a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

frictional discharge at fault asperities origin of fractal seismo electromagnetic radiation abstract to investigate the relation between the rock friction and the fractal electromagnetic radiation before the main shock of earthquakes we conducted a friction experiment simulating the motion of an asperity on a fault plane and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals this indicates that frictional discharges plasma generations could occur locally at microscopic asperities on fault surfaces from concepts on the fractal size distribution and temporal evolution of fault asperities the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation benioff electromagnetic radiation prior to earthquakes

dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

tectonic evolution of the sanga sanga block mahakam delta kalimantan indonesia the sanga sanga block contains four large to giant hydrocarbon fields in mid to upper miocene deltaic sandstones of the mahakam delta eastern kalimantan indonesia these fields occur in the northeast trending mahakam fold belt which is characterized by long tight fault bounded anticlines and broad synclines and cored by overpressured shales onshore sections of the fold belt are strongly deformed uplifted and eroded whereas the eastern offshore sections are little deformed and buried by the progradational delta wedge section balancing of depth converted seismic lines together with scaled analog modeling was used to develop a new tectonic model of inverted delta growth faults for the evolution of the mahakam fold belt section balancing shows that the fault bounded anticlines of the sanga sanga block are formed by contractional reactivation of early delta top extensional growth faults the change from gravity driven extension to regional contraction occurred at around 14 ma anticlinal folds controlled local sedimentation patterns and influenced the distribution of the reservoir channel sands in the main hydrocarbon fields scaled analog models of progradational loading above a ductile substrate produced delta top extensional growth faults and depobelts together with delta toe fold thrust contraction inverted the extensional growth faults and depobelts producing tight fault bounded anticlines the results support the model of delta inversion and thus the most viable explanation for the geometric kinematic and mechanical evolution of the structures in the sanga sanga block the inverted delta model has applications to other hydrocarbon bearing deltas around borneo and in other contracted delta systems

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

structural controls on the evolution of the kutai basin east kalimantan abstract the kutai basin formed in the middle eocene as a result of extension linked to the opening of the makassar straits and philippine sea seismic profiles across the northern margin of the kutai basin show inverted middle eocene half graben oriented nne ssw and n s field observations geophysical data and computer modelling elucidate the evolution of one such inversion fold nw se and ne sw trending fractures and vein sets in the cretaceous basement have been reactivated during the tertiary offset of middle eocene carbonate horizons and rapid syn tectonic thickening of upper oligocene sediments on seismic sections indicate late oligocene extension on nw se trending en echelon extensional faults early middle miocene n7 n8 inversion was concentrated on east facing half graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin slicken fibre measurements indicate a shortening direction oriented 290 310 ne sw faults were reactivated with a dominantly dextral transpressional sense of displacement faults oriented nw se were reactivated with both sinistral and dextral senses of movement leading to the offset of fold axes above basement faults the presence of dominantly wnw vergent thrusts indicates likely compression from the ese initial extension during the middle eocene was accommodated on nne ssw n s and ne sw trending faults renewed extension on nw se trending faults during the late oligocene occurred under a different kinematic regime indicating a rotation of the extension direction by between 45 and 90 miocene collisions with the margins of northern and eastern sundaland triggered the punctuated inversion of the basin inversion was concentrated in the weak continental crust underlying both the kutai basin and various tertiary basins in sulawesi whereas the stronger oceanic crust or attenuated continental crust underlying the makassar straits acted as a passive conduit for compressional stresses

present day stress field of southeast asia article i nfo it is now well established that ridge push forces provide a major control on the plate scale stress field in most of the earth s tectonic plates however the sunda plate that comprises much of southeast asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field the cenozoic tectonic evolution of the sunda plate is usually considered to be controlled by escape tectonics associated with india eurasia collision however the sunda plate is bounded by a poorly understood and complex range of convergent and strike slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region we compile the first extensive stress dataset for southeast asia containing 275 a d quality 177 a c horizontal stress orientations consisting of 72 stress indicators from earthquakes located mostly on the periphery of the plate 202 stress indicators from breakouts and drilling induced fractures and one hydraulic fracture test within 14 provinces in the plate interior this data reveals that a variable stress pattern exists throughout southeast asia that is largely inconsistent with the sunda plate s approximately ese absolute motion direction the present day maximum horizontal stress in thailand vietnam and the malay basin is predominately north south consistent with the radiating stress patterns arising from the eastern himalayan syntaxis however the present day maximum horizontal stress is primarily oriented nw se in borneo a direction that may reflect plate boundary forces or topographic stresses exerted by the central borneo highlands furthermore the south and central sumatra basins exhibit a ne sw maximum horizontal stress direction that is perpendicular to the indo australian subduction front hence the plate scale stress field in southeast asia appears to be controlled by a combination of himalayan orogeny related deformation forces related to subduction primarily trench suction and collision and intraplate sources of stress such as topography and basin geometry

on the dynamics of extensional basin geological and geophysical data from the north china bohai basin and basin and range province were examined and compared they are similar to each other in many respects surficial geological structures are characterized by a series of half grabens with their one flank constituted by normal fault those extensional structures usually extend to a depth of 6 8 km therefore the stress condition in the upper 8 km can be written as sigma 2 sigma x sigma y where x y denote the directions of maximum compression and maximum tension on the horizontal plane while z signifies the vertical direction

electromagnetic emissions during dilating fracture of a rock abstract a lot of experiments on electromagnetic emissions emes have been reported under axial compressive fracture shear fracture indentation fracture and stick slip friction in lab and blasting in situ but there are rare reports on the in lab experimental work on emes during dilating fracture of a rock which is helpful in studying and understanding emes related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs therefore in the present paper in order to check whether there are detectable emes during dilating fracture of a rock in lab dilating fracture experiments were conducted the dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space mffs at room temperature we arranged evenly 20 eme antennas whose resonance frequencies range from 2 5 khz to 540 khz close to rock specimens our experimental results strongly indicate that detectable emes could generate during dilating fracture of a rock they were recorded only associated with some but not all phases of fracture their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low amplitude oscillations the electromagnetic em signals after eliminating the effects of eme antennae via deconvolution had the maximum peak to peak amplitudes of about 80 0 mv and 40 5 mv for granodiorite and limestone respectively their main spectral components often concentrated in the band of several khz to 60 khz and of several khz to 280 khz the emission of electrons and charged particles from fracture surfaces and or micro fracture electrification could be possible mechanisms for our experimental results

p wave and s wave azimuthal anisotropy at a naturally fractured gas reservoir bluebell altamont field utah reflection p and s wave data were used in an investigation to determine the relative merits and strengths of these two data sets to characterize a naturally fractured gas reservoir in the tertiary upper green river formation the objective is to evaluate the viability of p wave seismic to detect the presence of gas filled fractures estimate fracture density and orientation and compare the results with estimates obtained from the s wave data the p wave response to vertical fractures must be evaluated at different source receiver azimuths travelpaths relative to fracture strike two perpendicular lines of multicomponent reflection data were acquired approximately parallel and normal to the dominant strike of upper green river fractures as obtained from outcrop core analysis and borehole image logs the p wave amplitude response is extracted from prestack amplitude variation with offset avo analysis which is compared to isotropic model avo responses of gas sand versus brine sand in the upper green

self potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes abstractlarge amplitude 100 mv negative electric self potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants to explain the physical and chemical mechanisms that generate such electrical signals a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox the 2d and 3d self potential sp data were collected at several time steps along with collocated ph and redox potential measurements large dipolar sp and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe although no anomalies were observed in the vicinity of the horizontal pipe this discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger eh gradient accounting for the electrical conductivity dis

stress orientations from well bore breakouts in the coalinga region borehole breakouts are caused by unequal stress concentrations around a borehole resulting in shear failure of the borehole wall and creating hole elongation perpendicular to the maximum horizontal in situ stress breakouts in tertiary sedimentary rocks were identified in 10 holes in the west coalinga cantua creek and west haven oil fields in the western san joaquin valley the deeper and more reliable 1 5 to 3 7 km breakouts were oriented northwest indicating northeast compressive stress perpendicular to the major fold axes in the san joaquin valley and at a 70 90 angle to the major strike slip faults in the coast ranges this stress direction is consistent with a reverse slip component on northwest trending faults in the region and with the focal mechanisms reported for the may 1983 coalinga earthquake the existing literature on stress measurements in central and southern california indicates that on a regional scale the stress regime is transitional between thrust and strike slip faulting a hydraulic fracture test in the kettleman hills oil field at 3 km depth indicates that this stress regime exists in the upper crust near coalinga as well

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock implication on mechanism of borehole breakouts abstract we conducted laboratory true triaxial experiments in the nearly impermeable pohang rhyolite to investigate failure mechanisms under dry and wet rock conditions under dry conditions prismatic specimens were jacketed all around to prevent confining fluid penetration under wet conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid kerosene applying the least principal stress in an attempt to simulate the case of an unlined borehole wall in both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises the unjacketed rhyolite strength is however only 60 to 85 of the strength under dry conditions depending on the magnitude of the intermediate principal stress in dry rhyolite the failure process begins upon dilatancy onset followed by microcrack localization and ending in a steeply dipping shear fracture on the other hand brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through going extensile fractures subparallel and adjacent to one of the unjacketed faces resembling the extensile cracks leading to borehole breakouts in crystalline rocks we infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress induced microcracks subparallel to the unjacketed faces leading to early failure

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

santonian to eocene palaeogeographic evolution of the rio grande rise south atlantic deduced from clay mineralogical data dsdp legs 3 and 39 abstract the late cretaceous to eocene morphologic evolution of the rio grande rise interpreted from variations in clay mineralogy progressed in four main stages 1 1 santonian early campanian the rio grande rise largely emerged consisted of flat areas and low relief undulant terrain where smectite formed 2 2 late campanian maastrichtian early paleocene the continental morphology did not change on the sao paulo plateau western rio grande rise where illite and mixed layers were abundant was marked by tectonism associated with the deepening of the vema channel eastern rio grande rise subsided leading to temporary submergence of flat areas and the formation of confined sedimentary basins where attapulgite formed 3 3 late paleocene early eocene the tectonic activity stopped and the continental relief was progressively peneplaned while the abundance of smectite increased subsidence continued in the eastern areas where attapulgite remained abundant 4 4 middle eocene the rio grande rise was almost completely submerged

fracture porosity creation and persistence in a basement involved laramide fold upper cretaceous frontier formation green river basin usa fracture hosted porosity and quartz distribution along with crack seal texture and fluid inclusion assemblage sequences in isolated bridging quartz deposits show that open fractures can persist through protracted burial and uplift in foreland basins fractures oriented at a high angle to current maximum compressive stress remain open and were weak mechanical discontinuities for millions of years even at great depth upper cretaceous frontier formation sandstones in the basement involved laramide table rock anticline eastern greater green river basin wyoming sampled by two horizontal wells cut parallel or nearly parallel to bedding and at a high angle to steeply dipping fractures have 41 5 m of rock in four cores at depths of 4538 4547 m cores intersect older e striking set 1 fractures are abutted by or locally cross cut by n striking set 2 fractures both sets contain quartz and porosity sequenced using quartz crack seal cement texture maps set 1 fluid inclusion assemblage fia trapping temperatures increase progressively from 140 to 165 c then decrease to c 150 c compatible with fracture opening over c 15 ma during rapid burial followed by uplift in eocene oligocene time set 2 opened at c 160 c probably near maximum burial after a period of quiescence set 2 reopened at c 5 ma at c 140 c on a cooling trajectory intermittent set 2 movement could reflect local basement involved fault movement followed after a pause by further set 2 reactivation in the modern stress field during uplift interpretations are sensitive to available burial thermal histories which have considerable uncertainty

contour mapping of relic structures in the precambrian basement of the reelfoot rift north american midcontinent a new contour map of the basement of the reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features the major features are two asymmetric intrarift basins bounded by three structural highs and the rift margins the basins are oriented normal to the northeast trend of the rift two of the highs appear to be ridges of undetermined width that extend across the rift the third high is an isolated dome or platform located between the basins the minor features are three linear structures of low relief oriented subparallel to the trend of the rift two of these located within the rift basins may divide the rift basins into paired subbasins these mapped features may be the remnants of initial extensional rifting half graben faulting and basement subsidence the rift basins are interpreted as having formed as opposing half graben and the structural highs are interpreted as having formed as associated accommodation zones some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime a detailed knowledge of the geometries of the reelfoot rift s basement features therefore is essential when evaluating their seismic risk potential

correlation between velocity dependence of friction and strain localization in large displacement experiments on feldspar muscovite and biotite gouge abstract room temperature rotary shear experiments on rock powders of albite feldspar and muscovite and biotite micas show that the degree of localization of shear strain in these materials correlates with the frictional behavior in both feldspar and mica experiments increasing localization correlates with a lower coefficient of friction and a more negative velocity dependence of friction feldspar gouges tend to have localized deformation along one or more boundary parallel shears and a negative velocity dependence more localized deformation correlates with a lower coefficient of friction and a more negative velocity dependence in general micas deform throughout a broader zone than feldspar and have a lower coefficient of friction compared to muscovite biotite is weaker has a negative rather than a positive velocity dependence and shows more localized deformation for materials as diverse as feldspars and micas localization along boundary parallel shears correlates with negative velocity dependence along compliant natural faults a negative velocity dependence would result in a greater tendency for unstable sliding thus localized boundary parallel shears may indicate negative velocity dependence and slip by earthquakes on natural faults

orientation of the stress field from breakouts in a crystalline well in a seismic active area abstract the orientation of the regional stress field in the swabian jura was determined from borehole breakouts caused by stress accumulation at the borehole wall the analysis is based on caliper data recorded in the urach 3 geothermal well within an intervall of about 1450 m the azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes

stress patterns in northern iraq and surrounding regions from formal stress inversion of earthquake focal mechanism solutions the collision zone between the arabian and eurasian plates is one of the most seismically active regions northern iraq represents the northeastern part of the arabian plate that has a suture zone with the turkish and iranian plates called the bitlis zagros suture zone the orientations of the principal stress axes can be estimated by the formal stress inversion of focal mechanism solutions the waveform moment tensor inversion method was used to derive a focal mechanism solution of 65 earthquakes with magnitudes range from 3 5 to 5 66 in the study area from focal mechanism solutions the direction of slip and the orientations of the moment stress axes p n and t on the causative fault surface during an earthquake were determined the dataset of the moment stress axes have been used to infer the regional principal stress axes 1 2 and 3 by the formal stress inversion method two inversion methods which are the new right dihedron and the rotational optimization methods were used the results show that six stress regime categories exist in the study area however the most common tectonic regimes are the strike slip faulting 43 94 unspecified oblique faulting 27 27 and thrust faulting 13 64 regimes in most cases the strike slip movement on the fault surfaces consists of left lateral sinistral movement the normal faulting is located in one small area and is due to a local tensional stress regime that develops in areas of strike slip displacements as pull apart basins the directions of the horizontal stress axes show that the compressional stress regime at the bitlis zagros suture zone has two directions one is perpendicular to the suture zone near the iraq iran border and the second is parallel in places as well as perpendicular in others to the suture zone near the iraq turkey border in addition the principal stress axes in the sinjar area near the iraq syria border have a e w direction these results are compatible with the tectonic setting of the arabian eurasian continental collision zone and the anticlockwise rotation of the arabian plate that is evidently responsible for the strike slip displacements on fault surfaces

thrust fault nucleation due to heterogeneous bedding plane slip evidence from an ohio coal mine abstract shales often form the roof and floor rocks of coal mines in the appalachian basin from a geologic perspective these mines offer outstanding 3d exposures of fresh rocks otherwise only accessible via boreholes or heavily weathered surface outcrops and present an excellent opportunity to directly observe pristine in situ natural fractures in shale in carroll county ohio small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal shale contacts are steepest causing ground instability we hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state resulting in localized thrust fault development using borehole and in mine survey data we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations our modeling results suggest that inherited non planarity of contact surfaces influenced the nucleation of secondary faults simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures for mining purposes recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards

folding in regions of extension summary many extension zones have been subjected to folding and shortening in a direction perpendicular to the stretching such deformation can be accounted for by the extension of a thin superficial elastic layer overlying a substrate that has small elastic moduli or that deforms in a viscous regime laboratory experiments are used to document the wavelength and amplitude of the folds for a range of geometrical configurations folding is observed even for very small amounts of extension less than 1 per cent with characteristics that are consistent with finite amplitude scaling laws because of the intrinsically 3 d nature of the deformation field the size of the region affected by folding and the direction of the fold axes depend on the orientation of the extension with respect to the rigid blocks that bound the deforming region for regions of extension where the elastic thickness is about 10 km as in the basin and range province for example it is predicted that folding occurs with wavelengths in a 20 40 km range such that it induces little deformation in the lower crust and maintains a flat moho discontinuity these predictions are consistent with the observations the characteristics of faulting that is associated with such deformation are discussed

strength and rheology of the western u s cordillera effective elastic thickness te depends primarily on temperature composition and state of stress of the lithosphere in this paper we examine high resolution spectral estimates of te and their relationships to regional heat flow age of the lithosphere seismic properties stress orientations and earthquake focal depths of the western u s cordillera the relationship of te to heat flow indicates that ductile flow accommodates long term 106 to 108 years isostatic response at different levels of the crust and upper mantle depending principally on age and by implication bulk composition of the lithosphere isostatic response is primarily controlled by the upper mantle in archean lithosphere of the middle rocky mountains whereas te depends on lower crustal flow in early proterozoic lithosphere of the colorado plateau the yellowstone snake river plain volcanic field and significantly extended regions in the basin range and northern rocky mountains are associated with latest proterozoic aged lithosphere and indicate middle to upper crustal control of long term te we also show that azimuthal variations of te reflect deviatoric stress in the lithosphere te is found empirically to approximate the 95th percentile focal depth of background seismicity the latter relationship is inconsistent with brittle ductile control of focal depth indicating that another rheological transition e g from stick slip to stable sliding frictional behavior is responsible tectonic and structural relationships expand upon the hypothesis that the geographic distribution of tectonic features depends fundamentally on spatial variations in strength of the lithosphere moreover we find a spatial correlation of the intermountain seismic belt to a marked transition in te implying that forces responsible for this active seismic zone are derived from local buoyancy anomalies rather than from current day plate boundary interactions

positive electrification on the floor of an underground mine gallery at the arrival of seismic waves and similar electrification on the surface of partially stressed rocks in laboratory terra nova 22 203 207 2010 abstract a large plate electrode in a mine gallery detected electric signals when seismic waves arrived this signal is equivalent to the generation of an electric field with the upward negative and the downward positive one possible reason for detection of the electric field is a positive electrification of the floor here we studied such electrification in the laboratory using an andesite block quarried from the same mine when partially loaded at one end the block exhibits positive electrification on the surface of the other unstressed end the activation of positive hole charge carriers reasonably explain the laboratory results the positive holes are activated by breaking peroxy bonds a common type of lattice defects in igneous rock forming minerals the positive holes spread to the surface thereby causing the electric field the same charge carriers may be activated upon arrival of seismic waves

electric potential source localization reveals a borehole leak during hydraulic fracturing abstracta laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory the cubic block was instrumented with 32 nonpolarizing sintered ag agcl electrodes during the test several events were detected corresponding to fluid leakoff along the seal of the well each event showed a quick burst in the electric field followed by an exponential type relaxation of the potential distribution over time the occurrence of these electric events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure these self potential data were inverted in two steps 1 using a deterministic least square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and 2 using a genetic algorithm to refine the position of the sou

regional stress alignments in the kutai basin east kalimantan indonesia a contribution from a borehole breakout study abstract borehole breakout data from 134 wells located within the kutai basin region east kalimantan were analyzed to determine the present day regional horizontal stress alignments the data were extracted from various types of dipmeter logs the study reveals that the majority of the data give a coherent picture of breakout orientation the mean azimuths for the entire unweighted ellipticity weighted and magnitude weighted data sets are preferentially aligned in the regional mean direction of 48 9 n or 128 9 n most of the data have a low dispersion value s o and the ranking of reliability in zoback s classification is a there is no significant azimuth variation with depth these relatively consistent alignments of breakout azimuths indicate that the maximum regional stress direction in the study area is nw se this regional mean of breakout azimuths deviates from the axis of the anticlinorium trends and from the strike of the thrust fault patterns in the region it is believed that these structural patterns are influenced by reactivation of weak zones related to sediment loading structural inversion

stress orientation profile to 3 5 km depth near the san andreas fault at cajon pass california a detailed profile of the orientation of the apparent maximum horizontal compressive stress was constructed over the depth interval 1 75 3 46 km in the cajon pass drill hole located 4 2 km from the san andreas fault in southern california the profile is based on the analysis of stress induced well bore breakouts and consists of 32 616 orientation determinations at a basic sampling interval of 4 cm the azimuth of the apparent maximum horizontal compressive stress around the borehole is 057 s d 19 depth dependent variations in breakout azimuths from a few degrees to as much as 100 occur over depth intervals of several centimeters to hundreds of meters in the borehole with wavelengths showing a self similar distribution over a range of depth intervals the variations in breakout orientation at depth seem to reflect stress fluctuations associated with active faults penetrated by the drill hole assuming linear elastic behavior perturbations in stress magnitude and orientation were computed for predrilling slip on these faults fault stress drops limited to the ambient shear stress i e up to total stress drop along with occasional local extreme stress drops and geometrical complications can explain the variations in breakout orientations in the drill hole the penetrative stress inhomogeneity may suggest that the average orientation of borehole breakouts in cajon pass which indicates left lateral shear on planes parallel to the san andreas fault may not be representative of the state of stress near the fault at depth in this region rather the stress orientation profile indicates the superposition of numerous local stress perturbations on an average stress field which is characterized by an absence of appreciable right lateral shear on planes parallel to the san andreas combining these observations with the highly variable stress state in shallow boreholes in the western mojave desert it is suggested that the heterogeneous stress field in this region representing a spectrum of seismic events may extend over substantial distances across and along the san andreas fault zone if the average measured breakout orientation in cajon pass is representative of the state of stress near the san andreas in this region then substantial left lateral shear stress is resolved on planes parallel to the fault in contradiction to the sense of its long term motion we use an elastic dislocation model to compute the net stress change near the cajon pass drill site since just prior to the large 1812 earthquake taking into account coseismic slip in major earthquakes and aseismic accumulation of slip on the san andreas and san jacinto faults the model suggests that the net change in fault parallel shear stress during the current earthquake cycle in the cajon pass area is nearly negligible the difference between the measured and computed results requires that additional left lateral shear stress be superimposed on a generally fault normal maximum horizontal compressive stress the results suggest that during the great fort tejon earthquake of 1857 left lateral shear stress parallel to the san andreas fault in the region of cajon pass may have played a role in terminating the southeastward extent of the rupture propagation

microbial domes and megaoncoids in miocene reefs in the mahakam delta in east kalimantan indonesia abstract coral patch reefs in the miocene mahakam delta in east kalimantan borneo indonesia developed in shallow marine turbid waters these reefs grew in delta front to prodelta environments under fluctuating siliciclastic input langhian patch reefs are well exposed in limestone quarries of the air putih area near the city of samarinda and include two different types of microbial carbonates in two sections 2 km apart in the northern section microbialites occur as low relief domes up to 2 m wide and 0 5 m high the domes show internal lamination and coralline algae and encrusting foraminifers interlayered with microbial micrite they developed around large coral fragments at the transition from reef deposits to fine grained siliciclastics microbialites in the southern section formed decimetre to metre scale nodules here termed megaoncoids around nuclei of large coral fragments microbial micrite with laminated to digitate fabrics intergrew with coralline algae and encrusting foraminifers to form the thick covers of megaoncoids small nodules were bound together in larger ones which are usually strongly asymmetric internally megaoncoids accumulated in a carbonate breccia laterally changing into coral boundstones in both sections microbialites grew on the flanks of shallow water low relief patch reefs in poorly illuminated low energy conditions flat domed microbialites formed on a nearly horizontal stable seafloor seawards of the patch reef the megaoncoids in the southern section formed as a result of downslope displacement of coral fragments coated by microbialite coralline algal encrusting foraminifer crusts the slope of the patch reef s flank favoured the falling and rolling of encrusted corals with the continued growth of microbial crusts on all sides of nodules in contrast to quaternary and recent occurrences of microbialites in indo pacific and caribbean reefs the samarinda microbialites are not components of the reef framework nor formed in deep water instead they developed in shallow turbid waters of the miocene mahakam delta in periods of arrested siliciclastic input

clay mineral associations and structural evolution of the south atlantic jurassic to eocene abstract clay minerals have been used to reconstruct the geological history of the south atlantic six mineralogical stages have been recognized from the middle jurassic to the eocene 1 1 prior to the oxfordian illite irregular mixed layers and kaolinite marked a period of tectonic extension between africa and antarctica 2 2 from the oxfordian to the early albian smectites developed during subsidence induced peneplanation of the relief along the southern margin while chlorite illite irregular mixed layers and kaolinite characterized a distensive regime in the cape and southern angola basins 3 3 from the albian to the early turonian smectites palygorskite and sepiolite linked to subsidence processes occurred from the southern ocean to the southern angola basin while chlorite illite irregular mixed layers and kaolinite characterized tectonic extension from gabon to nigeria 4 4 from the early turonian to the early campanian smectites palygorskite and sepiolite linked to subsidence were widespread in the south atlantic areas 5 5 from the early campanian to early paleocene chlorite illite irregular and subregular mixed layers and kaolinite marked a reactivation of continental reliefs in the northern areas of the south atlantic in relation to compression in nigeria and opening of the equatorial atlantic 6 6 after the early paleocene smectites palygorskite and sepiolite characterized the widespread subsidence in the south atlantic

high heat flow effects on a coalbed methane reservoir east kalimantan borneo indonesia abstract the balikpapan formation miocene age in sangatta east kalimantan is thick 1500 m containing abundant coal seams that range in thickness from less than a meter to over 5 m coal seams are distributed throughout the section and may represent 5 to 7 of the total formation thickness measured gas contents range from

electromagnetic signals associated with stick slip of quartz free rocks abstract we recorded clear transients in the electric and magnetic fields upon sudden slip in stick slip experiments on dry cylindrically shaped quartz free rock specimens of basalt and peridotite with a 30 saw cut representing a fault at confining pressures of up to 120 mpa the amplitudes of the measured electric field signals were always higher at the electrode pair oriented parallel to the strike of the fault than at the pair oriented perpendicular this anisotropy suggests a preferred electric polarization normal to the slip surface the transients in the electric and magnetic fields were observed only when the fault slip occurred by stick slip mode not by a stable mode of the sliding and the amplitudes of the electric field signals increased with increasing stress drop it is suggested that the generation process of the electromagnetic signals is closely related to the characteristic behavior of the fault at the time of the initiation of slip during stick slip events probably with respect to the intensity of the signals we propose that one or both of the following two processes characteristic of the fault at the time of the initiation of slip during stick slip events are essential for the generation of detectable electromagnetic signals rapid slip along the simulated fault and separation of the rock masses across the fault

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

short term earthquake prediction current status of seismo electromagnetics abstract loss of human lives as a result of earthquakes is caused overwhelmingly by the collapse of buildings within less than a few minutes of main shocks the most urgent countermeasure consists of two key elements one is strengthening of weak structures and the other is short term earthquake prediction short term prediction needs precursors although some promising precursors are reported the prevailing views in japan and elsewhere are overly pessimistic the pessimism largely roots in the fact that short term precursors are generally non seismic and tools developed for seismology are not designed to detect them nonetheless nationally funded large scale earthquake prediction programs always emphasize the need to reinforce seismometer networks they do not take into account the views of those in the science community who point to the importance of non seismic precursors while there are well founded causes to be skeptical the situation needs to be improved one reason for skepticism is that the observations of precursors have not yet been perfect enough and another is that some important fundamental aspects of non seismic precursors are still unresolved we review some of these problems

on the origin and evolution of electrical signals during frictional stick slip in sheared granular material electromagnetic signals have been reported in association with geophysical phenomena including earthquakes landslides and volcanic events mechanisms that suggested to explain seismoelectrical signals include triboelectricity piezoelectricity streaming potentials and the migration of electron holes yet the origin of such phenomena remains poorly understood we present results from laboratory experiments regarding the relationship between electrical and mechanical signals for frictional stick slip events in sheared soda lime glass bead layers the results are interpreted in the context of lattice defect migration and granular force chain mechanics during stick slip events we observe two distinct behaviors delineated by the attainment of a frictional stick slip steady state during initial shear loading layers charge during stick slip events and the potential of the system rises after steady state stick slip behavior is attained the system begins to discharge coseismic signals are characterized by potential drops superimposed on a longer term trend we suggest that the observed signal is a convolution of two effects charging of the forcing blocks and signals associated with the stress state of the material the long term charging of the blocks is accomplished by grain boundary movement during the initial establishment of force chain networks short term signals associated with stick slip events may originate from produced electron holes applied to tectonic faults our results suggest that electrical signals generated during frictional failure may provide a way to monitor stress and the onset of earthquake rupture potential changes could produce detectable signals that may forecast the early stages of failure providing a modest warning of the event

frictional discharge plasma and seismo electromagnetic phenomena abstract although several mechanisms of precursory electromagnetic emissions of earthquakes have been proposed there has been no in situ observation of electromagnetic phenomena occurring at the frictional contacts during rock frictions from an experiment simulating the motion of an asperity on a fault surface we report the generation of photon emissions around frictional contacts between natural rock minerals spectroscopic analysis clarified that the photon emissions are caused by dielectric breakdown of ambient gases electric discharge plasma due to frictional electrification the plasmas were found to occur under normal stress of 4 mpa and sliding speed of 10 2 m s this indicates that plasma generations do not require high normal stresses needed to fracture rocks and sliding speeds as high as seismic rates 1 m s thus frictional discharges could occur at microscopic asperities at the onset of the slips of earthquakes and might be one of the sources of the seismo electromagnetic emission

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

reconstruction of floral changes during deposition of the miocene embalut coal from kutai basin mahakam delta east kalimantan indonesia by use of aromatic hydrocarbon composition and stable carbon isotope ratios of organic matter the distribution of aromatic hydrocarbons and stable carbon isotope ratios of organic matter in a series of nine miocene embalut coal samples obtained from nine coal seams of kutai basin east kalimantan indonesia were studied the rank of the embalut coals ranged from lignites to low rank sub bituminous coals 0 36 0 50 rr based on measurements of huminite reflectance the aromatic hydrocarbon fractions of all coal samples were dominated by cadalene in the lower boiling point range and picene derivatives in the higher boiling point range of the gas chromatograms cadalene can be attributed to the contribution of dipterocarpaceae and various hydrated picenes to the contribution of additional angiosperms to the coal forming vegetation the picenes originate from alpha and beta amyrin however in some coal samples minor amounts of simonellite and retene were also detected which argues for an additional contribution of gymnosperms conifers to coal forming vegetation preferentially in the middle miocene and at the beginning of the late miocene the results of stable carbon isotope ratios d 13

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

origin of pseudotachylites in slow creep experiments we conducted a series of experiments on granitoid cataclasites under mid crustal conditions pc 500 mpa t 300 c and slow displacement rates 10 8 ms 1 d 10 7 ms 1 i e within an order of magnitude of plate tectonic velocities the samples reach high peak strength 1250 1375 mpa then weaken slightly by 40 mpa and continue to deform without any abrupt stress drops up to a of 4 microstructural observations show that at peak strength nanocrystalline mean grain size 34 nm smallest crystalline particles 8 nm to partly amorphous material develops weakening occurs once this material is abundant enough to form through going anastomozing slip zones where the strain partitions during higher strain deformation deformation localizes further and 1 to 2 multiply connected layers of fragment loaded amorphous material develop this material shares many similarities with naturally occurring pseudotachylites however was formed at velocities up to 8 orders of magnitude slower than those calculated for earthquakes 1 ms 1 we conclude that the use of pseudotachylites as indicators for paleoseismic events should be reconsidered

breakouts in alberta and stress in the north american plate the paper reports a detailed statistical study of breakout azimuths in 48 oil wells widely distributed in the alberta sedimentary basin bringing the number of oil wells contributing azimuths to 94 for the western canadian basin the azimuths show significant regional variation between the northern central and southern parts of the basin twenty one wells in which breakouts cover depth ranges greater than 600 m were used to investigate regression of breakout azimuths on depth ten wells give positive regression coefficients 11 are negative and no coefficient is significant at 95 confidence level if the dominant northwest southeast orientation of the long axes of breakouts gives the orientation of the lesser horizontal principal stress sh following the hypothesis of bell and gough the inferred stress orientations indicate that throughout the whole basin the direction of the maximum horizontal stress sh is northeast southwest stress measurements by strain relief techniques in a mine and from hyd

electric potential changes associated with nucleation of stick slip of simulated gouges our friction experiments using simulated gouges detected premonitory changes in electric potential before stick slip events these precursor electric signals have been detected both in piezoelectric quartz and non piezoelectric gabbroic gouges the changes in the potential were locally detected by electrodes set very close to the fault surface associated with slow slip prior to stick slip events the magnitude of electrification is proportional to fault slip associated with gradual stress releases indicating that the electrification is slip dependent process from the detailed microstructural analyses on a representative sample riedel r1 shears known to be formed during stable sliding were the most densely developed around the electrode pair which detected the precursory voltage changes this indicates that local increases in the voltages were likely caused by frictional electrification due to slow slip on r1 shears in nucleation phases of stick slip events our experimental results imply that natural faults with thicker gouge zones would require greater precursory slips resulting in larger electric signals in the nucleation phase of earthquakes

recent and future trends in paleopiezometry in the diagenetic domain insights into the tectonic paleostress and burial depth history of fold and thrust belts and sedimentary basins paleopiezometry provides an access to the past stress magnitude key to better understand the behaviour of the earth s crust over long period of time this contribution presents a review of some paleopiezometric techniques that can be used in the diagenetic domain in fold and thrust belts and sedimentary basins calcite twinning and stylolite roughness techniques have been selected and are presented through a critical description of their methodologies along with approaches to further reconstruct the complete effective stress tensor major geological lessons learned over the past decades from published studies are summarized and discussed along with a way forward to potential breakthroughs