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

a discontinuum modelling approach for investigation of longwall top coal caving mechanisms abstract this paper presents a discontinuum modelling approach to investigate longwall top coal caving ltcc behaviour including stress distribution coal and rock failures top coal caving and roof strata rupture and to analyse the impact of overburden movement on top coal caving the current model ia successful in using plastic material in a discontinuum code for intact rocks the model scale is large enough to capture the critical features of ltcc including steady state caving of top coal and repeatable periodic weighting of roof strata the applicability of the numerical model was assessed by calibration with field measurements obtained from a longwall mine site the numerical study found that the stress distribution caused by ltcc mining is in general similar to that caused by conventional longwall mining top coal predominantly fails in shear whereas roof rock mostly fails in tension top coal starts to cave in stress caving while main roof strata first rupture in crushing mode and roof strata weightings periodically increase and decrease top coal cavability the findings of this study should assist engineers in better understanding fundamental rock mechanics associated with ltcc identifying key geotechnical parameters dominating caving behaviour and managing top coal productivity and mine safety involved in ltcc operation

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

flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments thibault candela 1 2 emily e brodsky 2 chris marone 1 derek elsworth 1 1 dept geosciences penn state univ university park pa united states 2 dept earth sciences uc santa cruz santa cruz ca united states

a new observation of dynamically triggered regional seismicity earthquakes in greece following the august 1999 izmit turkey earthquake the m w 7 4 izmit turkey earthquake triggered widespread regional seismicity in greece over a study region extending from 400 km to nearly 1000 km away from the epicenter small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger the increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95 level unlike the previous example of distant triggering during the landers earthquake the activated seismicity occurred entirely in non volcanic areas the greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for imperial valley we speculate that dynamic triggering on a regional scale results in countrywide episodes of increased seismicity or superswarms in regions with low triggering thresholds such as greece

correlation of geoid and depth anomalies over the agulhas plateau abstract correlations of geoid anomalies with bathymetry are an important source of information in the compensation of submarine features we have used this technique to constrain models of the density structure of the lithosphere beneath the agulhas plateau south of africa we explain the correlation in terms of a two layer airy isostatic model the plateau is compensated in part by crustal thickening and in part by an underlying layer of anomalously low density mantle the anomalous mantle layer extends to a depth of about 50 km and has a density 1 2 lower than normal mantle crustal thickening alone is insufficient to explain the observed correlation between bathymetry and the geoid the anomalous mantle region may be the source for the excessive volumes of basalt which have intruded and thickened the crust of the plateau there is strong evidence that depleted mantle rock is lighter than undepleted mantle rock a similar model may hold for the walvis ridge

cavability control by hydraulic fracturing for top coal caving in hard thick coal seams abstract insufficient breaking and falling of top coal is a technical problem in hard thick or super thick coal seams during top coal mining based on top coal weakening by hydraulic fracturing and main roof hydraulic fracturing to induce coal crushing a method of improving the top coal cavability by top coal and roof hydraulic fracturing is proposed more specifically linear multi hole hydraulic fracturing and deep hole retreating hydraulic fracturing methods for top coal control in top coal caving of hard thick coal seams are proposed a set of high pressure 60 mpa hydraulic fracturing devices was developed the hydraulic fracturing technology and devices were applied in the 3 coal seam in the yulin district where the coal is hard the occurrence depth is shallow and the ground pressure is not extreme the top coal begins to fall when the working face advances 20 m from the setup room and begins to cave normally when the working face advances 40 m after the top coal begins to cave normally the recovery ratio in shallow hard thick coal seam conditions reaches over 80 reaching the average level of top coal caving faces these methods ensure efficient and safe top coal caving in the first coal face by control of the top coal and roof without explosive blasting compared to traditional methods of weakening the top coal and roof by blasting hydraulic fracturing is simpler and safer and requires less work and lower costs 10 of the cost of explosive blasting

dynamic triggering of microseismicity in southwest china following the 2004 sumatra and 2012 indian ocean earthquakes abstract we conduct a systematic detection of microseismicity around yunnan province southwest china following the 2004 mw9 1 sumatra and 2012 mw8 6 indian ocean earthquakes based on seismicity analysis on china earthquake network center cenc catalog and spectral analysis of continuous waveforms we find clear evidence of triggered seismicity in yunnan immediately after the 2004 mainshock including a magnitude 4 8 earthquake near tengchong volcanic region in comparison we do not find clear evidence of instantaneous triggering following the 2012 mainshock we further apply a matched filter technique to detect microearthquakes in tengchong volcanic region 15 days before and 15 days after the 2012 mainshock the seismicity rate remains stable immediately after the 2012 mainshock and increases in the next few days indicating a possible delayed triggering although similar changes can be seen at other times long before and after the mainshock in addition we find possible evidence of remote triggering near the city of yibin in southern sichuan province southwest china near the sites with ongoing shale gas development we also examine other magnitude 8 earthquakes from the sumatra region and do not find any additional evidence of dynamic triggering around yunnan we suggest that the absolute value of dynamic stress change is the most important factor to explain why the 2004 sumatra event triggered a widespread seismicity rate increase around yunnan while other great events around sumatra did not

earthquake triggering at alaskan volcanoes following the 3 november 2002 denali fault earthquake the 3 november 2002 m w 7 9 denali fault earthquake provided an excellent opportunity to investigate triggered earthquakes at alaskan volcanoes the alaska volcano observatory operates short period seismic networks on 24 historically active volcanoes in alaska 247 2159 km distant from the mainshock epicenter we searched for evidence of triggered seismicity by examining the unfiltered waveforms for all stations in each volcano network for 1 hr after the m w 7 9 arrival time at each network and for significant increases in located earthquakes in the hours after the mainshock we found compelling evidence for triggering only at the katmai volcanic cluster kvc 720 755 km southwest of the epicenter where small earthquakes with distinct p and s arrivals appeared within the mainshock coda at one station and a small increase in located earthquakes occurred for several hours after the mainshock peak dynamic stresses of 0 1 mpa at augustine volcano 560 km southwest of the epicenter are significantly lower than those recorded in yellowstone and utah 3000 km southeast of the epicenter suggesting that strong directivity effects were at least partly responsible for the lack of triggering at alaskan volcanoes we describe other incidents of earthquake induced triggering in the kvc and outline a qualitative magnitude distance dependent triggering threshold we argue that triggering results from the perturbation of magmatic hydrothermal systems in the kvc and suggest that the comparative lack of triggering at other alaskan volcanoes could be a result of differences in the nature of magmatic hydrothermal systems

absolute and relative plate motions and hypotheses on the origin of five aseismic ridges in the indian ocean abstract paleopositions of the african indian and antarctic plates are used as an independant set of data to test various hypotheses derived from geophysical data on the origin emplacement mechanism and evolution of five aseismic structures of the western and southern indian ocean crozet and kerguelen plateaus marion dufresne lena and ob seamount chain madagascar and mascarene ridges except for a continental fragment of very limited extent bearing the seychelles islands these structures together with the madagascar and mascarene ridges are probably due to anomalous volcanic episodes at or near active plate boundaries rather than to intraplate emplacement their creation processes are therefore mainly related to the relative motions between the antarctic african and indian plates the volcanic episodes are synchronous with major changes in the relative motions between these plates and thus substantiate the role played by frequent irregularities in the kinematic pattern of the western and southern indian ocean such as ridge jumps asymmetric spreading and rapid variations in spreading velocity or direction finally we think that thermal anomalies located not far from active spreading boundaries may have played a role in the physical processes creating the aseismic ridges

detecting remotely triggered microseismicity around changbaishan volcano following nuclear explosions in north korea and large distant earthquakes around the world we conduct a systematic survey on locally triggered earthquakes by large distant earthquakes in changbaishan volcano an active intraplate volcano on the border between china and north korea we examine waveforms of distant earthquakes recorded at broadband station changbaishan cbs near the volcano with estimated dynamic stresses over 5 kpa between 2000 and 2016 out of 26 selected distant earthquakes three of them show positive evidence of triggering during large amplitude surface waves the earthquakes that had positive or possible evidences of triggering generated larger long period surface waves indicating that they are more efficient in triggering microseismicity in addition since 2006 north korea has conducted five underground nuclear explosion une tests only 140 km away from changbaishan volcano by systematically examining waveforms of these unes recorded at station cbs we find that none of them have triggered microearthquakes in changbaishan volcano

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

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

analysis of satellite gravity and bathymetry data over ninety east ridge variation in the compensation mechanism and implication for emplacement process 1 we investigate the mode of compensation emplacement history and deep density structure of the ninety east ridge indian ocean using spectral analyses and forward modeling of satellite gravity and bathymetry data we find that the northern 0 10 n and the southern 20 30 s parts of the ridge are flexurally compensated with an effective elastic thickness 15 km whereas the central part 0 20 s is locally compensated furthermore we find that for a part of central block 10 20 s over osborn knoll the compensation depth is unreasonably very high 30 40 km therefore we favor a model with subsurface loading and interpret this to be due to underplating of mafic material at the base of the crust a hypothesis that is supported by seismic results and direct modeling of gravity data along some profiles these results suggest that the northern and southern parts of ninety east ridge were emplaced off to a ridge axis compared to the central one which might have been emplaced on or near a spreading center locally compensated large topography thick underplated crust in the central part near osborn knoll might result from an interaction of a hot spot with the extinct wharton spreading ridge

dynamic triggering of microearthquakes in three geothermal volcanic regions of california geothermal volcanic regions are most susceptible to local earthquake triggering by regional and remote earthquakes transient stresses caused by surface waves of these earthquakes can activate critically stressed faults though earthquakes can be triggered in geothermal volcanic regions it is less understood how these regions differ in their triggering responses to distant earthquakes we conduct a systematic survey of local earthquakes triggered by distant earthquakes in three geothermal volcanic regions of california long valley caldera coso geothermal field and geysers geothermal field we examine waveforms of distant earthquakes with magnitudes 5 5 occurring between 2000 and 2012 and compute statistics to confirm the significance of our findings we find that long valley coso and geysers vary in triggering frequency 2 0 3 8 and 6 8 in the 12 year period respectively and when compared to the triggering of deep tectonic tremors along the parkfield cholame section of san andreas fault 9 2 in the 12 year period stress triggering thresholds vary among the regions with long valley having the highest of 5 kpa and 1 kpa for the other regions because dynamic stresses from distant earthquakes are similar in these three regions the varying triggering behavior likely reflects faults having a tendency to be at or near failure this is compatible with geysers having a higher a value in the gutenberg richter relationship and higher geothermal productivity than the other two regions the observation of more frequent triggering of tremor than microearthquakes is consistent with recent laboratory studies on increasing triggerability with lower effective stress

the japan trench and its juncture with the kuril trench cruise results of the kaiko project leg 3 this paper presents the results of a detailed survey combining seabeam mapping gravity and geomagnetic measurements as well as single channel seismic reflection observations in the japan trench and the juncture with the kuril trench during the french japanese kaiko project northern sector of the leg 3 on the r v jean charcot the main data acquired during the cruise such as the seabeam maps magnetic anomalies pattern and preliminary interpretations are discussed these new data cover an area of 18 000 km2 and provide for the first time a detailed three dimensional image of the japan trench combined with the previous results the data indicate new structural interpretations a comparative study of seabeam morphology single channel and reprocessed multichannel records lead to the conclusion that along the northern japan trench there is little evidence of accretion but instead a tectonic erosion of the overriding plate the tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the japan trench axis which is a direct consequence of the downward flexure of the pacific plate in addition to these new faults ancient normal faults trending parallel to the n65 oceanic magnetic anomalies and oblique to the japan trench axis are reactivated so that two directions of normal faulting are observed seaward of the japan trench only one direction of faulting is observed seaward of the kuril trench because of the parallelism between the trench axis and the magnetic anomalies the convergent front of the kuril trench is offset left laterally by 20 km relative to those of the japan trench this transform fault and the lower slope of the southernmost kuril trench are represented by very steep scarps more than 2 km high slightly south of the juncture the erimo seamount riding on the pacific plate is now entering the subduction zone it has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches is it due to the collision of an already subducted chain of seamounts or does it correspond to one of the failure lines of the america eurasia plate boundary

non self similar source property for microforeshocks of the 2014 mw 6 2 northern nagano central japan earthquake foreshocks are considered a part of the preparation process for large earthquakes and as such can provide important constraints on earthquake generation we examine the characteristics of the four day long foreshock sequence of the 2014 northern nagano earthquake mw 6 2 using seismograms recorded by a dense seismic observation network including data from a deep borehole closest to the foreshock region the improved earthquake catalog shows a slow speed migration of the sequence toward the mainshock hypocenter implying possible slow slip transients which should have caused stress loading at the mainshock hypocenter analysis of source spectra reveals that foreshocks for mw 1 5 display a weaker dependence of corner frequency on magnitude than expected for self similar scaling suggesting that these micro foreshocks can be regarded as small low frequency earthquakes so far we might have missed the expected weak low frequency pre seismic signals because they emerge only below a certain magnitude and are generally embedded in background noise

an ultrasonic based method for longwall top coal cavability assessment abstract longwall top coal caving ltcc is widely employed in the underground mining of thick coal seams the technique divides a thick coal seam into a lower and an upper section the bottom coal is sheared by a cutting head and transported by a conveyor in front of the support while the top coal fails and caves under mining pressure transported by a conveyor at the rear of the support in an ltcc panel accurate assessment of top coal cavability is critical to the design of mining parameters required to achieve continuous caving of top coal in the present paper an integrated detection system in which fracture development and ultrasonic wave velocity are used to characterize top coal cavability is introduced the cavability is predicted conveniently due to ease of access of the ultrasonic wave velocity in the top coal accordingly an ultrasonic model is established and coupled to the mechanical model previously proposed by the authors to simulate the evolution of the wave velocity in stressed coal the mechanical ultrasonic coupling model is validated by comparison against experimental data and further extended to evaluate top coal cavability in dongzhouyao mine with a finite difference type code the predictions including the excavation damaged zone roof weighting interval stress distribution stress rotation and ultrasonic wave velocity evolution are consistent with the field measurements with the proposed model the influence provided by hydraulic fracturing on top coal cavability is investigated by conducting the finite difference type modeling

evolution of the southwest indian ridge from the late cretaceous anomaly 34 to the middle eocene anomaly 20 abstract the determination of the motion of antarctica relative to africa is particularly important when considering the breakup of gondwana two models have been proposed that describe the pattern of seafloor spreading between africa and antarctica during the late cretaceous starting at chron 34 84 ma through to the middle eocene chron 20 46 ma in the first model the motion of antarctica relative to africa can be simply described by a rotation about a single pole of rotation in the second model which we favor the relative motion of antarctica and africa is more complex and a major change in spreading direction between chron 32 74 ma and chron 24 56 ma times is required in this paper we present ten plate tectonic reconstructions of the southwest indian ridge that were produced using a new compilation of magnetic bathymetric and satellite altimetry data in combination with interactive computer graphics these reconstructions illustrate that spreading directions started to change at chron 32 74 ma between chrons 31 and 28 69 64 ma spreading was very slow

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

remotely triggered microearthquakes and tremor in central california following the 2010 mw 8 8 chile earthquake 1 we examine remotely triggered microearthquakes and tectonic tremor in central california following the 2010 mw 8 8 chile earthquake several microearthquakes near the coso geothermal field were apparently triggered with the largest earthquake ml 3 5 occurring during the large amplitude love surface waves the chile mainshock also triggered numerous tremor bursts near the parkfield cholame section of the san andreas fault saf the locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from coso but can be identified by applying high pass or matched filters both triggered tremor along the saf and the ml 3 5 earthquake in coso are consistent with frictional failure at different depths on critically stressed faults under the coulomb failure criteria the triggered tremor however appears to be more phase correlated with the surface waves than the triggered earthquakes likely reflecting differences in constitutive properties between the brittle seismogenic crust and the underlying lower crust

numerical investigation of the development of the excavation damaged zone around a deep polymetallic ore mine abstract this paper deals with the development of a non linear constitutive model of a rock mass and its application to predict the extension of the excavation damaged zone edz around openings a comparison of the model results with the simulations of triaxial compression tests shows a good agreement between predictions and theoretical values of peak and residual strengths as well as a good reproduction of the transition between brittle failure and ductile response the relevance of the proposed model to evaluate the potential failure around stopes of the garpenberg mine was examined the comparison of the results proved satisfactory and highlighted the interest of considering a more realistic mechanical behavior of hard rock masses in rock engineering compared with the elastic perfectly plastic models generally used in numerical modeling of underground deep mines finally a 3d simulation of the complete mine geometry was carried out in order to model the first phases of stope mining operations the predicted stresses were compared with the continuous measurements of induced in situ stresses recorded by stress cells at different points around the stope the predictions of the proposed constitutive model provided a much better agreement with stress measurements than those obtained with elastic perfectly plastic models

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

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

nonlinear soil amplification its corroboration in taiwan nonlinear ground response at two strong motion arrays in taiwan is studied using the spectral ratio technique at the smart1 array we calculate the frequency dependent soil amplification functions as a ratio of the spectra at alluvium to rock sites and study their dependence on the excitation level hor izontal components of shear waves are considered we compare 1 the average spectral ratios on weak and strong motions 2 the ratios for the mainshocks and aftershocks and 3 the ratios for the strong shear waves and their coda at the smart1 array weak motions have a peak horizontal acceleration pha less than 30 gal strong motions are in the range of 100 to 267 gal comparison of the average weak and strong motion spectral ratios shows a significant deamplification of strong motion between 2 and 9 hz exceeding the error margin estimated by the standard deviations the maximum deamplifi cation occurs at approximately 6 5 hz where the average weak motion ampli fication is 2 9 versus 0 40 in the strong motion a similar pattern is exhibited by the ratios calculated for the mainshocks and the aftershocks as well as for the shear waves and their coda the spectral ratio calculated from a single re alization of coda is identical to the average ratio obtained from many small earthquakes at the smart2 we analyze spectral ratios between the stations on pleistocene terrace deposits and recent alluvium which characterize the rel ative response at these two types of sediments weak motion is pha less than 13 gal while strong motion extends from 100 to 295 gal strong motion spec tral ratios between terrace and alluvial sites are consistently reduced in the fre quency range from 1 to 10 hz compared with the weak motion this effect is insensitive to the variation in distance between stations from 7 9 to 11 4 km as well as the azimuthal change of up to 80 in the station pair strike we attribute the observed discrepancies between weak and strong motion ampli fications to the differential nonlinear response occurring at terrace and alluvial sites our results document a significant nonlinear ground response at both ar rays

the absence of remotely triggered seismicity in japan remote dynamic triggering occurred in the western united states and greece following the following the denali hector mine landers and izmit main shocks in seismically active largely geothermal areas that experienced shaking from the mainshock typically exceeding 0 2 cm sec because triggered earthquakes are small often below mw 2 investigations of whether remote triggering is a generally occurring phenomena must be concentrated in well instrumented locations as a seismically active geothermal well instrumented location japan constitutes an ideal location for such study we systematically examine whether remote dynamic trig gering occurs following mainshocks in japan producing amplitudes in the study region above 0 2 cm sec at distances greater than two estimated fault lengths from 1998 to 2004 we use both catalog data and filtered waveforms to search for seis micity increases one significant regional increase follows a mw 7 6 mainshock in march 2000 largely due to a volcanic swarm that began the day before and increased in intensity in the following days two localized increases in cataloged seismicity occur in kyushu which is the only area in the study region with onshore tectonic extension two factors possibly inhibit regional triggering in japan 1 compres sional tectonics and 2 the frequent occurrence of large mainshocks the ambient seismicity in japan combined with the lack of observable widespread triggering ren ders rate state friction and stress corrosion to be improbable triggering mechanisms fracture unclogging as a triggering mechanism is consistent with the observations

high frequency identification of non volcanic tremor triggered by regional earthquakes 1 subsequent to the discovery of ambient non volcanic tremor activity along the parkfield cholame section of the san andreas fault in central california triggered tremors associated with the surface waves of large teleseismic earthquakes have been recognized however no evidence of triggered tremors from regional earthquakes has previously been found either here or in other tremor regions by systematically filtering seismograms to higher frequencies i e above 20 hz associated with 99 regional m5 earthquakes since 2001 we identify four regional earthquakes that have triggered tremors in central california significant high frequency energy is also observed in previously identified teleseismically triggered and ambient tremors suggesting a common mechanism we find that long period and large amplitude surface waves from both regional and teleseismic events have a greater potential of triggering tremor in the same region and that the inferred minimum triggering dynamic stress is 1 kpa

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

seismicity along st lawrence paleorift faults overprinted by a meteorite impact structure in charlevoix quebec eastern canada abstract the charlevoix seismic zone csz in quebec has the highest number of earthquakes in eastern canada with cataloged events diffusely distributed between the st lawrence paleorift faults in this study we relocate 1242 out of 1639 earthquakes in the csz from 1988 to 2010 using double difference relocations with phase arrivals from manual picks and waveform cross correlations and requiring a strict set of quality control criteria our results show a diffuse distribution of earthquakes beneath the st lawrence river within a meteorite impact structure and clear lineations of event hypocenters outside the inner boundary of the impact structure the diffuse seismicity distribution coupled with a lower cumulative seismic moment within the impact structure despite a higher number of events suggests the presence of highly fractured crust and weakened pre existing faults a lack of m n 4 0 earthquakes and a wide variation of focal mechanism p axis orientations also provide evidence for weakened pre existing faults relocated earthquakes beneath the north shore of the st lawrence river illuminate a broad southeast trending linear structure suggesting the geometry of the gouffre northwest river fault a paucity of seismicity between the north shore and the river may correspond to fault controlled basins of unconsolidated sediments at the surface and volumes of high seismic velocity material at midcrustal depths online material earthquake catalogs

elastic wave stimulation of oil reservoirs promising eor technology roughly 60 of oil resources in the world remains unproduced partially due to limitations in existing enhanced recovery methods this translates to approximately half a billion tons of oil left behind annually anecdotal production data as well as historic field and laboratory experiments have shown that low amplitude seismic waves in the frequency range of roughly 1 500 hz can enhance oil mobility and total recovery in mature reservoirs it is estimated that to date various types of seismic and acoustic oilfield stimulation activities have produced an additional 11 million tons of oil in the former soviet union alone unfortunately field tests with different seismic sources have often yielded mixed or inconclusive results in some cases seismic stimulation increased production rates by 50 or more but in other cases production was unchanged or actually declined so far laboratory and field experiments have not been sufficiently comprehensive to define the physical conditions under which stress wave stimulation is most effective an exhaustive review of observations and research on this subject from the 1950s up through 1992 was published by beresnev and johnson 1994 the paper summarizes the important early research including a large body of work published only in russian the major conclusion of the beresnev and johnson review was that the seismic stimulation method has produced promising results however further testing and understanding of the mechanisms are necessary this statement has motivated numerous sponsored research projects and industry evaluation programs over the last 10 years particularly in the united states efforts in russia have also been greatly expanded field tests are yielding more promising results as experimental controls and measurements are improved but questions remain about how to predict optimum stimulation parameters for a particular reservoir and what the statistical significance is of production changes observed during stimulation treatments laboratory experiments continue to

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

geoid height versus topography for oceanic plateaus and swells oceanic plateaus and swells are a major component of the seafloor topography yet they remain among the most poorly understood features this is especially true of the oceanic plateaus which show large variations in crustal thickness to determine the depth and mode of compensation for 53 of the largest plateaus and swells we analyzed the relationship between geoid height and topography in polygonal areas containing each feature both geoid height and topography were first band pass filtered 400 km i 4000 km to isolate the signal associated with local compensation from flexural and deep mantle signals the ratio of geoid height to topography was then determined by fitting a straight line to the data except for nine of the smaller features there is a high correlation between geoid height and topography that is positive in accordance with airy and thermal compensation models eighteen features have high geoid topography ratios that cannot be explained by the airy compensation model of crustal thickening these features thermal swells are partially supported by thermal buoyancy forces in the lower half of the lithosphere the ratios are highest for active hot spot swells and decay with the thermal age of the swell to values consistent with airy compensation of the enduring volcanic edifice the remaining features plateaus have lower geoid topography ratios in agreement with the airy compensation model those plateaus with average height greater than 4 km are thought to be continental fragments the shorter plateaus tend to be volcanic features modified continental plateaus presumably small fragments of extended and intruded continental margin crust cluster around heights of n3 km overlapping the range associated with oceanic plateaus since the origin of many plateaus is poorly understood this global geoid topography analysis provides a new technique for comparing the deep structure of oceanic plateaus and swells

precise location of unsurveyed seamounts in the austral archipelago area using seasat data summary seasat altimetric geoid data are used to detect uncharted seamounts in the austral archipelago area the various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location these parameters are the shape of the seamount its density the crustal model the effective elastic thickness of the lithosphere and the distance between the seamount and sub satellite tracks respectively the results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks it is possible to locate it with good confidence and to give an estimation of its height if the correct elastic thickness is assumed the precision on the location is order 15 km ten previously unsurveyed seamounts have been located in the austral archipelago it appears that they are emplaced along two well defined azimuths n 1 10 e and n 150 e and that two parallel distinct volcanic chains form the austral archipelago

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

linear pressurization method for determining hydraulic permeability and specific storage of a rock sample summary we studied the methodology and applicability of linear pressurization for determining simultaneously hydraulic permeability and specific storage of a rock sample we analytically solved the governing equation for 1 d pressure diffusion through a homogenous isotropic cylindrical rock specimen located between a downstream and an upstream reservoir considering linear pressurization of the upstream fluid as the boundary condition the solution consists of a transient and a steady state for which both differential pressure between the two reservoirs and injection rate at the upstream reservoir assume constant values since the steady state differential pressure is linearly proportional to the compressive storage of the downstream reservoir tests conducted with a systematic variation of the size of the downstream reservoir permit determining permeability and specific storage from the intercept and slope of the linear relationship alternatively simultaneous measurement of differential pressure and fluid injection rate at steady state conditions provides a basis for calculation of the hydraulic properties as previously presented for linear injection experiments were performed on fontainebleau sandstone samples to document the feasibility of the method the determined storage capacity value is used to calculate various poroelastic parameters such as bulk and pore space compressibility skempton and the effective pressure coefficient

remote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions based on a multiple station matched filter approachremote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

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

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

an integrated geophysical study east of the southern chagos laccadive ridge complex central indian ocean basin implications for the rodriguez triple junction dynamics in the late cretaceous abstract the central indian ocean basin east of the southern chagos laccadive ridge complex has evolved due to seafloor spreading in the n s direction since the late cretaceous the trace of the rodriguez triple junction rtj has been inferred in this basin but its exact location and dynamics prior to c29o are not known about 20 000 km of total magnetic intensity data along with satellite gravity mosaic were used to understand the dynamics of the rtj in the late cretaceous synthetic seafloor spreading models endorse the presence of late cretaceous to early palaeogene magnetic anomalies c34y to c24o in the study area half spreading rates are initially low 32 mm yr between c34y to c33y and increase up to 78 mm yr by c28y thereafter a decreasing trend is seen 57 mm yr towards the west in the study area higher spreading rates 120 mm yr between c33y and c32ay and distorted anomalies between chrons c32ay and c30y are observed detailed geophysical analysis suggests that the higher spreading rates are due to the presence of transferred crust and the distorted anomalies are caused by the presence of fragmented tectonic blocks depicting microplate formation and rotation plate reconstruction models suggest that the rtj at c34y time lay southwest of comorin ridge which coincided with the northern edge of the conrad rise until c33y the rtj left a linear trace parallel to the fracture zone trend on both the indian and antarctic plates while it gradually moved eastwards on the african plate the rtj migrated westwards until c31y causing the transfer of a considerable amount of crust from the african plate to both the indian and antarctic plates thereafter the rtj rapidly reversed its migration direction towards the east until c29o causing the formation and rotation of a microplate on the indian plate and lengthening of the southwest indian ridge the present study suggests that this episodic migration of the rtj may be due to ridge propagation under the influence of the marion hotspot which was in the vicinity during that period this rtj migration resulted in microplate formation lithospheric transfer and thickened lithosphere similar to the inferences made at many triple junctions in the pacific ocean thus the origin of anomalous structures such as the crozet bank may be related to triple junction dynamics under the influence of marion hotspot further the counter clockwise rotation of the southwest indian ridge between c33y and c29y may have a causal link with the formation and rotation of the microplate which occurred during the same period the present study thus facilitated the inference of the dynamics of the rtj trace between c34y and c29o on the three plates

modelling of the gravity effects of flexurally compensating thin layers under the afanasy nikitin seamount abstract modelling of the gravity data over the afanasy nikitin seamount is carried out to estimate the variation of the crustal and flexural parameters along the strike of the seamount it is inferred that the compensation of the seamount is due to both the bending of a very thin elastic plate and the occurence of low density material at depth the elastic plate thickness is inferred as 2 km and does not change significantly along the strike of the seamount furthermore the crustal thicknesses range within 12 22 km not showing any systematic variation along the strike of the seamount it is suggested that the afanasy nikitin seamount was emplaced on thin and weak lithosphere very near to a slowly migrating ridge which trapped a hot rising plume resulting in a higher crustal thickness

dynamic stresses coulomb failure and remote triggering corrected abstract dynamic stresses associated with crustal surface waves with 15 30 s periods and peak amplitudes

the geoid roughness a scanner for isostatic processes in oceanic areas maps of bandpass filtered geoid height anomalies deduced from seasat altimetry data which are referred to as geoid roughness maps are contoured over the indian ocean both in the short 30 90 km bandwith and in an intermediate one 90 230 km interpretation of these maps essentially provides a guide as to where further detailed studies should be conducted the roughness maps can thus be used as a fast and efficient scanner for isostatic processes at the scale of an entire ocean additionally roughness maps provide a qualitative appraisal of the emplacement mechanisms of intraplate features this can for example be appreciated by comparing the interpretations of the maps with the results of admittance studies over such features

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

relative positions of africa and antarctica in the upper cretaceous evidence for non stationary behaviour of fracture zones abstract new bathymetric and magnetic data have been collected in the enderby basin southern indian ocean during cruise md34 of the n o marion dufresne january february 1983 one can identify in this basin oceanic crust created along the same portion of the southwest indian ridge as the crust of the mozambique basin two sets of magnetic lineations with different amplitude split by a large offset fracture zone are localized in each basin and enable us to obtain accurate reconstructions of the africa antarctica plate boundary at the time of anomalies 34 33 and 32 the data west of prince edward fracture zone are taken into account to adjust the parameters of rotation these reconstructions of isochrons allow us to discuss the evolution of the geometry of accretionary plate boundaries and to emphasize the unstable behaviour of fractures zones in particular we give evidence for an important change in the spreading direction along prince edward fracture zone which demonstrates that stability of a pole of rotation is not guarantueed by major offset fracture zones

isostatic response of the lithosphere beneath the mozambique ridge sw indian ocean and geodynamic implications summary the sw indian ocean is characterized by the presence of several aseismic features the mozambique ridge an elongated feature lying roughly parallel to the se coast of africa is by far the least known of those structures mainly due to the scarcity of marine data to date the crustal nature and the origin of the ridge are still controversial points since knowledge of the origin of the mozambique ridge is important for a better understanding of the evolution of the sw indian ocean the isostatic response of the lithosphere beneath the ridge is analysed in order to characterize its effective elastic thickness and the emplacement process of the feature two different approaches are applied the direct computation of the geoid anomaly over the ridge by means of a 2 5 dimensional method and the computation of the admittances between the bathymetry and both the geoid and gravity anomalies both approaches point to a local isostatic response of the lithosphere the crustal thickness beneath the mozambique ridge ranges from 17 to 30 km and the average density from 2 78 to 2 7 103 kg m 3 varying with locality in good agreement with the few existing refraction profiles based on our results on the geochemical similarity between the basalts cored at the dsdp site 249 and the mor basalts erlank reid 1974 thompson et al 1982 and on the present knowledge of the sw indian ocean kinematics martin hartnady 1986 we propose an on ridge origin for the mozambique ridge the ridge would have been formed by the anomalous activity of a spreading axis linking the northern mozambique and the transkei basins accretion centres between m10 and m2 times at the m2 epoch a ridge jump event would have caused the spreading to cease the astrid ridge a poorly known aseismic structure lying close to the coast of antarctica near 15 e may be the antarctic counterpart of the mozambique ridge formed by the same accretionary phenomenon the two ridges breaking apart at m2 time due to the ridge jump event however any admittance computation at such high latitudes is impossible at present due to the very poor quality of both bathymetry and altimetry and so this hypothesis cannot be verified

seismic triggering by rectified diffusion in geothermal systems widespread seismicity was triggered by the june 28 1992 landers california earthquake at a rate which was maximum immediately after passage of the exciting seismic waves rectified diffusion of vapor from hydrothermal liquids and magma into bubbles oscillating in an earthquake can increase the local pore pressure to seismically significant levels within the duration of the earthquake in a hydrothermal system modeled as a two component h 2o co 2 fluid in porous rock the pressure initially increases linearly with time the rate of pressure buildup depends sensitively on the mean bubble radius and is large for small bubbles the diffusion induced pressure is relaxed by percolation and resorption of vapor into the liquid solution the induced seismicity itself also relieves stress values of parameters used in the present calculations give results consistent with observations of triggered seismicity at long valley caldera after the landers earthquake for one representative condition at 250 c and 5 6 km depth oscillating strain acting on 10 m diameter bubbles increases pore pressure at the rate of 151 pa s resulting in a pressure increase of 12 kpa in the 80 s duration of the landers earthquake the elevated pressure induced by a single 26 m diameter cloud of bubbles in saturated rock relaxes by percolation through soil of 0 2 mdarcy permeability in 53 6 hours observations of earthquake swarms at other locations suggest that self induced buildup of pore pressure by rectified diffusion can provide a positive feedback mechanism for amplifying seismicity

potential for earthquake triggering from transient deformations 1 we report on laboratory experiments in which stick slipping shear surfaces are subject to transient stressing to simulate earthquake triggering by seismic waves granular layers and bare granite surfaces were sheared in a servo controlled deformation apparatus in double direct shear the seismic waves from an earthquake and tectonic load were simulated by superimposing a loading rate sinusoid on a constant shear loading rate the dependence of triggered stick slip failure on fault stress state and architecture was analyzed fault architecture was evaluated by varying gouge layer thickness 2 6 mm and studying bare granite surfaces we compare the shortened recurrence times for faults under transient loading conditions to the consistent recurrence intervals under constant loading rate our results imply that triggering depends on oscillation amplitude and frequency as well as properties of the fault larger amplitude dynamic stresses reduce stick slip recurrence intervals for granular layers whereas failure times for granite surfaces are uncorrelated with oscillation amplitude granular layers have shorter recurrence rates at higher frequency whereas the recurrence intervals of granite surfaces are lengthened or unaffected by high frequency oscillations higher frequencies can inhibit failure when fault slip exceeds a critical distance dc prior to peak velocity and encourages failure if dc is achieved postpeak velocity increasing velocity temporarily strengthens faults whereas velocity reduction further weakens and promotes failure as predicted by the rate and state friction laws our results may explain variations in earthquake triggering thresholds and imply that high frequency thresholds may not be constant as has been previously proposed

origin and compensation of chagos laccadive ridge indian ocean from admittance analysis of gravity and bathymetry data abstract the chagos laccadive ridge clr is a prominent aseismic volcanic ridge in the northern indian ocean the ridge together with the southern mascarene plateau smp to which it is genetically related is considered as a volcanic trace of the reunion hotspot we have examined the isostatic compensation of the clr through transfer function analysis of gravity and bathymetry data along seven profiles the analysis suggests that the clr is compensated locally with an airy crustal thickness t c of 20 km the rather low elastic plate thickness t e of about 4 km implies that the volcanism of the ridge took place very near a spreading centre the proximity of the chagos fracture zone indicates that the emplacement was probably near a spreading centre transform junction

numerical modeling of influence parameters in cavabililty of rock mass in block caving mines abstract the prediction of rock mass cavability is needed in the design of block caves to estimate the undercut size required to achieve continuous caving the cavability of the rock mass will control mine design and economic issues for a given geological environment and is a fundamental issue in establishing a successful block caving mine with recent interest in applying caving techniques to stronger rock masses the reliable prediction of rock mass cavability is becoming increasingly important the two most universally applied methods for cavability prediction are the empirical stability graph approach developed by laubscher and numerical methods empirical approaches developed to predict rock mass cavability have been based on the assessment of rock mass conditions using recognized rock mass classification schemes rock mass classification is the first stage in empirical approaches to predicting rock mass cavability the numerical approaches also commonly utilize rock mass classification schemes to assign rock mass properties and apply failure criteria within the models a reliable prediction of cavability of rock mass depends on the accurate identification of the influence parameters in rock mass cavability the cavability of a rock mass is based on many factors such as natural and induced factors affect the caving performance in this paper the effect of seven parameters the compressive strength of intact rock ucs joint orientation joint persistence joint density p32 joint friction confined stress and hydraulic radius hr is investigated using numerical technique named the synthetic rock mass srm the srm is a numerical modeling technique which combines the bonded particle model pfc for intact rock and discrete fracture network dfn simulation to assess the influence of each parameter in numerical modeling the value of one parameter is changing while the values of other six parameters are fixed it is found that in situ stress and hydraulic radius are the most effective parameters in cavability of rock mass in block caving mines

emplacement of the marion dufresne lena and ob seamounts south indian ocean from a study of isostasy abstract three gravity and topographic profiles over the ob lena and marion dufresne seamount chain southwest indian ocean are analysed in terms of the isostatic response of the lithosphere these seamounts are regionally supported by both the bending of an elastic plate which varies significantly in thickness along the chain and by the presence of light material at depth this variation is correlated with the age of the lithosphere at the time of loading by the seamounts which varies between 6 and 40 m y these ages when combined with the identification of magnetic anomalies yield absolute emplacement ages for each seamount these results favour a creation of the marion dufresne and lena seamounts near the active southeast indian ridge during the upper cretaceous their emplacement due to intraplate volcanism as the result of the displacement of the antartic plate over a hot spot is therefore considered very unlikely interpretation of the results over ob seamount are somewhat less conclusive but support a similar upper cretaceous emplacement near the southwest indian ridge

the equivalent elastic thickness te seismicity and the long term rheology of continental lithosphere time to burn out creme brulee insights from large scale geodynamic modeling abstract depending on the conditions and time scale the lithosphere exhibits elastic brittle plastic or viscous ductile properties as suggested by rock mechanics experiments a large part of the long term lithospheric strength is supported in the ductile regime unfortunately these data validated for strain rates 10 6 s 1 small scales few cm and simplified conditions cannot be univocally interpolated to geological time and spatial scales strain rates 10 17 10 13 s 1 100 1000 km spatial scales complex conditions without additional parameterization an adequate parameterization has to be based on real time observations of large scale deformation indeed for the oceanic lithosphere the goetze and evan s brittle elastic ductile yield strength envelopes derived from data of experimental rock mechanics were successfully validated by a number of geodynamic scale observations such as the observations of plate flexure and the associated t e equivalent elastic thickness estimates yet for continents the uncertainties of flexural models and of the other data sources are much stronger due to the complex structure and history of continental plates for example in one continental rheology model dubbed jelly sandwich the strength mainly resides in the crust and mantle while in another dubbed creme brulee the mantle is weak and the strength is limited to the upper crust these models have arisen because of conflicting results from distributed earthquake elastic thickness t e and rheology data we address these problems by examining the plausibility of each rheological model from general physical considerations we review the elastic thickness t e estimates and their relationship to the seismogenic layer thickness t s to show that these two quantities have no direct physical relation we also show that some of small t e must be artifacts of inconsistent formulation of the mechanical problem in some free air anomaly admittance models we point out that this does not necessarily detract from the admittance method itself but refers to its incorrect application in the continental domain we then explore by analytical and numerical thermo mechanical modeling the implications of a weak and strong mantle for tectonic structural styles we conclude that rheological models such as creme brulee which invoke a weak lithosphere mantle are generally incompatible with observations the jelly sandwich is in better agreement and we believe provides a useful first order explanation for the long term support of the earth s main surface features

matched filter detection of the missing pre mainshock events and aftershocks in the 2015 gorkha nepal earthquake sequence abstract the 25 april 2015 mw 7 8 gorkha nepal earthquake occurred at the bottom edge of the locked portion of the main himalayan thrust where the indian plate underthrusts the himalayan wedge the earthquake was followed by a number of large aftershocks but not preceded by any foreshocks within 3 weeks according to the neic or isc catalog however due to the limited station coverage of the local seismic network a large portion of events may not be reported in routine catalogs here we employ the matched filter technique to recover the undocumented earthquakes for the period beginning 80 days before through 30 days after the 2015 gorkha earthquake we detect twice as many aftershocks as those listed in the isc catalog we observe an along strike aftershock expansion after the mainshock and before the largest mw 7 3 aftershock that occurred on 12 may 2015 repeating earthquakes are found to the ese of the mainshock rupture area suggesting that the expansion may be partially driven by afterslip in addition we observe a significant increase in seismicity rate 3 4 days prior to the mainshock initiating 6 h after a m 5 2 earthquake located 240 km to the nw of the mainshock the increase of seismic activities occurs in a wide region around the gorkha principal slip zone indicating the effect of delayed dynamic triggering may contribute to the large scale unloading process prior to the 2015 gorkha mainshock

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

emplacement of afanasy nikitin seamount based on transfer function analysis of gravity and bathymetry data abstract the nature of compensation of the afanasy nikitin seamount in the central indian ocean lithosphere is examined through transfer function analysis of gravity and bathymetry data along five profiles across the seamount the seamount appears to be regionally compensated by the bending of an elastic plate of only 2 5 km thickness from this low elastic thickness it is inferred that the seamount is formed near a spreading axis transform junction

seafloor spreading magnetic anomalies south off sri lanka abstract results obtained from compilation and reinterpretation of about 21 200 line km of bathymetry magnetic and satellite gravity data between 10 s to 10 n latitudes and 75 to 90 e longitudes south off sri lanka are presented here magnetic data and the synthetic seafloor spreading model reveal the presence of mesozoic anomaly sequence m11 through m0 south of sri lanka the oldest magnetic anomaly m11 134 ma occurs between 110 and 140 km away from the sri lankan coast the seafloor created during the early cretaceous is estimated to have evolved with variable half spreading rates ranging from 5 5 to 1 53 cm yr the trends of the fracture zones inferred from the offsets in the magnetic anomalies have been constrained using the satellite gravity mosaic the cretaceous magnetic quiet zone cmqz 121 84 ma crust between the isochrons m0 and a34 has an unequal width and widens from about 170 km in the west 80 e longitude to about 500 km towards east 85 e longitude plate reconstruction models for 160 fit 134 m11 121 m0 and 84 ma a34 are generated under the constraints of newly identified magnetic anomaly isochrons and fracture zones the mismatch in the a34 reconstruction is attributed to the emplacement of the ob lena and marion dufresne seamounts at the spreading ridge axis and or the frequent ridge jumps in the middle cretaceous during the major plate reorganization

origin and tectonic evolution of the caroline ridge and the sorol trough western tropical pacific from admittance and a tectonic modeling analysis abstract an independent caroline sea plate surrounded by prominent seismotectonic features is said to exist in the western tropical pacific the caroline sea plate is a transient feature existing only when the caroline philippine sea plate boundary is jumping to the caroline pacific boundary the origin and the tectonic evolution of the caroline ridge sorol trough region which forms the northern part of the caroline pacific plate boundary are examined using a standard admittance analysis a tectonic modeling study and additional direct gravity and magnetic analyses the observed admittance function is fitted well by shallow airy model in the 250 125 km 0 025 k 1 wavelength region whose average crustal thickness t c is 20 km and also by thin plate flexure model of isostasy within the diagnostic waveband of 250 80 km 0 025 k 1 with an effective elastic thickness t e of 5 7 km a simple interpretation of the observed admittance function is that the local airy model of isostasy is the main support mechanism in the study region for the longer wavelength more fundamental topography corresponding to that of the caroline ridge the caroline ridge is inferred to have formed in a near ridge tectonic setting on top of oceanic lithosphere which was young thin and weak at the time of emplacement the tectonic model study after an explanation for rifting along the mendana fracture zone in the nazca plate suggests that the sorol trough formed in the 17 7 ma interval splitting the caroline ridge into two longitudinal halves the rifting along the sorol trough which took place in the manner described in weissel and karner 1989 flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension j geophys res 94 13 919 13 950 necking of unbroken lithosphere post dated the formation of the caroline ridge by 10 15 m y during which time t e in the region increased to 5 10 km the rifting necking along the sorol trough represents a second loading event in the region the combined gravity effects of the rifting as well as the increase in the t e in the region from essentially nil to 5 10 km is reflected in the agreement between the observed admittance and the regional model with a 5 7 km t e in the wavelength region 80 km these results are consistent with the findings and the suggestions of the previous investigators in the region in that 1 the caroline ridge was constructed in the late oligocene by hot spot volcanism on top of oligocene seafloor of the caroline sea back arc basin 2 the eauripik rise genetically related to the caroline ridge formed on young and weak caroline basin lithosphere and is supported by airy manner crustal thickening and that 3 the lithosphere of the caroline ridge was young at the time of rifting necking along the sorol trough on the basis of the current results and the findings of the previous workers a tentative hypothetical rheological model for the crustal density structure of the caroline ridge sorol trough is also given the caroline sea plate appears to be bounded in the north and south by e w trending boundaries that deform diffusely while more normal narrow n s trending boundaries exhibiting more localized albeit slow deformation bound the plate in the east and west

mechanical and thermal isostatic response of the del cano rise and crozet bank southern indian ocean from altimetry data an analysis of the relationship between the bathymetry and the gravity field has been carried out both in the frequency domain admittance technique and in the space domain over the del cano rise and the crozet bank southern indian ocean a bathymetric map contoured from original shipboard data and a geoid anomaly map computed from a merged set of seasat and geos3 data were used the inversion of admittances for water depth crustal thickness crustal density and elastic plate thickness shows that the isostatic response of the lithosphere supporting the del cano rise differs very much from that of the one situated beneath the crozet bank the del cano rise appears to have been formed near the active southwest indian ridge before early eocene and is locally supported by a thickened crust shallow thermal processes contribute to the present topography of the crozet bank emplaced further away from the southeast indian ridge on older crust

surface wave potential for triggering tectonic nonvolcanic tremor source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle is anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction 0 2 however documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan is associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

laboratory simulation of fluid driven seismic sequences in shallow crustal conditions 1 we report new laboratory simulations of fluid induced seismicity on pre existing faults in sandstone by introducing pore pressure oscillations faults were activated or reactivated to generate seismic sequences these sequences were analysed using a slip forecast model furthermore field data from the monticello reservoir was used to verify the model our results suggest that short term forecasting is reliant upon the final stages when crack communication begins limiting reservoir induced seismicity ris forecasting strategies to short periods in addition our laboratory data confirms the general accuracy and robustness of short term forecast techniques dealing with natural crack linkage processes whether strain driven or fluid driven ranging from volcanic hazard mitigation to episodic tremors and slips finally oscillating pore pressure can prolong the period of fluid induced seismicity and the aftershock decay rate is slower than that without oscillations

assessment of excavation damaged zone around roadways under dynamic pressure induced by an active mining process abstract this study presents an investigation of the excavation damaged zone edz around roadways under dynamic pressure during longwall mining based on their geological conditions a total of fourteen typical roadways seven roadways under dynamic pressure seven roadways under static pressure in daxing coal mine liaoning province china were selected to investigate the characteristics of their edz under both dynamic and static pressure with borehole camera detection and nonmetallic ultrasonic detection techniques the results of the investigation indicate that the edz width around roadways under dynamic pressure was larger than those under static pressure due to mining induced disturbance and the effect of unstable overlying rocks in adjacent goaf the existence of faults and other adverse geological conditions can also contribute to the expansion of edzs the findings were incorporated in designing a more appropriate roadway support system if the width of edz is larger than the bolt length then the employment of bolts alone will not be sufficient to maintain roadway stability reinforcement with cables must be added to the support system the reason is that cables have an overhanging effect and can be anchored in the excavation influenced zone eiz which is adjacent to the edz in stable surrounding rock masses the installation of cables could increase the volume of stable strata participating in the support system