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

ground motion scaling in eastern sicily italy we describe the characteristics of crustal wave propagation in eastern sicily by using the background seismicity of the area we follow the approach de scribed by malagnini hermann and di bona 2000 and malagnini et al 2002 our data set consists of 106 earthquakes recorded by nine three component digital seismic stations between 1994 and 2001 we used only crustal events depths shal lower than 25 km with local magnitudes ranging from 1 0 to 4 3 and hypocentral distances from 10 to 130 km peak ground velocities from 1311 narrow bandpass filtered waveforms are mea sured in thefrequency range 1 0 16 0 hz and regressedtodefinecrustalpropagation excitation and site characteristics with respect to a reference station a subsequent modeling effort is carried out through the use of random vibration theory rvt for obtaining a quantitative evaluation of the apparent geometrical spreading g r and of the crustal quality factor q f an attenuation parameter j0 is also evaluated relative to a reference rock site the attenuation and source parameters estimated in this study are used through the rvt in order to predict the peak horizontal ground acceleration pga and the 5 damping pseudoacceleration spectra psa

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

source parameters and tectonic implications of aftershocks of the mw 7 6 bhuj earthquake of 26 january 2001 we present and discuss the spatial distribution of more than 1000 aftershocks of the largest continental intraplate earthquake to occur during the modern seismological period the data were recorded on a network of eight portable digital seismographs deployed for 3 weeks starting 17 days after the mainshock we have calculated high quality single event locations based on a 1d velocity model determined for the region for earthquakes with magnitudes between 2 and 5 aftershock locations reveal activity concentrated on a nearly east striking south dipping plane trapezoidal in outline the active zone tapers from about 45 km along strike at the shallow end which is about 5 km deep to no more than 25 km long at a depth of 35 km the total rupture area was about 1300 km 2 we estimate the static stress drop of the mainshock at 16 2 mpa aftershocks extend nearly through the entire crust with concentrations in the lower crust at about 26 km and in the upper crust at about 10 km the fault that ruptured was not mapped at the surface and not known to have been active prior to the 2001 earthquake the aftershock data are consistent with the bhuj earthquake resulting from reactivation in contraction of a fault formed under extension within a failed rift

high frequency ground motion in the erzincan region turkey inferences from small earthquakes this study has been supported by istituto nazionale di geofisica e vulcanologia ingv internal project attenuazione e leggi di scala nei paesi dell area mediterranea internally funded r b herrmann s participation was supported by ingv and by the earthquake engineering research centers program of the national science foundation under award number eec 9701785

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

source radiation invariant property of local and near regional shear wave coda application to source scaling for the mw 5 9 wells nevada sequence 1 this study documents another unique property of local and regional shear wave coda that scattering in the earth s crust averages out source heterogeneities such as focal mechanism and directivity we consider two recent events which exhibited significant source directivity the first an mw 4 2 oakland hills california strike slip event on july 20 2007 resulted in uncharacteristically large amounts of damage in the montclair and south berkeley neighborhoods along strike and north west of the hypocenter but almost no damage to the south east the second event the mw 5 9 wells nevada dip slip event of february 21 2008 was well recorded by the earthscope transportable array usarray and determined to exhibit south west directivity we conclude with an example of corner frequency fc estimates from the wells sequence which showcase the coda s low variance and find that scaling is non self similar suggesting a change in dynamics between the mainshock and aftershocks

the influence of magnitude range on empirical ground motion prediction a key issue in the assessment of seismic hazard in regions of low to moderate seismicity is the extent to which accelerograms obtained from small magnitude earthquakes can be used as the basis for predicting ground motions due to the larger magnitude events considered in seismic hazard analysis in essence the question is whether empirical ground motion prediction equations can be applied outside their strict range of applicability as defined by the magnitude and distance ranges covered by the datasets from which they are derived this question is explored by deriving new spectral prediction equations using an extended strong motion da taset from europe and the middle east covering the magnitude range mw 3 0 7 6 and comparing the predictions with previous equations derived using data from only mw 5 0 and above events the comparisons show that despite their complex func tional form including quadratic magnitude dependence and magnitude dependent attenuation the equations derived from larger magnitude events should not be extra polated to predict ground motions from earthquakes of small magnitude moreover the results suggest not only that ground motion prediction equations cannot be used outside the ranges of their underlying datasets but also that their applicability at the limits of these ranges may be questionable although only tested for smaller magni tudes the results could be interpreted to suggest that predictive equations also cannot be reliably extrapolated to higher magnitudes than those represented in the dataset from which they are derived a finding that has important implications for seismic hazard analysis the conclusion of the study is that empirical derivation of ground motion pre diction equations should be based on datasets extending at least one unit below the lower limit of magnitude considered in seismic hazard calculations the inclusion of small magnitude recordings results in a significant increase in the aleatory varia bility of the equations although it is yet to be established whether this is due to greater uncertainty in the associated metadata or whether ground motion variability is gen uinely dependent on earthquake magnitude

temporal variation of seismic velocity and anisotropy before the 2009 mw 6 3 l aquila earthquake italy we describe a set of seismological observations of the foreshock sequence preceding the 6 april 2009 m w 6 3 l9aquila earthquake the dense configuration of the seismic network in the epicenter area and the occurrence of a long foreshock sequence provide the opportunity for a detailed reconstruction of the preparatory phase of the main shock approaching the earthquake we observed clear variations in the seismic wave propagation properties the elastic properties of rocks in the fault region underwent a sharp change about a week before the earthquake from our observations we infer that a complex sequence of dilatancy diffusion processes takes place and that fluids play a key role in the fault failure process

proterozoic tectonic evolution and late svecokarelian plate deformation of the central baltic shield the continental crust of the central baltic shield evolved by accretion towards the west during the svecokarelian orogeny 1700 2200 ma ago the following features are consistent with a plate tectonic mechanism involving subduction of oceanic crust below an archean craton in the east flysch sediments with serpentinite masses and pillow lavas linear high grade metamorphic zones island arc type volcanic belts and late tectonic batholiths with porphyry type cu mo deposits semi consolidated new crust was affected by late svecokarelian deformation dn after 1850 ma nne trending folds with crenulation cleavage were overprinted on older structures together with associated nw trending ductile transcurrent shear zones that curve the fn folds into gentle s and z shapes the late tectonic batholiths intruded partly at the same time as and partly after the dn deformation

weak motion based attenuation relationships for israel summary we performed a regional study of earthquake ground motion scaling relations to provide the seismic hazard community of israel with a new attenuation relationship that could be used for the prediction of earthquake induced ground motion strong earthquakes are rather scarce in israel and the existing collection of records from strong earthquakes is not sufficient to allow the use of traditional regression methods to develop a regional attenuation relationship we used velocity seismograms from the israel seismic network to estimate the distance and frequency dependence of ground motion in the israel region from frequent smaller regional earthquakes our analyses included 4814 waveforms recorded by 30 stations of the israel seismic network from 2000 to 2005 we restricted our analysis to 330 events recorded at five or more stations with duration magnitudes ranging between 1 0 and 5 2 we derived empirical excitation site and regional attenuation terms by regressing the peak amplitudes of narrowband filtered seismograms around the shear wave arrivals and the rms fourier spectral amplitudes taken around the specific sampling frequency in order to optimize the attenuation parameters in our scaling model we used a simple grid search an optimal solution for minimal error between empirical and theoretical attenuation function was found for the quality parameter q f 298f0 67 and the geometrical spreading g r parametrized as a bilinear piecewise function r 0 74 for r 60 km and r 0 47 for r 60 km the spectral parameters of 0 015 s and stress drop increasing from 0 3 to 4 mpa were used to model the excitation spectra a theoretical modelling effort based on brune s source spectrum and random vibration theory rvt was performed on the attenuation and source parameters estimated in this study comparison of the attenuation relationship derived with locally measured ground motions shows excellent agreement with the data in the magnitude range for which we have observations and seems to be adequate for predictions of earthquake ground motion for the israel region comparison of peak ground acceleration pga predictions based on our scaling relationship with those that have been recently used for seismic hazard analysis in israel shows that our attenuation relationship predicts significantly lower ground motions than other relations

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

high frequency attenuation in the lake van region eastern turkey we provide a complete description of the characteristics of excitation and attenuation of the ground motion in the lake van region eastern turkey using a data set that includes three component seismograms from the 23 october 2011 m w 7 1 van earthquake as well as its aftershocks regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance frequency and magnitude peak ground velocities are measured in selected narrow frequency bands from 0 25 to 12 5 hz observed peaks are regressed to define a piecewise linear regional attenuation function a set of excitation terms and a set of site response terms results are modeled through random vibration theory see cartwright and longuet higgins 1956 in the log log space the regional crustal attenuation is modeled with a bilinear geometrical spreading graphic 1 characterized by a crossover distance at 40 km graphic 2 fits our results at short distances r is better at larger distances 40 r 200 km a frequency dependent quality factor q f 100 f f ref 0 43 in which f ref 1 0 hz is coupled to the geometrical spreading because of the inherent trade off of the excitation attenuation parameters and their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes after choosing a brune stress drop brune 4 mpa at m w 3 5 we were able to define 1 an effective high frequency distance and magnitude independent roll off spectral parameter eff 0 03 s and 2 a size dependent stress drop parameter which increases with moment magnitude from brune 4 mpa at m w 3 5 to brune 20 mpa at m w 7 1 the set of parameters mentioned here may be used in order to predict the earthquake induced ground motions expected from future earthquakes in the region surrounding lake van 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

empirical prediction equations for peak ground velocity derived from strong motion records from europe and the middle east peak ground velocity pgv has many applications in earthquake engineering but there are relatively few prediction equations for this parameter in comparison with the large numbers of equations for estimating peak ground accel eration and response spectral ordinates this lack of empirical equations for pgv has led to widespread use of the practice of scaling peak velocity from the 5 damped response spectral ordinate at 1 sec which is a poor substitute for direct prediction of the parameter responding to the need to provide equations for the prediction of pgv this article derives new equations using the strong motion database for the seismically active areas of europe and the middle east following a new processing of all of the records a total of 532 strong motion accelerograms recorded at distances of up to 100 km from 131 earthquakes with moment magnitudes ranging from m 5 to 7 6 are used to derive equations for both the larger and the geometric mean of the horizontal components the predictions are found to be broadly consistent with those from previous european equations and also with preliminary results from the next generation of attenuation nga project suggesting that systematic differences in ground motions from active crustal regions if any are sufficiently small not to prevent the combined use of strong motion data from southern europe western north america and other tectonically active areas of shallow crustal seismicity

unbiased moment rate spectra and absolute site effects in the kachchh basin india from the analysis of the aftershocks of the 2001 mw 7 6 bhuj earthquake what can be learned about absolute site effects on ground motions with no geotechnical information available in a very poorly instrumented region in addition can reliable source spectra be computed at a temporary deployment these challenges motivated our current study of aftershocks of the 2001 m w 7 6 bhuj earthquake in western india where we decouple the ambiguity between absolute source radiation and site effects by first computing robust estimates of coda derived moment rate spectra of about 200 aftershocks in each of two depth ranges crustal attenuation and spreading relationships based on the same data used here were determined in an an earlier study using our new estimates of source spectra and our understanding of regional wave propagation for direct s waves we isolate the absolute site terms for the stations of the temporary deployment absolute site terms for each station were determined in an average sense for the three components of the ground motion via an l1 norm minimization results for each site were averaged over wide ranges of azimuths and incidence angles the bhuj deployment is characterized by a variable shallow geology mostly of soft sedimentary units vertical site terms in the region were observed to be almost featureless i e flat with amplifications slightly 1 0 within wide frequency ranges as a result the horizontal to vertical h v spectral ratios observed at the deployment mimic the behavior of the corresponding absolute horizontal site terms and they generally overpredict them this differs significantly from results for sedimentary rock sites limestone dolomite obtained by malagnini et al 2004 in northeastern italy where the h v spectral ratios had little in common with the absolute horizontal site terms spectral ratios between the vector sum of the computed horizontal site terms for the temporary deployment with respect to the same quantity computed at the hardest rock station available bac1 are seriously biased by its nonflat nonunitary site response this indicates that occasionally the actual behavior of a rock outcrop may be far from that of an ideal reference site steidl et al 1996

ground motion scaling in the marmara region turkey summary predictive relationships for the ground motion in the marmara region northwestern turkey are parametrized after regressing three component waveforms from regional earthquakes in the frequency range 0 4 15 0 hz and in the distance range 10 200 km the data set consists of 2400 three component recordings from 462 earthquakes recorded at 53 stations moment magnitudes m w range between 2 5 and 7 2 the largest event for which we have waveforms available m w 7 2 occurred in duzce on 1999 november 12 the aftershocks of that earthquake together with the aftershocks of the 1999 august 17 izmit event m w 7 4 are included in the dataset regressions are performed independently on fourier velocity spectra and on peak ground velocities for a large number of sampling frequencies a simple model is used to relate the logarithm of the measured ground motion to excitation site and propagation terms results obtained for peak velocities are used to define a piecewise continuous geometrical spreading function g r a frequency dependent q f and a distance dependent duration function the latter is used through random vibration theory rvt in order to predict time domain characteristics i e peak values of the ground motion the complete model obtained for the peak ground motion was used to match the results of the regressions on the fourier amplitudes fourier velocity spectra for the combined horizontal motion are best fit by a hinged quadrilinear geometrical spreading function for observations in the 10 200 km hypocentral distance ranges as a function of frequency f 100 f 1 0 hz r 1 0 for r 30 km r 0 6 for 30 100 km the frequency dependent crustal shearwave quality factor q f coefficient q f 180 f 0 45 the t 5 75 per cent duration window provides good agreement between observed and predicted peak values by modelling the behaviour of the small earthquakes at high frequency we also quantified a regional parameter 0 055 s spectral models with one single corner frequency brune and with two corner frequencies atkinson and silva fit the observed high frequency excitation levels equally well whereas the model by atkinson and silva fits the low frequency observations slightly better than brune s rvt is used to predict the absolute levels of ground shaking following boore s implementation of the stochastic ground motion model boore s smsim codes our regional empirical predictive relationships are compared to the ones adopted in several regions of the world from california to western united states

vs30 κ regional attenuation and mw from accelerograms application to magnitude 3 5 french earthquakes summary we investigate recordings from weak to moderate earthquakes with magnitudes ranging between about 3 and 5 recorded by the french accelerometric network s wave spectra are modelled as a product of source propagation and site terms inverting large data sets of multiple earthquakes recorded at multiple stations allows us to separate the three contributions source parameters such as moment magnitude corner frequency and stress drop are estimated for each earthquake we provide the first complete and homogeneous catalogue of moment magnitudes for france for the events with magnitude greater than 3 that occurred between 1996 and 2006 stress drops are found to be regionally dependent as well as magnitude dependent and range from about 0 1 mpa 1 bar to about 30 mpa 300 bars the attenuation parameters show that in france on a nationwide scale variations of attenuation properties do exist site transfer functions are also computed giving the level of amplification at different frequencies with respect to the response of a generic rock site characterized by an average 30 m s wave velocity vs30 of 2000 m s 1 from these site terms we compute the high frequency fall off parameter modelled as exp f with f the frequency for 76 stations we also determine rock stations vs30 and we show the vs30 relationship for 21 rock stations

shear wave velocity structure of sediments from the inversion of explosion induced rayleigh waves comparison with cross hole measurements rayleigh waves generated by a 10 kg dynamite explosion were recorded along a dense linear array of 47 seismic stations the array had a total length of 1 4 km and it was deployed on the sediments of the po river floodplain near the city of ferrara northern italy the recorded signals were dominated by fundamental mode rayleigh waves several techniques including multiple filter analysis phase velocity stacking and single station cross correlation were used to obtain group and phase velocity dispersion from subsets for the data set synthetic seismograms were computed for one velocity structure showing a good match to the recorded waveforms late rayleigh wave codas were characterized by persistent monochromatic ringing interpreted as due to surface waves scattered by weak lateral heterogeneities scattering within the alluvium of the great po river valley likely occurred across a reticular system of ancient secondary river beds compared to the rest of the floodplain these preferential directions of local drainage are characterized by different sedimentary environments the availability of in situ cross hole measurements of shear wave velocities allowed the comparison with our results from surface observations demonstrating that the analysis of explosion induced rayleigh waves can be used for the geophysical characterization of flat layered structures at a local scale for seismic engineering purposes

local source tomography applications to italian areas we describe three study cases in which we used local earthquake and shot travel time residuals to investigate the upper crustal structure of three regions in italy we inverted for velocity and hypocentral parameters using a damped least squares technique making use of parameter velocity and hypocentre separation the three studied regions are in italy namely a the vulsinian volcanic complex latium where there is an active geothermal field b the irpinia campania lucania region in the southern appennines site of the strongest earthquake in italy for at least 65 years november 1980 ms 6 9 c the friuli region in northeastern italy where another strong earthquake ms 6 5 occurred in 1976 the computed shallow velocity models generally correspond with surface geological structures for the three studied areas the main results are respectively a a low velocity anomaly detected in the centre of the vulsinian volcanic complex at a depth of 5 8 km probably due to anomalous heat flow caused by a partially molten or cooling intrusive body b the identification of a deep 10 km discontinuity in the crust beneath the irpinia fault zone approximately corresponding with the fault extension at depth c the detection of a wedge of high velocity high density material at seismogenic depth 5 10 km beneath the friuli region interpreted as a buried thrust of the metamorphic basement

tomographic studies of the upper mantle beneath the italian region teleseismic p arrivals at seismological stations are inverted into a model of velocity perturbations down to a depth of about 470 km directionally independent average residuals computed from steeply inciding waves are transformed into a model of lithospheric thickness both models show a good correspondence with the main tectonic features of the italian peninsula positive velocity perturbations are observed beneath the alps and in depths over 200 km also beneath the po basin a high velocity anomaly of the tyrrhenian subduction is less pronounced probably due to a directional dependence of p velocities in the mantle negative velocity perturbations indicate several low velocity regions e g beneath the northern apennines the sicily region and in the upper 100 km beneath the po basin the amplitudes of velocity perturbations beneath the depth of 200 km are smaller on the average than those in the upper two layers the whole region is characterized by large undulations of the lithosphere base which reaches depths from less than 60 km to more than 150 km the most prominent lithospheric root beneath the alps is a product of the collision between the european and the adriatic plates while the lithospheric thickening beneath the calabrian coast is likely to be connected with the eastern wing of the tyrrhenian subduction the dramatic changes of lithosphere thickness between the northern and the southern apenninic arcs and northern calabria as well as the thinnings at the western closure of the po basin indicate important deep seated boundaries of lithospheric blocks of autonomous geodynamic development

a break in self similarity in the lunigiana garfagnana region northern apennines 1 in this study stable source parameters are determined for small earthquakes in the lunigiana garfagnana region using an empirical methodology based on coda envelope measurements that are significantly less affected by the source radiation pattern directivity and heterogeneous path variation than traditional direct wave measurements we find evidence that the scaled energy er m0 increases with moment and source spectra are not self similar for 3 0 mw 4 6 the calibration procedure allows for an independent check of three important features 1 that the empirical path corrections provide consistent amplitude measurements for the same event at different stations distances and azimuths 2 that the long period levels of the source spectra are consistent with independent m0 derived from long period waveform modeling 3 that small event spectra are flat below a conservative estimate of the corner frequency and thereby effectively accounting for near site attenuation

high stress strike slip faults in the apennines an example from the 2002 san giuliano earthquakes southern italy 1 under the hypotheses that the high frequency part of the seismic spectrum is controlled by source duration and by peak slip velocity we applied a recent coda envelope methodology to obtain stable relative source estimates between selected mainshocks and their aftershocks we computed stable mainshock aftershock s wave spectral ratios and used a simple source model in order to quantify the scaling of the seismic sources of the san giuliano sequence southern italy from the analysis of the ratios obtained between the main shock of 10 31 2002 and 11 aftershocks and of those computed between the other main event of the sequence of 11 01 2002 and 10 aftershocks we observe that the scaling relationships m0 fc 3 holds with 0 89 0 05 despite the strong discrepancy between the moment magnitude and the high frequency ground motion excited by the main shocks ml was much lower than mw that would indicate low stress drop sources we compute anomalously high stress parameters for both events by comparison the same analysis was carried out on seismic data of the hector mine seismic sequence the main event of october 16 1999 mw 7 0 and six of its aftershocks we found m0 fc 3 with 0 8 0 4

3d ground motion estimation in rome italy paleoseismic evidence and seismic hazard analysis suggest that the city of rome italy has experienced considerable earthquake ground motion since its establishment more than 2000 years ago seismic hazards in rome are mainly associated with two active seismogenic areas the alban hills and the central apennines regions located about 20 km southeast and 80 100 km east of central rome within the twentieth century m 6 8 and m 5 3 earthquakes in the apennines and the alban hills respectively have generated intensities up to mercalli cancani sieberg scale mcs vii in the city with a lack of strong motion records we have generated a 3d velocity model for rome embedded in a 1d regional model and estimated long period 1 hz ground motions for such scenarios from finite difference simulations of viscoelastic wave propagation we find 1 hz peak ground velocities pgvs and peak ground accelerations pgas of up to 14 cm sec and 44 cm sec2 respectively for a m 5 3 alban hills scenario largest near the northwestern edge of the tiber river our six simulations of a m 7 0 central apennine scenario generate 0 5 hz pgvs in rome of up to 9 cm sec as well as extended duration up to 60 sec the peak motions are similar to but the durations much longer than those from previous studies that omitted important wave guide effects between the source and the city the results from the two scenarios show that the strongest ground motion amplification in rome occurs in the holocene alluvial areas with strong basin edge effects in the tiber river valley our results are in agreement with earlier 2d sh wave results showing amplification of peak velocities by up to a factor of 2 in the alluvial sediments largest near the contact to the surrounding plio pleistocene formations our results suggest that both earthquakes from the alban hills and the central apennines regions contribute to the seismic hazards in rome although earthquakes from the former area may generate the larger peak motions seismic waves from the latter region may generate ground motions with extended durations capable of causing significant damage on the built environment

estimation of response spectra and simulation of nonstationary earthquake ground motions abstract italian strong motion data were used to study the attenuation of response spectra and to simulate artificial accelerograms as a function of magnitude distance and site geology the database has already been utilized for the study of the atten uation of peak ground acceleration pga and velocity and consists of 95 accelero grams from 17 earthquakes of magnitudes ranging from 4 6 to 6 8 using multiple regressions we developed empirical predictive equations for the vertical and hori zontal components of response spectra corresponding to 14 frequencies ranging from 0 25 to 25 hz predictive equations aimed at the ground motion simulation were also estimated for time dependent frequency parameters strong ground motion du ration and arias intensity the shape of the predicted spectra is strongly dependent on magnitude and nearly independent of distance alluvium sites show an amplification effect with respect to stiff sites in different frequency ranges according to the thickness of the soil deposit the vertical horizontal spectral ratio in far field varies with magnitude and frequency from 0 35 to 0 85 the resulting response spectra are compared with the predictions of some recent attenuation relationships and with those proposed by the eurocode ec8 the simulation of nonstationary strong ground motions is achieved through an empirical method where time and frequency features of the motion are represented through the physical spectrum extending the spectral moments theory to the nonsta tionary case the simulated time histories fit the recorded accelerograms in terms of several ground motion amplitude measures such as peak acceleration peak velocity fourier spectra and response spectra the principal advantage of the proposed method consists in correlating the simulation parameters with earthquake magnitude source distance and soil conditions introduction in the field of seismic risk assessment the prediction of shaking intensity in future earthquakes plays a key role re liable estimates of the ground motions that structures must be designed to withstand are obtained mainly through em pirical predictive relationships developed after statistical analysis of data recorded during strong earthquakes many predictive equations are by now available in dif ferent regions of the world campbell 1985 1993 for the prediction of peak ground acceleration pga many fewer are the relationships developed for the prediction of response spectral values idriss 1991 boore

layered seismogenic source model and probabilistic seismic hazard analyses in central italy we defined a seismogenic model for central italy based on three layers of sources and computed the relative seismic hazard maps one layer is constituted by individual structures liable to generate major earthquakes m 5 5 we defined them as seismogenic boxes by using geological information in terms of plan projec tion of active faults the seismicity rates associated with an individual source are based on the geometry and kinematics of the fault the recurrence model is controlled by the earthquake source association and when possible we defined the occurrence time of the last major event using it in a time dependent approach another layer is given by the instrumental seismicity analysis of the past two decades which allows us to evaluate the background seismicity m 5 5 using a sliding window selec tion of events we defined a model of regular adjacent cells of variable a and b values of the gutenberg richter relation the last layer utilizes all the instrumental earth quakes and the historical events not correlated to known structures 4 5 m 6 by separating them into seismotectonic provinces shaped on a geological structural basis the seismic hazard computations first use this layered model in a traditional probabilistic scheme the results indicate a narrow belt of peak ground acceleration pga higher than 0 30g with standard deviation in attenuation functions in the axial part of the apennine chain with a maximum spot of pga 0 40g southeast of the area damaged by the 1997 1998 umbria marche sequence pga expected not to be exceeded in 50 years at 90 probability level the background seismicity gives a nonnegligible contribution to the hazard at least for first damage levels then a simplified time dependent hypothesis has been introduced for the individual sources alone computing the conditional probability of occurrence of characteristic earth quakes for each source by brownian passage time distributions adopting equivalent fictitious seismicity rates we obtained maps referring to the next 50 years by using traditional codes these results show that the contribution of the recently active sources vanishes and the most hazardous sites are now located south of l aquila and in the sulmona area we consider that the methodology and results obtained are useful for seismic risk reduction strategies

strong ground motion simulation of the 6 april 2009 l aquila italy earthquake on 6 april 2009 an earthquake of mw 6 13 herrmann et al 2011 occurred in central italy close to the town of l aquila although the earthquake is considered to be a moderate size event it caused extensive damage to the surround ing area the earthquake is identified with significant directivity effects high amplitude short duration motions are observed at the stations that are oriented along the rupture direction whereas low amplitude long duration motions are observed at the stations oriented in the direction opposite to the rupture the complex nature of the earthquake combined with its damage potential brings the need for studies that assess the seismological characteristics of the 2009 l aquila mainshock in this study we present the strong ground motion simulation of this particular earthquake using a stochastic finite fault model with a dynamic corner frequency ap proach for modeling the resulting ground motions we choose two finite fault source models that take into account the source complexity of the l aquila mainshock in order to test the sensitivity of ground motion parameters to the seismic wave attenua tion parameters we use two different attenuation models obtained in the study region using weak motion and strong motion databases comparisons are made between the attenuation of synthetics and ground motion prediction equations gmpes synthetic ground motions are further compared with the observed ones in terms of fourier amplitude and response spectra at 21 strong ground motion stations that recorded the mainshock within an epicentral distance of 100 km the spatial distribution of shaking intensity obtained from the did you feel it project and site survey results are compared with the spatial distributions of simulated peak ground motion intensity parameters our results show that despite the limitations of the method in simulating the directivity effects the stochastic finite fault model seems an effective and fast tool to simulate the high frequency portion of ground motions

estimating absolute site effects the authors use previously determined direct wave attenuation functions as well as stable coda derived source excitation spectra to isolate the absolute s wave site effect for the horizontal and vertical components of weak ground motion they used selected stations in the seismic network of the eastern alps and find the following 1 all hard rock sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0 5 and 12 hz the available bandwidth on both the horizontal and vertical components 2 hard rock site transfer functions showed large variability at high frequency 3 vertical motion site transfer functions show strong frequency dependence and 4 h v spectral ratios do not reproduce the characteristics of the true horizontal site transfer functions 5 traditional relative site terms obtained by using reference rock sites can be misleading in inferring the behaviors of true site transfer functions since most rock sites have non flat responses due to shallow heterogeneities resulting from varying degrees of weathering they also use their stable source spectra to estimate total radiated seismic energy and compare against previous results they find that the earthquakes in this region exhibit non constant dynamic stress drop scaling which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes to correct the vertical and horizontal s wave spectra for attenuation they used detailed regional attenuation functions derived by malagnini et al 2002 who determined frequency dependent geometrical spreading and q for the region these corrections account for the gross path effects i e all distance dependent effects although the source and site effects are still present in the distance corrected spectra the main goal of this study is to isolate the absolute site effect as a function of frequency by removing the source spectrum moment rate spectrum from the distance corrected s wave spectra typically removing the s wave source spectrum is difficult because of inadequate corrections for the source radiation pattern directivity and random interference in addition to complexities near the source 2 d and 3 d structure beneath the recording site will result in an azimuth dependent site effect since the direct wave only samples a narrow range in take off and back azimuth angles multi station averaging is needed to minimize the inherent scatter to minimize these complicating effects they apply the coda methodology outlined by mayeda et al 2003 to obtain stable moment rate spectra this methodology provides source amplitude and derived source spectra that are a factor of 3 to 4 times more stable than those derived from direct waves since the coda is commonly thought of as scattered energy that samples all ray parameters and back azimuths it is not very sensitive to the source radiation pattern and 3 d structure this property makes it an excellent choice for use in obtaining average properties of the source site and path effects in a region due to the characteristics of the techniques used in this study all the inverted quantities are azimuthally averaged since the aximuthal information is lost in the processing

stress drop apparent stress and radiation efficiency of clustered earthquakes in the nucleation volume of the 6 april 2009 mw 6 1 l aquila earthquake

from velocity and attenuation tomography to rock physical modeling inferences on fluid driven earthquake processes at the irpinia fault system in southern italy we retrieve 3 d attenuation images of the crustal volume embedding the fault system associated with the destructive ms 6 9 1980 irpinia earthquake by tomographic inversion of t measurements a high qp anomaly is found to be correlated with the 1980 fault geometry while the qs model shows regional scale variations related to the ne edge of the uplifted pre tertiary limestone an upscaling strategy is used to infer rock properties such as porosity consolidation type of fluid mixing and relative saturation percentage at 8 10 km fault depth we constrain the porosity and consolidation in the ranges 4 5 and 5 9 respectively with the possible fluid mixes being both brine co2 and ch4 co2 the consolidation parameter range indicates high pore pressures at the same depths these results support the evidence for a fracture system highly saturated in gases and a seismicity triggering mechanism at the fault zone which is strongly controlled by fluid induced pore pressure changes

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

characterization of earthquake induced ground motion from the l aquila seismic sequence of 2009 italy summary based only on weak motion data we carried out a combined study on region specific source scaling and crustal attenuation in the central apennines italy our goal was to obtain a reappraisal of the existing predictive relationships for the ground motion and to test them against the strong motion data peak ground acceleration pga peak ground velocity pgv and spectral acceleration sa gathered during the mw 6 15 l aquila earthquake 2009 april 6 01 32 utc the l aquila main shock was not part of the predictive study and the validation test was an extrapolation to one magnitude unit above the largest earthquake of the calibration data set the regional attenuation was determined through a set of regressions on a data set of 12 777 high quality high gain waveforms with excellent s n ratios 4259 vertical and 8518 horizontal time histories seismograms were selected from the recordings of 170 foreshocks and aftershocks of the sequence the complete set of all earthquakes with ml 3 0 from 2008 october 1 to 2010 may 10 all waveforms were downloaded from the iside web page http iside rm ingv it iside standard index jsp a web site maintained by the istituto nazionale di geofisica e vulcanologia ingv weak motion data were used to obtain a moment tensor solution as well as a coda based moment rate source spectrum for each one of the 170 events of the l aquila sequence 2 8 mw 6 15 source spectra were used to verify the good agreement with the source scaling of the colfiorito seismic sequence of 1997 1998 recently described by malagnini et al 2008 finally results on source excitation and crustal attenuation were used to produce the absolute site terms for the 23 stations located within 80 km of the epicentral area the complete set of spectral corrections crustal attenuation and absolute site effects was used to implement a fast and accurate tool for the automatic computation of moment magnitudes in the central apennines

near real time ground motion updating for earthquake shaking prediction abstract one of the main challenges of modern engineering seismology is the mitigation of the adverse consequences of earthquakes although modern engineering techniques allow for the designing of earthquake resistant structures the ability to predict more reliable ground motion estimates and associated uncertainties is needed with this aim this study investigated the possibility of using data recorded during an earthquake to improve the empirical ground motion prediction equations gmpes in particular we propose a procedure that updates the coefficients of an initial gmpe to account for the specific features of a seismic source and propagation medium we applied the technique in the immediate postevent time period of three well recorded earthquakes that occurred recently in italy and caused casualties and significant damage the 6 april 2009 m w 6 3 l aquila earthquake the 20 may 2012 m w 5 9 emilia earthquake and the 25 october 2012 m w 5 2 pollino earthquake for possible future development using the same earthquakes and the networks with which they were recorded we also explored the potential of the technique as a possible real time application as in the case of earthquake early warning systems

effect of time dependence on probabilistic seismic hazard maps and deaggregation for the central apennines italy abstract we produce probabilistic seismic hazard assessments for the central apennines italy using time dependent models that are characterized using a brownian passage time recurrence model using aperiodicity parameters of 0 3 0 5 and 0 7 we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters for the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults we use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault floating fault model to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation we show maps for peak ground acceleration pga and 1 0 hz spectral acceleration sa 1 on rock having 10 probability of exceedence in 50 yr we produce maps to compare the separate contributions of smoothed seismicity and fault components in addition we construct maps that show sensitivity of the hazard for different parameters and the poisson model for the poisson model the addition of fault sources to the smoothed seismicity raises the hazard by 50 at locations where the smoothed seismicity contributes the highest hazard and up to 100 at locations where the hazard from smoothed seismicity is low for the strongest aperiodicity parameter smallest the hazard may further increase 60 80 or more or may decrease by as much as 20 depending on the recency of the last event on the fault that dominates the hazard at a given site in order to present the most likely earthquake magnitude and or the most likely source site distance for scenario studies we deaggregate the seismic hazard for sa 1 and pga for two important cities rome and l aquila for pga both locations show the predominance of local sources having magnitudes of about 5 3 and 6 5 respectively for sa 1 at a site in rome there is significant contribution from local smoothed seismicity and an additional contribution from the more distant apennine faults having magnitude around 6 8 for l aquila the predominant sources remain local in order to show the variety of impact of different values we also obtained deaggregations for another three sites in general as decreases periodicity increases the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates this effect is strongest for the long period 1 sec ground motions

separation of source and site effects in ground motions recorded in the village of onna during aftershocks of the 2009 april 6 mw 6 1 l aquila earthquake this article has been accepted for publication in geophysical journal internationa the authors 2017 published by oxford university press on behalf of the royal astronomical society all rights reserved

multifractality and punctuated equilibrium in the earth s magnetic field polarity reversals the earth s magnetic field has reversed its polarity hundreds of times in the earth s history this phenomenon is generally viewed as due to a poisson nonstationary process here the geomagnetic chron time length sequence for the past 166 ma is analyzed using a multifractal approach based on singularity analysis the existence of a multifractal structure is the signature of the occurrence of punctuated equilibrium which can be read as an indication of a critical configuration of the geodynamo the results obtained are compared with those from a prototypical model of a dynamical system introduced by seki ito 1993 and are discussed in the context of fluid motions within the earth s outer liquid core

apparent stress and corner frequency variations in the 1999 taiwan chi chi sequence evidence for a step wise increase at mw 5 5 1 apparent stress and corner frequencies are measured for the chi chi taiwan sequence beginning with the mw 7 6 mainshock on 20 september 1999 using the coda source ratio method we obtained stable source ratio estimates using broadband stations on taiwan we find the following 1 for the mainshock and 3 of the larger aftershocks apparent stress is clustered around 0 8 mpa 0 1 mpa 2 events below mw 5 5 exhibit lower apparent stress with larger scatter ranging between 0 08 and 0 8 mpa and are spatially variable 3 the brune 1970a 1970b omega square source model fits the spectral shape for events 4 7 mw 7 6 however a step wise break in self similarity exists at mw 5 5 we hypothesize that larger events are subject to the regional state of stress whereas smaller aftershocks are sensitive to the local state of stress from stress field redistribution following the mainshock and or fault zone lubrication that affects only larger events