a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

rate dependence of ae activity during frictional sliding 1 a velocity step test was performed to examine effects of the macroscopic sliding rate on ae activity during steady state frictional sliding on a pre cut fault in a granite sample both the amplitude frequency relation and the number of ae events per unit displacement changed in response to a change in the macroscopic sliding rate both the ae activity and its rate dependence evolved with sliding the rate dependence of cumulative seismic energy calculated from the ae activity shows a positive correlation to that of friction coefficient suggesting that the rate dependence of seismic energy is one of the origins of rate dependent friction because the seismic energy is a part of frictional energy loss further the rate dependence of seismic energy is much larger than that of friction meaning that a ratio of seismic energy to frictional energy loss depends on the macroscopic sliding rate

searching for hidden earthquakes in southern california earthquakes follow a well known power law size relation with smaller events occurring much more often than larger events earthquake catalogs are thus dominated by small earthquakes yet still missing a much larger number of even smaller events caused by signal fidelity issues to overcome these limitations we applied a template matching detection technique to the entire waveform archive of the regional seismic network in southern california this effort resulted in a catalog with 1 81 million earthquakes a factor of 10 increase which provides important new insights into the geometry of fault zones at depth foreshock behavior and nucleation processes and earthquake triggering mechanisms the extraordinary detail resolved in this type of catalog will facilitate a new generation of analyses of earthquakes and faults

frequency characteristics of acoustic emission in rocks under uniaxial compression and its relation to the fracturing process to failure acoustic emission generated during the uniaxial compression of brittle rocks were counted after band pass filtering throughout the whole process from application of load to failure the count rate monitored through a low pass window was compared statistically with the monitored through a high passs window the emission rate monitored through a low pas window increases more rapidly than that monitored through a high pass window as rock approaches failure two possible explanations for this effect are 1 generation of larger cracks or coalescence of cracks into larger sizes and 2 the relative attenuation of higher frequency wave components this finding is consistent with past observations i e the relative number of large amplitude events increases i e a decrease in b value as rock approaches failure we suggest that larger cracks tend to generate events with larger amplitudes and containing lower frequency components the frequency characteristics of acoustic emissions are used to characterize the microfracturing processes leading to failure the beginning of a sequence of acoustic emission activity is discussed in relation to the stress strain curve and the onset of dilatancy the present observations may be utilized in understanding structural instability of a region where rockbursts or earthquakes can potentially occur if a sizable microseismicmore population is observed through sensors placed near the fault then a potential exists for predicting major earthquakes less

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

characterization of nucleation during laboratory earthquakes 1 we observe the nucleation phase of in plane ruptures in the laboratory we show that the nucleation is composed of two distinct phases a quasi static and an acceleration stage followed by dynamic propagation we propose an empirical model which describes the rupture length evolution the quasi static phase is described by an exponential growth while the acceleration phase is described by an inverse power law of time the transition from quasi static to accelerating rupture is related to the critical nucleation length which scales inversely with normal stress in accordance with theoretical predictions and to a critical surfacic power which may be an intrinsic property of the interface finally we discuss these results in the frame of previous studies and propose a scaling up to natural earthquake dimensions

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

real time discrimination of earthquake foreshocks and aftershocks immediately after a large earthquake the main question asked by the public and decision makers is whether it was the mainshock or a foreshock to an even stronger event yet to come so far scientists can only offer empirical evidence from statistical compilations of past sequences arguing that normally the aftershock sequence will decay gradually whereas the occurrence of a forthcoming larger event has a probability of a few per cent here we analyse the average size distribution of aftershocks of the recent amatrice norcia and kumamoto earthquake sequences and we suggest that in many cases it may be possible to discriminate whether an ongoing sequence represents a decaying aftershock sequence or foreshocks to an upcoming large event we propose a simple traffic light classification to assess in real time the level of concern about a subsequent larger event and test it against 58 sequences achieving a classification accuracy of 95 per cent

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

multiscale anatomy of a reservoir geological characterization of pembina cardium pool west central alberta canada geological reservoir elements that control a reservoir s conduit system are mineralogy grain size packing pore network lithohydraulic units lithologic continuity fractures and faults and rock fluid interactions all occur at different scales we have focused on four scales typical of a developed reservoir to characterize geological reservoir heterogeneity in the pembina cardium pool 1 megascale the field wide view 2 macroscale the interwell continuity 3 mesoscale the neighborhood of the well and 4 microscale the domain of grains and pores 1 megascale observations the reservoir top is characterized by a ridge and swale topography oriented northwest southeast a similar but more subdued topography is also characteristic of the unconformity between conglomerates and sandstones conglomerates are distributed irregularly and are generally shaly in beds thinner than 1 m thick conglomerates are common on the east and south flanks of underlying ridges and impart northwest southeast fluid production trends and yield zones of reduced pressures in thick conglomerates high flow capacities are detrimental to hydrocarbon recovery as they result in bypassing of injection fluids the conglomerate is a lithohydraulic unit as it is a body of strata distinct from neighboring strata by depositional diagenetic and tectonic imprintin s and by a characteristic set of petrophysical properties 2 macroscale characteristics reservoir lithofacies and lithohydraulic units are laterally discontinuous and form irregular patterns that can possess an irregular northwest southeast orientation fluid production trends oriented northeast southwest in areas of thin shaly conglomerates appear to be the product of fractures in these areas reorientation of injector wells to line drives results in higher oil recoveries 3 mesoscale properties in cores five lithofacies characterize the field they are 1 dark gray mudstone and siltstone 2 bioturbated thin and very thin bedded shale siltstone and very fine and fine grained sandstone 3 thin and very thin bedded shale siltstone and very fine and fine grained sandstone 4 medium to thick bedded very fine and fine grained sandstone and 5 conglomerate as each lithofacies possesses contrasting but partially overlapping petrophysical properties they are lithohydraulic units lithofacies 1 acts as the reservoir seal and restricts flow within the reservoir lithofacies 2 has high porosities low permeabilities and dominates the bottom half of the reservoir lithofacies 2 has a high storage capacity phgrh but its flow capacity kh i low lithofacies 3 reduces cross flow because its vertical permeabilities are very low lithofacies 4 has modest permeabilities and high porosities and is common to the top half of the reservoir this lithofacies flow capacity in t47 r7 w5m is 17 times greater than that of lithofacies 2 lithofacies 5 has modest porosities but very high permeabilities resulting in intervals with very high flow capacities 4 microscale investigations in the sandstones the mineral framework consists predominantly of quartz and chert whereas chert prevails in the conglomerates these mineralogic differences lead to reduced cementation by silica on cherts and result in the preservation of pore spaces resembling original pores in chert rich zones although quartz grains are modified by megaquartz overgrowths chert particles are altered by pressure solution fracturing and crushing in both sandstones and conglomerates framework grains are cemented by siderite calcite kaolinite and illite experiments with reservoir cores flooded with co2 enriched brines and data from waterflooding indicate that siderite and calcite are unstable under reservoir conditions this behavior can result in perm ability losses from release of insoluble fine materials and weakened responses during polymer floods mercury capillary pressure data from 28 measurements of lithofacies 4 sandstones indicate that mercury end page 1233 recovery efficiency increases with decreasing permeability and porosity this behavior if confirmed elsewhere in the field may explain the performance of areas that have reduced permeabilities and porosities but are responding well to waterflooding

high resolution characterization and integrated study of a reservoir formation the danian carbonate platform in the aquitaine basin france abstract this paper provides an example of an integrated multi scale study of a carbonate reservoir the danian lower r2 carbonate reservoir is located in the south of the aquitaine basin france and represents a potential underground gas storage site for gaz de france the danian lower r2 reservoir was deposited as a prograding carbonate platform bordered by a reef barrier the effects of sedimentary and diagenetic events on the reservoir properties particularly dolomitization were evaluated in this study the reservoir quality has been assessed by seismic analyses at the basin scale by log analysis at the reservoir scale by petrographic methods and by petrophysical tools at the pore core scale two dolomitization stages separated by a compaction event with associated fracturing and stylolites have been identified these diagenetic events have significantly improved the lower r2 carbonate reservoir properties it is demonstrated that the reservoir quality is mainly controlled by the pore geometry which is determined by various diagenetic processes the permeability values of the reservoir range over 4 orders of magnitude from 0 1 to 5600 md and the porosity values range between 2 and 42 reservoir unit 4 a karstic dolomite shows the best reservoir properties with average porosity values ranging between 11 1 and 19 3 and an average permeability ranging between 379 and 766 md reservoir unit 2 a fine grained limestone shows the worst reservoir properties the cementation factors range from 1 68 to 2 48 the dolomitic crystal carbonate texture mainly units 3 and 4 shows the highest value of the cementation factor 1 98 2 48 and formation factor 9 54 36 97 which is due to its high degree of cementation the saturation exponents vary between 1 2 and 3 4 using these experimental electrical parameters and the resistivity laterolog tool we predicted the water saturation in the various reservoir units the permeability was predicted by combining the formation factor with the micro geometric characteristic length the best fit is obtained with the katz and thompson s model and for a constant of 1 171

moho interface beneath yakutat terrane southern alaska 1 we use air gun shots recorded by ocean bottom and land seismometers to constrain a 3 d velocity structure and a moho interface depth for the yakutat terrane in southern alaska we use a tomographic inversion of 61 000 first arrival picks from 64 receivers to create a 3 d velocity model the average velocity depth function north of the coastline has velocities at the surface of 4 5 km s increasing to velocities of 6 km s at 12 13 km below the surface average velocities at the surface are slower near the coast 3 8 km s than under the highest topography 4 7 km s we carry out an interface inversion of 19 000 pmp reflection picks from 50 receivers to constrain a 2 d moho interface model the average moho depth of the yakutat terrane in the marine portion of our study area is 30 km but depth rapidly increases onshore to 40 45 km beneath the high topography of the chugach st elias mountains moho depths are consistent with airy isostasy beneath the orogen our data set supports a continuous moho at the base of the yakutat terrane with no evidence for pacific oceanic crust underthrusting the yakutat terrane we present several geologic models for crustal thickening beneath the chugach st elias orogen that are consistent with the seismic observations and surface geology and compare these models with geologic mapping in the region we argue that crustal thickening and topography at the chugach st elias mountains is obtained via a duplex system that produces a vertically growing antiformal stack of sedimentary and metasedimentary material

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

decade scale decrease inb value prior to the m9 class 2011 tohoku and 2004 sumatra quakes 1 the gutenberg richter frequency magnitude distribution of earthquakes has become well established in seismology the slope of the relation between frequency and magnitude b value is typically 1 but it often shows variations around 1 based on an analysis of seismicity prior to the 2011 tohoku and 2004 sumatra earthquakes both in magnitude m 9 class we show that the pronounced decade scale decrease inbvalue was a common precursor to both mega quakes around their hypocenters this is the first report onm9 class quakes to confirm a change inb value which has been predicted based on the results of laboratory experiments we propose that the b value is an important indicator of an impending great earthquake and has great potential in terms of predicting a future large quake off the pacific coast of hokkaido japan

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

mineralogical control on porosity type in upper jurassic smackover ooid grainstones southern arkansas and northern louisiana abstract original mineralogy of ooids affects both their diagenetic history and therefore the reservoir quality of ooid lithologies previous studies have shown that ancient ooid cortices were composed either of aragonite mg calcite or calcite this study based on fabrics and geochemical analyses of smackover oolites suggests that both aragonite and calcite ooids were deposited on the upper jurassic smackover shelf of southern arkansas and northern louisiana smackover ooids exhibit both a blocky calcite spar fabric and a radial calcite fabric grainstones with blocky calcite spar ooids and oomoldic porosity have a higher strontium content than those with a radial calcite fabric the high strontium has a jurassic marine isotopic signature supporting the interpretation that the blocky cal ite spar is an early diagenetic fabric after aragonite radial calcite ooids were originally calcitic the ooids accumulated in a series of linear bars parallel to shore ooids with original aragonite mineralogy are older and were deposited in the north the younger more southern bars consisted of calcite ooids aragonite ooids in the north were susceptible to dissolution and formation of moldic porosity during freshwater diagenesis moldic porosity is generally accompanied by low permeability calcite ooids in the south however were less susceptible to dissolution in meteoric waters hence preserved porosity is interparticle porosity and permeability is generally higher porosity types in the upper smackover of arkansas and louisiana reflect both the original mineralogy of the ooids as well as their diagenetic history

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

a reinterpretation of the precursory seismic b value anomaly from fracture mechanics summary a new model is presented which can explain the major temporal fluctuations in seismic b value in terms of the underlying physical processes of time varying applied stress and crack growth under conditions of constant strain rate the model predicts two minima in the b value separated by a temporary maximum of inflexion point a corollary being that a single broad maximum would be expected in scattering attenuation these fluctuations in b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence we present preliminary results from controlled laboratory experiments and report recent field observations both of which are consistent with the predicted form and in particular exhibit the distinctive second short term anomaly which reaches a value bc 0 5 during the critical phase

microscale characterization of rupture nucleation unravels precursors to faulting in rocks abstract precursory signals manifestations of microscale damage that precedes dynamic faulting are key to earthquake forecasting and risk mitigation detections of precursors have primarily relied on measurements performed using sensors installed at some distance away from the rupture area in both field and laboratory experiments direct observations of continuous microscale damage accumulated during fault nucleation and propagation are scarce using an x ray transparent triaxial deformation apparatus we show the first quantitative high resolution three dimensional 3d information about damage evolution of rocks undergoing brittle failure the dynamic microtomography images documented a spectrum of damage characteristics and different fault growth patterns the interplay between various deformation mechanisms can result in either a positive negative or constant net volume change consequently changes in rock density and acoustic wave velocities before faulting are expected to vary in different tectonics settings hence making failure forecasting intrinsically dependent on rock type at depth

upper jurassic depositional systems and hydrocarbon potential of southeast mississippi abstract upper jurassic sedimentation in southeast mississippi was controlled by eustatic sea level fluctuations and locally modified by salt tectonism and basement structure the present study using conventional core data and geophysical logs indicates that a stable carbonate platform developed along the updip margin of the mississippi interior salt basin the basin was partially barred from the main gulf of mexico water mass by the wiggins uplift and became evaporitic during the upper jurassic the smackover and haynesville formations are separate sedimentologic packages deposited during two distinct sea level cycles high energy carbonates extended across the northern basin margin as sedimentation kept pace with subsidence and slowing sea level rise near the close of each transgression an effective shelf margin barrier did not develop lime mud generally accumulated under subtidal conditions within the interior salt basin however the basin was sufficiently shallow for wavebase sedimentation to occur on crests of salt cored bathymetric highs resulting in localized reservoir facies to the south eolian conditions initially prevailed on the wiggins uplift later as the wiggins subsided subaqueous shoals fringed and capped individual basement islands eustatic sea level fluctuations and salt movement controlled diagenesis and porosity formation limestone porosity dominates in upper smackover platform carbonates with a transition from secondary moldic porosity updip to preserved primary porosity downdip moldic intercrystalline and vuggy dolomite porosity is developed on the crests of intermediate and high amplitude salt highs and on the wiggins uplift jurassic source rocks are lower smackover laminated lime mudstones migration into adjacent reservoirs postdated formation of porosity and the growth of salt anticlines the most common trap type a large potential norphlet smackover gas play extends along the southern flank of the wiggins uplift salt anticlines within the interior basin remain viable targets small oil discoveries should continue in stratigraphic traps subtle salt structures and basement blocks on the platform

porosity preservation in the upper smackover jurassic carbonate grainstone walker creek field arkansas response of paleophreatic lenses to burial processes reply a section of the arco bodcaw no 1 core from the upper smackover jurassic of southern arkansas was studied in detail in an effort to understand the control of porosity petrographic isotopic atomic absorption and cathodoluminescence data on whole rocks and components were generated on 24 samples from a 115 foot length of core the core is composed almost entirely of accretionary and cryptocrystalline grains and cement porosity is unrelated to grain type size or sorting on a sample to sample basis the porous intervals are interpreted to have been stablized to calcite under fresh water phreatic conditions the porous intervals approach fresh water values of 5 0 per thousand delta 18 o 1 5 mol percent mg and 300 ppm sr and are further characterized by luminescent oolites and relatively slight solution compaction effects the nonporous intervals represent relict vadose and subphreatic environments which stabilized after burial the nonporous intervals approach burial values of 2 8 per thousand delta 18 o 2 5 mol percent mg and 600 ppm sr and are further characterized by nonluminescent grains and intense solution compaction data indicate that oolites were initially composed of a metastable mineralogy cryptocrystalline grains were composed of a more stable mineralogy and algal grains were composed of a mixture of mineralogies oolites in the vadose and subphreatic environments were not fully stabilized under fresh water conditions but vadose grains carried with them a light delta 13 c soil gas signal after burial these grains were fully stabilized under post fresh water burial conditions observed porosity distribution is readily explained in terms of solution compaction and cementation grains with metastable mineralogy in relict vadose and subphreatic intervals were heavily solution compacted at relatively shallow depths before being converted to stable calcite intense solution compaction destroyed pore space in these intervals dolomite cementation seems linked with the compaction process the stablized mineralogy of the phreatic lens together with associated meteoric cements resisted solution compaction and thereby preserved pore space

distribution of seismic wave speed changes associated with the 12 may 2008 mw 7 9 wenchuan earthquake 1 we used continuous recordings in sichuan china to track the temporal change of the seismic wave speed at a regional scale for 2 years including the wenchuan mw 7 9 earthquake the data are recorded by a temporary network of 156 broad band seismographs in a region that covers the southern 2 3 of the fault activated during the earthquake a doublet analysis applied on the codas of seismic noise cross correlation functions is used to detect temporal velocity changes we found clear evidence that the seismic velocity drops by up to 0 08 in the fault region just after the earthquake with fluctuations within 0 02 before the earthquake we compared the measurements in different sub arrays to get a spatial distribution of the velocity changes this distribution is consistent with the volumetric strain change during the wenchuan earthquake and shows that the co seismic velocity change is not controlled by the response of sediments

burial diagenesis and porosity evolution upper jurassic smackover arkansas and louisiana the jurassic upper smackover ooid lime grainstone of the central gulf coast has been a major hydrocarbon exploration target for nearly half a century study of the geologic and sedimentologic framework petrography two phase fluid inclusions and trace element and stable isotope chemistry indicates the following diagenetic history the upper smackover is a blanket ooid grainstone ranging in thickness from 300 to 400 ft 91 to 122 m and covering at least 4 000 sq mi 10 400 sq km in the northern part of the arkansas shelf a regional meteoric water system was established in the grainstone shortly after deposition and prior to significant burial this meteoric water system gave way to conditions which were increasingly more marine toward the south near the louisiana arkansas state line the fresh to marine hydrologic gradient is responsible for the strong precompaction regional diagenetic overprint that eventually controlled available diagenetic pathways for the unit during burial three diagenetic zones are present 1 a northern zone dominated by oomoldic porosity and preburial spar cementation 2 a sou hern zone characterized by compaction effects late subsurface cement primary porosity preservation and late secondary subsurface porosity generation and 3 a transitional zone having characteristics common to both the northern and southern zones during the shallow burial phase compaction became increasingly more important to the south in zones dominated by marine connate fluid whereas rock integrity and a secondary oomoldic porosity system had already been established in the northern zone as burial increased brine originating in the underlying louann salt reached the shelf grainstone and began to displace the original connate fluid the brine triggered the inversion to calcite of remaining grains and cement composed of unstable mineralogy when the louann brine had displaced the original connate fluid caso4 replacement as gypsum and anhydrite was common across all three diagenetic zones also precompaction fine cement associated with oomoldic porosity was recrystallized and reequilibrated with the concentrate brine localized replacement dolomitization may well have developed throughout the burial history of the sequence but was most commonly postcompactional postcompaction poikilitic calcite cement and baroque dolomite were precipitated from the louann brine under conditions of elevated temperature and pressure as subsidence continued organic material from the basinward equivalents of the upper smackover lime grainstone arrived on the shelf and catalyzed so4 reduction resulting in pyrite and galena replacement in the southern and transitional zones as hydrocarbon maturation continued in the fine grained equivalents of the upper smackover h2s and co2 by products of these processes began to increase in the brine of the southern and transitional zones ultimately causing regional dissolution of existing carbonate and significantly enhancing preserved porosity porosity in the northern zone was established early and preserved through moderate burial although porosity is well developed permeability has been largely destroyed by recrystallization dolomitization is a prerequisite for economic reservoir development in the northern zone porosity in the southern zone is solution enhanced preserved primary intergranular porosity compaction is the most important porosity destruction process compaction in the absence of an early diagenetic overprint is affected primarily by grain type and secondarily by size and sorting pellets and oncolites compact easily yet destroy porosity during burial ooids and rhodolites resist compaction during burial therefore are related to porosity preservation grain type distribution as well as size and sorting are controlled by depositional environment processes with the most favorable areas for porosity development concentrations of ooids and rhodolites associated with early salt related structural movement porosity distribution in the southern zone therefore can be outli ed with the aid of geophysical end page 597 techniques porosity in the transitional zone is early secondary or preserved primary intergranular or a combination porosity in this zone therefore is highly unpredictable and a strong potential exists for diagenetic traps unrelated to structure or original depositional environment documentation of significant deep subsurface secondary porosity possibly associated with hydrocarbon maturation opens the potential for hydrocarbon exploration in deeply buried carbonate dominated basins this would include carbonate rocks heretofore thought to be well below the depth of carbonate porosity maintenance because of lithostatic load

pervasive foreshock activity across southern california foreshocks have been documented as preceding less than half of all mainshock earthquakes these observations are difficult to reconcile with laboratory earthquake experiments and theoretical models of earthquake nucleation which both suggest that foreshock activity should be nearly ubiquitous here we use a state of the art high resolution earthquake catalog to study foreshock sequences of magnitude m4 and greater mainshocks in southern california from 2008 2017 this highly complete catalog provides a new opportunity to examine smaller magnitude precursory seismicity seventy two percent of mainshocks within this catalog are preceded by foreshock activity that is significantly elevated compared to the local background seismicity rate foreshock sequences vary in duration from several days to weeks with a median of 16 6 days the results suggest that foreshock occurrence in nature is more prevalent than previously thought and that our understanding of earthquake nucleation may improve in tandem with advances in our ability to detect small earthquakes

pore geometry control on reservoir properties walker creek field columbia and lafayette counties arkansas walker creek field in southern arkansas produces hydrocarbons from oolitic packstones and grainstones of the jurassic smackover formation the relationships between pore geometry and reservoir quality in these rocks were evaluated using petrographic methods and mercury injection capillary pressure analyses results indicate that reservoir quality is controlled by pore geometry which in turn is determined by depositional and diagenetic processes reservoir rocks at walker creek were deposited as prograding grainstone shoals in a shallow water high energy environment diagenetic processes including early marine cementation compaction and deeper burial pressure solution and calcite cementation modified the original pore system primary interparticle porosity is the dominant effective pore type and is most important in terms of reservoir performance secondary microporosity is also abundant comprising a significant percentage of total porosity locally up to 100 but is generally ineffective the rocks were subdivided into lithofacies based on their depositional and diagenetic origin within each lithofacies reservoir marginal reservoir and nonreservoir rock types are identified based on their pore geometry and characteristic capillary pressure curve the reservoir rock types are less cemented oolitic and oolitic skeletal grainstones with steeply sloping capillary pressure curves and flat plateaus indicating relatively homogeneous pore sizes that are well interconnected by large pore throats the marginal to nonreservoir rock types include mudstones wackestones muddy packstones and cemented grainstones with generally small interparticle and moldic pores gently sloping capillary pressure curves with poorly defined or no plateaus indicate variable pore and pore throat sizes a close correlation is found among parts of the capillary pressure curve shape such as slopes plateaus and displacement pressure and aspects of pore geometry such as pore throat size pore throat size distribution and pore interconnectivity in addition capillary pressure analyses provide guidance in evaluating overall reservoir quality by rock type as well as answer specific questions regarding net pay criteria as a function of height above free water level

similarity of fast and slow earthquakes illuminated by machine learning tectonic faults fail in a spectrum of modes ranging from earthquakes to slow slip events the physics of fast earthquakes are well described by stick slip friction and elastodynamic rupture however slow earthquakes are poorly understood key questions remain about how ruptures propagate quasi dynamically whether they obey different scaling laws from ordinary earthquakes and whether a single fault can host multiple slip modes we report on laboratory earthquakes and show that both slow and fast slip modes are preceded by a cascade of micro failure events that radiate elastic energy in a manner that foretells catastrophic failure using machine learning we find that acoustic emissions generated during shear of quartz fault gouge under normal stress of 1 10 mpa predict the timing and duration of laboratory earthquakes laboratory slow earthquakes reach peak slip velocities of the order of 1 10 4 m s 1 and do not radiate high frequency elastic energy consistent with tectonic slow slip acoustic signals generated in the early stages of impending fast laboratory earthquakes are systematically larger than those for slow slip events here we show that a broad range of stick slip and creep slip modes of failure can be predicted and share common mechanisms which suggests that catastrophic earthquake failure may be preceded by an organized potentially forecastable set of processes both fast and slow earthquakes are preceded by micro failure events that radiate energy according to machine learning these events can foretell catastrophic failure in laboratory experiment earthquakes

petrofacies analysis of carbonate rocks example from lower paleozoic hunton group of oklahoma and texas a petrophysical classification of hunton group dolomitized carbonates lower paleozoic in the anadarko basin of oklahoma and texas is based on porosity mercury recovery efficiency median pore throat size normalized pore throat size the shapes of capillary pressure curves and lithology five petrophysical facies petrofacies include i porous and permeable dolostones ii skeletal grainstones and packstones iii low porosity low permeability dolomitized oomoldic ooid grainstones iv cemented ooid grainstones cherts and cherty carbonates and v lime mudstones and tight fine grained dolostones petrofacies i porous dolostone is the most variable this variability reflects the inherent variability of dolostones and the probability that dolomitization of t e hunton group occurred in more than one episode four subpetrofacies include ia crystalline and sucrosic dolostones ib vuggy dolostones iva cemented ooid grainstones and ivb cherts and cherty mudstones and wackestones the petrofacies form mappable subsurface units that can be used to predict the distribution of petroleum reservoirs e g petrofacies i and ii and of potential sealing units petrofacies iii iv and v and to identify potential stratigraphic traps petrofacies and depositional lithofacies are discordant indicating that diagenetic processes did not respect lithofacies boundaries the best reservoir rocks sucrosic fossiliferous dolostones of subpetrofacies ia and crinoidal grainstones of petrofacies ii have both high porosities mean 5 2 6 9 and high mercury recovery efficiencies mean 30 7 36 1 these rocks are characterized by moderately sized throats median 2 6 8 8 m mesokurtic to platykurtic pore throat size distributions and intermediate or gently sloping cumulative mercury intrusion capillary pressure curves higher porosity rocks with low mercury recovery efficiencies mean porosity 11 8 re 25 for example vuggy and moldic dolostones of subpetrofacies ib would not perform well during primary oil recovery but would be good candidates for enhanced oil recovery for reservoir rocks that are oil wet capillary pressure dat must be interpreted differently than is done in this paper most petrofacies can be distinguished by the shapes of capillary pressure curves alone however bivariate plots of petrophysical parameters also allow discrimination between petrofacies the negative log of median pore throat size plotted vs either porosity or mercury recovery efficiency provides the most readily interpretable graphic method of assigning samples to petrofacies such plots are particularly useful in highlighting samples that are lithologically similar to but petrophysically different from samples typical of a particular petrofacies

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

acoustic energy release during the laboratory seismic cycle insights on laboratory earthquake precursors and prediction machine learning can predict the timing and magnitude of laboratory earthquakes using statistics of acoustic emissions the evolution of acoustic energy is critical for lab earthquake prediction however the connections between acoustic energy and fault zone processes leading to failure are poorly understood here we document in detail the temporal evolution of acoustic energy during the laboratory seismic cycle we report on friction experiments for a range of shearing velocities normal stresses and granular particle sizes acoustic emission data are recorded continuously throughout shear using broadband piezo ceramic sensors the coseismic acoustic energy release scales directly with stress drop and is consistent with concepts of frictional contact mechanics and time dependent fault healing experiments conducted with larger grains 10 5 m show that the temporal evolution of acoustic energy scales directly with fault slip rate in particular the acoustic energy is low when the fault is locked and increases to a maximum during coseismic failure data from traditional slide hold slide friction tests confirm that acoustic energy release is closely linked to fault slip rate furthermore variations in the true contact area of fault zone particles play a key role in the generation of acoustic energy our data show that acoustic radiation is related primarily to breaking sliding of frictional contact junctions which suggests that machine learning based laboratory earthquake prediction derives from frictional weakening processes that begin very early in the seismic cycle and well before macroscopic failure

preseismic fault creep and elastic wave amplitude precursors scale with lab earthquake magnitude for the continuum of tectonic failure modes tectonic faults fail in a continuum of modes from slow earthquakes to elastodynamic rupture precursory variations in elastic wavespeed and amplitude interpreted as indicators of imminent failure

evolution of b value during the seismic cycle insights from laboratory experiments on simulated faults abstract we investigate the evolution of the frequency magnitude b value during stable and unstable frictional sliding experiments using a biaxial shear configuration we record broadband acoustic emissions ae while shearing layers of simulated granular fault gouge under normal stresses of 2 8 mpa and shearing velocity of 11 m s ae event amplitude ranges over 3 4 orders of magnitude and we find an inverse correlation between b and shear stress the reduction of b occurs systematically as shear stress rises prior to stick slip failure and indicates a greater proportion of large events when faults are more highly stressed for quasi periodic stick slip events the temporal evolution of b has a characteristic saw tooth pattern it slowly drops as shear stress increases and quickly jumps back up at the time of failure the rate of decrease during the inter seismic period is independent of normal stress but the average value of b decreases systematically with normal stress for stable sliding b is roughly constant during shear however it exhibits large variability during irregular stick slip we see a mix of both behaviors b decreases during the interseismic period between events and then remains constant when shear stress stabilizes until the next event where a co seismic increase is observed our results will help improve seismic hazard assessment and ultimately could aid earthquake prediction efforts by providing a process based understanding of temporal changes in b value during the seismic cycle

precursory changes in seismic velocity for the spectrum of earthquake failure modes temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes tremor and low frequency earthquakes1 laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2 however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3 here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults we systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick slip and monitored ultrasonic wave speed during frictional sliding we find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure which suggests that real time monitoring of active faults may be a means to detect earthquake precursors

acoustic emissions document stress changes over many seismic cycles in stick slip experiments 1 the statistics of large earthquakes commonly involve large uncertainties due to the lack of long term robust earthquake recordings small scale seismic events are abundant and can be used to examine variations in fault structure and stress we report on the connection between stress and microseismic event statistics prior to the possibly smallest earthquakes those generated in the laboratory we investigate variations in seismic b value of acoustic emission events during the stress buildup and release on laboratory created fault zones we show that b values mirror periodic stress changes that occur during series of stick slip events and are correlated with stress over many seismic cycles moreover the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop consequently b value variations can be used to approximate the stress state on a fault a possible tool for the advancement of time dependent seismic hazard assessment citation goebel t h w d schorlemmer t w becker g dresen and c g sammis 2013 acoustic emissions document stress changes over many seismic cycles in stick slip experiments geophys res lett 40 2049 2054 doi 10 1002 grl 50507

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