focal mechanism inversion in the giudicarie lessini seismotectonic region southern alps italy insights on tectonic stress and strain abstract a set of 41 focal mechanisms 1989 2006 from p wave first polarities is computed from relocated seismic events in the giudicarie lessini region southern alps estimated hypocentral depths vary from 3 1 to 20 8 km for duration magnitudes md in the range 2 7 5 1 stress and strain inversions are performed for two seismotectonic zones namely g giudicarie and l lessini this subdivision is supported by geological evidence seismicity distribution and focal mechanism types the available number of data 16 in g 22 in l does not make possible any further subdivisions seismotectonic zones g and l are undergoing different kinematic regimes thrust with strike slip component in g and strike slip in l principal stress and strain axes in each sub region show similar orientations the direction of maximum horizontal compressive stress is roughly perpendicular to the thrust fronts along the giudicarie belt in zone g and compatible with right lateral strike slip reactivation of the faults belonging to the schio vicenza system in zone l on the whole kinematic regimes and horizontal stress orientations show a good fit with other stress data from focal mechanisms and breakouts and with geodetic strain rate axes

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

investigating rupture direction for three 2012 moderate earthquakes in northern italy from inversion of peak ground motion parameters we investigate the possibility of inferring the dominant horizontal rupture direction for moderate earthquakes from the inversion of peak ground motion parameters to this aim we adopt a technique that was devised and applied to large earthquakes for retrieving both the dominant rupture direction and the surface fault projection to be used with a proper distance metric to refine the shakemap computation in the present paper the procedure was applied to three moderate earthquakes that occurred in 2012 in northern italy three days apart the m 4 2 pre alpi venete earthquake on 24 january the m 4 9 reggio emilia earthquake on 25 january and the m 5 4 parma earthquake on 27 january for two of the three analyzed events the technique identifies a dominant horizontal rupture direction which is consistent with the strike directions inferred from the focal mechanisms for the m 5 4 event which is a deep about 61 km thrust faulting mechanism earthquake the inferred dominant rupture direction allows identification of the northeast dipping plane as the fault plane in accordance with the aftershocks distribution

the 2012 may 20 and 29 emilia earthquakes northern italy and the main aftershocks s wave attenuation acceleration source functions and site effects

large effects of moho reflections sms on peak ground motion in northwestern taiwan abstract a total of 336 three component strong motion recordings from the m w 6 35 niu dou earthquake of 25 june 1995 at a focal depth of 39 9 km in northern taiwan are used to study the effects on strong ground motion due to moho reflection of s waves the residuals of both horizontal peak ground acceleration pga and peak ground velocity pgv recorded from the earthquake are analyzed the results confirm that many class e soft soil stations in the taipei basin and the ilan plain had the expected large amplification of about 1 7 and 1 5 times respectively the predicted median pga values surprisingly a large group of class c or d dense and stiff soil sites in taoyuan tcu007 lungtan tcu013 guanshi tcu021 hsinchu tcu095 and miaoli tcu047 areas in northwestern taiwan had unusually large amplification of about 3 4 8 1 and 1 7 3 3 times the predicted median pga and pgv values respectively they are interpreted in terms of focusing and interference between sms waves reflected from the horizontal and inclined portions of an east dipping moho discontinuity in this area this interpretation is supported by the close agreement between the expected amplitudes and arrival times of the largest shear waves with the observed data our results suggest that when a damaging earthquake occurs near an inclined moho boundary the reflected sms waves can result in significantly amplified ground motions at distances beginning about 50 km the exact distance range will depend on the thickness of the crust and the dip angle of the moho boundary

evaluating the relevance of moho reflections in accelerometric data application to an inland japanese earthquake the relevance of sms seismic phase or multiple reflected sms on the ground motion away from the earthquake source has been discussed in many studies during the past 30 years the sms and multiples are normally recognized by analyzing travel time arrivals on the basis of a priori well known crustal models moho reflections in borehole and surface accelerometric data of the kik net network for an inland japanese earthquake are investigated when reflected phases are transmitted efficiently both amplitude and frequency content can be retrieved by using a simple time frequency analysis of accelerometric records for the 15 april 2007 m 5 4 kinki crustal earthquake moho reflections are found at epicentral distances from 70 to 180 km borehole data show that sms and multiples can be easily found in the frequency range from 0 25 to 2 s and in the group velocity window from 2 8 to 3 5 km s the coupling of borehole and surface stations of kik net data allows for the separate evaluation of the propagation effect along the source receiver path and of the transfer function due to soft soils for these specific phases an amplitude period scaling relationship is found between the national earthquake hazards reduction program site classification and the observed transfer function for sms phase and multiples online material figures showing the effect of the source time function duration on the multiple filter technique mft diagrams an mft analysis of surface and borehole accelerograms period distance domain spectral amplitudes and the average period velocity transfer function for different nehrp soil classes

far source long period displacement response spectra in the po and venetian plains italy from 3d wavefield simulations abstract design elastic displacement spectra for seismic codes and zoning studies of seismic hazard for long period structures are becoming of utmost importance in modern earthquake engineering the increase of displacement based design approaches together with the availability of good quality digital strong motion data allow the creation of reliable spectral shapes for seismic design of up to 10 s nevertheless to characterize the site amplification effects during large levels of shaking additional studies are needed especially in deep sedimentary basins and plains that can be strongly excited by large amplitude long period waves data within deep basins is rare because accelerometric seismic networks are normally deployed on rock or stiff soil and modeling of waveforms is hence necessary for bridging this gap focusing on the numerical modeling of the 3d wavefield in 1d flat layered and 3d structures in the po and venetian plains northern italy and on earthquakes with magnitudes m 6 6 and hypocentral distances greater than 50 km in this study we 1 estimate the displacement response spectra drs from 1 to 10 s in the po and venetian plains 2 compare the drs from numerical simulations using flat layered and heterogeneous 3d models against the currently available uniform hazard drs for italy and 3 evaluate the influence of deep sediments on drs shape and thus on seismic codes finally 1d and 3d simulated drs are compared with drs obtained from recordings in the kanto basin where similar long period displacement is observed

moho reflection effects in the po plain northern italy observed from instrumental and intensity data abstract recent moderate sized earthquakes m l 5 2 that occurred in northern italy demonstrate that the currently available ground motion prediction equations gmpes largely underestimate shaking in the po plain region at hypocentral distances greater than 70 km in order to investigate this phenomenon we collected a set of peak ground acceleration pga observations for weak and moderate earthquakes in the area nonparametric regression analysis of pga observations as a function of magnitude and hypocentral distance shows that pga is systematically enhanced for distances between 70 and 200 km an indirect estimation through the analysis of the attenuation of macroseismic intensities suggests that the effect also applies to strong earthquakes m l 5 5 we performed numerical modeling experiments to investigate the cause of the phenomenon the characteristics of the computed synthetic seismograms indicate that the enhancement of ground motion is mainly an effect of the reflection of s waves at the moho sms phase the analysis of both real and synthetic data shows that the moho reflection effect is maximized at hypocentral distances between 90 and 150 km where the pga increases by a factor larger than 2 4

the mw 5 4 reggio emilia 1996 earthquake active compressional tectonics in the po plain italy summary we have analysed the seismic sequence that occurred in october 1996 near the town of reggio emilia on the southern edge of the po plain the onset of the sequence was marked by a 5 4 moment magnitude main shock located at 15 km depth the main shock focal mechanism is a reverse solution with a strike slip component and the scalar moment is 1 46 1017 n m we used broad band digital recordings from a borehole station located at about 70 km from the epicentre for a spectral analysis in order to estimate attenuation and source parameters for the main shock in addition the empirical green s function method has been applied to evaluate the source time function in terms of both moment rate and stress rate we infer an asperity like rupture process for the main shock as suggested by the short duration of the stress release with respect to the overall duration of the moment rate function this analysis also allows us to estimate the average dynamic stress drop of the main shock 600 bar we analysed the digital recordings of the temporary local seismic network deployed after the main shock and of a permanent local network maintained by the italian petroleum agency agip during 15 days of field experiments we recorded more than 800 aftershocks which delineate a 9 km long ne elongated distribution confined between 12 and 15 km depth suggesting that the basement is involved in the deformation processes 102 focal mechanism of aftershocks have been computed from p wave polarities showing mainly pure reverse solutions we calculate the principal stress axes from a selected population of earthquakes providing a constraint on the stress regime of this part of the po plain the focal mechanisms are consistent with a n s subhorizontal 1 all the seismological data we have analysed confirm that this region is undergoing active compressional tectonics as already inferred from recent earthquakes geomorphological data and other stress indicators moreover the elongation of the reggio emilia aftershock sequence is consistent with the regional direction of the thrust fronts cropping out in the area suggesting that they are still active

source parameter analysis of microearthquakes recorded around the underground gas storage in the montello collalto area southeastern alps italy abstract the study of seismic source parameters is crucial for understanding the origin of seismicity and retrieving information on the energy balance and the stress involved in earthquake rupture processes in active tectonic areas where underground industrial activities are carried out such parameters may help to understand whether earthquakes are induced triggered or natural the montello collalto area southeastern alps is located in an active tectonic environment and hosts a depleted natural reservoir used to store gas since 2012 a high quality seismic network monitors the microseismicity occurring around the underground gas storage reservoir to understand if the storage activity might induce seismicity in this paper we estimate the source parameters of low magnitude events representative of the seismicity occurring in the area surrounding the reservoir the analysis includes a preliminary removal of the site effects specifically computed within this study from all the records then using a parametric multistep inversion scheme we estimate the seismic moment the corner frequency and the static stress drop that can be set as reference for the microseismicity occurring in the study area all the investigated earthquakes show low seismic efficiency compatible with overshoot processes which is typical of natural i e tectonic earthquakes our procedure can be implemented in other tectonic regions hosting underground industrial activities to support the decisional processes related to real time monitoring

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

the contribution of postcritical moho reflections sms to ground motions of the 2008 mw 7 9 wenchuan earthquakethe contribution of postcritical moho reflections sms to ground motions

p wave velocity density and vertical stress magnitude along the crustal po plain northern italy from sonic log drilling data in order to characterize better p wave velocities for the shallow crust of the po plain and surrounding regions we have selected 64 deep wells mainly located in the plain and also along the apennine belt and adriatic coast in particular we have analyzed the stratigraphic profiles for all wells and the available sonic logs 37 out of 64 from these data we have examined the p wave velocity trend with depth and estimated rock density following an empirical relationship between sonic velocity and density in sedimentary rocks then we have calculated notably for the first time in a large area of italy the overburden stress magnitude for each well for instance at a depth of 5 km we have found values varying from 105 to 130 mpa moving from the adriatic coast to the apennine belt consequently the apennine belt shows a maximum regional lithostatic gradient of around 26 mpa km while the po plain and adriatic region have values of around 21 mpa km the maximum density value that can be considered for the apennine crustal belt corresponds to 2 65 g cm3 in the po plain the mean density is around 2 25 g cm3 while in the adriatic area the average density has the lowest value in the region at 2 13 g cm3 although in this area a 2d crustal p wave velocity model does not adequately constrain the complicated and uneven tectonics we have nevertheless established a shallow model consisting of five separate layers the strength of this paper lies in the possible use of these direct data together with other derived geological and geophysical information to build a 3d model of the area

the italian cmt dataset from 1977 to the present abstract the ingv harvard european mediterranean regional centroid moment tensor rcmt catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude 4 5 m 5 5 in the mediterranean region the database represents an extension to smaller magnitudes of the harvard global cmt catalog based on analysis of seismograms recorded at regional distance and modeling of intermediate period surface waves the catalog includes about 600 events 200 of which in the italian region this study extends the catalog back in time for the italian region as long as made possible by available digital data i e since 1977 with the same analysis and inversion method used for current seismicity as a result we present here 65 new moment tensors for years between 1977 and 1997 these solutions represent 45 of the total number of events analyzed the existing seismograms being often too scarce to allow a stable solution the new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented e g the po plain the central to southern apennines and the adriatic sea the complete dataset including previously determined rcmts and cmts represents the seismic deformation in the italian area during the last 25 years

ground motion prediction equations for region specific probabilistic seismic hazard analysis abstract the goal of this article is to investigate the possibility of reducing the uncertainty of the ground motion predicted for a specific target area po plain and northeastern italy by calibrating a set of ad hoc ground motion prediction equations gmpes the derived gmpes account for peculiarities that are not generally considered by standard predictive models such as 1 an attenuation rate dependent on distance ranges and geological domains 2 enhancement of short period spectral ordinates due to the reflection of s waves at the moho discontinuity and 3 generation of surface waves inside an alluvial basin the analyzed strong motion dataset was compiled by selecting events in the 4 0 6 4 magnitude range records with distances shorter than 200 km and focal depths shallower than 30 km the major contribution comes from the recent 2012 emilia sequence first mainshock 20 may 2012 m w 6 1 second mainshock 29 may 2015 m w 6 0 the gmpes are derived for the geometrical mean of horizontal components of peak ground acceleration peak ground velocity and 5 damped spectral acceleration in the 0 04 4 s period range the derived region specific models led to a reduction of the hazard levels for several intensity measures with respect to the values obtained by considering the reference italian attenuation model bindi et al 2011 as exemplified by the comparison of the hazard curves computed for two specific sites online material database of northern italy dbni flat file and tables of northern italy ground motion prediction equations gmpes ni15 regression coefficients and variability components for use with joyner boore and hypocentral distances

stress and strain tensors based on focal mechanisms in the seismotectonic framework of the friuli venezia giulia region northeastern italy the principal axes of stress and strain are inferred for the seismotectonic zones of the friuli venezia giulia region which forms the eastern part of the european southern alps this region corresponds to a polyphase deformational belt formed during the meso and neoalpine compressions from the eocene to plio quaternary several distinct seismotectonic zones are recognized by comparing seismological and tectonic characteristics inference of the stress and strain tensors is based on 243 fault plane solutions corresponding to earthquakes occurring between 1984 and 2001 magnitude range 2 1 5 6 the analysis reveals two main regional stress patterns a strike slip regime active in the eastern and northwestern parts of the area under study and dominant thrusting processes in the central and western zones the orientation of the maximum principal stress varies from north northwest south southeast to north northeast south southwest the stress magnitude ratio of the calculated stress tensors varies from 0 4 to 0 7 the orientation of the maximum shortening axis is generally north northwest south southeast changing to north northeast south southwest in the southeastern part of the region for most seismotectonic domains the inferred strain pattern is quite concordant with the surface tectonics the orientations of the principal axes of stress and strain are in most cases similar the complex regional tectonic structure consisting of two indented tectonic wedges appears to control the patterns of horizontal stress and strain

quantification of the intrusive magma fluxes during magma chamber growth at soufriere hills volcano montserrat lesser antilles magma fluxes in the crust control the thermal viability and mechanical stability of magma chambers we estimated the magma fluxes required to generate the negative seismic velocity anomaly observed below soufriere hills volcano montserrat growth of a magma body by accretion of andesitic sills was simulated numerically and the resulting temperatures and melt fractions were used to calculate a synthetic anomaly of seismic wave velocity which was filtered to be comparable with the velocity anomaly obtained from a tomographic experiment petrology indicates that before it was reheated remobilized and erupted the temperature of the magma residing in the chamber was about 850 c we ran simulations where convection is assumed to be low and heat transfer is mostly by conduction and simulations where convection is assumed to be vigorous enough to rapidly cool the magma chamber to 850 c in both cases magma chamber growth over the last 350 years results in tomography anomalies that are too strong unless the magma was emplaced at an unlikely low melt fraction 0 5 good fits between the modelled and the observed velocity anomaly were obtained with sills 2 5 km in radius emplaced over 6000 150 000 years depending on the temperature and melt fraction of the emplaced magma because of a trade off between intrusion dimensions and emplacement durations the volumetric magma fluxes are restricted to 7 10 4 and 5 10 3 km3 a 1 the velocity anomaly can be reproduced with a chamber containing high melt fraction magma or with a mush of crystals and melt the range of magma ages in the modelled magma chamber is much wider than the crystal residence time of the erupted andesite this suggests that the eruption taps small pockets of recently assembled magma and that the velocity anomaly is mostly due to a non eruptible mush

reviewing pre transalp dss models abstract the interpretation of dss deep seismic soundings profiles in central and eastern alps is recalled in the paper and the models of the lower crust and moho proposed several years ago are compared to the results of the transalp seismic reflection profile this evaluation highlights a good agreement as far as the geometry of the deep crustal structure is concerned therefore the reliability of the interpretative models previously exclusively based on dss profiles becomes improved the deep structure beneath the whole alpine range is examined reconsidering the map of the moho boundary and the structural model already proposed for the central eastern sector five main interpretative transects are put side by side starting from the western alps and moving eastwards to the swiss lombardian central alps european geotraverse to the cross section from southern bavaria to the euganei hills to the transalp profile and finally to the easternmost profile available so far southern bavaria trieste the comparison outlines lateral variations of the deep crustal structure as well as a sharp contrast between the adria and the european lower crust and moho the transition from the adria plate to the dinaric domain remains up to now undefined

teleseisms as estimators of experimental long period site amplification application to the po plain italy for the 2011 mw 9 0 tohoku oki japan earthquake abstract this study focuses on the evaluation of teleseisms as estimators of long period seismic site amplification in correspondence to large alluvial basins using the recordings of the 11 march 2011 m w 9 0 tohoku oki japan earthquake the site response at low frequency of the po plain italy was investigated the interdistances among the analyzed sites compared to the travel paths of the tohoku oki waveforms with respect to the target area allowed us to investigate the reliability of the standard spectral ratio ssr technique applied to teleseismic recordings the results are presented as directional ssrs calculated considering 2 min of p s and rayleigh lr waves filtered from 0 025 to 1 0 hz considering the horizontal components at frequency from 0 04 to 0 3 hz the po plain stations show amplification factors up to 20 and 16 detected for the s and lr phases respectively in some cases the amplified ground motion appeared to be affected by polarization phenomena in particular in the north south direction moving from the center to the edge of the basin the lr wave amplification remarkably decreases in particular for frequencies between 0 1 and 0 3 hz this was not observed for the s wave amplification factors 10 were also detected for the vertical component with increasing resonance periods moving from p to lr waves comparing ssrs with the single station horizontal to vertical spectral ratios the latter case shows that the vertical amplifications lead to the partial masking of the actual response of a site in particular for frequencies 0 15 hz finally the relative p wave amplitudes were also investigated the results of the spectral analysis and the correlation between the relative p wave amplitudes and the geometry of the bedrock suggest that the proposed approach is appropriate for the investigation of long period seismic site response in similar settings

nonparametric description of peak acceleration as a function of magnitude distance and site in guerrero mexico this article describes the peak accelerations observed on a network of strong motion accelerographs above the subduction zone in guerrero mexico as a function of magnitude and hypocentral distance our empirical description differs from regression analysis however in that it produces a table of values of peak acceleration for selected values of m and r and an interpolation rule to obtain peak acceleration at intermediate values with this approach the existence and extent of saturation of peak acceleration as magnitude increases is dictated by the data and unlimited flexibility is allowed in the distance dependence of the peak acceleration this nonparametric approach does not allow extrapolation beyond the range of the data and is thus most useful when the data spans a large magnitude and distance range after 7 yr of recording the digital guerrero accelerograph network has obtained enough data to test the concept the records include events with magnitudes ranging from under 3 to 8 1 with all magnitudes recorded at distances ranging from nearly directly above the rupture to distances where acceleration has become too small to trigger the instruments the data used in this study consist of 528 recordings each three components from 146 earthquakes that occurred between 1985 and 1990 all but one station are on rock sites since all the accelerograms are recorded by one of 30 stations there is an average of about 18 records for each station the results suggest that at short distances about 14 to 25 km from the fault as magnitude increases the peak horizontal acceleration saturates at about 20 g however unlike small earthquakes peak accelerations decrease very slowly with increased distance from the rupture in a large magnitude station corrections for peak acceleration reduced the rms misfit by about 15 for the horizontal component by 12 for the vertical component and by 21 for the ratio for some stations horizontal corrections are close to vertical corrections but others show very different site effects on horizonal and vertical components the ratios of peak vertical acceleration to peak horizontal acceleration show a very weak tendency to decrease as magnitude increases and this tendency is further reduced at most distances after correction for average site effects the average value of this ratio is 0 70 before the station correction after these corrections for 55 events with known stress drop the residual between the predicted peak acceleration and the observed peak acceleration is correlated with stress drop although scattered the observations are consistent with a theoretical prediction that amax 0 80

earthquake sound perception 1 sound is an effect produced by almost all earthquakes using a web based questionnaire on earthquake effects that included questions relating to seismic sound we collected 77 000 responses for recent shallow italian earthquakes an analysis of audibility attenuation indicated that the decrease of the percentage of respondents hearing the sound was proportional to the logarithm of the epicentral distance and linearly dependent on earthquake magnitude in accordance with the behavior of ground displacement even if this result was based on italian data qualitative agreement with the results of theoretical displacement and of a similar study based on french seismicity suggests wider validity we also found that given earthquake magnitude audibility increased together with the observed macroseismic intensity leading to the possibility of accounting for sound audibility in intensity assessment magnitude influenced this behavior making small events easier to recognize as suggested by their frequency content

some remarks on the origin of foredeeps abstract geological observations show that there are two main types of foredeep basins on the base of their subsidence rate and their relationship with the associated orogen or accretionary wedge high rates of subsidence up to 1600 m myr and a ratio lower than 1 between the area of the elevated belt and the area of the basin characterize the foredeeps associated with w dipping subduction low rates of subsidence up to 300 m myr and a ratio higher than 1 between the area of the orogen and the area of the basin characterize the foredeeps associated with e or ne dipping subductions this observation enables us to interpret the slow filling of foredeeps of the first type and the much faster filling of foredeeps of the second type moreover w dipping subductions have a steeper and faster monocline bounding the base of the deep foredeep in contrast to e or ne dipping subductions which have a shallower monocline this differentiation supports the notion of the eastward mantle flow with respect to the lithosphere detected in the hot spot reference frame in this view the foredeep depth in w dipping subductions is mainly controlled by the roll back of the subduction hinge pushed by the relative eastward mantle flow while foredeep depth in e or ne dipping subductions is instead mainly generated by the load of the thrust sheets and by the roll back of the subduction hinge due to the advancing upper plate contrasting the upward push of the mantle the shape of the foredeeps is regularly arcuate in case of w dipping subduction while is linear or following the shape of the inherited continental margin in case of e or ne dipping subduction fold development in the two opposite foredeeps is significantly different in w dipping subduction the folds are transported down in subduction while they are forming and consequently they are poorly eroded syntectonic sediments drape a preserved fold in the e ne dipping subduction folds and thrust sheets are instead uplifted and deeply eroded this is also predicted by the envelope of the crests in the two distinct accretionary wedges in the w dipping case the envelope may dip toward the subduction while it is rising toward the hinterland in the other cases this approach may explain the differences in terms of geometries amount and rates of subsidence between the foredeeps around the adriatic plate for instance the foredeep of the southern alps back thrust belt foredeep is deformed in the western part by the later apenninic foredeep development associated with the sinistral oblique ramp of the w dipping adriatic plate subduction the relationship in the frontal parts of a thrust belt between accretion and eustacy has to be analyzed in terms of when where and how fast thrusts propagation took place with respect to the randomly distributed sea level third order fluctuations and by the type of subduction which is connected to the foredeep and thrust belt or accretionary wedge therefore the stratigraphic patterns in foredeep basins are peculiar and casual successions that record the combination of regional tectonic evolution with independent wider scale sea level changes

the attenuation of seismic intensity in italy a bilinear shape indicates the dominance of deep phases at epicentral distances longer than 45 km the attenuation of seismic intensity with distance in italy is analyzed by using felt intensity report data obtained from two comprehensive historical databases recently made available the observed attenuation pattern that in the past was interpreted as a logarithmic or root square or cubic attenuation law shows quite clearly two different linear trends in the near and in the far field at distances shorter than 45 km the decrease of the intensity with distance is about one degree per 20 km while at longer distances the slope is about one degree per 50 km this is in agreement with some recent findings of realistic modeling of seismic ground motion that has been explained as the transition from upper crust direct sg phases to waves reflected at the moho controlling the energy main release the slope of the curve in the far field shows a regional dependence in agreement with recent works on the attenuation of pn and sn phases in italy if effective this correlation might allow us to discriminate the contribution of crustal and subcrustal paths in seismic intensity attenuation studies manuscript received 31 may 2000

development and testing of a 3d seismic velocity model of the po plain sedimentary basin italy abstract we built a 3d seismic model of the po plain and neighboring regions of northern italy covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid we started by collecting an extensive and diverse set of geological and geophysical data including seismic reflection and refraction profiles borehole logs and available geological information major geological boundaries and discontinuities have thus been identified and mapped into the model we used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness seismic wave properties have been assigned to each unit using a rule based system and v p v s and derived from other studies sedimentary strata although with varying levels of compaction and hence material properties may locally reach a thickness of 15 km and give rise to significant effects in seismic wave propagation we have used our new model to compute the seismic response for two recent earthquakes to test its performance results show that the 3d model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments whereas paths outside the basin may be well fit by more homogeneous 1d hard rock structure we conclude that the new model is suited for simulation of wave propagation mostly for t 3 s and may serve well as a constraint for earthquake location and further improvements via body or surface wave inversion