statistical modeling and characterization of induced seismicity within the western canada sedimentary basin in western canada there has been an increase in seismic activity linked to anthropogenic energy related operations including conventional hydrocarbon production wastewater fluid injection and mor

stress drop estimates and hypocenter relocations of induced seismicity near crooked lake alberta we use a sequence of induced earthquakes near crooked lake alberta to investigate the physical differences between induced and tectonic earthquakes starting with the natural resources canada earthquake catalogue we use a spectral ratio method to calculate the static stress drops of a group of relocated earthquakes ranging from december 2013 to june 2015 we find that stress drops fall within the high side of the typical reported range of tectonic events and show no correlation with earthquake magnitude depth or distance from the well the stress drops appear roughly constant for events with mw 3 to 4 relocated hypocenters cluster both spatially and temporally around corresponding injection wells and appear to migrate deeper with increasing time from injection fine scale lineations apparent in relocated hypocenters could indicate the presence and orientation of fault planes consistent with the published focal mechanism solutions of m 4 events in the area

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

analyzing earthquake clustering features by using stochastic reconstruction 1 on the basis of the epidemic type aftershock sequence etas model and the thinning procedure this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically the key points of this method are the probabilities of one event being triggered by another previous event and being a background event making use of these probabilities we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena we applied this reconstruction method to the shallow seismic data in japan and also to a simulated catalogue the results show the following assertions 1 the functions for each component in the formulation of the space time etas model are good enough as a first order approximation for describing earthquake clusters 2 a background event triggers less offspring in expectation than a triggered event of the same magnitude 3 the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor 4 the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes while no evidence shows that each individual triggering process is diffusive and 5 the scale of the triggering region is still an exponential law as formulated in the model but not the same one for the expected number of offspring

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

geologic influence on induced seismicity constraints from potential field data in oklahoma recent oklahoma seismicity shows a regional correlation with increased wastewater injection activity but local variations suggest that some areas are more likely to exhibit induced seismicity than others we combine geophysical and drill hole data to map subsurface geologic features in the crystalline basement where most earthquakes are occurring and examine probable contributing factors we find that most earthquakes are located where the crystalline basement is likely composed of fractured intrusive or metamorphic rock areas with extrusive rock or thick 4 km sedimentary cover exhibit little seismicity even in high injection rate areas similar to deep sedimentary basins in michigan and western north dakota these differences in seismicity may be due to variations in permeability structure within intrusive rocks fluids can become narrowly focused in fractures and faults causing an increase in local pore fluid pressure whereas more distributed pore space in sedimentary and extrusive rocks may relax pore fluid pressure

linking fossil reefs with earthquakes geologic insight to where induced seismicity occurs in alberta recently a significant increase in north american midcontinent earthquakes has been associated with contemporaneous development of petroleum resources despite the proliferation of drilling throughout sedimentary basins worldwide earthquakes are only induced at a small fraction of wells in this study we focus on cases of induced seismicity where high resolution data are available in the central western canada sedimentary basin our regional comparison of induced earthquake depths suggests basement controlled tectonics complementary to these findings hypocenters of induced seismicity clusters coincide with the margins of devonian carbonate reefs we interpret this spatial correspondence as the result of geographically biased activation potential possibly as a consequence of reef nucleation preference to paleobathymetric highs associated with precambrian basement tectonics this finding demonstrates the importance of geologic tectonic factors to earthquake induction in addition to industrial operational parameters in fact the observation of induced seismicity silhouetting deep fossil reef systems may be a useful tool to identify future regions with increased seismogenic potential

retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

quantitative description of induced seismic activity before and after the 2011 tohoku oki earthquake by nonstationary etas models 1 the epidemic type aftershock sequence etas model is extended for application to nonstationary seismic activity including transient swarm activity or seismicity anomalies in a seismogenic region the time dependent rates of both background seismicity and aftershock productivity in the etas model are optimally estimated from hypocenter data these rates can provide quantitative evidence for abrupt or gradual changes in shear stress and or fault strength due to aseismic transient causes such as triggering by remote earthquakes slow slips or fluid intrusions within the region this extended model is applied to data sets from several seismic events including swarms that were induced by the m9 0 tohoku oki earthquake of 2011

aftershock statistics of major subduction earthquakes abstract large megathrust subduction earthquakes generate prolific aftershock sequences which last over an extended period of time and affect wide spatial areas among those aftershocks the largest ones can cause additional damage and pose significant risks to population and infrastructure therefore modeling aftershock sequences of large subduction earthquakes is of considerable importance for seismic hazard assessment and earthquake risk mitigation it can also play a prominent role in the ground shaking modeling of major mainshock aftershock sequences in this work we analyze statistical properties of aftershock sequences of large subduction earthquakes worldwide which occurred from 1973 to present including recent catastrophic events in sumatra chile and japan we use information provided in the national earthquake information center neic catalog to extract 70 aftershock sequences generated by mainshocks of m 7 0 and above we construct their temporal decay rates and magnitude frequency statistics to model their temporal behavior we estimate the parameters of the modified omori law in the magnitude domain we model the frequency magnitude statistics using the gutenberg richter scaling relationship we also analyze statistically the difference between the magnitude of the mainshock and the corresponding largest aftershock in the sequence and discuss this in terms of bath s law one of the main goals of this work is to investigate the variation in parameter values of the above empirical laws with respect to the magnitude of the mainshock our main finding indicates that most parameters do not depend on the magnitude of the mainshock however they show some variation in values across different subduction settings online material the location and spatial information for elliptical regions of aftershock zones

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

nontrivial clustering of microseismicity induced by hydraulic fracturing for induced microseismicity associated with hydraulic fracturing the frequency magnitude distribution is typically characterized by a falloff with increasing magnitude that is significantly faster than for seismicity along active fault systems this characteristic may arise from a break in scale invariance possibly due to mechanical layering that typifies fine grained sedimentary rocks in many shale gas and tight oil reservoirs the latter would imply the presence of spatio temporal magnitude correlations using three microseismic catalogs for well stimulations in widely separated locations with varying hydraulic fracturing methods we show that events with similar magnitudes indeed tend to cluster in space and time in addition we show that the inter event time distribution can be described by a universal functional form characterized by two power laws one exponent can be related to the presence of inter event triggering as in aftershock sequences and is a consequence of the omori utsu law the other one is a reflection of the intrinsic spatial variation in the microseismic response rates taken together these features are indicative of non trivial spatio temporal clustering of induced microseismicity and hence of direct relevance for time dependent seismic hazard assessment

earthquake clusters in southern california ii classification and relation to physical properties of the crust 1 this is a second paper in a study of statistical identification and classification of earthquake clusters using a relocated catalog of 1981 2011 seismicity in southern california and synthetic catalogs produced by the epidemic type aftershock sequence model here we focus on classification of event families statistically significant clusters composed of foreshocks mainshocks and aftershocks that are detected with the methodology discussed in part i of the study the families are analyzed using their representation as time oriented tree graphs the results 1 demonstrate that the clustering associated with the largest earthquakes m 7 is statistically different from that of small to medium earthquakes 2 establish the existence of two dominant types of small to medium magnitude earthquake families burst like and swarm like sequences and a variety of intermediate cluster forms obtained as a mixture of the two dominant types 3 suggest a simple new quantitative measure for identifying the cluster type based on its topological structure 4 demonstrate systematic spatial variability of the cluster characteristics on a scale of tens of kilometers in relation to heat flow and other properties governing the effective viscosity of a region and 5 establish correlation between the family topological structure and a dozen of metric properties traditionally considered in the literature number of aftershocks duration spatial properties b value parameters of omori utsu and bath law etc the burst like clusters likely reflect highly brittle failures in relatively cold regions while the swarm like clusters are likely associated with mixed brittle ductile failures in regions with relatively high temperature and or fluid content the results of this and paper i may be used to develop improved region specific hazard estimates and earthquake forecasts

space time etas models and an improved extension for sensitive detection of anomalous seismicity such as quiescence and activation in a given region we need a suitable statistical reference model that represents a normal seismic activity in the region the regional occurrence rate of the earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively this manuscript summarizes the development of the epidemic type aftershock sequence etas model and proposes an extended version of the best fitted space time model that was suggested in ogata ogata y 1998 space time point process models for earthquake occurrences ann inst statist math 50 379 402 this model indicates significantly better fit to seismicity in various regions in and around japan d 2005 elsevier b v all rights reserved

evidence for a constant b value above magnitude 0 in the southern san andreas san jacinto and san miguel fault zones and at the long valley caldera california the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes 3 some recent studies have suggested that this decrease in b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict brune allen 1967 recorded microseismicity in both the san andreas and san jacinto fault zones in southern california calculating that they were complete to magnitude 0 reyes et al 1975 performed a similar study of the san miguel fault zone baja california estimating completeness above magnitude 0 5 we compare the results of these studies with the occurrence rates of earthquakes on the same faults recorded by the southern california and resnor seismic networks the observed microseismicity rates are in good agreement with the rates predicted by extrapolating the b values of the larger earthquakes in a new microseismicity survey at the long valley caldera mammoth lakes california microearthquakes were recorded and counted within 24 km of stations clk and chs this study is estimated to be complete above 0 6 m at clk and 0 9 m at chs and the microseismicity rates are found to be in good agreement with the rate predicted by extrapolating the b value from the local network recorded seismicity the constant b value in the magnitude range 0 to 5 observed in all four areas considered is consistent with a scale invariant earthquake rupture process

a statistical model for seismic hazard assessment of hydraulic fracturing induced seismicity we analyze the interevent time distribution of hydraulic fracturing induced seismicity collected during 18 stages at four different regions we identify a universal statistical process describing the distribution of hydraulic fracturing induced events in time the distribution of waiting times between subsequently occurring events is given by the exponential probability density function of the homogeneous poisson process our findings suggest that hydraulic fracturing induced seismicity is directly triggered by the relaxation of stress and pore pressure perturbation initially created by the injection therefore compared to this relaxation the stress transfer caused by the occurrence of preceding seismic events is mainly insignificant for the seismogenesis of subsequently occurring events we develop a statistical model to compute the occurrence probability of hydraulic fracturing induced seismicity this model can be used to assess the seismic hazard associated with hydraulic fracturing operations no aftershock triggering has to be included in the statistical model

fault activation by hydraulic fracturing in western canada hydraulic fracturing has been inferred to trigger the majority of injection induced earthquakes in western canada in contrast to the midwestern united states where massive saltwater disposal is the dominant triggering mechanism a template based earthquake catalog from a seismically active canadian shale play combined with comprehensive injection data during a 4 month interval shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites the largest event moment magnitude mw 3 9 occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of 1 km whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months

detecting aseismic strain transients from seismicity data 1 aseismic deformation transients such as fluid flow magma migration and slow slip can trigger changes in seismicity rate we present a method that can detect these seismicity rate variations and utilize these anomalies to constrain the underlying variations in stressing rate because ordinary aftershock sequences often obscure changes in the background seismicity caused by aseismic processes we combine the stochastic epidemic type aftershock sequence model that describes aftershock sequences well and the physically based rate and state dependent friction seismicity model into a single seismicity rate model that models both aftershock activity and changes in background seismicity rate we implement this model into a data assimilation algorithm that inverts seismicity catalogs to estimate space time variations in stressing rate we evaluate the method using a synthetic catalog and then apply it to a catalog of m 1 5 events that occurred in the salton trough from 1990 to 2009 we validate our stressing rate estimates by comparing them to estimates from a geodetically derived slip model for a large creep event on the obsidian buttes fault the results demonstrate that our approach can identify large aseismic deformation transients in a multidecade long earthquake catalog and roughly constrain the absolute magnitude of the stressing rate transients our method can therefore provide a way to detect aseismic transients in regions where geodetic resolution in space or time is poor

displaced re worked rhodolith deposits infilling parts of a complex miocene multistorey submarine channel a case history from the sassari area sardinia italy abstract in the sassari area north western sardinia italy the miocene porto torres sub basin sequences represent the complex multistorey mixed carbonate siliciclastic submarine feature called the sassari channel during the late burdigalian early serravallian repeated terrigenous supplies from uplifted paleozoic crystalline substrata fed the sassari channel system by means of turbidity and locally hyper concentrated turbidity flows shelfal areas were the source of terrigenous clasts but open shelf rhodalgal foramol carbonate areas were very productive and largely also contributed to the channel infilling re worked sands and skeletal debris were discontinuously re sedimented offshore as pure terrigenous mixed and or carbonate deposits major sediment supply was introduced between the latest burdigalian and the start of the middle langhian during which a large amount of carbonate mixed and siliciclastic sediments reached the porto torres basin sassari channel i contributions from shallow proximal source areas typify the lower intervals unit a in marginal sectors of the channel upward these evolve into autochthonous rhodolith deposits winnowed by strong currents in relatively shallow well lit settings within a complex network of narrow tidally controlled channels unit d locally bearing coral assemblages conversely re sedimented rhodoliths from the units b and c accumulated under conditions of higher turbidity in deeper parts of the channel taxonomically diversified rhodoliths point to the mixing of re deposited skeletal components from different relatively deep bathmetric settings in the latest early langhian major re sedimentation episodes resulting in large prograding bodies unit d triggered by repeated regression pulses in a frame of persistent still stand during these episodes photophile assemblages dwelled in the elevated margin sectors of the channel a significant latest early langhian drop in relative sea level resulted in impressive mass flows involving early cemented channel margin and levee blocks and culminated in the formation of major erosional surface er e such events seemingly correlate with the long term global cooling trend of the mid miocene climatic transition episodes of middle langhian re sedimentation concluded with the channel abandon phase after which new erosive episodes followed overall this led to a shift in the sassari channel ii with phases presumably started during the earlymost serravallian subsequent to the major sea level drop at the langhian serravallian boundary

the cardston earthquake swarm and hydraulic fracturing of the exshaw formation alberta bakken play more than 60 small earthquakes m l 0 7 3 0 were detected from december 2011 to march 2012 north of cardston alberta an area with little evidence for previous seismic activity the timing of these events closely correlates 99 7 confidence with hydraulic fracturing completions of the devonian mississippian age exshaw formation at a nearby horizontal well unanimous waveform multiplicity within the swarm suggests that the events share a similar origin and source mechanism this observation is corroborated by the point like collocation of hypocenters within the crystalline basement during robust double difference relocations furthermore the presence of a pre existing fault is confirmed via formation top offset mapping and interpreted to be a late cretaceous extensional fault the confirmation of this fault at depth provides a plausible pathway for rapid hydraulic communication from the fracturing interval into the crystalline basement consistent with structural interpretations and available stress information moment tensor inversion of the largest magnitude event m w 3 0 indicates reactivation of a basement fault with normal slip we conclude that the genesis of this earthquake swarm was likely caused by increased pore pressure within the basement fault as a result of fracturing stimulation online material figure showing frequency magnitude distribution of earthquakes and table of the velocity models used in the study

characterizing potentially induced earthquake rate changes in the brawley seismic zone southern california the brawley seismic zone bsz in the salton trough of southern california has a history of earthquake swarms and geothermal energy exploitation some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields particularly at the north brawley geothermal field nbgf and at the salton sea geothermal field ssgf we explore this issue by examining earthquake rate changes and interevent distance distributions in these fields in oklahoma and arkansas where considerable wastewater injection occurs increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid injection induced seismicity here we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas we use stochastic epidemic type aftershock sequence models to detect changes in the underlying seismogenic processes shown by statistically significant changes in the model parameters the most robust model changes in the ssgf roughly occur when large changes in net fluid production occur but a similar correlation is not seen in the nbgf also although both background seismicity rate and aftershock productivity increased for fluid injection induced earthquake rate changes in oklahoma and arkansas the background rate increases significantly in the bsz only roughly corresponding with net fluid production rate increases moreover in both fields the interevent spacing does not change significantly during active energy projects this suggests that although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions earthquake rates may still be driven by fluid injection or extraction rates particularly in the ssgf

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

seismic clusters analysis in northeastern italy by the nearest neighbor approach abstract the main features of earthquake clusters in northeastern italy are explored with the aim to get new insights on local scale patterns of seismicity in the area the study is based on a systematic analysis of robustly and uniformly detected seismic clusters which are identified by a statistical method based on nearest neighbor distances of events in the space time energy domain the method permits us to highlight and investigate the internal structure of earthquake sequences and to differentiate the spatial properties of seismicity according to the different topological features of the clusters structure to analyze seismicity of northeastern italy we use information from local ogs bulletins compiled at the national institute of oceanography and experimental geophysics since 1977 a preliminary reappraisal of the earthquake bulletins is carried out and the area of sufficient completeness is outlined various techniques are considered to estimate the scaling parameters that characterize earthquakes occurrence in the region namely the b value and the fractal dimension of epicenters distribution required for the application of the nearest neighbor technique specifically average robust estimates of the parameters of the unified scaling law for earthquakes usle are assessed for the whole outlined region and are used to compute the nearest neighbor distances clusters identification by the nearest neighbor method turn out quite reliable and robust with respect to the minimum magnitude cutoff of the input catalog the identified clusters are well consistent with those obtained from manual aftershocks identification of selected sequences we demonstrate that the earthquake clusters have distinct preferred geographic locations and we identify two areas that differ substantially in the examined clustering properties specifically burst like sequences are associated with the north western part and swarm like sequences with the south eastern part of the study region the territorial heterogeneity of earthquakes clustering is in good agreement with spatial variability of scaling parameters identified by the usle in particular the fractal dimension is higher to the west about 1 2 1 4 suggesting a spatially more distributed seismicity compared to the eastern parte of the investigated territory where fractal dimension is very low about 0 8 1 0

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

detection and characterization of transient forcing episodes affecting earthquake activity in the aleutian arc system abstract crustal slow deformation transients can be caused by fluid or magmatic intrusions and by slow slip on faults they can affect earthquake dynamics if they occur close to or within seismically active zones we here further develop and test a statistical method for detecting and characterizing seismicity anomalies that is only based on earthquake occurrence times and locations we make use of this method to analyze the 2004 2013 seismicity at m c 3 5 in the aleutian subduction system to find six statistically significant anomalies with typical 1 day duration and 30 to 50 km size that are likely related to slow deformation transients they tend to be located in zones characterized by intermediate seismic coupling and to mark the termination of past large to mega thrust earthquakes these anomalies account for a non negligible 9 part of the total activity proving that non stationary aseismic loading plays an important role in the dynamics of crustal deformation

a seismological overview of the induced earthquakes in the duvernay play near fox creek alberta this paper summarizes the current state of understanding regarding the induced seismicity in connection with hydraulic fracturing operations targeting the duvernay formation in central alberta near the town of fox creek we demonstrate that earthquakes in this region cluster into distinct sequences in time space and focal mechanism using i cross correlation detection methods to delineate transient temporal relationships ii double difference relocations to confirm spatial clustering and iii moment tensor solutions to assess fault motion consistency the spatiotemporal clustering of the earthquake sequences is strongly related to the nearby hydraulic fracturing operations in addition we identify a preference for strike slip motions on subvertical faults with an approximate 45 p axis orientation consistent with expectation from the ambient stress field the hypocentral geometries for two of the largest magnitude m 4 sequences that are robustly constrained by local array data provide compelling evidence for planar features starting at duvernay formation depths and extending into the shallow precambrian basement we interpret these lineaments as subvertical faults orientated approximately north south consistent with the regional moment tensor solutions finally we conclude that the sequences were triggered by pore pressure increases in response to hydraulic fracturing stimulations along previously existing faults

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

maturity of nearby faults influences seismic hazard from hydraulic fracturing understanding the causes of human induced earthquakes is paramount to reducing societal risk we investigated five cases of seismicity associated with hydraulic fracturing hf in ohio since 2013 that because of their isolation from other injection activities provide an ideal setting for studying the relations between high pressure injection and earthquakes our analysis revealed two distinct groups i deeper earthquakes in the precambrian basement with larger magnitudes m 2 b values 1 5 and few post shut in earthquakes based on geologic history laboratory experiments and fault modeling we interpret the deep seismicity as slip on more mature faults in older crystalline rocks and the shallow seismicity as slip on immature faults in younger sedimentary rocks this suggests that hf inducing deeper seismicity may pose higher seismic hazards wells inducing deeper seismicity produced more water than wells with shallow seismicity indicating more extensive hydrologic connections outside the target formation consistent with pore pressure diffusion influencing seismicity however for both groups the 2 to 3 h between onset of hf and seismicity is too short for typical fluid pressure diffusion rates across distances of 1 km and argues for poroelastic stress transfer also having a primary influence on seismicity

estimating the etas model from an early aftershock sequence forecasting aftershock probabilities as early as possible after a main shock is required to mitigate seismic risks in the disaster area in general aftershock activity can be complex including secondary aftershocks or even triggering larger earthquakes however this early forecasting implementation has been difficult because numerous aftershocks are unobserved immediately after the main shock due to dense overlapping of seismic waves here we propose a method for estimating parameters of the epidemic type aftershock sequence etas model from incompletely observed aftershocks shortly after the main shock by modeling an empirical feature of data deficiency such an etas model can effectively forecast the following aftershock occurrences for example the etas model estimated from the first 24 h data after the main shock can well forecast secondary aftershocks after strong aftershocks this method can be useful in early and unbiased assessment of the aftershock hazard

a model for induced seismicity caused by hydrocarbon production in the western canada sedimentary basin over the past three decades a significant number of small magnitude and shallow earthquakes have occurred in the western canada sedimentary basin and are located along its western flank near areas of oil and gas production one of the better documented examples is the swarm of earthquakes associated with the strachan field in the alberta foothills a model based on segall s poroelastic theory is developed to account for the occurrence of earthquakes below the strachan reservoir using this methodology we show that the earthquake of 19 october 1996 underneath the strachan field was most probably triggered by gas extraction the numerical model also implies that gas extraction would cause subsidence and localized changes in in situ stress magnitudes there is a strong correlation between rates of production and the number of seismic events but the onset of major seismic activity postdates the commencement of production by approximately 5 years poroelastic modelling can account neatly for this observe

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

using the etas model for catalog declustering and seismic background assessment the concept of background seismicity is strictly related to the identification of spontaneous and triggered earthquakes the definition of foreshocks main shocks and aftershocks is currently based on procedures depending on parameters whose values are notoriously assumed by subjective criteria we propose a method for recognizing the background and the induced seismicity statistically rather than using a binary distinction of the events in these two categories we prefer to assign to each of them a probability of being independent or triggered this probability comes from an algorithm based on the etas model a certain degree of subjectivity is still present in this procedure but it is limited by the possibility of adjusting the free parameters of the algorithm by rigorous statistical criteria such as maximum likelihood we applied the method to the seismicity of southern california and analyzed the sensitivity of the results to the free parameters in the algorithm finally we show how our statistical declustering algorithm may be used for mapping the background seismicity or the moment rate in a seismic area

sr isotope variations in vent fluids from 9 46 9 54 n east pacific rise evidence of a non zero mg fluid component abstract sr isotopic variations in vent fluids from six high temperature hydrothermal vents from between 9 46 n and 9 54 n on the east pacific rise are reported the mg sr 87sr 86sr systematics of one vent biovent require the presence of a fluid component that has experienced significant mg depletion 50 but has undergone very little sr exchange with local basalts this fluid component accounts for 3 to 10 of the biovent samples by volume similarities between the composition of the inferred fluid component and that of bore hole fluids sampled from hole 504b suggest that this fluid component is modified seawater partially reacted with basalt at temperatures less than 150 c and subsequently entrained by high temperature vent fluids previously reported vent fluid data from 12 50 n east pacific rise suggest that the presence of the additional lower temperature fluid component admixed in biovent samples may not be unique among seafloor hydrothermal systems if such a fluid component is common in seafloor hydrothermal systems it will need to be considered in estimates of axial hydrothermal fluxes if not accounted for properly the presence of an additional fluid component can bias calculated end member 87sr 86sr ratios after correction for the influence of the additional fluid component on the biovent samples the calculated end member 87sr 86sr ratio of this vent is 0 7041 other nearby vents p vent and bio9 are slightly more radiogenic 0 7042 a and l vents from the southern portion of the study area have end member 87sr 86sr ratios that are less radiogenic 0 7039 and 0 7037 respectively the reason for the greater influence of seawater derived sr in the more northern vents is not known but it may be related to entrainment of seawater in the upflow zone

differentiating induced and natural seismicity using space time magnitude statistics applied to the coso geothermal field a remarkable characteristic of earthquakes is their clustering in time and space displaying their self similarity it remains to be tested if natural and induced earthquakes share the same behavior we study natural and induced earthquakes comparatively in the same tectonic setting at the coso geothermal field covering the preproduction and coproduction periods from 1981 to 2013 we analyze interevent times spatial dimension and frequency size distributions for natural and induced earthquakes individually these distributions are statistically indistinguishable determining the distribution of nearest neighbor distances in a combined space time magnitude metric lets us identify clear differences between both kinds of seismicity compared to natural earthquakes induced earthquakes feature a larger population of background seismicity and nearest neighbors at large magnitude rescaled times and small magnitude rescaled distances local stress perturbations induced by field operations appear to be strong enough to drive local faults through several seismic cycles and reactivate them after time periods on the order of a year

hydraulic fracturing and the crooked lake sequences insights gleaned from regional seismic networks within central alberta canada a new sequence of earthquakes has been recognized as of 1 december 2013 in a region of previous seismic quiescence near crooked lake 30 km west of the town of fox creek we utilize a cross correlation detection algorithm to detect more than 160 events to the end of 2014 which is temporally distinguished into five subsequences this observation is corroborated by the uniqueness of waveforms clustered by subsequence the crooked lake sequences have come under scrutiny due to its strong temporal correlation 99 99 to the timing of hydraulic fracturing operations in the duvernay formation we assert that individual subsequences are related to fracturing stimulation and despite adverse initial station geometry double difference techniques allow us to spatially relate each cluster back to a unique horizontal well overall we find that seismicity in the crooked lake sequences is consistent with first order observations of hydraulic fracturing induced seismicity

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

isolated cases of remote dynamic triggering in canada detected using cataloged earthquakes combined with a matched filter approach here we search for dynamically triggered earthquakes in canada following global main shocks between 2004 and 2014 with ms 6 depth 0 2 cm s we use the natural resources canada nrcan earthquake catalog to calculate statistical values in 1 1 bins in 10 day windows before and after the main shocks the statistical analysis suggests that triggering may occur near vancouver island along the border of the yukon and northwest territories in western alberta western ontario and the charlevoix seismic zone we also search for triggering in alberta where denser seismic station coverage renders regional earthquake catalogs with lower completeness thresholds we find remote triggering in alberta associated with three main shocks using a matched filter approach on continuous waveform data the increased number of local earthquakes following the passage of main shock surface waves suggests local faults may be in a critically stressed state

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

detecting periodicities and declustering in earthquake catalogs using the schuster spectrum application to himalayan seismicity we show that the schuster test alone does not provide a sufficient condition to assert the existence of a periodicity in an earthquake catalog such periodicities can be detected by computing a spectrum of schuster p values the probability to observe such a level of periodic variations in a catalog occurring out of a constant seismicity rate we show that the detection level is slightly period dependent and we provide an analytical expression relating the amplitude of seismicity rate variations to the confidence level at which the probability that the observed variations be due to chance can be discarded the schuster spectrum also provides information about the deviation from a sinusoidal function of the periodicity of the seismicity rate and identifies an eventual imperfect declustering of the catalog making it coincidently a potential tool to determine whether or not a catalog has been properly declustered applying this tool to the nepalese seismicity we demonstrate annual variations of the seismicity rate of amplitude up to 40 while no other periodicity appears in particular no variations of seismicity at any of the tidal periods are observed indicating that the relative amplitude response of the seismicity at these periods is less than 18

an objective method for the assessment of fluid injection induced seismicity and application to tectonically active regions in central california changes in seismicity rates whether of tectonic or of induced origin can readily be identified in regions where background rates are low but are difficult to detect in seismically active regions we present a novel method to identify likely induced seismicity in tectonically active regions based on short range spatiotemporal correlations between changes in fluid injection and seismicity rates the method searches through the entire parameter space of injection rate thresholds and determines the statistical significance of correlated changes in injection and seismicity rates applying our method to kern county central california we find that most earthquakes within the region are tectonic however fluid injection contributes to seismicity in four different cases three of these are connected to earthquake sequences with events above m4 each of these sequences followed an abrupt increase in monthly injection rates of at least 15 000 m 3 the probability that the seismicity sequences and the abrupt changes in injection rates in kern county coincide by chance is only 4 the identified earthquake sequences display low gutenberg richter b values of 0 6 0 7 and at times systematic migration patterns characteristic for a diffusive process our results show that injection induced pressure perturbations can influence seismic activity at distances of 10 km or more triggering of earthquakes at these large distances may be facilitated by complex local geology and faults in tectonically active regions our study provides the first comprehensive statistically robust assessment of likely injection induced seismicity within a large tectonically active region

characterizing aftershock sequences of the recent strong earthquakes in central italy the recent strong earthquakes in central italy allow for a comparative analysis of their aftershocks from the viewpoint of the unified scaling law for earthquakes usle which generalizes the gutenberg richter relationship making use of naturally fractal distribution of earthquake sources of different size in a seismic region in particular we consider aftershocks as a sequence of avalanches in self organized system of blocks and faults of the earth lithosphere each aftershock series characterized with the distribution of the usle control parameter we found the existence in a long term of different intermittent levels of rather steady seismic activity characterized with a near constant value of which switch in mid term at times of transition associated with catastrophic events on such a transition seismic activity may follow different scenarios with inter event time scaling of different kind including constant logarithmic power law exponential rise decay or a mixture of those as observed in the case of the ongoing one associated with the three strong earthquakes in 2016 evidently our results do not support the presence of universality of seismic energy release while providing constraints on modelling seismic sequences for earthquake physicists and supplying decision makers with information for improving local seismic hazard assessments

poroelastic stressing and induced seismicity near the lacq gas field southwestern france o hundreds of shallow small to moderate earthquakes have occurred near the lacq deep gas field in southwestern france since 1969 these earthquakes are clearly separated from tectonic seismicity occurring in the pyrenees 25 km to the southwest the induced seismicity began when the reservoir pressure had declined by 30 mpa repeated levehng over the field shows localized subsidence reaching a maximum of 60 mm in 1989 segall 1989 suggested that poroelastic stressing associated with volumetric contraction of the reservoir rocks is responsible for induced seismicity associated with fluid extraction to test this model we compare the observed subsidence and hypocentral distributions with the predicted displacement and stress fields we find that the relationship between average reservoir pressure drop and subsidence is remarkably linear lending support to the linear poroelastic model displacements and stresses are computed based on a priori knowledge of the reservoir geometry materim properties and reservoir pressure changes the computed vertical displacements are found to be in excellent agreement with the subsidence observed from leveling stress perturbations accompanying gas extraction computed using the same parameters are found to be 0 2 mpa or less changes in coulomb failure stress are computed assuming that shp occurs on optimally oriented planes the predicted failure zones correlate very well with the spatial distribution of earthquakes if the perturbing stresses are small in comparison to the ambient regional deviatoric stresses and if the minimum regional compresslye stress axis is vertical accurate determination of focal mechanisms of the induced events would allow a more rigorous test of the poroelastic model and could lead to important inferences about the crustal stress state

earthquakes induced by hydraulic fracturing in poland township ohio felt seismicity induced by hydraulic fracturing is very rare with only a handful of reported cases worldwide using an optimized multistation cross correlation template matching routine 77 earthquakes were identified in poland township mahoning county ohio that were closely related spatially and temporally to active hydraulic fracturing operations we identified earthquakes as small as local magnitudes m l 1 up to 3 potentially one of the largest earthquakes induced by hydraulic fracturing in the united states these events all occurred from 4 to 12 march 2014 and the rate decayed once the ohio department of natural resources issued a shutdown of hydraulic fracturing at a nearby well on 10 march using a locally derived velocity model and double difference relocation the earthquakes occurred during six stimulation stages along two horizontal well legs that were located 0 8 km away nearly 100 stimulation stages in nearby wells at greater distances from the earthquake source region did not coincide with detected seismicity during the sequence hypocenters migrated 600 m along an azimuth of 083 defining a vertically oriented plane of seismicity close to the top of the precambrian basement the focal mechanism determined for the m l 3 event had a vertically oriented left lateral fault plane consistent with the earthquake distribution and the regional stress field the focal mechanism orientation and depth of hypocenters were similar to those of the 2011 youngstown earthquake sequence that occurred 18 km to the northwest and was correlated with wastewater injection instead of hydraulic fracturing considering the relatively large magnitude of the poland township events and the b value of 0 89 it appears the hydraulic fracturing induced slip along a pre existing fault fracture zone optimally oriented in the regional stress field

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

decay rate of fluid induced seismicity after termination of reservoir stimulations we present a model describing the seismicity rate of fluid injection induced seismicity we put the focus on seismicity induced after termination of fluid injections here our primary objective is the identification of parameters controlling the decay rate of seismicity the particular importance of a theoretical model for postinjection seismicity is underlined by observations after stimulations of geothermal reservoirs at different locations for instance the postinjection phase is relevant for a seismic risk which up to now has been difficult to control because processes leading to postinjection events are not well understood based on the assumption of pore pressure diffusion as the governing mechanism leading to the triggering of seismic events we develop a method to calculate the seismicity rate during and after fluid injections we find that the decay rate of seismicity after termination of injection is very similar to the omori law which describes the decay rate of aftershock activity after t

seismic detection capability at noress and implications for the detection threshold of a hypothetical network in the soviet union the detection threshold of a network including noress type arrays in the soviet union is estimated using the frequency dependent attenuation of pn and lg observed at noress to normalize the threshold of individual stations the normalization begins with a parameterization of the magnitude and range dependence of the noress pn and lg spectra in terms of seismic moment and apparent attenuation a relationship between these spectral amplitudes and the time domain amplitudes used in signal detection at noress is then determined this allows an estimate of noress detection capability from the spectral parameterization and a prediction of the pn detection capability for regions with different wave propagation characteristics a comparable prediction is not possible for lg because of dispersion and the non stationarity of pre lg noise instead an empirical relationship for lg detectability based on observed temporal amplitudes is determined to validate the results for noress predictions based on our model are compared with observed detection statistics and with results obtained by ringdal 1986 who compared detections at noress to bulletins produced by local seismic networks the simulations represent the detection capability of a network of noress type arrays 20 within and 13 outside the soviet union the 90 ml threshold for detecting three pn phases for events in the soviet union is estimated to be between 2 4 and 2 7 if the frequency dependent attenuation and noise throughout the network are the same as those observed at noress this threshold is reduced by 0 1 ml if pn q is 50 higher in the soviet union than estimated for scandinavia and is increased by 0 2 0 3 ml if pn q is 50 lower the ml thresholds are reduced by 0 2 0 3 if the detection criteria include lg as well as pn phases while these simulations are carefully normalized by the actual detection capability of a prototype station for test ban treaty monitoring observations of attenuation and noise inside the soviet union are needed to determine how they actually differ from those at noress also it must be noted that the noress detection capability estimates and therefore the simulations are for average conditions and there are regular variations that must be considered when estimating treaty monitoring capability

source analysis of a potential hydraulic fracturing induced earthquake near fox creek alberta an earthquake with a reported magnitude of 4 4 ml was detected on 13 june 2015 in western central alberta canada this event was the third felt earthquake this year near fox creek a shale gas exploration region our results from full moment tensor inversions of regional broadband data show a strong strike slip mechanism with near vertical fault plane solutions the decomposition of the moment tensor solution is overwhelmingly double couple while only a modest 20 contribution is attributed to compensated linear vector dipole the depth of this earthquake is 3 4 km near the base of the sedimentary layer and the moment magnitude m 3 9 of this event is considerably smaller than the initial reported ml value the hypocenter location depth and mechanism are favorable to a possible association between this earthquake and hydraulic fracturing operations within the duvernay shale

spatial and temporal evolution of b values before large earthquakes in taiwan abstract we investigate the spatial and temporal variations of b values before twenty three earthquakes with ml 6 0 in the taiwan region from 1999 to 2009 we estimate the spatial distribution of b values within a one year period before the occurrence of investigated earthquakes it shows that the epicenters of those earthquakes are located predominately in the regions with low b values relative to the entire study area in terms of temporal evolutions the b values are slightly lower during the year prior to the investigated earthquakes in comparison to the periods two to five years earlier we propose that these anomalies may offer spatiotemporal constraints for the earthquake forecasting in taiwan in the future

source spectral properties of small to moderate earthquakes in southern kansas the source spectral properties of injection induced earthquakes give insight into their nucleation rupture processes and influence on ground motion here we apply a spectral decomposition approach to analyze p wave spectra and estimate brune type stress drop for more than 2000 ml1 5 5 2 earthquakes occurring in southern kansas from 2014 to 2016 we find that these earthquakes are characterized by low stress drop values median 0 4mpa compared to natural seismicity in california we observe a significant increase in stress drop as a function of depth but the shallow depth distribution of these events is not by itself sufficient to explain their lower stress drop stress drop increases with magnitude from m1 5 m3 5 but this scaling trend may weaken above m4 and also depends on the assumed source model although we observe a nonstationary sequence specific temporal evolution in stress drop we find no clear systematic relation with the activity of nearby injection wells

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

an investigation of seismicity clustered near the cordel field west central alberta and its relation to a nearby disposal well historically seismicity documented in the western canada sedimentary basin has been relatively quiescent and earthquakes are usually restricted to the foreland belt of the rocky mountains however exceptional clusters of events which have remained active for decades are recognized in alberta in this study we investigate the seismicity in this region using data obtained from recently established regional arrays emphasizing the relationship between a disposal well in the cordel field and a nearby cluster of previously reported earthquakes we explore temporal correlations of wastewater pumping rates and local seismic activity dating back to 1960 we find that the first statistically significant increase in seismicity lags the onset of wastewater injection october 1991 by 3 33 years in particular the waveform similarity of 32 events are analyzed from continuous data recorded at nor a nearby 30 km station operated by the university of alberta starting in september of 2006 results from this analysis suggest that many events are well correlated in the characteristics of the waveforms and thus are likely to share a similar origin and source mechanism the most prolific of these multiplets repeats more than 10 times sporadically throughout the entire duration of recorded data from october 2006 to march 2012 despite the limited availability of nearby stations which adversely affects the resolution of our analysis hypocenter depths could be relatively accurately determined from waveform synthesis and double difference methods the results of our analysis provide first order evidence that the seismicity is consistent with fluid injection induced events

transition from aftershock to normal activity the 1965 rat islands earthquake aftershock sequence a transition from aftershock to normal activity is identified 2200 days after the occurrence of the 1965 rat islands earthquake of mw 8 7 after this time we observe a significant departure of the seismicity in the focal region from the extrapolated trend of the aftershock activity predicted by the modified omori formula proposed by utsu in 1961 the maximum likelihood estimate of the parameters for the formula and the selection of a statistical model based on the akaike information criterion show that the whole aftershock sequence is best modeled by the combination of an ordinary aftershock sequence and secondary aftershock activity associated with the largest aftershock fitting of the activity after the transition period to the modified omori formula results in an unusually low value of the decay constant we interpret that this activity represents normal or background seismicity and not another secondary aftershock sequence defining background activity in a focal region of a large earthquake is essential for detection of seismic quiescence prior to the next major event

statistical discrimination of foreshocks from other earthquake clusters summary when earthquake activity begins it may be a foreshock sequence to a larger earthquake a swarm or a simple main shock aftershock sequence this paper is concerned with the conditional probability that it will be foreshock activity of a later larger earthquake depending on the occurrence pattern of some early events in the sequence the earthquake catalogue of the japan meteorological agency 1926 1993 m 24 is decomposed into a large number of clusters in time and space in order to compare statistical features of foreshocks with those of swarms and aftershocks using such a data set ogata utsu katsura 1995 revealed some discriminating features of foreshocks relative to the other types of clusters for example the events closer proximity in time and space and a tendency towards chronologically increasing magnitudes which encouraged us to construct models which forecast the probability of the earthquakes being foreshocks specifically the probability is a function of the history of magnitude differences spans between origin times and distances between epicentres within a cluster for purposes of illustration the models were fitted to the early part of the data 1926 1975 and the validity of the forecasting procedure was checked on data from the later period 1976 1993 two procedures for evaluating the performance of the probability forecast are suggested furthermore for the case where only a single event is available i e either it is the first event in a cluster or an isolated event we also forecast the probability of the event being a foreshock as a function of its geographic location then the validity of the forecast is demonstrated in a similar manner finally making use of the multi element prediction formula we show that the forecasting performance is enhanced by the joint use of the information in the location of the first event and that in the subsequent interevent history in the cluster

discriminating characteristics of tectonic and human induced seismicity we analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human induced and natural seismicity analysis of end member areas known to be dominated by human induced earthquakes the geyser geothermal field in northern california and tautona gold mine in south africa and regular tectonic activity the san jacinto fault zone in southern california and the coso region excluding the coso geothermal field in eastern central california reveals several distinguishing characteristics induced seismicity is shown to have 1 higher rate of background events both absolute and relative to the total rate 2 faster temporal offspring decay 3 higher rate of repeating events 4 larger proportion of small clusters and 5 larger spatial separation between parent and offspring compared to regular tectonic activity these differences also successfully discriminate seismicity within the coso and salton sea geothermal fields in california before and after the expansion of geothermal production during the 1980s online material figures of examined regions earthquake epicenters and joint distributions of the time and space components of the nearest neighbor distance

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

earthquakes near rocky mountain house alberta and their relationship to gas production facilities a 1980 field survey of earthquake activity near rocky mountain house alberta using one digital and six conventional seismographs recorded 146 microearthquakes m 3 4 in 23 days and located 67 of them the located events and probably the unlocated events as well all occurred in a small zone approximately 4 km north south by 4 km east west by 1 km thick centred near 52 12 5 n 115 15 w at a depth of 4 0 km with an uncertainty of 2 km on each of the location coordinates the activity occurred below and or in the strachan d 3a sour gas reservoir which is a devonian aged limestone reef complex in a section of nearly flat lying unfaulted sediments the earthquakes had a composite thrust faulting mechanism with generally north trending intermediate dipping planes in the presence of a regional deviatoric stress field that was horizontally compressive and oriented approximately east west the earthquake activity may be related to the extraction of the natural gas and related fluids from the reservo

on the increase of background seismicity rate during the 1997 1998 umbria marche central italy sequence apparent variation or fluid driven triggering abstract we investigate the temporal evolution of background seismicity rate in the umbria marche sector of the northern apennines that was struck by the 1997 1998 colfiorito seismic sequence specifically we apply the epidemic type aftershock sequences etas model to separate the background seismicity rate from the coseismic triggered rate of earthquake production analyzed data are extracted from the catalogo della sismicita italiana csi1 1 catalog of italian seismicity 1981 2002 which contains for the study area 12 163 events with m l 1 5 the capability of the etas model to match the observed seismicity rate is tested by analyzing the model residuals and by applying two nonparametric statistical tests the runs and the kolmogorov smirnov tests to verify the fit of residuals to poisson hypothesis we first apply the etas model to the seismicity that occurred in the study area during the whole period covered by the csi1 1 catalog our results show that the etas model does not explain the temporal evolution of seismicity in a time interval defined by change points identified from time evolution of residuals and encompassing the colfiorito seismic sequence we therefore restrict our analysis to this period and analyze only those events belonging to the 1997 1998 seismic sequence we again obtain the inadequacy of a stationary etas model with constant background rate to reproduce the temporal pattern of observed seismicity we verify that the failure of the etas model to fit the observed data is caused by the increase of the background seismicity rate associated with the repeated colfiorito mainshocks we interpret the inferred increase of background rate as a consequence of the perturbation to the coseismic stress field caused by fluid flow and or pore pressure relaxation in particular we show that the transient perturbation caused by poroelastic relaxation can explain the temporal increase of background rate that therefore represents a fluid signal in the seismicity pattern

spatiotemporal distribution of oklahoma earthquakes exploring relationships using a nearest neighbor approach determining the spatio temporal characteristics of natural and induced seismic events holds the opportunity to gain new insights into why these events occur linking the seismicity characteristics with other geologic geographic natural or anthropogenic factors could help to identify the causes and suggest mitigation strategies that reduce the risk associated with such events the nearest neighbor approach utilized in this work represents a practical first step toward identifying statistically correlated clusters of recorded earthquake events detailed study of the oklahoma earthquake catalog s inherent errors empirical model parameters and model assumptions is presented we found that the cluster analysis results are stable with respect to empirical parameters e g fractal dimension but were sensitive to epicenter location errors and seismicity rates most critically we show that the patterns in the distribution of earthquake clusters in oklahoma are primarily defined by spatial relationships between events this observation is a stark contrast to california also known for induced seismicity where a comparable cluster distribution is defined by both spatial and temporal interactions between events these results highlight the difficulty in understanding the mechanisms and behavior of induced seismicity but provide insights for future work

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing induced seismicity during december 2011 a swarm of moderate magnitude earthquakes was induced by hydraulic fracturing hf near cardston alberta despite seismological associations linking these two processes the hydrological and tectonic mechanisms involved remain unclear in this study we interpret a 3d reflection seismic survey to delve into the geological factors related to these earthquakes first we document a basement rooted fault on which the earthquake rupture occurred that extends above the targeted reservoir second at the reservoir s stratigraphic level anomalous subcircular features are recognized along the fault and are interpreted as resulting from fault associated karst processes these observations have implications for hf induced seismicity as they suggest hydraulic communication over a large vertical distance reconciling the discrepancy between the culprit well trajectory and earthquake hypocenters we speculate on how these newly identified geological factors could drive the sporadic appearance of induced seismicity and thus be utilized to avoid earthquake hazards

a preliminary statistical model for hydraulic fracture induced seismicity in the western canada sedimentary basin we characterize the statistical relationship between hydraulic fracturing and seismicity in western canada by using the concept of cellular seismicity we determine the regionally averaged probability that hydraulic fracture operations will be associated with m 3 seismicity within a 10 km grid cell this rate is 0 01 to 0 026 at the 95th percentile confidence limit monte carlo simulations confirm that the observed correlations are extremely unlikely 1 to have been obtained by chance proximity to a disposal well and proximity to the swan hills formation which has been suggested as a proxy for basement controlled faults appear to increase the likelihood that hydraulic fracturing will trigger seismicity

crustal heterogeneity highlighted by spatial b value map in the wellington region of new zealand summary we map the b value in the subduction zone of the wellington region new zealand using a high quality earthquake catalogue relocated with a 3 d seismic velocity model consisting of 50 314 events that occurred between 1990 and 2005 in order to investigate heterogeneity in the crust of the overlying plate and in the upper plane of the wadati benioff zone wbz we analyse a series of cross sections perpendicular to the strike of the subduction zone we calculate the b values selecting events with magnitude of completeness 2 4 and depth 65 km and projecting the seismicity within 20 km on each side of the cross sectional planes we observe areas of high b value 1 7 near the plate interface and regions of low b value anomalies are detected both in the wbz in the northwest region below 40 km depth and in the overlying plate in the northern south island at 10 km depth the anomalies are statistically significant based on utsu s p test and the bootstrap method and are not data processing method or parameter dependent we compare the b value distribution with previously determined 3 d distributions of vp vp vs and qp from seismic tomography this comparison suggests that material inhomogeneity caused by fluid filled cracks resulting from dehydration of the subducted slab and subducted sediments is the predominant cause of b value variation in the shallow part of this subduction zone our observations are consistent with a previously proposed conceptual model that fluid distribution in the shallow part of this subduction zone is controlled by the permeability of geological terranes in the overlying plate

hydraulic fracturing volume is associated with induced earthquake productivity in the duvernay play a sharp increase in the frequency of earthquakes near fox creek alberta began in december 2013 in response to hydraulic fracturing using a hydraulic fracturing database we explore relationships between injection parameters and seismicity response we show that induced earthquakes are associated with completions that used larger injection volumes 10 4 to 10 5 cubic meters and that seismic productivity scales linearly with injection volume injection pressure and rate have an insignificant association with seismic response further findings suggest that geological factors play a prominent role in seismic productivity as evidenced by spatial correlations together volume and geological factors account for 96 of the variability in the induced earthquake rate near fox creek this result is quantified by a seismogenic index modified frequency magnitude distribution providing a framework to forecast induced seismicity

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time

complex spatiotemporal evolution of the 2008 mw 4 9 mogul earthquake swarm reno nevada interplay of fluid and faulting after approximately two months of swarm like earthquakes in the mogul neighborhood of west reno nv seismicity rates and event magnitudes increased over several days culminating in an mw 4 9 dextral strike slip earthquake on 26 april 2008 although very shallow the mw 4 9 mainshock had a different sense of slip than locally mapped dip slip surface faults we relocate 7 549 earthquakes calculate 1 082 focal mechanisms and statistically cluster the relocated earthquake catalog to understand the character and interaction of active structures throughout the mogul nv earthquake sequence rapid temporary instrument deployment provides high resolution coverage of microseismicity enabling a detailed analysis of swarm behavior and faulting geometry relocations reveal an internally clustered sequence in which foreshocks evolved on multiple structures surrounding the eventual mainshock rupture the relocated seismicity defines a fault fracture mesh and detailed fault structure from approximately 2 6 km depth on the previously unknown mogul fault that may be an evolving incipient strike slip fault zone the seismicity volume expands before the mainshock consistent with pore pressure diffusion and the aftershock volume is much larger than is typical for an mw 4 9 earthquake we group events into clusters using space time magnitude nearest neighbor distances between events and develop a cluster criterion through randomization of the relocated catalog identified clusters are largely mainshock aftershock sequences without evidence for migration occurring within the diffuse background seismicity the migration rate of the largest foreshock cluster and simultaneous background events is consistent with it having triggered or having been triggered by an aseismic slip event