sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

the denver earthquakes of 1967 1968 abstract a detailed study of the earthquakes associated with the rocky mountain arsenal disposal well is presented long period surface wave studies are used together with p wave first motions to show that the 10 april 9 august and 27 november 1967 earthquakes occurred at depths of 3 to 5 km and were characterized by normal faulting along a northwest striking fault plane a joint hypocenter relocation of 103 microearthquakes of a data set of 279 recorded between 1967 and 1968 shows a hypocenter pattern striking n50 w with most of the events located about 5 km northwest of the disposal well at depths between 3 to 8 km a fault plane dipping southwest is tenuously suggested by those earthquakes with depths less than 5 km modeling of near field seismoscope observations lend support to the focal mechanisms derived

a 21 year record of arctic sea ice extents and their regional seasonal and monthly variability and trends satellite passive microwave data have been used to calculate sea ice extents over the period 1979 1999 for the north polar sea ice cover as a whole and for each of nine regions over this 21 year time period the trend in yearly average ice extents for the ice cover as a whole is 32 900 6 100 sq km yr 2 7 0 5 decade indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of 34 000 8 300 sq km yr 2 8 0 7 decade for the period 1979 1996 regionally the reductions are greatest in the arctic ocean the kara and barents seas and the seas of okhotsk and japan whereas seasonally the reductions are greatest in summer for which season the 1979 1999 trend in ice extents is 41 600 12 900 sq km yr 4 9 1 5 decade on a monthly basis the reductions are greatest in july and september for the north polar ice cover as a whole in september for the arctic ocean in june and july for the kara and barents seas and in april for the seas of okhotsk and japan only two of the nine regions show overall ice extent increases those being the bering sea and the gulf of st lawrence for neither of these two regions is the increase statistically significant whereas the 1079 1999 ice extent decreases are statistically significant at the 99 confidence level for the north polar region as a whole the arctic ocean the seas of okhotsk and japan and hudson bay

history of the newark east field and the barnett shale as a gas reservoir david martineau is a certified petroleum geologist and received his b s degree in geology from the university of texas in 1960 he joined pitts in 1972 and is the exploration manager pitts has been involved in the barnett play since its inception prior to pitts he worked for prudential drilling funds and coastal states gas producing company now el paso in 2006 the newark east field was the largest producing gas field in texas and according to the energy information administration eia latest reserves estimate eia 2006 tables b2 and b4 newark east field ranks third in the nation and second in the nation in terms of production the newark east field has generated considerable attention because the gas is produced from the barnett shale as opposed to conventional sandstone conglomerate or carbonate reservoirs the field was discovered in 1981 by mitchell energy corporation mec in wise county texas located in the fort worth basin in north central texas george mitchell founder and chief executive officer of mec had the vision and leadership behind mec s continued exploration and research for the correct technology to extract gas from this unconventional gas reservoir dan steward was the chief geologist for mec during the critical exploration development of the barnett shale and was honored by aapg with the 2007 outstanding explorer award the development of the field started slowly and only 100 wells were completed between 1981 and 1990 in 1998 a major breakthrough in completion technique occurred when water fracturing replaced gel fracturing from 1997 to 2006 more than 5829 wells were put on production and hundreds of additional wells were drilled completed or waiting on a pipeline the field has been divided into two areas 1 the original core area where the barnett sits on top of the viola limestone

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

injection induced seismicity and fault slip potential in the fort worth basin texasinjection induced seismicity and fault slip potential in the fort worth basin texas

tracking induced seismicity in the fort worth basin a summary of the 2008 2018 north texas earthquake study catalogtracking induced seismicity in the fwb a summary of the 2008 2018 north texas earthquake study catalog

the architecture of an anisotropic elastic plastic sea ice mechanics constitutive law the architecture for a new large scale anisotropic constitutive law intended for use in a sea ice dynamics model is presented here this architecture accounts directly for refrozen lead systems in the pack ice strength with an anisotropic failure surface and in the ice thickness distribution with an oriented thickness distribution the lower limit 5 km of the model resolution is controlled by the fracture spacing of old thicker ice and the maximum lead width the upper limit of the model resolution 100 km is controlled by curvature in the lead directions and variations in the lead width these in turn are controlled by the variations in internal ice stress due to driving forces winds and currents which set the time resolution this architecture features abrupt changes in the failure surface and the associated flow rule that cannot be averaged over a time step in addition the principal stress normal to a new lead must be zero as it opens this model has subscale simulations that allow for the inclusion of phenomena such as ridging rafting buckling and fracture on the behavior of the ice with this new ice constitutive law it is possible to test directly the ice failure strength plastic flow rule and ice thickness distribution the data most useful for this testing come from ice stress and position buoys together with synthetic aperture radar deformation data some data comparisons have already been made

results of the sea ice model intercomparison project evaluation of sea ice rheology schemes for use in climate simulations a hierarchy of sea ice rheologies is evaluated on the basis of a comprehensive set of observational data the investigations are part of the sea ice model intercomparison project simip four different sea ice rheology schemes are compared a viscous plastic rheology a cavitating fluid model a compressible newtonian fluid and a simple free drift approach with velocity correction the same grid land boundaries and forcing fields are applied to all models as verification data there are 1 ice thickness data from upward looking sonars uls 2 ice concentration data from the passive microwave radiometers smmr and ssm i 3 daily buoy drift data obtained by the international arctic buoy program iabp and 4 satellite derived ice drift fields based on the 85 ghz channel of ssm i all models are optimized individually with respect to mean drift speed and daily drift speed statistics the impact of ice strength on the ice cover is best revealed by the spatial pattern of ice thickness ice drift on different timescales daily drift speed statistics and the drift velocities in fram strait overall the viscous plastic rheology yields the most realistic simulation in contrast the results of the very simple free drift model with velocity correction clearly show large errors in simulated ice drift as well as in ice thicknesses and ice export through fram strait compared to observation the compressible newtonian fluid cannot prevent excessive ice thickness buildup in the central arctic and overestimates the internal forces in fram strait because of the lack of shear strength the cavitating fluid model shows marked differences to the statistics of observed ice drift and the observed spatial pattern of ice thickness comparison of required computer resources demonstrates that the additional cost for the viscous plastic sea ice rheology is minor compared with the atmospheric and oceanic model components in global climate simulations

improving the simulation of landfast ice by combining tensile strength and a parameterization for grounded ridges in some coastal regions of the arctic ocean grounded ice ridges contribute to stabilizing and maintaining a landfast ice cover recently a grounding scheme representing this effect on sea ice dynamics was introduced and tested in a viscous plastic sea ice model this grounding scheme based on a basal stress parameterization improves the simulation of landfast ice in many regions such as in the east siberian sea the laptev sea and along the coast of alaska nevertheless in some regions such as the kara sea the area of landfast ice is systematically underestimated this indicates that another mechanism such as ice arching is at play for maintaining the ice cover fast to address this problem the combination of the basal stress parameterization and tensile strength is investigated using a 0 25 pan arctic cice nemo configuration both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the kara sea but also in the laptev sea however the simulated landfast ice season for the kara sea is too short compared to observations this is especially obvious for the onset of the landfast ice season which systematically occurs later in the model and with a slower build up this suggests that improvements to the sea ice thermodynamics could reduce these discrepancies with the data this article is protected by copyright all rights reserved

application of new seismic attributes to collapse chimneys in the fort worth basin three dimensional seismic volumes from the central fort worth basin display roughly circular collapse chimneys that extend vertically about 800 m from the ordovician ellenburger formation to the atokan middle pennsylvanian caddo limestone collapse chimneys in carbonates may be caused by subaerial karst hydrothermal or tectonic extensional processes we use 3d multitrace geometric attributes including coherence volumetric curvature and energy weighted coherent amplitude gradients to investigate details of the origin of these structures the ordovician ellenburger surface resembles a subaerial karst landscape of cockpits dolines and frying pan valleys while resistivity based wireline image logs record 50 m of karst breccia facies however images from coherence and long wavelength most positive and most negative curvature volumes show many of the 800 m collapse features are associated with basement faults or with subtle pennsylvanian and younger tectonic features rather than with intra ellenburg

covariance of optimal parameters of an arctic sea ice ocean model abstractthe uniqueness of optimal parameter sets of an arctic sea ice simulation is investigated a set of parameter optimization experiments is performed using an automatic parameter optimization

induced seismic deformation in the cogdell oil field of west texas a sequence of induced earthquakes occurred at the cogdell oil field in west texas from about 1974 to 1982 the earthquakes occurred within an array of injecting wells which surrounded the perimeter of the field and which decreased in radius during the life of the injection project we examine this sequence of earthquakes in terms of two failure models in the first model seismic failure occurs when and where fluid pressures exceed some critical value in the second model earthquakes occur at the edges of low fluid pressure areas where stresses have been transferred as a result of aseismic deformation in adjacent high fluid pressure regions we calculate the history of fluid pressures in the cogdell field using the theis equation for fluid flow in an areally infinite aquifer the calculations show that the earthquakes occur in a region of relatively low pressure surrounded by regions of higher fluid pressure the cogdell earthquakes may occur on pre existing faults however fluid pressures are sufficiently high in surrounding portions of the field to also produce failure a long time delay between the start of injection and the onset of seismicity may correspond to the time required for fluid pressures on a pre existing fault to reach critical values or may be the result of an evolving injection pattern whereby the inward migration of injecting wells produces aseismic failure which loads stress onto stronger regions within the center of the field injection of fluids for secondary recovery occurs at over three thousand sites in the state of texas many of these sites are geographically near cogdell and many have higher injection pressures and volumes of injected fluid than cogdell however they do not exhibit any seismicity a failure model which incorporates stress loading suggests that the perimeter injection pattern is responsible for the onset of seismicity a consequence of this interpretation is that many other injection fields may be undergoing large amounts of aseismic deformation

optimization of a sea ice model using basinwide observations of arctic sea ice thickness extent and velocity a stand alone sea ice model is tuned and validated using satellite derived basinwide observations of sea ice thickness extent and velocity from the years 1993 to 2001 this is the first time that basin scale measurements of sea ice thickness have been used for this purpose the model is based on the cice sea ice model code developed at the los alamos national laboratory with some minor modifications and forcing consists of 40 yr ecmwf re analysis era 40 and polar exchange at the sea surface poles data three parameters are varied in the tuning process ca the air ice drag coefficient p the ice strength parameter and the broadband albedo of cold bare ice with the aim being to determine the subset of this three dimensional parameter space that gives the best simultaneous agreement with observations with this forcing set it is found that observations of sea ice extent and velocity alone are not sufficient to unambiguously tune the model and that sea ice thickness measurements are necessary to locate a unique subset of parameter space in which simultaneous agreement is achieved with all three observational datasets

impact of a new anisotropic rheology on simulations of arctic sea ice 1 a new rheology that explicitly accounts for the subcontinuum anisotropy of the sea ice cover is implemented into the los alamos sea ice model this is in contrast to all models of sea ice included in global circulation models that use an isotropic rheology the model contains one new prognostic variable the local structure tensor which quantifies the degree of anisotropy of the sea ice and two parameters that set the time scale of the evolution of this tensor the anisotropic rheology provides a subcontinuum description of the mechanical behavior of sea ice and accounts for a continuum scale stress with large shear to compression ratio and tensile stress component results over the arctic of a stand alone version of the model are presented and anisotropic model sensitivity runs are compared with a reference elasto visco plastic simulation under realistic forcing sea ice quickly becomes highly anisotropic over large length scales as is observed from satellite imagery the influence of the new rheology on the state and dynamics of the sea ice cover is discussed our reference anisotropic run reveals that the new rheology leads to a substantial change of the spatial distribution of ice thickness and ice drift relative to the reference standard visco plastic isotropic run with ice thickness regionally increased by more than 1 m and ice speed reduced by up to 50

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

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

simultaneous parameter optimization of an arctic sea ice ocean model by a genetic algorithm abstractimprovement and optimization of numerical sea ice models are of great relevance for understanding the role of sea ice in the climate system they are also a prerequisite for meaningful pred

revisiting the timpson induced earthquake sequence a system of two parallel faults the 17 may 2012 m4 8 timpson earthquake is the largest known earthquake in eastern texas it is suspected to have been induced by wastewater injection from two nearby high volume wells its catalo

analysis of the cleburne texas earthquake sequence from june 2009 to june 2010 on 9 june 2009 an graphic 1 2 8 earthquake shook cleburne texas a community not known to have previously experienced earthquakes over 50 small earthquakes followed by the end of december 2009 a temporary network of four and then five iris passcal broadband systems was deployed from june 2009 to june 2010 recording data that were used to locate 38 events with the most confident p and s arrival picks event locations were distributed along a 2 km long north northeast trend the location centroid was at 32 298 n 97 372 w and at 3 6 km depth this location is approximately 1 3 km from a saltwater disposal well that began injection in october 2007 and 3 2 km away from a second injection well that was active from september 2005 to late july 2009 focal mechanisms estimated for the best recorded events suggest a north northeast south southwest trending normal fault with a dip of 50 and a component of oblique motion rake of 80 this average solution is generally consistent with the north northeast trending extensional faults that are prevalent across parts of texas oklahoma louisiana and arkansas stress drops calculated from p and s spectra for seven different events ranged from 3 9 to 90 bars with most estimates between 40 and 50 bars typical values for intraplate earthquakes because there were no known previous earthquakes and the located events were close to the two injection wells and near the injection depth the possibility exists that earthquakes may be related to fluid injection online material tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions 1 embed inline graphic 1 gif

improving the spatial distribution of modeled arctic sea ice thickness 1 the spatial distribution of ice thickness draft in the arctic ocean is examined using a sea ice model a comparison of model predictions with submarine observations of sea ice draft made during cruises between 1987 and 1997 reveals that the model has the same deficiencies found in previous studies namely ice that is too thick in the beaufort sea and too thin near the north pole we find that increasing the large scale shear strength of the sea ice leads to substantial improvements in the model s spatial distribution of sea ice thickness and simultaneously improves the agreement between modeled and ers derived 1993 2001 mean winter ice thickness

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

the 17 may 2012 m4 8 earthquake near timpson east texas an event possibly triggered by fluid injection this study summarizes our investigation of the 17 may 2012 mw rmt4 8 earthquake near timpson texas the largest earthquake recorded historically in eastern texas to identify preshocks and aftershocks of the 17 may event we examined the arrivals recorded at nacogdoches natx 30 km from the 17 may epicenter at nearby usarray transportable array stations and at eight temporary stations deployed between 26 may 2012 and mid 2013 at natx we identified seven preshocks the earliest occurring in april 2008 reliably located aftershocks recorded by the temporary stations lie along a 6 km long nw se linear trend corresponding to a previously mapped basement fault that extends across the highest intensity mmi vii region of the 17 may main shock earthquakes in this sequence are relatively shallow with focal depths ranging from 1 6 to 4 6 km evidence supporting these depths include hypocentral locations of exceptionally well recorded aftershocks s p intervals at the nearest stations and comparisons of synthetics and observed seismograms within 3 km of the linear trend of aftershock activity there are two class ii injection disposal wells injecting at 1 9 km depth beginning in august 2006 and february 2007 with injection rates averaging 42 750 m3 mo and 15 600 m3 mo respectively several observations support the hypothesis that fluid injection triggered the timpson sequence well located epicenters are situated near a mapped basement fault and near high volume injection wells focal depths are at or below the depths of injection and the earliest preshock april 2008 occurred after the onset of injection in 2006

modeling landfast sea ice by adding tensile strength landfast ice is sea ice that forms and remains fixed along a coast where it is either attached to the shore or held between shoals or grounded icebergs the current generation of sea ice models is not capable of reproducing certain aspects of landfast ice behavior for example the persistence of landfast sea ice under the effect of offshore winds the authors develop a landfast sea ice model by adding tensile strength to the viscous plastic as well as two versions of the elastic viscous plastic sea ice rheologies one dimensional implementations of these rheologies are used to explore the ability of coastal sea ice to resist offshore winds over extended times while all modified rheologies are capable of maintaining landfast ice like structures in the model only the viscous plastic rheology fulfills theoretical expectations the elastic viscous plastic rheologies show initial elastic waves that weaken the ice and thus reduce its capacity of maintaining landfast ice further special care has to be taken when implementing the most commonly used version of the elastic viscous plastic rheology because the standard set of parameters is not adequate for landfast sea ice modeling

a fluid injection triggered earthquake sequence in ashtabula ohio implications for seismogenesis in stable continental regions a persistent earthquake sequence in northeast ohio includes many distinct fore main aftershock subsequences illuminates two faults and was triggered by fluid injection the first known earthquake from within 30 km of ashtabula was an m blg 3 8 mainshock that shook the downtown area in 1987 seismicity has continued at an average of about one felt event per year the largest magnitude so far m blg 4 3 caused slight damage modified mercalli intensity vi on 26 january 2001 the latest subsequence started in july 2003 with an m blg 2 6 event accurate hypocenters and focal mechanisms are available from three local seismograph deployments in 1987 2001 2003 and from regional broadband seismograms these hypocenters are in the precambrian basement 0 2 km below the 1 8 km deep paleozoic unconformity and illuminate two distinct planar east west striking sources zones 4 km apart one in 1987 about 1 5 km long the other in 2001 and 2003 about 5 km long we interpret them as steep subparallel faults slipping left laterally in the current regime like many of the faults that ruptured in hazardous stable continental region scr earthquakes these faults were previously unknown and probably have small post precambrian displacements the 1987 source was active a year after onset of class 1 fluid injection only 0 7 km north of the fault the second fault 5 km south of the injection well became active in 2000 while the 1987 source was inactive the well injected about 164 m 3 day of waste fluid into the 1 8 km deep basal sandstone with about 100 bars of wellhead pressure from may 1986 to june 1994 an annular high pore pressure anomaly is expected to expand along this hydraulically confined horizon at the top of the basement even after injection ends and pressure drops near the well over 16 years seismicity has shifted southward from 1 to 5 8 km from the point of injection it seems to initiate when and where a significant pore pressure rise intersects pre existing faults close to failure and to be turned off when pressure starts dropping back the largest earthquakes postdated the end of injection at both ashtabula and at the rocky mountain arsenal near denver colorado anthropogenic earthquake hazard may thus persist after the causative activity has ceased but can generally be closely monitored high stress and low strain rates in scrs can account for a larger proportion of triggered earthquakes in the eastern united states and other scrs than in active regions

using sea ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice we investigate the ability of viscous plastic vp sea ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the radarsat geophysical processor system rgps in particular we reformulate the vp elliptical rheology to allow independent changes in the ice compressive shear and isotropic tensile strength parameters p s t respectively in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters our 10 km vp simulation with standard ice mechanical strength parameters p 27 5 knm 2 s 6 9 knm 2 and t 0 knm 2 ellipse aspect ratio of e 2 does not reproduce the large shear and divergence deformations observed in the rgps deformation fields and specifically lacks well defined active linear kinematic features lkfs probability density functions pdfs for the shear and divergence of are nonetheless not gaussian simulations with a reduced compressive or increased shear strength are in good agreement with rgps derived shear and divergence pdfs with relatively more large deformations compared to small deformations the isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions when considering additional metrics such as the ice drift error mean ice thickness fields and spatial scaling of the deformations our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing arctic wide simulations of the sea ice cover with the vp elliptical rheology

an observationally based evaluation of subgrid scale ice thickness distributions simulated in a large scale sea ice ocean model of the arctic ocean a key parameterization in sea ice models describes the subgrid scale ice thickness distribution based on only a few observations the ice thickness distribution model was shown to be consistent with field data and to improve the simulation s large scale properties the available submarine and airborne observations enable to evaluate in greater detail the ability of a pan arctic sea ice ocean model with an ice thickness distribution parameterization to reproduce observed thickness distributions in different regions and seasons many observations are reproduced accurately some cases of poorly simulated modes and tails of the distributions are tentatively attributed to simplified thermodynamics and inaccurate deformation fields variability on decadal timescales however is generally underestimated thickness distributions in individual grid cells of the model show similar differences between regions and seasons as observed regional mean distributions but the modeled grid scale variability is lower than observed simulated modal thicknesses of first year ice are only insufficiently different from those of multiyear ice the modal thickness proves to be a useful metric for quantifying model biases in both dynamics and thermodynamics in addition to improving basin wide mean variables the ice thickness distribution parameterization provides reliable and valuable additional subgrid scale data at the same time the low climate sensitivity of the parameterization may affect longer simulations with strong climate change aspects

simultaneous inversion for q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock an inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite assuming a 2 source model the inversion fits the p wave spectra of microearthquake waveforms to determine individual values of corner frequency and low frequency spectral amplitude for each event and one average frequency independent q for all source receiver paths we also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra the waveforms analyzed were recorded by a borehole seismometer the p wave q was found to be 1070 for q values as low as 600 and as high as 3000 the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a q of 1070 average stress drop was 3 7 bars seismic moments obtained from spectra ranged from 1013 to 1018 dyne cm the low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock stress drops were found to be larger near the edges of the seismic zone in regions that had not been seismically active during previous injections the seismic moments determined from spectra were used to obtain a coda length to moment relation then moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal to noise ratio the constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions the slope is so high that the seismic energy release is dominated by the large number of small events in the absence of information about the number of events smaller than we studied we cannot estimate the total seismic energy released by the hydraulic injection

a decade of induced slip on the causative fault of the 2015 mw 4 0 venus earthquake northeast johnson county texas on 7 may 2015 a mw 4 0 earthquake occurred near venus northeast johnson county texas in an area of the bend arch fort worth basin that reports long term high volume wastewater disposal and that has hosted felt earthquakes since 2009 in the weeks following the mw 4 0 earthquake we deployed a local seismic network and purchased nearby active source seismic reflection data to capture additional events characterize the causative fault and explore potential links between ongoing industry activity and seismicity hypocenter relocations of the resulting local earthquake catalog span 4 6 km depth and indicate a fault striking 230 dipping to the west consistent with a nodal plane of the mw 4 0 regional moment tensor fault plane solutions indicate normal faulting with b axes striking parallel to maximum horizontal compressive stress seismic reflection data image the reactivated basement fault penetrating the ordovician disposal layer and mississippian production layer but not displacing post lower pennsylvanian units template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in april 2008 with increasing magnitude over time pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0 9 4 8 mpa above hydrostatic we suggest that the injection of 28 000 000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long lived earthquake sequence the 2015 mw 4 0 event represents the largest event in the continuing evolution of slip on the causative fault

q structure beneath the north and central indian ocean from the inversion of observed love and rayleigh wave attenuation data abstract the fundamental mode love and rayleigh waves generated by 57 earthquakes which occurred in the north and central indian ocean extending to 40 s and recorded at indian seismograph and other wwssn stations such as how shl vis mdr hyb kod chg trd poo bom goa ndi nil and que are analysed love and rayleigh wave attenuation coefficients are estimated at periods of 15 100 s using the spectral amplitude of these waves for 98 different paths across the bay of bengal fan the arabian fan and the north and central indian ocean the large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions love wave attenuation coefficients are found to vary from 0 000 03 to 0 000 45 km 1 for the bay of bengal fan from 0 000 03 to 0 000 85 km 1 for the arabian fan and from 0 000 03 to 0 000 35 km 1 for the north and central indian ocean similarly rayleigh wave attenuation coefficients vary from 0 000 03 to 0 0004 km 1 for the bay of bengal fan from 0 000 06 to 0 0007 km 1 for the arabian fan and from 0 000 03 to 0 0007 km 1 for the north and central indian ocean backus and gilbert inversion theory is applied to these surface wave attenuation data to obtain average q 1 models for the crust and upper mantle beneath the bay of bengal the arabian fan and the north and central indian ocean inversion of love and rayleigh wave attenuation data shows a high attenuation zone centred at a depth of 120 km q 125 for the bay of bengal fan similarly a high attenuation zone q 40 70 occurs at a depth of 60 160 km for the arabian fan at 100 160 km q 115 for the indian ocean off ninetyeast ridge and at 80 160 km q 80 for the indian ocean across the ninetyeast ridge the q 1 models show a lithosphere thickness of 120 km beneath the bay of bengal fan similarly lithosphere thickness of 70 100 and 80 km is estimated beneath the arabian fan and the indian ocean off ninetyeast ridge and across ninetyeast ridge respectively the base of the lithosphere is identified as the depth at which there is a significant increase in the q 1 value which attains its maximum value in the asthenosphere the thinning of indian lithosphere beneath the arabian fan suggests high temperature below moho depth 60 km from surface which has caused a high attenuation zone at this shallow depth

automatic time domain calculation of source parameters for the analysis of induced seismicity abstract a time domain methodology for the automatic on line calculation of source parameters is introduced the method is based on applying parseval9s theorem to the spectral equations proposed by andrews 1986 the appropriateness of the technique for the analysis of induced seismicity was tested by comparing on line values of seismic moment seismic energy and static stress drop with those obtained in the frequency domain off line for an aftershock sequence of events recorded underground at creighton mine ontario our analysis shows that the calculated on line and off line source parameters are in good agreement with an average slope offset of 4 from the 1 1 line suggesting that the proposed method is reliable additionally by applying empirical on line attenuation corrections coda q similar results are obtained to those calculated using off line corrections spectral decay improving the average slope offset to 1

consistent and contrasting decadal arctic sea ice thickness predictions from a highly optimized sea ice model decadal hindcast simulations of arctic ocean sea ice thickness made by a modern dynamic thermodynamic sea ice model and forced independently by both the era 40 and ncep ncar reanalysis data sets are compared for the first time using comprehensive data sets of observations made between 1979 and 2001 of sea ice thickness draft extent and speeds we find that it is possible to tune model parameters to give satisfactory agreement with observed data thereby highlighting the skill of modern sea ice models though the parameter values chosen differ according to the model forcing used we find a consistent decreasing trend in arctic ocean sea ice thickness since 1979 and a steady decline in the eastern arctic ocean over the full 40 year period of comparison that accelerated after 1980 but the predictions of western arctic ocean sea ice thickness between 1962 and 1980 differ substantially the origins of differing thickness trends and variability were isolated not to parameter differences but to differences in the forcing fields applied and in how they are applied it is argued that uncertainty differences and errors in sea ice model forcing sets complicate the use of models to determine the exact causes of the recently reported decline in arctic sea ice thickness but help in the determination of robust features if the models are tuned appropriately against observations

the arctic ice thickness anomaly of the 1990s a consistent view from observations and models 1 observations of sea ice draft from submarine cruises in much of the arctic ocean show that the ice cover was unusually thin in the mid 1990s here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11 year span comparisons of our modeled draft with observed draft show good agreement in the temporal change comparing average draft over entire cruises the rms discrepancy between modeled and observed draft is 0 3 m and the correlation is 0 98 agreement in the spatial patterns of draft is somewhat lower the rms discrepancy of 50 km averages of draft is 0 7 m and the correlation is 0 73 we review reports of interannual variations of ice thickness or volume from other model studies all models agree that thickness decreased by between 0 6 and 0 9 m from 1987 to 1996 our model shows a modest recovery in thickness from 1996 to 1999 for the 1950s 1960s and 1970s models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations

characteristics of rg waves recorded from quarry blasts in central texas abstract chemical blasts from quarrying operations in central texas are routinely recorded by the w m keck foundation seismological observatory near china spring texas the keck observatory consists of a single broadband three component borehole seismograph system five quarries located at distances ranging from 16 to 101 km from the observatory each detonate from 1 to 6 tons of ammonium nitrate fuel oil explosive on the average of twice per week for every quarry for which the orientation of the working face could be determined dispersed rg waves are recorded at the keck observatory from those quarries at which the working face is directed away from the observatory but are not observed or are severely attenuated from those quarries at which the working face is directed toward the observatory seismograms containing the dispersed rg are easily recognized as quarry blasts but those in which the dispersed rg is absent look like small earthquakes

spatio temporal evolution of frequency magnitude distribution and seismogenic index during initiation of induced seismicity at guy greenbrier arkansas abstract in this study we carry out detailed analyses of the spatio temporal variations of seismic b value during the onset of the potentially induced earthquake sequence between guy and greenbrier arkansas to investigate correlations with pore pressure change the range of b values suggests that the seismicity in the guy greenbrier area is mostly a result of the activation of pre existing faults the spatial distribution of b value correlates with modeled pore pressure changes in the northern segment of the fault b value increases with depth due to large pore pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts whereas in the southern segment the shallower part shows higher b values due to higher pore pressure fluctuations but the deeper part in the crystalline basement has low b value due to higher confining stress the correlation between the temporal variation of b value and hypocentral depth explains a previously observed temporal drop of b value this suggests that temporal variations should be interpreted along with the spatial variations estimation of the seismogenic indices for the guy greenbrier fault is provided our analysis suggests that monitoring changes in b value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times

arctic sea ice in the global eddy permitting ocean reanalysis orap5 we discuss the state of arctic sea ice in the global eddy permitting ocean reanalysis ocean reanalysis pilot 5 orap5 among other innovations orap5 now assimilates observations of sea ice concentration using a univariate 3dvar fgat scheme we focus on the period 1993 2012 and emphasize the evaluation of model performance with respect to recent observations of sea ice thickness we find that sea ice concentration in orap5 is close to assimilated observations with root mean square analysis residuals of less than 5 in most regions however larger discrepancies exist for the labrador sea and east of greenland during winter owing to biases in the free running model sea ice thickness is evaluated against three different observational data sets that have sufficient spatial and temporal coverage icesat icebridge and smosice large scale features like the gradient between the thickest ice in the canadian arctic and thinner ice in the siberian arctic are simulated well by orap5 however some biases remain of special note is the model s tendency to accumulate too thick ice in the beaufort gyre the root mean square error of orap5 sea ice thickness with respect to icesat observations is 1 0 m which is on par with the well established piomas model sea ice reconstruction interannual variability and trend of sea ice volume in orap5 also compare well with piomas and icesat estimates we conclude that notwithstanding a relatively simple sea ice data assimilation scheme the overall state of arctic sea ice in orap5 is in good agreement with observations and will provide useful initial conditions for predictions

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed