short migration of methane into a gas hydrate bearing sand layer at walker ridge gulf of mexico 1 the mechanisms governing distribution of natural gas hydrates in marine sediment systems are not well understood we focus on a hole in the gulf of mexico walker ridge block 313 hole h where a 2 5 m thick gas hydrate bearing sand occurs within a 152 m thick fine grained mud interval containing gas hydrate in fractures the gas hydrate bearing sand is surrounded by two distinct hydrate free zones 10 m thick above and 3 m thick below we hypothesize that microbial methane generated within the hydrate free zones diffused into the sand and formed gas hydrate we show that the amount of methane produced in the hydrate free zones is likely enough to explain the gas hydrate content of the sand layer additionally we show that there is enough time for dissolved methane to diffuse from the hydrate free zones into the sand we conclude that methane transport over significant distances via fluid flow is not required but that microbial methane could migrate short distances to form gas hydrate in the sand layer

developments in the characterization of complex rock slope deformation and failure using numerical modelling techniques recent advances in the characterization of complex rock slope deformation and failure using numerical techniques have demonstrated significant potential for furthering our understanding of both the mechanisms processes involved and the associated risk this paper illustrates how rock slope analyses may be undertaken using three levels of sophistication level i analyses include the conventional application of kinematic and limit equilibrium techniques with modifications to include probabilistic techniques coupling of groundwater simulations and simplistic treatment of intact fracture and plastic yield such analyses are primarily suited to simple translational failures involving release on smooth basal rear and lateral surfaces where the principle active damage mechanisms are progressive failure and or asperity breakdown level ii analyses involve the use of continuum and discontinuum numerical methods in addition to simple translation level ii techniques can be applied to complex translational rock slope deformations where step path failure necessitates degradation and failure of intact rock bridges along basal rear and lateral release surfaces active damage processes in this case comprise not only strength degradation along the release surface e g asperity breakdown but also a significant component of brittle intact rock fracture level iii analyses involve the use of hybrid continuum discontinuum codes with fracture simulation capabilities these codes are applicable to a wide spectrum of rock slope failure modes but are particularly well suited to complex translation rotational instabilities where failure requires internal yielding brittle fracturing and shearing in addition to strength degradation along release surfaces through a series of rock slope analyses the application of varied numerical methods are discussed particular emphasis is given to state of the art developments and potential use of level iii hybrid techniques d 2005 elsevier b v all rights reserved

acoustic response of gas hydrate formation in sediments from south china sea abstract gas hydrate has been recognized as a potential energy resource in south china sea scs understanding the acoustic response of gas hydrate formation in the scs sediments is essential for regional gas hydrate investigation and quantification the sediments were obtained from gravity core sampling at e 115 12 52363 n 19 48 40299 gas hydrate was formed within a gas water saturated scs sediments system combination of a new bender element technique and coated time domain reflectometry tdr was carried out to study the acoustic response of hydrate occurrence in scs sediments the results show the acoustic signal becomes weak when hydrate saturation sh is lower than 14 the acoustic velocities vp vs of the sediments increase with sh during hydrate formation and vs increases relatively faster when sh is higher than 14 these results indicate that tiny hydrate particles may firstly float in the pore fluid which causes a significant acoustic attenuation but has little influence on shear modulus as time lapses and sh approaches 14 numerous particles coalesce together and contact with sediment particles as a result vs has a sharp increase when hydrate saturation exceeds 14 several velocity models were validated with the experimental data which suggests a combination of the bgtl biot gassmann theory modified by lee model and the weighted equation is suitable to estimate sh in scs

microseismic emissions from flowslide type movements in south wales abstract many of the unstable hillslopes of south wales have landslides that turn into flowslides over part of their tract the valley slopes at pant teg and glynrhigos are unstable as they possess the optimum requirements for slope failure they have probably been affected by repeated movements during the last 10 000 years significant acoustic emissions ae have been recorded from two landslide sites both subsequent to a major failure pant teg and during continuous movement glynrhigos four distinct types of ae have been recognised so far with frequencies in the 1 7 khz bandwidth with particular peaks at 1 2 2 0 4 2 4 9 5 5 and 6 5 khz the results indicate that there is a potential in developing a warning system for identifying increasing instability

velocity structure of a gas hydrate reflector seismic reflection profiles across many continental margins have imaged bottom simulating reflectors bsrs parallel to the seabed these are often interpreted as the base of a zone in which methane hydrate ice is stable waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a bsr and its thickness a test of this method at a drill site of the ocean drilling program predicts that sediment pores beneath the bsr contain free methane for approximately 30 meters the hydrate and underlying gas represent a large global reservoir of methane which may have economic importance and may influence global climate

hydrate distribution off vancouver island from multifrequency single channel seismic reflection data on the northern cascadia margin single channel seismic data clearly image the bottom simulating reflector bsr that marks the base of the hydrate stability zone airguns with three distinct source frequencies 30 75 and 150 hz were recorded along several coincident lines and at all frequencies the bsr appears as a single pulse bsr reflection coefficients are slightly larger for the 30 hz data than for the 75 or 150 hz data multi frequency analysis indicates that the bsr is due to a single sharp interface at the base of the hydrate zone whereas the velocity structure away from the interface must be gradationally varying so as to produce no separate reflection and no tuning effects at the 75 and 150 hz frequencies in contrast the seafloor reflection in some areas has significantly larger amplitudes for data recorded with the 75 hz source relative to the 30 hz source synthetic seismogram analysis of the two data sets shows that the high amplitudes can be produced by a 2 m thick high velocity layer at the seafloor with velocities and densities corresponding to those of carbonate using the 75 hz source seafloor and bsr amplitudes and reflection coefficients were measured over a tight grid of lines nominally spaced at 200 m maximum bsr reflection coefficients of 0 15 0 18 were observed beneath topographic highs while maximum seafloor reflection coefficients of up to 0 5 0 6 were found on the flanks of the topographic highs this suggests that topography provides a major control on the flow of methane bearing fluids amplitude measurements converted to values of velocity above the bsr were used to estimate hydrate concentrations which reaches a maximum of 15 18 of the total sediment volume with mean values near 5 10 over the 100 km2 survey area the volume of methane gas in the hydrate reservoir is estimated as 6 4 l010 m3 or 2 1 trillion cubic feet

vertical tectonics and the origins of bsrs along the peru margin abstract the distribution of bottom simulating reflections bsrs which mark the base of the gas hydrate zone on marine seismic records across the peru margin is examined with respect to tectonic uplift sedimentation and carbon content of sediment where accretion of only deep ocean pelagic sediment containing less than 1 carbon is seismically imaged no bsr is observed no bsr is apparent on seismic records of carbon rich 4 8 sediment of rapidly subsiding basins bsrs are abundant on records of carbon rich sediment affected by tectonic uplift and or rapid sedimentation in areas of uplift the bottom simulating reflectors contain small amounts of free gas in contact with sediment containing small amounts of gas hydrate during uplift free gas is released from gas hydrates by dissociation as the hydrate phase boundary shifts upward with respect to sea level the strong effects of free gas in reducing seismic velocity and gas hydrate in increasing velocity can explain the relatively small total quantities of gas and hydrate indicated by observations of bsrs off peru

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

thermal evolution of the new zealand hikurangi subduction margin impact on natural gas generation and methane hydrate formation a model study abstract we present an integrated 2d model of thermal and microbial generation of methane migration into the gas hydrate stability zone hsz and formation of methane hydrates the model reconstructs the shallow 0 20 km thermal structure of the subduction interface between the australian plate and the subducting pacific plate and the trench basin pegasus basin modelled temperatures of less than 110 c within pegasus basin constrain the generation of oil and gas whilst a cool thermal regime is predicted to limit thermogenic generation of gas to a burial depth of 10 km it extends the interval where prolific microbial gas generation occurs the modelled rate of microbial generation of methane increases beneath the hsz and peaks at 1600 m below seafloor diffusive upward migration of microbially generated methane is interpreted to lead to widespread methane hydrate formation and the presence of a semi continuous bottom simulating reflector bsr predicted average hydrate saturation within the hsz is 0 9 for a modelled sedimentary organic matter content of 0 5 and 1 6 for 1 organic matter in fine grained pegasus basin sediments considerably higher concentrations of methane hydrate of up to 20 70 are predicted to occur where gas migration is focussed within the frontal anticline and proto thrust zone southeast of the modern accretionary wedge and in channel and basin floor sandstones related to the hikurangi channel the hikurangi channel sedimentary system transported coarse clastic sediments eroded from the rising southern alps along the eastern margin of the pegasus basin since the miocene it provides carrier beds specifically for transport of thermogenic gas generated close to the subduction interface a buried mesozoic accretionary wedge originating from subduction of the pacific plate beneath gondwana further focusses the migration of gas focussed migration of thermogenic gas leads to the highest predicted hydrate concentrations in potential channel sand reservoirs

geophysical investigations of large landslides in the carnic region of southern austria abstract the area under investigation for the past two decades is in the vicinity of the gailtal lineament which is the most dominant tectonic feature of the eastern alps of southern austria an area of about 8 km2 is in a state of constant instability as documented by movement of road tracks of several centimetres per year geotechnical and surveying techniques have been used to measure these movements in the past but without solving the problem of the mechanism of these failure processes geophysical methods seismic refraction geoelectrics and electromagnetics were applied in order to determine the validity of one of the discussed movement models in situ velocity measurements were used to identify different lithologies beneath surficial talus deposits the thickness of these talus deposits of about 4 30 m found by seismic refraction clearly demonstrates that huge blocks i e more or less undisturbed lithologic units within the talus debris are in close contact with the basement this basement which shows lower seismic velocities in different parts combined with low electric resistivities is obviously strongly disturbed by different failure surfaces the different gliding velocity of the blocks and the talus debris deposits leads to a geological model in which huge rock blocks move slowly in relation to the disintegrating basement whereas the talus debris deposits move over the surface of these blocks at a higher velocity the interpretation of these landslide studies is not a straightforward analysis it is a complex problem with a complex solution including all information from geotechnical geophysical and surveying investigations

reflectivity template a quantitative intercept gradient avo analysis to study gas hydrate resources a case study of iranian deep sea sediments abstract presence of gas hydrate and free gas in iranian part of makran accretionary prism changes the elastic properties of unconsolidated sediments and produces sharp bottom simulating reflectors bsrs which are observed on the 2 d seismic data different methods have been applied to estimate the gas hydrate and free gas saturations in marine sediments based on seismic measurements most of these methods are based on relating the elastic properties to the hydrate and free gas saturations and remotely estimating their concentration in this regard using the effective medium theory emt which was developed for different modes of hydrate distribution is more considered among other rock physics theories the main concern about saturation estimations based on emt is that the velocities of the hydrate bearing sediments primarily depend on how they are distributed within the pore space therefore understanding the modes of hydrate distribution at least cementing or non cementing modes is necessary to decrease the estimation uncertainties the first intention of paper is to investigate amplitude variation versus offset avo analysis of bsr to determine the hydrate distribution modes the results from the probable saturation revealed that if the hydrate cements the sediment grains bsr would show the avo class iv and if hydrate does not cement the sediment grains then bsr would show either the avo class ii or class iii depending on the free gas saturation just beneath the bsr the second intention of paper is to introduce some templates called reflectivity templates rts for quantitative study of hydrate resources these templates are provided based on the emt to quantify the hydrate and free gas near the bsr validation of this approach by synthetic data showed that a reliable quantification could be achieved by intercept gradient rts only if these attributes are determined with a high accuracy and good assumptions are made about the mineralogical composition and porosity of the unconsolidated host sediments the results of this approach applied to a 2 d marine pre stack time migrated seismic line showed that less than 10 of the gas hydrate accumulated near to the bsr in anticlinal ridge type structure of iranian deep sea sediments the free gas saturation near to the bsr by assuming a homogeneous distribution was less than 3 and by assuming patchy distribution was about 3 10

analysing sand dominated channel systems for potential gas hydrate reservoirs using an avo seismic inversion technique on the southern hikurangi margin new zealand abstract gas hydrates have recently been recognised as a class of unconventional petroleum resource and the economic viability of gas production from hydrates is now being viewed as a realistic possibility within the next decade therefore potential offshore hydrate accumulations in the world class endowed gas hydrate province the hikurangi margin new zealand represent a significant medium to long term opportunity to meet the country s future energy requirements in this paper we delineate a potential gas hydrate reservoir in the east coast basin new zealand and quantitatively estimate its gas hydrate concentrations from 2d seismic data with no well information available the target is interesting for exploration since it shows evidence for gas hydrate bearing sands in particular buried channel systems we use a combined analysis of high resolution velocity analysis amplitude versus offset avo attribute and avo inversion to investigate whether we can identify regions that are likely to contain highly concentrated gas hydrates and whether they are likely to be sand dominated to estimate hydrate concentrations we apply a rock physics model our results indicate the presence of several up to 200 m thick zones that are likely to host gas hydrates with one location predicted to consist of high permeable channel sands and an inferred gas hydrate saturation of 25 these findings suggest significant amounts of gas hydrates may be present in high quality reservoirs on this part of the margin

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

acquisition and processing strategies for 3d georadar surveying a region characterized by rugged topography efficiently performing 3d ground penetrating radar gpr or georadar surveys across rugged terrain and then processing the resultant data are challenging tasks conventional approaches using unconnected gpr and topographic surveying equipment are excessively time consuming for such environments and special migration schemes may be required to produce meaningful images we have collected gpr data across an unstable craggy mountain slope in the swiss alps using a novel acquisition system that records gpr and coincident coordinate information simultaneously undulating topography dips of 8 to 16 and boulders with diameters up to about 2 m complicated the field campaign after standard processing the data were found to be plagued by time shifts associated with minor coordinate inaccuracies uneven antenna ground coupling and numerous small gaps in data coverage these problems were resolved by passing the data sequentially through an adaptive f xy deconvolution routine and f kx and f ky filters this filtering also reduced incoherent noise finally the data were migrated using a 3d algorithm that accounted for the undulating topography the nonmigrated and migrated images contained gently and moderately dipping reflections from lithological boundaries and actively opening fracture zones a suite of prominent diffraction patterns was generated at a steeply dipping fracture zone that projected to the surface through this case history we introduce a general strategy for 3d gpr studies of topographically rugged land

logging while drilling and wireline velocities site nghp 01 10 krishna godavari basin india abstract at site nghp 01 10 krishna godavari basin india the downhole wireline logging tool measured higher porosity and sonic velocities in gas hydrate bearing sediments compared to the logging while drilling lwd acquired data in two closely spaced wells 10 m using a rock physics model that assumes random fractures in unconsolidated sediments using hashin shtrikman bounds we show that difference in physical properties could be due to intra site difference in the distribution and pattern of hydrate filled fractures rather than differences in the volume of gas hydrate our fracture inclusive model suggests that between the two holes the porosity and hydrate saturation of the background sediments is similar while porosity and hydrate saturation of the fracture systems change considerably resulting in the change of the sonic log responses relative changes in hydrate saturation between sediments and fractures at 90 m below the sea floor mbsf depth at a prominent seismic horizon suggests that fracture filling hydrate could have partly originated as pore filling material in the sediments and grew as fracture filling material as a result of fluid flow the volume fracture profile of hydrate fracture porosity fracture saturation between the two holes further suggests that the higher concentration of fractures in the wireline hole may not be a natural in situ condition but rather a manifestation of the drilling compounded with time lapse in data recording between the lwd and wireline log data frequently reported worldwide intra site variability in hydrate saturation from lwd and wireline logs in close proximity could be more related to interpretative methods than actual geologic variability

elastic wave velocity characterization of gas hydrate bearing fractured reservoirs in a permafrost area of the qilian mountain northwest china abstract there are two types of gas hydrate bearing reservoirs in the permafrost area of qilian mountain most of the gas hydrates occur mainly in the fractured mudstone reservoirs and rarely in the pores of the sandstone reservoirs in this study for the acoustic velocity characterization of the fractured gas hydrate reservoirs of the qilian mountain permafrost area some mudstone core samples were collected for physical rock experiments such as the acoustic experiment and the porosity and permeability experiment an acoustic velocity numerical simulation of gas hydrate reservoirs was performed according to the biot theory and the differential effective medium theory with the conditions of multiple gas hydrate occurrence models including the suspension model the semi cementation model and the cementation model and considering both infinite and penny shaped cracks fracture porosity was added to the core samples that only contain matrix porosity with fracture porosity ranging from 0 01 to 5 the variation laws between acoustic velocity with fractured porosity and hydrate saturation are obtained 1 in the case of an infinite crack if the fractured porosity is 0 01 1 the p wave velocity decreases rapidly in the case of the three occurrence models if the fractured porosity is higher than 1 the acoustic velocity decreases gradually if the crack shape is a penny shaped crack the p wave velocity decreases almost linearly with increasing fracture porosity 2 if the hydrate occurrence model is the suspension model the p wave velocity increases slightly with increasing hydrate saturation if the occurrence model is the semi cementation model or the cementation model when the gas hydrate saturation of the infinite crack ranges from 0 to 80 the acoustic velocity increases approximately linearly whereas when the gas hydrate saturation ranges from 80 to 100 the velocity increases rapidly if the crack is a penny shaped crack the velocity increases almost linearly with increasing gas hydrate saturation from 0 to 100 3 it is found that the fractured gas hydrate reservoirs of the qilian mountain permafrost area contain both penny shaped and infinite cracks of which the infinite crack is the main crack shape the gas hydrate occurrence in the qilian mountain permafrost area mainly follows the suspension model this has significance for the seismic exploration and log evaluation of gas hydrate bearing fractured reservoirs in the permafrost area of the qilian mountain in studying the acoustic velocity characterization the crack shapes and occurrence models of gas hydrate reservoirs in the study area

gas hydrate accumulations related to focused fluid flow in the pegasus basin southern hikurangi margin new zealand abstract the hikurangi margin east of the north island of new zealand is known to contain significant deposits of gas hydrates this has been demonstrated by several multidisciplinary studies in the area since 2005 these studies indicate that hydrates in the region are primarily located beneath thrust ridges that enable focused fluid flow and that the hydrates are associated with free gas in 2009 2010 a seismic dataset consisting of 2766 km of 2d seismic data was collected in the undrilled pegasus basin which has been accumulating sediments since the early cretaceous bottom simulating reflections bsrs are abundant in the data and they are accompanied by other features that indicate the presence of free gas and concentrated accumulations of gas hydrate we present results from a detailed qualitative analysis of the data that has made use of automated high density velocity analysis to highlight features related to the hydrate system in the pegasus basin two scenarios are presented that constitute contrasting mechanisms for gas charged fluids to breach the base of the gas hydrate stability zone the first mechanism is the vertical migration of fluids across layers where flow pathways do not appear to be influenced by stratigraphic layers or geological structures the second mechanism is non vertical fluid migration that follows specific strata that crosscut the bsr one of the most intriguing features observed is a presumed gas chimney within the regional gas hydrate stability zone that is surrounded by a triangular in 2d region of low reflectivity approximately 8 km wide interpreted to be the result of acoustic blanking this chimney structure is cored by a 200 m wide low velocity zone interpreted to contain free gas flanked by high velocity bands that are 200 400 m wide interpreted to contain concentrated hydrate deposits

forecasting giant catastrophic slope collapse lessons from vajont northern italy rapid giant landslides or sturzstroms are among the most powerful natural hazards on earth they have minimum volumes of similar to10 6 10 7 m 3 and normally preceded by prolonged intervals of accelerating creep are produced by catastrophic and deep seated slope collapse loads similar to1 10 mpa conventional analyses attribute rapid collapse to unusual mechanisms such as the vaporization of ground water during sliding here catastrophic collapse is related to self accelerating rock fracture common in crustal rocks at loads similar to1 10 mpa and readily catalysed by circulating fluids fracturing produces an abrupt drop in resisting stress measured stress drops in crustal rock account for minimum sturzstrom volumes and rapid collapse accelerations fracturing also provides a physical basis for quantitatively forecasting catastrophic slope failure c 2003 elsevier science b v all rights reserved

microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the soultz hdr site summary a high rate injection of 20 000 m3 of water into granite between 2 8 and 3 4 km depth at the soultz hot dry rock hdr test site in france in 1993 september led to a 200 fold increase in borehole transmissivity and produced a subvertical cloud of microseismicity of dimensions 0 5 km wide 1 2 km long 1 5 km high and oriented 25 nw the resulting data set is unusually complete and well suited to studying permeability creation enhancement processes in crystalline rock and the utility of microseismic data for revealing them although the microseismic cloud defined using joint hypocentre determination jhd locations was diffuse and showed little structure application of the collapsing method showed it to be composed largely of discrete tubes and planes that propagated coherently one prominent structure that extended 350 m downwards from the vicinity of a flow inlet early in the injection and that appears to contain a major flow path was subjected to detailed investigation to establish its hydrogeologic nature and the mechanisms underpinning its inferred permeability enhancement high resolution microseismic mapping techniques i e multiplets and clustering showed it to be a subvertical nnw sse striking fracture zone of width 10 20 m the strike and scale of the structure identifies it as a member of a family of hydrothermally altered cataclastic shear structures that constitute the primary permeable paths for fluid migration within the rock mass both under ambient and forced fluid flow conditions the microseismicity occurred on subvertical small scale fractures within the cataclastic shear zone whose azimuths scatter within 22 of parallel to the parent structure although the structure is likely to have been naturally permeable to some degree its permeability appears to have been significantly enhanced as a consequence of the injection the most likely mechanism of permeability enhancement which is in accord with the strong preference for the microseismicity to grow downwards involves strike slip shearing which produced the opening of vertical tubes at along strike jogs in the fault the so called hill mesh seismic moment release averaged over the structure suggests shear displacements of at least 0 3 mm occurred which are sufficient to generate aperture changes that are hydraulically significant the preponderance of discrete structures within the microseismic cloud after collapsing suggests that significant flow and permeability enhancement i e stimulation within the rock mass is largely confined to the interiors of shear zones that appear to have a spacing of approximately 100 m

seismic anisotropy in gas hydrate and gas bearing sediments on the blake ridge from a walkaway vertical seismic profile 1 we present results from an analysis of anisotropy in marine sediments using walkaway vertical seismic profiles from the blake ridge offshore south carolina we encountered transverse isotropy ti with a vertical symmetry axis in a gas hydrate bearing unit of clay and claystone with thomsen parameters e 0 05 0 02 and 0 04 0 06 ti increased to e 0 16 0 04 and 0 19 0 12 in the underlying gas zone rock physics modeling suggests that the observed ti is caused by a partial alignment of clay particles rather than high velocity gas hydrate veins similarly the increase of ti in the gas zone is not caused by thin low velocity gas layers but rather we speculate by the sharp contrast between seismic properties of an anisotropic sediment frame and elongated gas bearing pore voids our results underscore the significance of anisotropy for integrating near vertical and wide angle seismic data

site effect analysis around the seismically induced ananevo rockslide kyrgyzstan in 1911 the surface wave magnitude 8 2 kemin earthquake hit northeastern tien shan kyrgyzstan close to the cities of bishkek and almaty the capitals of kyrgyzstan and kazakhstan respectively several hundreds of people were killed by the earthquake some by indirect effects such as landslides and mudflows a particular but nonfatal landslide triggered by the kemin event was a rockslide in the vicinity of ananevo north of lake issyk kul kyrgyzstan rockslide located above the fault zone activated in 1911 in the summer of 1999 a geophysical seismological field trip was organized to study geology and to record seismic ground motions on and around the ananevo rockslide the work was part of project assessing seismogenic landslide hazard in northern kyrgyzstan based on various case studies of slope failures in connection with site specific ground motion dynamics the geophysical investigations consisted of seismic refraction tests processed as 2d seismic tomographies and surface wave inversion which were combined to build a 3d geophysical model of the landslide site ground motions from small earthquakes were analyzed using several techniques to define site effects over the mountain massif both h v and standard spectral ratios indicated lower dominant frequencies with stronger amplification in the crest region with respect to the mountain slope these effects could be partially simulated by 1d 2d and 3d finite element modeling by comparing the numerical results with the experimental data the presence of a surficial low velocity layer of varying thickness appeared to be the key factor controlling the ground motion around the rockslide

detecting slope deformation using two pass differential interferometry implications for landslide studies on earth and other planetary bodies landslide features have been identified on earth and the moon mars venus as well on the jovian moons by focusing on a terrestrial landslide complex we test the operational parameters of radarsat 1 and the use of two pass differential interferometry to detect change to map its extent and to measure the amount of movement over a given time period radarsat 1 was chosen because of its variable imaging modes and geometry for investigations of landslide motions using remote sensing techniques repeat pass data are required synthetic aperture radar sar interferometry insar can ideally monitor movements across the whole surface of a landslide to a millimeteric precision yielding a coverage significantly better than that obtained by ground instrumentation obtaining optimal data for insar analysis requires controlled orbital characteristics and imaging geometries an understanding of the landslide characteristics and behavior a cooperative surface and mitigation of the factors that can affect phase using two pass differential interferometry a slope deformation map has been generated from radarsat 1 data for part of the black ven landslide 2 52 w 50 40 n on the south coast of england four months separate the insar pair during which time 0 03 m of subsidence was measured from this a movement rate of 0 09 m yr can be calculated this agrees well with ground observations and an in situ record of movement thus demonstrating that the technique can be used to investigate landslides with further refinement it can provide more direct measurements of landslide deformation on earth and other planetary bodies than are currently available

velocity structure of a bottom simulating reflector offshore peru results from full waveform inversion abstract much of our knowledge of the worldwide distribution of submarine gas hydrates comes from seismic observations of bottom simulating reflectors bsrs full waveform inversion has proven to be a reliable technique for studying the fine structure of bsrs using the compressional wave velocity we applied a non linear full waveform inversion technique to a bsr at a location offshore peru we first determined the large scale features of seismic velocity variations using a statistical inversion technique to maximise coherent energy along travel time curves these velocities were used for a starting velocity model for the full waveform inversion which yielded a detailed velocity depth model in the vicinity of the bsr we found that the data are best fit by a model in which the bsr consists of a thin low velocity layer the compressional wave velocity drops from 2 15 km s down to an average of 1 70 km s in an 18 m thick interval with a minimum velocity of 1 62 km s in a 6 m interval the resulting compressional wave velocity was used to estimate gas content in the sediments our results suggest that the low velocity layer is a 6 18 m thick zone containing a few percent of free gas in the pore space the presence of the bsr coincides with a region of vertical uplift therefore we suggest that gas at this bsr is formed by a dissociation of hydrates at the base of the hydrate stability zone due to uplift and subsequently a decrease in pressure

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

gas hydrate saturations estimated from fractured reservoir at site nghp 01 10 krishna godavari basin india 1 during the indian national gas hydrate program expedition 01 nghp 01 one of the richest marine gas hydrate accumulations was discovered at site nghp 01 10 in the krishna godavari basin the occurrence of concentrated gas hydrate at this site is primarily controlled by the presence of fractures assuming the resistivity of gas hydrate bearing sediments is isotropic the conventional archie analysis using the logging while drilling resistivity log yields gas hydrate saturations greater than 50 as high as 80 of the pore space for the depth interval between 25 and 160 m below seafloor on the other hand gas hydrate saturations estimated from pressure cores from nearby wells were less than 26 of the pore space although intrasite variability may contribute to the difference the primary cause of the saturation difference is attributed to the anisotropic nature of the reservoir due to gas hydrate in high angle fractures archie s law can be used to estimate gas hydrate saturations in anisotropic reservoir with additional information such as elastic velocities to constrain archie cementation parameters m and the saturation exponent n theory indicates that m and n depend on the direction of the measurement relative to fracture orientation as well as depending on gas hydrate saturation by using higher values of m and n in the resistivity analysis for fractured reservoirs the difference between saturation estimates is significantly reduced although a sizable difference remains to better understand the nature of fractured reservoirs wireline p and s wave velocities were also incorporated into the analysis

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

characterizing an unstable mountain slope using shallow 2d and 3d seismic tomography as transport routes and population centers in mountainous areas expand risks associated with rockfalls and rockslides grow at an alarming rate as a consequence there is an urgent need to delineate mountain slopes susceptible to catastrophic collapse in a safe and noninvasive manner for this purpose we have developed a 3d tomographic seismic refraction technique and applied it to an unstable alpine mountain slope a significant segment of which is moving at 0 01 0 02 m year toward the adjacent valley floor first arrivals recorded across an extensive region of the exposed gneissic rock mass have extraordinarily low apparent velocities at short 0 2 m to long 100 m shot receiver offsets inversion of the first arrival traveltimes produces a 3d tomogram that reveals the presence of a huge volume of very low quality rock with ultralow to very low p wave velocities of 500 2700 m s these values are astonishingly low compared to the average horizontal p wave velocity of 5400 m s determined from labora

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

evolution of fluid expulsion and concentrated hydrate zones across the southern hikurangi subduction margin new zealand an analysis from depth migrated seismic data identification of methane sources controlling hydrate distribution and concentrations in continental margins remains a major challenge in gas hydrate research lack of deep fluid samples and high quality regional scale seismic reflection data may lead to underestimation of the significance of fluid escape from subducting and compacting sediments in the global inventory of methane reaching the hydrate zone the water column and the atmosphere the distribution of concentrated hydrate zones in relation to focused fluid flow across the southern hikurangi subduction margin was investigated using high quality long offset 10 km streamer pre stack depth migrated multichannel seismic data analysis of low p wave velocity zones bright reverse polarity reflections and dim amplitude anomalies reveals pathways for gas escape and zones of gas accumulation the study shows the structural and stratigraphic settings of three main areas of concentrated hydrates 1 the opouawe bank dominated by focused periodic fluid input along thrust faults sustaining dynamic hydrate concentrations and gas chimneys development 2 the frontal anticline with a basal set of protothrusts controlling permeability for fluids from deeply buried and subducted sediments sustaining hydrate concentrations at the crest of the anticline and 3 the hikurangi channel with buried sand dominated channels hosting significant amounts of gas beneath the base of the hydrate zone in sand dominated channels gas injection into the hydrate zone favors highly concentrated hydrate accumulations the evolution of fluid expulsion controlling hydrate formation offshore southern hikurangi is described in stages during which different methane sources in situ buried and thermogenic have been dominant

grain scale imaging and compositional characterization of cryo preserved india nghp 01 gas hydrate bearing cores abstract we report on grain scale characteristics and gas analyses of gas hydrate bearing samples retrieved by nghp expedition 01 as part of a large scale effort to study gas hydrate occurrences off the eastern indian peninsula and along the andaman convergent margin using cryogenic scanning electron microscopy x ray spectroscopy and gas chromatography we investigated gas hydrate grain morphology and distribution within sediments gas hydrate composition and methane isotopic composition of samples from krishna godavari kg basin and andaman back arc basin borehole sites from depths ranging 26 to 525 mbsf gas hydrate in kg basin samples commonly occurs as nodules or coarse veins with typical hydrate grain size of 30 80 m as small pods or thin veins 50 to several hundred microns in width or disseminated in sediment nodules contain abundant and commonly isolated macropores in some places suggesting the original presence of a free gas phase gas hydrate also occurs as faceted crystals lining the interiors of cavities while these vug like structures constitute a relatively minor mode of gas hydrate occurrence they were observed in near seafloor kg basin samples as well as in those of deeper origin 100 mbsf and may be original formation features other samples exhibit gas hydrate grains rimmed by nacl bearing material presumably produced by salt exclusion during original hydrate formation well preserved microfossil and other biogenic detritus are also found within several samples most abundantly in andaman core material where gas hydrate fills microfossil crevices the range of gas hydrate modes of occurrence observed in the full suite of samples suggests a range of formation processes were involved as influenced by local in situ conditions the hydrate forming gas is predominantly methane with trace quantities of higher molecular weight hydrocarbons of primarily microbial origin the composition indicates the gas hydrate is structure i

focussed fluid flow on the hikurangi margin new zealand evidence from possible local upwarping of the base of gas hydrate stability the southern hikurangi subduction margin is characterized by significant accretion with predicted high rates of fluid expulsion bottom simulating reflections bsrs are widespread on this margin predominantly occurring beneath thrust ridges we present seismic data across the porangahau ridge on the outer accretionary wedge the data show high amplitude reflections above the regional bsr level based on polarity and reflection strength we interpret these reflections as being caused by free gas we propose that the presence of gas above the regional level of bsrs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids although we cannot entirely rule out alternative processes simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low permeability slope basins into the porangahau ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability focussing of fluid flow is predicted to take place deep in the accretionary wedge and or the underthrust sediments above the high amplitude reflections sediment reflectivity is low a lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas hydrate related amplitude blanking structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge a gap in the bsr in the southern part of the study area may be caused by a loss of gas during fluid expulsion we speculate that gaps in otherwise continuous bsrs that are observed beneath some thrusts on the hikurangi margin may be characteristic of other locations experiencing focussed fluid expulsion

sources of methane for marine gas hydrate inferences from a comparison of observations and numerical models the supply of methane for marine gas hydrate is commonly attributed to local conversion of organic material within the zone of stability or to migration of methane bearing fluids from a deeper source area however the relative importance of these methane sources is not well known we use numerical models for the formation of gas hydrate to assess the influence of methane supply on observable features of hydrate occurrences model predictions for the pore fluid chlorinity and the volumes of hydrate and free gas are compared with observations from the blake ridge and cascadia margin we find that the observations from the blake ridge can be explained with a deep methane source if a saturated fluid rises with a velocity of 0 26 mm yr 1 an equally good fit to the observations is obtained by combining in situ production of methane with an upward fluid velocity of 0 08 mm yr 1 which is compatible with estimates of fluid velocity at site 997 observations from the cascadia margin can be explained with a deep methane source if the upward fluid velocity is 0 42 mm yr 1 the predicted volume of hydrate 2 of the pore space is much smaller than some previous estimates and a layer of free gas 1 of the pore space develops below the stability zone allowing for in situ production at the cascadia margin lowers the upward fluid velocity 0 35 mm yr 1 needed to explain the pore water chlorinity

fracture coalescence as a mechanism for earthquakes observations based on mining induced microseismicity abstract microseismic events with magnitudes less than zero recorded within a volume at depth in an underground mine are used to evaluate failure conditions associated with a magnitude 2 9 event rockburst the approach incorporated several independent methods of analysis including the principal component analysis pca of seismicity focal mechanisms stress inversion underground in situ stress measurements and structural mapping and three dimensional numerical modelling derived stresses a good correlation was found between stress inversion and pca derived microseismic failure planes and structural mapping and between the in situ principal stress orientations and those obtained through stress inversion and numerical modelling a few days prior to the large event and during the aftershock sequence a change in microseismic failure plane orientation to a shallower dip angle than mapped underground was found to coincide with the numerical modelling derived plane of maximum slip potential this orientation along with measured fracture characteristics persistence and spacing and an increase in event clustering into the plane suggests that the formation of the large event plane of rupture was likely related to the coalescence of mapped fractures an observed reduction in stress release accompanying the increased tendency towards planarity prior to the large event indicates that the development of a large rupture surface occurred under an increased effective shear stress build up as part of the earthquake generation process and the process of coalescence can be considered as the breakage of barriers new fracture growth accompanied by an increase in the effective shear stress on the remaining asperities pre existing fractures

seismic evidence of free gas migration through the gas hydrate stability zone ghsz and active methane seep in krishna godavari offshore basin abstract seismic amplitude versus offset avo analysis was performed on the multichannel seismic data in the vicinity of site nghp 01 10 where thick fracture filled gas hydrate is reported to understand the fluid migration in fracture dominated gas hydrate system amplitude preserved common image gathers cig are used in extracting the seismic amplitude with offset for seafloor bottom simulating reflectors bsr and different horizons within the gas hydrate stability zone ghsz the extracted amplitudes are fitted with three term shuey s avo approximation to estimate the intercept and gradient values based on the intercept and gradient values two distinct classes of seismic avo responses are observed class iv avo decreasing negative amplitudes with increasing offsets and class iii avo increasing negative amplitudes with increasing offsets for the bsr and other horizons above the bsr the large negative intercept and gradient values which indicate class iii avo ranges from 0 2 to 1 8 for the inline seismic profile and from 0 01 to 0 3 for the crossline profile the presence of class iii avo anomaly within the gas hydrate stability zone ghsz provides evidence of existence of free gas which may be migrating along the fault system some of the active faults are exposed on the surface and show gas venting signatures such as gas flares and pockmarks in the multibeam data

anisotropic seismic tomography of a potential hot dry rock reservoir before and during induced pressurization to assess the effects of changing fluid pressure in a potential hot dry rock reservoir two cross hole seismic surveys were conducted one at ambient pressures and one with the investigated volume hydraulically overpressured by 3 3 mpa sources and receivers were located in two straight subvertical boreholes 100 m apart traveltime data were inverted for velocity information in two phases during the first phase the seismic velocities were constrained to be isotropic and during the second they were allowed to be anisotropic accounting for anisotropy enhanced greatly the interpretability of the tomograms before pressurization a low velocity anomaly at 455 475 m depth correlated with a subhorizontal zone of hydraulically permeable fractures connecting the two boreholes although the absolute magnitude of anisotropy is not well constrained the dominant orientation of the ti axes is consistent with the local stress field hydraulic over pressurization resulted in a pronounced extension of the low velocity zone but had no significant effects on the velocity structure elsewhere the results of this study suggest that anisotropic seismic tomography may be a key method for characterizing hot dry rock reservoirs

on the application of sar interferometry to geomorphological studies estimation of landform attributes and mass movements this paper presents two examples of application of synthetic aperture radar sar interferometry insar to typical geomorphological problems the principles of insar are introduced taking care to clarify the limits and the potential of this technique for geomorphological studies the application of insar to the quantification of landform attributes such as the slope and to the estimation of landform variations is investigated two case studies are presented a first case study focuses on the problem of measuring landform attributes by interferometric sar data the interferometric result is compared with the corresponding one obtained by a digital elevation model dem in the second case study the use of insar for the estimation of landform variations caused by a landslide is detailed

ocean warming and gas hydrate stability on the mid norwegian margin at the storegga slide abstract the sensitivity of oceanic gas hydrates and submarine slope stability to the combined forcing of sea level changes and bottom water perturbation is a critical issue for risk assessment in the storegga slide area on the mid norwegian margin evidence for the existence of gas hydrates both inside and outside the storegga slide complex comes from reflection seismic profiles where a bottom simulating reflection marks today s base of the gas hydrate stability zone paleo bottom water temperatures show a relatively fast increase at approximately 12 5 10 ka calendar years following the younger dryas while stable warm water conditions have prevailed since then despite sea level rise this warm water inflow caused a major reduction in the thickness of the gas hydrate stability zone along the upper slope of the mid norwegian margin modelling results indicate that critical hydrate stability conditions and consequently the maximal potential pore pressure build up occur at the location of the storegga slide headwall although the major phase of hydrate melting predates the storegga slide event dated at 8 2 ka calendar years reduced hydrate stability conditions could have facilitated or contributed to sub marine slope failure additionally the bottom simulating reflections within the slide complex seem to have nearly adjusted to new equilibrium conditions highlighting the dynamics of hydrate stability in continental margin sediments under environmental changes climate change geohazards

the potential volume of oceanic methane hydrates with variable external conditions gas hydrate abundance in marine sediment depends on gas concentration and the available pore space within certain stability limits potentially gas hydrates can occur between the seafloor and a locus of subbottom depths where geothermal gradients intersect gas gas hydrate pore water equilibrium curves perpendicular to a given continental margin the lens shaped area between these two bounding surfaces a sl varies according to seven basic parameters gas composition water activity a w bottom water temperature t b geothermal gradient g slope depth z slb slope gradient z and sea level relative to the shelf break z 0 assuming pure ch 4 gas 35 km 2 of sediment can host gas hydrate across an average continental margin at a pleistocene lowstand a w 0 981 t b 0 c g 0 c z slb 4000 m z 0 04 z 0 0 however this potential area would decrease with smaller a w higher t b greater g shallower z slb steeper z and lower z 0 and increase with opposite external conditions of the basic parameters temperature t b and g and bathymetry z slb and z can particularly influence the distribution of gas hydrate on continental slopes a hydrothermal gradient with e g surface temperatures t b will also decrease a sl although minimally especially if t b is warm the sum of parallel cross sectional areas along a margin combined with porosity o gives the potential volume of gas hydrate v assuming 200 000 km of continental margin with a o of 50 3 5 10 6 km 3 of pore space can contain gas hydrates at present day a volume that compares favorably with previous estimates 1 2 to 6 4 10 6 km 3 although underlying approaches differ fundamentally since the triassic v glob probably has increased significantly because t b has cooled while total margin length has grown this trend was likely punctuated by at least one major decrease nominally 1 5 to 0 7 10 6 km 3 when t b suddenly rose by 5 c during the latest paleocene thermal maximum lptm a prominent global negative 13 c excursion across the lptm may signify massive release of ch 4 associated with this theoretical drop in v glob

characteristics and interpretation of fracture filled gas hydrate an example from the ulleung basin east sea of korea abstract through the use of 2 d and 3 d seismic data a total of thirteen sites were selected and drilled in the east sea of korea in 2010 a suite of logging while drilling lwd logs was acquired at each site lwd logs from the ubgh2 3a well indicate significant gas hydrate in clay bearing sediments including several zones with massive gas hydrate with a bulk density less than 1 0 g m 3 for depths between 5 and 103 m below the sea floor the ubgh2 3a well was drilled on a seismically identified chimney structure with a mound feature at the sea floor average gas hydrate saturations estimated from the isotropic analysis of ring resistivity and p wave velocity logs are 80 13 and 47 16 respectively whereas they are 46 17 and 45 16 respectively from the anisotropic analysis modeling indicates that the upper part of chimney between 5 and 45 m below sea floor mbsf is characterized by gas hydrate filling near horizontal fractures 7 dip and the lower part of chimney between 45 and 103 mbsf is characterized by gas hydrate filling high angle fractures on the basis of ring resistivity and p wave velocity the anisotropic analysis using p40h resistivity phase shift resistivity at 32 mhz with 40 inch spacing and the p wave velocity yields a gas hydrate saturation of 46 15 and 46 15 respectively similar to those estimated using ring resistivity and p wave velocity but with quite different fracture dip angles differences in vertical resolution depth of investigation and a finite fracture dimension relative to the tool separation appear to contribute to this discrepancy forward modeling of anisotropic resistivity and velocity are essential to identify gas hydrate in fractures and to estimate accurate gas hydrate amounts

anisotropic amplitude variation of the bottom simulating reflector beneath fracture filled gas hydrate deposit 1 for the first time we report the amplitude variation with angle ava pattern of bottom simulating reflectors bsrs beneath fracture filled gas hydrate deposits when the effective medium is anisotropic the common depth point cdp gathers of two mutually perpendicular multichannel seismic profiles located in the vicinity of site nghp 01 10 are appropriately processed such that they are fit for ava analysis ava analysis of the bsr shows normal incidence reflection coefficients of 0 04 to 0 11 with positive gradients of 0 04 to 0 31 indicating class iv pattern the acoustic properties from isotropic rock physics model predict class iii ava pattern which cannot explain the observed class iv ava pattern in krishna godavari basin due to the anisotropic nature of fracture filled gas hydrate deposits we modeled the observed class iv ava of the bsr by assuming that the gas hydrate bearing sediment can be represented by horizontally transversely isotropic hti medium after accounting for anisotropic wave propagation effects on bsr amplitudes the effective medium properties are estimated using backus averaging technique and the ava pattern of bsrs is modeled using the properties of overlying hti and underlying isotropy hti media with or without free gas anisotropic ava analysis of the bsr from the inline seismic profile shows 5 30 gas hydrate concentration equivalent to fracture density and the azimuth of fracture system fracture orientation with respect to the seismic profile is close to 45 free gas below the base of gas hydrate stability zone is interpreted in the vicinity of fault system f1

reconnaissance geophysical methods in landslide investigations abstract landslides are a natural hazard in many countries and often affect civil engineering structures and projects three aspects in particular require examination in a geotechnical appraisal of a landslide s stability in engineering terms 1 the definition of its three dimensional shape with particular reference to shear surfaces and failure planes 2 the definition of the hydrogeological regime with regard to water input to the landslide and its distribution within the slip mass 3 the detection of movement by or within the slip mass and the characterisation of such movements the site investigation costs may be very high since landslides may be extremely large structurally complex and topographically severe it is therefore advantageous in suitable circumstances to carry out reconnaissance geophysical surveys to define the structure and to guide optimum siting of boreholes and pits and ultimately the installation of piezometers inclinometers etc standard surface geophysical techniques including the seismic electrical resistivity acoustic emission and borehole methods have all been applied with varying success to look at a landslide before a major site investigation commences in recent years electromagnetic methods have been the subject of considerable research in this field and significant advances have been made in this paper the application of the above geophysical methods at the reconnaissance stage in a landslide investigation has been reviewed and illustrated with several case histories taken from different geological settings

high resolution deep towed multichannel seismic survey of deep sea gas hydrates off western canada a multichannel seismic survey was carried out using the high resolution deep towed acoustics geophysics system dtags to image the structure of deep sea gas hydrates on the continental slope off vancouver island and to determine the velocity profile of the hydrated sediments the high frequency dtags data provide the means to estimate the frequency response of the bottom simulating reflector bsr that defines the base of the hydrate stability field in these sediments over a broad frequency band from 15 to 650 hz the dtags sections resolved fine scale layering as thin as a few meters within the hydrated zone and below the bsr and they revealed small scale faults and vertically oriented zones of very low acoustic reflectivity that may represent channels for upward migration of fluids or gas interval velocities determined from the dtags data indicate uniformly low values of about 1500 m s to depths of 100 m below sea floor mbsf increasing to about 1850 m s at the bsr 250 mbsf the reflection from

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

shallow methane hydrate system controls ongoing downslope sediment transport in a low velocity active submarine landslide complex hikurangi margin new zealand morphological and seismic data from a submarine landslide complex east of new zealand indicate flow like deformation within gas hydrate bearing sediment this creeping deformation occurs immediately downslope of where the base of gas hydrate stability reaches the seafloor suggesting involvement of gas hydrates we present evidence that contrary to conventional views gas hydrates can directly destabilize the seafloor three mechanisms could explain how the shallow gas hydrate system could control these landslides 1 gas hydrate dissociation could result in excess pore pressure within the upper reaches of the landslide 2 overpressure below low permeability gas hydrate bearing sediments could cause hydrofracturing in the gas hydrate zone valving excess pore pressure into the landslide body 3 gas hydrate bearing sediment could exhibit time dependent plastic deformation enabling glacial style deformation we favor the final hypothesis that the landslides are actually creeping seafloor glaciers the viability of rheologically controlled deformation of a hydrate sediment mix is supported by recent laboratory observations of time dependent deformation behavior of gas hydrate bearing sands the controlling hydrate is likely to be strongly dependent on formation controls and intersediment hydrate morphology our results constitute a paradigm shift for evaluating the effect of gas hydrates on seafloor strength which given the widespread occurrence of gas hydrates in the submarine environment may require a reevaluation of slope stability following future climate forced variation in bottom water temperature

resolving vertical tectonics in the san francisco bay area from permanent scatterer insar and gps analysis using a combination of gps measured horizontal velocities of 200 sites and 115 487 range change rates determined with the permanent scatterer interferometric synthetic aperture radar insar method in the san francisco bay area we resolve vertical motions in the region at sub mm yr precision the highest displacement rates are due to nontectonic processes such as active landslides subsidence and rebound over aquifers and rapid settling of unconsolidated sediments along the bay margins residual displacement rates are determined by removing the contribution of the gps derived horizontal velocity field from the insar range change rates to isolate vertical tectonic rates we use only those insar measurements made on material that was not quaternary substrate which is susceptible to nontectonic and seasonally varying ground motions the insar residuals indicate significant uplift over the southern foothills of the active mount diablo anticlinorium the mission hills stepover region of the hayward and calaveras faults and the central and southern santa cruz mountains located along a restraining bend of the san andreas fault

microearthquake imaging of the parkfield asperity microearthquake data from a downhole seismometer network on the san andreas fault appear to outline two aseismic asperities that may correspond to the locations of the foreshocks and main shocks of the parkfield characteristic earthquakes the source parameters of the microearthquakes show that a few of the earthquakes have significantly higher stress drops than most furthermore the magnitude frequency statistics suggest that at local magnitude 0 6 the cumulative number of small events begins to fall off the usual gutenberg richter b 1 relation in which the number of events increases exponentially with decreasing magnitude the downhole seismometer data establish a baseline from which the evolution of the earthquake process at parkfield can be monitored and suggest that different mechanical conditions than those that lead to the typical gutenberg richter relation may be operating for the smallest of parkfield microearthquakes

erosion of the seafloor at the top of the gas hydrate stability zone on the hikurangi margin new zealand 1 the dissociation of gas hydrates in sediment pores is thought to decrease seafloor strength potentially facilitating submarine slides because of the generation of overpressured gas and the melting of load bearing or cementing solid hydrate here we present findings that suggest gas hydrates may lead to a previously unknown mechanism of seafloor erosion gas hydrate bearing sub sea ridges on the hikurangi margin are eroded close to the top of the hydrate stability field in the ocean we hypothesize that gas hydrate instability may lead to ridge erosion by a combination of two processes hydrate destabilization caused by depressurization during ridge uplift and repeated pore volume expansion and contraction from hydrate dissociation and formation triggered by fluctuating water temperatures

dynamics of slow moving landslides from permanent scatterer analysis high resolution interferometric synthetic aperture radar insar permanent scatterer data allow us to resolve the rates and variations in the rates of slow moving landslides satellite to ground distances range changes on landslides increase at rates of 5 to 7 millimeters per year indicating average downslope sliding velocities from 27 to 38 millimeters per year time series analysis shows that displacement occurs mainly during the high precipitation season during the 1997 1998 el nino event rates of range change increased to as much as 11 millimeters per year the observed nonlinear relationship of creep and precipitation rates suggests that increased pore fluid pressures within the shallow subsurface may initiate and accelerate these features changes in the slope of a hill resulting from increases in the pore pressure and lithostatic stress gradients may then lead to landslides

possible link between weak bottom simulating reflections and gas hydrate systems in fractures and macropores of fine grained sediments results from the hikurangi margin new zealand abstract small amounts of free gas in interstitial sediment pores are known to significantly lower compressional p wave velocity vp this effect combined with moderately elevated vp from the presence of gas hydrates is usually thought to be the cause for the often observed strong negative reflection coefficients of bottom simulating reflections bsrs at the base of gas hydrate stability bghs at several locations however weak bsrs have been observed which are difficult to reconcile with a presence of gas in sediment pores we here present a rock physics model for weak bsrs on the hikurangi margin east of new zealand thin sections of a fine grained mudstone sample from a submarine outcrop in the vicinity of a weak bsr show macroscopic porosity in the form of fractures and intrafossil macropores we apply the kuster toksoz theory to predict seismic velocities for a rock with water saturated interstitial micropores and gas or hydrates in macroscopic pore space simulating fractures or compliant macropores we match field observations of a weak bsr with a reflection coefficient of 0 016 with two end member models 1 rocks with gas hydrate filled voids with a concentration of

gas hydrate formation in compressional extensional and un faulted structural settings examples from new zealand s hikurangi margin abstract we investigate gas hydrate formation processes in compressional extensional and un faulted settings on new zealand s hikurangi margin using seismic reflection data the compressional setting is characterized by a prominent subduction wedge thrust fault that terminates beneath the base of gas hydrate stability as determined from a bottom simulating reflection bsr the thrust is surrounded by steeply dipping strata that cross the bsr at a high angle above the bsr these strata are associated with a high velocity anomaly that is likely indicative of relatively concentrated and broadly distributed gas hydrates the un faulted setting sedimentary infill of a slope basin on the landward side of a prominent thrust ridge is characterized by a strong bsr a thick underlying free gas zone and short positive polarity reflection segments that extend upward from the bsr we interpret the short reflection segments as the manifestation of gas hydrates within relatively coarse grained sediments the extensional setting is a localized shallow response to flexural bending of strata within an anticline gas has accumulated beneath the bsr in the apex of folding a high velocity zone directly above the bsr is probably mostly lithologically derived and only partly related to gas hydrates although each setting shows evidence for focused gas migration into the gas hydrate stability zone we interpret that the compressional tectonic setting is most likely to contain concentrated gas hydrates over a broad region indeed it is the only setting associated with a deep reaching fault meaning it is the most likely of the three settings to have thermogenic gas contributing to hydrate formation our results highlight the importance of anisotropic permeability in layered sediments and the role this plays in directing sub surface fluid flow and ultimately in the distribution of gas hydrate each of the three settings we describe would warrant further investigation in any future consideration of gas hydrates as an energy resource on the hikurangi margin

application of geophysical methods for the investigation of the large gravitational mass movement of sechilienne france several geophysical techniques electromagnetic profiling electrical tomography seismic refraction tomogra phy and spontaneous potential and seismic noise measurement were applied in the investigation of the large gravita tional mass movement of sechilienne france the aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists whose lateral and vertical limits are still uncertain a major observation of this study is that all the zones strongly deformed previously and at present by the movement are characterized by high electrical resistivity values 3 k m in contrast to the undis turbed mass which exhibits resistivity values between a few hundred and 1 k m as shown by the surface observa tions and the seismic results this resistivity increase is due to a high degree of fracturing associated with the creation of air filled voids inside the mass other geophysical techniques were tested along a horizontal transect through the movement and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve these preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass in volved in the movement results also suggest that monitoring the evolution of the rock mass movement with time lapse geophysical surveys could be beneficial resume plusieurs techniques geophysiques profil electromagnetique tomographie electrique tomographie sismique et potentiel spontane et bruit de fond sismique ont ete appliquees pour la reconnaissance du grand mouvement de ter rain de sechilienne france situe dans des micaschistes l objectif de cette etude etait de tester ces methodes geophy siques afin de caracteriser et de delimiter la masse de roche affectee par ce mouvement complexe dont la limite laterale reste incertaine l etude a montre que toutes les zones tres deformees encore actuellement et dans le passe par le mouvement sont caracterisees par de fortes valeurs de resistivite electrique superieur ea3k m tandis que dans la zone non perturbee les valeurs de resistivite sont de quelques centaines de m a1k m comme le montrent les observations de surface et les profils de tomographie sismique cette augmentation de resistivite est due a une frac turation importante associee a la creation de vides remplis d air au sein du massif les techniques electromagnetiques ps et de mesure de bruit ont ete testees le long d un profil transversal recoupant le mouvement une correlation remar quable est obtenue entre les anomalies geophysiques et le taux de deplacement ces resultats preliminaires soulignent l interet de combiner les methodes geophysiques pour caracteriser la masse de roche impliquee dans le mouvement et pour determiner l evolution du mouvement par un suivi temporel des parametres geophysiques mots cles mouvement gravitaire methodes geophysiques sechilienne meric et al 1115

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

geophysical characterisation of a rockslide in an alpine region a combination of geophysical methods has been used for the characterisation of a rockslide area located in the graie alps nw of italy where the construction of a roadway tunnel has been planned electrical resistivity tomography ert seismic refraction tomography srt and spectral analysis of surface waves swm have been adopted to determine the overburden thickness and the geometry of the sliding surfaces the geomechanical characterisation of rock mass was performed by means of horizontal seismic profiles hsp and sonic log in a horizontal borehole the results have been calibrated by comparing the geophysical responses with the geological evidence derived from boreholes and with the movements recorded using inclinometric probe moreover borehole geophysics results were validated by the results of laboratory measurements performed on core samples the integration of geophysical and geotechnical results allowed the definition of a subsoil model for the investigated area and provided the necessary data for the design of the roadway tunnel the study shows that surface and borehole geophysical techniques could be an efficient and cost effective tool in rockslide investigations

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

evidence of pore and fracture filling gas hydrates from geophysical logs in consolidated rocks of the muli area qinghai tibetan plateau permafrost china

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

reservoir characterization using oil production induced microseismicity clinton county kentucky abstract microseismic monitoring tests were conducted from 1993 to 1995 in the seventy six oil field clinton county kentucky oil is produced from low porosity fractured carbonate rocks at 3 no injection operations were conducted gross changes in production rate correlate with event rate event rate lags changes in production rate by 2 to 3 weeks hypocenters and first motion data have revealed previously undetected low angle thrust faults above and below the currently drained depth intervals production history well logs and drill tests indicate that the seismically active faults or fractures are previously drained intervals that have subsequently recovered to hydrostatic pressure via brine invasion storage capacity computed for one of these drained fractures implies that total oil production represents about 20 of total pore volume correlation of older production intervals and well log porosity anomalies with the seismically active faults indicate that the oil reservoir in the study area is primarily a set of compartmentalized low angle thrust faults although low angle fracture sets have not previously been considered in the exploration and development of the area the mapped thrust faults are consistent with other investigators interpretations of oil associated with secondary fracture sets occurring along deeper seated wrench fault structures stress determined from composite focal mechanisms indicates a near surface

seismic reflection character of the hikurangi subduction interface new zealand in the region of repeated gisborne slow slip events summary we use seismic reflection data to map the geometry and character of the subduction interface in the gisborne area of the hikurangi subduction margin new zealand which experiences repeated shallow 15 km slow slip events the reflection character and geometry in this area is highly variable which we interpret to be related to the subduction of seamounts and underthrust sediments three zones of high amplitude interface reflectivity hrz 1 2 and 3 are interpreted to be the result of fluid rich sediments that have been entrained with subducting seamounts the interface above the hrz zones is shallower than the surrounding areas by 2 4 km due to the warping of the interface to accommodate seamount subduction these zones of high amplitude reflectivity and shallower interface geometry correlate broadly with locations of recorded slow slip events from 2002 to 2008 we hypothesize that effective stresses on the interface may be lower along the northeast margin in areas of high amplitude reflectivity due to 1 the enhanced underthrusting of fluid rich sediment 2 reduced overburden stresses where the interface has been warped to shallower depths to accommodate seamount subduction and 3 potential fluid flow concentration effects leading to overpressure along these shallower interface corrugations from our observations we propose localized reductions in effective stress caused by interface structural relief may be a potential factor in promoting shallow slow slip events

geophysical models of the lesachriegel and gradenbach deep seated mass movements schober range austria two examples lesachriegel and gradenbach of deep seated gravitational creep of slopes or saggings located in the crystalline rocks of the schober mountain range austria have been examined the retreat of the alpine glaciers after the last ice age at 15 000 years bp is considered to have initiated these movements both mass movements have had phases of accelerated movement during the last 50 years the sagging masses and the escarpment areas have been delineated using existing geological and geomorphological information as well as field observations and digital terrain models models of the basal planes have been derived from seismic investigations and boreholes the areas and volumes of the creeping rock masses are 1 6 km 2 and 0 06 km 3 for lesachriegel and 1 7 km 2 and 0 12 km 3 for gradenbach the pre failure topography gives an idea of the slope topography before creep or sagging processes started the surfaces have been modeled taking morphological and kinematic plausibility and the dilation of the rock masses into account several geometric and physical parameters e g displacement of centre of gravity initial and average sliding angle porosity potential energy release have been derived from structural models total displacements of the centres of gravity and within flow channels have been calculated by applying a special form of the condition of continuity mass conservation from these results lesachriegel has been classified as a mature sagging and gradenbach as an early stage sagging at lesachriegel present creep rates and total displacements conform to the idea that glacial retreat after the ice age initiated creep processes at gradenbach the data indicate a significant acceleration in recent times it is assumed that either the development of deep gravitational creep after glacial retreat took a very long time n10 000 years or the creep process stopped at an early stage and was reactivated more recently our present knowledge of the history of the gradenbach mass movement is not sufficient to identify a particular factor responsible for a reactivation of the creep process d 2005 elsevier b v all rights reserved

precise hypocentre relocation of microearthquakes in a high temperature geothermal field the torfajokull central volcano iceland the torfaj okull volcanic system is one of approximately 30 active volcanoes comprising the neovolcanic zones of iceland the central volcano of the system is the largest silicic centre in iceland with a caldera of approximately 12 km diameter its high temperature geothermal system is one of the most powerful in iceland torfaj okull is a source of persistent seismicity where both high and low frequency earthquakes occur to study this microseismicity in detail a temporary array of 20 broad band seismic stations was deployed between 2002 june and november these temporary stations were embedded in the permanent south iceland lowland sil network and data from nine adjacent sil stationswere included in this study aminimum one dimensional 1 d velocity model with station corrections was computed for earthquake relocation by inverting manually picked p and s wave arrival times from events occurring in the torfaj okull volcanic centre and its surroundings high frequency earthquakes from the torfaj okull volcanic centre were then relocated calculating a non linear probabilistic solution to the earthquake location problem subsequently we correlated the waveforms of these 121 events 2000 observations to define linked events calculated the relative traveltime difference between event pairs and solved for the hypocentral separation between these events the resulting high resolution pattern shows a tighter clustering in epicentre and focal depth when compared with original locations earthquakes are mainly located beneath the caldera with hypocentres between 1 and 6 km depth and lie almost exclusively within the geothermal system a sharp cut off in seismicity at 3 km suggests either that there is a marked temperature increase or that this is a structural boundary no seismic activity was observed in the fissure swarms to the northeast ne and southwest sw of the volcanic centre

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

analysis of lidar derived topographic information for characterizing and differentiating landslide morphology and activity abstract this study used airborne laser altimetry lidar to examine the surface morphology of two canyon rim landslides in southern idaho the high resolution topographic data were used to calculate surface roughness slope semivariance and fractal dimension these data were combined with historical movement data global positioning systems gps and laser theodolite and field observations for the currently active landslide and the results suggest that topographic elements are related to the material types and the type of local motion of the landslide weak unconsolidated materials comprising the toe of the slide which were heavily fractured and locally thrust upward had relatively high surface roughness high fractal dimension and high vertical and lateral movement the body of the slide which predominantly moved laterally and consists mainly of undisturbed older canyon floor materials had relatively lower surface roughness than the toe the upper block consisting of a down dropped section of the canyon rim that has remained largely intact had a low surface roughness on its upper surface and high surface roughness along fractures and on its west face unrelated to landslide motion the upper block also had a higher semivariance than the toe and body the topographic data for a neighboring older and larger landslide complex which failed in 1937 are similarly used to understand surface morphology as well as to compare to the morphology of the active landslide and to understand scale dependent processes the morphometric analyses demonstrate that the active landslide has a similar failure mechanism and is topographically more variable than the 1937 landslide especially at scales 20 m weathering and the larger scale processes of the 1937 slide are hypothesized to cause the lower semivariance values of the 1937 slide at smaller scales

can a fractionally crystallized magma ocean explain the thermo chemical evolution of mars abstract the impact heat accumulated during the late stage of planetary accretion can melt a significant part or even the entire mantle of a terrestrial body giving rise to a global magma ocean the subsequent cooling of the interior causes the magma ocean to freeze from the core mantle boundary cmb to the surface due to the steeper slope of the mantle adiabat compared to the slope of the solidus assuming fractional crystallization of the magma ocean dense cumulates are produced close to the surface largely due to iron enrichment in the evolving magma ocean liquid a gravitationally unstable mantle thus forms which is prone to overturn we investigate the cumulate overturn and its influence on the thermal evolution of mars using mantle convection simulations in 2d cylindrical geometry we present a suite of simulations using different initial conditions and a strongly temperature dependent viscosity we assume that all radiogenic heat sources have been enriched during the freezing phase of the magma ocean in the uppermost 50 km and that the initial steam atmosphere created by the degassing of the freezing magma ocean was rapidly lost implying that the surface temperature is set to present day values in this case a stagnant lid quickly forms on top of the convective interior preventing the uppermost dense cumulates to sink even when allowing for a plastic yielding mechanism below this dense stagnant lid the mantle chemical gradient settles to a stable configuration the convection pattern is dominated by small scale structures which are difficult to reconcile with the large scale volcanic features observed over mars surface and partial melting ceases in less than 900 ma assuming that the stagnant lid can break because of additional mechanisms and allowing the uppermost dense layer to overturn a stable density gradient is obtained with the densest material and the entire amount of heat sources lying above the cmb this stratification leads to a strong overheating of the lowermost mantle whose temperature increases to values that exceed the liquidus the iron rich melt would most likely remain trapped in the lower part of the mantle the upper mantle in that scenario cools rapidly and only shows partial melting during the first billion year of evolution therefore a fractionated global and deep magma ocean is difficult to reconcile with observations different scenarios assuming for instance a hemispherical or shallow magma ocean or a crystallization sequence resulting in a lower density gradient than that implied by pure fractional crystallization will have to be considered