source mechanisms of micro earthquakes induced in a fluid injection experiment at the hdr site soultz sous forets alsace in 2003 and their temporal and spatial variations we have inverted the peak amplitudes of direct p waves of 45 micro earthquakes with magnitudes between m 1 4 and 2 9 which occurred during and after the 2003 massive fluid injection in the gpk3 borehole of the soultz sous for ets hot dry rock facility these events were recorded by a surface seismic network of 15 stations operated by the ecole et observatoire des sciences de la terre university of strasbourg the unconstrained moment tensor mt expression of the mechanism was applied allowing the description of a general system of dipoles that is both double couple dc and non dc sources as tensile fractures the mechanisms of all but one event are dominantly dcs with a few per cent additional components at the most we have checked carefully the reliability of the mt retrieval in bootstrap trials eliminating some data by simulating the mislocation of the hypocentre and by applying simplified velocity models of the area in constructing green s functions in some of the trials non dc components amounting to several tens of per cent appear but the f test classifies them as insignificant even the only micro earthquake with an exceptionally high non dc mechanism cannot be classified unambiguously the f test assigns similar significance to the pure dc solution the massive dominance of the dc indicates the shear slip as the mechanism of the micro earthquakes investigated the mechanisms display large variability and are of normal dip slip oblique normal to strike slip types the t axes are fairly stable being concentrated subhorizontally roughly in the e w direction on the contrary the p axes are ill constrained varying in the n s direction from nearly vertical to nearly horizontal which points to heterogeneous stress in the soultz injected volume this is in agreement with the stress pattern from in situ measurements the minimum stress axis is well constrained to e w whereas the maximum and intermediate stress values are close to one another enabling the ambiguity of the p axis direction we found no significant dependence of source mechanisms either on magnitudes or depths the time space distribution of the events analysed suggests that the injection activated two segments of the natural faults existing in the area i and ii in our notation showing different source mechanism patterns the dip slip regime is characteristic of fault segment i where the seismicity occurred during and also after injection whereas the strike slip regime prevails in segment ii where the seismicity was triggered only after the injection shut in this indicates that the tensile fractures which are assumed to be created during injection may have occurred on a smaller scale than the pure shear micro earthquakes investigated

adakite like potassic magmatism and crust mantle interaction in a postcollisional setting an experimental study of melting beneath the tibetan plateau

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

source parameters of injection induced microseismicity we analyze source parameters of microseismic events m 1 associated with high flow rate water injections in a shale formation at a depth of 220 m two types of events were observed several hundred impulsive events with clear p and s wave arrivals and continuous emissions with peaked spectra detected well into the experiment for a representative collection of impulsive events an 2 model provided satisfactory fits to displacement spectra corrected for attenuation and average quality factors of 34 and 15 were obtained for p and s waves p wave first motion analysis and e s e p ratios indicated the existence of a non double couple component in some events particularly early in the experiment a clear difference was observed for estimates of stress release parameters as non doublecouple events had smaller stress drops and apparent stresses the seismic efficiency of double couple and non double couple events was limited to 0 9 and 0 05 respectively with average values being 0 25 and 0 02 a comparison of our results with those reported for a similar magnitude range in a hard rock formation indicates considerably smaller estimates of stress drop and apparent stress in our case while seismic efficiencies are comparable

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

insight on seismic hazard studies for egypt abstract the seismic hazard studies for egypt have been initiated a long time ago aiming to predict the ground motion parameters at different geographical scales their review process had been routinely performed due to the increase of available instrumental observations rather than from methodological advances for the comprehensive understanding of the development of seismic hazard assessment sha studies in egypt we properly collect and test the existing sha maps computed at different geographic scales against the available observations data quality physical assumptions and adopted methodology most of these sha studies are probabilistic and the mapped ground motion acceleration values have been often largely exceeded by the observed values due to earthquakes occurred after their publication for each study we discuss and evaluate the input data methodology and the results obtained in order to understand the reasons behind the bad performance of the available seismic hazard maps and to avoid such shortcomings in future seismic hazard assessment finally we formulate suggestions that could be considered before new seismic hazard maps are released and then adopted for the real benefit of society

deterministic seismic hazard in egypt summary the regional seismic hazard in egypt is assessed using a deterministic approach based on the computation of synthetic seismograms at a set of gridpoints located at distances of 0 2u from each other the main input for this computation are earthquake sources and structural models the earthquake sources are parametrized using focal mechanisms seismogenic areas and regional seismicity a number of deep seismic profiles have been used to define the crustal structures similar sets of gravity profiles have been used to define the density of the layers the peak displacement dmax peak velocity vmax and design ground acceleration dga are chosen and plotted to construct the seismic hazard maps there are similarities between computed and observed amplitudes of ground motion in terms of their values and spatial distributions the results obtained from the deterministic and probabilistic approaches are comparable the areas of high seismic hazard level are of great socio economic importance

the system tonalite peridotite h 2 o at 30 kbar with applications to hybridization in subduction zone magmatism we present data on the phase relationships of mixtures between natural tonalite and peridotite compositions with excess h2o at 30 kbar and on the composition of the piercing point where the peridotite tonalite mixing line intersects the l ga opx reaction boundary these data in conjunction with earlier analogous data along peridotite granite and basalt granite mixing lines permit construction of a pseudoternary liquidus projection that is relevant to interaction of peridotite with slab derived magmas knowledge of the liquidus phase and temperature for a range of compositions within this projection enables us to map primary crystallization fields for quartz garnet orthopyroxene clinopyroxene and olivine and to estimate the distribution of isotherms across the projection using this projection we explore the consequences of peridotite assimilation by mafic to intermediate basalt to dacite hydrous slab derived melts progressive assimilation under isothermal conditions results in garnet precipitation as the melt composition traverses the garnet liquidus surface and then garnet orthopyroxene crystallization once the melt reaches the l ga opx field boundary the melt is constrained to remain on this field boundary and further assimilation of peridotite simply results in continued precipitation of garnet orthopyroxene until the melt is consumed the product is a hybrid solid assemblage consisting of ga opx it is noteworthy that this process drives the melt composition in a direction nearly perpendicular to the mixing line between peridotite and the initial melt if assimilation occurs with increasing temperature as might occur if a slab derived magma rises into the hotter mantle wedge intermediate magmas e g andesites will again precipitate garnet until they reach the l ga opx reaction boundary at which point ga re dissolves and orthopyroxene precipitates as the melt composition moves up temperature along this boundary the product of this process is a hybrid solid assemblage with garnet subordinate to orthopyroxene for more mafic initial compositions e g basalts originally plotting in the cpx field it appears possible to avoid field boundaries involving garnet and shift in composition more directly toward peridotite if assimilation is accompanied by a sharp increase in temperature considering published ree evidence arguing against garnet playing a significant role in the genesis of many subduction related magmas in light of our results it appears unlikely that peridotite assimilation by intermediate magmas under conditions of constant or increasing temperature is an important process in subduction zones however if assimilation is accompanied by an increase in temperature our data do permit the derivation of high mg basalts from less refractory precursors e g high al basalts by peridotite assimilation

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

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

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

up to date probabilistic earthquake hazard maps for egypt an up to date earthquake hazard analysis has been performed in egypt using a probabilistic seismic hazard approach through the current study we use a complete and homogenous earthquake catalog covering the time period between 2200 bc and 2015 ad three seismotectonic models representing the seismic activity in and around egypt are used a logic tree framework is applied to allow for the epistemic uncertainty in the declustering parameters minimum magnitude seismotectonic setting and ground motion prediction equations the hazard analysis is performed for a grid of 0 5 0 5 in terms of types of rock site for the peak ground acceleration pga and spectral acceleration at 0 2 0 5 1 0 and 2 0 s periods the hazard is estimated for three return periods 72 475 and 2475 years corresponding to 50 10 and 2 probability of exceedance in 50 years the uniform hazard spectra for the cities of cairo alexandria aswan and nuwbia are constructed the hazard maps show that the highest ground acceleration values are expected in the northeastern part of egypt around the gulf of aqaba pga up to 0 4 g for return period 475 years and in south egypt around the city of aswan pga up to 0 2 g for return period 475 years the western desert of egypt is characterized by the lowest level of hazard pga lower than 0 1 g for return period 475 years

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

non double couple mechanisms of microearthquakes induced during the 2000 injection experiment at the ktb site germany a result of tensile faulting or anisotropy of a rock abstract moment tensors of microearthquakes induced during the 2000 injection experiment at the ktb deep drilling borehole at a depth level of 5 4 km are studied a family of 37 most reliable moment tensors contains significant non double couple non dc components the dc is on average 60 and the non dc is 40 fault plane solutions computed from the dc part show preferred strike slip mechanisms with small normal or reverse components a predominant azimuth of p and t axes is in the range of n320 340 e and of n230 250 e respectively the non dc components contain both the isotropic iso and compensated linear vector dipole clvd components the mean value of iso is 1 5 the mean value of clvd is 5 7 the predominantly negative clvd components are inconsistent with the concept of the non dc mechanisms as a result of tensile faulting due to fluid injection into the rock the main origin of the non dc components is probably anisotropy in the focal area the other origins are errors produced by mismodelling of the medium when calculating the green functions and numerical errors produced by noise and limitations of input data adopting four alternative models of anisotropy obtained by other seismic measurements at the ktb we have employed the non dc components for estimating an optimum orientation of anisotropy in the focal area the optimum orientation of the symmetry plane of anisotropy is nearly vertical with a strike of n335 340 e this strike coincides well with the strike of 330 typical for many major lithological units and faults and with the orientation of the transversely isotropic model inferred by other authors after removing the anisotropy effects from the moment tensors by calculating the source tensors the distribution of iso is significantly narrowed this indicates predominantly shear but not tensile faulting

can small events m 0 it is becoming evident that under different circumstances such as injection rates and geologic conditions it might be possible to generate larger magnitude m 0 events during hydraulic fracture stimulations by utilizing fully integrated passive seismic monitoring programs we can examine the relationship between the occurrence of small magnitude events m 0 and the fracture and stress conditions that may lead to larger events in our investigations we identify that over all scales of observation the events follow a self similar behavior however the small magnitude events are generally lower in stress release than observed for the larger events these differences can be explained by the observed failure mechanisms where smaller events tend to be driven by shear tensile failures of pre existing discrete fractures joints whereas the larger events appear to be dominated by shear driven failure processes associated with pre existing faults these observations suggest that there can be sufficient

microseismic moment tensors a path to understanding frac growth microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process with sufficient resolution the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

phase relationships in the system kalsio 4 mg 2 sio 4 sio 2 h 2 o as a model for hybridization between hydrous siliceous melts and peridotite the system kalsio4 mg2sio4 sio2 h2o includes model representatives of 1 hydrous siliceous magma from subducted oceanic crust the eutectic liquid in kalsi3o8 sio2 h2o and 2 the overlying mantle peridotite the assemblage forsterite enstatite fo en in a series of partly schematic isobaric isothermal sections the products of hybridization between the model materials at pressures between 20 and 30 kbar have been determined the liquid dissolves peridotite components with little change in composition hybridization is not a simple mixing process because of the incongruent melting of peridotitic assemblages with phlogopite ph hybridization causes solidification of the liquid with products a sequence of three mineral assemblages ph ph quartz qz and ph en the products represent an absolute geochemical separation and local concentration of all potassium from the liquid hybridization is accompanied by h2o saturation of melts and evolution of aqueous fluid although there are significant differences between the melt composition and that of the magma rising from subducted oceanic slab and between fo en and the mantle rock extrapolation of the results suggests that the conclusions can probably be extended to mantle conditions with sodium in the melt and jadeitic clinopyroxene included in the hybrid products

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

site characterization in ismailia egypt using seismic ambient vibration array abstract seismic ambient vibration array measurements were carried out at seven sites in ismailia egypt in order to obtain one dimensional 1d shear wave velocity vs profiles and horizontal to vertical spectral ratios hvsr we applied the spatial autocorrelation spac method to the ambient vibration data for the estimating rayleigh wave dispersion curves and obtained 1d vs profiles the deeper parts 90 350 m of the estimated models have vs values ranging between 500 and 700 m s while the subsurface parts have vs varying between 140 and 200 m s the averaged vs in the upper 30 m based on the results indicate that site classes of all the sites are classified as c or d according to nehrp soil classification the computed site amplification factors derived from the estimated vs profiles show that the resonant frequencies at sites on the east side of the suez canal are below 1 hz while those at sites on the west side vary between 1 and 2 hz indicating the difference of subsurface geology across the suez canal the hvsr curves at each site are generally similar for all sensors indicating nearly flat subsurface layers beneath each site we also compared the dominant frequencies of hvsrs and those derived from 1d amplification factors the comparisons show that both the frequencies are similar to each other but there are slight differences possibly due to the lack of deeper sedimentary layer structures and lower resolution of hvsrs in the lower frequency range indicating the importance of further ambient vibration survey with broadband sensors the results show that the combination of spac and hvsr methods is advantageous to estimate proper vs profiles to evaluate site effects for earthquake disaster mitigation

update and sensitivity analysis of the neo deterministic seismic hazard assessment for egypt abstract the main goal of this work is to provide an update on the seismic hazard maps available for egypt that incorporates the results of recent studies i e revised historical earthquake catalogs morphostructural zonation data mz revised focal mechanism solutions and mechanical models of the lithospheric structure this is done within the framework of the neo deterministic seismic hazard assessment ndsha procedure that may effectively accommodate any reliable new information to adequately compute the earthquake ground motion maps i e pga pgv and pgd furthermore with the set of relevant scenario earthquakes this work provides a large dataset of synthetic seismograms particularly important for the areas that suffer from the endemic lack of useful strong motion time histories such as egypt setting the base toward detailed and comprehensive seismic microzonation studies ndsha aims to supply an envelope value in other words a value that should not be exceeded therefore it is immediately falsifiable and verifiable a sensitivity analysis based on the different ground motion maps computed adopting different a models for the earthquake source process b mechanical models of the crust and c mapmaker s preconceptions e g different seismotectonic models is provided the maps of difference and ratio between various ground motion maps computed for different variants are shown and discussed in order to explore the influence of using various input models the results provide the potential users with an adequate spectrum of choices and reliably assess and clearly communicate the possible uncertainties the availability of a wide spectrum of hazard maps is a prerequisite to supply valuable information for the significant improvement of a seismic code

source parameters and rupture velocity of small m 2 1 reservoir induced earthquakes summary we calculate stress drop and rupture speed for ml 2 1 shallow reservoir induced earthquakes and find them to be similar to those of large natural earthquakes previous studies have suggested that hydrofractures mining and reservoir induced earthquakes have lower average stress drop than natural tectonic earthquakes this difference might result from the different tectonic setting or the shallower hypocentral depths of induced earthquakes alternatively difficulties in correcting for attenuation and site effects in earlier studies may lead to underestimation of stress drop in addition most studies assume the rupture velocity of small reservoir induced earthquakes to be the same as for the large earthquakes we analyse a set of 101 ml 2 1 earthquakes induced by changing water level in the acu reservoir ne brazil the earthquakes are shallow depth 5 km and the region has negligible natural seismicity we use three different approaches to calculate the source parameters of the six largest 1 9 ml 2 1 earthquakes we model the individual spectra to find corner frequency frequency independent q and long period amplitude we use collocated small earthquakes as empirical green s functions to calculate the spectral ratios and determine the relative source time functions estimates of the source duration and corner frequency imply stress drops in the range of 26 179 mpa these are similar to or higher than tectonic earthquakes suggesting that the shallow hypocentral depth and the presence of water do not affect stress drop we observe clear directivity for one of the earthquakes and use the azimuthal variation in pulse width to estimate a rupture velocity of 0 6

shear and tensile earthquakes caused by fluid injection 1 we apply rock mechanics concepts to the seismological observations in order to explain why during hydraulic injection some events display tensile and some shear deformation the presence of non shear components depends on the differential stress and the fracture orientation with respect to the 1 direction provided the slip vector is parallel to the traction we define four types of earthquakes according to the ratio of the shear and tensile components assuming a griffith failure envelope hybrid events containing both shear and tensile components can occur for fractures striking within 22 5 of 1 we argue that pure tensile fractures striking parallel to 1 are unlikely in the presence of natural fractures the low shear traction of tensile events also implies their small stress drops by applying the analysis to two different data sets soultz sous forets and cotton valley we show that different orientations of natural fractures and differential stress in the targeted formations made each region favorable for different non dc components in the injection induced seismicity

source parameters of koyna earthquakes india abstract a seismic zone in southwestern india extending 30 km south from koyna dam has witnessed more than 150 earthquakes of m 4 and 10 of m 5 during the last 34 years during august 1993 to december 1994 a spurt of earthquakes occurred in the vicinity of the newly impounded warna reservoir 25 km south of koyna dam the epicenters are located between the two reservoirs but more near the new reservoir during 1994 digital data acquisition systems were deployed by the national geophysical research institute in the vicinity of the koyna warna reservoirs to help in understanding the physical processes responsible for generating earthquakes in the area source parameters were estimated at three stations using s wave spectrum for 193 selected earthquakes of m 1 5 to 4 7 that were recorded during october 1994 to june 1995 seismic moments of 10 11 to 10 16 n m source radii from 94 to 538 m and stress drops of 0 03 to 19 mpa for earthquakes of magnitude 1 5 to 4 7 were obtained from this analysis it is observed that earthquakes of m 3 are associated with larger stress drops of more than 2 mpa the larger energy release through more numbers of m 3 earthquakes and higher stress drop values are found in 0 to 1 km and 5 to 13 km depth ranges depth range of 1 to 4 km has low seismicity and low stress drop earthquakes higher energy release and stress drops are possibly caused by higher stress concentration and incremental stress on rocks with fluids in subhydrostatic conditions in 0 to 1 km depth range and suprahydrostatic conditions in 5 to 13 km depth range spatially the earthquakes of m 3 and high stress drop are now less near koyna reservoir but frequent near the new reservoir

petrogenesis and tectonic implications of the late carboniferous calc alkaline and shoshonitic magmatic rocks in the awulale mountain western tianshan abstract the widespread late carboniferous calc alkaline and shoshonitic magmatic rocks in the awulale mountain provide crucial constraints on the tectonic evolution of the western tianshan here we perform detailed petrological investigations as well as zircon u pb chronological whole rock geochemical and sr nd isotopic analyses on these magmatic rocks from two geological sections along the duku road magmatic rocks in the section i with zircon shrimp u pb ages of 306 8 ma and 306 4 ma are composed of medium k calc alkaline to shoshonitic basalt trachy andesite and trachyte while those in the section ii consist of shoshonitic trachy andesite trachyte with a u pb age of 308 1 ma and monzonite with a u pb age of 309 6 ma all these magmatic rocks are characterized by strong enrichments in large iron lithophile elements with depletions of nb ta and ti indicating the origination from subduction modified lithospheric mantle the end t values of the rock samples collected from the section i 2 80 5 45 and section ii 3 34 5 37 are generally higher than those of the devonian to early carboniferous arc type magmatic rocks in the yili central tianshan suggesting that depleted asthenosphere might also be involved in their generation based on these geochemical data and petrological observations we suggest that the early stage 308 1 309 6 ma shoshonitic monzonite trachy andesite and trachyte in the section ii were generated by mixing between mafic magmas and trachytic melts while the late stage 306 4 306 8 ma medium k calc alkaline to shoshonitic basalt trachy andesite and trachyte in the section i were produced by partial melting of depleted asthenospheric and metasomatized lithospheric mantle followed by the processes of fractional crystallization and crustal contamination taking into account the available regional geological data the subduction of south tianshan ocean was probably ceased at 310 ma and these calc alkaline and shoshonitic magmatic rocks in the awulale mountain formed in a post collisional setting subsequent to slab break off

multi scale seismicity model for seismic risk for a general use of the frequency magnitude fm relation in seismic risk assessment we formulate a multi scale approach that relies on the hypothesis that only the ensemble of events that are geometrically small compared with the elements of the seismotectonic regionalization can be described by a log linear fm relation it follows that the seismic zonation must be performed at several scales depending upon the self similarity conditions of the seismic events and the linearity of the log fm relation in the magnitude range of interest the analysis of worldwide seismicity using the harvard catalog where the seismic moment is recorded as the earthquake size corroborates the idea that a single fm relation is not universally applicable the multi scale model of the fm relation is tested in the italian region

the nile valley of egypt a major active graben that magnifies seismic waves the nile valley and the nile delta are part of the active rift that is probably connected with the red sea tectonism this zone is characterized by small to moderate size earthquakes that have caused extremely severe damage to recent and historical constructions the most vulnerable area along the nile valley is the one of cairo faiyoum small local and large distant earthquakes could be a source of huge socio economic damage in this area the loose soft alluvial sediments of the nile canyon are the main factor behind this potential damage because they may greatly amplify the ground motion as demonstrated by strong ground motion modelling the largest amplification is generally concentrated along the edges of the graben and occurs at frequencies between 1 hz and 2 hz this may explain the huge damage caused by distant earthquakes during recent and historical times the distribution of intensity values during the events of 1926 and 1992 is well correlated with the modelled spatial distribution of the spectral amplification

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

volcanic hybrid earthquakes that are brittle failure events 1 volcanoes generate a variety of pre eruptive low frequency seismic signals hybrid earthquakes comprise a class of these signals having high frequency onsets followed by low frequency ringing they are used empirically to predict eruptions but their ambiguous physical origin limits their diagnostic use the short duration near field hybrid seismograms associated with the 2004 mount st helens eruption indicate that much of the prolonged signal is due to path rather than resonating fluids we show using seismic source spectra that the hybrids have a corner frequency seismic moment relationship that scales consistently with brittle failure the unusually low frequency of these earthquakes can result from low rupture velocities combined with strong path effects due to their shallow sources this new application of near field instrumentation provides the first seismological evidence for brittle failure as a major process in dome building and suggests that hybrids should not be used as direct indicators of fluids

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

hybrid fracture and the transition from extension fracture to shear fracture fracture is a fundamental mechanism of material failure two basic types of brittle fractures are commonly observed in rock deformation experiments extension opening mode fractures and shear fractures for nearly half a century it has been hypothesized that extension and shear fractures represent end members of a continuous spectrum of brittle fracture types however observations of transitional fractures that display both opening and shear modes hybrids in naturally deformed rock have often remained ambiguous and a clear demonstration of hybrid fracture formation has not been provided by experiments here we present the results of triaxial extension experiments on carrara marble that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress hybrid fractures form under mixed tensile and compressive stress states at acute angles to the maximum principal compressive stress fracture angles are greater than those observed for extension fractures and less than those observed for shear fractures fracture surfaces also display a progressive change from an extension to shear fracture morphology

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

source parameters of seismic events at heinrich robert mine ruhr basin federal republic of germany evidence for nondouble couple events abstract a three component digital seismic station is in operation at heinrich robert coal mine in the ruhr basin at a depth of 890 m a cluster of seismic events occurred at the beginning of 1987 at a distance of about 5 km from the station and continued in 1988 source parameters of 46 tremors selected from the cluster with local magnitude from 1 2 to 2 3 are studied the ratio of p wave to s wave corner frequency is variable implying its dependence on the angle of observation and in turn the variability of focal mechanism with time the scaling relations indicate that characteristic tremors with a fault length of about 200 m are possibly generated in the area but the evidence is not conclusive the seismic energy for a given seismic moment can vary by a factor of 20 and the ratio of s wave to p wave energy ranges from 1 5 to 30 stress release estimates show low values not exceeding a few bars typical for tremors induced by mining a comparison of the apparent stress with the static stress drop divides the selected tremors into high and low apparent stress events the latter events are characterized by high p wave energy and almost constant and large ratio of p wave to s wave corner frequency which differs from the lower ratios of other events implying similar focal mechanism these high p wave energy tremors are the most likely candidates for nondouble couple events

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

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

seismogenic nodes m 5 0 in northeast egypt and implications for seismic hazard assessment seismogenic nodes capable of generating shallow earthquakes with m 5 0 have been identified in the northeast part of egypt using the pattern recognition approach the study region includes the sinai peninsula and the northern part of the eastern desert between the nile river and the red sea which comprises the new capital of egypt and suez canal projects and represents a place for much future development we apply a phenomenological approach based on pattern recognition for identifying seismogenic nodes the methodology is based on the idea that earthquakes nucleate at nodes specific structures forming around fault intersections morphostructural zoning mz is applied to map nodes over the entire study region without using a priori knowledge of regional seismicity the pattern recognition is employed to pinpoint seismogenic nodes where earthquakes with m 5 0 may occur in the future as a result seismogenic nodes capable of generating earthquakes with m 5 0 have been defined in the sinai peninsula and the northern part of the eastern desert we also found characteristic geological geophysical features that discriminate seismogenic nodes d from non seismogenic ones n information on the potential seismic sources represents the main issue in seismic hazard evaluation seismogenic nodes prone to earthquakes with m 5 0 as described in this work may contribute to the definition of earthquake source zones in the northeast of egypt because some of the d nodes are potential sources of seismic risk for critical facilities e g ismailia tunnels and large metropolitan areas e g nile valley this information can contribute to the revision of seismic zoning or microzoning and improve the performance of seismic hazard studies of egypt by adding a new source of information about seismogenic nodes to the seismogenic zones

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

low apparent stress observed for mw 0 6 microearthquakes recorded during hydraulic fracturing stimulation in the carthage cotton valley gas field understanding the source characteristics of hydraulic fracturing induced microearthquakes is expected to provide better understanding of both the fracturing process and the influence of pre existing structures on the distribution of events however details of the source characteristics of microearthquakes remain largely unknown one controversial issue is whether the mechanism of such events differs from natural tectonic events that is whether significant reductions of effective stress and or volumetric change occur because of the stimulation herein to address this question we estimated the apparent stress of the 61 m w 0 6 microearthquakes observed during the hydraulic fracturing in the carthage cotton valley gas field we first obtained the apparent stress by estimating the radiated seismic energy from the duration of the relative moment rate function and then adjusted the values considering the possibility of seismic energy underestimation the initial value range of 0 001 0 02 mpa is consistent with other past studies of hydraulic fracturing induced microearthquakes although the adjustment increases the original value by a factor of 10 it is still within the lower bound of the range of constant apparent stress commonly observed for natural tectonic events furthermore relatively lower apparent stress was observed for the events striking subparallel to the maximum horizontal compressional stress axis this implies the mechanism of these events could be different from that of events optimally oriented for failure although the uncertainty of their measurements was expected to be large compared with other events because of their small magnitude online material table with information on microearthquakes observed during the hydraulic stimulation in the carthage cotton valley gas field

non double couple mechanisms of microearthquakes induced by hydraulic fracturing 1 we have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the carthage cotton valley east texas gas field with vertical arrays of four and eight three component geophones in two monitoring wells respectively we were able to reliably determine source mechanisms of the strongest events with the best signal to noise ratio our analysis indicates predominantly non double couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation our observations suggest the induced events are directly the result of opening cracks by fluid injection in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

effects of seismicity models and new ground motion prediction equations on seismic hazard assessment for four canadian cities seismicityratesandground motionpredictionequations gmpes arethe key uncertainties in probabilistic seismic hazard analysis psha we explore the impact of new findings and knowledge from seismological and ground motion studies on seismic hazard assessment for eastern and western canada updated information includes the reevaluation of seismicity rates and their interpretation in terms of seismic source zones and the use of new gmpes we refer to our model as an interim updated seismic hazard model as it does not treat all uncertainties comprehensively rather we address the impact of key uncertainties based on our updated interim seismic hazard model uniform hazard spectra uhs at four major cities across canada are obtained and compared with uhs in the current seismic hazard maps of canada 2005 2010 whicharebasedona1995seismichazardmodeldevelopedbythegeologicalsurveyof canada sensitivity analysis highlights the significant impact of seismicity smoothing in low to moderate seismic regions eastern canada while gmpes are important for all regions moreover our interim updated seismic hazard model can readily produce seismic hazard curves as well as seismic hazard deaggregation results for various site conditionsandformultipleprobabilitylevels thiscapabilityisessentialforcarryingout advanced earthquake engineering analyses

moment tensor inversion of microseisms from the b sand propped hydrofracture m site colorado abstract we apply a moment tensor inversion algorithm to microseismic events generated by hydrofracturing our dataset consists of microseismic events associated with a hydraulic fracturing experiment conducted at the gri doe m site near rifle colorado the event recordings were from a vertical string of 3 component accelerometer pods that are cemented in a borehole the accelerograms clearly show p and s waves which can be rotated into the sh and sv components to invert the p and s amplitudes for moment tensors we use just the first two peaks after the first arrival using this amplitude information and the average pulse width we formed a symmetric stylized pulse for integration and we inverted for the moment tensor resolution tests revealed that with the source microseism to receiver geometry we have at the m site where all receivers are in one borehole and at the same azimuth from the source we can extract the five deviatoric components of the moment tensor using combinations of p sh and sv amplitudes for example a minimum data set of 3 p wave 2 sv wave and 1 sh wave amplitudes to obtain the sixth component which is the isotropic component requires amplitude information from receivers at another azimuth we studied seven high quality events in detail and tested their results against two alternative source geometries these microseismic events tend to have a major double couple nodal plane aligned parallel to the main hydrofracture plane rather than have their tension t axes aligned parallel to the regional minimum principal compressive stress direction the events have seismic moments m0 on the order of 10 5 nm and moment magnitudes mw of about 2 5

potassium rich magmatism from a phlogopite free source the generation of strongly potassic melts in the mantle is generally thought to require the presence of phlogopite in the melting assemblage in the mediterranean region trace element and isotope compositions indicate that continental crustal material is involved in the generation of many potassium rich lavas this is clearest in ultrapotassic rocks like lamproites and shoshonites for which the relevant chemical signals are less diluted by extensive melting of peridotite furthermore melting occurs here in young lithosphere so the continental crust was not stored for a long period of time in the mantle before reactivation we have undertaken two types of experiments to investigate the reaction between crust and mantle at 1000 1100 c and 2 3 gpa in the first continental crustal metasediment phyllite and depleted peridotite dunite were juxtaposed as separate blocks whereas in the second the same rock powders were intimately mixed in the first series a clear reaction zone dominated by orthopyroxene was formed between dunite and phyllite but no hybridized melt could be found whereas analyzable pools of hybridized melt occurred throughout the charges in the second series melt compositions show high abundances of rb 100 220 ppm and ba 400 870 ppm and consistent ratios of nb ta 10 12 zr hf 34 42 and rb cs 28 34 similar to bulk continental crust these experiments demonstrate that melts with as much as 5 wt k 2 o may result from reaction between melts of continent derived sediment and depleted peridotite at shallow mantle depths without the need for phlogopite or any other potassic phase in the residue

on the retrieval of moment tensors from borehole data the complete moment tensors of seismic sources in homogeneous or vertically inhomogeneous isotropic structures cannot be retrieved using receivers deployed in one vertical borehole the complete moment tensors can be retrieved from amplitudes of p waves provided that receivers are deployed in at least three boreholes using amplitudes of p and s waves two boreholes are in principle sufficient similar rules also apply to transversely isotropic media with a vertical axis of symmetry in the case of limited observations the inversion can be stabilized by imposing the zero trace constraint on the moment tensors however this constraint is valid only if applied to observations of shear faulting on planar faults in isotropic media which produces double couple mechanisms for shear faulting on non planar faults for tensile faulting and for shear faulting in anisotropic media the zero trace constraint is no longer valid and can distort the retrieved moment tensor and bias the fault plane solution numerical modelling simulating the inversion of the double couple mechanism from real data reveals that the errors in the double couple and non double couple percentages of the moment tensors rapidly decrease with increase in the number of boreholes used for noisy p and s wave amplitudes with noise of 15 of the top amplitude at each channel and for a velocity model biased by 10 the errors in the double couple percentage attain 25 13 and 6 when inverting for the double couple mechanism from one two and three boreholes

hot cold spots in italian macroseismic data site effect is usually associated with local geological conditions which increase or decrease the level of shaking compared with standard attenuation relations we made an attempt to see in the macroseismic data of italy some other effects namely hot cold spots in the terminology of olsen in bull seismol soc am 90 6b 577 594 2000 which are related to local fault geometry rather than to soil conditions we give a list of towns and villages liable to amplify or to reduce the level of shaking in comparison with the nearby settlements relief and soil conditions cannot always account for the anomalous sites further there are sites where both and effects are observed depending on the earthquake the opposite effects can be generated by events from the same seismotectonic zone and along the same direction to the site anomalous sites may group themselves into clusters of different scales all isolated anomalous patterns presented in this paper can be used in hazard analysis in particular for the modeling and testing of seismic effects

updated probabilistic seismic hazard values for egypt seismic hazard in terms of mean peak ground acceleration pga and spectral acceleration sa values has been computed for egypt using both historical and instrumental earthquake data for this purpose an updated earthquake catalog spanning the time period from 2200 b c to 2013 has been compiled for egypt as well as its surrounding regions and is prepared to be used in a new probabilistic seismic hazard assessment of egypt the earthquakes sizes were unified in terms of the moment magnitude scale a new seismic source model for the seismic activity in and around egypt consisting of a total of 88 seismic zones for shallow and intermediate depth seismicity was considered in this new assessment the seismicity parameters have been specifically computed for 35 seismic sources covering the egyptian territory and the eastern mediterranean region a logic tree design was set up to consider the epistemic uncertainty in the gutenberg richter b value maximum possible magnitude m max and the selected ground motion prediction equations seismic hazard computations for rock site conditions with 10 and 5 probability of exceedance in 50 years were carried out in addition uniform hazard spectra for twelve among the most important and populated cities in egypt are computed and compared with the most recent egyptian building code values it is interesting to highlight that the maximum hazard values are observed at the gulf of aqaba region specifically around the epicentral location of the biggest egyptian recorded earthquake of 22 november 1995 m w 7 2 aqaba earthquake the obtained seismic hazard values for nuweiba city located in this region for mean pga and sa 0 1 s are 0 29 g and 0 74 g respectively for a return period of 475 years

imaging hydraulic fractures in a geothermal reservoir 1 an injection experiment at the coso geothermal field in eastern california in march 2005 caused a swarm of microearthquakes that was recorded by a local network of three component digital seismometers high resolution relative hypocenter locations propagated upward and northward on a 700 600 m plane striking n 20 e and dipping 75 to the wnw this plane is a pre existing fault whose surface projection coincides with an active scarp the earthquakes have similar non double couple mechanisms that involve volume increases and the fault plane bisects their dilatational fields implying a process dominated by tensile failure the source types require the additional involvement of subsidiary shear faulting however events before and after the swarm have variable orientations and volume changes of both signs similar tensile shear failure is observed in some natural microearthquake swarms for example at long valley caldera california its occurrence under low fluid pressure may imply a heterogeneous stress field or the induction of thermal stresses by introduction of cold fluid