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

sedimentary geochemical record of human induced environmental changes in the lake brunnsviken watershed sweden environmental changes in lake brunnsviken its watershed and the greater stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments these humaninduced perturbations within the lake s watershed included agriculture urbanization sewage and industrial disposal and water column aeration smaller d 15 ntotal values high organic carbon mass accumulation rates low c n ratios and larger d 13 corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake c s ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity accumulations of redox sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake a recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy

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

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

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

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

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

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

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

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

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

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

measurement and implications of saturn s gravity field and ring mass the interior structure of saturn the depth of its winds and the mass and age of its rings constrain its formation and evolution in the final phase of the cassini mission the spacecraft dived between the planet and the innermost ring at altitudes 2600 3900 km above the cloud tops during six of these crossings a radio link with earth was monitored to determine the gravitational field of the planet and the mass of its rings we find that saturn s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 km the total mass of the rings is 1 54 0 49 10 19 kg 0 41 0 13 times that of the moon mimas indicating that the rings may have formed 10 7 10 8 years ago