interaction between normal faults and pre existing thrust systems in analogue models the influence of pre existing thrusts on the development of later normal faults was investigated using scaled laboratory analogue models experiments consisted of a phase of shortening followed by extension at variable angles of obliquity a to the shortening direction results suggest that the angle a has a major influence on the surface fault pattern and on the interaction between shortening related structures and later extensional structures three different modes of interactions were identified depending upon the extension kinematics 1 for orthogonal extension a 1 4 08 shortening related fold and thrust structures strongly influence the development of normal faults graben structures nucleate within anticlines and the normal faults reactivate thrusts at depth branching at depth mode of interaction 2 for highly oblique extension a 458 shortening related structures exert no influence on normal faults as extension related steeply dipping faults characterized by an oblique component of movement displace early thrusts no interaction mode 3 for intermediate obliquity angles a 1 4 158 308 an intermediate mode of interaction characterizes the experiments where the no interaction and branching at depth modes coexist in different regions of models modelling results can be used to infer regional extension directions as is shown for the northern appenines italy it has been shown that in many cases pre existing thrust systems play an important role in controlling the architecture of superimposed normal faults mechanical theory suggests that the probability of reactivation of pre existing thrust faults depends on their orientation with respect to the superimposed extensional stress field e g sibson 1985 the process was investigated in previous analogue models krantz 1991 faccenna et al 1995 and references therein suggesting that the initial dip of thrust faults has a major control on the development of successive normal faults both studies started with a phase of shortening that resulted in progressively steeper thrust faults prior to extension model results suggested that three different types of interactions between pre existing thrusts and successive normal faults may arise e g faccenna et al 1995 1 no interaction occurs in case of low dip thrusts 328 18 and normal faults form independently displacing pre existing thrusts 2 branching at depth of normal faults with thrusts is observed for intermediate dip angles 328 182 418 18 3 total reactivation occurs on thrusts dipping at angles higher than 418 18 these three basic mode of interaction between normal faults and thrust systems have been recognized and described in natural systems such as the central apennines italy and the north sea region faccenna et al 1995 active extensional structures interacting with early thrust systems have been also recognized in the northern apennines e g finetti et al 2001 in this fold and thrust belt the early compressive structures show a prominent curvature along strike and the successive normal faults display strong variations in terms of trend arrangement and kinematics in different sectors of the chain fig 1 in particular where thrusts are orthogonal to the regional ne sw extension direction e g mugello basin fig 1 normal faults are long and linear display a mainly pure dip slip kinematics and from buiter s j h schreurs g eds 2006 analogue and numerical modelling of crustal scale processes geological society london special publications 253 65 78 0305 8719 06 15 00 the geological society of london 2006 are subparallel to the early compressive structures delle donne et al 2003 conversely where thrusts are slightly oblique to the extension garfagnana lunigiana area fig 1 normal faults are arranged en echelon are characterized by an oblique slip kinematics and display a mean peak in distribution oriented at about 108 with respect to the earlier thrusts piccardi et al 1999 in case of high obliquity e g martani mounts terni basin area fig 1 normal faults are linear are characterized by an important locally dominant strike slip component of movement and form at an angle of 208 to the pre existing structures bonini et al 2003 these features suggest that the different orientation of thrusts with respect to the direction of extension may have exerted an important control on the pattern of successive extensional structures this influence is investigated in this study by means of analogue models we present a series of experiments on polyphase deformation consisting of orthogonal shortening followed by extension at variable angles of obliquity

controls on hydrothermal alteration in a section of fast spreading oceanic crust abstract young oceanic crustal sections that formed at the fast spreading east pacific rise epr were mapped by submersible along steep fault scarps that bound the hess deep rift valley excellent exposures allowed the documentation of the spatial distribution of alteration within the lava sequence sheeted dike complex and uppermost plutonic sequence alteration assemblages record the initiation and subsequent cooling of an axial hydrothermal system s that was periodically perturbed by the injection of sheeted dikes mineralogical and geochemical data indicate that temperatures increased across the lava dike transition 50 180 c and that the grade of metamorphism was heterogeneous within the sheeted dike complex in that temperatures varied laterally from 100 300 c to 600 800 c within the upper dikes and were 400 450 c within the lower sheeted dikes during vigorous hydrothermal circulation at the epr the base of the hydrothermal system was located within or at the top of a sequence of gabbros that is interpreted to be the root zone of the sheeted dike complex the base of the hydrothermal cell did not penetrate into the subjacent plutonic sequence until the section of crust had migrated off axis and the magma lens had solidified the vigor of the hydrothermal system would have waned by this time and hydrothermal fluids migrated into the lower crust along broadly distributed microfracture networks at temperatures between 450 and 650 c although locally temperatures may have reached 800 c the highest temperature alteration assemblages within the sheeted dikes formed in response to the injection of a dike or swarm of dikes that initiated a short lived hydrothermal system the sheeted dikes and plutonic rocks experienced very little retrograde alteration and there is no evidence for a discrete off axis hydrothermal event s incipient alteration conditions in crustal sections that formed at mid ocean ridges with slower rates of spreading than the epr are similar to hess deep although there are differences in the distribution and mineralogical expression of incipient alteration in plutonic sequences the evolution of alteration as a section of crust cools and moves off axis reflects its particular magmatic tectonic history and thus may vary significantly in ridges with all spreading rates

the 2001 adana landslide and its destructive effects turkey the current study deals with a catastrophic landslide that occurred due to heavy rainfall in adana southern turkey in 2001 the research area which is one of the largest populated districts in adana and one of the most tropical places between the middle east and southern europe has about 25 000 people on the basis of geological and geotechnical surveys the landslide phenomena and the effects of landslide are examined to understand the slide mechanism of the landslide ground reconnaissance laboratory and in situ tests are conducted it is observed that the clayey and silty layers of the site are heavily saturated due to extreme rainfall in winter and consequently sheared the landslide consists of a block sliding in the upper portions and a debris flow soil flow component around the margins of the sliding blocks in the middle parts and at the toe although there was no loss of human life it has caused significant economic losses besides it is determined that if precautions are not taken around the landslide area larger landslides could definitely occur in the future

modelling hanging wall accommodation above rigid thrust ramps abstract experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat ramp flat thrust footwalls the deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle ranging from 15 to 60 we model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ranging from 15 to 30 as well as above pre existing normal faults ranging from 45 to 60 for the hanging walls we used stratified frictional sand and viscous silicone putty materials in this paper we study three types of models type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer parallel thickening and by generating a series of back thrusts type 2 and 3 models represent stratified frictional viscous hanging walls in these models accommodation was by a complex association of reverse and normal faults mainly controlled by the rheological anisotropy as well as by the ramp inclination angle in type 2 models the silicone covered only the lower flat while in type 3 models it also covered the rigid ramp for 30 in type 2 models and 45 in type 3 models the viscous layer inhibited the development of back thrusts in the frictional hanging wall instead the silicone thickened to develop a ductile ramp for values higher than 30 in type 2 models and 45 in type 3 models back thrusts develop in response to the bulk compression the experiments simulate many structures observed above natural thrust ramps with 30 and pre existing normal faults with 45 the models emphasise the importance of a basal ductile layer which allows the hanging wall to step up over the rigid ramp by building up its own ductile ramp the models also emphasise that foreland directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end loading within a thrust wedge

the generation of oceanic rhyolites by crystal fractionation the basalt rhyolite association at volcan alcedo galapagos archipelago

application of the revised universal soil loss equation model on landslide prevention an example from n euboea evia island greece this study aims to evaluate the application of the revised universal soil loss equation rusle on predicting of sites susceptible to slope failures caused by the soil erosion it was carried out at the northern part of euboea island presenting one of the highest frequencies of landslide occurrence in greece all required datasets for the application of the rusle model were engaged to compile a potential soil erosion map of the study area in addition historical slope failure data were used to evaluate the produced map moreover the frequency ratio statistical analysis was applied for the verification of the soil erosion map the results showed a satisfactory agreement between the soil erosion intensity zones and distribution of landslides events therefore the rusle model can be applied for the localization of sites susceptible to landslides that were prepared or triggered by the soil erosion finally taking under consideration the contribution of erosion mechanisms over the landslides manifestation a combination of measures were proposed for preventing and supporting these catastrophic phenomena

hf isotope geochemistry of the galapagos islands 1 we report 176hf 177hf ratios determined by multicollector inductively coupled plasma mass spectrometry on 49 basalts from the galapagos islands the hf values range from about 8 a value typical of many oceanic island basalts to about 15 a value typical of mid ocean ridge basalt the hf shows the expected correlation with nd and inverse correlations with sr and pb isotope ratios the range of values and correlations observed is consistent with galapagos mantle plume asthenosphere mixing inferred from previous geochemical studies while oceanic island basalt isotopic arrays suggest that multicomponent mixing is common in the sources of such basalts the galapagos is unusual in that depleted upper mantle appears to be a principal component thermal and dynamic interaction between the galapagos mantle plume and the lithosphere and shallow asthenosphere is the most likely cause of mixing and of the geographic pattern of geochemical variation the galapagos hf nd sr pb isotopic array diverges toward the plume end indicating the plume is heterogeneous this heterogeneity is geographic with distinct northern central and southern components the central component and to a lesser degree the northern component are compositionally similar to the common component of plumes variously called phem fozo and c while the southern component is unique with relatively high hf and 206pb 204pb compared to 87sr 86sr and nd

stable isotopic composition of upper oceanic crust formed at a fast spreading ridge odp site 801 1 odp legs 129 and 185 sampled the upper 474 m of 170 ma ocean crust in the western pacific in order to investigate alteration processes in fast spread crust and to determine inputs to subduction fourteen composite bulk samples of altered upper oceanic crust from site 801 have 18o 8 7 25 7 d 69 4 to 90 4 and 13c 2 7 to 1 8 the intensity of alteration and the amount of sediment within the basement decrease with depth leading to corresponding decreases in 18o and d a super composite constructed to estimate the bulk composition of the upper crust has 18o 12 0 d 87 0 and 13c 0 7 compared to core descriptions and geophysical logs the super composite contains too much 18o rich sediment 18o 25 7 and a corrected 18o value of 10 8 is more reasonable for the upper crust at site 801 these values are higher than those for other bulk upper oceanic basement sections 18o 8 0 10 0 and result in part from 1 intense low temperature 100 c hydrothermal alteration of the upper 100 m of tholeiitic basement at site 801 that may not be representative of material subducting in the western pacific and 2 an aging effect whereby progressive addition of 18o rich secondary carbonate in veins and breccia cements contributed to the high bulk 18o of this old upper crustal section

forward modeling of the southern apennines forward kinematic modeling has been developed to reconstruct the successive geometries of geological sections the method is tested here on a geological section across the southern apeninnes where syntectonic neogene deposits are of help in determining the timing of the deformation that progressively affected more eastern parts of the apulian margin well known triassic and paleogene decollement levels induced thin skinned tectonics in the mesozoic and cenozoic sedimentary cover but the basement geometry is only poorly revealed by subsurface data two distinct hypotheses have been tested 1 thin skinned tectonics and 2 basement involved tectonics the shortening of the prism is estimated to be between 170 and 210 km whether or not the basement is involved in the imbricated stack of thrust sheets the results are discussed in the light of regional constraints i e regional flexure uplifts etc which favor basement involved structures at depth in addition to the effects of compression other phenomena affected the geometry of the prism and have to be taken into account because of the recent uplift of the belt the inner parts of the apenninic wedge have emerged and undergone erosion part of this eroded material has been simultaneously trapped in piggyback basins which record both the geometric and temporal evolution of the prism normal faulting also affected the western part of the southern apennines reactivating older thrust as detachment surfaces along which block rotation occurred

rainfall patterns and critical values associated with landslides in povoacao county sao miguel island azores relationships with the north atlantic oscillation sao miguel island azores has been affected by hundreds of destructive landslide episodes in the last five centuries triggered either by earthquakes volcanic eruptions or rainfall episodes which were responsible for many deaths and very important economic losses among the instability causes meteorological factors are of primary importance on povoacao county namely the high recurrence rate of calamitous rainfall triggering landslides the most recent catastrophic episode took place on the 31st october 1997 when almost 1000 soil slips and debris flows were triggered and 29 people died in the ribeira quente village the role of rainfall on regional landslide activity was analysed applying cumulative rainfall methods the method comprises the reconstruction of both absolute and calibrated antecedent rainfalls associated with each major landslide event the critical rainfall combination amount duration responsible for each landslide event was assessed and a rainfall critical threshold for landslide occurrence was calculated rainfall triggered landslides in the study area are ruled by the function i 144 06 d 0 5551 and they are related both to short duration precipitation events 1 3 days with high average intensity between 78 and 144 mm day and long lasting rainfall episodes 1 5 months with a lower intensity between 9 and 22 mm day the impact of the north atlantic oscillation nao on the regional precipitation regime was evaluated it is shown that the monthly precipitation of sao miguel is largely modulated by the nao mode presenting a significant negative correlation with the nao index this result arises from the nao control on the travelling latitude of most storm tracks that cross the northern atlantic ocean copyright 2007 john wiley sons ltd

fluid pressure and effective stress in sandbox models abstract we have done a series of simple tests on sandpacks involving upward flow of compressed air through the pores and its effect on the yield strength the ultimate objective is to model deformation coupled with fluid flow in sedimentary basins for all tests we used a single batch of fontainebleau sand sieved to a grain size between 0 200 and 0 315 mm poured into a cylindrical container and then fluidized the density of this sand was 1 585 g cm3 irrespective of sand thickness the lithostatic pressure was proportional to the thickness of the sandpack a yield envelope was obtained by shearing the sandpack horizontally compressed air entered the base of the sandpack and flowed upwards through the pore spaces for 69 measurements on air flow without shearing a plot of discharge velocity versus gradient of fluid pressure is close to a straight line verifying darcy s law and yielding an intrinsic permeability of about 1 7 darcy for the sand for 72 tests on simultaneous shearing and fluid flow the estimated effective stress lithostatic stress minus estimated pore fluid pressure ranged from 0 to 1600 pa and the pore fluid ratio between air pressure and lithostatic pressure from 0 0 to 1 0 a plot of shear stress versus effective stress at failure is almost linear verifying terzaghi s principle of effective stress the best fit slope coefficient of internal friction is about 0 55 and the intercept on the shear stress axis cohesion is less than 85 pa the tests show that it is feasible to use compressed air within sandpacks as a means of modelling deformation coupled with fluid flow the next step will be to build sandbox models of layered sequences and to investigate detachments caused by abnormal fluid pressures

the permian to cretaceous structural evolution of the western approaches basin melville sub basin uk summary the tectonic sedimentary evolution of the western part of the western approaches basin melville sub basin was initiated during early permian times when synrift clastic sedimentation and volcanism commenced within an ene trending half graben this sequence thickened to the south and onlapped a high to the north during the permian an early nnw sse basin extension was accommodated on an array of ene wsw trending normal faults linked by nnw sse orientated transfer faults this was followed by a period of ene wsw extension along the basin axis when the normal and transfer faults of the previous faulting episode swapped roles this was possibly related to early rifting in the bay of biscay both sets of faults appear to be controlled to some extent by variscan thrusts and strike slip faults within the basement during the upper triassic the ridge in the north subsided allowing a thick sequence of salt to be deposited where there had previously been a topographic high during jurassic times sedimentation extended across the permian triassic half graben into the french sector this was followed by an episode of rifting and wrench deformation and inversion during which the permian to jurassic basin was domed and uplifted the cretaceous to tertiary sedimentation which followed probably resulted from postrift thermal subsidence related to cooling of the continental platform adjacent to the opening atlantic ocean steep normal and or strike slip faults data from the earliest part of this postrifting stage

spatio temporal analysis of a complex landslide in the northern apennines italy by means of dendrochronology dendrochronology is used to determine the spatial and temporal development of movements in a complex landslide located in the northern apennines the analysis of trees growing on the landslide body enabled us to date their colonisation pattern which starts from the 1920s and increases mainly after 1950 since then sampled trees recorded with growth anomalies the movements involving the landslide body in 1956 1957 1982 1983 1990 1995 and 1998 these movements are reactivations of the main landslide that probably occurred in the last decades of the 19th century in 1980 trees on the upper landslide body were involved in a rock fall due to the expansion of the main scarp microsections cut out from selected tree ring sequences allowed seasonal dating of the highlighted movements which mostly occurred in early spring meteorological and seismic time series were analyzed in order to relate them with reactivations and to search for correlations and triggering events the seismic activity although characterized by low magnitudes could be able either to trigger the movements 1990 or to destabilize the ground where rainfalls could have been playing the first role in triggering the reactivation probably in 1982 1983 and 1995 the other reactivations seem to be linked either to long lasting rainfalls or to monthly rainfall peaks mostly following dry periods

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

landslide susceptibility mapping by comparing the wlc and wofe multi criteria methods in the west crete island greece in the current research the weighted linear combination wlc and the weights of evidence wofe methods were applied for landslide susceptibility zonation mapping in the chania prefecture of crete island greece several thematic maps representing various landslide conditioning factors such as geology formations faults proximity altitude slope gradient aspect curvature rivers proximity precipitation roads proximity and land use types have been generated in a gis environment three landslide susceptibility maps were created one for each method and a combined one by applying the logistic regression approach to the wlc and wofe susceptibility maps the maps were evaluated and validated using the efficiency rate curve the receiver operator curve and the spatially agreed areas methods the resulting landslide susceptibility maps have uncertainties introduced due to the subjective knowledge of experts in the case of wlc method and to the quality of the recorded landslides sample in the case of the wofe method nevertheless the performance of the three approaches was found to be almost equal with all methods to produce quite satisfactory results besides the comparison of the applied methods the current study contributes to the risk management of the area providing the first landslide susceptibility maps for chania prefecture

transient modeling of regional rainfall triggered shallow landslides this study investigates the transient modeling of regional rainfall triggered shallow landslides in unsaturated soil using the richards equation to model shallow landslides within a distributed regional scale framework infinite slope stability analysis coupled with the hydrological model with consideration of the fluctuation of time dependent pore water pressure and the soil water characteristic curve proposed by van genuchten was developed the validity of the proposed model is established through several test problems by comparing the numerical results with the analytical solutions a new procedure to set up wide range shallow landslide analysis and to integrate regional distribution variations for input data such as geology groundwater level hydrogeological characteristics and rainfall intensity and duration was presented the results obtained demonstrate that the computed distribution of the safety factor is consistent with the distribution of actual landslides in addition the fluctuation of pore water pressure in unsaturated soil dominates the stability of landslides during typhoons accompanied by heavy rainfall the findings observed in this study are a fundamental contribution to environmental effects for landslides in areas with higher occurrence and vulnerability to extreme precipitation

an automatic method for determining three dimensional normal fault geometries we describe a general kinematic method for automatically determining the three dimensional 3 d geometry of normal faults at depth from the 3 d geometry of deformed hanging wall horizons the method should be applicable to normal faults which do not change shape as deformation proceeds it is a generalization of two dimensional models and assumes that the hanging wall deforms by arbitrarily inclined bulk simple shear deformation in three dimensions is parameterized by the three euler angles which describe the horizontal slip vector the rake angle and the inclination of shear planes as in two dimensions differential compaction can be included by assuming that the axis of shortening is parallel to the direction of shear three dimensional fault geometry and the three euler angles can all be automatically determined provided the geometries of two or more hanging wall horizons are known here the method is tested on both synthetic data and on 3 d sand box models synthetic modeling shows that unique solutions can be found and more importantly that the horizontal slip vector can be constrained solutions obtained from sand box models are also encouraging in most cases the method can predict automatically the correct direction of extension and a 3 d fault geometry close to the fault geometry used hence arbitrarily inclined bulk simple shear appears to be a good approximation of hanging wall deformation in three dimensions this general method will allow 3 d palinspastic analysis to be undertaken on 3 d seismic reflection data sets

fluid flow patterns in fast spreading east pacific rise crust exposed at hess deep tectonic exposures of a volcanic sequence and sheeted dike complex over a 4 km wide region at hess deep equatorial pacific reveal significant spatial heterogeneity 10 103 m in the extent and nature of hydrothermal alteration in young fast spreading east pacific rise crust the volcanic sequence is fairly uniformly altered with only minor oxidation and alteration to clay minerals sheeted dikes in the eastern part of the field area are highly fractured with narrow intervals of intact dikes that dip up to 60 their alteration characteristics show a simple depth trend such that with increasing depth the dominant secondary mafic mineral changes from chlorite to amphibole clinopyroxene replacement increases 40 whole rock 18o values decreases 4 4 5 5 to 3 5 4 5 and calculated peak metamorphic temperatures increase 250 c to 450 700 c within the deepest dikes localized zones up to 400 m wide are chlorite rich and have low 18o 2 9 4 1 and low peak metamorphic temperatures 345 c these alteration patterns likely formed within broad recharge zones whereby the low 18o zones developed in the regions with the highest fluid flux in the west massive slightly rotated sheeted dikes near the volcanic sheeted dike transition are 18o and cu depleted and display higher peak temperatures 345 c than elsewhere in the shallow dikes these characteristics are consistent with formation within a high temperature hydrothermal discharge zone we propose that the spreading history of a fast spreading ridge segment can create significant spatial heterogeneity in fluid flow and alteration patterns within sheeted dike complexes similar to those preserved in many ophiolites

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

a complete oxygen isotope profile through the lower oceanic crust odp hole 735b abstract odp hole 735b located on the southwest indian ridge at 57 e is an in situ sampled long continuous section of lower oceanic crust oxygen isotope compositions of constituent minerals of leg 176 gabbros have been measured by uv laser oxygen isotope microprobe together with existing data from leg 118 a complete oxygen isotope profile through the lower oceanic crust has been obtained most clinopyroxenes and olivines have normal mantle values of 5 5 and 5 2 respectively while plagioclases show slight 18 o enrichment relative to its mantle value of 6 1 down hole variations of hole 735b gabbro indicate a downward decreasing 18 o profile with a kink at a depth of about 800 m below sea floor above this depth gabbros are depleted in 18 o relative to unaltered basalts while below 800 m they show nearly unmodified 18 o values abundant seawater penetration appears to be limited to the upper part of the lower crust at odp site 735 800 m into the gabbroic layer and 2 2 5 km into the oceanic crust from the top of pillow basalts mass balance calculations show that the lower crust formed under this ultra slow spreading ridge has an average 18 o value of 5 5 the whole crust at site 735 has an overall 18 o enrichment with 18 o values of 6 0 to 7 8 depending on the possible variation of the 18 o values of the upper pillow basalts and sheeted dykes the apparent difference in oxygen isotope compositions of ocean crusts formed with different spreading rates has important implications on the buffering of ocean water over geological time as well as on the oxygen recycling between crust and mantle through subduction the difference of seawater penetration between fast and slow spreading ridges could be related to their particular magmatic tectonic history during the formation and aging of the crust however more analyses on continuous sections through oceanic and ophiolitic crust in different tectonic settings are required to derive any predictive models

petrology of lavas from sierra negra volcano isabela island galapagos archipelago sierra negra volcano is a voluminous active basaltic shield situated in the western galapagos archipelago a hotspot related chain adjacent to the galapagos spreading center the volcano has erupted fe rich tholeiitic basalts of very limited compositional range comparison of lavas from each of five stratigraphic units covering the entire volcano indicates that the lavas are mineralogically similar and compositionally restricted 4 4 to 6 9 wt mgo the lavas are fe rich and hypersthene normative and plot in both the alkaline and tholeiite fields of the alkali silica diagram rare earth element ree patterns are steep and parallel the major and trace element data indicate a comagmatic relationship by fractional crystallization of the observed phenocryst phases projections into pseudoternary phase diagrams suggest that the magmas cooled and crystallized at pressures between 1 and 3 kbar calculated melt densities range from 2 73 to 2 77 g cm3 which are higher than those of typical mid ocean ridge basalt morb hawaiian tholeiite and other galapagos lavas the high calculated melt densities may be caused by fractionation at greater depths than is ordinary for the other basaltic magmas suppression of plagioclase and olivine crystallization in favor of augite may eliminate the minimum density window that has been proposed for morb fractionation sierra negra lavas have the most radiogenic lead and strontium isotopic ratios in the western galapagos indicating that the magmas have a relatively large contribution of plume material and have been minimally contaminated by entrainment of morb producing mantle magmatic 3he 4he isotopic ratios from sierra negra are approximately 15 times the atmospheric ratio although these ratios clearly indicate plume helium they are not the highest 3he 4he in the archipelago suggesting that helium is decoupled from the heavier isotopes high sm yb ratios light rare earth element lree enrichment and a steep ree slope are consistent with an origin by moderate extents 5 15 of partial melting of a garnet lherzolite source with ree characteristics that are between chondrite and depleted earth mantle sources sierra negra lavas are compositionally monotonous because homogeneous plume rich material has experienced long term exposure to a well regulated sublithospheric thermal environment with additional compositional restrictions imposed in the lithosphere by high magma flux

oxygen isotope trajectories of crystallizing melts insights from modeling and the plutonic record elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth the 18 o value of a melt however can also increase through closed system fractional crystallization in order to quantify the change in melt 18 o due to crystallization we develop a detailed closed system fractional crystallization mass balance model and apply it to six experimentally and naturally determined liquid lines of descent llds which cover nearly complete crystallization intervals melt fractions of 1 to 0 1 the studied llds vary from anhydrous tholeiitic basalts to hydrous high k and calc alkaline basalts and are characterized by distinct melt temperature sio 2 trajectories as well as crystallizing phase relationships our model results demonstrate that melt fraction temperature sio 2 relationships of crystallizing melts which are strongly a function of magmatic water content will control the specific 18 o path of a crystallizing melt hydrous melts typical of subduction zones undergo larger increases in 18 o during early stages of crystallization due to their lower magmatic temperatures greater initial increases in sio 2 content and high temperature stability of low 18 o phases such as oxides amphibole and anorthitic plagioclase versus albite conversely relatively dry tholeiitic melts only experience significant increases in 18 o at degrees of crystallization greater than 80 total calculated increases in melt 18 o of 1 0 to 1 5 can be attributed to crystallization from 50 to 70 wt sio 2 for modeled closed system crystallizing melt compositions as an example application we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences a relatively dry tholeiitic sequence from the upper and upper main zones uumz of the bushveld complex south africa and a high k hydrous sequence from the arc related dariv igneous complex mongolia these two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed system fractional crystallization and their llds have been modeled in detail we calculated equilibrium melt 18 o values using the measured mineral 18 o values and calculated mineral melt fractionation factors increases of 2 3 and 1 1 5 in the equilibrium melts are observed for the dariv igneous complex and the uumz of the bushveld complex respectively closed system fractional crystallization model results reproduce the 1 increase observed in the equilibrium melt 18 o for the bushveld uumz whereas for the dariv igneous complex assimilation of high 18 o material is necessary to account for the increase in melt 18 o values assimilation of evolved supracrustal material is also confirmed with sr and nd isotope analyses of clinopyroxene from the sequence beginning with a range of mantle derived basalt 18 o values of 5 7 pristine mantle to 7 0 heavily subduction influenced mantle our model results demonstrated that high silica melts i e granites with 18 o of up to 8 5 can be produced through fractional crystallization alone lastly we model the zircon melt 18 o fractionations of different llds emphasizing their dependence on the specific sio 2 t relationships of a given crystallizing melt wet relatively cool granitic melts will have larger zircon melt fractionations potentially by 1 5 compared to hot dry granites therefore it is critical to constrain zircon melt fractionations specific to a system of interest when using zircon 18 o values to calculate melt 18 o

oxygen isotope composition of a section of lower oceanic crust odp hole 735b 1 the oxygen and hydrogen isotope compositions of vein minerals and 18o values of 64 whole rocks from the deeper kilometer of the 1 5 km lower crustal section of odp hole 735b in the sw indian ocean were analyzed in order to investigate seawater penetration into and reaction with the lower oceanic crust vein amphiboles have d values of 35 to 65 indicating formation from seawater fluids and hydrothermal fluids containing a component of low d magmatic fluid crystal plastic shear zones reacted with 18o enriched fluids at high temperatures and have 18o values of 6 0 7 0 indistinguishable from surrounding rocks reaction with seawater dominated fluids over a range of temperatures 350 700 c led to local 18o depleted rocks but much of the section exhibits 18o enrichment 18o up to 7 6 as the result of static alteration of plagioclase over a range of temperatures 250 to 600 c and fluid compositions chloritic veins and associated alteration by 18o enriched fluids occurred at temperatures of 150 250 c and late carbonates and fe oxyhydroxides formed from cold 10 seawater associated with open fault related fractures bulk rock 18o values of the lower 1 km range from 3 7 to 10 2 but are mostly 5 6 7 6 and the section has a mean bulk 18o of 6 5 1 0 in contrast rocks from the shallower 500 m exhibit net 18o depletion 5 1 1 0 reflecting high temperature deformation and seawater hydrothermal alteration stakes 1991 the weighted average 18o for the entire gabbro section of hole 735b is 6 0 exhibiting little or no change compared to unaltered crust although tectonism at slow spreading rates may allow exposure of lower crust to greater amounts of low temperature alteration and 18o enrichment there is no evidence for a consistent difference in the bulk 18o of the plutonic sections of oceanic crust formed at fast versus slow spreading rates

detachment folding related miocene submarine slope instability in the romagna apennines italy 1 the relationships between slope failure and growing thrust related structures have been explored in the miocene marnoso arenacea foredeep basin romagna apennines impressive fossil slump layers are distributed along the footwall of the regional mount nero thrust which evolved from detachment fold to breakthrough thrust during the detachment fold stage development of growth strata on the rotating forelimb was preceded by the emplacement of slump layers that are currently part of the mount nero thrust footwall in this process sliding is assumed to nucleate along the contacts between different lithologies in the semiconsolidated rock mass the conditions of sliding specifically the critical angle of sliding crit are quantified by adding the influence of cohesion of sediments to the equilibrium analysis reported in hubbert and rubey s 1959 classical work the resulting angles crit are discussed with respect to the depth of the basal surface of sliding and pore fluid pressure states on the basis of such an analysis and field work results an evolutionary model is proposed in which slide sheets come from the crest and upper forelimb of growing detachment folds and attain a deeper detachment depth as the forelimb rotates and steepens pore fluid pressure is found to play a major role by radically decreasing the critical angle of sliding likewise localization of overpressures may also control the depth of sliding during progressive forelimb rotation to allow sliding along gently dipping bedding surfaces slope failure is interpreted as being related to the reactivation of anisotropies represented by lithological discontinuities

evolution of galapagos magmas mantle and crustal fractionation without assimilation summary of helium isotopic data from the gala pagos islands and dredged samples from the gala pagos platform data from graham et al 1993 and kurz et al 1993 data are normalized to the atmospheric value r ra most gala pagos samples are intermediate betweenmorb value of 8 1 and the fernandina value 22 material in those magmas the exception is floreana structure first the depth to the magma chambers mayisland which ranges from 14 5 to 7 7 ra it is possible be due to the rate at which magma is supplied from thethat the low value at floreana re ects assimilation of mantle as the volcano is carried away from the focus ofmaterial with excess radiogenic 4 he by a magma with the hotspot the volcanoes in a juvenile growing stage 3 he 4 he ra 14 most floreana lavas contain abundant of evolution those that have had numerous historicdisaggregated debris from ultrama c xenoliths bow eruptions are dominated by lavas with mgo con geist 1992 a potential source of helium contamination centrations between 5 and 6 e g reynolds geist 1995 a narrow deep caldera characterizes the juvenilestage e g cerro azul wolf and fernandina and iteventually broadens and shallows because of lling with

digital photogrammetric analysis and electrical resistivity tomography for investigating the picerno landslide basilicata region southern italy abstract digital photogrammetric analysis and electrical resistivity tomography ert techniques were applied to evaluate the volume of material involved in a complex roto translational slide occurred in the territory of picerno basilicata region southern italy analytical and digital photogrammetric techniques facilitated a multi temporal analysis of aerial photos for the years 1997 2004 and 2006 in order to identify different geomorphologic features scarps terraces and trenches of the landslide and their development the analytical and digital photo interpretation was performed at the maximum scale of 1 5000 geological and geomorphological surveys were carried out to verify photo interpretation results digital elevation models dems for 1997 2004 and 2006 were produced by applying the grid adaptive method the differential dems 2006 1997 2006 2004 2004 1997 for the most dangerous part of the landslide allowed us to recognize the areas affected either by deposition or erosion and also estimate any altitudinal changes in each geomorphologic unit to detect the sliding surface and estimate the thickness of the sliding material several transversal and longitudinal ert profiles were obtained the electrical images of subsurface supported by stratigraphical data from boreholes were integrated with the information from the dems the altitudinal changes and the sizes of the source and accumulation areas allowed us to estimate the volume of material involved in the mass movement the fusion of data from different sensors allows us to gather indications on the surface and subsurface characteristics of the landslide providing useful information for landslide mitigation activities such an approach can help both to improve our knowledge and overcome the drawbacks of each methodology

crustal structure beneath the galapagos archipelago from ambient noise tomography and its implications for plume lithosphere interactions 1 to constrain the seismic velocity structure of the crust beneath the galapagos archipelago we conducted a tomographic study using high frequency rayleigh waves obtained from cross correlations of ambient noise we analyzed waves with periods between 5 and 8 5 s sensitive to shear wave velocity vs structure between about 3 and 10 km depth after accounting for the effect of water depth crustal velocities are up to 25 lower than those of very young crust at the east pacific rise and are comparable to those of hawaii we attribute the lower than normal velocities to the combined effect of heating and the presence of melt in the crust above the galapagos plume as well as the construction of a highly porous volcanic platform emplaced atop preexisting oceanic crust on average vs between 3 and 10 km depth beneath the western archipelago is up to 15 lower than beneath the eastern archipelago we attribute the west to east velocity increase to a decrease in porosity of the volcanic platform and to cooling of the crust after its passage above the galapagos plume the results of this study in combination with previous work indicate that many of the unusual aspects of the galapagos archipelago are the result of variations in the thickness and internal structure of the chemical and thermal lithospheres our findings indicate that observed variations in the flexural response to loading observed in the galapagos cannot be explained by the current thermal state of the lithosphere instead the flexural response likely represents varying elastic strength at the time of loading we also propose that the northwest and northeast trending alignments of volcanic centers found throughout the archipelago the darwinian lineations may be associated with preexisting zones of weakness in the lithosphere formed during earlier episodes of ridge jumping and ridge propagation that were later reactivated by stresses generated by plume lithosphere interactions

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

pre processing algorithms and landslide modelling on remotely sensed dems abstract terrain analysis applications using remotely sensed digital elevation models dems nowadays easily available permit to quantify several river basin morphologic and hydrologic properties e g slope aspect curvature flow path lengths and indirect hydrogeomorphic indices e g specific upslope area topographic wetness index able to characterize the physical processes governing the landscape evolution e g surface saturation runoff erosion deposition such dems often contain artifacts and the automated hydrogeomorphic characterization of the watershed is influenced by terrain analysis procedures consisting in artificial depression pit and flat area treatment approaches combined with flow direction methods in shallow landslide deterministic models when applied using topographic dataset at medium scale e g 30 m of resolution the choice of the most suitable dem processing procedure is not trivial and can influence model results this also affects the selection of most critical areas for further finer resolution studies or for the implementation of countermeasures aiming to landslide risk mitigation in this paper such issue is investigated using as topographic input the aster dems and comparing two different combinations of dem correction and flow routing schemes the study areas comprise ten catchments in italy for which hydrogeomorphic processes are significant aims of this paper are 1 to introduce a parameter estimation procedure for the physically based dem correction method pem4pit physical erosion model for pit removal 2 to investigate the influence of different terrain analysis procedures on results of the slope stability model shalstab shallow landsliding stability using remotely sensed aster dems 3 trying to assess which of terrain analysis methods is more appropriate for describing terrain instability

oxygen osmium isotope systematics of west maui lavas a record of shallow level magmatic processes new 18 o and 187 os 188 os data from late shield building stage lavas from west maui volcano hawai i indicate that a range of distinct shallow level processes can affect compositions of plume generated ocean island magmas the relative ages of the samples studied were determined either on the basis of field relationships or from collection depth in a water well the stratigraphically lower lavas have os 61 399 ppt initial 187 os 188 os 0 1311 0 1324 and 18 o olivine 4 53 4 88 the stratigraphically higher lavas have os 20 273 ppt initial 187 os 188 os 0 1323 0 1390 with the exception of one low os sample with 187 os 188 os 0 1517 and 18 o olivine 4 73 5 21 these compositions are generally similar to those of kea type hawaiian lavas from mauna kea and kilauea volcanoes but in detail there are some significant differences between the west maui lavas and other kea type lavas the stratigraphically lower lavas have 187 os 188 os similar to those previously observed for mauna kea and kilauea lavas and define a nearly flat 87 sr 86 sr vs 187 os 188 os trend that is consistent with assimilation by these magmas of small degree melts of pacific oceanic crustal gabbros the stratigraphically higher west maui lavas extend to 187 os 188 os higher than observed at mauna kea or kilauea this probably results from interaction of these magmas with the hydrothermally altered volcanic edifice during the waning phases of the shield building stage this process is likely to affect the isotope systematics of os and o but will have little effect on those of hf nd pb or sr

experiments on basin inversion above reactivated domino faults abstract results are presented from scaled sand box experiments which investigate the structural inversion of half graben basins generated by the contractional reactivation of extensional domino fault systems the overburden was deformed above a series of rigid basement fault blocks that were extended in a domino manner the models were constructed from either 1 sand with mica interlayers anisotropic behaviour 2 pure sand isotropic behaviour or 3 a sand clay mixture behaviour with increased competence during the extensional phase of deformation sand or alternating sand mica layers were deposited in teh half grabens associated with individual domino faults to simulate a syn extensional stratigraphic sequence together with a component of overall subsidence after termination of the extensional phase sand layers were added to represent a post rift passive subsidence stratigraphy subsequent contraction of the experimental configuration resulted in progressive reactivation of the domino fault system which was accompanied by back rotation of both the footwall and hanging wall in each of the individual fault blocks this produced null points along the profile section of the fault planes which separated net contraction above from net extension below continued shortening of the system led to further contraction being accommodated along footwall shortcut faults it is suggested that these shortcuts developed in response to 1 the accommodation of space problems generated by increased bed length in the graben acquired during extension and 2 by more efficient low angle fault trajectories in keeping with coulomb failure during horizontal to subhorizontal compression during inversion in the anisotropic model folding in the footwall partially suppressed the initiation of footwall shortcut faults footwall shortcut faulting did not occur in experiments where the dips of the original extensional faults were decreased before the inversion in all inversion experiments the contractional deformation associated with the shortening of the half graben was concentrated in the footwall to each domino basin bounding fault a control experiment in which an undeformed sand pack was deposited above an extended series of basement fault blocks revealed that the early extensional architecture formed in the other experiments had a profound influence on the resultant inversion geometries the results show clear similarities to interpreted examples of natural basin inversion structures associated with reactivated domino fault systems as well as to inferred strike slip induced flower structures

the northern samail ophiolite an oxygen isotope microprobe and field study geological petrological and oxygen isotopic data are presented for 228 whole rock and mineral samples collected from a 100 20 km area of the northern samail ophiolite in oman most of these samples are from three detailed profiles through the pillow lavas sheeted dikes and layered gabbros of this laterally heterogeneous fragment of cretaceous oceanic crust down to and across the petrologic moho the profiles encompass a range of petrologic and tectonic styles and each profile exhibits distinctive 18 16 o variations compared to one another and to mid ocean ridge basalts as a result of pervasive seawater hydrothermal interaction that varied in intensity along strike in the ophiolite in general 18 o depletions are observed in the layered gabbros and 18 o enrichments in most of the sheeted dikes and pillow lavas similar to results previously observed in the southern part of the ophiolite ibra area where 18 o depletions within the gabbroic section are quantitatively balanced by 18 o enrichments in the shallower parts of the oceanic crust the wadi hilti profile selected as an example of relatively intact crust differs from ibra in having more uniform and slightly higher 18 o in the gabbros 5 4 to 6 3 as well as in containing more hydrous alteration minerals amphibole epidote chlorite and prehnite the profiles in the wadi kanut shafan and wadi rajmi sections are much more complex and reveal the impact of off axis intrusions and deep crustal shearing plagiogranite wehrlite intrusions in the shafan kanut area superimposed a local hydrothermal aureole on the ophiolite evident in dikes highly depleted in 18 o quartz sulfide veins abundant epidote thullite and chlorite in shallower rocks and low temperature hydrous alteration of deeper gabbroic rocks the latter produced an overall increase in whole rock 18 o 6 2 to 6 9 such late stage intrusions are found throughout the northern half of the samail ophiolite the wadi rajmi area which is a possible fossil transform or propagating rift represents the most complex of the three profiles it also contains the most abundant highly deformed and hydrothermally altered rocks together with the deepest and largest zone of 18 o depletion yet found in any ophiolite locally 18 o 2 0 conduits for large volumes of high temperature hydrothermal fluids were provided by fractures now occupied by low 18 o gabbro pegmatites and low 18 o dikes material balance estimates for the regional samples and from the various transects through the ophiolite give crustal bulk 18 o averages 5 9 to 6 3 that are within sampling error almost identical to the average morb basalt value of about 5 8 if both vertical and lateral crustal heterogeneities are integrated into a three dimensional model this supports and amplifies the conclusion of earlier workers that the 18 o of seawater is buffered and controlled by hydrothermal interaction with oceanic crust as long as the cumulative effects both spatial and temporal of all seafloor magmatic hydrothermal processes are considered the very slight out of balance enrichment of the integrated crustal average 18 o compared to morb may be explained by the ubiquitous mineralogical and isotopic evidence for a late low temperature alteration event in the basal gabbros these effects are prominent in the vicinity of the petrologic moho and may indicate exchange with low temperature aqueous fluids during or after detachment of the obducted slab

roof assimilation at fast spreading ridges an investigation combining geophysical geochemical and field evidence 1 the role of assimilation at the roof of the axial magma chamber amc at fast spreading mid ocean ridges is investigated using field geophysical and geochemical data field observations from ophiolites indicate that roof assimilation is a common process but provide little constraint on the amount of material assimilated arguments based on geophysical data that include the subsidence of the layer 2a 2b boundary across the width of the amc and the depth of large axial summit troughs require at least 50 100 m of assimilation however significant variations in the depth of the amc on the east pacific rise epr over short along axis distances suggest up to 500 m fluctuations in the depth of the amc may be common on short timescales geochemical modeling of the over enrichment of chlorine in epr basalts suggests that 20 of the oceanic crust may go through a cycle of crystallization alteration then assimilation this is far more than can be accounted for by roof subsidence and suggests that fluctuations in the level of the roof must account for the majority of the assimilation assimilation most likely occurs on a number of different timescales ranging from decadal due to perturbations in the thermal regime related to diking to longer period fluctuations controlled by magma supply from the mantle large scale roof assimilation has implications for the accretion of the lower crust due to heat losses associated with assimilation and for the interpretation of the geochemistry of the oceanic crust

using preexisting cleavage to define extensional fault geometries an example from glacier national park montana the geometry of the rocky mountain trench extensional fault system in northwest montana can be defined by using as reference features pervasive asymmetric cleavages associated with the preexisting lewis thrust these laramide fabrics act as preextensional markers of regional dip and elevation and thus deformation of these passive markers can be used to determine the specific hanging wall geometry of each extensional fault two types of extensional fault are distinguished 1 planar faults with tilt block geometries that cut through the lewis thrust and 2 curved faults with rollover geometries that reactivate the existing lewis thrust the deformed laramide markers indicated that the rocky mountain trench system is dominated by a series of tilt blocks upon with the preexisting thrust had only a localized effect

upper mantle structure beneath the galapagos archipelago from surface wave tomography 1 we present a rayleigh wave tomographic study of the upper mantle beneath the galapagos archipelago we analyze waves in 12 separate frequency bands 8 50 mhz sensitive to shear wave velocity vs structure in the upper 150 km average phase velocities are up to 2 and 8 lower than for 0 to 4 my old and 4 to 20 my old pacific seafloor respectively laterally averaged vs is 0 05 0 2 km s lower between 75 and 150 km depth than for normal pacific mantle of comparable age corresponding to an excess temperature of 30 to 150c and 0 5 melt a continuous low velocity volume that tilts in a northerly direction as it shoals extends from the bottom of our model to the base of a high velocity lid which is located at depths varying from 40 to 70 km we interpret this low velocity volume as an upwelling thermal plume that flattens against the base of the high velocity lid the high velocity lid is 30 km thicker than estimated lithospheric thickness beneath the southwestern archipelago above the main region of plume upwelling we attribute the thicker than normal high velocity lid to residuum from hot spot melting the thickness of the lid appears to control the final depth of melting and the variability of basalt composition in the archipelago at depths less than 100 120 km plume material spreads in directions both toward and against eastward plate motion indicating that plume buoyancy forces dominate over plate drag forces and suggesting a relatively high plume buoyancy flux b 2000 kg s

the role of rainfall in the landslide hazard the case of the avigliano urban area southern apennines italy abstract mass movements varying in type and size some of which are periodically reactivated affect the urban area of avigliano the disturbed and remoulded masses consist of sandy silty or silty clayey plastic material interbedded with stone fragments and conglomerate blocks five landslides that were markedly liable to rainfall associated instability phenomena were selected the relationships between landslides and rainfall were investigated using a hydrological and statistical model based on long term series of daily rainfall data the model was used to determine the return period of cumulative daily rainfall over 1 180 days the resulting hydrological and statistical findings are discussed with the aim of identifying the rainfall duration most critical to landslides the concept of a precipitation threshold was generalized by defining some probability classes of cumulative rainfall these classes indicate the thresholds beyond which reactivation is likely to occur the probability classes are defined according to the return period of the cumulative rainfall concomitant with landslide reactivation

sandbox experiments on basin inversion testing the influence of basin orientation and basin fill analogue modelling experiments using brittle materials are performed to study the inversion of extensional structures asymmetric grabens of two different orientations are first created during a phase of extension and progressively filled they are subsequently shortened in the same direction the aim of our experiments is to determine factors affecting the style of deformation during inversion we specifically investigate variations in thickness and distribution of strong and weak layers constituting the graben fill and in initial basin orientation the main advantage of our experimental set up is that we have a complete control on graben location width infill and orientation before inversion the experiments show that shortening results only in limited reactivation of pre existing normal faults in general forward thrusts and backthrusts cut across normal faults into the footwall of the graben the forward thrusts either propagate parallel to the enveloping surface of faulted blocks or they cut across basin limiting normal faults at various angles the graben fill is mechanically extruded by displacement along forward thrusts that accommodate most of the shortening both pre existing faults and weak graben fill act as zones of weakness during inversion and determine the orientation and location of both backthrusts and forward thrusts the results of our experiments conform well to natural examples of inverted graben structures

regional scale high plasticity clay bearing formation as controlling factor on landslides in southeast spain complex landslides in clay bearing sediments are investigated in two moderate relief regions of southeast spain both regions more than 100 km apart show landslides affecting the same flysch formation which outcrops widely in the central and western betic cordillera along the contact between the external south iberian domain and internal alboran domain zones intense rainfall episodes can be considered as the main triggering factor for slope failures in these two areas we have chosen two landslides diezma and riogordo landslides one from each area of study to investigate their morphological and geotechnical features in order to establish the relative importance of the different controlling factors from a kinematic point of view the two features studied in detail can be referred as to rotational failures evolving downhill to slow earthflows the movement was concentrated on several surfaces developed on a clay rich layer mostly constituted by smectite this clay mineral is of critical relevance to the mechanical behaviour of soils and flysch like formations being very consistent at dry conditions but rapidly losing its strength at wet conditions thus softened smectite rich clay layers with high water contents can approach the properties of a lubricant which in turn can be critical for slope stability in addition to their high plasticity these clays have a high swelling potential which can induce significant vertical overpressure thus reducing even more the strength properties of the flysch formation in southeast spain a region with a mediterranean rainfall regime slope stability can be seriously influenced by the presence of these smectite rich clay layers in a formation of regional extent as is the case of the flysch formation therefore this lithologically controlled factor should be taken into account when evaluating landslide hazard in the betic cordillera

submarine fernandina magmatism at the leading edge of the galapagos hot spot new multibeam and side scan sonar surveys of fernandina volcano and the geochemistry of lavas provide clues to the structural and magmatic development of galapagos volcanoes submarine fernandina has three well developed rift zones whereas the subaerial edifice has circumferential fissures associated with a large summit caldera and diffuse radial fissures on the lower slopes rift zone development is controlled by changes in deviatoric stresses with increasing distance from the caldera large lava flows are present on the gently sloping and deep seafloor west of fernandina fernandina s submarine lavas are petrographically more diverse than the subaerial suite and include picrites most submarine glasses are similar in composition to aphyric subaerially erupted lavas however these rocks are termed the normal series and are believed to result from cooling and crystallization in the subcaldera magma system which buffers the magmas both thermally and chemically these normal series magmas are extruded laterally through the flanks of the volcano where they scavenge and disaggregate olivine gabbro mush to produce picritic lavas a suite of lavas recovered from the terminus of the sw submarine rift and terraces to the south comprises evolved basalts and icelandites with mgo 3 1 to 5 0 wt this evolved series is believed to form by fractional crystallization at 3 to 5 kb involving extensive crystallization of clinopyroxene and titanomagnetite in addition to plagioclase high k lavas were recovered from the southwest rift and are attributed to hybridization between normal series basalt and evolved series magma the geochemical and structural findings are used to develop an evolutionary model for the construction of the galapagos platform and better understand the petrogenesis of the erupted lavas the earliest stage is represented by the deep water lava flows which over time construct a broad submarine platform the deep water lavas originate from the subcaldera plumbing system of the adjacent volcano after construction of the platform eruptions focus to a point source building an island with rift zones extending away from the adjacent buttressing volcanoes most rift zone magmas intrude laterally from the subcaldera magma chamber although a few evolve by crystallization in the upper mantle and deep crust

sandbox model studies of inversion tectonics abstract scaled plane strain sandbox models have been used to simulate basement controlled structural inversion in a sedimentary overburden two basement configurations were tested in the first one reversal of movement along vertical and normal faults that controlled a graben relief induced only a partial recovery of displacement along the pre existing overburden faults the inversion produced new reverse faults in the footwall of the pre existing overburden faults the reactivated normal faults and the new reverse faults defined wedge shaped fault blocks at the edges of the inverted structure in the second configuration the relationship between inversion and tilted fault blocks was tested when a tilting basement block does not move parallel to its bounding fault a compression is induced in the overburden which generates an inverted structure bounded by new reverse faults both experiments show that structural inversion not only reactivates pre existing faults but also generates new faults in the overburden faults related to inversion are the result of horizontal compression either associated with rotation of one of the fault blocks or with vertical uplift of basement blocks

mechanical behaviour of granular materials used in analogue modelling insights from grain characterisation ring shear tests and analogue experiments abstract the mechanical behaviour of several dry granular materials is investigated through ring shear tests grain characterisation and simple analogue experiments analysed by x ray computed tomography an improved knowledge of granular materials is essential to determine their suitability as analogues for upper crustal rocks in experimental models and to compare analogue and numerical experiments the ring shear tests show that the granular materials have an elastic frictional plastic behaviour with strain hardening preceding failure at peak strength followed by strain softening until a dynamic stable value is reached this is similar to the behaviour exhibited by experimentally deformed rocks the physical characteristics of the grains determine the amount of diffuse deformation before failure the percentage of strain softening and act on the thickness of the shear zones before broadening initial shear zone width in extensional and contractional experiments is between 11 and 16 times the mean grain size the angle of internal friction defining one of the mechanical properties of granular materials and thus fault dip is not only related to physical characteristics of the grains and to the handling technique used e g sieving or pouring but also to the overburden and to the experimental setup used

formation of caldera periphery faults an experimental study changing stresses in multi stage caldera volcanoes were simulated in scaled analogue experiments aiming to reconstruct the mechanism s associated with caldera formation and the corresponding zones of structural weakness we evaluate characteristic structures resulting from doming chamber inflation evacuation collapse chamber deflation and cyclic resurgence inflation and deflation and we analyse the consequential fault patterns and their statistical relationship to morphology and geometry doming results in radial fractures and subordinate concentric reverse faults which propagate divergently from the chamber upwards with increasing dilation the structural dome so produced is characterised bysteepening in the periphery whereas the broadening apex subsides pure evacuation causes the chamber roof to collapse along adjacent bell shaped reverse faults the distribution of concentric faults is influenced by the initial edifice morphology steep and irregular initial flanks result in a tilted or chaotic caldera floor the third set of experiments focused on the structural interaction of cyclic inflation and subsequent moderate deflation following doming caldera subsidence produces concentric faults that characteristically crosscut radial cracks of the dome the flanks of the edifice relax resulting in discontinuous circumferential faults that outline a structural network of radial and concentric faults the latter form locally uplifted and tiltedwedges half grabens that grade into horst and graben structures this superimposed fault pattern also extends inside the caldera we suggest that major pressure deviations in magma chamber s are reflected in the fault arrangement dissecting the volcanoflanks and may be used as a first order indication of the processes and mechanisms involved in caldera formation

oxygen isotope geochemistry of oceanic arc lavas variations of oxygen isotope ratios in arc related lavas can constrain the contributions of subducted crustal igneous rocks sediments and fluids to the sub arc mantle we have measured oxygen isotope ratios in 72 arc and back arc lavas from five ocean ocean subduction zone systems using laser fluorination analyses of olivine and other phenocrysts and glass eighty percent of our samples have delta 18o values for any given phase olivine plagioclase glass or biotite within 0 2 per thousand of the average value for that phase in upper mantle peridotites and mid ocean ridge basalt morb the range for each phase is 1 0 per thousand this result contrasts with previous studies of whole rock samples which are significantly more variable even after exclusion of samples believed to be altered or fractionated by magmatic differentiation and demonstrates that most arc related lavas contain 1 2 of 18o enriched crustal oxygen from any source i e assimilation or subducted contributions elevations in delta 18o that do occur in these basic arc derived magmas relative to values most common for mantle derived lavas are associated both with enriched radiogenic isotope signatures and even more strongly with chemical indices consistent with high integrated extents of melting of their peridotite sources we interpret these relationships as evidence that melting in the sources of the high delta 18o lavas we have studied was fluxed by addition of high delta 18o aqueous fluid or perhaps a hydrous melt from the subducted slab such that sources that contain relatively large components of slab derived fluid or melt are both relatively 18o enriched and also experienced relatively large amounts of melting we have developed a quantitative model linking the amount of melting to the extents of 18o radiogenic isotope and trace element enrichment in a mantle source being fluxed by addition of aqueous fluid comparison of this model with observed variations in the geochemistry of lavas from the vanuatu fiji new caledonia region the suite of related samples showing the greatest range in delta 18o observed in this study constrains the amounts and chemical and isotopic compositions of slab derived phases in the sources of these arc related lavas assuming a delta 18o value of 20 per thousand for the slab derived fluid 0 5 1 0 wt is added to the sources of most mantle derived arc magmas the maximum amount of slab derived flux in the sources of arc magmas according to our results is 2 5 wt

oxygen isotope compositions of lavas from the galapagos archipelago geochemical contributions from modern crustal sources new oxygen isotope compositions of olivine phenocrysts collected across the galapagos archipelago show a larger range of 18 o olivine values than previously reported 4 74 5 40 in the region olivines from fernandina floreana and pinta which represent the main radiogenic isotope end members of the galapagos hotspot have 18 o values of 5 02 0 08 1 within the accepted range of the oxygen isotope composition of mantle olivines in general 18 o olivine values do not correlate with radiogenic isotope compositions of hosting lavas instead the span of 18 o olivine values is more consistent with widespread lithospheric contamination 18 o olivine values at the higher end of the range in the galapagos are correlated with indices of crustal assimilation including sr sr values below the normal mantle range can be explained by assimilation and fractional crystallization processes olivines that have 18 o values below the normal mantle range come from the western part of the archipelago with the thickest lithosphere this is consistent with melt interacting with crust that underwent hydrothermal alteration at elevated temperature causing a decrease in 18 o values in contrast the highest 18 o values of the galapagos come from areas underlain by thin lithosphere in the eastern part of the archipelago this is consistent with shallow crust melt interaction that is generally associated with 18 o values above the normal mantle range these results suggest that while the three end member components of the galapagos mantle have a generally homogenous 18 o value indistinguishable from normal upper mantle there is a more widespread effect of lithospheric contamination in melts than previously thought

landslide triggering scenarios in homogeneous geological contexts the area surrounding acri calabria italy abstract the paper describes a methodology to detect landslide triggering scenarios in geological homogeneous areas and for some specific landslide categories in these scenarios the rainfall landslide relationship as well as the pluviometric load conditions influencing slope instability have to be investigated the methodology is applied to an area located in northern calabria italy and affected by widespread and different slope instability phenomena outcropped fractured and deeply weathered crystalline rock masses determining geologic homogeneous conditions are present in the same area suitable and homogeneous climatic features have also been found according to the methodology adopted the hydrologic analysis of rainfall time series is initially carried out notwithstanding historical data concerning landslide mobilization but using simple models to determine critical pluviometric scenarios for the three landslide categories shallow medium deep and deep landslide triggering scenarios individualized according to this procedure are less significant as compared to the landslide mobilization detected in the study area by means of historical research and ascribed to the three landslide categories according to geomorphologic analysis subsequently the possible landslide triggering scenarios are outlined by carefully investigating the hydrologic analysis limited to the periods identified according to the historical data in the study area and approximately for all the areas characterized by the outcrop of fractured and deeply weathered crystalline rocks significant triggering scenarios can be outlined in particular shallow landslide triggers could be activated by rainfall events with intensities exceeding 90 mm day and or with amounts exceeding 160 mm as for medium deep and deep landslides triggering mechanisms are more complicated and effective rainfall contribution must be taken into account compared to groundwater storage moreover a more complex link between deep landslides and precipitation is confirmed the results obtained to date highlight the potential of this methodology which enables us to define and progressively improve the knowledge framework by means of a work sequence integrating different disciplinary tools and results

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

wolf volcano galapagos archipelago melting and magmatic evolution at the margins of a mantle plume wolf volcano an active shield volcano on northern isabela island in the galapagos archipelago has undergone two major stages of caldera collapse with a phase of partial caldera refilling between wolf is a typical galapagos shield volcano with circumferential vents on the steep upper carapace and radial vents distributed in diffuse rift zones on the shallower sloping lower flanks the radial fissures continue into the submarine environment where they form more tightly focused rift zones wolf s magmas are strikingly monotonous estimated eruptive temperatures of the majority of lavas span a total of only 22 c this homogeneity is attributed to buffering of magmas as they ascend through a thick column of olivine gabbroic mush that has been deposited from a thin shallow 2 km deep subcaldera sill that is in a thermochemical steady state wolf s lavas have the most depleted isotopic compositions of any historically active intraplate ocean island volcano on the planet and have isotopic compositions except for he he indistinguishable from midocean ridge basalt erupted from the galapagos spreading center gsc 250 410 km away from the peak of influence of the galapagos plume wolf s lavas are enriched in incompatible trace elements and have systematic major element differences relative to gsc lavas however wolf s magmas result from lower extents of melting deeper melt extraction and a greater influence of garnet compared with gsc magmas but wolf and the gsc share the same sources these melt generation conditions are attributed to melting in a thermal and mechanical boundary layer of depleted asthenosphere at the margins of the galapagos plume the lower degrees of melting and extraction from deeper levels result from a thicker lithospheric cap at wolf than exists at the gsc

evaluation of landslide reactivation a modified rainfall threshold model based on historical records of rainfall and landslides abstract this study proposes a modification of the conventional threshold model for assessing the probability of rainfall induced landslide reactivation the modification is based on the consideration that exceedance of a pre determined rainfall threshold is a necessary but not sufficient condition to reactivate a landslide the proposed method calculates the probability of reactivation as a function of the probability of exceedance of a pre determined rainfall threshold as well as the probability of occurrence of a landslide after such exceedance the data for the calculation were obtained from historical records of landslides and rainfall the method was applied to two complex landslides san donato and la salsa involving fine grained debris in the southern section of the apennine foredeep the minimum rainfall threshold triggering landslide reactivation on the two slopes was determined by examining rainfall patterns during the 180 days preceding the slide events for the san donato and la salsa landslides the minimum triggering threshold consists of rainfall events lasting 15 days with cumulated rainfall exceeding 150 and 180 mm respectively based on hydrological and statistical analyses the annual probabilities of exceeding the thresholds were estimated to be 0 38 and 0 25 respectively during the period from 1950 to 1987 the minimum threshold was exceeded 14 times and four reactivations occurred at san donato whereas the threshold was exceeded 10 times and three reactivations occurred at la salsa hence the probabilities of landsliding after exceedance of the minimum rainfall threshold are 4 14 and 3 10 respectively finally annual reactivation probabilities were calculated to be 0 11 and 0 08 respectively the reliability of the minimum rainfall threshold was tested by i simulating variations in the stress strain behavior of the slopes as a result of fluctuations in the water table from normal to extreme values and ii analyzing the results of continuous multi year monitoring of pore pressure and rainfall variations on a slope composed of dominantly fine grained debris

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

analysis of physical testing of rainfall induced soil slope failures rainfall is a significant factor that triggers slope failures around the world this paper reports a series of physical tests which were conducted to simulate rain induced slope failures the experiments dealt with two scenarios including 1 rainwater infiltration into the slope and 2 slope failures induced by artificial rainfall with different initial conditions slope deformation and slope failures were observed and possible mechanisms were interpreted based on the experimental results the results confirm the hypothesis that pore water pressure and water content in a loose soil slope change rapidly and that water infiltration into cracks in the slope has a great impact on landslide development the observed slope failures can be divided into three types overall sliding failure partial sliding failure and flow slide the effect of slope gradient rainfall intensity and distribution of initial suction on the slope deformation and failure process are also summarized for possible applications under the similar conditions

the tectonic evolution of the southern dutch north sea during the palaeogene basin inversion in distinct pulses abstract in this paper we discuss the response of a sedimentary basin to compressional reactivation of extensional faults in distinct pulses the inversion of the broad fourteens basin in the southern dutch north sea is used as a case study the first pulse of inversion occurred during the late mesozoic as a result of the sub hercynean phase a second pulse occurred during the mid palaeocene laramide phase a final inversion pulse occurred around the eocene oligocene boundary coinciding with the pyrenean tectonic event we reconstructed the stratigraphic and structural development of the area during the palaeogene in detail basic data are two 2d seismic surveys supported by 74 geophysical wireline logs on which newly constructed depth and thickness maps are based the reconstruction is aided by a quantitative subsidence analysis cessation of compression resulted in relaxation and tensional reactivation of faults caused differential subsidence inheritance of geological structures is a key element in the tectonic activity in the broad fourteens basin during the palaeogene tectonic movement during the palaeogene was always accommodated by reactivation of palaeozoic mesozoic faults the intensity of inversion in the southern north sea basin during the pyrenean phase appears much larger than previously noticed moreover the area affected by the inversion is much wider than during previous phases minor differences in the direction of the local stress field between the tectonic phases and by the deposition of a thick sedimentary succession during the periods of tectonic quiescence between the inversion phases can account for this

geochemical constraints on the role of oceanic lithosphere in intra volcano heterogeneity at west maui hawaii 87 sr 86 sr 206 pb 204 pb variation in the stratigraphically lowest lavas is orthogonal to the all hawaii variation indicating that it is not the result of mixing between components normally sampled by hawaiian shield stage magmas we compare our west maui data with observed compositions of pacific oceanic basaltic and gabbroic crust and predicted compositions for 2ga basaltic and gabbroic oceanic crust the observed fine scale compositional variability in the stratigraphically lowest west maui lavas is consistent with 10 15 mixing of small degree 2 partial melts of the pacific gabbroic oceanic crust with plume derived kea type magmas mass balance considerations indicate that this geochemical signal can be present in no more than 5 of the total volume of lavas erupted at west maui

2d electrical resistivity imaging of some complex landslides in lucanian apennine chain southern italy we use high resolution electrical resistivity imaging to delineate the geometry of complex landslides in the lucanian apennine chain of southern italy to identify the discontinuity between the landslide material and bedrock and to locate possible surfaces of reactivation the lucanian apennine chain is characterized by high hydrogeological hazard and shows a complete panorama of mass movements in this area all typologies of landslides markedly predisposed and tightly controlled by the geostructural characteristics are found rotational and translational slides rototranslational slides earth and mudflows as well as deep seated gravitational slope phenomena with a predominance of rototranslational slides evolving as earthflow slides three test sites characterized by complex geology and a high hydrogeologic hazard are studied the giarrossa and varco izzo earthflow slides are located to the west and east of the town of potenza whereas the latronico slide is located close to the town of latronico

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

normal faulting block tilting and decollement in a stretched crust extensional tectonics cover a wide range of crustal structures from narrow continental rifts to large continental areas if we except continental and oceanic rifts stretched portions of the crust exhibit complex faulting patterns at upper levels with high angle and low angle normal faults very little is known concerning the geometry of structures and physical processes at depth it is therefore difficult to extrapolate surface observations to the crustal scale five general models are proposed that combine continuous and discontinuous deformation and geometrical and geological tests are proposed two natural examples the west armorican atlantic margin and eldorado mountains basin and range province are presented they are characterized by an association of high angle normal faults tilted blocks and low angle normal faults field and geometrical arguments are given to demonstrate that low angle faults are controlled by decollement surfaces along preexisting interfaces geometrical implications of the tilted block pattern are presented and the gravity gliding hypothesis is proposed as a possible explanation of block tilting when associated with low angle normal faults in such cases the amount of stretching cannot be related to bulk thinning of the crust

dynamics of a complex mass movement triggered by heavy rainfall a case study from nw turkey abstract following a period of heavy precipitation a large and complex mass movement namely the dagkoy landslide occurred in the west black sea region of turkey on may 21 1998 this paper describes the conditioning factors of the landslide and interprets the mass transport processes in terms of a movement scenario geology geomorphology and vegetation cover were considered as the conditioning factors of the failure observations showed that the gently sloping about 10 area is mostly covered by dense forest trees at the crown where the motion initiated significant intersection of the collapsed slope with dip of the local marls seems to have contributed to the formation and geometry of the landslide the distance from the crown down to the toe of the landslide measured more than 600 m with about 0 6 km 3 total earth material displaced the landslide has both a block sliding characteristics in the upper portions and a debris flow soil flow component around the margins of the sliding blocks in the middle parts and at the toe the proposed scenario for the landslide reveals that the movement was initiated near crown as a result of the excess water content in the marls at the end of 3 days of heavy rainfall the early perturbations transverse cracks ridges etc lasted for 6 7 h after which the central part of the zone started to move as a soil flow in which very large intact blocks were transported even though the movement was very rapid 1 2 m min there was no loss of life however the movement destroyed 38 houses one mosque and a considerable amount of farmland

deep structure of the foreland to the caledonian orogen nw scotland results of the birps winch profile the winch marine deep seismic reflection profile crosses the hebridean shelf the proterozoic foreland to the caledonian orogen west of scotland the data quality is very good the upper crust is largely devoid of coherent seismic reflections although this may in part be due to acquisition techniques being inappropriate for this problem in contrast the middle and lower crust 10 25 km depth exhibits good reflections the mid crust contains reflectors which may be relics of early palaeozoic caledonian or earlier grenvillian eastward dipping thrust zones which pass into an acoustically strongly layered lower crust the outer isles thrust is mapped from the surface to the mid crust and tied into its land outcrop on north lewis reactivation of this thrust offshore in a normal sense in mesozoic times caused the formation of the minch and north lewis basins the mono is defined by a strong band of reflections at about 27 km depth which correlates well with results from the hmse explosion seismic survey moho depth is apparently rather uniform in the area of the foreland crossed by winch winch and hmse results together suggest a mean crustal velocity for the hebridean shelf of 6 4 0 1 km s 1 the eastward dipping flannan thrust can be mapped into the upper mantle on three lines from about 15 to 45 km depth well into the upper mantle neither the flannan thrust nor the outer isles thrust appear to pass straight through the reflective lower crust suggesting that the lower crust is a region of high strain the outer hebrides is a positive block probably formed as an isostatic response to mesozoic normal faulting which reactivated the outer isles thrust

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

displacement properties of landslide masses at the initiation of failure in quick clay deposits and the effects of meteorological and hydrological factors abstract this study aimed to identify displacement properties of landslide masses at the initiation of failure and factors that affect the landslides activities in areas where quick clay is found we set up a research site in a quick clay deposit area in norway and monitored the displacements of landslide masses and meteorological and hydrological factors for a long period of time using an automatic monitoring system the system collected data for two landslides that occurred at the site from the start of their movement until their ultimate collapse the two landslides that were monitored showed definite secondary and tertiary creep stages before they collapsed one of the landslides moved from the secondary stage to the tertiary creep stage when another landslide occurred nearby the tertiary stage of this landslide showed reconstruction of short primary secondary and tertiary creep stages these phenomena suggested that 1 the stress at the end of the landslide mass was released during the nearby landslide and 2 a new stress distribution was formed in the landslide mass the critical strain differed for 14 times between the two landslide masses we monitored the difference was likely attributable to the difference in the contents of quick clay which shows small critical stress against slope failure as well as topological factors our analyses of the effects of hydrological and meteorological factors on landslides showed that the precipitation of 3 and 10 days before six slope failures as the final stages of the landslides that had occurred in the research area was no different from the mean precipitation of periods that showed no slope failure suggesting that precipitation had no direct effects on the collapse of the landslide masses on the other hand the traveling velocities of the landslide masses during the secondary creep stage which was prior to their collapse were affected by the water content of the soil and precipitation and the amount of snowmelt water but was little correlated with the pore water pressure of the quick clay layer we also found that the presence of snow cover scarcely affected landslide movements

lithospheric structure and compensation mechanisms of the galapagos archipelago volcanic islands of the galapagos archipelago are the most recent subaerial expression of the galapagos hotspot these islands and numerous seamounts are constructed mainly upon a broad volcanic platform that overlies very young 10 m y oceanic lithosphere just south of the active galapagos spreading center the 91 w fracture zone crosses the platform and creates an estimated 5 m y age discontinuity in the lithosphere major tectonic features of the galapagos include an unusually broad distribution of volcanic centers pronounced structural trends such as the nw se wolf darwin lineament wdl and a steep escarpment along the western and southern margins of the archipelago we use shipboard gravity and bathymetry data along with geosat geoid data to explain the tectonic and structural evolution of the galapagos region we model the gravity anomalies using a variety of compensation models including airy isostasy continuous elastic flexure of the lithosphere and an elastic plate with embedded weaknesses and we infer significant lithospheric strength variations across the archipelago the outboard parts of the southern and western escarpment are flexurally supported with an effective elastic thickness of 12 km this area includes the large shield volcanoes of fenandina and isabela islands where the lithosphere regionally supports these volcanic loads the central platform is weaker with an elastic thickness of 6 km or less and close to airy isostasy the greatest depths to the moho are located beneath eastern isabela island and the central platform thinner lithosphere in this region may account for the broad distribution of volcanoes the extended period of eruption of the central volcanoes and their reduced size the transition from strong to weak lithosphere along the southern escarpment appears to be abrupt within the resolution of our models and can be best represented by a free end or faultlike discontinuity also modeling the wdl as a lithospheric fault increases the match to the observed gravity anomalies the primary feature is the weak central platform whose existence is a logical convergence of several factors the 91 w transform age offset the possible increase in age of the lithosphere along the southern part of the platform due to ridge jumping and the formation of the central platform at a spreading ridge

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

plagioclase ultraphyric basalts of the galapagos archipelago abstract basalts containing as much as 50 plagioclase phenocrysts that attain lengths of several centimeters are common on the northern islands of the galapagos archipelago mineralogic and geochemical evidence requires that the large anorthitic phenocrysts nucleated and grew from a less evolved magma than that in which they were erupted we suggest that plagioclase ultraphyric basalts pubs form when a buoyant phenocryst laden magma enters a chamber containing a denser more evolved magma as the new magma mixes with the old anorthitic plagioclase phenocrysts may accumulate near the roof in a hybrid liquid thinner crust under the northern islands increases the probability that viscous plagioclase rich magmas can ascend to shallow magma chambers and may account for the fact that pubs are more common on the northern islands than in the rest of the archipelago

cyclic caldera collapse piston or piecemeal subsidence field and experimental evidence many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution on gran canaria canary islands the miocene tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone sheet swarm obscuring intracaldera structural relations extracaldera radial and circumferential faults and dikes are well exposed we used field data and experiments scaled to the island of gran canaria to clarify the poorly understood structural temporal and genetic relationship of peripheral faults to the central caldera the experimental setup comprises a cone of medium grained sand in which a rubber balloon was repeatedly inflated and deflated balloon inflation resulted in updoming and a dominantly radial fault pattern whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks a complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the tejeda caldera on gran canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes

hydrothermal activity in a peculiar oceanic ridge oxygen and hydrogen isotope evidence in the xigaze ophiolite tibet china the xigaze ophiolite locally displays a 7 km thick continuous sequence which probably represents an oceanic crust formed at a slow spreading ridge it consists from top to bottom of 1 1 pillow lavas with 18o between 9 and 16 and d around 90 vs smow 2 2 rare trondjhemites 9 7 18o 13 4 and d around 75 3 3 dolerite sills and dikes with 18o between 7 0 and 9 5 and d between 77 and 40 4 4 isotropic gabbros occurring as screens of the sills and dikes and rare layered gabbros these gabbros have 18o between 4 8 and 11 0 and d around 65 and bear high 18o albitized plagioclases 18o 10 which coexist with clinopyroxenes of mantle values 18o 5 5 or having values being slightly depleted down to 3 0 5 5 ultramafic rocks are either fresh or serpentinized they have 18o mainly around mantle values and d s are between 250 and 100 for the mafic part of the ophiolite the isotopic compositions correspond to hydrothermal interaction with seawater derived fluids under zeolite to greenschist facies but the trondjhemites were additionally affected by fluids poorer in d in particular the gabbros reacted with seawater derived fluids under amphibolite facies conditions as seen from their secondary mineralogy and their 18o depleted pyroxenes and subsequently were pervasively reacted under greenschist zeolite facies conditions during which the high 18o albitized plagioclase formed this occurrence of amphibolite facies conditions followed by greenschist zeolite facies conditions can be interpreted either to be a result of slow cooling of the oceanic crust at the ridge or to result from a fundamentally lower temperature hydrothermal interaction if compared with other ophiolites in contrast the d s of the serpentine 100 from the ultramafics are attributed to fluids of meteoric origin at high elevation nevertheless the particular location of the serpentinized harzburgites just beneath the gabbros and the high d dolerite sills and dikes 60 d 40 enclosed in these serpentinized harzburgites suggests an oceanic origin and therefore the possibility of hydrogen isotope exchange between serpentine and meteoric fluids after the obduction the xigaze ophiolite sequence displays very little 18o depleted rocks relative to mantle oxygen composition they cannot balance the amount of 18o enriched rocks consequently the result of the hydrothermal interaction between the xigaze ophiolite sequence and the seawater is an 18o depletion of the seawater however the contribution of xigaze type ridges to the buffering of 18o in cretaceous seawater was probably small