the impact of frictional healing on stick slip recurrence interval and stress drop implications for earthquake scaling interseismic frictional healing is an essential process in the seismic cycle observations of both natural and laboratory earthquakes demonstrate that the magnitude of stress drop scales with the logarithm of recurrence time which is a cornerstone of the rate and state friction rsf laws however the origin of this log linear behavior and short time cut off for small recurrence intervals remains poorly understood here we use rsf laws to demonstrate that the back projected time of null healing intrinsically scales with the initial frictional state i we explore this behavior and its implications for 1 the short term cutoff time of frictional healing and 2 the connection between healing rates derived from stick slip sliding versus slide hold slide tests we use a novel continuous solution of rsf for a one dimensional spring slider system with inertia the numerical solution continuously traces frictional state evolution and healing and shows that stick slip cut off time also scales with frictional state at the conclusion of the dynamic slip process i dc vpeak this numerical investigation on the origins of stick slip response is verified by comparing laboratory data for a range of peak slip velocities slower slip motions yield lesser magnitude of friction drop at a given time due to higher frictional state at the end of each slip event our results provide insight on the origin of log linear stick slip evolution and suggest an approach to estimating the critical slip distance on faults that exhibit gradual accelerations such as for slow earthquakes

seismic and aseismic weakening effects in transtension field and microstructural observations on the mechanics and architecture of a large fault zone in se tibet

effects of simulated fault gouge on the sliding behavior of tennessee sandstone nonclay gouges stick slip has been considered to be a mechanism of shallow focus earthquakes along pre existing faults and thus laboratory studies relevant to stick slip may lead to a better understanding of the mechanisms of the earthquakes and eventually to an effective prediction and or control of them this paper deals with the effects of various simulated gouges on the sliding behavior of rocks with special emphasis on how fault gouge alters potentially unstable behavior of a brittle rock about 150 specimens of tennessee sandstone with various simulated gouges along a 35 precut are deformed dry in a triaxial apparatus at room temperature with shortening rate of about 2 10 4cm s and at confining pressures to 300 mpa tennessee sandstone is a brittle and strong rock quartz cemented quartzose sandstone which consistently shows stick slip without simulated gouge at confining pressures above 30 40 mpa sliding behavior with a gouge layer depends markedly on the material used to simulate the gouge experimental results from monomineralic gouges show that mohs hardness of a mineral is a useful parameter to predict the general sliding behavior the most unstable sliding is associated with gouge composed of minerals with intermediate hardness dolomite anhydrite and calcite these gouges undergo the transition from stable sliding to stick slip at pressures of 50 80 mpa gouge composed of hard mineral such as quartz or feldspar behave more stably but stick slip occurs at pressures above 250 mpa only stable sliding is observed for gouge composed of soft minerals like halite although anhydrite gouge shows violent stick slip at 100 mpa pressure whereas only stable sliding occurs for quartz at the same pressure when they are mixed the behavior changes systematically with composition the inclusion of only 10 anhydrite permits stick slip and hence even a minor constituent mineral of fault gouge may alter the sliding mode for gouge composed of two distinct layers the more stabilizing member of the two dominates the behavior and the behavior is considerably different from that of homogeneously mixed gouge with the same bulk composition this suggests the significance of internal structures of natural fault zone in understanding the effects of fault zone materials on the fault motion the gouge composed of calcite or a mineral harder than calcite all show high and approximately the same ultimate frictional strength with an exception of fluorite the frictional strength is intermediate for fluorite galena and barite gouges and it is low for halite gouge

the role of mineral composition on the frictional and stability properties of powdered reservoir rocks national natural science foundation of china 41672268 41772286 u s department of energy doe de fe0023354

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

on palaeozoic mesozoic brittle normal faults along the sw barents sea margin fault processes and implications for basement permeability and margin evolution palaeozoic mesozoic brittle normal faults onshore along the sw barents sea passive margin off northern norway give valuable insight into fault and fluid flow processes from the lower brittle crust microstructural evidence suggests that late permian early triassic faulting took place during multiple phases with initial fault movement at minimum p t conditions of c 300 c and c 240 mpa c 10 km depth followed by later fault movement at minimum p t conditions of c 275 c and c 220 mpa c 8 5 km depth the study shows that pore pressures locally reached lithostatic levels 240 mpa during faulting and that faulting came to a halt during early deep stages of rifting along the margin fault permeability has been controlled by healing and precipitation processes through time which have sealed off the core zone and eventually the damage zones after faulting a minimum average exhumation rate of c 40 m ma 1 since the late permian is estimated it implies that the debated late cenozoic uplift of the margin may be explained by increased erosion rates in the coastal regions owing to climate detoriation which caused subsequent isostatic recalibration and uplift of the marginal crust the studied faults may be used as analogues of basement involved fault complexes offshore revealing details about the offshore nature of faulting including past and present basement and fault zone permeability

effects of shear stress applied to surfaces in stationary contact on rock friction in this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact we develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test a series of experiments conducted at a single normal stress of 5 mpa show the following effects first unloading the shear stress during the hold period increases frictional resistance by up to 10 20 a decrease in shear stress linearly increases the frictional resistance of the interface secondly the static friction coefficient increases with the logarithm of contact time the friction coefficient increases by 0 01 per decade of contact time at near zero shear stress levels and by more than 0 02 at shear stress levels that are greater than half the sliding friction

geology of offshore new ireland basin in northern papua new guinea abstract the 62 mi 100 km wide new ireland basin extends north westward from southwest of bougainville to north of the admiralty islands we have studied some 5 000 mi 8 000 km of geophysical data from the basin north of bougainville to west of manus island the data were gathered by ccop sopac the australian bureau of mineral resources gulf oil co and a french consortium the part of the new ireland basin studied here is a fore arc basin which contains neogene sediments and lies between two ridges formed as part of an old north facing arc trench system in the oligocene and miocene the southern ridge is the old volcanic axis and consists of volcanic rocks forming new ireland new hannover and the admiralty islands the northern ridge appears to be an accretionary prism which forms the southern flank of the west melanesian trench uplifted during its active phase in oligocene miocene times the central new ireland basin is generally a simple little deformed synclinal basin with as much as 3 mi 5 km of well stratified sediment along its axis the basin fill contains several seismic discontinuities and unconformities and probably consists of miocene pliocene quaternary volcaniclastic and carbonate sediments the older sequences are lateral equivalents of sediments outcropping on new ireland and other islands but younger flat lying carbonate oozes and turbidites are ponded in the basin north of new ireland a number of volcanic islands consisting largely of pyroclastic rocks and lavas have cut through the basin northeast of manus island folding and faulting in the basin increase markedly with faults forming large scarps on the sea floor volcanism may have had a more active role in sedimentation reducing seismic penetration in the sediments in areas of extensive flows north of manus island young deformation and volcanism have replaced the flat lying strata common to the central basins area obliterating further traces of the deeper basin if it exists the thickness of the sedimentary sequence and the possible presence of some carbonate buildups at depth in the central basin indicates that the basin may have some petroleum potential major unknowns are source rock potential and the thermal gradient history in the basin carbonate buildups are the most likely reservoir rocks for any petroleum generated in the basin end of article last page 966

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

a microphysical interpretation of rate and state dependent friction for fault gouge the evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip nature of earthquake stress drop and earthquake nucleation laboratory based rate and state dependent friction rsf laws can describe changes in fault strength during slip but the connections between fault strength and the mechanisms that dictate the mode of failure from aseismic creep to earthquake rupture remain poorly understood the empirical nature of rsf laws remains a drawback to their application in nature here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling rsf we document robust relationships between 1 the initial value of sliding or kinetic friction 2 rsf parameters and 3 the time rates of frictional strengthening aging we derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by 1 an activation energy that controls the rate of asperity growth by plastic creep and 2 an inverse relationship between material hardness and the activation volume of plastic deformation collectively our results illuminate the physics expressed by the rsf parameters and which describe the absolute value of frictional strength and its dependence on time and slip rate moreover we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain scale asperity contacts

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

carbon deposition during brittle rock deformation changes in electrical properties of fault zones and potential geoelectric phenomena during earthquakes 1 to investigate potential mechanisms for geoelectric phenomena accompanying earthquakes we have deformed hollow cylinders of sioux quartzite to failure in the presence of carbonaceous pore fluids and investigated the resulting changes in electrical conductivity and carbon distribution samples were loaded at room temperature or 400 c by a hydrostatic pressure at their outer diameter increasing pressure at a constant rate to 290 mpa pore fluids consisted of pure co co2 and ch4 and a 1 1 mixture of co2 and ch4 each with pore pressures of 2 0 to 4 1 mpa failure occurred by the formation of mode ii shear fractures transecting the hollow cylinder walls radial resistivities of the cylinders fell to 2 9 to 3 1 m m for co tests and 15 2 to 16 5 m m for co2 ch4 tests compared with 23 m m for dry undeformed cylinders carbonaceous fluids had no discernable influence on rock strength on the basis of mapping using electron microprobe techniques carbon occurs preferentially as quasi continuous films on newly formed fracture surfaces but these films are absent from preexisting surfaces in those same experiments the observations support the hypothesis that electrical conductivity of rocks is enhanced by the deposition of carbon on fracture surfaces and imply that electrical properties may change in direct response to brittle deformation they also suggest that the carbon films formed nearly instantaneously as the cracks formed carbon film deposition may accompany the development of microfracture arrays prior to and during fault rupture and thus may be capable of explaining precursory and coseismic geoelectric phenomena

effects of load point velocity on frictional instability behavior abstract triaxial experiments were conducted on sawcut westerly granite specimens sandwiched with a simulated gouge layer of ultrafine quartz over a wide range of normal stresses from 25 to 250 mpa tens and sometimes hundreds of repeated stick slip events were observed to persist over a total slip displacement up to 10 mm a transition from stick slip to stable sliding was observed as the result of cumulative slip displacement the total slip displacement over which repeated stick slip instabilities occurred before the transition to stable sliding decreases with increasing normal stress the stress drop amplitude decreases with increasing load point velocity the experimentally determined stress drop amplitude was also found to increase as a function of the time of stationary contact the dependence of stress drop amplitude on load point velocity and on time of stationary contact can be characterized empirically by a power law preliminary data suggest that the two effects are coupled the seismological implications of the experimental data are discussed at relatively high normal stresses above 250 mpa no systematic dependence of stress drop amplitude on load point velocity was observed an increase in gouge particle size stabilizes the frictional instability behavior a mixed mode of velocity weakening and velocity strengthening behavior was occasionally observed

nucleation of dynamic slip on a hydraulically fractured fault this work is concerned with the relationship between hydraulic fracturing injection into a fault and the possibility of a seismic slip the results of this study show that the nucleation of dynamic slip on a fault with slip weakening friction is only weakly dependent on the magnitude of the stress perturbation ahead of the propagating hydraulic fracture hf or the hf propagation regime and is mainly controlled by the hydraulic fracture length i e the size of the fully unloaded fault segment at a given time the growth of the fault slipping patch remains stable when the background shear stress 0 is smaller than the residual fault strength r under ambient conditions otherwise 0 r nucleation of dynamic slip takes place when the hydraulic fracture grows to the critical size lc which is vanishingly small p 0 for critically stressed faults i e when the background stress approaches the fault peak strength 0 p and is diverging as 1 0 r when the stability boundary is approached 0 r our solution for the critical hf size allows to infer the corresponding fluid injection volume that may lead to slip instability on a fault with given frictional properties and background stress

cohesive strengthening of fault zones during the interseismic period an experimental study 1 there is widespread evidence indicating that faults regain a portion of their strength during the interseismic period here we present experiments designed to understand and quantify the interseismic cohesive strengthening resulting from fluid rock reactions in fault zones the triaxial experiments consisted of fracturing cores of fontainebleau sandstone under dry conditions forming a localized shear failure zone stage 1 the specimens were then reacted hydrothermally under isostatic conditions allowing the fault damage zone to compact consolidate and strengthen stage 2 following reaction the specimens were then reloaded to failure under nominally dry conditions so that the increase in cohesive strength of the fault could be measured stage 3 experiments show that cohesion increase is positively correlated to temperature and pore pressure during reaction after 6 hours of reaction at the highest temperatures 927 c and pore pressures 200 mpa cohesion increases by as much as 35 mpa microstructural examination of the specimens showed that the gouge particles within the fault compacted and cemented together exhibiting textures typical of pressure solution and that fractures in the surrounding damage zone had healed a theoretical treatment of the data was conducted using these experiments in combination with results on time dependent changes in fault cohesion presented by tenthorey et al 2003 we find that the rate controlling process in our experiments has an activation energy q of approximately 70 kj mol 1 we use this information to develop a model for time dependent cohesive strengthening in fault zones within the continental seismogenic regime we conclude that significant cohesive strengthening of fault zones can occur during the interseismic period of medium to large earthquakes given the presence of reactive pore fluids

pressure solution lithification as a mechanism for the stick slip behavior of faults many major faults including a large fraction of the san andreas appear to be virtually quiescent between great earthquakes the locked sections of the san andreas near san francisco and los angeles have little or no seismic activity on the primary fault trace although secondary faults may be active stick slip behavior on a fault can be explained in terms of a static coefficient of friction which is larger than the dynamic or sliding coefficient in this paper we propose a modification of the friction hypothesis in which chemical lithification cementation occurs on the fault between earthquakes as the stress on the fault increases it becomes large enough to break the cemented bonds between particles causing slip on the fault we treat this problem quantitatively assuming that pressure solution is responsible for the cementation an advantage of this model is that the hydrostatic pressure approaches the lithostatic pressure during cementation so that low fault strengths are predicted

frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere 1 faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults oceanic detachment faults subduction zones and continental rifts however few data exist that directly explore the frictional properties of peridotite rocks improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere furthermore our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes it has been hypothesized and some experimental data indicate that plastic yielding by dislocation glide low temperature plasticity determines the direct effect in the rate and state frictional constitutive formulation plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and or displacement dependent friction evolution effect and frictional healing we present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas medium deformation apparatus in the temperature range of 400 1000 c with 100 mpa confining pressure we conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability we also conducted slide hold slide experiments to investigate the time and temperature dependence of fault zone restrengthening frictional healing the mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding the data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts we explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere

mechanisms of fracture propagation in experimentally extended sioux quartzite abstract notched samples of sioux quartzite have been extended to failure at temperatures t between 25 and 710 c strain rates e from 5 2 10 6 to 6 7 10 4 s 1 and 100 mpa confining pressure and fracture morphologies examined by optical and scanning electron microscopy in all the extension tests performed sample failure occurred by the formation of a tensile fracture in or near the notch mid plane differential stress magnitudes at failure are insensitive to variations in t and e and calculated tensile strengths are comparable to previously reported values for unconfined tests at room temperature force displacement records show a change in mechanical response from linear elastic behavior at temperatures between 25 and 412 c to significant yielding in compression prior to failure in the 500 to 710 c tests in all cases fractures consist almost entirely of intragranular cracks igc which exhibit characteristic surface features which can be used to infer local crack propagation directions in one test in which fracturing was initiated at an edge flaw igc propagation directions show no overall trend the observations indicate that the mechanism of fracture propagation involves nucleation growth and coalescence of igc which are themselves propagating in all directions in the plane of the main fracture the onset of inelastic yielding prior to failure at elevated temperatures is attributed to the formation of thermally induced gbc which act as nucleation sites for igc during extension

interseismic re strengthening and stabilization of carbonate faults by non dieterich healing under hydrothermal conditions abstract friction experiments consisting of a velocity stepping stage a slide hold slide shs stage and a second velocity stepping stage have been performed to study the frictional healing behavior of carbonate fault gouge and the effects of healing on the velocity dependence of friction at 20 140 c and at 50 mpa effective normal stress dry experiments show classical dieterich healing characterized by a transient peak in friction after each hold period with no effects of shs testing on steady state friction or velocity dependence by contrast the wet tests show 1 an increase in apparent steady state friction upon re sliding after a hold period and 2 a pronounced increase in the velocity dependence parameter a b after the shs stage while the first of these non dieterich type healing effects has been observed in previous hydrothermal experiments on simulated quartz gouges it has not been reported previously for carbonate gouges the observed effect of shs testing on a b has never been reported our findings suggest that under in situ hydrothermal conditions interseismic fluid assisted deformation processes such as pressure solution can significantly promote fault re strengthening in carbonates and can cause slip stabilization if the results are applicable to active faults in carbonate terrains they have important implications for understanding how the extent of the seismogenic zone and how earthquake magnitude and aftershock distributions may evolve with repeated cycles of natural seismicity and interseismic healing

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

how strong is an asperity a recent study of repeating earthquakes on the san andreas fault in central california by nadeau and johnson 1998 found that the smallest events occurred on patches having a linear dimension of the order of 0 5 m displacements of about 2 cm and stress drops of the order of 2000 mpa roughly 10 times larger than rock strengths measured in the laboratory the stress drop for larger events was observed to decrease as a power law of the seismic moment reaching the commonly observed value of 10 mpa at about magnitude 6 these large strengths are shown here to be consistent with laboratory data if the preexisting microcracks are all healed a hierarchical fractal asperity model is presented which is based on recent laboratory observations of contact distributions in sliding friction experiments this cantor dust model is shown to be consistent with the observed power law decrease in stress drop and increase in displacement with increasing event size the spatial distribution of hypocenters in the parkfield area is shown to be consistent with this simple fractal model and with a hierarchical clustering of asperities having a fractal dimension of d 1 and discrete rescaling factor of about 20

effects of temperature and sliding rate on frictional strength of granite layers of artificial granite gouge have been deformed on saw cut granite surfaces inclined 30 to the sample axes samples were deformed at a constant confining pressure of 250 mpa and temperatures of 22 to 845 c the velocity dependence of the steady state coefficient of friction ss was determined by comparing sliding strengths at different sliding rates the results of these measurements are consistent with those reported bysolberg andbyerlee 1984 at room temperature andstesky 1975 between 300 and 400 c stesky found that the slip rate dependence of ss increased above 400 c in the present study however the velocity dependence of ss was nearly independent of temperature

new zealand and southwest pacific islands in new zealand new incentives by the government have greatly stimulated interest in exploration on land four wells were completed during 1980 at a total depth of 10 120 m one well was a commercial oil and gas discovery offshore the first exploratory well since 1978 was spudded shortly before the end of 1980 offshore concession areas have increased over ten fold to 107 044 km2 on land licenses which are all owned by the government company petrocorp decreased to 11 591 km2 during 1980 the combined output of kapuni and maui gas was 1 069 049 106 m3 a decrease of 18 23 this reflects the new gas recycling operation at the kapuni field which started in april combined condensate production was down only 12 15 amounting to 418 941 m3 natural gasoline was down 17 44 to 7 093 m3 whereas lpg production went up 39 44 to 27 301 m3 in tonga 925 km of offshore multichannel seismic gravity and magnetic surveys run in 1979 have been processed and interpreted firm drilling proposals must be submitted by july 1 1981 otherwise the petroleum agreement will be terminated outside the presently held license area of 15 540 km2 ccop sopac have conducted two single channel seismic surveys a 900 km survey north of vava u and a 2 140 km survey over the tonga platform south of tongatapu widespread occurrence of relatively thick sediments has been encountered particularly in the southern area in fiji the first two exploratory wells ever drilled were dry total depths of the wells were 2 743 m and 2 839 m the wells were drilled in bligh water north of the island of viti levu and terminated in a lower tertiary sequence without reaching basement in vanuatu the newly independent republic of the former new hebrides condominium no petroleum legislation has so far been introduced ccop sopac and orstom jointly ran a 4 000 km single channel reflection seismic survey between the northern islands several sedimentary basins with over 2 500 m of slightly deformed sediments of miocene pliocene age have been delineated however the water depth is generally about 2 000 3 000 m in the solomon islands there is still no petroleum legislation but the draft of the petroleum exploration and development act has been completed and will go before parliament during 1981 in papua new guinea one well was drilled to 3 027 m and abandoned as dry it confirmed the regional stratigraphic interpretation and had encouraging hydrocarbon indications in the mesozoic part of the sequence concession holdings increased to 815 blocks with another 394 blocks under application

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

influence of grain boundary structural evolution on pressure solution creep rates intergranular pressure solution is a well known rock deformation mechanism in wet regions of the upper crust and has been widely studied especially in the framework of compaction of granular materials such as reservoir sandstones and fault rocks several analytical models exist that describe compaction creep by stress induced mass transport and the parameters involved are relatively well constrained by laboratory experiments while these models are capable of predicting compaction behavior observed at relatively high porosities they often overestimate compaction rates at porosities below 20 by up to several orders of magnitude this suggests that the microphysical processes operating at low porosities are different and are not captured well by existing models the implication is that available models cannot be extrapolated to describe compaction of sediments and fault rocks to the low porosities often reached under natural conditions to address this problem we propose a new thermodynamic model that describes the decline of pressure solution rates within individual grain contacts as a result of time averaged growth of asperities or islands and associated constriction of the grain boundary diffusion path here termed grain boundary evolution the resulting constitutive equations for single grain grain contacts are then combined and solved semianalytically the compaction rates predicted by the model are compared with those measured in high strain compaction experiments on wet granular halite a significant reduction in compaction rate is predicted when grain boundary evolution is considered which compares favorably with the experimental compaction data

oil and gas developments in new zealand and southwest pacific islands in 1981 new zealand has experienced a strong increase in exploration activity offshore license holdings are up to 164 015 km2 an increase of 53 onshore licences are 20 467 km2 an increase of 77 four offshore wells were drilled to a total depth of 13 690 m they were all dry onshore drilling amounted to 8 548 m and was concentrated around last year s oil discovery of mckee 2a the field was confirmed by 1 extension well mckee 3a whereas 2 other wells were dry and a fourth extension well still drilling by year end onland seismic surveys covered 484 line km while marine seismic work amounted to 6 561 km because of increased re injection of gas in the kapuni field the saleable production slightly went down but condensate production rose by nearly 50 000 m3 i e 21 more than last year with the strongly increased output from the offshore maui field total gas production for sale was 1 286 106 m3 up 20 2 while the total production of condensate was 550 101 m3 up 31 3 lpg production rose to 41 179 m3 up 50 8 tonga has experienced a virtual standstill in exploration but ccop sopac has completed and prepared for publication its interpretation of a single channel seismic survey over the southern tongan platform conducted the year before in fiji license areas remained unchanged but a new company bennett petroleum corp acquired a 75 interest in block d extensive geochemical sampling and minor geophysical surveys were undertaken in several blocks and a shallow stratigraphic hole was drilled to 307 m in vanuatu which still lacks petroleum legislation no exploration licenses were granted a ccop sopac sponsored study of all existing marine seismic surveys has been completed and a summary of results has been prepared for publication the solomon islands too has no petroleum legislation as yet ccop sopac ran single channel seismic surveys to a total of 1 115 line km mainly near rennell island but also some in the central solomons trough in papua new guinea the total concession areas increased to 72 600 km2 oil companies recorded 550 km of seismic lines onshore and 1 716 km offshore aeromagnetic surveys covered 9 779 line km outside concession areas ccop sopac conducted single channel seismic surveys in the new ireland basin between bougainville and manus island for a total length of 4 964 km interpretation of these surveys has been completed and prepared for publication an appraisal well barikewa 2 was spudded shortly before year end initial reserve estimates for this large anticline had run as high as 10 tcf of gas in place drilling depth will be about 2 120 m

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

mineral precipitation as a mechanism of fault core growth abstract faults vary in structural style from simple planes to complex systems composed of fault cores and damage zones increased fault complexity results from the interaction of mechanical and chemical processes including fracture growth shear and linkage and mineral dissolution and precipitation although water rock interaction is traditionally associated with fault rock weakening and shear localization we investigate processes of fault core widening by water rock interactions that resulted in quartz precipitation we combine field and petrographic observations with prior mechanical characterization to assess the impact of alteration and cementation on fault architecture at the dixie comstock epithermal gold deposit nevada usa mineralized portions of the fault contain strong thick silicified fault cores and wide weak damage zones with evidence for widening of the core through entrainment of damage zone material and repeated cycles of embrittlement dilation and cementation we present a model of fault zone evolution in which the hydrothermal regimes favoring either alteration weakening or precipitation strengthening result in distinct fault zone architecture and mechanical and flow properties of fault systems alteration weakening favors localization of the fault into thinner clay rich low permeability fault cores precipitation strengthening promotes thick strong and low permeability fault cores with mineralization embrittlement enhancing transient permeability following coseismic failure

oil and gas developments in new zealand and southwest pacific islands in 1984 new zealand had an increase in petroleum production while exploration drilling continued at 1983 s high level although there was an overall drop in licensed acreage the amount of seismic exploration increased markedly with 1 100 km of acquisition onshore and 4 300 km offshore a new oil discovery toetoe 1a was made near mckee field combined production from kapuni maut mckee and kaimiro fields was 2 978 56 106 million m3 of gas up 25 and 962 323 m3 of condensate up 14 the combined mckee and pouri fields which came on line in november are producing oil at about 5 200 b d 830 m3 day all licenses in tonga have been relinquished and all company data are on open file new petroleum legislation will be in force in 1985 fiji had no exploration activities three license blocks have been renewed at reduced acreage vanuatu and the solomon islands are still awaiting legislation for petroleum exploration a second stage of a ccop sopac sponsored tripartite project s p lee cruise was carried out in both countries and also in tonga and the new ireland basin of papua new guinea on the mainland of papua new guinea 5 wells were drilled to a combined depth of 10 158 m up 10 9 an were dry concession areas comprise 11 petroleum prospecting licences with a total of 1 062 blocks at 5 min graticules

frictional strength of fault gouge in taiwan chelungpu fault obtained from tcdp hole b abstract three fault zones fzb1136 fzb1194 and fzb1243 are found in core samples in hole b borehole penetrating through the chelungpu fault central taiwan that activated at the 1999 taiwan chi chi earthquake each fault zone is composed of a black gouge zone bgz and a gray gouge zone ggz surrounded by a fault breccia zone bz and or fracture damaged zone fz we conducted tri axial friction experiments on samples collected from subzones of the above three fault zones under the 1 km depth ambient condition with axial shortening rates of 0 1 to 10 m s to investigate frictional strength and its velocity dependence we found that the coefficient of friction is 0 3 for the bgz at fzb1136 1136bgz which is lower than those at other fault zones this result indicates that fault slip at the chi chi earthquake occurred at the 1136bgz the estimated frictional strength profile across fzb1136 was that the frictional strength was the lowest the coefficient of friction was 0 3 for the bgz and increased up to 0 5 for undeformed host rock with increasing distance from the bgz presence of the intermediate frictional strength zone consisting of the ggz and the bz suggests a development of off fault damage zone where deformation occurred not only in the bgz but also in the intermediate zone this feature should be important to estimate total fracture energy released during earthquakes we also suggest that coefficients of friction and the velocity dependences of the samples are closely related to localization of shear deformation and clay content respectively

systematic variations in recurrence interval and moment of repeating aftershocks 1 the recurrence intervals for 194 repeating clusters on the calaveras fault follow a power law decay relation with elapsed time after the 1984 m6 2 morgan hill california mainshock the decay rates of repeating aftershocks in the immediate vicinity of a high slip patch that failed during the mainshock systematically exceed those that are farther away the trend between relative moment and recurrence interval which is a measure of the fault healing rate varies systematically with depth and changes from negative to positive value as the distance between the repeating aftershock and the mainshock slip patch increases we speculate that high strain rate in the early postseismic period may cause transient embrittlement and strengthening of the deep repeating clusters in the areas adjacent to the mainshock slip patch resulting in large moments that decrease with time as the strain rate diminishes our observations suggest that systematic behavior of repeating aftershocks reflect variations in the fault zone rheology

frictional and hydraulic behaviour of carbonate fault gouge during fault reactivation an experimental study abstract we present a novel experimental approach devised to test the hydro mechanical behaviour of different structural elements of carbonate fault rocks during experimental re activation experimentally faulted core plugs were subject to triaxial tests under water saturated conditions simulating depletion processes in reservoirs different fault zone structural elements were created by shearing initially intact travertine blocks nominal size 240 110 150 mm to a maximum displacement of 20 and 120 mm under different normal stresses meso and microstructural features of these sample and the thickness to displacement ratio characteristics of their deformation zones allowed to classify them as experimentally created damage zones displacement of 20 mm and fault cores displacement of 120 mm following direct shear testing cylindrical plugs with diameter of 38 mm were drilled across the slip surface to be re activated in a conventional triaxial configuration monitoring the permeability and frictional behaviour of the samples as a function of applied stress all re activation experiments on faulted plugs showed consistent frictional response consisting of an initial fast hardening followed by apparent yield up to a friction coefficient of approximately 0 6 attained at around 2 mm of displacement permeability in the re activation experiments shows exponential decay with increasing mean effective stress the rate of permeability decline with mean effective stress is higher in the fault core plugs than in the simulated damage zone ones it can be concluded that the presence of gouge in un cemented carbonate faults results in their sealing character and that leakage cannot be achieved by renewed movement on the fault plane alone at least not within the range of slip measureable with our apparatus i e approximately 7 mm of cumulative displacement additionally it is shown that under sub seismic slip rates re activated carbonate faults remain strong and no frictional weakening was observed during re activation

reconstructing the geomorphic evolution of large coastal dunes along the southeastern shore of lake michigan abstract coastal dunes are common along the eastern shore of lake michigan with the most common being large 30 m high parabolic dunes that mantle lake terraces south of manistee mi although these dunes are an important resource in michigan and thus intensely managed by various state agencies their geomorphic history is poorly understood this study examines four sites near holland mi through stratigraphic and radiocarbon analyses and is the most detailed geomorphic reconstruction conducted of coastal parabolic dunes in the region results from this study could benefit the environmental agencies in their management of the coastal dune ecosystem deposition of eolian sand apparently began 5500 cal years bp i e during the nipissing high stand most 75 dune building occurred between 4000 and 2500 cal years bp but was punctuated by brief periods of stability that resulted in the development of entisols a c horizonation entisol burial occurred because the sand supply apparently increased during both the receding and rising lake levels subsequently each dune stabilized for 2000 years allowing the formation of inceptisols i e a e bs c horizonation this interval of dune stability correlates with sites south of holland and occurred while lake michigan fluctuated slowly and the beach potentially prograded these combined variables of slow fluctuation and potential beach progradation hypothetically protected the dunes from wave erosion dunes near holland became active again 1000 500 cal years bp and grew both vertically and laterally this activity intensified in the past 500 cal years bp and hypothetically occurred due to recession of the lake shore such that wave erosion at the modern bluff base resumed results from this study indicate that coastal dunes along lake michigan are similar to many coastal dunes around the world including those along the intermediate beaches in se australia

oil and gas developments in new zealand and southwest pacific islands in 1983 new zealand had an increase in exploration activity particularly drilling 30 876 m were drilled onshore up 62 and 14 034 m offshore concession holdings slightly increased offshore to 230 665 km2 but dropped to nearly half onshore to 34 353 km2 seismic surveys decreased to 477 5 line km onshore and 1 128 km offshore down 56 and 93 respectively oil gas and condensate were found in several wells on small structures close to the recently discovered mckee field regular production from mckee began in april 1984 at an initial rate of 1 000 bopd production from kapuni and maui fields combined was 2 381 313 106 m3 of gas up 9 4 and 845 286 m3 of condensate down 2 3 construction of a 1 200 mt day methanol plant which uses natural gas from these fields was completed no exploration was carried out in tonga fiji vanuatu and the solomon islands in fiji all prospecting licenses expired but renewal terms on areas reduced by 50 were agreed on in principle papua new guinea had 4 wells drilled to a combined depth of 9 158 m up 23 2 the juha 2x appraisal well confirmed the discovery of gas and condensate in the juha anticline in the gulf of papua the offshore appraisal well pasca a3 blew out and was abandoned the total area of petroleum prospecting licenses slightly increased to 74 715 km2

oil and gas developments in new zealand and southwest pacific islands in 1982 new zealand experienced a marked increase in activity concession holdings went up 205 onshore to 62 429 km2 and 31 offshore to 215 439 km2 seismic coverage more than doubled both onshore and offshore to 1 075 and 15 321 line km respectively several new targets have been delineated offshore and 2 drillships are scheduled to arrive in the country and start drilling during 1983 onshore the total depth drilled more than doubled to 18 993 m drilling was concentrated in the recently discovered mckee field where 2 additional oil producers were completed and on 3 other structures nearby where 1 well tested gas and condensate production of gas and condensate from the kapuni and maui fields combined was 2 177 122 106 m3 up up 69 3 and 865 454 m3 up 57 3 respectively expansion of the only refinery in new zealand and the realization of large petrochemical projects using natural gas are well under way these projects include an ammonia urea plant which was completed by year end a methanol plant and a methanol to synthetic petrol plant now under construction fiji also saw increased exploration activity there were no changes in the license holdings but marine and land seismic surveys covered 242 58 and 42 04 line km respectively four wells were drilled to a total depth of 5 697 m all were dry papua new guinea had active exploration carried out in nearly all of its 11 petroleum prospecting licenses a total of 2 750 line km of marine seismic data was acquired whereas onshore 654 line km were obtained the appraisal well barikewa 2 was drilled to a total depth of 1 820 m and plugged and abandoned in the western highlands 2 wildcat wells were drilled lavani 1 which was dry plugged and abandoned and juha 1 which was drilling ahead at 2 625 m at year end total depth drilled was 7 433 m in the gulf of papua an appraisal well pasca a3 was spudded in january 1983 a reservoir engineering study of the pasca field which is being considered for commercial development has been completed for the papua new guinea government no exploration activities took place in tonga vanuatu or the solomon islands but a ccop sopac sponsored project funded by a tripartite agreement between the governments of australia new zealand and the united states did comprehensive geophysical studies in some offshore areas of these 3 countries

healing behavior of simulated fault gouges from the groningen gas field and implications for induced fault reactivation we investigated the frictional strength recovery healing and subsequent reactivation and slip weakening behavior of simulated fault gouges derived from key stratigraphic units in the seismogenic groningen gas field n e netherlands direct shear slide hold slide shs experiments were performed at in situ conditions of 100 c 40 mpa effective normal stress and 10 15 mpa pore fluid pressure synthetic formation brine sheared gouges were allowed to heal for periods up to 100 days before subsequent reshearing the initial coefficient of steady sliding friction was highest in the basal zechstein caprock 0 65 0 02 and slochteren sandstone reservoir 0 61 0 02 gouges and the lowest in the ten boer claystone at the reservoir top 0 38 0 01 and in the carboniferous shale substrate 0 45 healing and subsequent reactivation led to a marked increase in static friction coefficient of up to 0 16 in basal zechstein and 0 07 in slochteren sandstone gouges for the longest hold periods investigated followed by a sharp strength drop up to 25 and slip weakening trajectory by contrast the ten boer and carboniferous gouges showed virtually no healing or strength drop healing rates in the basal zechstein and slochteren sandstone gouges were significantly affected by the stiffness of different machines used in line with the ruina slip law and with a microphysical model for gouge healing our results point to marked stratigraphic variation in healed frictional strength and healing rate of faults in the groningen system and high seismogenic potential of healed faults cutting the reservoir and basal zechstein caprock units upon reactivation

an analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress the moment magnitude 7 2 el mayor cucapah emc earthquake of 2010 in northern baja california mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults these faults have been exhumed from depths of 6 10 km since the late miocene based on low temperature thermochronology synkinematic alteration and deformational fabrics coseismic slip of 1 6 m of the emc event was accommodated by fault zones that displayed the full spectrum of architectural styles from simple narrow fault zones 100 m in width that have multiple anastomosing high strain cores as fault zone complexity and width increase the full spectrum of observed widths 20 200 m coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays thus the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long term history of slip on the faults at deeper levels of the seismogenic crust we find that factors such as protolith normal stress and displacement which control gouge production in laboratory experiments also affect the architectural complexity of natural faults fault zones developed in phyllosilicate rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo feldspathic granitoid rocks we hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad multi stranded fault zones fault orientation also strongly affects fault zone complexity which we find to increase with decreasing fault dip we attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting the conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone promoting complex branching and development of multiple high strain cores overall we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress

petroleum potential of southern part of tonga platform abstract the tonga platform is roughly outlined by the 2 000 m isobath with an average width of about 60 to 75 mi 100 to 120 km surrounding the tongan islands of vava u ha apal and tongatapu single channel seismic profiles across the platform were acquired between 1977 and 1979 by scientific expeditions sponsored by ccop sopac committee for cooperation of joint prospecting for mineral resources in south pacific offshore areas and orstom office de la recherche scientific et technique outre mer this survey and a five well drilling program on tongatapu were inspired by the discovery of seeps of weathered crude oil from vuggy coralline limestone reef buildups and normal fault structures are interpreted from seismic data and the wells penetrated miocene and eocene limestone volcanogenic clastics and some reached volcanic basement few oil and gas fields are found in fore arc basins of which the tonga platform is typical but the reefs offer prospects and the seeps suggest that the requirements of source rock and maturation may be satisfied end of article last page 986

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

fault healing inferred from time dependent variations in source properties of repeating earthquakes we analyze two sets of repeating earthquakes on the calaveras fault to estimate in situ rates of fault strengthening healing earthquake recurrence intervals tr range from 3 to 803 days variations in relative moment and duration are combined to study changes in stress drop rupture dimension rupture veloc ity and particle velocity as a function of t healing rates and source variations are compared with predictions of laboratory derived friction laws two interpretations of event duration z are used one in which is given by the ratio of slip to particle ve locity and one in which it scales as rupture dimension divided by rupture velocity our data indicate that faults strengthen during the interseismic period we infer that source dimension de creases with t r due to aseismic creep within the region surround ing the repeating events stress drop increases 1 3mpa per dec ade increase in twhich represents an increase of a factor of 2 3 relative to events with tbetween 10 and 100 days this rate of fault healing is consistent with extrapolations of laboratory meas urements of healing rates if fault strength is high on order of 60mpa and stress drop is roughly 10 of this value

oil and gas developments in new zealand and southwest pacific islands in 1987 in new zealand 14 new licenses were granted 6 in the east coast region 6 offshore taranaki and 2 in the south island two licenses were relinquished and the onshore taranaki license held by petrocorp expired onshore seismic activity totaled 525 km offshore seismic activity totaled 3 221 km reconnaissance seismic surveys by tcpl accounted for much of the offshore activity drilling decreased slightly with 18 wells drilled 13 onshore and 5 offshore totaling 55 203 m the drilling of kora 1 on a volcanic structure in the north taranaki basin has led to speculation about a possible oil discovery total petroleum production remained steady at 4 360 million m3 of gas 1 127 thousand m3 of condensate 190 thousand m3 of lpg and 509 t ousand m3 of oil in papua new guinea further discoveries in the overthrust belt of the papuan basin have confirmed the highly prospective nature of this area a major gas and condensate field with 4 pay zones was established in the hides structure east of juha field and early in 1988 gas condensate and oil were found in the hedinia structure south of the iagifu oil field discovered in 1986 total drilling amounted to 15 725 55 m during 1987 seismic surveys covered 858 km onshore and 4 747 km offshore there are 36 active petroleum prospecting licences 32 in the papuan basin and 4 in the north new guinea basin no new developments were reported in solomon islands tonga and vanuatu

on the mechanical properties of synthetic kaolinite quartz fault gouge summary the mechanical properties and microstructures of mixed kaolinite quartz fault gouge have been studied by means of triaxial tests wherein a 1 mm thickness of fault gouge was sheared between rigid sintered alumina sliders test conditions ranged up to 200 mpa confining pressure 175 mpa pore water pressure and temperatures to 600 c constant displacement rate tests were carried out at 5 10 4 mm s 1 and the stress relaxation technique was used to access a wide range of lower displacement rates down to 10 10 mm s 1 the effects of different ratios of clay quartz were studied and some experiments were cafried out using crushed tennessee sandstone gouge and pre faulted cylinders of tennessee sandstone deformation induced microstructures were studied by optical scanning and transmission electron microscopy and mineral chemistry changes were identified using eds analysis in the stem the most important factor determining the strength of these gouges is effective confining pressure and the effective stress law was obeyed at all test conditions increasing the proportion of quartz in the gouge slightly increases the strength as does increase of temperature under all test conditions the gouges deformed by strain hardening stable sliding at 2 mm displacement the friction coefficient is similar to that for rock and rock sliding 0 85 over wide ranges of strain rate and temperature the strength of these gouges is little affected if the effective pressure is high but strength drops rapidly with decreasing strain rate if effective pressure is low or if pore water pressure is high reloading of the gouge after stress relaxation at high temperatures demonstrated hardening arising from hydrothermal cementation during stress relaxation which led to sudden rupture of the cemented gouge this phenomenon may be responsible for cyclic rupture of natural faults new mineral phases were produced in these experiments only at 600 c at 400 c anticipated production of pyrophyllite from kaolinite plus quartz was not found but recrystallization of kaolinite is believed to have occurred and evidence of healing of cracks in quartz was seen microstructural studies revealed the ubiquitous development of p and r1 foliations and other features which are identical to those found in natural clay bearing fault zones microstructural evolution is associated with the strain hardening and apparent hardening is strongly associated with the stress path during loading

faults smooth gradually as a function of slip abstract geometry and roughness of fault surfaces plays a central role in the dynamics and kinematics of faulting faults smooth with increasing slip but the degree of the smoothing has not previously been well constrained for natural faults we measure the roughness as a function of displacement for a suite of 16 faults with cumulative offsets ranging from 0 1 m to approximately 500 m we find that slip parallel roughness evolves gradually with slip for instance for segments of length 0 5 m h 2 10 3 d 0 1 where h is the rms roughness and d is the displacement on the fault strand with both quantities measured in meters the gradual nature of the smoothing is robust to varying lithology and erosion the weak function implies a decrease in the rate of gouge formation for a model with increasing slip for a model in which gouge is generated by abrading an asperity tip the relatively gradual evolution of roughness could be explained by lubrication by the accumulated gouge that mitigates the abrasional smoothing that occurs during slip and or re roughening processes

southwest pacific island arcs sedimentary basins and petroleum prospects in new hebrides and solomons abstract several thousand meters of miocene pliocene sediments are predominantly fine to coarse grained volcaniclastics deposited in shelf to deep marine environments commonly as turbidites coralgal reef limestones and fore reef calcarenites formed locally original basins in both the solomons and new hebrides measured 375 to 435 mi 600 to 700 km by 62 to 125 mi 100 to 200 km but parts of their margins are strongly deformed uplifted and eroded cross faulting and holocene volcanism caused segmentation and further reduction of basinal areas in both island arcs the sediments are little deformed along a median structural basin which was downfaulted in pleistocene to recent time in the solomons and from pliocene onward in the central new hebrides no downfaulting occurred i the northern new hebrides little is known of hydrocarbon source potential and degree of maturation back reef or rapidly buried fore reef environments may be the principal areas for source rock formation reefal limestones are the main potential reservoir rocks they have however lost porosity locally because of recrystallization turbidite sandstones may form additional reservoirs but volcanic derivation keeps permeability generally low the main structural traps are fault controlled near basin margins but limited folding also occurs the pre pliocene unconformity in the northern new hebrides could generate stratigraphic traps water depth in the main prospective areas is several hundred to 5 000 ft 1 500 m in the solomons and up to 10 000 ft 3 000 m in the new hebrides nearshore and onland prospect are extremely limited in both island arcs end of article last page 972

evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions an experimental study we performed flow through laboratory experiments on five cylindrically cored samples of ultramafic rocks in which we generated a well mated through going tensile fracture to investigate evolution of fracture permeability during serpentinization the samples were tested in a triaxial loading machine at a confining pressure of 50 mpa pore pressure of 20 mpa and temperature of 260 c simulating a depth of 2 km under hydrostatic conditions a pore pressure difference of up to 2 mpa was imposed across the ends of the sample fracture permeability decreased by 1 2 orders of magnitude during the 200 330 h experiments electron microprobe and sem data indicated the formation of needle shaped crystals of serpentine composition along the walls of the fracture and chemical analyses of sampled pore fluids were consistent with dissolution of ferro magnesian minerals by comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture the experimental results suggest that the fracture network in long lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation and generation of new permeability resulting from a combination of tectonic and crystallization induced stresses is required to maintain fluid circulation

fluid assisted healing processes in gouge bearing faults insights from experiments on a rock analogue system on the basis of both experimental and field studies solution transfer processes are expected to be important in contributing to fault strength recovery healing under the hydrothermal conditions prevailing in large parts of the seismogenic zone however most experimental work on healing effects in faults has been done using quartzo feldspathic sliding surfaces or fault gouges under conditions in which solution transfer processes are very slow mechanisms of fluid assisted fault healing are accordingly rather poorly understood we have performed slide hold slide fault healing experiments on simulated faults containing brine saturated granular halite as a fault rock analogue halite was used because solution transfer processes are known to be rapid in this system under easily accessible conditions we studied the effects of hold time duration shear stress during hold pre hold sliding velocity and pore fluid composition on strength evolution the results show rapid fluid assisted compaction and stress relaxation during hold periods and a significant hold time dependent strengthening upon re shear the data reveal that healing resulted from both a packing density increase and a contact area strength increase during hold periods the general type of behaviour observed is similar to that observed in quartzo feldspathic gouges at room temperature although important differences were observed as well notably the time dependence of healing deviates from the log linear trend observed in gouges where solution transfer processes are absent this means that if pressure solution is an important healing mechanism in natural faults applying a log linear trend will underestimate natural fault healing rates

the effect of shear load on frictional healing in simulated fault gouge we report on frictional strengthening healing in granular quartz gouge as a function of time of true stationary contact to distinguish between the slip dependent ruina 1983 and time dependent dieterich 1979 friction constitutive laws we designed tests similar to conventional slide hold slide shs tests except that shear load was completely removed prior to holds we find large healing values 0 033 0 054 for holds of 101 102 s compared with quasi static shs experiments and our data indicate time dependent weakening in contrast with strengthening observed from shs tests gouge layer compaction increases with increasing hold time comparable to observations from conventional shs tests our data indicate that purely time dependent processes have a minor influence on healing under the conditions studied and or that such effects are efficiently erased by particle rearrangement during removal reapplication of shear load the data are not adequately described by either the time dieterich or slip ruina dependent state evolution laws

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact