joint inversion of source location and focal mechanism of microseismicity abstractthe seismic focal mechanism fm is an effective property to indicate source physics as well as stress and strain distribution in regional local and microscales we have developed an algorithm to jointly invert for the fm and source locations for a given velocity structure all possible combinations of source locations x y and z and fm strike dip and rake were used to compute traveltimes and polarities of waveforms correcting normal moveout times and polarities and stacking all waveforms the x y z strike dip and rake combination that gave the strongest stacking power was identified as the optimal solution compared with the traditional source scanning algorithm ssa that only scanned source locations this algorithm was thereby called the joint source scanning algorithm jssa the jssa method was tested rigorously and it was applied to a hydraulic fracturing data set our work determined several advantages against the ssa method 1 the jssa method could identify many shea

reactivated faulting near cushing oklahoma increased potential for a triggered earthquake in an area of united states strategic infrastructure in october 2014 two moderate sized earthquakes mw 4 0 and 4 3 struck south of cushing oklahoma below the largest crude oil storage facility in the world combined analysis of the spatial distribution of earthquakes and regional moment tensor focal mechanisms indicate reactivation of a subsurface unnamed and unmapped left lateral strike slip fault coulomb failure stress change calculations using the relocated seismicity and slip distribution determined from regional moment tensors allow for the possibility that the wilzetta whitetail fault zone south of cushing oklahoma could produce a large damaging earthquake comparable to the 2011 prague event resultant very strong shaking levels mmi vii in the epicentral region present the possibility of this potential earthquake causing moderate to heavy damage to national strategic infrastructure and local communities

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

seismic arrival enhancement through the use of noise whitening abstract a constant feature in seismic data noise is particularly troublesome for passive seismic monitoring where noise commonly masks microseismic events we propose a statistics driven noise suppression technique that whitens the noise through the calculation and removal of the noise s covariance noise whitening is shown to reduce the noise energy by a factor of 3 5 resulting in microseismic events being observed and imaged at lower signal to noise ratios than originally possible whilst having negligible effect on the seismic wavelet the procedure is shown to be highly resistant to most changes in the noise properties and has the flexibility of being used as a stand alone technique or as a first step before standard random noise attenuation methods

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

microseismic hydraulic fracture imaging the path toward optimizing shale gas production economic shale gas production involves hydraulic fracture stimulation in order to create permeable flow paths within these low permeability reservoirs microseismic monitoring has shown that often these fracs consist of complex fracture networks with large surface contact areas with the reservoir optimized production is therefore dependent on the ability of the stimulation to activate an extensive fracture network much of the current attention around hydraulic fractures focuses on microseismic imaging of the activated network however the path toward optimized shale gas production also requires methods to both predict and model the fracture networks along the path engineers will be able to close the loop for an optimally designed stimulation being able to predict monitor and assess the stimulated fracture network as an industry we are just starting down this path and this paper describes a few case studies that highlight recent advancements before we can ultimately predict the fracture netw

sedimentation calcrete cycles in the mesozoic red formations from the central high atlas telouet area morocco abstract in the telouet ighrem area southern side of the central high atlas morocco the mesozoic couches rouges or red formations are composed of conglomerates sandstones and siltstones organized into upward fining sequences locally capped by swamp deposits epigenetic calcretes developed within these formations subsequent to indeindependent of the initial sedimentation several types occur controlled mainly by the permeability and structures of the original sediment nodules prismatic pillars small columns etc these carbonate bodies appear in field sections as metric to plurimetric commonly overhanging lenses or beds siliceous micro features are locally associated with the carbonate accumulations these calcretes are the result of polyphase epigenetic processes among which surface weathering in a semi arid context is predominant during the wet season carbonates in the upper part of the profile dissolve and migrate downwards by the end of the wet season and the beginning of the dry season solute concentration occurs which induces hydrolysis of quartz and silicates including clay minerals during the dry season palygorskite develops and carbonates are precipitated these pedogenic processes may have succeeded localized and ephemeral palustrine processes related to observed lateral water circulation or to an exposed water table the latter being particularly sensitive to exceptional events e g heavy rainfall in this type of climate the accumulation of detrital deposits followed by the epigenetic wrocesses which occur according to the sometimes partial sequence of calcitization palygorskitization dolomitization silicification characterize sedimentation calcretization cycles the thickness of the carbonate bodies depends on the stability of the environment which is probably controlled by climate and tectonics michard 1976 jenny et al 1981 jacobshagen 1988 a new insight is thus provided on the mesozoic palaeogeography of the central high atlas

turonian to neogene palaeokarst in israel abstract the extensive karstic system found today in cretaceous carbonates in central and northern israel has been developing since late turonian times initial late turonian karstic activity is evidenced by small sand filled solution cavities within the upper turonian sequence senonian palaeodolines are found in central and northern israel but are missing from the southern negev and sinai areas this is attributed to the emergence of northern israel during the lowermost senonian coniacian stage while southern israel was submerged the palaeodolines take the form of circular to irregular depressions a few tens of meters in diameter cut into turonian and or santonian rocks in many of these palaeodolines the turonian bedrock dips concentrically towards the center of the depression a feature characteristic of dolines resulting from the collapse of bedrock into underlying conduits most of the palaeodolines are filled with collapsed beds of turonian limestones and marine chalks of senonian mostly campanian age marine sediments of eocene and miocene age are locally found as doline fill overlying the senonian chalks indicating repeated phases of emergence and karstic erosion in late coniacian post santonian pre campanian pre middle eocene and pre late miocene times followed by submergence and marine deposition pockets of dolomite crystal sands are found in some senonian dolines their 18 o ranges between 1 and 2 3 and 13 c between 0 8 o and 1 8 o pdb it is suggested that these dolomites were formed at the seawater freshwater inferface during one of the later transgressive phases between the karstic stages the senonian palaeodolines are cut only into horizontally bedded strata of late turonian age showing only moderate development of paleokarst at this time considerable uplifting of this region and the entailing incision of erosional canyons prior to the late miocene tortonian marine transgression created favorable conditions for a very developed karstic phase

the magnesium isotope δ26mg signature of dolomites abstract dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments using well established isotope systems 18 o 13 c 87 sr 86 sr fluid inclusions and elemental data as well as a detailed sedimentological and petrographic data set we established the precipitation environment and subsequent diagenetic pathways of a series of proterozoic to pleistocene syn depositional marine evaporative sabkha dolomites syn depositional non marine evaporative lacustrine and palustrine dolomites altered marine mixing zone dolomites and late diagenetic hydrothermal dolomites these data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios 26 mg dol dolomite 26 mg ratios documented here range from 2 49 to 0 45 26 mg mean 1 75 1 08 n 42 the isotopically most depleted end member is represented by earliest diagenetic marine evaporative sabkha dolomites 2 11 0 54 2 n 14 in comparing ancient compositions to modern ones some of the variation is probably due to alteration altered marine 1 41 0 64 2 n 4 and earliest diagenetic lacustrine and palustrine dolomites 1 25 0 86 2 n 14 are less negative than sabkha dolomites but not distinct in composition various hydrothermal dolomites are characterized by a comparatively wide range of 26 mg ratios with values of 1 44 1 33 2 n 10 by using fluid inclusion data and clumped isotope thermometry 47 to represent temperature of precipitation for hydrothermal dolomites there is no correlation between fluid temperature 100 to 180 c and dolomite mg isotope signature r 2 0 14 nor is there a correlation between 26 mg dol and 18 o dol magnesium isotope values of different dolomite types are affected by a complex array of different mg sources and sinks dissolution precipitation and non equilibrium fractionation processes and overprinted during diagenetic resetting further progress on the use of 26 mg dol as a proxy will require new theoretical and experimental data for 26 mg fluid dol that includes dehydration effects of the free mg aquo ion versus fluid temperature in ancient diagenetic systems complex variables must be considered these include fluid chemistry and physical properties mg sources and sinks temporal changes during precipitation and post precipitation processes including open and closed system geochemical exchange with ambient fluids all of these factors complicate the application of 26 mg dol as proxy for their depositional or diagenetic environments nevertheless the data shown here also indicate that 26 mg dol can in principle be interpreted within a detailed framework of understanding

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

neocomian deltaic complex in central tunisia a particular example of ancient sedimentation and basin evolution abstract sedimentologic and stratigraphic study of the neocomian series of central tunisia has demonstrated that these sediments form a regressive megasequence dominated by development of a deltaic complex this deltaic complex consists of three prograding environments 1 a clayey prodelta passing seawards into a deep marly calcareous shelf 2 a delta platform characterized by coarsening upward sequences of mouth bars and fining upward sequences of channel bars and intercalated with oolitic carbonate beds and 3 a fluvial plain with coarse sands deposited in braided channels the general organization of deposits and the progradation of the environments is comparable to many modern deltaic systems however it differs from modern deltas by the absence of classic deltaic form and by the intimate association of siliciclastic and carbonate sediments reflecting fluctuating terrigenous supply and minor marine ingressions non marine sedimentation occurred mainly on a fluvial plain deficient both in swamps and in tidal flats the coarse sand was deposited not by a single river but in numerous braided channels the construction of this deltaic complex within the weakly subsiding central tunisia basin was controlled by three main factors 1 a semi arid paleoclimate 2 tectonic movements occurring at the end of jurassic and neocomian and 3 a hinterland the saharan platform lacking both relief and channelized drainage systems

trace element and stable c o and radiogenic sr isotope geochemistry of stromatolitic carbonate rocks of the mesoarchaean pongola supergroup implications for seawater composition abstract the mesoarchaean pongola supergroup hosts one of the oldest well preserved stromatolitic carbonate successions major and trace element geochemistry along with c o and sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment and to unravel the chemical characteristics of contemporaneous seawater the carbonate rocks consist mainly of dolomite and to a lesser extent ankerite their variable sr concentrations of 95 to 450 mg kg are interpreted as resulting from early to late dolomitization of metastable carbonates aragonite and or high mg calcite facies control and calcitization during meteoric diagenesis 18o values range from 19 6 to 12 0 vpdb and reflect recrystallization of carbonates caused by high water rock interactions during diagenesis and metamorphism a 13c value of 2 5 vpdb was measured in carbonate samples least affected by alteration and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater the samples display variable 87sr 86sr isotopic ratios from as low as 0 708 to 0 777 these ratios are considerably higher than those expected in archaean open ocean water masses buffered by hydrothermal interaction with the mantle we interpret the highly radiogenic sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic sr from siliciclastic volcaniclastic components in the samples and fluids from clay rich layers intercalated with the carbonates the least radiogenic sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the kaapvaal craton the dolomitic carbonate samples show shale normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive lasn gdsn and ysn anomalies superchondritic y ho ratios a small negative cesn anomaly and depleted light rare earth elements relative to the heavy rare earth elements these anomalies are not as pronounced as expected for an open marine setting which together with the sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions a convex upward shale normalized rare earth element and yttrium pattern is probably a result of several factors including organic matter complexation and element fractionation during estuarine mixing the small negative cesn anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity

fine grained volcanic hydrothermal sedimentary rocks in permian lucaogou formation santanghu basin nw china implications on hydrocarbon source rocks and accumulation in lacustrine rift basins abstract subaqueous volcanic hydrothermal field is a complex hybrid geological system where sediments originated from volcanic hydrothermal lacustrine terrestrial and biotic sources are mixed recent petrological studies on such sediments have indicated a potential relationship between volcanic hydrothermal activities and oil generation and accumulation here we explore the mechanisms of sedimentation and oil accumulation in well laminated organic rich fine grained sedimentary rocks in permian lucaogou formation deposited in the lacustrine santanghu rift basin nw china we conducted petrographic carbon and oxygen isotopic and organic geochemical analyses of fifty four core samples from three wells forty eight samples from well w1 two from w2 four from w3 designed for tight oil exploration four main observations and interpretations are 1 the fine grained sediments are a mixture of volcanic hydrothermal detrital feldspar grains authigenic quartz crystals and primary lacustrine dolomite forming interbedded tuffaceous shale and dolostone 2 authigenic quartz crystals were precipitated from acidic hydrothermal fluids whereas fine grained angular alkaline feldspars were derived from subaqueous volcanic eruption 3 the toc content and oil generation potential increase with increased mixing of feldspars and carbonate minerals hence the dolomite bearing tuffaceous shale and tuffaceous dolostone are the best source rocks and 4 the fine grained sedimentary rocks are interpreted as a subaqueous volcanic hydrothermal deposit that controls the source potential the sedimentary processes of an ancient sediment hosted geothermal system and its implications on hydrocarbon source rocks and accumulation were first identified algal bloom induced by subaqueous eruptions is the main cause for episodic deposition of organic matter and extreme heterogeneity in both lithofacies and source rock distribution the results suggest that cone shaped buildups on seismic sections which were formed by volcanic hydrothermal deposits and contain highly mixed feldspar and carbonate sediments are the best hydrocarbon reservoirs and demonstrate a strong relationship between volcanic hydrothermal activities and hydrocarbon accumulation in an extensional tectonic setting

probabilistic assessment of potential fault slip related to injection induced earthquakes application to north central oklahoma usa we utilize quantitative risk assessment qra to calculate the conditional probability of slip on mapped faults in response to injection related increases in pore pressure in north central oklahoma usa where widespread injection of produced saltwater has triggered thousands of small to medium sized earthquakes in the past 7 yr the conditional probability incorporates the uncertainty in each mohr coulomb parameter stress tensor pore pressure coefficient of friction and fault orientation through qra the result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment the results can be used to assess the probability of induced slip on a known fault from a given injection related pore pressure increase after dividing north central oklahoma into six study areas we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses the qra identifies the potential for slip on the fault that produced the m 5 6 prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the m 5 1 fairview earthquake sequence that occurred in early 2016 and had the 289 striking fault of the september 2016 m 5 8 pawnee event been mapped it would have been identified as potentially active

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

source modeling of the 2015 mw 7 8 nepal gorkha earthquake sequence implications for geodynamics and earthquake hazards abstract the gorkha earthquake on april 25th 2015 was a long anticipated low angle thrust faulting event on the shallow decollement between the india and eurasia plates we present a detailed multiple event hypocenter relocation analysis of the mw 7 8 gorkha nepal earthquake sequence constrained by local seismic stations and a geodetic rupture model based on insar and gps data we integrate these observations to place the gorkha earthquake sequence into a seismotectonic context and evaluate potential earthquake hazard major results from this study include 1 a comprehensive catalog of calibrated hypocenters for the gorkha earthquake sequence 2 the gorkha earthquake ruptured a 150 60 km patch of the main himalayan thrust mht the decollement defining the plate boundary at depth over an area surrounding but predominantly north of the capital city of kathmandu 3 the distribution of aftershock seismicity surrounds the mainshock maximum slip patch 4 aftershocks occur at or below the mainshock rupture plane with depths generally increasing to the north beneath the higher himalaya possibly outlining a 10 15 km thick subduction channel between the overriding eurasian and subducting indian plates 5 the largest mw 7 3 aftershock and the highest concentration of aftershocks occurred to the southeast the mainshock rupture on a segment of the mht decollement that was positively stressed towards failure 6 the near surface portion of the mht south of kathmandu shows no aftershocks or slip during the mainshock results from this study characterize the details of the gorkha earthquake sequence and provide constraints on where earthquake hazard remains high and thus where future damaging earthquakes may occur in this densely populated region up dip segments of the mht should be considered to be high hazard for future damaging earthquakes

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

finite fault slip model of the 2011 mw 5 6 prague oklahoma earthquake from regional waveforms the slip model for the 2011 mw 5 6 prague oklahoma earthquake is inferred using a linear least squares methodology waveforms of six aftershocks recorded at 21 regional stations are used as empirical green s functions egfs the solution indicates two large slip patches one located around the hypocenter with a depth range of 3 5 5 km the other located to the southwest of the epicenter with a depth range from 7 5 to 9 5 km the total moment of the solution is estimated at 3 37 1024 dyne cm mw 5 65 the peak slip and average stress drop for the source at the hypocenter are 70 cm and 90 bars respectively approximately one half the values for the mw 5 8 2011 mineral virginia earthquake the stress drop averaged over all areas of slip is 16 bars the relatively low peak slip and stress drop may indicate an induced component in the origin of the prague earthquake from deep fluid injection

multiple episodes of dolomitization and dolomite recrystallization during shallow burial in upper jurassic shelf carbonates eastern swabian alb southern germany abstract the upper jurassic of the eastern swabian alb is composed of oolitic platform sands with associated microbe siliceous sponge mounds at the platform margins they are surrounded by argillaceous or calcareous mudstones and marl limestone alternations deposited in adjacent marl basins partial to complete dolomitization is predominantly confined to the mound facies six types of dolomite as well as one type of ankerite document a complex diagenetic history during shallow burial with multiple episodes of dolomite formation and recrystallization the earliest massive matrix dolomitization is ca rich has slightly depleted oxygen isotope values relative to late jurassic seawater and carbon isotopic values in equilibrium with late jurassic seawater this initial massive matrix dolomitization occurred during latest jurassic to earliest cretaceous and is related to pressure dissolution during very shallow burial at temperatures of at least 50 c hydrologic conditions and mass balance calculations indicate that burial compaction provided sufficient fluids for dolomitization mg is derived from negligibly modified seawater that was expelled from the adjacent off reef strata into the mound facies position of the mounds along the platform margins controlled the distribution of the shallow burial dolomite covariant trends between textural modification increasing stoichiometry partial changes in trace element content mn fe sr and depletion in stable isotopes as well as distinctive cl pattern illustrate two recrystallization phases of the precursor matrix dolomite during further burial at elevated temperatures strong sr enrichment of the second phase of recrystallized dolomite is ascribed to sr rich meteoric waters descending from overlying aragonite bearing reef limestones or evaporite bearing peritidal carbonates late stage coarsely crystalline dolomite cements occur as vug and fracture fillings and formed during burial ankerite associated with sulphide and sulphate minerals and saddle dolomite are assumed to have formed from hydrothermal waters that moved to higher stratigraphic levels along fracture conduit systems that developed during late cretaceous to tertiary alpine orogenesis

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

geophysical evidence for crustal and mantle weak zones controlling intra plate seismicity the 2017 botswana earthquake sequence abstract large earthquakes away from plate boundaries pose a significant threat to human lives and infrastructure but such events typically occur on previously unknown faults most cases of intra plate seismicity result from compression related to far field plate boundary stresses the april 2017 mw 6 5 earthquake in central botswana and subsequent events occurred in a region with no previously known large earthquakes occurred away from major present day tectonic activity and accommodate extension rather than compression here we present results from an integrated geophysical study that suggests the recent earthquakes may be a sign of future activity controlled by the collocation of a weak upper mantle and weak crustal structure between otherwise strong precambrian blocks magnetotelluric data highlights proterozoic continent accretion structure within the region and shows that recent extension and seismicity occurred along ancient thrust faults within the crust our seismic velocity and resistivity models suggest a weak zone in the uppermost mantle that does not persist to greater depths and is therefore unlikely to represent mantle upwelling the botswana events may therefore be indicative of top down extension as a response to large scale extensional forces

ground motions for induced earthquakes in oklahoma we examine ground motions for a sequence of earthquakes in oklahoma where assessment of hazard contributions from induced seismicity is of particular interest we aim to empirically calibrate a model driven equation that was derived for central and eastern north america cena so that it will match the observed ground motions of the 2011 prague oklahoma sequence we first show that ground motions in oklahoma decay at a rate similar to the average attenuation observed in the stable continental region of cena we then search for any needed adjustments to the cena source model to match ground motions from the induced seismicity sequence that occurred near prague in 2011 an interesting feature noted in the ground motion analysis is that the stress parameters for the prague mainshock events m 5 are notably higher than those for aftershocks moreover the stress parameter that characterizes the high frequency ground motion decays in both time and space relative to the three largest events the largest events in the prague sequence have similar source parameters to natural cena events of the same magnitude and focal depth but their aftershocks have weaker motions

efforts to monitor and characterize the recent increasing seismicity in central oklahoma abstract the sharp increase in seismicity over a broad region of central oklahoma has raised concerns regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure efforts to monitor and characterize the earthquake sequences in central oklahoma are reviewed since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma to record the evolving seismicity a multiple event relocation method is applied to produce a catalog of central oklahoma earthquakes from late 2009 into early 2015 regional moment tensor rmt source parameters were determined for the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled determination of the length depth and style of faulting occurring on reactivated subsurface fault systems it was found that the majority of earthquakes occur on near vertical optimally oriented northeast southwest and northwest southeast strike slip fault

aftershock patterns of ms 7 earthquakes in the india asia collision belt anomalous results from the muzaffarabad earthquake sequence kashmir 2005 the seismicity rate triggered by the muzaffarabad kashmir 2005 m w 7 6 m s 7 7 earthquake is above the average when analyzing the aftershock rate of the 18 m s 7 0 events in the india asia collision belt between 1973 and 2008 all 17 m s 7 0 events occurred within 10 latitude and 20 longitude distance from the 2005 muzaffarabad earthquake epicenter we determined the huge aftershock productivity for this earthquake is not driven by a specific omori law parameter this anomaly in aftershock rate value corresponds to a relatively higher rate decay as measured by the p value and a larger density value in a higher background seismicity rate setting prestress conditions than the other 17 sequences respectively after normalizing by the mainshock size and by the magnitude range of observation we resolved the anomalies with a 95 confidence level for five aftershock sequences for either the duration the productivity the density or the background seismicity rate when we did not include the local processes that drive these specific anomalies two other global results emerged for the averaged data from the 18 m s 7 0 aftershock sequences first for all sequences background seismicity and duration are anticorrelated graphic 1 within the framework of rate and state friction law this result supports the assertion that the observed background seismicity rate can be used as a proxy for the stressing rate dieterich 1994 second we robustly resolve the dependence of aftershock productivity on the mainshock faulting styles for example the aftershock productivity for strike slip mainshocks is on average four times smaller than the productivity of thrust faulting mainshocks 1 embed inline graphic 1 gif

hydromechanical controls on the spatiotemporal patterns of injection induced seismicity in different fault architecture implication for 2013 2014 azle earthquakes

activation of optimally and unfavourably oriented faults in a uniform local stress field during the 2011 prague oklahoma sequence the orientations of faults activated relative to the local principal stress directions can provide insights into the role of pore pressure changes in induced earthquake sequences here we examine the 2011 m 5 7 prague earthquake sequence that was induced by nearby wastewater disposal we estimate the local principal compressive stress direction near the rupture as inferred from shear wave splitting measurements at spatial resolutions as small as 750 m we find that the dominant azimuth observed is parallel to previous estimates of the regional compressive stress with some secondary azimuths oriented subparallel to the strike of the major fault structures from an extended catalogue we map ten distinct fault segments activated during the sequence that exhibit a wide array of orientations we assess whether the five near vertical fault planes are optimally oriented to fail in the determined stress field we find that only two of the fault planes including the m 5 7 main shock fault are optimally oriented both the m 4 8 foreshock and m 4 8 aftershock occur on fault planes that deviate 20 29 from the optimal orientation for slip our results confirm that induced event sequences can occur on faults not optimally oriented for failure in the local stress field the results suggest elevated pore fluid pressures likely induced failure along several of the faults activated in the 2011 prague sequence

on the nature of long period long duration seismic events detected during hydraulic fracturing abstractlong period long duration lpld seismic events are low amplitude tremor like seismic signals that have been observed in some microseismic monitoring data sets acquired during hydraulic fracturing operations the lpld events have been interpreted to be associated with slow slip along preexisting fractures presumed to either have high clay content or be misaligned with respect to the current day principal stress directions however a recent study indicates that regional earthquakes when recorded on vertical downhole monitoring arrays have similar signal characteristics to lpld events and that care must be taken when analyzing and interpreting such signals using data from a hydraulic fracturing microseismic data set in which lpld events have previously been identified and well documented together with data from the earthscope transportable usarray we have investigated the hypothesis that the documented lpld events were regional earthquakes we have determined that the lpld events corresponded

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

numerical simulation of the atmospheric signature of artificial and natural seismic events the mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere we numerically simulate this coupled system for two application cases active seismic experiments ases and passive seismic experiments a recent ase krishnamoorthy et al 2018 https doi org 10 1002 2018gl077481 observed the infrasonic signals produced by a seismic hammer to measure the sensitivity of observations to seismic parameters we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock solid subsurface at long range we investigate the influence of the source by using two focal mechanisms we found surface waves generate an infrasonic plane head wave in the ase case of the rock solid material for the passive seismic experiments the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail despite some limitations the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties

low limit of mn2 activated cathodoluminescence of calcite state of the art in the literature the lower limit for mn2 activated cathodoluminescence cl of calcite is variously reputed to over a very wide range of values above 10 ppm mn our spectroscopic investigations of the cl response in natural calcite reveal that below 10 ppm manganese content mn2 activation is also present using the quantitative high resolution spectral analysis of cl qhrs cl an activation by mn2 in the range of 700 ppb is proved which cannot be determined visually so if not quenched the minimum mn2 content for mn2 activation is one atom in the irradiated calcite crystal lattice volume as the intrinsic background blue luminescence is used to determine non altered biogenic calcite the limit of mn2 activation plays an important role in the interpretation of diagenetic processes our results of spectroscopic analyses require a revision of current opinions about the diagenesis of calcite as revealed by cl investigation

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

differentiation of environments of dolomite formation lower cretaceous of central tunisia combined field sedimentological mineralogical isotopic and geochemical study of the lower cretaceous dolomites of central tunisia has demonstrated considerable diversity in origin environments of dolomite formation include deep phreatic karst lacustrine and evaporitic sabkha all four groups of dolomite are composed of non stoichiometric and or disordered crystals which are more or less rich in calcium and in iron petrographic fabrics are of three types replacement recrystallization and cementation these three fabrics are proposed among the various criteria for the different environments of dolomitization average isotope 18 o and 13 c contents for these four dolomite groups range from 10 5 to 0 4 o pdb and 3 9 to 3 7 o respectively the distribution of strontium is related both to the degree of recrystallization and to the palaeosalinity ferrous iron also very common is regarded as an indicator of relatively deep reducing conditions mainly in meteoric groundwaters sodium distribution is related to inclusions within the dolomite its distribution being relatively constant in all four groups it cannot be regarded as a reliable criterion for palaeosalinity of dolomitizing fluids this study confirms that dolomitization may occur under widely different palaeoenvironments either at the surface or during burial with the exception of the sabkha environment dolomitizing fluids seem to have been essentially meteoric

moment tensor analysis of very shallow sources an issue for moment tensor mt inversion of shallow seismic sources is that some components of the green s functions have vanishing amplitudes at the free surface which can result in bias in the mt solution the effects of the free surface on the stability of the mt method become important as we continue to investigate and improve the capabilities of regional full mt inversion for source type identification and discrimination it is important to understand free surface effects on discriminating shallow explosive sources for nuclear monitoring purposes it may also be important in natural systems that have very shallow seismicity such as volcanic and geothermal systems we examine the effects of the free surface on the mt via synthetic testing and apply the mt based discrimination method to three quarry blasts from the humming albatross experiment these shallow chemical explosions at 10 m depth and recorded up to several kilometers distance represent rather severe source station geometry in terms of free surface effects we show that the method is capable of recovering a predominantly explosive source mechanism and the combined waveform and first motion method enables the unique discrimination of these events recovering the design yield using seismic moment estimates from mt inversion remains challenging but we can begin to put error bounds on our moment estimates using the network sensitivity solution technique ford et al 2010 online material figures showing synthetic tests for a pure explosion and a composite source at local distances and table of moment tensor components

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

a comparative study of the rare earth element ree distributions within the lower cretaceous dolomites and limestones of central tunisia ree distribution strontium content and oxygen isotopic composition have been studied in the lower cretaceous dolomites and their interbedded and or parental limestones of central tunisia dolomites as indicated by previous sedimentologic geochemical and isotopic study are different in origin environments of dolomite formation include evaporitic sabkha deep phreatic karst and lacustrine with the exception of the sabkha environment dolomitizing fluids presumably have been essentially meteoric the comparison between ree distributions in dolomites and limestones clearly suggests that the general shapes of the ree patterns are preserved during dolomitization nevertheless the total ree amounts are somewhat lowered in dolomites comparatively to parental limestones moreover within the dolomites the total ree contents are positively correlated to the sr and 18o contents thus indicating that the decrease in ree sr and 18o contents is related to a decrease in the salinity of dolomitizing fluids in addition dolomites associated with emergence surfaces karst are the most impoverished in ree furthermore they are relatively enriched in light ree indicating a more or less important fractionation with the ree distributions this enrichment has been related to the influence of the inorganic complexes which favours the greatest solubility of the heavy ree in basic solution with respect to the lightest members of the ree group

spatiotemporal evolution of the 2011 prague oklahoma aftershock sequence revealed using subspace detection and relocation the 6 november 2011 mw 5 7 earthquake near prague oklahoma is the second largest earthquake ever recorded in the state a mw 4 8 foreshock and the mw 5 7 mainshock triggered a prolific aftershock sequence utilizing a subspace detection method we increase by fivefold the number of precisely located events between 4 november and 5 december 2011 we find that while most aftershock energy is released in the crystalline basement a significant number of the events occur in the overlying arbuckle group indicating that active meeker prague faulting extends into the sedimentary zone of wastewater disposal although the number of aftershocks in the arbuckle group is large comprising 40 of the aftershock catalog the moment contribution of arbuckle group earthquakes is much less than 1 of the total aftershock moment budget aftershock locations are sparse in patches that experienced large slip during the mainshock

anisotropy in fracking a percolation model for observed microseismicity hydraulic fracturing fracking using high pressures and a low viscosity fluid allow the extraction of large quantiles of oil and gas from very low permeability shale formations the initial production of oil and gas at depth leads to high pressures and an extensive distribution of natural fractures which reduce the pressures with time these fractures heal sealing the remaining oil and gas in place high volume fracking opens the healed fractures allowing the oil and gas to flow to horizontal production wells we model the injection process using invasion percolation we use a 2d square lattice of bonds to model the sealed natural fractures the bonds are assigned random strengths and the fluid injected at a point opens the weakest bond adjacent to the growing cluster of opened bonds our model exhibits burst dynamics in which the clusters extend rapidly into regions with weak bonds we associate these bursts with the microseismic activity generated by fracking injections a principal object of this paper is to study the role of anisotropic stress distributions bonds in the y direction are assigned higher random strengths than bonds in the x direction we illustrate the spatial distribution of clusters and the spatial distribution of bursts small earthquakes for several degrees of anisotropy the results are compared with observed distributions of microseismicity in a fracking injection both our bursts and the observed microseismicity satisfy gutenberg richter frequency size statistics

fracking in tight shales what is it what does it accomplish and what are its consequences fracking is a popular term referring to hydraulic fracturing when it is used to extract hydrocarbons we distinguish between low volume traditional fracking and the high volume modern fracking used to recover large volumes of hydrocarbons from shales shales are fine grained rocks with low granular permeabilities during the formation of oil and gas large fluid pressures are generated these pressures result in natural fracking and the resulting fracture permeability allows oil and gas to escape reducing the fluid pressures these fractures may subsequently be sealed by mineral deposition resulting in tight shale formations the objective of modern fracking is to reopen these fractures and or create new fractures on a wide range of scales modern fracking has had a major impact on the availability of oil and gas globally however there are serious environmental objections to modern fracking which should be weighed carefully against its benefits

petroleum geology of east central tunisia the tectonic features of tunisia are complex and include folds all types of faults evaporite diapirs and the saharan flexure which separates a stable paleozoic province on the south from a subsidence zone of mesozoic and cenozoic strata of the offshore ashtart and tripolitania basins the remainder of the offshore region is mostly stable shelf of the pelagian craton which also extends onshore the present study focused on this shelf where two carbonate intervals contain proven hydrocarbon reservoirs the metlaoui formation of earliest eocene ypresian age and the zebbag formation of late cretaceous turonian age regionally well defined belts of metlaoui carbonates trend northwest on the northeast are open marine deep water micrites and marls with abundant planktonic foraminifers thick bars of nummulitid packstone grainstone were deposited in shallow water at an angle to the paleoshelf the reservoir is confined largely to the bars and visible effective porosity is best developed in those areas among the foraminifers filled with sand size nummulitid debris where secondary solution enlargement has occurred this lithology tested oil in two recent wildcat wells and is a commercial reservoir at sidi el itayem and ashtart fields distribution of zebbag carbonates is more complex a northwest trending platform was bounded on three sides by deep water where shale and micrite with planktonic foraminifers were deposited predominately back reef and lagoonal foraminifer rudist wackestones and packstones occur in narrow belts apparently controlled at least locally by block faulting they tested oil in two recent discoveries the most significant porosity is interparticle generally enlarged by solution in foraminifer packstones but intraparticle voids in foraminifers and rudists commonly contribute to the porosity analyses of surface and subsurface samples identified the bahloul basal turonian and bou dabbous ypresian formations as source rocks fluorescence spectra of several oils were compared with extracts from these samples and indicate the bahloul to be the source of oils in recent metlaoui and zebbag discoveries

geological evolution of the offshore tunisia gabes basin pelagian domain since the cretaceous constraints from subsidence curves from hydrocarbon wells data abstract the comparison of subsidence curves obtained from deep wells in sedimentary basins represents a powerful tool to identify major changes in subsidence distribution both in time and space the construction of subsidence curves from 19 wells covering a time interval from the cretaceous to the present in the gabes basin pelagian domain of the eastern tunisian platform provided the opportunity to reconstruct the subsidence patterns across the basin changes in the subsidence rates in different wells allowed the identification of six time intervals stages stage boundaries are defined by major changes in subsidence trends in the 19 wells each stage is characterized by changes in the subsidence pattern of groups of wells likely reflecting episodes of re organization of the distribution of domains with different trends increase or decrease of subsidence comparisons among the subsidence curves highlighted for each stage parts of the basins with higher or lower subsidence permitting to identify highs and lows and to reconstruct their significance in the different stages identified the basin scale changes in the distribution of subsidence rates reflect regional events of basin re organization potentially controlled by syndepositional faults or for some stages by halokinesis due to the presence of salt deposits in the southern part of the study area the comparison of the subsidence curves permitted to identify domains characterized in different time intervals by different patterns of subsidence rates providing important elements for the characterization of the different stages in the stratigraphic and tectonic evolution of the basin

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

petrographic and geochemical characteristics of dolomite types and the origin of ferroan dolomite in the trenton formation ordovician michigan basin u s a three major types of dolomite occur in the trenton formation mid ordovician of the michigan basin these are 1 regional dolomite which is confined to the extreme western edge of the basin 2 cap dolomite which occurs in the upper portion of the trenton and is confined to the basin s southern margin and 3 fracture related dolomite which occurs in association with both large and small scale faults and fractures these three dolomite types can be distinguished from one another by their major element chemistry oxygen isotope ratios and rock texture the regional dolomite is fine grained has 0 34 mol feco3 and mean 18o of 6 8 opbd the cap dolomite is texturally similar to regional dolomite but contains 3 13 0 mol feco3 and has a mean 18o of 7 7 fracture related dolomites are coarse grained low in iron and have the most depleted 18o ratios x 9 0 pdb petrographic relationships imply that the regional dolomite formed prior to the cap dolomite probably during early diagenesis the cap dolomite formed at relatively shallow depths as a result of the interaction of the overlying utica shale and the trenton limestone fracture related dolomites post date the cap dolomite and formed during deeper burial a temperature of precipitation of approximately 80 c was calculated for fracture related dolomites using oxygen isotope data the distribution of the cap dolomite was controlled by the availability of fe2 which was in turn controlled by the availability of s2 in the centre of the basin trenton utica deposition was continuous the upper trenton contained relatively high concentrations of organic matter which was used by sulphate reducing bacteria to produce h2s from seawater sulphate the precipitation of iron sulphides pyrite iron monosulphide followed and used up most of the available fe2 as a result only small amounts of ferroan dolomite formed on the periphery of the basin subaerial exposure resulted in the oxidation of most of the available organic matter sulphate reducing bacteria were therefore limited and produced limited amounts of h2s as a result only a minor amount of iron sulphide iron monosulphide formed the remaining fe2 was then available for the formation of the ferroan cap dolomite this model is supported by the following 1 in the southern margin of the basin the contact between trenton cap dolomite and the overlying utica shale is sharp and probably unconformable in the centre of the basin the contact is gradational 2 in the centre of the basin the total organic carbon content in the upper trenton is an order of magnitude higher than in the cap dolomite 3 the whole rock concentration of iron is high in both the cap dolomite and in slightly dolomitized equivalent beds in the basin centre 4 iron sulphides are abundant in the centre of the basin and mostly in the form of pyrite in the cap dolomite iron sulphide is minor and primarily in the form of iron monosulphide