evidence for postseismic viscoelastic relaxation following the 1959 m 7 5 hebgen lake montana earthquake a 1983 releveling survey conducted by the national geodetic survey combined with previous surveys in 1923 1960 1967 and 1975 provides evidence for ongoing vertical deformation of a broad region diameter of 150 km surrounding the site of the 1959 hebgen lake earthquake deformation consists of relative uplift centered roughly on the coseismic fault and a smaller amplitude zone of relative subsidence south of the fault maximum observed elevation change during the postseismic period 1960 1983 exceeds 30 cm assuming that the entire uplift i e 1923 1983 occurred following the 1959 earthquake i e uplift measured between 1923 and 1960 was entirely postseismic the rate of vertical deformation appears to have decreased exponentially with a characteristic decay time of about 10 years the spatial pattern and time behavior of the observed movements are consistent with simple models of postseismic deformation following normal faulting in an elastic layer thickness of 30 40 km overlying a viscoelastic half space viscosity of 1019 pa s this model may also account for the anomalously large horizontal strain around the hebgen lake region measured by repeated trilateration surveys during the period 1973 1984 the releveling measurements in the hebgen lake region appear to provide the first observations of viscoelastic relaxation in the asthenosphere following an intraplate earthquake in the united states

sulfur diffusion in basaltic melts abstract we measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions i e in the sulfide stability field temperatures from 1225 c to 1450 c pressures of 0 5 and 1 gpa and water concentrations of 0 and 3 5 wt although each melt is characterized by slightly different sulfur diffusion coefficients the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts d 2 19 10 4 exp 226 3 58 3 r t where d is the diffusion coefficient in m2s 1 the activation energy is in kj mol 1 r is the gas constant and t is the temperature in k sulfur diffusion in basalts with 3 5 wt water is a factor of three to seven higher than in anhydrous melts and can be described by d 5 91 10 7 exp 130 8 82 6 r t at the conditions of this study the pressure does not measurably affect sulfur diffusion sulfur diffusion in dry basaltic melts is one order of magnitude higher than sulfur diffusion in dry andesitic and dacitic melts whereas sulfur diffusion in hydrous basaltic and andesitic melts is within the same order of magnitude when compared to the diffusivity of other volatile species in nominally dry basaltic melts sulfur diffusion appears to be two times lower than co2 diffusion and two orders of magnitude lower than h2o diffusion

the quaternary evolution of the gulf of corinth central greece coupling between surface processes and flow in the lower continental crust abstract the gulf of corinth in central greece is an active normal fault zone with particularly clear evidence of isostatic footwall uplift constrained by quaternary marine terraces and hanging wall subsidence and sedimentation it is bounded to the south by a pliocene to early pleistocene sedimentary basin which is now eroding into the gulf previous work has suggested that the relief across this region has increased dramatically since the early pleistocene due to the isostatic response to increased rates of footwall erosion and hanging wall sedimentation it is indeed assumed here that incision accompanying the draw down of global sea level at 0 9 ma during the first major pleistocene glaciation initiated the erosion of the basin south of the gulf of corinth and so abruptly increased the sedimentation rate in the gulf the resulting transient thermal and isostatic response to these changes is modelled with the subsiding depocentre and eroding sediment source coupled by flow in the lower continental crust the subsequent enhancement of relief involving an increase in bathymetry from near zero to 900 m and 500 m of uplift of the eroding land surface in the sediment source is shown to be a direct consequence of this change the model is sensitive to the effective viscosity of the lower crust and can thus resolve this parameter by matching observations a value of 6 1019 pa s is indicated suggesting a viscosity at the moho no greater than 1018 pa s similar transient topographic effects caused by increased rates of sedimentation and erosion are likely to be widespread within the geological record suggesting that this coupling process involving flow in the weak lower crust may be of major geological and geomorphological importance

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

a note on the surface volume change of shallow earthquakes summary this note presents an exact analytical formula for determining the magnitude of coseismic surface volume change v of earthquake faults in a half space for a poisson solid the formula is remarkably simple v mzz 8 where mzz is one of the moment tensor elements of the source maximum v values derive from dip slip on faults plunging 45 for these events surface volume changes of 0 0001 and 4 3 km3 can be expected for magnitude 5 and 8 earthquakes respectively all of the coseismic surface volume change is recovered in the interseismic period through relaxation of the earth and rebound of the surface a useful rule of thumb for estimating the magnitude of vertical rebound in 45 dip slip events is hp s 24 where s is the coseismic slip on the fault

a melt inclusion study of the toba tuffs sumatra indonesia the toba caldera in northern sumatra indonesia is the site of earth s largest quaternary volcanic eruption this eruption dated at 74 ka produced the 2800 km3 youngest toba tuff ytt and ash fall quartz bearing silicic pumices ranging from 68 to 77 wt sio2 indicate that the ytt magma was zoned compositionally and mineralogically prior to the ytt eruption two other silicic quartz bearing tuffs known as the middle toba tuff mtt and the oldest toba tuff ott were erupted from toba at 0 501 ma and 0 840 ma respectively although the volatile contents of the toba magmas are poorly constrained aerosols generated by the ytt eruption are generally thought to have caused a global volcanic winter an evaluation of the pre eruptive dissolved gas contents of the ytt magma is fundamental to understanding the global effects of this eruption we used melt inclusions in quartz crystals to determine the dissolved h2o co2 s cl and f contents of the ytt mtt and ott magmas quartz crystals selected from pumice blocks and welded tuffs that spanned the compositional ranges of the three units were chosen for study major and trace element analyses of melt inclusions were also conducted to characterize melt evolution and provide context to the volatile data melt inclusions from the ytt mtt and ott are rhyolitic in composition 73 77 wt sio2 and have overlapping indistinguishable major element trends inclusions from the large eruptions ytt and ott have similar geochemical relationships where the most evolved melt inclusions occur in the least silicic bulk rock samples and are more evolved than their matrix glasses in contrast the least evolved melt inclusions occur in the most silicic samples and either overlap with or are less evolved than their matrix glasses these patterns can be explained if quartz crystals in the least silicic magmas were inherited from more evolved melt while those in the most silicic melt formed in situ several lines of evidence suggest that crystal settling of early formed quartz crystals in long lived magma bodies was an important process in the ytt and ott magmas trace element data from the ytt melt inclusions have wide ranges rb 250 830 ppm ba 10 485 ppm and mostly support these models however incompatible trace elements are enriched 2 3 over their matrix glass compositions in all samples in the smaller mtt melt inclusions overlapped with the compositional range of the bulk rock samples and are consistent with in situ crystallization ftir analyses indicate that the ytt mtt and ott melts contained about 4 0 5 5 2 0 5 5 and 2 0 5 5 wt h2o respectively co2 contents in all units are generally 100 ppm and cl is 2000 ppm water gradients occur in all 3 tuffs cl gradients are evident only in the ytt and the least silicic samples from all units had no detectable co2 sulfur contents in melt inclusions are low in all samples 32 ppm and overlap with matrix glass s contents applying broad degassing constraints about 1014 g of h2so4 aerosols were likely loaded into the atmosphere during the ytt eruption 2 orders of magnitude less than previous petrologic estimates considerably more cl and f about 1015 g of each may have been part of the ytt aerosol cloud

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

diffusion of dissolved co2 and cl in hydrous silicic to intermediate magmas the bulk diffusivity of dissolved co sub 2 in obsidian and dacite melts containing 0 11 wt dissolved water at 800 1 100c and 1 gpa was characterized using a sup 14 c radiotracer technique five values were also obtained for cl in melts containing 8 h sub 2 o carbon dioxide diffusivity d sub co sub 2 in nominally dry molten obsidian is similar to previously reported values for a simple melt in the na sub 2 o al sub 2 o sub 3 sio sub 2 system and for dry basalt indicating little effect of melt composition on bulk co sub 2 diffusion three d sub co sub 2 values for hydrous dacite melt are consistent with this lack of a melt composition effect dissolved water however causes an increase of d sub co sub 2 in molten obsidian by about an order of magnitude for each 5 of added water the activation energy of approximately 18 kcal mol is lower by a factor of approximately 3 than that for diffusion in dry basalt in comparison with existing data for diffusion of water in silicic melts at their typical liquidus temperatures d sub co sub 2 is generally lower unless the melt contains more than about 6 dissolved h sub 2 o in which case d sub co sub 2 approximately d sub h sub 2 0 the few data obtained frommore chlorine diffusion reveal the d sub cl is lower by a factor of 5 10 than d sub co sub 2 in the same melt the overall systematics of the new data on dissolved volatile diffusion indicate that diffusional fractionation effects are likely to be most significant in silicic to intermediate magmas having water contents in the 0 4 range less

the 1983 borah peak idaho earthquake and its aftershocks abstract the 28 october 1983 borah peak idaho earthquake m s 7 3 occurred in an area of low historic seismicity within east central idaho along a segment of the lost river fault active during the holocene a dense network of portable short period seismographs up to 45 stations station spacings of 2 to 10 km was installed beginning several hours after the main shock and operated for 22 days in addition to records from the portable instrumentation data from permanent seismograph stations operating in idaho utah montana oregon washington and wyoming provide a good regional data base no foreshock activity above m c coda magnitude 2 0 was detected for the 2 month period preceding the main shock the epicenter of the main shock is 14 km south southwest of the end of the surface faulting this relationship suggests unilateral rupture propagating to the northwest the distribution of 421 aftershocks of m c 2 defines an epicentral pattern 75 km 10 km trending north northwest parallel to the surface rupture but displaced laterally southwest by 5 to 10 km aftershocks extend to depths of approximately 16 km and in the central and southeastern portion of the aftershock pattern define a zone dipping approximately 45 southwest that intersects the surface near the fault scarp the entire aftershock zone as observed during the first 3 weeks was active shortly after the main shock occurred fault plane solutions for 47 aftershocks show predominantly normal faulting with varying amounts of strike slip motion tension axis orientations indicate a dominant extension direction of nne ssw during the aftershock sequence there is considerable diversity among the aftershock focal mechanisms even along the central and southeast portions of the fault where the hypocenters appear to outline the main fault break we therefore interpret most of the aftershocks to represent complex fracturing on subsidiary structures adjacent to the main fault

volatiles in a peralkaline system abiogenic hydrocarbons and f cl br systematics in the naujaite of the ilimaussaq intrusion south greenland agpaitic rocks comprise most of the exposed part of the 1 16 ga old 8 17 km large and about 1700 m thick ilimaussaq intrusion in south greenland within these more than 600 m thick sequence of sodalite rich naujaites mainly sodalite arfvedsonite alkali feldspar nepheline eudialyte aenigmatite are interpreted as a sodalite flotation cumulate sodalites show two to three different zones in cathodoluminescence cl and at least two zones in thin sections the cl zones can be related to chemical differences detectable by electron microprobe whereas relations with optical zonations are less obvious compositional trends in sodalite reflect trends in the evolution of volatile contents in the melt the sodalite at ilimaussaq is almost free of ca and closely corresponds to the pure na cl sodalite endmember with about 7 wt of cl s contents reach up to 0 9 wt cl br ratios range from 500 to 1700 raman spectroscopy shows that s is present as so4 2 in sodalite although sphalerite zns is a stable phase in naujaites peralkalinity and fo2 conditions allow s2 and so4 2 to be present contemporaneously the whole naujaite sequence is divided into two parts an upper part with low homogeneous s contents and cl br ratios in the sodalite cores and a lower part with strongly variable and higher s contents and with cl br ratios which are decreasing downwards the details of the s content and the cl br ratio evolution show that sodalite strongly influences the halogen contents of the melt by scavenging cl and br the naujaites were formed from a highly reduced halogen rich magma in equilibrium with magmatic methane at about 800 c which upon ascent cooling and fractionation exsolved an aqueous fluid phase both fluids were trapped in separate inclusions indicating their immiscibility micrometer sized aegirine crystals and primary hydrocarbon bearing inclusions are abundant in the crystal cores the inclusions were trapped at pressures up to 4 kbar although the emplacement pressure of the intrusion is about 1 kbar this indicates growth of the sodalite during melt ascent and a very effective mechanism of trace element scavenging during sodalite growth sodalite rims are devoid of aegirine or primary hydrocarbon inclusions and probably reflect the emplacement stage

evidence for dynamic coupling of surface processes with isostatic compensation in the lower crust during active extension of western turkey western turkey in the eastern part of the aegean region is extending slowly with extension no faster than 0 5 mm yr 1 across any individual active normal fault up to 15 km of southward extension has occurred in the most active 100 km wide part of this region since 15 ma indicating a typical strain rate of 3 10 16 s 1 rivers carry a sediment flux of 4 106 m3 yr 1 westward to the aegean sea coast with offshore sedimentation at 1 mm yr 1 sediment loading causes coastal areas to subside much faster than would be expected from the extension alone most of this sediment is derived from regional erosion of inland areas to the east at a typical rate of 0 1 mm yr 1 this erosion being isostatically compensated by uplift it is suggested that the lower crustal material displaced by sediment loading near the coast flows east to isostatically compensate the erosion the average eastward velocity of this lower crustal channel flow beneath the aegean coast is estimated as 1 mm yr 1 the maximum velocity is 2 mm yr 1 this case study thus indicates the general point that isostatically compensated erosion and lower crustal channel flow can affect the evolution of sedimentary basins that are surrounded by eroding landmasses factors that are often neglected

forces associated with mantle plumes this study addresses first order aspects of the physics of continental lithosphere extension above mantle plumes developing a testable model that predicts extension rates from flow parameters radial flow in the head of a plume causes a viscous force and uplift over this head causes a buoyancy force which both drive extension the viscous force is roughly proportional to the plume s volume flux and given my best estimates for flow parameters predominates for the most vigorous plumes extension is opposed by a viscous force beyond the plume head and its rate is thus affected by the dimensions of the plate on which this force acts extension rates are 2 mm yr 1 above yellowstone 1mm yr 1 above baikal and 0 7 mm yr 1 above the east african plume volume fluxes for all these plumes are 50 m3 s 1 the extension rates depend mainly on plate dimensions

sulfur speciation oxidation state and sulfur concentration in backarc magmas we have determined the fe3 fe2 ratio s content and the so2 4s2 ratio by sk x ray peak shift for a suite of twelve mid ocean ridge and backarc basin glasses these samples range in oxidation state from two orders of magnitude below to 1 5 orders of magnitude above the ni nio oxygen buffer sulfur speciation in the glasses is strongly dependent on magmatic oxidation state we propose that the solubility mechanism for s in basaltic melts changes over the o2 range which characterizes convergent margin magmas in low o2 sulfide saturated basaltic melts such as most morbs s is present largely as s2 and its concentration is controlled by sulfide melt silicate melt equilibrium and varies positively with o2 at higher o2 s where sulfide melt becomes unstable s concentration is controlled by melt vapor equilibrium and decreases with increasing o2 for the range of o2 s in the back arc basin basalts in this study nno 1 to nno 1 5 s is dissolved in the silicate in both oxidized and reduced forms for the lower o2 end of this range s2 dominates and equilibria involving reduced s species control s melt concentration at higher o2 s the proportion of oxidized s increases and melt vapor equilibria involving these species become more important because s partitions strongly into the vapor phase over the o2 range investigated magmatic degassing may be effective at stripping s from the melt the low s concentrations in island arc and backarc lavas do not necessarily reflect a low s source but rather result from higher o2 in the convergent margin environment

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over quaternary timescales on the basis of the rheological knowledge gained it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust this view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation it is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity and by instances of seasonal seismicity that correlates with seasonal climate human interference in the environment can affect surface loading for instance deforestation for agriculture or urban development can cause increased erosion rates global warming is expected to cause increased storminess and thus increased erosion rates and or global sea level rise the possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment copyright 2006 john wiley sons ltd

natural and human induced landsliding in the garhwal himalaya of northern india after the march 28 1999 garhwal earthquake 338 active landslides including 56 earthquake induced landslides were mapped in a 226 km 2 study area in the garhwal himalaya northern india these landslides mainly comprised shallow failures in regolith and highly weathered bedrock involving avalanches slides and flows the total volume of active 33 landslide debris in the region was estimated to be 1 3 million m including 0 02 million m 2 of the total volume moved during and within a few days of the earthquake the denudation produced by the active landsliding within the study area is equivalent to a maximum landscape lowering of 5 7 mm if active landsliding persists for a duration of between 1 and 10 years then denudation due to landsliding is in the order of 0 6 6 mm a y1 approximately two thirds of the landslides in this region were initiated or accelerated by human activity mostly by the removal of slope toes at road cuts suggesting that human activity is accelerating denudation in this region three ancient catastrophic landslides each involving 1 million m 3 of debris were identified and two were dated to the early middle holocene using cosmogenic radionuclide 10 be and 26 al cosmogenic radionuclide 10 be and 26 al were also used to date strath terraces along the alaknanda river in lower garhwal himalaya to provide an estimate of 4m m a y1 for the rate of regional denudation throughout the holocene natural landsliding therefore contributes 5 50 of the overall denudation in this region and is important as a formative process in shaping the landscape q 2001 elsevier science b v all rights reserved

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

the growth of fault bounded tilt blocks a series of uniformly tilted fault bounded blocks is a common feature in actively extending regions such as the basin and range province if the tilted blocks were produced by rigid domino style rotation one would predict large voids at either end of a series of these blocks using tilt data and a simple flexural calculation we suggest that much of the apparent rigid behavior could also be produced by internal block deformation in our model of normal fault growth isostatic elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults resulting in the appearance of a tilted rigid block we present tilt data sampled at varying distances from several block defining faults within the northeast basin and range province tilt measurements between a series of 30 km spaced block defining faults are found to be uniform while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km using a simple flexural calculation for internal block deformation we show that for this region the patterns of tilt are consistent with a flexural length scale of 8 12 km and deflections of 2 4 km these estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies

cu and fe diffusion in rhyolitic melts during chalcocite dissolution implications for porphyry ore deposits and tektites copper diffusion plays an important role in natural processes such as metal transport during the formation of magmatic hydrothermal porphyry type ore deposits and cu isotope fractionation during tektite formation copper diffusion data in natural silicate melts however are limited in this study chalcocite cu 2 s dissolution experiments were carried out using chalcocite rhyolite diffusion couples to study cu and s diffusion in rhyolitic melts instead of chalcocite dissolution as initially expected our experiments show that cu is transferred from the chalcocite crystal to the rhyolitic melt and fe is transferred from the rhyolitic melt to chalcocite whereas the s concentration profile in the rhyolitic melt is essentially flat from the cu and fe exchange profiles in the rhyolitic melts cu diffusivities and fe diffusivities are obtained and reported copper diffusivity in rhyolitic melts containing 0 10 to 5 95 wt h 2 o at temperatures of 750 to 1391 c and pressures of 0 5 to 1 0 gpa can be described as d cu rhy exp 14 75 0 35 0 23 0 10 w 11647 491 698 117 w t which allows the estimation of an activation energy for diffusion in dry rhyolitic melts to be 96 8 4 1 kj mol in the above equation diffusivity d is in m 2 s t is the temperature in k w is the h 2 o concentration in the rhyolitic melts in wt and all errors reported are at 1 level combining cu diffusion data from this study and previous data in basaltic melt gives a general equation for cu diffusivity in natural silicate melts d cu exp 17 3 0 9 3 8 1 5 si al h 4403 1094 9700 1921 si al h t where si al h is the cation mole fraction of si plus al minus h in the silicate melt on a wet basis iron diffusivities obtained in this study in anhydrous to 6 wt h 2 o rhyolite are combined with previous data to get a general equation for fe diffusion in rhyolitic melts d fe rhy exp 16 1 1 7 19859 2541 1218 135 w t our data demonstrate that cu diffusion is faster than h 2 o or cl in rhyolitic melts containing 6 wt water which indicates that the scavenging and transport of cu by a magmatic volatile phase during formation of porphyry type ore deposits is not limited by diffusion of cu based on our experimental data cu diffusivity is almost four orders of magnitude higher than zn in anhydrous rhyolitic melts which supports the explanation of more diffusive loss of cu leading to more fractionated cu isotopes than zn isotopes in tektites

case history of controlling a landslide at panluo open pit mine in china controlling of landsides safely and economically is a great challenge to mine operators because landslides are major geological problems especially in open pit mines in this paper a case history at panluo open pit mine is presented in detail to share the experiences and lessons with mine operators panluo open pit mine is located in the southwestern fujian province of china it is the largest open pit iron mine in the fujian province and was planned in 1965 and is in full operation from 1978 in july 1990 an earthquake of magnitude 5 3 in taiwan strait and big rainstorms impacted the mine slope causing tension cracks and rather large scale failures and forming a u shaped landslide total potential volume was estimated to be up to 1 0 106 m3 this directly threatened the mine production in order to protect the mine production and the dwellers safety around a dynamic comprehensive method was implemented including geotechnical investigations in situ testing and monitoring stability analysis and many mitigation and preventive measures these measures slowed down the development and further occurrence of the landslide the results showed that the landslides were still active it was slowed with the control measures and moved rapidly with rainfall and mining down however no catastrophic accidents occurred and the pit mining was continued till it was closed at the elevation of 887 m in 2000 as a successful case of landslide control at an open pit mine for 10 years this paper reports the controlling measures in details these experiences of landslide control may be beneficial to other similar mines for landslide control

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

textural characterization major and volatile element quantification and ar ar systematics of spherulites in the rocche rosse obsidian flow lipari aeolian islands a temperature continuum growth model spherulitic textures in the rocche rosse obsidian flow lipari aeolian islands italy have been characterized through petrographic crystal size distribution csd and in situ major and volatile elemental analyses to assess the mode temperature and timescales of spherulite formation bulk glass chemistry and spherulite chemistry analyzed along transects across the spherulite growth front glass boundary reveal major oxide and volatile h2o co2 f cl and s chemical variations and heterogeneities at a 5 m scale numerous bulk volatile data in non vesicular glass spatially removed from spherulitic textures reveal homogenous distributions of volatile concentrations h2o 0 089 0 012 wt f 950 40 ppm and cl 4 100 330 ppm with co2 and s consistently below detection limits suggesting either complete degassing of these volatiles or an originally volatile poor melt volatile concentrations across the spherulite boundary and within the spherulitic textures are highly variable these observations are consistent with diffusive expulsion of volatiles into melt leaving a volatile poor rim advancing ahead of anhydrous crystallite growth which is envisaged to have had a pronounced effect on spherulite crystallization dynamics argon concentrations dissolved in the glass and spherulites differ by a factor of 20 with ar sequestered preferentially in the glass phase petrographic observation csd analysis volatile and ar data as well as diffusion modeling support continuous spherulite nucleation and growth starting at magmatic emplacement temperatures of 790 825 c and progressing through the glass transition temperature range tg 750 620 c being further modified in the solid state we propose that nucleation and growth rate are isothermally constant but vary between differing stages of spherulite growth with continued cooling from magmatic temperatures such that there is an evolution from a high to a low rate of crystallization and low to high crystal nucleation based on the diffusion of h2o across these temperature ranges 800 300 c timescales of spherulite crystallization occur on a timescale of 4 days with further modification up to 400 years growth is prohibitively slow 400 c and would become diffusion reliant selective deformation of spherulites supports a down temperature continuum of spherulite formation in the rocche rosse obsidian indeed petrographic evidence suggests that high strain zones may have catalyzed progressive nucleation and growth of further generations of spherulites during syn and post emplacement cooling

landslides in a densely populated county at the footslopes of mount elgon uganda characteristics and causal factors manjiya county on the ugandan slopes of mount elgon is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century the numerous fatalities and the damage done during the extreme rainfall events of 1997 to 1999 drew attention to this phenomenon in order to better understand the causal factors of these landslides 98 recent landslides in the study area mostly debris slumps were mapped and investigated together they displaced 11 millions m 3 of slope material statistical analysis shows that landslides dominate on steep concave slope segments that are oriented to the dominant rainfall direction northeast and at a relatively large distance from the water divide based on landslide occurrence and impact four different zones can be distinguished within the study area causal factors as well as landslide characteristics differ greatly between the four zones besides the fact that steep slopes high rainfall and typical soil properties and stratification turn manjiya into an inherently unstable area human interference cannot be neglected whereas deforestation has reduced the stability of the shallow soils on the eastern slopes of the study area the excavation of slopes mainly for house building is an important destabilizing factor for the western slopes the growing population density not only increases the risk on damage but hampers the search for solutions for the landslide problem as well d 2005 elsevier b v all rights reserved

sulfur partition coefficient between apatite and rhyolite the role of bulk s content experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt kd s apatite melt at oxidizing conditions crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents 0 15 to 2 wt s at 900 and 1 000 c 200 mpa and log f rm o 2 nno 3 6 the sulfur content in the glass increases with increasing amount of added s anhydrite crystallizes for s added 0 75 wt 0 10 and 0 13 wt so3 in glass at 900 and 1 000 c respectively the amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur the sulfur exchange reaction in apatite is influenced by the bulk composition of the melt e g p content however changing melt composition has only little effect on kd s apatite melt for the investigated rhyolitic composition the kd s apatite melt does not depend directly on temperature decreases from 14 2 to 2 7 with increasing s content in glass from so3 0 03 to 0 19 wt respectively and can be predicted from the following equation ln kd 0 0025 s in melt in ppm 2 9178 the combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high sulfur content in the glass 0 2 wt so3 using s in apatite as proxy for determining s content in melt is promising but additional experimental data are needed to clarify the individual effects of t f rm s 2 and p and ca content in the melt on s partitioning

comment on the southern italy earthquake of 23 november 1980 an unusual pattern of faulting by r s crosson m martini r scarpa and s c key

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

pre eruptive conditions of the huerto andesite fish canyon system san juan volcanic field colorado influence of volatiles c o h s on phase equilibria and mineral composition crystallization experiments at 400 mpa oxidized condition logfo2 nno 1 where nno is nickel nickel oxide buffer and over a range of temperatures 850 950 c and fluid composition xh2oin 0 3 1 have been carried out to constrain the storage conditions of the sulphur rich magma of the huerto andesite an anhydrite pyrrhotite and s rich apatite bearing post fish canyon tuff mafic lava the results are used to evaluate the role of fluids released from the crystallization of magmas such as the huerto andesite on the remobilization of the largely crystallized dacitic fish canyon magma body experiments were performed using the natural andesitic bulk composition with and without added sulphur the presence of sulphur slightly affects the phase equilibria by changing the phase proportions stability fields of plagioclase pyroxenes and ilmenite and also affects the plagioclase composition phase equilibria and mineral composition data indicate that the magma may have contained 4 5 wt water in the melt and that the pre eruptive temperature was 875 25 c assuming that the magma was in equilibrium with a fluid phase the co2 concentration of the melt is estimated to be in the range 2000 4000 ppm at 400 mpa before eruption the andesite had an oxidation state very close to or slightly within the co stability field of anhydrite pyrrhotite at nno 1 1 at these conditions the sulphur content in the melt is 500 ppm assuming open system degassing resulting from continuing crystallization at depth most of the co2 dissolved in the andesitic melt should be released after the crystallization of 10 vol of the magma corresponding to a cooling from 875 to 825 850 c thus the fluids released owing to crystallization processes should be mainly composed of water at temperatures below 825 c

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

diffusion of ar in rhyolite orthoclase and albite composition glasses the diffusivity of ar has been determined in a natural rhyolite obsidian rhy and in glasses of naalsi3o8 ab and kalsi3o8 or composition at temperatures between 400 and 900 c at pressures from 1150 to 3700 bar the observed variations in the ar diffusion coefficient d with temperature can be described by the arrhenius relationshipd d0exp e rt with the following results for pressures from 1100 to 2500 bar d in cm2 s r in cal mole ab d 1 62 10 3 exp 32780rt or d 6 64 10 3 exp 29000rt rhy d 6 86 10 3 exp 34490rt the data although of limited extent also indicate a slight decrease ind with increasing pressure and the calculated activation volume of 36 8 cm3 mole for ar in rhy at 800 c agrees with the idea that the volume change associated with a diffusive jump is similar to the size of the diffusing species comparison of the ar results with cation tracer diffusivities indicates that ar diffusivity is similar to that of rubidium in rhy and ab argon diffusivity is several orders of magnitude slower than h2o att 900 c and exsolution of h2o to form bubbles might leave a residual rhyolitic melt enriched in ar and kr xe due to kinetic effects noble gases show lower activation energies for diffusion than are observed for tracer diffusion of cations with comparable radii a systematic increase in activation energy for diffusion with increasing size of the noble gas atoms and similarities in activation energies in rhyolitic through basaltic melts suggests that in basaltic melts he ne and probably ar can diffuse faster than co2 the major volatile component in basalts in contrast xe and possibly kr due to their estimated high activation energies may diffuse more slowly than co2 at temperatures below 1200 c this implies that kinetic factors may influence noble gas abundance patterns during separation of a co2 rich vapor phase from degasing basaltic magma during ascent

sulfur diffusion in rhyolite melts diffusion rates for sulfur in rhyolite melt have been measured at temperatures of 800 1100 c water contents of 0 7 3 wt and oxygen fugacities from the quartz fayalite magnetite buffer to air experiments involved dissolution of anhydrite or pyrrhotite into rhyolite melt over time scales of hours to days electron microprobe analysis was used to measure sulfur concentration profiles in the quenched glasses regression of the diffusion data in dry rhyolite melt gives dsulfur 0 05 exp 221 80rt which is one to two orders of magnitude slower than diffusion of other common magmatic volatiles such as h2o co2 and cl diffusion of sulfur in melt with 7 wt dissolved water is 1 5 to 2 orders of magnitude faster than diffusion in the anhydrous melt depending on temperature sulfur is known to dissolve in silicate melts as at least two different species s2 and s6 the proportions of which vary with oxygen fugacity despite this oxygen fugacity does not appear to affect sulfur diffusivity except under extremely oxidizing conditions this result suggests that diffusion of sulfur is controlled by one species over a large range in oxygen fugacity the most likely candidate for the diffusing species is the sulfide ion s2 re equilibration between s2 and s6 in oxidized melts must generally be slow compared to s2 diffusion in order to explain the observed results in a silicic melt undergoing degassing sulfur will tend to be fractionated from other volatile species which diffuse more rapidly this is consistent with analyses of tephra from the 1991 eruption of mount pinatubo philippines and from other high silica volcanic eruptions

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

regional structural synthesis wyoming salient of western overthrust belt surface geologic mapping regional and high density reflection seismic data and information from approximately 370 wells have been combined to describe geometrically that area of the western overthrust belt between the snake river plain and the uinta uplift particular care has been taken to verify two dimensional interpretations of multiple thrust sheets by linear restoration by establishing equivalence of pre thrust lengths of affected beds one can gain confidence in interpreted structural geometries as well as generate data in regard to internal shortening and deformation intensity because of irresoluable geometric problems within sections 47 cross sections were developed at roughly 6 mi 10 km spacing to help verify changes in displacement or placement of key st uctural elements displacements of 0 to 32 mi 0 to 51 km have been demonstrated jurassic to paleocene sevier thrusts were active across a previously deformed cratonic shelf terrane and interacted with active structural elements such as the uinta uplift gros ventre range and moxa arch thrusts are progressively younger to the east except for the darby prospect pair in which the darby system is younger

dip analysis as a tool for estimating regional kinematics in extensional terranes abstract in basin analyses that rely almost solely on seismic reflection data to configure the underlying structure it has become common practice to use extensional fault geometries to infer kinematic histories this procedure relies on the existence of fault geometries predicted by ideal orthogonal extension and assumes the structure is well constrained in areas where data are sparse or of equivocal quality this often leads to circular analysis that is ideal orthogonal extension is assumed to have been operative then under constrained fault geometries are mapped according to model predictions fault geometries so derived are subsequently used as evidence that orthogonal extension was operative and that the direction of extension is determinable we develop an alternative tool for inferring kinematics which is independent of fault geometries the method relies on the empirical evidence that the dip of the hangingwall s is systematic and predictable in extensional systems even when fault geometries are non ideal although not without significant limitations dip analysis can provide additional constraints for structural and kinematic interpretations especially where seismic reflection data are the main source of information and dip domains define discrete crustal blocks

analysis and remedies of landslides of cut slopes due to the presence of weak cohesive layers within stronger formations several cases of instability of cut slopes along major highways in jordan were reviewed in this study in some detail emphasis was placed on the amman irbid highway but some cases along the na ur dead sea highway were also reviewed with the aim of establishing a wider database of case studies and examining all possible mechanisms and factors influencing stability the study showed that major cut slope failures were caused by the presence of weak cohesive layers mainly clayey marl interbedded within mostly stronger formations in addition to the steep cutting angles and unfavorable dip of strata combined with relatively high piezometric surface brought about by poor surface and subsurface drainage no remedies were implemented to stabilize major cut slope failures at km 39 200 44 300 and 56 400 along the irbid jerash amman highway the three major cut slope failures require extensive remedial work and probably advanced geotechnology which is expected to be expensive to investigate the influence of various parameters on slope stability several analyses were performed in addition to back analyses to determine shear strength parameters parametric sensitivity studies were also performed on some cases data was obtained from previous investigations by local and international firms and were screened and modified where needed before being used in stability analyses considerable difference between back analysis and test result values for shear strength parameters were observed in many cases failure surfaces and mechanisms were accurately depicted in most cases allowing back analyses to be performed with considerable confidence the effective residual shear strength parameters for clayey marl needed for stability analysis were found to be c r 5 18 kpa and r 13 18 the relation between total annual rainfall and occurrence of landslides was investigated it was shown that all landslides occurred in years of very high rainfall with values always exceeding 400 mm the probability of exceeding the average total annual rainfall was found to be approximately 0 42 for the three gauging stations considered

quaternary deformation of the isthmus and gulf of corinthos greece interdisciplinary data suggest that the quaternary late holocene and present day deformation patterns of the isthmus of corinthos greece are very similar and can be compared to a platelike body under torsion this hypothesis is consistent with the vertical differential motions observed in the adjacent corinthiakos gulf a possible explanation is that the back arc compressional zone is much wider than formerly believed and extends to an area of normal faulting parallel to the direction of the compression this stress field produces a central bulging in the southern coast and a depression in the northern coast of the corinthiakos gulf the easternmost ends of this depression and bulging are the southern and northern parts of the isthmus tilted to the east and to the west respectively

analysis of tilting near normal faults using calculus of variations implications for upper crustal stress and rheology abstract an initially horizontal surface in the surroundings to a normal fault will after extension tilt towards the fault if in the hanging wall or away from it if in the footwall coseismic deformation of these surroundings can be validly modelled as flexure cumulative deformation on geological time scales has been regarded as flexure also but this has led to the apparent paradox that many observed structures require the effective elastic thickness of the brittle upper crust to be much smaller than its seismogenic thickness this article presents a possible alternative that cumulative deformation of the upper crust near some active normal faults may be regarded instead as partitioned into separation of the blocks that comprise their surroundings through the horizontal component of dip slip on the fault and distributed vertical simple shear in their surroundings which causes them to tilt and takes up the vertical slip on the fault a generalized profile of tilting near a normal fault which approximates a parabola can be derived following two assumptions first the brittle layer retains an elastic term in its rheology on geological time scales such that it resists arbitrary length changes second the brittle layer minimizes its overall vertical deflection thus minimizing the buoyancy force acting on it maximum stress and total strain energy associated with observed profiles of tilting are typically smaller for distributed vertical simple shear favouring this mechanism over flexure

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

the effect of nonlinear decompression history on h2o co2 vesiculation in rhyolitic magmas magma ascent rate is one of the key parameters that controls volcanic eruption style tephra dispersion and volcanic atmospheric impact many methods have been employed to investigate the magma ascent rate in volcanic eruptions and most rely on equilibrium thermodynamics combining the mixed h2o co2 solubility model liu et al 2005 with the diffusivities of both h2o and co2 for normal rhyolitic melt zhang et al 2007 behrens and zhang 2009 we model the kinetics of h2o and co2 in rhyolitic eruptions that involve non linear decompression rates our study focuses on the effects of the total magma ascent time the non linearity of decompression paths and the influence of different initial co2 h2o content on the post eruptive h2o and co2 concentration profiles around bubbles within the melt our results show that under most circumstances volatile diffusion profiles do not constrain a unique solution for the decompression rate of magmas during an eruption but instead provide a family of decompression paths with a well defined trade off between ascent time and non linearity an important consequence of our analysis is that the common assumption of a constant decompression rate averaged value tends to overestimate the actual magma ascent time

comparison of the 1959 hebgen lake montana and the 1983 borah peak idaho earthquakes from geodetic observations abstract we deduce the fault geometry coseismic slip and moment for two of the largest historic earthquakes that have occurred in the basin and range of the western united states the m 7 3 1959 hebgen lake montana earthquake and the m 6 9 1983 borah peak idaho event newly augmented data sets of vertical deformation from geodetic leveling and from lake shoreline changes were modeled by simple dislocations in an elastic half space the rms signal to noise ratio is 12 for the hebgen lake data and 38 for the borah peak set the residuals for both models are about twice as large as the noise the hebgen lake earthquake struck on the 15 to 25 km long en echelon hebgen and red canyon faults dipping 45 to 50 and extending to a depth of 10 to 15 km the 7 0 and 7 8 m of dip slip on these faults produced a combined moment of 1 2 10 20 n m the dip of the red canyon fault may decrease slightly with depth in a listric manner abutting the planar hebgen fault at a depth of 8 km in addition up to 1 m of deep slip occurred on the holocene segment of the adjacent madison range fault 10 km west of the hebgen fault the borah peak segment of the lost river fault was found to dip 49 slip of 2 1 m occurred at the south fault end extending to a depth of 14 km 1 4 m of slip occurred at the north end where the fault reached only to 6 km depth a listric fault shape is not permitted by the geodetic data at borah peak both the hebgen red canyon and the lost river faults are high angle and nearly planar despite the much greater age and length of the lost river fault in comparison to the en echelon hebgen faults the chief difference between the earthquakes is the 3 to 4 fold higher slip at hebgen relative to borah peak and all other well studied basin and range shocks thrust faults located close to these active normal faults must either dip steeply at depth or were not reactivated

re evaluation of extension across the pearl river mouth basin south china sea implications for continental lithosphere deformation mechanisms abstract the tertiary pearl river mouth basin in the south china sea is one of relatively few localities where independent estimates of extension from upper crustal normal faulting crustal thinning and subsidence have been compared previous work indicates that these methods all support extension factor 1 8 for this basin however the estimate from faulting used the controversial rigid domino method whereas summing normal fault heaves gives only 1 3 instead this study pursues the possibility that the true value for this basin is 1 3 and the published estimates of extension from subsidence and crustal thinning are exaggerated because they do not take account of outflow of lower crustal material from beneath this basin such outward channel flow will occur when the lithostatic pressure at the base of the brittle upper crust is greater beneath a basin than beneath its surroundings in response to such a pressure gradient material lost from beneath this basin has probably flowed to beneath the adjacent chinese landmass where it isostatically compensates the erosion that has supplied much of the basin s sediment

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

an elastic rebound model for normal fault earthquakes a viscoelastic finite element method is used to formulate an elastic rebound model for normal fault earthquake cycles model generated displacements correlate well with geodetic survey data collected before and after the 1954 m 7 1 fairview peak nevada and the 1959 m 7 1 hebgen lake montana earthquakes model coseismic deformation results in an uplift of the footwall block and a depression of the hanging wall block as has been reported by savage and hastie 1966 the interseismic phase of the deformation is characterized by a regional doming of the crust in the vicinity of the modeled normal faults doming observed before and after and adjacent to the faults which ruptured during the hebgen lake earthquake indicate that areas which are experiencing doming may be the future sites of normal fault earthquakes two areas which are presently experiencing crustal doming and are in the vicinity of a normal fault are the socorro new mexico and diablo plateau texas brown et al 1978 regions the interseismic doming will not occur if the modeled fault ruptures through the entire lithosphere if a single normal fault is active then model generated coseismic and interseismic deformations result in sum to a tilt block topography if two normal faults are active one master fault and a minor fault which dips toward the master fault then the resultant deformation is a horst and graben type of topography the rate at which the doming proceeds is primarily a function of the seismic stress drop and the effective viscosity of the asthenosphere doming rates following the hebgen lake earthquake indicate an asthenospheric viscosity of about 2 1021 p model recurrence intervals for the fairview peak and hebgen lake earthquakes are on the order of 103 yr

deformation of the ne basin and range province the response of the lithosphere to the yellowstone plume summary tectonic deformation in the ne basin and range province of the western united states is concentrated in two zones the n s trending northern part of the intermountain seismic belt in northern utah se idaho and sw wyoming and the e w trending central idaho seismic zone which converge at yellowstone in nw wyoming accepting the popular view that the yellowstone volcanic field is above an upwelling plume from the deep mantle i explore the possibility that deformation of the brittle upper crust in these two seismic zones may be caused by return flow from this plume this return flow is assumed sheared sw in the direction of motion of the north american plate relative to yellowstone the snake river plain srp a linear outcrop of neogene and quaternary basalt that trends sw from yellowstone for more than 400 km bisecting the angle between the two seismic zones may be a trail formed as the plate moves sw across the upwelling plume beyond 150 km from yellowstone slip vectors on active normal faults in both deforming zones are oriented inwards at 45 towards the sw azimuth along the srp normal slip rates on these faults are typically 1 mm yr 1 implying extensional strain rate 10 15 s 1 proportions of normal slip and strike slip suggest faults in the intermountain seismic belt are rotating anticlockwise at 2 myr 1 around vertical axes and faults in the central idaho seismic zone are rotating clockwise at similar rates within 100 km of yellowstone observed sense of rotation around vertical axes in both zones appears reversed tilt rates of hanging wall beds suggest most faults in both zones are rotating at 2 myr 1 also 10 15 s 1 around horizontal axes oriented nw the relative size of rotation rate around vertical axes and horizontal extensional strain rate is shown to imply that velocity in the underlying deforming fluid is small in the direction perpendicular to the axis of the srp in an initial model this velocity is set to zero enabling the two dimensional pattern of flow at the horizontal upper boundary of this deforming fluid to be solved straightforwardly this approximation enables observed rates and senses of horizontal extension and rotation around a vertical axis to be explained as consequences of the pattern of horizontal gradients of velocity parallel to the axis of the srp in the deforming fluid beneath the brittle layer a refinement suggests that velocity perpendicular to the srp near the upper boundary of the deforming fluid is small but inward towards the srp from both sides and is accompanied by downwelling beneath the srp beyond 100 km sw of yellowstone this pattern of flow will act to move magma in the uppermost mantle beneath the srp from its sides it may thus reconcile petrological observations that srp basalts do not show deep mantle characteristics expected had they been extruded from the yellowstone plume with the existence of this plume nearby conservation of angular momentum around horizontal axes perpendicular to the srp for the combined system of the plume interacting with the north american plate leads to the deduction that the plume radius is 50 km consistent with results of other investigations and its upwelling velocity is 60 mm yr 1

the solubility of sulphur in hydrous rhyolitic melts experiments performed at 2 kbar in the temperature range 800 1000 c with fo2 between nno 2 3 and nno 2 9 where nno is the nickel nickel oxide buffer and varying amounts of sulphur added to hydrous metaluminous rhyolite bulk compositions were used to constrain the solubility of sulphur in rhyolite melts the results show that fs2 exerts a dominant control on the sulphur solubility in hydrous silicate melts and that depending on fo2 a rhyolitic melt can reach sulphur contents close to 1000 ppm at high fs2 at fo2 below nno 1 the addition of iron to a sulphur bearing rhyolite magma produces massive crystallization of pyrrhotite and does not enhance the sulphur solubility of the melt for a given fo2 the melt sulphur content increases with fs2 for fixed fo2 and fs2 temperature exerts a positive control on sulphur solubilities at least for fo2 below nno 1 the mole fraction of dissolved sulphur exhibits essentially linear dependence on fh2s at low fo2 and although the experimental evidence is less clear on fso2 at high fo2 the minimum in sulphur solubility corresponds to the redox range where both fh2s and fso2 are approximately equal a thermodynamic model of sulphur solubility in hydrous rhyolite melts is derived assuming that total dissolved sulphur results from the additive effects of h2s and so2 dissolution reactions the model reproduces well the minimum of sulphur solubility at around nno 1 in addition to the variation of the sulphide to sulphate ratio with fo2 a simple empirical model of sulphur solubility in rhyolitic melts is derived and shows good correspondence between model and observations for high silica rhyolites

sulfur isotopic systematics of granitoids from southwestern new brunswick canada implications for magmatic hydrothermal processes redox conditions and gold mineralization bulk 34srock values sulfur contents and magnetic susceptibility were determined for 12 gold related granitoid intrusions in southwestern new brunswick the canadian appalachians the sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed this new dataset was used to characterize two distinctive groups of granitoids 1 a late devonian granitic series gs and 2 a late silurian to early devonian granodioritic to monzogranitic series gms the gs rocks have a large range in 34s values of 7 1 to 13 with an average of 2 2 5 0 1 low bulk s contents 33 to 7 710 ppm and low magnetic susceptibility values 10 3 si indicative of oxidized magnetite series granites the exceptions for the gms rocks are the lake george granodiorite and tower hill granite that display reduced characteristics which may have resulted from interaction of the magmas forming these intrusions with graphite or organic carbon bearing sedimentary rocks the bulk 34s values and s contents of the gms rocks are interpreted in terms of selective assimilation fractional crystallization safc processes degassing processes may account for the 34s values and s contents of some gs rocks the characteristics of our sulfur isotope and abundance data suggest that mineralizing components s and au in intrusion related gold systems are dominantly derived from magmatic sources although minor contaminants derived from country rocks are evident in addition the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the 34srock value of the whole rock sample and the 34ssulfide or 34ssulfate value of sulfide and or sulfate mineral in the sample on the basis of s isotope fractionation and mass balance under the condition of magmatic equilibrium this may be used to predict the speciation of sulfur in granitic rocks which can be a potential exploration tool for intrusion related gold systems

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

in situ xanes study of the influence of varying temperature and oxygen fugacity on iron oxidation state and coordination in a phonolitic melt iron oxidation state and environment in magmas affect their phase diagram and their properties including viscosity and density which determine magma mobility and eruptive potential in turn magma composition pressure temperature and oxygen fugacity affect iron oxidation state and coordination potentially leading to complex feedbacks associated with magma ascent degassing and eruption while equilibrium experiments and models have led to a deep understanding of the role of iron in melts our knowledge of the effects of disequilibrium processes on iron oxidation state and its structural role in lavas and magmas remains limited accordingly we performed a series of dynamic disequilibrium experiments on a natural melt composition a phonolite lava from erebus volcano antarctica at atmospheric pressure in which oxygen fugacity and temperature were controlled and varied during the experiments we continuously measured iron oxidation and coordination using fe k edge dispersive x ray absorption spectroscopy xas we found that iron oxidation state changes in the phonolite melt are reversible and well reproduced by existing models changes in iron oxidation state are driven by joint diffusion of alkali cations and oxygen anions at magmatic temperatures 1000 c for erebus phonolite however redox diffusion timescales are too slow for any significant oxygen exchange with the atmosphere at the lava air interface or via air entrainment turning to iron coordination while fe 2 and fe 3 are present mostly in an average five fold coordination complex coordination variations decoupled from redox changes were detected the data suggest transitions between fe 3 in four fold and six fold coordination prior to reduction or as a consequence of oxidation this questions the possible implication of fe coordination changes in triggering crystallisation of magnetite nanolites upon magma ascent and through such crystallisation events in promoting magma explosivity

sulfur evolution of the 1991 pinatubo magmas based on apatite abstract using electron microprobe emp and laser ablation inductively coupled plasma mass spectrometry la icp ms to collect major and rare earth elements ree respectively from apatites from the 1991 mt pinatubo juvenile eruption products we have determined that two statistically distinct populations of apatite exist one population crystallized from the juvenile basaltic melt basalt apatites and the other population crystallized from the main dacitic magma body silicic apatites both populations contain high s apatites 0 7 wt so3 apatite has previously been shown to be a potential monitor for magmatic sulfur contents via numerous proposed coupled substitutions of p5 for s6 however simple apatite melt partitioning cannot account for high s silicic apatites which grew from a silicic melt with an apparent maximum s concentration of 80 ppm disparate apatite morphology i e skeletal and acicular for basalt apatites and euhedral for silicic apatites as well as compositional evidence reveal that high s silicic apatites were not inherited from the juvenile basalt during mingling mixing prior to eruption sulfur gain from neighboring anhydrite phenocrysts can also be ruled out as a source of high sulfur emp sulfur mapping of silicic apatites shows highly irregular patterns of sulfur enrichment that do not correspond with adjacent anhydrite and can be found within apatites hosted by other minerals e g hornblende and fe ti oxides with these data in mind we propose high s silicic apatites from pinatubo and other sulfur rich systems achieved elevated sulfur concentrations during high sulfur fluxing events that originated from underplated basalt during degassing of a so2 rich fluid phase that basalts were indeed sulfur rich and oxidized is here indicated by high s contents of apatites growing in basalt the predominant location of s rich areas of silicic apatite is crystal interiors of apatite inclusions in other mineral phases while large apatite microphenocrysts surrounded by groundmass glass have low sulfur contents this is evidence for placing sulfur fluxing periods long before events that ultimately led to the 1991 eruption

halogen diffusion in magmatic systems our current state of knowledge diffusion of halogens has the potential to influence petrogenetic processes in magma chambers and conduit degassing processes this contribution reviews our current state of knowledge concerning halogen diffusion and the influence of halogens on the diffusion of major elements in silicate melts the addition of halogens to silicate melts at common natural concentration levels will have little effect on the diffusion of major elements however the differences between the diffusivity of water the diffusivities of halogens and the diffusivity of sulfur are significant enough that during melt inclusion entrapment or during rapid bubble or crystal growth diffusive fractionation between water and the halogens and between halogens and sulfur are expected to occur and can influence the compositions of melt inclusions crystals and volcanic gases

mechanism of reactivated badu landslide in the badu mountain area southwest china this paper presented the reactivated mechanism of badu landslide according to site investigations monitoring finite element and limit equilibrium analyses finite element analysis incorporating a stability analysis with the finite element stress based method revealed a large railway cut triggered a localized slide in the upper part of badu landslide rather than a global failure and piles in three rows were effective in stabilizing the reactivated zone monitoring results and the limit equilibrium analysis showed that the landslide underwent multi instabilities rather than a global failure due to a rise in groundwater table in rainy season the mechanism of reactivated badu landslide was finally proposed i e grading creeping sliding mechanism which helped designers to propose the most suitable mitigation measures to stabilize the landslide

sulfur isotope behavior during metamorphism and anatexis of archean sedimentary rocks a case study from the ghost lake batholith ontario canada abstract recycling of surface derived sulfur into the deep earth can impart distinct sulfur isotope signatures to magmas the details of sulfur transfer from sedimentary rocks to magmas and ultimately igneous rocks through metamorphism and devolatilization and or partial melting however is difficult to trace to understand this process in detail we studied multiple sulfur isotope compositions of sulfides in the archean c 2685 ma ghost lake batholith glb and its surrounding host metasedimentary rocks of the superior craton ontario canada by high spatial resolution secondary ion mass spectrometry complemented by high precision gas source isotope ratio mass spectrometry measurements the glb comprises strongly peraluminous biotite cordierite biotite muscovite and muscovite garnet tourmaline granites to leucogranites which are thought to represent the partial melts of surrounding metagreywackes and metapelites the metasedimentary rocks display a range of metamorphic grades increasing from biotite chlorite 280 380 c at 5 km away from the glb to sillimanite k feldspar grade 660 c immediately adjacent to the batholith thus providing a natural experiment to understand sulfur isotope variations from low to high grade archean sedimentary rocks as well as granites representative of their partial melts we find that metasedimentary sulfide 34 s values increase with progressive metamorphism at most 2 3 from 1 up to 1 to 2 an increase in 34 s values in pyrrhotite during prograde metamorphism can be explained through rayleigh fractionation during pyrite desulfidation reactions pyrite from all but one of the granite samples preserve 34 s values similar to that of the high grade metasedimentary rocks indicating that partial melting did not result in significant fractionation of 34 s the exception to this is one granite sample from a part of the batholith characterized by abundant metasedimentary inclusions this sample contains pyrite with heterogeneous and low 34 s values down to 16 which likely resulted from incomplete homogenization of sulfur between the granitic melt and metasedimentary inclusions small several tenths of a permil mostly positive 33 s are observed in both the metasedimentary rocks and granites our results suggest that archean strongly peraluminous granites could be a high fidelity archive to quantify the bulk sulfur isotope composition of the archean siliciclastic sediments further our findings indicate that subduction of reduced sulfur bearing sediments in the archean with 34 s at or near 0 should result in release of sulfur bearing fluids in the mantle wedge with similar values within a few permil s mif if initially present in archean surface material may be preserved during this process however the absence of s mif in igneous rocks does not preclude assimilation of archean sedimentary material as either s mif may not be originally present in the archean sedimentary sulfur and or homogenization or dilution could obscure any s mif originally present in assimilated archean sediments

fault and bed rotation during continental extension block rotation or vertical shear abstract for almost a century the view has existed that the tilting of blocks between closely spaced planar normal faults is rigid body rotation this interpretation requires only simple geometry and has consequently found widespread application however it is not consistent with the deformation expected around normal faults given the present knowledge of stress fields and rheology in basement in the brittle upper crust which is better regarded instead as distributed vertical simple shear rigid body rotation and vertical shear involve different relations between fault and bed tilting and thus predict different initial fault dips for particular present day dips of faults and beds these two schemes also predict different amounts of extension and it is consequently important to establish which is correct with this aim in mind we examine normal faults associated with neogene extension in western turkey and the western united states and with mesozoic extension in the north sea except where extension and the associated tilting are minimal rigid body rotation predicts unrealistically steep initial fault dips some extensional basins also exhibit reversals of normal fault polarity and tilt polarity of beds which are incompatible with rigid body rotation we therefore conclude that the general cause of the tilting is vertical shear not rigid body rotation this has three main observational consequences first the heave on any normal fault equals the amount of extension across it second no feature near a normal fault can rotate through the vertical a normal fault thus cannot rotate through the vertical and appear as a reverse fault third any initially vertical feature near a normal fault will remain vertical a vertical dyke in the tilted surroundings of a normal fault is thus not necessarily younger than the extension that caused the tilting

volatile heavy metal mobility in silicate liquids implications for volcanic degassing and eruption prediction abstract the volatilization of cd re tl pb sb and te from melts in the system cao mgo al 2 o 3 sio 2 cmas and na 2 o mgo al 2 o 3 sio 2 nmas has been investigated at 0 1 mpa and 1200 1350 c experiments were conducted in air using metal doped melts in pt crucibles analysis of quenched glasses by laser ablation inductively coupled plasma mass spectrometry la icp ms normal to the melt gas interface produced concentration profiles for cd re tl pb sb and te to which a semi infinite one dimensional diffusion model could be applied to extract diffusion coefficients d the melt was also doped with cu zn in mo sn and w but concentration profiles for these metals did not develop in the cmas composition at 1300 c the fastest diffusing element was cd having a log d cd 6 5 0 2 the slowest element was re with log d re 7 5 0 3 diffusivities of sb te pb and tl have intermediate values where log d sb 7 1 0 1 log d te 7 2 0 3 log d pb 7 1 0 2 log d tl 7 0 0 2 cm 2 s in the nmas composition log d re 6 5 0 2 log d sb 6 0 0 2 log d pb 6 1 0 1 log d tl 5 8 0 2 cm 2 s values for cd and te were not determined differences in diffusivity of volatile heavy metal ions to a melt gas interface lead to significant fractionation between these metals in magmas during degassing given the observed differences in cd and re diffusivities in the cmas composition we predict an increase in the normalized cd re ratio in the gas phase with increasing bubble growth rate monitoring of the cd re ratios in aerosols from degassing volcanoes may provide a tool for predicting volcanic eruption

diffusion and redox reactions of sulfur in silicate melts although large scale transport in magmas is usually controlled by convection diffusion of sulfur in silicate melts nevertheless plays a crucial role in the kinetics of various magmatic processes the most important process is probably the degassing of magmas and melts initiated by an oversaturation of the melt with respect to dissolved volatiles such oversaturation can be caused in nature i e by decompression when a magma ascends to the earth surface but the degassing of melts is also of major interest for technical applications e g during fining of melts in industrial glass production the kinetics of volcanic eruptions and the fining of glass melts are basically controlled by the dynamics of bubble nucleation and growth and these properties are strongly affected by the diffusion of volatiles from the melt into bubbles nemec 1980a b sparks et al 1994 muller simon 2011 this volume hence understanding the diffusion of volatiles in melts provides a necessary tool for modeling bubble nucleation and growth however the diffusivities of volatiles such as h2o co2 so2 and h2s in the melt do not only affect the degassing rate they may also cause a fractionation of volatiles between gas phase and melt as well due to different diffusivities for instance in hydrous magmas the diffusion of h2o is usually much faster than co2 and sulfur diffusion baker et al 2005 zhang and ni 2010 so rapid disequilibrium removal of bubbles from the melt may cause an artificial enrichment of some components in the bubbles other processes which may be governed by sulfur diffusion in the melts are the dissolution and precipitation of minerals in glass manufacturing crucial problems are the kinetics of dissolution of the raw materials in the melt batch and of

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

gold contents of sulfide minerals in granitoids from southwestern new brunswick canada the abundance of gold and selected trace elements in magmatic sulfide and rock forming minerals from silurian devonian granitoids in southwestern new brunswick were quantitatively analyzed by laser ablation inductively coupled plasma mass spectrometry gold is mainly hosted in sulfide minerals i e chalcopyrite pyrrhotite and pyrite in some cases perhaps as submicron inclusions nanonuggets gold is below detection 0 02 ppm in major rock forming minerals i e plagioclase k feldspar biotite hornblende and muscovite and oxides i e magnetite and ilmenite gold distribution coefficients between sulfide and granitoid melt are calculated empirically as d text cpy melt text au 948 pm 269 text d text po melt text au 150 pm 83 text and d text py melt text au 362 pm 96 this result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity gold behaves incompatibly prior to the formation of sulfide liquids or minerals but it becomes compatible at their appearance gold would be enriched in sulfur undersaturated granitoid magmas during fractionation partitioning into evolved magmatic fluids and favoring the formation of intrusion related gold deposits however gold becomes depleted in residual melts if these melts become sulfur saturated during differentiation leading to gold precipitation in the early sulfide phases of a granitoid suite late stage cl bearing magmatic hydrothermal fluids with low ph and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon bearing sediments may scavenge gold from early sulfide minerals if a significant amount of gold produced in this manner is concentrated in a suitable geological environment e g shear zones or fracture systems intrusion related gold deposits may also be generated exploration for intrusion related gold systems should focus on the areas around evolved phases of granitoid suites that remained sulfur undersaturated for sulfur saturated granitoid suites the less differentiated phase and associated structures are the most prospective targets

open system degassing of sulfur from krakatau 1883 magma we present the first sulfur and oxygen isotopic data for tephra from the catastrophic 1883 eruption of krakatau sulfur isotopic ratios in unaltered krakatau tephra erupted august 26 27 1883 are markedly enriched in 34s relative to mantle sulfur high 34s values of 6 3 to 16 4 can best be explained by open system or multi stage degassing of so2 from the oxidized rhyodacitic and gray dacitic magmas with 34s enrichment of so2 4 remaining in the melt lower whole rock 34s values of 2 6 and 4 0 in two oxidized gray dacitic samples indicate more primitive subarc mantle sulfur in the 1883 magma chamber initial 34s of the rhyodacitic magma was probably in the 1 5 to 4 0 range and similar to 34s values measured in arc volcanic rocks from the mariana arc

neogene evolution of the denizli region of western turkey the denizli region contains one of the easternmost neogene sedimentary basins in the part of western turkey that takes up ssw extension this isolated active normal fault zone which contains closely spaced en echelon normal fault branches is investigated using field measurements of fault exposures and tilted sediments and seismological observations as a case study to address its style of extension the denizli basin is no more than 1 km thick and has accommodated up to 4 km of extension substantial 20 sediment dips are readily explicable assuming extension is accompanied by distributed vertical simple shear with initial and present day dips of the main normal faults that control extension most likely 54 57 and 45 50 other aspects of the form of this basin require regional uplift at 0 1 mm yr 1 providing the first indication of major tectonic elevation changes in this actively extending region that are not directly related to throw on normal faults

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

anhydrite pyrrhotite and sulfur rich apatite tracing the sulfur evolution of an oligocene andesite eagle mountain co usa abstract the oldest known occurrence of magmatic anhydrite in a shallow sub volcanic rock is at the oligocene andesitic eagle mountain volcanic center huerto formation san juan volcanic field which immediately postdates the pyrrhotite bearing fish canyon tuff estimates of intensive parameters derived from the compositions of coexisting minerals hornblende plagioclase anhydrite pyrrhotite s rich apatite augite hypersthene feti oxides indicate that the eagle mountain magma was wet oxidized and s rich it was much like k rich andesitic and dacitic anhydrite bearing magmas recently erupted from the subduction related volcanoes el chichon mt pinatubo and lascar although the oligocene geodynamic setting of the san juan volcanic field is poorly constrained and its enormous volume is not easily reconciled with an arc setting the eagle mountain occurrence emphasizes how closely some of its magmas resemble those from active continental margin arcs s rich magmas similar to the eagle mountain andesite also may have contributed to the formation of some hydrothermal ore deposits of the san juan volcanic field

landslides in sado island of japan part i case studies monitoring techniques and environmental considerations abstract a sufficient knowledge on the kinematics and development of landslides helps to adopt proper measures that can be used to protect slopes and the environment in general this can be achieved by adequate monitoring programs this paper presents the findings of intensive monitoring activities carried out on shiidomari and katanoo landslides found in sado island of japan more than one year of observation of the two landslides allowed defining some peculiar futures of their kinematics and style of development the problem of slope instability in the two areas is generally accredited to various factors but both landslides were triggered by heavy rainfalls and snowmelt because of the outline of the area and the presence of relict topographic features the shiidomari landslide is considered to be a large scale reactivation of old slope failures the katanoo landslide is however a first time case geophysical investigations and drilling activities in shiidomari indicated the presence of two slip planes the deepest 80 100 m of these is controlled by existing lineaments monitoring data suggests that the body of the landslide has subsided as much as 1 16 m just below the main scarp but a centimeter in the central region the toe sector also experienced a significant amount of subsidence but this was counter balanced by an uplift on the opposite side of the landslide hence the landslide seems not any more active along the deepest slip surface although it may extend upward and define a series of shallow shear planes around the crown in the case of katanoo the landform characteristics differential weathering the road cut and groundwater fluctuations appeared to contribute much to determine the exact location of the landslide extensional cracks that preceded the landslide can be related to heavy rainfalls and the cold and warm cycles thereafter subsurface investigations and monitoring works indicated that the landslide has two slide blocks with different slip planes during the observation period the upper part of the landslide responded more effectively to rainfall and snowmelt than the middle and lower sections the corresponding movements however appeared to settle about three months after failure there were also little strain transmissions in boreholes and no significant change in the characteristics of the landslide the kinematics of deformation of many of the slopes in sado island resembles that of shiidomari landslide but mass movements along highways and mountain roads are usually similar to katanoo landslides of the type like shiidomari may not show sudden and drastic failures but are usually long lasting and can reactivate repeatedly along new shallow shear planes monitoring works and long term supervisions in these types of landslides are useful to identify impending failures and take the right measures before they brought about large scale destruction to the environment

constraints on dacite magma degassing and regime of the june 15 1991 climactic eruption of mount pinatubo philippines new data on melt and crystal inclusions in quartz abstract to better constrain processes that operated prior to and during the dacite magma eruption of mount pinatubo on june 15 1991 primary inclusions found in quartz phenocrysts of white dacite pumice have been studied by combining micro analytical techniques with homogenisation experiments inclusion morphology and composition before and after homogenisation experiments performed in gas pressure vessels at 760 780 c and 185 200 mpa distinguish two stages of magma degassing during the first stage which occurred prior to eruption the host quartz trapped a fluid saturated rhyolitic melt with an average of 78 6 0 7 wt sio2 12 4 0 5 wt al2o3 and 7 0 3 wt h2o and a water rich fluid microanalyses on the quartz hosted multiphase and crystal inclusions indicate that the dacite magma crystallised at 750 5 c an oxygen fugacity of 1 5 1 7 log fo2 units above the nno nickel nickel oxide buffer and a total pressure of 190 50 mpa corresponding to depths from 4 to 7 km in the second stage which corresponds to the magma eruption and decompression to 12 23 mpa volatile exsolution provoked decrepitation of unstable melt inclusions and the loss of initially high h2o contents from all 80 m glassy and hourglass inclusions to 1 7 0 3 wt h2o the exsolution of 5 wt h2o from the dacite magma might have occurred at depths of 300 700 m due to vent blockage caused by the sudden collapse of the conduit walls these conditions of the climactic eruption in combination with an extreme mass eruption rate reaching 2 109 kg s 1 could create oscillations between convecting and collapsing columns which explains the alternation of pyroclastic flow deposits with plinian pumice fall deposits reported in previous studies

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment

toward a quantitative model for the formation of gravitational magmatic sulfide deposits abstract a preliminary quantitative model for the formation of magmatic sulfide deposits through gravitational sulfide droplet settling is developed the model incorporates thermodynamic consideration of the oversaturation of sulfide liquid from a silicate melt and the coupled growth kinetics and settling dynamics of sulfide droplets the conditions for the sulfide droplets to have enough time to grow and settle to form a sulfide liquid layer at the bottom of a magma chamber are referred to as the necessary criteria for sulfide ore formation simulations are carried out for dry etna basaltic melt because their melt viscosity and sulfur diffusivity have been measured so that the simulations are more realistic rather than parametric furthermore the effects of empirical nucleation rate and condition and of the variation of solubility viscosity and diffusivity have been parametrically evaluated the simulations show that for a given magma containing about 0 1 to 0 3 wt sulfur sulfide melt layer can form for realistic magma body size with cooling time of 1000 yr or more and realistic solubility viscosity and diffusivity the ability of the sulfide melt to collect ore elements depends critically on the diffusivity of individual ore elements when the diffusivity of an ore element is similar to or greater than that of sulfur near equilibrium partitioning is reached when the diffusivity of an ore element is much smaller than that of sulfur which is often the case for trivalent and tetravalent ions the concentration of the element in the sulfide melt would be far below the equilibrium concentration it is hoped that the model will help both researchers and exploration geologists