temporal variation in the magnitude frequency distribution during the guy greenbrier earthquake sequence the recent increase in earthquake activity in the central u s has led to concerns about the hazard posed by induced earthquakes understanding earthquake phenomena and monitoring in all settings can be improved by the detection of small events however the catalog of induced earthquakes is incomplete for small events due to the sparse instrumentation this is particularly true in settings of low background seismicity like the central u s we apply single station template matching to detect small earthquakes during the guy greenbrier sequence in central arkansas and find over 100 times more earthquakes than are registered in the advanced national seismic system catalog between july 2010 and october 2011 a complete catalog over nearly 4 units of magnitude enables us to analyze the magnitude frequency distribution of induced earthquakes we find that earthquakes deviated from the gutenberg richter statistics during the operation of nearby injection wells but returned to gutenberg richter statistics after the wells were shut in

influence of pore pressure on the event size distribution of induced earthquakes 1 during an enhanced geothermal system egs experiment fluid is injected at high pressure into crystalline rock to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted the fracturing of the basement caused by these high pore pressures is associated with microseismicity however the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates and thus pore pressure is unknown here we show how pore pressure can be linked to the seismic frequency magnitude distribution described by its slope theb value we evaluate the dataset of an egs in basel switzerland and compare the observed event size distribution with the outcome of a minimalistic model of pore pressure evolution that relates event sizes to the differential stress d we observe that the decrease of b values with increasing distance of the injection point is likely caused by a decrease in pore pressure this leads to an increase of the probability of a large magnitude event with distance and time

temporal correlation between seismic moment and injection volume for an induced earthquake sequence in central oklahoma the rapidly increased earthquake rate in the central united states has been linked with wastewater injection while the overall understanding appears clear at large scales the interaction between injection and faulting at smaller scales within individual sequences is still not clear for an earthquake sequence in central oklahoma we conduct finer scale analysis of the spatiotemporal evolution of seismicity and pore pressure modeling the pore pressure modeling suggests that nearby wells show much stronger correlation with earthquake sequence evolution detailed temporal analysis found correlation between earthquake rate seismic moment and injection rates from wells in close proximity however the observed maximum magnitude mmax is about one order of magnitude smaller than expected based on a theoretical relationship between mmax and cumulative volume this discrepancy may point toward additional parameters such as fault size and stress which influence mmax the lower mmax is consistent with the truncated gutenberg richter distribution observed from matched filter detected catalog overall the detailed observations suggest that it is possible to resolve relationships between individual disposal wells and induced earthquake sequences

analysis of foreshock sequences in california and implications for earthquake triggering we analyze foreshock activity in california and compare observations with simulated catalogs based on a branching aftershock triggering model we first examine foreshock occurrence patterns for isolated m ge 5 earthquakes in southern california from 1981 to 2011 and in northern california from 1984 to 2009 among the 64 m ge 5 mainshocks excluding 3 swarms and 3 doubles 53 of the rest are preceded by at least one foreshock within 30 days and 5 km foreshock occurrence appears correlated with mainshock faulting type and depth foreshock area is correlated with the magnitude of the largest foreshock and the number of foreshocks however it is not correlated with mainshock magnitude we then examine the occurrence pattern of all seismicity clusters without a minimum magnitude requirement and the possibility that they are foreshocks of larger mainshocks only about 30 of the small clusters lead to a larger cluster about 66 of the larger clusters have foreshock activities and the spatial distribution pattern is similar to m ge 5 mainshocks with lower occurrence rates in the transverse range and central california and higher occurrence rates in the eastern california shear zone and the bay area these results suggest that foreshock occurrence is largely controlled by the regional tectonic stress field and fault zone properties in special cases foreshock occurrence may be useful for short term forecasting however foreshock properties are not reliably predictive of the magnitude of the eventual mainshock comparison with simulated catalogs suggest that the swarmy features and foreshock occurrence rate in the observed catalogs are not well reproduced from common statistical models of earthquake triggering

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

late quaternary glacial history of george vi sound area west antarctica during the last glacial maximum in west antarctica separate ice caps developed on alexander island and on palmer land became confluent in george vi sound and discharged northward from latitude 72 s radiocarbon 32 000 yr and amino acid approximately 120 000 yr age determinations on shell fragments hiatella solida found in basal till suggest a wisconsin age for the glaciation that incorporated them the pattern of ice flow differed from that deduced for this area in the climap reconstruction following the maximum stage there was a stadial event when outlet valley glaciers flowed from smaller ice caps into george vi sound more widespread recession permitted the george vi ice shelf to deposit palmer land erratics on eastern alexander island before isostatic recovery raised them to final elevations of about 82 m the ice shelf may have been absent at about 6500 yr b p when large barnacles bathylasma corolliforme were living in the sound small glaciers readvanced to form at least two terminal moraines before the ice shelf re formed and incorporated the barnacle shells into its moraine on alexander island the shells gave a 14c age corrected for antarctic conditions of about 6500 yr b p and an amino acid ratio consistent with a holocene age valley glaciers readvanced over the ice shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice cored moraines probably during the little ice age such oscillations may represent a climatic control not yet observed in the dry valleys of victoria land the only other part of antarctica studied in detail for glacier fluctuations

baroclinic instability in a downstream varying channel shelikof strait alaska abstract moored current meter observations obtained from upstream and downstream locations in shelikof strait between kodiak and afognak islands and the alaskan mainland in the northwest gulf of alaska show a considerable amount of low frequency variability superimposed upon the mean southwestward along channel flow moreover the spectral properties of these low frequency current fluctuations varied seasonally and according to location within the channel during fag 1976 the variance spectra of the along channel fluctuations at the upstream end of shelikof strait were sharply peaked at 2 86 days at the downstream end of the strait some 150 km to the southwest the variance spectrum of the cross channel fluctuations at 100 m was peaked at 6 15 days however the upstream 2 86 day signal was coherent with 2 86 day fluctuations downstream and the phase relationship between the two locations implied the presence of a downstream traveling wave with a wavelength of 74 km and a phase speed of 26 km day 1

maximum magnitude estimations of induced earthquakes at paradox valley colorado from cumulative injection volume and geometry of seismicity clusters the paradox valley unit pvu a salinity control project in southwest colorado disposes of brine in a single deep injection well since the initiation of injection at the pvu in 1991 earthquakes have been repeatedly induced pvu closely monitors all seismicity in the paradox valley region with a dense surface seismic network a key factor for understanding the seismic hazard from pvu injection is the maximum magnitude earthquake that can be induced the estimate of maximum magnitude of induced earthquakes is difficult to constrain as unlike naturally occurring earthquakes the maximum magnitude of induced earthquakes changes over time and is affected by injection parameters we investigate temporal variations in maximum magnitudes of induced earthquakes at the pvu using two methods first we consider the relationship between the total cumulative injected volume and the history of observed largest earthquakes at the pvu second we explore the relationship between maximum magnitude and the geometry of individual seismicity clusters under the assumptions that i elevated pore pressures must be distributed over an entire fault surface to initiate rupture and ii the location of induced events delineates volumes of sufficiently high pore pressure to induce rupture we calculate the largest allowable vertical penny shaped faults and investigate the potential earthquake magnitudes represented by their rupture results from both the injection volume and geometrical methods suggest that the pvu has the potential to induce events up to roughly mw 5 in the region directly surrounding the well however the largest observed earthquake to date has been about a magnitude unit smaller than this predicted maximum in the seismicity cluster surrounding the injection well the maximum potential earthquake size estimated by these methods and the observed maximum magnitudes have remained steady since the mid 2000s these observations suggest that either these methods overpredict maximum magnitude for this area or that long time delays are required for sufficient pore pressure diffusion to occur to cause rupture along an entire fault segment we note that earthquake clusters can initiate and grow rapidly over the course of 1 or 2 yr thus making it difficult to predict maximum earthquake magnitudes far into the future the abrupt onset of seismicity with injection indicates that pore pressure increases near the well have been sufficient to trigger earthquakes under pre existing tectonic stresses however we do not observe remote triggering from large teleseismic earthquakes which suggests that the stress perturbations generated from those events are too small to trigger rupture even with the increased pore pressures

sediment and organic carbon focusing in the shelikof strait alaska abstract profiles of excess 210 pb and 137 cs in sediment cores were used to determine sediment accumulation rates in outer cook inlet and the shelikof strait alaska in outer cook inlet and the northern shelikof strait sediment accumulation rates averaged 0 16 cm yr 1 and ranged from 0 10 to 0 21 cm yr 1 in contrast sediment accumulation rates were 4 times higher in the central and southern shelikof strait where the average was 0 68 cm yr 1 with a range of 0 46 to 0 94 cm yr 1 in addition to higher rates of sedimentation higher activities of excess 210 pb and higher levels of silt clay total organic carbon pb and mn also were found in surface sediments from the central and southern shelikof strait relative to outer cook inlet and the northern shelikof strait these trends are directly related to the progressive sorting and focusing of sediments along the transport pathway from cook inlet to the shelikof strait the flux of excess 210 pb and organic carbon to the sediments increased by 2 and 4 8 fold respectively from outer cook inlet and the northern shelikof strait to the central and southern shelikof strait based on 13 c values for surface sediments the amount of carbon derived from marine sources increased from 30 in outer cook inlet and the northern shelikof strait to 60 in the central and southern shelikof strait the good correlation between the accumulation rate of sediment organic carbon and excess 210 pb fluxes r 0 93 suggests that scavenging of excess 210 pb by organic carbon is an important process in this region modern sediment budgets for outer cook inlet and the shelikof strait indicate that 70 of the total sediment accumulation of 61 10 6 tons yr 1 is deposited in the central and southern shelikof strait these sediment budgets are in good agreement with the calculated value of 70 10 6 tons yr 1 of riverine and erosional sediment transported into outer cook inlet and the shelikof strait collectively the data support focusing of fine grained sediments and organic carbon to the central and southern shelikof strait

precise relative earthquake magnitudes from cross correlation abstract we present a method to estimate precise relative magnitudes using cross correlation of seismic waveforms our method incorporates the intercorrelation of all events in a group of earthquakes as opposed to individual event pairings relative to a reference event this method works well when a reliable reference event does not exist we illustrate the method using vertical strike slip earthquakes located in the northeast pacific and panama fracture zone regions our results are generally consistent with the global centroid moment tensor catalog which we use to establish a baseline for the relative event sizes online material supplementary description and formulation of uncertainty and tables of relative magnitudes

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

volcanic rock mass properties from snowdonia and tenerife implications for volcano edifice strength although volcano instability is increasingly recognized as a societal hazard numerical data on the relevant mechanical properties remain sparse we report new field data on the rock mass properties of volcanic materials from snowdonia north wales uk and tenerife canary islands using rock types that range in composition from phonolite to rhyolite we summarize a method for estimating the overall strength of a volcanic edifice based on the rock mass rating index rmr and the hoek brown criterion we show that the average rock mass compressive cm and cohesive c strengths decrease exponentially with rmr according to cm 0 652 0 0559rmr and c 0 035 0 0669rmr respectively and appear insensitive to both initial magma composition and relative age this exponential relationship provides a new predictive tool for directly estimating rock mass strength from the rmr our analysis further predicts a marked reduction of up to 96 in the rock mass compressive strength relative to the intact rock value based on laboratory tests and that overall the combined results from both study areas yield cohesive strength values from 4 8 to 0 44 mpa estimated values of rock mass angle of friction range from 28 to c 38 recent modifications to the hoek brown criterion in particular the inclusion of the disturbance factor d suggest that even these low values of rock mass strength and cohesion may be optimistic and the true values of rock parameters relevant for accurate predictions of volcano edifice strength may be up to 30 weaker still

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

the importance of sediment gravity flow to sediment transport and sorting in a glacial marine environment eastern weddell sea antarctica offshore sediment transport on the eastern weddell sea continental margin cannot be modeled after examples from nonglaciated margins transport of terrigenous material to the marine environment is accomplished by floating or grounded ice instead of fluvial processes there is no coastal zone where sediments are washed as they enter the marine environment and because the average shelf depth is 400 m wind or wave generated currents have little if any influence on sediments texturally immature glacial sediment on the continental shelf and slope remains unsorted except by processes of sediment gravity flow piston core coverage demonstrates that downslope transitions between slumps debris flows and turbidity currents are active on the unstable intercanyon slope areas and on the glacially scoured continental shelf sediment textural analyses indicate that size sorting and mineralogic maturity are achieved within sediment gravity flow transitions and that lithic 40 lithics glacial sediment is transformed into sorted arkosic sand 3 lithics over distances of less than 10 km on the upper continental slope and shelf arkosic or quartz sand thus generated is often interbedded with diamictons which are either glacial or nonglacial slumps and debris flows in origin therefore such associations in ancient sequences do not rule out a glacial origin for diamictites or mixtites nor do they mandate deep water sedimentation canyon systems are at present isolated from major sediment input however an extensive 662 000 km2 abyssal submarine fan complex containing glaciogenic sands implies canyon activity since initial glaciation of the region sediment may have been supplied to canyons in the past by subglacial meltwater discharge at times of maximum ice grounding sand may also have been generated directly at canyon heads by strong contour currents impinging on the shelf break as typically occurs elsewhere around the antarctic margin today this focus of current energy at the shelf break does not exist in the eastern weddell sea today thus given the great depth of the continental shelf eustasy is far less important than glacial and oceanographic conditions that is the position of the ice sheet grounding line relative to the shelf break and the level and intensity of contour currents in regulating sediment supply to submarine canyons in the absence of major canyon activity intercanyon sediment transport appears to be the most significant source of slope and abyssal sands

optimizing multi station earthquake template matching through re examination of the youngstown ohio sequence abstract a series of earthquakes in 2011 near youngstown oh has been a focal point for discussions of seismicity induced by a nearby wastewater disposal well utilizing an efficient waveform template matching procedure the optimal correlation template to study the youngstown sequence was identified by varying parameters such as the stations utilized frequency passband and seismogram length a catalog composed of 566 events was identified between january 2011 and february 2014 double difference relocation refines seismicity to a 800 m linear streak from the northstar 1 injection well to the wsw along the same strike as the fault plane of the largest event calculated gutenberg richter b values are consistent with trends observed in other regions with seismicity induced by fluid injection

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

clay mineralogy and chemistry as indicators of hemipelagic sediment dispersal south of the aleutian arc abstract near surface hemipelagic sediments from across the aleutian arc trench system were analyzed for clay mineral composition by x ray diffraction in addition oriented aggregates of clay sized fractions were analyzed for their chemical compositions by energy dispersive x ray analysis eds in conjunction with scanning electron microscopy the main clay minerals are illite chlorite and expandable clay minerals principally smectite smectite is diagnostic of sediment derived from the aleutian volcanic arc in contrast continental sources on the alaskan mainland produce mainly illite and chlorite backarc samples adjacent to the central arc segment contain an average of 71 smectite in the central forearc however smectite values are generally less than 30 and decrease progressively eastward only on meiji sediment tongue in the far western aleutian segment do smectite contents begin to dominate the eds data correlate well with clay mineral abundances al 2 o 3 mgo and feo all increase in abundance with increasing chlorite content and al 2 o 3 and k 2 o increase in illite rich mud silica is the only oxide which increases in abundance with increasing smectite content the compositional and chemical disparity between forearc and backarc sediments is due to dilution of arc derived mud by suspended sediment derived from mainland alaska the westward transport of mud for thousands of kilometers occurs both through isobath parallel bottom currents and by westward flowing turbidity currents these results show that interpretations of tectonic provenance cannot be based on elemental concentrations or mineralogy without also taking into account the possibility of long distance transport

comprehensive analysis of earthquake source spectra and swarms in the salton trough california 1 we study earthquakes within california s salton trough from 1981 to 2009 from a precisely relocated catalog we process the seismic waveforms to isolate source spectra station spectra and travel time dependent spectra the results suggest an average p wave q of 340 agreeing with previous results indicating relatively high attenuation in the salton trough stress drops estimated from the source spectra using an empirical green s function egf method reveal large scatter among individual events but a low median stress drop of 0 56 mpa for the region the distribution of stress drop after applying a spatial median filter indicates lower stress drops near geothermal sites we explore the relationships between seismicity stress drops and geothermal injection activities seismicity within the salton trough shows strong spatial clustering with 20 distinct earthquake swarms with at least 50 events they can be separated into early mmax and late mmax groups based on the normalized occurrence time of their largest event these swarms generally have a low skew value of moment release history ranging from 9 to 3 0 the major temporal difference between the two groups is the excess of seismicity and an inverse power law increase of seismicity before the largest event for the late mmax group all swarms exhibit spatial migration of seismicity at a statistical significance greater than 85 a weighted l1 norm inversion of linear migration parameters yields migration velocities from 0 008 to 0 8 km hour to explore the influence of fluid injection in geothermal sites we also model the migration behavior with the diffusion equation and obtain a hydraulic diffusion coefficient of approximately 0 25 m2 s for the salton sea geothermal site which is within the range of expected values for a typical geothermal reservoir the swarms with migration velocities over 0 1 km hour cannot be explained by the diffusion curve rather their velocity is consistent with the propagation velocity of creep and slow slip events these variations in migration behavior allow us to distinguish among different driving processes

glaciotectonic origin of the massachusetts coastal end moraines and a fluctuating late wisconsinan ice margin late wisconsinan end moraines on cape cod and islands south and west of cape cod are believed to be glaciotectonic features formed by advancing ice fronts evidence of a glaciotectonic origin includes the stratified drift composition of the moraines dislocated preglacial and glaciolacustrine deposits tilted preglacial and glacial beds folding and thrust faulting and morphologic similarity to ancient and modern glaciotectonic moraines evidence for major ice readvances during over all general recession includes the moraines themselves till atop stratified drift and the numerous basal tills that are inferred to exist beneath cape cod bay the thompson glacier end moraine in the canadian arctic archipelago is considered to be a modern example of how late wisconsinan end moraines on cape cod and the islands were formed the thompson glacier is overriding its outwash plain displacing outwash deposits forward and upward beyond the ice front new sheets are added to the base of the moraine and till is deposited atop the moraine as the ice overrides it evidence from cape cod and the nearby islands indicates that over all recession of late wisconsinan ice was characterized by alternating episodes of ice front retreat during which the outwash plains were formed and of ice front advance during which the moraines were built retreat of the ice from cape cod and the islands may have been similar to the retreat of the lake michigan lobe deposits of which contain evidence of at least 12 moraine building episodes caused by readvancing ice during the over all retreat of the late wisconsinan ice sheet

seismic reflection characteristics of glacial and glacimarine sediment in the gulf of alaska and adjacent fjords abstract glaciation together with tectonism have been dominant factors affecting sedimentation in the gulf of alaska area from at least the late miocene throughout the quaternary the effects of tectonism are apparent in high mountains that border the gulf raised terraces of middleton island and the eastern gulf coastal zone and numerous active faults and related earthquakes glacial evidence includes magnificent glaciers and their onshore deposits spectacular fjords large sea valleys incised in the continental shelf submarine morainal ridges at mouths of bays and sea valleys and thick glacimarine sedimentary sequences diamicts that are exposed onshore and at the sea floor along the outer shelf seismic reflection profiling and sampling of the uppermost marine sedimentary sequences in the gulf of alaska and adjacent fjords and bays have allowed identification of three discrete glacially related stratigraphic units these units were delineated on the basis of seismic signature geometry physiographic location stratigraphic position and sedimentologic characteristics the oldest unit a quaternary diamict is portrayed on seismic profiles by irregular discontinuous reflections this unit probably includes till outwash and glacimarine sediment a geographically restricted unit one incorporating holocene end moraines at bay mouths and associated with some sea valleys consists of jumbled masses of discontinuous reflections and very irregular surface morphology the youngest unit a blanket of holocene sand to clayey silt prograding as a sediment wedge across the shelf contains nearly horizontal parallel reflections except where disrupted by mass movement although seismic reflection data alone cannot provide definitive proof of the presence of glacial sediment when combined with sea floor sampling seismic profiling is a powerful tool for determining the continuity of marine sedimentary units and relationships to past and modern glaciers

the role of coulomb stress changes for injection induced seismicity the basel enhanced geothermal system 1 we estimate coulomb stress variations cfs by considering interactions among 163 earthquakes ml 3 4 that occurred during the hydraulic stimulation of the enhanced geothermal system in basel switzerland in 2006 we observe that overall 75 of event locations are consistent with positive cfs the performance of the model increases with time and distance from injection accordingly with the presumed less dominant role of the pore pressure further from the injection well and after shut in we analyze the sensitivity of results to location and focal mechanism uncertainties the fault plane ambiguity and the friction coefficient we find that cfs are highly sensitive to location accuracy but robust with regard to uncertainties of the other parameters our results suggest that i the coulomb model may complement conventional pore pressure triggering models and ii implementing it for time dependent seismic hazard assessment during fluid injection may improve the forecasting ability but will require highly accurate hypocenter estimates

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

california foreshock sequences suggest aseismic triggering process 1 foreshocks are one of the few well documented precursors to large earthquakes therefore understanding their nature is very important for earthquake prediction and hazard mitigation however the triggering role of foreshocks is not yet clear it is possible that foreshocks are a self triggering cascade of events that simply happen to trigger an unusually large aftershock alternatively foreshocks might originate from an external aseismic process that ultimately triggers the mainshock in the former case the foreshocks will have limited utility for forecasting the latter case has been observed for several individual large earthquakes however it remains unclear how common it is and how to distinguish foreshock sequences from other seismicity clusters that do not lead to large earthquakes here we analyze foreshocks of three m 7 mainshocks in southern california these foreshock sequences appear similar to earthquake swarms in that they do not start with their largest events and they exhibit spatial migration of seismicity analysis of source spectra shows that all three foreshock sequences feature lower average stress drops and depletion of high frequency energy compared with the aftershocks of their corresponding mainshocks using a longer term stress drop catalog we find that the average stress drop of the landers and hector mine foreshock sequences is comparable to nearby swarms our observations suggest that these foreshock sequences are manifestations of aseismic transients occurring close to the mainshock hypocenters possibly related to localized fault zone complexity which have promoted the occurrence of both the foreshocks and the eventual mainshock

induced earthquake magnitudes are as large as statistically expected a major question for the hazard posed by injection induced seismicity is how large induced earthquakes can be are their maximum magnitudes determined by injection parameters or by tectonics deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected however if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field then they may be limited only by the regional tectonics and connectivity of the fault network in this study we show that the largest magnitudes observed at fluid injection sites are consistent with the sampling statistics of the gutenberg richter distribution for tectonic earthquakes assuming no upper magnitude bound the data pass three specific tests 1 the largest observed earthquake at each site scales with the log of the total number of induced earthquakes 2 the order of occurrence of the largest event is random within the induced sequence and 3 the injected volume controls the total number of earthquakes rather than the total seismic moment all three tests point to an injection control on earthquake nucleation but a tectonic control on earthquake magnitude given that the largest observed earthquakes are exactly as large as expected from the sampling statistics we should not conclude that these are the largest earthquakes possible instead the results imply that induced earthquake magnitudes should be treated with the same maximum magnitude bound that is currently used to treat seismic hazard from tectonic earthquakes

in situ stress and active faulting in oklahoma abstract appreciable injection induced seismicity has been occurring in north central oklahoma since 2009 to better understand these earthquakes we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms seventy five new in situ stress orientations are available from wellbores throughout the state in the north central part of the state where the induced seismicity is occurring stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations all of the data show remarkably uniform stress directions the azimuth of s hmax the maximum horizontal stress is about n85 5 e strike slip faulting is occurring in central oklahoma with strike slip normal and normal faulting observed in northern oklahoma and southern kansas as very few of the thousands of m 2 5 earthquakes that have recently occurred are located on or near already mapped faults we utilize the stress information to interpret the likely fault planes associated with over 300 well constrained focal plane mechanisms in the vicinity of the january 2016 sequence of magnitude 4 and 5 earthquakes in the fairview oklahoma region we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area the september 2016 m w 5 8 pawnee event occurred on an unmapped n70 w trending strike slip fault expected to be active in the local stress field

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

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

submarine debris flow deposits from the upper carboniferous dwyka tillite formation in the kalahari basin south africa four types of sediment gravity flow deposits occur interbedded with rhythmite shale siltsone mudstone and minor diamictite in a 230 m thick carboniferous glacial sequence shear and plug zones are present in the cohesive debris flow deposits which have a diamictic texture the high density turbidity flow deposits which consist of coarse to medium grained clastics are characterized by both normal and reverse grading the medium to fine grained low density turbidity flow deposits show normal grading and consist of bouma units a b d and e deposition occurred by gravity flow suspension settling and minor basal melt out during ice retreat along the southern margin of the kalahari basin immediately basinwards of the ice grounding line a proximal diamictite facies consisting predominantly of cohesive and high density turbidity flow deposits and minor melt out tills formed a distal sedimentary facies of graded sandstone and siltstone units deposited by low density turbidity flows and suspension settling of muds with ice rafted debris is located basinwards

quaternary sedimentation in shelikof strait alaska abstract shelikof strait a nearly parallel sided marine channel between the kodiak island group and the alaska penninsula has experienced a succession of distinct sedimentary environments during quaternary time pleistocene glaciers carved a deep basin into bedrock in the southwest part of the strait and a shallower platform surface with incised channels in the northeast the basin and channels were filled with glacial and glacialmarine sediment before and during the time that ice retreated and oceanic conditions returned restricted marine conditions prevailed in early holocene time and sediment prograded transversely into the strait from the adjacent landmasses with some localized dispersal to the deep central strait onset of modern open marine conditions commenced when regional currents breached the sill across kennedy and stevenson entrances to combine with sediment laden outflow from cook inlet and deposit a blanket of well stratified sediment throughout the strait

possible precursory signals in damage zone foreshocks foreshocks may provide a precursory signal of an impending earthquake but their role in nucleation of the mainshock is unclear one way to further our understanding of foreshock failure mechanisms is to determine where they occur in the fault zone however earthquake locations commonly include uncertainties large enough to allow rupture on either the main fault interface or on subsidiary fractures within a surrounding damage zone here we obtain precise earthquake locations with 10 m uncertainty for foreshocks and aftershocks of an mw5 0 near prague ok usa repeating earthquakes imply that some precursory slow slip occurred before the mainshock in addition we show that foreshocks initially rupture faults and fractures throughout the 300 meter thick fault damage zone and later localize onto a narrower zone 100 m thick nearer the mainshock hypocenter focal mechanisms corroborate that foreshocks occur in the surrounding damage zone as well as on the mainshock rupture interface these results highlight that earthquake nucleation is most likely a complex feedback between frictional failure processes on the fault interface and deformation in the surrounding damaged rock not just nucleation on a single surface

extent and timing of the last glacial maximum in southwestern alaska a glacier complex composed of confluent alpine glaciers island ice caps and piedmont lobes covered much of the alaska peninsula and kodiak island during the last glacial maximum lgm because this glacier complex formed the southeastern border of beringia its dynamics may have been important in the timing and feasibility of the northwest coast route for human migration into lower latitude north america radiocarbon dates from stratigraphic sections on kodiak island and in the bristol bay lowlands bracket the lgm in southwestern alaska between 23 000 and 14 700 yr b p reconstruction of ice thickness based on glacier trimlines moraines and calculations of basal shear stress depict the alaska peninsula glacier complex flowing to the outer edge of the continental shelf in the gulf of alaska equilibrium line altitudes elas were 300 to 700 m lower than today and approached sea level on the southwestern alaska peninsula in northeastern areas where elas were higher bedrock topography largely controlled ice flow except where ice saddles bridged straits and inlets

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast