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

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

coulomb stress changes caused by repeated normal faulting earthquakes during the 1997 umbria marche central italy seismic sequence 1 we investigate fault interaction through elastic stress transfer among a sequence of moderate magnitude main shocks 5 mw 6 which ruptured distinct normal fault segments during a seismic sequence in the umbria marche region central apennines we also model the spatial pattern of aftershocks and their faulting mechanisms through coulomb stress changes we compute stress perturbations caused by earthquake dislocations in a homogeneous half space our modeling results show that seven out of eight main shocks of the sequence occur in areas of enhanced coulomb stress implying that elastic stress transfer may have promoted the occurrence of these moderate magnitude events our modeling results show that stress changes caused by normal faulting events reactivated and inverted the slip of a secondary n s trending strike slip fault inherited from compressional tectonics in its shallowest part 1 3 km of the 1517 available aftershocks 82 are located in areas of positive stress changes for optimally oriented planes oops for coulomb failure however only 45 of the 322 available fault plane solutions computed from polarity data is consistent with corresponding focal mechanisms associated with the oops the comparison does not improve if we compute the optimally oriented planes for coulomb failure by fixing the strike orientation of oops using information derived from structural geology our interpretation of these modeling results is that elastic stress transfer alone cannot jointly explain the aftershock spatial distribution and their focal mechanisms

on the geometry of an earthquake fault system abstract invariants of a two point correlation function of the seismic moment tensor were used to investigate an earthquake fault system the geometry of the fault system is significantly different from the standard model of an earthquake fault i e coherent rupture on a planar surface contrary to the flat fault model we see clear evidence for non planarity of the fault system geometry and observe that the focal mechanisms of neighboring events may have very different orientation i e they undergo large three dimensional rotations therefore earthquake deformation models need to be fully three dimensional and should include large rotations the spatial behavior of the invariants is approximately the same for earthquakes in different depth intervals shallow intermediate and deep the temporal behavior of the invariants differs only in that shallow earthquakes are clustered in time whereas for deeper events the clustering is much less pronounced as soon as we decluster shallow seismicity the invariants temporal properties become similar for earthquakes of all depths this demonstrates that the basic geometrical properties of earthquake rupture do not depend on depth and therefore they are generally independent of rheological properties of rocks lithostatic pressure or the presence of a free boundary for strong shallow earthquakes

a stress inversion procedure for polyphase calcite twin and fault slip data sets in rocks that are polydeformed an approach which separates faults prior to stress inversion is more appropriate the traditional stress inversion approach involving the concept of the best fit stress tensor e g a tensor which minimises the misfit between calculated and measured fault striae data often risks computing artificial stress tensors that are some form of average of mixed sets of real stress tensors a new approach is proposed in which fault data are pre processed to group the faults on the basis of their response to all possible orientations and magnitudes of applied stress a computer method is described which utilises cluster analysis based on the right dihedra method to divide dynamically mixed fault populations to monophase subsets this division is based on the ranked similarity coefficients of each fault pair from the raw data set the data clusters form dynamically homogeneous subsets which are used for the composite right dihedra solution this solution is re computed for the reduced stress tensor defined by the orientation of principal stress axes and the ratio of their magnitudes

palaeomagnetic and structural evidence of neogene tectonic rotation of the gran sasso range central apennines italy abstract interference between discordant tectonic trends in the central apennines italy was investigated in a palaeomagnetic study of the arc shaped e w to n s oriented overthrust units of the lazio abruzzi carbonate platform gran sasso and the underlying n s oriented imbricates of the marche pelagic domain mt dei fiori samples were taken from 26 sites in the cretaceous palaeogene scaglia formation and in the messinian lower pliocene laga flysch stepwise thermal demagnetization was used to remove secondary components and a stable direction of the characteristic remanent magnetization chrm was determined for 24 sites the palaeomagnetic results point to counter clockwise rotation of the marche domain similar to that of the southern umbria directions in both the scaglia and laga formations of the lazio abruzzi units show counter clockwise rotations up to 90 in the easternmost segment of the gran sasso belt this setting may be framed in a structural context wherein superposition of the e w oriented gran sasso belt onto the n s oriented marche imbricates derives from progressive rotation of the lazio abruzzi platform decoupled by right lateral shearing along the n s oriented rigopiano bussi rivisondoli shear zone

imaging the complexity of an active normal fault system the 1997 colfiorito central italy case study 1 six moderate magnitude earthquakes 5 mw 6 ruptured normal fault segments of the southern sector of the north apennine belt central italy in the 1997 colfiorito earthquake sequence we study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using 1650 earthquake locations obtained by applying a double difference location method using travel time picks and waveform cross correlation measurements the lateral extent of the fault segments range from 5 to 10 km and make up a broad 45 km long nw trending fault system the geometry of each segment is quite simple and consists of planar faults gently dipping toward sw with an average dip of 40 45 the fault planes are not listric but maintain a constant dip through the entire seismogenic volume down to 8 km depth we observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure the observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust preexisting thrusts inherited from neogene s compressional tectonic intersect the active normal faults and control their maximum length the stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the apennine revealing a clear ne trending extension direction aftershock focal mechanisms show a consistent extensional kinematics 70 of which are mechanically consistent with the main shock stress field

anomalous stress diffusion in earthquake triggering correlation length time dependence and directionality 1 it has been recently suggested that moderate and large earthquakes can be triggered by similarly sized events at very long range here we study the main characteristics of earthquake triggering by determining its correlation length time dependence and directionality the problem is examined at a global level by using the harvard centroid moment tensor catalogue our results show that the correlation lengths depend only weakly on the magnitude thresholds involved no significant systematic triggering is observed for distances greater than the lithospheric thickness 100 150 km and the correlation length magnitude is similar to the seismogenic thickness 10 20 km the mean triggering distance and correlation length both increase with time very slowly compared with what would be expected from a normal diffusion process this is consistent with a clock advance on the failure time based on the constitutive rules for subcritical crack growth following a transient change in the loading stress the power law scaling disappears after a few months a functional form for the probability of triggering as a function of time and distance is proposed on the basis of the properties of near critical point systems the model fits the data well and could be used to calculate conditional probabilities for time dependent seismic hazard due to earthquake triggering an apparent directionality effect that was observed in the data set can be attributed to an artefact of poor depth determination these results do not preclude individual long range triggering with a potential directionality effect but they do rule out a statistical correlation at distances much greater than the thickness of the lithosphere

a stress inversion procedure for polyphase fault slip data sets palaeostress estimation from striated fault data is frequently frustrated by the fact that natural fault data are heterogeneous in the sense that they cannot satisfactorily be explained by reactivation brought about by a single stress tensor in many instances there is clear evidence to show that striation data can record the effects of multiple stress events any attempt to find the tensor which best fits or explains such dynamically mixed data sets risks determining a spurious stress state which is some form of compromise between the real stress states corresponding to different tectonic phases to avoid this problem a strategy is proposed here which involves an initial separation of the raw data into coherent sub sets prior to formal stress inversion this separation is performed by assigning attributes to each fault which describe the fault s compatibility with trial stress tensors using these attributes faults can be grouped into dynamically homogeneous families using the statistical techniques of cluster analysis

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

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

looking at fault reactivation matching structural geology and seismological data abstract we investigate fault reactivation that occurred during the 1997 colfiorito seismic sequence central italy matching detailed structural geology precise earthquake locations and mechanical models of fault interaction the colfiorito area within the northern apennines is characterised by a relatively recent inversion of the tectonic stress field from compression late miocene to extension late pliocene quaternary in september october 1997 the area experienced a protracted seismic sequence consisting of six moderate magnitude earthquakes 5 we analyse the coseismic elastic static stress changes due to the occurrence of the normal fault events in order to investigate the mechanical coupling and interaction between the nw se oriented normal fault system and the intervening n10 inherited fault we show that the elastic stress perturbation increased on the shallow portion of the activated volume where the n10 structure is located and promoted its reactivation with a strike slip motion the different amount of slip experienced along the two normal faults responsible for the greater mainshocks favoured the left lateral strike slip kinematics

origin and tectonic interpretation of multiple fault patterns abstract it is shown that in two dimensional and three dimensional deformation accommodated by fracture the symmetry of the fault patterns is an intrinsic attribute because it reflects the symmetry of either stress or strain tensors the deformation accommodated by sliding along pre existing planes when there is kinematic interaction between that planes forms multiple fault pattern and multiple slickenline sets during a single deformation event these fault patterns have no restrictions with respect to symmetry number of fault sets or fault orientation the kinematic analysis developed here shows that an interacting system is formed by two cross cutting faults and three slickenlines one slickenline must be parallel to the intersection line between the planes also it is demonstrated that the slickenlines generally do not correspond to the shear stress solution on the planes thus the interaction between planes does not satisfy the assumption of parallelism between shear stress and slip vector we conclude that the inversion methods to calculate paleostress tensors can lead to erroneous interpretations in structurally complex zones with many pre existing planes of weakness we propose four possibilities to form multiple fault patterns 1 two or more events of faulting obeying coulomb s law with a change of orientation of the principal stresses in each event 2 reactivation of non interacting planes according to the bott 1959 model 3 one three dimensional strain event that obeys the slip model this mechanism will form an orthorhombic four fault pattern and two slickenline sets in a single strain event and 4 one or more events obeying the interacting block model proposed here with or without rotation of the principal stresses we propose the last origin as the most common in continental regions

random stress and earthquake statistics spatial dependence summary we calculate the 3 d stochastic rotations of focal mechanisms disorientations caused by stresses arising from the presence of many small random point defects that may surround the tip of an earthquake fault these random stresses can be shown to be distributed according to a cauchy distribution as a consequence the next episode of fracture of a fault cannot be planar the disorientation of focal mechanisms of these new rupture episodes is closely approximated by a rotational cauchy distribution as observed previously the geometry of fault systems for natural earthquakes is consistent with these observations since it too can be modelled by the cauchy distribution these observations indicate how the 3 d rupture process in rocks and other materials can be modelled we also calculate distributions of disorientations caused by a uniformly random 3 d rotation of sources these distributions are governed by symmetry properties of earthquake focal mechanisms to take into account the source symmetry we compare the cauchy distribution which is due to influence of random stresses to the distributions caused by random rotations

spatial variations in the similarity of earthquake populations the case of the 1997 colfiorito sellano northern apennines italy seismic sequence abstract the spatial properties of events in the 1997 colfiorito sellano seismic sequence northern apennines italy were investigated using coherence a parameter derived from seismic moment tensors that quantifies the kinematic similarity between focal mechanisms the 1997 colfiorito sellano seismic sequence predominantly consists of normal faulting earthquakes with a few strike slip and reverse faulting episodes this kinematic heterogeneity is possibly related to the contemporaneous activity of two different sets of faults nw se normal faults and nne ssw sub vertical faults the latter inherited from the previous miocene compressional phase the study used two independently derived data sets of the same seismic sequence characterized by a different number of events and by different precision of spatial localisation their statistical significances assessed through a reshuffling procedure reveal that data sets with at least some hundreds of events and good positional precision are required to obtain significant results through coherence analysis results from the better quality data set indicate that this seismic sequence is characterized by a rapid decrease in the kinematic similarity between earthquake pairs within 2 km of separation particularly along directions sub perpendicular to the normal fault strike the decrease rate seems to be controlled by the geometric characteristics of the normal faults given that the mean along dip distance between fault segments is 2 km in proximity to pre existing tectonic lineaments the relative abundance of strike slip and reverse faults tends to decrease the kinematic similarity between events but does not influence the coherence decrease rate the presence of mixed focal mechanisms normal reverse and strike slip in a single seismic phase implies that mixed fault types are not restricted to polyphase tectonic histories such heterogeneous kinematics during a single phase may be induced by the presence of inherited discontinuities

spatial structures in earthquakes and faults quantifying similarity in simulated stress fields and natural data sets abstract this paper presents an adaptation for fault analysis of the coherence method of kagan and knopoff kagan y y knopoff l 1985b the two point correlation function of the seismic moment tensor geophysical journal of the royal astronomical society 83 637 656 understanding coherence as a measure of the similarity between fault slip data for two faults which can be analytically computed from earthquake or fault moment tensors through the use of a customized gis routine the degree and distribution of similarity in synthetic and natural fault populations can be calculated as a function of distance between fault earthquake pairs and their relative orientation stress simulations using synthetic data sets reveal that fault populations which developed under homogeneous stress fields have a high degree of similarity that increases with the slip tendency of faults stress ratio variations and especially stress axis rotations lower the coherence values spatial analysis of natural earthquake and fault data sets from the umbria marche region northern apennines italy reveals a common pattern of coherence spatial cyclicities in faults earthquakes controlled by two consecutive tectonic phases miocene compression and plio pleistocene extension the proposed interpretation attributes the spatial cyclicities of miocene data to syn to post faulting folding in agreement with wavelengths derived from field data the observed periodicities in earthquakes 1997 colfiorito sellano umbria marche seismic sequence could in turn have been controlled by the miocene thrust structures with possible spatial stress field axis rotations and or stress ratio variations the spatial characteristics of younger fault earthquake populations are thus possibly controlled by the characteristics of older tectonic structures such as fold wavelength or fault spacing

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

the densest meteorite collection area in hot deserts the san juan meteorite field atacama desert chile we describe the geological morphological and climatic setting of the san juan meteorite collection area in the central depression of the atacama desert chile our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3 88 km 2 area the recovery density is in the range 9 12 falls km 2 depending on pairing making it the densest among meteorite collection areas in hot deserts this high meteorite concentration is linked to the long standing hyperaridity of the area the stability of the surface pebbles ma and very low erosion rates of surface pebbles approximately 30 cm ma 1 maximum the san juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka and limited weathering compared with other dense collection areas in hot desert chemical weathering in san juan is slow and mainly controlled by the initial porosity of meteorites as in the antarctic and other hot deserts there is an overabundance of h chondrites and a shortage of ll chondrites compared with the modern falls population suggesting a recent few ka change in the composition of the meteorite flux to earth

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

connecting seismically active normal faults with quaternary geological structures in a complex extensional environment the colfiorito 1997 case history northern apennines italy 1 the northern apennines of italy are characterized by a complex tertiary tectonic history where superposed compressional and extensional deformation occurred in such regions characterized by low active extensional strain rate the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between geological faults i e faults which can be mapped at the surface and seismological faults i e faults which actually generate earthquakes the availability of detailed geological mapping and high resolution seismological data for the colfiorito area struck in 1997 by a sequence of six 5 mw 6 normal faulting earthquakes allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological quaternary faults and the activated structures in map view the earthquakes distribution reflects the fault pattern mapped at the surface the length of activated and mapped faults is quite similar 7 10 km the coseismic subsided region imaged by interferometric synthetic aperture radar data is located in the hanging wall of the mapped normal faults that bound the quaternary basins in section view there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency this study points out that the quaternary tectonosedimentary evolution and the present day geological and geomorphologic setting of the colfiorito area can be interpreted as the result of repeated extensional earthquakes similar to the 1997 events occurring on nw se trending normal faults our data also show that the main shocks of the colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional transpressional structures which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size

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

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

vp and vp vs images in the mw 6 0 colfiorito fault region central italy a contribution to the understanding of seismotectonic and seismogenic processes 1 in 1997 the umbria marche apennines central italy was struck by a series of moderate magnitude normal faulting earthquakes accompanied by a prolonged sequence of aftershocks seismological analysis revealed a 40 km long nw trending structure composed by several low angle normal fault segments in this paper we present the three dimensional 3 d vp and vp vs structure of the fault zone determined by the inversion of p and s wave arrival times from 1982 aftershocks the high resolution tomographic images reveal strong heterogeneity along and across the fault zone and allow us along with the 3 d location of earthquakes to define the fault geometry at depth and to improve our understanding on the seismotectonics of this part of the northern apennines thrust and fold belt the relocated aftershocks suggest that the main ruptures occurred on planes slightly steeper than previously hypothesized and at depths shallower than those evidenced by 1 d locations we find that the preexisting structure which developed during the neogene compressional tectonics plays an important role in the earthquake generation and rupture evolution of the normal faulting events we propose that the main shocks whose hypocenters are all located at 6 km depth originated along a shallow decollement of the meso cenozoic cover thrust over the metamorphic basement geometrical discontinuities and lateral steps along the inherited structures control the lateral fault extent and determine fault segmentation this study offers a good example of how lithological heterogeneities and the complexity of the upper crust structure strongly affect the faulting process

paleosols as an indicator of climatic change at the early late cretaceous boundary southwestern new mexico abstract cretaceous aptian to lower campanian alluvial paleosols in southwestern new mexico suggest that a paleoclimatic change from arid or semi arid to humid or subhumid occurred near the boundary between early and late cretaceous lower cretaceous paleosols of the hell to finish lower aptian and mojado upper albian formations are primarily aridisols characterized by a dark reddish brown pedoturbated bw horizon underlain by a bk horizon composed of calcareous nodules and tubules or a massive calcareous bkm horizon retention of carbonate in the paleosol profiles suggests that annual precipitation was less than 60 cm in contrast upper cretaceous paleosols consist of non calcic alfisols and inceptisols inceptisols consist of two types 1 a gleyed variety displaying a bg and bc or cg horizons in the satten formation uppermost albian to lowermost cenomanian and in the crevasse canyon formation upper coniacian to lower campanian and 2 a non gleyed variety consisting of a bw and c horizons in the moreno hill and tres hermanos formations middle turonian and in the crevasse canyon formation in addition alfisols in the tres hermanos and crevasse canyon formations are composed of a e bt bc and c horizons the argillic b horizons bt contain kaolinite and mixed layer clay and display blocky peds vertical clay filled root traces and argillans indicative of relatively well drained woodland soils modern counterparts of the upper cretaceous alfisols exist in humid and subhumid regions receiving greater than 75 cm yr precipitation comparison of the data resented in this study with paleosol and paleobotanical data from other locations in the western interior of the u s suggests that the paleoclimatic change proposed for southwestern new mexico may have been of regional extent

global creepex distribution and its relation to earthquake source geometry and tectonic origin summary the ms mb ratio conventionally used for the discrimination of earthquakes and underground nuclear explosions has been studied for a pure earthquake catalogue in an attempt to classify earthquakes into two categories one related to extremely lowfrequency events of creep and the other to relatively high frequency explosions ms and mb measured at 20 s and 1 s respectively are considered as estimates of source spectra at two separate points thus allowing one to compare large samples of earthquakes from the spectral point of view creepex or the deviation of ms mfc points from the orthogonal regression of ms on mb is by definition a parameter independent of the size of seismic events it has been estimated from neic magnitudes and is studied in relation to parameters of central moment tensor solutions of the harvard group for this purpose the parameters of central moment tensors have been factorized to make classes of equivalence of events with the same dip and rake and arbitrary strike and size the resulting triangle representation of source mechanisms has been used to correct the global distribution of creepex for the type of source mechanism dip slip events have consistently lower creepex than strike slip ones however the global distribution of creepex either corrected or uncorrected for source mechanism has a clear tectonic pattern negative values in most of the subduction zones and positive ones in mid ocean ridges the dependence of creepex on focal depth is negligible according to empirical data for events shallower than 40 km limitation of the sample by considering only events in this depth range does not diminish considerably the amount of data and does not change the tectonic pattern of the creepex