neogene caribbean plate rotation and associated central american tectonic evolution during the neogene the caribbean plate moved eastward with respect to the north and south american plates reconstructing this motion by closing the cayman trough along its bounding transform faults creates a gore of ocean between northern central america and southern mexico we present instead a reconstruction which juxtaposes these two continental areas by strike slip motion using geological evidence from around the cayman trough the strike slip fault zones of northern central america and the continental margin of southern mexico as our constraints we propose that seafloor spreading began in the cayman trough at 30 5 ma and that subsequently there was 1100 km of relative plate displacement at an average rate of 3 7 0 6 cm yr this neogene plate motion cannot be achieved by rigid plate rotation about a single pole which implies that central america must have rotated anticlockwise relative to the rest of the plate there is evidence for internal plate deformation in central america consistent with such a sense of rotation our suggestion of an originally easterly trending arc in southern central america is more consistent with the timing and geometry of the collision of panama with northern colombia and the resultant deformation than were earlier models that depicted collision of a northerly trending arc

paleomagnetic results from honduras and their bearing on caribbean tectonics paleomagnetic results have been obtained from 37 sites in central and western honduras and one site in north western nicaragua the rocks are limestones sandstones and granites and range in age from 140 to 60 m y regional fold tests demonstrate that the rocks carry a prefolding pre laramide magnetization the data indicate a very large clockwise rotation of the sampling area during the early cretaceous followed by a counter clockwise rotation in the late cretaceous the changes in latitude are minor during this time period it is highly unlikely that these large rotations apply to the entire caribbean plate rather they reflect the motion of a smaller area known as the chortis block this interpretation is supported by paleomagnetic data from neighboring areas the results also suggest that the chortis block sutured onto southern mexico guatemala in latest cretaceous time in agreement with geochemical data and several plate tectonic models these new data together with published paleomagnetic data from around the caribbean imply that a rigid caribbean plate did not exist until well into the tertiary

new geochemical investigations in platanares and azacualpa geothermal sites honduras abstract platanares and azacualpa geothermal sites of honduras are located in an inner part of the caribbean plate far from the active volcanic front of central america here geology indicates that there are not the conditions for the occurrence of shallow magmatic heat sources for high enthalpy geothermal resources geothermal perspectives are related to the possibility of a deep circulation of meteoric water along faults and the storage of the heated fluid in fractured permeable reservoirs geochemical geothermometers indicate a temperature for the deeper part of the geothermal reservoir close to 200 c for platanares and of 150 170 c for azacualpa calcite scaling with subordinate silica deposition has to be expected in both sites co 2 soil flux investigations have been carried out in both areas and reveal the presence of positive anomalies likely corresponding to the presence at depth of fractured degassing geothermal reservoirs compared with the geothermal areas of central italy whose reservoirs are hosted in carbonate rocks e g latera chiodini et al 2007 the co 2 soil flux measured in honduras is significantly lower mean of 17 g m 2 day at platanares and of 163 g m 2 day at azacualpa probably because of the dominant silicate nature of the deep reservoirs

accelerated thawing of subarctic peatland permafrost over the last 50 years 1 in this study we provide a quantification of the main patterns of change of a subarctic peatland caused by permafrost decay monitored between 1957 and 2003 up thrusting of the peatland surface due to permafrost aggradation during the little ice age resulted in the formation of an extensive peat plateau that gradually fragmented into residual palsas from the 19th century to the present only about 18 of the original surface occupied by permafrost was thawed in 1957 whereas only 13 was still surviving in 2003 rapid permafrost melting over the last 50 years caused the concurrent formation of thermokarst ponds and fen bog vegetation with rapid peat accumulation through natural successional processes of terrestrialization the main climatic driver for accelerated permafrost thawing was snow precipitation which increased from 1957 to present while annual and seasonal temperatures remained relatively stable until about the mid 1990s when annual temperature rose well above the mean contrary to current expectations the melting of permafrost caused by recent climate change does not transform the peatland to a carbon source ecosystem as rapid terrestrialization exacerbates carbon sink conditions and tends to balance the local carbon budget

the triple junction of the north america cocos and caribbean plates seismicity and tectonics the triple junction of the north america cocos and caribbean plates is ambiguously defined mainly because the north america caribbean plate boundary does not clearly continue beyond its known surface trace the motagua fault zone in western guatemala to intersect the middle america trench well located regional shallow earthquakes h 70 km show that there is no intermediate or large magnitude seismic activity associated with a presumed extension of the north america caribbean plate boundary to the west beyond its well defined surface trace there is however a clear zone of shallow seismic activity from the western section of the fault system through southern mexico fault plane solutions for these events indicate a left lateral strike slip displacement which is in good agreement with surface faulting we suggest that these strike slip faults together with the salina cruz fault in the isthmus of tehuantepec mark the boundaries of a broad zone of deformation in southern mexico and northern central america which takes up the interactions of the three plates in this sense no single point constitutes the triple junction the geologic record suggests that the motagua fault zone developed because the westernmost portion of the caribbean plate became locked against north america

rotation of the chortis block causes dextral slip on the guayape fault the chortis block is undergoing deformation as a direct result of large magnitude sinistral strike slip faulting on the north america caribbean plate boundary we have studied the chortis block using geologic mapping remote imagery and earthquake seismology to evaluate the effect that large magnitude strike slip faulting has on an adjacent microcontinental block in the eastern part of the chortis block recent geologic mapping has shown that the northeast striking guayape fault is dextral instead of sinistral as previously assumed because this is a major fault that cuts most of the central america isthmus the new evidence for dextral slip necessitates a reinterpretation of the active tectonics of the chortis block the presence of several north trending rifts in the western part of the chortis block has led previous workers to propose that the chortis block is divided into smaller independently rotating blocks we use earthquake seismology and remote imagery data to extend this interpretation to the central portion of the chortis block however we have modified their model to account for dextral slip on the guayape fault we believe that rotation of the chortis block causes dextral slip on the guayape fault even though central america is undergoing large sinistral displacement with respect to north america

geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone heubeck ch and mann p 1991 geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone tectonophysics 191 l 26 four published plate kinematic models for the present day north american caribbean plate boundary predict significantly different fault behavior along this dominantly strike slip plate boundary zone pbz using a computer graphics system we compare the deformational pattern predicted by the four kinematic models with geologic and seismic observations along the entire length of the pbz from central america to the northern lesser antilles our results indicate that none of the kinematic models predict all the geologic and seismic observations across the entire pbz however all four models predict mapped fault character and observed earthquake focal mechanisms along certain segments of the pbz we conclude that the present day deformation within the north american caribbean plate boundary zone cannot be described by rotation about a single pole instead the caribbean plate appears to be segmented into at least three major sub plates or blocks each of which requires an individual pole of rotation to describe its motion relative to the north american plate sub plate boundaries correspond to two poorly studied zones of diffuse deformation within the caribbean plate honduras depression of central america and beata ridge of the caribbean sea

review of crustal seismicity in the aleutian arc and implications for arc deformation abstract central and eastern aleutian arc is characterized by oblique convergence between the subducting pacific and overriding bering plates this results in westward arc translation and formation of rotating crustal blocks in the forearc in 2006 2010 several moderate shallow crustal earthquakes up to magnitude 6 7 occurred in the region these events are located about 150 km away from the trench on the volcanic axis and have either strike slip west of 174 w or normal east of 174 w faulting mechanisms we improve aftershock locations by applying precise relocation methods to aid in identifying preferred fault planes we also review similar earthquakes that occurred prior to 2006 for the central aleutian arc we conclude that while some of these events occurred along the boundaries of the rotating blocks the majority are left lateral strike slip events on nw to n oriented fault planes in the unrotated bering massif these manifest riedel shearing in response slip partitioning due to the oblique convergence normal faulting events in eastern aleutian arc reflect along arc extension

geomorphological approaches to the study of neotectonics the study of morphotectonics is concerned with the analysis of landforms whose form or origins have been affected by neotectonic activity traditional morphotectonic studies have been used as a basis for more refined e g statistical analyses after the 1960s however there emerged new techniques and new approaches to the study of morphotectonics these have made more precise not only the recognition of morphotectonic features but have also improved their dating the time has come to integrate morphotectonic studies more fully both with the approaches used by other disciplines and with modern geomorphological theory

the interaction between volcanoes and strike slip transtensional and transpressional fault zones analogue models and natural examples regional strike slip faulting can control magma movements deform volcanoes and may destabilise their flanks the aim of this study is to address this problem by comparing two natural examples basse terre island volcanoes lesser antilles and maderas volcano nicaragua with analogue experiments the field and remote sensing analyses of their structures reveal that guadeloupe volcanoes which developed in a1 45 striking sinistral transtensional fault zone are dominantly fractured in a 090 e120 direction which is parallel to the maximum principal horizontal stress and to the elongation direction of the summit graben of analogue models this graben is bordered by the sigmoid i fault or y shear structure and has facilitated the formation of the beaugendre and vieux habitants valleys by faulting erosion or collapse this structure has also influenced the injection of dykes and the transport of hydrothermal fluids the comparison of maderas volcano with the analogue models confirms that the volcano has developed parallel to a 135

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

semiquantitative modeling of strain and kinematics along the caribbean north america strike slip plate boundary zone recent structural and geophysical studies conducted along the northern caribbean plate boundary at sea and on land have led to a precise description of the geometry and the tectonic regimes along this major transcurrent zone which separates the caribbean and north american plates in order to interpret its tectonic features in terms of plate motion we use a simple numerical model of strike slip faulting to test previously proposed kinematic models and to compute new motion parameters we show that none of the previously proposed models correctly accounts for the observed deformation along the whole plate boundary on the basis of the deformation pattern obtained from geological data we compute a motion parameters set that integrate rigid plate rotation and a plate boundary zone deformation component our results show that the deformation along the northern caribbean plate boundary zone is controled by regional kinematics i e the caribbean north america relative motion rather than by local effects e g small block rotation intraplate deformation

extension and rotation of crustal blocks in northern central america and effect on the volcanic arc sinistral displacements across the north american caribbean plate boundary in northern central america are distributed among major arcuate faults that have been active in neogene time south of the jocotan and motagua faults in guatemala extensional tectonics has accompanied rotation of the trailing edge of the caribbean plate around these faults segmentation of the volcanic arc in northern central america hitherto attributed to transverse breaks in the subducting cocos plate may instead be a result of this block rotation accompanying changes along the arc are observed in seismicity gravity anomaly patterns volume and composition of volcanic products and topography therefore the complex volcano tectonic geology south of the main boundary faults may be explained by interaction and rotation of crustal blocks in the overriding caribbean plate above the magma production zone along the downgoing cocos slab

depth and age in the cayman trough abstract caribbean plate boundaries are almost everywhere either strike slip or convergent so oceanic crust accreted at the spreading axis within the cayman trough provides information critical to determining the relative motions and tectonic interactions among the caribbean and surrounding plates the tectonic evolution of the trough as inferred from magnetic anomaly identifications is not entirely compatible with either its crustal subsidence or the geological evidence for time of opening and rate of offset movement along the north american caribbean plate boundary a close examination of basement topography and depth within the trough suggests that the total opening of the cayman trough is about 1100 km and that this opening occurred in two stages crust generated by the present ongoing stage of very slow spreading has extensive relief and shows a distinct increase of crustal depth with increasing distance from the spreading center crust generated by an earlier episode of faster spreading is characterized by reduced topographic relief and no appreciable differential subsidence and is separated from the younger crust by distinct topographic breaks the rate of spreading of the current slow spreading episode is15 5mm yr based upon a new crustal subsidence curve which accommodates lateral as well as vertical cooling of the accreting slab the trough has opened at this rate for about 30 ma the rate of opening prior to 30 ma cannot be determined with any reliability from crustal subsidence a reexamination of magnetic anomalies in the central part of the trough shows that these anomalies can be generated at a much slower spreading rate than previously thought this revised interpretation of cayman trough evolution brings magnetic subsidence and geological evidence into much better agreement

cenozoic tectonics of the nicaraguan depression nicaragua and median trough el salvador based on seismic reflection profiling and remote sensing data lakes nicaragua and managua are the two largest lakes in central america and they cover a combined area of 9000 km 2 of the presently active nicaraguan depression and central america volcanic front as part of the subduction factory focus area of the u s national science margins program 1925 km of shallow geophysical data were acquired over lakes nicaragua and managua in may 2006 to establish their late quaternary structural and stratigraphic history and to better constrain regional models for active tectonics in western nicaragua the gulf of fonseca and the median trough in el salvador in order to investigate regional upper crustal deformation resulting from forearc sliver transport and or slab rollback of the cocos plate these new data were integrated with relocated earthquake epicenters earthquake focal mechanisms high resolution digital topography from the national aeronautics and space administration nasa shuttle radar topography mission srtm published global positioning system gps vectors onland geologic maps previous maps of lake bathymetry and bottom sediment types a previously unpublished regional aeromagnetic data set and multichannel seismic reflection profiles from the gulf of fonseca and pacific ocean these new data sets have improved bathymetric bottom sediment and recent fault maps for both nicaraguan lakes and can be used as new constraints on the regional geology and tectonics three regional structural cross sections across the nicaraguan depression indicate that the basin is a highly asymmetrical half graben bounded to the southwest by northeast dipping oblique slip normal faults late oligocene to holocene extension resulted in footwall uplift along the elevated and folded area of the nicaraguan isthmus and the area of greatest subsidence occurs on the footwall block underlying lake nicaragua in the southeast a similar but younger pattern of footwall uplift adjacent to the down thrown footwall block is present to the northeast beneath lake managua and the gulf of fonseca we interpret this structural pattern as a time transgressive rift opening where the oldest extension late oligocene early miocene began in the southeast and migrated to the northwest gps data indicate that this earlier phase of intra arc normal rifting is presently being superimposed by arc parallel right lateral shear related to the northwestward transport of the central america forearc sliver

geophysical investigations of the platanares geothermal site honduras central america abstract geophysical studies were carried out in platanares in western honduras as part of an investigation of the geothermal resource potential of honduras by los alamos national laboratory in cooperation with the honduran government and the u s geological survey geological and geochemical studies later followed by exploratory bore holes indicate this area of rugged topography has the best geothermal potential in honduras in order to better understand the geology of the area gravity audiomagnetotelluric and telluric surveys were carried out the site is in a graben of tertiary volcanics and cretaceous red beds with numerous hot springs along faults in the center of the graben gravity mapped the thickness of low density tuffs and the position of associated normal faults it also indicated the presence of persuasive shallow highly silicified high density tuffs and gravels the electrical surveys mapped shallow high resistivity silicified zones and faults as low resistivity zones the red beds below the tuffs are considered to contain the geothermal reservoir but their maximum thickness could not be determined by these surveys due to the lack of density contrast and the high surface electrical conductivities three geologic cross sections constructed by others have been re evaluated using gravity modeling and analysis of eletrical anomalies showing general agreement but in detail significant differences

drivers of holocene palsa distribution in north america abstract palsas and peat plateaus are climatically sensitive landforms in permafrost peatlands climate envelope models have previously related palsa peat plateau distributions in europe to modern climate but similar bioclimatic modelling has not been attempted for north america recent climate change has rendered many palsas peat plateaus in this region and their valuable carbon stores vulnerable we fitted a binary logistic regression model to predict palsa peat plateau presence for north america by relating the distribution of 352 extant landforms to gridded modern climate data our model accurately classified 85 3 of grid cells that contain observed palsas peat plateaus and 77 1 of grid cells without observed palsas peat plateaus the model indicates that modern north american palsas peat plateaus are supported by cold dry climates with large seasonal temperature ranges and mild growing seasons we used palaeoclimate simulations from a general circulation model to simulate holocene distributions of palsas peat plateaus at 500 year intervals we constrained these outputs with timings of peat initiation deglaciation and postglacial drainage across the continent our palaeoclimate simulations indicate that this climate envelope remained stationary in western north america throughout the holocene but further east it migrated northwards during 11 5 6 0 ka bp however palsa extents in eastern north america were restricted from following this moving climate envelope by late deglaciation drainage and peat initiation we validated our holocene simulations against available palaeoecological records and whilst they agree that permafrost peatlands aggraded earliest in western north america our simulations contest previous suggestions that late permafrost aggradation in central canada was climatically driven

a gps and modelling study of deformation in northern central america summary we use gps measurements at 37 stations in honduras and el salvador to describe active deformation of the western end of the caribbean plate between the motagua fault and central american volcanic arc all gps sites located in eastern honduras move with the caribbean plate in accord with geologic evidence for an absence of neotectonic deformation in this region relative to the caribbean plate the other stations in the study area move west to west northwest at rates that increase gradually from 3 3 0 6 mm yr 1 in central honduras to 4 1 0 6 mm yr 1 in western honduras to as high as 11 12 mm yr 1 in southern guatemala the site motions are consistent with slow westward extension that has been inferred by previous authors from the north striking grabens and earthquake focal mechanisms in this region we examine the factors that influence the regional deformation by comparing the new gps velocity field to velocity fields predicted by finite element models fems that incorporate the regional plate boundary faults and known plate motions our modelling suggests that the obliquely convergent 20 direction of caribbean north american plate motion relative to the motagua fault west of 90 w impedes the ene directed motion of the caribbean plate in southern guatemala giving rise to extension in southern guatemala and western honduras the fem predictions agree even better with the measured velocities if the plate motion west of the central american volcanic arc is forced to occur over a broad zone rather than along a single throughgoing plate boundary fault our analysis confirms key predictions of a previous numerical model for deformation in this region and also indicates that the curvature of the motagua fault causes significant along strike changes in the orientations of the principal strainrate axes in the fault borderlands in accord with earthquake focal mechanisms and conclusions reached in a recent synthesis of the structural and morphologic data from honduras poor fits of our preferred models to the velocities of gps sites near the gulf of fonseca may be an artefact of the still short gps time series in this region or the simplifying assumptions of our fems

a statistical model for presence of late season frozen ground in discontinuous permafrost at dublin gulch yukon this paper describes geostatistical analyses completed at a discontinuous permafrost site in central yukon to develop a predictive model for the presence of late season frozen ground in support of planning and design for potential site develop ment the most important factors in the bivariate statistical model were soil type as determined through terrain analysis and slope aspect as inferred from available topographic data the other three factors included in the final model were profile curvature slope angle and ground elevation each interpreted from available topographic data the resulting model subdivides the site into three broad classes of frozen ground likelihood low where frozen ground can be expected to be encountered in late summer at 15 of observation locations medium where 50 of the ground is expected to remain frozen and high where 85 of the ground is expected to remain frozen new test pit and borehole data from the summer of 2012 were used to verify model performance the inferred correlations between frozen ground and soil type aspect curvature slope and elevation obtained in this case study may provide useful information relative to expected permafrost occurrence at sites in central yukon with similar geology and physiography

neogene north american caribbean plate boundary across northern central america offset along the polochic fault abstract the polochic fault was a segment of the north american caribbean plate boundary across central america in the neogene its 130 km of left slip was previously determined by matching structures and stratigraphie outcrop patterns of northwest and central guatemala across the fault additional support for the model and the youthfulness of the recorded offset comes from an essentially perfect match of major geomorphic features across the fault a reconstruction process which eliminates 123 km of left slip brings together rivers and drainage divides that existed before the polochic became active with the reconstruction carried across the isthmus on an east west fault the regional structural geology assumes the coherent pattern of a continuous orogenic belt whose geometry is compatible with the model of collisional tectonics centered on the motagua suture zone confined within this belt narrowed to some 60 km by the reconstruction lie the major laramide thrusts folds and tectonically emplaced serpentinites of guatemala crystalline rocks of guatemala re join the chiapas massif and paleozoic sedimentary rocks exposed in the core of an almost continuous anticlinorium extend from southern chiapas to lake izabal the polochic does not bend in eastern guatemala but continues eastward to the motagua fault where it dies westward drift of the northern block resulted in rifting which extended from eastern guatemala into the caribbean along the cayman trough the honduras depression may represent an element of a triple junction along with the polochic and izabal cayman rift the polochic continues westward into the pacific ocean and offsets the middle america trench the polochic has offset the miocene volcanic belt of northern central america confirming the previous estimate of a neogene time of movement about 300 km of relative east west neogene displacement has been recorded on the mid cayman rise only 130 km of which can be accounted for across the polochic it is suggested that cumulative extension on north south faults south of the motagua fault zone between the trench and the honduras depression might make up that difference

rotation of stress and blocks in the lake mead nevada fault system the coulomb criterion has been widely used to infer paleostresses from fault slip data assuming that faults are optimally oriented relative to the tectonic stress direction consequently if the stress direction is fixed during deformation so must be the faults freund 1974 has shown however that faults when arranged in sets must generally rotate as they slip nur et al 1986 showed that large rotations require the development of new faults more favorably oriented to the principal direction of stress this leads to older faults sets offset by younger ones both having the same sense of slip because stress rotates as well paleostress analysis must include the possible effect of stress field rotation the combined effects of stress field rotation and material rotation were found in the lake mead nevada fault system lmfs fault inversion results imply an apparent 60 clockwise cw rotation of the stress field since mid miocene time in contrast structural data from the great basin suggest only a 30 cw stress field rotation by incorporating paleomagnetic declination anomalies it is inferred that slip on faults caused a local 30 counterclockwise ccw rotation of blocks and faults in the lake mead area so that the inferred 60 cw rotation of the stress field in the lmfs is actually only 30

recent changes in climate and permafrost temperatures at forested and polar desert sites in northern canada climate and ground temperature records up to 30 years in length from permafrost monitoring sites in a polar desert at alert nunavut and a boreal forest at table mountain northwest territories were analyzed by season and year to assess the ground thermal response to recent climate warming methods were developed to standardize incomplete ground temperature data sets and to hindcast air temperatures for comparative analysis the timing and magnitude of climate warming varied beginning in the 1960s in the mackenzie valley and the 1970s in the high arctic ground temperature increases occurred in both regions but varied in magnitude and timing in relation to the external forcing and permafrost conditions significant increases in winter air temperatures in both regions appear to be largely responsible for recent increases in ground temperature particularly at the polar desert sites where snow cover is minimal

block rotation and deformation by strike slip faults 2 the properties of a type of macroscopic discontinuous deformation study of the general features of deformation by systems of subparallel strike slip faults shows that the governing constraints are kinematic the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings as a result fault blocks that move laterally without significant internal deformation also rotate about vertical axes relative to boundaries of the fault domain by an amount that is quantitatively related to fault slip spacing and orientation areas where left and right lateral faults move simultaneously are usually divided into domains that contain faults of one kind only deformation of such multidomain areas is nonhomogeneous but the differences between domains can compensate for each other so that the regional deformation is quite simple strike slip faulting combined with block rotation is an efficient mechanism of deformation because modest offsets and rotations change the linear dimensions of faulted areas by several tens of percents which may often greatly exceed the results of other types of coeval deformation paleomagnetic data can provide an independent measure of block rotations and should be used to supplement structural data block rotation changes the initial angles between right and left lateral faults and also their orientation relative to the stress field the faults probably tend to rotate away from the axis of maximum compression rotated faults continue to move because they are weak surfaces since the deformation depends on geometric factors such as fault orientation and domain geometry it is not simply related to the stress field these properties including rotation of material units characterize discontinuous deformation in general

noble gases from honduras geothermal sites the elemental and isotopic composition of noble gases in hot springs and geothermal test wells were determined as part of a collaborative project to evaluate the potential for geothermal development in honduras central america the relative abundances of the noble gases in samples from the test wells indicate recharge temperatures for the geothermal systems equivalent to mean annual temperatures a common ratio of radiogenic 40ar to 4he of 0 35 corresponding to a k u ratio of 2 104 was found in samples from three of the studied areas platanares azacualpa and san ignacio a constant ratio may imply a common reservoir rock possibly the valle de angeles group of cretaceous to eocene age 3he 4he ratios are correlated in a positive sense with so4 concentration and in a negative sense with geothermal reservoir temperatures determined from chemical geothermometers these correlations are best explained by dilution of primary geothermal fluids with cooler sulfate rich waters the cooler waters inhibit deep boiling preserving high 3he 4he ratios in the surface springs in the el olivar region either the cool diluting fluid is sulfate poor or there is additional excess 3he provided by nearby quaternary trachytic to basaltic volcanism of the southern yojoa graben

a case study on large deformation failure mechanism of deep soft rock roadway in xin an coal mine china abstract large deformation of soft rock roadway has always been a major difficulty in deep mining practices this paper describes a case study of the failure mechanisms and stability control technology of deep roadway with soft rock mass in xin an coal mine in gansu province china rock mass properties around the roadway are evaluated using geological strength index gsi based on the field data and the mechanical properties of intact rock specimens the universal discrete element code udec software program is adopted to establish the numerical model of a ventilation roadway in xin an coal mine and the micro parameter calibration is conducted with the rock mass properties the failure process of roadway under unsupported and primary support conditions is simulated the deformation stress and crack evolution characteristics were clearly illustrated failure first appears around the roadway surface because there is a high stress concentration around the roadway surface after excavation the failure area propagates further into the deep surrounding rock as the stresses applied on the surface gradually decreases finally resulting in a large zone of stress relaxation there exists a large scale of tensile failure in the shallow rock which leads to swelling and fracturing around the roadway the primary support is low in strength with no support in the floor which results in serious floor heave side shrinking and roof subsidence a new bolt cable mesh shotcrete shell combined support is proposed to support the ventilation roadway the monitoring data in the experiment section show that the new support design successfully controls the large deformation of the roadway which can provide helpful references for support designing of engineering in deep soft rock roadway

geology of the platanares geothermal area departamento de copan honduras abstract the platanares geothermal area departamento de copan honduras is located within a graben that is complexly faulted the graben is bounded on the north by a highland composed of paleozoic metamorphic rocks in contact with cretaceous tertiary redbeds of unknown thickness these are unconformably overlain by tertiary andesitic lavas rhyolitic ignimbrites and associated sedimentary rocks the volcanic rocks are mostly older than 14 ma and thus are too old to represent the surface expression of an active crustal magma body thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240 c within the cretaceous redbed sequence three continuously cored geothermal gradient holes have been drilled fluids of about 165 c have been produced from two drilled along a nw trending fault zone from depths of 250 to 680 m a conductive thermal gradient of 139 c km at a depth of 400 m was determined from the third well drilled 0 6 km west of that fault zone these data indicate that the platanares geothermal area holds considerable promise for electrical generation by moderate to hightemperature geothermal fluids

mesozoic stratigraphy of central honduras geologic mapping near lake yojoa in central honduras has shown the need to modify the published mesozoic stratigraphic column the ilama formation is not a useful unit for regional mapping inasmuch as ilama type strata are discontinuous and in various stratigraphic positions the formal name ilama formation should be abandoned a new formal name the jaitique formation is introduced to designate a major cenomanian limestone unit that is stratigraphically about midway in the valle de angeles group in the santa barbara lake yojoa region the jaitique formation consists of up to 140 m of shallow marine strata that can be divided into two members 1 a lower member of thick bedded shelf carbonate strata and 2 a distinctive upper member of thin bedded laminated nonfossiliferous limestone which may represent a shallow possibly hypersaline lagoon or intertidal mud flat environment because the lower member of this cenomanian limestone was formerly misidentified as the atima formation of the yojoa group the upper thin bedded member was originally defined as the guare formation of the yojoa group the name guare is retained but the unit is downgraded to the guare member of the newly defined jaitique formation within the valle de angeles group although the jaitique formation is similar in stratigraphic position and age to the esquias formation in the minas de oro area on the east it is lithologically distinct and probably slightly older the two units are not thought to be lithostratigraphically contiguous recognition of major cenomanian limestone units within the valle de angeles group has led to reappraisal of the hydrocarbon potential of certain structural zones in honduras

monitoring surface deformation over permafrost with an improved sbas insar algorithm with emphasis on climatic factors modeling abstract changes of permafrost not only affect regional and global water circulation carbon deposit and climate warming but also influence ground ecological geophysical and biogeochemical processes in cold region monitoring surface deformation over permafrost will help to understand the dynamics of these processes assess climate changes and prevent potential damages to engineering structures underlain by permafrost this article employs an improved small baseline subset interferometric synthetic aperture radar sbas insar technique to monitor the surface deformation over the danxiong yangbajing area in the southern qinghai tibet plateau qtp with emphasis on climatic factors modeling a new deformation model considering both the external mainly climatic and internal factors such as tectonic activities and thermal character of frozen soil is constructed and introduced into the sbas insar to estimate the surface deformation over permafrost the results show that the peak to peak annual deformation over natural surface is 3 6 5 0 cm while that along the qinghai tibet highway qth and the qinghai tibet railway qtr is 2 8 3 7 cm we also find that the surface deformation over frozen soil is negatively correlated to air temperature and precipitation with the correlation being 0 80 to 0 45 and 0 95 to 0 75 respectively the root mean squares rmss of the residual un modeled deformation got by the proposed method are much smaller than that by the existing methods we also successfully examine a time lag of about 60 days between the retrieved maximal subsidence and the highest air temperature in warm seasons from may to september after compensating for this time lag the rmss of the residual deformation reduce significantly and the correlation between the deformation and the temperature rises considerably varying from 0 95 to 0 65 the method presented in this paper is more suitable to model and analyze the surface deformation in permafrost areas

the elasto plastic response of underground excavations in rock masses that satisfy the hoek brown failure criterion abstract this paper is intended to illustrate the relationship between the hoek brown parameters describing the strength of rock masses and the mechanical response of underground openings a formulation of the elasto plastic behavior of rock in terms of the hoek brown criterion is presented the analysis assumes that the joint system present in the rock mass has no preferred orientation so that the medium can be considered to behave as an isotropic continuum it is shown that appropriate scaling of the hoek brown parameters leads to considerable simplification in defining the elasto plastic response of the rock mass the classical case in which the excavation process is treated as a uniform reduction of internal pressure in symmetrically loaded cylindrical and spherical cavities is considered closed form expressions are given for the extent of plastic behavior and the related stress and displacement fields a dimensionless graphical representation of these solutions is provided that allows accurate estimates of the response of excavations in hoek brown materials to be made quickly and easily examples are given to illustrate the use of the graphs illustrative applications of the derived closed form solutions are also described the construction of ground reaction curves for the design of cylindrical tunnels according to the convergence confinement method and a case study of stability analysis of spherical cavities produced by underground nuclear explosions in french polynesian atolls are discussed

neotectonic development of western nicaragua this study presents a reconstruction of the neotectonic evolution of western nicaragua by means of structural analysis of outcrop scale joints faults and bedding planes integrated with macroscale structures the results indicate three clearly separable deformation phases which are closely related to specific volcanic events and account for the major tectonic features of nicaragua the first deformation phase was a late miocene to early pliocene shortening that produced the pacific plain anticlines and controlled the contemporaneous extrusion of the el coyol group volcanic rocks the second phase active between the pliocene and the pleistocene resulted in extensional structures such as the 500 km long and 50 km wide nw se trending nicaragua depression this phase was accompanied by a gradual trenchward migration of the volcanic activity responsible for the formation of the las sierras group the third deformation phase is still active and is responsible for the present shallow focus seismic activity associated with n s trending volcanic vents and the n s managua pull apart graben the neotectonic development of western nicaragua as interpreted here is closely related to the contemporaneous evolution of the neighboring areas of guatemala south of the jocotan fault honduras el salvador and costa rica north of the valle central the valle central of costa rica represents the southern boundary of this structurally homogeneous domain and may indicate the southern boundary of the neogene chortis block changes in deformation style and the trenchward migration of volcanism which occurred during the pliocene may indicate an increase in the subduction angle of the cocos plate and may also be correlated to pliocene shortening of jamaica and hispaniola

recent warming of mountain permafrost in svalbard and scandinavia 1 three deep boreholes 100 m in mountain permafrost were recently drilled in svalbard janssonhaugen and in scandinavia tarfalaryggen and juvvasshoe for long term permafrost monitoring these holes form part of a latitudinal transect of boreholes in permafrost through europe established by the permafrost and climate in europe pace project six year thermal time series data collected from the three boreholes are presented these data provide the first opportunity for temporal trends in permafrost temperatures in svalbard and scandinavia to be analyzed results show that the permafrost has warmed considerably at all three sites significant warming is detectable down to at least 60 m depth and present decadal warming rates at the permafrost surface are on the order of 0 04 0 07 c yr 1 with greatest warming in svalbard and in northern scandinavia the present regional trend shows accelerated warming during the last decade

heat flow at the platanares honduras geothermal site meert j g and smith d l 1991 heat flow at the platanares honduras geothermal site in f goff editor honduras a geothermal investigation j volcanol geotherm res 45 91 99 three boreholes pltg 1 pltg 2 and pltg 3 were drilled in the platanares honduras geothermal system to evaluate the geothermal energy potential of the site the maximum reservoir temperature was previously estimated at 225 240 c using various types of chemical and isotopic geothermometry geothermal gradients of 139 239 c km calculated from two segments of the temperature depth profile for borehole pltg 2 were used to project a minimum depth to the geothermal reservoir of 1 2 1 7 km borehole pltg 1 exhibited an erratic temperature distribution attributed to fluid movement through a series of isolated horizontal and subhorizontal fractures the maximum measured temperature in borehole pltg 1 was 150 4 c and in pltg 2 the maximum measured temperature was 104 3 c pltg 3 was drilled after this study and the maximum recorded temperature of 165 c is similar to the temperature encountered in pltg 1 heat flow values of 392 mwm 2 and 266 mwm 2 represent the first directly measured heat flow values for honduras and northen central america radioactive heat generation based on gamma ray analyses of uranium thorium and potassium in five core samples is less than 2 0 wm 3 and does not appear to be a major source of the high heat flow several authors have proposed a variety of extensional tectonic environments for western honduras and these heat flow values along with published estimates of heat flow are supportive of this type of tectonic regime

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

tectonic interpretation of the morphology of honduras the morphotectonics of honduras have been studied using existing geologic and topographic maps and imaging done from satellites and the following interpretations have been made during the late oligocene to early miocene a wide strike slip boundary existed in western honduras and eastern guatemala and produced east west trending basins containing the coarse clastic rocks of the subinal formation marine geophysical studies of the continental shelf of honduras show that during the rest of the miocene and the early pliocene the boundary was inactive but motion resumed in the late pliocene to pleistocene and produced horsts on the north coast of honduras in northwestern honduras the east northeast trending alignment of the jocotan copan and charnelecon river valleys may result from crustal flexuring rather than from faulting as previously proposed because the postulated fault the jocotan chamelecon fault cannot be reconciled with available geologic maps the northwest and northeast flowing rivers of central and eastern honduras define domains of strike slip faulting that have probably rotated 30 from an original set of conjugate fractures widespread deposition of conglomerates suggests that strike slip movements began in the mid cretaceous and reoccurred at intervals culminating in the development of pull apart basins in western honduras during the late pliocene at the present time no further strike slip movement is possible as the faults defining each domain lie parallel and perpendicular to the middle america trench new conjugate fractures however cut honduras along north south and east northeast trends and have also separated into domains in the domain of north south fractures easterly directed ductile extension of the lithosphere beneath western honduras and guatemala is opening up rifts but the domain of east northeast fractures is characterized by strike slip motion that has produced left lateral pull aparts in central honduras early workers identified no rift valley extending from the gulf of fonseca to the caribbean and there is no fresh evidence upon which to base the existence of one today the notion of the honduras depression which has persisted over the last half century stems from misinterpretation of the maps and writings of karl sapper

geology of the ahuas area in the mosquitia basin of honduras preliminary report following a 36 fold seismic survey that covered 460 km two exploratory wells were drilled between july 1991 and august 1993 in the ahuas area on the patuca tectonic belt in the mosquitia savannah in northeastern honduras the embarcadero 1 well encountered only dense barren gray and red siliciclastics and some phyllite at total depth the raiti tara 1 well also drilled mostly barren but less dense red beds that included some upper cretaceous limestone conglomerate in the lower section we did not find source or reservoir rocks in either well nor did we find hydrocarbon shows the absence of lower cretaceous limestone in both wells is significant because more than 1500 m of limestone are exposed 35 50 km southwest in the colon mountains the lithology of the clastics in the embarcadero well is similar to middle and upper jurassic formations in central honduras the lithology of the softer red beds in the raiti tara well suggests they are tertiary fill in a pull apart basin the mosquitia basin including the ahuas area probably was on the seaward side of the chortis block once part of mexico and received only jurassic sediments until it was elevated by arc magmatism in the early cretaceous however thick lower cretaceous platform carbonates were deposited some distance inland lateral forces in the early late cretaceous caused the outer edge of chortis to break up carrying the colon carbonate block up to 50 km northwest by sinistral fault movement later antithetic dextral displacement offset the various blocks and created pull apart basins that filled with tertiary sediments in the early paleocene compression from a spreading center to the southeast ruptured the jurassic rocks creating a decollement and later thrusting no complete petroleum system seems to exist along the axis of the uplifted patuca tectonic belt largely because of the lack of organic rich source rocks and the presence of complicated young structures

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

a geo engineering classification for rocks and rock masses abstract in this article an attempt is made to assess the reliability of predicting the uniaxial compressive strength and the corresponding modulus of a rock mass by current approaches these two basic engineering properties when estimated from rock mass rating rmr q and geological strength index gsi indicate hardly any change in the modulus ratio with the change in the quality of the rock mass from very good to very poor however the modulus ratio obtained from the relations involving the joint factor j f indicate a definite decrease in the modulus ratio with a decrease in the quality of the rock mass the strength and modulus in the unconfined and confined states the modulus ratio and failure strain in the unconfined case were linked to j f in earlier publications based on a large experimental database some of these relations were adopted to verify the response of jointed test specimens the response of the rock mass during excavations for mining and civil underground chambers in establishing ground reaction curves including the extent of the broken zone and the bearing capacity of shallow foundations the joint factor is now linked to rmr q and gsi the prediction of compressive strength and modulus of the rock mass appears to be more suitable for classifying the rock based on these properties the deere and miller engineering classification applicable to intact rocks has been suitably modified and adopted the results of different modes of failure of jointed specimens establish definite trends of changes in the modulus ratio originating from the intact rock value on the modified deere and miller plot a geo engineering classification is evolved by considering strength modulus quantifiable weathering index and lithological aspects of the rock

indirect determination of the modulus of deformation of rock masses based on the gsi system today as a result of the increase in the number of large tunnel constructions and underground excavations required for civil engineering and waste disposal and the operation of deep open pit mines determination of rock mass properties has become one of the most important stages in design and construction for rock engineering when rocks and rock masses are classified for geotechnical purposes this needs to be on the basis of strength or static modulus of deformation to give an indication of their stability or deformational response in addition the strength and modulus of deformation are the necessary input parameters of the rock masses to be utilized by numerical methods the modulus of elasticity of the rock material is undoubtly the geomechanical parameter that best represents the mechanical behaviour of rock material a similar conclusion can also be made for rock masses however the modulus of deformation of rock masses should be determined in situ by carrying out special tests which normally implies considerable costs and operational difficulties because of such difficulties the determination of the modulus of deformation of the rock masses continues to attract the attention of rock engineers and engineering geologists given the importance of having the value of the modulus of deformation available and at the same time the operational and economical difficulties mentioned above many researchers mentioned below were led to consider several cost effective and not too time consuming indirect procedures that can provide information on the modulus of deformation these attempts

changing coastal levels of south america and the caribbean region from tide gauge records abstract tide gauge records from southern mexico the caribbean islands and central and south america that span the interval 1940 1970 reveal long term changes of relative sea level according to regression analysis and eigenanalysis the results indicate such large variations in both direction and rate of secular movement as to rule out changes in volume of ocean water as being more than a subordinate factor the only satisfactory explanation is that the land level beneath the tide gauges is rising in some places and sinking in others complex spatial patterns of relative seal level change in southern mexico and the caribbean mirror the tectonic regime of these regions exhibiting both submergence and emergence of the land central american tide gauge records similarly show considerable complexity responding to relative movement along plate boundaries the pacific coast of south america appears to correlate with the depth of the benioff zone subduction of aseismic ridges produces local highs in the benioff zone flanked by troughs at either side near the benioff highs relative land level is rising between these ridges relative land level is falling sea level trends in southern and atlantic coasts of south america are closely linked with continental crustal rifting and subsidence data do not allow unambiguous separation of changes in ocean level from changes in land level and no simple eustatic ocean level change can be estimated accurately from these data

structural geology and stress history of the platanares geothermal site honduras implications on the tectonics of the northwestern caribbean plate boundary abstract the structural geology of the platanares geothermal site in western honduras located about 25 km south of the northern boundary of the caribbean plate is the result of post early miocene extensional deformation normal faults many with listric geometries are numerous throughout the area strike slip faulting has mostly occurred on reactived normal faults analysis of the fault slip data shows an older minimum principal stress 3 oriented approximately n s and a contemporary 3 tensional and oriented ene wsw the analysis suggests that 3 has rotated clockwise since the early miocene although some of the change in orientation of 3 might reflect counterclockwise rotation of the crust about a vertical axis the 1 and 2 stress axes apparently switched recently with the 3 axis remaining unchanged these results are consistent with a tectonic model in which the east drifting caribbean plate is pinned against north america by the subducting cocos plate malfait and dinkleman 1972 and the northern and southern margins of the caribbean plate are broad mobile zones that are undergoing counterclockwise and clockwise rotations respectively gose 1985 the majority of the hot springs at platanares lie along quebrada del agua caliente fractures control the movement of the geothermal waters hot springs occur along joints and faults and in places hot water flows laterally along bedding planes if the fractures also control the movement of water at depth then the source reservoir of the geothermal waters may be located northeast of the principal hot spring areas along the quebrada since the majority of the faults dip in that direction however if the fault that seems to have controlled the development of quebrada del agua caliente is vertical as inferred then the main reservoir may lie directly beneath this drainage

constraints from finite element modeling on the active tectonics of northern central america and the middle america trench 1 we have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the central american volcanic arc and the chortis block we present synthetic focal mechanisms maps of tectonic regime and strain crosses to analyze the results the models show that to achieve the observed state of stress on the volcanic arc the arc must be modeled as a lithospheric weak zone also the forces related to the eastward drift of the caribbean plate must be higher than those related to the subduction of the cocos plate the coupling on the subduction interface must be low with or without slip partitioning due to the obliquity of the subduction at the trench at guatemala the western edge of the chortis block is pinned against north america even with low trench normal forces making the triple junction between the cocos north american and caribbean plates a zone of diffuse deformation the extension in the western part of the chortis block from guatemala to the honduras depression is explained by the geometry of the north american caribbean plate boundary and the direction of motion of the caribbean plate with respect to north america the direction of extension in the chortis block is always e w regardless of the magnitude of the applied forces and the main part of the deformation is absorbed between the ipala graben and the honduras depression both features being consistent with our models

late holocene earthquakes on the aeropuerto fault managua nicaragua managua capital of nicaragua is built on the shore of lake managua within a densely faulted graben at a major discontinuity in the central american volcanic chain shallow moderate earthquakes m s 6 6 2 ruptured faults with devastating effect at the heart of urban managua in 1931 and 1972 and damaging earthquakes are cataloged in the earlier history of the surrounding region the aeropuerto fault is a major structure in the managua graben but like other faults in this area its behavior is little understood paleoseismic investigations now suggest that the most recent large earthquake on this fault occurred sometime during the interval a d 1650 1810 an earlier earthquake on this fault occurred prior to a d 1390 and possibly around 2000 b p on the basis of stratigraphic correlations we estimate the ages of two shorelines associated with former high stands of lake managua to be less than 6 4 ka and approximately 2 ka respectively deformation of these abandoned shorelines adjacent to the aeropuerto fault implies a vertical slip rate of 0 3 to 0 9 mm yr strike slip movement on this fault is also expected but no direct measurement could be performed by comparison with faults of similar geometry in the managua area that ruptured in 1931 and 1972 we suspect a left lateral component of horizontal slip that is higher than the vertical one but less than 5 mm yr additional data on slip rate and timing of paleoearthquakes are needed to better assess the holocene behavior of the managua faults and to investigate the influence of magmatic processes on the nature of faulting in the managua graben manuscript received 15 january 2002

modeling deformation modulus of a stratified sedimentary rock mass using neural network fuzzy inference and genetic programming abstract this paper investigates a series of experimental results and numerical simulations employed to estimate the deformation modulus of a stratified rock mass the deformation modulus of rock mass has a significant importance for some applications in engineering geology and geotechnical projects including foundation slope and tunnel designs deformation modulus of a rock mass can be determined using large scale in situ tests this large scale sophisticated in situ testing equipments are sometimes difficult to install plus time consuming to be employed in the field therefore this study aims to estimate indirectly the deformation modulus values via empirical methods such as the neural network neuro fuzzy and genetic programming approaches a series of analyses have been developed for correlating various relationships between the deformation modulus of rock mass rock mass rating rock quality designation uniaxial compressive strength and elasticity modulus of intact rock parameters the performance capacities of proposed models are assessed and found as quite satisfactory at the completion of a comparative study on the accuracy of models in the results it is seen that overall genetic programming models yielded more precise results than neural network and neuro fuzzy models

thermal regimes at the snow ground interface and their implications for permafrost investigation abstract snow cover is a critical factor determining the presence or absence of permafrost in mid latitude high mountain regions this paper discusses the relation between temporal changes in temperature at the snow ground interface and permafrost distribution four fundamental types of temporal change in winter ground surface temperature gst are identified 1 nearly constant at 0 c 2 short term fluctuation 3 gradual increase without short term fluctuation and 4 gradual decrease without short term fluctuation the latter three are favorable for permafrost growth and result from direct cold penetration throughout winter ground cooling before the onset of seasonal snow cover and cold air funneling and concentrating in voids between coarse blocks respectively the fourth thermal effect predominantly contributes to growth of permafrost and thus should be included in the bottom temperature of snow cover bts concept which involves mainly the third effect monitoring gst over a winter provides a new tool for investigating the distribution of permafrost as well as information on the thermal regimes that control permafrost development

late cretaceous cenozoic tectonic transition from collision to transtension honduran borderlands and nicaraguan rise nw caribbean plate boundary

multiple strike slip fault sets a case study from the dead sea transform in many strike slip tectonic settings large rotations of crustal blocks about vertical axes have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which presumably accommodate the relative motion between the blocks as regional deformation progresses a mechanical model suggests that rotations greater than c 25 to 45 must be accommodated by more than one set of faults with the angle c between their directions consequently the sum of the angles between sets must be roughly equal to the total tectonic material rotation to test this model we investigated the fault geometry and field relationship of fault sets in the mt hermon area in northern israel where paleomagnetic declination data imply 69 13 counterclockwise ccw block rotation the statistical and field relationship analysis of over 315 faults shows that the faulting is predominantly right lateral strike slip consisting of three distinct sets the oldest set strikes 254 the second oldest set strikes 295 and the youngest strikes 331 this last direction is consistent also with the current north south direction of the maximum principal stress axis the angle c between the first and second sets is 41 and between the second and third sets 36 in good agreement with the c angle predicted from mechanical considerations the sum of the two angles is 77 ccw in good agreement with the 69 13 ccw paleomagnetically derived rotation the results suggest specifically that the sequential development of multiple intersecting fault sets is responsible for the faulting in the mt hermon area and generally that the model of block rotation with multiple faults provides very good simple rules for analyzing very complex fault patterns

prediction of critical strains and critical support pressures for circular tunnel excavated in strain softening rock mass abstract the critical strain is a strain level at the tunnel periphery beyond which the instability and squeezing problems are likely to occur thereby it provides helpful guide to assess the tunnel stability among the current studies for predicting the critical strain the influence factors such as the required support pressure the strain softening behaviour of the rock mass and the in situ stress condition have not been comprehensively considered this paper aims to overcome the limitation by proposing an improved tunnel critical strain classification which consists of five typical critical strains and critical support pressures specifically two critical levels correspond to the occurrences of the plastic softening and residual zones of the strain softening rock mass at the tunnel periphery three tunnel strains of 2 5 5 and 10 represent the squeezing potentials of the rock mass the correlations between the input geological parameters and the geological strength index gsi are proposed on the basis of the existing empirical equations a numerical procedure is presented to solve the five critical strains and critical support pressures according to a large amount of the calculation result the response surfaces for the critical support pressures in relation to the gsi and in situ stress are obtained by the nonlinear regression method the obtained critical strains are compared with the critical strain levels and measured tunnel strains by the current studies the results indicate that the reason for the unexpected secure condition with the large deformation in the rock mass can be attributed to the non existence of the plastic residual zone as the rock mass strength improves the critical strain level reveals an unexpected growth which is correlative to the considerations of the in situ stress condition and the strain softening behaviour of the rock mass

regional gravity investigation of honduras central america abstract a regional gravity study of honduras was performed as part of a major study of the geothermal resource potential of honduras this study was conducted by los alamos national laboratory in cooperation with the honduras government regional offshore free air and onshore bouguer gravity maps and residual isostatic gravity maps of honduras and surrounding regions were produced from these data several regional crustal and upper mantle models were produced these models pass through two local geothermal sites platanares and san ignacio the regional geologic and tectonic implications of the models and their relevance to the geothermal potential of honduras and to six well known geothermal sites in particular are examined no obvious regional structures observed in the gravity data can explain the thermal enhancement in general or the specific geothermal sites more local tectonic or structural conditions must control the distribution of the thermally enhanced areas

climate and ground temperature relations at sites across the continuous and discontinuous permafrost zones northern canada1 21this article is one of a series of papers published in this cjes special issue on the theme of fundamental and applied research on permafrost in canada 2earth science sector ess contribution 20110128 climate ground temperature relations are examined under a range of conditions for 10 sites across northern canada the sites are located between 60 n and 83 n and at elevations of 40 to 1840 m ab

the new central american seismic hazard zonation mutual consensus based on up to day seismotectonic framework abstract central america is one of the most active seismic zones in the world due to the interaction of five tectonic plates north america caribbean coco nazca and south america and its internal deformation which generates almost one destructive earthquakes 5 4 mw 8 1 every year a new seismological zonation for central america is proposed based on seismotectonic framework a geological context tectonic and geological maps geophysical and geodetic evidence gravimetric maps magnetometric gps observations and previous works as a main source of data a depurated earthquake catalog was collected covering the period from 1522 to 2015 this catalog was homogenized to a moment magnitude scale mw after a careful analysis of all the integrated geological and seismological information the seismogenic zones were established into seismic areas defined by similar patterns of faulting seismicity and rupture mechanism the tectonic environment has required considering seismic zones in two particular seismological regimes a crustal faulting including local faults major fracture zones of plate boundary limits and thrust fault of deformed belts and b subduction taking into account the change in the subduction angle along the trench and the type and location of the rupture the seismicity in the subduction zone is divided into interplate and intraplate inslab seismicity the regional seismic zonation proposed for the whole of central america include local seismic zonations avoiding discontinuities at the national boundaries because of a consensus between the 7 countries based on the cooperative work of specialists on central american seismotectonics and related topics

relations between air and surface temperature in discontinuous permafrost terrain near mayo yukon territory the association of site characteristics with the n factor a ratio of air to ground surface temperature was investigated at five sites in the boreal forest near mayo yukon territory permafrost was in equilibrium with surface conditions at three sites was degrading at another and was absent from the fifth air and near surface ground temperatures were recorded by data loggers between september 2000 and april 2002 and mean daily temperatures were accumulated to calculate n factors for the freezing nf and thawing nt seasons air temperature did not vary between the sites so inter site differences in nf and nt were because of variations in surface temperature variations in nf between the sites over the two winters were primarily because of differences in snow depth but at sites with similar snow cover the surface temperatures were relatively high when the site was underlain by unfrozen ground during summer daily mean surface temperatures were initially less than air temperatures however once

tertiary geodynamical evolution of northwestern greece paleomagnetic results abstract paleomagnetic results have been obtained from 29 sites sampled in lower to upper oligocene flysch sections of the ionian zone in northwestern greece they indicate a clockwise rotation of about 45 of the entire region a comparison with previously published results relative to both younger and older formations shows that this rotation has occurred in two phases of comparable amplitude one during middle miocene and the other during pliocene and quaternary separated by a period of at least 7 ma during which no significant rotation has occurred no major rotation has occurred during the entire paleocene and eocene stages this large measured rotation implies a horizontal displacement of at least 100 km in epirus possible mechanisms involving a rotation of the nappe sheets rotation of the basement or a combination of the two are discussed the two phases of paleomagnetic rotation can be correlated with the tertiary and quaternary calc alkaline volcanic activity in the aegean sea a palinspastic reconstruction shows that the orientation of the major structures now striking n155 was almost east west in the middle miocene at the epoch of their formation

empirical and numerical analyses of support requirements for a diversion tunnel at the boztepe dam site eastern turkey abstract this paper presents the engineering geological properties and support design of a planned diversion tunnel at the boztepe dam site that contains units of basalt and tuffites empirical theoretical and numerical approaches were used and compared in this study focusing on tunnel design safety rock masses at the site were characterized using three empirical methods namely rock mass rating rmr rock mass quality q and geological strength index gsi the rmr q and gsi ratings were determined by using field data and the mechanical properties of intact rock samples were evaluated in the laboratory support requirements were proposed accordingly in terms of different rock mass classification systems the convergence confinement method was used as the theoretical approach support systems were also analyzed using a commercial software based on the finite element method fem the parameters calculated by empirical methods were used as input parameters for the fem analysis the results from the two methods were compared with each other this comparison suggests that a more reliable and safe design could be achieved by using a combination of empirical analytical and numerical approaches

bookshelf faulting in nicaragua oblique subduction at a high rate of convergence along much of the middle america trench results in northwest directed trench parallel block motion accommodation of this motion along northwest striking dextral strike slip faults has been postulated however in nicaragua such faults are not well developed we suggest instead that this motion is accommodated by bookshelf faulting that includes northeast striking left lateral faults we present earthquake epicenter and focal mechanism data and mapped fracture and fault data consistent with this model trenchward migration of the volcanic arc since the miocene and reactivation of northeast striking miocene structures may have led to the development of this arc and trench normal fault system

empirical estimation of rock mass modulus the deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations field tests to determine this parameter directly are time consuming expensive and the reliability of the results of these tests is sometimes questionable consequently several authors have proposed empirical relationships for estimating the value of rock mass deformation modulus on the basis of classification schemes these relationships are reviewed and their limitations are discussed based on data from a large number of in situ measurements from china and taiwan a new relationship based upon a sigmoid function is proposed the properties of the intact rock as well as the effects of disturbance due to blast damage and or stress relaxation are also included in this new relationship