the influence of erosional processes on the visibility of permanent scatterers features from sar remote sensing on mount etna e sicily abstract analysis of 1549 dinsar interferograms covering the period from 2003 to 2010 has highlighted significant motion along the entire set of the active faults identified by advanced dinsar analyses i e permanent scatterers features psf affecting the mount etna volcano in eastern sicily in the analysed period the absence of significant seismicity producing co seismic ground deformation suggests that the overall deformation that has been recognized on the interferograms is to be associated with interseismic almost continuous creep which is well documented along most of the active faults according to field evidence the structures should accumulate displacements resulting in their permanent visibility on the interferograms progressively increases through time this expected behaviour has been recognised only for part of the entire set of structures other tectonic features in fact show episodic appearances alternating with periods of absence of ground displacement on the interferograms simulating a stick slip mechanism of deformation conflicting with field evidence this apparently incongruous behaviour can be interpreted as the result of topographic changes due to the combination of the tectonic displacements with related amounts of the differential erosion and deposition across the fault line the comparison between the history of the appearances and the monthly rainfall in the region seems to demonstrate that these structures appear when one of the two interacting processes governing the topographic changes around the fault i e tectonic vs erosional prevails over the other otherwise the same structures are not evident on the interferograms when the two components are in balance

comment on magnetic studies of magma supply and sea floor metamorphism troodos ophiolite dikes by g j borradaile and d gauthier anisotropy of magnetic susceptibility is used as a proxy for the determination of magmatic flow direction in mafic dykes here we take advantage of the dataset from g j borradaile and d gauthier to comment three points 1 the sampling strategy 2 the geometric relationship between magnetic axis dyke and 3 an alternative interpretation to obtain a flow direction the magnetic lineations published by borradaile and gauthier correspond to the zone axis of the dyke and magnetic foliation poles questioning the reliability of the magnetic lineation as a flow estimate an alternative interpretation is based on the use of the tiling of the magnetic foliation plane against the dyke wall

magnetic fabric development in the lower seve thrust from the cosc 1 drilling swedish caledonides abstract the cosc 1 project drilled the several hundred meters thick basal shear zone of the lower seve nappe with mylonites in mica schists amphibole schists and gneisses in zones of high magnetic susceptibility from 1910 to 2450 m we studied magnetic and petrographic fabrics and magnetic mineralogy borehole imaging allowed for geographic reorientation of the samples and offered the opportunity to study anisotropy of magnetic susceptibility ams in relation to tectonic evolution of the seve thrust we measured ams at room temperature added low temperature and field dependent ams for a subset of samples and compared magnetic with petrographic fabrics triaxial and prolate magnetic fabrics with degree of anisotropy p up to 3 2 together with abundant s c fabrics and strain partitioning around porphyroclasts indicate dominant simple shear until 2300 m magnetite and ilmenohematite mimic the rock fabric due to fabric parallel alignment and or magnetic interaction and either contribute to increase or decrease of p depending on the dominating rock fabric elements field dependency of pyrrhotite and magnetite in kmax direction further increases p homogeneous and oblate petrographic and magnetic fabrics in the greenschist grade overprinted rocks below 2300 m with subhorizontal kmax kint girdle distributions indicate dominant flattening ams depicts shear fabrics including magnetite and ilmenohematite and is additionally increased by retrograde magnetite rutile intergrowth in ilmenohematites we interpret that shape and degree of ams are controlled by a tectonic deformation and strain b alteration and magnetic grain interaction and c field dependency of deformed pyrrhotite and or magnetite we observed that all petrographic and magnetic subfabrics are coaxial and lineations are mainly e w to se nw directed confirming the transport direction of the caledonian allochthonous from our microstructural and ams results we suggest that thrusting of the lower seve unit commenced under simple shear conditions at higher metamorphic grades and subsequently switched to more pure shear under greenschist grade conditions

new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

transpressional tectonics during the emplacement of pasupugallu gabbro pluton western margin of eastern ghats mobile belt india evidence from ams fabrics abstract the pasupugallu gabbro anorthosite pluton intruded the transition zone between the mesoproterozoic eastern ghats granulites and the meso to paleoproterozoic amphibolites and migmatitic gneisses of east dharwar craton southern india the pluton is bound by shear zones at its entire eastern northern and southwestern margins the objective of this work is to study the internal fabric of the pluton to understand the tectonic setting during its emplacement essentially by means of anisotropy of magnetic susceptibility ams a total number of 107 samples have been subjected to ams and irm studies the magnetic fabric is principally ferromagnetic in origin as the magnetic susceptibility values are 10 3 si which is further supported by irm studies the magnetic fabrics correspond well with the field measurements and petrographic studies they show two lobes in both the northern and southern parts which display concentric inward dipping helicoidal foliation trajectories with interlayered steep and gently dipping domains the magnetic lineation pattern suggests that the magma might have ascended through the central lobes and extended towards outer margins particularly to the west the constrictional strains occur at the eastern margin while flattening strains mark the western margin ams studies together with our field structural observations suggest that the magma has been emplaced into a chamber dilational jog induced by crustal scale dextral transpressional tectonic regime probably during the onset of grenvilian event

emplacement and temporal constraints of the gondwanan intrusive complexes of northern patagonia la esperanza plutono volcanic case abstract two main lines of evidence disagree whether or not the patagonian blocks collided with gondwana all models invoke the voluminous magmatism of the la esperanza complex as evidence for active subduction magmatic arc or to a postcollisional setting the evolution of this bimodal igneous suite is reassessed with field geochronological shrimp u pb zircon and k ar mica and petrophysical data emplacement of high k calk alkaline granitic magmas occurred at shallow crustal levels 2 8 2 km depth related to the development and collapse of a caldera associated with a regional nw se structural trend magmatism involved intermediate hybrid pulses at 273 2 ma and 255 2 ma prieto granodiorite that shifted like a yo yo to acidic magmas at 260 2 ma and 250 2 ma donosa and calvo granites absence of solid state deformation features and the low anisotropy degrees in the granites indicate that its fabric is magmatic in origin magnetic fabric in granodiorites displays a concentrical pattern with subhorizontal foliations and lineations parallel to the volcanic axis magnetic foliations and moderately plunging lineations indicate a common feeder system for plutonics and volcanics donosa granite shows a discordant pattern with wnw ese ene wsw trending low plunging lineations and foliations the plutono volcanic system construction 273 255 ma followed nw se and ne sw diamond shape faults trends and supracrustal discontinuities magmatic climax is bracketed at 260 ma the collapse of the edifice is evidenced by the intrusion of acid magma plugs and dike swarms between 250 and 246 ma a similar age range was identified in other areas of patagonia related to syn and postcollisional tectonic events no evidence of tectonic activity such as major uplift metamorphism or thrusting was found excepting regional strike slip faulting and extension therefore la esperanza complex is a high crustal level episode and as such may not have structurally recorded an active collision during its crystallization and cooling

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

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

structural control on the directional amplification of seismic noise campo imperatore central italy abstract seismic signals propagating across a fault may yield information on the internal structure of the fault zone here we have assessed the amplification of seismic noise i e ambient vibrations generated by natural or anthropogenic disturbances across the vado di corno fault campo imperatore central italy the fault zone is considered as an exhumed analogue of the normal faults activated during the l aquila 2009 earthquake sequence detailed structural geological survey of the footwall block revealed that the fault zone is highly anisotropic and is affected by a complex network of faults and fractures with dominant wnw ese strike we measured seismic noise with portable seismometers along a 500 m long transect perpendicular to the average fault strike seismic signals were processed calculating the horizontal to vertical spectral ratios and performing wavefield polarization analyses we found a predominant ne sw to nne ssw i e ca perpendicular to the average strike of the fault fracture network amplification of the horizontal component of the seismic waves numerical simulations of earthquake induced ground motions ruled out the role of topography in controlling the polarization and the amplitude of the waves therefore the higher seismic noise amplitude observed in the fault perpendicular direction was related to the measured fracture network and the resulting stiffness anisotropy of the rock mass these observations open new perspectives in using measures of ambient seismic noise which are fast and inexpensive to estimate the dominant orientation of fracture networks within fault zones

new evidence for the form and extent of the pernicana fault system mt etna from structural and soil gas surveying a multidisciplinary study based on structural and soil gas surveys was carried out in order to investigate the relationship between soil co2 degassing and the tectonic setting of the lower northeastern flank of mt etna volcano the results show that anomalous soil co2 emissions occur mainly along faults trending wnw ese and also where these faults intersect the other main fault set trending ne sw that displaces the study area in particular anomalies in co2 degassing were revealed both along the pernicana fault and along another fault fiumefreddo fault which may represent the prolongation of the former towards the ionian sea coast in the areas where these structures show evident surface faulting they are all characterised by left lateral displacements and aseismic creep behaviour furthermore the geochemical survey revealed that these faults join in an area devoid of geological evidence of surface faulting and continue underneath an apparently unfaulted alluvial cover near the coastline in the light of these findings we suggest that the pernicana and fiumefreddo faults are discrete segments of a near continuous left lateral shear zone affecting the whole north eastern flank of mt etna as far as the ionian coast

wavefield polarization in fault zones of the western flank of mt etna observations and fracture orientation modelling ambient noise measurements performed on the western flank of mt etna are analyzed to infer the occurrence of directional amplification effects in fault zones the data were recorded along short 500 m profiles crossing the ragalna fault system ambient noise records were processed to compute the horizontal to vertical noise spectral ratio as a function of frequency and direction of motion wavefield polarization was investigated in the time frequency domain as well peaks of the spectral ratios generally fall in the frequency band 1 0 6 0 hz pointing out directional amplifications that are also confirmed by the results of the time frequency analysis the largest amplification occurring with high angle to the fault strike a variation of the frequency of the spectral peak is observed between the two sides of the fault possibly related to a damage fault asymmetry measurements performed several kilometers away from the fault zone do not show behavior that is as systematic as in the fault zone and this suggests that the observed directional effects can be ascribed to the fault fabric we relate the polarization effect to compliance anisotropy in the fault zone where the presence of predominantly oriented fractures makes the normal component of ground motion larger than the transversal one in order to test the direction and the type of fractures that are expected in the fault zone we modeled the brittle deformation pattern of the investigated fault theoretical results are in good agreement with field observations of the fracture strike

active faulting and seismicity along the siculo calabrian rift zone southern italy abstract southern italy is dominated by extensional tectonics that in the calabrian arc and eastern sicily produced the development of the siculo calabrian rift zone scrz this zone is represented by a 370 km long fault belt consisting of 10 to 50 km long distinct fault segments which extend both offshore and on land being also responsible of the crustal seismicity of this region the geological and morphological observations indicate that the active normal faults of the scrz are characterized by throw rates ranging from 0 7 to 3 1 mm a they accommodate an almost uniform horizontal extension rate of about 3 0 mm a along a wnw ese regional extension direction based on our field observations and following empirical relationships between magnitude and surface rupture length connections between large crustal earthquakes and distinct fault segments of the scrz have been also tentatively tested our data indicate moreover that the magnitudes m of the historical and instrumental earthquakes are consistent with the estimated values and that the geometry and kinematics of the fault segments and the related different crustal features of the scrz control the different seismic behaviours of adjacent portions of the active rift zone

geological evolution of mount etna volcano italy from earliest products until the first central volcanism between 500 and 100 ka ago inferred from geochronological and stratigraphic data we present an updated geological evolution of mount etna volcano based on new 40ar 39ar age determinations and stratigraphic data integrating the previous k ar ages volcanism began at about 500 ka ago through submarine eruptions on the gela catania foredeep basin about 300 ka ago fissure type eruptions occurred on the ancient alluvial plain of the simeto river forming a lava plateau from about 220 ka ago the eruptive activity was localised mainly along the ionian coast where fissure type eruptions built a shield volcano between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano val calanna moscarello area furthermore scattered effusive eruptions on the southern periphery of etna edifice occurred until about 121 ka ago the stabilization of the plumbing system on the valle del bove area is marked by the building of two small polygenic edifices tarderia and rocche volcanoes their eruptive activity was rather coeval ending 106 and 102 ka ago respectively during the investigated time span volcanism in etna region was controlled by a main e w extensional tectonic related to the reactivation of malta escarpment fault system in eastern sicily

long term uplift rate of the etna volcano basement southern italy based on biochronological data from pleistocene sediments the eastern flank of mt etna volcano rests on pleistocene marine sediments which unconformably cover the apenninic maghrebian chain units a quantitative biostratigraphic analysis was carried out based on the calcareous nannofossil content of the pleistocene deposits outcropping along the s and ne periphery of the volcano sediments were constrained to the mnn19e and mnn19f biozones deposited from 1 2 to 0 589 ma according to the depth of deposition and the present altitude of the pleistocene succession uplift rates are estimated between 1 1 and 1 7 mm yr 1 for the northeastern sector of the etna edifice and between 0 36 and 0 61 mm yr 1 for the southern one this inhomogeneous long term uplift rate affecting the etna region probably results from a buried thrust below the northern flank of etna which is related to the post tortonian geodynamic evolution of ne sicily

local and regional controls on the lateral emplacement of the ben hiant dolerite intrusion ardnamurchan nw scotland abstract sub volcanic and related satellite intrusions record the delivery storage and accommodation of magma before eruption however when several volcanic centres are in close proximity the relationship between centre and satellites may be ambiguous here we examine the structure of the ben hiant dolerite satellite intrusion discuss its relationship with the ardnamurchan central complex located 2 km to the northwest and explore the possibility of a genetic connection with the next nearest centre the mull central complex 35 km to the southeast structural field observations and anisotropy of magnetic susceptibility ams fabric analyses reveal that the ben hiant dolerite was emplaced as a series of lobes in a sequence of stacked sheets the ams fabric data further indicate that the ben hiant dolerite intruded laterally and may have been sourced from either the ardnamurchan central complex or the mull central complex testing either model and discriminating between these two possible source reservoirs remains an outstanding challenge however the potential implications of the lateral movement of magma over many 10 s of kilometres between upper crustal magmatic centres suggests hidden complexities associated with volcanic plumbing systems that must be tested structurally as well as geochemically

evidences for strong directional resonances in intensely deformed zones of the pernicana fault mount etna italy 1 in this paper we investigate ground motion properties in the western part of the pernicana fault this is the major fault of mount etna and drives the dynamic evolution of the area in a previous work rigano et al 2008 showed that a significant horizontal polarization characterizes ground motion in fault zones of mount etna both during earthquakes and ambient vibrations we have performed denser microtremor measurements in the ne rift segment and in intensely deformed zones of the pernicana fault at piano pernicana this study includes mapping of azimuth dependent horizontal to vertical spectral ratios along and across the fault frequency wave number techniques applied to array data to investigate the nature of ambient vibrations and polarization analysis through the conventional covariance matrix method our results indicate that microtremors are likely composed of volcanic tremor spectral ratios show strong directional resonances of horizontal components around 1 hz when measurements enter the most damaged part of the fault zone their polarization directions show an abrupt change by 20 to 40 at close measurements between the northern and southern part of the fault zone recordings of local earthquakes at one site in the fault zone confirm the occurrence of polarization with the same angle found using volcanic tremor we have also found that the directional effect is not time dependent at least at a seasonal scale this observation and the similar behavior of volcanic tremors and earthquake induced ground motions suggest that horizontal polarization is the effect of local fault properties however the 1 hz resonant frequency cannot be reproduced using the 1 d vertically varying model inferred from the array data analysis suggesting a role of lateral variations of the fault zone although the actual cause of polarization is unknown a role of stress induced anisotropy and microfracture orientation in the near surface lavas of the pernicana fault can be hypothesized consistently with the sharp rotation of the polarization angle within the damaged fault zone

a typical calanchi landscape on the eastern apennine margin atri central italy geomorphological features and evolution abstract the surroundings of the town of atri abruzzo region central italy situated about 10 km from the adriatic shoreline can be considered as representative of most part of the italian seaward peninsular landscape the subject of this research the calanchi landscape often generally considered as badlands by non italian authors is in fact made up of many singular landforms each of which calanco corresponds to a more or less extended hydrographic unit the dynamics are mainly the result of the action of the particularly aggressive climatic factors such as the mediterranean rainfall regime on weak substrata clay silt and sand of the plio pleistocene marine cycles the morphogenetic activity is not only limited to channel erosion but it is also due to repeated superficial slides so that it should in fact be better to consider the calanco as the result of a combined erosion process sensu zachar d 1982 soil erosion elsevier amsterdam since the mechanism regulating this process remains unclear this work wants to offer a contribution to this research field multitemporal geomorphological analysis has helped us to distinguish the different areas in which the calanchi evolution has been more or less important in the past in such a way it has been possible to characterize the landscape evolution as a function of the parameters that influence soil loss especially in areas such as that of atri where calanchi like landforms are highly developed moreover this analysis coupled with the processing of 40 years rainfall data also taking into account the concurrent land use changes has clearly shown that the areas affected by calanchi erosion on the eastern apennine margin still tectonically active are progressively diminishing

the relation between magnetite and silicate fabric in granitoids of the adamello batholith abstract the link between the macroscopic silicate fabric and the magnetite controlled ams anisotropy of magnetic susceptibility fabric in ferromagnetic rocks was investigated through a comprehensive comparison between different fabric measurement techniques sample lithologies include tonalites and granodiorites from the lago della vacca complex adamello batholith italy the datasets used to assess the link between subfabrics and the coherence between methods include 1 macroscopic silicate fabric measured directly in the field 2 macroscopic silicate fabric derived from image analysis ia of outcrop pictures and sample pictures 3 shape preferred orientations spo of mafic silicates 4 spo of magnetite and 5 calculated distribution of magnetite grains from computer assisted high resolution x ray tomography x ray ct images 6 fabrics derived from the ams macroscopic mineral fabrics measured in the field agree with the ia results and with the spo of mafic silicates obtained from the x ray ct imaging the x ray ct results show that the spo of the magnetite grains are consistent with the ams data whereas the spatial distribution of the magnetite grains is less compatible with the ams fabric this implies that the ams signal is mainly controlled by the shape of the magnetic carrier mineral rather than by the spatial arrangement of the magnetite grains an exception is the presence of magnetite clusters furthermore the spo of mafic silicates and the spo of the magnetite grains are consistent with the ams data another finding of this study is that the magnetic susceptibility correlates linearly with the amount of magnetite in the samples the coherent results obtained from a variety of methods reinforce the application of both ams measurements and ia as robust tools to analyse fabrics in granitic intrusions

ambient vibration measurements to support morphometric analysis of a pyroclastic cone pyroclastic cones are a typical feature on volcanoes characterized by flank activity their distribution and orientation are important markers to obtain information on the maximum horizontal compressional stress acting on a volcano a geophysical survey was performed on the pyroclastic cone of mt vetore mt etna volcano southern italy to obtain information on its internal structural setting and to support the standard morphometric analysis results highlighted evident frequency peaks at 1 0 hz inside the cone which are attenuated away from it the random decrement method was applied to this peak to compute damping and then to exclude links with anthropogenic sources moreover time frequency polarization analysis revealed that ambient vibrations are strongly polarized in a narrow frequency band centered at a frequency of 1 0 hz with a preferred oscillation azimuth of 70 90 n array measurement of ambient vibrations was also used to obtain a shear wave velocity profile and then to retrieve the main interfaces with high seismic impedance results suggest a cone structure having a feeder dike consisting of fractured rocks with thickness of about 50 m surrounded by pyroclastic material lying on a high velocity substrate finally a 3d model of mt vetore cone was built employing the finite element method to reproduce an experimental modal frequency of the cone itself the numerical results successfully reproduced the experimental ones collected by the geophysical survey

the valle del bove mount etna its origin and relation to the stratigraphy and structure of the volcano abstract the valle del bove is a major horseshoe shaped depression some 5 km in diameter and over 1000 m deep carved into the eastern flank of mount etna volcano the origin of the valle del bove has been a subject of debate for over a century but recent models relate it to the collapse of the ancient trifoglietto ii centre of etna either by caldera collapse or phreatomagmatic explosive activity careful morphological analysis shows the valle del bove to have formed after the post trifoglietto ii ellittico and leone centres and therefore to be considerably younger than the trifoglietto ii centre it has also been argued that the pyroclastic deposits that occur on the flanks of the volcano in close spatial relationship with the valle del bove were produced by the same event these pyroclastics are divided on the basis of age and composition into two groups the upper and lower tephra deposits the stratigraphy petrology and radiocarbon date of the lower tephra deposits indicate a trifoglietto ii age at least 20 000 years before the formation of the valle del bove the upper tephra deposits have a strong phreatomagmatic character and are closest in age to the valle del bove there is no evidence however to link them with its formation morphological study shows the valle del bove to consist of a series of coalescing scallops indicative of formation by landsliding the material removed by slope failure and subsequent fluvial transport followed a valley to the coast where it forms a fan shaped accumulation the chiancone consisting of volcaniclastics of fluvial and mudflow origin it is argued that the valle del bove did not result from simple caldera collapse but formed from a series of collapses caused by gravitational slope failure the chiancone is considered to be the product of this collapse

magnetic fabric studies of the nipissing sill province and senneterre dykes canadian shield and implications for emplacement the 2 21 ga nipissing diabase sills intrude the huronian supergroup of the southern province coeval senneterre dykes in the adjacent portion of the superior province are potential feeders for the sills anisotropy of magnetic susceptibility ams data were obtained from both of these units to study flow patterns and test emplacement models the sills exhibit three distinct paleomagnetic directions that are likely primary and represent a time correlation tool within the magmatic event two of the three directions are also found in senneterre dykes sites in the northern cobalt embayment carry an n1 reverse paleomagnetic signature they possess maximum ams axes that trend north northwest south southeast interpreted as the direction of magma emplacement in one area the data rule out a cone sheet emplacement mechanism the n3 paleomagnetic signature is restricted to a sill and or dyke like bodies near lake timiskaming where the ams axes are dominantly north northwest south southeast similar to that of the nearby n1 reverse sites sites in a geographically restricted area farther south carry an n1 normal paleomagnetic direction the ams patterns in these sites exhibit very poor within and between site consistency compatible with the magma having crystallized statically in this volumetrically minor magmatic pulse in the sudbury elliot lake area the nipissing diabase is deformed and outcrops exhibit east west elongation parallel to the fold axes of the enclosing huronian sedimentary rocks ams fabrics are interpreted as reflecting this deformation rather than primary magmatic flow three of eight senneterre dyke sites show horizontal flow patterns whereas the remainder have more complicated ams patterns

remanence stability and magnetic fabric development in synthetic shear zones deformed at 500 c shear experiments were performed on magnetite bearing calcite aggregates to examine magnetic fabric development and remanence stability in a deforming system using elevated temperature and pressure to encourage deformation by crystal plastic processes samples composed of 1 wt pseudo single domain magnetite 1 2 m in a calcite matrix were created with either strong or weak initial fabrics and deformed in coaxial simple shear to strains up to 1 5 at constant strain rates between 6 10 5 and 1 10 4 s 1 at 500 c and confining pressure of 300 mpa samples were given weak field thermal remanent magnetizations prior to deformation demagnetization of postdeformation remanence reveals that a primary remanent magnetization can withstand deformation at pressures and temperatures approximately equivalent to greenschist facies metamorphic conditions on laboratory time scales but this stability is found to depend on the character of the predeformation fabric the origin of secondary remanence components acquired during deformation is uncertain but is likely to partially result from thermal viscous remagnetization complete postdeformation remagnetization in initially anisotropic samples appears to involve a stress softening or piezoremanent magnetization mechanism postdeformation anisotropy measurements show progressive changes in magnetic fabric strength with strain in the absence of a strong initial magnetic anisotropy magnetic fabric intensity increases linearly as a function of strain however deformation that overprinted an existing fabric results in an apparent decrease of the initial anisotropy at low strains followed by rapid increases in magnetic fabric strength with increasing strain our results underscore the important role that initial fabric can play in determining the character of deformation fabrics

changing in crust mechanical behaviour due to raising magma a fracturing model of se flank of mt etna sicily abstract associated with the remarkable flank eruption which started in late october 2002 a series of earthquakes occurred on the lower eastern flank of mt etna the m d 4 4 bongiardo s venerina earthquake at 10 02 am gmt 29th october affected a large nnw sse area severely damaging nearby villages the faulting model proposed in this paper seeks to justify the two causes of the fracturing process as well as its spatiotemporal development for this purpose a preliminary analysis of the morphotectonic framework and the detected fractures linked to october 2002 earthquakes has been carried out we will therefore consider the seismic activity which affected the volcano in 2001 and 2002 additionally we will review previous scientific studies of seismic tomography and macroseismic data in particular the fracturing mechanisms appear to be linked to the volcanic area uplift as a consequence of rising magma the consequent change in the rheology beneath this sector of the volcano explains the differing reaction of the crust at different levels

empirical evidence of orthogonal relationship between directional site effects and fracture azimuths in an active fault zone the case of the mt etna lower eastern flank abstract mt etna in eastern sicily is a composite active volcano whose eastern flank is affected by several normal and strike slip active faults in this study geological structural field survey and ambient vibration measurements are performed in the lower eastern flank of mt etna in order to define the role of the tectono stratigraphic setting in the seismic site response the sites of measurements are mainly distributed inside the few hundreds of meters long s caterina graben which is located between two main seismogenic active faults of this volcano sector the acireale and the fiandaca faults our study aims at defining the contribution of the fault related active deformation in determining the local ground motion amplification also providing a subsoil geological model based on the integration of geological and geophysical investigation therefore structural measurements were made in seven sites revealing coseismic and aseismic extensional fractures mainly striking nnw the seismic site response was studied processing the ambient vibration measurements through horizontal to vertical spectral ratio the measured fundamental frequency falls in the range 1 0 4 0 hz that we linked to the presence of a velocity contrast at depth of 80 200 m by calibrating a frequency depth function moreover the seismic site effect is due to the stratigraphic setting and is markedly directional showing maximum amplification along the direction orthogonal to the strike of the observed isooriented extensional fracture field produced by the activity of the s caterina graben it is noteworthy that far from the graben on sites of measurements located near the fiandaca fault we observed directional effects parallel to the direction of maximum extension inferred for this tectonic lineament our results suggest a linkage between directional site effects and local stress tensors and fractures field orientation

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

horizontal polarization of ground motion in the hayward fault zone at fremont california dominant fault high angle polarization and fault induced cracks summary we investigate shear wave polarization in the hayward fault zone near niles canyon fremont ca waveforms of 12 earthquakes recorded by a seven accelerometer seismic array around the fault are analysed to clarify directional site effects in the fault damage zone the analysis is performed in the frequency domain through h v spectral ratios with horizontal components rotated from 0 to 180 and in the time domain using the eigenvectors and eigenvalues of the covariance matrix method employing three component records the near fault ground motion tends to be polarized in the horizontal plane at two on fault stations where the local strike is n160 ground motion polarization is oriented n88 19 and n83 32 respectively at a third on fault station the motion is more complex with horizontal polarization varying in different frequency bands however a polarization of n86 7 similar to the results at the other two on fault stations is found in the frequency band 6 8 hz the predominantly high angle polarization from the fault strike at the hayward fault is consistent with similar results at the parkfield section of the san andreas fault and the val d agri area a quaternary extensional basin in italy in all these cases comparisons of the observed polarization directions with models of fracture orientation based on the fault movement indicate that the dominant horizontal polarization is near orthogonal to the orientation of the expected predominant cracking direction the results help to develop improved connections between fault mechanics and near fault ground motion

the nuuanu and wailau giant landslides insights from paleomagnetic and anisotropy of magnetic susceptibility ams studies abstract the koolau volcano on the northeastern flank of the island of oahu in hawaii is the source area for one of the largest landslides on earth the nuuanu debris avalanche the offshore expression of this slide is an extensive rubbly field of debris extending approximately 230 km from the island across the hawaiian deep and onto the hawaiian arch we have studied the subaerial lavas of the koolau volcano as well as the deep sea sediments on top of the nuuanu and wailau landslides by means of magnetostratigraphy and magnetic anisotropy studies to investigate the volcanic evolution the plumbing of the koolau volcano and the timing of the nuuanu detachment in addition we have conducted deep sea magnetostratigraphic studies of a 20 and 7 m piston core recovered by the rv kana keoki and the rv bertha ann as well as three 7 m piston cores recovered by the rv kairei to understand the origins of the giant landslides the results derived from these investigations indicate that the plumbing of the koolau volcano is characterized by a very coherent dike complex and by a high dike injection nature parts of the koolau complex are a sheeted dike swarm as in ophiolites as demonstrated by geologic and anisotropy of magnetic susceptibility ams studies on the other hand the magnetostratigraphic results of the subaerial part of the koolau complex indicate that at least one of the normal reunion subchrons ca reunion ii 2 15 0 04 to 2 11 0 04 ma had been registered at two different locations deep sea cores have recorded several reversals the oldest one is the top of the olduvai subchron ca 1 78 ma land and deep sea paleomagnetic and plumbing investigations indicate that the collapse of the koolau volcano had to be relatively rapid in a period of less than 0 5 ma due to forceful injection of dikes associated with extension and gravitational effects therefore the timing of the main collapse of the koolau volcano that originated the nuuanu landslide had to occur between 2 1 and 1 78 million years ago based on the magnetostratigraphic evidence

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

deep characterization of the santiago basin using hvsr and cross correlation of ambient seismic noise abstract continuously recorded seismic ambient noise is used to investigate the intermediate and deep structure of the santiago basin for seismic site response evaluation single station h v spectral ratios hvsr were used as a proxy to identify zones with high stiffness soils and low impedance contrast with the underlying bedrock as a complement of available surface geology information frequency domain cross correlation of the vertical components of ambient noise were calculated and used to estimate phase velocity dispersion curves associated to station pairs over different soil deposits in addition noise correlation functions ncfs calculated from time domain cross correlation of the vertical seismic noise records were used to estimate group velocity dispersion curves and to verify results from the spectral method data processing from both methods resolves a frequency band between 0 1 and 8 0 hz a critical band for civil infrastructure that is difficult to determine with traditional local scale passive surface wave methods station pairs with high signal correlation over stiff soils in the center south and east part of the basin mainly associated to flat hvsr response yielded robust phase velocity dispersion curves that vary approximately from 3 5 km s at 0 1 hz to 1 km s at 4 hz shear wave velocity profiles inverted from the dispersion curves show high average shear wave velocities that also have a pronounced increase rate with depth and a lack of clear soil bedrock interface at depths predicted by available gravimetric data

investigating the magmatic plumbing system of a monogenetic scoria cone a field and laboratory study of the cienega scoria cone cerros del rio volcanic field new mexico

magnetite grain shape fabric and distribution anisotropy vs rock magnetic fabric a three dimensional case study abstract shape fabric and distribution anisotropy of magnetite grains in a highly ferromagnetic s l syenite are determined for three mutually perpendicular planes on about 600 magnetite grains the grains are lenticular with an average aspect ratio of about 2 0 their preferred orientation determined by the inertia tensor method is consistent with the principal directions of the magnetic susceptibility ellipsoid and the axial ratios of the magnetic fabric ellipses are very close to those of the shape fabric ellipses e g 1 41 and 1 39 in the section plane perpendicular to the magnetic foliation and parallel to the magnetic lineation the anisotropic wavelet transform can detect and quantify the anisotropic distribution of the magnetite grains which are located interstitially along the feldspar grain boundaries this anisotropic distribution has no noticeable effect on the rock s anisotropy of magnetic susceptibility ams since only a few percent of grains are close enough to interact magnetically therefore it is realistic to consider that the ams of ferromagnetic granitic rocks originates mainly from the shape fabric of anisotropic magnetite grains and a close correlation between the magnetic fabric and the magnetite grain shape fabric is expected

directional site resonances observed from aftershocks of the 18 october 1989 loma prieta earthquake abstract two weeks after the 18 october 1989 loma prieta california earthquake 18 three component digital seismometers were deployed in the epicentral area to form three six station subarrays the subarray configuration allowed us to investigate the presence of direction and frequency dependent site resonances we measured the shear wave polarization from the recordings of 10 aftershocks from the loma prieta earthquake our observations show that the site response has a strong azimuthal dependence and that both the shear wave polarization and the spectral amplitude of the ground motions are affected by site characteristics in the frequency range from 1 to 18 hz the majority of stations examined showed preferred azimuths of ground motion for the scattered waves that did not depend either on the earthquake location or on the polarization of the shear waves expected from the known focal mechanism the measurements were made from 5 sec windows that included direct and scattered shear waves which contain the largest amplitude motions in the near source region and are therefore of most interest to earthquake engineers however in the 0 to 2 hz frequency range the first pulse of shear waves shows a polarization that is well predicted by the mechanism and location of the earthquake the rapid spatial variation of the preferred directions and their corresponding frequencies indicate that geologic structures within a distance of the order of 50 m probably control these site effects we suggest that the site amplified the motion of scattered waves in one preferred direction altering the resulting polarization and modulating the spectral amplitude

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

determination of flow directions by combining ams and thin section analyses implications for oligocene volcanism in the kerguelen archipelago southern indian ocean we report an anisotropy of magnetic susceptibility ams study carried out on seven oligocene volcanic sections widely distributed on the surface of the kerguelen archipelago the statistical results at flow scale and at section scale were checked with ams density diagrams and thin section analysis because of the axis permutations frequently observed for lava flows two possible flow directions were nicely defined for the majority of the sections we then used two alternative approaches imbrication of the minimum axis and symmetry of the ams distribution to infer a flow direction for each section these two methods and thin section analysis not being decisive for choosing between the two solutions geological and geomorphological observations were finally used to obtain confident interpretations the results of this study enable the supposed eruptive centres of the kerguelen archipelago to be located more precisely

magma flow inferred from ams fabrics in a layered mafic sill insizwa south africa the insizwa sill is a 25 km diameter 1000 m thick layered mafic intrusion part of the karoo igneous province in south africa the peridotitic and gabbronoritic rocks are undeformed and mineral fabrics demonstrably result from magma flow a horizontal centimeter scale model layering is visible in numerous outcrops plagioclase crystals are both tabular and elongated their preferred orientation parallel to the layering forms a foliation and a nw se lineation respectively interpreted as the magma flow plane and flow direction throughout the 78 stations of this study 699 specimens magnetic susceptibilities km range from 750 to 10 000 10 6 si the magnetic anisotropy pj ranges from 1 03 to 1 08 magnetic ellipsoids are both prolate and oblate average tjc0 anisotropy of magnetic susceptibility ams fabrics are dominated by multidomain to pseudo single domain magnetite high field magnetic experiments indicate that the paramagnetic contribution from the mafic silicates is less than 50 for low susceptibility rock types the anisotropy results from magnetite grain shape solely as shown by no significant increase in pj with increasing km the magnetic lineation 305j 0 5j is consistent throughout the sill at various scales and coincides with the mineral lineation in average in contrast the magnetic foliation 125j ne 10j is generally perpendicular to the mineral foliation and to the layering several explanations for this odd configuration are discussed the variations of magnetic parameters across the layering and field observations point to a multiple injection the magnetic lineation is consistent with the presence of a single feeder dike situated to the se of the sill d 2002 elsevier science b v all rights reserved

the relationship between late quaternary deformation and volcanism of mt etna eastern sicily new evidence from the sedimentary substratum in the catania region abstract stratigraphical and structural analyses have been carried out on the late quaternary foredeep succession forming the etnean substratum in the catania region eastern sicily in order to investigate in detail the chronology of deformation events that have accompanied a significant period of the eruptive activity of mt etna i e from 240 ka to the present this episode was characterised at about 200 ka by a main change of the petrochemical features of the emitted products from sub alkaline to alkaline this can be related to an evolving mantle diapir located beneath the volcano the new stratigraphical and structural field data presented in this paper constrain the development from 240 to 125 ka of nw se trending dextral faults associated with minor e w to ne sw oriented accommodation thrusts and nnw sse trending normal faults that originated in a dominant transpressive regime strike slip tectonics were active during the earlier emissions of sub alkaline lavas 320 200 ka old and part of the ancient alkaline products 180 100 ka old from scattered eruptive systems which developed in local transtensive zones distributed throughout the whole etnean region a major change in the mode of deformation since 125 ka bp was related to the propagation of a normal fault belt along the ionian coast of the catania region and the eastern sectors of the etnean edifice this process was associated with the growth of open folds that deformed the entire foredeep sequence exposed along the southern boundary of the etnean edifice during this period eruptive activity concentrated along the main extensional features where steady and very efficient feeding systems originated this resulted in a rapid increase in the volume of emitted alkaline products that gave rise to the construction of the modern stratovolcano during the last 80 ka the collected data emphasise some main aspects of the relationship between tectonic deformation at a regional scale and volcanism in the etna area firstly the mode of deformation at the onset of etnean volcanism seems to be inadequate to explain the emplacement at depth of a mantle diapir related to the occurrence of a hotspot almost independent from the local crustal dynamics on the other hand the late quaternary structural assemblages recognised on the surface can be interpreted as direct effects of the europe africa convergence rather than as the products of deformation induced by the emplacement of the mantle diapir in the different stages of etnean evolution a direct relationship exists between the mode of deformation and the distribution as well as the capacity of the feeding systems in particular the amounts of emitted products in the different stages depend on the intensity of crustal stretching associated with deformation rather than the volume of available molten material at depth these conclusions represent a new perspective for the interpretion of the early stages and subsequent evolution of the volcanic activity of mt etna the proposed model also represents an useful tool in deciphering the relationship between the deformation path seismicity and volcanic activity of mt etna

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

a multidisciplinary study of the volcanoclastic deposit named chiancone inland and offshore in the frame of the evolution of volcanism in the etna area abstract in this work a detailed study about the volcanoclastic deposit pyroclastic cone called chiancone is carried out by 98 vertical electrical soundings vess and by analysis of the surface morphology made by two digital elevation model dem with high resolution the results seem to confirm what has been suggested by other researchers and shed some light on some dark aspects of this volcanoclastic deposit in particular it was found that the chiancone is quite a complex geologic formation whose deposition took place in several steps filling in depressions of various conductive substrate to depths of at least 300 m below the sea level the conductive substrate generally shows a higher resistivity than a clay one and is strongly tectonized and eroded the multibeam surveys carried out offshore in the ionian sea allow us to identify the geolithological nature of the substrate never before detected in the past they show the existence of an outcrop of a large cone shaped submarine pyroclastic body about 600 m deep covered near the coast by chiancone deposits the authors believe therefore that this pyroclastic body may form inland the conductive substrate of the formations outcropping in the studied area lava and chiancone and representing the product of the demolition of one or more existing volcanic apparatuses prior to the trifoglietto and mongibello which was given in the past the name of ancient etna

paleocurrent direction measurements in a volcanic setting by means of anisotropy of magnetic susceptibility a case study from the lower miocene tepoztlan formation transmexican volcanic belt central mexico sources of ancient volcanic rocks are often unknown if they are either eroded and or covered by younger deposits this problem as well as the provenance of reworked volcaniclastic fluvial and mass flow deposits can be partially solved by the application of anisotropy of the magnetic susceptibility ams for massive and poorly sorted volcaniclastic rocks in particular this may be the only way of finding reliable transport directions and therefore allowing for paleogeographic reconstructions here we present a data set of 428 ams measurements and 249 measurements of sedimentary paleocurrent indicators from the miocene tepoztlan formation at the southern edge of the transmexican volcanic belt central mexico the highest degree of reliability of ams measurements is gained for data from lava samples and the lowest from mass flows sedimentary structures in sandstones and conglomerates such as trough cross stratification asymmetric ripple marks and the shape of scours and channels could be used to calibrate the results from ams data and to prove their reliability ams data on fluvial deposits point to a drainage system with a w e flow direction indicating an outflow of the river system into the ancient gulf of mexico

magnetic and shape fabrics of magnetite in simple shear flows abstract the magnetite fabrics measured by anisotropy of magnetic susceptibility ams and by shape preferred orientation spo optical methods are classically used as flow kinematics indicators in lava flows the development of magnetite fabrics during simple shear strains 20 was performed using a suspension of 1 volume fraction of multidomain magnetite randomly contained in a mixture of silicone and wax we measured ams fabric and spo ellipsoids by calculating a quadratic shape tensor from oriented thin sections for jeffery 1922 fabrics are usable to determine the flow kinematics including the amount of applied finite strain for 8 fabric elements foliation and lineation are stabilised closely parallel to the flow plane and the shear direction respectively two and three dimensional numerical simulations using measured aspect ratios of magnetite point out that the large scattering of aspect ratios and the initial orientation distribution of particles are together responsible for a wide ranging loss of periodicity the stable ams and spo fabrics observed at large strains in experiments are the result of these primary fabric properties combined to collisions between particles and possibly their complex three dimensional shapes in addition the constant angular relationship observed at large strains between fabrics and flow components is related to the transient collisions consequently the determination of the lava flow kinematics by using fabric properties measured either by ams or by spo analyses should be indubitably associated to a detailed study of the three dimensional shape of the solid carriers regularly shaped populations of low elongated particles will be capable to produce cyclic to oscillating fabrics while the fabric of elongated particles will be more sensitive to the shape parameters and collisions ultimately favouring stable fabrics at large strains

internal fabric and strike slip emplacement of the pan african granite of solli hills northern nigeria the solli hills pluton 250 km2 in northern nigeria is an example of a pan african granite emplaced circa 580 ma ago in the jos adamawa block its micro structures and internal fabrics have been studied in order to help constrain the kinematics of the pan african orogeny in this block we used field observations and measurements petrographic examinations and measurements of the magnetic susceptibility and anisotropy of magnetic susceptibility of 124 regularly spaced stations most samples are ferromagnetic i e belong to the magnetite series granites and present predominantly magmatic microstructures particularly remarkable are the asymmetrical zoning of the petrographic types the susceptibility magnitudes and the planar linear magnetic fabrics the magnetic foliations and lineations are very consistent in the pluton around n 20 e 60 w and n 205 e 10 respectively field and microscopic observations reveal that deformation occurred everywhere in the pluton and immediate country rock envelope during a dextral strike slip synplutonic episode it is suggested that the solli hills pluton was emplaced in a late pan african dextral tear fault system the striking fabric asymmetry of the pluton strongly suggests a shear zone termination emplacement model

late quaternary tectonics and active ground deformation in the catania urban area eastern sicily new constraints from a geological investigation abstract new surface and subsurface geological data on the catania urban area in eastern sicily are here illustrated by a detailed geological map of the city and by four significant cross sections our study aims at defining the prolongation of the principal regional late quaternary tectonic features beneath the city the resulting geometry of the investigated structures completes the tectonic pictures of two different stages of deformation the earlier structural association ranging in age from 600 to 125 ka consists of a transpressive dextral belt that include e w oblique thrust ramp located to the south and the north of the city respectively connected by a wide ne sw oriented anticline crossing the urban area the younger structural association developed since the late pleistocene and includes a set of ene trending folds that originated at the hangingwall of a main thrust ramp running just beneath the old town catania thrust ramp these contractional features have been active during the last 60 ka and their geometry is consistent with the active ground deformation observed by the available geodetic data gps vectors and dinsar analyses the entire set of the recent structures are bordered to the north by a dextral transfer zone reactivating part of the previous e w alignment that now represents the tectonic boundary with the mt etna volcano transtensional domain our data suggest that the catania thrust ramp could play a main role in the active deformation pattern of the region thus representing a potential seismotectonic feature to be carefully investigated for the re evaluation of the seismic hazard of the area

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

stratigraphic constraints for explosive activity in the past 100 ka at etna volcano italy the pyroclastic deposits of etna have been correlated over the whole volcanic edifice for the first time allowing the construction of a continuous record of tephra producing events which extends from approximately 100 ka to the present in this interval five main periods of explosive activity have been identified a 100 ka strombolian to subplinian activity b 80 to 100 ka plinian benmoreitic activity c 16 to 80 ka strombolian to subplinian from basaltic to mugearitic activity d 15 5 to 15 ka plinian benmoreitic activity accompanying the caldera forming eruptions of the ellittico volcano and e the most recent 13 ka basaltic explosive activity of strombolian and subplinian type of the present edifice that also includes the 122 b c plinian eruption this study results in a semi quantitative and in some cases quantitative definition of the intensity and chronology of the explosive activity at etna moreover this work gives a new significance to the volcanic hazards of etna a volcano generally considered to be the site of gentle effusive eruptions

microtremors hvsr and its correlation with surface geology and damage observed after the 2010 maule earthquake mw 8 8 at talca and curico central chile nowadays microtremors horizontal to vertical spectral ratio hvsr has been extensively used in the estimation of the predominant vibration frequency of soils mainly for microzonation purposes in the present study we show results from extensive microtremor measurements performed at the cities of talca and curico central chile we found a strong correlation between surface geology and microtremors hvsr even in complex geological settings considering the damage produced by the 2010 maule earthquake mw 8 8 we also estimated high density macroseismic intensities at these cities with values ranging from vi up to viii on the msk64 scale we believe that the main responsible of these variations are the surface geological conditions also reflected in the variations of the resonance frequencies of the soils the evidence presented here supports the use of microtremors hvsr in combination with surface geology to improve seismic microzonation studies particularly in an andean context

new results of 40ar 39ar dating constrain the timing of transition from fissure type to central volcanism at mount etna italy recent geological studies performed at etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined this stratigraphic reconstruction was chronologically constrained on the basis of a limited number of u th and k ar age determinations whose uncertainty margins are sometimes too wide for this reason we successfully adopted at etna the 40ar 39ar technique that allowed obtaining more precise age determinations the incremental heating technique also gives information on sample homogeneity and potential problems of trapped argon five samples were collected from stratigraphically well controlled volcanic units in order to chronologically define the transition between the fissure type volcanism of the timpe phase to the central volcanism of the valle del bove centers isotopic ages with an uncertainty margin of 2 4 have been obtained emphasizing that this transition occurred 130 126 ka without significant temporal hiatus

correlation between earthquake damage and seismic site effects the study case of lentini and carlentini italy abstract on december 13th 1990 a magnitude 5 6 seismic event felt throughout sicily and having maximum seismic intensity vii viii occurred although it is classified as moderate magnitude it caused causalities and the collapse of a few buildings two of the most struck cities were carlentini and lentini located in south eastern sicily at about 20 km from the instrumental epicenter in order to evaluate the influence of ground features on the damage distribution both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments significant damage observed in some portions of the investigated areas appears related to the modest quality of the buildings that were classified as medium to high vulnerability to evaluate the role played by the geologic setting two sites were instrumented to measure shear wave velocity of the main lithotypes sixty three ambient vibrations measurements were also performed both in free field and inside some buildings moreover using information coming from geological and geophysical surveys 1d numerical modelling were done to achieve information about the main ground motion parameters the results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event seismic site amplifications together with the buildings vulnerability observed through damage surveys contributed to enhance the inherent seismic risk of the investigated area

paleo environmental and volcano tectonic evolution of the southeastern flank of mt etna during the last 225 ka inferred from the volcanic succession of the timpe acireale sicily abstract the tectonic escarpments locally known as timpe cut a large sector of the eastern flank of etna and allow an ancient volcanic succession dating back to 225 ka to be exposed geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures as well as important changes in the nature composition and magmatic affinity of the exposed volcanics in particular the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward dipping to the progressive tectonic tilting of strata these elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka bp and their relationship with tectonic structures active in the eastern flank of etna we propose a complex paleo environmental and volcano tectonic evolution of the southeastern flank of mt etna in which the timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span

magma emplacement into the lemptegy scoria cone chaine des puys france explored with structural anisotropy of magnetic susceptibility and paleomagnetic data the lemptegy volcano is a small monogenetic scoria cone located in the chaine des puys auvergne france which erupted about 32 000 years ago a first edifice lemptegy 1 formed during a trachybasalt eruption as a group of satellite vents of the puy de gouttes scoria cone a second trachyandesitic edifice lemptegy 2 formed soon after and completely covered lemptegy 1 with an 80 m high breached cone since 1946 the lemptegy volcano has been quarried for scoria and today offers unprecedented three dimensional exposure of the subvolcanic plumbing system to map the internal flow architecture of the plumbing system and to study the subvolcanic deformation of lemptegy 2 structural mapping petrographic observations anisotropy of magnetic susceptibility ams rock magnetic and paleomagnetic data were collected field structural mapping and thin section study of tension gashes riedel shears striations as well as ductile shear zones and bubbles allow the direction and sense of the magma flow to be determined twenty ams sites were established in ten dikes one to four sites in each dike with 504 specimens analyzed and 479 specimens used to infer magma flow patterns structural data the maximum susceptibility axis k 1 and the imbrication of the magnetic foliation k 1 k 2 planes indicate both upward and downward sense of flow as well as flow toward and away from the central vent rock magnetic experiments reveal that a cubic fe ti oxide phase likely low ti titanomagnetite is the principal magnetic phase carrying both the remanence and anisotropy paleomagnetic data from some sites yield statistically distinct at the 95 confidence level remanence directions while at other sites the data are indistinguishable at the 95 confidence level the paleomagnetic results observed steeply tilted scoria layers internal unconformities and faults show that as each dike was emplaced it displaced earlier dikes evidencing subvolcanic deformation the lemptegy 2 volcano shares similarities in terms of inferred eruption style and structures with other scoria cones such as cerro negro nicaragua and thus provides an excellent field laboratory to investigate active scoria cones world wide

magma rheology variations in sheet intrusions of the ardnamurchan central complex scotland inferred from gabbro inclusion characteristics entrainment of xenoliths and their consequent assimilation are key processes in modifying the crystallization kinetics and magma dynamics of conduit systems here an integrated textural and mineral chemical study of the evolution of a suite of gabbroic inclusions within a set of sheet intrusions from the ardnamurchan central complex nw scotland is presented the key findings are as follows 1 the host magma sheets and inclusions are not cognate 2 there are microstructural and mineral chemical similarities between the gabbroic inclusions and the textures and mineralogy of the major hypersthene gabbro on ardnamurchan 3 orientations of magnetic fabrics within the host sheet groundmass and within the gabbroic inclusions are virtually identical field observations suggest that the inclusions were derived from the hypersthene gabbro and were entrained in a few laterally restricted magma segments that subsequently coalesced with inclusion free segments into continuous sheets using stokes law and adaptations thereof we calculate that the magma within the inclusion free segments behaved as a newtonian fluid with a potential settling velocity of50 028 m s in contrast the presence of gabbro inclusions probably modified the magma dynamics to bingham like behaviour we infer that this variation in the magma rheology of separate segments continued after coalescence and internally partitioned the magma sheet preventing lateral mixing and inclusion transport

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and their bearing on the yinshan yanshan orogenic belt part ii anisotropy of magnetic susceptibility and gravity modeling abstract granitoids play an important role in deciphering both crustal growth and tectonic evolution of earth in the eastern end of the yinshan yanshan belt of north china craton the yiwulushan massif is a typical region that presents the tectonic evolution features of this belt our field work on the host rocks has demonstrated two phases of opposite tectonics compressional and extensional however the deformation is almost invisible in the intrusive rocks to improve the understanding of the tectonic evolution of the yiwulushan massif and the late mesozoic tectonics of east asia a multidisciplinary study has been carried out in this study anisotropy of magnetic susceptibility ams and gravity modeling have been applied on these jurassic plutons lushan jishilazi and guanyindong which intrude into the yiwulushan massif according to laboratory measurements and microscopic observations on thin sections the ams of the yiwulushan massif is characterized by secondary fabrics indicating that the intensive post solidus deformation has reset the primary magmatic magnetic fabrics a relatively gentle nw dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of n34 e and n335 e orientations namely lm1 and lm2 relatively gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif integrating all results from structural observation geochronological investigation ams measurement and gravity modeling two tectonic phases have been identified in the yiwulushan massif posterior to the jurassic 180 160 ma magmatism in the yinshan yanshan area the early one concerns a late jurassic early cretaceous 141 ma compressional event with a top to the south to southwest sense of shear the second one shows an early cretaceous 126 ma nw se ductile extensional shearing at that time sedimentary basins widened and jurassic plutons started to be deformed under post solidus conditions in fact the nw se trend of the maximum stretching direction is a general feature of east asian continent during late mesozoic

fracture related wavefield polarization and seismic anisotropy across the greendale fault we investigate seismic signatures of fracturing in a newly ruptured strike slip fault by determining the wavefield polarization in the new zealand canterbury plains area and across the greendale fault which was responsible for the 3 september 2010 darfield mw 7 1 earthquake previous studies suggested that fractured rocks in fault damage zones cause directional amplification and ground motion polarization in the fracture perpendicular direction as an effect of stiffness anisotropy and cause velocity anisotropy with shear wave velocity larger in the fracture parallel component an array of 14 stations was installed following the darfield earthquake we assess polarization both in the frequency and time domains through the individual station horizontal to vertical spectral ratio and covariance matrix analysis respectively and compare the results to previously reported anisotropy measurements from shear wave splitting stations installed in the canterbury plains have an amplification peak between 0 1 and 0 3 hz for both earthquakes and ambient noise we relate the amplification to the resonance of a considerable thickness c 1 km of soft sediments lying over the metamorphic bedrock analysis of seismic events revealed the existence of another peak in amplification between 2 and 5 hz at two on fault stations which was not visible in the noise analysis in contrast to the lower frequency peak the ones between 2 and 5 hz are more strongly anisotropic attaining amplitudes up to a factor of 4 in the n52 direction to interpret this effect we model the fracture pattern in the fault damage zone produced by the fault kinematics we conclude that the horizontal polarization is orthogonal to extensional fractures which predominate in the shallow layers 2 km expected in n101 direction on the basis of the model thus different fracture distribution at different depths may explain different results for amplification compared to anisotropy we propose polarization amplification analysis as a complementary method to s wave splitting analysis polarization analysis is rapidly computed and robust and it can be applied to either earthquakes or ambient noise recordings giving useful information about the predominant fracture patterns at various depths

quaternary negative tectonic inversion along the sibillini mts thrust zone the arquata del tronto case history central italy geological and geophysical investigations have been carried out in the surroundings of the villages of pretare and piedilama in the central apennines this area located at the footwall of the prominent nne ssw oriented sibillini thrust front was struck by the august 24th 2016 mw 6 earthquake the results of the geological field survey combined with geological and geophysical subsurface investigations are here illustrated by a detailed geological map and by two significant cross sections the studied area is crossed by the fosso di morricone valley that entrenched within the messinian pelitic arenaceous succession of the laga formation hosts a late pleistocene palaeo landslide the study evidences the occurrence of a n 10 oriented west dipping normal fault here named pretare piedilama fault that controlled the left side of the fosso di morricone valley producing a vertical displacement of the palaeo landslide deposits of about 50 m the geological geomorphological and geophysical data indicate that the fault was active during the late pleistocene and part of the holocene thus constraining a minimum vertical displacement rate of 0 4 mm a in the last 125 ka the geometry of the deformed laga formation cut by the fault suggests to relate it to the late quaternary negative tectonic inversion of a previous thrust plane located in the footwall of the sibillini thrust front the pretare piedilama fault would represent the easternmost tectonic expression of this main potentially active structure future researches could be addressed to detail the age and the actual motion rate of the structure and to define its seismic hazard assessment

anisotropy of magnetic susceptibility in welded tuffs application to a welded tuff dyke in the tertiary trans pecos texas volcanic province usa consideration of published anisotropy of magnetic susceptibility ams studies on welded ignimbrites suggests that ams fabrics are controlled by groundmass microlites distributed within the existing tuff fabric the sum result of directional fabrics imposed by primary flow lineation welding and if relevant rheomorphism ams is a more sensitive indicator of fabric elements within welded tuffs than conventional methods and usually yields primary flow azimuth estimates detailed study of a single densely welded tuff sample demonstrates that the overall ams fabric is insensitive to the relative abundances of fiamme matrix and lithics within individual drilled cores ams determinations on a welded tuff dyke occurring in a choked vent in the trans pecos texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width the dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit followed by residual squeezing between the failed block and in situ wallrock irrespective of the precise mechanism widespread occurrence of both welded tuff dykes and point welded aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process

shallow high resolution geophysical investigation along the western segment of the victoria lines fault island of malta abstract the victoria lines fault island of malta is a 15 km long and n260 striking segmented normal fault system which is probably inactive since the late pliocene in the westernmost part the fomm ir rih segment displays comparable geologic throw and escarpment height 150 170 m moreover its hangingwall hosts thin patches of middle pleistocene clastic continental deposits red beds which are poorly preserved elsewhere we acquired two seismic transects by collecting ambient vibration recordings processed by using horizontal to vertical spectral ratios complemented by one high resolution 2 d refraction tomography survey crossing this fault where it is locally covered by red beds and recent colluvial deposits we found a resonance peak at 1 0 hz in the hangingwall block whereas clear peaks in the range 5 0 10 0 hz appear when approaching the subsurface fault and we relate them to the fractured bedrock within the fault zone the best fit tomographic model shows a relatively high vp shallow body vp 2200 2400 m s that we relate to the weathered top of the miocene upper coralline limestone fm bounded on both sides by low vp regions 230 m s above the weathered top bedrock our results depict a clear seismic signature of the victoria lines fault characterized by low seismic velocity and high amplification of ground motion we hypothesize that during the middle pleistocene faulting may have affected the basal part of the red beds so that this part of the investigated complex fault system may be considered inactive since 0 6 myr ago

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

structure of a hypovolcanic acid complex inferred from magnetic susceptibility anisotropy measurements the western red hills granites skye scotland thulean igneous province the geochemistry and the injection mechanism of hypovolcanic ring dykes have been extensively studied but such is not the case for their internal fabric the tertiary western red hills epigranites of the isle of skye are a classic example of such intrusions using anisotropy of magnetic susceptibility measurements we present the first structural data of their internal magmatic fabric the magnetic foliations equated with the magmatic flow planes have strikes which roughly follow the walls of the different intrusions they dip steeply toward the convex wall of each intrusion the lineations or maximal magnetic susceptibility axes generally have shallow plunges except in the latest granite intrusion these structures appear to be related to the compressional deformation of each intrusion toward the end of its crystallization this shortening would be a consequence of a radial and compressive stress field acting after each injection of magma this radial stress field is interpreted as the effect of high magma pressures originating from the acid magma chamber underlying the ring dyke complex at a shallow depth

directional resonance variations across the pernicana fault mt etna in relation to brittle deformation fields summary the pernicana fault pf is the main structural element of mt etna and the northern boundary of a section sliding to the southeast observed ground motion records in the damage zone of the pf show strong variations of directional resonance in the horizontal plane the observed resonance directions exhibit an abrupt rotation of azimuth by about 30 across the fault varying from n166 on the north side to n139 on the south we interpret the directional resonance observations in terms of changes in the kinematics and deformation fields on the opposite sides of the fault the northern side is affected primarily by the left lateral strike slip movement whereas the southern side that is subjected also to sliding is under a dominant extensional stress regime brittle deformation models based on the observed kinematic field predict different sets of fractures on the opposite sides of the fault synthetic cleavages and extensional fractures are expected to dominate in the northern and southern sides respectively these two fracture fields have different orientations n74 and n42 respectively and both show a near orthogonal relation 88 in the northern sector and 83 to the south with the azimuth of the observed directional resonance we conclude that the direction of the largest resonance motions is sensitive to and has transversal relationship with the dominant fracture orientation the directional amplification is inferred to be produced by stiffness anisotropy of the fault damage zone with larger seismic motions normal to the fractures

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

magnetic fabric and its significance in the 1400 ma mealy diabase dykes of labrador canada an anistropy of magnetic susceptibility ams study of the relatively fresh mealy diabase dyke swarm indicates a correlation between the ams and the deformational effects in the rocks several ams components were revealed during experimental work on 211 samples that had been heated to 640 c during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields seventeen sites with slight or no deformation have a magnetic fabric composed of two major components the stable component attributed to a primary shape anisotropy has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike n 60 e respectively this configuration is consistent with an origin due to a post emplacement stress field whereby horizontal extension acted on a vertical sheet of partially crystallized magma the orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement the unstable component removed by fields up to 250 mt is attributed to induced domain anisotropy produced by mild tectonic stress during the grenville orogeny the approximate orientation of its principal components as found by the method of substitutional ellipsoids suggests an east west directed maximum stress four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed but which may be largely composed of domain and stress induced anisotropies developed during the grenville orogeny

magma flow in the east greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility magmatic growth of a volcanic margin summary volcanic passive margins vpms are characterized by large volumes of melt emplaced within the lithosphere during break up processes several data and a recently proposed conceptual model of volcanic margin development suggest that vpms are fed from localized crustal zones of magma storage underlying large polygenetic volcanoes localized above diapir like instabilities of the asthenosphere we investigated the magma flow pattern within the coastparallel dyke swarm of the east greenland vpm which is the only outcropping vpm over a distance of 125 km the 44 sampled dykes are representative of the successive families of intrusions igneous petrofabrics are constrained by the measurements of the anisotropy of magnetic susceptibility the magnetic fabrics are of medium to low anisotropy p 0 flow related fabrics are recorded in 75 per cent of the sampled dykes we infer the flow directions from the imbrication geometry of the magnetic foliation planes at the dyke margins and check the results by measuring the preferred orientation of plagioclase in thin sections cut in the magnetic principal planes due to probable fabric superposition the magnetic lineation represents the zone axis for the distribution of magnetic foliation plane we obtained 23 reliable flow directions that are predominantly horizontal and directed away from identified crustal reservoirs this flow pattern supports the proposed model of vpm growth and emphasizes the localized nature of the magma sources in the mantle the entire flood basalt sequence appears to have been fed by a restricted number of crustal reservoirs and associated dyke swarms

evidence for ground motion polarization on fault zones of mount etna volcano 1 during local and regional earthquakes an evident amplification of horizontal ground motion is observed at two seismological stations near the tremestieri fault on the southeastern flank of mount etna volcano rotated component spectral ratios show a narrow spectral peak around 4 hz along a n40 e direction a conventional polarization analysis using the eigenvectors of the covariance matrix confirms the very stable directional effect enhancing the approximately ne sw elongation of the horizontal ground motion in the fault zone the effect is evident during the entire seismogram and independent of source back azimuth as well as distance and depth of earthquakes the same polarization is observed in ambient noise as well this consistency allowed us to use microtremors for checking ground motion polarization along and across the tremestieri fault zone with a high spatial resolution the result is a stable polarization of horizontal motion in the entire area that can be observed in a broad frequency band to check whether this ground motion property is recurrent and to understand a possible relationship with fault strike faulting style or orientation of fractures ambient noise was recorded on other mapped faults of the mount etna area the moscarello acicatena and pernicana faults the latter in particular is characterized by different strike and faulting style a systematic tendency of ambient noise to be polarized is found in all of the faults a picture emerges where normal faults of the eastern flank show an e w to ne sw polarization that changes on the pernicana fault which develops approximately e w and is characterized by a prevailing nw se to n s polarization directions of polarization were never parallel to the fault strike moreover polarization persists too far away from the fault trace excluding an effect limited to a narrow low velocity zone hosted between harder wall rocks both these observations rule out an interpretation in terms of fault trapped waves the cause of observed polarizations will be the subject of future studies however the consistency with recent results of velocity anisotropy in a part of the investigated area suggests a possible role of attenuation anisotropy on horizontal amplitude variations versus azimuth

can seismic waves be trapped inside an inactive fault zone the case study of nocera umbra central italy in march 1998 a small aperture 350 m linear array of five broadband stations was installed across a pliocene strike slip fault crossing the town of nocera umbra central italy three component seismograms of local earthquakes recorded during the umbria marche seismic sequence have shown that the degradation of mechanical properties in damaged rock causes a significant amplification of ground motion within the fault zone marra et al 2000 during the operation of the array an m w 5 3 subcrustal earthquake occurred at a depth of 48 km and an epicentral distance of 10 km from nocera umbra the near vertical incidence of this event offers a unique opportunity for constraining the 2d geometry of the laterally heterogeneous low velocity structure responsible for the large amplification across the fault based on the observed symmetry of the amplification pattern a 2d wedge shaped model of the fault zone is used for the computation of antiplane sh synthetic waveforms to be compared with observations along the array two parameters of the wedge model can be constrained by independent geophysical and geological data 1 shear wave velocity in pristine rock outside the fault zone v s 2200 m sec and 2 the lateral extent of the damaged rock zone l 160 m the other two model parameters namely the wedge depth h and shear wave velocity of the fault zone v f s are varied computer simulations show that trapped waves which have been observed so far for earthquakes occurring inside the fault zone can develop inside a 2d wedge model when struck by external vertically incident seismic radiation results of numerical modeling indicate that in spite of its extreme simplicity such an idealized model is successful in reproducing many of the essential characters of ground motion within the fault zone of nocera umbra even though the best fit solution is not unique and the model parameters trade off each other a study of parameter sensitivity comparing synthetics with recorded data indicates that the variability of h and v f s can be restricted to a limited range of values the quality of fit is optimal when the shear velocity reduction lies in the range of 40 50 and the depth of the trapping zone is comprised between 1 and 2 km