paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

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

geodynamic evolution of the mauritanide bassaride and rokelide orogens west africa abstract the mauritanide bassaride and rokelide orogens occur along the western edge of the west african craton these record a polyphase tectonothermal evolution including pan african i c 650 ma and pan african ii c 550 ma events together with local hercynian late paleozoic overprinting pan african i activity is most penetratively recorded in the bassarides and resulted from late proterozoic collision of a western continental structural block pan african ii orogenesis increases in intensity from the southern mauritanides through the bassarides and dominates the rokelides this tectonothermal activity appears to reflect collision of the west african and guyanean cratons during assembly of gondwana hercynian activity is concentrated along the margin of a western continental block which underwent relative eastward translation during collision of gondwana and laurentia this resulted in extensive thrusting of intracontinental foreland sequences external nappes and more ductile imbrications of pre deformed and metamorphosed late proterozoic rift sequences and western calc alkaline igneous successions internal nappes

geodetic strain in peninsular italy between 1875 and 2001 1 we determine geodetic strain in peninsular italy by the gps reoccupation of the first order triangulation network of italy installed from 1860 the uncertainties in the original measurements about 3 ppm and the time span between the two observations imply that tectonic signals larger than about 0 03 ppm yr are resolvable along the apenninic belt where the largest earthquakes are concentrated the geodetic deformation has a clear and consistent strain pattern between adjacent regions well above the uncertainties and shows a pervasive ne sw extension along the tyrrhenian and adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements seismic deformation calculated over the same time interval agrees well with estimated extensional direction but the magnitudes of geodetic and seismic strain differ suggesting that in part of the apennines significant strain accumulation over the past 130 years may not have been released in earthquakes

crustal structure at colliding plates boundary from receiver functions analysis a close look beneath the northern apennines italy 1 teleseismic receiver functions from a seismic experiment in a small area of the northern apennines italy reveal strong crustal structure variations across the mountain chain receiver functions imaging and full waveform inversion technique are used to constrain the s wave velocity profile in the crust and to reconstruct the geometry of the main seismic discontinuities at depth we highlight the presence of the main mode converting discontinuities in the study area most importantly we identify the crust mantle transition which is represented almost everywhere in the study area by a sharp s wave velocity increase over 4 km s at depth between 35 and 40 km however farther west the s wave velocity reaches values typical for the sub crustal mantle at about 54 km depth possibly marking the locus where the subducting adriatic plate starts to dip into the mantle here the presence of a shallower discontinuity at about 36 km depth with s velocity values around 4 km s can be interpreted as the moho signature of the overriding tyrrhenian plate

the structure of the moho in the northern apennines evidence for an incipient slab tear fault abstract this study investigates the geometry of the crust mantle boundary along the northern apennines italy and its relationship to the tectonic evolution of a retreating subduction system using receiver function analysis from teleseismic records the moho depth was computed beneath 26 seismic stations located in key positions along the orogen the results show a relatively shallow 20 km moho in the tyrrhenian side as expected from an extended overriding plate and a deeper moho 40 km in the subducted adriatic plate sw dipping 15 45 beneath the chain stations deployed on the northeastern edge of the plio quaternary extensional basins provide maximum moho depth estimates thus supporting the hypothesis that these basins define the zone where the two plates separate at depth in addition an abrupt change in the moho depth is recognized along strike of the orogen attributed to a 45 km wide trench normal deformation zone that crosses the northern apennines in the proximity of the livorno sillaro lineament this zone is interpreted as an incipient lithospheric tear fault which accommodates varying rates of trench retreat along the length of the subduction zone

response of moist convection to multi scale surface flux heterogeneity we investigate the response of moist convection to the spatial variation of surface sensible heat flux shf in a mesoscale domain during the evolution of the afternoon convective boundary layer cbl using large eddy simulation the surface shf heterogeneity in the domain is analytically created as a function of the spectral slope in the wavelength range from a few tens of kilometres to a few hundreds of metres in the shf spectrum on a log log scale assuming surface energy balance and spatially uniform available energy the prescribed shf has a phase lag of 180 with respect to the latent heat flux lhf in the domain two sets of three simulations are forced by heterogeneous surface shf fields which are characterized by similar statistics one set however is created with a spectral slope of k 3 where k is wave number and the other with a slope of k 2 all of the simulations are integrated with the same observation based initial sounding favourable for moist convection in all of the k 3 slope cases early non precipitating shallow clouds further develop into deep thunderstorms but in all of the k 2 slope cases only shallow clouds develop a key process in the transition to deep convection is the formation of a mesoscale pool of cool and moist air just above the top of the cbl this high relative humidity rh pool is formed by repeated deep penetrations of turbulent plumes into the free atmosphere over a mesoscale surface of high shf these cross scale fluxes the vertical transports of mesoscale moisture and heat fluctuations by turbulent updraughts are critical for the formation of the mesoscale pool of high rh however these cross scale fluxes are cancelled out in the process of averaging and thus appear negligible in the vertical profiles of domain averaged moisture and heat fluxes

variance estimate in frequency domain deconvolution for teleseismic receiver function computation summary in this study the problem of estimating the receiver function variance is discussed the receiver function computation is performed through a frequency domain deconvolution oldenburg 1981 of the vertical seismogram from the radial and tangential seismograms this technique requires a knowledge of the noise contaminating the seismic signals and provides an estimate of the receiver function variance oldenburg 1981 modelled this noise as additive amnion 1992 proposed to estimate the noise level from the power spectral density in a pre signal time window in this paper this approach is used jointly with an additional inversion which yields a sequence of spikes as a model for the true receiver function the resulting residual in a time window preceding the direct p pulse is used in order to evaluate the receiver function variance and the actual noise level involved in the frequency domain deconvolution this variance estimate is compared with the one provided by oldenburg s original method the application of this method to teleseismic recordings of earthquakes 5 1 mb 6 1 with similar backazimuths and distances shows that considering the additive noise only is not sufficient to explain the uncertainty measured from the pre signal in the receiver function moreover the estimated uncertainty seems to be independent of the seismic event magnitude suggesting a signal generated noise affecting the receiver function the proposed approach provides a variance estimate for a single receiver function allowing one to assess the statistical accuracy of its amplitudes in agreement with the uncertainty involved in a stacking procedure this is particularly useful when poor quality waveforms from relatively small earthquakes mb 5 1 are analysed and data from nearly co located events are not available for stacking

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

sensitivity of deep convection to terrain forcing over mediterranean islands the influence of mountainous islands on the initiation of deep convection is investigated using the consortium for small scale modeling cosmo model a case study and sensitivity analysis is performed for 26 august 2009 when moist convection occurred over both corsica and sardinia islands in the western mediterranean sea sensitivity runs with systematically modified topography are explored to evaluate the relative importance of the land sea contrast and the terrain height for convection initiation whereas no island precipitation is simulated when the islands are completely removed all simulations that represent these land surfaces develop convective precipitation although convection initiates progressively earlier in the day over taller islands the precipitation rates and accumulations do not show a fixed relationship with terrain height this is due to the competing effects of different physical processes firstly whereas the forcing for low level ascent increases over taller islands the boundary layer moisture supply decreases which diminishes the conditional instability and precipitable water secondly whereas taller islands enhance the inland propagation speeds of sea breeze fronts they also block these fronts mechanically and prevent them from reaching the island interior as a result the island precipitation is rather insensitive to island terrain height except for one particular case in which the island precipitation increases considerably due to an optimal superposition of the sea breeze and upslope flow comparing the two islands convective precipitation develops earlier over corsica due to its increased terrain height and reduced convective inhibition however precipitation amounts are substantially larger over sardinia where a stronger land sea contrast gives rise to a more intense and organized line of sea breeze convergence these results demonstrate the complexity of interactions between sea breezes and orography and reinforce that an adequate representation of detailed topographic features is necessary to account for thermally induced wind systems that initiate deep convection

contrasting accreted terranes in the southern appalachian orogen basement beneath the atlantic and gulf coastal plains and west african orogens abstract a variety of lithostratigraphic units may be outlined within the pre mesozoic crystalline basement of the atlantic and gulf coastal plains these include 1 a group of metamorphic rocks of variable grade together with deformed and retrogressed granite in southwestern alabama and southeastern mississippi wiggins uplift hornblende and biotite within higher grade units record 40ar 39ar post metamorphic cooling ages of 310 300 ma 2 a suite of contrasting igneous rocks granite basalt and agglomerate and serpentinite which occurs along the brunswick altamaha magnetic anomaly in southwestern alabama and 3 an extensive apparently coherent tectonic element the suwannee terrane comprised of undeformed granite in which biotite records 40ar 39ar post magmatic cooling ages of 530 525 ma low grade felsic metavolcanic rocks a suite of high grade metamorphic lithologies st lucie metamorphic complex in which hornblende yields 40ar 39ar post metamorphic cooling ages of 515 510 ma and a succession of lower ordovician middle devonian sedimentary rocks characterized by gondwanan fauna the west african orogens mauritanides bassarides and rokelides record a locally complex polyphase tectonothermal evolution the earliest event corresponded to westward rifting of a continental fragment from the west african craton at 700 ma this led to development of a rift facies lithotectonic succession which included sedimentary units and intracontinental igneous sequences rifting was limited and a western ensialic arc began to develop by 680 ma the associated convergence culminated in an episode of folding and metamorphism at 650 ma pan african i orogenesis following widespread deposition of late paleozoic glacial and flyschoid sediments a second tectonothermal event occurred between 550 and 500 ma pan african ii orogenesis the west african orogens were marked by general tectonic quiescence throughout most of the early and middle paleozoic late paleozoic 300 ma collision of gondwana and laurentia resulted in eastward translation of previously tectonized mauritanide units over their foreland and emplacement at highest structural levels of previously imbricated nappes which include sequences with uncertain palinspastic origins the late paleozoic hercynian transport was largely intracontinental and only westernmost portions of the exposed mauritanides record an associated penetrative tectonothermal overprint characteristics of pre mesozoic basement units which comprise the suwannee terrane in the florida subsurface suggest they represent extensions of the bassaride rokelide orogen there is no apparent record of paleozoic tectonothermal activity in the suwannee terrane this contrasts markedly with penetrative late paleozoic reworking of basement units in the wiggins uplift this suggests that a major dextral transcurrent fault was active during the late paleozoic and that proximal basement units were directly involved in collisional aspects of pangea assembly the various basement units of the coastal plain are not correlative with any of the non laurentian terranes exposed in the southern appalachian orogen e g carolina terrane of the eastern piedmont which accreted in the ordovician devonian to exterior positions along the eastern margin of the north american craton these exotic appalachian terranes were transported into their present structural positions during late paleozoic collision of gondwana and laurentia they are separated from gondwanan elements of the suwannee terrane by a suture approximately marked by the brunswick altamaha magnetic anomaly

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

influence of the wind profile on the initiation of convection in mountainous terrain a number of days with small precipitating convective cells were investigated using weather radars during the cops convective and orographically induced precipitation study field campaign in the region of the vosges and the rhine valley in central europe depending on the weather situation two distinct mechanisms could be identified for the initiation of convection on some days cells were initiated over the ridge of the vosges whereas on other days cells were initiated in the lee of the vosges the initiation of convection appeared to be concentrated in a few favourable locations using the froude number it was possible to describe the two distinct mechanisms when the froude number was low the flow was diverted around the vosges and thermally driven convergence at the ridge initiated convection whereas when the froude number was high the flow passed through mountain gaps and then converged on the lee side with the flow in the rhine valley the convergence on the lee side was enhanced at locations where the outflows through valleys converged low froude numbers were accompanied by weak winds varying with height whereas high froude numbers were observed during situations with stronger southwesterly winds increasing with height

flow over heated terrain part ii generation of convective precipitation previous studies have shown that thunderstorms in the rocky mountain region have preferred areas in which to form there has been some indication that these areas depend on the midtropospheric wind direction a nonhydrostatic model with a terrain following horizontal grid is employed to investigate the initiation of precipitating convection over heated topography horizontally homogeneous meteorological conditions with no directional shear in the vertical wind profile are used the numerical simulations indicate that precipitating convection was more likely to be generated downwind of ridges than upwind of them initiation of these storms was more likely downwind of ridges with their long axis parallel to the wind direction than downwind of ridges with their long axis perpendicular to the wind direction in part i of this study it was shown that heating induced convergence is larger downwind of a ridge with its longer axis parallel to the wind direction for the orographic configuration of the rocky mountains total precipitation is maximized for southerly and northwesterly winds slower wind speeds are more likely and faster wind speeds are less likely to produce convective storms soundings with larger instability are more likely to produce convection the soundings with a greater temperature lapse rate produce more initiation locations and soundings with greater moisture produce greater amounts of precipitation even though a number of assumptions were made for this study the authors believe the results explain a significant amount of the observed variability in the initiation locations of precipitating convection in the rocky mountains during the summer because of the theoretical basis for this work detailed in part i of this study the authors believe it should explain convective initiation in other mountainous areas that are subject to strong solar heating

deep crustal roots beneath the northern apennines inferred from teleseismic receiver functions abstract teleseismic waveforms recorded by a regional array crossing the northern italian peninsula and northern corsica are analyzed using the receiver function technique to determine the first order crustal structure the receiver function approach is used to isolate receiver side ps conversions generated at the crust mantle boundary and any major velocity discontinuity beneath the stations we used the time delay between the direct p wave and the ps wave converted at the moho discontinuity to infer crustal thickness beneath the stations the crust mantle boundary is estimated at 25 1 km of depth in northern corsica 20 2 km beneath the elba island and 20 to 24 2 km beneath tuscany in the eastern portion of the array moho depth increases from 28 2 km beneath the adriatic coast to 49 3 km beneath the apennine chain in a distance of about 100 km a double ps conversion produced beneath the val tiberina graben to the west of the apennines corresponds to interfaces as deep as 20 2 and 52 2 km this observation supports the hypothesis of partial overlapping between the shallow tuscan moho and the deeper adriatic moho the westward deepening of the adriatic moho beneath the northern apennines can be explained by lithosphere delamination that has dragged downward the adriatic lower crust the deep crustal root estimated beneath the northern apennines indicates that this portion of the chain is isostatically overcompensated

lithospheric sources of north florida usa tholeiites and implications for the origin of the suwannee terrane abstract sr nd and pb isotopic data for mesozoic tholeiites from six drillholes in northern florida suwannee terrane indicate derivation of the magmas from a source that was slightly incompatible element enriched with respect to bulk earth probably continental lithospheric mantle variably contaminated by more enriched crust initial isotopic compositions of the florida tholeiites show a considerable range 87 sr 86 sr 0 7059 to 0 7097 end 4 6 to 0 1 206 pb 204 pb 18 30 to 18 65 207 pb 204 pb 15 57 to 15 66 and 208 pb 204 pb 38 22 to 38 35 these compositions are distinctly different from those of mesozoic alkali basalts from the subsurface of southwestern florida heatherington a l mueller p a 1991 geochemical evidence for triassic rifting in southwestern florida tectonophysics 188 291 302 it is suggested that the north florida tholeiites were derived from within the continental lithosphere in contrast with mesozoic volcanic rocks from southwestern florida which have been previously suggested to be related to a mantle plume sm nd isotope systematics suggest derivation of the tholeiites from a 1 ga source a similar age to that proposed by pegram pegram w j 1990 development of continental lithospheric mantle as reflected in the chemistry of the mesozoic appalachian tholeiites usa earth and planetary science letters 97 316 331 for the source of tholeiitic basalts within the carolina terrane this supports proterozoic tectonic models which suggest that both the suwannee and carolina terranes had affinities with south american portions of gondwana containing 1 ga crust specifically the sunsas rondonian province nance murphy 1996 mueller p a kozuch m heatherington a l wooden j l offield t w koeppen r p klein t l nutman a p 1996 evidence for mesoproterozoic basement in the carolina terrane and speculations on its origin in nance r d thompson m d eds avalonian and related peri gondwanan terranes of the circum north atlantic gsa special paper 304 pp 207 218

on thermally forced circulations over heated terrain abstracta combination of analytical and numerical models is used to gain insight into the dynamics of thermally forced circulations over diurnally heated terrain solutions are obtained for two layer flows representing the boundary layer and the overlying free troposphere over an isolated mountainlike heat source a scaling based on the linearized boussinesq system of equations is developed to quantify the strength of thermally forced updrafts and to identify three flow regimes each with distinct dynamics and parameter sensitivities this scaling closely matches corresponding numerical simulations in two of these regimes the first characterized by a weakly stable boundary layer and significant background winds and the second by a strongly stable boundary layer in the third regime characterized by weak winds and weak boundary layer stability this scaling is outperformed by a fundamentally different scaling based on thermodynamic heat engines within this regime the inability of wind ventilation or

idealized large eddy and convection resolving simulations of moist convection over mountainous terrain abstracton summertime fair weather days thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain this study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized double ridge system in large eddy less and convection resolving crm simulations first les at a horizontal grid spacing of 200 m is employed to analyze the developing circulations and associated clouds and precipitation second crm simulations at horizontal grid length of 1 km are conducted to evaluate the performance of a kilometer scale model in reproducing the discussed mechanisms mass convergence and a weaker inhibition over the two ridges flanking the valley combine with water vapor advection by upslope winds to initiate deep convection in the crm simulations the spatial distribution of clouds and precipitation is generally well captured ho

possible fault plane in a seismic gap area of the southern apennines italy revealed by receiver function analysis 1 unusual features in teleseismic receiver function computed at a single three component seismic station reveal the presence of a dipping interface in the shallow crust with a pronounced seismic velocity contrast in the campania lucania region southern apennines italy the locus of this finding is the pergola melandro basin situated between the maximum intensity areas of two of the most destructive earthquakes reported in the italian seismic catalogue the m 7 0 val d agri earthquake 1857 and the ms 6 9 irpinia earthquake 1980 this area is not associated with known historical events and for this reason is currently object of investigation as a potential seismic gap where the probability of future ruptures is higher than in surrounding regions also for the static stress increase caused by the two above mentioned earthquakes through an inversion procedure applied to the computed receiver functions we are able to satisfactorily constrain the strike dip depth and velocity contrast of this crustal discontinuity whose geometric characteristics closely match those proposed by some authors for the sources of the two neighboring earthquakes we argue that the detected interface is the seismogenic source which fills the gap the findings of this study could open new perspectives both in the study of seismic gap areas and in the identification of historical earthquake sources offering a new and effective tool to locate investigate and constrain buried or unknown faults

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

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

orographic precipitation and air mass transformation an alpine example a case of orographic precipitation in the alps on 20 september 1999 was studied using several models along with rain gauge and radar data the objective of the study is to describe the orographic transformation of an air mass including multi scale aspects several new and some conventional diagnostic quantities are estimated including drying ratio precipitation efficiency buoyancy work condensed water residence time parcel changes in heat moisture and altitude and dominant space and time scales for the case considered the drying ratio was about 35 precipitation efficiency values are ambiguous due to repeated ascent and descent over small scale terrain the sign of buoyancy work changed during the event indicating a shift from stratiform orographic to weak convective clouds cloud water residence times are different for the two mesoscale models 400 compared to 1000 s due to different cloud physical formulations the two mesoscale models agree that the dominant spatial scale of lifting and precipitation is about 10 km smaller than the scale of the main alpine massif trajectory analysis of air crossing the alps casts doubt on the classic model of fohn few parcels exhibit classic pattern of moist ascent followed by dry descent parcels that gain latent heat descend only briefly before rising into the middle troposphere parcels that descend along the lee slope originate in the middle troposphere and gain little or even lose latent heat during the transit as parcels seek their proper buoyancy level downstream a surprising scrambling of the air mass occurs radar data confirm the model prediction that the rainfall field is tightly controlled by local terrain on scales as small as 10 km rather than the full 100 km cross alpine scale a curious pulsing of the precipitation is seen indicating either drifting moisture anomalies or weak convection copyright 2003 royal meteorological society

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

boundary layer energy transport and cumulus development over a heated mountain an observational study abstract aircraft and surface measurements of the boundary layer transport of mass and moisture toward an isolated heated mountain are presented the data were collected around the santa catalina mountains in arizona 20 30 km in diameter during the north american monsoon on days with weak winds and cumulus congestus to cumulonimbus development over the mountain flights in the boundary layer around the mountain and surface station data indicate that mountain scale anabatic surface wind generally develops shortly after sunrise peaking at 1 m s 1 in strength close to solar noon there is some evidence for a toroidal heat island circulation with divergence in the upper boundary layer the aircraft data and mainly the diurnal surface temperature and pressure patterns confirm that this circulation is driven by surface heating over the mountain three case studies suggest that growth spurts of orographic cumulus and cumulonimbus are not preceded by enhanced mountain scale mass convergence near the surfac

40ar 39ar polyorogenic mineral age record in the northern mauritanide orogen west africa abstract northern segments of the mauritanide orogen in the akjoujt region are dominated by suprastructural nappe complexes these structurally overlie other tectonic elements including 1 autochthonous parautochthonous foreland units composed of late proterozoic late paleozoic frasnian sedimentary cover sequences and unconformably underlying crystalline basement late archean middle proterozoic of the west african shield 2 parautochthonous successions largely represented by low grade metasedimentary rocks and 3 allochthonous infrastructural complexes with characteristics similar to those of late proterozoic early paleozoic pan african tectonic elements exposed in central and southern parts of the mauritanide orogen amphibole from various structural levels of the ijibiten and akjoujt suprastructural nappe complexes generally display internally discordant saddle shaped 40 ar 39 ar release spectra suggestive of extraneous excess argon contamination one sample records a well defined intermediate temperature plateau of 2420 ma muscovite within lower and intermediate structural levels of the complexes displays variably discordant 40 ar 39 ar age spectra which suggest that variable thermal rejuvenation of older up to 2600 ma mineral systems occurred during a ca 310 300 ma metamorphism uppermost structural levels of the complexes are represented in part by penetratively mylonitic metagranite muscovite within these rocks displays internally concordant 40 ar 39 ar age spectra which define plateau ages of 300 310 ma there is no indication in either amphibole or muscovite results of any late proterozoic early paleozoic pan african thermal record together with field relationships the 40 ar 39 ar results suggest that structural units of the suprastructural nappe complexes are in part composed of variably overprinted basement rocks these structurally overlie allochthonous pan african sequences and therefore must have been derived west of and now largely conceal the pan african orogen the complexes were transported eastward to higher structural levels during late paleozoic orogenesis the extent of late paleozoic thrusting within the akjoujt region contrasts with more limited transport distances documented southward in the orogen this contrast probably reflects a kinematic influence of the reguibat promentory of the west african shield which during the late paleozoic collision of gondwana and laurentia effected extensive compression in proximal sequences

application of theory to simulations of observed cases of orographically forced convective rainfall abstractin two recent papers the authors reported on numerical simulations of conditionally unstable flows past an idealized mesoscale mountain ridge these idealized simulations which were performed with a three dimensional explicitly cloud resolving model allowed the investigation of simulated precipitation characteristics as a function of the prescribed environment the numerical solutions were carried out for a uniform wind flowing past a bell shaped ridge and using an idealized unstable sounding with prescribed values of the relevant parameters in the present work the application of these theoretical results to observed cases of orographically forced convective rainfall including the big thompson flood 1976 colorado the oahu flood 1974 hawaii and the gard flood 2002 france is reported specifically numerical simulations have been carried out using observed and idealized soundings relevant to these cases but with idealized topography it is found that using the observed soundings but

the evolution of convective storms initiated by an isolated mountain ridge abstractthe evolution of convective storms over the black hills an isolated mountain ridge in south dakota and wyoming and a regional convection hotspot is investigated using a 10 yr observational climatology and quasi idealized numerical simulations radar observed diurnally forced mountain convection events are classified according to their maximum cell track length and duration which are quantified using an automated cell tracking algorithm environmental conditions during these events are obtained from operational radiosonde and model analysis data these data suggest that mountain forced convective cells generally struggle to survive in the convectively inhibited flow downwind of the black hills those cells that do survive downwind prefer environments with strong bulk vertical shear over the 0 6 km layer which favors organized multicellular or supercellular convection under slightly weaker shear the cells tend to dissipate rapidly as they propagate downwind relatively weak winds aloft when c

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

emplacement age of post tectonic granites in southern guinea west africa and the peninsular florida subsurface implications for origins of southern appalachian exotic terranes the coyah granite of guinea intruded western portions of the rokelide orogen following a tectonothermal event at ca 550 ma it records a biotite muscovite plus whole rock rb sr isochron age of 533 7 m y mswd 1 6 which is interpreted to closely date crystallization the osceola granite represents a major lithotectonic element in the pre cretaceous crystalline basement of peninsular florida five biotite concentrates from cuttings recovered from four wells penetrating the pluton record 40ar 39ar plateau ages ranging between 527 4 1 9 m y and 534 6 2 0 m y petrographic characteristics of the four samples suggest relatively rapid post magmatic cooling and the plateau ages are interpreted to closely date emplacement of the pluton similarities in age and petrographic characteristics combine to suggest that the coyah and osceola granites were initially part of a sequence of plutons emplaced along the northwestern margin of the gondwana continent portions of this terrane amalgamated with laurentia during late paleozoic assembly of pangea various exotic lithotectonic terranes which had previously accreted or were at least proximal to the north american craton were transported to their present structural position in the southern central appalachian orogen during this collision

crustal structure in the southern apennines from teleseismic receiver functions while the upper crustal structure of the southern apennines is known lack of control on the deep structure allows competing thin skinned and thick skinned models of the orogen in thin skinned models the detachment decouples a stack of rootless nappes from the basement in thick skinned models basement is involved in the most recent phase of thrusting to examine crustal structure we use teleseismic data from the calabria apennine tyrrhenian subductionaccretion collision network cat scan array in southern italy we use receiver functions rf processed into a common conversion point stack to generate images of the crust interpretation and correlation to geological structure are done using inversions of individual station rfs we focus on a shallow discontinuity where p to s conversions occur in the foreland it corresponds to velocity jumps between carbonate and clastic strata with basement a similar interpretation for the apennines provides the most parsimonious explanation and supports a thick skinned interpretation in a thick skinned reconstruction the amount of shortening is much smaller than for a thin skinned model this implies considerably less pliocene pleistocene shortening across the apennines and suggests an east southeast motion of the calabrian arc subparallel to the southern apennines rather than a radial expansion of the arc

effects of lateral variations of crustal rheology on the occurrence of post orogenic normal faults the alto tiberina fault northern apennines central italy abstract the northern apennines na are characterized by formerly compressive structures partly overprinted by subsequent extensional structures the area of extensional tectonics migrated eastward since the miocene the youngest and easternmost major expression of extension is the alto tiberina fault atf we estimate 2d rheological profiles across the na and conclude that lateral rheological crustal variations have played an important role in the formation of the atf and similar previously active faults to the west lithospheric delamination and mantle degassing resulted in an easterly migrating extension compression boundary coinciding at present with the atf where i the thickness of the upper crust brittle layer reaches a maximum ii the critical stress difference required to initiate faulting at the base of the brittle layer is at a minimum and iii the total strengths of both the brittle layer and the whole lithosphere are at a minimum although the location of the fault is correlated with lithospheric rheological properties the rheology by itself does not account for the low dip 20 of the atf two hypotheses are considered a the low dip of the atf is related to a rotation of the stress tensor at the time of initiation of the fault caused by a basal shear stress 100 mpa possibly related to corner flow associated with delamination or b the low dip is associated to low values of the friction coefficient 0 5 coupled with high pore pressures related to mantle degassing our results establishing the correlation between crustal rheology and the location of the atf are relatively robust as we have examined various possible compositions and rheological parameters they also provide possible general indications on the mechanisms of localized extension in post orogenic extensional setting the hypotheses to account for the low dip of the atf on the other hand are intended simply to suggest possible solutions worthy of further study

the rokelides of west africa pan african aulacogen or back arc basin abstract a reassessment of the stratigraphy structure and metamorphism of the pan african rokelides tectono thermal belt in senegal guinea bissau guinea sierra leone and liberia indicates that the belt developed not as a plate margin collision orogen but as either an aulacogen or a back arc basin oblique to the main trend of the west african fold belt the main southern part of the late proterozoic to mid phanerozoic west african fold belt trends southwestwards via the koulountou belt of senegal and guinea bissau into south america where relics of pan african age occur within the andean cordilleras

passive seismology and deep structure in central italy in the last decade temporary teleseismic transects have become a powerful tool for investigating the crustal and upper mantle structure in order to gain a clearer picture of the lithosphere asthenosphere structure in peninsular italy between 1994 and 1996 we have deployed three teleseismic transects in northern central and southern apennines in the framework of the project geo modap european community contract ev5v ct94 0464 some hundreds of teleseisms were recorded at each deployment which lasted between 3 and 4 months although many analyses are still in progress the availability of this high quality data allowed us to refine tomographic images of the lithosphere asthenosphere structure with an improved resolution in the northern and central apennines and to study the deformation of the upper mantle looking at seismic anisotropy through shear wave splitting analysis also a study of the depth and geometry of the moho through the receiver function technique is in progress tomographic results from the northernmost 1994 and the central 1995 teleseismic experiments confirm that a high velocity anomaly hva does exist in the upper 200 250 km and is confined to the northern apenninic arc this hva already interpreted as a fragment of subducted lithosphere is better defined by the new temporary data compared to previous works based only on data from permanent stations no clear high velocity anomalies are detected in the upper 250 km below the central apennines suggesting either a slab window due to a detachment below southern peninsular italy or a thinner perhaps continental slab of adriatic lithosphere not detectable by standard tomography we found clear evidence of seismic anisotropy in the uppermost mantle related to the main tectonic processes which affected the studied regions either ne sw compressional deformation of the lithosphere beneath the mountain belt or arc parallel asthenospheric flow both giving nw se fast polarization direction and successive extensional deformation e w trending in the back arc basin of northern tyrrhenian and tuscany preliminary results of receiver function studies in the northern apennines show that the moho depth is well defined in the tyrrhenian and adriatic regions while its geometry underneath the mountain belt is not yet well constrained due to the observed high complexity

surface rupture of the 1857 southern italian earthquake in october 1862 robert mallet published an extensive study of a large earthquake that occurred on 16 december 1857 150 km south east of naples this event is one of the most destructive ever recorded in italy although continental earthquakes of similar size are almost invariably associated with surface faulting mallet did not identify any surface rupture and subsequent workers have also failed to find surface traces using satellite images and aerial photographs as a guide we examined two prominent quaternary normal fault systems in the field flanking the val d agri and the val di diano both trend nw se and dip to the sw the distribution of damage suggests that one or both moved in 1857 on one fault segment in val d agri we found a 2 5 m high scarp whose youthfulness and height suggest it is due to the 1857 earthquake comparison of the observed slip with rates derived from geomorphic evidence suggests a recurrence time for 1857 type events of about 3000 years while the new data we provide are consistent with the event having a magnitude of ms 7 0 there are also grounds for supposing it might have been bigger

character of the alleghanian orogeny in the southern appalachians part iii regional tectonic relations geological and geochronological studies in the eastern piedmont of the southern appalachians have documented a polyphase late paleozoic deformational chronology d 2 d 4 that is contemporaneous with the alleghanian orogeny recorded in the western appalachian foreland the scale and vergence of d 3 anticlinoria in the eastern piedmont are similar to those of anticlinoria in the western appalachians which are related to ramping of underlying thrust surfaces we suggest that the appalachian decollement extends southeastward beneath the entire piedmont province and that all of the piedmont rocks were displaced at least 175 km northwestward relative to north america during the alleghanian orogeny late paleozoic deformational effects in the eastern piedmont thus are considered cogenetic with alleghanian foreland deformation we interpret the alleghanian orogeny to be the result of oblique dextral convergence and collision of gondwana and laurentia

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

40ar 39ar mineral age record of polyphase tectonothermal evolution in the southern mauritanide orogen southeastern senegal 40 ar 39 ar incremental release mineral ages have been determined for several tectonostratigraphic units in southernmost portions of the maiuritanide orogen in senegal here middle proterozoic crystalline basement rocks of the west african craton are unconformably overlain by an upper proterozoic ca 1100 ma continental sedimentary succession madina kouta group transitional into volcanic and intercalated deep marine sediments tennesse group western portions of the volcano sedimentary unit were variably deformed and metamorphosed prior to deposition of an unconformably overlying upper precambrian lower cambrian sedimentary succession mali group muscovite within cleavage domains in the low grade metamorphic terrane records 40 ar 39 ar plateau dates of ca 655 665 ma and are interpreted to closely date the pan african i phase of orogenic activity the mali group itself was locally folded during a second phase of pan african tectonothermal activity which also affected a western calc alkaline volcanic plutonic sequence niokolo koba group igneous hornblende from several granites within this sequence displays internally discordant 40 ar 39 ar release spectra which record variably developed plateaus of ca 640 660 ma these are interpreted to approximately date initial postmagmatic cooling through 500 c and are consistent with a previously published rb sr whole rock iso chron crystallization age of 683 18 ma for one of the plutons associated calc alkaline volcanic and volcaniclastic rocks are more penetratively deformed muscovite that is aligned along a regional cleavage records 40 ar 39 ar plateau ages of ca 550 560 ma which are interpreted to closely date the pan african ii orogenesis widespread deposition of a molassic sequence youkoukoun formation occurred in the middle cambrian early ordovician this was disconformably overlain by upper ordovician upper devonian sedimentary rocks bove basin succession which are locally folded more significant late paleozoic tectonothermal activity is recorded in north westernmost portions of the study area where the calc alkaline upper proterozoic granites locally display penetrative mylonitic fabrics development of these fabrics is interpreted to be closely dated by the 40 ar 39 ar 270 to 280 ma plateau ages recorded by dynamically recrystallized muscovite developed along fluxion foliations these results allow demarcation of a late paleozoic tectonic front and permit correlations with genetically related events in southeastern portions of the appalachian orogen

moho depth and vp vs ratio in peninsular italy from teleseismic receiver functions 1 we present a new data set of moho depth estimates for peninsular italy obtained from receiver functions analysis and a grid search approach teleseismic records from 174 broadband seismic stations were used to compute the receiver function data set in general our results agree well with previous knowledge adding original information in many regions where previous data were lacking or uncertain we find broad regions with consistent moho depth namely 1 the peri tyrrhenian areas bordering the homonymous sea have a 20 to 25 km deep moho 2 the foreland regions adriatic apulia iblean with 30 35 km deep moho 3 the apennines belt where we find westward deepening of the adriatic moho down to 50 km depth that well delineate the westward adria subduction overlayed by the shallow tyrrhenian moho 4 calabria shows a flat 40 km deep moho suddenly dipping at high angle from the tyrrhenian coast westward defining the ionian subduction and 5 a clear separation between northern and southern apennines is marked by a region of almost flat moho possible evidence of a detached slab in between we also find that in the northern apennines the shallow tyrrhenian moho is continuous for more than 200 km from the sea to under the northern apennines with a generally flat geometry and a few undulations suggesting either the boudinage or episodic pulses of extension of the tyrrhenian crust during its pliocene quaternary stretching the eastward extent of the tyrrhenian moho below the apenninic belt approximately corresponds to the eastward extent of the observed extension in the upper crust as mapped by the normal faulting earthquakes in this portion of the apennines we interpret an intracrustal discontinuity sw dipping below the belt parallel to the adria moho as the top of the lower crust being subducted beneath the apennines the subcrustal earthquakes of this region down to 80 km depth seem to be located within this subducted crustal layer the southern apennines show the same general geometry of subduction as the northern arc although the former have a less defined on land extended region and no earthquakes in the lower crust uppermost mantle in between the central apennines present a different moho geometry no clear doubling of the two plates but rather a constant bilateral deepening possibly associated to a crustal root with no evidence of a subduction setting this reinforces the hypothesis of a detached slab in this area we also present the first large scale mapping of average crustal vp vs ratios for peninsular italy the results although representing averages over the whole crust enhance some interesting features the most evident are belts of high vp vs in the thinned crust of the apennines where extension has long been active in the quaternary probably as an effect of highly fractured rocks with abundant fluid circulation strong correlation exists between areas of high vp vs and quaternary volcanoes suggesting the presence of fluids at depth

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

thick skinned tectonics in the external apennines italy new evidence from magnetic anomaly analysis 1 we discuss the tectonic implications of a new residual magnetic map of the apennine belt adriatic apulian foreland obtained by integrating ground and offshore data sets chiappini et al 2000a negative anomalies are documented over the adriatic apulian foreland areas whereas the external apennine belt is characterized by a ubiquitous low amplitude 30 nt long wavelength positive anomaly in the central northern apennines three 100 km wide more intense 100 200 nt round shaped anomalies are superimposed to the long wavelength feature finally in the tyrrhenian sea and margins high intensity short wavelength positive negative couplets coincide with magmatic outcrops or bodies at shallow depth the low amplitude anomaly pattern over italy suggests that the magnetic basement beneath the triassic evaporites is ubiquitously incorporated in the external belt compressive fronts implying a thick skinned tectonic style for the external apennines the new residual magnetic map resolves the inconsistency between previous aeromagnetic data agip spa italia 1981 which suggested a lack of basement involvement in the apennine belt and recent seismic data which imaged deep reflectors penetrating the basement two magnetic models along ne sw transects in the northern and southern apennines suggest consistent structural styles in the northern apennines positive anomalies roughly coincide with the external compressive fronts although there are local second order differences between the belt front and the edges of the anomaly here the magnetic data show that the basement rises southwestward along the thrust fronts from 6 7 km depth in the adriatic foreland to 2 3 km depth in the axial belt where some exploration wells have penetrated basement within the belt front basement exhumation is inferred to occur along high angle low displacement thrust faults inverting preexisting normal faults in the southern apennines a remarkable positive magnetic anomaly is parallel with and tens of kilometers southwest of the belt front seismic data and oil wells show that the basement surface cannot be shallower in the belt than in the foreland therefore the observed magnetic anomaly is produced by strongly magnetic basement beneath the belt likely an internal crustal wedge tectonically interposed between the apulian carbonate sequences and basement

a tectonic linkage between the rodelide orogen sierra leone and the st lucie metamorphic complex in the florida subsurface the st lucie metamorphic complex comprises part of the non laurentian paleozoic suwannee terrane beneath the gulf and atlantic coastal plains of the southeastern united states hornblende concentrates prepared from cuttings from two deep test wells penetrating the complex display internally concordant 40 ar 39 ar incremental release spectra defining plateau ages of 510 8 pm 1 1 ma and 513 1 pm 1 8 ma which are interpreted to date post metamorphic cooling through temperatures required for intracrystalline argon retention the kasila group constitutes the western segment of the rokelide orogen in sierra leone four hornblende concentrates prepared from amphibolite within the kasila group yield 40 ar 39 ar ar plateau ages of 505 0 pm 5 2 508 2 pm 2 1 510 5 pm 2 6 and 546 1 pm 6 8 ma they are interpreted to date post metamorphic cooling through appropriate argon closure temperatures following a ca 550 560 ma pan african ii phase of tectonothermal activity

mountain volume control on deep convective rain amount during episodes of weak synoptic forcing abstractthermally driven upslope flows in mountainous areas provide favorable conditions for diurnal deep moist convection especially during episodes of weak synoptic forcing the present study inv

the crustal structure of the northern apennines central italy an insight by the crop03 seismic line in this paper the crop03 deep seismic reflection profile in the northern apennines is described and re considered in light of new geophysical data and interpretations made available in the last five years particularly from heat flow measurements aeromagnetics tomography active stress determination and passive seismology the crustal structure of the northern apennines is shown to be composed of two distinct domains to the west is the tyrrhenian domain and to the east is the adriatic domain these domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels in the tyrrhenian domain the upper oligocene lower miocene compressive structures are no longer recognizable because they are dissected by subsequent extensional tectonic features the seismic profile highlights the strong asymmetry of extensional deformation and the upper crust is affected by a set of six major east dipping low angle normal faults in the adriatic domain compressive tectonics have acted since the middle miocene and the pattern of shallow contractional structures is well preserved the geological interpretation of the seismic data supports a thick skinned style of deformation where the basement is involved in the major thrust sheets the good quality of seismic data also allows for determining the total shortening produced by the contractional structures in the central part of the profile at the border between the tyrrhenian and adriatic domains seismic data shows the presence of an intermediate sector the sector consists of a highly reflective window where the refraction data indicate a local doubling of the crust for about 30 km a scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the northern apennines since the upper oligocene

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

the rupture process of the 1980 irpinia italy earthquake from the inversion of strong motion waveforms abstract the distribution of slip and the behaviour of rupture propagation during the 23rd november 1980 irpinia earthquake ms 6 9 was investigated by analysing strong motion accelerograms the rupture was assumed to develop on a two dimensional purely normal fault whose geometry was constrained by geologic and geodetic data and by the aftershock space distribution theoretical seismograms have been computed using the isochron approach with a spatially variable slip intensity the asymptotic ray theory is used to evaluate the far field green functions the rupture model was updated following a trial and error approach the fit of observed waveforms with synthetic seismograms allowed several peculiarities in the rupture history to be pointed out the source model resulting from the solution of the forward waveform modelling was then used as starting model for the inversion of ground velocities therefore we performed a linearized inversion for slip velocity and rupture times on the fault by iteratively perturbing the assumed starting model the inverse problem is solved by means of a tomographic back projection technique the inferred source model shows a bilateral rupture which does not propagate uniformly away from the hypocentre the rupture velocity and the slip distribution on the fault plane are rather variable the solution confirms the shallow dislocation gap in the central part of the fault suggested by the behaviour of the surface rupture the results indicate that the rupture propagated northwestward along a further fault fragment for which no surface evidence is observed the aftershocks occurred mostly inside of or near to the edges of the source areas of maximum co seismic slip

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

crustal shortening and duplication of the moho in the northern apennines a view from seismic refraction data abstract a reappraisal of the dss refraction seismic campaigns of 1978 and 1974 in the northern apennines and the northern tyrrhenian sea after digitization of the original analog data and a new interpretation of crustal structures are presented in this paper the layering of the adria crust consists of a low velocity lower crust topped by a 6 7 km s horizon and an upper crust again formed by a low velocity layer capped by a faster one in the tuscany sector the crust mantle boundary and lower crust show attenuated velocities and a reduced thickness with respect to the adriatic counterpart these differences are due to the extensional tectonics restricted to tuscany and occurred in a high heat flow regime related to an uplifting astenosphere it has been confirmed that a deep thrust is responsible for moho doubling in correspondence with the zero bouguer anomaly line the tuscan moho overlaps the umbro marchean one for a length of about 30 km it is hypothesized that another shallower thrust involves upper crust in the mid tuscany range mt cetona and perugia massifs had their roots in the mantle and that subsequent extensional tectonics obliterated every trace of thrusting in lower crust and mantle rocks no conclusive proof of the existence of a european moho below a tuscan one in the area underneath elba has yet been found revision of dss data excludes the presence of a refractor reflector 60 km deep the same data however are compatible with the existence of a crust mantle boundary at 30 35 km depth

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

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

geochemical evidence for triassic rifting in southwestern florida abstract mesozoic rhyolites and basalts from three drillholes penetrating the pre cretaceous basement of southwestern florida were analyzed for their trace element and sr and nd isotopic compositions major and trace element abundances suggest the suite was erupted in an extensional environment and isotopic data indicate derivation primarily from aged enriched precambrian continental lithosphere combined to varying degrees with an asthenospheric component nd model ages show no significant difference in the age of the lithosphere from which these rocks and volcanic rocks of paleozoic age from north florida were derived arguing against major displacement across the peninsula including along proposed extensions of the jay fault and or bahamas fracture zone we suggest that the geophysically inferred boundary across the peninsula if a fault may have had a strong normal component consistent with the greater depth to basement south of the boundary in this view the southwestern florida mesozoic volcanic province sfmv may represent a part of a major triassic rift basin associated with the breakup of pangaea

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

crustal structure and moho geometry beneath the northern apennines italy 1 we used receiver functions rfs from broad band seismic stations to investigate the crustal structure of the northern apennines italy additionally we use data obtained in this study to provide initial constraints for a map of the moho depth of italy ten stations were deployed along a transect n75 e during the 1994 geomodap project rf analysis shows the presence of lateral variations in the crust we observed patterns of symmetric and anti symmetric converted phases from radial and tangential rfs vs back azimuth these patterns can be explained by the presence of dipping interfaces and or anisotropy within the crust we then inverted rfs following the inversion scheme proposed by sambridge 1999 the results show the presence of s velocity inversions in the lower crust beneath the apennines the upwelling of moho in the tyrrhenian area and its progressive deepening from the tyrrhenian sea toward the adriatic coast

cloud resolving simulations of deep convection over a heated mountain abstract cloud resolving numerical simulations of airflow over a diurnally heated mountain ridge are conducted to explore the mechanisms and sensitivities of convective initiation under high pressure conditions the simulations are based on a well observed convection event from the convective and orographically induced precipitation study cops during summer 2007 where an isolated afternoon thunderstorm developed over the black forest mountains of central europe but they are idealized to facilitate understanding and reduce computational expense in the conditionally unstable but strongly inhibited flow under consideration sharp horizontal convergence over the mountain acts to locally weaken the inhibition and moisten the dry midtroposphere through shallow cumulus detrainment the onset of deep convection occurs not through the deep ascent of a single updraft but rather through a rapid succession of thermals that are vented through the mountain convergence zone into the deepening cloud mass emerging t

insights on the seismogenic layer thickness from the upper crust structure of the umbria marche apennines central italy 1 we reconstruct the subsurface geology in a region of the northern apennines central italy where a protracted extensional sequence occurred in 1997 1998 with maximum magnitude m 6 0 our study is mainly based on the interpretation of three reprocessed seismic reflection profiles crossing the epicentral area which constrain the subsurface geometry to a depth of about 12 km where most of the shallow seismicity occurs comparing the subsurface setting with accurately determined earthquake locations we find that the seismicity is located entirely within the sedimentary cover and does not penetrate the underlying basement this is explained by considering that the sedimentary cover is rather thick and composed of relatively strong lithologies platform carbonates and evaporites while the upper part of the basement consists of weak phyllites and siliciclastic rocks this weak horizon is also evidenced by the low vp values measured in deep wells of the region its effect is to decouple the sedimentary cover from the crystalline basement where only microseismicity occurs our study indicates that local structure and stratigraphy can significantly influence the distribution of seismicity within the upper crust particularly in complex geological environments such as thrust and fold belts

numerical simulations of conditionally unstable flows over a mountain ridge abstractin two recent papers the authors performed numerical simulations with a three dimensional explicitly cloud resolving model for a uniform wind flowing past a bell shaped ridge and using an idealized unstable weisman klemp sounding with prescribed values of the relevant parameters more recently some observed cases of orographically forced wind profiles were analyzed showing that in order to reproduce larger rainfall rates it was necessary to initialize the sounding with low level flow toward the mountain with weak flow aloft as observed additional experiments using the weisman klemp sounding but with nonuniform wind profiles are performed here to identify the conditions in which the presence of a low level cross mountain flow together with calm flow aloft may increase the rain rates in conditionally unstable flows over the orography the sensitivity of the solutions to the wind speed at the bottom and the top of a shear layer and the effect of different mountain widths and heights are

effect of sinusoidal interfaces on teleseismic p wave receiver functions summary using the t matrix or extended boundary condition method we model seismic wave scattering from earth models with irregular interfaces this is motivated by numerous observations that surface and subsurface topography is responsible for the amplification and de amplification of seismic waves and the generation of coda waves we demonstrate that irregular moho and free surface scattering significantly affects teleseismic p wave receiver function waveforms receiver functions are routinely used to obtain detailed crustal and upper mantle structure for a layer over halfspace model we perform a sensitivity study on the effects of ray parameter interface roughness and wavelength receiver position and incident wave frequency content the free surface responses vary significantly with receiver position interface wavelength and with incident wave frequency content using frequency wavenumber analysis the coda is shown to contain scattered rg waves and s waves receiver functions are formed from the free surface responses by deconvolution and these are then inverted as synthetic data for plane layered velocity structure to show how scattered energy maps onto the final velocity models spurious structure models result with the amplitude of the spurious features for example low velocity zones decreasing with interface roughness the resulting velocity models also vary appreciably with receiver position

recognition of extraneous argon components through incremental release 40ar39ar analysis of biotite and hornblende across the grenvillian metamorphic gradient in southwestern labrador 40ar39ar incremental release ages have been determined for 15 hornblende and 20 biotite concentrates separated from rocks collected across the garnet and kyanite zones of grenvillian metamorphism in southwestern labrador most hornblende spectra from the kyanite zone are slightly discordant with low temperature increments yielding ages older than the ca 1000 ma date suggested for culmination of grenvillian metamorphism in the area however all the hornblende concentrates record well defined plateau ages these range from 968 to 905 ma across the kyanite zone and date times of diachronous post metamorphic cooling the discordant spectra are interpreted to result from low temperature liberation of excess 40ar components from grain margins two hornblende concentrates from the garnet zone display very discordant spectra total gas ages of 2100 and 3017 ma in which incremental dates systematically decrease during analysis this pattern of discordance suggests that excess argon components are inhomogeneously distributed throughout these hornblende grains most biotites from the garnet and kyanite zones record total gas or plateau ages in excess of 1000 ma 2066 857 ma reflecting the widespread presence of excess argon components because most of the 40ar39ar age spectra are internally concordant the ratios of excess 40ar relative to radiogenic 40ar must have been uniform in the various gas fractions liberated from each sample this is also reflected in the inability of isotope correlation diagrams to differentiate between excess radiogenic and atmospheric argon components the biotite total gas or plateau dates show marked local variation this is interpreted to indicate that the biotite grains were in contact with a post metamorphic intergranular vapor phase that was characterized by large and variable 40ar36ar ratios such ratios most likely resulted from widespread diffusion of the argon liberated from adjacent archean basement gneisses during the grenvillian metamorphic overprint

three dimensional moho topography in italy new constraints from receiver functions and controlled source seismology in complex tectonics regions seismological geophysical and geodynamic modeling require accurate definition of the moho geometry various active and passive seismic experiments performed in the central mediterranean region revealed local information on the moho depth in some cases used to produce interpolated maps in this paper we present a new and original map of the 3 d moho geometry obtained by integrating selected high quality controlled source seismic and teleseismic receiver function data the very small cell size makes the retrieved model suitable for detailed regional studies crustal corrections in teleseismic tomography advanced 3 d ray tracing in regional earthquake location and local earthquake tomography our results show the geometry of three different moho interfaces the european adriatic ionian and tyrrhenian the three distinct moho are fashioned following the alpine and apennines subduction collision and back arc spreading and show medium to high frequency topographic undulations reflecting the complexity of the geodynamic evolution

new cocorp profiling in the southeastern united states part i late paleozoic suture and mesozoic rift basin new cocorp profiling in the southeastern united states has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western georgia the zone is over 50 km wide and most of the reflections dip moderately steeply toward the south regional considerations suggest that this feature marks the late paleozoic suture between north america and africa where crossed by the cocorp survey the suture occurs beneath the north flank of the triassic early jurassic south georgia basin the main depocenter of the south georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill farther south the paleozoic suwannee basin sequence beneath northern florida is poorly imaged on the cocorp profiles however weak reflections suggest that these strata including basal felsic volcanics may have an aggregate thickness of about 6 km in north central florida at the northwest end of the cocorp traverse a prominent horizon imaged in the upper crust beneath the inner piedmont probably marks the southern appalachian detachment the detachment appears to be cut off by the towaliga fault implying that the towaliga fault is in part a down to the north normal fault intermittent moho reflections occur at 11 12 s two way time along the length of the cocorp survey indicating that the crust in the region has a roughly uniform thickness of about 33 36 km assuming an average crustal velocity of 6 km s

three dimensional evolution of simulated long lived squall lines abstract simulations of squall lines using nonhydrostatic convection resolving models have been limited to two dimensions or three dimensions with the assumption of along line periodicity the authors present 3d nonhydrostatic convection resolving simulations produced using an adaptive grid model where the lines are finite in length and the restriction to along line periodicity is removed the base state for the simulations is characterized by weak shallow shear and high convective available potential energy cape an environment in which longlived midlatitude mesoscale convective systems mcss are observed the simulated systems bear strong resemblance to many observed systems suggesting that large scale forcing absent in the horizontally homogeneous environment is not needed to produce many of the distinguishing features of midlatitude mcss in simulations without coriolis forcing the presence of line ends leads to mature symmetric systems characterized by a central region of strong convectio

mapping seismic anisotropy using harmonic decomposition of receiver functions an application to northern apennines italy 1 isotropic and anisotropic seismic structures across the northern apennines italy subduction zone are imaged using a new method for the analysis of teleseismic receiver functions rfs more than 13 000 p wave coda of teleseismic records from the 2003 2007 retreating trench extension and accretion tectonics retreat experiment are used to provide new insights into a peculiar subduction zone between two continental plates that is considered a focal point of mediterranean evolution a new methodology for the analysis of receiver functions is developed which combines both migration and harmonic decomposition of the receiver function data set the migration technique follows a classical common conversion point scheme and helps to focus on a crucial depth range 20 70 km where the mantle wedge develops harmonic decomposition of a receiver function data set is a novel and less explored approach to the analysis of p to s converted phases the separation of the back azimuth harmonics is achieved through a numerical regression of the stacked radial and transverse receiver functions from which we obtain independent constraints on both isotropic and anisotropic seismic structures the application of our method to the retreat data set succeeds both in confirming previous knowledge about seismic structure in the area and in highlighting new structures beneath the northern apennines chain where previous studies failed to clearly retrieve the geometry of the subducted interfaces we present our results in closely spaced profiles across and along the northern apennines chain to highlight the convergence of the tyrrhenian and the adriatic microplates which differ in their crustal structure where the adriatic microplate subducts beneath tuscany and the tyrrhenian sea a signature of the dipping adriatic moho is clearly observed beneath the tyrrhenian moho in a large portion of the forearc region in the area where the two mohos overlap our new analysis reveals the presence of an anisotropic body above the subducted moho there is a strong ps converted phase with anisotropic characteristics from the top of the adriatic plate to a depth of at least 80 km because the ps conversion occurs much deeper than similar ps phases in cascadia and japan dehydration of oceanic crust seems unlikely as a causative factor rather the existence of this body trapped between the two interfaces supports the hypothesis of lower crustal delamination in a postsubduction tectonic setting

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

the mississippi valley convection minimum on summer afternoons observations and numerical simulations abstractanalysis of 15 years of composite radar images over the continental united states reveals a distinct minimum of deep convection occurrence over the interior lower mississippi valley on summer afternoons relative to surrounding areas to understand the mechanisms behind this convection signature quasi idealized numerical simulations with the weather research and forecasting wrf model are performed the simulations which broadly reproduce the valley convection minimum suggest that convective inhibition is maximized and low level ascent minimized over the flat valley terrain by contrast weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily although the orography of the region is unremarkable it has a stronger influence on the regional convection pattern than do variations in land use

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others