stress drops of the 1997 1998 colfiorito central italy earthquakes hints for a common behaviour of normal faults in the apennines stress drop estimates of moderate magnitude earthquakes in the umbria marche region in the northern apennines exhibit a large scatter for the two mw 5 7 and 6 0 main shocks of 26 september 1997 near colfiorito several papers resulted in stress drop estimates of 20 mpa but values as low as 2 3 mpa were proposed as well also for the largest aftershocks mw 4 estimates spread from 1 mpa up to values ten times larger we have critically revisited methods and data used in the literature we have specifically faced the trade off between source and propagation effects as we believe that it is responsible for a part of the large scatter to keep this trade off under control we have applied a methodology that combines the best fit of both source spectra after empirical green s function egf deconvolution and observed ground motion spectra finding that the results of the two different data sets converge independently at the same solution we have used ground motions observed in the colfiorito basin where an accelerograph and a co located seismological broad band station recorded three clusters of earthquakes in a broad magnitude interval 1 7 mw 6 0 we have found that the mainshock aftershock sequences result in stress drops of 2 5 mpa at mw 5 6 with an average tendency to decrease at smaller magnitudes where stress drop variability increases these findings confirm the source scaling recently assessed through empirical green s function deconvolution for another well monitored seismic sequence of normal faulting earthquakes which struck the city of l aquila in the central apennines in april 2009 the similar scaling law of the two areas suggests common mechanisms of stress release for the shallow normal faults in the apennines the propensity of smaller earthquakes to increase in variability with a tendency toward smaller stress drops may reflect an effect of fault strength heterogeneities for smaller size ruptures

on strike slip faulting in layered media summary we study the effects of structural inhomogeneities on the stress and displacement fields induced by strike slip faults in layered media an elastic medium is considered made up of an upper layer bounded by a free surface and welded to a lower half space characterized by different elastic parameters shear cracks with assigned stress drop are employed as mathematical models of strike slip faults which are assumed to be vertical and planar if the crack is entirely embedded within the lower medium case a a cauchy kernel integral equation is obtained which is solved by employing an expansion of the dislocation density in chebyshev polynomials if the crack is within the lower medium but it terminates at the interface case b a generalized cauchy singularity appears in the integral kernel this singularity affects the singular behaviour of the dislocation density at the crack tip touching the interface finally the case of a crack crossing the interface is considered case c the crack is split into two interacting sections each placed in a homogeneous medium and both open at the interface two coupled generalized cauchy equations are obtained and solved for the dislocation density distribution of each crack section an asymptotic study near the intersection between the crack and the interface shows that the dislocation densities for each crack section are bounded at the interface where a jump discontinuity is present as a corollary the stress drop must be discontinuous at the interface with a jump proportional to the rigidity contrast between the adjoining media this finding is shown to have important implications for the development of geometrical complexities within transform fault zones planar strike slip faults cutting across layer discontinuities with arbitrary stress drop values are shown to be admissible only if the interface between different layers becomes unwelded during the earthquake at the crack interface junction planar strike slip faulting may take place only in mature transform zones where a repetitive earthquake cycle has already developed if the rheology is perfectly elastic otherwise the fault cannot be planar we infer that strike slip faulting at depth is plausibly accompanied by en echelon surface breaks in a shallow sedimentary layer where the stress drop is lower than prescribed by the discontinuity condition while ductile deformation or steady sliding at depth may be accommodated by multiple fault branching or by antithetic faulting in the upper brittle layer endowed with lower rigidity but higher stress

source characteristics of the nw himalaya and its adjoining region geodynamical implications abstract in this study we propose a novel interpretation of source parameters estimated using brune model for the nw himalaya and its adjoining region analysis of 157 events 2 2 mw 4 9 resulted in the scaling relationship between seismic moment m0 and corner frequency fc for the region as m0 8 1022 fc 2 89 which is in good unison to the garhwal and the kumaon himalaya with analogous seismogenic potential variability of kappa 0 01 s 0 08 s with varying number of events 2 5 m 5 0 at different depths is indicative of nature and extent of structural heterogeneity beneath the source zone which controls the propensity of background seismicity that provides enough testimony to complex geodynamical set up of the nw himalaya and its adjoining region source radii of source zone varying from 148 m to 975 m with static stress drops calculated for a given constant stress of 0 1 bar 1 bar 10 bar and 100 bar correspond to an average stress drop varied from 0 4 bar to 99 9 bar seismic moments of events vary from 2 64 1019 dyne cm to 2 32 1023 dyne cm with increase of the source radii we infer that variability in stress drop for seismic moment mo is attributed to different seismic sources of varying strengths associated with different structural heterogeneities stress drop of the events has good correspondence with source depth having the linear relationship of shear stress regime in the brittle crust with stress drop and source depth suggesting the presence of intricate subsurface seismogenic sources beneath the nw himalaya and its adjoining region

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

fault plane orientations of small earthquakes of the 1997 umbria marche italy seismic sequence from p wave polarities and rise times summary a two step technique has been developed with the aim of retrieving the fault plane orientation of a small magnitude earthquake the technique uses a set of non linear equations which relate the rise times of first p waves to source parameters source dimension l dip and strike of the fault and intrinsic qp at the first step of the technique the inversion of p polarities provides two fault plane orientations for each focal mechanism solution at the second step the inversion of rise times is carried out to retrieve l and qp by fixing and to the values of the fault plane orientation inferred at the first step a robust analysis based on the random deviates technique allows us to evaluate if one fault plane exists which systematically better fits data and can be considered the true fault plane a parameter is introduced to quantify the level of resolution of the true fault plane a probabilistic approach based on the assumption that errors on data are gaussian distributed allows us to a posteriori validate or reject the true fault plane the technique has been applied to 47 small earthquakes 1 3 ml 3 9 occurred below the town of sellano during the 1997 umbria marche central italy seismic crisis the strike of the inferred fault planes is generally along the apennine direction fault plane solutions can be mainly subdivided into two groups a first group of sw dipping faults and a second group of ne dipping faults these results agree with the present day knowledge of the fault systems in the area an average qp equal to 354 63 has been estimated in agreement with previous attenuation studies

qc qβ qi and qs attenuation parameters in the umbria marche italy region the attenuation of coda and s waves has been inferred for the umbria marche region central italy using seismic waveforms collected during the 1997 seismic crisis the selected dataset is composed of 343 small magnitude 1 4 ml 4 2 earthquakes recorded at a temporary array composed of 23 seismic stations the sato 1977 method based on the assumption of single isotropic scattering has been used to infer qc considering three different lapse times 20 30 and 40 s the coda normalization method aki 1980 has been used to infer q both qc and q show a clear frequency dependence with a different frequency dependent parameter the frequency dependence of qc is comparable with that previously found in the same area and around it using the method of wennerberg 1993 intrinsic and scattering attenuation have been separated intrinsic attenuation is found to be close to coda attenuation and dominates over scattering dissipation coda q increases with increasing lapse time but at a rate smaller than that observed in other areas of the earth coda and intrinsic attenuation in the umbria marche region are very high compared to other seismic active regions of the earth the retrieved high values of intrinsic attenuation may be explained in terms of the previously hypothesized fluid pressurized regime of the crust in the central apennines miller et al 2004

source parameters estimated from the aftershocks of the 1997 umbria marche italy seismic sequence we derived the source parameters of 563 aftershocks 1 4 m l 4 5 of the 1997 umbria marche seismic sequence by analyzing three component digital recordings of a temporary network and developed a local magnitude scale using the whole available data set more than 25 000 waveforms from synthetic wood anderson seismograms then considering a subnetwork composed of nine portable stations more than 12 000 earthquake spectra were corrected for the near surface attenuation parameter k and the path attenuation the corrected spectra were used to compute the seismic moment the source radius and stress drop assuming an 2 brune source model we calculate the relationship log m 17 46 1 12 m l between seismic moment and local magnitude for the studied area the source dimension versus seismic moment relationship did not show any breakdown in the similarity of the rupture process even when events of magnitude less than 2 2 the threshold value for the completeness of the considered catalog were considered the average stress drop obtained analyzing the s wave spectra was 38 10 bar and the source dimension ranged between about 40 and 500 m

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

long period regional wave moment tensor inversion for earthquakes in the western united states source parameters of moderate to large size mw 4 5 earthquakes in the western united states from 1992 to 1994 are determined by point source moment tensor inversion of complete long period t 35 50 s ground motions recorded at regional distances 1 12 stable long period signals are obtained by low pass filtering records from the very broadband seismometers recently deployed in several networks in the western united states these signals are dominated by fundamental mode rayleigh and love waves which have very simple waveforms due to the limited dispersion on the short paths to regional stations since long period motions are relatively insensitive to the attenuation model and crustal structure used in the inversion they provide robust constraints on the seismic moment and faulting geometry as long as adequate azimuthal coverage is available comparisons of solutions for 21 events with results of other regional and teleseismic wave inversions are made to assess the model dependence and uncertainties of our regional centroid moment tensor rcmt solutions rcmt inversion has limited source depth resolution for shallow crustal events but the focal mechanism and seismic moment determinations prove quite stable over a range of source depths in the crust as well as over a range of crustal propagation models simultaneous waveform inversion of shorter period body wave signals can improve the source depth resolution by applying path corrections for heterogeneous crustal structure shorter period surface wave energy can also be inverted allowing the methodology to be extended to lower magnitude regional events as well the rcmt procedure requires minimal signal processing only a sparse broadband network and a simple laterally homogeneous propagation model thus it can readily be automated and applied in near real time to events in the magnitude range from 4 5 to 7 5 distributed over an area as large as the western united states

estimation of source parameters of local earthquakes originated in shillong mikir plateau and its adjoining region of northeastern india abstract we estimate the source parameters seismic moment source radius stress drop and source displacement and scaling laws for local earthquakes that occurred in the shillong mikir plateau assam valley and arunachal himalaya in northeast india during 2001 2008 the source parameters were determined using the spectral analysis of p waves from the vertical component seismograms after correction for attenuation seismic moments are observed within the range from 9 51 10 12 to stress drop ranges from 4 10 5 to 9 10 7 pa for the brune model and 7 10 5 to 1 10 8 pa for the madariaga model seismic events in this study are prominent with an average stress drop of 0 1 10 mpa the effect of site geology may be a contributing factor for such a variation in stress drop source dimensions are however found to be smaller within the major part of the plateau it is suggested that local earthquakes in the region are associated with a brittle shear failure mechanism on fault segments and or the presence of weakened zones and earthquakes are triggered by low deviatoric stress empirical relations between m w m l and m 0 m l are developed leading to the future prediction of calibration coefficients for the local earthquakes in the shillong mikir plateau and its adjoining region online material tables of source parameters

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

non planar fault models complexities induced by crustal layering in transcurrent faulting processes summary crack models suitable to describe transcurrent faulting in the presence of a softer shallow layer are presented we employ the asymptotic theory of generalized cauchy kernel equations to study the singular behaviour of a strike slip crack crossing the welded interface between two different media if a planar crack cuts vertically across a material discontinuity the dislocation density is bounded at the interface but a stress drop discontinuity condition must be met in which the stress drop is proportional to the local rigidity such a condition cannot be fulfilled in several cases two antiplane strain models are proposed to avoid this difficulty in the first model fault bending model the fault surface is affected by a sharp change of the dip angle at the intersection with the interface an unbounded singularity in the dislocation density distribution and in the stress field appears at the interface and its dependence from model parameters is studied a generalized stress drop condition is obtained which can be interpreted in terms of the interaction of the crack with the welded boundary condition in the second model fault branching model the crack is split into three interacting sections with the lower section vertical and the other two sections inclined with respect to the vertical in this case the order of the singularity at the interface remains undetermined this result may be interpreted in terms of the further degree of freedom introduced by the presence of a second fracture in the upper layer in the case of branching two conditions are obtained for the stress drop on the three sections according to both models the generalized stress drop conditions may account for a stress drop ratio between the soft layer and the hard basement lower than the rigidity ratio

variations in the osmium isotope composition of sea water over the past 200 000 years the first osmium isotope data are presented for marine sediments spanning the past 200 000 years two full glacial cycles and establish that there have been ocean wide variations in sea water osmium isotope composition over this time while the osmium isotope composition of sea water has been relatively invariant over much of this interval 187os 186os of 8 5 to 8 6 excursions to lower isotope ratios 187os 186os 8 1 occur late in the last two glacial periods at 20 ka and 160 ka these are times of high global aridity low global temperature and maximum ice extent while various interpretations are possible a likely explanation is that the low sea water ratios reflect reduced chemical weathering of the continents during times of extreme cold and aridity there is no evidence that there is a net enhancement of chemical weathering during periods of continental glaciation the response of ocean composition to changes in input flux constrain the oceanic residence time of osmium to be less than 12 000 years

p and s wave attenuation in the region of marche italy we have found empirical functions to describe the amplitude decay with distance of p and s waves in the marche region of italy these functions result from the analysis of spectral amplitudes of 161 three component digital records from 26 earthquakes recorded by the marchesan seismograph network rsm jointly run by the italian seismological survey of rome ssn and the geophysical observatory of macerata ogsm the events have magnitudes in the range 1 8 m 3 6 and were recorded at hypocentral distances between 9 and 125 km in order to study the possible variations of the quality factor q with the direction of wave propagation q anisotropy we made independent estimates of the attenuation for p sv and sh waves using the longitudinal vertically polarized and transversely polarized components respectively for the whole distance range and in the frequency band analyzed 1 f 25 hz the frequency dependence of q can be approximated as qp 108 4 f0 70 for the p waves qsv 105 6 f0 65 for sv waves and qsh 86 1 f0 70 for sh waves the small difference between the sh and sv spectral decay is within the statistical uncertainties of the estimates suggesting that q anisotropy is negligible however when only deeper wave paths are used in the analysis we observed that at low frequencies f 4 hz the values of qsv are significantly above the estimates of qsh this observation provides additional evidence of the seismic anisotropy reported by margheriti et al geophys res lett 23 2721 2724 1996 for the region the low q anisotropy is possibly related with the weakly deformed adriatic foreland the high attenuation observed for both p and s waves can be explained by the double low velocity layer reported by ponziani et al tectonophysics 252 391 418 1995 since the seismic energy can be trapped between these layers in addition the low values of q obtained for distance ranges between 5 and 50 km can be due to the presence of hot material in the lower crust beneath the northern apennines as suggested by mele et al j geophys res 102 11863 11875 1997

site response of strong motion stations in the umbria central italy region we used near field and regional records from 16 earthquakes m l 4 6 5 9 located in the epicentral area of the 1997 umbria marche sequence to estimate the site response of 40 strong motion stations the distribution of hypocenters covers a distance range from 5 to 100 km we estimated site amplification factors using two techniques namely a generalized spectral inversion method and horizontal to vertical component spectral ratios hvsrs of ground acceleration for the first approach we inverted observed spectral amplitudes for site q and source using a reference site since the site response estimated using hvsrs assumes that the vertical component of motion is amplification free we also separated source and site effects by inverting the vertical component of the acceleration spectra we found that although most of the stations do not show important amplifications on the vertical component a few of them have a significant vertical amplification at low frequencies f q representative of the s wave train shows a frequency dependence that can be approximated by the relation q s 31 2 f 1 2 between 0 3 and 9 5 hz however at high frequencies f 10 hz this dependence weakens and q s takes an approximately constant value of 438

the 1997 umbria marche italy earthquake sequence relationship between ground deformation and seismogenic structure a field survey performed during the 1997 umbria marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks mw 5 7 the ruptures are concentrated in narrow bands that in part are on and near previously mapped high angle normal faults the geometry of the ground deformation is consistent with the ne trending extension indicated by cmt focal solutions of the mainshocks the distribution of aftershocks suggests that the three mainshocks occurred on 40 sw dipping normal faults geological investigations modelling of expected coseismic elevation changes and seismic data suggest that the surface deformation is not the direct result of primary rupture of faults at depth

a california statewide three dimensional seismic velocity model from both absolute and differential times abstract we obtain a seismic velocity model of the california crust and uppermost mantle using a regional scale double difference tomography algorithm we begin by using absolute arrival time picks to solve for a coarse three dimensional 3d p velocity v p model with a uniform 30 km horizontal node spacing which we then use as the starting model for a finer scale inversion using double difference tomography applied to absolute and differential pick times for computational reasons we split the state into 5 subregions with a grid spacing of 10 to 20 km and assemble our final statewide v p model by stitching together these local models we also solve for a statewide s wave model using s picks from both the southern california seismic network and usarray assuming a starting model based on the v p results and a v p v s ratio of 1 732 our new model has improved areal coverage compared with previous models extending 570 km in the sw ne direction and 1320 km in the nw se direction it also extends to greater depth due to the inclusion of substantial data at large epicentral distances our v p model generally agrees with previous separate regional models for northern and southern california but we also observe some new features such as high velocity anomalies at shallow depths in the klamath mountains and mount shasta area somewhat slow velocities in the northern coast ranges and slow anomalies beneath the sierra nevada at midcrustal and greater depths this model can be applied to a variety of regional scale studies in california such as developing a unified statewide earthquake location catalog and performing regional waveform modeling

the ml scale in southern california measurements 9 941 of peak amplitudes on wood anderson instruments or simulated wood anderson instruments in the southern california seismographic network for 972 earthquakes primarily located in southern california were studied with the aim of determining a new distance correction curve for use in determining the local magnitude m l events in the mammoth lakes area were found to give an unusual attenuation pattern and were excluded from the analysis as were readings from any one earthquake at distances beyond the first occurrence of amplitudes less than 0 3 mm the remaining 7 355 amplitudes from 814 earthquakes yielded the following equation for m l distance correction log a 0 log a 0 1 110log r 100 0 00189 r 100 3 0 where r is hypocentral distance in kilometers a new set of station corrections was also determined from the analysis the standard deviation of the m l residuals obtained by using this curve and the station corrections was 0 21 the data used to derive the equation came from earthquakes with hypocentral distances ranging from about 10 to 700 km and focal depths down to 20 km with most depths less than 10 km the log a 0 values from this equation are similar to the standard values listed in richter 1958 for 50 200 km the effect at close distances is consistent with that found in several other studies and is simply due to a difference in the observed 1 r geometrical spreading for body waves and the 1 r 2 spreading assumed by gutenberg and richter in the construction of the log a 0 table m l s computed from our curve and those reported in the caltech catalog show a systematic dependence on magnitude small earthquakes have larger magnitudes than in the catalog and large earthquakes have smaller magnitudes by as much as 0 6 units to a large extent these systematic differences are due to the nonuniform distribution of data in magnitude distance space small earthquakes are preferentially recorded at close distances relative to large earthquakes for large earthquakes however the difference in the two magnitudes is not solely due to the new correction for attenuation magnitudes computed using richter s log a 0 curve are also low relative to the catalog values the differences in that case may be due to subjective judgment on the part of those determining the catalog magnitudes the use of data other than the caltech wood anderson seismographs the use of different station corrections or the use of teleseismic magnitude determinations whatever their cause the departures at large magnitude may explain a 1 0 0 7 proportionality found by luco 1982 between m l s determined from real wood anderson records and those from records synthesized from strong motion instruments if it were not for the biases in reported magnitudes luco s finding would imply a magnitude dependent shape in the attenuation curves we studied residuals in three magnitude classes 2 0 m l 3 5 3 5 m l 5 5 and 5 5 m l 7 0 and found no support for such a magnitude dependence based on our results we propose that local magnitude scales be defined such that m l 3 correspond to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance rather than 1 mm of motion at 100 km this is consistent with the original definition of magnitude in southern california and will allow more meaningful comparison of earthquakes in regions having very different attenuation of waves within the first 100 km

local magnitude scale and seismicity rate for tanzania east africa abstract a local magnitude scale is developed for tanzania east africa using data collected by the 1994 1995 tanzania broadband seismic experiment the waveform data from 1189 local and regional earthquakes located within east africa were corrected for instrument response and convolved with the nominal wood anderson torsion seismograph response appropriate for the original definition of local magnitude a total of 24 710 maximum s wave amplitudes were incorporated into an iterative regression for individual event local magnitudes 38 horizontal component station factors and 2 linear distance dependent factors in the log a 0 term of the equation for m l the resulting distance correction log a 0 is given by log a 0 0 776 log r 17 0 000902 r 17 2 0 where r is hypocentral distance in kilometers this distance correction yields much less ground motion attenuation than observed for southern california and is similar to that observed for local s waves and regional lg waves propagating in eastern north america normalizing the distance correction using the standard constraint of 1 mm ground motion at 100 km for a magnitude 3 0 earthquake results in a bias of nearly half of a magnitude unit between m b and m l with m l being larger normalizing using the constraint of 10 mm of motion at 17 km for m l 3 0 removes the bias in magnitude measures and indicates that structure within tanzania is relatively high q the seismicity rate of tanzania for 1994 1995 was examined using the gutenberg richter seismicity distribution and is seen to follow the relation log n 4 63 0 84 m l where n is the number of earthquakes per year of local magnitude m l or greater the catalog of events used in this study is seen to be complete to magnitude 2 to 2 5

residence time of osmium in the oceans 1 estimates of osmium residence time in the oceans that are based on oceanic mass balance calculations 35 50 kyr appear irreconcilable with those inferred from the recent evolution of the osmium isotope composition of seawater 3 4 kyr it is argued that the osmium budget of the oceans is currently close to steady state and thus that the estimates made by the two methods should agree as the inventory of osmium in the oceans is relatively well constrained these disparate residence time estimates imply wildly different osmium input fluxes to the oceans an osmium residence time of 8 10 kyr is proposed by evaluating the uncertainties and limitations of both methods and it is argued that osmium inputs to the ocean are currently underestimated by a factor of 3 this reflects in part the underestimation of the river input of osmium to the oceans owing to a bias within the existing data set and in part the probable existence of sources of osmium to the oceans that have not yet been identified the very short residence time of 3 4 kyr inferred from the postglacial change in seawater composition assuming a single step change in input flux is rejected as it implies unreasonably high osmium input fluxes to the oceans it is concluded that a postglacial spike in osmium flux associated with a meltwater event must have driven part of the change in seawater composition however it is also shown that such a spike cannot be the dominant cause of the most recent shift in seawater 187os 188os

an empirical method to assess the seismic vulnerability of existing buildings using the hvsr technique the seismic vulnerability of existing buildings is usually estimated according to procedures based on checklists of main structural features the relationship with damage is then assessed using experience from past events an approach used in seismology for the evaluation of site amplification based on horizontal to vertical ratio of weak motion and microtremors has been applied to the structural field this methodology provides an alternative promising tool towards a quick and reliable estimate of seismic vulnerability the advantages are the measurements are quick simple and stable they are non invasive and do not affect at all even temporarily the functions housed in the buildings studied the site effect and the soil structure interaction are explicitly accounted for in the vulnerability estimate when they are excluded in the traditional approaches the relationship with damage is established using meaningful physical parameters related to the construction technology instead of adimensional normalised indexes the procedure has been applied to several case histories of buildings damaged in the recent umbria marche earthquake which occurred in italy in 1997 the same model has been applied to different structures brick stone masonry and infilled r c frames on different geological conditions and under very different seismic loads using this combined site building approach it was possible to explain very sharp variations in the damage pattern

the transport of osmium and strontium isotopes through a tropical estuary abstract we have determined the concentration and isotopic composition of os and sr in the estuarine waters from the godavari delta in peninsular india additionally we have obtained the concentration and isotopic composition of os and al concentration in selected suspended particulate matter recovered on 0 45 m filters the na k mg and ca concentrations of water samples obtained along salinity gradients from two distributary channels in the delta display a general two component mixing between river and sea water the data also reveal that al behaves non conservatively and is affected by interactions with suspended particulates the 87 sr 86 sr ratio of the riverine end member is 0 716303 and shows a linear decrease with salinity to seawater value and sr isotope systematics indicate that its behavior is conservative in the estuary the 187 os 188 os ratio of the godavari river end member is 1 24 and within error of the average eroding upper continental crust the concentration and isotopic composition of os through the two salinity transects shows that its behavior in the godavari estuary is complex and non conservative by comparing the al os ratios and os isotopes in the waters with those of the suspended particulate we find that both os gains and losses occur in the water column however in one of the distributaries vasishta the os concentration of suspended load increases and that of dissolved load decreases with increasing salinity towards the bay of bengal end member we infer that there is removal of seawater os at higher salinities the estimated mean residence time of os in the oceans is 37 14 2 kyr a comparison of the os concentration of the bay of bengal and the indian ocean waters indicates that the rainout rate of os in bay of bengal is 30 faster than that in the open ocean and suggests that the observed discrepancy between the mean residence time calculated from mass balance considerations and that estimated from the relaxation of the os isotopic ratio in marine record may not be real as the relaxation time experiments likely estimate the residence time for a basin sub basin and not for the entire ocean

on the influence of fault bends on the growth of sub rayleigh and intersonic dynamic shear ruptures earthquake ruptures are modeled as dynamically propagating shear cracks with the aim of gaining insight into the physical mechanisms governing their arrest or otherwise the often observed variations in rupture speeds fault bends have been proposed as being the main cause for these variations following this line of reasoning the existence of deviations from fault planarity is chosen as the main focus of this study asymmetric impact is used to generate shear loading and to propagate dynamic mode ii cracks along the bonded interfaces of two otherwise identical homogeneous constituents secondary paths inclined at various angles are also introduced to represent fault bends or kinks the experiments show that certain fault bend inclinations are favored as alternate paths for rupture continuation whereas others suppress further motion of the incoming rupture the asymptotic elastodynamic stress fields at the tip of the growing rupture are used to develop two criteria one energetic and one stress based for rupture propagation or arrest at the kinked interfaces these criteria correlate very well with the experimental results since most field evidence suggests that the average rupture speeds during crustal earthquakes are sub rayleigh this work first focuses on incoming rupture speeds that are just below the rayleigh wave speed reports of intersonic crustal fault rupture speeds having surfaced recently experiments and analyses are also performed within that speed regime

stress changes due to recent seismic events in the central apennines italy the central apennines italy are characterized by moderate seismic activity on normal faults oriented in directions parallel to the apenninic chain the subject of this study is the umbria marche apennines a segment approximately 200 km long where three main seismic events occurred in the last three decades the 1979 norcia earthquake was a mw 5 8 event taking place at the south end of the considered segment the 1984 gubbio earthquake was a mw 5 6 event which took place at the north end the 1997 1998 colfiorito sequence constituted 8 main shocks with magnitudes mw between 5 and 6 and epicenters located between the gubbio and the norcia earthquake areas a model made of an elastic half space is considered in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters and in which the static stress field produced by each event is calculated the analysis of the coulomb stress change c as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades 7 earthquakes of the 9 considered took place where c 0 such an interaction has been confirmed by the analysis of the aftershocks in the colfiorito zone post september 26 1997 about the 61 of the aftershocks considered took place where c 0 the comparison between the cs due to the coseismic stress transfer and the rate t due to the tectonic stress allows us to quantify the time advance of the earthquakes the cs pattern shows positive values in two areas that can be regarded as historical seismic gaps

geodetic and seismologic evidence for slip variability along a blind normal fault in the umbria marche 1997 1998 earthquakes central italy summary we analysed elevation changes induced by the 1997 1998 umbria marche central apennines italy earthquakes we employed data from a first order geodetic levelling line measured in 1951 1992 and 1998 the line bears a record of pre seismic and coseismic strains associated with the causative fault of the 1997 september 26 09 40 mainshock mw 6 0 a first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry a more detailed analysis based on a distribution of coseismic slip obtained from broad band seismograms provides a better fit and is in agreement with 1951 1992 elevation changes interpreted as precursory slip by previous investigators the levelling data sets new constraints on the location extent dip and depth of the fault in full agreement with seismological evidence and images from sar interferometry the data show no evidence for slip in the uppermost 3 km of the crust suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting

evidence for the variation of stress drop between normal and thrust faulting earthquakes in italy the horizontal components of 45 strong motion accelerograms recorded in friuli italy from may to september 1976 have been analyzed in order to estimate the stress drop of eight thrust faulting earthquakes two different stress parameters the brune stress drop and the apparent stress a have been considered the friuli main shock has a strong stress drop 800 bars while the aftershocks have stress drops which range from 250 to 400 bars five accelerograms written by the montenegro yugoslavia earthquake of april 1979 have also been analyzed this thrust faulting earthquake had a stress drop of 900 bars the stress drops of these thrust faulting earthquakes are compared to the stress drops determined by rovelli et al 1988a for nine normal faulting earthquakes which occurred in the apennines region from 1979 to 1984 the radiated energies and apparent stresses have also been calculated for the set of apennine earthquakes the thrust faulting earthquakes in the alpine dynaride region exhibit higher values for both the brune and the apparent stress than the normal faulting earthquakes in the apennines region excluding the friuli and montenegro main shocks the brune stress drops of the thrust faults are approximately 3 times those of the normal faults while the apparent stresses are twice as large this difference is statistically significant at a confidence level of 95 the same difference also emerges from the scaling of the peak ground motions recorded in these two regions suggesting an enhanced severity of the seismic input in the alpine dynaride environment compared with the apennines

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

the 1999 izmit turkey earthquake nonplanar fault structure dynamic rupture process and strong ground motion we simulated dynamic rupture propagation along various nonplanar fault models of the 1999 izmit turkey earthquake using a boundary integral equation method these models were inferred from geological and geodetic observations based on these results we modeled seismic wave propagation around the fault system using a finite difference method we focused on the effect of different fault geometries on the rupture process and seismic wave propagation numerical simulation results imply a rapid and continuous rupture propagation from the izmit sapanca lake segment to the sapanca akyazi segment the rupture under sapanca lake appears to have propagated not on a disconnected fault segment but along a smooth fault structure with a bend of only a few degrees the observational complexity of the surface breaks however can be best simulated by a highly segmented fault model this infers that fault geometric characters observed in the field reflect near surface structure and that seismological and geodetic features are controlled by global fault structure at depth then we investigated the effect of frictional parameters and the initial stress field in order to explain near field seismograms at station skr located a distance of a few kilometers from the fault we had to force the rupture to propagate at shallow depth close to the station in order to obtain this we had to introduce a finite cohesive force in the friction law that allows stress accumulation and release in the shallow crust the external stress field had to be large enough for the rupture to propagate at very rapid speed our simulation results show that it is important to include detailed fault geometry in the numerical simulation and to constrain frictional parameters and the initial stress field for understanding of the full dynamic process of an earthquake

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

automated near realtime cmt inversion the earthquake research institute eri of the university of tokyo has completely automated the process of determining source mechanisms of earthquakes using waveform data the solutions are automatically distributed using the internet without being checked the process is initiated by receipt of e mail giving the origin time and location of an earthquake to determine the source mechanism we apply the harvard centroid moment tensor cmt inversion method to long period body wave data the portion of the seismogram from the first arrival to the initial surface wave the method has been successfully applied since october 1993 to all of the major earthquakes in the world for which we received event e mail 108 of the 242 cmt solutions in 1994 were determined within 6 hours of the event with an average delay of 3 8 hours for local events e g events around japan it is also possible to determine cmt solutions within 30 minutes from the occurrence of the earthquakes using an efficient dialup data retrieval system operated by eri

the 1997 1998 umbria marche sequence central italy source path and site effects estimated from strong motion data recorded in the epicentral area 1 we apply a nonparametric spectral inversion scheme to calculate source spectra s wave attenuation and site transfer functions from strong motion records in the epicentral region of the 1997 1998 umbria marche seismic sequence central italy we use records from moderate size earthquakes 4 6 ml 5 9 to parameterize the spectral amplitude decay in the distance range from 5 to 40 km we find that the average quality factor q can be approximated by q f 49 f0 9 between 0 5 and 8 hz and the geometrical spreading by r 0 9 at high frequencies f 8 hz the dependence of q on frequency weakens and it takes an approximate constant value of 318 we fit the source spectra to the square model and calculate an average stress drop of 2 1 mpa the average value is consistent with the previous estimates from the weak events 1 4 ml 4 5 of the umbria marche seismic sequence the most remarkable site effects are found in correspondence of large sedimentary basins filled by alternation of sandy clayey deposits the estimated spectral parameters are used to simulate acceleration spectra recorded during several earthquakes of the umbria marche sequence both point source and finite fault effects are considered furthermore attenuation relationships for peak ground velocity and ground acceleration are estimated using synthetic data and compared to existing relationships

the relationship between seismic deformation and deep seated gravitational movements during the 1997 umbria marche central italy earthquakes abstract this paper re evaluates the origin of some peculiar patterns of ground deformation in the central apennines observed by space geodetic techniques during the two earthquakes of the colfiorito seismic sequence on september 26th 1997 the surface displacement field due to the fault dislocation as modelled with the classic okada elastic formulations shows some areas with high residuals which cannot be attributed to non simulated model complexities the residuals were investigated using geomorphological analysis recognising the geologic evidence of deep seated gravitational slope deformations dsgsd of the block slide type the shape and direction of the co seismic ground displacement observed in these areas are correlated with the expected pattern of movement produced by the reactivation of the identified dsgsd at least a few centimetres of negative line of sight ground displacement was determined for the costa picchio mt pennino and mt prefoglio areas a considerable horizontal component of movement in the costa picchio dsgsd is evident from a qualitative analysis of ascending and descending interferograms the timing of the geodetic data indicates that the ground movement occurred during the seismic shaking and that it did not progress appreciably during the following months this work has verified the seismic triggering of dsgsd previously hypothesized by many researchers a further implication is that in the assessment of dsgsd hazard seismic input needs to be considered as an important cause of accelerated deformation

an egf technique to infer the rupture velocity history of a small magnitude earthquake 1 an empirical green s function egf technique has been developed to detect the rupture velocity history of a small earthquake the assumed source model is a circular crack that is characterized by a single and unipolar moment rate function mrf the deconvolution is treated as an inverse problem in the time domain which involves an assumed form of the moment rate function mrf the source parameters of the mrf are determined by adopting a global nonlinear inversion scheme a thorough synthetic study on both synthetic and real seismograms allowed us to evaluate the degree of reliability of the retrieved model parameters the technique was applied to four small events that occurred in the umbria marche region italy in 1997 to test the hypothesis of a single rupture process the inversion results were compared with those arising from another egf technique which assumes a multiple rupture process for each event the best fit model was selected using the corrected akaike information criterion for all the considered events the most interesting result is that the selected best fit model favors the hypothesis of a single faulting process with a clear variability of the rupture velocity during the process for the studied events the maximum rupture speed can even approach the p wave velocity at the source as theoretically foreseen in studies of the physics of the rupture and recently observed for high magnitude earthquakes

deep structure of a fault discontinuity relocated aftershocks at a fault discontinuity that ruptured in the 1992 landers earthquake show that there is no simple connection between the homestead valley and emerson faults at depth rather faulting within the discontinuity is as complex as observed at the surface both aftershocks and mainshock slip on the far side of the discontinuity that is on the emerson fault were confined primarily to depths above 10 km whereas slip and aftershock activity on the near side of the discontinuity extended to 17 km similar behavior was also observed at a fault discontinuity in the 1979 coyote lake earthquake and may be attributable to the greater effectiveness of dynamic stress in inducing fault rupture at shallow depths

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

stress drop variations and source scaling relations of moderate earthquakes of the indian tectonic plate we investigate the source characteristics of 53 earthquakes in and around the indian subcontinent through a grid search technique applied to the p and s wave displacement spectra of regional waveforms registered at 42 broadband seismic stations in addition we estimate the p and s wave attenuation factors representative of the various tectonic regions that constitute the indian shield we discuss the sensitivity of the displacement spectrum to various parameters and demonstrate that for a brune type source model the seismic moment is the best estimated parameter compared to others such as the corner frequency our estimates of moment magnitudes are within the range of 1014 1020 n m with the crack radii being less than 12 km the nonuniform distribution of the static stress drop along the himalaya burmese arc and the western indian regions indicates that the central himalayas are prone to frequent failures owing to the lesser stress drop in contrast with the northwestern himalaya and burmese arc regions our results suggest that median stress drops are independent of the earthquake mechanism online material list of events and associated estimated parameters

complex normal faulting in the apennines thrust and fold belt the 1997 seismic sequence in central italy a long sequence of moderate magnitude earthquakes 5 m 6 struck central italy in september and october 1997 at the end of the sequence a year later the seismogenic area extends for about 60 km along the apennines the analysis of historical seismicity suggests that this seismic sequence filled a 700 year gap in this portion of the chain other historical sequences in the same area are characterized by prolonged seismic release on adjacent fault segments probably due to the in volvement of shallow and complex structures inherited by the compressive tectonics the distribution of seismicity and the fault plane solutions show that the extension in this region is accomplished by normal faults dipping at relatively low angles 40 to the southwest the focal mechanisms of the largest shocks reveal normal faulting with extension perpendicular to the apenninic chain northeast southwest consistently with the quaternary tectonics of the internal sector of the northern apen nine belt and with previous earthquakes in adjacent regions three mainshocks oc curred on distinct 5 to 10 km long fault segments adjacent and slightly offset be tween each other high quality aftershock locations show that seismicity is confined within the sedimentary mesozoic cover in the upper 8 km of the crust and that most of the aftershocks are shallower than the largest shocks which nucleated at 6 km depth faults evidenced by aftershock locations have a planar geometry and show increased complexity toward the surface most of the aftershock focal mechanisms are dominated by normal faulting several strike slip events occurred at shallow depths reactivating portions of pre existing thrust planes that segment the normal fault system the spatiotemporal evolution of seismicity shows a peculiar migration of hypocenters along the strike of the main faults with multiple ruptures and the activation of fault segments before the occurrence of the main rupture episodes

analysis of ground deformation detected using the sbas dinsar technique in umbria central italy ground deformation affecting the umbria region central italy in the 9 year period from 1992 to 2000 was investigated through multi temporal differential synthetic aperture radar interferometry dinsar for the purpose the small baseline subset sbas technique was adopted which allows studying the temporal evolution of the detected deformation at two spatial scales a low resolution regional scale and a full resolution local scale for the analysis sar data acquired by the european remote sensing ers 1 2 satellites along ascending and descending orbits were used the detected deformation was analysed to investigate its relevance to geophysical geomorphologic and human induced processes that may result in hazardous conditions to the population of umbria low resolution deformation data were used to i determine the amount of displacement caused by the umbria marche earthquake sequence from september 1997 to april 1998 in the foligno area ii determine the number and percentage of the known landslides that can be monitored by the dinsar technology in the investigated area and iii identify and measure subsidence induced by exploitation of a confined aquifer in the valle umbra results indicate that earthquakes moved through the foligno area westwards up to 3 9 cm and with an uplift reaching 1 7 cm intersection in a gis of the low resolution deformation maps with a detailed landslide inventory map allowed the determination that the portion of landslides that can be monitored by the sbas dinsar technique in umbria ranges from 2 7 to 3 4 and the percentage of the total landslide area ranges from 10 4 to 12 8 in the valle umbra a dependency was found between the time and the amount of detected ground deformation and the record of water withdrawal the full resolution deformation data were used to investigate the movement of the ivancich landslide in the assisi municipality joint analysis of the spatial and the temporal characteristics of the ground displacement allowed the formulation of a hypothesis on the landslide geometry and deformation pattern

source parameters of the december 2011 january 2012 earthquake sequence in southern carpathians romania abstract the seismicity at the contact between the getic depression and the south carpathians is part of the overall seismicity characterizing the contact of the moesian platform and the south carpathians orogen the december 2011 january 2012 earthquake sequence that occurred close to tg jiu city provides the best data set for the seismic activity in the region the seismic source parameters are estimated for 15 events of the sequence using the empirical green s function and spectral ratio techniques we selected 3 main events and 12 associated collocated small events as empirical green s functions to calculate the spectral ratios and determine the relative source time functions estimates of the source duration and corner frequency imply stress drop values in the range of 6 112 mpa relative small radius of the source and high stress drops suggest an intraplate type behaviour the scaling relationships investigated comply well with similar relationships in other regions in the world and in other seismogenic areas in the south carpathians region

determination of δσ and κ0 from response spectra of large earthquakes in greece we fit an 09 2 model to response spectra from eight recent greek earth quakes ranging in size from m 5 8 to m 6 9 the diminution parameter k o was determined for each site with a value near 0 06 for a typical soil site the stress parameter aa showed little variation from earthquake to earthquake and had a mean value of 56 bars over all earthquakes predictions of peak velocity peak acceleration rupture duration and fault length using the derived stress parameters are consistent with observations frequency dependent site amplifications were included in all es timates the combined effect of amplification and attenuation had a maximum value close to a factor of 2 5 for a typical soil site relative to the motions at the surface of a perfectly elastic uniform half space composed of materials near the source the results form the foundation for predictions of strong motions in greece for distances and magnitudes other than those for which data are available

the magnitude frequency distribution of earthquakes recorded with deep seismometers at cajon pass southern california abstract the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict in the cajon pass area southern california the b value of seismicity recorded by the local network scsn appears to decrease below about m l 1 6 in order to investigate whether this decrease is real or simply represents the network detection threshold we use seismicity recorded by the deep 1 5 and 2 5 km seismometers deployed in the cajon pass scientific drillhole between april 1992 and october 1994 the maximum amplitudes recorded downhole are compared to scsn magnitudes for events recorded by the network to determine the relationship between amplitude and m l as a function of hypocentral distance from the borehole magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole magnitude frequency curves are calculated for those events within 18 km of the borehole and a constant b value is observed to m l 0 5

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

attenuation and source parameters of shallow microearthquakes at mt etna volcano italy we estimated the attenuation laws of high frequency seismic waves in the shallow crust depth 5 km and earthquake source parameters by using a se lected data set of 320 shallow events 2 6 md 4 2 recorded at mt etna volcano during the last two flank eruptions occurring in 2001 and 2002 2003 the quality factor q was estimated from spectra of p and s waves for 24 stations of the local permanent network by applying a spectral ratio technique the results show varia tions in both qp and qs as a function of frequency according to the power law q q0f n with n ranging between 0 3 and 1 3 for p waves and between 0 2 and 0 9 for s waves as typical of volcanic environments strong azimuthal variations of qp were also found suggesting the presence of local strong lateral heterogeneities and or of fluid filled cracked volumes after correction for attenuation we estimated the source parameters seismic moment source radius and stress drop of a subset of 66 shallow events under the assumption of a circular dislocation the estimated seismic moments m0 range from 10 13 to 10 15 n m the source radii r are confined between 100 and 1000 m and stress drop dr ranges between 0 2 mpa and about 4 mpa combining the source parameters obtained in this study with those calculated by pataneet al 1997 for an old data set of smaller microearthquakes 10 9 m0 10 14 n m recorded in the same area we re evaluated the scaling relationship between seismic moment m 0 and corner frequency f c for the earthquakes with m 0 ranging between 10 13 and 10 15 n m we confirm that microearthquakes at mt etna seem not to obey a

quasi static analysis of strike fault growth in layered media summary we study the effects of structural inhomogeneity on the quasi static growth of strike slip faults a layered medium is considered made up of an upper layer bounded by a free surface and welded to a lower half space with different elastic property mode iii crack is employed as a mathematical model of strike slip fault which is nucleated in the lower half space and then propagates towards the interface we adopt fem newly proposed analysis method for failure to simulate the quasi statistic crack growth governed by the stress distribution in layered media our results show that along planar traces across interfaces a compliant upper layer has significant effects on promoting suppressing crack growth before after its extension into the layer and vice versa for a rigid one this proposes a possibility that surface breaks due to strike slip faulting could be arrested by deposit layers at the topmost part of the earth s crust

rupture directivity of the major shocks in the 1997 umbria marche central italy sequence from regional broadband waveforms we derive the relative moment rate function for the main shocks in the fall 1997 central italy seismic sequence mw 5 7 6 0 5 6 by applying an empirical green function method by using three conveniently placed broad band mednet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one taking a simple source model forward modeling is utilized for determining fault parameters such as length rupture propagation velocity and direction and slip distribution

multicycle dynamics of nonplanar strike slip faults 1 we perform two dimensional dynamic models of strike slip faults with a change in strike a bend over multiple earthquake cycles to examine the long term effects of nonplanar fault geometry a viscoelastic model a proxy for off fault deformation and tectonic loading is introduced for the interseismic process to avoid pathological stress buildup around the bend a finite element method with an elastodynamic model is used to simulate dynamic earthquake ruptures we find that stresses near the bend differ strongly from the regional stress field and that the fault develops a relatively steady state in which the stress level and the event pattern on the fault are stable reduced normal stress on the dilatational side and increased normal stress on the compressive side of the bend during dynamic ruptures result in the bend serving as an initiation and or a termination point s for rupture typical events on such a fault consist of two classes unilateral events that rupture only the favorable segment and bilateral events that rupture the favorable segment and part of or the entire unfavorable segment in the latter class of events a time delay in rupture around the bend results from a high yield stress on the compressive side of the bend other effects of the bent fault geometry include higher displacement on the inward wall than on the outward wall higher slip on the more favorable segment than on the less favorable segment and a large slip velocity on the compressive side of the bend

the 1997 umbria marche central italy earthquake sequence insights on the mainshock ruptures from near source strong motion records a small size foreshock and the two mainshocks of the umbria marche earthquake sequence which occurred on september 26 1997 have been recorded by two digital 3c accelerometers located at near source distances the close epicentral distance and azimuthal location relative to the fault orientation and geometry make these records relevant to look at the detail of the rupture kinematics s wave polarizations apparent source time duration and waveforms from strong motion records are used to constrain the location of the fracture origin point the fault geometry the final slip distribution size and mechanism of the events the final model shows that the seismic ruptures occurred along two adjacent sub parallel low angle dipping normal faults the relative timing location and geometry of the mainshock faults suggest the presence of a transfer zone barrier which has probably controlled the amplitude increase of local stress released by the first rupture at its nw edge which triggered about 9 hours later the second rupture

san andreas fault geometry in the parkfield california region in map view aftershocks of the 2004 parkfield earthquake lie along a line that forms a straighter connection between san andreas fault segments north and south of the parkfield reach than does the mapped trace of the fault itself a straightedge laid on a geologic map of central california reveals a 50 km long asymmetric northeastward warp in the parkfield reach of the fault the warp tapers gradually as it joins the straight creeping segment of the san andreas to the northwest but bends abruptly across cholame valley at its southeast end to join the straight locked segment that last ruptured in 1857 we speculate that the san andreas fault surface near parkfield has been deflected in its upper 6 km by nonelastic behavior of upper crustal rock units these units and the fault surface itself are warped during periods between large 1857 type earthquakes by the presence of the 1857 locked segment to the south which buttresses intermittent coseismic and continuous aseismic slip on the parkfield reach because of nonelastic behavior the warping is not completely undone when an 1857 type event occurs and the upper portion of the three dimensional fault surface is slowly ratcheted into an increasingly prominent bulge ultimately the fault surface probably becomes too deformed for strike slip motion and a new more vertical connection to the earth s surface takes over perhaps along the southwest fracture zone when this happens a wedge of material currently west of the main trace will be stranded on the east side of the new main trace

analysis of the static stress field around faults lying along and intersecting a bimaterial interface summary major faults are known to lie along material interfaces including plate interfaces and tectonic lines recent high precision observations have revealed that there are also faults in the vicinity of material interfaces this suggests that slip on a fault and stress changes near one can be affected significantly by the presence of a material interface in this paper we develop a new mathematical framework to derive an expression for a static slip response function by drawing on properties of complex functions our method is characterized by its unique ability to analyse both a fault lying along a material interface and a fault intersecting a material interface under a unified framework a few previous studies have theoretically dealt with the problem of slip on a fault that intersects a material interface but their mathematical techniques were so complicated that they had only limited utility for seismological applications by contrast our mathematical framework has a simple structure thanks to the characteristics of the complex functions using our formula one can easily calculate the fault slip and the static stress changes nearby if only the stress drop on the fault is given the static stress is represented as a sum of stress changes due to the slip and a background stress that is generally discontinuous across a material interface understanding of the static stress state around a fault has important implications for evaluating the likelihood of secondary failures we find that when the fault is located along or in the vicinity of a material interface the background stress plays a key role in the formation of the stress state around a fault and accordingly also in the triggering of secondary failures

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

effects of geological complexities on coseismic displacement hints from 2d numerical modelling by means of a 2d finite element procedure we tested how heterogeneities at the scale of seismogenic fault affect the displacement we defined one or more slip distributions for two typical normal faulting earthquakes in the central apennines computed the displacement occurred within different structures including lateral heterogeneities and compared the different displacement profiles to isolate the effect of the crustal structure to understand at what magnitude the heterogeneities affect the observation significantly we compared the predicted coseismic displacement with gps and dinsar data for the colfiorito 1997 earthquake we find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes whereas for smaller quakes they affect horizontal displacement close to the fault trace only

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

faulting in vertically inhomogeneous media and its geophysical implications faulting of strike slip type in vertically inhomogeneous media is analyzed using the classical fracture theory the analysis makes it possible to get a better insight into various aspects of faulting and earthquakes in real media the major conclusions are that both low rigidity media and those with regions in which a rapid transition from high to low pore pressure occurs may form barriers for a propagating rupture the permanent deficit of the driving stress small or negative stress drop in sediments that represent the most distinguished class of such media may be one of the main reasons of the generally observed lack of seismicity and rupture suppression there

monitoring volcanic and geothermal areas by full seismic moment tensor inversion are non double couple components always artefacts of modelling non double couple mechanisms ndc in volcanic environments are good indicators of local modifications of stress induced by dike injection high fluid pressure movements or by thermal cooling nevertheless the possible biasing effects of wave propagation in structurally complicated regions the presence of noise or a not appropriate station coverage can make the identification of ndc as true source phenomena uncertain in this paper we illustrate possible sources of fake ndc and we demonstrate that by the error analysis that we apply it is possible to discriminate spurious artifacts and physically meaningful solutions tests with synthetic seismograms and the analysis of observed ones in volcanic and geothermal areas are thoroughly discussed

comparison between reprocessed seismic profiles seismologic and geologic data a case study of the colfiorito earthquake area seismic reflection data are used to reconstruct the subsurface geologic structures below the umbria marche region in italy a highly seismogenic area with a recent history of seismic activity the 1997 1998 colfiorito sequence we reprocess three vibroseis seismic profiles acquired in the early 1980s for hydrocarbon exploration whose stacked sections were optimized for relatively deep oil targets on the reprocessed seismic profile closest to the epicentral area we construct the main reflectors to a depth of about 4 s two way time and compare this interpretation with the available hypocenters of the 1997 earthquakes the improvements in visualizing the shallow and deep reflections provide a better correlation between the reflectors and the observed surface structures as well as a better delineation of the basement rock geometry we find that part of the colfiorito sequence is localized around some of the reflectors in the reflection profile which we interpret as related to the active normal faults

mechanics of fault junctions a sharp bend in a fault must be part of a triple junction and slip on the three fault segments at the junction must have a vector sum of zero in order to avoid an unphysical 1 r stress singularity accompanying the slip a volume change occurs at the junction either a void opens or intense local deformation is required to avoid material overlap the energy absorbed due to the volume change is proportional to the slip increment times the total past slip accumulated at the junction at a new junction the energy absorbed is a small fraction of the energy released by slip on the fault system but after a number of earthquakes proportional to shear modulus over confining stress the junction becomes a strong barrier to further slip although slip occurs more easily on old rupture surfaces than on fresh fractures the growing barrier strength of junctions requires that there be some fresh fracture in earthquakes perhaps a small fraction of the surface that slips in any earthquake is fresh fracture which could provide the instability needed to explain earthquakes a numerical model in two dimensional static plane strain shows even without accounting for energy absorbed at the junction that a bend in a fault acts as a barrier if slip is impeded on the associated fault spur the stress concentration at the bend will tend to induce slip on the spur slip occurring on the spur unstably with a drop in the coefficient of friction can induce increased slip on the main fault segments with no change in the coefficient of friction a fault junction provides a natural realization of barrier and asperity models without appealing to arbitrary variations of fault strength the location of the fresh fracture that occurs after a junction becomes a strong barrier remains an unanswered question it is likely to be initiated near the stress concentration at the old junction a model simulating the effect of fresh fracture near old junctions might explain earthquakes without appealing to an unstable friction law anywhere

source parameters of earthquakes recorded near the itoiz dam northern spain we calculate the source parameters and attenuation from earthquakes recorded near the itoiz dam from 2004 to 2009 with magnitudes ranging between 1 2 and 5 2 we use a genetic algorithm in order to fit the three component p wave spectra with the spectral level corner frequency and attenuation factor as searching parameters the obtained moments range from 1 72 1011 to 2 65 1015 nm the radii span from 0 09 to 1 00 km and the stress drops vary from 0 006 to 29 462 mpa the maximum value for the q attenuation factor is 794 and the minimum value is 53 we find a good agreement between empirical and theoretical relationships between moment and magnitude there seems to be a breakdown of self similarity but it could be due to the method used we group the data by means of a self organizing map and the clusters found are related by their magnitude and not by other considerations

source parameters of microearthquakes in southeastern sicily italy we computed the source parameters of 135 local earthquakes that occurred in southeastern sicily italy between 1994 and 2001 magnitudes ranged from 0 6 to 2 5 the source parameters were determined from the spectral analysis of p waves after corrections for attenuation and site effects p wave quality qp and site s factors are known in the two frequency ranges 3 9 hz and 16 27 hz giampiccolo et al 2003 because the correction for qp and s over the whole spectrum could not be performed a new approach to estimate spectral parameters was applied we defined the new notion of holed spectrum to specify a spectrum lacking corrected spectral amplitude values within a certain frequency range whereas we referred to a whole spectrum to specify when the entire analyzed frequency band was used a detailed statistical analysis showed that dealing with the holed spectrum did not lead to significant differences in the estimate of spectral parameters displacement holed spectra corrected by the attenuation and site response were then used to estimate source parameters seismic moments ranged from 1017 to 1020 dyne cm and source dimensions from 150 to 500 m in general the stress drop values obtained analyzing p wave spectra were very low because they mainly span the range of 0 05 5 bars

source parameter scaling and radiation efficiency of microearthquakes along the irpinia fault zone in southern apennines italy we analyzed the p and s wave displacement spectra of 717 microearthquakes in the moment range 4 109 2 1014 n m recorded at the dense networks operating in southern apennines italy and deployed along the 1980 ms 6 9 irpinia earthquake fault zone source attenuation and site parameters are estimated by using a parametric modeling approach which is combined with a multistep nonlinear inversion strategy we found that in the analyzed frequency band an attenuation model with constant q has to be preferred to frequency dependent q models consistent estimates of the median p and s quality factors q p 167 90 296 and q s 226 114 417 are obtained from two different techniques and relatively high values of qs qp median value 1 3 0 8 2 1 are found in the same depth range where high vp vs and a peak in seismicity distribution are observed this is the evidence for a highly fractured partially or completely fluid saturated medium embedding the irpinia fault zone down to crustal depths of 15 20 km a nearly constant stress drop 1 4mpa 0 4 5 0 and apparent stress a 0 1mpa 0 03 0 4 scaling of p and s corner frequencies and seismic energies is observed above a seismic moment value of about 1011 n m the measured radiation efficiency is low sw 0 06 0 030 13 e g the radiated energy is only a small fraction of the whole energy spent by friction and fracture development a large positive dynamic overshoot high dynamic shear strength can be the dominant mechanism controlling the microearthquake fractures along the irpinia fault zone

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

stress redistribution following unwelding of near surface layers in strike slip fault zones summary major strike slip earthquakes are often associated with a complex pattern of surface fractures organized in hierarchic order en echelon shear fracture arrays open tensile fractures and hillocks which are oriented differently from the strike of the main fault and often extend laterally 1 or 2 km in the attempt to understand why the main fault remains confined at depth we have considered the possibility that during the earthquake a soft shallow sedimentary layer unwelds from the lower basement rock along a horizontal interface the stress redistribution provided by the unwelding process in the shallow layer is studied in terms of a dislocation model employing the boundary element method we show that a nearly uniform coulomb failure function develops above the main fault over a km wide strip along the fault strike explaining shear fracture arrays and positive tensile stresses appear near the surface over a similarly wide strip explaining open fractures a parametric study is performed to show when the unwelding process can take place and how the resulting stress redistribution in the shallow layer depends on the depth of the unwelded layer and on the coefficient of friction

seismic deformation in the mediterranean area estimated by moment tensor summation summary theoretical relationships allow the distributed deformation due to seismic activity to be quantified on the basis of the analysis of moment tensors we apply this method to a data set consisting of seismic events that have occurred in the past 85 yr 1908 1992 along the most important seismogenic zones of the mediterranean region we use the centroid moment tensor cmt catalog prepared at harvard university covering the last 16yr and older data from jackson mckenzie 1988 we determine the seismic deformation and compare it to estimates of the overall deformation as obtained from global plate motion and geological studies we generally find that the geometry of seismic deformation is similar to tectonic predictions even though spanning a shorter time interval the cmt catalog often gives a better estimate of deformation geometry than the whole data set 85yr seismic deformation generally ranges from less than 10 per cent to more than 90 per cent of the total deformation uncertainties arise because data sets may not be representative of the long term seismic behaviour of each zone more reliable estimates for comparison with geodynamic processes should result from analysis of a longer time period for which no instrumental data are available the similarity of the deformation geometry using cmt data with tectonic expectations suggests for several zones the possibility of using historical data to infer longer term deformation rates based on current deformation geometry

source parameters of microearthquakes at mount st helens usa summary we estimate the source parameters for a selection of microearthquakes that occurred at mount st helens in the period 1995 1998 excluding the activity of 2004 september this time period includes the most intense episode of earthquake activity since the last dome building eruption in 1986 october 200 seismograms were processed to obtain seismic moments source radii stress drops and average fault slip the source parameters were determined from the spectral analysis of p waves after correction for attenuation and site effects in particular p wave quality qp and site s factors have been previously calculated in the frequency ranges 2 7 hz and 18 30 hz because it was impossible to perform corrections for qp and s over the whole spectrum we applied a new approach based on the notion of holed spectrum to estimate spectral parameters the term holed spectrum indicates a spectrum lacking corrected spectral amplitude values at certain frequencies we carried out a statistical study to verify that dealing with the holed spectrum does not lead to significant differences in the estimates of spectral parameters we also investigated the dependence of spectral parameters low frequency level corner frequency and high frequency decay on the bandwidth of spectral hole and defined the threshold values for three different spectral models displacement holed spectra corrected by attenuation and site response are then used to determine spectral parameters in order to calculate seismic source parameters seismic moments range from 1017 to 1019 dyne cm source dimensions from 100 to 350 m and average fault slip from 0 003 to 0 1 cm self similarity seems to break down in that stress drops are very low 0 1 1 bars we postulate that seismicity is associated with a brittle shear failure mechanism occurring in a highly heterogeneous material under a relatively low stress regime

earthquake prediction research and the earthquakes of 2000 in the south iceland seismic zone abstract the purpose of this paper is to describe and to model long and short term processes that preceded two large earthquakes that occurred in 2000 in the south iceland seismic zone sisz the results are based on some key findings from multinational earthquake prediction research projects in the sisz since 1988 it involves a fusion of significant old and new results the paper presents a new hypothesis for earthquake build up processes in the region followed by a discussion on how interseismic and preseismic observations can be explained by this model and a discussion about a plausible earthquake cycle in light of the new hypothesis the research described here started in 1988 with the south iceland lowland sil project a significant outcome was the development of a seismic acquisition and evaluation system the sil system retrieving source information from earthquakes down to magnitude zero the research continued with the use of more multidisciplinary and multinational projects revealing new information about crustal processes related to large earthquakes in the area the validity of the work was tested in 2000 when two magnitude 6 6 m s earthquakes occurred in the central part of the sisz the earthquakes had a long term assessment of place a short term warning within short about the location and size of a probable impending earthquake was issued 25 hours before the second earthquake

bootstrap inversion for vertical and lateral variations of the s wave structure and the υp υs ratio from shallow earthquakes in the rhinegraben seismic zone germany using s wave arrival times of 400 earthquakes in the southern rhinegraben 1 d and 3 d inversions for the shear s wave crustal structure of that region are performed these models are then combined with previously obtained 1 d and 3 d p wave models to compute vertical and lateral variations of the p s poisson s ratio such an independent p and s wave inversion approach circumvents many of the limitations of the classical wadati diagram method usually used for the determination of crustal p s ratios for the statistical evaluation of the 1 d models we have used a new monte carlo bootstrap resampling technique which has been found useful in many statistical estimation problems where the underlying statistics of the data is poorly known the 1 d bootstrap p s crustal models exhibit significant vertical variations whereas the upper sedimentary and crystalline layer of the crust is characterized by a significant increase of p s over the reference value p s in the upper and middle crust is lowered this correlates well with several findings from wadati diagrams for p s in other seismically active zones and might be explained through the gradual closing of saturated microcracks in that depth range however the p s reduction can also be interpreted in terms of a particular petrological composition such as orthoclase feldspar without the indispensable need for fluids a lowering of p gus is also observed for the lower crust which might reflect the strong lamination found here from previous deep seismic sounding experiments for the upper mantle a strong increase of p s is observed which is primarily triggered by a decrease of s and is best explained by an eclogite petrological assemblage for the 3 d s wave models significant reductions of more than 100 were obtained for the unexplained travel time residuals variations of p s in the upper and middle crust are mostly induced by changes in p rather than s for the upper crust slight decreases of p s are observed for the rhinegraben but increases are detected for the adjacent vosges and black forest areas in the middle crust the refraction seismic deduced reduction of p s under parts of the black forest can neither be corroborated nor rejected however because of some experimental ambiguity on the effects of petrological composition and interstitial pore fluids this does not rule out the presence of the latter in the lower crust a local reduction of p s is observed under the kaiserstuhl and graben black forest shoulder and has been explained in terms of a metamorphic dehydrating phase change of the hydrous amphibolite facies to the anhydrous granulite facies depending on the pore pressure of the dehydrated water and the fractional amount of interstitial co2 granulite facies metamorphism occurs in the 650 800 c temperature range temperatures at the upper end of this interval can be generated by the mechanism of accretionary magmatic underplating as it has been proposed for some extensional rift zones where asthenospheric upwelling as in the rhinegraben occurs

osmium isotope geochemistry in the mackenzie river basin the cenozoic marine osmium isotope record is largely driven by changes in the continental input we aid its interpretation by supplying direct measurements of present day riverine os in known geological and environmental settings we analyzed os concentrations and isotopic ratios in the dissolved suspended and bed materials of the mackenzie river in canada and smaller rivers draining the western cordillera into the pacific ocean rhenium content was measured for suspended and bed materials to provide further constraint dissolved 187os 188os ratios range from 0 74 to 4 5 and are controlled to first order by age and lithology of the bedrock the rivers draining jurassic volcanic rocks are unradiogenic as low as 0 74 and those draining the precambrian canadian shield are radiogenic as high as 3 5 the headwaters of the mackenzie left bank tributaries draining metamorphic carbonates in the eastern cordillera and paleozoic black and gray shales in the transition zone and the interior platform are especially radiogenic 3 0 4 5 with relatively high concentrations of os these latter rivers are responsible for the mackenzie being above world average in os concentration and yield mol os km2 year as well as in 187os 188os the dissolved load is more radiogenic than the suspended or bed loads and constitutes a significant fraction of total fluvial os

gravity magnetic and high precision relocated seismicity profiles suggest a connection between the hayward and calaveras faults northern california 1 gravity magnetic and seismicity data profiled across the hayward fault zone were generated as part of ongoing studies to help determine the geologic and tectonic setting of the san francisco bay region these data combined with previous geophysical studies that indicate that the hayward fault zone dips 75 ne near san leandro and follows a preexisting structure reveal a possible direct connection between the seismogenic portion of the hayward and calaveras faults at depth although the relocated seismicity data are regional in nature they suggest that the dip of the hayward fault zone may vary from near vertical in the northwestern part of the fault to about 75 ne at san leandro in the central part of the fault to about 50 ne in the southeastern part of the fault gravity and magnetic data profiled across the hayward fault zone were processed using standard geophysical techniques cross sections of high precision relocated hypocenters were constructed along each profile from the northwestern to the southeastern end of the hayward fault zone profiles and cross sections are referenced to pinole point where the hayward fault enters san pablo bay and are spaced 2 5 km apart topographic profiles shown on the seismicity cross sections were generated using u s geological survey usgs 7 5 min 30 m digital elevation models relocation of seismicity data was accomplished using a regional double difference method the double difference method incorporates ordinary travel time measurements and cross correlation of p and s wave differential travel time measurements relative locations between earthquakes have hypocentral errors of about 100 m horizontally and 250 m vertically absolute location uncertainties were not determined but are probably dramatically improved compared to the usgs s northern california seismic network catalog data

secondary earthquake fractures generated by a strike slip fault in the south iceland seismic zone most large earthquakes in the south iceland seismic zone occur on n s trending dextral strike slip faults the resulting rupture zones display complex en echelon patterns of secondary structures including nne trending arrays of mostly ne trending open fractures and hillocks three spatial scales characterize the surface faulting pattern the length of the main fault mf 104 m the arrays of fractures here interpreted as surface evidence of subordinate faults sf 102 m and the individual open fractures of 10 m in order to improve our understanding of the genetic relationship between the of and the mf we computed the stress field induced by slip on a buried mf using a dislocation model in a layered half space where the fault surface is assumed to be embedded in the basement rock topped by a softer tens of meters thick near surface layer the of were modeled as secondary fractures of either of the following types 1 pure mode i cracks opening in the near surface layer in the direction of the tensile principal stress or 2 mixed mode cracks slipping at depth as shear cracks and opening near the surface due to low confining pressure assuming that both types of secondary fractures occur in the sisz we can explain their first order characteristics by reasoning that they are the end product of a hierarchy of deformation produced by the main fault the coulomb failure function after the earthquake obtained by summing the mf stress change and the lithostatic stress suggests that subordinate faulting sf must be expected to occur in response to the main rupture below the upper soft layer extending to a depth of 100 m the total stress change induced by the mf and the sf is shown to yield quantitative explanations of the spatial extent the double en echelon arrangement and the orientation of surface fractures observed in the field in terms of a simple frictional model of rupture

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

source attenuation and site parameters of the 1997 umbria marche seismic sequence from the inversion of p wave spectra a comparison between constant qp and frequency dependent qp models 1 the attenuation of p waves the site responses and the source parameters seismic moment corner frequency source dimension of 490 seismic events that occurred during the 1997 colfiorito umbria marche seismic sequence have been inferred from the inversion of p wave velocity spectra the boatwright source model has been assumed to model the source spectra a global nonlinear inversion scheme was developed to avoid any a priori selection of the initial qp and the corner frequency to establish if a frequency dependent qp model fits the data better than a constant qp model two inversion results have been compared application of the akaike information criterion indicates that the constant qp model represents the best compromise between model simplicity and data misfit the station qp values are small in the range of 50 to 200 a one dimensional qp model is obtained by back projecting the inverted t our results indicate both well defined near site attenuation effects at some sites and heterogeneity in the inelastic properties of the crust with the exception of the amplification response at five seismic stations most of the recording sites did not show amplification peaks at particular frequencies the stress drop clearly increases as a function of the seismic moment which indicates a deviation from self similarity whereas it does not show an increase with depth probably owing to the effects of fluid pressurization in the crust a stress drop of about 39 mpa is inferred the relationship between the seismic moment and the local magnitude for p waves has been calibrated

slip distribution of the 1997 umbria marche earthquake sequence joint inversion of gps and synthetic aperture radar interferometry data 1 in september october 1997 a seismic sequence struck the southern part of the umbria marche region in central italy the three largest earthquakes took place on 26 september 0033 ut mw 5 7 09 40 gu mw 6 0 near colfiorito and on 14 october mw 5 6 near sellano we present a slip model for the main sequence over two separate fault planes we use previously published global positioning system gps and differential interferometric synthetic aperture radar dinsar data as well as new dinsar data covering the sellano event as input to a simulated annealing solution for the distribution of fault slip the combination of both types of geodetic data as well as the combination of sar interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes for the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence we find the slip was concentrated in a zone at 4 5 5 km depth with a shallower tail extending to near the surface at the northern end of the colfiorito sequence for both the second colfiorito event and the sellano event individual patches were calculated with maximum slip of 2 m implying stress drops as high as 20 mpa coulomb stress calculations show that the coseismic slip distribution for the colfiorito events facilitated slip of the adjacent sellano earthquake

can seismic waves be trapped inside an inactive fault zone the case study of nocera umbra central italy in march 1998 a small aperture 350 m linear array of five broadband stations was installed across a pliocene strike slip fault crossing the town of nocera umbra central italy three component seismograms of local earthquakes recorded during the umbria marche seismic sequence have shown that the degradation of mechanical properties in damaged rock causes a significant amplification of ground motion within the fault zone marra et al 2000 during the operation of the array an m w 5 3 subcrustal earthquake occurred at a depth of 48 km and an epicentral distance of 10 km from nocera umbra the near vertical incidence of this event offers a unique opportunity for constraining the 2d geometry of the laterally heterogeneous low velocity structure responsible for the large amplification across the fault based on the observed symmetry of the amplification pattern a 2d wedge shaped model of the fault zone is used for the computation of antiplane sh synthetic waveforms to be compared with observations along the array two parameters of the wedge model can be constrained by independent geophysical and geological data 1 shear wave velocity in pristine rock outside the fault zone v s 2200 m sec and 2 the lateral extent of the damaged rock zone l 160 m the other two model parameters namely the wedge depth h and shear wave velocity of the fault zone v f s are varied computer simulations show that trapped waves which have been observed so far for earthquakes occurring inside the fault zone can develop inside a 2d wedge model when struck by external vertically incident seismic radiation results of numerical modeling indicate that in spite of its extreme simplicity such an idealized model is successful in reproducing many of the essential characters of ground motion within the fault zone of nocera umbra even though the best fit solution is not unique and the model parameters trade off each other a study of parameter sensitivity comparing synthetics with recorded data indicates that the variability of h and v f s can be restricted to a limited range of values the quality of fit is optimal when the shear velocity reduction lies in the range of 40 50 and the depth of the trapping zone is comprised between 1 and 2 km

determination of near surface attenuation with κ parameter to obtain the seismic moment stress drop source dimension and seismic energy for microearthquakes in the granada basin southern spain abstract a set of 43 microearthquakes of the granada basin with magnitude duration m d from 1 4 to 3 5 have been spectrally analysed the digital data used in this study was recorded by two short period digital seismic network five permanent stations using andalusian seismic network red sismica de andalucia rsa and three stations of a portable digital seismic network red sismica portatil rsp the displacement spectra for p and s waves were analysed with brune s j geophys res 75 1970 4997 j geophys res 76 1971 5002 source model and the spectra parameters were determined by snoke s model to correct spectra from path attenuation coda q was used for the spectra correction from near surface attenuation parameter was calculated obtaining it from acceleration spectra the values of parameter range from 0 01 to 0 04 s for p waves and from 0 006 to 0 04 s to s waves once the spectra of these attenuation effects was corrected we obtained the seismic moments that range from 5 45 10 17 dyne cm to 1 53 10 20 dyne cm the source radii are between 0 13 and 0 39 km the seismic energy ranges from 7 17 10 3 j to 1 13 10 8 j the stress drop values were below 4 bars the scaling relations between seismic moment and stress drop indicated decreasing stress drop with decreasing seismic moment