vp vs distribution in the northern taiwan area implications for the tectonic structures and rock property variations abstract the ratio of compressional wave velocity vp to shear wave velocity vs is often indicative of lithology and rock conditions in this study we determine the vp vs characteristics for the different tectonic features in northern taiwan and quantify the crack density and saturation by using the ob74 method the result shows that the highest vp vs values are located beneath the western foothills at depths between 4 and 21 km these vp vs highs are simultaneously characterized by low vp and low vs suggesting the presence of fluids the average crack density and saturation for each depth can reach as high as 25 and 91 at depths of 7 and 11 km respectively this distribution could be caused by the presence of less compacted sediments within the foreland basin and the progressive convergence of crustal faults with depth as the shallow portion of the foreland basin is highly fractured fluids could infiltrate into deeper parts to create a highly saturated environment however when the depth is deeper than 11 km the high crack density and saturation area migrate from the west to the east of the shanchiao fault this observation may indicate the presence of a preexisting syn rift basin buried at depth during the collision in the ilan plain the highest crack density and saturation are observed in its northeastern portion at a depth of 4 km with values of 17 1 and 60 3 respectively however slightly high saturation values spread throughout the plain at a depth of 15 km which may indicate a possible fluid conduit from a deep hot rock body to the surface and could be applied toward studies on geothermal fluid activity

three dimensional p and s velocity structure in the coalinga region california the coalinga earthquake sequence of 1983 provided a unique opportunity to perform a three dimensional velocity and hypocenter inversion in an area of complex three dimensional structure dominated by folding and blind thrusts additionally since other varied geological and geophysical studies have been completed in this area the three dimensional inversion solution could be compared to other interpretations inversion of 7696 p and 1511 s first arrivals from earthquakes and 696 p first arrivals from refraction shots produced a three dimensional velocity model with grid spacing of 1 2 km in the hypocentral area the overall shape and location of velocity features correspond well to the mapped surface geology the three dimensional inversion yields details of folds where the resolution is good and the general shape where resolution is lower the amounts of structural relief inferred for the local folds are similar to values inferred from geologic data the three dimensional velocity solution has several distinctive features there is a linear high velocity body 6 1 6 5 km s about 25 km long from 6 to 8 km depth that may represent a fragment of coast range ophiolite a shallow low velocity zone lvz which extends for 20 km along the fold axis at about 6 km depth and correlates with lvzs observed in both the refraction and the reflection data may indicate high pore pressure caused by lateral compressive strain deeper lvzs occur within inferred franciscan material and are characterized by horizontal or southwest dipping zones of varied thickness 4 8 km wide and 5 10 km long these lvzs may represent multiple thrust faults their locations and geometry are consistent with thrust faults inferred with seismic reflection data the three dimensional velocity solution compares well to prior two dimensional seismic reflection and refraction models and observed gravity the shape of the inferred sedimentary section agrees well with the reflections from the cenozoic strata compared to the refraction model the three dimensional solution has similar velocities and similar locations of velocity features but is more detailed in the hypocentral zone where it uses more data the gravity computed from the three dimensional velocities is similar to the observed gravity in both shape and amplitude both a simple one dimensional initial model and a complex initial model derived from the refraction interpretation were tried a simple starting model gave the best results the s velocity solution has different resolution than the p velocity solution because it uses a different set of stations and it has lower resolution because it uses fewer arrival times while the general patterns of velocity variation are similar for both vp and vs the vs solution tends to have more smearing of velocity features and can have somewhat different locations of velocity features

neotectonic rotations in the orava nowy targ intramontane basin western carpathians an integrated palaeomagnetic and fractured clasts study abstract the objectives of this contribution are 1 to promote the application of fractured clasts analysis in conglomerates for regional stress reconstructions and 2 to advance reconstruction of the western carpathians structural development our results show that the neogene fill of the orava nowy targ intramontane basin underwent ccw rotation of about 30 we infer that the rotation terminated after 8 ma and was related to shift along nw se to nnw sse trending faults at the ne termination of the sinistral mur ilina fault zone our results show that fractured clasts analysis can be good tool for regional tectonic reconstructions the tool is especially useful when other tectonic tools are scarce or absent results of our palaeomagnetic study and fractured clasts analysis verify and supplement each others in the studied case palaeomagnetic results allow to distinguish between regional stress field rotation and rotation of the orava nowy targ basin neogene fill whereas results of fractured clast analysis help to constrain the age of rotation

p s velocity and vp vs ratio beneath the toba caldera complex northern sumatra from local earthquake tomography summary in this paper we investigate the crustal and uppermost mantle structure beneath toba caldera which is known as the location of one of the largest cenozoic eruptions on earth the most recent event occurred 74 000 yr bp and had a significant global impact on climate and the biosphere in this study we revise data on local seismicity in the toba area recorded by a temporary passcal network in 1995 we applied the newest version of the lotos 07 algorithm which includes absolute source location optimization of the starting 1 d velocity model and iterative tomographic inversion for 3 d seismicp s or thevp vs ratio and source parameters special attention is paid to verification of the obtained results beneath the toba caldera and other volcanoes of the arc we observe relatively moderate for volcanic areas negative p and s velocity anomalies that reach 18 per cent in the uppermost layer 10 12 per cent in the lower crust and about 7 per cent in the uppermost mantle much stronger contrasts are observed for the vp vs ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies at a depth of 5 km beneath active volcanoes we observe small patterns 7 15 km size with a high vp vs ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes in the mantle wedge we observe a vertical anomaly with low p and s velocities and a high vp vs ratio that link the cluster of events at 120 140 km depth with toba caldera this may be an image of ascending fluids and melts released from the subducted slab due to phase transitions however taking into account poor vertical resolution these results should be interpreted with prudence although the results show clear signatures that are quite typical for volcanic areas low velocity and high vp vs ratio beneath volcanoes we do not observe any specific features in seismic structure that could characterize toba as a super volcano

seismic tomography of the north anatolian fault new insights into structural heterogeneity along a continental strike slip fault major funding was provided by the uk natural environment research council nerc under grant ne i028017 1 equipment was provided and supported by the nerc geophysical equipment facility seis uk this project is also supported by bogazici university scientific research projects bap under grant 6922 and turkish state planning organization dpt under the tam project number 2007k120610

estimation of magma depth for resurgent domes an experimental approach post collapse resurgence is a phenomenon affecting many calderas attributed to a renewed magma rise the process is still poorly understood and the associated source parameters remain poorly constrained a set of experiments has been conducted to gain insight into the structural evolution of caldera resurgent domes a sand plaster mixture was chosen as an analogue for the brittle pile of volcanic rocks and silicone putty simulates the ductile behavior of the intruding magma resurgence is driven by the vertical uplift of the silicone with variable shape and depth similarity conditions are achieved through eight dimensionless numbers which are of the same order of magnitude in both nature and experiments results show that extension due to doming is in many cases accommodated by one axial graben opposite master faults of this graben intersect at depth at the junction with the rising viscous silicone the simplicity of the geometry of the whole analogue system provides equations which allow the estimation of the silicone depth from surface parameters these equations are then used in some field examples to assess the magma depth beneath natural resurgent domes

damage and strain localization around a pressurized shallow level magma reservoir structures developing above long term growing shallow level magma reservoirs such as resurgent domes may contain information on the reservoir itself to understand the formation of such tectonic features we have investigated the deformation process around a shallow pressurized magma reservoir embedded in a damaging elastic volcanic edifice our model allows evidencing the effect of the progressive damage in producing the fault pattern associated to tectonic surface deformation damage is first isotropic around the cavity and constitutes a damaged zone then the free surface effect appears and an anisotropic shear strain develops from the boundary of the damaged zone it localizes on reverse faults that propagate upward to the surface when the surface deformation is sufficient normal faulting appears finally the complete structure shows an undeformed wedge above the damaged zone this structure is similar to those found by analogue modelling and from field geologic observations from this model we found a relation to estimate the reservoir radius and depth from the graben and dome widths from limit analysis we deduced an analytical expression of the magma reservoir pressure which provides a better understanding of the magma pressure build up during doming the dip of reverse faults limiting the dome can be inferred from the minimal pressure required to rupture the crust around the reservoir finally the magma reservoir overpressure the dip of the faults the reservoir depth and the damaged zone radius is inferred from three parameters the ratio r computed from the dome and graben widths the cohesion and the friction angle

three dimensional vp vs variations along the loma prieta rupture zone an inversion of s p seismic wave arrival time data primarily from the program for array seismic studies of the continental lithosphere passcal array deployed in the aftershock zone of the 1989 loma prieta california earthquake has yielded a 3 d model for vp vs variations along the loma prieta rupture zone significant effort was devoted to identifying s to p converted waves which were prevalent at a few of the stations used the inversion method uses 3 d ray tracing in an existing laterally heterogeneous p wave velocity model to determine the initial paths for s waves assuming a constant vp vs the model represents spatial variations in vp vs on a 3 d grid with node spacings of 3 to 15 km horizontally and 3 to 5 km vertically the reduction in data variance computed exactly by applying the vp vs perturbations to the s velocity structure exceeds 65 for the single step inversion we interpret the vp vs model in conjunction with other available geological and geophysical information our major findings are 1 high vp vs along the fault zone in the upper crust indicative of upthrust gabbroic rocks 2 predominantly low vp vs in the lower crust indicative of an underlying quartz rich basement and 3 two areas of low vp vs in the near surface associated with known quartz rich rock sequences one a sandstone and the other granite and or granodiorite we also tentatively identify a boundary between areas of low and slightly high vp vs at depth in the immediate vicinity of the loma prieta mainshock hypocenter our results indicate the diagnostic power of a 3 d vp vs model when it is combined with other geological and geophysical information

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

nature and composition of shore zone sediments between jeddah and yanbu eastern red sea abstract the shore zone sediments between jeddah and yanbu west coast of saudi arabia are composed mostly of skeletal carbonate sands the nearshore sediments containing benthic foraminifera algal fragments and molluscs are multimodal the mean grain size varying between 0 76 and 2 35 o the beach sediments except samples dominated by cerithid gastropods in some localities are relatively finer than the nearshore sediments although the beaches to a great extent comprise sand sized material fine lime muds and coarse clastic gravels occur in certain areas the dune sediments comprising mostly algal grains and ooids are very fine with 50 percent of the material in the 0 25 0 18 mm size grade except a general northward decrease in mean grain size regional trends in the textural parameters of the sediments between jeddah and yanbu are not quite apparent lateral variations in the textural characteristics suggest a landward migration of the sediments in the shore zone under the influence of northerly and northwesterly winds the carbon and oxygen 13 c 4 80 to 4 84 pdb 13 o 0 04 to 0 53 pdb isotopic ratios of the lime muds occurring in certain shallow margins in the shore zone which are much higher than those of the green algae indicate that the fine carbonates are at least in part inorganic in origin like the shallow water carbonates in tropical seas aragonite and high mg calcite are the dominant carbonate minerals in the shore zone sediments there is a landward increase in aragonite contents caused by the landward migration of fine material from the nearshore the dominant clay mineral in the nearshore sediments is kaolinite with subordinate swelling chlorite and little illite kaolinite is contributed by the coastal regions under the sub tropical humid climate swelling chlorite is considered to have been formed in the nearshore by mechanical mixture of chlorite and montmorillonite derived from the metamorphic and igneous terrains of the tertiary mountains bordering the coastal plain

a cross correlation method for chemical profiles in minerals with an application to zircons of the kilgore tuff usa magmatic crystals are characterised by chemical zonation patterns that reflect the thermal and chemical conditions within magma reservoirs in which they grew crystals that exhibit similar patterns of zonation are often interpreted to have experienced similar conditions of growth these patterns of zonation may represent continuous processes such as cooling or more instantaneous events such as magma injection and provide an insight into the structure and evolution of a magmatic system both temporally and spatially we have developed an algorithm that is objectively able to quantify the similarity within and between suites of magmatic crystals from different samples significantly the algorithm is able to identify correlation that occurs between the interiors of two crystals but does not extend to the rim which provides an opportunity to understand the long term evolution of magmatic systems we develop and explain the mathematical basis for our algorithm and introduce its application using cathodoluminescence images of zircons from the kilgore tuff usa the results allow us to correlate samples from two different outcrops that are found over 80 km apart

crustal structure and magmato tectonic processes in an active rift asal ghoubbet afar east africa 2 insights from the 23 year recording of seismicity since the last rifting event 1 the asal ghoubbet ag rift has sustained a major volcano tectonic rifting episode in 1978 and has been subsequently monitored with continuous geodetic and seismological surveys it is therefore an ideal place to study the transient magmato tectonic processes that operate after a rifting episode we examine the space time evolution of 2500 md 2 8 earthquakes recorded in the rift from 1979 to 2001 we focus on the relationships between this seismic activity and both the three dimensional structure of the rift and its postrifting behavior depicted from geodesy the results highlight the major role of the central magmatic system fieale shark bay on the structure seismic activity and overall behavior of the rift from 1978 to 1986 the rift opens at a fast rate yet mainly aseismically the opening is magmatically driven and accommodated since 1986 when the opening rate abruptly decreased the seismicity is concentrated in the central part of the rift and reveals pulses of activity of the central volcanic system these pulses result from that magmatic zone undergoing alternating stretching and inflating episodes thus while the plate driven induced stresses have been rebuilding in the rift since 1987 the rift opening is still essentially accommodated in the axial magmatic zone the ag rift has thus sustained a postrifting unsteady opening over more than 23 years following its stretching episode that transient opening has essentially occurred aseismically and most tectonic faults remain relaxed and locked

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

combining controlled source seismology and local earthquake tomography to derive a 3 d crustal model of the western alpine region summary we present a newly developed approach of combining controlled source seismology css and local earthquake tomography let data to obtain a new 3 d crustal model of the western alpine region our approach combines either data by taking into account the strengths of the individual seismic methods our western alpine 3 d model is primarily based on a welldefined moho constrained by css and let data and includes smooth lateral variations in seismic velocities mainly constrained by let data but locally also by css data the consistent combination of results from the two different seismic methods is feasible due to let moho elements as defined by characteristic p wave velocities and their uncertainty estimates these uncertainty estimates are based on values of the diagonal element of the resolution matrix absolute p wave velocities that are typical for crust and mantle and a specific velocity gradient across the moho discontinuity finally our definition of let moho elements and their uncertainties is validated by comparisons of highest quality moho results from both methods coinciding in 353 localities our model clearly shows three moho surfaces being europe adria and liguria as well as major tectonic structures like suture zones and the high velocity ivrea body in general it is in a good agreement with previous studies the biggest differences occur along plate boundaries where the strong lateral velocity variations arebestresolvedbylet duetothelargernumberofavailablemohoreflectorelementsamore accurate definition of plate boundaries at moho level is possible and therefore new insights in deep lithosphere structures of the alpine collision zone can be expected furthermore our new 3 d crustal model directly includes a 3 d migrated image of the ivrea body

probabilistic earthquake relocation in three dimensional velocity models for the yellowstone national park region wyoming recorded seismicity for the yellowstone national park region comprising 25 267 earthquakes from november 1972 to december 2002 has been relocated using three dimensional velocity models and probabilistic earthquake location in addition new coda magnitudes for earthquakes between 1984 and 2002 were computed by using an improved coda magnitude equation three dimensional velocity models for earthquake location were computed by inverting subsets of high quality data of three different periods 1973 1981 1984 1994 and 1995 2002 for hypocenter locations and seismic velocities earthquakes were relocated by using a nonlinear probabilistic solution to the earthquake location problem fully nonlinear location uncertainties included in the probabilistic solution allow a better and more reliable classification of earthquake locations into four quality classes earthquake locations show an improvement in location accuracy with time which we attribute to improved network geometry and more precise timing of arrival times no large systematic shifts of the relocated earthquake locations are observed except a systematic shift of 2 km to greater depth the new relocated earthquake locations show tighter clustering of epicenters and focal depths when compared with original earthquake locations the most intense seismicity in terms of number of earthquakes and cumulative seismic moment release in the yellowstone national park region occurs northwest of the yellowstone caldera between hebgen lake and the northern rim of the caldera seismicity within the yellowstone caldera is diffuse and shallow individual clusters of earthquakes can be associated with major hydrothermal areas

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

high frequency earthquake ground motion scaling in utah and yellowstone velocity seismograms from the university of utah seismograph stations are used to quantify high frequency ground motion scaling for the yellowstone region and the wasatch front in utah this study uses a data set consisting of over 3000 waveforms from 93 stations and 506 regional earthquakes and mining associated seismic events that occurred in the years 1995 2001 all events lie within the upper crust with magnitudes less than 5 5 the signals were processed to examine the peak ground velocity and fourier velocity spectra in the frequency range of 1 0 16 0 hz regression results for utah are characterized by rapid decreases of amplitude at short distances which requires low q and a rapid geometrical spreading g r for the forward modeling q f 160 f 0 75 eff 0 05 sec and 300 bars are selected to predict the excitation terms when combined with the derived geometrical spreading the frequency dependent excitation of mining associated events differs significantly from that of earthquakes because of either an additional attenuation due to shallow source depth or apparent low stress drops associated with the slow collapse of long tunnels a q f 140 f 0 70 and geometrical spreading less rapid than r 1 0 at short distance ranges are used to describe the wave propagation distance dependence in the yellowstone region the yellowstone attenuation functional d r f is very different from that of utah perhaps because a shallow wave guide in the caldera traps more energy the yellowstone excitation spectra were modeled using 30 bars and eff 0 04 sec manuscript received 24 october 2003

classification of lithology from seismic tomography a case study from the messum igneous complex namibia 1 combined analysis of seismic p and s velocity information provides a reasonable and efficient basis for the petrologic interpretation of seismic cross sections in this paper a methodology is presented which allows extraction of prominent features related to well defined p velocities and poisson s ratios from a tomographic velocity model using a classification approach we used first arrival travel time data from a near vertical seismic experiment and independently determined p and s velocities by forward and inverse modeling resolution and uncertainties were estimated from inverting synthetic data the classification procedure was carried out in two subsequent steps first prominent classes were identified in the parameter space spanned by poisson s ratios and p wave velocities for this purpose a probability density function was calculated from the tomograms a function measuring the topography of the probability density was then determined and a histogram analysis was carried out to detect significant classes in the second step the results from principal component analysis for the identified classes were used to map their distribution along the seismic profile we applied the method to the messum intrusive complex of namibia and identified three prominent classes on the basis of the integration of petrophysical data and comparison with surface geology we conclude that quartz syenite composition dominates the upper 800 m of the crust under the complex outside of the intrusion the upper crust has properties corresponding to felsic metasediments and granites which are abundant in the local basement this material shows strong depth dependent changes of seismic properties which are ascribed to decreasing porosity and fluid saturation with depth

upper crustal structure of the yellowstone caldera from seismic delay time analyses and gravity correlations the 1978 yellowstone snake river plain seismic experiment provided detailed refraction data that were recorded across a two dimensional array of seismographs in yellowstone national park a delay time analysis was applied to 173 crystalline basement pg arrivals from these data to determine the three dimensional distribution of velocities and the layer configuration of the upper crust beneath the yellowstone caldera the p wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows averaging 2 8 km s that range in thickness from 1 5 to 2 0 km adjacent to the caldera the crystalline upper crustal layer has a velocity of 6 05 0 01 km s but this layer decreases by 6 to 5 70 km s beneath the caldera and extends northeast 15 km beyond the caldera smaller zones of very low p velocity 4 0 km s a 30 velocity reduction compared to the 6 05 km s layer occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the upper and midway geyser basins a three dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of 60 mgal over the caldera correlates directly with 1 the surface layer of combined sediments and rhyolite flows 2 the low velocity 5 7 km s upper crustal layer and 3 the 4 0 km s low velocity zone beneath the northeastern caldera rim an interpretation of the seismic velocities and densities based on experimental data and theoretical models suggests that the 6 05 km s 2 70 g cm3 regional pg velocity is characteristic of crystalline basement rocks such as the precambrian granitic gneisses that are exposed north and south of the yellowstone caldera the 5 7 km s velocity layer 2 65 g cm3 is interpreted to be a 10 km thick hot body of granitic composition the 4 0 km s low velocity body 2 40 g cm3 beneath the northeastern caldera rim is associated with a local 20 mgal gravity anomaly with a range of interpretations from a large steam dominated system to a felsic body of 10 to 50 partial melt the postulated 4 0 km s low velocity layer beneath the southwestern caldera does not have a corresponding gravity signature and may reflect a zone of high seismic attenuation attributed to a saturated fracture zone this seismic velocity model of the yellowstone caldera suggests that the source of the quaternary silicic volcanic rocks corresponds to the 5 7 km s layer in the upper crust that appears to contribute the principal source of heat to the yellowstone hydrothermal systems the anomalous low velocity body in the northeastern caldera rim area may be a cupola of partial melt with an overlying vapor dominated carapace and may represent the waning stages of the third cycle of quaternary volcanism or the beginning of a new cycle of volcanism that will continue the northeastward progression of the silicic volcanism of the yellowstone snake river plain propagating system

buoyant replenishment in silicic magma reservoirs experimental approach and implications for magma dynamics crystal mush remobilization and eruption 1 we present new experiments on replenishment of rhyolite magma chambers by rhyolite magma using corn syrup water solutions we emphasize small density contrasts and show that buoyancy is the key controlling factor for whether injections will rise to the top if buoyant or pond at the base if denser during emplacement we observe little or no mixing of the injected liquid with the reservoir liquid as predicted by the fact that our injections have low reynolds numbers 10 typically at later stages the low buoyancy 1 kg m 3 injected liquid which has accumulated at the top of the reservoir undergoes mixing with the reservoir liquid which may originate by the gravitational destabilization of a thin layer of denser resident liquid trapped above the injected liquid layer the presence of a basal crystal mush modeled by acrylic beads in a corn syrup water solution matrix is also considered slightly buoyant injections entrain a small fraction of mush particles to the top of the overlying liquid layer entrainment efficiency increases dramatically for high buoyancy injections we hypothesize that the injected liquid can entrain a maximum quantity of mush particles which corresponds to the amount required for the injected liquid mush particle suspension to attain neutral buoyancy in the resident liquid hence for silicic systems a replenishing melt can entrain up to 12 5 crystals during its ascent through the mush our results have implications for rhyolites bearing crystals with disequilibrium features as they may represent mush crystals remobilized by a replenishing silicic magma

seismicity and earthquake hazard analysis of the teton yellowstone region wyoming abstract earthquakes of the teton yellowstone region represent a high level of seismicity in the intermountain west u s a that is associated with intraplate extension associated with the yellowstone hotspot including the nearby teton and hebgen lake faults the seismicity and the occurrence of high slip rate late quaternary faults in this region leads to a high level of seismic hazard that was evaluated using new earthquake catalogues determined from three dimensional 3 d seismic velocity models followed by the estimation of the probabilistic seismic hazard incorporating fault slip and background earthquake occurrence rates the 3 d p wave velocity structure of the teton region was determined using local earthquake data from the jackson lake seismic network that operated from 1986 2002 an earthquake catalog was then developed for 1986 2002 for the teton region using relocated hypocenters the resulting data revealed a seismically quiescent teton fault at m l local magnitude 3 with diffuse seismicity in the southern jackson hole valley area but notable seismicity eastward into the gros ventre range relocated yellowstone earthquakes determined by the same methods highlight a dominant e w zone of seismicity that extends from the aftershock area of the 1959 m s surface wave magnitude 7 5 hebgen lake montana earthquake along the north side of the 0 64 ma yellowstone caldera earthquakes are less frequent and shallow beneath the yellowstone caldera and notably occur along northward trending zones of activity sub parallel to the post caldera volcanic vents stress field orientations derived from inversion of focal mechanism data reveal dominant e w extension across the teton fault with a ne sw extension along the northern teton fault area and southern yellowstone the minimum stress axes directions then rotate to e w extension across the yellowstone caldera to n s extension northwest of the caldera and along the hebgen lake fault zone the combination of accurate hypocenters unified magnitudes and seismotectonic analysis helped refine the characterization of the background seismicity that was used as input into a probabilistic seismic hazards analysis our results reveals the highest seismic hazard is associated with the teton fault because of its high slip rate of approximately 1 3 mm yr compared to the highest rate of 1 4 mm yr in southern yellowstone on the mt sheridan fault this study demonstrates that the teton yellowstone area is among the regions highest seismic hazard in the western u s

inversion for sources of crustal deformation and gravity change at the yellowstone caldera the 3100 km2 yellowstone caldera yellowstone national park was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totalling 3700 km3 at 2 1 2 and 0 6 m y before present its youthful volcanic history widespread hydrothermal activity intense seismicity and extremely high heat flow in excess of 30 times the continental average marks the yellowstone volcanic system as a giant caldera at unrest orthometric height increases of the caldera of up to 76 cm measured from precise leveling surveys from 1923 to 1975 1977 were inverted to determine volume expansion source models for the caldera wide deformation for the 1923 to 1977 uplift episode two regions of expansion were found 1 in the northern part of the caldera near the sour creek resurgent dome of 0 37 km3 and 2 in the southern part of the caldera near the mallard lake resurgent dome of 0 41 km3 both bodies occur in the upper crust from near surface depths to 6 0 km but the largest volume expansions were found in the 3 0 6 0 tan depth range the southern caldera source volume near the mallard lake dome may extend down to 9 0 km the data are however unable to resolve if these two resurgent domes separated laterally by 40 km are connected prom 1976 to 1987 nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9 0 km and involved a density perturbation greater than 0 002 g cm3 the modeled volumetric sources are in the same general locations as bodies of low p wave velocities high seismic attenuation and large negative bouguer gravity anomalies in view of the intense quaternary volcanism the anomalously high heat flow and the correlation of the source volumes with the regional geophysical anomalies it is likely that the modeled volumetric increases were caused by migration of magmas and or the introduction of large volumes of hydrothermal fluids into the upper crust

isotope geochemistry of the miocene and quaternary carbonate rocks in rabigh area red sea coast saudi arabia abstract the rabigh area a coastal region north of jeddah city saudi arabia contains raised quaternary coral reefal terraces and reworked coral fragments mixed with sand and gravel this area has a thin exposure lower miocene shallow marine carbonate rocks that laterally pass into evaporites the miocene carbonate and evaporite rocks conformably overly the lower miocene siliciclastic sequence are in turn capped by the harrat basaltic boulders the miocene carbonates are made up of dolomitic packstone wackestone and mudstone whereas the overlying quaternary reefal terraces are composed of coral boundstone and grainstones the quaternary reefal terraces of rabigh area have been dated using the uranium series dating method to obtain precise dates for these corals the calculated ages 128 212 and 235 ka indicate that deposition took place during high sea level stands associated with interglacial times during oxygen isotope stages ois 5 and 7 the youngest age 128 ka clearly corresponds to stage 5e of the last interglacial period the obtained ages correlate well with those of the emerged reefs on the sudanese and egyptian coasts at the western side of the red sea the broad distribution of wet climate pluvial deposits on the continents and high sea level stands indicate a wide geographical range of the interglacial events of the oxygen isotope stages ois 5 and 7 the oxygen and carbon isotopic composition of the miocene and quaternary carbonate rocks in rabigh area show a broad range of 13c and 18o the quaternary carbonate rocks have significantly higher 13c than the miocene ones but low 13c values of the miocene samples likely indicate a high contribution of carbon from organic sources at the time of deposition linear trends are evident in both groups of samples supporting the likelihood of secondary alteration

marine transgressions in the west coast of saudi arabia red sea between mid pleistocene and present abstract marine abrasion terraces cut in coralline limestone formations are to be noticed at various elevations in the coastal plain of the west coast of saudi arabia in between jeddah and yanbu three prominent terraces occur at altitudes of 1 3 and 10 m above the present level coral limestone samples from the terraces were dated by the carbon 14 method the radiometric ages reveal four marine transgressions in the west coast of saudi arabia eastern red sea from the mid pleistocene to present sea level maxima were recorded at about 31 000 16 600 18 100 9980 yrs b p and mid holocene the absolute altitude of the sea levels during the transgressions could not be evaluated because of the tectonic instability of the region however it is evident that relative to the first marine transgression mid wurm interglacial upto 31 000 yrs b p the successive transgressions in the west coast of saudi arabia occurred at progressively lower levels

mushy magma beneath yellowstone a recent prospective on the yellowstone caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body in this study we show that many of the first teleseismic p wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge after applying a number of waveform modeling tools we obtain much lower seismic velocities than previous studies 2 3 km sec v p and 1 1 km sec v s we estimate the physical state of the magma body by assuming a fluid saturated porous material consisting of granite and a mixture of rhyolite melt and water and co 2 at a temperature of 800 c and pressure at 5 km 0 1 gpa we found that this relatively shallow magma body has a volume of over 4 300 km 3 and is about 32 melt saturated with about 8 water plus co 2 by volume

the relocation of microearthquakes in the northern mississippi embayment three component seismograms recorded by a small array of digital instruments in the northern mississippi embayment consistently show a high amplitude phase on the vertical component that arrives approximately 0 8 s before the shear wave on the basis of its timing and apparent velocity this phase is identified as an s p conversion from the boundary between the unconsolidated cenozoic sediments and the underlying paleozoic rocks synthetic models of ground motion in the mississippi embayment indicate that vertical displacement amplitudes are higher for s p conversions than for transmitted shear waves at all angles of incidence the models and their agreement with observations of the three component seismograms suggest that true shear waves cannot be reliably identified from vertical component seismograms recorded in this area the travel times of converted phases are used together with crustal velocity models derived from a recent seismic refraction survey to relocate approximately 500 microearthquakes recorded by the central mississippi valley regional seismic network since the network data are recorded by vertical component seismographs we assume that the s phases observed at the stations sited on unconsolidated sediments are s p conversions this assumption significantly reduces the average rms residual and provides well constrained hypocentral locations for 350 earthquakes the relocated microearthquakes cluster tightly along previously identified epicentral trends focal depths range from 0 5 to 22 km but events deeper than 14 km are rare and events shallower than 3 km are confined almost exclusively to the area between ridgely tennessee and new madrid missouri focal mechanisms are generally consistent with the results of previous studies the axial seismicity trend which extends from caruthersville missouri to marked tree arkansas is characterized by right lateral strike slip motion on a northeast trending nearly vertical fault plane the events between ridgely tennessee and new madrid missouri commonly show strike slip focal mechanisms with minor components of both normal and reverse dip slip

the 1978 yellowstone eastern snake river plain seismic profiling experiment data and upper crustal structure of the yellowstone region eleven in line refraction profiles recorded to distances of 300 km and one azimuthal fan plot were constructed from data recorded with a 150 station array in the yellowstone national park area during the 1978 yellowstone snake river plain seismic experiment interpretations of the data suggest that the crustal p wave velocity model for the yellowstone region is characterized by 1 an averaged 10 km thick upper crustal layer v sub p 6 0 km s 2 an average crustal velocity of 6 3 km s and 3 a total crustal thickness of 44 km velocity models are presented for profiles that emphasize the upper crust and show 1 a decrease in the depth to the top of the upper crustal crystalline basement from 5 km in southwestern yellowstone near island park to 1 km at the northeast side of the yellowstone plateau that is interpreted as a progressive thinning of the silicic surface volcanic layer to the northeast and 2 evidence for a large lateral inhomogeneity interpreted to be a low velocity body with a decrease of at least 10 in p wave velocity located beneath the northeast corner of the yellowstone plateau the low velocity zone coincides with a local 30 mgal residual gravity anomaly and is located beneath partmore of the sour creek resurgent dome and part of the hot springs basin the largest hydrothermal system in yellowstone the low velocity body has a maximum depth to the top of 3 km and a minimum depth to the bottom of 9 km and may represent a zone of partial melt in comparison to the thermally undisturbed upper crust of the surrounding rocky mountains the upper crust of the northeastern yellowstone plateau appears laterally inhomogeneous in velocity and layer thickness suggesting effects of thermal and magma intrusion whereas the lower crust appears relatively homogeneous less

probabilistic earthquake location in complex three dimensional velocity models application to switzerland 1 we present a new approach to determine precise and reliable hypocenter locations in the tectonically complex region of switzerland a three dimensional 3 d p wave velocity model to be used for earthquake relocation is obtained by simultaneously inverting arrival times of local earthquakes for hypocenter locations and 3 d p wave velocity structure a 3 d p wave velocity model derived from controlled source seismology css is used as an initial reference model the final 3 d model thus combines all available information from both css and local earthquake data the probabilistic nonlinear formulation of the earthquake location problem includes a complete description of location uncertainties and can be used with any kind of velocity model in particular the combination of nonlinear global search algorithms such as the oct tree importance sampling with probabilistic earthquake location provides a fast and reliable tool for earthquake location the comparison of hypocenter locations obtained routinely by the swiss seismological service sed to those relocated in the new 3 d velocity model using a probabilistic approach reveals no systematic shifts but does exhibit large individual shifts in some epicenter locations and focal depths we can attribute these large shifts in part to large uncertainties in the hypocenter location events with a low number of observations 8 and no observation within the critical focal depth distance typically show large location uncertainties improved hypocentral locations particularly for mine blasts and earthquakes whose routine hypocenter locations had been questionable confirm that improved velocity model and probabilistic earthquake location yield more precise and reliable hypocenter locations and associated location uncertainties for switzerland

carbonate cements in a modern red sea reef north of jeddah saudi arabia abstract subsea carbonate cements vary in their types and distribution in a modern coral reef formation north of jeddah saudi arabia the petrographic characteristics of cemented reefs were studied by scanning electron microscope and x ray diffraction methods the cements consist basically of acicular aragonite and magnesium calcite containing 17 mole mgco3 the predominant cement in the red sea reefs is aragonite which is generally restricted to the intraskeletal cavities of coral whereas the mg calcite develops as a cryptocrystalline cement filling and coating the reef components

human induced changes in sedimentary facies and depositional environments sarum area red sea coast saudi arabia this paper aims to study the environmental impact of the human inference on the coastal zone of sarum area red sea coast saudi arabia in the past the study area was occupied by coastal lagoons that were connected with the sea with several inlets change detection technique based on multi date satellite images in the last 44 years indicated the occurrence of environmental changes accompanied the construction of the main asphaltic road of the red sea that separated some coastal lagoons at the studied area from the red sea field investigation and litho and bio facies distribution indicated the existence of six lateral facies types gypsum microbial mats halite quaternary coral reef terrace bioclasts and siliciclastic sand sheets the lateral distribution of these facies is related to the following changes 1 disconnection between the coastal lagoons and the sea 2 extensive contraction of the coastal lagoons and formation of saline ponds 3 exposure of the submerged quaternary coral reef terrace 4 increasing of the salinity of the ponds up to 270 and 5 deposition of the evaporitic facies types gypsum and halite over intertidal and subtidal marine carbonates based on the above mentioned criteria the human activity leads to environmental changes in the sarum area from coastal lagoons dominated with carbonate deposits into hypersaline ponds dominated with evaporitic deposits

seismic velocity structure of the central taupo volcanic zone new zealand from local earthquake tomography abstract the 3 d distribution of p wave velocity vp and the p wave s wave velocity ratio vp vs are derived for the crust in the central taupo volcanic zone tvz new zealand by tomographic inversion of p and s wave arrival time data from local earthquakes resolution in the seismogenic mid crust 4 6 km is good but poorer above and below these depths the 3 d velocity model has several vp anomalies as large as 5 in the mid lower crust 4 10 km and more than 10 in the upper crust 0 4 km the model achieves a 55 reduction in data variance from an initial 1 d model young caldera structures okataina rotorua and reporoa are characterised by low vp anomalies at a depth of about 4 km and these coincide with large negative residual gravity anomalies we attribute these anomalies to large volumes of low vp low density volcaniclastic sediments that have filled these caldera collapse structures although there are no vp anomalies which suggest the presence of molten or semi molten magma beneath the tvz a large high vp anomaly of more than 15 and a high vp vs anomaly are observed coincident with a diorite pluton beneath the ngatamariki geothermal field however vp anomalies cannot be seen beneath the largest geothermal fields waimangu waiotapu and reporoa and consequently if such anomalies exist they must be below the resolution of our data a prominent vp contrast of 5 10 occurs at a depth of about 6 km beneath the boundary between the taupo reporoa depression and the taupo fault belt tfb coincident with the eastern limit of the seismic activity beneath the tfb we interpret this velocity contrast as being caused by the presence of extensive non molten intrusives beneath the taupo reporoa depression we suggest that the high velocity material beneath the taupo reporoa depression is isolated from regional extension in the tvz and from the resulting faulting and seismicity which occurs preferentially within the weaker material of the tfb we are unable to determine whether greywacke which forms the basement beneath the eastern most part of the tvz continues further west or is replaced by a volcanic rock such as andesite which has similar vp and density vp vs anomalies are much smaller than vp anomalies and generally have little spatial relationship to the vp pattern there is a widespread decrease in vp vs from 1 76 to 1 70 1 73 between 4 and 6 km depth over much of the study area and vp vs is high southwest of the okataina caldera where vp is low hypocentres calculated using the 3 d velocity model differ little from those obtained using a 1 d model with station terms however some groups of earthquakes are more tightly clustered following relocation there is a slight decrease in the estimated thickness of the seismogenic zone with 73 of hypocentres between 4 and 7 km depth and a slight increase in the depth of the brittle ductile transition from 6 to 6 5 km

the managua graben and las sierras masaya volcanic complex nicaragua pull apart localization by an intrusive complex results from analogue modeling abstract there is a well documented association between pull apart basins in strike slip zones and large volcanic caldera complexes las sierras masaya volcanic complex nicaragua is a large basaltic lava and ignimbrite shield with nested calderas the widest caldera is partly underlain by a large and dense intrusive complex evidenced by a positive gravity anomaly the las sierras caldera relating to this cumulate complex is less than 30 000 years old and is probably still hot and ductile the inner masaya caldera hosts an active magmatic system the volcanic complex is in a dextral transtensional tectonic context of the nicaraguan depression the highly active managua graben is on the northern part of the volcano we speculate that the graben and volcano are linked tectonically with the graben initiating in response of a regional stress field modified around the dense ductile intrusive complex previous field work and reappraisal of structures with digital elevation model morphological analysis show that the volcano is surrounded by a rhombic fault pattern that may form a nascent pull apart basin we have done scaled analogue models to test the effect of intrusion density and rheology anomalies on strike slip fault geometries the models show that intrusion density variations alone do not significantly change fault patterns in contrast ductile rocks silicone in the models as analogue for hot mafic intrusive rocks markedly alter strike slip fault patterns in transtension the presence of a ductile intrusion causes the formation of a pull apart while in pure strike slip or transpression uplift and thrusting is generated pull apart and uplift structures are rhomb shaped even when the ductile inclusion is circular we conclude that a pull apart is developing at las sierras masaya volcanic complex in response to the transtensive regional deformation regime and the dense ductile intrusive complex we suggest that the volcano and graben are one dynamic system and should be monitored as one entity

p and s velocity structure of the yellowstone volcanic field from local earthquake and controlled source tomography the three dimensional p and s velocity from vp vs ratios distribution and improved hypocenters for the yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled source explosions the p velocity model has an rms residual of 0 09 s whereas the vp vs ratio model calculated from 511 earthquakes has an rms residual of 0 29 s high p and s velocities outside the yellowstone caldera represent thermally undisturbed basement and sedimentary rocks a caldera wide 15 decrease from regional p velocities at depths of 6 to 12 km is coincident with a 60 mgal gravity anomaly and is interpreted as a hot subsolidus granitic batholith with a quasi plastic rheology localized 30 reductions from regional seismic velocities and higher vp vs ratios 8 km beneath yellowstone s resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful less than 2 ma silicic volcanism additional low seismic velocities and vp vs ratios and a 20 mgal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt hypocenters relocated with the three dimensional p velocity model show subparallel alignment with nw se trending postcaldera volcanic vents and normal faults northwest of the caldera focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera reflecting thinning and heating of the seismogenic crust

hypocenter velocity structure coupling in local earthquake tomography abstract local earthquake tomography involves the use of seismic wave arrival times from earthquake sources with uncertain locations for the inference of three dimensional variations in seismic velocity formally this inverse problem contains explicit coupling between the earthquake hypocenters and the velocity structure however many studies fail to treat the hypocenter velocity structure coupling explicitly an examination of previous studies provides evidence that this failure can lead to significant bias in the resulting velocity model a set of simple hypothetical test cases clearly demonstrates the seriousness of the potential bias when coupling is neglected producing models that underestimate the actual velocity perturbations by about a factor of four under the same conditions strict simultaneous inversion and simultaneous inversion with parameter separation both produce accurate inverted models the use of appropriate station corrections and iteration of the solution can improve the results when the coupling is ignored but velocity anomalies will still be underestimated by about a factor of two at best

origin of the southern okinawa trough volcanism from detailed seismic tomography 1 magmatism associated with subducting plate edges or slab tears has been suggested in the southern okinawa trough the cross back arc volcanic trail which consists of a cluster of about 70 seamounts is located above a ryukyu slab tear lying along the 123 3 e meridian in november 2003 more than 3300 earthquakes recorded in this area by 15 ocean bottom seismometers and surrounding land stations during a period of 12 days were used to determine the three dimensional vp and vs velocity structures and vp vs ratios a mantle inflow characterized by low vp and vs and high vp vs passing through the slab tear is imaged the fluid and or melt component is rising obliquely from the slab tear in the directions of the cross back arc volcanic trail the northern slope of the southern okinawa trough and to north of iriomote island the asthenospheric intake is also imaged by an inclined chip like high vp vs and low vp and vs body dipping northerly which might be linked to the slab retreat west of the slab tear most of the earthquakes are located around low vp and vs and high vp vs bodies which suggests that the seismicity is related to magmatic and or fluid activities east of it earthquakes are concentrated in an area characterized by high vp and vs velocities and low vp vs suggesting that the magma chamber is absent beneath the axial part of the trough and that normal faulting is the main factor controlling the seismicity

dating quaternary raised coral terraces along the saudi arabian red sea coast abstract late pleistocene raised coral reef terraces form extensive outcrops up to 5 km wide along the saudi coast porites coral were dated using u th while clastic sediment from jeddah was dated using thermoluminescence the pooled mean age for the coral samples is 121 5 0 2 ka suggesting mis 5e even for the uplifted 16 20 m high terrace in the north at haql in jeddah the mis 5e back reef succession is overlain by fluvial sediment that gave a tl age of 66 13 ka the structure and faunal composition of the coral terraces suggests that they accumulated in broad shallow embayments following the last interglacial transgression the consistent elevation of these terraces suggests that the central and southern saudi coast has been tectonically stable for at least the past 125 000 years and the coral reef terraces at 3 5 5 5 m elevation are consistent with the mis 5e sea level high stand that peaked at 6 9 m above present sea level the saudi coastal coral terrace north of duba shows progressive uplift to 16 20 m near haql since 108 120 ka as a result of ongoing transform faulting in the gulf of aqaba

gas driven filter pressing in magmas insights into in situ melt segregation from crystal mushes gas driven filter pressing is the process of melt expulsion from a volatile saturated crystal mush induced by the buildup and subsequent release of gas pressure filter pressing is inferred to play a major role in magma fractionation at shallow depths 10 km by moving melt and gas relative to the solid crystalline framework however the magmatic conditions at which this process operates remain poorly constrained we present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas driven filter pressing to segregate melt hydrous haplogranite 2 1 wt water in the melt and dacite 4 2 wt water in the melt crystal mushes with a wide range of crystallinities 34 80 vol crystals were investigated using in situ high temperature 500 800 c synchrotron x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 8 s per three dimensional data set our experimental results show that gas driven filter pressing operates only below the maximum packing of bubbles and crystals 74 vol above this threshold the mush tends to fracture and gas escapes via fractures therefore the efficiency of gas driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build up of pressure and expulsion of melt such observations offer a likely explanation for the production of eruptible crystal poor magmas within earth s crust

the use of the textural parameters of sand in studying the characteristics and depositional processes of coastal sediments south of jeddah saudi arabia abstract the subtidal sediments of four coastal environments beach swash zone lagoon and nearshore bar south of jeddah have been studied in terms of their textural characteristics and depositional process the skeletal grains are composed mainly of fragments of corals benthic foraminifera and different types of shells together with sand sized rock fragments and quartz and feldspar grains the skeletal material of the sediments has been derived from the mechanical breakdown of the adjacent reefs while the small clastic portion was provided from the hinterland by rivers bimodal and polymodal grain size distributions are common and can be attributed to heterogeneity in the types of skeletal debris the size distribution of such sediments suggests that the various processes that are responsible for their transportation and deposition are wave current and wind action the different energy conditions and the morphology of each coastal environment seem to be reflected in the characteristics of the sediments in each environment

cenozoic epeirogeny of the arabian peninsula from drainage modeling it is generally accepted that the arabian peninsula has been uplifted by subcrustal processes positive residual depth anomalies from oceanic crust in the red sea and in the gulf of aden suggest that a region surrounding this peninsula is dynamically supported admittance calculations surface wave tomography studies and receiver function analyses all imply that regional topography is generated and maintained by some combination of mantle convective circulation and lithospheric thickness changes despite these significant advances the spatial and temporal uplift rate history of the arabian peninsula is not well known here we show that a regional uplift rate history can be obtained by jointly inverting 225 longitudinal river profiles that drain this peninsula our strategy assumes that shapes of individual river profiles are controlled by uplift rate history and moderated by erosional processes we used local measurements of incision rate to calibrate the relevant erosional parameters in our inverse algorithm uplift rate is permitted to vary smoothly as a function of space and time but upstream drainage area remains invariant we also assume that knickzone migration is not lithologically controlled implications of these important assumptions have been investigated our results suggest that the arabian peninsula underwent two phases of asymmetric uplift during the last 20 30 ma at rates of 0 05 0 1 mm a 1 the southwestern flank of the peninsula has been uplifted by 1 5 2 5 km regional stratigraphic constraints the age and composition of volcanism paleosol formation incised peneplains emergent marine terraces and thermochronometric measurements corroborate our calculated patterns of uplift progressive development of three domal swells along the western margin of the peninsula is consistent with localized upwelling of hot asthenospheric mantle

evidence for a sea level lowstand between 4500 and 2400 years b p on the southeast coast of the united states abstract distribution of dated archaeological sites dredged pottery sherds 14c dates of submerged inplace stumps and the presence of numerous buried trees indicate a sea level lowstand of at least 3 m msl between 3000 and 2400 years before present b p on the georgia coast

geodynamics of the yellowstone hotspot and mantle plume seismic and gps imaging kinematics and mantle flow abstract integration of geophysical and geological data show that the yellowstone hotspot resulted from a mantle plume interacting with the overriding north america plate a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16 17 ma 700 km long yellowstone snake river plain ysrp silicic volcanic system accessibility of the ysrp allowed large scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements seismic tomography reveals a crustal magma reservoir of 8 to 15 melt 6 km to 16 km deep beneath the yellowstone caldera an upper mantle low p wave velocity body extends vertically from 80 km to 250 km beneath yellowstone but the anomalous body tilts 60 wnw and extends to 660 km depth into the mantle transition zone we interpret this conduit shaped low velocity body as a plume of up to 3 5 vp and 5 5 vs perturbation that corresponds to a 1 2 partial melt models of whole mantle convection reveal eastward upper mantle flow beneath yellowstone at relatively high rates of 5 cm yr that deflects the ascending plume into its west tilted geometry a geodynamic model of the yellowstone plume constrained by vp and vs velocities and attenuation parameters suggests low excess temperatures of up to 120 k corresponding to a maximum 2 5 melt and a small buoyancy flux of 0 25 mg s i e properties of a cool weak plume the buoyancy flux is many times smaller than for oceanic plumes nonetheless plume buoyancy has produced a 400 km wide 500 m high topographic swell centered on the yellowstone plateau contemporary deformation derived from gps measurements reveals sw extension of 2 3 mm yr across the yellowstone plateau one fourth of the total basin range opening rate which we consider to be part of basin range intraplate extension locally decadal episodes of subsidence and uplift averaging 2 cm yr characterize the 80 year yellowstone caldera monitored history and are modeled as hydrothermal magmatic sources moreover a recent episode 2004 2009 of accelerated uplift of the yellowstone caldera at rates up to 7 cm yr has been modeled as resulting from magmatic recharge of a 10 km deep sill at the top of the crustal magma reservoir regionally gravitational potential energy of the yellowstone swell drives the lithosphere southwest and downhill from the yellowstone plateau 400 km where it coalesces with basin range province wide westward extension based on the geometry and its assumed 660 km depth we extrapolate the plume source southwest to its original location at 17 ma and 600 km southwest and 200 km north of the ysrp importantly this location is beneath the southern part of the columbia plateau flood basalt field of the same age and implies that the yellowstone mantle plume may be the common source for both of these large volcanic fields our time progression model suggests that the original plume head rose vertically behind the juan de fuca plate but at 12 ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler thicker continental lithosphere becoming entrained in eastward upper mantle flow these results reveal that yellowstone plume plate processes have had a profound effect on late cenozoic geologic evolution and topography of a large part of the western u s

insights into the evolution of the yenkahe resurgent dome siwi caldera tanna island vanuatu inferred from aerial high resolution photogrammetry the yenkahe dome tanna island vanuatu is one of the most spectacular examples of presently active post caldera resurgence exhibiting a very high uplift rate over the past 1000 years 156 mm year on average although numerous inhabited areas are scattered around the dome the dynamics of this structure and associated hazards remain poorly studied because of its remote location and dense vegetation cover a high resolution photogrammetric campaign was carried out in november 2011 over the dome georeferenced photographs were treated by structure from motion and multiple view stereophotogrammetry methods to produce a 3d digital surface model dsm of the area and its associated orthophotograph this dsm is much more accurate than previously available srtm and aster digital elevation models dems particularly at minimal coastline and maximal altitudes yasur culmination point 390 m while previous mapping relied mostly on low resolution dems and satellite images the high precision of the dsm allows for a detailed structural analysis of the yenkahe dome notably based on the quantification of fault displacements the new structural map inferred from the 3d reconstruction and morphological analysis of the dome reveals a complex pattern of faults and destabilization scars reflecting a succession of constructive and destructive events numerous landslide scars directed toward the sea highlight the probable occurrence of a tsunami event affecting the south eastern coast of tanna simulations of landslide triggered tsunamis show the short time propagation of such a wave 1 2 min which could affect coastal localities even following relatively small destabilized volumes a few million cubic meters

p wave velocity variations in the coso region california derived from local earthquake travel times inversion of 4036 p wave travel time residuals from 429 local earthquakes using a tomographic scheme provides information about three dimensional upper crustal velocity variations in the indian wells valley coso region of southeastern california the residuals are calculated relative to a coso specific velocity model corrected for station elevation weighted and back projected along their ray paths through models defined with layers of blocks slowness variations in the surface layer reflect local geology including slow velocities for the sedimentary basins of indian wells and rose valleys and relatively fast velocities for the sierra nevada and argus mountains in the depth range of 3 5 km the inversion images an area of reduced compressional velocity in western and northern indian wells valley but finds no major velocity variations beneath the coso volcanic field to the north these results are consistent with a recent study of anomalous shear wave attenuation in the coso region between 5 and 10 km depth low velocity areas 7 slow appear at the southern end of the coso volcanics reaching east to the coso basin numerical tests of the inversion s resolution and sensitivity to noise indicate that these major anomalies are significant and well resolved while other apparent velocity variations in poorly sampled areas are probably artifacts the seismic data alone are not sufficient to uniquely characterize the physical state of these low velocity regions because of the coso region s history of pleistocene bimodal volcanism high heat flow geothermal activity geodetic deformation and seismic activity one possibility is to link the zones of decreased p velocity to contemporary magmatic activity

geomorphological changes in the coastal area of farasan al kabir island saudi arabia since mid holocene based on a multi proxy approach abstract the geomorphological evolution of the southeastern coastal area of farasan al kabir island saudi arabia is revealed by the mapping of modern landforms and a multi proxy and high spatial resolution study including grain size particulate organic carbon mineralogy element geochemistry benthic foraminifera analysis and radiocarbon dating of a 3 3 m long sediment core the modern geomorphological features comprise a variety of arid landforms such as plateau cliffs and pediments of pleistocene coral limestones playa depressions located on plateau surfaces alluvial fans butte and sandy beaches the mid holocene evolution of the borehole area is resulted from the detailed analysis of five sedimentary units detected along the core matar 1 and includes three distinct stages a from 5253 223 y cal bp to 3138 223 y cal bp carbonate coarse grained material consisting of coral fragments molluscs calcareous algae and benthic foraminifera are deposited on a shallow marine fringing reefal platform which becomes progressively a nearshore backreef around 3675 215 y cal bp and later around 3138 223 y cal bp a reef ramp b since 3040 220 y cal bp the borehole area obtains the characteristics of a high energy beach that receives increasing inputs of terrigenous material c subsequently a supratidal backshore setting is established influenced mostly by terrestrial processes and occasionally by marine processes as it is indicated by the decreasing and sometimes sporadic presence of benthic foraminifera and recently a sedimentary veneer consisting of terrigenous carbonate and evaporite material is formed by terrestrial mainly wadi and aeolian processes

chronological link between deep seated processes in magma chambers and eruptions permo carboniferous magmatism in the core of pangaea southern pyrenees abstract in the southern pyrenees there are upper carboniferous lower permian sedimentary basins with a significant volume of volcanic material derived from explosive eruptions rhyolitic ignimbrites and andesitic flows these basins are spatially associated with granodiorites and dacitic dykes emplaced in variscan basement rocks u pb shrimp dating of zircons extracted from three granodiorites an andesitic flow a dacitic dyke and six ignimbrites revealed that magmatism occurred over an extended period of thirty eight million years from ca 304 ma to ca 266 ma upper carboniferous middle permian a scattering of zircon ages in each sample shows that the history of melt crystallization was complex with more than one zircon forming event in each magma chamber the prolonged crystallization history was transferred to the product of the eruptions a chronological link between the deep seated magma chambers and processes in eruptions was identified on the basis of four overlapping intervals at ca 309 307 ma upper carboniferous ca 304 296 ma upper carboniferous lower permian ca 294 282 ma lower permian and ca 276 ma lower permian the variation of zircon u th ratios exposes a tendency for an increase in mafic sources as crystallization advances in the permian zircons probably crystallized from melt phases related to both a felsic intermediate metaluminous source from ca 310 293 ma mostly 0 1

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

locating hydrothermal acoustic sources at old faithful geyser using matched field processing in 1992 a large and dense array of geophones was placed around the geyser vent of old faithful in the yellowstone national park to determine the origin of the seismic hydrothermal noise recorded at the surface of the geyser and to understand its dynamics old faithful geyser ofg is a small scale hydrothermal system where a two phase flow mixture erupts every 40 to 100 min in a high continuous vertical jet using matched field processing mfp techniques on 10 min long signal we localize the source of the seismic pulses recorded at the surface of the geyser several mfp approaches are compared in this study the frequency incoherent and frequency coherent approach as well as the linear bartlett processing and the non linear minimum variance distorsionless response mvdr processing the different mfp techniques used give the same source position with better focalization in the case of the mvdr processing the retrieved source position corresponds to the geyser conduit at a depth of 12 m and the localization is in good agreement with in situ measurements made at old faithful in past studies

models of lithosphere and asthenosphere anisotropic structure of the yellowstone hot spot from shear wave splitting 1 teleseismic shear wave splitting measured at 56 continuous and temporary seismographs deployed in a 500 km by 600 km area around the yellowstone hot spot indicates that fast anisotropy in the mantle is parallel to the direction of plate motion under most of the array the average split time from all stations of 0 9 s is typical of continental stations there is little evidence for plume induced radial strain suggesting that any contribution of gravitationally spreading plume material is undetectably small with respect to the plate motion velocity two stations within yellowstone have splitting measurements indicating the apparent fast anisotropy direction is nearly perpendicular to plate motion these stations are 30 km from stations with parallel to plate motion the 70 rotation over 30 km suggests a shallow source of anisotropy however split times for these stations are more than 2 s we suggest melt filled stress oriented cracks in the lithosphere are responsible for the anomalous orientations within yellowstone stations southeast of yellowstone have measurements of oriented nnw to wnw at high angles to the plate motion direction the archean lithosphere beneath these stations may have significant anisotropy capable of producing the observed splitting

constraints on the upper crustal magma reservoir beneath yellowstone caldera inferred from lake seiche induced strain observations 1 seiche waves in yellowstone lake with a 78 minute period and heights 10 cm act as a load on the solid earth observed by borehole strainmeters with subnanostrain sensitivity throughout the yellowstone caldera the far field strain induced by the load of the seiche waves calculated with a homogeneous elastic model representing the upper crust is more than an order of magnitude smaller than the measured strain amplitude 30 km from the lake shore by contrast the observed far field strain amplitudes are consistent with the seiche load on a two layered viscoelastic model representing an elastic upper crust overlying a partially molten body deeper than 3 6 km with maxwell viscosity less than 1011 pa s these strain observations and models provide independent evidence for the presence of partially molten material in the upper crust consistent with seismic tomography studies that inferred 10 30 melt fraction in the upper crust

evaluation of the evolving stress field of the yellowstone volcanic plateau 1988 to 2010 from earthquake first motion inversions abstract although the last rhyolite eruption occurred around 70 ka ago the silicic yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field we use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail earthquake relocations and a set of 369 well constrained double couple focal mechanism solutions were computed events were grouped according to location and time to investigate trends in faulting the majority of the events have normal faulting solutions subordinate strike slip kinematics and very rarely reverse motions the dominant direction of extension throughout the 0 64 ma yellowstone caldera is nearly ene consistent with the perpendicular direction of alignments of volcanic vents within the caldera but our study also reveals spatial and temporal variations stress field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion a well resolved rotation of 3 was found from nne ssw near the hebgen lake fault zone to ene wsw near norris junction in particular the 3 direction changed throughout the years around norris geyser basin from being ene wsw as calculated in the study by waite and smith 2004 to nne ssw while the other 3 directions are mostly unchanged over time the presence of chocolate tablet structures with two sets of nearly perpendicular normal faults was identified in many stages of the deformation history both in the norris geyser basin area and inside the caldera

the temporal evolution of chemical and physical properties of magmatic systems exactly 100 years ago the great canadian born petrologist n l bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physico chemical understanding of the fractionation of crystals from melts in molten rock a subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution the image of sub volcanic magmatic systems has evolved greatly in that time from a simple boiling vat concept of molten rock in which bubbles crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten or mushy state real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma and heat at different fluxes magma fluxes between the different portions of this plumbing system and the variation of the chemical and physical properties of magma as it rises through the crust exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products this book presents a collection of contributions that use petrology geochemistry geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them

the 1978 yellowstone eastern snake river plain seismic profiling experiment crustal structure of the yellowstone region and experiment design in 1978 a major seismic profiling experiment was conducted in the yellowstone eastern snake river plain region of idaho and wyoming fifteen shots were recorded that provided coverage to distances of 300 km in this paper travel time and synthetic seismogram modeling was used to evaluate an average p wave velocity and apparent q structure of the crust from two seismic profiles reversed across the yellowstone national park region this area includes the well known hydrothermal features of yellowstone national park geysers fumeroles etc a large collapse caldera and extensive silicic volcanism of quaternary age features attributed to shallow crustal sources of magma the averaged crustal structure for this region as interpreted from the seismic data consists of 1 a highly variable near surface layer approximately 2 km thick with variable velocities of 3 0 to 4 8 km s and a low apparent q of 30 that is interpreted to be composed of weathered rhyolites and sedimentary infill 2 an upper crustal layer 3 to 4 km thick with variable velocities of 4 9 to 5 5 km s and apparent q of 50 to 200 that is thought to represent the accumulation of the pleistocene quaternary rhyolite flows ash flow tuffs and possible paleozoic and precambrian metamorphic equivalents 3 the crystalline upper crust that is characterized by a laterally inhomogeneous layer that varies in velocity from 4 0 to 6 1 km s averaging 5 km thick with a q of 300 this layer appears to be a cooling but still hot body of granitic composition beneath the yellowstone caldera it is thought to be a remnant of the magma chambers that produced the quaternary silicic volcanic rocks of the yellowstone plateau and may still be a major contributor to the high heat flow 4 a laterally homogeneous intermediate crustal layer 8 to 10 km thick with a velocity of 6 5 km s and apparent q of 100 to 300 5 a homogeneous 25 km thick lower crust with a velocity of 6 7 to 6 8 km s and an apparent q of 300 and 6 a total crustal thickness of 43 km the upper crustal layer 5 5 to 6 0 km s is thought to be the thermally altered equivalent of the continental crystalline basement that is normally 15 to 20 km thick in the surrounding thermally undisturbed archean crust an interpretation from these results suggests that mafic melts from the mantle have penetrated the lower crust without significant variations in the velocity structure but produce the main source of heat that drives the volcanic and hydrothermal systems of yellowstone the high apparent attenuation and large lateral velocity variations in the upper crust are consistent with a model in which partial fractionation partial melting and metamorphism differentiate the original upper crust to produce silicic melts that were extruded as rhyolites and ash flow tuffs across the yellowstone plateau this seismic model is consistent with the evidence for a systematic northeastward propogation of silicic volcanic centers along the eastern snake river plain to their present location beneath the yellowstone hydrothermal system while these findings do not bear directly on the origin and source of the heat i e mantle lumes lithospheric fractures mantle radiogenetic heat basal lithospheric shearing etc they provide a constraint on the configuration and lateral extent of crustal layers that reflect thermal and compositional boundaries

linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved yellowstone type supervolcanoes the geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations the a d 1815 tambora indonesia eruption perhaps nowhere on earth are deposits of such supereruptions more prominent than in the snake river plain yellowstone plateau srp yp volcanic province northwest united states while magmatic activity at yellowstone is still ongoing the heise volcanic field in eastern idaho represents the youngest complete caldera cycle in the srp yp and thus is particularly instructive for current and future volcanic activity at yellowstone the heise caldera cycle culminated 4 5 ma ago in the eruption of the 1800 km3 kilgore tuff accessory zircons in the kilgore tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity and the vast majority are 18o depleted this suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low 18o meteoric hydrothermal fluids prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir u pb geochronology of isotopically diverse zircons using chemical abrasion isotope dilution thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206pb 238u date of 4 4876 0 0023 ma mswd 1 5 n 24 these zircon crystallization ages are also indistinguishable from the sanidine 40ar 39ar dates and thus zircons crystallized close to eruption this requires that shallow crustal melting assembly of isolated batches into a supervolcanic magma reservoir homogenization and eruption occurred extremely rapidly within the resolution of our geochronology 103 104 yr the crystal scale image of the reservoir configuration with several isolated magma batches is very similar to the reservoir configurations inferred from seismic data at active supervolcanoes the connection of magma batches vertically distributed over several kilometers in the upper crust would cause a substantial increase of buoyancy overpressure providing an eruption trigger mechanism that is the direct consequence of the reservoir assembly process

spatial and temporal geochemical trends in the hydrothermal system of yellowstone national park inferences from river solute fluxes we present and analyze a chemical dataset that includes the concentrations and fluxes of hco3 s o4 c l and f in the major rivers draining yellowstone national park ynp for the 2002 2004 water years 1 october 2001 30 september 2004 the total molar flux in all rivers decreases in the following order hco3 ncl nso4 nf but each river is characterized by a distinct chemical composition implying large scale spatial heterogeneity in the inputs of the various solutes the data also display nonuniform temporal trends whereas solute concentrations and fluxes are nearly constant during base flow conditions concentrations decrease solute fluxes increase and hco3 cl and so4 cl increase during the late spring high flow period hco3 so4 decreases with increasing discharge in the madison and falls rivers but increases with discharge in the yellowstone and snake rivers the non linear relations between solute concentrations and river discharge and the change in anion ratios associated with spring runoff are explained by mixing between two components 1 a component that is discharged during base flow conditions and 2 a component associated with snow melt runoff characterized by higher hco3 cl and so4 cl the fraction of the second component is greater in the yellowstone and snake rivers which host lakes in their drainage basins and where a large fraction of the solute flux follows thaw of ice cover in the spring months although the total river hco3 flux is larger than the flux of other solutes hco3 cl 3 the co2 equivalent flux is only 1 of the estimated emission of magmatic co2 soil emissions from yellowstone no anomalous solute flux in response to perturbations in the hydrothermal system was observed possibly because gage locations are too distant from areas of disturbance or because of the relatively low sampling frequency in order to detect changes in river hydrothermal solute fluxes sampling at higher frequencies with better spatial coverage would be required our analysis also suggests that it might be more feasible to detect large scale heating or cooling of the hydrothermal system by tracking changes in gas and steam flux than by tracking changes in river solute flux published by elsevier b v

simultaneous inversion for lateral velocity variations and hypocenters in the yellowstone region using earthquake and refraction data a three dimensional upper crustal p wave velocity structure of the yellowstone region was determined by simultaneous inversion using pg refracted arrival times and earthquake generated direct p wave arrival times the velocity structure was modeled by a two layer block configuration with the velocity of the surface layer fixed the inversion was performed on a 14 4 km thick second layer 5 6 blocks using an optimal block size of 21 2 18 3 km and incorporated the method of separation of parameters results show volumes of higher velocities approximately 6 3 km s north of the yellowstone caldera that correlate with gravity anomaly highs and are interpreted to be associated with near surface crystalline basement the upper crust beneath the caldera showed an average velocity of 5 8 km s with prominent low velocity zones of 4 9 and 5 2 km s in the northeast and southwest portions of the caldera respectively the 4 9 km s low velocity layer in the northeast corner of the caldera coincides with a localized 20 mgal bouguer gravity low and the largest area of hydrothermal activity in yellowstone national park relocating earthquakes with the new velocity model showed a systematic migration of epicenters radially toward the caldera by an average of 1 2 km relative to locations using a homogeneous velocity model

three dimensional p wave velocity structure derived from local earthquakes at the katmai group of volcanoes alaska abstract the three dimensional p wave velocity structure beneath the katmai group of volcanoes is determined by inversion of more than 10 000 rays from over 1000 earthquakes recorded on a local 18 station short period network between september 1996 and may 2001 the inversion is well constrained from sea level to about 6 km below sea level and encompasses all of the katmai volcanoes martin mageik trident griggs novarupta snowy and katmai caldera the inversion reduced the average rms travel time error from 0 22 s for locations from the standard one dimensional model to 0 13 s for the best three dimensional model the final model from the 6th inversion step reveals a prominent low velocity zone 3 6 5 0 km s centered at katmai pass and extending from mageik to trident volcanoes the anomaly has values about 20 25 slower than velocities outboard of the region 5 0 6 5 km s moderately low velocities 4 5 6 0 km s are observed along the volcanic axis between martin and katmai caldera griggs volcano located about 10 km behind northwest of the volcanic axis has unremarkable velocities 5 0 5 7 km s compared to non volcanic regions the highest velocities are observed between snowy and griggs volcanoes 5 5 6 5 km s relocated hypocenters for the best 3 d model are shifted significantly relative to the standard model with clusters of seismicity at martin volcano shifting systematically deeper by about 1 km to depths of 0 to 4 km below sea level hypocenters for the katmai caldera are more tightly clustered relocating beneath the 1912 scarp walls the relocated hypocenters allow us to compare spatial frequency size distributions b values using one dimensional and three dimensional models we find that the distribution of b is significantly changed for martin volcano which was characterized by variable values 0 8 b b b b b b values indicating the robustness of the observations the strong high b value region at mageik volcano is mainly associated with an earthquake swarm in october 1996 that possibly indicates a shallow intrusion or influx of gas the new velocity and spatial b value results in conjunction with prior gravity bouguer anomalies up to 40 mgal and interferometry several cm uplift data provide strong evidence in favor of partially molten rock at shallow depths beneath the mageik katmai novarupta region moderately low velocities beneath martin and katmai suggest that old mostly solidified intrusions exist beneath these volcanoes higher relative velocities beneath the griggs and snowy vents suggest that no magma is resident in the shallow crust beneath these volcanoes

distribution of magma beneath the toba caldera complex north sumatra indonesia constrained by three dimensional p wave velocities seismicity and gravity data 1 we estimate the one and three dimensional p wave velocity structure beneath the toba caldera complex a 30 100 km topographic depression in north sumatra using arrival time data of local earthquakes recorded by a 40 station seismic network that operated for 4 months inversions reveal the presence of p velocities up to 37 below normal that likely map the distribution of magma within this subduction related volcanic system considered the world s largest in the upper 10 km of crust the largest low velocity region underlies the southern two thirds of the depression and coincides with a gravity low centered over the resurgent dome a smaller volume of low velocities is observed in the upper crust under the north end of the depression separating the two regions is a zone of locally high velocities indicating that the shallow subcaldera magma system is composed of two separate reservoirs not a single one that extends the entire length of the caldera complex above each low velocity region is a postcollapse volcano that erupted mostly mafic lavas after the last major caldera collapse 74 kyr ago a low velocity column below one of these volcanoes can be traced into the uppermost mantle and corresponds with a planar distribution of low frequency earthquakes in the 20 to 40 km depth range the low frequency earthquakes apparently record the migration of melt in the mafic roots of this large volume crustal magma system

intertidal conglomerate south of yanbu an episodic clastic deposit in the eastern red sea abstract a thin sheet of clastic conglomerate has been located overlying the pleistocene coral limestone in the intertidal zone south of yanbu on the west coast of saudi arabia the conglomerate exhibits a polymodal grain size distribution with gravel to cobble size clasts and sand silt matrix grain and fabric characters of the conglomerate are consistent with a flash flood deposit rather than with a wave processed nearshore sediment wadi wasit draining the adjacent highlands and the coastal plain covered with alluvial deposits derived from the tertiary volcanic and metamorphic rocks provided the coarse grained sediments to the shelf the carbonate cement in the conglomerate is composed of low mg calcite and appears to have been precipitated in non marine conditions the void filling low mg calcite exhibits a coarsening of crystal size away from the grains towards pore interiors the 14 c dating of the carbonate material gave an age of 3580 80 yr b p all evidences suggest that the conglomerate was deposited on the emergent reef flat during an episodic flood stage of the wadi during the middle holocene pluvial period on the west coast of saudi arabia

a late pleistocene transgression in thailand a marine molluscan fauna from ban praksa samut prakan province abstract a late pleistocene molluscan fauna sampled at ban praksa near the chao phraya river mouth lower central plain of bangkok thailand is herein analyzed and paleoecologically characterized revealing a shallow infralittoral coarse hard bottomed environment the comparison of the ban praksa association with several coeval ones recovered from phra pradaeng formation seems to be evidence of a 10 000 year hiatus between two separate groups of marine faunas possibly belonging to different interstadial transgressive peaks that occurred during the long term sea level regression following the last interglacial

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

vp vs ratios in the yellowstone national park region wyoming abstract in this paper we study the variation of v p v s and poisson s ratio in the yellowstone national park region using earthquakes which were well recorded by a local seismic network we find that the average v p v s value within the geothermally active yellowstone caldera is about 7 lower than in the area outside the caldera within the caldera itself there may be a further 2 7 reduction of v p v s in the hydrothermally active norris geyser basin the upper and lower geyser basins and the yellowstone lake and mud volcano regions after considering various possible causes for v p v s changes such as geologic and structural differences thermal effects partial melting and hydrothermal activity we conclude that the most plausible explanation for the observed v p v s reduction is the presence of hot water at temperatures and pore pressures near the water steam transition in the caldera geothermal reservoirs

early mixed water dolomitization in the pleistocene reef limestones west coast of saudi arabia abstract raised pleistocene reef limestone characterizes the western coastal plain of jeddah on the eastern margin of the red sea soon after the mid pleistocene regression the subaerially exposed limestone was subjected to meteoric processes during which mg calcite was converted to stable low mg calcite and partial or complete dissolution of aragonite occurred at various depths early meteoric diagenesis through dissolution precipitation processes had produced sparry calcite in the voids formed by the dissolution of aragonite in the limestone following the late pleistocene holocene marine transgression dolomitization was initiated in the reef in a meteoric marine water mixing zone lack of correlation between dolomite and the evaporite minerals and the low sr concentrations argue against hypersaline solutions as agents of dolomitization mineralogical and chemical data suggest that most diagenetic dolomite is formed at the expense of primary aragonite vertical and lateral variations in the distribution of dolomite aragonite and calcite indicate that dolomitization processes have been affected by the fluctuating mixed water zone associated with sea level oscillations holocene rise in the sea level terminated dolomitization in the lower layers and shifted the dolomitizing front to the upper sections of the limestone dolomite is low in the upper horizons of the reef and occurs as scattered perfect rhombs while in the lower layers it is fine grained and subhedral

high temperature hydrothermal vent fluids in yellowstone lake observations and insights from in situ ph and redox measurements abstract rov investigation of hydrothermal fluids issuing from vents on the floor of yellowstone lake revealed temperatures in excess of 170 c the highest temperature yet reported for vent fluids within yellowstone national park ynp the study site is east of stevenson island at depth of approximately 100 125 m in situ ph and redox measurements of vent fluids were made using solid state sensors designed to sustain the elevated temperatures and pressures ysz membrane electrode with ag ag 2 o internal element and internal pressure balanced ag agcl reference electrode were used to measure ph while a platinum electrode provided redox constraints lab verification of the ph sensor confirmed excellent agreement with nernst law predictions especially at temperatures in excess of 120 c in situ ph values of between 4 2 and 4 5 were measured for the vent fluids at temperatures of 120 to 150 c the slightly acidic vent fluids are likely caused by co 2 enrichment in association with magmatic degassing effects that occur throughout ynp this is consistent with results of simple model calculations and direct observation of co 2 bubbles in the immediate vicinity of the lake floor vents simultaneous redox measurements indicated moderate to highly reducing conditions 0 2 to 0 3 v as typical of measurements of this kind internal and external redox disequilibria likely preclude unambiguous determination of redox controlling reactions redox disequilibria however can be expected to drive microbial metabolism and diversity in the near vent environment thus the combination of in situ ph and redox sensor deployments may ultimately provide the requisite framework to better understand the microbiology of the newly discovered hot vents on yellowstone lake floor