near end member magnesiochloritoid in prograde zoned pyrope dora maira massif western alps in the ultrahigh pressure metamorphic terrane of the dora maira massif western alps magnesiochloritoid up to 97 mol end member occurs along with ellenbergerite talc chlorite or kyanite as prograde inclusions in a few pyrope megablasts whereas most pyrope megablasts in this terrane are relatively homogeneous prp90 prp98 the magnesiochloritoid bearing megablasts commonly preserve a clear prograde fe mg zonation pattern from prp70 to prp98 the nearly homogeneous chloritoid inclusions also record this zonation pattern their xmg increasing from 0 70 to 0 96 from garnet core to garnet rim these zonations are shown to be prograde and to record increasing p and t conditions up to about 700 c 30 kbar the occurrence of magnesiochloritoid in some garnets simply reflects either a slightly more fe rich system general case or a more al rich and originally corundum bearing system one unzoned near end member pyrope megablast fe mg partitioning between chloritoid and zoned host garnet changes from normal to reverse i e xmgcld xmggrt from core to rim or from rim to core in other megablasts of yet similar composition in case of reverse partitioning a diffusion zone of a few tens of mu m wide exists in garnet around the inclusions toward which xmggrt decreases and reaches a normal partitioning value at the contact these features are interpreted in terms of disequilibrium and tentatively ascribed to slow diffusion in chloritoid with respect to garnet growth rate or to two competing garnet forming reactions with the metastable one which produces a more mg rich garnet being kinetically favoured the prograde inclusions of magnesiostaurolite show a consistent fe mg reversal with garnet i e xmgst xmggrt which is interpreted as an equilibrium feature at high pressure and high xmg magnesiochloritoid locally breaks down into symplectites of chlorite and an extremely low si magnesiostaurolite down to 7 0 si per formula unit which is probably metastable with respect to magnesiostaurolite corundum

exploiting the airwave for time lapse reservoir monitoring with csem on land in the application of controlled source electromagnetics for reservoir monitoring on land repeatability errors in the source will mask the time lapse signal due to hydrocarbon production when recording surface data close to the source we demonstrate that at larger distances the airwave will still provide sufficient illumination of the target the primary airwave diffuses downward into the earth and then is scattered back to the surface the time lapse difference of its recorded signal reveals the outline on the surface of the resistivity changes in a hydrocarbon reservoir under production however repeatability errors in the primary airwave can destroy the signal to noise ratio of the time lapse data we present a simple and effective method to remove the primary airwave from the data which we call partial airwave removal for a homogeneous half space and a delta function type of source the surface expression of the airwave does not depend on frequency for this reason the primary airwave can be subtracted from the data using recordings at two frequencies one low enough with a skin depth of the order of the reservoir depth that is sensitive to the reservoir the other high enough to only sense the near surface the method does not affect secondary airwave components created by signals that have propagated through the earth and returned to the surface we show that the method provides a direct indicator of production related time lapse changes in the reservoir we illustrate this for several models including a general 3d heterogeneous model and one with strong surface topography for situations where survey repeatability errors are large

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

reversals in fe mg partitioning between chloritoid and staurolite chloritoid and staurolite coexist with al silicate chlorite or garnet or biotite in precambrian quartzite and schist from northern new mexico the observed fe mg reversal is not related to variable p t or minor element content including fe super 3 however it could arise from any of three factors 1 fe and mg may occur on several crystallographic sites in one or both minerals 2 some mg may not be exchangeable with fe in staurolite or 3 fe and mg may mix non ideally in one or both phases modified journal abstract

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

inversion of magnetotelluric data in the presence of strong bathymetry topography we describe an algorithm for inverting magnetotelluric mt data in the presence of strong bathymetry or topography instead of correcting distortions due to bathymetry or topography we incorporate them directly into the inversion to achieve a high accuracy in computing mt responses we use finite difference approximations that permit sloping discrete boundaries inside model elements the same approach is applicable to any seafloor electromagnetic calculation and can also be used to incorporate steep topography on land we test our approach on various topographic features and compare our results to that of a finite element approach finally we present inversion examples that illustrate the effectiveness of our inversion algorithm in recovering true subsurface structures in the presence of strong bathymetry and topography

the stress field in europe optimal orientations with confidence limits this article has been accepted for publication in geophysical journal international the authors 2003 published by oxford university press on behalf of the royal astronomical society all rights reserved

nanocoatings of clay and creep of the san andreas fault at parkfield california mudrock samples were investigated from two fault zones at 3066 m and 3296 m measured depth md located outside and within the main damage zone of the san andreas fault observatory at depth safod drillhole at parkfield california all studied fault rocks show features typical of those reported across creep zones with variably spaced and interconnected networks of polished displacement surfaces coated by abundant polished films and occasional striations electron microscopy and x ray diffraction study of the surfaces reveal the occurrence of neocrystallized thin film clay coatings containing illite smectite i s and chlorite smectite c s minerals 40 ar 39 ar dating of the illitic mix layered coatings demonstrated miocene to pliocene crystallization and revealed an older fault strand 8 1 3 ma at 3066 m md and a probably younger fault strand 4 4 9 ma at 3296 m md today the younger strand is the site of active creep behavior reflecting a possible re activation of these clay weakened zones we propose that the majority of slow fault creep is controlled by the high density of thin

petrology of fe mg carpholite bearing metasediments from ne oman abstract fe mg carpholite occurs in metasediments of tectonically disrupted basement shelf and foreland basin units that structurally underlie the semail ophiolite in ne oman in the lower grade structurally higher units fe rich carpholite coexists with paragonite quartz illite kaolinite and chlorite whereas in deeper units fe mg carpholite occurs with pyrophyllite sudoite phengite and or chloritoid mineral compositions in these units indicate that chlorite is more magnesian than coexisting fe mg carpholite at low temperatures and pressures but at higher metamorphic grades xmg decreases in the order sudoite carpholite chlorite chloritoid this suggests a reversal in fe mg partitioning between fe mg carpholite and chlorite at temperatures below or close to those of the breakdown of kaolinite quartz to pyrophyllite and at xmg 0 35 phase relations and mineral equilibria indicate that the p t conditions of formation of the fe mg carpholite bearing rocks of ne oman range from 280 315 c 3 6 kbar for the structurally highest units to 325 440 c 6 9 5 kbar for the deepest units indicating a systematic down section increase in metamorphic grade textural relations in these rocks interpreted in the context of pertinent equilibria are consistent with the clockwise p t paths previously constrained for these units from petrological studies of interlayered isofacial mafic rocks

holocene paleoearthquakes and early late pleistocene slip rate on the sulmona fault central apeninnes italy abstract the 23 km long sulmona normal fault flanks the southwestern slope of the mount morrone range in the central apennines to date the recent activity of this structure is uncertain as the faulting evidence concerns only undated deposits and the fault cannot be associated with any of the strong historical earthquakes m w 6 5 of the region our observation from 1 ma offset slope breccias coupled with new tephrochronological data on faulted early last glacial lacustrine infilling of the sulmona basin implies a vertical slip rate of 0 5 mm yr over both the long term and middle term moreover at the apex of a late pleistocene alluvial fan radiocarbon dating of offset stratigraphy uncovered in four paleoseismological trenches shows that repeated earthquakes resulted in more than 4 m of vertical offset since 9 ka providing again a minimum holocene vertical slip rate of 0 5 mm yr in combination with the results of the trench exposure we define four faulting events in the past 9 ky b p and at least one before then the most recent is constrained by robust radiocarbon dates as the middle of the second century a d the penultimate event was around the middle of the fifth millennium b p whereas the other two events are dated in a time between 8 5 ky to 6 5 ky b p and around 9 ky cal b p the oldest occurred before 9 5 ky b p as well as revealing the unexpected paleoseismic history of the sulmona silent fault our data provide a recurrence time for m w 6 5 earthquakes of 2 4 ky versus an elapsed time of 1 85 ky since the last event the latter matches with an earthquake previously hypothesized through archaeoseismic clues collected from several roman settlements of the sulmona plain all of which were dated to halfway through the second century a d online material table of major element compositions field photos and harker diagrams

rheology of the northern apennines lateral variations of lithospheric strength abstract a thermorheological wsw ene profile along the northern apennines is presented the variations in rheology are estimated using two different models the conventional model in which only frictional sliding and power law creep are taken into account and a new model in which in addition to the previous two mechanisms a high pressure brittle fracture mechanism is included upper and lower bounds for the rheology are considered a hard case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite and a soft case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite important differences in lithospheric rheological structure are inferred between the western and the eastern sectors of the chain in the former a creme brulee structure generally applies in the latter a jelly sandwich structure applies these rheological models therefore are not alternative but end members of a continuous spectrum of rheological behaviours

the effects of 3d topography on controlled source audio frequency magnetotelluric responses we are investigating the 3d topographic effects on controlled source audio frequency magnetotelluric data two 3d topographic models are considered a trapezoidal hill model and a trapezoidal valley model different responses are generated including the amplitude of electric field amplitude of magnetic field apparent resistivity and phase data the responses distorted by the 3d topography are simulated for the source located both next to and on the hill valley our study indicates that all the electric field magnetic field apparent resistivity and phase data are influenced by 3d topography but to different extents these topographic effects depend on the transmission receiver topography geometry the transmission frequency earth resistivity and the roughness of the surface the effects in the near field generated by topography in the survey area are quite different from those in the far field because of the existence of the source compared to those in the far field zone the magnetic field and pha

experimental evidence for mantle drag in the mediterranean 1 what forces control active deformation in the central mediterranean slab pull has long been debated but no other hypothesis has been generally accepted here we analyze the role of shear basal tractions by using a thin shell modeling technique we generated a large number of models that span different sets of boundary conditions from the literature we then explored acceptable ranges of model parameters we computed residuals between model predictions and several datasets of stress directions gps measurements and tectonic stress regimes that have been produced in recent studies and then compared the best models obtained in the presence of tractions with those obtained in the absence of tractions for all tested boundary conditions and all considered datasets our results show that the only successful models are those with significant basal shear traction exerted by eastward mantle flow

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

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

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 upper thermal stability of chlorite quartz an experimental study in the system mgo al2o3 sio2 h2o experiments up to water pressures of 21 kbar have been undertaken to bracket the reactions chlorite quartz talc kyanite h2o chlorite quartz talc cordierite h2o and talc kyanite quartz cordierite h2o by reversed runs in the system mgo al2o3 sio2 h2o mash these reaction curves intersect at an invariant point ip1 at ph2o 6 4 0 2 kbar and a temperature of 624 4 c the curve of the chlorite quartz breakdown to talc kyanite h2o at water pressures above 6 4 kbar shows a negative dp dt with the slope decreasing with rising pressure whereas the slope of the breakdown curve to talc cordierite h2o at water pressures is clearly positive the composition of the chlorite solid solution reacting with quartz has been estimated to be approximately mg4 85al1 15 al1 15si2 85o10 oh 8 over the entire pressure range investigated the composition of the talc solid solution forming by the breakdown of chlorite quartz appears to be mg2 94al0 06 al0 06si3 94o10 oh 2 at ph2o 2kbar with increasing pressure the al content of talc decreases reaching a value of about 0 06 atoms per formula unit at p h2o 21 kbar as a consequence of the new experimental data the existing phase topologies of the mash system and k2o mash system have been revised for example the invariant point ip1 and the univariant reaction curve kyanite talc h2o chlorite cordierite are stable for this reason the development of medium to high temperature metamorphic rocks compositionally approximating the mash system must be reconsidered the whiteschists from sar e sang afghanistan are treated as an example the application of the present experimental data to metamorphic rocks of more normal composition requires the examination of the influence of further components this leads to the conclusion that the introduction of fe2 into magnesian chlorite extends its stability field in the presence of quartz by 10 15 c in comparison with pure mg chlorite

2d marine controlled source electromagnetic modeling part 2 the effect of bathymetry marine controlled source electromagnetic csem data are strongly affected by bathymetry because of the conductivity contrast between seawater and the crust below the seafloor we simulate the marine csem response to 2d bathymetry using our new finite element fe code and our numerical modeling shows that all electric and magnetic components are influenced by bathymery but to different extents bathymetry effects depend upon transmission frequency seabed conductivity seawater depth transmitter receiver geometry and roughness of the seafloor topography bathymetry effects clearly have to be take into account to avoid the misinterpretation of marine csem data sets

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

bathymetric effects and corrections in marine csem data the effect of seafloor topographic variations on controlled source electromagnetic csem responses is investigated using a finite difference modeling approach for both petroleum and gas hydrate exploration scenarios in a deepwater reservoir model distortions in the inline electric field responses are mainly due to galvanic effects particularly at long transmitter receiver tx rx offsets and are characterized by persistent short wavelength anomalies at all tx rx offsets in the amplitude profiles in a shallow water reservoir model the contribution of inductive effects to bathymetric distortions is large at short tx rx offsets compared to the deepwater case whereas at long offsets the distortion pattern is mainly determined by the source receiver geometry relative to the sea surface because of the airwave effect rather than by the resistivity variations associated with the seafloor topography a simple correction technique which is an extension of the topographic correction procedure for magnetotelluric data is effective in removing the bathymetric distortions for the deep marine case but cannot be used for the shallow water case because of the airwave effect for a gas hydrate exploration model it is shown that the bathymetric response can be large enough to mask the target response because higher frequencies and shorter offsets need to be used to detect the shallow targets however the modeling study suggests that the shallow target response can be separated from the bathymetric distortions using the correction method

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

earthquake depth distributions in central asia and their relations with lithosphere thickness shortening and extension this paper examines the relationship between seismogenic thickness lithosphere structure and rheology in central and northeastern asia we accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust these variations exert a fundamental control on the active tectonics and the morphological evolution of the continents we consider 323 earthquakes across the tibetan plateau the tien shan and their forelands as well as the baikal rift ne siberia and the laptev sea and present the source parameters of 94 of these here for the first time these parameters have been determined through body wave inversion the identification of depth phases or the modelling of regional waveforms lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening and to locations where rifting coincides with abrupt changes in lithosphere thickness such as the ne baikal rift and w laptev sea the lower crust in these areas is seismogenic at temperatures that may be as high as 600 c suggesting that it is anhydrous and is likely to have great long term strength lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity topography relations the variation in crustal rheology indicated by the distribution of lower crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts to the localization and orientation of rifting in combination these processes can also be responsible for the separation of the front of the thin skinned mountain belts from their hinterlands when continents separate

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

fault mechanism of the 40 seconds subevent of the 1980 irpinia southern italy earthquake from levelling data a model for the 40 s subevent of the 1980 irpinia earthquake is obtained from levelling data an inverse method has been used to compute fault parameters based on the computation of the probability density on strike and dip angles and midpoint fault location the highest probability model consists of a fault almost parallel to the one associated to the first subevent this fault dips about 80 sw forming a small graben like structure with the main fault fault strike and dip parameters appear well constrained by levelling data to within 10 at 95 confidence level it is noteworthy that seismological and accelerometric data were not able to well constrain the fracture mechanism of this subevent which was the most controversial one in literature crosson et al 1986 westaway 1987 crosson et al 1987 westaway and jackson 1987 bernard and zollo 1989

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

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

prograde reactions and garnet zoning reversals in staurolite schist british columbia significance for thermobarometric interpretations an outcrop of staurolite bearing pelitic schist from the solitude range in the south western rocky mountains british columbia was examined in order to determine the nature of prograde garnet and staurolite producing reactions using information from garnet zoning and inclusion mineralogy although not present as a matrix phase chloritoid is present as inclusions in garnet and is interpreted to have participated in the simultaneous growth of garnet and staurolite by a reaction such as chloritoid quartz garnet staurolite h2o a garnet zoning trend reversal which is most pronounced with respect to almandine and grossular components is present in the outer core of garnets the location of the zoning reversal corresponds to the outer limit of chloritoid inclusions in garnet as there is no evidence for polymetamorphism the zoning reversal is interpreted to indicate continued garnet growth by prograde reaction s during a single metamorphic event after the exhaustion of chloritoid as a matrix phase metamorphic conditions recorded by mineral rim compositions are 550 600 c at 6 7 kbar because there is no evidence for partial resorption of garnet during production of staurolite we interpret these results to represent peak conditions

a new technique for the incorporation of seafloor topography in electromagnetic modelling summary we describe a new technique for incorporating seafloor topography in electromagnetic modelling it is based on a transformation of the topographic relief into a change in electrical conductivity and magnetic permeability within a flat seafloor since the technique allows us to model arbitrary topographic changes without extra grid cells and any restriction by vertical discretization we can model very precise topographic changes easily without an extra burden in terms of computer memory or calculation time the reliability and stability of the technique are tested by comparing the magnetotelluric responses from two synthetic seafloor topography models with three different approaches these incorporate the topographic change in terms of 1 the change in conductance using the thin sheet approximation 2 a series of rectangular block like steps and 3 triangular finite elements the technique is easily applied to any modelling method including 3d modelling allowing us to model complex structure in the earth while taking full account of the 3d seafloor topography

two dimensional topographic responses in magnetotellurics modeled using finite elements we simulate the magnetotelluric response to two dimensional earth topography using finite elements linear interpolation of the secondary field parallel to strike over triangular elements allows accurate modeling of inclined resistivity boundaries including topographic surfaces to avoid discontinuities in field derivatives or resistivity care must be taken that the nodal values of the field parallal to strike used to obtain the auxiliary secondary fields are kept within uniform earth media the nodal locations may be shifted but the derivatives still are evaluated at the field points of interest correct values may be returned at gentle breaks in slope as well as along straight surfaces the finite element program is verified by comparison with the analytic transverse magnetic response of a hemicylindrical depression and with rayleigh scattering and transmission surface results for transverse electric and transverse magnetic polarization agreement with the other methods generally is excellent with t

3d magnetotelluric modelling including surface topography an edge finite element method has been applied to compute magnetotelluric mt responses to three dimensional 3d earth topography the finite element algorithm uses a single edge shape function at each edge of hexahedral elements guaranteeing the continuity of the tangential electric field while conserving the continuity of magnetic flux at boundaries we solve the resulting system of equations using the biconjugate gradient method with a jacobian preconditioner the solution gives electric fields parallel to the slope of a surface relief that is often encountered in mt surveys the algorithm is successfully verified by comparison with other numerical solutions for a 3d 2 model for comparison of modelling methods for em induction and a ridge model we use a 3d trapezoidal hill model to investigate 3d topographic effects which are caused mainly by galvanic effects not only in the zxy mode but also in the zyx mode if a 3d topography were approximated by a two dimensional topography therefore errors occurring in the transverse electric mode would be more serious than those in the transverse magnetic mode

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

3d modeling of a deepwater em exploration survey analysis of a current offshore prospect employed 3d numerical modeling of a controlled source electromagnetic csem exploration system the analysis considers the sensitivity of data presentations to assumptions about the background model the numerical simulations show that false anomalies and significant distortion to anomaly magnitude can be caused by normalization of the observed electric fields by reference fields calculated from an incorrect or oversimplified background model bathymetry effects on the measured electric fields if not accounted for can produce anomalies as large as those of target sands the maximum sensitivity to oil water contacts or other strong lateral variations within the modeled channel sands is achieved by profiling along the length of the channel profiles run offset from a simulated oil water contact by as little as 2 km show a response below the expected noise levels good background models can be constructed by taking advantage of the magnetotelluric data recorded by m

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

a thermal tectonic model for high pressure metamorphism and deformation in the sesia zone western alps the sesia zone western alps is a slice of austroalpine continental crust that was once metamorphosed at t 500 560 c and p 14 16 kbar at 130 100 ma b p pervasive blueschist eclogite facies assemblages record this event and a later greenschist facies overprint is only well developed in the nw part of the zone on the basis of thermal calculations it is difficult to explain the preservation of high pressure assemblages in a simple model of underthrusting and subsequent uplift erosion an alternative model is proposed in which the sesia zone was emplaced by underthrusting of the austroalpine continental margin prior to subduction of oceanic lithosphere of the piemonte basin subduction of relatively cool oceanic lithosphere below the underthrust sesia zone then continued for a period of time e g 20 ma thus suppressing thermal recovery of this latter unit exhumation of sesia zone rocks began during this subduction episode by uplift on the insubric line erosion and by underplating of oceanic

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

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

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

new gps constraints on the kinematics of the apennines subduction abstract we present the velocity field of the italian area derived from continuous gps observations from 2003 to 2007 the gps sites were installed by different institutions and for different purposes they cover the whole country with a mean inter site distance of about 60 km and provide a valuable source of data to map the present day kinematics of the region the absolute itrf2005 rotation poles and rates of eurasia africa and adriatic plates are estimated to study the kinematics along their boundaries in the apennines belt the corsica sardinia block coherently moving as the eurasia plate is used as reference of the upper plate for the apennines subduction zone we apply a simple kinematic model to estimate the rates and spatial pattern of the subduction along the apennines we identify at least four different independently moving lower plates i e the adriatic diverging and internally segmented ionian sicily and africa converging plates with different subduction rates the conservative estimates of the subduction rate are 5 mm yr in the calabrian arc 1 5 mm yr in sicily and 0 9 mm yr in the northern apennines this variegate mixture of behaviors seems to reflect the variable lithospheric thickness and composition of the lower plates inherited from the mesozoic rifting an unexpected along strike contraction is observed along the western side of the central northern apennines velocities are estimated both relative to eurasia and relative to the deep and shallow hotspot reference frames hsrf the hotspot representation seems more coherent with the geophysical and geological constraints along the subduction system in which the adriatic and ionian plates move sw ward and their deeper slab portions provide an obstacle to the opposite relative mantle flow all these patterns better reconcile if the subduction process is conceived as a passive feature controlled by the far field plate velocities and the relative eastward mantle flow acting on a disrupted slab

twenty years of paleoseismology in italy abstract italy has one of the most complete and historically extensive seismic catalogues in the world due to a unique and uninterrupted flow of written sources that have narrated its seismic history since about the end of the iron age seismic hazard studies have therefore always been mainly based upon this huge mass of data nevertheless the italian catalogue probably lacks many m 6 5 events the seismogenetic structures responsible for which are characterized by recurrence times that are longer than the time span covered by our historical sources for these reasons and as in other countries earthquake data that in italy have been derived from paleoseismological studies should finally become a necessary ingredient in seismic risk assessment indeed over the past 20 years some hundred trenches have been excavated supplying reliable and conclusive data on the recent activities of many faults through to many robust datings of surface fault events these studies have provided the ages of several unknown or poorly known m 6 5 earthquakes here we summarize the state of the art of paleoseismology in italy and present a first catalogue of 56 paleoearthquakes pci that occurred mainly in the past 6 kyr the pci integrates the historical instrumental seismic catalogue and extends it beyond the recurrence time of the seismogenetic faults 2000 1000 yr we feel confident that the use of the pci will enhance future probabilistic seismic hazard assessment and thus contribute to more reliable seismic risk mitigation programs

global patterns of radiated seismic energy and apparent stress radiated energies from shallow earthquakes with magnitudes 5 8 that occurred between 1986 and 1991 are used to examine global patterns of energy release and apparent stress in contrast to traditional methods which have relied upon empirical formulas these energies are computed through direct spectral analysis of broadband seismic waveforms velocity squared spectra of body waves are integrated after they have been corrected for effects arising from depth phases frequency dependent attenuation and focal mechanism the least squares regression fit of energy es to surface wave magnitude ms for a global set of 397 earthquakes yields log es 4 4 1 5ms which implies that the gutenberg richter relationship overestimates the energies of earthquakes the least squares fit between es and seismic moment m0 is given by the relationship es 1 6 10 5 m0 which yields 0 47 mpa as the average global value of apparent stress however the regression lines of both es ms and es m0 yield poor empirical predictors for the actual energy radiated by any given earthquake the scatter of data is more than an order of magnitude about each of the regression lines on the other hand global variations between es and mo while large are not random when subsets of es m0 are plotted as a function of seismic region and faulting type the scatter in data is substantially reduced the es m0 fits for many seismic regions and tectonic environments are very distinctive and a characteristic apparent stress c can be derived the lowest apparent stresses 3 0 mpa are associated with strike slip earthquakes that occur at oceanic ridge ridge transforms and in intraplate environments seaward of island arcs intermediate values of apparent stress 1 5 a 3 0 mpa are associated with strike slip earthquakes at incipient or transitional plate boundaries in general the dominant mode of failure for a tectonic environment is associated with the faulting type that has the lowest apparent stress an energy magnitude me can complement moment magnitude mw in describing the size of an earthquake me being derived from velocity power spectra is a measure of seismic potential for damage mw being derived from the low frequency asymptote of displacement spectra is more physically related to the final static displacement of an earthquake when earthquake size is ranked by moment a list of the largest events is dominated by earthquakes with thrust mechanisms when earthquake size is ranked by energy the list of the largest events is dominated by strike slip earthquakes

on the number and spacing of faults orogens and rift zones have a finite number of regional faults the accretionary prisms analysed here have a number of thrusts 50 whereas extensional areas have a number of normal faults ranging between six and 44 the average spacing of thrusts is between 5 and 25 km spacing of normal faults is more restricted into two peaks at 25 29 km and 4 6 km in which the latter is the most common the number and spacing of faults appear to be mainly controlled by the depth of the decollement plane which seems to be more variable in compressive settings with respect to rift zones basementinvolved orogens present fewer and more spaced thrusts by contrast a greater number of thrusts with shorter spacing characterize thin skinned thrust belts the shallower the decollement is the stronger it appears to control the palaeogeography in the sense of rheological lateral variations in the sedimentary cover

the cenozoic graben system of sardinia italy geodynamic evolution from new seismic and field data abstract a tectono sedimentary scenario for the southern sardinia italy cenozoic graben system is proposed using field observations and the interpretation of onshore and offshore seismic profiles the major structural events are tied to the general geodynamic evolution of the western central mediterranean thus the extensional late oligocene aquitanian event is a consequence of an apenninic westward subduction process associated with a volcanic arc 29 30 to 15 16 my which is particularly well exposed in sardinia deposition of sub aerial clastics was followed by transgression of the rift depression at the beginning of the aquitanian subduction terminated at the opening of the oceanic provencal basin and the rotation of sardinia corsica during burdigalian time 20 21 to 15 16 my the messinian compressional event ne sw oriented documented from microtectonic data strongly affected the oligo miocene basin the superimposed plio quaternary campidano graben which is probably related to the formation of the tyrrhenian basin contains more than 600 m of syntectonic deposits a change in polarity of the master faults bounding the oligo miocene rift created a central horst type twist zone separating two depocenters in the oristano and cagliari regions emplacement of large volcanic bodies and inversion of the basin during the messinian in cagliari area has reduced the areas with potential for hydrocarbon exploration the two remaining prospective zones are the oristano sub basin and the offshore south of cagliari where burial of lower miocene marine organic matter may have been sufficient to generate hydrocarbons potential reservoirs could be pre rift mesozoic or eocene strata but are mainly excellent miocene sands derived from erosion of the granitic basement in tilted blocks

a strong topographic valley effect in amt and vlf r measurements summary the topographic effects of sharply embanked deep and narrow valleys cut in resistive rock are very strong on mt amt and vlf r soundings when the widths of the valley floors are of the same order as the skin depths the electromagnetic responses of such 2 d valley models have been calculated by means of a finite element numerical method for both e and h polarization field configurations the most striking effects occur in the h polarization geometry where the entire current flow must round the bottom of the valley in concentrated bundles thereby creating large electric fields and high apparent resistivities ph with e polarization there is a sharp reduction of both electric and magnetic fields at the centre of the valley but the reduction is stronger for the electric field so the apparent resistivity pe decreases below the matrix resistivity when the bottom of the valley contains a fill of conducting material like sediments or alluviums it is found that both ph and pe are dramatically reduced to values below even the fill resistivity these effects are studied for a variety of ratios between skin depth and width of valley floor

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

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

geodetic strain rate and earthquake size new clues for seismic hazard studies abstract earthquakes deliver in few seconds the elastic energy accumulated in hundreds of years where and when will be the next earthquake remains a difficult task due to the chaotic behaviour of seismicity and the present lack of available tools to measure the threshold of the crustal strength however the analysis of the background strain rate in italy and the comparison with seismicity shows that larger earthquakes occur with higher probability in areas of lower strain rate we present a statistical study in which a relationship linking the earthquake size magnitude and the total strain rate sr is found we combine the information provided by the gutenberg richter law gr of earthquake occurrence and the probability density distribution of sr in the italian area following a bayesian approach we found a simple family of exponential decrease curves describing the probability that an event of a given size occurs within a given class of sr this approach relies on the evidence that elastic energy accumulates in those areas where faults are locked and the sr is lower therefore in tectonically active areas sr lows are more prone to release larger amount of energy with respect to adjacent zones characterised by higher strain rates the sr map of italy compared with 5 years seismicity supports this result and may become a powerful tool for identifying the areas more prone to the next earthquakes

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

strain rate relaxation of normal and thrust faults in italy summary we find that geodetic strain rate sr integrated with the knowledge of active faults points out that hazardous seismic areas are those with lower sr where active faults are possibly approaching the end of seismic cycle sr values estimated from gps velocities at epicentral areas of large historical earthquakes in italy decrease with increasing elapsed time thus highlighting faults more prone to reactivation we have modelled an exponential decrease relationship between sr and the time elapsed since the last largest earthquake differencing historical earthquakes according to their fault rupture style then we have estimated the characteristic times of relaxation by a non linear inversion showing that events with thrust mechanism exhibit a characteristic time 990yr about three times larger than those with normal mechanism assuming standard rigidity and viscosity values we can infer an average recurrence time of about 600yr for normal faults and about 2000yr for thrust faults

li rich zincostaurolite and its decompression related breakdown products in a diaspore bearing metabauxite from east samos greece an emp and sims study li h rich zincostaurolite locally formed at a metabauxite marble contact along the eastern coast of samos during early alpine high p low t metamorphism the staurolite which probably grew from gahnite cookeite kaolinite pyrophyllite diaspore and minor fe oxide occurs as prismatic crystals up to several mm long in a calcite matrix it has an unusual composition with 7 5 12 9 wt zno 1 0 4 9 wt feo 0 66 0 82 wt li 2 o up to 2 6 wt nio and 0 59 wt coo and 0 32 wt mgo calculated structural formulae point to high h 2 o contents 4 14 h atoms per 48 oxygen atoms during late alpine uplift of the samos rocks the staurolite was at greenschist facies conditions variably replaced by bluish cobaltoan gahnite x zn 0 82 white na ca li mica ni rich chlorite x ni 0 42 0 59 zincohogbomite x zn 0 68 0 80 diaspore and fe hydr oxide detailed emp work and determination of li in staurolite and mica by sims indicates systematic zn fe mg ni co li partitioning between staurolite and its decomposition products implying local scale chemical equilibrium balanced reaction equations based on mineral chemical data indicate that the breakdown of staurolite occurred largely isochemically with only introduction of water na and ca into the reacting system the breakdown of high p staurolite during uplift and decompression is thought to be related to the sensitivity of its complex crystal chemistry to changes in physico chemical conditions

the dilatancy diffusion hypothesis and earthquake predictability the dilatancy diffusion hypothesis was one of the first attempts to predict the form of potential geophysical signals that may precede earthquakes and hence provide a possible physical basis for earthquake prediction the basic hypothesis has stood up well in the laboratory where catastrophic failure of intact rocks has been observed to be associated with geophysical signals associated both with dilatancy and pore pressure changes in contrast the precursors invoked to determine the predicted earthquake time and event magnitude have not stood up to independent scrutiny there are several reasons for the lack of simple scaling between the laboratory and the field scales but key differences are those of scale in time and space and in material boundary con ditions coupled with the sheer complexity and non linearity of the processes involved upscaling is recognized as a difficult task in multi scale complex systems generally and in oil and gas reser voir engineering specifically it may however provide a clue as to why simple local laws for dila tancy and diffusion do not scale simply to bulk properties at a greater scale even when the fracture system that controls the mechanical and hydraulic properties of the reservoir rock is itself scale invariant

the effect of seafloor topography on magnetotelluric fields an analytical formulation confirmed with numerical results summary magnetotelluric fields and impedances are distorted at undulating interfaces an analytical formulation is presented to calculate magnetotelluric effects in the presence of a sinusoidal interface in contrast to previous analytical approaches this formulation is not based on perturbation theory it is applicable to observations both on land and on the seafloor electric and magnetic fields as well as apparent resistivities and phases are calculated on the interface the topographic distortion on land mainly influences the tm mode data where the electric field is perpendicular to the geological strike both the tm mode and the orthogonal te mode data are distorted on the seafloor systematic parameter tests indicate which modes are independent of the period and the conductivity contrast provided that the induction depths are large relative to the amplitude of the topography the differing physics of the seafloor and land surface is illustrated by plotting current streamlines for the land model contour lines diverge below a hill and converge below a valley for the seafloor model electric currents mainly flow in the conductive sea water contour lines converge above a hill and diverge above a valley numerical results derived from finite element modelling support the analytical solutions streamlines of the electric current derived from a model for the central andes illustrate the connection between a graphical display of electromagnetic fields and an algebraic sensitivity analysis of the magnetotelluric impedance tensor