contemporaneous extension and compression in the northern apennines from earthquake fault plane solutions summary the northern apenninic arc belongs to the deformation zones surrounding the adriatic plate which behaves as a rigid block it is a ne verging fold and thrust belt which developed since the miocene with the migration of an extensional compressional pair previous seismological data are roughly in agreement with this deformation picture although the outer compressional front was not clearly defined by the few available solutions in this work we confirm the existence of two adjacent zones of contemporaneous extension and compression in the northern apennines defining the extent of these two zones and their interim1 deformation better than was previously done this is accomplished through the analysis of 125 new focal mechanisms of earthquakes 2 6 md 4 8 recorded by the national network of the lstituto nazionale di geofisica in the period 1988 1995 the two deformation zones are clearly separated and lie very close to each other with a partial overlapping in the emilian tuscan apennines strikeslip events are scattered in most of the study area thrust faulting earthquakes are located in the internal part of the most recently active thrust front middle upper pleistocene there is a general trend of the compressional p axes of thrust fault and strike slip solutions to be perpendicular to the apenninic direction in the external zone while the tensional axes of the normal fault and strike slip solutions in the belt do not show a uniform orientation however clearly evident is the ene direction of extension in the peri tyrrhenian region consistent with the direction of shmln in the quaternary volcanoes of this region inferred from borehole breakouts and microearthquake fault plane solutions we determined the orientation of the stress tensor in the two main deformation zones by inversion of the 125 fault plane solutions determined in this study we found that the external belt is characterized by ne sw compression ol horizontal oriented n45 e while a normal faulting regime with o3 e w oriented is characteristic of the umbria tuscany back arc region

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

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

models of the complex source of the el asnam earthquake abstract the el asnam earthquake of 10 october 1980 was originated by a thrust across a sw ne oriented fault 36 km long and 15 km wide it is a complex event with a rupture propagating from the sw to the ne fault mapping hypocenter distribution and b factor studies indicate fault branching to the ne a dislocation model is used to explain the branch with normal faulting at beni rached as a consequence of the thrust across a main fault that changes orientation the mechanism of the 1954 earthquake must be similar even though only normal faulting was observed at the surface

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

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

the perugia italy earthquake of 29 april 1984 a microearthquake survey a field study after the perugia earthquake of 29 april 1984 provided more than 300 well recorded events concentrated within two parallel clusters separated by 2 km and trending along the apenninic direction the length of the aftershock area is 14 km focal depths being shallower than 8 km relocation of the main event places the epicenter at the southern end of the aftershock zone suggesting a rupture propagation from se to nw most focal mechanisms are consistent with normal faulting the spatial distribution of seismicity suggests that the gubbio normal fault was activated during the main shock this earthquake together with the norcia 1979 and the abruzzi 1984 shocks is typical of the extension in the high apennines generated by the flexure of the mountain chain in response to regional compression the parma 1983 event a thrust belongs to the compres sion zone at the eastern flank of the chain these results are consistent with the ew continental collision along the apennines

viscoelastic relaxation and long lasting after slip following the 1997 umbria marche central italy earthquakes summary we combine global positioning system gps measurements with forward modelling of vis coelastic relaxation and after slip to study the post seismic deformation of the 1997 umbria marche central apennines moderate shallow earthquake sequence campaign gps mea surements spanning the time period 1999 2003 are depicting a clear post seismic deformation signal our results favour a normal faulting rupture model where most of the slip is located in the lower part of the seismogenic upper crust consistent with the rupture models obtained from the inversion of strong motion data the preferred rheological model obtained from viscoelastic relaxation modelling consists of an elastic upper crust underlain by a transition zone with a viscosity of 10 18 pa s while the rheology of deeper layers is not relevant for the observed time span shallow fault creep and after slip at the base of the seismogenic upper crust are the first order processes behind the observed post seismic deformation the deep after slip below the fault zone at about 8 km depth acting as a basal shear through localized time dependent deformation identifies a rheological discontinuity decoupling the seismogenic upper crust from the low viscosity transition zone

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

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

anatomy of late orogenic extension the northern apennines case abstract late orogenic extensional structures overprint the compressional structures of the northern apennines fold and thrust belt the tyrrhenian sea is the result of major continental extension and rifting which started in the thickened zone of the apulian corso sardinian collision it is believed to have commenced as early as in the late oligocene or early miocene in the corsica basin extension post dates the collision by approximately 20 ma the extensional stress field observed in the internal part of the northern apennines co exists with compression in the foreland part of the belt field borehole and refraction and reflection data were used to investigate the geometry of extension and how it affected the compressional abric in the northern apennines analysis of the collected data has revealed a complex geometry for the extension across the belt a geological cross section from the island of elba to the west of the italian peninsula to ancona in the east as well as a geodynamic model for the evolution of the northern apennines is presented and discussed from the early miocene stretching of the collision thickened crust created a n s rift which evolved into the present northern tyrrhenian sea typically two sets of extensional faults a low angle e dipping and a w dipping one are observed across the chain usually the w dipping faults have similar attitudes to those of the older reverse faults reactivating some of the thrusts as normal faults the e dipping normal faults however cut down section through the pre existing thrusts and in the internal part of the belt accommodate most of the displacement associated with extension a change in fault polarity occurs in the tuscan region and major faults dip towards the west a type subduction of the apulian crust under the corso sardinian block occurred after collision leading to the delamination of the apulian lithospheric mantle away from the crust collision induced delamination of the mantle lithosphere away from the zone of collision resulted in mechanical thinning of the lithosphere beneath the orogenic belt this process induced late orogenic crustal stretching in the internal zone of the northern apennines as the convergence between the apulian and corso sardinian blocks continued the extensional and compressional fronts accompanied by the delamination migrated from the hinterland towards the foreland of the orogen

the sequence of moderate size earthquakes at the junction of the ligurian basin and the corsica margin western mediterranean the initiation of an active deformation zone revealed a new seismically active zone is found in the southern part of the ligurian basin 80 km west of corsica western mediterranean the activity began in february 2011 with a foreshock ml 4 and a mainshock ml 5 3 5 days later followed by numerous aftershocks we first analyze the fore and mainshock in detail we compare the results obtained using classical methods linear location in a 1d medium and focal mechanisms from p and s polarities and new approaches non linear location in a 3d medium and waveform modeling for determining the seismic moment and the focal mechanism both methods provided similar results for location depth in the range of 6 13 km and focal mechanisms which reveal reverse faulting with nodal planes oriented n s and ne sw we then locate 27 of the aftershocks in the 3d model and find a 10 km long ne sw alignment with a depth between 7 and 16 km in 2012 and 2013 three other moderate size events ml 3 8 4 and 4 5 occurred and confirm that this zone is still active the epicentral area is located in the oceanic domain of the ligurian basin from analysis of the bathymetry and high resolution multi channel seismic profiles no morphologic anomaly at surface and no inherited fault in the shallow 4 km depth were imaged which suggest that no significant deformation occurred in the area since 5 ma thus the structure s activated during the 2011 2013 sequence remain unknown in light of these results we point out a notable difference on both sides of the ligurian basin the northern margin close to the alpine chain suffered strong earthquakes and large cumulated deformation since 5 ma while the southern margin close to the corsica sardinia continental block is poorly deformed since 5 ma

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

architecture and seismotectonics of a regional low angle normal fault zone in central italy information from surface geology subsurface geology boreholes seismic reflection and refraction profiles and seismicity are used to depict the geometry and the possible seismogenic role of the altotiberina fault af a low angle normal fault in central italy the af extends along the inner umbria region for a length of 70 km with an average dip of 30 and an horizontal displacement up to 5 km it emerges west of the inner border of the tiber basin and deepens beneath the umbria marche carbonate fold and thrust belt to a depth of 12 14 km close to the af surface trace low angle synthetic east dipping normal faults extensively outcrop whereas high angle antithetic west dipping normal faults prevail farther east integrating geological and seismologic information it can be stated that the af behaves as an active extensional fault zone and represents the basal detachment of the west dipping seismogenic normal faults of the umbria marche region the af belongs to a regional ne dipping low angle normal fault system etrurian fault system efs which extends for 350 km from northwestern tuscany to southern umbria early preliminary considerations suggest that the efs may play an important role in controlling active extension and related seismicity in northern central italy

assessment of hydrogeochemistry and contamination of varamin deep aquifer tehran province iran the present study investigates the hydrogeochemistry and contamination of varamin deep aquifer located in the southeast of tehran province iran the study also evaluates groundwater suitability for irrigation uses the hydrogeochemical study was conducted by collecting and analyzing 154 groundwater samples seasonally during 2014 based on evolutionary sequence of chebotarev the aquifer is in the stage of so4 hco3 in the north half of the plain and it has evolved into so4 cl in the south half the unusual increase in tds and cl toward the western boundaries of the aquifer indicates some anomalies these anomalies have originated from discharge of untreated wastewater of tehran city in these areas the studied aquifer contains four dominant groundwater types including na ca so4 55 na ca hco3 22 na cl 13 and ca cl 10 the spatial distributions of na cl and ca cl water types coincide with observed anomalies ionic relationships of so4 2 versus cl and na versus cl confirm that water rock interaction and anthropogenic contribution are main sources of these ions in the groundwater the main processes governing the chemistry of the groundwater are the dissolution of calcite dolomite and gypsum along the flow path and direct ion exchange reverse ion exchange controls the groundwater chemistry in the areas contaminated with untreated wastewater based on na and sar 10 3 and 27 of water samples are unsuitable for irrigation purposes respectively regarding residual sodium carbonate there is no treat for crop yields only 6 of water samples represent magnesium adsorption ratios more than 50 which are harmful and unsuitable for irrigation

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

sedimentary iron cycling in the benguela upwelling system off namibia abstract iron fe is an essential micronutrient and its availability controls primary production in large parts of the ocean further the variability of oxygen minimum zones omz exerts a major control on the availability of fe concentrations of which are elevated off namibia therefore to understand the sources and processes involved in the cycling of fe off namibia we determined major and trace element contents fe al si k p organic carbon mn co zr and the isotopic composition of fe 56 fe in seven sediment cores along a transect from the shelf to the abyssal plain at 5 km water depth meteor cruise m76 1 as well as in the local lithogenic background namibian river bed sediments and dust the depletion of mn vs the local lithogenic background llb reflects the reducing character of sediments from the shelf to the lower slope while depletion of mn and enrichment of co indicates the anoxic sulfidic environment on the shelf the enrichment of both elements in abyssal sediments documents highly oxidizing conditions there iron al ratios are elevated 0 6 to 1 6 and therefore equal to or higher than the llb the highest fe enrichment is seen on the shelf core 1 and the shelf break core 2 with a clear decrease towards the abyss the bulk 56 fe values range from 0 30 to 0 05 in the marine sediments with an average of 0 08 which is slightly lighter than the 56 fe of the llb 0 16 to 0 21 further combined enrichments of k and fe suggest the presence of detrital biotite core 1 and authigenic glauconite core 2 both of which are perfectly correlated with zr al ratios reflecting the highly dynamic conditions of the shelf environment 0 300 m water depth the absent large sedimentary fe isotope fractionation in the sediments of this study compared to peru sediments is likely due to a combination of the following i a highly variable omz leading to random re oxidation of any sediment sourced fe which prevents the export of larger amounts of dissolved fe to the interior of the ocean and which also prevents focused enrichments of fe and ii an enhanced dust flux which frequently resupplies terrestrial fe dampening any fe isotope fractionation this study is a snapshot on sedimentary fe cycling in one area from the vast namibian margin compared to the peruvian margin the data suggest little sedimentary fe release transport and redeposition however previous water column data suggest substantial fe release hence for a more subtle investigation of the fe loss and re supply a higher sampling resolution of multiple cores across the shelf and slope will be required

seismological geological and geophysical constraints for the gualdo tadino fault umbria marche apennines central italy abstract the april 3 1998 mw 5 1 gualdo tadino earthquake central italy was the last significant event in the 6 month long umbria marche seismic crisis this event and its aftershocks occurred in an area where active faulting produces no striking geological and geomorphological effects in this study we investigated the ruptured fault using detailed seismological data and a re processed and re interpreted seismic reflection profile aftershock location and focal mechanisms were used to constrain the geometry and kinematics of the ruptured fault and a comparison was made with the subsurface image provided by the seismic profile we found that the 1998 gualdo tadino earthquake occurred on a wsw dipping normal fault with a length of about 8 km and a relatively gentle dip 30 40 confined between 3 5 and 7 km in depth kinematics of the mainshock and aftershocks revealed a ne trending extension in agreement with the regional stress field active in the northern apennines belt the mw 5 1 earthquake originated above the top of the basement and ruptured within the sedimentary cover which consists of an evaporites carbonates multilayer we hypothesised that the active fault does not reach the surface blind normal fault

very detailed seismic pattern and migration inferred from the april 2010 pietralunga northern italian apennines micro earthquake sequence abstract we propose a very detailed picture of seismicity that occurred in the proximity of the alto tiberina fault atf northern italian apennines a low angle normal fault by presenting the pattern and evolution of a seismic sequence on the hanging wall of the atf in the first months of 2010 that was characterized by about 1000 events with m l ranging from 0 7 to 3 8 to capture the rupture kinematics of the investigated area a cross correlation technique was initially applied to calculate very accurate time shifts among the events of the sequence and then to relocate them the whole sequence was relocated with the double difference method which includes both absolute travel time measurements and cross correlation differential travel times the new locations confirm that the seismic activity was mainly arranged along a nw se oriented structure that ranged in depth from 4 km to 6 km with dipping towards ne at an angle of ca 65 in comparison with geological data the position of the seismic sequence is compatible with the evaporite triassic layer the main nodal planes are consistent with the spatial evolution of the aftershocks and with the tensional state of stress in the area an analysis of waveform similarity was performed at a reference station by merging the capability of the cross correlation technique and the bridging algorithm the detected mutiplets allow us to emphasize the anisotropic spatial and temporal migrations of the seismicity that occurred along a 307 n strike direction with an averaged propagation velocity of ca 0 4 km day we explain the highlighted anisotropic behavior of the migration with the hypothesized presence of overpressured fluids and with physical properties of triassic evaporites this suggests the importance of such very detailed relocation of weak and micro seismicity for improvement of our knowledge of fault system geometry and its evolution

detailed study of the potentino seismic zone in the southern apennines italy abstract most relevant macroseismic and instrumental data concerning past and current seismic activity of the potentino southern italy have been collected in order to study the seismic behaviour of this area ten among the most important recent and historical earthquakes occurred in the area from 1826 to 1990 have been studied by means of macroseismic methodologies macroseismic fields for all the events indicate a general isoseismal lengthening in the direction of the apennines chain northwest southeast a rapid attenuation of intensity westward of the studied area and a strong propagation eastwards this configuration is strongly dependent on the source mechanisms of the seismic events and the geological dishomogeneities of the concerned areas as regards earthquakes which have been instrumentally recorded in the campania basilicata area from 1980 to 1991 more than 1300 accurate hypocentral locations have been computed for events with m d 2 5 using data from osservatorio vesuviano o v and istituto nazionale di geofisica i n g seismic networks special emphasis is put on the potenza may 5 1990 earthquake m s 5 4 neic national earthquake information center i vii msk which was the strongest recent event in the area and was felt in a large sector of southern italy as regards the seismic sequence following this event about 110 aftershocks with m d 1 9 have been located very close to the town of potenza northeast of it with a clustering type space distribution the occurrence of the events is strongly time concentrated in so defining a main shock aftershocks typical sequence moreover the macroseismic investigation of the main event has allowed to map out isoseismal lines bounding vii vi v and iv msk areas the isoseismals pattern shows that attenuation and amplification of intensity are observed in the same areas as for the previous events beginning from may 26 1991 an increase of seismicity initiated by an earthquake of m l 4 7 neic and i vi vii msk was observed nearly in the same area as the 1990 sequence accurate locations of 84 events with m d 1 9 have been computed however this sequence seems to have a slightly different character from the 1990 one in that events are scattered in time and seismic energy release is comparable to a swarm type seismic sequence as regards the previous sequences fault plane solutions for the highest magnitude events and for appropriate groups of events have been worked out the mechanisms indicate normal faulting motion with t axes oriented orthogonal to the apenninic chain in conclusion detailed analyses on the historical and recent seismicity of the potentino area and adjacent ones have allowed to identify at least four seismogenic zones which show activity with different features such zoning represents a contribution to the seismic hazard assessment in the southern apennines on a regional scale

intermittent slip along the alto tiberina low angle normal fault in central italy the alto tiberina normal fault atf in central italy is a 50 km long crustal structure that deepens at a low angle 15 20 events on the fault plane are about ten times less than those located i

a decade of passive seismic monitoring experiments with local networks in four italian regions we report on four seismic monitoring experiments that in the past ten years we carried out with dense local networks in seismically active italian areas where for at least a year tens of three component seismic stations were set up to record microseismicity the areas observed are alpago cansiglio located in the venetian alps citta di castello in the northern apennines marsica in the central apennines and val d agri located in the southern apennines we produced homogeneous catalogues regarding earthquake locations and local magnitudes to investigate seismicity patterns during an inter seismic period the four regions are characterised by different kinematics strain rates and historical recent seismicity we investigate earthquake distribution in space time and size obtaining reference seismic rates and parameters of the gutenberg and richter law we declustered the catalogues to look for coherent signs in the background seismic activity despite a difference in the catalogues magnitudes of completeness due both to the diverse detection threshold of the local networks and different seismic release we detect and observe two common main behaviours a the alpago cansiglio and marsica regions are characterised by a relatively lower rate of seismic release associated to the episodic occurrence of seismic sequences with the largest event being 3 ml 4 in these areas the seismicity is not localised around the main faults b the citta di castello and val d agri regions have a relatively high rate of seismicity release almost continuously with time and the increase in earthquake production is not clearly related to seismic sequences in these areas the seismicity nucleates around defined fault systems and is usually lower than ml 3 we suggest that the presence of over pressured fluids in the citta di castello and val d agri uppermost crustal volume may favour and mould the higher rate of microseismic release

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

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

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

contemporary crustal extension in the umbria marche apennines from regional cgps networks and comparison between geodetic and seismic deformation abstract here we report the results of the analysis of a gps velocity field in the umbria marche apennines central italy obtained from the integration of diverse geodetic networks the velocity field obtained shows a high degree of consistency both spatially and in terms of comparison with independent information despite the limited time span of some gps stations starting from the velocity field we derive a continuous strain rate field applying a spline interpolation technique which provide a smooth estimate of the deformation field the main feature of the resulting strain rate field is a continuous high 50 nanostrain year strain rate belt coincident with the area of largest historical and instrumental seismic release the model directions of the principal axes agree with geological and seismological information indicating ne sw extension we transform the strain rate field into geodetic moment rate using the kostrov formula to evaluate the potential seismic activity of the region and compare it with actual seismic release in the last 720 years from mw 5 5 earthquakes this comparison highlights a large possible deficit in the seismic release with respect to the overall potential seismic activity particularly concentrated in the northern part of the study area this discrepancy can be resolved with either a large amount of seismicity to be released in the near future or significant aseismic slip and deformation

the gubbio normal fault central italy geometry displacement distribution and tectonic evolution abstract normal faults within orogenic belts can be pre syn or post orogenic features we studied the gubbio normal fault central italy which is an example of a pre orogenic fault reactivated in a post orogenic stage the gubbio fault is a 22 km long fault bordering a quaternary basin and part of an active faults system in the umbria marche region central italy the interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike seismic data indicate that the gubbio fault represents an example of multiple reactivation at least a portion of the fault was active in the miocene and only a part of the total displacement was achieved in the quaternary the reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry the fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth as the fault is commonly addressed as presently active the maximum fault dimensions are correlated to the maximum expected earthquake and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation

is the adriatic an african promontory seismicity patterns and fault plane solutions for the largest recent earthquakes in the adriatic region are used to test the hypothesis that the adriatic is a promontory of the african continental mass the horizontal projections of the slip vectors for the 24 best constrained focal mechanisms trend at a high angle to those predicted for the africa eurasia collision and so the adriatic cannot be thought of as a promontory of africa the slip vectors define an instantaneous pole of rotation that describes anticlockwise rotation of the adriatic relative to eurasia the adriatic is a stable continental block moving within the broad zone of deformation between africa and eurasia