regional deformation of the earth model for the los angeles region california abstract a mathematical model for historical horizontal crustal deformation is presented for the los angeles region of california model parameters are estimated from triangulation trilateration and astronomic azimuth data observed during the past 120 years also geologic and seismic data are used indirectly in specifying the model which relates crustal deformation to strain rates over large geographic areas secular slip rates along geologic faults and to episodic movements associated with large m 6 earthquakes the episodic movements are modeled in accordance with the theory of dislocation in an elastic halfspace for the secular motion the region is partitioned into a mosaic of proposed microplates or districts that are allowed to individually translate rotate and deform homogeneously as a linear function of time the model thus accounts for the secular and episodic time variability of the geodetic markers coordinates the results are compared with geodetic geologic and seismic studies by other investigators to evaluate the reliability of the procedure and the estimates in some cases the model provides the first geodetic determinations of strain rates slip rates directions of maximum right lateral shears and values of coseismic displacements experienced within the region the shear strain rates reveal that maximum right lateral shears are oriented parallel to the san andreas fault system and decrease in magnitude with distance from the central transverse ranges the directions of shear strain form a funnel shaped pattern that converges on the point outside the region where the san andreas garlock big pine and san gabriel faults meet the velocity for a point near san pedro relative to a point at the region s northeast corner is 1 8 0 6 cm yr in the direction n 15 w 11 these results are discussed in light of data limitations and modeling inadequacies subsidence due to oil and gas withdrawal and postseismic relaxation following the 1971 san fernando earthquake

crustal velocity field near the big bend of california s san andreas fault we use geodetic data spanning the 1920 1992 interval to estimate the horizontal velocity field near the big bend segment of california s san andreas fault saf more specifically we estimate a horizontal velocity vector for each node of a two dimensional grid that has a 15 min by 15 min mesh and that extends between latitudes 34 0 n and 36 0 n and longitudes 117 5 w and 120 5 w for this estimation process we apply bilinear interpolation to transfer crustal deformation information from geodetic sites to the grid nodes the data include over a half century of triangulation measurements over two decades of repeated electronic distance measurements a decade of repeated very long baseline interferometry measurements and several years of global positioning system measurements magnitudes for our estimated velocity vectors have formal standard errors ranging from 0 7 to 6 8 mm yr our derived velocity field shows that 1 relative motion associated with the saf exceeds 30 mm yr and is distributed on the earth s surface across a band 100 km wide that is roughly centered on this fault 2 when velocities are expressed relative to a fixed north america plate the motion within our primary study region has a mean orientation of n44 w 2 and the surface trace of the saf is congruent in shape to nearby contours of constant speed yet this trace is oriented between 5 and 10 counterclockwise relative to these contours and 3 large strain rates shear rates 150 nrad yr and or areal dilatation rates 150 nstr yr exist near the garlock fault near the white wolf fault and in the ventura basin

a rigorous analysis of gps data to detect crustal deformations application in the area of the ionian sea an analysis of a deformation process in dynamic models is presented where time is considered as the essential part a rigorous adjustment model of unregularly spanned observations in space and time is proposed for the estimation of point velocities and strain rate parameters the problem of the reference frame definition and choices of deformation models are discussed finally an application is given in order to illustrate the method using real data from gps observations at the geodynamically unstable area of the ionian sea 1998 elsevier science b v all rights reserved

a varve based calibration of the bridge river tephra fall a 1 cm thick layer of bridge river tephra is preserved in a core of varved lake sediments recovered from hector lake alberta the varve sequence extends from the core top to well below the tephra layer and has bseen calibrated to calendar years a varve count yields a calendar age of 2332 bp for the ash layer with a potential error of about 50 years this age is about 30 years younger than the current best radiocarbon based estimate of the time of the eruption however in light of the potential errors in both the varve count and the radiocarbon age the two ages are not inconsistent the tephra contains no biotite in the past biotite free bridge river tephra has been associated with a possible late ca 2000 bp tephra fall but the tephra from hector lake is clearly associated with the main 2300 2400 bp eruptive event

a new look at the u s geological survey 1970 1980 horizontal crustal deformation data around hollister california a compact mathematical formulation is presented for the estimation of crustal strain and fault displacement parameters from repeated geodetic observations on the basis of the theory of hubert space optimization complex linear forms are used to model spatially and temporally piecewise continuous relative horizontal displacement fields a mathematical model for the simultaneous network adjustment and strain approximation is elaborated in an application of the method to the hollister network reobserved several times during the 1970s several approximation models are evaluated the final model which incorporates a third degree complex algebraic polynomial with four block translation terms in space and a fifth degree algebraic polynomial with three episodic terms in time is presented in detail this approximation estimates coseismic fault slip and strain release associated with three moderate earthquakes which occurred in the hollister area within the time interval spanned by the observations

8000 year old wood from the athabasca glacier alberta several wood fragments of pinus sp dated at 8230 80 and 8000 90 years bp and abies sp were recovered from the snout of the athabasca glacier this wood derived from an unknown source up valley indicates that the glacier was less extensive than at present during the hypsithermal and that an area up valley of the present snout was tree covered ca 8000 8300 years bp

horizontal deformation in the imperial valley california between 1934 and 1980 a triangulation trilateration survey was performed by the national ocean survey national geodetic survey four months prior to the october 15 1979 imperial valley m 6 6 earthquake the survey was repeated in february march 1980 to gauge the coseismic displacement these data combined with triangulation surveys performed in 1934 1935 1939 1941 1954 1955 and 1967 provide a historical record of crustal deformation over a time period that also includes the 1940 el centro m 7 1 earthquake the total data set was analyzed in terms of a dislocation model that relates the observed surface deformation to slip on prescribed geologic faults according to the model the 1941 1980 fault slip at depths 10 km and greater is 1 9 0 3 m this value is approximately twice the 1 0 0 1 m estimated for the 1941 1980 slip on the imperial fault in the 0 to 10 km depth range this discrepancy can be explained by a range of possibilities including the following 1 some of the deep fault slip is due to aftereffects of the 1940 earthquake in which case the seismic cycle over which deep slip and shallow slip are equal is not the interval between large earthquakes but is delayed a few years 2 the deep slip should be equated to the shallow slip over several parallel faults 3 the crust experienced permanent inelastic deformation and 4 deep deformation is accommodated by a mechanism other than slip

horizontal strain across the wasatch front near salt lake city utah two adjacent geodetic networks span a 105 km extent of the wasatch fault zone in north central utah one of the networks located in the vicinity of salt lake city was observed by the national ocean service national geodetic survey nos ngs in 1962 1963 triangulation mode and again in 1973 1974 combined triangulation trilateration mode to the north in the vicinity of ogden the u s geological survey usgs performed five separate trilateration surveys of the second network during the 1972 1981 interval when fit to a model assuming both temporal and spatial homogeneity for the strain rate the two independent data sets yield mutually consistent strain rate tensors subsets of the nos ngs data however suggest spatial variation in the strain field and a subset of the usgs data indicates a possible temporal variation in the strain rate the quality of the data is such that we are uncertain whether or not these apparent variations represent actual tectonic signals the strain rate tensors for the two complete data sets suggest an underlying deformational pattern characterized by east west e w maximum principal strain extension positive this pattern may also be inferred from regional seismicity and quaternary geology the suspected variations would imply that the area to the north of salt lake city experienced significant e w compression preceding 1978 in contradiction to the underlying strain pattern this compression may be caused by the mountainous block eastward adjacent to the fault zone displacing westward along a shallow angle west dipping detachment surface we speculate on the existence of an e w trending zone of weakness for example secondary faults located north of salt lake city to explain how the stress field to the north may be decoupled from that to the south where e w compression has not been detected while seismic and geologic information contribute some plausibility to our speculations the evidence for the existence of the suspected variations is inconclusive

a continuous holocene glacial record inferred from proglacial lake sediments in banff national park alberta canada abstract sediment cores from three proglacial lakes in northern banff national park alberta preserve a record of holocene glacial activity upvalley which is more continuous and better dated than available surficial records dating of the cores is based on tephrochronology and 16 ams14c ages of terrestrial macrofossils all cores contain a threefold sequence of lacustrine sediments overlying a late pleistocene diamicton basal lacustrine sediments 10 10014c yr old contain little organic matter sediment composition indicates a large glacigenic contribution a sharp increase in organic content marks the beginning of the altithermal interval at all three lakes this transition occurred abruptly at about 10 10014c yr b p at crowfoot lake and possibly more gradually at the other lakes altithermal sediments contain relatively little glacigenic material and during most of the altithermal glaciers may have been absent above crowfoot and bow lakes glaciers draining into hector lake appear to have persisted through the altithermal a subsequent decrease in organic content in each lake reflecting increased clastic sedimentation marks the end of the altithermal and the onset of neoglacial ice advances the transition took place between about 5800 and 400014c yr b p and may be time transgressive beginning earlier in hector lake than in crowfoot lake changing neoglacial clastic sedimentation rates through the neoglacial interval indicate two main periods of increased glacier extent between ca 3000 and 1800 varve yr ago ca 2900 190014c yr b p and during the last several hundred years during the intervening period glaciers were less extensive but much more extensive than during the recessions of the altithermal interval

identification and significance of tephras encountered in a core from mary lake yoho national park british columbia mary lake is a small subalpine lake located proximal 3 km to the continental divide near lake o hara in yoho national park british columbia a 1 25 m core recovered from surficial bottom sediments was found to contain both bridge river tephra 2350 years bp and mazama tephra 6800 years bp identification of the tephras was initially based on distinctive colour texture phenocryst assemblages and glass shard habits and was confirmed by electron microprobe analysis of the constituent glass shards the microprobe technique employed backscattered and secondary electron imagery and both energy dispersive and wavelength dispersive analyses mean annual sedimentation rates calculated from tephra depths in the mary lake core were found to be of the order of 0 15 mm year for the post bridge river time period and 0 02 mm year for the mazama bridge river interval the preservation of mazama tephra in mary lake lacustrine sediments indicates that deglaciation had proceeded upvalley from the mary lake basin

grading in mud volcanic breccia from the mediterranean ridge abstract an analysis was made of mud breccia sampled from mud diapir fields on the crest of the mediterranean ridge to investigate whether they are emplaced by extrusion resulting in debris flows or by intrusion into the hemipelagic sediments descriptive sedimentological analyses was combined with the measurements of clast sizes and grading and the determination of the ratio of clasts to the mud matrix in the upper and lower parts of the mud breccia units in 15 cores taken from the tops and flanks of mud volcanoes observed grading in clast size in the upper and or lower boundary layers of most mud breccias is inferred to be the result of extrusion and flow on the seafloor such mud flows may be divided into three sections consisting of graded beds at the top and bottom separated by a massive intermediate part the best developed grading may result from further reworking of extruded mud breccia through debris flows down the flanks of the mud structures the composition of the clasts show five lithologies for which the dominant one is pebbles of silty mudstone

age variation in the source of the diapiric mud breccia along and across the axis of the mediterranean ridge accretionary complex abstract pleistocene or younger mud diapirism is recorded along the arcuated crest of the mediterranean ridge accretionary complex over a distance of more than 450 km the extruded mud supported breccia named mud breccia is poorly fossiliferous but the matrix may be dated as late aptian to albian and late burdigalian to langhian in age based on the calcareous plankton content calcareous nannofossils and planktonic foraminifera diagnostic of other ages are sparse within the two above mentioned major assemblages they indicate the presence of sediments attributable 1 to the santonian and cenomanian which occur in association with the mid cretaceous assemblages toronto unnamed and aros domes and 2 to the serravallian which occur in association with the late burdigalian langhian assemblages in the gelendzhik dome aptian albian to late cretaceous sediments are pelagic in origin and are similar to the scisti a fucoidi and scaglia rossa formations well known from continental italy mixed dolomitic clasts and crystals also occur within the matrix indicating the presence of portions of the evaporitic sequence of messinian age in four cores from the western locations single very rare plankton specimens indicative of other ages different from those mentioned above also occur within the matrix at various places they are interpreted as reworked primarily within the late burdigalian langhian sediments the age of the emplacement of the breccia should be older than the middle pleistocene as supported by the occurrence of clasts of this age in the mud breccia and is still an ongoing process at least in the napoli dome

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

sedimentary succession and evolution of the mediterranean ridge western sector as derived from lithology of mud breccia clasts abstract rock fragments from mud breccia extruded by mud volcanoes discovered during the ttr 4 cruise of the r v gelendzhik on the western mediterranean ridge are represented by a number of different lithologies they provide important information on the composition genesis and age of the deep seated sedimentary series of the basin lithological description and age determination of the main rock types obtained as clasts from mud breccia were made on the basis of a study of ninety seven samples depositional processes and environments of their accumulation were determined using sedimentological criteria the sedimentary section through which mud volcanoes erupted on the western mediterranean ridge includes aptian albian claystones late cretaceous limestones paleogene siliciclastic rocks and a variety of miocene limestones and mudstones the rock clasts studied throw insight into the evolution of the western sector of the eastern mediterranean basin from at least aptian time the aptian albian clayey series have been deposited in the marine conditions of a relatively narrow basin with a high input of terrigenous clayey material during the late cretaceous the basin enlarged terrigenous input into deep parts of the basin decreased and carbonate pelagic sedimentation became prevalent regression in paleogene time led to the deposition of thick terrigenous siliciclastic series of deltaic prodeltaic sediments extensive turbidite systems were emplaced in the western sector of the eastern mediterranean during the miocene along with predominantly carbonate pelagic sedimentation

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

structural features of mud volcanoes and the fold system of the mediterranean ridge south of crete abstract new information on the geometry of the mud volcanoes folds and faults located in the central part of the mediterranean ridge is provided from long range and deep tow sidescan sonar images high resolution seismic and low frequency echosounder profiles and gravity cores obtained on the r v gelendzhik during the 1993 unesco esf training through research cruise symmetrical gentle folds with a mean wavelength of 750 m deform predominantly pliocene quaternary sediments but also perhaps as old as messinian in most areas of the mediterranean ridge the north northeast directed subduction of the african plate below the eurasian plate at the hellenic arc produces folds with hinge lines subparallel to the trend of the ridge however the hinge lines of the folds curve around the southern part of the area with highest concentration of mud volcanoes and produce an irregular u shape fold belt some of the folds show an intrusive nucleus and in some of them mud breccia appears to have flowed from the flanks of the folds into the troughs the mud volcanoes consist of domes of interlayered pelagic sediments and mud breccias containing sediments and rock fragments of late aptian to pleistocene ages mud breccia flows are mainly extruded radially from vents although rare fissure extrusions are also observed the mud volcanoes have an irregular to elliptical shape with diameters up to 16 km the distribution of mud volcanoes in the area is irregular but they are more frequent in an area called the olimpi field faults in the uppermost part of the mediterranean ridge are rare most of the faults are normal and subparallel to fold limbs in addition n20 e and n100 e subvertical faults are found controlling the shape of the mud volcanoes

readjustment of leveling networks to account for vertical coseismic motions abstract in tectonically active regions the geodesist is confronted with the problem of updating heights where the earth s surface has been vertically deformed by an earthquake dislocation theory can be used as a basis for modeling coseismic elevation changes and be incorporated within a general least squares adjustment scheme to correct a network of old leveling measurements and heights that are within the deformed area releveling and information obtained from seismologists about the general nature of the earthquake serve as input to the modeling process fundamental equations and considerations are presented in this paper to develop dislocation models of vertical coseismic motions leveling data sets corresponding to the fairview peak nevada coalinga california and borah peak idaho earthquakes are analyzed these examples show potential for the method when applied in other areas even when the physical setting is made complex by ongoing subsidence the primary benefit of modeling coseismic motion is to avoid the cost of releveling for some lines in a deformed region rough modeling prior to any resurveying helps to select the lines to relevel that are most critical to a successful final model a good model for coseismic motion cannot restore geodetic levelings to their original reliability but corrected heights can be used in applications not requiring accuracy better than a few centimeters

models of crustal deformation this review is principally concerned with theoretical models of crustal deformation developed during this quadrennium observational data as well as topics in lithospheric flexure and isostasy are covered in companion reviews in this volume progress has been made toward constructing both new inelastic and inhomogeneous elastic models of earthquake induced crustal deformation most of the inelastic models involve dislocations or green s functions in an elastic or anelastic lithosphere which overlies a maxwell viscoelastic asthenosphere

dynap software for estimating crustal deformation from geodetic data abstract the acronym dynap dynamic adjustment program identifies a software package for estimating crustal dynamic parameters from a collection of geodetic data dynap accepts various data types including horizontal directions and angles distances azimuths zenith distances and intersite vectors such as those obtainable with the global positioning system gps or with very long baseline interferometry vlbi dynap incorporates the simultaneous reduction technique whereby crustal dynamic parameters are estimated simultaneously along with station positional coordinates and various nuisance parameters all via the least squares process the estimated crustal dynamics parameters come in groups of six or fewer where each group corresponds to a prespecified geographic region and period of time the six parameters convert mathematically to yield the three components of the horizontal strain rate tensor the horizontal rotation rate and the two components of the vertical tilt rate vector dynap s applicability is illustrated with two examples the first involves over 60 years of triangulation trilateration data in the cascadia subduction zone of northwestern california here a maximum shearing rate was found of 0 161 0 074 radians yr with the corresponding axis of maximum contraction oriented n25 e 14 the second involves a 1980 triangulation trilateration survey and a 1986 gps survey both spanning the imperial fault of southern california here a maximum dextral shearing rate was found of 1 073 0 171 radians yr in the direction of n31 w 5

holocene glacier fluctuations in the canadian cordillera alberta and british columbia abstract although the record of holocene glacier fluctuations in british columbia and alberta is still very fragmentary much recent progress has been made in their study dating of end moraines has been supplemented by studies of lateral moraine stratigraphy and dating of glacially overridden organic matter upstream of end moraines dates from sites close to contemporary glaciers indicate that ice had retreated to about its present limits before 10 ka bp prior to deposition of mazama tephra a minor pre hypsithermal readvance the crowfoot advance left deposits in the rockies and the interior of british columbia the earliest known neoglacial advances occurred 5 6 ka bp in the coast mountains and shortly after 4 ka bp in the rockies an advance culminating ca 4 3 ka bp has been reported from bugaboo glacier while evidence of another advance culminating in the period ca 2 5 1 8 ka bp the tiedemann advance is reported from more than one site following a recession the little ice age expansion the cavell advance began shortly after 900 bp this advance culminated in most cases in the 18th or 19th centuries the crowfoot tiedemann and little ice age advances were apparently of roughly the same magnitude the latter was most extensive in most cases but at several sites crowfoot moraines lie slightly farther downvalley than little ice age moraines during the present century ice fronts have generally retreated particularly rapidly in the period 1920 1950 a d although rates of retreat have decreased in the last three decades and some glaciers have readvanced slightly

holocene and latest pleistocene fluctuations of stutfield glacier canadian rockies the holocene and late glacial history of fluctuations of stutfield glacier are reconstructed using moraine stratigraphy tephrochronology and dendroglaciology stratigraphic sections in the lateral moraines contain tills from at least three glacier advances separated by volcanic tephras and paleosols the oldest pre mazama till is correlated with the crowfoot advance dated elsewhere to be younger dryas equivalent a neoglacial till is found between the mazama tephra and a paleosol developed on the bridge river tephra a log dating 2400 bp from the upper part of this till indicates that this glacier advance correlated with the peyto advance culminated shortly before deposition of the bridge river tephra radiocarbon and tree ring dates from overridden trees exposed in moraine sections indicate that the initial cavell little ice age lia advance overrode this paleosol and trees after a d 1271 three subsequent phases of the cavell advance were dated by dendrochronology the maximum glacier extent occurred in the mid 18th century predating 1743 on the southern lateral although ice still occupied and tilted a tree on the north lateral in 1758 subsequent glacier advances occurred ca 1800 1816 and in the late 19th century the relative extent of the lia advances at stutfield differs from that of other major eastward flowing outlets of the columbia icefield which have maxima in the mid late 19th century this is the first study from the canadian rockies to demonstrate that the large morphologically simple lateral moraines defining the lia glacier limits are actually composite features built up pro gressively but discontinuously over the holocene and contain evidence of multiple holocene and crowfoot age gla cier advances resume la stratigraphie des moraines la tephrochronologie et la dendroglaciologie des moraines ont servi a recons truire les fluctuations a l holocene et au cours de l histoire glaciaire tardive du glacier stutfield les sections stratigra phiques dans les moraines laterales contiennent des tills d au moins trois avancees glaciaires separees par des tephras volcaniques et des paleosols le plus ancien le till pre mazama est correle a l avancee crowfoot dont on a determine l ge ailleurs comme etant un equivalent du dryas recent un till de l epoque neo glaciaire se retrouve entre le tephra mazama et un paleosol developpe sur le tephra de bridge river un billot date 2400 bp provenant de la partie supe rieure de ce till indique que cette avancee glaciaire correlee a l avancee de peyto a culmine peu de temps avant la deposition du tephra de bridge river des datations au 14 c et des series chronlogiques provenant d arbres recouverts puis exposes dans des sections de moraine indiquent que l avancee cavell initiale petit ge glaciaire a chevauche ce paleosol et les arbres apres l an 1271 la dendrochronologie a permis la datation de trois phases subsequentes de l avancee cavell l etendue glaciaire maximale eut lieu au milieu du 18e siecle avant 1743 sur le cote sud bien que la glace fut encore presente sur le cote nord et y ait bascule un arbre en 1758 des avancees glaciaires subsequentes ont eu lieu vers 1800 1816 et vers la fin du 19e siecle l etendue relative des avancees du petit ge glaciaire a stutfield differe de celles d autres glaciers majeurs du champ de glace columbia s ecoulant vers l est et qui ont eu leur maxi mum dans la deuxieme moitie du 19e siecle cette etude est la premiere provenant des rocheuses canadiennes a de monter que les grandes moraines laterales morphologiquement simples definissant les limites du glacier au petit ge glaciaire sont en fait des elements composites developpes progressivement mais de facon discontinue tout au cours de l holocene et qu elles contiennent des evidences d avancees glaciaires multiples d ge holocene et crowfoot

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

lithology of mud breccia clasts from the mediterranean ridge abstract clasts from mud breccia extruded by mud volcanoes discovered during the ttr 3 cruise of the r v gelendzhik 1993 on the mediterranean ridge are represented by a number of different source rocks they provide important information about the composition and genesis of the deep seated deposits of the mediterranean ridge detailed descriptions of the main rock types obtained as clasts from the mediterranean ridge mud breccia were made on the basis of a study of more than three hundred thin sections and x ray data the genetic features of the rock types indicate deep sea conditions during their accumulation and the presence of turbidities in the sedimentary sequence of the mediterranean ridge this suggests that turbidity currents from the african margin were capable of reaching the area presently forming the modern mediterranean ridge crest and that the mediterranean ridge was not a positive morphologic structure during the accumulation of lithologies which were extruded from depth by mud volcanoes the dating of the clasts should shed some light on the history of the mediterranean ridge

severe drought in the early holocene 10 000 6800 bp interpreted from lake sediment cores southwestern alberta canada abstract six lake sediment vibracores from the foothills and mountain valleys of southwestern alberta were analysed on the basis of ams radiocarbon dates tephrochronology and sediment geochemistry from these results the magnitude timing and duration of the early holocene warm period are presented at about 10 000 bp immediately following the younger dryas cold period climate warmed dramatically precipitation decreased and surface evaporation increased previous research has identified this warm interval but new results have improved resolution of regional scale effects specific timing and severity sedimentation changed from extra basinal clastic to intra basinal organic between 10 000 and 9400 bp changes in subalpine lakes from sand silt deposition to biogenic carbonate precipitation suggest decreases in suspended sediment load caused by complete ablation of glacial sediment sources peat which formed in lakes of less than 4 m present depth indicates climate induced lake level lowering in the foothills water depth and stratigraphic position of the peat suggest that regional water table levels decreased by up to 6 5 m at cartwright lake an erosional unconformity 6 5 m below the modern lake surface indicates the lake had completely dried out either during or immediately after mazama tephra time 6800 bp

cementation patterns and genetic implications of holocene beachrocks from northeastern brazil abstract this paper describes the complex patterns of diagenesis in holocene beachrock ledges located along both the eastern and northern coasts of the state of rio grande do norte northeastern brazil these beachrocks show highly variable diagenetic processes fabrics and textures carbonate cements are exclusively composed by high mg calcite and occur in seven main morphologies 1 cryptocrystalline coatings 2 isopachous prismatic rims 3 equant spar 4 cryptocrystalline or micritic pore filling 5 pseudo peloidal aggregates 6 radial aggregates 7 isolated and randomly oriented clumps of scalenohedral crystals other diagenetic features include a carbonate siliciclastic mixed sediment b infiltrated micrite c authigenic smectitic clay minerals d organic films e chalcedony pore filling cement f vadose silty internal sediment the texture and composition of the cements are indicative of precipitation in the active marine phreatic zone the presence of vadose features and planktonic foraminifers within the infiltrated materials suggest that they were introduced in the backshore sands by muddy waters dislocated from the shelf during storms a general succession of diagenetic phases can be recognized comprising the precipitation of authigenic smectite micritic coatings radial aggregates isopachous rims of prismatic crystals or equant spar cryptocrystalline and pseudo peloidal pore filling cements and vadose infiltration of micritic carbonate siliciclastic mixed sediments or silty materials the absence of organic structures such as microbial bacteria or fungi filaments and bodies within the cements suggests that the mechanism behind beachrock cementation is essentially inorganic most probably the evaporation of entrapped seawater in response to the dry climatic conditions

the summit area antaeus pan di zucchero of the mediterranean ridge a mud diapir field abstract this paper presents a state of knowledge of the antaeus pan di zucchero field the summit area of the mediterranean ridge including morphological geological geophysical and micropaleontological data the area is characterized by elongated elevations the newly discovered antaeus elevation is probably the highest point of the mediterranean ridge diapiric mud breccias have been found in two places 1 in a mean relief level 2 in a relief depression but not on morphological highs the sediment cores record the occurrence of mud breccias in several stratigraphic levels during late pleistocene holocene time partly as discrete breccia bodies partly reworked in clastic layers the oldest presence of reworked mud breccia material documented in the cores is dated to about 40 000 yrs b p older than tephra y 5 the youngest event is dated as post sapropel s 1 less than 9000 yrs b p for a breccia layer the mud breccia layers from both places are interpreted to be emplaced by intrusion

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

latest pleistocene and early holocene fluctuations of glaciers in the canadian and northern american rockies in the canadian and northern american rockies small scale fluctuations of glaciers during and after late wisconsinan deglaciation have been identified using stratigraphy of superimposed glacial deposits geomorphology and records of glacial advance in lake and peat sediments several authors have proposed that valley glacier readvances of relatively modest scale followed the late wisconsinan maximum evidence for some of these is difficult to evaluate from the literature and no deposits recording such readvances have been numerically dated several minimum limiting radiocarbon dates for deglaciation suggest ice had retreated to within a few tens of km of present limits by ca 12 ka bp and to very near present limits by ca 11 ka bp one or more minor glacial advances or stillstands during recession evidently occurred in valley heads prior to 11 ka bp part of the evidence consists of moraines a few km downvalley from subsequently emplaced little ice age and crowfoot moraines the piper lake moraine in the mission mountains of montana is overlain by glacier peak g tephra and thus has a minimum age of 11 200 14c years bp the crowfoot advance a minor advance of about the same magnitude as little ice age advances occurred between ca 11 300 and 10 000 14c years bp and is thought to be related to the younger dryas climatic reversal crowfoot moraines have been found from jasper national park on the north to the mission mountains on the south crowfoot elas were an average of 40 m lower than modern elas around the canada u s border there have been past proposals of significant early holocene glacial advances in the rockies i e after crowfoot time but before the lia but recent evidence indicates that glaciers then were less extensive than at present

some aspects of the analysis of geodetic strain observations in kinematic models abstract frequently deformation processes are analyzed in static models in many cases this procedure is justified in particular if the deformation occurring is a singular event if however the deformation is a continuous process as is the case for instance with recent crustal movements the analysis in kinematic models is more commensurate with the problem because the factor time is considered an essential part of the model some specialities have to be considered when analyzing geodetic strain observations in kinematic models they are dealt with in this paper after a brief derivation of the basic kinematic model and the kinematic strain model the following subjects are treated the adjustment of the pointwise velocity field and the derivation of strain rate parameters the fixing of the kinematic reference system as part of the geodetic datum statistical tests of models by testing linear hypotheses the invariance of kinematic strain rate parameters with respect to transformations of the coordinate system and the geodetic datum the interpolation of strain rates by finite element methods after the representation of some advanced models for the description of secular and episodic kinematic processes the data analysis in dynamic models is regarded as a further generalization of deformation analysis

activation of gas bubble emissions indicated by the upward decreasing lead 210 activity at a submarine mud volcano ty1 offshore southwestern taiwan abstract a submarine mud volcano mv known as ty1 is one of the largest conical structures found offshore southwestern taiwan active gas bubble emissions at the flat crest of the mud volcano disperse sediment particles into the water column changes in the mud volcanism of ty1 were revealed by radiograph and grain size analysis of the sediment cores 210 pb geochronology was applied to the near seafloor sediments to reveal the detailed mud volcanism from the deposition rate in a 58 cm long sediment core taken from the northern margin of the crest known as ty1 n 170 the size and frequency of the mud clasts decrease upward the clasts are smaller than 8 mm above a sediment depth of 34 cm below the sea floor cmbsf sediments between 0 and 19 cmbsf are massive and particles larger than 2 mm are absent an enrichment of coarse silt sized particles in the massive sediment unit and the restricted distribution of the unit suggest that the massive unit was generated by re deposition of sediment particles that were dispersed into the water column by gas bubble emission these characteristics suggest that during the last mud volcanism of ty1 there was a decrease in mud eruption energy and gas bubble emission became the main activity in core ty1 s 440 taken from the southern slope a massive sediment unit enriched with coarse silt sized particles is intercalated between mud breccia structures this suggests repeated mud breccia flows caused by ty1 the excess 210 pb activity present in the massive sediment unit of ty1 n 170 suggests activation of gas bubble emission in the massive unit a decrease in excess 210 pb activity appears upward toward the seafloor the highest value is 3 1 dpm g at 19 8 cmbsf 26 4 g cm 2 in cumulative mass values lower than 1 0 dpm g are distributed 2 8 6 8 cmbsf 3 6 8 8 g cm 2 the upwardly decreasing trend is opposite that of the reference core from which a reasonable areal sedimentation rate was obtained using a constant flux constant sedimentation model the anomalous depth profile at the massive unit indicates an increasing rate of sediment deposition which originated from the activation of gas bubble emission

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

regional deformation of the earth model for the san diego region california a mathematical model for historical horizontal crustal deformation is presented for the southern california region that extends northward from mexico for approximately 100 km to 33 5 n latitude model parameters are estimated from triangulation trilateration and astronomic azimuth data observed during the past century also geologic and seismic data indirectly participate in specifying the model the model relates crustal deformation to the episodic movement experienced during large earthquakes m 6 secular slip rates on geologic faults and secular strain rates over large geographic areas the episodic movement is modeled in accordance with the theory of dislocation in an elastic halfspace for the secular motion the modeled region is partitioned into a mosaic of districts that are allowed to individually translate rotate and homogeneously deform as a linear function of time the derived strain pattern supports the hypothesis that the modeled region spans the pacific north american plate boundary secular shear strain is maximum in the nw direction parallel to the major faults and shear strain rates decrease with distance from a nw se trending strip to the region s north this strip is 40 km wide and is bounded on the west by the san jacinto fault zone and on the east by the southern extension of the san andreas fault to the south this strip converges in width onto the imperial fault the secular velocity for a point near the city of san diego relative to a point at the region s northeast corner is 4 3 3 1 cm yr in the direction n 17 w 5 this rate provides a rough estimate for the relative velocity between the pacific and north american plates

revised 14c age for st helens y tephra at tonquin pass british columbia the age of a mount st helens set y tephra at tonquin pass british columbia previously assumed to be 4300 years bp is revised to ca 3400 years bp based on bracketing 14c dates of 3140 70 beta 13558 and 3680 80 years bp beta 13559 the implications of this revision for tephrostratigraphy of this area are discussed

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

neoglacial glacier fluctuations in the canadian rockies abstract the little ice age was the most extensive neoglacial glacier advance in the canadian rockies evidence of earlier less extensive neoglacial glacier advances is based on wood recovered from several glacier forefields wood flushed out of athabasca glacier 7550 8230 yr b p three dates and dome glacier 6120 6380 yr b p two dates indicates that forests occurred upvalley of present glacier termini during the hypsithermal detrital logs from peyto 14 dates saskatchewan 3 dates robson 3 dates and yoho 1 date glaciers plus in situ slumps at peyto and robson glaciers have yielded 14 c dates between 2490 and 3300 yr b p 12 dates between 2800 and 2990 this wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca 3100 and 2500 yr b p treeline was higher than present immediately prior to this advance this advance which did not extend beyond the little ice age maximum position is designated the peyto advance and correlated with the tiedemann advance in western british columbia earliest little ice age advances at peyto and robson glaciers are dated ca 800 600 yr b p at positions ca 500 m upvalley from little ice age limits

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc

geodetic measurement of tectonic deformation in the santa maria fold and thrust belt california we have analyzed geodetic observations to resolve tectonic deformation across the santa maria fold and thrust belt northwest of santa barbara california the geodetic network forms a braced quadrilateral with 40 km sides whose southwest corner is the vandenberg very long baseline interferometry station the data include 1 historical triangulation from the 1880s 1920s and 1950s 2 electronic distance measurement trilateration from 1971 and 1985 and 3 global positioning system observations from 1986 and 1987 we combine the three different types of data to estimate two dimensional station positions and strain rate parameters simultaneously using a model which constrains the relative velocity field to be linear in space and constant in time we find significant strain rates the maximum compressive strain is oriented n17 e 5 e and the compressive strain rate in this direction is 0 13 0 03 strain yr under the assumption that the unresolved rotational component of the velocity field is zero we estimate that the integrated rate of deformation across the basin is 7 1 mm yr oriented at n03 e 13 this vector can be decomposed into 6 2 mm yr of crustal shortening on the general structural trend of n30 e and 3 1 mm yr of right lateral shear across this axis on the basis of these values and earthquake focal mechanisms in the area we infer that the deformation occurs on northwest trending folds and thrusts within the belt these results are consistent with the rate and direction of deformation across the central california coast ranges inferred by balancing pacific north america plate motion against san andreas slip and basin and range extension they imply that the santa maria fold and thrust belt is the primary active element in transforming motion from the coast ranges to the western transverse ranges and the santa barbara channel