reservoir induced changes to fluvial fluxes and their downstream impacts on sedimentary processes the changjiang yangtze river china abstract reservoir interception has significantly affected the fluvial sediment budget as well as the sedimentary processes of the entire changjiang catchment to evaluate the impact of reservoirs we analyze the combined effects of 1037 large and medium sized reservoirs on the fluvial flux in general and more specifically on the sedimentary processes in the middle and lower reaches results indicate that reservoir emplacement in the changjiang catchment currently reduces the sediment load towards the east china sea by 453 mt y 1 estimates at yichang station show that the sediment discharge would exceed 555 mt y 1 if there were no reservoirs involved it is expected that in the near future more dams will be constructed the entire reach of the changjiang river can be divided at yichang station into two distinctly characterised reaches with regard to sedimentation where the upper reach exhibits mostly siltation over 589 mt y 1 of sediment deposition and the lower reach is affected by erosion sediment loss including sand extraction exceeding 112 mt y 1 as a consequence the sediment flux to the sea will further decrease to 100 mt y 1 due to human interference the upstream sediment load reduced and caused significant changes in the erosion deposition pattern of the middle and lower reaches which together altered the terrestrial sediment input to the sea before 2003 the upstream reaches were the dominant sediment source after 2003 the sediment contribution of the middle and lower reaches became more important and its sediment contribution will further increase to 78 of the total sediment load reaching the sea after completion of the cascade reservoirs at the jinsha tributary hence the middle and lower reaches are converting from a sediment sink to a major sediment source

the structure of the crust and upper mantle in the dead sea rift abstract the previously published results of a deep seismic refraction study of the dead sea gulf of elat rift show crustal thinning underneath the rift and the presence of a 5 km thick velocity transition zone in the lower crust along the rift the structural interpretation of the first arrival data was revised using the detailed velocity depth distribution the revised crustal thicknesses are 35 km near elat and 27 km 160 km south of elat the crustal thinning and the presence of the velocity transition zone are interpreted as being the result of intrusion of upper mantle material into the lower crust possibly representing the initial shape of the processes which have been active further south in the red sea since earlier times

moment magnitude local magnitude calibration for earthquakes off canada s west coast local magnitude m l values of earthquakes off canada9s west coast are known to be underestimated by at least 0 5 magnitude units compared with other magnitude scales moment magnitude m w derived from moment tensor analysis provides the most robust estimate of the magnitude of earthquakes moment tensor analysis of regional seismic data in western canada is now possible due to the installation of more than 40 three component broadband stations in western canada the u s pacific northwest and southeast alaska moment tensor solutions are now possible down to m 4 0 more than 230 regional moment tensor solutions have been calculated off canada9s west coast at the geological survey of canada for 1995 2002 these solutions along with 14 previous solutions by oregon state university in 1994 1995 and 13 harvard solutions for 1984 1993 allow a systematic m w m l calibration for earthquakes in this region the study area extends from the queen charlotte islands region in the north to the area off the west coast of southern vancouver island at the northern end of the study area where there is little oceanic crust in the source receiver travel path m w is systematically larger than m l by 0 28 0 08 magnitude units at the southern end of the study area where there is a significant amount of ocean crust in the source receiver travel path m w is systematically larger than m l by 0 62 0 08 magnitude units calibration of m l with m w will allow the western canadian earthquake database to be used more effectively for tectonic studies and seismic hazard analysis

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

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

microearthquake activity in the dead sea region summary small earthquakes in the dead sea depression part of the jordan valley dead sea rift were recorded and analysed with 117 identified events of 0 5 ml 4 2 the microseismicity recorded by a local portable network during a period of about 20 months shows a normal rate of seismicity for the region with b values around 0 8 the recorded seismicity is mainly confined to the basin and its boundaries in the southern part of the dead sea basin we found a tendency to clustering which is clearly demonstrated in very similar seismograms of several events recorded at the same station two clusters on the eastern fault are separated by an area with no seismicity for at least 5 yr relative location of events in one of the clusters exhibits a clear north south lineament two active north south left lateral strike slip faults along the east and west boundaries of the southern section of the dead sea basin are distinguished and confirmed by using composite focal mechanism solutions in four out of more than 60 events we found normal faulting where one has a ml 4 1 for 34 events with 1 6 ml 4 2 we found seismic moment estimates m0 of 1 2 1019 m0 2 3 times 1022 dyne cm and brune stress drop estimates s between 0 6 and 92 bars for earthquakes of m0 smaller than about 5 times 1021 dyne cm we found only small variations in corner frequency f0 resulting in decreasing s with decreasing m0 this breakdown of the scaling relation for small earthquakes suggests an fmax slightly lower than 10 hz for the dead sea region the fmax is confirmed by available accelerometer data

the tectonic development of the western margin of the gulf of elat aqaba rift abstract along the western coast of the gulf of elat a 30 km wide shear belt of subparallel faults trending n s to ne sw is developed this shear belt is observed mainly within the precambrian basement terrain sinistral movements on these faults have been recognized based on offsets of magmatic bodies and lithological contacts in rocks of precambrian age the cumulative displacement measured independently at several localities across the belt attains a total of 24 km early neogene volcanism in the form of long dikes trending nw se is known from the eastern desert of egypt of the gulf of suez and along the red sea coast of saudi arabia volcanic bodies of a similar pattern have been identified in eastern sinai these bodies mainly dolerites and basalts intruding mesozoic sediments are parallel to each other and to the gulf of suez they are tens to hundreds of kilometers long and spaced several tens of kilometers apart dating k ar of bodies in sinai saudi arabia and in the eastern desert of egypt suggest an age of 20 22 m y for this extensive volcanism all the dikes are sinistrally displaced by the individual faults of the eastern sinai shear belt the amount of movement recorded using the precambrian markers is identical to movement recorded by offsets of the early neogene dikes this proves that the total 24 km shear of this fault system postdates the 20 22 m y volcanic phase it is assumed that the recorded movements are part of the 105 110 km shear persumed to exist along the gulf of elat which is also younger than 20 22 m y preliminary results suggest that a similar amount of movement is observable along a shear zone developed on the eastern coast of the gulf of elat thus only some 60 km movement are taken up by faults in the gulf itself the evolving model suggests that 1 a the intrusion of very long basaltic dikes in a nw se direction on both sides of the red sea accompanied the initial stage of development of the red sea gulf of suez rift valley 2 b a basic change in the geotectonic regime occurs after the intrusion of this volcanic suite large scale horizontal movements are initiated being recorded as a 105 110 km sinistral movement along the arava jordan rift this movement implies a synchronous opening of the red sea

oil migration driven by exhumation of the canol formation oil shale a new conceptual model for the norman wells oil field northwestern canada abstract thermal history petroleum system structural and tectonic constraints are reviewed and integrated in order to derive a new conceptual model for the norman wells oil field and a new play type for tectonically active foreland regions the thermal history recorded by devonian rocks suggests that source rocks experienced peak thermal conditions in the triassic jurassic during which time oil was likely generated after initial oil generation and expulsion the canol formation oil shale retained a certain fraction of hydrocarbons the shallow reservoir 650 350 m is a devonian carbonate bank overlain by the canol formation and resides within a hanging wall block of the norman range thrust fault both reservoir and source rocks are naturally fractured and have produced high api non biodegraded oil thrust faults in the region formed after the paleocene and a structural cross section of the field shows that the source and reservoir rocks at norman wells have been exhumed by over 1 km since then the key proposition of the exhumation model is that as canol formation rocks underwent thrust driven exhumation they crossed a ductile brittle transition zone and dip oriented fractures formed sympathetic to the thrust fault the combination of pore overpressure and new dip directed subvertical fractures liberated oil from the canol formation and allowed for up dip oil migration reservoir rocks were similarly fractured and improved permeability enhanced charging and pooling of oil gps and seismicity data indicate that strain transfer across the northern cordillera is a response to accretion of the yakutat terrane along the northern pacific margin of north america which is also the probable driving force for foreland shortening and rock exhumation at norman wells

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

lithospheric structure across the craton cordilleran transition of northeastern british columbia the lithospheric structure of the transition from the craton to the cordillera in northeastern british columbia is interpreted from inversion of seismic refraction wide angle reflection data along a 460 km profile and from 3 d 3 dimensional inversion and 2 5 d forward modelling of bouguer gravity data the seismic profile extends westward from the sediment covered edge of cratonic north america across the foreland and omineca morphogeological belts to the eastern boundary of accreted terranes beyond the tintina fault across the ancient cratonic margin the resultant models reveal a westward thickening package of low upper crustal velocities 6 2 km s and less and low densities to almost 20 km depth below the western canada sedimentary basin overlying a west facing ramp of higher velocities and densities in the middle and lower crust these features are inferred to represent passive margin sediments deposited on the ancient rifted margin during the mid to late proterozoic and early paleozoic a we

seismicity in the vicinity of the snorcle corridors of the northern canadian cordillera the slave northern cordillera lithospheric evolution snorcle corridors of the northern cordillera sample some of the most and least seismically active regions of canada the earthquake history of this region is short precise determination of earthquake locations and depths is not possible even today nonetheless significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earth quakes microseismicity studies and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes this article summarizes our current knowledge of the seismicity and seismic hazards across the region these detailed analyses have shown that i the largest historical earthquakes have occurred in regions of ongoing microseismicity ii the largest earthquakes have occurred in pairs or in swarms suggesting that stress triggering is important in this region iii the active faults are concentrated in the offshore region iv there is a concentration of seismicity in the fold and thrust belt several hun dred kilometres from the active plate margin and v there is no seismicity associated with the quaternary volcanic zone in northern british columbia potentially damaging magnitude m 5 earthquakes can be expected every few years in the vicinity of the northern cordillera the mw 7 9 denali alaska earthquake where mw is the moment magnitude was a good reminder that the effects of a large earthquake can be substantial even hundreds of kilometres from the epicentre detailed studies of seismicity earth structure and tectonics with the latter made possible in large part by the snorcle transect will allow for informed decision making for resource development and the design of safe structures and infrastructure in the northern canadian cordillera resume les corridors du projet snorcle de la cordillere septentrionale permettent d echantillonner quelques unes des regions sismiques les plus et les moins actives du canada l histoire des seismes de cette region est breve meme

three dimensional structure across the tintina strike slip fault northern canadian cordillera from seismic refraction and reflection tomography accepted 2006 june 5 received 2006 june 3 in original form 2005 september 4 summary the development of the northern canadian cordillera involved major strike slip displacement of accreted terranes relative to north america along faults such as the tintina which has experienced 425 km of dextral motion since the palaeocene the snore seismic refraction wideangle reflection experiment was carried out in 1997 as one component of lithoprobe s slavenorthern cordillera lithospheric evolution snorcle transect in addition to four 2 d profiles two sets of broadside recordings were acquired to image the 3 d structure across the tintina fault tf in areas centred at about 59 5 n and 62 n simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity moho depth and upper mantle velocity structure consistent with the data our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data the preferred 3 d models are generally consistent with the 2 d models obtained from the inline data in previous independent studies there are along strike variations across the tf perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south in the lower crust the only correlation with the tf that is required by the data is a 0 1 km s 1 drop in velocity to the southwest of the fault in the northern study area the absence of a strong correlation with the tf in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the snorcle reflection data the moho is relatively flat throughout the study area 34 35 km depth but there is broad crustal thickening of a few kilometres centred 50 km southwest of the tf in the northern and southern study areas this thickening may be the result of a period when there was a component of compression along the tf there is strong evidence for a 0 3 0 4 km s 1 drop in upper mantle velocity to the west of the tf in the south and weak evidence for 0 1 km s 1 drop to the southwest in the north the upper mantle variations in the south indicate that the tf is the boundary between cooler and or more refractory ancestral north american mantle to the east and warmer and or more fertile mantle beneath accreted north america to the west in the north the mantle appears to be more intermediate in its properties on both sides of the tf

river channel change during the last 50 years in the middle yangtze river the jianli reach intensive anthropogenic disturbances have affected the channel of the middle yangtze river since the 1950s this paper selects the jianli reach as an example to examine human impact on channel change in the middle yangtze river 1 100 000 channel distribution maps from 1951 1961 and 1975 and 1 25 000 navigation charts from 1981 and 1997 were employed to reconstruct channel change in the study reach the result indicates that the channel under the constraint of levees along the riverbanks underwent a minor widening but frequent bank failure due to susceptible bank structure and increase in water discharge the bank failure promoted bar growth in the channel cross section changes and quantitative calculations of erosion and deposition based on the dem derived from navigation charts present a pattern of over bank sedimentation and riverbed incision the stage and duration of floods have increased following levee construction and bank revetment

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

structural features in the dead sea jordan rift zone interpreted from a combined magnetic gravity study abstract the results of a combined analysis of aeromagnetic and gravity data covering the rift and adjacent areas show two different deep structural models a across the northern and central portions of the rift zone the crustal thickness and the character of the upper mantle remain unchanged on the other hand the lithology of the upper crust varies laterally so that the mafic composition of the rock type probably increases from east to west b the southern portion of the rift may be underlain by an anomalous low density upper mantle local negative gravity anomalies within the rift zone delineate deep depressions separated by structural highs the dead sea depression is interpreted to be filled by 7 5 km of young low density sediments local magnetic anomalies which cover the northern portion only are interpreted as basalt flows this approach enables delineation of fault patterns which support the classic view of sinistral strike slip movement along a complicated fault system

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

micro and macroseismicity of the dead sea rift and off coast eastern mediterranean abstract the seismicity of israel has been evaluated from documented earthquake records of the present century and two years of routine monitoring of microearthquake activity by means of eleven stations spreading from the gulf of elat to northern galilee the dead sea rift asserts itself as the tectonic feature that accounts for the seismicity of our region the activity peaks at zones where the fault branches sideways or at a junction with other fault systems in particular the crescent fault of wadi faria seems to be a zone of high strain accumulation this is probably the site of many historical earthquakes which caused inland and coastal damage it is thus found that the most active fault today which constitutes the greatest seismic risk to israeli metropolitan areas extends along the dead sea rift from 31 2 n to 33 4 n the seismicity around the dead sea conforms with the proposed movement along en echelon faults while the southwest segment is presently inactive most of the seismic activity there is limited to the neighbourhood of its eastern shore with extreme seismicity at its southern tip near the prehistorical site of bab a dara a the seismicity of the arava is much lower than the jordan dead sea section the seismicity of the israeli coast was found to be somewhat higher than that of the arava

asymmetry and basin migration in the dead sea rift the dead sea depression sensu stricto forms the deepest continental part of the dead sea rift a transfer which separates the levanthine and arabian plates it is occupied by three distinct sedimentary bodies deposited in basins whose depocenters are displaced northward with time they are the continental red beds of the hazeva formation miocene the bira lido gesher marls and the exceptionally thick rocksalt of the sedom formation pliocene early pleistocene and the successive amora lisan and dead sea evaporites and clastics early pleistocene recent lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to leftlateral shear combined with anticlockwise rotation of the arabian eastern plate steeper faulting of the crustal eastern margin than of the western sedimentary margin and modification of depositional pattern by twice filling up of basins by hazeva red beds during late miocene pause of shear and by sedom rocksalt during pliocene marine ingression

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

on the river lake relationship of the middle yangtze reaches abstract the geological and meteorological setting of the jianghan dongting lake area leads to high precipitation and siltation but poor water discharge thus the area is frequently flooded in the past the river lake relationship of the middle yangtze has been variable but has deteriorated recently under increasing human influence the jianghan plain of the middle yangtze becomes a waterlogged lowland under the constant threat of flooding from the perched jingjiang river due to siltation and land reclamation the dongting lake has lost most of its regulatory function for the river and has become increasingly vulnerable to flood disasters the middle yangtze river has been undergoing siltation resulting from a downstream decline of sediment transport capacity resulting in the elevation of the flood level above the lowlands heightening of the levees has caused further siltation of the channel the three gorges reservoir will provide a buffering period of 50 80 years during which much of the silt will be trapped in the reservoir and scouring downstream may occur we should utilize this period to work out an overall resolution to the problem construction of a water and silt diversion project in the honghu lake and surrounding areas may resolve this problem in the dangerous chenglingji wuhan segment of the yangtze widening the canals connecting the middle yangtze and han rivers may function as a discharge dividing channel of the yangtze which may prove to be beneficial

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

provenance study of the holocene sediments in the changjiang yangtze river estuary and inner shelf of the east china sea abstract the source to sink process of terrigenous sediment from east asia continent to the marginal seas is crucial for the understanding of land ocean interaction and marine sedimentary process in the west pacific continental margin this paper presents element geochemical and sr nd isotopic records of core cm97 in the changjiang yangtze river estuary and core md06 3040 on the inner shelf of east china sea aiming to reconstruct the changjiang sediment source to sink transport process and its major controlling mechanism during the holocene driven by the asynchronous evolution of the indian and east asian summer monsoon the provenance of sediments accumulated in the changjiang estuary gradually changed from the upper catchment during the late glacial period to the mid lower valley in the early mid holocene with the intensive agricultural cultivation and urbanization development in the catchment during the late holocene the major source of changjiang sediment into the sea shifted back to the upper catchment again the high frequency enso activity may superimpose the effect of human disturbances on sediment source to sink process in the late holocene therefore the holocene provenance evolution of changjiang sediments in the east china sea witnessed the changes of governing sediment erosion process within a large catchment from monsoon climate dominated to anthropogenic driving our study also suggests the strong effect of hydrodynamics in coastal and shelf environments on sedimentary geochemical compositions which deserves more attention in further sediment provenance study

source parameters of the 29 may and 5 june 1940 richardson mountains yukon territory earthquakes the 29 may and 5 june 1940 richardson mountains earthquakes are the two largest events ms 6 2 and 6 5 respectively known to have occurred in the northern yukon territory near the boundary of the canadian cordillera and the stable continental craton the earthquakes were located 20 km apart at 66 87 n 135 33 w and 66 85 n 135 80 w respectively for the may event mb 6 3 ms 6 2 and m 3 5 1025 dyne cm and for the june event mb 6 4 ms 6 5 and m 7 5 1025 dyne cm modeling of teleseismic and regional body waves for these earthquakes indicates a complex rupture sequence for each consisting of two to three subevents focal depths ranged from 14 5 to 11 km for the may rupture sequence and 10 to 7 km for the june sequence the focal mechanisms determined from modeling body waves are primarily strike slip along either n s or e w trending planes the former is preferred based on mapped surface faults in this region and the relative locations determined for the subevents the mechanisms are similar to those of other earthquakes in the richardson mountains but different from the pure thrust events that are observed in the mackenzie mountains 200 km to the southwest the alignment of the near horizontal pressure axes for the richardson mountains earthquakes suggests reactivation of pre existing zones of weakness within the crust by the contemporary stress field stress drops for these earthquakes 22 to 28 bars are low for intraplate events but similar to those estimated for other earthquakes in the eastern canadian cordillera

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

oldest dated earthquake in yukon territory canada a strong earthquake was recorded by hudson s bay company trader explorer robert campbell on december 27 1850 at fort selkirk yukon territory a search of records from the region failed to find an

the mw 7 9 denali fault earthquake of 3 november 2002 felt reports and unusual effects across western canada the 3 november 2002 m w 7 9 denali fault earthquake was one of the largest north american earthquakes of the past 100 years this earthquake located 330 km to the west of the yukon alaska border generated 260 reports of shaking and other unusual effects to distances of 3500 km across western canada felt intensity for this earthquake ranged from v at communities in the yukon closest to the epicenter about 350 km distance iv across much of the yukon territory distances of 350 to 750 km iii across much of northern british columbia to ii in southern british columbia and alberta about 2400 km distance in many instances people reported feeling nauseous or seasick and having trouble standing the long period ground motions generated by this earthquake displacements greater than 10 cm were recorded in the yukon caused water to spill from swimming pools generated seiches in lakes and rivers and affected wells instances of dirty well water to distances of 3500 km across western canada

interpretation of the environmental change of dongting lake middle reach of yangtze river china by 210pb measurement and satellite image analysis abstract the present study examined the recent environmental history of the dongting lake located in the middle yangtze river region central china the sediment was recovered by 22 vibrocores in different lake sectors primarily characterizing subaqueous delta and bay subfacies high sedimentation rates revealed by 210pb measurement in different subfacies of the lake ranged from 0 77 to 2 33 cm year these rates equate to deltaic sedimentation associated with mobile channels resulting from yangtze flood events satellite images confirm that the dongting lake does not contain the biggest yangtze floods moreover comparative bathymetric surveys verify that the dongting lake has lost almost two thirds of its total area in the past century due primarily to siltation by yangtze sediment in the late 19th century a major flood induced channel avulsion resulted in the coupling of the four tributary subbasin to the dongting lake causing a massive increase in the sediment supply into the lake since then hydrological data demonstrate that about 83 of the lake s annual sediment influx are derived from the yangtze in addition pressures from a growing population and associated human activities such as reclamation embanking aquaculture slope modification and deforestation are compounding the loss of the lake surface area and associated storage capacity

the recent history of hydro geomorphological processes in the upper hangbu river system anhui province china abstract this paper describes 20th century climate and human impacts on terrestrial and fluvial systems in the dabie mountains anhui province china based on analyses of four types of information analyses of particle size mineral magnetism organic carbon nitrogen and phosphorus in a sediment core taken from the longhekou reservoir built in 1958 ad in the upper reaches of hangbu river provide an 45 year record of fluvial responses while monitored meteorological and hydrological data provide records of climate and river discharge census data compiled for the local shucheng county provide records of population and land use complemented with analyses of satellite images the xiaotian river delivers over 65 of the total water and silt to the reservoir analyses indicate that the fluvial regime tracks the monsoon climate over seasonal timescales but human activities have a strongly mediating effect on sediment supply sediment delivery and to a lesser extent runoff over longer timescales notable periods of human impact on erosion include the great leap forward 1958 1960 and great cultural revolution 1966 1976 a rising trend in precipitation and new land use changes at the present time may be leading to an enhanced flood risk

silicon isotope compositions of dissolved silicon and suspended matter in the yangtze river china abstract silicon isotope compositions of main channel samples of the yangtze river were systematically investigated along with their chemical compositions the concentration of suspended matter in the yangtze river tends to decrease from the upper reaches to the lower reaches corresponding to settling of the sediments in the lakes and reservoirs due to reduction of the velocity of water flow the silica contents of suspended matter vary from 52 1 to 56 9 and their 30si values vary from 0 to 0 7 both similar to those of shales from the upper to lower reaches the silica contents of suspended matter tend to increase whilst their 30si values tend to decrease both trends reflect the increase of clay minerals and decrease of carbonates in suspended matter the concentrations of dissolved silicon vary from 97 to 121 mol l and their 30si values vary over a wide range from 0 7 to 3 4 from the upper to lower reaches dissolved silica concentrations tend to decrease and their 30si values tend to increase these trends mainly reflect the change of chemical and isotopic characteristics of the tributaries from the upper to lower reaches the major factors responsible for these changes may be the high meteoric precipitation and significant silicon absorption by grass in wetlands and rice in paddy fields in drainage areas of the middle and lower reaches there is no correlation between 30si of dissolved silicon and that of suspended matter the 30sidiss spm values vary over a wide range of 1 0 3 7 indicating that 1 they are out of isotopic equilibrium 2 dissolved silicon and the associated suspended matter do not belong to one physico chemical system and 3 isotopic exchange rate between them is very slow the 30si value of dissolved silicon output from the yangtze river to the east sea is estimated to be 3 0 much higher than the values reported for the amazon and congo rivers this increases the 30si range of dissolved silicon in the world s rivers from 0 4 1 2 to 0 4 3 4

structure of the dead sea pull apart basin from gravity analyses analyses and modeling of gravity data in the dead sea pull apart basin reveal the geometry of the basin and constrain models for its evolution the basin is located within a valley which defines the dead sea transform plate boundary between africa and arabia three hundred kilometers of continuous marine gravity data collected in a lake occupying the northern part of the basin were integrated with land gravity data from israel and jordan to provide coverage to 30 km either side of the basin free air and variable density bouguer anomaly maps a horizontal first derivative map of the bouguer anomaly and gravity models of profiles across and along the basin were used with existing geological and geophysical information to infer the structure of the basin the basin is a long 132 km narrow 7 10 km and deep 10 km full graben which is bounded by subvertical faults along its long sides the bouguer anomaly along the axis of the basin decreases gradually from both the northern and southern ends suggesting that the basin sags toward the center and is not bounded by faults at its narrow ends the surface expression of the basin is wider at its center 16 km and covers the entire width of the transform valley due to the presence of shallower blocks that dip toward the basin these blocks are interpreted to represent the widening of the basin by a passive collapse of the valley floor as the full graben deepened the collapse was probably facilitated by movement along the normal faults that bound the transform valley we present a model in which the geometry of the dead sea basin i e full graben with relative along axis symmetry may be controlled by stretching of the entire brittle and ductile crust along its long axis there is no evidence for the participation of the upper mantle in the deformation of the basin and the moho is not significantly elevated the basin is probably close to being isostatically uncompensated and thermal effects related to stretching are expected to be minimal the amount of crustal stretching calculated from this model is 21 km and the stretching factor is 1 19 if the rate of crustal stretching is similar to the rate of relative plate motion 6 mm yr the basin should be 3 5 m y old in accord with geological evidence

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

holocene tectonic deformation along the western margins of the dead sea abstract to assess the young tectonic activity along the western margins of the dead sea and north of the lake faults were studied within sediments which are up to 60 000 years old the western margins of the dead sea are dominated by normal step faults which are exposed up to 2 km east of the morphological escarpment of the basin the rate of subsidence accommodated by these normal faults is estimated to be about 0 85 mm y the distribution of the faults suggests that holocene fault activity was most intense in the northwestern corner of the dead sea north of the lake left lateral slip along the jordan fault produced both local compression and extension small reverse faults and folds exposed along this fault indicate a minimum left lateral slip rate of 0 7 mm y

anastomosing river system along the subsiding middle yangtze river basin southern china the study focuses on the formation processes of the uprivermost jingjiang reach of three anastomosing river reaches along the middle yangtze river downstream of the three gorges dam site and 1700 km upriver from the seacoast at shanghai in southern china the jingjiang reach consists of large anastomosing channels the songzi hudu anxiang and ouchi rivers which depart from the yangtze trunk channel and flow southward and southeastward up to 200 km into the dongting basin and lake the lake rejoins the yangtze at chenglingji the 7000 km 2 anastomosing reach is characterized by multiple stable low gradient channels 0 00004 m m 4 cm km with low width depth ratios 40 low stream powers 7 w m 2 with very high sedimentation rates 33 5 123 3 mm year in some channels tectonic subsidence caused by the himalayan orogeny is thought to be the primary forcing mechanism in causing the anastomosing channel processes and deposition historical documents have shown that the jingjiang channels were caused by repetitive avulsions southward from the yangtze channel the earliest recorded avulsion occurred in a high flood period before 1644 and subsequent avulsions have continued to modify the topography three major avulsion channels have diverted 14 33 of the discharge and 17 47 of suspended sediment load from the yangtze channel these channels have remained laterally stable a characteristic of anastomosing rivers due to their low gradient silt clay banks densely vegetated natural levees and stable interchannel islands consisting of clayey silt that supports dense riparian vegetation data derived from hydrological gauging stations over the last 45 years demonstrate that total discharge and sediment load of anastomosing channels has decreased by two thirds largely due to sediment aggradation on channel beds reduced sediment load and discharge and human caused channel modification were more pronounced in the eastern channels with the completion of the 3 gorges dam in 2009 the anastomosing channels will cease to carry significant quantities of water and sediment to maintain fluvial vigor in the next 100 years the yangtze main channel may become the only active channel as the anastomosing channels slowly will be infilled c 2004 elsevier b v all rights reserved

a fault model for the nahanni earthquakes from aftershock studies abstract relative locations of 323 large aftershocks m 3 0 or greater in the period from 5 october 1985 to 25 march 1988 show that the m s 6 6 event on 5 october 1985 initiated at 62 208 n 124 217 w about 2 5 km northeast of the m s 6 9 main shock on 23 december 1985 the overall aftershock distribution suggests the october rupture was primarily a west dipping low angle thrust in subsequent aftershock activity the main rupture plane was marked by a distinct quiescent area of about 200 km 2 that persisted until the 23 december event most of the stress drop and slip occurred in this area following the 23 december rupture a similar sized quiescent zone was also observed however it was only evident during the first 24 hr of the aftershock sequence and the area was about 50 per cent too small to yield the overall stress drop the additional area appeared to come from secondary rupture zones that developed coincident with the main shock rupture precise locations of 182 small m 3 0 or less aftershocks recorded during a third field survey from 12 to 21 september 1986 indicated at least one and probably three high angle faults composite mechanism solutions showed thrust faulting except in a region directly south of the main shock rupture areas where there is a bend in one of the secondary fault zones and a concentration of aftershock activity mechanism solutions calculated for five of the largest aftershocks in the same region also indicated a similar variability development of secondary fault zones explained the increased complexity of the december event and may also provide an explanation for the vertical peak acceleration exceeding 2 g that was recorded about 10 sec after the december rupture initiated

determination of geochronology and sedimentation rates of shallow lakes in the middle yangtze reaches using 210pb 137cs and spheroidal carbonaceous particles abstract accurate chronologies for recent sediments of shallow lakes in the yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century this study presents the results of detailed 210pb analysis from eight lake sediment cores collected from the middle yangtze reaches southeast china unsupported 210pb activities generally declined exponentially with mass depth in the eight cores the chronologies and sedimentation rates for the sediment cores were calculated using different 210pb based mathematical models the 137cs chronomarker i e the 1963 fallout peak and the spheroidal carbonaceous particle scp chronomarker i e the start of the rapid increase in 1970 ce were selected to validate the 210pb dating sedimentation rates derived from different models were validated using historical data including lake area arable land area sediment discharge and reservoir volume in the yangtze basin the scp corrected crs constant rate of supply model performs better than other models based on validation using historical documents in the yangtze basin the 137cs chronomarker might be erroneous due to catchment driven 137cs inputs from soil erosion and post depositional diffusion both scps and 137cs are susceptible to inputs from catchment soil erosion but scps show no apparent degradation and post depositional changes in lake sediments the scp profile provides a relatively reliable chronomarker which can be used for validating 210pb chronologies in these floodplain lakes generally sedimentation rates in the eight lakes were

analysis of historical floods on the yangtze river china characteristics and explanations abstract this paper examines the characteristics of historical floods and associated monsoon precipitation in the yangtze catchment with specific attention given to the middle and lower yangtze basin based on in situ field observations and historical discharge flood duration and land use information etc we propose a number of flood characteristics of the basin 1 floods have occurred more frequently after 1950s however changes in discharge can only partially explain the occurrence of the floods 2 spectral analysis on the annual mean water discharge during 1860 1985 in hankou hydrological gauging station of the middle yangtze river reveals 16 4 year and 2 5 year flood recurrences which become shortened from what has been recorded in the chinese historical literature on millennial time scale 3 floods after 1950s tend to have higher water levels both mean and peak and longer duration than before but with remarkably limited inundation area and 4 a series of flood waves generated by monsoon precipitation in 1998 initiated from the middle yangtze highlights the basin wide climate hazards with a recurrence of around 60 years intensifying anthropogenic activity in the last century including deforestation dyking and lake coast reclamation etc that results directly in riverbeds aggradation and shrinkage of lake water area in the middle yangtze basin are the key causes for recently human induced floods in the basin threatened land property in the basin reminds us to harmonize with the river and provide more space for flooding

magnetic field over the dead sea and vicinity abstract a detailed magnetic survey was conducted in the dead sea a large sedimentary basin within the dead sea rift the magnetic anomaly map shows two distinct provinces in the north the anomaly field trends north south and decreases towards the east with a gradient of 10 to 20 nt km in the south the field trends east west the magnetic field is generally smooth and most of the magnetic anomalies have long wavelengths and low amplitudes however a few short wavelength anomalies exist some of which have high amplitudes they may indicate the presence of small basaltic bodies buried at shallow depths a comparison between the magnetic anomaly map of the dead sea and aeromagnetic maps over the land areas to the west and east show that the magnetic anomalies extend uninterrupted from the land area to the west into the basin this configuration suggests that faulting on the western margin of the basin is basically normal in the east the magnetic contours are discontinous across the eastern margin of the basin which suggests that the eastern fault is a strike slip fault a very active fault of unknown nature borders the basin in the south this is associated with magnetic anomalies seismic activity and possibly hydrothermal activity there is no indication of faulting on the northern margin of the lake

seismic investigation of crust mantle transition in continental rift systems jordan dead sea rift and rhinegraben abstract the recent acquisition of high quality seismic refraction data in the jordan dead sea rift and adjacent areas has made possible the investigation of the dynamic properties of seismic p waves refracted and reflected at the crust upper mantle boundary these waves cause high amplitude arrivals near the outer cusp of the travel time curve which are followed by an abrupt decrease in amplitudes at increasing distances beyond the cusp it has been shown that such amplitude distributions can only be the result of a smooth rapid increase of velocity with depth in the case of the jordan dead sea rift the amplitude distribution indicates the presence of a transition zone between the lower crust and upper mantle in which the velocity increases smoothly the interpretation of seismic refraction data in the rhinegraben indicates the existence of a similar transition zone in both rifts the crust mantle boundary outside the rift is represented by sharp velocity discontinuity the comparison of the velocity structure of the crust upper mantle boundary suggests that a smooth transition zone at the base of the lower crust is a characteristic property of continental rifts which could be interpreted in terms of crust mantle interaction

rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock mechanics based yield criteria for the inelastic deformations at the top and base at mid plate depths stresses are likely to be supported elastically because bending strains and elastic stresses are low the collisional tectonic regime however is far more complex because very large permanent strains are sustained at mid plate depths and this requires us to include the broad transition between brittle and ductile flow moreover important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid plate depths two specific contributions of laboratory rock rheology research are considered in this paper first the high temperature steady state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere the thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm tc above which at geologic strain rates the high temperature ductile strength falls below some arbitrary strength isobar e g 100 mpa for olivine tc is about 700 800 c but for other crustal silicates tc may be as low as 400 600 c suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the moho as suggested by a number of workers on independent grounds put another way the moho is a rheological discontinuity a second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant strain rate tests or as an accelerating creep rate stage at constant differential stress a number of physical mechanisms have been identified that may be responsible for ductile faulting including the onset of dynamic recrystallization phase changes hydrothermal alteration and hydrolytic weakening microscopic evidence for these processes as well as larger scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere

assessing the potential for change in the middle yangtze river channel following impoundment of the three gorges dam abstract the geomorphic impacts of dams on downstream river channels are complex not readily predictable for specific cases but widely reported in the literature for the three gorges dam on the yangtze changjiang river in china no studies of the impact of the changed flow and sediment conditions below the dam on the behaviour of the channel were included in the pre dam feasibility report we have assembled a database of flow and sediment data for the middle yangtze river from yichang to hankou and used this to analyse changes following the closure of the dam while total flow is little affected the operating strategy for the dam that provides for storage of part of the summer high flows to maintain hydroelectric power generation in winter the low flow season is reflected in changes to the seasonal distribution of flow below the dam we calculated potential sediment carrying capacity and compared it with measured sediment concentrations for both pre and post dam conditions while channel sedimentation is indicated along the middle yangtze for pre dam conditions scour is indicated for post dam conditions highest at yichang immediately below the dam and decreasing downstream

a rock avalanche triggered by the october 1985 north nahanni earthquake district of mackenzie n w t a major rock avalanche estimated volume 5 7 106 m3 was triggered by the october 1985 north nahanni earthquake ms 6 6 the landslide is located at 62 27 n 124 18 w 23 km southwest of carlson lake in an uninhabited part of the district of mackenzie n w t it occurred within 10 km of the epicentre the rock avalanche detached from the northeast flank of a ridge located along the axis of the english chief anticline and involved massively bedded limestones of the middle devonian nahanni formation whilst most of the landslide mass was deposited at the foot of the original slope a mobile tongue of debris turned at right angles to the direction of initial sliding and travelled down valley coming to rest on a slope of about 5 the distal margin of the mobile tongue is approximately 1 55 km from the top of the rupture surface the fahrboschung of the landslide is estimated to be 14 5 and the rock avalanche exhibits exceptional mobility in relation to its volume the rupture surface is well expose

new constraints on tectonics of interior alaska earthquake locations source mechanisms and stress regime we used the joint hypocenter determination jhd method to relocate 3611 crustal earthquakes that occurred from 1988 to 1999 in central alaska the new earthquake locations provide more details on the structure of the kantishna cluster and better locations for the aftershock sequence of the 29 november 2000 m l 5 6 earthquake in the minto flats seismic zone the jhd locations for the aftershocks of the 1995 m w 6 0 minto flats earthquake and 22 october 1996 m w 5 8 earthquake near the denali fault are also available a catalog of 196 fault plane solutions consisting of the moment tensor solutions for the earthquakes with magnitude 4 0 or above and p wave first motion solutions for the earthquakes with magnitude 3 4 and above that occurred from 1988 to 2000 was composed moment tensor solutions were calculated using regional broadband data this catalog was used to calculate principal stress orientations in the crust the stress orientations change across central alaska in particular the maximum principal stress orientation rotates clockwise from se nw to ssw nne direction as one moves from west to east these stress orientations are consistent with the stress field transferred from the plate convergence in southern alaska in addition we tested different velocity structures in the moment tensor inversion procedure to identify velocity models for calculating the green s functions the moment tensor inversion study shows that it is possible to obtain a reliable moment tensor solution for moderate sized earthquakes m l 4 using three component records from a single broadband station when the epicentral distances are between 50 and 300 km manuscript received 8 june 2001

distribution of holocene sediments and neotectonics in the deep north basin of the dead sea abstract the distribution of holocene sediments and active faults in the central portion of the northern dead sea basin was analyzed from high resolution seismic reflection data the seismic reflection profiles reveal that sediments buried at a shallow depth are flat lying continuous and unfaulted within the central basin floor four prominent subsurface seismic reflectors were identified that based on limited core data represent the contact between rock salt and marl layers isopach and structural maps of recent sediments indicate an asymmetry of active subsidence with thick accumulations located closer to the east margin of the basin sediment thickness increases within a rhomb shaped depression whose long axis is oriented approximately 20 30 counterclockwise to the regional basin bounding faults the morphology and trend of the locus of maximum subsidence suggests tectonic control of the depression however the proximity of the depocenter of recent sediments to the ein gedi diapir and rim depression suggests that local sub basinal subsidence may also be related to movement of rock salt at depth the basinal strata are deformed along the faults that form a bathymetric escarpment along the west east and south margins of the north basin of the dead sea thinning of recent sediments toward the faults indicates syntectonic deposition

holocene seismic and tectonic activity in the dead sea area abstract the dead sea is a large active graben within the dead sea rift which is bounded by two major strike slip faults the jericho and the arava faults we investigated the young tectonic activity along the jericho fault by excavating trenches up to 3 5 m deep across its trace the trenches penetrate through late pleistocene and holocene sediments we found that a zone up to 15 m wide of disturbed sediments exists along the fault these disturbed sediments provide evidence for two periods of intensive activity or more likely for two major earthquakes that occurred during the last 2000 years the earthquakes are evident in small faults vertical throw of a few layers cracks unconformities and wide fissures we further documented evidence for recent sinistral shear along the jericho fault in deformed sediments and damage to an 8th century palace on a subsidiary fault we suggest that the two earthquakes may be correlated with the 31 b c earthquake and the 748 a d earthquake reported by the ancients

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

fault geometry and spatial clustering of microearthquakes along the dead sea jordan rift fault zone abstract earthquakes 1 0 m l 5 3 in the region around the dead sea jordan rift fault zone recorded by the israel scismograph station network issn from 1982 until the beginning of 1989 have been analyzed and interpreted the scismicity pattern clearly reveals activity along three fault zones the dead sea jordan rift fault zone the carmel faraa fault zone and the central sinai negev shear zone microearthquake occurrence tends to cluster in or near tensional features rhomb shaped grabens such as the hula sea of gallilee and dead sea depressions further eight representative focal mechanisms of individual earthquakes or earthquake clusters have been derived the seismicity and focal mechanism solutions near the branching of the carmel faraa and the dead sea jordan rift fault zones suggest a complicated tectonic breakup in this region microearthquakes in the arava may indicate a more complex pattern of active faults than was previously assumed

the rotation of arabia and the levant fault system abstract we establish the kinematics of the rotation of arabia with respect to africa and show that the rotation rate of africa increased by a factor of about four in late serravallian time about 12 13 ma ago we discuss evidence that oceanic accretion started simultaneously in the gulf of aden and in the red sea at this time it is also at this time that the levant and anatolian fault systems were initiated our initial reconstruction of the red sea rift in late oligocene early miocene time approximately superposes the present shore lines which coincide with the mid point of the zones of rapid crustal thinning the future continental slopes the amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension and by checking these estimates through closure around the sinai triple junction in the late miocene the southern evant fault zone was a zone of distributed shear deformation through counterclockwise block rotation extending soul h ward within the northernmost red sea since the early pliocene the shear motion has been localized within the gulf of aqaba changing the tectonic pattern in the northern red sea

acoustic doppler current profiler surveys along the yangtze river an acoustic doppler current profiler is used to characterize the river velocity against the morphology of the yangtze river from chonqing to the sea high flow velocities occur in the three gorges section and lower velocities in the middle and lower reaches of the river this is largely due to the change in river pattern from a high gradient deeply cut valley to a flat fluvial plain flow velocities fluctuate in the middle yangtze due to the presence of meander bends of different length there are numerous smaller velocity fluctuations in the lower yangtze channel that reflect multichannel pattern with numerous sand bars and a river morphology affected by bedrock outcrops water depths of 40 100 m occur in the three gorges valley but decrease to 15 40 m in the middle and lower yangtze at the gezhou reservoir 30 km downstream of the three gorges damsite velocity drops to low 1 0 m s 1 20 km reach a second low velocity 0 5 m s 1 zone about 20 km in length is located in the lower yangtze near the coast probably due to the tidal influence the results from this research will serve as a datum for evaluating changes to the river once the three gorges dam is completed in 2009

structure and fabric of the crust and uppermost mantle in the northern canadian cordillera from rayleigh wave tomography abstract the seismic structure and fabric of the lithosphere and underlying mantle beneath the northern canadian cordillera provides important constraints on its evolution and current tectonics however it is poorly characterized due to historically sparse networks of seismic instruments we use data from past and recently deployed networks of broadband seismic stations in northwestern canada and measure rayleigh waves propagating between all available pairs of seismic stations using two complementary techniques ambient noise and teleseismic two station interferometry the rayleigh wave data are processed to obtain phase velocity dispersion curves that are inverted for phase velocity maps at periods between 8 and 80 s to first order these maps show high velocity anomalies within the canadian shield and low velocity anomalies within the cordillera at all periods at short periods 30 s mostly sensitive to uppermost mantle depths high velocity anomalies of the canadian shield extend west past the cordilleran deformation front and suggest the presence of cratonic lithosphere beneath the cordillera whereas the lowest velocities underlie the allochtonous terranes anisotropy within the crust and uppermost mantle exhibits fast axis orientations aligned with the major faults and fabric of the cordillera and show evidence for vertical changes in anisotropy these results provide new constraints on geodynamic models proposed to explain neotectonic deformation in this area

sinistral strike slip motion on the dead sea rift confirmation from new magnetic data new aeromagnetic data from jordan provide information about basement structures that were previously unknown large east west magnetic anomalies are truncated by the dead sea rift comparison of these data with aeromagnetic data from west of the rift strongly suggests that these anomalies have undergone slightly more than 100 km of left lateral offset this is the same amount of offset concluded from several studies of surface bedrock geology offset of magnetic anomalies provides confirmation of the total amount of offset but no sense of timing or the polyphase history of motion suggested by other studies

seismic velocity model of the crust in the northern canadian cordillera from rayleigh wave dispersion data models of the seismic velocity structure of the crust in the seismically active northern canadian cordillera remain poorly constrained despite their importance in the accurate location and characterization of regional earthquakes on 29 august 2014 a moderate earthquake with magnitude 5 0 which generated high quality rayleigh wave data occurred in the northwest territories canada 100 km to the east of the cordilleran deformation front we carefully selected 23 seismic stations that recorded the rayleigh waves and divided them into 13 groups according to the azimuth angle between the earthquake and the stations these groups mostly sample the cordillera in each group we measured rayleigh wave group velocity dispersion which we inverted for one dimensional shear wave velocity models of the crust we thus obtained 13 models that consistently show low seismic velocities with respect to reference models with a slow upper and lower crust surrounding a relatively fast mid crustal layer the average of

a crustal structure study of jordan derived from seismic refraction data abstract the interpretation of a deep seismic refraction study in jordan performed in may 1984 shows that much of the country is underlain by continental crust 32 35 km thick and normal mantle with a velocity of 8 0 8 2 km s in the aqaba region southwest and central jordan east of wadi araba the crustal thickness is of the order of 32 35 km while in the amman region it is not less than 35 km in southeast jordan the crust thickens to at least 37 km in what is probably the transition to the arabian shield type of crust the boundaries between the upper and lower crust at about 20 km depth and the lower crust and uppermost mantle are probably transition zones the upper crystalline crust has velocities of 5 8 6 5 km s while the lower crust has velocities greater than or around 6 65 km s while the crystalline basement is exposed in southwest jordan and is at a depth of 2 2 5 km north of amman it is at a depth of not less than 5 km in central jordan a comparison of the crustal type and structure of jordan and the adjacent dead sea rift with that of the black forest and the rhine valley yields a striking resemblance the situation of the jordan dead sea rift is explained in terms of the continental crust of arabia rifting in preference to the thin oceanic crust of the mediterranean sea

structural geometry and evolution of the dead sea jordan rift system as deduced from new subsurface data abstract analysis of deep drilling data and seismic reflection surveys obtained in recent years permit establishment of a tectonic model of the dead sea jordan rift system that is in part conformable with some of the many often controversial theories on this subject but which also introduces new information negating some concepts that are widely accepted in the literature the dead sea jordan rift system is not a tensional graben between two parallel sets of faults but instead can be best defined as a sinistral transform connecting an incipient oceanic ridge the red sea with an upthrusted collision zone the taurus range the shear is caused by the opening of the red sea and the motion of the arabian sub plate away from the african plate the shearing occurs along a largely south north trending slightly arcuate une consisting of a series of en echelon left stepping left lateral strike slip master faults of varying lengths these faults characteristically die out to the north by bending outward northeast and the movement is taken up by the strike slip faults to the left i e to the west where overlap of the two faults occurs very narrow and very deep grabens have evolved in places the width being equal to the depth the narrowness of these grabens is dictated by the closeness of the overlapping segments of the successive strike slip faults this feature points to the probability that the en echelon strike slip faults have a common root zone at great depth these grabens are not typical leaky pull aparts in that they have no gravimetric magnetic or heat flow anomalies nor are they closed on all four sides by large faults their northern ends are characterized by gradually rising graben floors without major diagonal cross faults the dead sea jordan rift system sensu stricto extends over a distance of 420 km from the northern shore of the gulf of elat to the northern margin of the hula valley southward it is connected with the red sea along the gulf of elat transition zone which has elements of strike slip as well as tensional opening a northern transition zone exists between the hula valley and the taurus arc where diminishing strike slip movement is compensated by several underthrust belts the time of the beginning of the movement along the rift can be established as pre middle miocene because mid miocene sediments overlie an upper cretaceous graben floor rifting has continued intermittently to the present volcanism in the northern fifth of the rift is genetically associated with the seismically active tensional golan hauran jebel drouz wadi sirhan tectonic trend which has a north west southeast orientation and not with the north south trending dead sea jordan rift

sediment deposition and erosion during the extreme flood events in the middle and lower reaches of the yangtze river abstract floods often are accompanied by intensified soil erosion and thus high sediment supply from the catchment into the main channel of the river this paper examined the sediment processes especially deposition and erosion during the two extreme flood years in 1954 and 1998 in the middle and low reaches of the yangtze river the total amount of sediment supplied to the middle and lower reaches from yichang hankou and hankou datong was 1095 mt in 1954 and 855 9 mt in 1998 or 176 and 137 of the averaged 622 mt a from 1950 to 2006 a high deposition occurred in the floodplains lakes and channels along the section yichang hankou both in 1954 and 1998 the total deposition reached 635 mt and 499 mt in 1954 and 1998 or 138 and 124 of the sediment load measured at the datong station respectively however different processes in the downstream section hankou datong during the two flood events were found severe erosion 140 mt happened in 1954 but only a slight erosion occurred 22 mt in 1998 thus the floodplains and channels in the middle and lower reaches of the yangtze river play an important role in regulating sediment discharge during extreme flood events the heavy deposition in the middle reaches effectively reduced the amount of sediment discharged into the river mouth and thus acted as a major depocenter in the extreme flood year the results also suggested that the yichang hankou tended to shift from a depositional section to an erosional section whereas the hankou datong changed from an erosion dominated section to a deposition dominated section even before the three gorges reservoir infilling in 2003 it is anticipated that this tendency would be accelerated and the historical role of sediment regulation by the two reaches could eventually be changed due to the reduced sediment supply from the upper yangtze

development of asymmetric basins along continental transform faults abstract many basins associated with wrench or transform faults are asymmetrical both longitudinally and laterally the sense of basin asymmetry changes along the strike of transform faults geophysical data from the dead sea rift and other transforms indicate that wrench induced asymmetric basins are bounded on only one side by a transform fault this implies that during the evolution of such basins maximum compression was parallel to the transform the direction of extension can change during the geologic evolution of a basin a possible explanation of this observation takes the strength of the fault into into consideration in the case of a weak fault in a strong crust the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault thus minimizing the shear stress on the main fault basins formed by regional extension such as in the east african rift system sometimes show similar features recent studies have shown that these basins often undergo oblique extension this suggests that the asymmetry in these basins may result from simultaneous strike slip motion and fault normal extension similar to the way asymmetry is produced in large transform basins periods of oblique extension can alternate with periods of orthogonal extension the asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record

palynological evidence for the age and rate of sedimentation along the dead sea rift and structural implications abstract pollen diagrams obtained for eight deep boreholes penetrating the thick sequences of the dead sea rift fill correlated with dated marine sequences of the coastal plain in israel enable stratigraphie assignment of the continental deposits to be made the sedimentary units of the rift valley are of two main provenances those deposited in troughs within the rift limits of predominantly lacustrine environment attaining thicknesses in the order of 1 2 km for which the trough is the final erosion base level and those not limited to the rift boundaries but known from wide areas in israel mostly laid down in river systems that crossed the rift region on their way to the sea these fluviatile formations are in the order of hundreds of meters thick in the rift valley region which acted as an intermediate basin the first group of rock units of late miocene through early middle pliocene to glacial pleistocene ages indicate phases of considerable subsidence the earlier termed the erythrean and the later the levantine phase these are predated in the late oligocene through middle miocene by gentle subsidence and separated during the late pliocene preglacial pleistocene by another period of relative quietness in tectonic activity

stress in western canada from regional moment tensor analysis more than 180 regional moment tensor rmt solutions for moderate sized earthquakes m 4 are used to examine the contemporary stress regime of western canada and provide valuable information relating to earthquake hazard analysis the overall regional stress pattern shows mainly ne sw oriented p axes for most of western canada with local variations in the northern cordillera the maximum compressive stress direction 1 varies from east west to north south to ne sw from south to north the stress direction 1 is consistent with the p axis direction for the largest earthquakes except in the central and northern mackenzie mountains where there is a 16 difference the yakutat collision zone shows a steady change in 1 from east west in the east to north south in the west in the canada united states border region rmt solutions suggest a north south compressional regime may extend through southern british columbia and northern washington to the eastern cordillera in the vancouver island puget sou

transverse faults at the northern end of the southern basin of the dead sea graben abstract classical models for pull apart basins along strike slip faults predict normal motion along the transverse faults which cross the basin a detailed geophysical investigation was carried out across the northern end of the southern sub basin of the dead sea depression the study included analysis of newly obtained 3 5 khz seismic profiles and reinterpretation of existing single channel sparker seismic profiles and multichannel seismic profiles the unique combination of very shallow and deep seismic profiles reveals the recent activity of a transverse fault in the study area and helps trace its direction the northern end of the southern sub basin was probably characterized by normal movement during the miocene early pleistocene thereafter during the late pleistocene present the mode of its activity changed to strike slip movement