a laboratory study of surface boundary currents application to the algerian current the problem of a gravity current along a coast is considered in the laboratory the flow originates from a continuous pointsource and when facing downstream has the shore to its right the shore is the vertical wall of a 13 m diameter rotating basin the density of the current r1 is slightly less than that of the surrounding fluid this buoyant flow is shown to depend upon three parameters namely the burger and ekman numbers and the aspect ratio of the current at its source disregarding friction and taking the flow as hydrostatic so that the current aspect ratio does not need to be considered the stability characteristics of the current are shown to depend mostly upon the burger number to study its role in the flow we performed several experiments by varying the burger number bu between 0 15 and 0 82 for large burger numbers the current is stable but as it decreases increasing numbers of anticyclonic disturbances develop and grow along the axis of the current measurements of the normalized distance from the source and times for these disturbances to develop are given as functions of the burger number the dependence of the normalized separation distance of disturbances upon the burger number in cases of multiple instabilities is also discussed finally these laboratory results are compared with the algerian current where both anticyclonic and cyclonic eddies have been observed the experimental current simulates the algerian current when the burger number is 0 15

seismic images of the transition fault and the unstable yakutat pacific north american triple junction in southern alaska the pacific plate and yakutat terrane subduct beneath the north american plate along the aleutian trench and pamplona zone respectively and are sliding past each other at minimal rates along the transition fault as the deformation front of the pamplona zone stepped eastward during the pliocene pleistocene the pacific north american yakutat triple junction became unstable four recent seismic images reveal that the transition fault changes from a single strike slip boundary east of the deformation front to three strands that step increasingly seaward between the deformation front and the aleutian trench the southern two strands deform the pacific crust and the outermost of these became increasingly convergent sometime since 1 ma as demonstrated by young growth strata we propose that this internal deformation of the pacific plate is an attempt to re attain stability which can only be reached by creating a tectonic boundary collinear with the pamplona zone the plate reorganization will result in initiation of subduction such that a portion of former pacific crust will become accreted to the north american plate such accretion events caused by triple junction instability may be an important mechanism for transferring oceanic crust to continental margins

sedimentary processes and origin of sediment gravity flow deposits on the western algerian margin during late pleistocene and holocene seven piston cores retrieved from the algerian margin from oran to 80 km east of algiers were studied to identify sediment gravity flow deposits and their sources at the foot of the slope five sediment cores indicate a decreasing frequency of turbidite sequences from the transgressive systems tract to the highstand systems tract resulting in lower off shelf sediment fluxes during the last highstand episode there is an approximately log normal frequency distribution of bed thickness that increases for larger grain size class but this relationship is frequently altered by truncation of the top of the turbidite sequence in the deep basin off algeria two sediment cores indicate that turbidite sequences are both thicker and more preserved than at the foot of the slope and are observed through the entire sediment core implying various origin of the gravity flow eustatic change seismicity

seismicity in the st elias region of northwestern canada and southeastern alaska abstract low level monitoring in the st elias region between september 1978 and march 1981 has identified two principal zones of seismicity that are consistent with the historical pattern of seismicity at higher magnitude levels the most active zone follows the plate boundary along the coast of southeast alaska a recurrence relation based on completeness over varying time intervals is log n m 0 74 m 3 77 a less active zone is observed generally following the duke river and dalton segments of the denali fault system through the southwest yukon instead of continuing into chatham strait this trend of seismicity turns south into the glacier bay region to connect with the fairweather fault north of cross sound the seismicity and high rate of uplift observed in the glacier bay region is probably the result of convergence across the fairweather fault north of cross sound the recurrence relation for the denali zone is log n m 0 90 m 3 77 a similiar recurrence curve is found for activity with magnitudes down to about 2 0 observed over the 39 month low level monitoring program the rate of activity in the denali zone appeared to decrease for a period of about 1 yr following the 28 february 1979 m 7 2 st elias earthquake the rate of aftershock activity was also found to vary with the b value decreasing throughout the sequence only minor seismicity is observed northeast of the denali fault system in the southwest yukon and east of chatham strait in northwest british columbia a prominent cluster east of juneau near the british columbia border may be related to volcanic activity a 5 week microearthquake survey over a 40 km segment of the denali fault system found activity in a highly faulted zone about 15 km wide at depths of less than about 15 km a composite p nodal solution indicates motion on either east west or north south striking planes neither of which are consistent with the general trend of the denali system in the area an average slip rate of no more than about 1 mm yr is estimated from the seismicity for the denali fault system through the southwest yukon an estimate of the minimum present accumulated elastic strain suggests the potential for a magnitude 6 1 2 earthquake

characterization of glacial silt and clay using automated mineralogy glacial erosion produces vast quantities of fine grained sediment that has a far reaching impact on earth surface processes to gain a better understanding of the production of glacial silt and clay we use automated mineralogy to quantify the microstructure and mineralogy of rock and sediment samples from 20 basins in the st elias mountains yukon canada sediments were collected from proglacial streams while rock samples were collected from ice marginal outcrops and fragmented using electrical pulse disaggregation for both rock fragments and sediments we observe a log normal distribution of grain sizes and a sub micrometer terminal grain size we find that the abrasion of silt and clay results in both rounding and the exploitation of through going fractures the abundance of inter versus intragranular fractures depends on mineralogy and size unlike the relatively larger grains where crushing and abrasion are thought to exploit and produce discrete populations of grain sizes the comminution of fines leads to a grain size composition and rounding that is continuously distributed across size and highly dependent on source rock properties

the circulation of the levantine intermediate water in the algerian basin markedly different scenarios have been proposed for the circulation of the levantine intermediate water liw in the southern part of the western mediterranean sea discrepancies result from the fact that large temperature and salinity values which characterize liw are encountered both in the vicinity of sardinia and off algeria thus it was assumed that the circulation of liw was divided into two major branches one northward along the sardinian continental slope and the other across the algerian basin being dissatisfied with such a branch image of the circulation we have put forth hypotheses millot 1985 1987 which now appear to be supported by the results of the mediprod 5 experiment conducted in june 1986 we propose a scheme for the circulation of liw in the algerian basin wherein a gravity flow is constrained by the topography around sardinia and is subjected to sporadic spreading toward the open basin due to erosion of this vein by mesoscale eddies therefore it seems admissible that no branch of liw flows off the algerian coast

deformation rates estimated from earthquakes in the northern cordillera of canada and eastern alaska 1 we estimate deformation rates from earthquake catalog statistics to investigate current strain distribution resulting from the collision of the yakutat block with north america the collision is accommodated over a broad region of alaska and nw canada in a variety of tectonic regimes our estimates have significant uncertainties but the results are generally in agreement with other deformation rate estimates gps and geological data and provide useful first order constraints on local long term tectonic deformation and seismic hazard we estimate that 50 75 of relative plate motion is taken up by earthquakes on the yakutat north america boundaries with lateral crustal extrusion other far field strain and possibly aseismic creep accommodating the remainder we calculate dextral strike slip of 4 5 10 2 mm a on the denali fault system in alaska remarkably similar to late pleistocene holocene rates from geomorphic offsets right lateral motion essentially bypasses the denali fault in easternmost alaska and westernmost yukon passing instead along the totschunda and duke river fault systems right lateral transpression of 5 10 mm a suggests that the alaskan fore arc does not have fully block like behavior between the denali and tintina kaltag faults in alaska 10 20 mm a of dextral shear is accommodated by several ne trending bookshelf faults significant seismic deformation in cases higher than expected from gps data is indicated in the ne cordillera where preexisting faults have a strong control on the pattern and mechanisms of current deformation

inversion of source parameters for moderate earthquakes using short period teleseismic p waves in this paper we introduce a new method for estimating the source parameters of moderate earthquakes mw 5 0 by modeling short period teleseismic waveforms this method uses a grid search algorithm to minimize misfits between observed data and synthetic seismograms in depth magnitude and mechanism domain in a relative high frequency range of 0 8 2 0 hz similar to the traditional cut and paste method used in regional modeling zhu and helmberger bull sesimol soc am 86 1634 1641 1996 in this frequency range a significant challenge is determining the initial p wave polarity because of a low signal to noise ratio snr therefore we first determine source properties for a master earthquake with a relative strong snr both the travel time and amplitude corrections are developed relative to the reference 1d model along each path used in inverting the master event we then applied these corrections to other earthquakes clustered in the same area to constrain the initial p polarities thus the focal mechanisms can be determined reasonably well we inverted focal mechanisms for a small set of events beneath qeshm island in southern iran and demonstrate the importance of radiation pattern at short periods

geophysical insights into the transition fault debate propagating strike slip in response to stalling yakutat block subduction in the gulf of alaska on the basis of faulting mapped on seismic reflection and bathymetric data seismicity current plate motions and evidence that the yakutat block may be anomalously thick we propose a tectonic model for yakutat pacific interactions including the often debated transition fault to the east deformation associated with the queen charlotte fairweather fault system is extending offshore facilitating westward propagation of strike slip motion along the eastern segment of the transition fault to the west the oblique slip pamplona zone and transition faults merge at an embayment in the continental margin where a north south dextral strike slip fault within the pacific plate illuminated by the 1987 1992 earthquake swarm intersects the pacific yakutat tectonic boundary these fault patterns are consistent with modern plate motions and reflect a plate boundary reorganization that may be caused by resistance to subduction by the yakutat block a possible moderate sized oceanic plateau

current deformation in the northern canadian cordillera inferred from gps measurements 1 continuous and campaign style global positioning system gps measurements provide new constraints on the first order current deformation pattern of the northern cordillera of nw canada and eastern alaska the yakutat block is currently colliding with north america in the corner of the gulf of alaska our data infer that relative yakutat north america motion is accommodated across the eastern boundary by right lateral motion 40 mm a mainly on the fairweather fault and minor shortening 6 mm a to the north collision is taken up by shortening 31 mm a mainly on the chugach st elias fault system with westward extrusion and possible counterclockwise rotation of the yakutat block and alaskan fore arc facilitated by 23 mm a right lateral motion that is shared by several faults the seismicity pattern indicates that plate boundary deformation is far reaching producing strain throughout eastern alaska yukon and western northwest territories our gps data confirm the transfer of strain from the yakutat collision zone and enable the extent of plate boundary deformation to be mapped thereby defining the western edge of stable north america gps sites in sw yukon show motion of 3 10 mm a to the ne confirming that strain is transferred at least 400 km from the yakutat collision continued transfer north toward the mackenzie delta and ne to the mackenzie mountains indicated by current seismicity is not yet well resolved by the campaign gps data which are hampered by coseismic and postseismic effects of the 2002 mw 7 9 earthquake on the denali fault in eastern alaska

the transition from strike slip to oblique subduction in southeastern alaska from seismological studies abstract body waveform modeling of 11 moderate to large earthquakes within southeastern alaska has been incorporated with earthquake relocations and the results of previous seismicity studies to examine the transition from strike slip to oblique subduction in southeastern alaska in the sitka region of extreme southeastern alaska earthquakes indicate seismic slip is parallel to the direction of motion between north america and the pacific plate as the plate margin begins to bend to the west near cross sound and encounters the southeastern edge of the yakutat block partitioning of seismic slip is evident both onshore and offshore although the largest earthquakes magnitude 6 0 in this region have slip parallel to plate motion most moderate sized events have slip vectors rotated clockwise from plate motion offshore the 1973 cross sound sequence indicates that the southern end of the transition zone is seismogenic with the pacific plate being thrust beneath the yakutat block while onshore strike slip faulting has occurred along the fairweather border ranges and denali faults in the st elias region thrust faulting is occurring along and above the plate interface moderate sized events in the st elias show a mix of slip vector orientations in the pamplona zone slip vectors of offshore earthquakes and deformation directions determined onshore from gps studies show a counter clockwise rotation relative to plate motion suggesting that a change in strain field occurs just west of the st elias region

active tectonics of the st elias orogen alaska observed with gps measurements 1 we use data from campaign and continuous gps sites in southeast and south central alaska to constrain a regional tectonic block model for the st elias orogen active tectonic deformation in the orogen is dominated by the effects of the collision of the yakutat block with southern alaska our results indicate that 37 mm yr of convergence is accommodated along a relatively narrow belt of n nw dipping thrust faults in the eastern half of the orogen with the present day deformation front running through icy bay and beneath the malaspina glacier near the bering glacier the collisional thrust fault regime transitions into a broad northwest dipping decollement as the yakutat block basement begins to subduct beneath the counterclockwise rotating elias block the location of this transition aligns with the gulf of alaska shear zone implying that the pacific plate is fragmenting in response to the yakutat collision our model indicates that the bering glacier region is undergoing internal deformation and could correspond to the final stage of offscraping and accretion of sediments from the yakutat block prior to subduction predicted block motions at the western edge of the orogen suggest that the crust is laterally escaping along the aleutian fore arc

role of grain boundaries and micro defects on the mechanical response of a crystalline rock at multiscale the paper examines the cracks initiation propagation and coalescence until failure in a crystalline rock under stress states involving rock volumes varying in size from nano berkovich indentation in continuous stiffness measurement mode to micro vickers indentation scratching and macro rockwell indentation rock impact hardness number scales the experimental work was performed on a calcitic marble characterized by two different textures xenoblastic and granoblastic the grain boundaries microcracks were deeply studied with focused ion beam scanning electron microscopy technique innovative approach in rock mechanics the experimental results show that at the three investigation scales the microcracks give rise to the rock failure with fractures propagation mechanisms varying with the microstructure in the granoblastic texture fracturing is ruled by grain boundaries microcracks which often appear almost open conversely the fracture behavior of the xenoblastic marble seems dominated by the grains cleavage even at the macroscale

paleoseismological evidence from lake sediments for recent movement on the denali and other faults yukon territory canada abstract most of the pacific north america plate motion in northwestern canada and southeastern alaska occurs along coastal faults that are the inland extension of the queen charlotte dextral transform fault more ancient faults farther east such as the denali and duke river faults exhibit moderate earthquake activity and may be accommodating part of the pacific plate motion paleoseismological results based on seismic resuspension of lake sediments covering a period of up to 3000 years show that the seismicity on the denali duke river fault system is remarkably recent spanning just the last three to five centuries there is a northerly trending zone of seismicity from the active fairweather contact fault system on the coast across to the part of the denali fault that is currently as well as prehistorically active this partial transfer eastward of pacific plate motion may be analogous to a similar proposed transfer of motion northward to the denali fault from the same fairweather contact fault system farther west in alaska

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

new constraints on the motion of the fairweather fault alaska from gps observations 1 gps velocities from sites near to the fairweather fault in southern alaska are combined with line length data from geodetic surveys by the u s geological survey usgs to estimate the slip rate and locking depth of the fairweather fault using dislocation theory we perform a weighted least squares inversion of the geodetic data and obtain a best fitting slip rate of 45 6 2 0 mm yr and locking depth of 9 0 0 8 km the slip rate we estimate is one of the highest observed across any strike slip fault we also include the dalton creek segment of the denali fault in our model and estimate a slip rate of 3 8 1 4 mm yr for this section of the fault this is substantially lower than the rate observed for the denali fault segment to the northwest which ruptured in the november 3 2002 mw 7 9 denali fault earthquake

late holocene fine grained sediments of the balearic abyssal plain western mediterranean sea abstract the late holocene fine grained sedimentation in the deep central balearic abyssal plain western mediterranean sea has been studied after the analysis of high quality sediment cores from three multicoring stations named a b and c the coring stations are 25 km apart from each other and form a triangle that is at the greatest distance from the nearest landmasses the sediments consist of foraminifer pteropod oozes layers u1 and u4 from bottom to top two pteropod oozes u2 and u5 and a turbidite layer u3 the same sequence has been identified in the three cores the turbidite layer u3 that lies on top of u2 14 c ams dated at 1814 cal yrs bp ranges from 5 to 11 cm thick and is clearly distinguished from the dominating hemipelagic sediments by colour variations higher water content and the absence of planktonic foraminifer shells rather uniform values of organic carbon and nitrogen are also characteristic of the u3 turbidite unit likely because of homogenisation during transport and emplacement in addition u3 unit shows higher contents of terrigenous elements such as k and fe otherwise the presence of zeolites in the turbidite layer supports the hypothesis of the sardinian continental margin where pyroclastic deposits are known as the most likely source area for u3 our results demonstrate the ability of turbidity currents originating on the margins surrounding the balearic abyssal plain to reach the very centre of the basin during high sea level still stands as the present one

a methodology for assessing the postconvection mesoscale dynamics in the gulf of lion from composite datasets in order to access the statistical properties of the mesoscale dynamics in the western mediterranean and its associated transport and heat fluxes during the postconvection period the authors have applied data combination methods for analyzing a wide range of in situ measurements collected during the thetis 1 and convhiv experiments ctd and xbt profiles were merged with times series at a fixed or moving point and also with integral time series obtained from acoustic tomography data estimates of temperature and currents within a box of approximately one degree square over a time period of 35 days during the postconvection period were produced during this winter convection has been only partial rarely penetrating deeper than 1200 m the analysis concentrates on the upper 1000 m where most changes occur geostrophy is used as a dynamical constraint relating the parameters the time evolution is controlled by a kalman filter using simple persistence the contribution of the different datasets to the estimation indicates their complementarity in the time and space dimensions hydrography and eulerian measurements provide a major contribution to the estimation of the baroclinic modes tomography data complement the estimate at all horizontal scales float data bring some information on the barotropic mode but the major contribution on this mode comes from the reciprocal tomography data particularly at the largest scales the period analyzed mostly covers the postconvection estimation of the kinetic energy indicates that the barotropic contribution represents 85 of the total energy horizontal advection transfers heat toward the central area at a mean rate of 50 w m 2 compensating for the heat losses through the surface the mesoscale flow field observed is characterized by strongly barotropic coherent vortices with a size o 30 40 km these barotropic eddies are present during all phases of convection

the algerian eddies abstract this paper synthetizes various previous analyses of the algerian eddies these mesoscale anticyclonic eddies are of primary importance to the circulation of all the water masses in the western mediterranean they are generated by instability processes disturbing the flow of modified atlantic water maw shortly after it reaches the african coast near 0 e namely the algerian current young eddies which have diameters of 50 100 km and the upwelling generally attached to their southwestern edges drift eastward along the coast at a few km per day sometimes during several months as they grow older and larger the most vigorous ones leave the coastal zone and drift seaward some of them may reach the sardinian continental slope where a well defined vein of levantine intermediate water liw flows we suspect them to be capable to pull fragments of liw seaward and in fact the least modified liw we encountered in the middle of the algerian basin had the form of rings or filaments trapped by one eddy eddies several months old may have diameters as large as 200km they also entrain the mediterranean deep water mdw and they probably extend down to the bottom in 1984 two such eddies occupied most of the algerian basin the maw was deflected seaward by the westernmost one from the algerian coast at 3 e as far as the balearic islands and was then dispatched by other eddies through the whole basin as though by a set of paddle wheels such interactions are perhaps not as exceptional as was previously expected these mesoscale phenomena have strong biological implications the western mediterranean sea thus appears to be a very suitable place for the observation and modelling of such mesoscale coherent structures

complex empirical orthogonal functions analysis of ers 1 and topex poseidon combined altimetric data in the region of the algerian current maps of sea level anomalies sla relative to the 1993 annual mean sea level combine the data from the two altimetric missions ers 1 and topex poseidon during the overlap period october 1992 to december 1993 these regular maps in space and time of residual sea level every 10 days on a 0 2 regular grid are used in the region of the algerian current where the mesoscale eddies are of primary importance to the circulation of all the mediterranean water masses they are first compared with ers 1 along track scanning radiometer sea surface temperature images to get information on two anticyclonic eddies produced by instabilities of the algerian current and visible in both infrared and altimetric data sets then an analysis of complex empirical orthogonal functions ceofs is performed on the sla data set to see the correlation of the different dynamic features of the observed variability the ceof analysis is applied to the complex time series formed from the original sla time series and their hubert transforms to separate the variability into spatially coherent modes the spatially correlated signal in the study area 0 15 e and 35 40 n was found to be dominated by the first two ceofs these first two modes explain nearly 85 of the variability with 80 of the total variance for the first one and 5 of the total variance for the second one the temporal phase of the first mode indicates that a constant frequency of one cycle per year is clearly dominant corresponding to the seasonal signal the strongest amplitude is obtained in the southern part of the channel of sardinia and south of the strait of sicily the temporal amplitude and the temporal phase of the second mode show a periodicity of about 6 months which appears to be associated with the variability of the algerian current as the phase isolines are parallel to the mean current path along the algerian coast the strongest amplitude of the second mode is located near the african coast at 4 e and 8 e these two points of high variability could correspond to eddy detachments from the main current

paleobathymetric history of the western mediterranean sea shelf during the latest glacial period and the holocene quantitative reconstructions based on foraminiferal transfer functions abstract we present results of the palaeobathymetric evolution in cool water shelf carbonate environments of the western mediterranean sea during the latest glacial period and the holocene for this quantitative approach we used the weighted averaging partial least squares wa pls regression method for the development of benthic foraminifera based transfer functions and the modern analog technique mat to test the robustness of the models transfer functions were created on the basis of recent benthic foraminiferal assemblages in surface samples modern data sets and were then applied to fossil samples in sediment cores from the alboran platform the oran bight and the mallorca shelf the performance of the wa pls transfer functions suggests a close relationship between the observed and estimated water depths in the modern data sets with a precision of 11 m root mean squared error of prediction rmsep within water depths ranging from 38 to 160 m the estimated relative sea level histories of the alboran platform and the mallorca shelf show a total relative sea level rise of 50 m with sample specific errors of approximately 7 m and generally match the global and regional mediterranean sea records inconsistencies in the paleobathymetric estimates are strongly attributed to redeposition processes dating problems and to minor effects of an under representation of modern samples from shallower water depths

a seismotectonic study of the southeastern alaska region abstract we compare relocations of recent 1973 2005 and historic 1919 1972 earthquakes to geologic and geophysical gravity aeromagnetic and uplift information to determine the relationship of seismicity to crustal deformation in southeastern alaska our results suggest that along strike changes in the structure of the pacific plate may control the location of the ends of rupture zones for large earthquakes along the offshore queen charlotte fault system in the southern portion of the study area there is a marked increase in background seismicity in the northern portion of the study area where the fairweather fault begins to bend toward the northwest and crustal uplift due to glacial unloading exceeds 20 mm year focal mechanisms indicate that thrust and reverse mechanisms predominate in the region of maximum uplift as might be expected by the decrease in ice sheet thickness the diffuse nature of seismicity between the fairweather and denali faults in the northern study area suggests a complex interaction between plate microplate interactions and glacial unloading making it difficult to determine the optimal fault orientation for failure in moderate magnitude 5 5 to 6 5 earthquakes within this region

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

some features of the algerian current an analysis of infrared images leads to a new conception of the dynamics of the atlantic water in the algerian basin in situ current measurements are not yet available but coherent hypotheses are presented with the aim to initiate further experimental and theoretical works the algerian current flows steadily along the coast near 0 and becomes unstable near 1 2 e eddies of both signs are generated that are advected by the mean current but only the anticyclonic eddies increase in size diameter about 100 km as they extract more energy from the mean current they are advected more slowly and they may detach from the coast and drift for several weeks in the algerian basin they grow as deep as 1000m at least and they are able to pull lenses of intermediate water seaward from the sardinian continental slope coastal upwelling cells are generated near 1 2 e between the cyclonic and the anticyclonic eddies they are also advected by the mean current and are definitively not wind induced these turbulent structures create intense mixing between the atlantic and mediterranean waters which account for the large eastward gradient of salinity encountered in the surface layer therefore the algerian basin is characterized by a large mesoscale variability mainly due to the instability of the algerian current it appears to be a reservoir in which the water of atlantic origin is amassed and it forms a buffer zone which disconnects the flow of atlantic water coming in at gibraltar from the flow of hygly modified atlantic water exiting the basin through the strait of sardinia and into the ligurian sea

the 1998 mw 5 7 zhangbei shangyi china earthquake revisited a buried thrust fault revealed with interferometric synthetic aperture radar 1 the 1998 mw 5 7 zhangbei shangyi china earthquake is the largest to have occurred in northern china since the large 1976 ms 7 8 tangshan earthquake due to its proximity to beijing the capital of china it has therefore gained a lot of attention a great number of studies have been conducted using seismic and geodetic data but few are able to identify conclusively the orientation of the primary fault plane for this earthquake in this paper two independent ers synthetic aperture radar interferograms are used to determine precisely the location and magnitude of coseismic surface displacements 11 cm in the radar line of sight modeling the event as dislocation in an elastic half space suggests that the earthquake is associated with a buried shallow nne ssw oriented thrust fault with a limited amount of lateral displacement which is consistent with seismic intensity distribution and aftershock locations

resolution of fault slip along the 470 km long rupture of the great 1906 san francisco earthquake and its implications data from all available triangulation networks affected by the 1906 earthquake have been combined to assess the trade off between slip resolution and its uncertainty and to construct a conservative image of coseismic slip along the rupture because of varying network aperture and station density slip resolution is very uneven although slip is determined within uncertainties of 1 0 m along 60 of the fault constraints are poor on the remaining mostly offshore portions of the rupture slip decreases from maxima of 8 6 and 7 5 m at shelter cove and tomales bay to 4 5 m near mount tamalpais and 2 7 m at loma prieta the geodetically derived slip distribution is in poor agreement with estimates based on analysis of s wave seismograms probably because these waves register only 20 30 of the total seismic moment obtained from longer period surface waves consideration of a range of fault geometries for 1906 slip near loma prieta indicates right lateral motions lie between 2 3 and 3 1 m these values are considerably greater than the 1 5 m of measured surface slip on which several assessments of high earthquake hazard for this fault segment were based this factor along with the absence of 1989 slippage where 1906 surface slip was used to make the forecasts casts doubt on some claims of success in predicting the 1989 m 6 9 loma prieta earthquake

using 1 hz gps data to measure deformations caused by the denali fault earthquake the 3 november 2002 moment magnitude 7 9 denali fault earthquake generated large permanent surface displacements in alaska and large amplitude surface waves throughout western north america we find good agreement between strong ground motion records integrated to displacement and 1 hertz global positioning system gps position estimates collected 140 kilometers from the earthquake epicenter one hertz gps receivers also detected seismic surface waves 750 to 3800 kilometers from the epicenter whereas these waves saturated many of the seismicinstruments in the same region high frequency gps increases the dynamic range and frequency bandwidth of ground motion observations providing another tool for studying earthquake processes

new gps constraints on the motion of the yakutat block global positioning system gps measurements were made at yakutat on the yakutat terrane of southern alaska to investigate the motion of the yakutat block with respect to the north american plate and to help constrain motion along the fairweather fault the velocity of yakutat derived from the gps data is 44 1 1 9 mm yr toward n37 4 w relative to stable north america the magnitude of this velocity is similar to that of the pacific plate predicted by nuvel1a although there is a significant difference in the azimuth of these two vectors the motion of yakutat relative to north america is almost exactly parallel to the strike of the fairweather fault suggesting that most deformation inboard of yakutat is right lateral strike slip on the fairweather fault or faults parallel to it and that significant motion normal to the fairweather fault occurs offshore of yakutat the gps velocity at yakutat is also used to help constrain the slip rate and locking depth of the fairweather fault

spreading of levantine intermediate waters by submesoscale coherent vortices in the northwestern mediterranean sea as observed with gliders since 2007 gliders have been regularly deployed in the northwestern mediterranean sea a crucial region regarding the thermohaline circulation of the mediterranean sea it revealed for the first time very warm 10 48c and saline 10 1 submesoscale anticyclones at intermediate depth characterized by a small radius 5 km high rossby 0 3 and burger 0 7 numbers they are likely order of 10 to be formed each year have a life time order a year and certainly contribute significantly to the spreading of the levantine intermediate waters liw toward the whole subbasin thus potentially impacting wintertime vertical mixing through hydrographical and dynamical preconditioning they could be mainly formed by the combined action of turbulent mixing and flow detachment of the northward flow of liw at the northwestern headland of sardinia upwelling conditions along the western coast of sardinia associated with a southward geostrophic flow within the upper layers seem to play a key role in their formation process

indentor corner tectonics in the yakutat st elias collision constrained by gps the yakutat st elias collision in se alaska and adjacent canada represents a prime example of present day tectonics associated with an indentor corner its eastern syntaxis is marked by high exhumation a sharp structural bend and strain concentration at the transition from shortening to oblique transpression here we present gps velocity and strain rate fields that cover the syntaxis including 11 new stations in the core of the st elias mountains these data are corrected for transient deformation glacial isostatic adjustment and postseismic and interseismic loading to produce residual velocities and strain rates representative of long term tectonics the main features of these velocity and strain rate fields are a peak in strain rates strain knot in the syntaxis at the junction between the main fault systems and a rapid rotation from convergence parallel to convergence normal orientations of the velocities and shortening axes around the syntaxis leading to shortening across the southern denali fault these features are consistent with the strain and tectonic patterns expected near an indentor corner at the transition from shortening to transpression with a combination of diffuse and localized deformation the gps velocities and strain rates show diffuse deformation around the syntaxis from pure convergence parallel shortening in the orogenic wedge to oblique extension that accommodates the strain rotation at the front of the syntaxis this indentor corner model also results in a near zero strike slip rate on the southern denali fault and shows no clear evidence for a throughgoing fault hypothesized to link the fairweather and totschunda faults

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

potential use of ers 1 and topex poseidon altimeters for resolving oceanographic patterns in the algerian basin two independent and concurrent 1992 1993 sources of data obtained from ers 1 and topex poseidon satellites provide a first look at the spatial distribution of mesoscale sea surface variability in the algerian basin values higher than 6 cm rms were found in a narrow band extending along the algerian slope between 0 and 4 e where meander formation and eastward eddy propagation occurred east of 4 e patterns of higher variability were also seen in the interior of the basin resulting from detachment of eddies from the algerian current that drift seaward based on geostrophic velocity estimates at crossover points the eddy field variability appeared to be anisotropic especially in the vicinity of the algerian current two mesoscale features whose signatures were clearly identified from altimeter transects were supported by cloud free avhrr infrared imagery in particular the path of an anticyclonic eddy 140 km diameter with drift of 3 cm s 1 was sufficiently coherent with the temporal and spatial sampling of altimeters to describe its kinematic behaviour the results thus demonstrate the potential usefulness of satellite altimetry for monitoring oceanographic conditions in the algerian basin

mean sea level and surface circulation variability of the mediterranean sea from 2 years of topex poseidon altimetry we describe the circulation and mean sea level variations of the mediterranean sea from 2 years of topex poseidon altimetric data it is first shown that the response of the mediterranean sea to atmospheric pressure forcing is close to an inverse barometer except at high frequencies which means that the adjustment is accompanied by a flow through the straits of sicily and gibraltar we then use topex poseidon to study the mean sea level variations representing steric effects and integrated large scale changes of the mass of the mediterranean sea we observe an annual cycle with a fast drop during winter steric effects account for about half of the observed variations the remaining signal is believed to be driven by evaporation minus precipitation e p forcing and internal hydraulic control in the straits of gibraltar using suboptimal space time objective analysis the classic components of the mediterranean surface circulation are recovered despite low signal to noise ratio the rms of sea level variability is less than 10 cm the variable mediterranean circulation is seen as a complex combination of mesoscale and large scale variations the surface circulation is more complex in the eastern basin than in the western basin in the east it is composed of subbasin scale gyres such as the so called mersa matruh and shikmona gyres which do not have an obvious recurrence period we also observe an intensification of the large scale cyclonic winter circulation in the western and in the ionian basins several mesoscale structures such as the alboran gyres and the ierepetra gyre show a clear seasonal cycle with a maximum in summer the good qualitative and quantitative agreement of the results with previous data from the mediterranean illustrates the improved accurary of topex poseidon over its predecessors

seismicity of southwestern yukon canada and its relation to slip transfer between the fairweather and denali fault systems abstract several researchers have postulated the existence of a fault termed the connector fault that transfers slip from the fairweather to the denali fault systems in order to match the observed regional variations in fault slip and gps deformation earthquake locations seismic moment tensor information and gravity data presented in this study suggest that the connector fault is an active seismogenic structure that extends from the fairweather fault near hubbard glacier to the intersection of the duke river and totschunda fault systems seismicity and potential field data also suggest the existence of an east west trending cross structure between the totschunda and denali faults just north of 62 n that appears to be taking up compressional deformation similar to the duke river fault system to the south the intersection of this cross structure with the totschunda fault occurs near the termination of the 2002 denali fault mainshock rupture zone

field examples of strike slip fault terminations in mongolia and their tectonic significance deformation at the ends of large intracontinental strike slip faults that do not simply link other major structures often involves rotations about a vertical axis we use earthquake slip vectors surface rupture in earthquakes and geomorphology to examine the ends of three major strike slip faults in mongolia in these places a simple pattern is seen consisting of a thrust fault on one side with a displacement that decreases away from the strike slip fault consistent with local rotational deformation strike slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area for example from dominantly strike slip to dominantly dip slip while still accommodating the overall deformation required by larger scale regional motions such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis which may be detected paleomagnetically the kind of strike slip fault termination described here may have consequences for how large strike slip fxaults evolve and grow and for the variation in displacement along their length

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out