evidence of large scale deformation patterns from gps data in the italian subduction boundary abstract we present the velocity field in italy derived from over 300 continuous gps stations operated in the 1998 2009 time span the gps network maps the whole country with a mean inter site distance of about 50 km and provides a valuable source of data to study the ongoing deformation processes in the central mediterranean the estimated horizontal and vertical velocity fields show major significant features and also less known second order kinematic features a general uplift characterizes the whole apennines and alpine belts that follow the topographic ridge whereas the po plain shows a gradually increasing subsidence from west to east the apennines belt displays a distinctive extension 50 80 10 9 yr 1 while compressive tectonic regimes characterize northern sicily eastern alps and the northeast front of the northern apennines 25 50 10 9 yr 1 second order deformation patterns on large scale wavelength 100 km have been detected on the accretionary prism of central and southern apennines that are highly correlated with other geophysical data vp anomalies seismic anisotropy etc and related to deep rooted sections 70 100 km marked by different subduction regimes apparently at this scale length the observed deformations are governed by the lithosphere as a whole we interpret these deformations as a result of different subduction mechanisms such as variations of the subduction rollback velocity affecting different segments of the subduction zone and or to mantle flows in proximity of the slab edges further south in central southern sicily we detect a contraction of 1 1 0 2 mm yr that probably accommodates part of the africa eurasia convergence on the outer thrust front of the apennines maghrebides belt this hypothesis agrees with an independent analysis of the seismicity associated to the sicilian basal thrust thought to be still active the itrf2005 estimates of the new gps velocity field are available also in sinex format as supplementary file s1

a seismic source zone model for the seismic hazard assessment of the italian territory abstract we designed a new seismic source model for italy to be used as an input for country wide probabilistic seismic hazard assessment psha in the frame of the compilation of a new national reference map we started off by reviewing existing models available for italy and for other european countries then discussed the main open issues in the current practice of seismogenic zoning the new model termed zs9 is largely based on data collected in the past 10 years including historical earthquakes and instrumental seismicity active faults and their seismogenic potential and seismotectonic evidence from recent earthquakes this information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model zs4 zs9 is made out of 36 zones where earthquakes with m w 5 are expected it also assumes that earthquakes with m w up to 5 may occur anywhere outside the seismogenic zones although the associated probability is rather low special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates although it was drawn following criteria that are standard practice in psha zs9 is also innovative in that every zone is characterised also by its mean seismogenic depth the depth of the crustal volume that will presumably release future earthquakes and predominant focal mechanism their most likely rupture mechanism these properties were determined using instrumental data and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications these attributes allow zs9 to be used with more accurate regionalized depth dependent attenuation relations and are ultimately expected to increase significantly the reliability of seismic hazard estimates

finite fault inversion of dinsar coseismic displacement of the 2009 l aquila earthquake central italy 1 we define the geometric and kinematic characteristics of the fault activated during the mw 6 3 6 april 2009 l aquila earthquake from the modeling of envisat and cosmo skymed the first ever x band interferogram inverted for a coseismic dislocation study dinsar interferograms our best fit solution for the main shock is represented by a normal fault 16 km long and 12 km wide with a small right lateral component dipping 47 sw with a maximum slip of 90 cm although the seismic dislocation probably ended at 1 km depth the updip projection of the fault plane corresponds to the northern segment of the mapped paganica s demetrio fault where alignment of surface breaks was observed in the field the absence of this fault in existing seismic source catalogues suggests that an improved approach involving detailed surface and subsurface geological and geophysical investigations is needed for a better assessment of the seismic hazard at the local scale

seismicity at the southern east pacific rise from recordings of an ocean bottom seismometer array 1 seismic data recorded by ocean bottom seismometers obss at the southern east pacific rise sepr were analyzed to characterize seismicity at fast spreading mid ocean ridges an automated event detection algorithm based on pattern recognition was developed to identify earthquake generated t phases the waveform cross correlation and least squares method was found to provide more robust estimates of t phase relative travel times than the method of picking t phase maximum amplitude the obss and subsequent equatorial pacific hydrophones recorded earthquakes near an earthquake swarm in 1992 which was located 300 km west of the ridge axis at about 18 s and 116 w the process that generated the 1992 swarm either was reactivated 3 years later during the obs experiment or has been continuously active in the past decade this longterm activity suggests renewable stresses which are consistent with the interpretation that magma injection was the cause of the 1992 swarm in contrast to the swarm characteristics of earthquakes on the west flank of the ridge axis earthquakes on the nazca flank were randomly distributed in time and space this difference in seismicity may result from the difference in the thermal structure of the pacific and nazca plates the few earthquakes located at or near the ridge axis had very small magnitudes reflecting the presence of shallow magma chambers and the thin elastic layer of the sepr this result suggests that acoustic monitoring of earthquakes associated with dike intrusion is difficult at regional scales at the sepr there is no apparent correlation between seismicity and off axis seamounts index terms 3025 marine geology and geophysics marine seismics 0935 3035 marine geology and geophysics midocean ridge processes 4259 oceanography general ocean acoustics 7230 seismology seismicity and seismotectonics 9355 information related to geographic region pacific ocean keywords t phase ocean bottom seismology mid ocean ridges east pacific rise marine seismics seismicity citation shen y seismicity at the southern east pacific rise from recordings of an ocean bottom seismometer array j geophys res 107 b12 2368 doi 10 1029 2001jb001742 2002

an observation of the horizontal and vertical diffusion of a passive tracer in the deep ocean an experiment to measure the dispersion of a passive tracer injected at 300 and 1000 m depth in the pacific 600 miles southwest of san diego is described rhodamine dye was released as a very nearly point source and the subsequent growth of the patch was mapped at various times up to 66 2 hours after release using a self propelled underwater research vehicle spurv which carried temperature conductivity pressure and dye sensors on a depth cycling trajectory through the patch the analysis shows that the horizontal diffusion rates decrease with depth that it is difficult to resolve the mixing in terms of a constant diffusion parameter based on any one of a number of models that the 300 m results agree with those obtained by schuert 1970 and that the patch growth began to develop eddy behavior at 66 2 hours when the rms second moment of the dye distribution was r2 l 2 210 m for the purpose of predicting horizontal mixing the results indicate that eddy diffusivities of 1150 and 360 cm2 s at 300 and 1000 m respectively are the best fit values for spatial scales 200 m horizontally although we have focused on horizontal isopycnal diffusion a few aspects of the vertical diapycnal characteristics of the patch are also discussed

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

the santa monica basin tracer experiment a study of diapycnal and isopycnal mixing we have studied cross isopycnal diapycnal and lateral mixing and stirring below the sill of santa monica basin by releasing two tracers sulfur hexafluoride and perfluorodecalin as close as possible to an isopycnal surface and measuring their subsequent dispersion the target for the release was a potential temperature surface at about 790 m depth roughly 100 m above the bottom and 50 m below the sill three surveys performed immediately after about 7 weeks after and about 6 months after the release showed that the time scales for lateral stirring and mixing in the basin were between 2 and 5 months the diapycnal diffusivity for the whole period was found to be 0 29 0 06cm2 s near the injection surface where the buoyancy frequency was about 1 1 cph this estimate may include some mixing in the turbulent boundary layer near the walls of the basin our best estimate for the diapycnal diffusivity in the basin interior is 0 25 0 08 cm2 s

dye dispersion in the seasonal thermocline abstract a dye dispersion experiment was performed in september 1979 in the open ocean approximately 180 km off the east coast of florida an initially vertical sheet of dye extending from about 60 to 100 meters in depth and about 10 kilometers long was dispensed into the seasonal thermocline its subsequent evolution was recorded with an instrumented chain that included 25 fluorometers which was towed back and forth across the dye sheet by another vessel the dye sheet was crossed 17 times at ages varying from 6 minutes to slightly less than 4 hours two of the most apparent effects in the data were the important of vertical shear and the presence of intermittency in the dye time series it is found that the depth averaged width of the dye sheet grows as time to the 3 2 power there is good evidence that a shear diffusion interaction is responsible for this growth which implies an effective vertical diffusivity of 1 0 0 5 cm 2 s 1 even though this is an upper ocean experiment there is some cons

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

fecycle attempting an iron biogeochemical budget from a mesoscale sf6 tracer experiment in unperturbed low iron waters 1 an improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high nitrate low chlorophyll hnlc oceanic regions iron budgets for hnlc waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics in summer 2003 we conducted fecycle a 10 day mesoscale tracer release in hnlc waters se of new zealand and measured concurrently all sources with the exception of aerosol deposition to sinks of iron from and rates of iron recycling within the surface mixed layer a pelagic iron budget timescale of days indicated that oceanic supply terms lateral advection and vertical diffusion were relatively small compared to the main sink downward particulate export remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in australia prior to and during fecycle one of which may have deposited iron at the study location however iron deposition rates cannot be derived from such observations illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric supply despite the threefold uncertainties reported for rates of aerosol deposition duce et al 1991 published atmospheric iron supply for the new zealand region is 50 fold i e 7 to 150 fold greater than the oceanic iron supply measured in our budget and thus was comparable i e a third to threefold to our estimates of downward export of particulate iron during fecycle the fluxes due to short term hours biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron i e estimated atmospheric and measured oceanic supply giving an fe ratio uptake of new iron uptake of new regenerated iron of 0 17 i e a range of 0 06 to 0 51 due to uncertainties on aerosol iron supply and an fe ratio biogenic fe export uptake of new regenerated iron of 0 09 i e 0 03 to 0 24

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

determining rheology from deformation data the case of central italy 1 the study of geodynamics relies on an understanding of the strength of the lithosphere however our knowledge of kilometer scale rheology has generally been obtained from centimeter sized laboratory samples or from microstructural studies of naturally deformed rocks in this study we present a method that allows rheological examination at a larger scale utilizing forward numerical modeling we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities stress directions and the tectonic regime to select the best solutions we compared the model predictions with experimental data we applied this method in italy and found that the rheology shows significant variations at small distances the strength ranged from 0 6 0 2 tn m within the apennines belt to 21 6 tn m in the external adriatic thrust these strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the adriatic lithosphere with respect to the internal thrust we found that strike slip or transpressive but not compressive earthquakes can occur along the deeper portion of the thrust the differences in the lithospheric strength are greater than our estimated uncertainties and occur across the adriatic subduction margin using the proposed method the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

mechanics of continental rift architecture continental rifts are long narrow features bounded on one or both sides by normal faults along which several kilometers of displacement has occurred resulting in deep rift valleys that form sedimentary basins continental rifts all share the same geometrical features they have widths that are characteristic of the region in which they form they are predominantly asymmetric and they are segmented along axes at a length scale that is also characteristic of the region we describe a very simple mechanical model to explain these three features the rift initiates with the formation of a conjugate set of normal faults that intersect at the center of the seismogenic layer one of these becomes the boundary fault system the other the failed conjugate fault being offset by the former becomes locked early in the rifting history hence an asymmetric graben is formed which is the basic building block of rifts the failed conjugate fault has distinctive properties that allow it to be easily distinguished from other faults examples of these faults from the tanganyika and malawi rifts show excellent agreement with predictions about their positions with respect to the boundary fault system and their net displacement and slip history the width of the asymmetric graben is a simple function of seismogenic thickness the net displacement on the boundary fault system is limited by the resistive friction and the flexural restoring force we calculate this limiting boundary fault system displacement and using the displacement length scaling law for normal faults suggest that this controls the along axis segmentation length both maximum fault slip and segmentation length are functions of the seismogenic thickness and the effective elastic thickness of the crust these calculations agree very well with observations of segmentation from the african rifts and the maximum length of range fronting normal faults in nevada

low angle normal fault earthquakes and triggering geologic evidence for low angle normal faulting is overwhelming and recent seismic geodetic and neotectonic studies have identified probable active examples thus apparent low levels of historical seismicity on such faults is enigmatic however one large mainshock was a low angle normal event and three others may have been one earthquake sequence had significant moment release from a triggered low angle normal fault and three earthquakes may have had normal subevents on low angle planes such sub events are hard to recognize may be underrepresented in catalogs helping to explain the apparent seismic enigma and pose increased seismic hazard due to delayed strong motions triggered sub events may be along strike or down dip from their triggering shock in cases where the triggered slip is downdip of the steep fault and under its hanging wall elevated pore fluid pressure or fault weakness may be required

clay clast aggregates in gouges new textural evidence for seismic faulting 1 spherical aggregates named clay clast aggregates ccas have been reported from recent investigations on retrieved clay bearing fault gouges from shallow depth seismogenic faults and rotary shear experiments conducted on clay bearing gouge at seismic slip rates the formation of ccas appears to be related to the shearing of a smectite rich granular material that expands and becomes fluidized we have conducted additional high velocity rotary shear experiments and low velocity double shear experiments we demonstrate that a critical temperature depending on dynamic pressure temperature conditions is needed for the formation of ccas this temperature corresponds to the phase transition of pore water from liquid to vapor or to critical which induced gouge pore fluid expansion and therefore a thermal pressurization of the fault a detailed examination by energy dispersive x ray spectrometry edx sem element mapping sem and transmission electron microscopy tem shows strong similar characteristics of experimental and natural ccas with a concentric well organized fabric of the cortex and reveals that their development may result from the combination of electrostatic and capillary forces in a critical reactive medium during the dynamic slip weakening accordingly the occurrence of ccas in natural clay rich fault gouges constitutes new unequivocal textural evidence for shallow depth thermal pressurization and consequently for past seismic faulting

isotopic evidence for ecological and climate change in the richly fossiliferous plio pleistocene upper siwalik deposits exposed around chandigarh india abstract the plio pleistocene siwalik deposits around chandigarh well known for their great wealth of mammalian fossils preserve a continuous record of calcareous paleosols ranging in age from 2 7 to 0 6 ma the carbon isotope composition 13c relative to vienna peedee belemnite vpdb of 140 pedogenic carbonates from ghaggar and nadah sections and 13 gastropod samples from nadah section record a landscape primarily occupied by c4 grasses during this interval however a mixed c3 c4 vegetation between 2 15 and 1 7 ma and a progressive increase in the percentage of c3 plants from 1 1 to 0 6 ma has been recorded most of the pedogenic carbonate 18o values vpdb in the ghaggar river section range between 5 29 and 8 93 indicating the dominance of monsoon climate these 18o values exhibit somewhat consistent trend in relation to 13c values suggesting influence of climate on the vegetation at two instances 1 07 and 0 66 ma there is significant depletion in carbonate 18o and 13c values suggesting monsoon intensification and a synchronous development of c3 vegetation pedogenic carbonate and gastropod 18o values vpdb in the nadah paleoswamp also exhibit consistent trends in relation to 13c values indicating steady relationship between short term climatic fluctuations in terms of warm humid and cool dry conditions and the abundance of c3 c4 biomass on the landscape nearly 1 8 ma ago the vegetation change on the siwalik landscape during early and middle pleistocene appears to have been influenced mainly by the regional tectonics sedimentation patterns and monsoonal rains rather than global climate changes

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

evaluation of stresses in two geodynamically different areas stable foreland and extensional backarc areas which are geodynamically different have different behaviors both in their thermal regime and seismic activity a stable area has a geotherm which can be considered as standard extensional and compressional areas have respectively high and low temperature gradients the italian region includes different geodynamical areas and all such situations are present we consider the apulian platform as an example of a stable area and the tuscany latium as an example of an extensional area for both of them the present geotherms are calculated taking into account for the tuscany latium its thermal history assuming that each region is subject to a constant strain rate the stresses are calculated as functions of depth and time the rheological behavior is assumed to be linear viscoelastic with viscosity dependent on temperature and elastic parameters dependent on lithology the geothermal profile and the rheological structure of the lithosphere remarkably affect the processes of stress accumulation which control the distribution of seismic activity the abrupt decrease of the temperature gradient at the moho produces considerably higher stress values with respect to the case of uniform gradient thus favoring subcrustal seismicity in the case of a standard temperature gradient subcrustal seismicity is predicted and a gap in seismicity indicating a soft intracrustal layer exists if there is a discontinuity in rheology by contrast in the case of a high temperature gradient subcrustal seismicity is not to be expected even in the presence of a discontinuity in rheology since subcrustal temperatures are already too high to permit a sufficient stress accumluation

tectonic evolution of a low angle extensional fault system from restored cross sections in the northern apennines italy 1 broad geological and geophysical documentation is available on regional extensional systems driven by low angle normal faults however little information exists about the three dimensional geometry and the offset distribution of such extensional structures we present a new set of balanced geological sections across the extensional fault system driven by the altotiberina low angle normal fault in the northern apennines of italy we document this extensional system throughout a large set of surface field surveys and geological maps and subsurface data seismic reflection profiles and boreholes the subsurface data allowed us to define the fault deep geometry and to obtain its structural contours the fault geometry is characterized by both along dip and along strike irregularities in cross section the fault displays a staircase trajectory with the shallowest part being dome shaped and flattened to horizontal this bending could be due to the footwall uplift triggered by a footwall uploading greater than about 115 mpa the sequential restoration of five geological cross sections yields a maximum extension of about 10 km accumulated over approximately 3 ma the resulting long term slip rate is about 3 mm yr which is of the same order as the present day extensional rate measured by gps 2 5 3 0 mm yr suggesting an almost steady state extension over the last 3 ma the distribution of the extension values along the fault strike is bell shaped as expected for a continuous surface

new paleoseismic data from the irpinia fault a different seismogenic perspective for southern apennines italy abstract the irpinia fault i e mount marzano fault system mmfs was responsible for the devastating 1980 earthquake mw 6 9 that caused the longest surface faulting ever observed in italy 30 km early paleoseismological studies have revealed a 2 kyr recurrence time for 1980 like characteristic earthquakes on this fault system during the holocene however this appears to clash with both the catastrophic historical seismicity and high gps derived strain rate of the area to explain this apparent discrepancy we investigated the mmfs through a multidisciplinary approach first on the basis of recent archives and archaeological research we reassessed the historical seismicity of the area analysing the highest intensity distribution of the major earthquakes of the upper ofanto valley with respect to the mmfs hanging wall then we carried out a step by step survey along the entire 43 km long fault system through both high precision topographic levelling along the compound fault scarp and geostructural analyses finally we excavated trenches and pits across different fault segments to explore the recent paleoseismological history of the structure based on the combined results that we have obtained we propose a different point of view concerning the seismogenic behaviour of the mmfs from the holocene to the present at the end fault parameters have been compared with those of all the apennines active faults and cross checked with the newest gps results in peninsular italy providing some relevant observation of the relationships between seismogenesis and geodetic deformation

role of the brittle ductile transition on fault activation abstract we model a fault cross cutting the brittle upper crust and the ductile lower crust in the brittle layer the fault is assumed to have stick slip behaviour whereas the lower ductile crust is inferred to deform in a steady state shear therefore the brittle ductile transition bdt separates two layers with different strain rates and structural styles this contrasting behaviour determines a stress gradient at the bdt that is eventually dissipated during the earthquake during the interseismic period along a normal fault it should form a dilated hinge at and above the bdt conversely an over compressed volume should rather develop above a thrust plane at the bdt on a normal fault the earthquake is associated with the coseismic closure of the dilated fractures generated in the stretched hangingwall during the interseismic period in addition to the shear stress overcoming the friction of the fault the brittle fault moves when the weight of the hangingwall exceeds the strength of the dilated band above the bdt on a thrust fault the seismic event is instead associated with the sudden dilation of the previously over compressed volume in the hangingwall above the bdt a mechanism requiring much more energy because it acts against gravity in both cases the deeper the bdt the larger the involved volume and the bigger the related magnitude we tested two scenarios with two examples from l aquila 2009 italy and chi chi 1999 taiwan events gps data energy dissipation and strain rate analysis support these contrasting evolutions our model also predicts consistently with data that the interseismic strain rate is lower along the fault segment more prone to seismic activation

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

mapping moho depth variations in central italy from psmoho p delay times evidence of an e w transition in the adriatic moho at 42 n latitude 1 along the italian peninsula adjoin two crustal domains peri tyrrhenian and adriatic whose boundary is not univocal in central italy in this area we attempt to map the extent of the moho in the two terrains from variations of the travel time difference between the direct p wave and the p to s wave converted at the crust mantle boundary called psmoho we use teleseismic receiver functions computed at 38 broad band stations in this and previous studies and assigned each of the recording sites to the adriatic or peri tyrrhenian terrains based on station location geologic and geophysical data and interpretation and consistency of delays with the regional moho trend the results of the present study show that the psmoho arrival time varies from 2 3 to 4 1 s in the peri tyrrhenian domain and from 3 7 to 5 5 s in the adriatic domain as expected the lowest time difference is observed along the tyrrhenian coastline and the largest values are observed in the axial zone of the apennine chain a key new result of this study is a sharp e w boundary in the adriatic domain that separates a deeper moho north of about 42 n latitude from a shallower moho to the south this feature is constrained for a length of about 40 km by the observations available in this study the e w boundary requires a revision of prior mapping of the moho in central italy and supports previous hypotheses of lithosphere segmentation

the database of individual seismogenic sources diss version 3 summarizing 20 years of research on italy s earthquake geology abstract this paper describes the main characteristics the evolution and the structure of the database of individual seismogenic sources diss and particularly of its release of early 2007 the database contains the results of the investigations of the active tectonics in italy during the past 20 years the first two sections of this paper document the recent evolution in mapping and archiving italian active fault data in relation to important achievements in the understanding of italian tectonics some of which were spurred by significant earthquakes the central sections describe the current structure of the database the reasons for its assumptions and data categories its current contents its evolution through several years of improvements the last section describes how the current contents of the database correspond with the existing strain and stress data available from focal mechanism borehole breakout and gps data for the whole of italy the database supplies a fresh and unified view of active and seismogenic processes in italy by building on basic physical constraints concerning rates of crustal deformation on the continuity of deformation belts and on the spatial relationships between adjacent faults both at the surface and at depth

seismology tectonic strain in plate interiors arising from r smalley jr m a ellis j paul r b van arsdale nature 435 1088 1090 2005 r smalley et al reply it is not fully understood how or why the inner areas of tectonic plates deform leading to large although infrequent earthquakes smalley et al 1 offer a potential breakthrough by suggesting that surface deformation in the central united states accumulates at rates comparable to those across plate boundaries however we find no statistically significant deformation in three independent analyses of the data set used by smalley et al and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present

experimental constraints on energy partitioning during stick slip and stable sliding within analog fault gouge abstract the lack of substantial frictional heat anomalies across major fault zones has been a key observation suggesting that faults support low shear stress during slip some studies have suggested that the lack of large thermal anomalies across faults may be a result of considerably less energy going to frictional heat than generally thought and that a large fraction of energy is dissipated by other processes such as the creation of new surface area we evaluate this hypothesis through the analysis of laboratory shear experiments for both stick slip seismic and stably sliding aseismic analog fault gouges these experiments differ from previous laboratory studies in that they 1 provide independent constraints on frictional heat generation and energy consumed generating new surface area 2 cover a broader range of shear stresses 2 20 mpa than most previous studies and 3 evaluate both stick slip and stable sliding within granular material based on the analysis of high precision temperature measurements and comparisons with numerical model simulations 90 of the total energy appears to go to frictional heat generation e h for all of our experiments we also show based on grain size analysis that 1 of total work is consumed generating new surface area e sa these results are consistent with assumptions allowing frictional resistance to be inferred from thermal data furthermore we observe no resolvable difference in the fraction of energy going to fracturing or frictional heat between stick slip and stable sliding experiments

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

local regional and plate scale sources for the stress field in the adriatic and periadriatic region abstract the stress field at a specific location is the sum of regional stress controlled by plate scale tectonic processes with local sources here we evaluate and discuss the different sources from geodynamic to local scale and the controlling factors including the jurassic paleogeography of the adriatic passive margin of present day stress in the adriatic sea and periadriatic regions of italy using two kinds of numerical models 3d mantle scale viscoelastic models and 2 5d lithosphere scale thin shell models the subcrustal stress field of the slabs in the dinarides hellenic and apennines calabrian subduction zones are characterized by downdip extension and compression respectively this difference is explained by the velocity of the adriatic slab with respect to the upper mantle in the hotspot reference frame the slab in the calabrian subduction zone is encroached and down pushed whereas the slab in the hellenic subduction zone is sustained by the mantle flow at the plate scale the upper crustal stress field at the apennines front is governed by the different nature of the lithosphere probably oceanic in the ionian sea and continental elsewhere which in turn determines first order rotations of the stress axes second order rotations of the stress axes depend on the jurassic paleogeography and consequent differential advancement of the thrust fronts with recesses and salient occurring in correspondence with jurassic structural highs and lows respectively the eastward relative motion of the mantle with respect of the lithosphere enhances the onset of nw se oriented compression within the adriatic plate consistent with observations finally 2 5d thin shell models demonstrate that present day stress does not simply follow the long wavelength pattern 500 1000 km due to plate tectonics and mantle interaction but is greatly affected by the presence of second and third order sources like crustal structure faults and topography most importantly these factors give an observable effect in data

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

extension on the tibetan plateau recent normal faulting measured by insar and body wave seismology we use insar and body wave modelling to determine the faulting parameters for a series of five mw 5 9 7 1 normal faulting earthquakes that occurred during 2008 including the march 20 yutian earthquake mw 7 1 one of the largest normal faulting events to have occurred recently on the continents we also study three earlier normal faulting earthquakes that occurred in southern tibet between 1992 and 2005 coseismic deformation for each of these eight events is measured with ascending and descending interferograms from envisat ers and alos sar data elastic dislocation modelling of the line of sight insar displacements and body wave seismological modelling of p and sh waves are used to estimate fault parameters and are found to be in good agreement for all the events studied the use of insar to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity only five of the eight events are associated with a clear surface topographic feature suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone the observations in all cases are consistent with slip on planar surfaces with dips in the range 40 50 that penetrates the uppermost crust to a depth of 10 15 km we find no evidence for active low angle dip less than 30 normal faulting the contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3 4 mm yr 1 or 15 20 per cent of the rates of extension measured across the plateau using gps 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km this observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

graviquakes in italy abstract we discuss the mechanics of crustal normal fault related earthquakes and show that they represent dissipation of gravitational potential energy graviquakes and their magnitude increases with the involved volume delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall and the fault dip the magnitude increases with the deepening of the brittle ductile transition bdt which in turn enlarges the involved volume the fault dip seems rather controlled by the static friction of the involved crustal layers we apply the model to the extensional area of the italian peninsula whose geodynamics is controlled by the alpine and apennines subduction zones the latter has a well developed backarc basin and a large part of the accretionary prism is affected by on going extensional tectonics which is responsible for most of peninsular italy seismicity analyzing the seismic record of the apennines the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth we compile a map of the brittle ductile transition depth and assuming a fixed 45 or 60 fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane we compute the maximum volume of the hangingwall collapsing at the coseismic stage and estimate the maximum expected magnitude lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow moreover lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values

sulphur hexafluoride as a tracer of biogeochemical and physical processes in an open ocean iron fertilisation experiment abstract the first open ocean experiment to test the iron hypothesis in the equatorial pacific was undertaken using the tracer gas sulphur hexafluoride sf 6 to locate and track the fertilised surface water continuous surface measurements showed that the sf 6 patch spread rapidly in the first 24 h from an initial release area of 64 km 2 to a total area of 214 km 2 and remained relatively constant in size for the following three day period sf 6 data was mapped in a lagrangian frame of reference by the use of a drogued gps buoy released at the centre of the patch the sf 6 patch remained coherent and exhibited a slow anti cyclonic oscillation during the first four days the buoy was transported downwind of the patch in a northwesterly direction within two days which has implications for the future use of buoys in surface water advection studies following subduction below a low salinity front 3 4 days after release the patch centre was relocated by its sf 6 signal at a depth of 25 30 m to the east of the residual surface patch the latter spread rapidly to the southwest during the remainder of the experiment whilst the subducted patch remained relatively stationary density corrected sf 6 profiles were used to calculate a mean vertical eddy diffusivity of 0 25 cm 2 s across the thermocline following the subduction event a vertical flux of nitrate of 2 5 mmol m 2 d 1 into the mixed layer was estimated which implied an f ratio value of 0 4 on comparison with productivity data the results demonstrate that sf 6 is a successful tracer of water masses and emphasise the potential of this technique for the in situ measurement and manipulation of open ocean processes

normal faults and thrusts reactivated by deep fluids the 6 april 2009 mw 6 3 l aquila earthquake central italy 1 on 6 april 2009 a mw 6 3 earthquake occurred in the central apennines italy damaging the city of l aquila and the surrounding country we relocate the october 2008 to 6 april 2009 foreshocks and about 2000 aftershocks occurred between 6 and 30 april 2009 by applying a double difference technique and determine the stress field from focal mechanisms the events concentrate in the upper 15 km of the crust three main nw se to nnw sse striking 30 45 and 80 90 dipping faults were activated during the seismic sequence among these a normal fault and a thrust were reactivated with dip slip movements in response to ne sw extension the structural maturity of the seismogenic fault system is lower than that displayed by other systems in southern apennines because of the lower strain rate of the central sector of the chain with respect to the southern one vp vs increases progressively from october 2008 to the 6 april 2009 main shock occurrence along a nw se strike because of an increment in pore fluid pressure along the fault planes pore pressure diffusion controls the space time evolution of aftershocks a hydraulic diffusivity of 80 m2 s 1 and a seismogenic permeability of about 10 12 m2 suggest the involvement of gas rich co2 fluids within a highly fractured medium suprahydrostatic high fluid pressure about 200 mpa at 10 km of depth within overpressurized traps bounded by preexisting structural and or lithological discontinuities at the lower upper crust boundary are required to activate the april 2009 sequence traps are the storage zone of co2 rich fluids uprising from the underlying about 20 km deep metasomatized mantle wedge these traps easily occur in extensional regimes like in the axial sector of apennines but are difficult to form in strike slip regimes where subvertical faults may cross the entire crust in the apennines fluids may activate faults responsible for earthquakes up to mw 5 6 deep fluids more than tectonic stress may control the seismotectogenesis of accretionary wedges

assessing the work budget and efficiency of fault systems using mechanical models 1 we examine the work energy budget of actively deforming fault systems in order to develop a means of examining the systemic behavior of complex fault networks work done in the deformation of a faulted area consists of five components 1 work done against gravity in uplift of topography wgrav 2 internal energy of the strained host rock wint 3 work done resisting friction during slip on faults wfric 4 seismic energy released in earthquake events as ground shaking wseis and 5 work done in initializing new faults and propagating existing faults wprop the energy budget of a fault system can be expressed as wtot wgrav wint wfric wseis wprop for a balanced energy budget the total of these five components will equal the external tectonic work applied to the system we examine the work balance within hypothetical and simulated two dimensional static fault systems using mechanical models the boundary element method models produce a balanced work budget for both simple and complex fault system models the presence of slipping faults reduces the internal strain energy of the faulted area wint at a cost of work done against friction and gravity and propagation and seismic energy where applicable calculations of minimum work deformation match expected deformation paths indicating the usefulness of this approach for evaluating efficiency in more complex systems the partitioning of various work terms may express the relative efficiency or maturity of fault systems furthermore calculation of potential seismic energy release can provide an upper bound to earthquake seismic moment assessments

active aseismic creep on the alto tiberina low angle normal fault italy the existence of active low angle normal faults has been questioned because the standard theory of fault mechanics precludes normal faults from slipping at low

parameter sensitivity of primitive equation ocean general circulation models abstract experiments with a low resolution primitive equation ocean general circulation model with idealized basin geometry and surface forcing have been carried out in order to identify the processes controlling the climatically important aspects of the circulation emphasis was placed on the sensitivity of the model solutions to the magnitude of the vertical diffusivity scaling arguments suggest and the numerical experiments confirm that the solutions are most sensitive to the magnitudes of the wind stress curl and the vertical diffusivity for small vertical diffusivity wind forcing dominates the solution the vertical scale of the thermocline is set by the strength of the ekman pumping and there is a multiple gyre circulation in the upper layers for large vertical diffusivity diabatic surface forcing dominates the solution vertical diffusion controls the vertical scale of the thermocline and there is a single large anticyclonic gyre in the upper layers both the meridionally and zonally inte