estimation and testing of standard molar thermodynamic properties of tourmaline end members using data of natural samples different estimation methods have been combined with calorimetric data for a natural mg rich tourmaline and dumortierite a structurally similar borosilicate to estimate thermodynamic properties of five tourmaline end members dravite schorl alkali free dravite aluminofoitite and ferrifoitite the results were tested by predicting the solubility of fe rich tourmaline in natural low variance hydrothermal mineral assemblages for which the b concentration was independently known from laser ablation icp ms analysis of coexisting fluid inclusions agreement within the uncertainty of experimental and thermodynamic data supports the validity of the estimation methods that used the fictive properties of the iiib2o3 polyhedron for calculating standard enthalpy and entropy and reactions involving dumortierite to estimate the heat capacity functions this study indicates more generally that the development of new microanalytical techniques for measuring the composition of natural fluid inclusions in well constrained mineral assemblages represents a promising approach to estimating or testing thermodynamic data for complex silicates

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

detritic tourmalines with complex zonation in the cretaceous exotic flysches of the western carpathians where did they come from abstract the period of the cretaceous marked a time of convergence in the tethyan realm characterized by both collisions and local ophiolitic obduction sedimentary records from this period are full of detritic materials of unknown provenance so called exotics among these exotic rocks and minerals was tourmaline with complex zonation which began to appear in considerable amounts research conducted in albian to senonian exotics of the western carpathians has shown that there are two kinds of complex zoned grains 1 grains with a fabric consisting of several tourmaline phases which are chaotically arranged as laths and 2 grains displaying a fine intergrowth of tourmaline and quartz the first type of tourmaline shows a continuous trend of al and its substitution by fe3 at the y and z sites thus shifting from a schorl dravitic composition to a bosiite one the second type consists of a dominant presence of schorl dravitic tourmaline however with a scarce occurrence of al enriched oxy dravitic foititic and magnesio foititic compositions tourmaline with complex zonation occurs in metamorphics which include hp and uhp facies evaporitic complexes and hydrothermal deposits they also appear locally in granites and pegmatites in most of the rocks saline and boron rich fluids played a substantial role in the high pressure metamorphics there was an influx of fluids during their exhumation because the examined exotics are rich in ophiolitic material including hp to uhp rock pebbles it is substantiated to assume that the also represented the main source of the complex zoned tourmaline they may have also combined with permian lower triassic evaporites where the dismembered ophiolites are often embedded hydrothermal veins and granitoids did not represent a regionally significant and widespread source at that time

petrology geochemistry and zircon u pb lu hf isotopes of paleoproterozoic granite gneiss from bomdila in the western arunachal himalaya ne india

modelling coseismic displacements during the 1997 umbria marche earthquake central italy summary we propose a dislocation model for the two normal faulting earthquakes that struckthe central apennines umbria marche italy on 1997 september 26 at 00 33 mw 5 7 and 09 40 gmt mw 6 0 we t coseismic horizontal and vertical displacements resulting from gps measurements at several monuments of the igmi istituto geogra co militare italiano by means of a dislocation model in an elastic homogeneous isotropic half space our best tting model consists of two normal faults whose mechanisms and seismic moments have been taken from cmt solutions it is consistent with other seismological and geophysical observations the rst fault which is 6 km long and 7 km wide ruptured during the 00 33 event with a unilateral rupture towards the se and an average slip of 27 cm the second fault is 12 km long and 10 km wide and ruptured during the 09 40 event with a nearly unilateral rupture towards the nw slip distribution on this second fault is non uniform and is concentrated in its se portion maximum slip is 65 cm where rupture initiated the 00 33 fault is deeper than the 09 40 one the top of the rst rupture is deeper than 1 7 km the top of the second is 0 6 km deep in order to interpret the observed epicentral subsidence we have also considered the contributions of two further moderate magnitude earthquakes that occurred on 1997 october 3 mw 5 2 and 6 mw 5 4 immediately before the gps survey and were located very close to the 09 40 event of september 26 we compare the pattern of vertical displacements resulting from our forward modelling of gps data with that derived from sar interferograms the t to sar data is very good con rming the reliability of the proposed dislocation model

qualitative effects of local geology on damage pattern september 1997 registered the onset of a seismic sequence striking the umbria marche region central italy in which earthquakes up to intensity ix caused widespread damage with respect to villages settled in an intermountain basin near the epicentral area the resulting damage pattern is investigated to give a better understanding of future local ground motion sensitivity macroseismic data are collected and compared with the surface geology of 26 villages and hamlets within a restricted area among these 26 settlements seven individual groups of different geological conditions are discernible showing a gradual variation to the damage severity the greatest damage occurred within the basin in villages settled close to border faults significant damage also occurred at locations on the contact between fan debris with bedrock or alluvium in support of models existing in literature these observations show that strong shaking can be generated at the edge of basins

slip distribution of the 1997 umbria marche earthquake sequence joint inversion of gps and synthetic aperture radar interferometry data 1 in september october 1997 a seismic sequence struck the southern part of the umbria marche region in central italy the three largest earthquakes took place on 26 september 0033 ut mw 5 7 09 40 gu mw 6 0 near colfiorito and on 14 october mw 5 6 near sellano we present a slip model for the main sequence over two separate fault planes we use previously published global positioning system gps and differential interferometric synthetic aperture radar dinsar data as well as new dinsar data covering the sellano event as input to a simulated annealing solution for the distribution of fault slip the combination of both types of geodetic data as well as the combination of sar interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes for the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence we find the slip was concentrated in a zone at 4 5 5 km depth with a shallower tail extending to near the surface at the northern end of the colfiorito sequence for both the second colfiorito event and the sellano event individual patches were calculated with maximum slip of 2 m implying stress drops as high as 20 mpa coulomb stress calculations show that the coseismic slip distribution for the colfiorito events facilitated slip of the adjacent sellano earthquake

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

evidence for li rich brines and early magmatic fluid rock interactionin the larderello geothermal system abstract the geochemical features of fluids accompanying the first stages of geothermal activity linked to magmatic intrusions have been documented for the larderello geothermal system italy deep drilling has provided samples which preserve evidence of this early geothermal activity four wells san pompeo 2 monteverdi 7 sasso 22 and serrazzano vc 11 penetrated the deeper parts of the larderello system located in a metamorphic basement underlying the tertiary nappe complex which constitutes the main aquifer at larderello the drill holes terminated close to the inferred roof of a granitic complex thought to be responsible for geothermal activity fluid inclusion data were obtained from recrystallized quartz lenses and quartz veins in samples displaying high temperature assemblages plagioclase actinolite biotite tourmaline clinopyroxene andradite wollastonite and also from magmatic quartz in a leucogranite dike the inclusions are mainly secondary in origin oriented in fluid inclusion planes fip related to hydrothermal circulation in the larderello system several generations of high temperature fluids were trapped and include 1 1 h2o co2 dominated vapors displaying variable but significant contents of ch4 and n2 2 2 aqueous vapors containing licl with variable salinity 3 3 aqueous licl brine often oversaturated with respect to halite at room temperature 4 4 complex brine always oversaturated at room temperature with respect to two halite and sylvite or more n 4 salts the presence of licl was confirmed by identification of the salt hydrate licl 5h2o at very low temperature using raman spectroscopy bulk salinities could be roughly estimated at around 30 wt eq licl for the licl brine geometric and chronologic relationships between fip reveal close relationships and mutual contamination between the h2o co2 vapors and licl brine indicating synchronism in their trapping these fluids were generated and trapped at pressures of 100 130 mpa nearly 23 mpa above the estimated present day lithostatic pressure this implies a denudation rate between 0 2 and 0 5 mrn a 1 since the onset of hydrothermal activity compatible with the setting of larderello in a young tortonian collision belt fluid inclusion trapping temperatures 425 650 c show a monotonous increase towards the inferred granite and are around 100 200 c higher than the highest present day temperatures the results are interpreted as recording the interaction between magmatic and contact metamorphic fluids in the early larderello system the h2o co2 vapors resulted from the reheating of the basement metamorphic series often c rich under relatively high temperatures during contact metamorphism lirich fluids expelled from an underlying li rich leucogranite migrated through the metamorphic series and the already cooled granite dikes and experienced local boiling the fluid inclusion data demonstrate the involvement of magmatic fluids during the initial development of this high energy geothermal field

crystal chemical characterization of tourmalines from the english lake district electron microprobe analyses and mossbauer spectroscopy electron microprobe analyses empa and mossbauer spectra ms have been acquired for natural tourmalines sampled near crummock water and haweswater english lake district in the former the dravite schorl series is prevalent whereas in the latter the dravite species is dominant all tourmaline samples presently studied are chemically disordered the compositional and ms data give an insight into the thermal and fluid evolution experienced by the tourmalinite rocks the tourmalines from crummock water crystallized in a closed low f o 2 environment under the influence of a magmatic fluid the tourmalines from haweswater are of hydrothermal origin and were formed under low variable t and low f o 2 conditions from a fluid of constant composition

alpine tectonothermal evolution of the tuscan metamorphic complex in the larderello geothermal field northern apennines italy on the internal tyrrhenian side of the northern apennines high heat flow and geothermal gradient in the larderello geothermal field are evidence of a large scale thermal anomaly related to the emplacement of a large batholith of pliocene age extending from the upper to middle crust these intrusions relate to the miocene to recent northern apennines magmatism which developed as a result of crustal extension and upwelling of the asthenosphere at the base of the thinned crust in the subsurface of the larderello geothermal field medium and high grade metamorphic rocks tuscan metamorphic complex cored in several geothermal wells have previously been considered to be variscan basement new structural and petrographic data on these metamorphic rocks indicate an alpine tectonometamorphic history and provide evidence that medium to high grade mineral assemblages are related to pliocene thermal metamorphism centred on intrusions at shallow depth these data allow a new interpretation of the tuscan metamorphic complex as a tectonic wedge of the late palaeozoic triassic units and in particular highlight the considerable extent of pliocene thermal metamorphism and hydrothermal circulation as a result of convective cooling of intrusions

coseismic ruptures of the 24 august 2016 mw 6 0 amatrice earthquake central italy on 24 august 2016 a mw 6 0 normal faulting earthquake struck central italy causing about 300 fatalities and heavy damage a geological survey collected the coseismic effects observed at the surface in order to evaluate two competing hypotheses about their nature surface faulting versus gravitational deformation we find that the most significant geological effect is a 5 2 km long alignment of ground ruptures along the mt vettore fault system these ruptures are independent from lithology topography morphology and change in slope and exhibit an average dip slip displacement of 13 cm geometry kinematics and dimensional properties of this zone of deformation strongly lead us to favor the primary surface faulting hypothesis that fits well the predicted estimates from experimental scaling law relationships our study provides relevant hints for surface faulting in extensional domains contributing to implement the worldwide database of the moderate earthquakes

analysis of seismological and geological observations formoderate size earthquakes the colfiorito fault system central apennines italy to contribute to the understanding of the relationships between moderate earthquakes and the faults that are recognisable in the geological record we analysed seismological and geological data related to the 1997 98 umbria marche central italy earthquake swarm the seismological recordings collected by local networks allowed accurate location of about 1000 events whereas the geological field observations provided a picture of the structural features and the ground surface deformations we also re examined and utilised some already published data and results mostly about the fault plane solutions and the geology on the basis of earthquake locations fault plane solutions and geological mapping we explored the possible correlation between the earthquake causative fault planes and the normal faults exposed in the area our results show that the two mainshocks that occurred on september 26 1997 mw 5 7 and mw 6 0 originated on the same structure reactivating at depth the colfiorito normal faults both ruptures did not propagate up to the ground surface but triggered gravitational sliding that occurred along pre existing fault scarps the earthquake that occurred on october 14 1997 mw 5 6 originated on another fault branch at a much shallower depth in spite of the lower magnitude this earthquake produced tectonic ruptures where the fault plane projects to the surface in an area where no faults were previously mapped by comparing the paleostress reconstruction based on slickenside lineations analysis and the focal mechanism solutions we also suggest a possible correlation between the long term early middle pleistocene cumulative effects of the colfiorito fault system and the short term behaviour of the fault planes observed during this earthquake swarm favouring the idea of a seismogenic source producing clustered moderate size earthquakes rather than large events scattered in time our results suggest that the integration of geological and seismological observations can constrain the seismotectonic interpretations in regions of low level seismicity and that this integration can pose a reliable basis in the seismic hazard assessment

the 1997 umbria marche italy earthquake sequence relationship between ground deformation and seismogenic structure a field survey performed during the 1997 umbria marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks mw 5 7 the ruptures are concentrated in narrow bands that in part are on and near previously mapped high angle normal faults the geometry of the ground deformation is consistent with the ne trending extension indicated by cmt focal solutions of the mainshocks the distribution of aftershocks suggests that the three mainshocks occurred on 40 sw dipping normal faults geological investigations modelling of expected coseismic elevation changes and seismic data suggest that the surface deformation is not the direct result of primary rupture of faults at depth

observation and prediction of dynamic ground strains tilts and torsions caused by the mw 6 0 2004 parkfield california earthquake and aftershocks derived from upsar array observationsdynamic ground strains tilts and torsions caused by the 2004 parkfield california earthquake

the perugia italy earthquake of 29 april 1984 a microearthquake survey a field study after the perugia earthquake of 29 april 1984 provided more than 300 well recorded events concentrated within two parallel clusters separated by 2 km and trending along the apenninic direction the length of the aftershock area is 14 km focal depths being shallower than 8 km relocation of the main event places the epicenter at the southern end of the aftershock zone suggesting a rupture propagation from se to nw most focal mechanisms are consistent with normal faulting the spatial distribution of seismicity suggests that the gubbio normal fault was activated during the main shock this earthquake together with the norcia 1979 and the abruzzi 1984 shocks is typical of the extension in the high apennines generated by the flexure of the mountain chain in response to regional compression the parma 1983 event a thrust belongs to the compres sion zone at the eastern flank of the chain these results are consistent with the ew continental collision along the apennines

multi stage fluid circulation in a hydraulic fracture breccia of the larderello geothermal field italy abstract the deep well mv5a drilled in the western part of the larderello geothermal field crossed a 20 cm thick hydraulic fracture breccia unit at a depth of 1090 m below ground level b g l this breccia occurs in a fine grained triassic metasandstone and consists of angular to subangular clasts of up to some centimeters in size pervasive alteration has affected the breccia clasts and wall rock around the breccia with the formation of mg fe chlorite after such alteration hydrothermal circulation caused the precipitation of two generations of calcite cement then ankerite partially replaced these two calcite generations ankerite also precipitated in late veinlets with chlorite late hydrothermal activity led to the crystallization of albite quartz and finally anhydrite the calcite contains vapor rich inclusions and two populations of liquid rich l1 and l2 inclusions l1 inclusions are characterized by homogenization temperatures between 304 and 361 c and salinities from 7 4 to 11 6 wt nacl equivalent l2 inclusions revealed homogenization temperatures in the range of 189 245 c and salinities from 2 6 to 6 3 wt nacl equivalent the fluids contained in l2 inclusions were probably trapped coevally with some vapor rich inclusions under boiling conditions after the l1 inclusions formed some of the abundant vapor rich inclusions in calcite may also represent early low temperature inclusions affected by decrepitation and or stretching and or leaking during l1 trapping the liquid rich l inclusions trapped at later stages in ankerite albite and anhydrite display respectively homogenization temperature ranges of 189 198 c 132 145 c and 139 171 c and salinities ranging from 1 6 to 1 7 wt nacl equivalent 1 4 to 2 1 wt nacl equivalent and 3 7 to 6 2 wt nacl equivalent the inclusions studied record the evolution over time of the fluids flowing in the breccia level l1 inclusions capture high temperature fluid about 300 to 350 c of high salinity around 10 wt nacl equivalent at above hydrostatic pressures up to about 150 bar the l2 inclusions in calcite and liquid rich inclusions in ankerite and albite represent subsequent hydrothermal fluid evolution toward lower temperatures about 250 to 130 c pressures 45 to a few bar and salinities 6 3 to 1 4 wt nacl equivalent during this stage boiling processes and infiltration of meteoric waters probably occurred finally moderately saline fluids around 5 wt nacl equivalent at a temperature about 160 c close to that of present day in hole measurements was trapped in the anhydrite inclusions the liquids trapped in liquid rich inclusions circulated at 41 000 years maximum age of calcite or later this age represents an upper limit for the development of vapor dominated condition in this part of the geothermal system the fluids circulating at the breccia level were probably meteoric and or connate waters these fluids may have interacted with the anhydrite and carbonate bearing formations present in the larderello area the occurrence of the hot and saline fluids trapped in l1 inclusions at above hydrostatic pressure suggests that similar fluids but with higher pressure 167 bar and temperature 360 c may have been responsible for rock fracturing

geodetic and seismologic evidence for slip variability along a blind normal fault in the umbria marche 1997 1998 earthquakes central italy summary we analysed elevation changes induced by the 1997 1998 umbria marche central apennines italy earthquakes we employed data from a first order geodetic levelling line measured in 1951 1992 and 1998 the line bears a record of pre seismic and coseismic strains associated with the causative fault of the 1997 september 26 09 40 mainshock mw 6 0 a first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry a more detailed analysis based on a distribution of coseismic slip obtained from broad band seismograms provides a better fit and is in agreement with 1951 1992 elevation changes interpreted as precursory slip by previous investigators the levelling data sets new constraints on the location extent dip and depth of the fault in full agreement with seismological evidence and images from sar interferometry the data show no evidence for slip in the uppermost 3 km of the crust suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting

geochronology of the larderello geothermal field new data and the closure temperature issue the larderello geothermal field is generally accepted to have been produced by a granite intrusion at 4 9 km depth hydrothermal parageneses and fluid inclusions always formed at temperatures greater than or equal to the current ones which implies that the field has always undergone a roughly monotonic cooling history fluctuations 40 k since intrusion of the granite at 4 ma the heat required to maintain the thermal anomaly over such a long period is supplied by a seismically anomalous body of 32000 km3 rooted in the mantle borehole minerals from larderello are thus a unique well calibrated natural example of thermally induced ar and sr loss under geological conditions and time spans the observations biotites retain ar above 450 c agree well with other albeit less precise geological determinations but contrast with laboratory determinations of diffusivity from the literature we therefore performed a hydrothermal experiment on two larderello biotites and derived a diffusivity dlab 370 c 5 3 10 18 cm2s 1 in agreement with published estimates of diffusivity in annite from dlab and the rejuvenation of the k ar ages we calculate maximum survival times at the present in hole temperatures they trend smoothly over almost two orders of magnitude from 352 ka to 5 3 ka anticorrelating with depth laboratory diffusivities are inconsistent not only with geological facts but also among themselves from the geologically constrained lifetime of the thermal anomaly we derive a diffusivity dg 370 c 3 81 1021 cm2s 1 3 1 orders of magnitude lower than dlab the cause of these discrepancies must be sought among various laboratory artefacts overstepping of a critical temperature t enhanced diffusivities in wet experiments presence of fast pathway dislocation and pipe diffusion and of dissolution reprecipitation reactions which we imaged by scanning electron microscopy these phenomena are minor in geological settings in the absence of mineral transformation reactions complete or near complete resetting is achieved only by volume diffusion therefore laboratory determinations will necessarily result in apparent diffusivities that are too high compared to those actually effecting the resetting of natural geochronometers

crustal deformation associated with east mediterranean strike slip earthquakes the 8 june 2008 movri nw peloponnese greece earthquake mw6 4 abstract the 2008 mainshock mw 6 4 was the first modern strong strike slip earthquake in the greek mainland the fault strikes ne sw dips 85 nw while the motion was right lateral with small reverse component historical seismicity showed no evidence that the fault ruptured in the last 300 years for rectangular planar fault we estimated fault dimensions from aftershock locations dimensions are consistent with that a buried fault was activated lateral expansion occurred only along length and the rupture stopped at depth 20 km implying that more rupture along length was favoured we concluded that no major asperities remained unbroken and that the aftershock activity was dominated rather by creeping mechanism than by the presence of locked patches for mo 4 56 1025 dyn cm we calculated average slip of 76 cm and stress drop 13 bars this is high for greek strike slip earthquakes due rather to increased rigidity because of the relatively long recurrence 300 years of strong earthquakes in the fault than to high slip values of and indicated that the fault is neither a typical strong nor a typical weak fault dislocation modeling of a buried fault showed uplift of 8 0 cm in kato achaia 20 km at the hanging wall of the reverse fault component dinsar analysis detected co seismic motion only in kato achaia where interferogram fringes pattern showed vertical displacement from 3 0 to 6 0 cm from field surveys we estimated maximum intensity of viii in kato achaia the most important liquefaction spots were also observed there these observations are attributable neither to surface fault breaks nor to site effects but possibly to high ground acceleration due to the co seismic uplift the causal association between displacement and earthquake damage in the hanging wall described for dip slip faults in taiwan greece and elsewhere becomes possible also for strike slip faults with dip slip component as the 2008 earthquake

schorl dravite ferridravite tourmalines deposited by hydrothermal magmatic fluids during early evolution of the larderello geothermal field italy electron microprobe and petrographic data on tourmaline rich assemblages in addition to available data from fluid inclusions and geochronological studies are used to model the early stage of hydrothermal metamorphism in the larderello geothermal field italy during this early stage different hydrothermal events are characterized by deposition of tourmaline biotite calcic plagioclase k feldspar quartz and pyrrhotite at lithostatic pressures of 0 75 to 1 kbarsand temperatures in the range 400 degrees to 600 degrees c pressures exceeding hydrostatic values and inferred temperatures of 450 degrees to 460 degrees c at the bottom of well san pompeo 2 suggest a possible present day deposition of tourmaline in the deepest levels of the central and hottest part of the field hydrothermal tourmalines appear to have crystallized at temperatures in excess of 370 degrees c they show significant replacement of al by fe super 3 in the z site substitutions of al for si in the tetrahedral site and slight vacancies in the x and y sites produced by limited cation and proton deficient substitutions in the hydrothermal tourmaline nearest to the inferred granitic contact and in the tourmaline of a leucogranitic dike crossed by well vcll a negative correlation existing between mg and fe super 2 reveals significant reciprocal substitutions of these elements in the y site tschermak9s and aluminobuergerite substitutions and an increase in the molecular fractions of schorl and elbaite in the schorl dravite and schorl elbaite solid solutions were observed from rim to core of the vcll magmatic tourmalines rims and intermediate growth zones of magmatic tourmalines and most of the hydrothermal tourmalines have compositions falling in the field of metamorphic tourmalines this behavior reveals the dominant control of the host rock on fluid chemistry some growth zones and most cores have compositions that plot in the field of tourmalines from granitoids a gradual schorl or ferridravite enrichment from magmatic to hydrothermal tourmalines with increasing distance from the granite contact is also present in a microprobe traverse from the base to the tip of an acicular tourmaline four peaks of fe super 3 replacing al can be ascribed to four distinct hydrothermal events generated by episodic ascent from below of magmatic fluids that became more and more oxidized with increasing distance from the granite contact owing to an easier hydrogen leakage in the shallower and more fractured levels the studied mineral assemblages and available fluid inclusion data reveal close analogies between the deepest and hottest part of the larderello geothermal system and quartz tour maline and k silicate alteration zones of porphyry tin and copper deposits the mineralizing fluids are inferred to have been of magmatic origin and were characterized by t 400 degrees to 600 degrees c pressure varying between hydrostatic 0 2 0 35 kbars and lithostatic 0 75 1 kbars commonly near lithostatic values high f sub o 2 as inferred by the presence of hematite and anhydrite among fluid inclusion daughter minerals and very high salinities up to 50 60 equiv wt nacl

tourmaline occurrences within the penamacor monsanto granitic pluton and host rocks central portugal genetic implications of crystal chemical and isotopic features tourmalinization associated with peraluminous granitic intrusions in metapelitic host rocks has been widely recorded in the iberian peninsula given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of sn w mineralizations in the penamacor monsanto granite pluton central eastern portugal central iberian zone tourmaline occurs 1 as accessory phase in two mica granitic rocks muscovite granites and aplites 2 in quartz mica tourmaline rocks tourmalinites in several exocontact locations and 3 as a rare detrital phase in contact zone hornfels and metapelitic host rocks electron microprobe and stable isotope 18o d 11b data provide clear distinctions between tourmaline populations from these different settings a schorl oxyschorl tourmalines from granitic rocks have variable foititic component x 17 57 and mg mg fe ratios 0 19 0 50 in two mica granitic rocks and 0 05 0 19 in the more differentiated muscovite granite and aplites granitic tourmalines have constant 18o values 12 1 0 1 with wider ranging d 78 2 4 7 and 11b 10 7 to 9 0 values b vein breccia oxyschorl mg mg fe 0 31 0 44 results from late b and fe enriched magma derived fluids and is characterized by 18o 12 4 d 29 5 and 11b 9 3 while replacement tourmalines have more dravitic compositions mg mg fe 0 26 0 64 close to that of detrital tourmaline in the surrounding metapelitic rocks and yield relatively constant 18o values 13 1 13 3 though wider ranging d 58 5 to 36 5 and 11b 10 2 to 8 8 values and c detrital tourmaline in contact rocks and regional host metasediments is mainly dravite mg mg fe 0 35 0 78 and oxydravite mg mg fe 0 51 0 58 respectively boron contents of the granitic rocks are low 650 ppm compared to the minimum b contents normally required for tourmaline saturation in granitic melts implying loss of b and other volatiles to the surrounding host rocks during the late magmatic stages this process was responsible for tourmalinization at the exocontact of the penamacor monsanto pluton either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin vein breccia tourmalinites or as replacement of mafic minerals chlorite or biotite in the host rocks replacement tourmalinites along the exocontact of the granite thermometry based on 18o equilibrium fractionation between tourmaline and fluid indicates that a late b enriched magmatic aqueous fluid av 18o 12 1 at 600 c precipitated the vein breccia tourmaline 18o 12 4 at 500 550 c and later interacted with the cooler surrounding host rocks to produce tourmaline at lower temperatures 400 450 c and an average 18o 13 2 closer to the values for the host rock although b metasomatism associated with some granitic plutons in the iberian peninsula seems to be relatively confined in space extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of variscan magmatism and related mineralizations

tourmalinization related to late proterozoic early palaeozoic lode gold mineralization in the bin yauri area nigeria three types of tourmaline occurrence have been identified in the area of bin yauri nigeria mesothermal lode gold mineralization these are 1 stratabound tourmalinites in pelitic metasediments 2 tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks 3 tourmaline in auriferous quartz and quartz carbonate veins although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source two stages of tourmalinization are envisaged the earlier ca 1100 ma involved syngenetic diagenetic formation of tourmalinites while the later ca 500 ma involved epigenetic hydrothermal tourmaline gold mineralization possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline rich rocks or tourmalinites electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl dravite solid solution series plots involving feo mgo and or al2o3 from these analyses are used to constrain the sources and processes of tourmalinization two metallogenic implications are derived from this study one is that although the tourmalinites are barren of gold and base metal mineralization their occurrences nevertheless encourages exploration for syngenetic exhalative massive sulphide deposits in the region the other implication applies to the potential use of tourmaline in deciphering the physico chemical conditions of gold mineralizing fluids in the bin yauri area

early proterozoic cu au and fe ore deposits associated with regional nacl metasomatism in northern fennoscandia scapolite is widely distributed in 1 9 2 5 ga volcano sedimentary rocks and 1 77 2 2 ga igneous rocks over several hundred square kilometres in northern fennoscandia comprising northern sweden no

helium isotopes in paleofluids and present day fluids of the larderello geothermal field constraints on the heat source 1 the he isotope composition of paleofluids entrapped in fluid inclusions of hydrothermal minerals is compared with the present day fluid composition of the larderello geothermal field almost constant values of 3he 4he m 3he 4he air r ra over time indicate that no important changes have occurred in the deep source of gases at least during the last 3 8 million years on a regional scale a correlation has been found between the r ra spatial distribution heat flow and bouguer gravity anomaly high values of r ra and heat flow and low bouguer anomaly values indicate that the larderello field is an area of preferential escape for mantle derived fluids a positive correlation has also been found between the r ra spatial distribution and a major seismic reflector named the k horizon a deep magma source refilled by periodic gas input from the mantle is the most likely source of 3he enriched fluids and the anomalously high heat flow the nearly constant value of r ra clearly indicates that input of fresh mantle material has occurred up to recent times clear evidence of mixing between mantle and crustal fluids indicates that the high r ra is the lower limit of the actual mantle value which is suggested to be similar to the subcontinental european mantle the decrease of r ra over time in the peripheral part of the larderello field indicates that important changes in the feeding fracture system and or cooling rate have occurred in these areas

breccia hosted manganese rich minerals of alpi apuane italy a marine redox generated deposit mn rich beds occur within the brecce di seravezza formation bsfm intercalated between norian metadolostone megalodontic marble and hettangian marble in the alpi apuane italy the bsfm is a rockfall talus deposit that accumulates at the base of the footwall scarp of normal faults bordering extensional marine coastal basins the type sequence of metabreccia ends with a bed of chloritoid schist interpreted as the metamorphic equivalent of lateritic soils the four main types of mn mineral assemblages are 1 braunite piemontite and rare hausmannite 2 piemontite braunite hollandite and minor rhodochrosite and kutnahorite 3 braunite hollandite and rare piemontite the other minerals are quartz calcite muscovite phlogopite baryte and minor hematite rutile and apatite during the alpine orogeny pressures of 4 6 kb and temperatures of 350 380 c were attained mn assemblages with hematite and phlogopite indicate o2 10 8 for t 350 c and o2 10 6 when braunite appears on the mn rich rocks ti fe nb sn ta hf th ga rb pr k na nd were identified as detrital in origin and are positively correlated with al u is positively correlated with co pb bi mo the rare earth element patterns normalized to seawater show a negative slope towards the heavy rare earth elements with positive ce anomalies in some samples positive ce and eu anomalies in other samples and negative ce and positive eu anomalies in a third group the eu concentrations are nearly constant and the eu anomalies reflect differences in the concentration of other rare earth elements for ce a positive correlation with al2o3 sio2 indicate that a detrital signature prevails on that produced by duration of seawater exposure but a significant good correlation of la tm lu with mg could indicate at least for these elements a seawater signature only in some samples ba eu sr show anomalously high concentrations likely of hydrothermal origin however generally in all the chemical variation diagrams the bsfm samples fall outside the field of hydrothermal and hydrogenous deposits as defined in the literature for other mn deposits in addition metabasites and metavolcaniclastic beds are absent from the bsfm sequence and bsfm coastal basins were for the most part separated from the open ocean and related streams that must be excluded as possible mn sources owing to the arid climate of late triassic the runoff was negligible and the groundwater oxidizing and alkaline were unable to mobilize mn the bsfm basins are then the most suitable depositional environment for mn the water column was stagnant and stratified only where bottom of the basin was deeper than the oxic anoxic boundary reducing marine bottom waters percolated within the fractured basement and leached mn from disseminated minerals of metamorphic rocks and then rising along fault and fractures supplied mn to the bottom waters afterwards when tectonic uplift and sealevel drop brought the bottom into the oxic field mn precipitated and formed the mn rich matrix of the bsfm deposits

the relationship between seismic deformation and deep seated gravitational movements during the 1997 umbria marche central italy earthquakes abstract this paper re evaluates the origin of some peculiar patterns of ground deformation in the central apennines observed by space geodetic techniques during the two earthquakes of the colfiorito seismic sequence on september 26th 1997 the surface displacement field due to the fault dislocation as modelled with the classic okada elastic formulations shows some areas with high residuals which cannot be attributed to non simulated model complexities the residuals were investigated using geomorphological analysis recognising the geologic evidence of deep seated gravitational slope deformations dsgsd of the block slide type the shape and direction of the co seismic ground displacement observed in these areas are correlated with the expected pattern of movement produced by the reactivation of the identified dsgsd at least a few centimetres of negative line of sight ground displacement was determined for the costa picchio mt pennino and mt prefoglio areas a considerable horizontal component of movement in the costa picchio dsgsd is evident from a qualitative analysis of ascending and descending interferograms the timing of the geodetic data indicates that the ground movement occurred during the seismic shaking and that it did not progress appreciably during the following months this work has verified the seismic triggering of dsgsd previously hypothesized by many researchers a further implication is that in the assessment of dsgsd hazard seismic input needs to be considered as an important cause of accelerated deformation

age and temperature constraints on metamorphism and exhumation of the syn orogenic metamorphic complexes of northern apennines italy abstract the apennine range is a young convergent orogen that formed over a retreating subduction zone syn orogenic metamorphic rocks are exposed in the mid tuscan ridge tuscan coast and tuscan archipelago and provide information about processes of continental subduction and exhumation associated with accretion and retreat apatite and zircon fission track analyses were applied to some of these syn orogenic metamorphic rocks the new low temperature thermochronological data helped to constrain the timing of the metamorphic peak and the age and modality of exhumation of these rocks that were structurally buried at 20 to 40 km depth during the main tectonogenic phase of the northern appenine belt in the giglio and elba islands and in the monti dell uccellina along the coast minimum ages of partially reset zircon samples yielded a first time constraint on the late oligocene age of the metamorphic peak the ca 27 ma obtained at the monti dell uccellina is coeval to that found in the alpi apuane located at the northern termination of the mid tuscan ridge the data from the tuscan archipelago point to a slightly older age in the monti pisani south of the alpi apuane and in the argentario promontary along the coast south of the monti dell uccellina completely reset zircon samples but composed by different populations were behaving as multiple thermochronometers and confirm the already proposed isothermal nature of the exhumation occurred after the metamorphic peak zircon p1 peak indicated that at 13 10 ma rocks were already at shallow crustal levels

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

analysis of ground deformation detected using the sbas dinsar technique in umbria central italy ground deformation affecting the umbria region central italy in the 9 year period from 1992 to 2000 was investigated through multi temporal differential synthetic aperture radar interferometry dinsar for the purpose the small baseline subset sbas technique was adopted which allows studying the temporal evolution of the detected deformation at two spatial scales a low resolution regional scale and a full resolution local scale for the analysis sar data acquired by the european remote sensing ers 1 2 satellites along ascending and descending orbits were used the detected deformation was analysed to investigate its relevance to geophysical geomorphologic and human induced processes that may result in hazardous conditions to the population of umbria low resolution deformation data were used to i determine the amount of displacement caused by the umbria marche earthquake sequence from september 1997 to april 1998 in the foligno area ii determine the number and percentage of the known landslides that can be monitored by the dinsar technology in the investigated area and iii identify and measure subsidence induced by exploitation of a confined aquifer in the valle umbra results indicate that earthquakes moved through the foligno area westwards up to 3 9 cm and with an uplift reaching 1 7 cm intersection in a gis of the low resolution deformation maps with a detailed landslide inventory map allowed the determination that the portion of landslides that can be monitored by the sbas dinsar technique in umbria ranges from 2 7 to 3 4 and the percentage of the total landslide area ranges from 10 4 to 12 8 in the valle umbra a dependency was found between the time and the amount of detected ground deformation and the record of water withdrawal the full resolution deformation data were used to investigate the movement of the ivancich landslide in the assisi municipality joint analysis of the spatial and the temporal characteristics of the ground displacement allowed the formulation of a hypothesis on the landslide geometry and deformation pattern

the boron isotopic composition of tourmaline as a guide to fluid processes in the southwestern england orefield an ion microprobe study the boron isotopic composition 11b and chemistry of tourmalines from a series of sites in the western southwest england orefield has been determined using ion microprobe and electron microprobe techniques respectively the range of 11b values determined is relatively wide 0 6 to 12 7 and falls at the lighter end of the range for typical continental crust within this range granite tourmalines show a depletion in 11b from coarse grained early magmatic examples to fine grained late magmatic tourmaline we attribute this to fractionation of boron isotopes between aqueous and melt species during the exsolution of an aqueous fluid phase from the magma the aqueous phase formed by degassing of the magma is considered to have crystallised to form the tourmalinites and quartz topaztourmaline rocks common throughout the area decreases in the 11b values occur within certain zones of individual tourmaline crystals from these rocks this is ascribed to loss of 11b in the vapour phase during boiling caused by decompression of the aqueous fluid on fracturing the calculated boron isotope composition of fluids in equilibrium with tourmalines from the cligga head greisen bordered vein system agrees closely with that calculated for the tourmalinite fluid and suggests a constant granite derived source of boron during the early hydrothermal evolution of the stock the lack of isotopic zoning within the tourmalines from the cligga head hydrothermal veins suggests that phase separation did not occur or was very limited during hydrothermal circulation in the vein system

diverse tourmaline compositions from orogenic gold deposits in the hutti maski greenstone belt india implications for sources of ore forming fluids the late archean hutti maski greenstone belt hosts the largest operational gold mine in india at hutti as well as two satellite mines at hira buddini and uti tourmaline is a common accessory mineral in the auriferous altered wall rocks proximal to the gold bearing veins of these orogenic gold deposits we report here major rare earth element ree and selected trace element compositions of tourmalines from these alteration zones at hutti and hira buddini and from spatially associated volcaniclastic rocks at uti in order to compare and evaluate possible fluid sources related to tourmaline precipitation and gold mineralization tourmalines at hutti occur as tourmaline calcite microveins within proximal alteration zones and as disseminated grains along the biotite chlorite defined mylonitic foliation these tourmalines belong to the dravite oxydravite group with an evolutionary trend towards magnesio foitite and commonly are mg rich up to 2 06 apfu with low na 0 61 apfu and up to 53 x site vacancies characteristics are low abundances of total ree 0 25 0 67 chondrite and a flat trend with minor hree enrichment accompanied by strong positive eu anomalies at hira buddini tourmalines of the oxydravite povondraite series replace amphiboles and hydrothermal biotite based on textural and chemical characteristics three generations of tourmalines are present at hira buddini earliest type i tourmaline has moderate fe content up to 1 46 apfu high na average 0 80 apfu and moderate x site vacancies up to 22 type ii tends to be relatively enriched in fe up to 2 08 apfu have similar na contents average 0 79 apfu and low x site vacancies up to 8 these tourmalines contain higher total ree 0 93 2 23 chondrite and display a flat trend with slight middle rare earth element mree depletion accompanied by a small positive eu anomaly the latest tourmalines type iii are fe poor up to 1 52 apfu and na poor average 0 67 apfu with relatively high x site vacancies up to 21 this tourmaline type has relatively low total rees 0 21 1 05 chondrite and similar abundance patterns to those of hutti tourmalines accompanied by large positive eu anomalies similarity in tourmaline compositions with evolutionary trends in compositional space from different textural associations suggests that a single low salinity and reduced metamorphogenic fluid with inherently low ree was responsible for proximal alteration and gold mineralization at hutti the type i and type ii tourmalines from hira buddini display oxydravite povondraite trends with compositional overlap that suggests fluid mixing at a paragenetically early stage the early hydrothermal fluid was more saline oxidizing and likely had a granite derived component with high ree contents a later evolved relatively low salinity and reduced fluid is recorded by the last generation type iii tourmalines at hira buddini the tourmalines from uti metapelites are characterized by dravitic composition low na contents high x site vacancies 31 47 and an evolutionary trend toward magnesio foitite these tourmalines have higher ree contents 1 16 2 08 chondrite lree enriched patterns together with large positive eu anomalies and low concentrations of most trace elements all features that suggest a metamorphic origin

water rock interaction in the larderello geothermal field southern tuscany italy an 18o16o and dh isotope study abstract stable isotope and fluid inclusions investigations were carried out on metamorphic rocks belonging to the southern tuscany paleozoic basement that constitutes the main deep fluid reservoir 1000 m below ground level of the larderello geothermal field whole rock samples have 18o and d values ranging from 2 9 to 11 6 and from 65 to 76 respectively most negative 18o and d values have been obtained on rocks from highly fractured levels calculated 18o and d values for the fluids in equilibrium with the rocks are from 3 to 8 and 31 to 43 respectively temperatures of homogenization of fluid inclusions range from 245 c to 324 c and salinities from 1 0 to 12 8 wt nacl eq the combined data are consistent with mixing between a deep circulating 2500 m below ground level meteoric hydrothermal water and a deep thermal water of probable magmatic or metamorphic origin after mixing and exchange the water rock mass ratios are small typically 250 c in the deeper explored levels contrast with the much less strongly 18o shifted meteoric hydrothermal waters which circulate in the upper 1000 m or so of the system at t these new stable isotope data and other petrological geophysical and geochemical data are all consistent with the existence of two apparently separate hydrothermal systems and productive horizons at different depths bearing fluids of different physico chemical characteristics the shallow upper meteoric system may not be continuosly connected to the lower meteoric magmatic system because at least locally fluid pressures in the lower levels are higher than hydrostatic pressures

rupture directivity of the major shocks in the 1997 umbria marche central italy sequence from regional broadband waveforms we derive the relative moment rate function for the main shocks in the fall 1997 central italy seismic sequence mw 5 7 6 0 5 6 by applying an empirical green function method by using three conveniently placed broad band mednet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one taking a simple source model forward modeling is utilized for determining fault parameters such as length rupture propagation velocity and direction and slip distribution

tourmaline at diagenetic to low grade metamorphic conditions its petrologic applicability article i nfo tourmaline developed under low temperature conditions b 300 c typically has distinctive morphological and chemical characteristics that reveal significant information about the environments in which they crys tallize under diagenetic conditions tourmaline can develop as overgrowths on detrital tourmaline cores or as new authigenic crystals tourmaline as monopolar crystal overgrowths is found in sandstones shales conglomerates dolostones and limestones nucleating exclusively at the positive end of the c axis cpole on the detrital grain a feature related to the mineral s polar nature these overgrowths tend to have compo sitions dominated by x site vacant tourmaline species e g foitite and can be linked to growth in aqueous environments low in na with other chemical characteristics related to the host rocks as temperature in creases tourmaline overgrowths develop at both the cpole andc pole but continue to exhibit a signif icant degree of morphological and chemical asymmetries these differences at either pole diminish as a function of increasing temperature such that it can be used as an intramineral geothermometer authigenic tourmalines without detrital tourmaline nuclei are found in many sedimentary or weakly meta morphosed metasedimentary rocks as well as fluid dominated geothermal systems here tourmalines are commonly foititic but have mg fe contents influenced by the host rock composition low temperature tour malines developed in hypersaline environments e g salt domes have distinct chemical characteristics high na fe 3 and w o and follow a trend between oxy dravite and povondraite o p trend this composi tional trend can be used as a guide to indicate tourmaline development within low temperature hypersaline environments and appears to be diagnostic of an oxidizing environment with high na in the fluid and high sa linity with the resulting reduction of the activity of h2o the o p trend is retained in some meta evaporite de posits that are relatively high grade and is found in tourmaline from some types of economically important metal deposits although tourmalines in low temperature environments are largely overlooked they have po tential to be a useful indicator of the chemical and thermal environments in a regime largely absent of such indicators

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

static stress interactions in extensional earthquake sequences an example from the south lunggar rift tibet 1 an extensional earthquake sequence occurred in 2004 8 across a graben in the south lunggar rift on the tibetan plateau we use insar data to determine the location fault geometry and slip distribution of these earthquakes and to test whether the sequence is compatible with static stress triggering the mw 6 2 and 6 3 earthquakes in 2004 and 2005 both ruptured west dipping faults on the east side of a graben in 2008 a mw 6 7 earthquake ruptured a pair of east dipping fault segments on the other side of the graben offset from the earlier ruptures we compute first order dislocation models of stress change and demonstrate that the order and spatial configuration of this sequence of events is compatible with triggering by static stress transfer a continuation of the sequence would be most likely to occur on the northern extension of the 2008 rupture although variable slip rate along the rift may mean that the sequence has run its course the insar data for the 2008 earthquake also reveal slip on a fault that cuts the graben at a highly oblique angle we suggest that this is a release fault accommodating differential throw in the hanging wall and associate the deformation with a mw 6 0 aftershock activity on such a release fault has not been directly imaged before the zhongba sequence is one of several examples of recent clustered normal fault earthquakes on the plateau and may be an example of phase locking of similar faults

fault geometry and active stress from earthquakes and field geology data analysis the colfiorito 1997 and l aquila 2009 cases central italy the fault segmentation pattern and the regional stress tensor acting since the early quaternary in the intra apennine area of central italy was constrained by integrating two large geological and seismological fault slip data sets collected for the areas struck by the two most energetic seismic sequences of the last 15 years colfiorito 1997 m w 6 0 and l aquila 2009 m w 6 1 the integrated analysis of the earthquake fault association and the reconstruction of the 3d shape of the seismogenic sources were exploited to identify homogeneous seismogenic volumes associated with subsets of geological and focal mechanism data the independent analysis of geological and seismological data allowed us to observe and highlight similarities between the attitude of the long term e g quaternary and the instantaneous present day seismogenic extensional deformations and to reveal their substantial coaxiality coherently with the results from the kinematic analysis the stress field inversion also noted a prevailing tensional seismotectonic regime associated with a subhorizontal ne sw minimum stress axis a minor very local and shallow 5 km strike slip component of the stress field was observed in the colfiorito sector where an inherited n s oriented right lateral fault was reactivated with sinistral kinematics instead an almost total absence of strike slip solutions was observed in the l aquila area these results do not agree with those indicating quaternary regional strike slip regimes or wide areas characterized by strike slip deformation during the colfiorito and l aquila seismic sequences

rupture depths and source processes of the 1997 1998 earthquake sequence in central italy abstract the focal depths and the rupture processes of four moderate earthquakes which occurred in central italy during 1997 and 1998 are investigated using broadband teleseismic data the earthquakes the largest with m w 6 0 caused significant damage in the epicentral area and are part of an unusual sequence of moderate sized earthquakes to strike the central apennines for three of the events the waveforms are found to be consistent with seismic ruptures confined to the top 5 to 7 km of the crust directivity effects are evident in the waveforms of the largest earthquake and waveform inversion suggests an upward rupture with a horizontal component oriented toward the north one earthquake m w 5 2 is confirmed from waveform modeling to have occurred at 50 km depth this is the first event of this magnitude to have been located in the mantle beneath the apennines

an advanced slip model for the umbria marche earthquake sequence coseismic displacements observed by sar interferometry and model inversion summary we report an improved slip model for the 1997 september october umbria marche earthquake sequence in central italy the model is based on coseismic displacements estimated by differential synthetic aperture radar dinsar interferometry using an advanced inverse modelling approach that enables the characteristics of the sar data especially their dense spatial sampling to be fully exploited the paper first looks at dinsar analysis using the simplest configuration that is a single image pair that temporally covers the earthquake sequence yet given that this dinsar configuration is often used for coseismic studies and the limited availability of sar data we duly consider the limitations of the dinsar results and discuss the rigorous dinsar procedure carried out highlighting key errors associated with such observations we then focus on the inversion of the estimated dinsar displacements and on our advanced heterogeneous slip model for this earthquake sequence s main shocks emphasizing its most significant features

the 1997 98 umbria marche earthquake sequence geological vs seismological faults abstract the 1997 98 umbria marche earthquake provided a huge amount of good quality seismological data the geology of the region has been extensively mapped for over a century by geologists from all over the world the subsurface geology is constrained by a set of seismic reflection profiles and deep boreholes acquired for oil exploration the earthquake stimulated the acquisition of many other geological and geophysical data sets surface ruptures structural analysis geodetic data geoeletrical data etc as a consequence the 1997 98 earthquake is one of the best case studies in the world for extensional earthquakes driving the possibility of building up an integrated model of an extensional system we use this favourable test site to discuss the possibility of integrating and connecting the seismological faults i e the short term instantaneous ruptures generated during the earthquakes representing the effect of a single event and the geological faults i e the long term active faults exposed at the surface that are the effects of multiple repeated events of faulting the review of this complex data set points to an integrated model where the moderate seismicity of the region is driven by sw dipping normal faults whose dip changes with depth from 60 70 the fault surfaces mapped at the surface to 35 45 the fault segments ruptured during the earthquake at depths of 2 8 km to less than 20 at depth 8 km these normal faults are not inherited from previous tectonic events however the pre existing arc shaped compressional structures act as barriers segmenting the extensional fault system the depth and thickness of the seismogenic layer is lithologically controlled since the seismicity is confined within the sedimentary cover and do not penetrate the underlying basement the mainshocks are located close to the bottom of the seismogenic layer within the triassic evaporites

the evolution of volcano hosted geothermal systems based on deep wells from karaha telaga bodas indonesia temperature and pressure surveys fluid samples and petrologic analyses of rock samples from deep drill holes at the karaha telaga bodas geothermal field on the volcanic ridge extending northward from galunggung volcano west java have provided a unique opportunity to characterize the evolution of an active volcano hosted geothermal system wells up to 3 km in depth have encountered temperatures as high as 353 c and a weakly altered granodiorite that intruded to within 2 to 3 km of the surface the intrusion is shallowest beneath the southern end of the field where an acid lake overlies a nearly vertical low resistivity structure 10 ohm m defined by magnetotelluric measurements this structure is interpreted to represent a vapor dominated chimney that provides a pathway to the surface for magmatic gases four distinct hydrothermal mineral assemblages document the evolution of the geothermal system and the transition from liquid to vapor dominated conditions the earliest assemblage represents the initial liquid dominated system generated during emplacement of the granodiorite between 5910 76 and 4200 150 y bp tourmaline biotite actinolite epidote and clay minerals were deposited contemporaneously at progressively greater distances from the intrusive contact assemblage 1 at 4200 150 y bp flank collapse and the formation of the volcano s crater kawah galunggung resulted in catastrophic decompression and boiling of the hydrothermal fluids this event initiated development of the modern vapor dominated regime chalcedony and then quartz were deposited as the early low salinity liquids boiled assemblage 2 both vapor and liquid rich fluid inclusions were trapped in the quartz crystals liquid rich fluid inclusions from the southern part of the field record salinities ranging from 0 to 26 weight percent nacl cacl 2 equivalent and locally contain fluorite daughter crystals we suggest based on temperature salinity relationships and evidence of boiling that these fluids were progressively concentrated as steam was lost from the system however mixing with fluids derived from the underlying intrusion or generated during the formation of acid so 4 water on the vapor dominated chimney margins could have contributed to the observed salinities as pressures declined co 2 and so 4 rich steam heated water drained downward depositing anhydrite and calcite assemblage 3 in the fractures limiting further recharge fluid inclusions with salinities up to 31 weight percent nacl equivalent were trapped in these minerals as the descending water vaporized the final assemblage is represented by precipitates of nacl kcl and fecl x deposited on rock surfaces in portions of the vapor dominated zone that boiled dry vapor dominated conditions extend over a distance of at least 10 km and to depths below sea level deep wells drilled into the underlying liquid dominated reservoir in the northern and central part of the volcanic ridge produce low salinity fluids representing recent recharge of meteoric and steam heated water the evolution of volcanic hosted vapor dominated geothermal systems can be described by a five stage model stage 1 involves the formation of an over pressured liquid dominated geothermal system soon after magmatic intrusion in stages 2 and 3 pressures progressively decrease and a curtain of steam heated water surrounding a magmatic vapor dominated chimney at 350 c and 14 2 mpa develops the relatively low pressure near the base of the chimney causes liquid inflow adjacent to the intrusion and the development of a secondary marginal vapor dominated zone in stage 4 the magmatic vapor discharge from the intrusion becomes small vapor pressure declines and the secondary vapor dominated zone expands above the intrusion in stage 5 the vapor dominated zone floods because heat from the intrusion is insufficient to boil all liquid inflow a more common liquid dominated volcanic hosted system then develops

primary diagenetic copper carbonate at the malbunka copper deposit amadeus basin northern territory australia abstract the malbunka copper deposit located about 220 km west of alice springs in the northern territory of australia may be a rare example of primary formation of copper carbonate mineralization this deposit consists of unusual azurite disks up to 25 cm diameter and lesser amounts of secondary azurite crystals and malachite carbon isotope values of the copper carbonate minerals are consistent with formation from groundwater dissolved inorganic carbon oxygen isotope thermometry formation temperature estimates are 5 16 c above ambient temperatures suggesting the copper carbonates formed at a depth between 0 3 and 1 6 km in the amadeus basin azurite fluid inclusion waters are rich in boron chlorine and other elements suggestive of dilute oil basin formation fluids in addition presence of euhedral tourmaline with strong chemical zonation suggest that this was a low temperature diagenetic setting the strong correlation of structures associated with hydraulic fracturing and rich copper carbonate mineralization suggest a strongly compartmentalized overpressure environment it is proposed that copper carbonates of the malbunka deposit formed when deep copper rich formation fluids were released upward by overpressure induced failure of basin sediments permitting mixing with carbonate rich fluids above this work bears directly upon exploration for a new type of primary copper deposit through understanding of the conditions of genesis

complex behavior of magma hydrothermal processes role of supercritical fluid abstract magmas emplaced into the upper portions of the earth s crust are accompanied by extensive hydrothermal activity hydrothermal activity is represented as a system of coupled processes that dissipate thermal mechanical and chemical energy into the magma s lithocap primarily by convection of h2o rich fluids to investigate dynamical behavior of the system a serial experiment was undertaken in which t t and p t values are computed for a pluton location during the time the region was subjected to near critical hydrothermal convective flow the consequent evolution of fluid buoyancy x f ion stability and fracture extension l l0 during this time indicates that variations in density gradients increase smoothly until 70 000 yr then burst into frequent 100 yr oscillations oscillations first increase in magnitude then decrease oscillatory behavior of state conditions derived from numerical experiments illustrate resonant effects in chemical equilibrium and fracture extension processes and show the sensitivity of the stable mineral assemblage to either of the competing chemical and mechanical transport processes an oscillatory zoned tourmaline that formed at near critical conditions of h2o from the geysers geothermal deposit appears to provide evidence of nonlinear systematics in hydrothermal activity mathematical analogs to this system demonstrate that processes in this system record their dynamical behavior in the supercritical region and suggest that alteration events are generated by the complex chaotic behavior of these processes this type of behavior appears to be further augmented by strong divergence of h2o fluid properties toward infinity at commonly encountered state conditions in the shallow reaches of magma hydrothermal activity system behavior elucidated here arises from affording for connectivity of processes by numerical experiments of hydrothermal activity for a region near the contact of a magma and its lithocap the cumulative data from numerical experiments equation of state eos relationships geologic and geochemical observations support the proposition that magma hydrothermal processes should be thought of as complex dynamical systems whose behavior at state conditions near the supercritical region of the fluid is likely chaotic

quaternary basin evolution and present tectonic regime in the area of the 1997 1998 umbria marche seismic sequence central italy abstract geological and geomorphological surveys have been performed in the area affected by the 1997 1998 umbria marche seismic sequence m max 6 0 aimed at defining the quaternary tectonic history and the characteristics of the present tectonic regime data have been collected from 1 the analysis of the remnant landsurfaces by means of aerial photos and field surveys 2 geological surveys in the cesi san martino basin and in the easternmost sector of the colfiorito basin in order to identify deformative features affecting the quaternary deposits 3 the analysis of boreholes and geo electrical data derived from previous surveys performed in the 1960s in order to reconstruct the top of the pre quaternary substratum in the colfiorito basin two different successions of remnant landsurfaces have been identified along the faults bounding the basins to the east in the hangingwall and the footwall respectively the difference accounts for a fault controlled evolution of the landscape at least during the upper pliocene early pleistocene the deformation affecting the quaternary deposits and landforms in the investigated basins indicates a decreasing tectonic activity along the master faults since the middle pleistocene surface deformation due to tectonics is faint and displayed by gentle warping of the landforms during the late quaternary as for the basin geometry subsurface data show that two minor depressions formed in the colfiorito basin during the quaternary the oldest one close to the fault bounding the basin while the youngest and deepest formed in the inner portion of the basin therefore the present geometry is different from that of other fault bounded quaternary depressions of the central apennines typically half graben basins showing the maximum depth of the substratum in the area close to the master fault tectonic history may be summarised as follows 1 origin of the quaternary fault bounded colfiorito and cesi san martino basins 2 evolution of the basins with a half graben style 3 significant reduction of tectonic activity since the middle pleistocene during the third phase the evolution of the basins is no longer related to a half graben style in the case of the colfiorito basin a new depression is superimposed to on the previous half graben whose evolution is related to the lowering of the inner portion of the basin through warping moreover present activity does not result in fault related surficial displacements but only in continuous deformation spread over the basins these conclusions have fundamental implications for the seismotectonic framework of the 1997 1998 earthquake sequence this deformation style is indeed in agreement with the coseismic deformation modelled by means of the sar interferometry analyses carried out by other institutions during the seismic sequence and with the lack of evident surface faulting related to the mentioned events in the investigated area this evidence indicates that the evolution of the investigated area since the middle pleistocene resulted from the summation of deformative episodes similar to that which occurred during the recent seismic sequence as a consequence no earthquakes with magnitude larger than 6 are expected in the area

episodic hydrothermal alteration recorded by microscale oxygen isotope analysis of white mica in the larderello travale geothermal field italy abstract microscale oxygen isotope analysis 18o 16o of minerals can identify distinct events of fluid rock interaction this method is however still limited to a few major and accessory minerals of which most are anhydrous minerals we present the systematic study of oxygen isotope distribution in white mica by secondary ion mass spectrometry sims texturally and chemically distinct white mica populations in granitic and contact metamorphic rocks from the larderello travale geothermal field ltgf italy record stages of magmatic crystallization metamorphic hydrothermal replacement and fluid rock interaction the large range in intra and inter grain white mica 18o values between 1 and 14 reflects varying protoliths and degrees of fluid mineral interaction at variable temperatures 180 450 c present day temperatures p d t this variability reflects the large scale circulation of both 1 magmatic syn intrusive to early contact metamorphic hydrothermal fluids with high 18o values and 2 meteoric fluids with 18o values of 7 during a post intrusive late hydrothermal stage metasedimentary rocks from the upper reservoir contain distinct white mica populations occurring in close proximity m scale including detrital grains 18o 12 14 high na low mg partially altered white mica 18o 8 9 and late hydrothermal white mica 1 6 low na mid mg the late hydrothermal white mica has similar 18o values to other secondary minerals and is in equilibrium with meteoric dominated fluids with a 18o of 6 to 0 5 which circulated in the late hydrothermal stage downhole towards the lower reservoir white mica from two contact metamorphic micaschist samples shows either 1 homogeneous 18o values of ca 9 likely due to recrystallization in the contact metamorphic hydrothermal stage t ca 600 c or 2 a large spread in 18o from 2 to 12 within and across grains of variable texture and chemistry in the host rock and a cross cutting quartz white mica vein ca 300 c present day temperature hereafter p d t this contrasting 18o signature of white mica is also recorded in granite cored at up to 4 6 km depth the carboli granite contains white mica with a homogeneous magmatic 18o of 10 0 6 whereas older granite samples from radicondoli have magmatic to hydrothermal white micas that vary in 18o from 4 to 10 a pronounced intra grain 18o variability of up to 6 occurs in white mica domains with higher fe mg ti halos around inclusions of chloritized biotite as a result of interaction with dominantly meteoric fluids that infiltrated to depths of at least 4 6 km in the porto azzurro granite on elba italy altered white mica has 18o values of 2 6 down from 10 in unaltered grains the distribution of oxygen isotope ratios in white mica is thus firstly a result of pervasive versus selective fluid alteration at depth sample and grain scale secondly the actual preservation of these m scale variabilities indicates that volume diffusion is not detectable at microscale at p d t at or below 350 c where most of the heterogeneous white mica is found selective sample and grain scale fluid penetration occurs episodically and anisotropically on micro and megascale along faults fractures and cleavages producing lower 18o white mica at various times in zones of higher secondary permeability and active hydrothermal fluid circulation

connecting seismically active normal faults with quaternary geological structures in a complex extensional environment the colfiorito 1997 case history northern apennines italy 1 the northern apennines of italy are characterized by a complex tertiary tectonic history where superposed compressional and extensional deformation occurred in such regions characterized by low active extensional strain rate the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between geological faults i e faults which can be mapped at the surface and seismological faults i e faults which actually generate earthquakes the availability of detailed geological mapping and high resolution seismological data for the colfiorito area struck in 1997 by a sequence of six 5 mw 6 normal faulting earthquakes allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological quaternary faults and the activated structures in map view the earthquakes distribution reflects the fault pattern mapped at the surface the length of activated and mapped faults is quite similar 7 10 km the coseismic subsided region imaged by interferometric synthetic aperture radar data is located in the hanging wall of the mapped normal faults that bound the quaternary basins in section view there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency this study points out that the quaternary tectonosedimentary evolution and the present day geological and geomorphologic setting of the colfiorito area can be interpreted as the result of repeated extensional earthquakes similar to the 1997 events occurring on nw se trending normal faults our data also show that the main shocks of the colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional transpressional structures which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

li b rich rhaetian metabauxite tuscany italy reworking of older bauxites and igneous rocks abstract li b rich metabauxite layers occur in two outcrops of talus metabreccias intercalated between norian and liassic marbles in the alpi apuane tuscany italy field evidence petrographical geochemical and paleogeographic paleoclimatologic considerations suggest that bauxitic material was derived from a multistage reworking of late carboniferous early autunian primary deposits now completely removed the identified lithotypes are cookeite rich metabauxite cookeite bearing metabreccia chloritoid schist and chloritoid phyllite the mg content of calcite and the si content of muscovite and mineral assemblages indicate temperatures of 350 380 c pressures of f o 2 values of 10 30 to 10 24 for the alpine metamorphism in comparison with the average mesozoic bauxite of bronevoy et al 1985 the metabauxite is strongly enriched in si k ca mg li b be ni and ce it shows comparable contents of co la eu tb ta and th it is depleted in ga cr v zn mn hf u and is strongly depleted in sr f cu a metabauxite layer shows decreasing abundance of fe and ga from bottom to top with a pattern opposite to that of primary bauxite deposits inverted profile the strong enrichment of li and b is not related to evaporitic conditions since the mgo na 2 o and sr contents are too low and indicator minerals such as dravitic tourmaline albite and scapolite are missing during the permian volcanic products similar to the coeval peralkaline peraluminous rocks of corsica sardinia were widespread in tuscany b li rich minerals were produced by circulation of hot hydrothermal fluids within the permian volcanic rocks during and soon after their emplacement the erosion of such hydrothermal products supplied detrital material to the talus metabreccia

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

upper crust tomographic structure of the central apennines italy from local earthquakes abstract we derived a three dimensional p and s waves velocity model of the first 9 km of crust in the central apennine from local earthquakes the data set used for the tomographic inversion was recorded from three component regional and local networks which operated in the region from 1979 to 1998 and consists of 984 earthquakes for these earthquakes we have at least eight phases a gap smaller than 200 and a total rms residual smaller than 0 6 s giving a total of 13190 p and 10257 s phases first arrivals the inversion is performed using the simulps12 code this technique iterates the estimated velocity model parameters defined at the nodes of a grid relocating the earthquakes with an approximate 3 d ray tracing a large positive p and s wave velocity anomaly is observed in correspondence to the main seismogenetic volume of the central apennines a synthetic test demonstrates that this anomaly is not artificially produced by the substantially higher density of earthquakes within the seismic velocity anomaly this anomaly corresponds to the carbonatic rocks that form the core of the fold and thrust central apennines belt these rocks are underlain by ductile evaporite formations which were justaposed during the tectonic evolution of the belt we suggest that the evaporite layers effectively decouple the upper crustal seismogenetic volume from the middle and lower crust we conclude that the accumulation of seismic energy could be induced by gravitational tectonic processes explaining the fact that most of the seismicity is confined above the evaporites

velocity and attenuation tomography of the umbria marche 1997 fault system evidence of a fluid governed seismic sequence abstract the 1997 umbria marche is probably the best ever monitored normal faulting seismic sequence seismicity migration and multiple main shocks characterize the activation of a 40 km long system of contiguous fault segments as documented by seismological data many authors as indicative of fault weakening by fluids migration have interpreted this behaviour in this study we create a new catalogue of high quality p and s wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations we show that the relocated earthquakes and the joint interpretation of p and s wave velocity and attenuation models help in understanding the faulting processes revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume we observe that large aftershocks occur on the top and within the triassic evaporitic layer a rock volume locally characterised by fluid over pressured as evidenced by high vp vs and low qp qs anomalies velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence

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