the limits of seaward spreading and slope instability at the continental margin offshore mt etna imaged by high resolution 2d seismic data highlights analysis of a combined new high resolution 2d seismic and bathymetric data set offshore mt etna extensional domains are mapped at the shallow subsurface of the continental margin compressional structures are mapped at the toe of the continental margin a coupled volcano edifice continental margin instability is proposed mount etna is the largest active volcano in europe instability of its eastern flank is well documented onshore and continuously monitored by geodetic and insar measurements little is known however about the offshore extension of the eastern volcano flank defining a serious shortcoming in stability models in order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano we acquired a new high resolution 2d reflection seismic dataset the data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore mt etna the submarine realm is characterized by different blocks which are controlled by local and regional tectonics a compressional regime is found at the toe of the continental margin which is bound to a complex basin system both the clear link between on and offshore tectonic structures as well as the compressional regime at the easternmost flank edge indicate a continental margin gravitational collapse as well as spreading to be present at mt etna moreover we find evidence for the offshore southern boundary of the moving flank which is identified as a right lateral oblique fault north of catania canyon our findings suggest a coupled volcano edifice continental margin instability at mt etna demonstrating first order linkage between on and offshore tectonic processes

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

a recent tectonic reorganization in the south central mediterranean abstract new geodetic data combined with seismicity geologic and geochemical information document a major tectonic reorganization in the central mediterranean around 0 8 0 5 ma when rapid trench migration and consequent tyrrhenian back arc extension which dominated the region s evolution since the tortonian 10 8 ma essentially stopped in response the african convergence in sicily was transferred to a back thrust in the southern tyrrhenian characterized by frequent m5 6 earthquakes in the last 20 years a diffuse transform boundary formed across northeastern sicily to connect the sicilian and calabrian plate boundaries causing opening of the messina straits home to large historical earthquakes and unusual volcanism in the aeolian island arc and the intraplate mount etna a divergence of the ionian region from the main part of africa with northeastward motions that reflect the joint influence of african push and hellenic slab pull and are transmitted to calabria and adria could explain motions observed in the sicily channel calabria and apulia as well as the high level of southeastern sicilian seismic activity

the results of the taormina 2006 seismic survey possible implications for active tectonics in the messina straits abstract the straits of messina and its surroundings are considered as one of the most tectonically active area of the mediterranean but in spite of their hazard potential modern geophysical data aimed at investigating their hidden structures are lacking in order to bridge this gap we carried out a marine multichannel seismic survey primarily aimed at i studying the regional fault pattern in the area of the messina 1908 earthquake and ii checking the existence of a potentially seismogenic fault the taormina fault which many authors locate offshore along the coast between taormina and messina our seismic profiles show a great structural complexity within the messina straits with the best imaged faults occurring on the calabrian side in particular a more than 30 km long nw trending fault located at the sw tip of calabria is cutting the sea floor moreover our data did not image any extensional fault plane attributable to the taormina fault rather the whole slope has been tilted east ward the geodynamic implication is that extension in south eastern sicily on the ionian side of the hyblean plateau and extension in southern calabria and messina straits belong to two different tectonic systems and cannot be mechanically linked

structural styles and regional tectonic setting of the gela nappe and frontal part of the maghrebian thrust belt in sicily the gela nappe of south central sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening synorogenic sediments allow the deformation to be dated two distinct structural styles are observed in the gela nappe the central salient part of the nappe caltanissetta basin consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe sciacca and monte judica consist of a stack of several thrust sheets these different structural styles correspond to the pretectonic mesozoic stratigraphy of the foreland plate carbonate platforms exist on the adventure bank and hyblean plateau ahead of sciacca and monte judica respectively while the caltanissetta basin region appears to have accumulated basinal clay facies where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front deformation is taken up by imbrication on steep ramps through the carbonates generating a relatively thick orogenic wedge in the basinal setting where no strong rheology exists the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas producing a nonlinear thrust front in the basinal region accretion of foreland material to the nappe by imbrication was only prominent during the messinian when subaerial exposure prevented low friction transport of the nappe across the highest levels of the stratigraphy a steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment possibly due to progressive compaction of the clays

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

the deformation offshore of mount etna as imaged by multichannel seismic reflection profiles abstract despite the clear evidence of active flank dynamics that is affecting the eastern side of mount etna the contribution of tectonic processes has not been yet understood so far the various models proposed to explain the observed flank deformation have been based on onshore structural data coming from the volcanic edifice the ionian offshore of mount etna has been only recently investigated using multichannel seismic profiles and offers the opportunity to image the structural features of the substrate of the unstable flank of the volcano this contribution aims at describing the deformation located offshore mount etna using multichannel seismic profiles recently acquired during three seismic surveys the onshore flank deformation of mount etna appears to be laterally confined by two tectonic guidelines trending roughly e w located to the north and south of the deforming flank the northern guideline in particular takes the surface expression of a sharp fault pernicana fault though often assumed that these boundary structures continue offshore as linear features connected to a frontal thrust ramp the occurrence of this simple offshore structural system has not been imaged in fact seismic data show a remarkable degree of structural complexity offshore mount etna the pernicana fault for instance is not continuing offshore as a sharp feature rather the deformation is expressed as ene wsw folds located very close to the coastline it is possible that these tectonic structures might have affected the offshore of mount etna before the pernicana fault system was developed less than 15 ka ago the southern guideline of the collapsing eastern flank of the volcano is poorly expressed onshore and does not show up offshore in fact seismic data indicate that the catania canyon a remarkable e w trending feature does not reflect a tectonic control seismic interpretation also shows the occurrence of a structural high located just offshore the edifice of mount etna whereas a complex deformation affects the boundary of this offshore bulge it shows only limited internal deformation part of the topography of the offshore bulge pre existed the constructional phase of mount etna being an extension of the hyblean plateau only in the northern part the bulge is a recent tectonic feature being composed by plio quaternary strata that were folded before and during the building of mount etna the offshore bulge is bounded by a thrust fault that can be related to the intrusion of the large scale magmatic body below mount etna

seismotomography of the crust in the transition zone between the southern tyrrhenian and sicilian tectonic domains 1 a crustal tomography of seismic wave velocity was performed in the contact zone between the southern tyrrhenian sicilian and ionian tectonic units a zone where the lithospheric structure can be expected to furnish evident signatures of dynamics related to the tyrrhenian subduction process a dataset of 10241 p and 5597 s readings from 932 local earthquakes recorded between 1978 and 2001 by stations operating in sicily and calabria was inverted by the simulps12 algorithm for simultaneous computation of hypocenter parameters and vp and vp vs three dimensional distributions the study brought significant improvement in the knowledge of the local velocity structure furnishing new information useful to better identify the local tectonic units the results appear to be compatible with the most recent hypotheses regarding the geodynamics of the study region

tectono stratigraphic modelling of the north sicily continental margin southern tyrrhenian sea abstract a two dimensional numerical modelling that simulate the kinematic and thermal response of the lithosphere to thinning was used for the quantitative reconstruction of the late neogene to recent times tectonic and stratigraphic evolution of the north sicily continental margin southern tyrrhenian sea the numerical study of the evolution of the north sicily margin builds on the crustal image and kinematic interpretation of the margin obtained by pepe et al tectonics 19 2000 241 on the basis of seismic data and gravity modelling tectonic modeling indicate that different segments of the margin were undergoing different vertical movements which are mainly expression of the rifting and thinning of the lithosphere occurred during tectonic evolution of the southern tyrrhenian sea a prediction of the pre rift basement topography and the moho along the margin converges to a value of 6 5 km for the depth of necking and a temperature dependent eet 500 isotherm the model fails to reproduce the morphology of the solunto high confirming its non extensional origin a polyphase evolution is required to reproduce the observed syn and post rift stratigraphy during the first rifting stage between 9 and 5 ma crustal thinning factors reach maximum values of 1 27 in the cefalu basin a similar value is predicted for the subcrustal thinning around 60 km nne of the profile margin crustal thinning factors increase during the second rifting stage from 4 to 2 ma and reach values of 2 and up to 3 5 in the cefalu basin and in the continent oceanic transition zone respectively similarly subcrustal lithospheric thinning factors reach values up to 2 5 in the distal sector of the margin an uplift of more than 100 m is predicted for the north sicily shelf and surrounding onshore areas during the post rift stage the evolution of thermal structure with time is very sensitive to the partial thinning factors describing the evolution of the thinning itself during time the lithosphere preserved part of its strength during extension the effective elastic thickness eet along the margin through time is 24 km at the onset of rifting and reaches values less to 8 km during the second rifting stage in the northeastern end of the margin

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

crustal and upper mantle responses to lithospheric segmentation in the northern apennines lithospheric tear faults are expected to develop in response to along strike variations in the rates of slab rollback however the exact geometry of such structures and their crustal and upper mantle expressions are still debated we present an analysis of seismic structural and morphological features that possibly represent the expression of lithospheric segmentation in the northern apennines geophysical observations show evidence for the existence of a discontinuity in the lithospheric structure beneath the northern apennines characterized by a change in the spatial distribution of intermediate depth seismicity along strike variations in the pattern of crustal seismicity and a bend in the moho topography the near surface expression of this discontinuity is associated with an abrupt change in the morphology and exhumation history of the northern apennines in the proximity of the livorno sillaro lineament we interpret these features as evidence for incipient tearing of the lithospheric slab beneath the northern apennines marking the boundary between domains that underwent contrasting styles of lithospheric deformation which are either associated with different rates of slab rollback or a transition from underplating to retreat we suggest that similar types of structures may play a crucial role in the evolution of convergent plate boundaries allowing segmentation of orogenic belts and facilitating the development of orogenic curvatures ultimately further tearing along such structures could potentially lead to the occurrence of tear related magmatism and the formation of slab windows

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

fault parameters in the messina strait southern italy and relations with the seismogenic source abstract the messina strait is characterized by strong deformations in pliocene and pleistocene times but considering the historical seismicity significant uncertainity exists as to whether any of the surface fault systems reflects the location geometry and mechanisms of the seismogenic source based on field data and structural analyses the parameters length l displacement d age of activity t minimum slip rate min and total geological moment m g have been derived for all the faults exposed on the sicilian and calabrian sides of the strait the analysis of these parameters shows that the highest rates of activity pertain to interconnected faults of different orientation and length which bound the uplifted crystalline basement relative to the pliocene pleistocene foundered zones of the calabrian side the comparison between the fault slip rates and the regional uplift rates shows that each single fault contributes for a limited fraction only to the whole deformation release in the area the contribution of the whole fault population expressed as cumulative m g release is still one order of magnitude less than the seismic moment release taking into account the underestimation of the geological parameters the lack of information on the offshore faults and the role of anelastic deformation by aseismic creep the data suggest that the long term recurrence of seismic breaks is partitioned at the surface in a complex array of interconnected faults some of these faults might represent basement inherited structures repeatedly and preferentially reactivated over geological time

late oligocene early miocene sedimentary evolution of the foreland basins in the sicilian mobile belt the example of the peloritani area in the northeastern corner of sicily peloritani mountains thin bodies of hercynian crystalline basement covered by meso cenozoic veneers of sedimentary rocks represent the highest and innermost africa vergent group of thrust units of the sicilian belt the peloritani tectonic edifice consists of a set of prevalently middle to high grade crystalline rocks so called fondachelli unit mandanici unit and aspromonte unit and thrusts over a thin tectonic wedge made of prevalently mesozoic to tertiary sedimentary covers overlying pre triassic low grade metamorphic rocks longi taormina unit the tectonic bodies of the peloritani thrust system are overlain by thick clastic sequences of late oligoceneearly miocene age the so called stilo capo d orlando formation previous work has pointed out the molassic character of these clastic sequences which postdate the main deformation phase of the peloritani belt started during oligocene time new structural data on the crystalline and sedimentary terrains sedimentological analysis of the outcropping oligo miocene foreland clastic deposits and their geometric relationships with the substrate make it possible to recognize the syn tectonic character and the timing of deformation of these basin fill deposits which are expressed by prograding clastic fans in the active margin of a foreland foredeep system this system has progressively been involved in the accretion of the sicilian belt and migration during the early miocene towards the more external areas represented by the sicilide sector seen in this light three different lithological units have been distinguished to prdvide a framework for a review of the palaeotectonic significance of the overall oligo miocene terrigenous covers of the peloritani thrust belt

orogenic gold in the new lycksele storuman ore province northern sweden the palaeoproterozoic faboliden deposit abstract southwest of the well known skellefte district northern sweden a new gold ore province the so called gold line is presently being explored during the past decade a number of gold occurrences have been discovered in this area the largest known gold occurrence is the faboliden deposit late to post orogenic ca 1 81 to 1 77 ga revsund granite constitutes the main rock type in the faboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks the supracrustal rocks are strongly deformed within a roughly n s trending subvertical shear zone the mineralization constitutes a 30 to 50 m wide n s striking steeply dipping zone the mineralization is commonly hosted by arsenopyrite bearing quartz veins within the supracrustal rocks the quartz veins parallel the main foliation in the shear zone gold is closely associated with arsenopyrite lollingite and stibnite and found in fractures and as intergrowths in the arsenopyrite lollingite gold is also seen as free grains in the silicate matrix of the host rock the proximal alteration zone displays positive correlation with ca s as ag sb sn w pb bi cd se and hg whereas k and na show a slightly negative correlation the hydrothermal mineral assemblage in the proximal alteration zone is diopside calcic amphibole biotite and minor andalusite and tourmaline this type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide garnet biotite geothermometry indicates amphibolite facies in the faboliden area the ductile fabric that hosts the mineralization is also found in the margin of the surrounding revsund granitoid it is therefore suggested that at least the final stages of the gold mineralization are syn to late kinematic and the minimum age for the mineralization is thus constrained at ca 1 80 ga revsund age

polyphase tectonic evolution of fore arc basin related to step fault as revealed by seismic reflection data from the alboran sea w mediterranean 25 pages 14 figures 1 table seismic reflection and bathymetric data collected during the marlboro and saras cruises are stored at sismer and seanoe sea scientific open data edition https doi org 10 17600 11480100 https doi org 10 17600 12450090 and https campagnes flotteoceanographique fr campagnes 12000010

geodynamic implications of earthquake data in the southern tyrrhenian sea abstract data from short period seismic stations operating in calabria sicily and the aeolian islands have been used to investigate earthquake properties of the southern tyrrhenian lithosphere the results have been analyzed taking into account other geophysical and geological information available in the literature for the same region with the main purpose of contributing to the definition of local geodynamic processes space distribution and focal mechanisms of earthquakes support the hypothesis of southeastward migration of the southern tyrrhenian lithosphere shared by several authors in their tectonic modelling of the area we find that most seismicity appears to be related to two main faults crossing the aeolian island archipelago sisifo and vulcano and propose that these faults are important dislocation structures associated with the lithosphere migration process we also give a detailed picture of the seismic behaviour of the above mentioned fault systems by analyzing the earthquake depth distribution focal mechanisms seismic clustering and strain release some degree of activity was also detected at the eastern boundary of the southern tyrrhenian area calabrian arc in particular our results demonstrate that in this highly stressed zone of contact between different tectonic units tyrrhenian and ionian basins strain is released under seismic form up to depths of the order of 25 km in the crust and not just in the shallowest structures as proposed by other authors

the 2011 yingjiang china earthquake a volcano related fluid driven earthquake abstract a high resolution tomographic model inferred from local and teleseismic arrival time data under yunnan southwest china shows that the 2011 yingjiang earthquake m 5 8 occurred around a low velocity anomaly that extends down to the top of the mantle transition zone and is attributable to upwelling flow of the active tengchong volcano fluids in the flow may mainly originate from the dehydration of the eastward subduction of the indian plate in the mantle transition zone and have reached the fault zone our results suggest that the occurrence of the yingjiang earthquake could be closely related to fluids that might enhance the stress concentration on the seismogenic layer as well as decrease the effective normal stress across the fault planes of the da yingjiang fault we conclude that the yingjiang earthquake might be a volcano related fluid driven earthquake the successive occurrence of small earthquakes m 4 0 and the yingjiang aftershocks may imply recent magmatism at the tengchong volcano the 4 february 2011 indo burma earthquake m 6 4 occurred at 90 km depth suggesting that the indian plate is still active and currently subducting eastward which may explain why several moderate large earthquakes such as the 24 march 2011 burma earthquake m 7 2 have occurred recently in the region

fault pattern and seismotectonic potential at the south western edge of the ionian subduction system southern italy new field and geophysical constraints abstract the south western edge of the calabrian arc in southern italy has been investigated throughout a joint analysis of field marine and geophysical data which provided constraints on the fault pattern and on the seismotectonic potential the study was focused on a poorly known sector of a larger belt of seismically active faults slicing across the ne corner of sicily the so called tindari fault system our data pointed out that the investigated area including the mainland and the ionian offshore is deformed by oblique faulting with a general nw se tectonic trend earthquake distribution and seismic profiles pointed out active deformation in the offshore while the mainland is characterized by the occurrence of a nw se oriented 20 km long structural belt however scarce seismicity has been recorded in the last 30 years alongside this tectonic structure accounting for a possible silent segment of the larger fault system tomographic images revealed that the moho discontinuity is deformed by a ne dipping lithospheric tectonic structure which has been here retained the main mode of deformation and responsible for coseismic displacement in the area as a whole field and geophysical data agree with a general nw se trend segmented pattern of recent active faults that have the potentiality of generating magnitude 6 5 7 earthquakes

propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy the rollback of a segmented slab of oceanic lithosphere is typically accompanied by vertical lithospheric tear fault s along the lateral slab edge s and by strike slip movement in the upper plate defined as a step fault subduction tear edge propagator the neogene evolution of the central mediterranean is dominated by the interaction between the slow africa eurasia convergence and the se ward rollback of the ionian slab that leads to the back arc opening of the tyrrhenian sea here we present post stack time migrated and pre stack depth migrated archimede 1997 multichannel seismic lines that were acquired offshore eastern sicily at the foot of the malta escarpment first we identify the recent deformation along the lateral ramp of the calabrian accretionary wedge towards the east the calabrian wedge is formed by the accretion of the post evaporitic sediments above a decollement at the base of the messinian evaporites at the latitude of syracuse 50 km east of the malta escarpment a major n150 degrees e trending crustal scale and vertical fault slices through the entire accretionary wedge this fault cuts by several kilometers through the pre evaporitic messinian sediments and into the basement the vertical offset along this vertical fault decreases from north to south and the fault is no longer observed on the seismic lines 50 km se of the alfeo seamount a previously published moho depth isocontour map offshore sicily and the recent gps data combined with the presence of strike slip movements ne onshore sicily allow us to identify this 200 km long crustal scale fault as the surface expression of a step fault the presence of syntectonic pleistocene sediments on top this crustal scale fault suggests a recent lithospheric vertical movement of the step fault in response to the rollback of the ionian slab and to the se ward advance of the calabria peloritan block

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

ore petrology chemistry and timing of electrum in the archean hypozonal transvaal lode gold deposit western australia the transvaal lode gold deposit is hosted in ultramafic schists and graphite bearing pelites that are metamorphosed to lower and mid amphibolite facies assemblages the orebody is structurally controlled by the transvaal shear zone which overprinted and reactivated the penetrative regional fabric the main tabular orebody is formed of a massive quartz sulfide vein and related splays and adjacent hydrothermally altered wall rock prograde alteration in the ultramafic rocks consists of a proximal diopside actinolite quartz zone which grades outward into a distal amphibole hornblende actinolite biotite plagioclase quartz schist in pelitic metasedimentary rocks a proximal biotite muscovite quartz graphite zone grades outward into a distal cordierite quartz biotite graphite schist retrograde chlorite talc and zoisite replaced prograde hydrothermal alteration minerals and exhibit generally postkinematic fabrics the dominant sulfide assemblages in the hydrothermal alteration zones at transvaal are pyrrhotite loellingite pyrrhotite arsenopyrite 1 and loellingite arsenopyrite 1 other assemblages include chalcopyrite pyrrhotite pyrite loellingite and pyrrhotite cubanite these assemblages are interpreted to consist of a mixture of equilibrium assemblages that relate to a prograde hydrothermal alteration event and disequilibrium assemblages that formed during cooling and reequilibration of the rocks arsenopyrite 1 is interpreted to have formed both during the prograde alteration event and during high temperature retrogressive replacement of loellingite average compositions of arsenopyrite 1 in equilibrium with loellingite and pyrrhotite indicate paleotemperatures of about 510 degrees or 20 degrees c about 40 degrees c lower than estimates of the peak metamorphic temperatures low and high fe pyrrhotite and arsenopyrite 2 for instance would not be in equilibrium with other sulfides and are interpreted to be retrograde both electrum and gold occur in the transvaal gold deposits but electrum is the more abundant gold bearing phase and contains between 24 and 56 wt percent silver the compositions of electrum grains correspond to gold finenesses of about 431 to 732 with silver the dominant impurity electrum occurs mostly at the interface between arsenopyrite 1 loellingite or as inclusions in loellingite pyrrhotite and arsenopyrite 1 more rarely it occurs as as fracture fill within arsenopyrite 1 the differing silver contents of electrum can be explained by differing fluid rock reactions low ag electrum about 24 wt ag occurs where the lode is entirely hosted by ultramafic schists whereas high ag electrum is at the ultramafic schist graphitic pelite contact it is proposed that fluid interaction with reducing pelites produced ag rich electrum through destabilization of gold bisulfide and silver chloride complexes whereas fluid that reacted with more oxidized ultramafic rocks formed au rich electrum as silver chloride complexes were not destabilized the main phase of hydrothermal alteration which included the crystallization of prograde silicates pyrrhotite and loellingite was syntectonic with respect to the transvaal shear zone and at approximately peak metamorphic conditions electrum in equilibrium with pyrrhotite and or loellingite was thus deposited at synpeak metamorphic conditions however the majority of electrum grains coexist with arsenopyrite 1 and composite loellingite arsenopyrite 1 grains and are interpreted to have formed from submicroscopic gold released from loellingite during high temperature retrogressive replacement by arsenopyrite these are also considered to be part of the main gold bearing hydrothermal event retrograde low temperature postmetamorphic silicate and sulfide minerals such as chlorite muscovite pyrite and cubanite are evidence for processes that occurred after the main gold depositing hydrothermal activity took place renewed flux of hydrothermal fluids during the protracted metamorphic history of the terrane could have produced the low temperature retrogression the occurrence of low temperature sulfides is likely the result of in situ reequilibration during cooling of the rocks

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

fluid chemical evolution as a factor in controlling the distribution of gold at the archean golden crown lode gold deposit murchison province western australia the golden crown lode gold deposit is one of a number of northwest southeast to north south trending quartz veins hosted by a steeply dipping 500 m thick differentiated dolerite sill the great fingall sill and adjacent graphitic shale in the day dawn district of the murchison province in the archean yilgarn craton western australia quartz veins of the golden crown deposit are shear zone hosted crosscut the dominant host rock stratigraphy at a high angle and are laminated partly boudinaged and generally bifurcate at their extremities veins are dominated by dark gray or milky white quartz with subordinate calcite and ankerite and in order of abundance arsenopyrite pyrrhotite pyrite galena chalcopyrite and minor sphalerite the vein sulfides coexist with native gold and are most abundant at vein margins textural evidence indicates that precipitation of the majority of these minerals overlapped and that most phases can be considered to have been in equilibrium during vein genesis mineral chemistry fluid inclusions alteration and ore assemblages show that there are significant systematic gradients in intensive variables within the golden crown deposit these are recorded over the approximately 450 m of vertical exposure of the vein system and over up to 30 m into the wall rocks based on proximal alteration assemblages and zoning patterns zoned wall rock alteration haloes are divisible into four sequences three of which are closely related to gold mineralization specific alteration sequences occur within different parts of the vein system biotite alteration predominates in the deeper portions whereas muscovite alteration characterizes the upper and southern portions of the system higher grade gold zones within the golden crown deposit are limited to the northern end of the system in the deeper portion of the veins and expand along strike to the south in the upper portions fluid inclusions interpreted to be trapped during gold mineralization are low salinity 10 wt nacl equiv h2o co2 ch4 inclusions with variable carbonic to aqueous contents that are interpreted to be due to fluid immiscibility inferred methane concentrations in the carbonic phase vary significantly from 19 7 mole percent in the vicinity of the shale contact to 5 2 mole percent in the shallower southern end of the deposit carbon and oxygen isotope compositions of carbonates 13ccalcite 10 5 to 1 9 13cankerite 5 3 to 4 1 18ocalcite 7 0 18 3 and 18oankerite 7 7 9 2 and oxygen isotope compositions of vein quartz 18oquartz 10 2 12 5 are well within the range of known archean orogenic lode gold deposits combining the results of all geothermometers and geobarometers a temperature of 300 to 400 c and pressure of 2 5 0 5 kbars are determined with temperature variations over the exposed quartz vein of less than 40 c the as content at of arsenopyrite and au ag ratios of native gold show significant compositional variation which appears to be controlled by parameters such as a h2s aq and f o2 not temperature gradients on the basis of the variations in fluid composition determined in the reefs the two major processes responsible for high grade gold mineralization are interpreted to have been phase separation in the deeper portions of the ore forming system approximately below 400 m level and above these levels mixing between two modified ore fluids one reduced fluid that had reacted with graphitic shale and a relatively oxidized fluid that had partly equilibrated with dolerite

a 125 kyr long geological record of seismic source repeatability the messina straits southern italy and the 1908 earthquake ms7 2 the occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century the large 1908 messina straits blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time scale in the order of 100 kyr we have compared seismological and geodetic descriptions of the 1908 rupture process with long term crustal deformation recorded at different stratigraphic levels by marine terraces marine sedimentary units and landscape features the wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale we investigated in detail the pattern of deformation of the 125 kyr old lowest emergent terrace and found that it mimics the pattern of elevation changes observed following the earthquake this suggests 1 that the 1908 earthquake is characteristic 2 that its segment boundaries have been stationary during the past 125 kyr and 3 that even the locations of the regions of largest coseismic release do not change through many seismic cycles based on a comparison between observed heights of the 125 kyr terrace and 1908 displacements we estimated an average repeat time of 1000 yr for a 1908 type earthquake we also investigated the height position age and state of deformation of older terraces and found 1 that uplift of the region started about 1 ma and has since continued rather uniformly at 0 9 1 4 mm yr 1 2 that during this time the straits have narrowed at a rate of 10 20 mm yr 1 and 3 that all the main geomorphic features of the messina straits result from the interaction of fast regional uplift 1908 type coseismic subsidence and global sea level fluctuations

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

coseismic velocity change in the rupture zone of the 2008 mw 7 9 wenchuan earthquake observed from ambient seismic noise we investigated seismic velocity and structural changes along the long men shan fault associated with the 2008 mw 7 9 wenchuan earthquake using ambient seismic noise data recorded by the regional seismic network of the china earthquake administration we computed cross correlograms of continuous records of station pairs from which we obtained clear rayleigh wave signals at periods of 10 to 25 s we measured the travel speeds of these rayleigh waves from ambient noise data recorded before and after the earthquake and obtained a total of 77 estimates of group velocity along paths running across the rupture zone of the earthquake most of the ray paths showed increasing travel times of rayleigh waves right after the earth quake we inverted the measured differential travel times along different ray paths to constrain regions with significant changes in seismic velocity our 2d tomographic image showed a distinct region with an 0 4 velocity decrease the strike and extension of this region match remarkably well with the deep rupture area of the earth quake because the rayleigh waves that we used in this study travel as deep as 25 km below the surface it is difficult to explain the observed velocity changes solely with shallow damages 100 m resulting from strong shaking numerous laboratory studies have shown that the speed at which seismic waves travel through rocks changes with the level of stress the velocity decrease observed here thus may be caused by a large stress drop associated with the earthquake assuming a stress drop of 3 mpa we obtained a stress sensitivity of 1 3 10 9 pa 1 consistent with both laboratory and field observations our results suggest that time lapse seismic imaging with ambient noise data provides a promising probe for monitoring temporal structural changes at seismogenic depths

tectono sedimentary constraints to the oligocene to miocene evolution of the peloritani thrust belt ne sicily abstract the peloritani thrust belt belongs to the southern sector of the calabrian arc and is formed by a set of south verging tectonic units including crystalline basement and sedimentary cover from the top aspromonte u mela u mandanici u fondachelli u longi taormina u piled up starting from late oligocene at least two main terrigenous clastic formations lie with complicated relationships on top of the previous units the frazzano fm oligocene and the stilo capo d orlando fm late oligocene early miocene as syn to post tectonic deposits these clastic deposits have different characteristics in space and time representing or flysch like sequences involved in several thrust events frazzano fm or molassic like sequences stilo capo d orlando fm which unconformably overlie the tectonic units in the present paper we describe a kinematic model of the progressive foreland migration of the peloritani thrust belt starting from oligocene carrying piggy back basins and incorporating foredeep deposits recognised in the frazzano stilo capo d orlando terrigenous successions in general the facies and structural observations on the overall oligo miocene clastic sequences outcropping in the western peloritani mts indicate a the distal character of the frazzano fm b a complex group of terrigenous facies of the stilo capo d orlando fm with lateral to vertical organisation characterised by a distal to proximal to distal facies trend c facies analogies of the basal portions of the stilo capo d orlando fm with the frazzano fm d the involvement of the frazzano fm in lowermost and more external thrusting and of the basal late oligocene distal stilo capo d orlando facies in the higher and inner thrusting during the early stages of deformation e the involvement of the proximal stilo capo d orlando facies in the tectonic edifice during the early miocene deformation f the generally unconformable stratigraphical contacts of the higher proximal to distal early miocene stilo capo d orlando facies on the constructing mobile belt and g the presence of various thrust faults distinguished in a sequential order the collected data allow us to hypothesise that the oligo miocene tectono sedimentary history was characterised by a foredeep with a deforming internal flank probably lying in onlap on the constructing tectonic edifice frazzano lower stilo capo d orlando fms and then deformed and covered by a piggy back like sequence middle upper stilo capo d orlando fm which was subsequently also deformed the tectono sedimentary evolution of the peloritani belt has been probably developed through a progressive migration towards the foreland of a foredeep compressional front couple and the chain body the thrust stack progressively incorporates terrigenous foredeep deposits and in turn carried piggy back basins

tectonic expression of an active slab tear from high resolution seismic and bathymetric data offshore sicily ionian sea subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault while the calabrian subduction beneath southern italy is considered to be the type example of this geodynamic setting the geometry kinematics and surface expression of the associated lateral slab tear fault offshore eastern sicily remain controversial results from a new marine geophysical survey conducted in the ionian sea using high resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long two branched fault system near alfeo seamount the previously unidentified 60 km long nw trending north alfeo fault system shows primarily strike slip kinematics as indicated by the morphology and steep dipping transpressional and transtensional faults available earthquake focal mechanisms indicate dextral strike slip motion along this fault segment the 80 km long sse trending south alfeo fault system is expressed by one or two steeply dipping normal faults bounding the western side of a 500 m thick 5 km wide elongate syntectonic plio quaternary sedimentary basin both branches of the fault system are mechanically capable of generating magnitude 6 7 earthquakes like those that struck eastern sicily in 1169 1542 and 1693

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

structural evolution of the tyrrhenian back arc basin abstract the tyrrhenian basin has developed as a marginal basin through drifting of the calabrian sicilian arc system towards the east southeast the main structural features of the basin result from this movement the tensional structures normal faults of the margins are mainly aligned n10 to n30 e the transform faults are oriented n110 n120 e except for a previous structuralization linked to the western mediterranean rifting and drifting the first extensional movements affected the tyrrhenian area as early as lower miocene time during the post burdigalian nevertheless the main rifting phase which led to oceanic accretion was initiated during the late tortonian the narrow central oceanic area generated mainly around the early pliocene is restricted to the rift s axis the marginal basin type of evolution of the tyrrhenian sea is most probably directly linked to subduction of the ionian lithosphere nevertheless interferences between collision in the surrounding apennines calabria or sicilides and subduction processes have dominated this special back arc basin evolution since late tortonian time the tyrrhenian arc shows a regional n120 e oriented tensional pattern short compressional events occur briefly in middle pliocene and middle pleistocene times correlated with brief paroxysmal phases of extension and subsidence the deformation depends on the presence of a subduction zone parallel to the calabrian arc swell which allows the migration of the unblocked segments of the arc in a n120 e direction

seismotectonics of northeastern sicily and southern calabria italy new constraints on the tectonic structures featuring in a crucial sector for the central mediterranean geodynamics

evolution of the calabrian accretionary wedge central mediterranean 1 the neogene tectonics of the central mediterranean are related to the subduction and trench rollback of the ionian basin under eurasia causing the opening of the liguro provencal and tyrrhenian back arc basins and the formation of the calabrian accretionary wedge the calabrian accretionary wedge is a partially submerged accretionary complex located in the ionian offshore and laterally bounded by the apulia and malta escarpments while the history of the back arc extension process is fairly well defined the structure and evolution of the wedge are still poorly known we have analyzed and interpreted the available reflection multichannel and single channel seismic profiles in the ionian offshore and integrated them with other geological and geophysical data acquired in the last 40 years here we present unpublished seismic profiles to provide a new map of the tectonic structure of the ionian offshore and to define the structure of the wedge and its evolution during the last 15 myr our reconstruction points out that the messinian salinity crisis represents an important break in the evolution of the wedge as the basal decollement ramps up onto the messinian salt deposits producing a dramatic and fast forward propagation of the frontal thrust and resulting underplating of the underlying crustal ionian sequence during progressive trench rollback our results provide new insight into the style of accretion in a weakly converging setting which is typical for the mediterranean region

geological and geochemical characteristics of the sawaya erdun gold deposit southwestern chinese tianshan the sawaya erdun gold deposit in the western segment of the south tianshan xinjiang china is a large low grade orogenic gold deposit an abundance of index fossils in the ore hosting strata including brachiopoda corals and schwagerina show that the fossil age of the country rocks ranges from late carboniferous to early permian whole rock rb sr and sm nd isochron ages ranging from 292 43 0 38 to 304 7 11 6 ma are concordant with a late carboniferous age gold mineralization is strictly controlled by a fault zone ore minerals are dominated by sulfides with gold inhomogeneously distributed within them gangue minerals are quartz siderite or calcite data suggest that the ore forming fluid was derived predominantly from an active meteoric groundwater system ore forming temperatures are estimated to have been within the range 110 to 220 c new 40 ar 39 ar isotope age determinations of auriferous quartz are in excellent agreement with rb sr ages obtained from fluid inclusions in quartz they suggest gold mineralization at 206 to 213 ma late indosinian such an age is consistent with the age of formation given for other gold deposits in the region such as bulong and dashankou combined with k ar geochronological data and observed geological features it is concluded that the indosinian metallogentic epoch represents a previously unrecognized major period of gold metallogeny in the southwestern chinese tianshan in some ways the sawaya erdun gold deposit can be compared with the muruntau gold deposit in uzbekistan with respect to geological setting host lithology mineralization style mineral assemblages geochemical association and metallogenic processes involved despite this the sawaya erdun gold deposit possesses a number of characteristics typical of only low temperature metallogenesis 2007 elsevier b v all rights reserved

the italian cmt dataset from 1977 to the present abstract the ingv harvard european mediterranean regional centroid moment tensor rcmt catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude 4 5 m 5 5 in the mediterranean region the database represents an extension to smaller magnitudes of the harvard global cmt catalog based on analysis of seismograms recorded at regional distance and modeling of intermediate period surface waves the catalog includes about 600 events 200 of which in the italian region this study extends the catalog back in time for the italian region as long as made possible by available digital data i e since 1977 with the same analysis and inversion method used for current seismicity as a result we present here 65 new moment tensors for years between 1977 and 1997 these solutions represent 45 of the total number of events analyzed the existing seismograms being often too scarce to allow a stable solution the new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented e g the po plain the central to southern apennines and the adriatic sea the complete dataset including previously determined rcmts and cmts represents the seismic deformation in the italian area during the last 25 years

thermal constriction and slab tearing at the origin of a superinflated spreading ridge marsili volcano tyrrhenian sea 1 recently acquired swath bathymetry of the marsili basin has offered an unprecedented opportunity to study the processes of back arc ocean basin development in the tyrrhenian sea in particular the detailed morphology of marsili seamount a large strongly elongated volcano located in an axial position within the 2 ma ocean crust floored marsili basin is a key to understanding the mechanisms governing lithosphere formation in this young basin the basin is near circular in shape with diameter on the order of 120 km and is positioned in the southern tyrrhenian sea above the steeply dipping ionian oceanic slab of mesozoic age it is bounded southward by the aeolian volcanic arc and the calabrian accretionary wedge surface evidence of the northwesterly directed subduction the most outstanding feature of the basin is the elongated 3000 m high marsili volcano which reveals distinctive morphology strikingly akin to the high order segmentation and volcanic landforms described in mid ocean slow spreading ridges on the basis of its distinctive morphology and incremental growth relationship we propose that marsili volcano represents a superinflated spreading ridge resulting from a distinct thermal pulse of increased melt production occurring within the young and immature marsili basin surrounding cooler continental lithosphere thermally constricts ridge propagation and crust production in marsili basin to the finite scale of marsili volcano increased melt production to feed the superinflated marsili ridge is generated by deep lateral asthenospheric mantle flow produced at the edges of tears that bound the subducting ocean crust of the ionian plate slow spreading plate separation outpaced by the increase in magma generation results in vertical accretion to produce the superinflated ridge the existence of dip directed tears delimiting the narrow ionian slab is supported by the geological evolution of the surrounding foreland and apennine maghrebid mountain belt during early middle pleistocene i e the time of formation of the marsili volcano present day structure and volcanism furnish direct and indirect surface evidence of the presence and location of the slab tears

the archean chalice gold deposit a record of complex multistage high temperature hydrothermal activity and gold mineralisation associated with granitic rocks in the yilgarn craton western australia abstract the chalice gold deposit 20 t au produced in the southwestern portion of the late archean norseman wiluna greenstone belt of the yilgarn craton western australia is hosted both in a sequence of intercalated mafic and ultramafic amphibolites and a post peak metamorphism monzogranite dike the deposit is flanked on the western side by calc alkaline plutonic rocks and to the east by a predominantly monzogranitic pluton with at least four generations of monzogranitic dikes that intrude the local mine stratigraphy locally four deformation events d 1 d 4 have affected this sequence of amphibolites and two stages of gold mineralisation are recognised controlled by the progressive d 2 event main stage gold mineralisation 95 of the resource which is demonstrably later than all granitic bodies except second generation and subsequent monzogranite dikes is controlled by localised d 2 asymmetric folds developed in the mafic amphibolite it is expressed as veins and wall rock replacement characterised by a prograde assemblage of quartz diopside plagioclase k feldspar titanite pyrrhotite pyrite magnetite garnet hornblende scheelite and biotite second stage gold mineralisation 5 of the resource is associated with the intrusion of a monzogranite dike and is expressed as disseminated gold in the dike as well as foliation discordant veins of quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold detailed field mapping and petrography suggest that main stage gold mineralisation at chalice is equivalent to hypozonal orogenic lode gold mineralisation in other archean greenstone belts of the yilgarn craton whereas monzogranite associated second stage gold mineralisation is atypical of such deposits the main stage mineralisation cannot be correlated to any particular granitoid in the local environment although temporally it is bracketed by granitic magmatism a deep magmatic or metamorphic source cannot be resolved from the field data it is also uncertain as to whether second stage mineralisation represents a true magmatic gold event or is a product of the assimilation and remobilisation of main stage gold during the intrusion of the monzogranite dike however its distinctive metal association of au bi mo te w suggests the former irrespective of this uncertainty chalice remains as a deposit which is more intimately related both spatially and temporally to granitic magmatism than other yilgarn deposits

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

coseismic velocity variations caused by static stress changes associated with the 2001 mw 4 3 agios ioanis earthquake in the gulf of corinth greece 1 the analysis of temporal variations in the seismic velocity across faults can be used to estimate in situ stress changes seismic velocity of propagation depends on the fault stiffness which is a function of stress the coda wave interferometry technique is applied to seven families of repeating earthquakes multiplets recorded on the southern shore of the gulf of corinth greece to estimate high precision velocity changes in the earth s crust associated with the mw 4 3 agios ioanis earthquake results show that the agios ioanis event causes a perturbation in elastic properties at seismogenic depth resulting in a reduction of 0 2 in the seismic velocity the results are not consistent with either damage induced by dynamic stresses nor a fluid transient origin in contrast both the spatial distribution and magnitude of the velocity perturbation correlate well with modeled static stress variations this suggests that the measured changes in the mechanical properties of the seismogenic crust can be attributed to a change in static stress field associated with the mw 4 3 agios ioanis earthquake the velocity changes indicate an unclamping of the pyrgaki fault at depth which has local hazard implications

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

high frequency wave propagation from mantle earthquakes in the tyrrhenian sea new constraints for the geometry of the south tyrrhenian subduction zone propagation of shear waves produced by 25 mantle earthquakes 80 600 km depth in the subduction zone of the south tyrrhenian sea southern italy has been investigated to infer the geometry and extent of the descending lithosphere from all hypocentral depths high frequency high amplitude shear waves are recorded at most of the stations in southern italy and easternmost sicily this shear wave energy is interpreted to travel as a guided wave within the descending slab in contrast shear waves are either not recorded at all or they are recorded as low frequency low amplitude signals at stations located in the peninsular part of italy north of the calabrian arc in western sicily and in sardinia this systematic s wave attenuation is interpreted in terms of an active and continuous slab correlated with and limited to the calabrian arc

coseismic and postseismic velocity changes measured by repeating earthquakes 1 repeating earthquakes that rupture approximately the same fault patch and have nearly identical waveforms are a useful tool for measuring temporal changes in wave propagation in the earth s crust since source and path effects are common to all earthquakes in a repeating earthquake sequence multiplet differences in their waveforms can be attributed to changes in the characteristics of the medium we have identified over 20 multiplets containing between 5 and 40 repeating events in the aftershock zones of the 1989 loma prieta and 1984 morgan hill california earthquakes postmain shock events reveal delays of phases in the early s wave coda of as much as 0 2 s relative to premain shock events the delay amounts to a path averaged coseismic velocity decrease of about 1 5 for p waves and 3 5 for s waves since most of the multiplets are aftershocks and follow omori s law we have excellent temporal sampling in the immediate postmain shock period we find that the amplitude of the velocity decrease decays logarithmically in time following the main shock in some cases it returns to the premain shock values while in others it does not similar results are obtained for the morgan hill main shock because the fractional change in s wave velocity is greater than the fractional change in p wave velocity it suggests that the opening or connection of fluid filled fractures is the underlying cause the magnitude of the velocity change implies that low effective pressures are present in the source region of the velocity change our results suggest that the changes are predominantly near the stations and shallow but we cannot exclude the possibility that changes occur at greater depth as well if the variations are shallow we may be detecting the lingering effects of nonlinearity during main shock strong ground motion if the variations are deep it suggests that pore pressures at seismogenic depths are high which would likely play a key role in the earthquake process

new gps constraints on the africa eurasia plate boundary zone in southern italy 1 southern italy is a key area for understanding the tectonic processes in the africa eurasia collision zone we analyze new gps measurements carried out between 1994 and 2001 the results are presented in terms of time series trajectories and velocities of crustal motion as well as a geodetic strain rate field while central italy corsica sardinia and the tyrrhenian sea move like the eurasian plate the overall motion of the sicily rift zone region matches african plate motion unexpected are the north northwest directed motions of northeastern sicily and the eolian islands most striking on the deformation field are a north south oriented compression along the northern sicilian coast compression between apulia and northwestern greece as well as extension in the sicily rift zone and the interior of sicily

u pb ages constraining batholith emplacement contact metamorphism and the formation of gold and w mo skarns in the southern cross area yilgarn craton western australia gold mines in the archean southern cross greenstone belt central yilgarn craton have produced more than 220 metric tons t of gold the deposits are characterized by a pyroxene rich gangue and have been interpreted as synmetamorphic amphibolite facies replacement deposits and as postmetamorphic intrusion related skarns we present ion microprobe u pb zircon data constraining the age of amphibolite facies contact metamorphism in the aureole of the ghooli dome the largest granitoid batholith intruding the southern cross belt drill cores from the copperhead gold mine provided zircons from an altered quartz porphyry sill located 300 m southwest of the ghooli dome and zircons from the monzogranite gneiss at the border of the batholith the porphyry sill contains embayed igneous zircons dated by a concordant u pb age of 2912 5 ma and euhedral zircons of metamorphic crystal habitus dated by a second concordant age of 2772 5 ma the igneous zircons are slightly younger than those recovered from another sill of quartz porphyry sampled at the southern star mine which define a single concordant u pb age of 2934 7 ma the metamorphic zircons in the porphyry at copperhead record the same age as the igneous zircons 2775 10 ma in the monzogranite gneiss of the ghooli dome this pluton extends more than 40 km to the southeast of copperhead and also forms the batholith border at the corinthian and fraser s mines these gold deposits too are hosted by amphibolite facies greenstones contact metamorphosed at 2772 5 ma the corinthian skarn 2620 6 ma formed 150 m y after high grade metamorphism and consequently cannot be classified as synmetamorphic or metamorphogenic a review of field relationships and of published geochronometric data suggests that the gold skarns in the southern cross area are related in space and time to a suite of magnetite series granite pegmatite complexes these granites dated regionally at 2 66 to 2 60 ga are also associated with gold bearing w mo skarn greisen or skarn systems of up to 6 km strike length the numerous skarns exposed in the deeply eroded 14 km paleodepth central yilgarn craton are members of a recently recognized group of intrusion related gold deposits which are part of continental margin tungsten tin provinces

comment on geometry of the deep calabrian subduction central mediterranean sea from wide angle seismic data and 3 d gravity modeling by dellong et al

malta escarpment fault zone offshore eastern sicily pliocene quaternary tectonic evolution based on new multichannel seismic data 1 the malta escarpment represents the dominant morphological feature offshore eastern sicily linking the deep ionian basin to the east with the hyblean carbonate platform to the west interpretation of purposely acquired multichannel seismic data allows division of the malta escarpment into two portions characterized by different tectonic structures along the segment south of siracusa the malta escarpment is not affected by recent faulting and appears as a steep surface that flattens out toward the ionian basin a recent deformation characterized by a broad area of uplift occurs 20 30 km east from the slope along a nnw sse trend the segment of the malta escarpment extending north of siracusa on the other hand is characterized by the presence of nnw sse east dipping recent extensional faults and related sedimentary basins the observed structural features support the occurrence of a lithospheric tear between the ionian oceanic basin and the hyblean plateau

comment on the article propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy by gallais et al 2013 tectonophysics abstract the oceanic lithosphere of the ionian sea is subducted under the calabrian arc and it has been proposed that the ionian lithosphere has been torn apart step fault sensu govers and wortel 2005 on its western side close to the malta escarpment a major morphological feature inherited from the mesozoic palaeogeography in a recent paper gallais et al tectonophysics 2013 have traced a right lateral strike slip fault that extends from south of the alfeo seamount all the way to the tyrrhenian sea they also argue that the position of the step fault is distinct from and located ca 50 km east of the malta escarpment gallais et al document with some additional details a fault segment that was already reported in the literature and that is located south of the alfeo seamount however gallais et al have little constraints to trace the step fault further to the north in this sector a belt of surface deformation that can be related to the step fault has been mapped from a denser grid of seismic profiles and is located west ward close to the malta escarpment argnani and bonazzi 2005 this undermines the conclusion of gallais et al that the lithospheric tear is distinct from the malta escarpment it is therefore likely that surface deformation associated with the lithospheric tear fault is more complex and is not represented by a single strike slip fault

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

seismic strain and seismogenic stress regimes in the crust of the southern tyrrhenian region abstract an investigation has been performed to identify and characterize the seismic deformation zones active over the last decades in the region of italy that has experienced the strongest seismicity during the last centuries the study is based on the estimate of hypocenter locations fault plane solutions seismogenic stress and seismic strain tensor orientations carried out using the entire dataset of the national and local seismic networks and the recently improved three dimensional 3d crustal velocity model of the study area a series of simulation tests have been performed to evaluate the significance of the earthquake space distribution obtained and whether it was influenced by network geometry problems related to the sea and the lack of ocean bottom seismometers in the sectors where hypocentral location was synthetically proved to be reliable space distributions of earthquakes located with epicenter and focal depth errors less than 3 and 4 km respectively have been compared with local geology in order to identify seismogenic faults the dataset of 32 fault plane solutions estimated with fault parameter errors less than 20 has been used to investigate space variations of seismogenic stress and seismic strain orientations over the study area stress was found to be uniform in the messina strait and southern calabria where inversion of the available set of 11 fault plane solutions showed clear evidence of an extensional regime the different orientations of the minimum compressive stress and strain found in this sector together with the information available on local geology and tectonics lead us to propose that the seismicity occurring over the last decades in the messina strait and southern calabria was not in general produced at the main faults but at minor faults activated by the main tectonic stress field acting in the area to the west in the sector including western etna the nebrodi chain and the western aeolian islands analysis of the available set of 16 fault plane solutions revealed a certain degree of stress heterogeneity with an apparent prevalence of north south compression this east to west change of stress strain regimes is evaluated in the light of current hypotheses regarding the geodynamics of the study region

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

evolution of the southern tyrrhenian slab tear and active tectonics along the western edge of the tyrrhenian subducted slab abstract the evolution of the southern tyrrhenian subduction has been possibly controlled by distinct episodes of slab break off as indicated by a critical review of the geological literature and by the analysis of purposely acquired multichannel seismic profiles within the proposed interpretation the first episode occurred from 8 5 to 4 0 ma and affected the segment of the slab located in the sardinia channel causing the abandonment of the adventure thrust front in western sicily the second episode occurred between 2 5 and 1 6 ma affecting the segment of slab located north of sicily and was preceeded by rifting in the strait of sicily the space and time location of these episodes appear controlled by discontinuities pre existing within the subducted african plate that trend at high angle to the advancing subduction front these discontinuities delimit segment of subducted slab that can be affected by slab break off and can act as wayouts for magma and mantle derived he the major of these discontinuities the malta escarpment has been reactivated in the quaternary as a trench perpendicular tear step faults ultimately the hierarchy in strength of these trench perpendicular features could have affected the timing and amount of trench retreat and backarc opening

convergence vs retreat in southern tyrrhenian sea insights from kinematics 1 the tyrrhenian sea is an extensional basin opened by trench retreat and back arc extension during subduction of the calabrian slab in the last 10 12 my subduction is still active beneath the semost part of the tyrrhenian sea as testified by seismicity down to 500 km depth by analyzing seismicity and geodetic data together with recent tomographic images we define the present day situation an evident n s compressional regime prevails in the tyrrhenian region west of the aeolian archipelago while east of them a nnw sse extension is documented by focal mechanisms and gps data with a much smaller strain rate with respect to the past the transition between these two domains is accommodated by a n s discontinuity zone which runs from aeolian islands to mt etna with an extensional to strike slip deformation

ambient noise rayleigh wave tomography in western sichuan and eastern tibet abstract we perform rayleigh wave tomography in western sichuan and eastern tibet by applying the ambient noise method to broadband data recorded at 49 stations from the sichuan digital seismic network cross correlations of vertical component ambient noise data are computed in one hour segments and stacked over 7 months from june to december 2007 then rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple filter analysis method group velocity maps at periods from 8 to 44 s were inverted the resulting group velocity maps generally show good correlations with tectonic features the sichuan basin is clearly resolved with lower group velocities at the short periods 8 to 20 s due to thick sedimentary layers and a prominent low velocity zone exhibits in the middle crust beneath the eastern margin of the tibetan plateau the longmen shan thrust belt marks not only the rapid lateral velocity variation between the topographically high tibetan plateau and low elevation sichuan basin but also the transition from the thick crust beneath the tibetan plateau to the normal continental crust beneath the sichuan basin

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

pattern of deformation around the central aeolian islands evidence from multichannel seismics and gps data the tectonics of the central aeolian islands which are located within the tyrrhenian backarc basin has been investigated through a marine seismic reflection survey we find that compressional structures dominate around the islands whereas extensional faults occur only to the north of salina and filicudi towards the marsili basin this pattern of deformation although different from previously reported is in agreement with the strain field and stress regime obtained from gps measurements and seismological data age constraints suggest that contractional deformation was active since middle pleistocene being coeval with the building of the volcanic edifices of the aeolian islands and is superimposed on pre existing extensional deformation compressional and extensional regimes therefore can coexist within a backarc setting seismic profiles show that the tindari letojanni fault considered as a major tectonic element does not extend to the north towards the island of vulcano as a throughgoing fault rather deformation is accommodated in a broader belt displaying greater structural complexity

crustal image of the ionian basin and its calabrian margins abstract previous seismic investigation of the crustal structure in the ionian basin has been limited to shallow penetration seismics of the 1970 s characterized by inadequate source power and low fold earlier obs and esp seismic refraction experiments have not been able to firmly resolve one of the principal scientific problems for this region which is whether the ionian basin is floored by oceanic crust or by highly attenuated continental crust a second elusive problem is the nature of the transition of the boundaries between the ionian basin and its margins in this paper we describe and interpret new deep seismic reflection and wide angle data collected in the western ionian sea and the calabria region of italy one of the principal features of our multichannel reflection data beneath the ionian basin is a band of layered high amplitude reflections near the base of the crust this band shows a quasi monochromatic ca 8 to 10 hz frequency and a traveltime thickness of 1 to 1 5 s these images contrast with the well known reflection patterns of mesozoic oceanic crust investigated in the atlantic ocean there is evidence that the low frequency band dips down towards the edge of the malta escarpment me where landward dipping reflectors separate continental and intermediate type crust in the central tract of the me the increased traveltimes of the lower crustal reflectors and moho from the basin towards the southern and eastern margins of southern calabria could be partially due to the velocity pull down effect of the sedimentary pile of the arc although a true dip of 15 to 18 over 60 km distance can be substantiated moreover the reflecting band maintains its reflectivity and thickness until its abrupt termination beneath the ionian continuation of the calabrian compressional crustal structures the coincident acquisition of wide angle seismic data and marine reflection seismic data provided a landward extension of the survey which will complement existing geologic information on the deep framework of the ionian basin and its calabrian margin

midcrustal low velocity layer beneath the central himalaya and southern tibet revealed by ambient noise array tomography 1 ambient noise tomography has been becoming an important tool to image the shallow lithospheric structure of the earth using 2 months of ambient noise data from 20 stations of the himalayan nepal tibet seismic experiment we investigate the upper and middle crustal structure in the central himalaya and southern tibet about 120 interstation rayleigh wave empirical green s functions with sufficient signal to noise ratio are obtained and used for group velocity dispersion analysis in the period range 6 25 s using frequency time analysis technique the obtained dispersion data are then used to construct 2 d group velocity maps at the short periods from 9 to 15 s the distribution of rayleigh wave velocities delineates several distinct low and high velocity zones separated mainly by geological boundaries the high group velocity zone is located mainly around regions with plutonic rocks and the low group velocity zone is located around regions with sedimentary or metasedimentary rocks finally we invert for the shear velocity structure in the upper and middle crust along a n s trending cross section at the longitude 86 5 e we observe a clear low velocity layer in the middle crust about 10 25 km depth distributed on both sides of the indus yarlung suture zone the existence of this midcrustal low velocity zone suggests a mechanically weaker middle crust beneath the central himalaya and southern tibet which might decouple the upper crustal deformation from that of the lower crust in the tibetan himalayan orogenic processes

time dependent seismic tomography summary of methods for measuring temporal changes in seismic wave speeds in the earth seismic tomography is among those that offer the highest spatial resolution 3 d tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations this assumption is dangerous because the results of independent inversions would differ even if the structure in the earth did not change due to observational errors and differences in the seismic ray distributions the latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant a better approach which makes it possible to assess what changes are truly required by the data is to invert multiple data sets simultaneously minimizing the difference between models for different epochs as well as the rms arrival time residuals this problem leads in the case of two epochs to a system of normal equations whose order is twice as great as for a single epoch the direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions we present an algorithm tomo4d that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require

recent and active tectonics in the calabrian arc southern italy normal faulting which has developed since the middle pleistocene with an overall ese wnw extension is the dominant mode of deformation which has characterized the calabrian arc up to the present quaternary normal faults extend for a total length of about 180 km along the inner side of the arc the different normal fault segments which during the pleistocene controlled the evolution of the main marine sedimentary basins are varying in length from 10 to 20 km and have fault escarpments showing a very young morphology which define the fronts of the major mountain ranges of the arc the morphological features of the fault escarpments suggest slip rates of 0 8 1 1 mm yr for the last 700 k y and values of 0 6 0 9 mm yr for the last 120 k y indicating a uniform rate of faulting since the middle pleistocene crustal seismicity and the mesoseismic areas of historical large events 6 5 m 7 1 which occurred in the calabrian arc are located within a narrow belt along the hanging walls of the quaternary normal fault segments this suggests that the normal faults which dissect the inner side of the calabrian arc may be seismically active

tectonics and seismicity of the tindari fault system southern italy crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab 1 the tindari fault system southern tyrrhenian sea italy is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab onshore structural data an offshore seismic reflection profile and earthquake data are analyzed to constrain the present geometry of the tindari fault system and its tectonic evolution since neogene including the present seismicity results show that this zone of deformation consists of a broad nnw trending system of faults including sets of right lateral left lateral and extensional faults as well as early strike slip faults reworked under late extension earthquakes and other neotectonic data provide evidence that the tindari fault system is still active in the central and northern sectors and mostly accommodates extensional or right lateral transtensional displacements on a diffuse array of faults from these data a multiphase tectonic history is inferred including an early phase as a right lateral strike slip fault and a late extensional reworking under the influence of the subduction related processes which have led to the formation of the tyrrhenian back arc basin within the present regional geodynamic context the tindari fault system is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments these tectonic compartments relating to the complex processes of plate convergence occurring in the region the tindari fault system might also be included in an incipient oblique extensional transfer zone linking the ongoing contractional belts in the calabrian ionian and southern tyrrhenian compartments

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries

active upper crust deformation pattern along the southern edge of the tyrrhenian subduction zone ne sicily insights from a multidisciplinary approach abstract using a multidisciplinary dataset based on gravimetric seismic geodetic and geological observations we provide an improved picture of the shallow structure and dynamics of the southern edge of the tyrrhenian subduction zone with a local earthquake tomography we clearly identify two main crustal domains in the upper 15 km characterized by different p wave velocity values a high velocity domain comprising southeasternmost tyrrhenian sea ne sicily and messina straits and a low velocity domain comprising mt etna and eastern sicily the transition between the two domains shows a good spatial correspondence with a wider set of faults including the taormina fault system tfs and the aeolian tindari letojanni fault system atlfs two nearly se striking fault systems crossing northeastern sicily and ending on the ionian shoreline of sicily according to many investigators within this set of faults most of the deformation seismicity occurs along the northern and central segments of atlfs compared to low activity along tfs a lack of seismicity both recent and historical is observed in the southern sector of atlfs where however geodetic data reveal significant deformation our multidisciplinary dataset including offshore observations suggests the southeastward continuation of the atlfs into the ionian sea until joining with the faults cutting the ionian accretionary wedge described in the recent literature our findings imply the existence of a highly segmented crustal shear zone extending from the aeolian islands to the ionian abyssal plain that we believe plays the role of accommodating differential motion between the southern tyrrhenian unit and the western compressional domain of sicily the atlfs which is a main part of the inferred shear zone behaves similarly to what often observed at the edges of retreating subduction slabs where the overriding plate drifts with a highly non uniform transform motion along the lateral borders

the impact of the 24 march 2011 myanmar earthquake ms 7 2 on seismic structure of the yunnan region abstract the temporal and spatial variations of the velocity structure 60 days before and after the march 24 2011 myanmar m7 2 earthquake in the yunnan region are studied by using the ambient noise cross correlation method with the continuous seismic waveform records in addition the response ratio of strain energy release is obtained using moderate and small earthquakes and the coulomb stress changes along different faults are calculated using the source parameters of the myanmar earthquake there are three regions where the velocities increased the area from the zemuhe xiaojiang fault zone to the yuanmou lvzhi fault zone the southern segment of the honghe fault zone and the area from the nantinghe fault zone northward extending to the dayingjiang fault zone the seismic activity and the coulomb stress of these regions are also enhanced by contrast there are several regions where velocities decreased such as the area from the nantinghe fault zone southward extending to the simao region the seismic activity and the coulomb stress of these regions are decreased as well the consistency of the variation indicates some relationship between the variation and the myanmar earthquake