a comparison of spectral parameter kappa from small and moderate earthquakes using southern california anza seismic network data kappa is a one parameter estimator of the spectral amplitude decay with frequency of a seismogram low values 5 ms indicate limited attenuation of high frequency energy whereas higher values 40 ms indicate high frequency energy has been removed kappa is often assumed to be a site term and used in seismic designs we address two key questions about kappa 1 how to identify source path and site contributions to kappa and 2 can kappa estimates from smaller earthquakes and more readily accessible weak motion recordings be reasonably extrapolated to esti mate kappa of larger earthquakes the use of small earthquakes ml 3 5 earthquakes inside the network we find kappa from small earthquakes predicts the relative values of kappa for larger earthquakes e g measurements at stations pfo and knw are small compared with those at stations tro and snd for the snd and tro data however kappa values from small earth quakes overpredict those from moderate and large earthquakes site effects are the most important contributor to kappa estimates but the scatter within kappa measure ments at a given station is likely caused by a significant contribution from near the source perhaps related to near source scattering because of this source side varia bility care is recommended in using individual small events as green s functions to study source time effects of moderate and large events

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

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

solving for source parameters using nested array data a case study from the canterbury new zealand earthquake sequence the seismic spectrum can be constructed by assuming a brune spectral model and estimating the parameters of seismic moment m 0 corner frequency f c and high frequency site attenuation using seismic data collected during the 2010 2011 canterbury new zealand earthquake sequence we apply the non linear least squares gauss newton method a deterministic downhill optimization technique to simultaneously determine the m 0 f c and for each event station pair we fit the brune spectral acceleration model to fourier transformed s wave records following application of path and site corrections to the data for each event we solve for a single m 0 and f c while any remaining residual kappa kappa text r is allowed to differ per station record to reflect varying high frequency falloff due to path and site attenuation we use a parametric forward modeling method calculating initial m 0 and f c values from the local gns new zealand catalog m w gns magnitudes and measuring an initial kappa text r using an automated high frequency linear regression method final solutions for m 0 f c and kappa text r are iteratively computed through minimization of the residual function and the brune model stress drop is then calculated from the final best fit f c we perform the spectral fitting routine on nested array seismic data that include the permanent geonet accelerometer network as well as a dense network of nearly 200 quake catcher network qcn mems accelerometers analyzing over 180 aftershocks m w gns 3 5 that occurred from 9 september 2010 to 31 july 2011 qcn stations were hosted by public volunteers and served to fill spatial gaps between existing geonet stations moment magnitudes determined using the spectral fitting procedure m w sf range from 3 5 to 5 7 and agree well with m w gns with a median difference of 0 09 and 0 17 for geonet and qcn records respectively and 0 11 when data from both networks are combined the majority of events are calculated to have stress drops between 1 7 and 13 mpa 20th and 80th percentile correspondingly for the combined networks the overall median stress drop for the combined networks is 3 2 mpa which is similar to median stress drops previously reported for the canterbury sequence we do not observe a correlation between stress drop and depth for this region nor a relationship between stress drop and magnitude over the catalog considered lateral spatial patterns in stress drop such as a cluster of aftershocks near the eastern extent of the greendale fault with higher stress drops and lower stress drops for aftershocks of the 2011 m w gns 6 2 christchurch mainshock are found to be in agreement with previous reports as stress drop is arguably a method dependent calculation and subject to high spatial variability our results using the parametric gauss newton algorithm strengthen conclusions that the canterbury sequence has stress drops that are more similar to those found in intraplate regions with overall higher stress drops that are typically observed in tectonically active areas

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

long wavelength gravity and topography anomalies it is shown that gravity and topography anomalies on the earth s surface may provide new information about deep processes occurring in the earth such as those associated with mantle convection two main reasons are cited for this the first is the steady improvement that has occurred in the resolution of the long wavelength gravity field particularly in the wavelength range of a few hundred to a few thousand km mainly due to increased coverage of terrestrial gravity measurements and the development of radar altimeters in orbiting satellites the second reason is the large number of numerical and laboratory experiments of convection in the earth including some with deformable upper and lower boundaries and temperature dependent viscosity the oceans are thought to hold the most promise for determining long wavelength gravity and topography anomalies since their evolution has been relatively simple in comparison with that of the continents it is also shown that good correlation between long wavelength gravity and topography anomalies exists over some portions of the ocean floor

gondwana breakup and plate kinematics business as usual 1 a tectonic model of the weddell sea is built by composing a simple circuit with optimized rotations describing the growth of the south atlantic and sw indian oceans the model independently and accurately reproduces the consensus elements of the weddell sea s spreading record and continental margins and offers solutions to remaining controversies there at their present resolutions plate kinematic data from the south atlantic and sw indian oceans and weddell sea rule against the proposed but controversial independent movements of small plates during gondwana breakup that have been attributed to the presence or impact of a mantle plume hence although supercontinent breakup here was accompanied by extraordinary excess volcanism there is no indication from plate kinematics that the causes of that volcanism provided a unique driving mechanism for it

the 2002 m5 au sable forks ny earthquake sequence source scaling relationships and energy budget 1 we find invariant high stress drops and radiated energies for a sequence of intraplate earthquakes we estimate source parameters of the au sable forks ny earthquake m5 2002 and aftershocks this intraplate earthquake was the largest to occur in eastern north america since 1988 and the largest to be recorded by regional broadband networks we use the empirical green s function egf method and define a set of qualitative and quantitative rules for the selection of egf earthquake pairs and for the quality verification of the obtained egf spectral ratio we use a multitaper code that performs the complex spectral division with minimum frequency leakage and allows transformation back to the time domain to check the validity of the egf event we estimate source parameters for 22 earthquakes m1 m5 in the sequence the median stress drop of 104 mpa using madariaga source model and 19 mpa for a brune model is significantly larger than estimates for interplate earthquakes the lower crustal strain rates and longer fault healing times in intraplate environments may be responsible for this high average value we find constant stress drop between m2 and m5 up to the bandwidth resolution limit 80 hz of the study and no evidence of stress drop breakdown for m2 to m1 earthquakes we find consistently high radiated seismic energy and apparent stress and a median radiated energy to seismic moment ratio of 9 10 5 this is significantly larger than estimates for interplate earthquakes 2 10 5 and consistent with higher stress drops and stronger faults

a machine learning based surrogate model of mars thermal evolution constraining initial conditions and parameters of mantle convection for a planet often requires running several hundred computationally expensive simulations in order to find those matching certain observables such as crustal thickness duration of volcanism or radial contraction a lower fidelity alternative is to use 1 d evolution models based on scaling laws that parametrize convective heat transfer however this approach is often limited in the amount of physics that scaling laws can accurately represent e g temperature and pressure dependent rheologies or mineralogical phase transitions can only be marginally simulated we leverage neural networks to build a surrogate model that can predict the entire evolution 0 4 5 gyr of the 1 d temperature profile of a mars like planet for a wide range of values of five different parameters reference viscosity activation energy and activation volume of diffusion creep enrichment factor of heat producing elements in the crust and initial temperature of the mantle the neural network we evaluate and present here has been trained from a subset of 10 000 evolution simulations of mars ran on a 2 d quarter cylindrical grid from which we extracted laterally averaged 1 d temperature profiles the temperature profiles predicted by this trained network match those of an unseen batch of 2 d simulations with an average accuracy of 99 7per cent

the sedimentary structure in the western weddell sea abstract the western weddell sea was one of the regions where breakup of gondwana was initiated about 180 ma the perennial ice coverage makes it difficult to obtain knowledge about the thickness and structure of the sediments that might reveal information about the break up process and the evolution of the weddell sea basin seismic investigations south of 66 s provide a first detailed view of the sediment structure of the westernmost weddell sea in addition four wide angle seismic measurements with offsets up to 31 km were undertaken the sediment thickness ranges from 4 8 0 3 to 7 3 0 3 km but seems to be relatively uniform in the area between the eastern continental margin of the antarctic peninsula at 52 w and 35 w three out of four measurements of the sediment thickness in this area are between 4 8 and 5 7 km the depth of the acoustic basement is constrained by both the wide angle data and by seismic reflection profiles acquired at the same time a comparison of the two western wide angle seismic measurements with estimates for the non magnetic overburden derived from aeromagnetic data show a deviation of more than 1 km the depth velocity functions reveal that the sediments of the western weddell sea are divided into two sequences that are separated by a broad transition zone at a depth of 6 7 km

revised tectonic implications for the magnetic anomalies of the western weddell sea abstract ten years after the usac u s a rgentina c hile project which was the most comprehensive aeromagnetic effort in the antarctic peninsula and surrounding ocean basins questions remain regarding the kinematics of the early opening history of the weddell sea key elements in this complex issue are a better resolution of the magnetic sequence in the western part of the weddell sea and merging the usac data set with the other magnetic data sets in the region for this purpose we reprocessed the usac data set using a continuation between arbitrary surfaces and equivalent magnetic sources the equivalent sources are located at a smooth crustal surface derived from the existing bathymetry topography and depths estimated by magnetic inversions the most critical area processed was the transition between the high altitude survey over the antarctic peninsula and the low altitude survey over the weddell sea that required downward continuation to equalize the distance to the magnetic source this procedure was performed with eigenvalue analysis to stabilize the equivalent magnetic source inversion the enhancement of the mesozoic sequence permits refining the interpretation of the seafloor spreading anomalies in particular the change in shape and wavelength of an elongated positive in the central weddell sea suggests that it was formed during the cretaceous normal polarity interval the older lineations in the southwestern weddell sea are tentatively attributed to susceptibility contrasts modeled as fracture zones numerical experimentation to adjust synthetic isochrons to seafloor spreading lineations and flow lines to fracture zones yields stage poles for the opening of the weddell sea since 160 ma to anomaly 34 time the corresponding reconstructions look reasonable within the known constraints for the motions of the antarctic and south america plates however closure is not attained between 160 and 118 ma if independent published east antarctica africa south america rotations are considered the lack of closure may be overcome by considering relative motion between the antarctic peninsula and east antarctica until 118 ma time an important component of convergence

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

rock and stiff soil site amplification dependency on vs30 and kappa κ0 abstract a ground motion prediction equation gmpe specific to rock and stiff soil sites is derived using seismic motion recorded on high v s 30 sites in japan this gmpe applies to events with 4 5 m w 6 9 and v s 30 ranging from 500 to 1500 m s stiff soil to rock sites the empirical site coefficients obtained and the comparison with the simulated site functions show that seismic motion on rock and stiff soil sites does not depend only on v s 30 but also on the high frequency attenuation site properties 0 the effects of the site specific 0 on site amplification are analyzed using stochastic simulations with the need to take into account both of these parameters for rock site adjustments adding the site specific 0 into the gmpes thus appears to be essential in future work the rock site stochastic ground motion simulations show that the site specific 0 controls the frequency corresponding to the maximum response spectral acceleration f amp 1 this observation is used to link the peak of the response spectral shape to 0 in this specific japanese dataset and then to add the effects of high frequency attenuation into the previous gmpe from the peak ground acceleration and up to periods of 0 2 s the inclusion of 0 allows the observed bias to be corrected for the intraevent residuals and thus reduces sigma however this 0 determination is limited to a minimum number of rock site records with m w 4 5 and to distances of less than 50 km

an airborne gravity study of eastern north carolina the naval research laboratory nrl has developed a prototype airborne gravity measurement system the core of the system is a lacoste and romberg air sea gravity meter mounted on a three axis stable platform corrections to the gravimeter data for altitude and variations in altitude are determined from a combination of highly precise radar and pressure altimeters the original prototype system was designed for use over oceanic areas we recently incorporated the pressure measurement to extend use of the airborne system to terrestrial regions where occasional radar altitudes over points of known topographic height can be obtained the radar heights are used to relate the pressure altitudes to absolute altitudes and to determine the slopes of the isobaric surfaces vertical accelerations due to horizontal velocity over a curved rotating earth the eotvos correction and precise two dimensional positions are determined from a texas instrument p code global positioning system the updated system was tested

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

variability of seismic source spectra estimated stress drop and radiated energy derived from cohesive zone models of symmetrical and asymmetrical circular and elliptical ruptures large variability of earthquake stress drops and scaled energy has been commonly reported in the literature but it is difficult to assess how much of this variability is caused by underlying physical source processes rather than simply observational uncertainties here we examine a variety of dynamically realistic rupture scenarios for circular and elliptical faults and investigate to what extent the variability in seismically estimated stress drops and scaled energy comes from differences in source geometry rupture directivity and rupture speeds we numerically simulate earthquake source scenarios using a cohesive zone model with the small scale yielding limit where the solution approaches a singular crack model with spontaneous healing of slip compared to symmetrical circular source models asymmetrical models result in larger variability of estimated corner frequencies and scaled energy over the focal sphere the general behavior of the spherical averages of corner frequencies and scaled energy in the subshear regime extends to the supershear regime although shear mach waves generated by the propagation of supershear rupture lead to much higher corner frequency and scaled energy estimates locally our results suggest that at least a factor of 2 difference in the spherical average of corner frequencies is expected in observational studies simply from variability in source characteristics almost independent of the actual stress drops translating into a factor of 8 difference in estimated stress drops furthermore radiation efficiency estimates derived from observed seismic spectra should not be directly interpreted as describing rupture properties unless there are independent constraints on rupture speed and geometry

on the characteristics of earthquake stress release variations in japan abstract the amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process as such it represents a key parameter for improving our understanding of earthquake source physics and for reliable ground motion prediction large earthquake populations usually show variations in stress release as large as three orders of magnitude but the underlying mechanisms have remained largely elusive and particularly the dependence of stress release on earthquake size is still a matter of debate here i use a unique dataset from japan encompassing earthquakes of a wide magnitude range and spatial coverage to show that stress release variations of crustal earthquakes are strongly correlated with heat flow variations indicating that they are thermally controlled in contrast subcrustal events depict highest stress release in regions of strong subduction interface coupling and overall less pronounced variability as compared with crustal earthquakes stress release is overall only weakly dependent on earthquake size but at local scales i e within individual earthquake sequences the dependence can be very strong and apparently varies with stress regime accounting for these systematic variations reduces the stress release variability on local scale by a factor of two to three as compared with the full earthquake population a finding that is of key significance in the endeavor to reduce the uncertainties in future ground motion predictions

earthquake stress drops and inferred fault strength on the hayward fault east san francisco bay california we study variations in earthquake stress drop with respect to depth faulting regime creeping versus locked fault behavior and wall rock geology we use the p wave displacement spectra from borehole seismic recordings of m 1 0 4 2 earthquakes in the east san francisco bay to estimate stress drop using a stack and invert empirical green s function method the median stress drop is 8 7 mpa and most stress drops are in the range between 0 4 and 130 mpa an apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4 55 hz there is a trend of increasing stress drop with depth with a median stress drop of 5 mpa for 1 7 km depth 10 mpa for 7 13 km depth and 50 mpa deeper than 13 km we use s p amplitude ratios measured from the borehole records to better constrain the first motion focal mechanisms high stress drops are observed for a deep cluster of thrust faulting earthquakes the correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress we compare the spatial distribution of stress drops on the hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near oakland this also suggests a connection between stress drop and applied shear stress as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher strength material the stress drops do not directly correlate with the strength of the proposed wall rock geology at depth suggesting that the relationship between fault strength and the strength of the wall rock is complex

a preliminary assessment of the hydrocarbon potential of the larsen basin antarctica abstract the larsen basin on the northwest margin of the weddell sea formed as a mesozoic ensialic basin during gondwana breakup deposition was either in half grabens on the extending weddell sea margin or in a restricted back arc basin at the northern end of this basin 5 6 km of sedimentary rock crop out on james ross island exposing elements of a large potential hydrocarbon system aeromagnetic and outcrop data suggest that the basin structure inferred from james ross island can be recognised at least as far south as 70 s upper jurassic anoxic marine strata deposited prior to the main phase of arc development form a rich potential source t o c up to 3 5 with both marine and terrestrial kerogens arc derived volcaniclastic sediments of barremian oligocene age form a regressive megasequence basal strata represent slope apron and rudaceous submarine fan deposits proximal to the margin fan conglomerates form lenticular bodies hundreds of metres thick and tens of kilometres across enveloped in slope apron mudstones late cretaceous fault reactivation and uplift led to dramatic shallowing of the basin with deposition of shelf facies although there are many potentially attractive reservoir targets there may be problems of pore occlusion due to the abundant labile volcanic grains however there is evidence of more quartzose sandstone towards the top of the section and inferentially toward the basin centre in the larsen basin there is moderate potential for oil generated from upper jurassic source rocks and reservoired in cretaceous and tertiary sandstones and conglomerates in large stratigraphic or structural traps caused by partial basin inversion during deposition

finite fault slip model of the 2011 mw 5 6 prague oklahoma earthquake from regional waveforms the slip model for the 2011 mw 5 6 prague oklahoma earthquake is inferred using a linear least squares methodology waveforms of six aftershocks recorded at 21 regional stations are used as empirical green s functions egfs the solution indicates two large slip patches one located around the hypocenter with a depth range of 3 5 5 km the other located to the southwest of the epicenter with a depth range from 7 5 to 9 5 km the total moment of the solution is estimated at 3 37 1024 dyne cm mw 5 65 the peak slip and average stress drop for the source at the hypocenter are 70 cm and 90 bars respectively approximately one half the values for the mw 5 8 2011 mineral virginia earthquake the stress drop averaged over all areas of slip is 16 bars the relatively low peak slip and stress drop may indicate an induced component in the origin of the prague earthquake from deep fluid injection

seismic stratigraphy and tectonics of the northwestern weddell sea antarctica inferred from marine geophysical surveys abstract marine geophysical studies of the northwestern weddell sea show several interesting stratigraphic and tectonic features synthesis of the odp drilling results on the south orkney microcontinent with the circum antarctic depositional model allows identification of the main reflectors within the cretaceous cenozoic sedimentary cover the age and composition of pre rift syn rift and post rift units probably vary throughout the region the observed seismic pattern of the jane bank suggests a young asymmetric zone of extension a seismic record across the south orkney trough and central scotia basin indicates an association with an accretion zone and spreading centre

small earthquakes deviate from the omega square model as revealed by multiple spectral ratio analysis we examine the omega square model by estimating the source spectra of 196 m w 3 2 4 0 shallow earthquakes in the northern ibaraki prefecture and the fukushima prefecture hamadori area of japan using multiple spectral ratio analysis spectral ratios of the seismograms of target events to those of multiple nearby small events empirical green s function egf events allow for negation of path and site effects and are fitted by the omega square model the residual spectra for different egf events exhibit similar curves indicating how the source spectra of the target events deviate from the omega square model many earthquakes deviate remarkably whereas other events fit well the possible implications of these findings are incoherencies in the rupture process the double corner frequency model and a high frequency falloff exponent value slightly higher than 2 although this is still an open question this study will help to improve the source spectrum model enhancing not only source studies but strong motion assessments and other seismological studies online material figures showing results of spectral analysis of the events with the largest and smallest peak to peak amplitudes

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

ground motions for induced earthquakes in oklahoma we examine ground motions for a sequence of earthquakes in oklahoma where assessment of hazard contributions from induced seismicity is of particular interest we aim to empirically calibrate a model driven equation that was derived for central and eastern north america cena so that it will match the observed ground motions of the 2011 prague oklahoma sequence we first show that ground motions in oklahoma decay at a rate similar to the average attenuation observed in the stable continental region of cena we then search for any needed adjustments to the cena source model to match ground motions from the induced seismicity sequence that occurred near prague in 2011 an interesting feature noted in the ground motion analysis is that the stress parameters for the prague mainshock events m 5 are notably higher than those for aftershocks moreover the stress parameter that characterizes the high frequency ground motion decays in both time and space relative to the three largest events the largest events in the prague sequence have similar source parameters to natural cena events of the same magnitude and focal depth but their aftershocks have weaker motions

discriminating induced seismicity from natural earthquakes using moment tensors and source spectra earthquake source mechanisms and spectra can provide important clues to aid in discriminating between natural and induced events in this study we calculate moment tensors and stress drop values for eight recent induced earthquakes in the western canadian sedimentary basin with magnitudes between 3 2 and 4 4 as well as a nearby magnitude 5 3 event that is interpreted as a natural earthquake we calculate full moment tensor solutions by performing a waveform fitting procedure based on a 1 d transversely isotropic velocity model in addition to a dominant double couple dc signature that is common to nearly all events most induced events exhibit significant non double couple components a parameter sensitivity analysis indicates that spurious non dc components are negligible if the signal to noise ratio snr exceeds 10 and if the 1 d model differs from the true velocity structure by less than 5 estimated focal depths of induced events are significantly shallower than the typical range of focal depths for intraplate earthquakes in the canadian shield stress drops of the eight induced events were estimated using a generalized spectral fitting method and fall within the typical range of 2 to 90 mpa for tectonic earthquakes elastic moduli changes due to the brittle damage production at the source presence of multiple intersecting fractures dilatant jogs created at the overlapping areas of multiple fractures or non planar pre existing faults may explain the non dc components for induced events

new perspectives on self similarity for shallow thrust earthquakes scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment large subduction earthquakes are typically remote and we mostly rely on teleseismic body waves to extract information on their slip rate functions we estimate the p wave source spectra of 942 thrust earthquakes of magnitude mw 5 5 and above by carefully removing wave propagation effects geometrical spreading attenuation and free surface effects the conventional spectral model of a single corner frequency and high frequency falloff rate does not explain our data and we instead introduce a double corner frequency model modified from the haskell propagating source model with an intermediate falloff of f 1 the first corner frequency f1 relates closely to the source duration t1 its scaling follows m0 t13 for mw 7 5 and changes to m0 t12 for larger earthquakes an elliptical rupture geometry better explains the observed scaling than circular crack models the second time scale t2 varies more weakly with moment m0 t25 varies weakly with depth and can be interpreted either as expressions of starting and stopping phases as a pulse like rupture or a dynamic weakening process estimated stress drops and scaled energy ratio of radiated energy over seismic moment are both invariant with seismic moment however the observed earthquakes are not self similar because their source geometry and spectral shapes vary with earthquake size we find and map global variations of these source parameters

does strong tropospheric forcing cause large amplitude mesospheric gravity waves a deepwave case study the deepwave deep propagating wave experiment campaign was designed for an airborne and ground based exploration of gravity waves from their tropospheric sources up to their dissipation at high altitudes it was performed in and around new zealand from 24 may till 27 july 2014 being the first comprehensive field campaign of this kind a variety of airborne instruments was deployed onboard the research aircraft nsf ncar gulfstream v gv and the dlr falcon additionally ground based measurements were conducted at different sites across the southern island of new zealand including the dlr rayleigh lidar located at lauder 45 04 s 169 68 e we focus on the intensive observing period iop 10 on the 4 july 2014 when strong wsw winds of about 40 m s at 700 hpa provided intense forcing conditions for mountain waves at tropopause level the horizontal wind exceeded 50 m s and favored the vertical propagation of gravity waves into the stratosphere the dlr rayleigh lidar measured temperature fluctuations with peak to peak amplitudes of about 20 k in the mesosphere 60 km to 80 km msl over a period of more than 10 hours two research flights were conducted by the dlr falcon falcon flight 04 and 05 during this period with straight transects mt aspiring 2a over new zealand s alps at three different flight levels around the tropopause approx 11 km msl these research flights were coordinated with the gv research flight 16 where the largest mountain wave amplitudes at flight level approx 13 km msl were measured during deepwave additionally a first analysis of falcon s in situ flight level data revealed amplitudes in the vertical wind larger than 4 m s at all altitudes in the vicinity of the highest peaks of the southern alps here we present a comprehensive picture of the gravity wave characteristics and propagation properties during this interesting gravity wave event we use the airborne observations combined with a comprehensive set of ground based measurements consisting of 13 radiosoundings 1 5 hourly interval together with the dlr rayleigh lidar to cover the altitude range from the troposphere to the mesosphere high resolution 1 hourly ecmwf analyses and forecasts are used to estimate the propagation conditions of the excited mountain waves the goal of our investigation is to find out whether the large amplitude mesospheric gravity waves are caused by the strong tropospheric forcing

late mesozoic sedimentation in the northern antarctic peninsula and its relationship to the southern andes two distinct phases of island are evolution are recognized in late mesozoic sedimentary rocks of the northern antarctic peninsula during late jurassic kimmeridgian tithonian times alternating radiolaria rich mudstones and ash fall tuffs were deposited under shallow marine euxinic conditions in association with restricted volcanic centres the name nordenskjold formation is proposed for this lithostratigraphic unit subsequently during the early cretaceous a major episode of volcanism and uplift led to the construction of an emergent are terrane simultaneous development of a retro arc basin resulted in the accumulation of coarse volcaniclastic detritus along the eastern side of the arc retro are sedimentation and intermittent volcanism continued into the late cretaceous and early tertiary although the pattern of sedimentation in the northern antarctic peninsula is broadly comparable to that of the southern andes an active marginal basin has not been recognized in the former area interbedded mudstones and tuffs identical to those of the nordenskjold formation were deposited in the southern andes and south georgia during the late jurassic early cretaceous

relics of a complex triple junction in the weddell sea embayment antarctica abstract interpretation of an airborne magnetic data compilation containing a key new survey together with re tracked satellite gravity data from the weddell sea embayment wse west antarctica suggests rift rift rift triple junction formation at the onset of gondwana breakup in the early middle jurassic a complex system of northwest southeast rifts was active contemporaneously with an east west trending rift this rift activity led to northward separation of the falkland plateau and formation of the weddell sea by sea floor spreading atypically the jurassic passive margin of gondwana shows evidence for coeval extension in two directions and a large volume of interpreted magmatic material this is consistent with initial doming above a mantle plume and we suggest that this resulted in the formation of a triple junction magnetic anomalies indicate a series of faults perpendicular to igneous intrusions and extrusions with outlines that range in shape from lozenges to parallel ridges they show remarkably good spatial correlation with free air gravity anomalies even in areas of sea ice we base a structural elements map and timing sequence for the events in the wse during early gondwana breakup on anomaly cross cutting relationships

an alternative explanation for intermediate wavelength magnetic anomalies harrison and carle this issue and others have examined very long profiles of the magnetic field and have calculated one dimensional power spectra in these they expect to see but do not find a minimum in power at intermediate wavelengths between 65 and 150 km conventional one dimensional models of the field predict very little power in this band which lies between the spectral peaks arising from sources in the crust and the core mantle sources or high intensity long wavelength magnetizations have been proposed to account for the observations an alternative more plausible explanation is that one dimensional spectra of two dimensional fields contain contributions from wavenumbers in the perpendicular i e nonsampled direction unless the seafloor spreading anomalies are perfectly lineated at right angles to the profile some low wavenumber energy must be attributed to this effect we propose that such directional aliasing is a major factor in the power spectra to support this idea we discuss theoretical models and analyze a large scale marine survey

bathymetry depth to magnetic basement and sediment thickness estimates from aerogeophysical data over the western weddell basin we estimated the bathymetry and sediment thickness of a remote and difficult to access portion of the antarctic continental margin using aerogeophysical surveying techniques the u s argentina chile aerogeophysical survey collected magnetic and gravity data over the basins surrounding the antarctic peninsula thirty seven of these flight lines were used to estimate bathymetry and depth to magnetic basement for the western weddell basin a wavenumber technique was applied to individual magnetic anomaly profiles in an automated fashion to obtain estimates of the depth to magnetic basement the bathymetric estimates were obtained by admittance inversions of the gravity field the results were then gridded at a 40 km interval for the region 64 w 44 w 73 s and 62 s bathymetric estimates and depth to magnetic basement estimates were differenced at each grid point to obtain a regional estimate of the thickness of nonmagnetic overburden assumed to be sediment subsequent spot measurements of topography in the estimated region of the continental margin generally agree to about 52 m the estimated magnetic basement deepens from the antarctic peninsula margin eastward to a maximum of 10 12 km near 54 w we also postulate the existence of two moderately large basins flanking the eastward continuation of the jason peninsula farther east the basement steps upward with a correspondent thinning of the sedimentary layer along the east coast of the peninsula results agree well with seismic studies on james ross island and magnetotelluric studies on marambio island and the larsen nunatak as well as the british antarctic survey basement estimates from aeromagnetic data this study further demonstrates the utility of combined application of airborne and satellite geophysical techniques in the study of structure and tectonic evolution of continental margins and marine basins

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

investigating uncertainties in empirical green s function analysis of earthquake source parameters i use a well recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical green s function egf approach the earthquakes in the largest m 2 1 repeating sequence targeted by the san andreas observatory at depth safod parkfield california are recorded by multiple borehole stations and have simple sources well constrained stress drops and abundant smaller earthquakes to use as egfs i perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings i use egf earthquakes with a range of cross correlation values and separation distances from the main earthquakes the stress drop measurements decrease by a factor of 3 as the quality of the egf assumption decreases a good egf must be located within approximately one source dimension of the large earthquake with high cross correlation i subsample the large number of measurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or egfs are available if only one measurement is available the uncertainties are likely to be at least 50 the uncertainties decrease to 20 with five or more measurements using multiple egfs is a good alternative to multiple stations to investigate the effects of limited frequency bandwidth i recalculate the corner frequencies after progressively decimating the sample rate decreasing the high frequency limit of the bandwidth decreases the estimate of the corner frequency and stress drop the corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal

the age of the weddell basin the deep oceanic basin occupied by the weddell sea separates the east antarctic craton from the antarctic peninsula a largely post palaeozoic orogenic belt an understanding of the tectonic evolution of the basin would resolve most of the remaining problems of gondwanaland reconstruction which revolve around the relative positions of these two fragments and south america norton and sclater1 conclude that indian ocean marine geophysical data essentially support the smith and hallam fit2 but the unacceptable overlap ofundoubtedly old continental crust3 5 on the antarctic peninsula and falkland plateau implies relative motion between the peninsula and east antarctica such motion is not required by the reconstruction of barron and others7 8 which however can be criticized on other grounds9 10 the marine geophysical observations within the intervening ocean basins have proved useful in formulating plate tectonic reconstructions fracture zone trends seafloor spreading type magnetic anomalies crustal heat flux and crustal depth all provide clues to the timing and direction of the continental motions the acquisition of geophysical data from the weddell sea region has been slow11 13 however the combined interpretation of the two largest data sets extant12 13 now being undertaken seems likely to provide a more tightly constrained gondwanaland solution as a first step we report here an estimated age for the weddell sea floor in the area bounded by 60 and 73 s 5 and 35 w shown in fig 1

temporal changes in stress drop frictional strength and earthquake size distribution in the 2011 yamagata fukushima ne japan earthquake swarm caused by fluid migration

spectral analysis of k net and kik net data in japan part ii on attenuation characteristics source spectra and site response of borehole and surface stations abstract in this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the k net and kik net networks in japan in order to derive attenuation characteristics source spectra and site response for this purpose we use a total of more than 67 000 s wave records from 2178 earthquakes m jma 2 7 8 obtained at 1555 stations at the earth s surface and more than 29 000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m attenuation characteristics are investigated in five separate regions showing that crustal q depicts lower values in central compared to southern japan and a significant frequency dependence is observed in every region the source spectra follow the 2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones while strong amplification effects dominate the site contributions for the surface sensors those for the borehole sensors are characterized by smaller variability nevertheless consistent with observations from deconvolution of borehole surface recording pairs downgoing wave effects are visible in the site contributions for many borehole stations finally the site amplification functions obtained at the surface are compared with surface to borehole s b and horizontal to vertical h v spectral ratios showing that the s b ratios generally provide better estimates of the horizontal amplification than the h v ratios due to amplification of the vertical component of ground motion

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

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

stress drops of repeating earthquakes on the san andreas fault at parkfield i calculate well resolved corner frequencies and stress drops for 25 earthquakes 1989 2006 in the three repeating sequences targeted by the san andreas fault observatory at depth using borehole data and multiple highly correlated empirical green s functions egfs the earthquakes in the largest magnitude m 2 1 cluster exhibit source spectra well fit by a circular source model the corner frequencies correlate with those from the regional study by allmann and shearer 2007 suggesting that the interevent variability is resolvable the earthquakes have stress drops between 25 and 65 mpa with a gradual increase before the 2004 m6 earthquake followed by an immediate decrease then a rapid return to previous levels the spectra of the cluster of m 1 9 earthquakes include high frequency energy not fit by simple source models and so stress drops are unreliable and probably underestimated 1 20 mpa there is no correlation with previous studies and interevent variation is not resolvable the earthquakes in the smallest magnitude cluster m 1 8 have the highest corner frequencies but similar stress drops 4 120 mpa the stress drops exhibit the same temporal variation as the first cluster but there is poor correlation with allmann and shearer 2007 probably because their frequency bandwidth is too limited

deep and bottom water of the weddell sea s western rim oceanographic observations from the ice station weddell 1 show that the western rim of the weddell gyre contributes to weddell sea bottom water a thin 300 meters highly oxygenated benthic layer is composed of a low salinity type of bottom water overlying a high salinity component this complex layering disappears near 66 s because of vertical mixing and further inflow from the continental margin the bottom water flowing out of the western rim is a blend of the two types additionally the data show that a narrow band of warmer weddell deep water hugged the continental margin as it flowed into the western rim providing the continental margin with the salt required for bottom water production

antarctica geology and hydrocarbon potential antarctica covers approximately 14 million sq km 5 405 800 sq mi and hosts an estimated 90 of the world s ice glacial ice covers about 98 of the continent with an average thickness of 2 000 m 6 562 ft based on limited data geologists have identified 21 sedimentary basins for the antarctic and immediately adjacent areas these include 6 onshore subglacial basins and 15 offshore basins excluding 11 basins considered to have little or no potential the other 10 basins contain an estimated 16 9 million cu km 4 05 million cu mi of sediment having a potential hydrocarbon yield of 203 billion barrels oil equivalent end page 55

spatial and temporal stress drop variations in small earthquakes near parkfield california 1 we estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the parkfield segment of the san andreas fault in central california we use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed p wave source spectra with a spatially varying empirical green s function egf our brune type stress drop estimates vary from 0 1 to over 100 mpa with a median value of 6 75 mpa which is nearly constant with moment implying self similarity over the ml 0 5 to 3 0 range of our data the corner frequency decreases for earthquakes at shallower depths consistent with slower rupture velocities and reduced shear wave velocities in local velocity models the estimated median stress drops show significant lateral variations we find lower stress drops in the middle mountain asperity and along the creeping fault section and higher stress drops in the hypocentral region of the 2004 m6 0 parkfield earthquake the main shock did not alter the overall pattern of high and low stress drop regions however a statistical test reveals areas with significant changes in computed stress drops after the main shock which we compare to estimated absolute shear stress changes from a main shock slip model by calculating t from the spectral egf ratio we also identify areas with increased attenuation after the main shock and we are able to distinguish source effects and near source attenuation effects in the spectral analysis these results are confirmed independently from spectral ratios of repeating microearthquake clusters

mesozoic evolution of west antarctica and the weddell sea basin new paleomagnetic constraints paleomagnetic data from the antarctic peninsula and our recent results from the ellsworth whitmore mountains block suggest that since the middle jurassic these two west antarctic blocks have undergone little relative movement and together have rotated relative to the east antarctic craton new data from lower cretaceous rocks from the thurston island region of west antarctica suggest that on the basis of paleomagnetic constraints the antarctic peninsula ellsworth whitmore mountains and thurston island blocks define a single entity which we call weddellia some motion between these blocks is possible within the limits of the paleomagnetic data between the middle jurassic and early cretaceous weddellia remained attached to west gondwanaland while east antarctica moved southward dextrally relative to weddellia from the early cretaceous to mid cretaceous weddellia rotated clockwise 30 and moved sinistrally approximately 2500 km relative to east antarctica to its present day position we suggest the early to mid cretaceous to be the time of the main if not initial opening of the weddell sea

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

internal waves and tides in the western weddell sea observations from ice station weddell the upper ocean current and temperature fields in the western weddell sea were measured from the drifting pack ice at ice station weddell 1 isw and nearby sites using a vertical profiler and an array of moored sensors in january june 1992 these data document the structure and variability of the internal gravity wave field and tidal currents in this remote region the variance of the internal wave continuum frequency n at isw was 0 2 0 6 of the garrett munk gm universal level for the first 60 days increasing to near gm levels during the final 10 days of the deployment in contrast the energy density at site c 50 km west of isw and farther up the continental slope was always near gm levels variations may be due to a combination of spatial and temporal gradients of the internal wave field at isw coherence between vertically separated sensors was used to estimate vertical wave number bandwidth energy and bandwidth estimates are compared with previous studies in both ice covered and temperate oceans using our measurements of the internal wave field and existing parameterizations of mixing we estimate the vertical heat flux from the warm deep water toward the surface at isw the upward heat flux due to mixing associated with the internal waves was about 1 w m 2 much less than the 20 w m 2 average flux required to balance the heat budget for the weddell gyre tidal currents contributed significantly to the total measured horizontal velocity variance the tides were primarily barotropic and increased toward the west in both the semidiurnal and diurnal frequency bands it is suggested that the stronger tidal currents to the west over the shallower water of the upper continental slope are indirectly responsible for the higher internal wave energy at site c relative to isw

comparison of direct and coda wave stress drop measurements for the wells nevada earthquake sequence 1 i calculate the corner frequencies and stress drops of the seven largest earthquakes m4 6 in the wells nevada sequence 2008 using both coda and direct waves i use spectral ratio empirical green s function egf and methods to investigate whether differences and uncertainties in the analyses could affect the calculated source parameters i find that the source spectral ratios from the coda and direct s waves are similar for the same pairs of earthquakes but that the source spectra and corresponding source parameters depend systematically on whether the earthquake of interest is the larger or smaller within the spectral ratio mayeda and malagnini 2009a calculated coda spectral ratios between the m6 main shock and six large aftershocks m 4 and performed a combined inversion to calculate source parameters they found that the main shock had a higher stress drop than the large aftershocks i model the identical spectral ratios individually in the manner that i use for direct waves i find that the choice of source model and fitting procedure produces significant random scatter but no systematic biases i calculate direct wave ratios for the same earthquake pairs and find higher variability but no systematic difference in the results lastly i use m2 8 3 2 aftershocks as egfs for the large aftershocks these spectral ratios yield significantly higher corner frequencies and stress drops for the large aftershocks than when the same earthquakes are the denominator in ratios with the main shock to improve the quality of egf analyses i propose strict objective criteria for acceptance of a spectral ratio fit 1 observable source pulse 2 the amplitude ratio of the low to high frequency limits of the fit is at least 5 and 3 the corner frequency only varies by 50 when the variance is within 5 of the minimum

present day stress orientations and tectonic provinces of the nw borneo collisional margin received 23 september 2009 revised 17 may 2010 accepted 9 june 2010 published 16 october 2010 1 borehole failure observed on image and dipmeter logs from 55 petroleum wells across the nw borneo collisional margin were used to determine maximum horizontal stress sh orientations combined with seismic and outcrop data they define seven tectonic provinces the baram delta deepwater fold thrust belt exhibits three tectonic provinces its inner shelf inverted province sh is nw se margin normal its outer shelf extension province sh is ne sw margin parallel and its slope to basin floor compression province sh is nw se margin normal in the inverted province sh reflects inversion of deltaic normal faults the sh orientations in the extension and compression provinces reflect deltaic gravitational tectonics the shale and minibasin provinces have been recognized in offshore sabah in the shale province sh is n010 e which aligns around the boundary of a massif of mobile shale currently no data are available to determine sh in the minibasin province in the balingian province sh is ese wnw reflecting ese absolute sunda plate motions due to the absence of a thick detachment seen elsewhere in nw borneo the central luconia province demonstrates poorly constrained and variable sh orientations these seven provinces result from the heterogeneous structural and stratigraphic development of the nw borneo margin and formed due to complex collisional tectonics and the varied distribution and thicknesses of stratigraphic packages

analysis of james ross island volcanic complex and sedimentary basin based on high resolution aeromagnetic data abstract high resolution aeromagnetic surveys provide a geophysical tool to help image the subsurface structure of volcanoes and their tectonic framework here we interpret high resolution aeromagnetic data and models for james ross archipelago and surrounding regions to provide a new perspective on neogene magmatism emplaced along the eastern margin of the antarctic peninsula based on the analysis and modelling of magnetic anomalies we were able to image the subglacial extent of miocene to recent alkaline rocks of the james ross island volcanic group and map tectonic structures that appear to have exerted important controls on neogene magmatism high amplitude linear anomalies detected over mount haddington stratovolcano were modelled as caused by subvertical feeder bodies extending to a depth of at least 3 km these feeder bodies may have been emplaced along a n s oriented volcano tectonic rift zone we also identified several effusive subglacial centres and imaged two concentric magnetic arcs which we related to neogene volcanic and subvolcanic lineaments likely controlled by mid cretaceous strike slip fault belts and associated deformation zones the regional magnetic quiet zone that encompasses james ross island is caused by the thick sedimentary infill of the larsen basin and a low amplitude magnetic high within the basin is inferred to reflect a basement push up structure associated with strike slip faulting along the eastern edge of the antarctic peninsula in the offshore regions magnetic anomalies southwest of tabarin peninsula and west of vega island may reflect recent volcanic structures that have yet to emerge from the sea floor

high frequency ice motion and divergence in the weddell sea we describe the spatial variability of high frequency ice velocity in the weddell sea using satellite tracked ice mounted buoys ice motion is analyzed separately for diurnal 1 36 1 18 cph and semidiurnal 1 18 1 6 cph bands ice motion in both bands is caused by a combination of ocean tidal currents and wind stress monthly mean diurnal band ice speeds over the deep basin range from 2 to 4 cm s 1 depending on wind stress variance and ice concentration cice higher speeds 10 cm s 1 are found in the semidiurnal band in regions of low cice notably the northern weddell sea where the ice velocity is dominated by the inertial response to wind stress variations monthly mean tidal band ice speeds over the continental slope and shelves often exceed 10 cm s 1 we use comparisons between buoy velocities moored current meter data and an ocean tidal model to demonstrate that ice motion is frequently a good indicator of ocean tidal currents in strongly tidal regions the standard deviation of the divergence of ocean tidal currents estimated from an ocean only tidal model is small 0 1 10 6 s 1 over most of the weddell sea but has values of 1 5 10 6 s 1 along the ronne ice front and the continental shelf break high frequency ice divergence is dominated by ice response to wind stress rather than by tides except along the shelf break and ice fronts in these tidally dominated regions the periodic divergence maintains a mean lead open water area of 2 5 this increased lead fraction implies an increase in area averaged winter ocean to atmosphere heat exchange rate of 4 10 w m 2 and an increase in salt flux into the upper ocean as new ice forms in the leads

a new magnetic map of the weddell sea and the antarctic peninsula abstract as part of the antarctic digital magnetic mapping project admap workers from vniiokeangeologia russia the british antarctic survey uk and the naval research laboratory usa have brought together almost all of the available magnetic data in the area 0 120 w 60 90 s the final map covers the whole weddell sea and adjacent land areas the antarctic peninsula and the seas to the west an area comparable in size with that of the usa this paper describes the methods used during the compilation of the map and reviews briefly some of the main features shown on it distinct magnetic provinces are associated with precambrian rocks of the east antarctic craton highly extended continental crust in the weddell sea embayment the arc batholith of the antarctic peninsula and oceanic crust of the northern weddell sea which was created as a direct consequence of south america antarctica plate motion and oceanic crust generated at the pacific antarctic ridge the magnetic anomaly map thus provides an overview of the fragmentation of south western gondwana and the tectonic development of the weddell sea sector of antarctica

investigating microearthquake finite source attributes with iris community wavefield demonstration experiment in oklahoma author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 1072 1087 doi 10 1093 gji ggy203