the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

stable sr isotope sr ca mg ca li ca and mg li ratios in the scleractinian cold water coral lophelia pertusa the aragonitic skeletons of scleractinian cold water corals can serve as valuable archives in paleoceanographic studies the potential of 88 86sr sr ca mg ca li ca and mg li ratios of the cold water coral lophelia pertusa to record intermediate water mass properties has been investigated here we used samples from several locations along the european continental margin spanning a large temperature range from 6 to 14 c stable strontium isotope measurements were carried out with the recently developed double spike tims technique and our results differ from those obtained with less precise methods in contrast to the strong positive relationship with temperature of previous studies our results suggest that 88 86sr measured in scleractinian cold water corals is not controlled by seawater temperature but reflects the sr isotopic composition of seawater with an offset of 88 86sr 0 196 as found in previous studies the elemental ratios sr ca li ca and mg li measured in corals are significantly related to water temperature and do not correlate with salinity moreover sr ca ratios in l pertusa display the expected inverse correlation with temperature however the variance in the sr ca data severely limits the accuracy of paleotemperature estimates the li ca and mg ca ratios reveal other influences besides temperature such as ph and or growth or calcification rate however corresponding mg li ratios in l pertusa are more tightly related to temperature as they remove these secondary effects in particular the mg li ratio in l pertusa may serve as a new promising paleotemperature proxy for intermediate water masses our dataset represents the most extensive geochemical examination of l pertusa to date revealing a temperature sensitivity of 0 015 mol mmol c for mg li however using this temperature dependence and the precision of 5 3 2sd only temperature variations larger than 1 5 c can be resolved with 95 confidence

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

magma chamber evolution prior to the campanian ignimbrite and neapolitan yellow tuff eruptions campi flegrei italy the campi flegrei campanian region italy experienced two cataclysmic caldera forming eruptions which produced the campanian ignimbrite 39 ka ci and the neapolitan yellow tuff 15 ka nyt we studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions major trace element and sr and nd isotope compositions of pre campanian ignimbrite and pre neapolitan yellow tuff products define distinct geochemical groups which are here interpreted as distinct magma batches these batches do not show any transitional trend towards the ci and nyt eruptions the ci and nyt systems are decoupled geochemically and isotopically at least one of the pre ci and one of the pre nyt erupted magma batches qualifies as mixing endmembers for the large ci and nyt eruptions and thus must have been stored in reservoirs for some time to remain available for the ci and nyt eruptions the least evolved isotopically distinct magma compositions that are typical of the last phases of the nyt and ci eruptions did not occur before caldera forming events based on the new data we propose the following scenario multiple magma chambers with distinct compositions existed below the campi flegrei before the ci and nyt eruptions and remained generally separated for some time unless new magma was recharged in each case one of the residing magma reservoirs was recharged by a new large volume magma input of intermediate composition from a deeper differentiating magma reservoir this may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera forming eruption large magma chambers in the campi flegrei may therefore be ephemeral features interrupted by periods of evolution in individual separated magma reservoirs

mantle and crustal processes in the magmatism of the campania region inferences from mineralogy geochemistry and sr nd o isotopes of young hybrid volcanics of the ischia island south italy ischia one active volcano of the phlegraean volcanic district prone to very high risk is dominated by a caldera formed 55 ka bp followed by resurgence of the collapsed area over the past 3 ka the activity extruded evolved potassic magmas only a few low energy explosive events were fed by less evolved magmas a geochemical and sr nd o isotope investigation has been performed on minerals and glass from products of three of such eruptions molara vateliero and cava nocelle 2 6 ka bp data document strong mineralogical geochemical and isotopic heterogeneities likely resulting from mingling mixing processes among mafic and felsic magmas that already fed the ischia volcanism in the past detailed study on the most mafic magma has permitted to investigate its origin the mantle sector below ischia underwent subduction processes that modified its pristine chemical isotopic and redox conditions by addition of 1 of sediment fluids melts similar processes occurred from southeast to northwest along the apennine compressive margin with addition of up to 2 5 of sediment derived material this is shown by volcanics with poorly variable typical 18o mantle values and 87sr 86sr progressively increasing toward typical continental crust values multiple partial melting of this modified mantle generated distinct primary magmas that occasionally assimilated continental crust acquiring more 18o than 87sr at ischia 7 of hercynian granodiorite assimilation produced isotopically distinct k basaltic to latitic magmas a sw ne regional tectonic structure gave these magmas coming from large depth the opportunity to mingle mix with felsic magmas stagnating in shallower reservoirs eventually triggering explosive eruptions

space time distribution patterns of destructive earthquakes in the inner belt of central japan part 2 moment release rates and earthquake prediction the inner belt of central japan between the itoigawa shizuoka tectonic line istl and tsurugawan isewan tectonic line titl can be divided into four blocks by boundaries linking major nw se trending left lateral active faults historical earthquakes of magnitude 6 4 or greater which caused significant damage mainly occurred along the four block boundaries and have been recorded or documented since 715 a d the average rates of seismic moments released along the block boundaries in the inner belt of central japan have been estimated since no destructive earthquakes were recorded or documented between 888 a d and 1585 a d this period is regarded as a time of seismic quiescence the average rates re of the seismic moments released by destructive earthquakes since 1586 a d the present active period were estimated from the amount of the released moment inferred from the magnitude of the earthquakes average rates rs of seismic moments are also calculated from the average rates of quaternary displacements along the major active faults constituting the block boundaries the average rates re during the active period were found to be0 031 1026dyne cm yr for the istl those for the other three boundaries ranged from 0 087 to0 095 1026dyne cm yr the average release rate re through the quiet and active periods since 888 a d ranged from 0 023 to0 031 1026dyne yr with exception of0 008 1026dyne cm yr for the istl these values were found to be in good agreement with the estimation ofs this suggests that destructive earthquakes are a manifestation of the movement of the block boundary thus it is important to assess the block boundary movements when designing large earthquake resistant structures regions having no incidences of earthquakes seismic gaps during the present active period since 1586 a d have already been detected by us in previous work destructive earthquakes are predicted to occur in these seismic gaps the dates of the future earthquakes are then estimated assuming that the moment accumulated since the last earthquake exceeds the moment inferred from the possible magnitude in the region of the seismic gap future earthquakes are predicted to occur between 2007 and 2076 a d

earthquake cycles in a model of interacting fault patches complex behavior at transition from seismic to aseismic slip numerical simulations of complex earthquake cycles are conducted using a model with two patches asperities on a fault where friction obeys a rate and state dependent law the patches are represented by regions of steady state velocity weakening friction and are in contact with each other or are separated by a region of steady state velocity strengthening friction simulated earthquake cycles are examined by changing the characteristic slip distance of friction in one patch while that in the other patch is maintained at a constant as the characteristic slip distance in a patch increases the slip at the patch tends to be aseismic and rupture tends to be delayed as compared to rupture at the other patch or arrested due to an increase in fracture energy as a result the slip pattern changes in a complicated manner with the change of the parameter a complex multiperiodic or aperiodic slip pattern occurs in the simulation and this pattern tends to occur near the boundaries between regions of different slip behavior characteristics such as the boundary between seismic and aseismic slip in the patch with a larger characteristic slip distance iteration maps of the recurrence intervals of simulated earthquakes for an aperiodic sequence are sometimes expressed by simple curves suggesting that the simulated earthquake cycles exhibit deterministic chaos in the two patch models of the present study an aperiodic slip pattern is observed for narrower parameter ranges than in a model of a two degree of freedom spring block system which is usually regarded as a simplified model of a fault with two patches online material simulated histories of moment release rate and recurrence interval of simulated slip events in the two patches and seismic coupling coefficients

the baia fondi di baia eruption at campi flegrei stratigraphy and dynamics of a multi stage caldera reactivation event the baia fondi di baia eruption is one of the sporadic events that have occurred in the western sector of the campi flegrei caldera it dates back to 9525 9696 bp and opened epoch 2 of the caldera activity after a 1000 year long period of quiescence although relatively small in terms of erupted volume with respect to most of the events of the past 15 ka the baia fondi di baia eruption was characterized by a complex series of events which have led to different interpretations in the literature we present a detailed stratigraphic study of 40 outcrops in a sector of about 90 km2 coupled with sedimentological grain size componentry physical density vesicularity textural and compositional analyses of the erupted deposits based on these data we interpret the stratigraphic succession as being related to two distinct eruptive episodes baia and fondi di baia these were separated by a short time interval and each was characterized by different eruptive phases the baia eruptive episode started in a shallow water environment with an explosive vent opening phase that formed a breccia deposit unit i rapidly followed by alternating fallout activity and dense pyroclastic density current deposits generation unit ii sedimentological features and pumice textural analyses suggest that deposition of unit ii coincided with the intensity peak of the eruption with the fallout deposit being characterized by a volume of 0 06 0 008 km3 corresponding to a total erupted mass of 4 06 0 5 1010 kg a column height of 17 km and a corresponding mass flow rate of 1 8 107 kg s 1 the associated tephra also shows the highest vesicularity up to 81 vol the highest vesicle number density 1 01 108 cm 3 and decompression rate 0 69 mpa s 1 this peak phase waned to turbulent surge like activity possibly associated with vulcanian explosions and characterized by progressively lower intensity as shown by density vesicularity and textural properties of the erupted juvenile material unit iii this first eruptive episode was followed by a short quiescence interrupted by the onset of a second eruptive episode fondi di baia whose vent opening deposited a breccia bed unit iv which at some key outcrops directly overlies the fallout deposit of unit ii the final phase of the fondi di baia episode strongly resembles unit ii although sedimentological presence of obsidian clasts which are absent in the baia deposits and textural lower vesicularity vesicle number density and decompression rate values features together with a more limited dispersal suggest that this phase of the eruption had a lower intensity the large range of groundmass glass compositions associated with variable proportions of highly phonolitic trachytic and mildly tephriphonolitic latitic evolved end members in the erupted products also suggests that these eruptive episodes were fed by at least two different magma batches that interacted during the different phases with an increase of tephriphonolitic latitic magma occurring during the fondi di baia stage

a laboratory model of a replenished magma chamber abstract it has recently been suggested that periodic influxes of hot but heavy magma into the base of a basaltic magma chamber can remain isolated from the rest of the chamber while the new magma cools and crystallization proceeds when thermal equilibrium is almost complete the suspended crystals settle out and the residual less dense liquid can then mix with the fluid above in the present paper the basic fluid dynamical processes underlying this model have been investigated in laboratory experiments using aqueous solutions the lower layer was hot kno3 solution for which saturated solutions become less dense as the temperature decreases with a cold deeper layer of less dense nano3 or k2co3 above the lower layer there was strong convective transfer of heat through a sharp interface separating the layers at a rate which is predicted here drawing on previous studies carried out with oceanographic applications in mind once crystallization began non equilibrium effects became important and the observed temperatures differ somewhat from those predicted in the experiments crystals grew mainly from the bottom rather than while in suspension but this is not an essential aspect of the model the important fact is that the density of the residual liquid in the lower layer decreased until it became equal to that of the upper layer and then the interface broke down so that the two layers mixed thoroughly together leaving a layer of kno3 crystals at the base no crystallization at all occurred when the hot input liquid was forced to mix initially with the cold solution already in the chamber

simple spring mass model simulation of earthquake cycle along the nankai trough in southwest japan along the nankai trough in southwest japan due to the subduction of the philippine sea plate great earthquakes have occurred repeatedly the rupture zone is divided into five segments historical documents show the characteristic features of the past several earthquake cycles such as almost simultaneous rupture occurrence in segments in spite of different convergence rates the recurrence time of 90 to 150 years the existence of segment pairing in earthquake ruptures and the different coseismic slip behaviors in respective segments

temporally unstable recurrence of earthquakes due to breaks in fractal scaling observed sequences of large earthquakes are not consistent in either recurrence time or energy release long term prediction has been impossible even in areas such as parkfield with well defined recurrence intervals the seismic gap hypothesis which predicts characteristic earthquakes in areas of the circum pacific belt that have not produced recent great earthquakes has also failed to predict the observed clustering of high energy events models in which fractal scaling is broken at high magnitude predict that characteristic events and recurrence behavior will be unstable in time the central predictions of these models are supported by recent observations at landers and big bear in california

step filling and development of a three layer magma chamber the neapolitan yellow tuff case history abstract the neapolitan yellow tuff the product of the largest known trachytic phreatoplinian eruption gives a good opportunity to investigate the filling mechanisms and internal dynamics of a trachytic magma chamber a detailed study of the geochemical mineralogical and isotopical features of the deposit was carried out to investigate the behaviour of the magma chamber before the eruption the collected data show three distinct compositional groups separated by gaps single depositional units contain glass shards formed contemporaneously although each of these shards is homogeneous they display the same compositional variations and gaps detected in pumice clasts this feature is taken as an evidence for interpreting the detected compositional gaps as real gaps in the chamber therefore the chamber was filled by three distinct magma bodies separated by compositional gaps the uppermost magma was alkali trachyte and highly homogeneous likely a consequence of vigorous convection the intermediate magma was trachyte with a slight and continuous compositional variation likely resulting from less intense convection the lowermost magma was compositionally zoned from alkali trachyte to latite downward this compositional zonation was most likely acquired during uprise from a deeper reservoir the three magmas entered the chamber sequentially from the uppermost to the lowermost the latter entered the chamber short before the beginning of the eruption its input was interpreted as a possible triggering factor for the eruption the results of this study strongly support a step filling mechanism for the neapolitan yellow tuff magma chamber and allow definition of the temporal succession of input of magma batches furthermore they also suggest that the magma bodies did not mix although at least the uppermost two coexisted inside the chamber for a time long enough to allow internal homogeneization by convection

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

long term dynamics of a fault with two asperities of different strengths summary a fault made of two segments or asperities having different strengths and subject to a constant strain rate is considered the fault is modelled by a discrete dynamical system made of two blockscoupledbyaspringandpulledatconstantvelocityonaroughplane wegiveacomplete analytical solution for the evolution of the system the long term behaviour of the fault is studied by calculating the orbits of the system in the phase space the dynamics of the system has four different modes and produces a variety of behaviours the asperities may slip one at a time originating a medium size earthquake or simultaneously originating a large earthquake in the latter case the focus may be at one asperity or at the other in some cases the weaker asperity may slip twice both before and after the failure of the stronger asperity the time pattern of the seismic events generated by the fault is controlled by the stress distribution on the asperities and may include many different behaviours we devise suitable correspondence rules allowing application of the discrete model to real fault systems as an example the model is applied to the 1964 great alaska earthquake which was originated by the failure of two asperities and a possible evolution of this fault system is discussed

a sequence of destructive earthquakes and the coupling of fault systems in central japan abstract in the western part of central japan large successive inland earthquakes have occurred causing serious damage the 1891 m 8 0 nobi earthquake was followed by the 1909 m 6 8 anegawa the 1945 m 6 8 mikawa and the 1948 m 7 1 fukui earthquakes the two major fault systems termed the tsurugawan isewan tectonic line titl and the fukui neodani block boundary line fnbb have been identified as lines linking nw se oriented active faults in the study area an examination of the vertical displacement of ground surfaces indicates that tilting of the central part of the fnbb caused by the nobi earthquake begins around the sekigahara fault on the central part of the titl ruptures and vertical displacements can also be found along the ogaki kisozaki fault close to the titl therefore it was concluded that the influence of the nobi earthquake extended to a part of the titl eighteen years after the nobi earthquake the anegawa earthquake occurred along the sekigahara fault these features and the earthquake sequence can be explained by a block rotation model with strike slip faulting the nobi earthquake created en echelon ruptures over an 80 km long line with a left lateral slip of up to 8 m along the neodani fault according to the model this left lateral slip must be accompanied by a clockwise rotation of the block between the fnbb and titl the block rotation should in turn induce a left lateral slip on the titl since the titl exhibits a sharp bend along the sekigahara fault a transtensional region should appear along the fault owing to the left lateral slip of the titl the expected transtensional region is consistent with areas damaged by the anegawa earthquake suggesting that the earthquake occurred in the transtensional regime about 40 years after the anegawa earthquake the mikawa and fukui earthquakes were generated on the southern and northern ends of the fnbb respectively this implies that the fault movement of the nobi and anegawa earthquakes created a concentration of stress at both ends of the fnbb resulting in the mikawa and fukui earthquakes approximately two years prior to the nobi earthquake seismic activity was initiated over a wide zone along the fnbb also notable earthquakes aligned along the titl were observed ten years prior to the anegawa earthquake the onset of seismicity along a fault system can be used in predicting destructive inland earthquakes which eventually occur along the fault

geochemical and b sr nd isotopic evidence for mingling and mixing processes in the magmatic system that fed the astroni volcano 4 1 3 8 ka within the campi flegrei caldera southern italy abstract the astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes within the campi flegrei caldera southern italy 4 1 3 8 ka bp whole rock geochemical and b sr nd isotopic investigations were carried out on representative samples of all seven eruptions the products vary from tephriphonolites to phonolites and from latites to trachytes they show textural mineralogical and isotopic evidence of disequilibrium including distinct clinopyroxene populations rounded and or resorbed plagioclase and alkali feldspar and reverse zoned phenocrysts of all these mineral phases the sr nd and b isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution suggesting open system processes in addition to fractional crystallisation moreover significant sr isotopic disequilibrium between the phenocrysts and glass has been documented for one sample the chemostratigraphy of the products indicates that astroni eruptions 1 through 5 were fed by magmas of trachytic to phonolitic composition that were less enriched in radiogenic sr and 11b up section this variability has been interpreted as the result of mingling between at least two distinct magmatic end members one more evolved and the other less evolved another heterogeneous batch of magma resulting from almost complete mixing between the same two end members was drained during eruptions 6 and 7 the more evolved end member characterised by 87sr 86sr 0 7075 143nd 144nd 0 51247 and 11b 8 was very similar to the magma that fed the final phases of the agnano monte spina eruption which occurred a few centuries earlier in the astroni vent area the less evolved end member had 87sr 86sr 0 70726 143nd 144nd 0 51251 and 11b 10 and was likely derived by fractional crystallisation of a mantle derived magma an abrupt decrease in both the sr isotope ratio and the th content detected at the transition between unit 4 and 5 suggests that another magma with a 87sr 86sr ratio intermediate between those of the two identified end members may have been involved in astroni activity the more evolved end member is interpreted as a residue of the agnano monte spina eruption that was invaded by either the intermediate or the less evolved magmatic end member promoting mingling and triggering astroni activity this study of astroni provides insights for both short and long term volcanic hazard assessment as the astroni volcano is the best example of a very close sequence of eruptions from the same vent area in the campi flegrei caldera

time scales of recent phlegrean fields eruptions inferred from the application of a diffusive fractionation model of trace elements the variation of chemical element compositions in two pyroclastic sequences astroni 6 and averno 2 phlegrean fields italy is studied both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior to eruption a clear dichotomy between the behaviour of major vs trace elements is also observed in both sequences with major elements displaying nearly linear inter elemental trends and trace elements showing a variable scattered behaviour together with previous petrological investigations these observations are consistent with the hypothesis that magma mixing processes played a key role in the evolution of these two magmatic systems recently it has been suggested that mixing processes in igneous systems may strongly influence the mobility of trace elements inducing a diffusive fractionation phenomenon whose extent depends on the mixing time scale here we merge information from 1 numerical simulations of magma mixing and 2 magma mixing experiments using as end members natural compositions from phlegrean fields to derive a relationship relating the degree of diffusive fractionation to the mixing time scales application of the diffusive fractionation model to the two studied pyroclastic sequences allowed us to apply the relationship derived by numerical simulations and experiments to estimate the mixing time scales for these two magmatic systems results indicate that mixing processes in astroni 6 and averno 2 systems lasted for approximately 2 and 9 days respectively prior to eruption

the role of transfer structures on volcanic activity at campi flegrei southern italy abstract the tyrrhenian margin of central italy underwent extension during pliocene and quaternary extension occurred mainly through nw se normal faults bordering a sequence of plio quaternary basins these basins are offset by coeval ne sw faults which show strike slip and normal motions and have been interpreted as transfer faults plio quaternary volcanic activity along the margin occurred along a nw se belt systematically in correspondence with ne sw transverse systems the campi flegrei volcanic district cfvd on the southern tyrrhenian margin consists of an active ne sw volcanic ridge developed along ne sw fractures we performed a structural field analysis with analogue and mechanical models to investigate the role of transverse structures upon volcanism at campi flegrei field analysis at campi flegrei recognized ne sw and to a lesser extent coeval nw se active fractures analogue experiments have simulated the development of transfer fault systems in brittle extensional domains the experiments show that subvertical transfer faults connect offset adjacent normal faults dipping 60 the mechanical model is based on the stress equations in uniaxial lithostatic conditions and absence of regional stresses it shows how pre existing subvertical fractures require the smallest magmatic pressures to be penetrated for a given magmatic pressure subvertical fractures might be penetrated more deeply tapping more easily primitive magmas these results suggest that the cfvd is located along a ne sw transfer zone connecting nw se regional normal faults volcanic activity along such ne sw trend would be induced by the subvertical dip of the transfer faults the subvertical dip of transfer faults also suggests an explanation for the emission of the more primitive products along ne sw systems at campi flegrei these considerations find a wider application on the remaining volcanic districts of the margin located in the same overall structural setting

the thermal regime of the campi flegrei magmatic system reconstructed through 3d numerical simulations abstract we illustrate a quantitative conductive convective thermal model incorporating a wide range of geophysical petrological geological geochemical and isotopical observations that constrain the thermal evolution and present state of the campi flegrei caldera cfc magmatic system the proposed model has been computed on the basis of the current knowledge of 1 the volcanic and magmatic history of the volcano over the last 44 ka 2 its underlying crustal structure and 3 the physical properties of the erupted magmas 3d numerical simulations of heat conduction and convection within heterogeneous rock magma materials with evolving heat sources and boundary conditions that simulate magma rise from a deep 8 km depth to shallow 2 6 km reservoirs magma chamber formation magma extrusion caldera collapse and intra caldera hydrothermal convection have been carried out the evolution of the cfc magmatic system through time has been simulated through different steps related to its changes in terms of depth location and size of magma reservoirs and their replenishment the thermal modeling results show that both heat conduction and convection have played an important role in the cfc thermal evolution although with different timing the simulated present heat distribution is in agreement with the measured geothermal profiles agip 1987 reproduces the thermal gradient peaks at the cfc margins in correspondence to the anomalies in surface gradients corrado et al 1998 and suggests temperatures of 700 c at depth of 4 km in the central portion of the caldera in agreement with the estimated temperature for the brittle ductile transition hill 1992

evidence for chaotic fault interactions in the seismicity of the san andreas fault and nankai trough interactions between fault segments are one of the main sources of complexity in the seismicity of active tectonic regions such interactions are likely to influence the spatial and temporal patterns of earthquakes here we examine the dynamical behaviour introduced by fault interactions using a simple spring loaded slider block model with velocity weakening friction the model consists of two slider blocks coupled to each other and to a constant velocity driver by elastic springs for an asymmetric system in which the frictional forces on the two blocks are not equal the solutions exhibit chaotic behaviour the system s behaviour over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault we see similarities between our model simulations and observed patterns of seismicity on the south central san andreas fault in california and in the nankai trough along the coast of southwestern japan

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

sea level change and volcano tectonic interplay the gulf of pozzuoli campi flegrei eastern tyrrhenian sea during the last 39 ka a geological study based on seismic profiles and sediment cores has been accomplished on the gulf of pozzuoli the marine sector of the campi flegrei an active volcanic area located west of the city of naples italy detailed seismo stratigraphic analysis led to the correlation between marine units and the on land volcanic deposits the absence of primary pyroclastic beds in cores highlights the role of the shallow marine environment in the reworking of the volcani clastic sediments the evolution of the area during the last 39 ka evidences the role of the eustatic change and volcano tectonic phenomena in the development of the local sedimentary record four main phases in the geological evolution have been distinguished in a first phase the emplacement of two volcanic units v1 between 60 and 39 ka and ci 39 ka took place a second phase developed between 39 and 15 ka and led to the formation of regressive depositional wedges fw and lw sedimentary bodies in the external sectors of the area outer shelf the eruption of the neapolitan yellow tuff 15 ka and the following eruptions that occurred up to 11 ka constitute the third phase during the fourth phase 11 ka to present generalized marine conditions were established in the area distribution and thickness of the sedimentary bodies formed during the latter time span are highly variable and constitute the result of a complex interplay between volcano tectonic movements and sea level change

introduction to special section paleoseismology a proverb of confucius states study the past if you would divine the future if we could learn about the past history of earthquakes on a specific fault then we could serve society well by better forecasting the future earthquake behavior of that fault for most of the world the period of historical records is short about 200 years in california and less than that in new zealand oregon and other parts of the world and even where the historical record is thousands of years long such as in north central china or the eastern mediterranean region it is commonly difficult to correlate a major historical earthquake with a specific active fault even if this correlation could be made without ambiguity the recurrence intervals for many faults are longer than even a historical record of several thousand years for these reasons the history of large earthquakes on faults must for the most part be learned from the geological record

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

statistical model for the stick slip behaviour of faults summary inspired by an earlier work by smalley turcotte solla 1985 in this paper we consider a fault consisting of large sets of asperities with a statistical distribution of strength it is argued that the principle of equal load sharing between asperities inside a segment is necessary to account for the stick slip behaviour this principle is responsible for amplifying or damping the effective probability for the displacement of crustal blocks the antecedents of this idea in the seismological literature are commented on

the averno 2 fissure eruption a recent small size explosive event at the campi flegrei caldera italy the averno 2 eruption 3 700 50 a b p was an explosive low magnitude event characterized by magmatic and phreatomagmatic explosions generating mainly fall and surge beds respectively it occurred in the western sector of the campi flegrei caldera campanian region south italy at the intersection of two active fault systems oriented ne and nw the morphologically complex crater area largely filled by the averno lake resulted from vent activation and migration along the ne trending fault system the eruption generated a complex sequence of pyroclastic deposits including pumice fall deposits in the lower portion and prevailing surge beds in the intermediate upper portion the pyroclastic sequence has been studied through stratigraphical morphostructural and petrological investigations and subdivided into three members named a through c member a was emplaced during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of 10 km during this phase the eruption reached its climax with a mass discharge rate of 3 2 106 kg s intense fracturing and fault activation favored entry of a significant amount of water into the system which produced explosions driven by variably efficient water magma interaction these explosions generated wet to dry surge deposits that emplaced member b and c respectively isopachs and isopleths maps as well as areal distribution of ballistic fragments and facies variation of surge deposits allow definition of four vents that opened along a ne oriented 2 km long fissure the total volume of magma extruded during the eruption has been estimated at about 0 07 km3 dre the erupted products range in composition from initial weakly peralkaline alkali trachyte to last emplaced alkali trachyte isotopic data and modeling suggest that mixing occurred during the averno 2 eruption between a more evolved less radiogenic stored magma and a less evolved more radiogenic magma that entered the shallow reservoir to trigger the eruption the early phases of the eruption during which the vent migrated from sw to the center of the present lake were fed by the more evolved uppermost magma while the following phases extruded the less evolved lowermost magma integration of the geological and petrological results suggests that the averno 2 complex eruption was fed from a dyke shaped shallow reservoir intruded into the ne sw fault system bordering to the west the la starza resurgent block within the caldera floor

interaction between particles transported by fallout and surge in the deposits of the agnano monte spina eruption campi flegrei southern italy abstract the agnano monte spina tephra amst is a complex sequence of beds generated by contrasting fragmentation and transportation dynamics the 4 1 ka eruption was accompanied by a volcano tectonic collapse part of which is the present agnano plain the pyroclastic sequence is subdivided into members and submembers each characterized by different lithological and sedimentological features plinian subplinian fallout deposits frequently alternate with base surge beds of phreatomagmatic origin analysis of lateral facies variations and vertical facies associations of correlated layers of submembers b2 d2 and e2 reveals that during some eruption phases the contrasting eruptive dynamics were almost contemporaneous base surge deposits of submember b2 formed during the declining stage of a plinian column they resulted from highly energetic and steady pyroclastic density currents that traveled long distances from the vent area and surmounted topographic obstacles such as the posillipo hill 150 m and the northern sector of the camaldoli hill 250 m submember d2 pyroclastic density currents formed when contemporaneous fallout from an eruptive column was present coarse particles from the column settled throughout the pyroclastic density current determining a significant increase of the solid load of the base surge the consequent increase of supply rate from the transportation to the depositional zone of the base surge led to the formation of unsteady flows that could not efficiently transport the solid load and did not have the ability to travel long distances base surge deposits of submember e2 were fed by a pulsating phreatomagmatic activity which was punctuated by a short lived fallout phase fallout material which was incorporated as an additional load to the base surges was partially transported by low energy steady pyroclastic density currents that traveled over the agnano plain but did not surmount either the camaldoli or the posillipo hills only the very fine material in continuous suspension in the upper no shearing part of the base surge cloud was dispersed higher in the atmosphere and quietly settled over a large area outside the caldera rim the phreatomagmatic origin of base surges which contrasts with the magmatic origin of fallout activity suggests that the pyroclastic density currents of the agnano monte spina eruption did not result from eruption column collapses they were most likely related to radially spreading clouds which were contemporaneous with fallout activity but issued from distinct zones in the vent area the turbulent nature and the high expansion of base surges made them capable under certain conditions of passing over high topographic obstacles with hazardous effects in distal areas

magnetic modeling of the phlegraean volcanic district with extension to the ponza archipelago italy abstract a 3d modeling of the residual aeromagnetic anomalies of the area including the phlegraean volcanic district pvd campi flegrei caldera cfc and ischia and procida vivara islands and two volcanic islands of the ponza archipelago ventotene and s stefano has been carried out the observed residual anomalies have been reproduced with several large magnetized bodies located at 2 10 km depth in the crust a volcanological interpretation has been made possible only for those bodies that have been constrained by geological geothermal and other geophysical data the magnetized structures associated with cfc and ischia procida vivara ventotene and santo stefano islands have been interpreted as igneous bodies that may be solidified intrusions or magma reservoirs on the basis of magnetic data volcanological and magmatological history and geothermal heat flux distribution the existence of a partially solidified magma chamber is suggested at ischia a speculation shows that the magnetization intensity assumed for the magnetic bodies located at procida and south west of ventotene matches quite well with the calculated composition of a cooled residual magma resulting from crystallization processes within a chamber

a new lateglacial chronostratigraphic tephra marker for the south eastern alps the neapolitan yellow tuff nyt in langsee austria in the context of a regional biostratigraphy and palaeoclimate langsee is a small meromictic lake in carinthia se alps with partially varved lateglacial sediments the langsee tephra correlates to the neapolitan yellow tuff nyt an eruption from the campanian volcanic province italy this tephra provides a lateglacial chronostratigraphic time marker from central italy across the adriatic sea to the southeastern alps the langsee tephra is discussed in the context of pollen geochemical and microstratigraphical data from a profundal sediment core from langsee the age of 14 120 cal yr bp for the nyt has been accepted from the monticchio chronology the timescale for the lateglacial in the langsee record is based on laminae counts and has been linked to calendar year ages using the nyt tephrachronological marker consequently the mass expansion of betula has been dated at 14 270 cal yr bp the expansion of p sylvestris started concurrent with the nyt and about 180 yr later at 13 940 cal yr bp p sylvestris forests were established the younger dryas biozone at langsee is characterized only by a slight increase in non arboreal pollen and dominated by pine with visible variations only in pine pollen types differentiation of pine pollen types allowed the recognition of three minor fluctuations during the lateglacial interstadial two of these oscillations tentatively have been correlated with the aegelsee and gerzensee oscillations in switzerland as well as with vegetation changes in nw germany

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

petro chemical features and source areas of volcanic aggregates used in ancient roman maritime concretes abstract we present and discuss data from petrographic observation at the optical microscope electron microprobe analyses on selected glass shards and trace element analyses on 14 mortar aggregates collected at the ancient harbors and other maritime structures of latium and campania spanning the third century bce through the second ce aimed at identify the volcanic products employed in the concretes and their area of exploitation according to latin author vitruvius assertion about the ubiquitous use of campanian pozzolan in the ancient roman sea water concretes results of this study show a very selective and homogeneous choice in the material employed to produce the concretes for the different investigated maritime structures evidencing three main pumice compositions all corresponding to those of the products of the post neapolitan yellow tuff activity of the phlegraean fields and a systematic use of the local neapolitan yellow tuff to produce the coarse aggregate of these concretes however mixing with local products of the colli albani volcanic district located 20 km east of rome has been evidenced at two fishponds of latium in punta della vipera and torre astura based on these petrographic and geochemical data we conclude that the selective use of pozzolan from campania rather than of unproved different chemical properties was the consequence of a series of logistic economic industrial and historical reasons

hydrothermal fluid venting in the offshore sector of campi flegrei caldera a geochemical geophysical and volcanological study the ongoing unrest at the campi flegrei caldera cfc in southern italy is prompting exploration of its poorly studied offshore sector we report on a multidisciplinary investigation of the secca delle fumose sdf a submarine relief known since antiquity as the largest degassing structure of the offshore sector of cfc we combined high resolution morpho bathymetric and seismo stratigraphic data with onshore geological information to propose that the present day sdf morphology and structure developed during the initial stages of the last cfc eruption at monte nuovo in ad 1538 we suggest that the sdf relief stands on the eastern uplifted border of a n s trending graben like structure formed during the shallow emplacement of the monte nuovo feeding dike we also infer that the high angle bordering faults that generated the sdf relief now preferentially allow the ascent of hot brines with an equilibrium temperature of 179 c thereby sustaining hydrothermal degassing on the seafloor systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable co2 ph and temperature anomaly in the overlying seawater column data for the seawater vertical profile can be used to estimate the co2 and energy heat outputs from the sdf area at 50 tons day 0 53 kg s and 80mw respectively in view of the cause effect relationship with the monte nuovo eruption and the substantial gas and energy outputs we consider that the sdf hydrothermal system needs to be included in monitoring programs of the ongoing cfc unrest this article is protected by copyright all rights reserved

power law random behaviour of seismic reflectivity in boreholes and its relationship to crustal deformation models abstract there is good evidence for the fractal nature of some fault systems both from field observations and the frequency magnitude distribution of earthquakes recently two models with fundamentally different dynamics have been employed to explain seismicity low order non linear slider block models have successfully explained activity on part of the san andreas fault system and in the nankai trough while high dimensional self organised critical cellular automaton models convincingly reproduce the gutenberg richter frequency magnitude relationship output variables from these two models fall respectively into two distinct data classes chaotic deterministic and random using a predictability algorithm which can distinguish between random and chaotic datasets we examine the distribution class of in situ fractures as inferred from borehole seismic reflectivity logs in three chalk layers off the south coast of ireland we find that fractures are distributed in a non deterministic manner consistent with self organised critical dynamics therefore we may infer that deterministic seismicity should not occur on structures over the scale range covered by the logs at least in the end member case where the frequency magnitude distribution of earthquakes is controlled by the fractal distribution of faults

space time distribution patterns of destructive earthquakes in the inner belt of central japan activity intervals and locations of earthquakes abstract based on a block structure model of the inner belt of central japan an examination was conducted of the space time distribution patterns of destructiv magnitudes m 6 4 or greater m japan meteorological agency scale the distribution patterns revealed a periodicity in earthquake activit seismic gaps major nw se trending left lateral active faults divide the inner belt of central japan into four blocks 20 80 km wide the occurrenc a d with m 6 4 which have caused significant damage were documented in the inner belt of central japan the epicenters of these earthquakes close to the block boundaries using the relationship between the magnitude of earthquakes which occurred in the japanese islands and the active length of faults that generated them movement is calculated for each historical earthquake space time distributions of earthquakes were obtained from the calculated lengths the latitud of generation when an active period begins a portion or segment of the block boundary creates an earthquake which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central japan it is predicted that the gaps will generate ea magnitudes of 7 0 these data are of significance for estimating a regional earthquake risk over central japan in the design of large earthquake resist the time sequences of earthquakes on the block boundaries reveal a similar tendency with alternating active periods with seismic activity and quiet pe activity the inner belt of central japan is now in the last stage of an active period the next active period is predicted to occur around 2500 a d

structure of volcanic glasses from the nmr epr perspective a preliminary application to the neapolitan yellow tuff glass samples from alkali trachytic pumice of the lower member lm level lm1 and upper member um of the neapolitan yellow tuff at campi flegrei caldera were studied by nuclear magnetic resonance nmr and electron paramagnetic resonance epr spectroscopy the epr data show that the relative occupancy of the different iron sites varies in samples from the lower member lm1 and upper member of the eruptive sequence the lm1 glasses are characterized by a more homogeneous distribution of the cationic site population of iron compared with um and by a different fe3 al3 substitution in the c2v symmetrical sites of the silicate framework 29si mas nmr spectra on glasses indicate that lm1 glasses are more depolymerized than um glasses indicating the existence of structurally distinct magma batches 27al mas nmr spectra indicate the occurrence in um glasses of aluminum in both tetrahedral and octahedral coordination the observed alvi is believed to be a primary feature of the glass since 27al cp mas nmr experiments do not reveal detectable esa hydrated al the al in sixfold coordination could be ascribed either to the more abundant alkali oh terminations in um in which alkalies would be extracted from their charge balance role for al thus altering its fourfold structural position or to permanent compaction during fast cooling and decompression of high pressure melts 23na cp mas nmr experiments indicate the existence of na oh groups in both lm1 and um glasses relatively more abundant in the latter although preliminary the results indicate the possible application of atomic scale studies to variables that determine the regimes of explosive volcanism

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

geochemical characterization of quaternary tephras from the campanian province italy the campanian province has a rich history of human interaction with volcanic eruptions in a region currently inhabited by 3 million people it is crucial to have precise and accurate geochemical characterization of volcanic units within the region so as to identify the spatial distribution of past events furthermore tephrochronology is becoming an important tool in the region for correlating past environmental records unfortunately many of the key units have been geochemically analysed using relatively imprecise methods making correlation problematic although robust correlations have been established in the campanian province using a range of methods including stratigraphy and geochronology more distal correlation requires precise geochemical characterisation of individual glass shards here we report major oxide data geochemically characterising 17 key tephra units within the campanian province using wavelength dispersive spectrometry wds the new data confirm the trachytic nature of most of the eruptions to effect more precise correlations between units especially in distal locations proximal units must be individually analysed for major oxides using wds on the vitreous phase and statistically analysed for robust correlations in cases where similar geochemistry exists analysis of trace and rare earth elements may be necessary

co2 driven large mafic explosive eruptions the pozzolane rosse case study from the colli albani volcanic district italy generally the intensity and magnitude of explo sive volcanic activity increase in parallel with sio2 content pyroclastic flow forming eruptions in the colli albani ultrapotassic volcanic district italy represent the most striking exception on a global scale with volumes on the order of tens of cubic kilometres and k foiditic composi tions sio2 even 42 wt here we reconstruct the pre eruptive scenario and event dynamics of the 456 ka pozzolane rosse pr eruption the largest mafic explosive event of the colli albani district in particular we focus on the driving mechanisms for the unusually explosive eruption of a low viscosity mafic magma geologic petrographic and geochemical data with mass balance calculations supported by experimental data for colli albani magma compositions provide evidence for signif icant ingestion of carbonate wall rocks by the pozzolane rosse k foiditic magma moreover the scattered occurrence of cored bombs in pozzolane rosse pyroclastic flow deposits records carbonate entrainment even at the eruptive time scale as also tested quantitatively by thermal modelling of magma carbonate interaction and carbonate assimilation experiments we suggest that the addition of free co2 from decarbonation of country rocks was the major factor controlling magma explosivity high co2 activity in the volatile component coupled with magma depressurisation produced extensive leucite crystallisation at short time scales resulting in a dramatic increase in magma viscosity and volatile pressurisation which was manifested a change of eruptive dynamics from early effusion to the pozzolane rosse s highly explosive eruption climax

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

mechanical and thermo fluid behaviour during unrest at the campi flegrei caldera italy abstract the campi flegrei caldera cfc is a resurgent nested structure resulting from the two main collapses of the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the whole structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the young nested caldera structure the caldera has shown signs of unrest during the past 30 years with two uplift events that have generated a net displacement of 3 5 m each followed by subsidence the time evolution of both ground deformation and seismicity recorded in campi flegrei in the last 30 years since 1969 up to the present shows aspects not completely explainable by means of mechanical models in particular the occurrence of an intense seismic activity during uplift and its absence during subsidence lead us to infer that these two phases might be related to two variable mechanisms the large amount of magma and the shallow convective fluids circulation needed to explain the very high temperature gradient 100 c km measured also in marginal areas of the caldera suggest the presence of a thermo dynamical system in supercritical conditions we have carried out an analysis of the unrest episodes by means of 3d finite element method simulating the mechanical and fluid dynamical response of a two phase medium solid fluid to a sudden stepwise pressure or volume increase at a depth of 4 km according to geological and geophysical constraints in our scheme we have subdivided the caldera floor into a central and a peripheral zone the central zone represents the resurgent block and has high permeability while the peripheral zone is less permeable we have performed a parametric analysis assuming both young modulus and permeability of each zone as variables the basic test for each solution was how well it simulates the time evolution of ground deformation during the last unrest episode 1982 1984 the results obtained clearly show that fluids diffusion accounts for some peculiar features of the ground deformation such as the variable behavior between the resurgent block and the peripheral part of the caldera floor subsidence is explained in terms of lateral diffusion of fluids instead of a regression of source processes consequently no variation of shear stress occurs during this phase providing a physical explanation to the absence of seismicity

a facies interpretation of the eruption and emplacement mechanisms of the upper part of the neapolitan yellow tuff campi flegrei southern italy this study focuses on the upper part member b of the neapolitan yellow tuff nyt detailed measurements of stratigraphic sections within the unlithified pozzolana facies show that member b is composed of at least six distinct depositional units which each record a complex fluctuation between different styles of deposition from pyroclastic density flows six lithofacies have been identified 1 massive valleyponded facies the product of non turbulent flows 2 inverse graded facies formed by flows that were turbulent for the majority of transport but were deposited through a non tubulent basal regime 3 regressive sand wave facies the product of high concentration turbulent flows 4 stratified facies the product of deposition from turbulent low particle concentration flows 5 particle aggregate and 6 vesicular ash lithofacies both of which are considered to have formed by deposition from turbulent low concentration flows although the whole eruption may have been phreatomagmatic facies 1 4 are interpreted to be the product of dry eruptive activity whereas facies 5 and 6 are considered to be of wet phreatomagmatic eruptive phases small scale horizontal variations between facies include inverse graded lithofacies that pass laterally into regressive sand wave structures and stratified deposits this indicates rapid transition from non turbulent to turbulent deposition within the same flow thin vesicular ash and particle aggregate layers pass laterally into massive valley ponded vesicular lithofacies suggesting contemporaneous wet pyroclastic surges and cohesive mud flows three common vertical facies relations were recognised 1 massive valley ponded and inverse graded facies are overlain by stratified facies suggesting decreasing particle concentration with time during passage of a flow 2 repeated vertical gradation from massive up into stratified facies and back into massive beds is indicative of flow fluctuating between non turbulent and turbulent depositional conditions 3 vertical alternation between particle aggregates and vesicular facies is interpreted as the product of many flow pulses each of which involved deposition of a single particle aggregate and vesicular ash layer it is possible that the different facies record stages in a continuum of flow processes the deposits formed are dependent on the presence thickness and behaviour of a high concentration non turbulent boundary layer at the base of the flow the end members of this process are a flows that transported and deposited material from a non turbulent flow regime and b flows that transported and deposited material from a turbulent flow regime

an earthquake model with magnitude sensitive dynamics considerations of the dimensionality of earthquake generating mechanisms as assessed by prediction regression analysis show that complete earthquake populations are best described by complex high dimensional dynamics cellular automata which allow individual degrees of freedom to many small areal increments of a fault face reproduce realistic event sequences which follow the gutenberg richter relation simple spring block models with as few as two blocks have been shown however to neatly explain the coupling between adjacent segments of transform faults which has been observed in the stratigraphic record here we propose a hierarchical earthquake model in which there is an explicit change in the generating dynamics with magnitude and which may be appropriate for seismicity on a section of a transform fault which includes more than one active segment in the model a high dimensional cellular automaton is responsible for the production of low energy events and a low dimensional double block model represents the dynamics of events in which an entire fault face slips frequency magnitude distributions of the model seismicity show a change in b value with magnitude which is the result of the change in universality class of the underlying dynamics similar changes in b value related to the finite width of the seismogenic layer have been reported in the literature

simulations of magma withdrawal from compositionally zoned bodies heterogeneities in the form of continuous less common or discontinuous more common mineralogical geochemical and thermal gradients within volcanic deposits are ubiquitous in the geologic record examples cover a wide spectrum of eruptive volumes 10 2 km3 to 103 km3 compositions felsic to mafic mass discharges 103 to 109 kg s and eruptive styles plinian air falls pyroclastic flows lava flows an understanding of the dynamics of the magma withdrawal process is essential for accurate reconstruction of pre emptive chemical and thermal fields within crustal magma bodies a model based on numerical solution of the governing conservation equations has been devised in order to investigate the dynamics and systematics of central vent and ring fracture eruptions from flat roofed and sloped roof magma bodies strongly zoned in density and viscosity scale analysis of the conservation equations together with about 150 numerical experiments enables development of quantitative correlations for the mass discharge m and the duration of mixed magma eruption t with the effective driving pressure natural eruptions span the entire range of dynamic regimes from viscous through inertial for central vent eruptions in the viscous regime m is proportional to d where d is the conduit length and is the viscosity in the transitional and inertial regimes the intensity varies as 3 5 and respectively where is the density similarly t depends on d 5 3 5 and in the viscous transitional and inertial regimes respectively for systems with layered viscosity structure t is nearly independent of the viscosity ratio pressures above hydrostatic needed to drive eruptions are proportional to m m 5 3 and m 2 in the three dynamic regimes typical eruptions in the viscous and transitional regimes require pressure anomalies of order 102 103 pa whereas high intensity inertial eruptions demand anomalies of order 106 pa because the lower values are less than or equal to maximum tidally induced stresses earth tides appear capable of exciting eruptions several scenarios for producing variable discharge during a single eruptive phase were also studied these include arbitrary changes in the basal pressure and eruptions controlled by density and viscosity gradients it is demonstrated quantitatively that compositional gaps and episodes of mixed magma eruption can originate due to the withdrawal process itself and are not necessarily related to pre eruptive gradients within the magma body

the campanian plain and phlegrean fields structural setting from potential field data abstract a boundary analysis of the gravity and magnetic fields of the phlegrean fields volcanic area and of the surrounding campanian plain reveals a complex structural setting the campanian plain results well defined from sharp density boundaries a set of major e w lineaments occurs within the plain we derive a framework of the structural control to the volcanological evolution of campanian plain which appears strongly influenced by a set of ne sw lineaments bordering the acerra depression the density and magnetization boundaries of the phlegrean fields are significantly consistent both indicating for the collapsed phlegrean caldera an area considerably less extended than that based on previous geologically defined models many other structures are evidenced in the phlegrean area often with agreement between density and magnetization boundaries inside the caldera a strong consistence between the structures we identified and recent seismicity has been noted

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

seismicity simulation with a rate and state dependent friction law the dynamic motions and stabilities of a single degree of freedom elastic system controlled by different friction laws are compared the system consists of a sliding block connected to an elastic spring driven at a constant velocity the friction laws are a laboratory inferred friction law called the rate and state dependent friction law proposed by dieterich and ruina and a simple friction law described by dynamic and static frictions we further extend the solution to a one dimensional mass spring model which is an analog of a fault controlled by the rate and state dependent friction law this model predicts non uniform slip and stress drop along the rupture length of a heterogeneous fault this result is very different from some earlier modelings based on the simple friction law and a slip weakening friction law in those earlier modelings the stress and slip functions become smoother with time along the length of the fault rupture owing to the interactions between fault segments during slip because of this smoothing process the number of small events will decrease with time and the universilly observed stationary magnitude frequency relation cannot be explained the interaction between a fault segment and its neighboring segments can be measured when the post slip stress on this segment is compared with the stress on an identical segment represented by a block in this modeling without neighboring segments if the post slip stress of the former is much higher than that of the latter strong interaction exists if the two are close only weak interaction exists the interaction is determined by the relative motion between fault segments and the time duration of interaction our new modeling with the rate and state dependent friction law appears to show no such smoothing effect and provides a physical mechanism for the roughening process in the difference between the fault strength and stress that is necessary to explain the observed stationary magnitude frequency relation the noninstantaneous healing predicted by the rate and state dependent friction law may be repsonsible for the recurring nonuniform slip and stress drop and may be explained by the reduction of interaction among fault segments due to the low frictional strength during the fault stopping the very low friction during slip stopping allows much longer times than does the higher friction due to instantaneous healing for the fault segments to adjust their motions from an upper limit slip velocity to almost rest according to newton s second law a process with fixed masses and constant velocity changes involves low forces and weak interactions if it is accomplished in a long time period and vice versa our modeling also indicates that the existence of strong patches with higher effective stress on a fault is needed for the occurrence of major events the creeping section of a fault such as the one along the san andreas fault in central california on the other hand can be simulated with the rate and state dependent friction law by certain model parameters which however must not include strong patches in this case small earthquakes and aseismic creep relieve the accumulating strain without any large events

timing of magma extraction during the campanian ignimbrite eruption campi flegrei caldera a core drilled within the northern part of the city of napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the campanian ignimbrite ci eruption such a stratigraphic succession has never been encountered before in natural or in man made exposures therefore the ci sequence was reconstructed only on the basis of stratigraphic correlations and compositional data in literature the occurrence of four superposed ci flows together with all the data available in literature allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the ci magma chamber the ci magma chamber includes two cogenetic magma layers separated by a compositional gap the upper magma layer was contaminated by interaction with radiogenic fluids the two magma layers were extruded either individually or simultaneously during the course of the eruption in the latter case they produced a hybrid magma but no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found comparison with the exposed ci deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes the eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and or activation of fractures formed an unstable pulsating column that was fed only by the most evolved magma layer this plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation at this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated during the following major caldera collapse episode the maximum mass discharge rate was reached and both magma layers were tapped generating expanded pyroclastic flows towards the end of the eruption only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances

effect of a large outer rise earthquake on seismic cycles of interplate earthquakes a model study a numerical simulation of the sliding process of a plate interface is performed to investigate the effect of stress perturbation due to a large outer rise earthquake on seismic cycles of large interplate earthquakes in a subduction zone a two dimensional model of uniform elastic half space is set up for repeatedly occurring large interplate earthquakes by assuming that the frictional stress on the plate interface obeys a rate and state dependent friction law derived from laboratory experiments an increase in shear stress on a shallow part of the plate interface due to a tensional outer rise earthquake promotes aseismic sliding on the shallower aseismic zone of the plate interface this aseismic sliding advances the occurrence time of the next interplate earthquake on the other hand a compressional outer rise earthquake tends to delay the occurrence time of the next interplate earthquake the magnitude of time advance or delay of the next interplate earthquake depends on the time of the outer rise earthquake in a seismic cycle due mainly to the complex behavior in propagation of aseismic sliding governed by the rate and state dependent friction law

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

helium strontium isotope constraints on mantle evolution beneath the roman comagmatic province italy european social fund scottish universities carnegie trust for the universities of scotland

lithology of the basement underlying the campi flegrei caldera volcanological and petrological constraints abstract a geologically reasonable working hypothesis is proposed for the lithology of the basement underlying the campi flegrei caldera in the ca 4 8 km depth range in most current geophysical modeling this portion of crust is interpreted as composed of meso cenozoic carbonate rocks underlain by a ca 1 km thick sill of partially molten rock thought to be a main magma reservoir shallower magma reservoirs likely occur in the 3 4 km depth range however the lack of carbonate lithics in any campi flegrei caldera volcanic rocks does not support the hypothesis of a limestone basement considering the major caldera forming eruptions which generated widespread and voluminous ignimbrites during late quaternary times including the campanian ignimbrite and neapolitan yellow tuff eruptions the total volume of trachytic to phonolitic ejected magma is conservatively estimated at not less than 350 km 3 results of least squared mass balance calculations suggest that this evolved magma formed through fractional crystallization from at least 2500 km 3 of parent shoshonitic magma in turn derived from even more voluminous more mafic k basaltic magma calculations suggest that shoshonitic magma likely emplaced at ca 8 km depth must have crystallized about 2100 km 3 of solid material dominated by alkali feldspar and plagioclase with a slightly lower amount of mafic minerals during its route toward shallower magma reservoirs before feeding the campi flegrei large volume eruptions the calculated volume of cumulate material likely syenitic in composition at least in its upper portions is more than enough to completely fill the basement volume in the 4 8 km depth range beneath the campi flegrei caldera estimated at ca 1250 km 3 thus it is proposed that the basement underlying the campi flegrei caldera below 4 km is composed mostly of crystalline igneous rocks as for many large calderas worldwide syenite sensu lato would meet physical properties requirements for geophysical data interpretations explain some geochemical and isotopic features of the past 15 ka volcanics and justify the carbon isotopic composition of fumaroles at the campi flegrei caldera this implies that meso cenozoic limestones if still present today beneath the campi flegrei caldera no longer constitute significant portions of its basement

turbulent boundary layer shear flows as an approximation of base surges at campi flegrei southern italy abstract small volume base surge deposits of astroni and agnano monte spina eruptions at campi flegrei consist of sets of beds formed by the passage of multiple pyroclastic density currents each set is made by a fining upward sequence consisting from base to top of 1 an inversely graded layer made of bombs and lapilli 2 a finely laminated layer with wavy bedforms made of coarse ash and fine lapilli 3 a structureless fine ash bed lack of discontinuities at layer contacts allows us to hypothesize that each set of beds represents the passage of one pyroclastic density current the sequence formed as a function of the decreasing particle transportation capability of the base surge during the waxing sustained waning phases of flowage we make the simplifying assumptions that the flow on passing from the deposition of the inversely graded layer to the deposition of the finely laminated layer had low particle concentration was quasi steady and incompressible by such assumptions some of the equations that regulate sediment mechanics are applicable to the base surges of campi flegrei to reconstruct flow density and shear velocity in between the deposition of the two layers structural and textural features of deposits stress the importance of shear and turbulence during transportation and suggest that the turbulent boundary layer shear flow is a good approximation to such pyroclastic density currents we used the coles formula to reconstruct velocity as a function of flow height during the formation of the finely laminated layer of astroni and agnano monte spina base surges the methodology we used allows the reconstruction of flow parameters just at a particular point in time and space of base surge evolution and does not provide the complete picture of the flow history of pyroclastic density currents nevertheless flow velocity and density data as obtained with the proposed approach point to dynamic pressure values that are compatible with those reported for similar currents on other volcanoes we conclude therefore that the results obtained give approximate but helpful information on the nature of such hazardous events at campi flegrei

ground deformation at campi flegrei italy implications for hazard assessment campi flegrei caldera west of naples in southern italy has an exceptional documented record of ground deformation from roman times onwards systematic recording began in the nineteenth century for earlier dates information has been obtained from archaeological studies and from contemporary descriptions of the locations of buildings usually roman with respect to sea level especially important have been accounts related to the serapis a roman market place built in the second century bc and now incorporated within the modern town of pozzuoli the long term patterns of ground deformation have conventionally been investigated on the premise that campi flegrei naturally tends to a state of static equilibrium this study argues that instead the area naturally tends to a steady rate of subsidence at about 17 mm a 1 after this background rate has been removed the data indicate that a permanent uplift of some 33 m has occurred from roman times up until the present day 2005 at the time of writing attributable to the intrusion of 1 85 km3 of magma of which only 1 has been erupted uplift has occurred in three episodes the third of which is still in progress the behaviour can be interpreted in terms of the intermittent ascent of magma between a reservoir of c 102 103 km3 at depths of 8 15 km or greater to a much smaller shallower system at depths of about 3 4 km should the current pattern of deformation follow previous trends uplift is expected to continue for another 80 90 years during whieh time campi flegrei will be characterized by an elevated possibility of eruption the geological society of london

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

replenishment and crystallization in epicontinental silicic magma chambers evidence from the bandelier magmatic system abstract the cerro toledo rhyolite jemez volcanic field new mexico records the volcanism that occurred after the eruption of the lower bandelier tuff ignimbrite which formed toledo caldera at 1 51 0 03 ma pumice samples from the top of this ignimbrite and from the base of the cerro toledo rhyolite tephra sequence are stratigraphically and geochemically distinct from younger cerro toledo rhyolite tephras that overlie this basal suite all samples exhibit decreasing la lu with increasing lu concentrations for a given lu content however the lower bandelier tuff and basal member cerro toledo rhyolites have higher la lu compared to overlying cerro toledo rhyolites this difference can be explained either by 1 differentiation of a single batch of magma in which trace mineral solubilities increased with time due to higher volatile contents or 2 replenishment of the magma chamber by an input of silicic magma after caldera collapse at 1 51 ma large scale replenishment of epicontinental silicic magma chambers may be restricted to timescales of 10 5 years

recurrent magma mingling in successive ignimbrites from amealco caldera central mexico the amealco tuff is a widespread 2880 km2 trachyandesitic to rhyolitic pyroclastic deposit in the central mexican volcanic belt that was erupted from the amealco caldera at 4 7 0 1 ma it includes three major ignimbrites each showing complex mingling of pumice fragments and matrix glass with andesitic to rhyolitic compositions the different glasses are well mingled throughout each of the pyroclastic flow deposits mingling of glasses may have occurred just before and during the explosive eruptions that produced the pyroclastic flows as the distinct melts had insufficient time to homogenize mingling of glasses is evident in each of the three separate major ignimbrites of the amealco tuff thus the processes that caused it were repetitive it is infered that the repetitive mingling of melts was due to repeated mafic magma inputs to an evolved magma chamber

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

mineralogical geochemical and isotopic features of tuffs from the cfddp drill hole hydrothermal activity in the eastern side of the campi flegrei volcano southern italy abstract a 506 m drill hole has been recently drilled in the framework of the campi flegrei deep drilling project cfddp and the international continental scientific drilling program icdp with the intention of coring the subsurface in the eastern sector of the campi flegrei caldera the borehole located in the western district of the neapolitan city bagnoli plain 3 km to the east of the most active volcanic area and about 5 m above sea level is now targeted for monitoring purposes this paper reports the results obtained from the analysis of two short cores collected at depths of 443 and 506 m below the ground level the cores sampled two pre caldera tuffs observations performed by optical and scanning electron microscopy energy dispersive spectroscopy and powder x ray diffraction were used to achieve data on the primary lithology both primary and secondary mineralogical assemblages and the relationship between texture and secondary mineralization sr isotope ratios were determined on selected primary feldspars whereas 13c and 18o analyses were performed on carbonates from veins and filled voids in tuffs our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions a paleo temperature of ca 160 c has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface by using carbon and oxygen isotope data the temperature measured at the bottom of the drilling is about 80 c

modeling of the interaction between destructive inland earthquakes and large off coast earthquakes in central and south west japan abstract a one dimensional stick slip model which is introduced to explain the fractal features of earthquake phenomena is applied to describe he destructive earthquake occurrences in central and south west japan space time patterns of events are simulated and the predictablity is discussed on the basis of the block rotation model epicenters of historical destructive earthquakes with magnitude 6 4 or greater are relocated to the tectonic or block boundary lines this model has revealed that these events show a periodicity of about 1000 years of active and quiet alternative intervals in each active period individual block boundary lines generate several large earthquakes without overlapping rupture areas the space time pattern and moment release rate for the hanaore kongo fault line hkfl can be represented well with the one dimensional stick slip model the seismic coupling of large offshore earthquakes along the nankai trough is also found to be well modeled by this model this model may be useful for estimation of seismic risk in this region further this model can be applied to see the situation of the m7 2 kobe earthquake and interpret this earthquake to be the event that comes from the block structure in later section

evidence of crystallization in residual cl f rich agpaitic trachyphonolitic magmas and primitive mg rich basalt trachyphonolite interaction in the lava domes of the phlegrean fields italy the lava domes in the northwestern cuma northern punta marmolite and central accademia parts of the phlegrean fields are the subject of this study the cuma and punta marmolite trachyphonolitic lava domes are among the oldest phlegrean products cropping out the cuma rocks have an agpaitic groundmass with early alkali feldspar fe rich clinopyroxene fe edenite and sodalite and late rosenbuschite fluorite baddeleyite pyrochlore britholite monazite aegirine often zr rich and exceptionally fe mn rich olivine the bulk rock compositions at cuma have some of the highest concentrations of zn mn zr nb th u and lanthanides among the phlegrean fields rocks and some of the lowest mgo p 2 o 5 sr eu and ba the punta marmolite dome is chemically less evolved and lacks characteristic agpaitic minerals but features alkali feldspar sodalite nepheline and relatively na poor fe rich hedenbergite with rare ca rich plagioclase xenocryst cores the accademia dome belonging to the recent activity is latitic to trachytic in composition has highly forsteritic olivine with chromiferous spinel inclusions calcic plagioclase and mg rich diopside phlogopite xenocrysts in an evolved host rock with phenocrysts and microlites of alkali feldspar fe rich clinopyroxene fe rich amphibole magnetite fe rich olivine and accessory baddeleyite zirconolite and fluorite there is clear evidence of open system magma crystallization in the form of interaction between a crystallizing primitive shoshonitic basalt in a reservoir already filled by rather evolved trachytic magma the magmatic evolution towards the evolved compositions is dominated by crystallization of more and more na rich alkali feldspar in a cl f rich and relatively h 2 o poor environment input of mafic magma is evident in many trachytic eruptions of the phlegrean fields and even in the products of the campanian ignimbrite but eruptions having mineral assemblages rich in xenocryst phases as well as eruptions virtually free of mafic magma input are also frequently observed throughout the history this suggests a variable pattern of open and closed system crystallization which may or may not be linked to explosive activity and that can be caused by intermittent supply of basaltic magma from depth

the neapolitan yellow tuff a large magnitude trachytic phreatoplinian eruption eruptive dynamics magma withdrawal and caldera collapse the results of a detailed stratigraphical and volcanological study has allowed the definition of the neapolitan yellow tuff nyt as the largest known trachytic phreatoplinian eruption with an estimated volume of not less than 30 km3 dre the nyt sequence can be subdivided in a lower and an upper member sedimentological and textural variations in time and space indicate that different eruptive and depositional mechanisms operated during the eruption the lower member eruptive phase was characterized by alternating phreatoplinian and magmatic explosions while the upper member eruptive phase was characterized by a random sequence of phreatomagmatic and magmatic explosions particles produced by the same explosion were deposited contemporaneously by fallout and surge mechanisms either at different or at the same distance from the vent compositional variations show that the nyt sequence cannot be modeled as an inverted compositionally zoned magma body with magma becoming more basic in the course of the eruption the chamber composed of three geochemically distinct magma layers was tapped at different depths according to the eruption dynamics each phreatoplinian explosion tapped concurrently all the magma layers while magmatic explosions tapped only one of them the onset of the nyt caldera collapse is well constrained between lower and upper member eruptive phases the collapse which is only gravimetrically detectable occurred inside the larger phlegrean fields caldera which therefore can be defined as a nested caldera

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

hazard of pyroclastic density currents at the campi flegrei caldera southern italy as deduced from the combined use of facies architecture physical modeling and statistics of the impact parameters abstract pyroclastic density currents of the recent eruptions at campi flegrei caldera cfc southern italy have been studied with the aim of assessing the potential impact of similar events in the future eruptions of different scales have been investigated by means of the combined use of facies architecture laboratory analysis and physical modeling both in the small averno 2 and intermediate astroni scales facies analysis indicates that deposits result from the emplacement of pyroclastic density currents like base surge formed by multiple closely timed impulses of phreatomagmatic origin in the large scale event agnano monte spina the facies architecture suggests that the currents started as concentrated flows near the vent as originating from the collapse of a dense eruptive column and evolved laterally into expanded flows by the propagation of the basal shear current laboratory analyses on samples from the main layers of deposits allowed obtaining the input data for the pyflow code which was used for reconstructing the flow dynamic characteristics of the currents the expected damage is discussed in terms of the probability density function of dynamic pressure and particle volumetric concentration in this way the range of potential impact that similar pyroclastic density currents could cause to buildings infrastructures and population is defined in the large scale event the dynamic pressure ranges from 9 38 to 1 00 kpa integrating the basal 10 m of the current at distances of 1 5 and 4 0 km from the vent respectively the values are highly influenced by the local topography in the intermediate scale event the dynamic pressure ranges from 2 43 to 0 26 kpa at distances of 1 1 and 1 4 km from the vent respectively in the small scale event the dynamic pressure ranges from 1 49 to 0 39 kpa at distances of 0 5 and 1 1 km from the vent respectively the particle volumetric concentration at a height of 2 m within the current is always lower than 0 01 but typically it is higher than 0 001 inside the caldera and could have severe effects on the unsheltered population also at locations topographic highs where velocity and dynamic pressures are low in distal reaches outside the caldera the widespread fine ash originated by buoyancy from the currents which was transported by lower atmosphere winds is to be considered as a fallout load slowly accumulating on the ground surface and building roofs during the waning stage of the current

the present state of the magmatic system of the campi flegrei caldera based on a reconstruction of its behavior in the past 12 ka abstract new geochemical and sr isotope data have been acquired on samples representative of volcanic units erupted inside the resurgent campi flegrei caldera cfc over the past 12 ka these data integrated with previous published petrological and with newly acquired geochronological volcanological and geothermal data shed light on the nature and timing of the processes that controlled the evolution of the phlegraean magmatic system in the past 12 ka three isotopically and geochemically distinct magmatic components were erupted at the cfc as either homogeneous or mixed magma batches one component campanian ignimbrite component cic 87 sr 86 sr 0 70735 0 70740 is similar to the trachytic magma extruded during the first phase of the campanian ignimbrite ci eruption 37 ka a second component neapolitan yellow tuff component nytc 87 sr 86 sr 0 70750 0 70757 is similar to the latitic alkali trachytic magma batches extruded during the course of the neapolitan yellow tuff nyt eruption 12 ka a third component minopoli component mic 87 sr 86 sr 0 7086 is similar to the trachybasaltic magma of the minopoli 2 mi eruption 9 7 ka these components were erupted as either single batches of magma or mixed ci nyt or mi nyt batches of magma through vents located either along the structural boundary of the nyt caldera or inside the nyt caldera mainly on portions of the resurgent block under extensional stress the ci and nyt components represent residual portions of older large volume magma reservoirs which have fed eruptions since about 60 and 15 ka respectively the least evolved mi component was erupted only during the 12 9 5 ka and 8 6 8 2 ka epochs of activity through vents located on a ne sw regional fault system this component could represent a deeper reservoir tapped by the ne sw regional fault system reactivated after the nyt caldera collapse deeper mi and shallower ci and nyt magmatic systems interacted by mixing among batches of magma during their rise to surface overall the data suggest that the cfc magmatic system today is characterized by the presence of two larger independent reservoirs filled by residual portions of the ci and nyt magmas these generated many smaller shallower pockets of evolved magma that fed most of the eruptions that occurred in the cfc over the past 12 ka moreover a deeper reservoir mi tapped by the ne sw regional fault system provided batches of less evolved magma that mixed with magma present in the shallower pockets

fractals chaos self organized criticality and tectonics some geological structures have simple geometrical forms and can be analysed using deterministic equations examples include alluvial fans and many sedimentary basins but most geological structures are complex and appear to defy mathematical analyses yet in the complexity there is an order complex geological structures generally obey fractal statistics examples include topography distributions of earthquakes and faults and mineral deposits an unresolved question is whether the fractal order is simply the result of scale invariance or the result of governing equations that yield deterministic chaos in order to try to answer this question a variety of slider block models have been considered the stick slip behaviour of slider block models is a simple analogy to earthquakes a pair of slider blocks has been shown to behave chaotically models that use many slider blocks exhibit self organized criticality and generate fractal statistics similar to the statistics of regional seismicity

a general viscosity model of campi flegrei italy melts abstract viscosities of shoshonitic and latitic melts relevant to the campi flegrei caldera magmas have been experimentally determined at atmospheric pressure and 0 5 gpa temperatures between 840 k and 1870 k and h2o contents from 0 02 to 3 30 wt the concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101 5 103 pa s the micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range 1010 pa s falling sphere experiments were performed at 0 5 gpa in the low viscosity range from 100 35 to 102 79 pa s in order to obtain viscosity data of anhydrous and hydrous melts the combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified vft equation l o g a b t c d t e e x p g w t where is the viscosity in pa s t the temperature in k w the h2o content in wt and a b c d e and g are the vft parameters this model reproduces the experimental data 95 measurements with a 1 standard deviation of 0 19 and 0 22 log units for shoshonite and latite respectively the proposed model has been applied also to a more evolved composition trachyte from the same area in order to create a general model applicable to the whole compositional range of campi flegrei products moreover speed data have been used to constrain the ascent velocity of latitic shoshonitic and trachytic melts within dikes using petrological data and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate a time scale for the ascent of melt from 9 km to 4 km depth where deep and shallow reservoirs respectively are located in the order of few minutes such a rapid ascent should be taken into account for the hazard assessment in the campi flegrei area