seismicity following the 1985 eruption of nevado del ruiz colombia abstract over 200 of the best recorded earthquakes occurring near nevado del ruiz colombia between december 1985 and may 1986 are examined for spatial patterns information on local stress orientations and evidence for seismogenic structures that may be related to magma transport processes these earthquakes occurred following the devastating eruption of november 13 1985 earthquake activity that is probably related to the volcanic system occurs over a large area of the order of 50 km 2 a pattern of earthquakes beneath the southern half of ruiz may be the expression of a conduit system but evidence is inconclusive due to low spatial resolution of most hypocenters epicenter and first motion plots suggest most earthquakes occur on small faults of varying orientation most seismicity during this time period was unrelated to mapped faults including some with holocene offsets except for the villamaria fault near ruiz s northeast sector composite focal mechanisms show a variation of nearly 90 in the strike of t axes and indicate ruiz is in a zone of local extension

recently exposed vegetation reveals holocene changes in the extent of the quelccaya ice cap peru abstract radiocarbon dating of well preserved in place vegetation exposed by the retreating quelccaya ice cap of southeastern peru constrains the last time the ice cap s extent was smaller than at present seventeen plant samples from two sites along the central western margin collectively date to 4700 and 5100 cal yr bp and strongly indicate that current ice cap retreat is unprecedented over the past 5 millennia seventeen vegetation samples interbedded in a nearby clastic sedimentary sequence suggest ice free conditions at this site from 5200 to at least 7000 cal yr bp and place minimum constraint on early to mid holocene ice cap extent

deep structure of northern mississippi embayment in september 1980 the u s geological survey conducted a seismic refraction investigation of the northern mississippi embayment during the investigation 34 shots from nine shotpoints were recorded along a series of profiles the profiles were parallel to and across an inferred precambrian rift zone which is outlined by a series of magnetic anomalies and covers an area at least 200 km 125 mi long and 70 km 45 mi wide along the northeast southwest trending axis of the rift a 0 7 to 1 1 km 2 297 to 3 609 ft thick 1 8 km sec layer representing the unconsolidated tertiary and cretaceous sediments overlies a 2 km 6 562 ft thick 5 95 km sec layer representing a paleozoic carbonate sequence beneath the carbonates is a 3 km 9 843 ft thick low velocity layer which probably consists of late precambrian clastics the presence of this low velocity layer is indicated on the seismic profiles by an abrupt cutoff of the 5 95 km sec arrivals at about 20 km 12 mi from the shotpoints this cutoff is followed by a 30 to 40 km 20 to 25 mi long zone of no arrivals beyond which are seen delayed arrivals from a 6 2 km sec crystalline basement the 11 km 6 8 mi thick 6 2 km sec basement overlies a lower crus composed of a 6 6 km sec layer whose thickness decreases to the northeast owing to its replacement by an anomalous high velocity 7 3 km sec basal layer the base of the crust ranges from a 39 km 24 mi depth at the southern end of the profile to a 46 km 29 mi depth at the northern end where the 7 3 km sec layer is 20 km 12 mi thick below the base of the crust moho the upper mantle has a velocity of 8 0 km sec the velocity structure beneath the west flank of the embayment is simpler than that of the axis 5 95 6 2 6 6 7 3 and 8 0 km sec the low velocity layer is absent and the anomalous 7 3 km sec layer is thinner than along the axial profile the profiles perpendicular to the rift show that the low velocity layer is restricted to the axial zone and that the anomalous 7 3 km sec basal crustal layer reaches maximum thickness there the tectonic model proposed to explain the origin of this embayment velocity structure includes a late precambrian mantle plume that intruded the lower crust of the northern embayment causing uplift and or crustal stretching and subsequent rifting of the axial area this was followed by erosion subsidence and subsequent deposition of sediments in the resulting trough

tectonic stress within the new madrid seismic zone refraction data indicate a significant high density rift pillow beneath the new madrid seismic zone we present results of linear and nonlinear viscoelastic finite element modeling to determine whether support of the rift pillow may contribute significantly to the total present day stress field and we consider the implications for intraplate seismicity these models were run for a loading time of 100 m y to account for relaxation and transfer of stress since the last reactivation of the rift in the mid mesozoic results indicate that the nonlinear viscoelastic model with rheological stratification based on composition and temperature agrees well with the observed deformation within the seismic zone and with estimates of regional stress magnitudes the model predicts a maximum compression of 30 40 mpa above the rift pillow in the center of the rift axis if the magnitude of local compression predicted by the nonlinear model produces the inferred clockwise rotation of the order of 10 30 in the direction of shmax maximum horizontal compression near the rift axis the magnitude of regional compression is a factor of 1 to 2 times the magnitude of local compression and consistent with an origin due to ridge push forces the addition of the local stress associated with the rift pillow however results in an approximately 30 reduction in the resolved maximum horizontal shear stress thus while the stress associated with the rift pillow can rotate the stress field into an orientation favorable for failure reduction in the resolved shear stress requires a separate mechanism for strength reduction results of the modeling indicate that stresses from the load of the rift pillow may still be present in the upper crust even after 100 m y and may still play a role in present day deformation and seismicity of the new madrid seismic zone local stress fields of significant tectonic magnitudes may also occur around other ancient rift pillows and help explain the observed correlation between intraplate seismicity and failed rift zones

contribution of icelandic ice caps to sea level rise trends and variability since the little ice age 1 in total icelandic ice caps contain 3600 km3 of ice which if melted would raise sea level by 1 cm here we present an overview of mass changes of icelandic ice masses since the end of the 19th century they have both gained and lost mass during this period changes in ice volume have been estimated both through surface mass balance measurements performed annually since 1990 and differencing of digital elevation models derived from various satellite and airborne observations while the glaciers showed little mass loss as the 20th century began losses increased rapidly after 1925 peaked in the 1930s and 1940s and remained significant until the 1960s after being near zero or even positive during the 1980s and early 1990s glacier mass budgets declined considerably and have since the mid 1990s shown an average annual loss of 9 5 1 5 gt a 1 contributing 0 03 mm a 1 to sea level rise since 1995 interannual variability in mass loss is high ranging from 2 7 to 25 3 1 5 gt a 1 corresponding to surface mass balances of 0 2 to 2 2 0 15 m we a 1 this variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

quaternary grabens in southernmost illinois deformation near an active intraplate seismic zone abstract narrow grabens displace quaternary sediments near the northern edge of the mississippi embayment in extreme southern illinois east central united states grabens are part of the fluorspar area fault complex fafc which has been recurrently active throughout phanerozoic time the fafc strikes directly toward the new madrid seismic zone nmsz scene of some of the largest intra plate earthquakes in history the nmsz and fafc share origin in a failed cambrian rift reelfoot rift every major fault zone of the fafc in illinois exhibits quaternary displacement the structures appear to be strike slip pull apart grabens but the magnitude and direction of horizontal slip and their relationship to the current stress field are unknown upper tertiary strata are vertically displaced more than 100 m illinoian and older pleistocene strata 10 to 30 m and wisconsinan deposits 1 m or less no holocene deformation has been observed average vertical slip rates are estimated at 0 01 to 0 03 mm year and recurrence intervals for earthquakes of magnitude 6 to 7 are on the order of 10 000s of years for any given fault previous authors remarked that the small amount of surface deformation in the new madrid area implies that the nmsz is a young feature our findings show that tectonic activity has shifted around throughout the quaternary in the central mississippi valley in addition to the nmsz and southern illinois the wabash valley illinois indiana benton hills missouri crowley s ridge arkansas missouri and possibly other sites have experienced quaternary tectonism the nmsz may be only the latest manifestation of seismicity in an intensely fractured intra plate region

simulation and analysis of 1991 u s geological survey refraction data from the new madrid seismic zone two orthogonal wide aperture seismic refraction lines were acquired in the new madrid seismic zone by the u s geological survey in 1991 these n s and e w oriented lines cross the blytheville arch and adjacent portions of the reelfoot rift ten shots were fired along the e w line eight shots were fired along the n s line iterative numerical modeling including scattering and viscoelasticity has been performed for all shots on both lines using a new eighth order staggered grid two dimensional finite difference solution based on superposition of relaxation mechanisms the main features in the data can be explained by the existence of a strong 15 km wide low velocity cap lying beneath the center of the blytheville arch between 1 5 and 2 5 km depth the data do not allow estimation of its extent along the axis of the arch but it is at least 30 km long and appears to become less prominant toward the southwest the arch itself has a low velocity background that extends to at least 5 km depth an additional low velocity layer the elvins shale lies generally between 3 and 4 km depth is upwarped at the edges of the arch and thins toward the edges of the reelfoot rift there is no evidence for anomalously low intrinsic q but the data may be interpreted to indicate strong local scattering that occurs west of the low velocity cap of the blytheville arch at depths that are similar to and slightly shallower than the cap additional strong scattering occurs at the western edge of the reelfoot rift an alternative interpretation attributes the apparent scattering at the blytheville arch to instrument noise

a seismic structure study in the kaoping area southwestern taiwan the difference between s wave and s to p wave conversion s p phase arrival times is enhanced with rectilinear motion detector filtering to describe alluvial sediment thickness in the kaohsiung pingtung kaoping plains area a more complete understanding of the underground structures of the kaoping area is provided in this paper and explains why the surrounding regions in taiwan experience more earthquakes than the kaoping area data are based on seismic activity recorded by the portable array for numerical data acquisition panda for the period from 1995 to 1997 the difference between s wave and s p phase arrival times shows that the sedimentary layer is thicker along the west and southwest coasts p wave travel time residuals high frequency attenuation parameters kappa and quality factor q p q s and coda waves confirm this result we also determined the orientation of the chaochou fault using the first motion of p wave arrivals to the east of the chaochou fault stress trends southeast northwest while to the west it trends northeast southwest the change in stress trends east and west of chaochou fault suggests the presence of a highly fluid accretionary wedge in the kaoping area the chaochou fault forms a seismically active tectonic boundary with the uplift of the hanging wall leading to westward tilting of the basement of the kaoping plains we demonstrate that these features are the reason there are relatively few earthquakes in the kaoping area the presence of a highly fluid accretionary wedge is indicated by a thick alluvial layer in the west and southwest kaoping coasts the peikung high acts as the indenter that may allow seismic energy to escape and reduce the number of earthquakes in the region online material figures illustrating calculations of kappa q c p and s wave spectra q p and q s from ground motion data

three dimensional s wave velocity structure and vp vs ratios in the new madrid seismic zone a three dimensional s wave velocity model for the new madrid seismic zone nmsz has been developed using nonlinear travel time tomography the inversion utilized 5544 s wave arrival times from 720 earthquakes recorded by digital three component stations deployed in the nmsz over the time period 1989 through 1992 we imaged s wave velocity anomalies ranging from 5 to 8 relative to the starting one dimensional velocity model lowest s wave velocities are found south of ridgley tennessee in an area characterized by a high earthquake swarm rate and shallower than normal hypocenters two centers of higher than average s wave velocity are located west of the mississippi river north of caruthersville missouri the s wave model is similar to a p wave velocity model generated using the same earthquake data set the similarity in ray coverage in both the p and s wave solutions allowed calculation of vp vs ratios most of the seismicity in the nw trending central arm of the nmsz is associated with normal vp vs values that border regions with high vp vs north of ridgely high vp vs values are associated with higher than average compressional and shear wave velocities and are interpreted to be due to mafic intrusions along the axis and edges of the reelfoot rift se of ridgley the end of the central arm coincides with high vp vs values that are due to a significant shear wave low velocity zone and are interpreted to be the result of highly fractured and fluid saturated crust

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

microearthquakes near the sleepy hollow oil field southwestern nebraska between april 1982 and june 1984 311 earthquakes were detected and 176 earthquakes were located in the vicinity of the sleepy hollow oil field southwestern nebraska the oil field is being injected with water to enhance oil production and the earthquakes may be related to production there is geologic evidence however to suggest that the earthquakes are tectonic in origin and are related to uplift along the axis of the cambridge arch on which the field is located first motion data from these events do not yield a well constrained fault plane solution furthermore first motion detections are inconsistent for earthquakes with nearly coincident hypocenters indicating that more than one faulting mechanism is active in the oil field injection pressures do not correlate well with earthquake occurrence

recent sea level contributions of the antarctic and greenland ice sheets after a century of polar exploration the past decade of satellite measurements has painted an altogether new picture of how earth s ice sheets are changing as global temperatures have risen so have rates of snowfall ice melting and glacier flow although the balance between these opposing processes has varied considerably on a regional scale data show that antarctica and greenland are each losing mass overall our best estimate of their combined imbalance is about 125 gigatons per year of ice enough to raise sea level by 0 35 millimeters per year this is only a modest contribution to the present rate of sea level rise of 3 0 millimeters per year however much of the loss from antarctica and greenland is the result of the flow of ice to the ocean from ice streams and glaciers which has accelerated over the past decade in both continents there are suspected triggers for the accelerated ice discharge surface and ocean warming respectively and over the course of the 21st century these processes could rapidly counteract the snowfall gains predicted by present coupled climate models

rupture properties of clustered microearthquakes near intersecting intraplate faults of new madrid seismic zone implications for fault weakening seismic waveforms from the portable array for numerical data acquisition network were used to identify sets of 21 similar microearthquakes near ridgely tennessee where two major segments of the new madrid seismic zone nmsz intersect the events are relocated with a precision of about 30 m and are found to have occurred along four subfaults that are aligned to n50 e subparallel to the southern arkansas segment of the nmsz the separations among the subfaults are a few hundred meters while the span of hypocenters within each subfault is typically a few tens of meters these subfaults are inferred from focal mechanism solutions to be oriented at high angles to n50 e trend striking roughly north northwest and dipping moderately with reverse slip this indicates that the subfaults belong to the central segment of the nmsz and are en echelon the similar events also cluster in time the typical time span of events over one subfaults is about 3 weeks while the intercluster times are a few months or more an empirical green s function analysis of the largest event placed a lower bound of its rupture dimension at 121 32 m suggesting that this rupture overlapped with the smaller ruptures along the same subfault on the basis of variations in fault zone properties previously inferred for the ridgely junction the rupture properties of the similar events and the result of a stress calculation we infer that the similar events may be triggered by temporal weakening of the subfaults possibly associated with a temporal elevation of pore fluid pressure the nearly constant depths 5 7 km and the reverse dip of the ruptures suggest that the en echelon subfaults may be intersected by subhorizontal veins which could have been developed by episodic influx of fluid at superhydrostatic pressures

ground motion simulations of 1811 1812 new madrid earthquakes central united states we performed a suite of numerical simulations based on the 1811 1812 new madrid seismic zone nmsz earthquakes which demonstrate the importance of 3d geologic structure and rupture directivity on the ground motion response throughout a broad region of the central united states cus for these events our simulation set consists of 20 hypothetical earthquakes located along two faults associated with the current seismicity trends in the nmsz the hypothetical scenarios range in magnitude from m 7 0 to 7 7 and consider various epicenters slip distributions and rupture characterization approaches the low frequency component of our simulations was computed deterministically up to a frequency of 1 hz using a regional 3d seismic velocity model and was combined with higher frequency motions calculated for a 1d medium to generate broadband synthetics 0 40 hz in some cases for strike slip earthquakes located on the southwest northeast striking nmsz axial arm of seismicity our simulations show 2 10 s period energy channeling along the trend of the reelfoot rift and focusing strong shaking northeast toward paducah kentucky and evansville indiana and southwest toward little rock arkansas these waveguide effects are further accentuated by rupture directivity such that an event with a western epicenter creates strong amplification toward the northeast whereas an eastern epicenter creates strong amplification toward the southwest these effects are not as prevalent for simulations on the reverse mechanism reelfoot fault and large peak ground velocities 40 cm s are typically confined to the near source region along the up dip projection of the fault nonetheless these basin response and rupture directivity effects have a significant impact on the pattern and level of the estimated intensities which leads to additional uncertainty not previously considered in magnitude estimates of the 1811 1812 sequence based only on historical reports the region covered by our simulation domain encompasses a large portion of the cus centered on the nmsz including several major metropolitan areas based on our simulations more than eight million people living and working near the nmsz would experience potentially damaging ground motion and modified mercalli intensities ranging from vi to viii if a repeat of the 1811 1812 earthquakes occurred today moreover the duration of strong ground shaking in the greater memphis metropolitan area could last from 30 to more than 60 s depending on the magnitude and epicenter online material tables of 1d velocity models used to generate the high frequency synthetics and figures of source models and peak ground motion synthetics

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

analysis of local ice crystal growth in snow the structural evolution of snow under metamorphism is one of the key challenges in snow modeling the main driving forces for metamorphism are curvature differences and temperature gradients inducing water vapor transport and corresponding crystal growth which is detectable by the motion of the ice air interface to provide quantitative means for a microscopic validation of metamorphism models a vtk based image analysis method is developed to track the ice air interface in time lapse ct experiments to measure local interface velocities under both isothermal and temperature gradient conditions using estimates of local temperatures from microstructure based finite element simulations a quantitative comparison of measured interface velocities with theoretical expressions is facilitated for isothermal metamorphism the data are compared with a kinetics and a diffusion limited growth law in both cases the data are largely scattered but consistently show a mean curvature dependency of the interface velocity for temperature gradient metamorphism we confirm that the main contribution stems from the temperature gradient induced vapor flux accompanied by effects of mean curvature as a secondary process the scatter and uncertainties are discussed in view of the present theoretical understanding the experimental setup and complications such as mechanical deformations

explicit iterative computation of diffusive vapour field in the 3 d snow matrix preliminary results for low flux metamorphism the metamorphism of seasonal snow is classically considered as limited by vapour diffusion in the pore phase to account for the lack of knowledge of the ice vapour reaction coefficient near 0 c the assumption of a reaction limited metamorphism was first tested in three dimensional simulations at low and very low temperature gradients however the validity of such results is difficult to verify experimentally by a reasoned use of traditional iterative schemes vapour diffusion is now simulated in three dimensions on tomographic snow data mapping the gradient of vapour pressure near the grains repeating this process may provide a way to simulate the isothermal metamorphism without grain packing at a reasonable expense of computation time preliminary results are compared with existing computations made within the reaction limited hypothesis

global distributions of glacier properties a stochastic scaling paradigm many problems in global climate and earth systems science require knowledge of regional or global scale distributions of glacier properties which includes mass balance ice velocity flux thickness volume and surface area among others with roughly 160 000 glaciers worldwide obtaining information on the global probability distributions of most ice properties is expensive and often infeasible only surface area distributions are relatively easy to measure either by direct observation or remote sensing while other properties are difficult to observe this work shows that scaling relationships from the continuum dynamics of ice can link the distribution of surface areas to the global and regional distributions of any other continuum property some data inventories already exist for constructing reasonable distributions of glacier sizes and this analysis presents theoretical arguments based on glacier network topologies similar in concept to river networks to suggest a power law times an exponential distribution of surface areas in agreement with the data therefore by using existing data or the theoretical distributions of surface areas specific distributions for other glacier properties in any region of the world can be constructed as an example predictions up to a scaling constant are made for the distribution of glacier volumes characteristic thicknesses characteristic velocities and characteristic response times in the alps

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

an ancient rift complex and its relation to contemporary seismicity in the new madrid seismic zone gravity magnetic geologic and seismicity data have been combined in a seismotectonic analysis of the new madrid seismic zone previous studies have presented evidence for several rift zones in this area upper mississippi embayment including the reelfoot rift a late precambrian early paleozoic failed arm which extends n ne from the ancient continental margin in this study we propose that the northern terminus of the reelfoot rift forms a rift complex which appears to correlate well with the seismicity in the area this correlation suggests that faults associated with this rift complex are being reactivated in the contemporary stress field ene compression if this interpretation is valid it represents a seismotectonic model which can be used to predict the extent of future seismicity in the new madrid seismic zone the proposed rift complex also provides a coherent model for the tectonic development of this region of the north american midcontinent

model for the tectonic evolution of the mississippi embayment and its contemporary seismicity aeromagnetic and gravity surveys of the northern mississippi embayment have delineated a northeast trending basement depression about 70 km wide and more than 300 km long the feature the mississippi valley graben is remarkably linear over its known length has nearly parallel sides and has estimated depths relative to surrounding basement of more than 2 km both gravity and magnetic anomalies show an alignment of dense magnetic plutons along the boundaries of the graben estimated magnetization directions for the plutons indicate a mesozoic age the graben of probable earliest paleozoic age underlies the northwest side of the embayment and contains the area of major seismicity in particular much of the instrumentally located contemporary seismicity and the estimated locations of the large magnitude 1811 1812 earthquakes are in the central part of the graben we interpret the early paleozoic graben the mesozoic plutonism and the sedimentation cycles as evidence of stretching events seismicity is attributed to strain in and below the central graben area which would appear to be a focal point of deformation in the stretching model we suggest that the sequence of events can be explained by the action of a rotating horizontal stress field on a crustal flaw that persisted well back in pre cambrian time the postulated rotating stress field is presumably controlled by the system that drives the global plates

a simplified energy and mixing budget for a small river plume discharge 1 the formation and evolution of a tidally modulated river plume that spreads and mixes into english channel waters is investigated by combining results from two observational studies remote sensing imagery showed a near semicircular plume expansion as its diameter increased linearly during the ebb tide subsequent ship surveys made repeated transects across the plume front and showed that regions of mixing and instability froude numbers 1 were confined to horizontal length scales 1 suggesting that a plume cannot form

state of stress and intraplate earthquakes in the united states recently compiled data on the state of stress have been used to define stress provinces in the conterminous united states in which the orientation and relative magnitude of the horizontal principal stresses are fairly uniform the observed pattems of stress constrain mechanisms for generating intraplate lithospheric stresses coupled with new information on geologic structure and tectonism in seismically active areas of the midcontinent and east these data help to define some characteristics common to these areas and to identify key questions regarding why certain faults seem to be seismically active

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

the temperature gradient metamorphism of snow vapour diffusion model and application to tomographic images a simple physical model describing the temperature gradient metamorphism of snow is presented this model based on kelvin s equation and fick s law takes into account the local variation of the saturating vapour pressure with temperature it can determine locally whether the ice is condensing or subliming depending on both the pressure and temperature fields in the snow structure this model can also explain the formation of facets that occurs during the metamorphism using x ray microtomo graphic images of snow samples obtained under low to moderate temperature gradient conditions this model has been tested and compared to the reaction limited model proposed in a previous work

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100

climate sensitivity implications for the response of geomorphological systems to future climate change climate sensitivity is defined as the equilibrium temperature response of the climate system to a doubling of atmospheric co2 levels from pre industrial levels despite three decades of debate in the climatological literature on the estimation and significance of climate sensitivity very little appears in the geomorphological literature on the implications of this for geomorphological systems this paper reviews the concept of climate sensitivity and applies its findings to an assessment of future landscape change in cold regions it is concluded that paraglacial processes will become the dominant mechanism of sediment transfer in currently glaciated catchments and that this period of sediment mobilization will be the last episode of major sediment movement for geological time periods there is a scientific consensus oreskes 2004 that the mean surface temperature of the earth has increased in recent decades and that the warming amounts to around 0 8 8c since the beginning of the twentieth century ipcc 2007 from this nasa goddard institute of space studies giss estimates that 2005 was the warmest year to date since reliable instrumental measurements become available although the world meteorological office wmo and climatic research unit cru place it just behind 1998 detection and attribution studies show that there is high probability at least 90 that this warming is largely the result of anthropogenic emissions of greenhouse gases ghg mainly co2 in the troposphere and that the amount and rate of warming lie outside of the range of natural variation and are unprecedented within the context of the holocene the last 11 000 years continued future warming is expected to have important consequences for a range of earth systems including the atmosphere cryosphere oceans hydrological systems and the biosphere and there are compelling reasons to expect increases in the magnitude and frequency of some natural hazards such as floods huntington 2006 droughts mason goddard 2001 and landslides e g fischer et al 2006 and increases in the intensity of tropical cyclones emanuel 2005 there are also concerns about the stability of several of the large ice sheets on earth e g overpeck et al 2006 as break up of these has the ability to impact upon global sea levels and regulate ocean currents given that climate is a major driver of many earth systems the rate nature and extent of future climate changes are important variables for understanding the future behaviour of geomorphological processes and the likely evolution of geomorphological systems as a result it is surprising that little appears in the geomorphological literature assessing climate sensitivity as a factor in landform and landscape evolution it is therefore the purpose of this paper to synthesize current understanding of climate sensitivity defined later and discuss briefly the implications of this for assessing the response of mountain geomorphological systems to future temperature rises metrics for climate change metrics are of interest to geomorphologists and other earth scientists modelling the response of earth systems to changes in climate as they provide a baseline measurement from which to calculate change the most widely used metric is the global mean surface temperature which is estimated by the hadcru hadley climatic research unit data set which excludes the polar regions or by the nasa giss assessment which extrapolates to the poles the warming of mean surface temperature is related theoretically and empirically to the idea of radiative forcing at the top of the atmosphere radiative forcing is measured in w m and can be defined as a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the earth atmosphere system and is an index of the importance of the factor as a potential climate change mechanism ipcc 2001 despite this metric having been used by the ipcc assessment reports and adopted by from knight j harrison s eds periglacial and paraglacial processes and environments the geological society london special publications 320 257 265 doi 10 1144 sp320 16 0305 8719 09 15 00 the geological society publishing house 2009 policy makers there have been a number of challenges to its use the most credible challenge comes from the suggestion that a global heat budget measures the warming of the earth in a more complete way than the global mean surface temperature e g pielke 2003 in addition there are important uncertainties and limitations associated with the concept national academies of sciences 2005 especially as radiative forcing fails to account adequately with regional forcings such as by aerosols and land use changes that may have significant climatic effects at the local scale

a 2000 yr long multi proxy lacustrine record from eastern baffin island arctic canada reveals first millennium ad cold period abstract we generate a multi proxy sub centennial scale reconstruction of environmental change during the past two millennia from itilliq lake baffin island arctic canada our reconstruction arises from a finely subsectioned 210pb and 14c dated surface sediment core and includes measures of organic matter e g chlorophyll a carbon nitrogen ratio and insect diptera chironomidae assemblages within the past millennium the least productive and by inference coldest conditions occurred ca ad 1700 1850 late in the little ice age the 2000 yr sediment record also reveals an episode of reduced organic matter deposition during the 6th 7th century ad combined with the few other records comparable in resolution that span this time interval from baffin island we suggest that this cold episode was experienced regionally a comparable cold climatic episode occurred in alaska and western canada at this time suggesting that the first millennium ad cold climate anomaly may have occurred throughout the arctic dramatic increases in aquatic biological productivity at multiple trophic levels are indicated by increased chlorophyll a concentrations since ad 1800 and chironomid concentrations since ad 1900 both of which have risen to levels unprecedented over the past 2000 yr

qp qs relations in the sedimentary basin of the upper mississippi embayment using converted phases abstract three component digital seismograms recorded by the 40 panda portable array for numerical data acquisition stations in the new madrid seismic zone were analyzed to study seismic wave attenuation in the sedimentary basin using the spectral ratio method a prominent s to p s p converted phase was generated at the boundary between the uppermost sedimentary basin and the underlying paleozoic rocks the direct s wave on the horizontal component is characterized by a lower frequency content than that of the converted s p wave on the vertical component the differences in frequency content between the direct s and the s p converted waves can be attributed to the different attenuation effects between p and s waves in the unconsolidated sediments the spectral ratio between the low frequency s wave and the high frequency converted s p wave from the bottom of the sediments can be used to yield a relationship between q p and q s in the sediments results from panda stations with well constrained spectral ratios in the frequency range from 2 to 25 hz give the q p value ranging from 25 to 60 and q s from 25 to 30 for the sedimentary basin in the upper mississippi embayment

a cocorp deep reflection profile across the buried reelfoot rift south central united states abstract a cocorp deep reflection survey across the northern mississippi embayment reveals essential features of the late precambrian early paleozoic reelfoot rift stratified reflections delineating the sedimentary fill of the rift basin are of variable thickness the base ranging from 2 0 to a maximum of 3 5 s twt 4 to 8 km depth in contrast the base of phanerozoic the sedimentary section immediately east of the rift is at 1 4 s 2 8 km depth correlation with a basement penetrating well indicates that the base of the upper cretaceous holocene mississippi embayment supergroup base of the cambrian ordovician knox group and the lower upper cambrian bonneterre formation are basin wide seismic stratigraphic markers clastic sedimentary strata of the lamotte formation which immediately overlie precambrian basement show clear angular discordance with the overlying subhorizontal bonneterre formation indicating that the base of the bonneterre marks the transition from active extension to passive subsidence within the reelfoot rift palinspastic restoration of the basement suggests relatively modest extension associated with rift formation 17 the blytheville arch an axial antiformal feature as well as a number of lesser structures indicative of multiple episodes of fault reactivation are also evident on the cocorp profile the crystalline basement beneath the reelfoot rift is relatively devoid of reflections down to 5 0 s 12 15 km depth beyond which it passes gradationally into a complexly reflective diffractive middle and lower crust the lower crust however does not exhibit the distinctly laminated character commonly observed in mesozoic cenozoic extensional provinces the crust mantle transition beneath the rift is characterized by a gradational downward cessation of crustal reflectivity at 12 13 s 40 km depth followed by an unreflective zone which in turn is followed by a distinct horizontal reflection at 14 5 s the latter is not observed on existing profiles outside the rift at present it is not possible to determine strictly whether the deep horizon represents moho or alternatively a discrete feature sill within the uppermost mantle however its spatial association with the reelfoot rift suggests that the two are genetically related regional relations together with the existence of dipping fabric in the deep crust beneath the rift suggest the possibility that the reelfoot rift formed along the southern extension of the circa 1 ga grenville front

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

changes in the glacier extent and surface elevation along the ningchan and shuiguan river source eastern qilian mountains china we investigate the changes at nine glaciers in the ningchan and shuiguan river source eastern qilian mountains between 1972 and 2010 according to analysis of topographic maps and multispectral satellite data all nine glaciers in the study area have retreated by a maximum of 250 57 4 m and a minimum of 91 57 4 m the total glacier area decreased by 1 20 km 2 corresponding to 9 9 of the glacierized area in 1972 comparing the two dems generated from the topographic maps and real time kinematic gps data the mean glacier thinning rate was 0 64 m yr 1 between 1972 and 2010 the most significant thinning generally occurred on the termini the ice volume loss was about 106 8 46 7 x 10 3 km 3 equal to 90 8 39 7 x 10 3 km 3 w e which suggested a mean water discharge of 0 1 0 05 m 3 s during 1972 2010 based on analysis of meteorological data the summer temperature june august tends to increase over a similar time period the consistency of temperature increase and glacier shrinkage allows us to suggest that air temperature plays an important role in glacier changes in this region c 2014 university of washington published by elsevier inc all rights reserved

low sea level rise projections from mountain glaciers and icecaps under global warming the mean sea level has been projected to rise in the 21st century as a result of global warming such projections of sea level change depend on estimated future greenhouse emissions and on differing models but model average results from a mid range scenario a1b suggests a 0 387 m rise by 2100 refs 1 2 the largest contributions to sea level rise are estimated to come from thermal expansion 0 288 m and the melting of mountain glaciers and icecaps 0 106 m with smaller inputs from greenland 0 024 m and antarctica 0 074 m here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise excluding those in greenland and antarctica we provide the first separate assessment of melt contributions from mountain glaciers and icecaps as well as an improved treatment of volume shrinkage we find that icecaps melt more slowly than mountain glaciers whose area declines rapidly in the 21st century making glaciers a limiting source for ice melt using two climate models we project sea level rise due to melting of mountain glaciers and icecaps to be 0 046 and 0 051 m by 2100 about half that of previous projections

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

the significance of the crustal velocity model in local earthquake locations from a case example of a panda experiment in the central united states reliable local earthquake locations depend on many factors including the quality of earthquake data the spatial distribution of network stations the location algorithms and the local and regional seismic velocity models the uncertainties of p and s wave arrival times at various seismic stations are in large part responsible for the uncertainty in the determination of crustal velocity models and earthquake locations we took the advantage of the high quality and high dynamic range panda data from a 33 month seismic array experiment in the central united states to investigate the importance of crustal velocity models especially the s wave model on earthquake locations several crustal models are used to relocate a group of selected earthquakes from the panda database it is clear that earthquake depths are determined less reliably than the epicenters when the shear wave velocity model is not properly determined the mislocations in some examples are significant that the importance of determining reliable p and s velocity models independently cannot be overlooked if the crustal p and s wave velocity structures in the region can be well determined reliable earthquake locations are possible even with only a few accurate p and s readings

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

a simple algorithm for local earthquake location using 3d vp and vs models test examples in the central united states and in central eastern taiwan traditional local earthquake location using a horizontally layered homogeneous velocity model is limited in its resolution and reliability due to the existence of frequently overlooked 3d complexity of the real earth during traditional 3d seismic tomography simultaneous earthquake relocation using the resultant 3d velocity model has produced reliable earthquake locations however only a small subset of events are typically used and thus relocated in the inversion the rest of the events in a catalog must then be relocated using the 3d models the repeated calculation of travel times across 3d v p and v s models is also not efficient and not practical for a routine network earthquake location when the very time consuming exact 3d raytracing is used because high resolution earthquake data are now available from many modern seismic networks representative high resolution 3d v p and v s models for a region can be better determined by taking advantage of recently available high speed computer technology and large disk space we implemented a simple algorithm to efficiently locate every local earthquake using the best available regional 3d v p and v s models once the v p and v s information for all cubic cells in a 3d grid model are determined p and s travel times from each grid point to all seismic stations can be calculated and stored on disk files for later usage during the iteration process for earthquake location travel times from a trial hypocenter to all recording stations can be determined simply by a linear interpolation from those of the adjacent eight grid points available in the previously stored disk files without the need for raytracing the iterations continue until the hypocenter adjustments at the end of the last iteration are below the given criteria and the travel time residual or the difference between the observed and the calculated travel times is a minimum therefore any local earthquake can be efficiently and reliably located using the available 3d velocity models this simple location program has been applied to relocate earthquakes in the new madrid seismic zone nmsz of the central united states and in the central eastern taiwan region preliminary results in both regions reveal that earthquake hypocenters can be efficiently relocated in spite of the very significant lateral structural variations tests with data from taiwan further demonstrate that the resolution of seismic tomography and the relocated seismicity is sensitive to relative distribution of seismic network stations and background seismicity thus this single event location program can be applied to relocate all earthquakes in a seismic network catalog and more importantly to allow routine earthquake location for any seismic network using the available 3d velocity models

comment on the potential for sea level rise new estimates from glacier and ice cap area and volume distribution by s c b raper and r j braithwaite

contour mapping of relic structures in the precambrian basement of the reelfoot rift north american midcontinent a new contour map of the basement of the reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features the major features are two asymmetric intrarift basins bounded by three structural highs and the rift margins the basins are oriented normal to the northeast trend of the rift two of the highs appear to be ridges of undetermined width that extend across the rift the third high is an isolated dome or platform located between the basins the minor features are three linear structures of low relief oriented subparallel to the trend of the rift two of these located within the rift basins may divide the rift basins into paired subbasins these mapped features may be the remnants of initial extensional rifting half graben faulting and basement subsidence the rift basins are interpreted as having formed as opposing half graben and the structural highs are interpreted as having formed as associated accommodation zones some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime a detailed knowledge of the geometries of the reelfoot rift s basement features therefore is essential when evaluating their seismic risk potential

using airborne ku band altimeter waveforms to investigate winter accumulation and glacier facies on austfonna svalbard winter balance is an important metric for assessing the change on glaciers and ice caps yet measuring it using ground based techniques can be challenging we use the european space agency prototype airborne sar interferometric radar altimeter system asiras to extract snow depths from the received altimeter waveforms over austfonna ice cap svalbard additionally we attempt to distinguish the long term firn area from other glacier facies we validate our results using snow depth and glacier facies characterizations determined from ground based radar profiles snow pits and a multi look satellite synthetic aperture radar image we show that the depth of the winter snowpack can be extracted from the altimeter data over most of the accumulation zone comprising wet snow zone and a superimposed ice zone the method struggles at lower elevations where internal reflections within the winter snowpack are strong and the winter snow depth is less than 1m we use the abruptness of the reflection from the last summer surface lss to attempt to distinguish glacier facies while there is a general correlation between lss abruptness and glacier facies we do not find a relationship that warrants a distinct classification based on asiras waveforms alone

the information content of high frequency seismograms and the near surface geologic structure of hard rock recording sites due to hardware developments in the last decade the high frequency end of the frequency band of seismic waves analyzed for source mechanisms has been extended into the audio frequency range 20 hz in principle the short wavelengths corresponding to these frequencies can provide information about the details of seismic sources but in fact much of the signal is the site response of the nearsurface several examples of waveform data recorded at hard rock sites which are generally assumed to have a flat transfer function are presented to demonstrate the severe signal distortions includingfmax produced by near surface structures analysis of the geology of a number of sites indicates that the overall attenuation of high frequency 1 hz seismic waves is controlled by the whole path q between source and receiver but the presence of distinctfmax site resonance peaks is controlled by the nature of the surface layer and the underlying near surface structure models of vertical decoupling of the surface and nearsurface and horizontal decoupling of adjacent sites on hard rock outcrops are proposed and their behaviour is compared to the observations of hard rock site response the upper bound to the frequency band of the seismic waves that contain significant source information which can be deconvolved from a site response or an array response is discussed in terms offmax and the correlation of waveform distortion with the outcrop scale geologic structure of hard rock sites it is concluded that although the velocity structures of hard rock sites unlike those of alluvium sites allow some audio frequency seismic energy to propagate to the surface the resulting signals are a highly distorted limited subset of the source spectra

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

estimation of ground motion at deep soil sites in eastern north america the stochastic model used previously to estimate motions at hard rock sites in eastern north america has been modified to include the effect of deep soils we simulated motions for a number of distances and magnitudes for a representative soil column and used these motions to derive equations giving ground motion as a simple function of magnitude and distance these new equations are intended for use in building codes and those engineering applications that do not require detailed site evaluations the ground motions for which we derived equations include 5 damped response spectra at 13 periods ranging from 0 05 to 4 sec peak acceleration and the maximum pseudovelocity and maximum pseudoacceleration responses the latter two quantities are introduced here for the first time they represent the maxima over the period range 0 1 to 4 sec for a given magnitude and distance and they may be useful as a basis for determining the seismic coefficient in building codes

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

three dimensional vp vs variations for the coso region california recent seismological studies of the coso region of southeastern california document both low p wave velocities and abnormal sv attenuation in indian wells valley south of the pleistocene volcanics of the coso range in order to learn more about the physical nature of these colocated anomalies a tomographic inversion for the three dimensional variations of vp vs the ratio of compressional to shear velocity was performed iterative back projection of 2966 shear and compressional wave travel time residuals from local earthquakes recorded on vertical instruments reveals that vp vs is generally high at the surface and decreases systematically to 10 km depth superimposed on this trend are several large anomalies near devil s kitchen in the coso geothermal area vp vs values are very low near the surface consistent with measured values for steam dominated geothermal systems abnormally high values of vp vs are observed in portions of indian wells valley and also below the cactus peak rhyolite dome from 2 to 5 km in depth in indian wells valley the co occurrence of low p velocities low s velocities high vp vs and anomalous sv attenuation are indicative of subsurface partial melt because the inversion is based on vertical data only however the results cannot be considered conclusive only suggestive

rift structure of the northern mississippi embayment from the analysis of gravity and magnetic data gravity and magnetic data have been simultaneously inverted to derive a crustal model of the northern mississippi embayment which is compatible with geologic and seismic refraction data the results indicate that this region is a site of a late precambrian early paleozoic rift system an anomalously dense layer is present at the base of the crust and thickens beneath a broad northeast trending graben that formed during the initial phases of rifting the thickest part of anomalous crust occurs beneath the region of greatest seismic activity which lies within the geographic limits of the graben it is suggested from this correlation that strain accumulates within the anomalous crust layer which acts as an inhomogeneity in a relatively homogeneous lithosphere based on the results of this study and previous geophysical studies the complex tectonic evolution of the upper mississippi embayment since late precambrian time is rift formation possibly along a pre existing shear zone graben development in cambrian time reactivations in permian and cretaceous time and subsequent formation of the present mississippi embayment and fault zones with large influences from rift structures

snow patch and glacier size distributions a simple theoretical model demonstrates that some amount of randomness in snow and ice mass balance is sufficient to reproduce empirically observed power law and exponential distributions of snow patch and glacier sizes no other assumptions about the underlying topography or snow accumulation and ablation processes are necessary to extract this important spatial property the inclusion of additional geometrical and physical processes can alter the specific scaling constants of the size distributions but the fundamental behavior remains unchanged specifically for snow patch and glacier sizes less than some correlation length the size distribution is a decreasing power law and for sizes larger than the correlation length the distribution decreases rapidly as an exponential the solution is based on a mapping to a relatively well explored class of problems in percolation theory

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

refinement of thrust faulting models for the central new madrid seismic zone abstract we present the results of the joint relocation of events recorded during 1989 1992 by the panda network in the central new madrid seismic zone the near surface material in the study area is a gently dipping layer of poorly consolidated sediments with low p wave velocity and high v p v s estimated values 1 8 km s 1 and 3 the sediments are underlain by high velocity paleozoic rocks under the network the difference in sediment thickness is only 0 6 km but because of the low velocities the location of the events using layered models is affected by errors application of the joint hypocentral determination jhd technique to a subset of 580 events shows that the single event locations may be in error by as much as 1 km in depth depending on where the events are located analysis of synthetic data generated for a realistic 3 d velocity model supports the jhd results the analysis of synthetic data also suggests that a v p v s 2 3 is more appropriate for the post paleozoic mississippi embayment sediments based on the jhd locations we present a new interpretation of the seismicity with two en echelon sw dipping thrust faults connected by a west dipping thrust fault these faults appear associated with the reelfoot scarp and its northern extension the kentucky bend scarp

attenuation of body waves in the central new madrid seismic zone abstract data from the portable array for numerical data acquisition panda deployment in the central part of the new madrid seismic zone have been used to study the attenuation of body waves the spectral decay technique is used to analyze acceleration amplitude spectra of both p and s waves in a frequency range of 5 to 25 hz in order to obtain the high frequency attenuation parameter a multiple weighted least squares method is applied to obtain the site attenuation factor 0 at each station and to get d dr which were interpreted in terms of a two layer q structure consisting of a sedimentary layer overlying the upper crust the 0 values for s waves are stable and show a positive correlation with sediment thickness the 0 values for p waves in the sediments show significant scatter which may be due to greater sensitivity of p wave attenuation to water content of the soils than that of s waves which gave more stable 0 values consistency checks on the assumptions made in obtaining the p and s values are made by studying the source spectrum of several events and the differential sp s from the spectral ratio of the converted sp to s phases the three sets of values are found to be internally consistent but our results are limited to deep sediment sites since the complete vertical distribution of q with sediment depth is not known

flow dynamics and iceberg calving rates of devon ice cap nunavut canada the surface velocity field of devon ice cap nunavut canada was mapped using interferometric synthetic aperture radar insar ascending european remote sensing satellite 1 and 2 ers 1 2 tandem mode data were used for the western and southeast sectors and 3 day repeat pass ers 1 imagery for the northeast sector speckle tracking procedures were used with radarsat 1 imagery to obtain surface velocities over the terminus of belcher glacier a major calving front where decorrelation between ers data occurred the insar data highlight a significant contrast in ice flow dynamics between the east and west sides of the ice cap ice movement west of the main north south divide is dominated by relatively uniform sheet flow but three fast flowing outlet glaciers that extend 14 23 km beyond the ice cap margin also drain this region several outlet glaciers that extend up to 60km inland from the eastern margin drain the eastern side of the ice cap the dominant ice flow regimes were classified based on the relationship between the driving stress averaged over a length scale often ice thicknesses and the ratio of surface velocity to ice thickness the mapped distribution of flow regimes appears to depict the spatial extent of basal sliding across the ice cap this is supported by a close relationship between the occurrence of flow stripes on the ice surface and flow regimes where basal sliding was found to be an important component of the glacier motion iceberg calving rates were computed using measured surface velocities and ice thicknesses derived from airborne radio echo sounding the volume of ice calved between 1960 and 1999 was estimated to be 20 5 4 7 km 3 or 0 57km 3 a 1 approximately 89 of this loss occurred along the eastern margin the largest single source is belcher glacier which accounts for 50 of the total amount of ice calved

crustal studies velocity inversions and fault tectonics results from a microearthquake survey in the new madrid seismic zone a dense network of portable seismographs was operated in the ridgely area of western tennessee in may of 1978 during 32 days of operation 122 earthquakes were detected of which 90 were located the high quality p and s arrivals recorded exhibit travel time ratios ts tp that decrease significantly with depth this decrease is most rapid in the upper few kilometers and necessarily reflects similar changes in the velocity ratio vp vs based on laboratory and theoretical studies such observations are consistent with a decrease in crack density with increasing confining pressure a special study of vp vs and vp vs revealed strong variations with depth that also correlate with rock type inversion of the data for both p and s velocity structures confirms the presence of a low velocity zone in the depth range 2 to 5 km a high velocity lid with high vp vs and thus high crack density and a boundary at the near surface for s to p conversion associated with the unconsolidated saturated sediments of the mississippi embayment relocated hypocenters using independent velocity structures for p and s are systematically deeper and define a seismogenic layer between 4 and 13 km depth the earthquakes near ridgely show that most of the activity is occurring on a northwest striking reverse fault that dips to the southwest minor off fault activity within the hanging wall was also observed representing motion on a series of small normal faults dipping to the northeast other composite focal mechanisms were determined for nearby regions these solutions are all in general agreement with a horizontal compressive stress field striking northeast to east favoring right lateral strike slip motion on left stepping northeast trending faults or reverse motion on faults trending northwest and north these results are consistent with the stress field found in a large area interior to the united states and imply a rotation of the regional stress field since the late cretaceous when extensional faulting occurred in the area

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

three dimensional p wave velocity structure in the new madrid seismic zone a three dimensional p wave velocity model for the new madrid seismic zone nmsz has been developed using a nonlinear travel time tomography method the inversion involved 709 earthquakes recorded by digital three component portable array for numerical data acquisition stations deployed in the nmsz over the time period 1989 through 1992 analysis of ray coverage and inversion of a synthetic data set showed that the model has high resolution to a depth of 11 km low velocity anomalies correlate with the prominent northwest and northeast trending arms of seismicity lowest velocity anomalies 8 occur at the intersection of these arms and are associated with shallow seismicity and a high swarm rate these low velocity regions are interpreted to be the result of increased fluid pressure associated with structurally disrupted rocks beneath the blytheville pascola arch complex small regions of high velocity limited to the upper few km of the crust correlate with gravity and magnetic anomalies and are interpreted to be igneous intrusions high velocity anomalies also parallel the edges of the reelfoot rift margin and probably are associated with crystalline precambrian rocks that form the margin of the reelfoot rift graben most earthquakes are associated with low velocity regions and avoid regions of high velocity

wave conversions from earthquakes and a new velocity model for the south carolina coastal plain phase conversions from p to sv and from sv to p occur at a high impedance boundary near the surface in charleston south carolina four arrivals p converted p converted s and s are observed on three component records of earthquakes in this area using arrival time differences between paired arrivals of direct and converted phases a shallow surface layer vp vs ratio of 2 9 was determined applying the wadati method to travel times derived at the base of the surface layer yields a vp vs ratio in deeper layers of 1 73 relocating earthquakes using this more appropriate velocity structure for direct and converted shear waves alters hypocentral parameters such that epicenters diverge and depths converge it is inferred that these relocated earthquakes are not exclusively associated with a single seismogenic fault

analysis of low frequency seismic signals generated during a multiple iceberg calving event at jakobshavn isbrae greenland 1 we investigated seismic signals generated during a large scale multiple iceberg calving event that occurred at jakobshavn isbrae greenland on 21 august 2009 the event was recorded by a high rate time lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus during the event two full glacier thickness icebergs calved from the grounded or nearly grounded terminus and immediately capsized the second iceberg to calve was two to three times smaller than the first the individual calving and capsize events were well correlated with the radiation of low frequency seismic signals 0 1 hz dominated by love and rayleigh waves in agreement with regional records from previously published glacial earthquakes these low frequency seismic signals had maximum power and or signal to noise ratios in the 0 05 0 1 hz band similarly full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus the signals therefore appear to be local manifestations of glacial earthquakes although the magnitudes of the signals twice time integrated force histories were considerably smaller than previously reported glacial earthquakes we thus speculate that such earthquakes may be a common if not pervasive feature of all full glacier thickness calving events from grounded termini finally a key result from our study is that waveform inversions performed on low frequency calving generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving in particular the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude accordingly in our analysis it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal

sharply increased mass loss from glaciers and ice caps in the canadian arctic archipelago the canadian arctic archipelago contains one third of the global volume of land ice outside the ice sheets but its contribution to sea level change is largely unknown gardner et al use three independent techniques to reveal that mass loss from the archipelago was 92 12 gigatonnes per year in 2007 09 about three times greater than in 2004 06 and coincident with warmer summer temperatures the record is too short to allow a firm conclusion on longer term trends but it is clear that the canadian arctic archipelago is a significant contributor to sea level rise mountain glaciers and ice caps are contributing significantly to present rates of sea level rise and will continue to do so over the next century and beyond1 2 3 4 5 the canadian arctic archipelago located off the northwestern shore of greenland contains one third of the global volume of land ice outside the ice sheets6 but its contribution to sea level change remains largely unknown here we show that the canadian arctic archipelago has recently lost 61 7 gigatonnes per year gt yr 1 of ice contributing 0 17 0 02 mm yr 1 to sea level rise our estimates are of regional mass changes for the ice caps and glaciers of the canadian arctic archipelago referring to the years 2004 to 2009 and are based on three independent approaches surface mass budget modelling plus an estimate of ice discharge smb d repeat satellite laser altimetry icesat and repeat satellite gravimetry grace all three approaches show consistent and large mass loss estimates between the periods 2004 2006 and 2007 2009 the rate of mass loss sharply increased from 31 8 gt yr 1 to 92 12 gt yr 1 in direct response to warmer summer temperatures to which rates of ice loss are highly sensitive 64 14 gt yr 1 per 1 k increase the duration of the study is too short to establish a long term trend but for 2007 2009 the increase in the rate of mass loss makes the canadian arctic archipelago the single largest contributor to eustatic sea level rise outside greenland and antarctica

quaternary deformation and fault structure in the northern mississippi embayment as imaged by near surface seismic reflection data seismicity in the new madrid seismic zone nmsz in the central united states constrains the location of present deformation at depth along four main distinct arms while the surface expression of the ongoing deformation is still unclear to better constrain the surface deformation in the nmsz we integrate existing seismic reflection data with a new 300 km long high resolution seismic reflection profile acquired along the mississippi river from cape girardeau mo to caruthersville mo based on the data we interpret the reelfoot thrust and the new markham fault as upward splays of a blind master fault defined by the seismicity and extending at depth farther north to the south two faults the axial fault and the cottonwood grove fault are imaged above the southern arm of the nmsz both fault display deformation of the paleozoic through the tertiary sediments and a relief of 20 25 m at the base of the quaternary alluvium which we interpret as the result of strike slip motion along a complex fault plane geometry we propose two alternative interpretations for the relationship between the shallow faults and the seismicity in this area 1 the faults merge at depth and are presently both active and 2 the faults are distinct at depth and were active during the quaternary and only the axial fault is presently deforming geological structures mapped at the surface as part of this study show that quaternary deformation is accommodated along a fault network that is more complex than the simple four arm system illuminated by the seismicity a behavior predicted by analog and computer models

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

energy based binary segmentation of snow microtomographic images x ray microtomography has become an essential tool for investigating the mechanical and physical properties of snow which are tied to its microstructure to allow a quantitative characterization of the microstructure the grayscale x ray attenuation coefficient image has to be segmented into a binary ice pore image this step called binary segmentation is crucial and affects all subsequent analysis and modeling common segmentation methods are based on thresholding in practice these methods present some drawbacks and often require time consuming manual post processing here we present a binary segmentation algorithm based on the minimization of a segmentation energy this energy is composed of a data fidelity term and a regularization term penalizing large interface area which is of particular interest for snow where sintering naturally tends to reduce the surface energy the accuracy of the method is demonstrated on a synthetic image the method is then successfully applied on microtomographic images of snow and compared to the threshold based segmentation the main advantage of the presented approach is that it benefits from local spatial information moreover the effective resolution of the segmented image is clearly defined and can be chosen a priori

the challenge of monitoring glaciers with extreme altitudinal range mass balance reconstruction for kahiltna glacier alaska glaciers spanning large altitudinal ranges often experience different climatic regimes with elevation creating challenges in acquiring mass balance and climate observations that represent the entire glacier we use mixed methods to reconstruct the 1991 2014 mass balance of the kahiltna glacier in alaska a large 503 km 2 glacier with one of the greatest elevation ranges globally 264 6108 m a s l we calibrate an enhanced temperature index model to glacier wide mass balances from repeat laser altimetry and point observations finding a mean net mass balance rate of 0 74 mw e a 1 0 04 std dev of the best performing model simulations results are validated against mass changes from nasa s gravity recovery and climate experiment grace satellites a novel approach at the individual glacier scale correlation is strong between the detrended model and grace derived mass change time series r 2 0 58 and p 0 001 and between summer r 2 0 69 and p 0 003 and annual r 2 0 63 and p 0 006 balances lending greater confidence to our modeling results we find poor correlation however between modeled glacier wide balances and recent single stake monitoring finally we make recommendations for monitoring glaciers with extreme altitudinal ranges including characterizing precipitation via snow radar profiling

array observations of microseismic noise and the nature of h v in the mississippi embayment abstract ambient ground motion data were collected using phased seismic arrays in fall 2002 and spring 2007 within the mississippi embayment and at a single station external to the embayment these data allowed us to determine the wave field composition of ambient noise for understanding wave propagation mechanisms giving rise to spectral peaks using nakamura s h v technique ambient ground motions in the frequency band of 0 1 0 33 hz 10 3 sec period were dominated by spatially localized rayleigh and love wave microseisms generated by high ocean waves along the north american seaboard in the time periods of analysis seismic waves important in forming the h v peak near 4 sec period are composed of relatively high phase velocity rayleigh and love waves that convert to propagating homogeneous shear waves in the thick unconsolidated sediments of the embayment the h v resonant period is controlled by both constructive and destructive interference of these shear waves a simple relationship for the h v peak is given using a propagator matrix formulation that predicts the resonance frequency of a layered medium for surface wave motion at the base of the system the amplitude of the observed h v peak however does not give an accurate estimate of shear wave amplification because it depends on the slowness of the incident wave the inconsistency in estimated average shear wave velocities using the h v method and differential travel times of local earthquake sp phases in the mississippi embayment may be explained by misidentification of sp wave conversion points from deeper interfaces

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

high resolution 3 d p wave attenuation structure of the new madrid seismic zone using local earthquake tomography a three dimensional 3 d high resolution p wave seismic attenuation model for the new madrid seismic zone nmsz is determined using p wave path attenuation t values of small magnitude earthquakes md 3 9 events were recorded at 89 broadband and short period seismometers of the cooperative new madrid seismic zone network and 40 short period seismometers of the portable array for numerical data acquisition experiment the amplitude spectra of all the earthquakes are simultaneously inverted for source path t and site parameters the t values are inverted for qp using local earthquake tomography methods and a known 3 d p wave velocity model for the region the four major seismicity arms of the nmsz exhibit reduced qp higher attenuation than the surrounding crust the highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid rich fractures along the southeast extension of the reelfoot fault the qp results are consistent with previous attenuation studies in the region which showed that active fault zones and fractured crust in the nmsz are highly attenuating

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

relocation of earthquakes in the new madrid seismic zone estimation of 1d velocity structure and geometry of a seismogenic fault abstract determination of reliable hypocenters of earthquakes is crucial to earthquake seismology and to evaluate hazards associated with earthquakes there are many associated computer codes for this purpose however most of the location algorithms are designed to determine hypocentral parameters based on previously determined velocity models in contrast we employed a location method that is independent of the initial velocity model using a genetic algorithm ga to determine an optimal 1d velocity model and the locations of earthquakes using this ga we relocated earthquakes that occurred in the new madrid seismic zone nmsz in the central united states between october 1989 and august 1992 the goal of this work was to delineate the possible fault planes by reliable relocation of those earthquakes and to determine a 1d velocity structure for the nmsz a total of 502 earthquakes recorded by 37 portable array for numerical data acquisition panda stations were used in the relocation study in the relocation process the root mean square travel time residuals were reduced by 35 corresponding to an average of 2 3 km deeper in depth 0 7 km shift in latitude and 0 8 km shift in longitude compared with those in the initial catalog locations the hypocenters of the earthquakes can be subdivided into four groups based on their spatial distributions the group that corresponds to the cottonwood grove fault cgf in the southwestern nmsz represents a very steep plane whereas the other three groups fall into reelfoot fault rf we inverted p and s wave travel times from the new hypocentral parameters to determine 1d velocity models the resulting eight layered velocity models consist of a 2 km thick surface layer followed by seven 2 km thick layers with v p ranges from 5 36 to 6 74 km s and v s ranges from 2 83 to 3 90 km s for both cgf and rf regions online material interactive visualizations of hypocentral distributions

progressive inversion for hypocenters and p wave and s wave velocity structure application to the geysers california geothermal field seismicity at the geysers is induced by some aspect of steam production accurate earthquake locations particularly hypocentral depth are needed to determine the relationship between geothermal energy production and seismicity progressive p and s wave velocity hypocenter inversions were done using data from 39 microearthquakes at the geysers to estimate microearthquake locations and determine if the geothermal field has a distinctive seismic signature comparable final vp vs and vp vs velocity models were obtained from four different starting velocity models the elevation interval of maximum steam production coincides with minimum observed vp vs and vp vs increases below the primary production zone suggesting that reservoir rock becomes more fluid saturated with increasing depth a vp vs peak at the condensation zone production zone elevation delineates the top of the stream reservoir earthquake locations are confined to two depth intervals a zone of shallow seismicity occurs immediately below the condensation zone and above maximum depths of steam production a more arealy restricted zone of seismicity is located below maximum production depths and is abruptly terminated at an elevation of 3 7 km

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

mysterious tremor like signals seen on the reelfoot fault northern tennessee abstract a phased array of 19 broadband seismometers was deployed from november 2009 to september 2011 in an effort to detect nonvolcanic tremor or tectonic tremor associated with the reelfoot fault northern tennessee an autodetection algorithm using broadband frequency wavenumber analysis was used to search for the recurrence of signals first reported during an active source experiment in 2006 the original signals appeared as short duration impulsive arrivals with a high phase velocity ranging from 3 to 25 km s we have identified thousands of similar signals on the 2 year long array data two distinct detection peaks are observed with event azimuths from the west and northeast the detections are most similar to the events seen in 2006 and are inferred to come from very small m l 1 microearthquakes that occur in the shallow basement on faults adjacent to the reelfoot fault these include detections with coherent s wave energy that reinforce the interpretation of very small local and regional events other signals detected show distinct changes in slowness and azimuth as a function of time these events were interpreted as atmospheric acoustic sources the high frequency content and impulsive arrivals of the nonacoustic arrivals are not consistent with tectonic tremor as seen in other parts of the world but do indicate seismic activity in the crust near the reelfoot thrust fault that was previously unknown