate level of mineralogical maturity and high values of chemical proxy of alteration cpa 88 29 coupled with a high th u ratio 9 37 which reveals intense weathering in the source area the zr nb y and th concentrations are comparable to upper continental crust ucc values and trends in th cr th co and cr zr ratios support contribution from a felsic source however enrichment in ni and cr reinforced by trends in ni co cr v v ni and y ni ratios reveals mixing of the felsic source with mafic ultramafic source terrains tectonic discrimination plots suggest continental arc to active continental margin setting this study supports the katawaz delta panjgur submarine fan model and upholds the initial southward transport of predominantly felsic detritus from the himalayan orogenic belt controlled by the chaman ornach nal transform fault system this study further adds that the bela muslimbagh ophiolites associated melanges and the west pakistan fold thrust belt from the east and the chagai raskoh volcanic arc from the west were also concurrently shedding mafic ultramafic detritus to the basin and that the depositional system in the makran region turned westward roughly parallel to the present active margin of the makran accretionary wedge

the effect of texture and porosity on seismic reflection amplitude in granular sediments theory and examples from a high resolution shallow seismic experiment sediment properties such as grain shape sorting porosity and the effective stress applied on the grains affect the elastic behavior of granular aggregates and with it the propagation of seismic waves seismic reflections from boundaries within granular sedimentary packs such as sands carry information about variation in the sediment properties in this paper we analyze elastic contact mechanics models of granular media to show that within mineralogically uniform homogeneously saturated sediments the reflection strength can be theoretically related to variations in texture and porosity the theoretical formulation indicates that in dry mineralogically uniform sediments seismic reflection amplitude depends strongly on changes in textures such as angularity or sorting in saturated sediments at low confining pressures the reflection amplitude is primarily related to changes in porosity shallow seismic field data are interpreted quantitatively within the context of the theory the field seismic data and supportive evidence from a nearby well are consistent with our interpretation of reflections arising from changes in textural properties of the sediment above the water table this analysis can be used to quantify texture and porosity changes within sedimentary packets from measurements of seismic reflection strength and thus spatially map sedimentary properties in aquifers

role of hydraulic sorting in the origin of fluvial placers a necessary condition for placer development is selective sorting at the grain scale by size and density the effects of differential entrainment suspension and transport on an initial distribution composed of medium size quartz and 10 fine size magnetite were modeled by solving the einstein bedload function for specific grain friction velocities u super in the range 3 63 cm sec super 1 and bed roughnesses of 0 55 2 5 and 10 mm for any value of u super and for both mineral densities the transport rate for all sizes in the initial distribution decreases with increasing roughness the decrease being greatest in the finer sizes the concentration of magnetite transported in the flow increases with increasing u super for each roughness and decreases with increasing roughness for each u super the settling velocity ratio of magnetite to quartz in transport decreases with increasing u super for any value of roughness for any value of u super the ratio first decreases then increases with increasing roughness ranging from 1 36 at low u super and roughness to 0 76 at high u super and intermediate roughness these results are due to variations in the reactive angles of grains and the extent to which grains hide in the lower inner zone of the boundary layer concentrations of heavy minerals at the bed bar and system scales are explained using these results

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

measurements of frictional heating in granite a large 150 150 40 cm granite sample sawn diagonally in half to simulate a fault was deformed in a biaxial rock press at normal stress up to 6 41 mpa displacements and local shear stress were monitored along the fault 200 40 cm temperature transients as large as 10 m c were recorded following stick slip events at distances of 0 2 to 1 0 cm from the fault and were related to stress displacement and total work the temperature measurements were used to calculate the heat generated on the fault during slip frictional heating was found to be 94 2 of the total work expended in each event implying a seismic efficiency of 4 8 when water was injected onto the fault both fractional stress drop and static frictional stress increased the efficiency of frictional heating was not lowered by the presence of water heat generated during deformation of a 0 15 cm thick layer of simulated gouge was also measured for sliding rates from 0 09 to 9 1 m s in these gouge experiments temperature rises were less than 0 1 c and were proportional to sliding rate

compositional variations in deep sea gravity flow deposits a case study from the voirons flysch voirons wagital complex chablais prealps france abstract grain size control is frequently invoked to explain the compositional variation of detrital sediments in fluvial sediments a similar possibility is here investigated in the fossil deep sea gravity flow deposits from the voirons flysch voirons wagital complex chablais prealps about 270 samples of diverse depositional settings were analysed using the framework composition including cement and porosity mutti facies and grain size measurements six lithofacies have been identified from cluster analysis they correspond to channel l1 to l3 and lobe l4 and l5 depositional settings and to reworked turbidites l6 our results emphasize the close relationship between petrography and grain size which alters the detrital signal from extrabasinal sources the abundant polycrystalline component of proximal deposits is progressively removed while skeletal grains and additional intrabasinal grains become more abundant in distal deposits alongside porosity is reduced by the simultaneous increase of cement which constrains subsequent diagenetic modifications hence proximal depositional settings keep most of the inherited signal from extrabasinal sources whereas distal deposits will be homogenised when plotted in provenance analysis diagrams the successive depositional settings show distinct fields possibly corresponding to different tectonic settings of the dickinson model this compositional variation thus creates a bias in provenance interpretation resulting from both grain size control and flow mechanisms finally our results emphasize that petrographic data must be handled with care in provenance analyses especially when comparing various deep sea gravity flow systems with different grain size ranges

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

evidence for shear heating musgrave block central australia the phenomenon of shear heating is generally difficult to recognise from petrologic evidence alone establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients in the musgrave block central australia there is a clear spatial association between shear zones and interpreted elevated temperatures eclogite facies shear zones that formed at 550 ma record temperatures of 650 700 c outside the high pressure shear zones minerals with low closure temperatures such as biotite 450 c in the 40ar 39ar and rb sr systems preserve ages 800 ma suggesting that these rocks did not experience temperatures greater than about 450 c at 550 ma for any extended period thus the shear zones record temperatures that are 200 c higher than the surrounding country rocks simple calculations show that the combination of relatively high shear stresses 100 mpa and high strain rates 10 11 s 1 for short durations 1 ma can account for the observed apparent temperature variations the evidence indicates that shear heating is the dominant mechanism for localised temperature increases in the shear zones while the country rock remained at relatively lower temperatures

stratification and particle segregation in flowing polydisperse suspensions with applications to the transport and sedimentation of pyroclastic density currents abstract pyroclastic density currents pdcs are particle laden gravity driven flows of volcanic origin they typically contain solid particles with a wide range of sizes and densities resulting in complicated segregation effects during transport and sedimentation this paper describes experimental high density aqueous suspension flows scaled approximately to turbulent pyroclastic density currents it provides information on the development of concentration and particle size gradients in such flows and their relationships to vertical and stream wise grading in the resulting deposit the currents were generated by lock exchange release of initially homogeneous suspensions of highly polydispersed particles with concentrations of 13 8 23 0 vol size distributions were chosen to encompass a wide range of rouse pn numbers from particles that were fully supported by turbulence in the currents pn 2 5 to those whose motion was essentially decoupled from turbulent eddies pn 2 5 as in many pyroclastic density currents experimental currents of two different particle populations were studied one containing particles of a single density and another with particles of two different densities in each case the current head was sampled at different locations along the flume in order to study the evolution of vertical gradients in particle size concentration and density distribution in the propagating flow these gradients were then related to grading observed in the resulting deposits differential settling resulted in rapid segregation of particles of different sizes and densities in the currents and the development of both vertical and longitudinal gradients in particle concentrations sizes and proportions longitudinal gradients developed as vertical gradients were pulled out longitudinally by the vertical velocity profile in the fluid gradient development involved principally large particles capable of moving independently of turbulent eddies in the fluid the segregation behaviour of large light particles equivalent to pumice in the natural system in the bidensity currents was strongly influenced by buoyancy forces in the dense initial suspension sedimentation of large light particles was delayed and reverse vertical and longitudinal grading of these particles was generated in the resulting deposit reverse grading in the deposit was not caused by flotation of the large light particles which were normally stratified in the current during transport deposition of large light particles was probably delayed by a thin boundary layer of sufficiently high bulk density at the base of the rapidly evolving density stratified current vertical or longitudinal reverse grading of large pumices in pyroclastic density current deposits does not necessarily imply flotation during transport

short length scale variability of hybrid event beds and its applied significance abstract hybrid event beds hebs are a type of deep water sediment gravity flow deposit that generally comprise a basal clean sandstone overlain by a variety of muddier and less permeable sandy facies they are thought to be emplaced by combinations of turbidity currents transitional flows and debris flows all as part of the same transport event to date a number of studies have highlighted the common presence of hebs mainly in the outer and marginal parts of deep water systems where they replace beds composed dominantly of clean sand up dip and or axially over scales of km to 10 s km in addition to these broad patterns important yet poorly understood short length facies changes over metres to 100 s m occur modifying the overall texture and reservoir characteristics at or beneath typical spacing of production wells the nature and origin of the short length scale transitions is here addressed in four well exposed heb prone outcrops the cretaceous paleocene gottero sandstone and the miocene cilento flysch both in italy the carboniferous mam tor sandstone in northern england and the carboniferous basal ross sandstone formation western ireland a series of detailed correlation panels show marked lateral variations in internal bed make up for most of the hybrid event beds studied this variability typically involves lateral changes in the proportions of the cleaner basal sandstone and the overlying muddy sandstone division that occur without substantial change in the overall event bed thickness the variability is inferred to reflect the complex fingering between the up dip sandstone dominated part of the event bed and the down dip linked debrite due to internal erosion ploughing of the debrite into the basal clean sand where the upper part of the bed is dominated by large mudstone rafts these may have foundered into liquefied sand and been injected and partly fragmented by the sand intrusions the variable thickness and continuity of the basal clean sandstones have important implications for reservoir characterisation significant variability in bed character at interwell scale can be anticipated rugose contacts between the intra bed facies divisions may impact on drainage and sweep efficiency during hydrocarbon production

experiments on bidisperse constant volume gravity currents propagation and sediment deposition laboratory experiments show that the propagation and sedimentation patterns of particle laden gravity currents are strongly influenced by the size of suspended particles the main series of experiments consisted of fixed volume releases of dilute mixtures containing two sizes of silicon carbide particles 25 m and 69 m mean diameter within a 6 m flume polydisperse experiments involved mixtures of five different particle sizes and variation of the amounts of the finest and coarsest particles all variables apart from the initial relative proportions of particles were identical in the experiments the effects of mixing different proportions of fine and coarse particles is markedly non linear adding small amounts of fine sediment to a coarse grained gravity current has a much larger influence on flow velocity run out distance and sedimentation patterns than adding a small amount of coarse sediment to a fine grained gravity current the experiments show that adding small amounts of fine particles to a coarse grained current results in enhanced flow velocities because the fine sediment remains suspended and maintains an excess current density for a much longer time thus the distance to which coarse particles are transported increases substantially as the proportion of fines in the flow is increased our experiments suggest that sandy turbidity currents containing suspended fines will be much more extensive than turbidity currents composed of clean sand

field evidences for the role of static friction on fracture orientation in extensional relays along strike slip faults comparison with photoelasticity and 3 d numerical modeling fault friction is a parameter that is difficult to assess along fault zones since its determination depends on the knowledge of any factor controlling the state of stress around faults in brittle homogeneous rocks a limited number of these factors such as the shape of the fault surface the vicinity of fault tips or the remote stress ratio are crucial to constrain for this determination in this paper we propose to analyse a field example in which all these properties are met and where the nature of the slipped structure suggest differences in static friction we compare the orientations of branching fractures at strike slip relay zones between en echelon stylolites and en echelon joints both reactivated in shear the field data are compared with both photoelastic and 3 d numerical models that consider the remote stress conditions and the role of the geometry of the strike slip segments based on field observations these analyses quantitatively demonstrate the significant role of fault friction on the local stress field orientation and subsequent fracture formation this work points out that estimations of fault friction based on analyses of fracture patterns or in situ stresses must be accompanied with a thorough investigation of the 3 d fault shape its segmentation and the remote stress state

hybrid event bed character and distribution linked to turbidite system sub environments the north apennine gottero sandstone north west italy this study documents the character and occurrence of hybrid event beds deposited across a range of deep water sub environments in the cretaceous palaeocene gottero system north west italy detailed fieldwork 5200 m of sedimentary logs has shown that hybrid event beds are most abundant in the distal confined basin plain domain 31 of total thickness in more proximal sectors hebs occur within outer fan and mid fan lobes up to 15 of total thickness whereas they are not observed in the inner fan channelised area six hybrid event bed types heb 1 to heb 6 were differentiated mainly on basis of the texture of their muddier and chaotic central division h3 the confined basin plain sector is dominated by thick max 9 57 m average 2 15 m and tabular hybrid event beds heb 1 to heb 4 their h3 division can include very large substrate slabs evidence of extensive auto injection and clast break up and abundant mudstone clasts set in a sandy matrix dispersed clay ca 20 these beds are thought to have been generated by highly energetic flows capable of delaminating the sea floor locally and carrying large rip up clasts for relatively short distances before arresting the unconfined lobes of the mid fan sector are dominated by thinner average 0 38 m hybrid event beds heb 5 and heb 6 their h3 divisions are characterised by floating mudstone clasts and clay enriched matrices dispersed clay 25 with hydraulically fractionated components mica organic matter and clay flocs these hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport although there is a tendency to look to external factors to account for hybrid event bed development systems like the gottero imply that intrabasinal factors can also be important specifically the type of substrate available muddy or sandy and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts this article is protected by copyright all rights reserved

textural and dispersal patterns of thick mud turbidites from the madeira abyssal plain abstract the madeira abyssal plain is the site of a thick sequence of thick pleistocene turbidites that are almost entirely of material less than 63 m in grain size the major turbidites are 1 to 5 m in maximum thickness concentrating on three turbidites cored at 24 locations detailed patterns of thickness and vertical and lateral grain size changes reveal flow paths on the plain in general the bases of the units are of graded silt showing thick and thin planar lamination and occasionally ripple cross lamination a new idealised sequence of changes in size and structures with distance along the flow path is developed closer to source the beds comprise a graded structured silty base overlain by structureless mud which may also be graded down current the silty base becomes thinner with less apparent structure and the upper homogeneous part becomes thicker and more uniform in an overall thickening trend at the distal end uniform beds up to 5 m in thickness are found in one turbidite the modal size structure shows some silt modes which are hydrodynamically sorted and change size vertically and spatially while one particular mode is constant in size due to a particular species of coccolith the turbidites originated from slumps on the northwest african continental margin and from the vicinity of madeira and the canaries some of which exceeded 100 km3 in volume

evidence for cool extrusion of the north indochina block along the ailao shan red river shear zone a diancang shan perspective abstractmuch debate surrounds the temporal thermal structural evolution of the 1000 km nw se trending ailao shan red river asrr shear zone this mainly reflects the contradictory interpretations of the timing and p t conditions for the occurrence of left lateral shearing event due to a diverse data set of mineral ages our new microstructural petrological and geochronological data from the southern section of the diancang shan dcs block along the west wall of the asrr support slow cooling from 300 c to 150 c from the middle eocene to the late miocene accompanied by left lateral shearing activity this conclusion is based on the following 1 the lower greenschist facies assemblages of biotite replaced by muscovite or chlorite the albitized k feldspar and the stable association of k feldspar chlorite rather than muscovite biotite are universally observed for the synkinematic sn 1 and mylonitic s c fabrics from both quartzofeldspathic and amphibolite domains 2 new 40ar 39ar data for k fe

hot on the trail coseismic heating on a localized structure along the muddy mountain fault nevada abstract recent advances in the use of thermal proxies to identify past earthquake slip in exhumed faults have created an extraordinary opportunity to map the geometry of past ruptures in unprecedented detail this approach can reveal along strike differences in the structure and speed of earthquake slip here we present organic thermal maturity data collected along the muddy mountain thrust in nevada to investigate where it was within the fault that earthquake slip occurred and whether this is consistent along strike we observe large changes in thermal maturity which represent temperature rise variations along the fault modeling of thermal maturity measurements yield peak temperatures of 760 1090 c where the principal slip zone psz is narrowest 0 8 mm nearby where the psz is thicker 1 5 mm these temperatures did not exceed 500 c based upon estimates of temperature rise within a submillimeter psz mean frictional work during earthquake slip was 6 3 7 1 mjm 2 these results show that thickness of the active slipping zone can vary at small spatial scales and development of a continuously narrow

esr detection of seismic frictional heating events in the nojima fault drill core samples japan abstract we have analyzed the nojima fault nied 1800 m drill core samples by esr electron spin resonance to detect seismic frictional heating events especially during the 1995 kobe earthquake dark gray fault gouge with foliation 10 cm away from the fault plane at about 1140 m in depth which was produced by ancient fault movements has a fmr ferrimagnetic resonance signal heating experiments show that this fmr signal is derived from ferrimagnetic trivalent ion oxides fe 2 o 3 maghemite with imperfect crystallinity which is produced by thermal dehydration of feooh lepidocrocite or fe oh 3 limonite the existence of the fmr signal means that dry heating such as frictional heating once occurred and that the frictional heat temperature along the dark gray fault gouge may have risen to over 350 c during ancient seismic fault slip in order to detect frictional heating events in fault zones the increase of the fmr signal and the color change of fault gouge into dark gray or black are important indexes on the other hand no fmr signal is detected from the fault gouges just on two fault planes at about 1140 m and 1300 m in depth which are considered to be possible main fault planes in the 1995 kobe earthquake these two fault planes may not have played an important role of fault slip in the earthquake