dynamical mechanisms for the south china sea seasonal circulation and thermohaline variabilities abstract the seasonal ocean circulation and the seasonal thermal structure in the south china sea scs were studied numerically using the princeton ocean model pom with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography a 16 month control run was performed using climatological monthly mean wind stresses restoring type surface salt and heat and observational oceanic inflow outflow at the open boundaries the seasonally averaged effects of isolated forcing terms are presented and analyzed from the following experiments 1 nonlinear dynamic effects removed 2 wind effects removed and 3 open boundary inflow outflow set to zero this procedure allowed analysis of the contribution of individual parameters to the general hydrology and specific features of the scs for example coastal jets mesoscale topographic gyres and countercurrents the results show that the pom model has the capability of simulating seasonal variations of the scs circulation and thermoha

observed evidence of the anomalous south china sea western boundary current during the summers of 2010 and 2011 seven years of directly measured current data from a mooring in the xisha area of the south china sea scs together with shipboard adcp and satellite data have shown the western boundary current wbc anomaly and its vertical structure during the summers of 2010 and 2011 the observed wbc presented obvious year to year variability especially in the summer overall the summer mean velocity at the mooring site over 7 year 2007 2013 was northeastward the moored adcp showed that the northeastward velocity was particularly strong in the summer of 2010 but the increase was confined in the upper 120 m in contrast the northeastward current disappeared throughout the observed depth range from 50 to 450 m in the summer of 2011 even at the deepest observed position the monthly velocity anomalies reached 14 cm s 1 westward and 12 cm s 1 southward in the zonal and meridional directions respectively both the vietnam offshore current voc and double gyres in the western scs disappeared and the southern anticyclonic gyre expanded to strengthened the northward wbc in the summer of 2010 however in summer of 2011 the voc intensified and the northern cyclonic gyre enlarged with its northern edge reaching 18 degrees n slightly north of mooring site which weakened the northeastward wbc the observed scs circulation anomalies during 2010 and 2011 were mainly induced by the basin scale wind field anomalies associated with the 2009 2010 el nino and 2010 2011 la nina

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

triggered slip along the san andreas fault after the 8 july 1986 north palm springs earthquake in addition to minor surface cracks in the region of the 8 july 1986 north palm springs earthquake minor aseismic surficial rupture occurred along three segments of the san andreas fault 44 to 86 km southeast of the epicenter data from a creepmeter and a tiltmeter at one locality suggest that triggered slip occurred coseismically beneath the instruments but took 33 hr to propagate to the surface that slippage occurred coseismically at depth favors mechanisms for triggered slip that involve dynamic or static strain changes rather than creep migrating from the source region the distribution of slip along the san andreas fault associated with the north palm springs earthquake differed significantly from that recorded after the moderate 1968 borrego mountain california and 1979 imperial valley california earthquakes during these earthquakes triggered slip occurred along the san andreas fault in the durmid hill area and in the mecca hills triggered slip associated with the north palm springs earthquake occurred in these two areas again but also extended farther northwest into the indio hills where as much as 9 mm of dextral slip occurred in the mecca hills surface cracks in 1986 appeared over a shorter fault length than in previous events and the dextral displacement was smaller with maximum values of only 2 to 3 mm on durmid hill surface cracks in 1986 were localized along a 200 m long stretch of the fault spanning the mecca beach creepmeter and extending about 150 m to the southeast right lateral displacements on surface cracks in this area were 1 4 to 2 0 mm smaller than those observed in previous events although the mechanism of triggered aseismic slip is poorly understood examination of displacement rates for the past several decades to centuries may indicate whether the aseismic slip rate is constant or represents accelerating premonitory failiure of the southernmost san andreas fault

a revisit of the interannual variation of the south china sea upper layer circulation in summer correlation between the eastward jet and northward branch the interannual variation of the south china sea upper layer circulation in summer is revisited based on analysis of current derived from altimetry data acoustic doppler current profilers moorings and numerical simulations results show not only the interannual variation of the eastward jet eastward branch but also its anti correlation with the northward branch on interannual time scale when the eastward branch is enhanced the northward branch is weakened and vice versa their variations are largely related to the change of the south china sea summer monsoon scssm and are strongly influenced by the luzon strait transport lst composite analysis reveals a stronger scssm and lst into the scs in the developing phase of el nino would lead to an eastward branch dominant circulation pattern whereas a weaker scssm and reduced lst into the scs in the decaying phase of el nino favors a northward branch dominant circulation pattern the distinct composite patterns appear in el nino and southern oscillation cycles rather than episodic event or multiyear el nino or la nina contribution of the transport of major straits in the scs to the interannual variation of the scs summer circulation is quantitatively evaluated for the first time and the results show that the change of the planetary vorticity flux through three major straits luzon strait contributes most is as equally important as the vorticity input change from local wind stress curl

interannual variability of south china sea winter circulation response to luzon strait transport and el nino wind the el nino wind and luzon strait transport are important factors modulating the interannual variability of the southern and northern south china sea scs winter circulation respectively the joint effect of el nino wind and westward luzon strait transport drives a dipolar gyre with an anticyclonic cyclonic circulation anomaly in the southern northern scs which enhances the cross basin current that connects the scs western boundary current with the eastern boundary of the scs around the mindoro strait and then effectively modulates the interannual variability of mindoro strait transport an extreme el nino and large luzon strait intrusion occurred in winter 2015 16 and mooring observations and remote sensing data confirmed the presence of an intense dipolar gyre this resulted in an extreme eastward cross basin current and outward scs mindoro strait transport anomaly in 2015 16

interannual variability of the south china sea throughflow inferred from wind data and an ocean data assimilation product 1 the luzon strait transport as an index for the south china sea throughflow has attracted much attention recently in this study the interannual variability of luzon strait transport is examined using the island rule and results from ocean data assimilation transport variability obtained from these two approaches is consistent with each other assessment of contribution from each integral segment involved in the island rule indicates that wind stress in the western and central equatorial pacific is the key factor regulating the interannual variability of the luzon strait transport whereas the effect of local wind stress in the vicinity of the luzon strait is secondary analysis also shows that when the westerly easterly wind anomalies in the tropical pacific break out the luzon strait transport increases decreases associated with the variations in the

on two characteristic frequencies of acceleration spectra patch corner frequency and fmax abstract we examine two issues related to the radiation of tectonic earthquake sources i the complexity of the shape of observed source spectra and ii the effect of recording site characteristics on the cut off frequency f max of acceleration spectra beyond which spectral amplitudes diminish sharply we compute the far field spectra of the 1979 imperial valley and the 1984 morgan hill earthquakes from the slip functions that were inferred from detailed inversion studies of strong motion and teleseismic data of these two california strike slip events these spectra along with data from the 1983 central japan sea earthquake sequence main shock and aftershocks demonstrate the existence of the so called patch corner frequency which is related to the scale length of heterogeneities of the fault plane such a frequency is a distinct feature of the source spectrum of the specific barrier model of papageorgiou and aki by analyzing accelerograms of the san fernando earthquake of 1971 we found that f max determined from records at soil stations is nearly the same as that determined from records at hard rock stations

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd

meridional overturning circulation in the south china sea envisioned from the high resolution global reanalysis data glba0 08 the pattern of meridional overturning circulation moc in the south china sea scs is studied using a numerical lagrangian tracing method with the hycom ncoda global 1 12 degrees analysis glba0 08 data the scs moc has a sandwich structure which consists of a layer of stronger clockwise circulation above 500 m depth a counterclockwise layer in the mid layer between 500 and 1000 m depth and a weaker clockwise layer below 1000 m the deep below 1000 m depth clockwise layer is divided into three cells namely the deep southern moc cell dsmoc the deep middle moc cell dmmoc and the unclosed deep northern moc cell dnmoc the inflow through the luzon strait is the main source for the scs mocs the upper layer luzon strait inflow dominates the upper scs moc structure but has relatively less contribution to the dnmoc whereas the deep layer luzon strait inflow mainly influences the dnmoc and it mostly rises near 18 degrees n the inflow through the taiwan strait mainly contributes to the upper layer moc moreover inflows from the mindoro and karimata straits contribute negatively to the upper moc but play a significant role on the dsmoc the backward integration of lagrangian trajectories further validates that the scs deep water comes not only from the deep inflow but also from the entrainment of the middle and upper layer inflow through the luzon strait in the scs basin there are three northwest southeast tilted zones where tracers upwell which correspond to the three deep moc cells one possible mechanism for these upwelling zones is the interaction between the continental slope trapped waves and the westward planetary rossby waves

fault plane solutions for the 1984 morgan hill california earthquake sequence evidence for the state of stress on the calaveras fault fault plane solutions for 946 aftershocks of the april 24 1984 morgan hill california m6 2 earthquake reveal a pattern of complex faulting within a 10 km wide zone surrounding the calaveras fault the fault plane solutions fall into three groups strike slip mechanisms located along the calaveras fault with north northwest striking dextral slip planes nearly parallel to the fault strike slip mechanisms located northeast of the calaveras fault with north striking dextral slip planes and reverse mechanisms located southwest of the calaveras fault with northeast or southwest dipping slip planes the average azimuth of p axes for aftershocks located on the calaveras fault is n10 1 e in contrast the average azimuths of p axes for aftershocks northeast and southwest of the calaveras fault are n49 7 e and n37 3 e respectively by assuming that the earthquakes occur on preexisting cracks in response to a uniformly oriented regional stress field we are able to infer from the observed average slip directions an orientation for 1 the axis of maximum horizontal compression 63 80 from the local strike of the calaveras fault such a high angle orientation of 1 is incompatible with the classical andersonian model of strike slip faulting but is consistent with an alternate model in which a weak calaveras fault is driven by plate motion slightly convergent with respect to the san andreas fault system in central california if this inferred high angle uniform stress field is combined with the changes in the static stress field calculated with elastic dislocation theory for the 1984 morgan hill main shock the resulting stress field predicts most of the observed spatial pattern of the aftershocks and their fault plane solutions the orientations of the inferred aftershock slip planes are generally consstent with the fracture orientations predicted by the coulomb failure criterion areas with predicted increases in the coulomb failure function of only a few tenths of a megapascal correspond to areas of intense aftershock activity the invariance of focal mechanisms in the vicinity of the south end of the main shock rupture before and after the main shock suggests that the magnitude of compressive stress in this area is at least 10 mpa in addition to explaining a preponderance of the seismic observations of the aftershock sequence the presence of a predominantly fault normal compressive regional stress field accounts for the contemporary development of folds reverse faults and topographic relief observed throughout the central california coast ranges

glacier bed characteristics of midtre lovenbreen svalbard from high resolution seismic and radar surveying we conducted a seismic and radar survey of the central part of midtre lovenbreen a small polythermal valley glacier in svalbard we determined the physical properties of the material beneath the glacier by measuring the reflection coefficient of the bed by comparing the energy of the primary and multiple reflections and deriving the acoustic impedance by making reasonable assumptions about the properties of the basal ice we determined the acoustic impedance of the bed material as 6 78 1 53 x 10 6 kg m 2 s 1 we interpret the material beneath the glacier to be permafrost with up to 50 ice and we speculate that the material may be frozen talus similar to a deposit observed directly by others beneath another svalbard glacier the implication for midtre lovenbreen is that the basal material beneath the present glacier is not able to support fast flow we conclude that midtre lovenbreen has most likely had limited capability for faster flow in the past with motion dominated by internal deformation midtre lovenbreen is used as a study glacier for the scientific community in svalbard and a large number of studies have been based there our results show that it cannot be used as an analogue for larger glaciers in svalbard having distinct basal boundary conditions

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

interannual variability of the south china sea in a data assimilation model 1 sea surface height ssh variations in the south china sea are examined using results from a data assimilation model after the ssh data have had the annual cycle removed principal component analysis illustrates two distinct anomaly patterns the first mode strongest off vietnam would affect the basin wide gyre intensity the second mode consists of a meridional dipole feature with a nodal line around 12 n and is related to the development of the eastward jet and upwelling off vietnam both eof modes have significant interannual variations and are highly correlated to the enso events the leading phase of mode 2 coefficient provides preliminary evidence for the air sea interaction and the pacific east asian teleconnection an innovative mechanism is proposed to describe a weakened upwelling off luzon in winter 1998 an extra strong basin wide warming in summer 1998 persists into fall and winter preventing the formation of winter upwelling off luzon in that year

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

assimilating altimetric data into a south china sea model sea surface heights from the topex poseidon altimeter are assimilated into a three dimensional primitive equation model to derive the circulation in the south china sea with data assimilation the model resolves not only the basin wide circulation but also a dipole off vietnam and a low high feature near the luzon strait mesoscale features are missing in the simulation without data assimilation because of poor resolution in the wind field and inadequate knowledge of the transport through the luzon strait compared to the case without data assimilation data assimilation reduces the root mean square error between the simulated and observed sea surface heights by a factor of 2 3 circulation derived from data assimilation under climatological conditions is contrasted with that during el nino in the normal winter of 1993 1994 flow at 50 m depth is strong and cyclonic flow at 900 m depth is cyclonic as well the deep cyclone persists into the following summer during the 1994 1995 el nino winter features in the flow field at 50 m depth either weaken or disappear and circulation at 900 m depth is anticyclonic in the summer of 1995 the dipole and the eastward jet off vietnam at 50 m depth are missing and the anticyclonic circulation at 900 m depth persists temperature at 65 m shows significant warming from fall 1994 to summer 1995 a weakened flow field and warming in the upper ocean are consistent with findings from earlier el nino events

upper layer circulation in the south china sea abstract upper layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature salinity relationships in the south china sea two cyclonic eddies are revealed one is located east of vietnam called the east vietnam eddy and the other is off northwest luzon called the west luzon eddy both local ekman pumping and remotely forced basin scale circulation are important mechanisms controlling these two eddies the luzon strait transport relative to 400 db is estimated to be of the order 3 0 sv 1 sv 1 106 m3 s 1 in the mean and has a seasonal cycle dominated by the annual signal with a maximum 5 3 sv in january february and a minimum 0 2 sv in june july pressure gradients are also examined to explore the dynamics of the intrusion of waters from the pacific into the south china sea through the luzon strait

spatial mapping of multi year superimposed ice on the glacier kongsvegen svalbard ground penetrating radar gpr and satellite ers 2 synthetic aperture radar sar are used to map the thickness and extent of the superimposed ice si zone on the surge type glacier kongsvegen svalbard gpr imagery shows sub horizontal si layers lying unconformably above a discrete boundary below this boundary the ice has a gpr signature similar to that of ice further down glacier in the ablation zone this boundary is posited to represent the closing of crevasses that were created during the last surge of kongsvegen in 1948 open crevasses would have interrupted the formation of sheet layers of si due to efficient vertical drainage of the snowpack aerial photographs suggest that the crevasses closed sometime in the period 1956 66 a classified sar image from 2003 is used to delineate the extent of the si zone the si extent in the sar image agrees well with the si zone mapped by gpr using the si spatial depth distribution we estimate the mean annual accumulation of superimposed ice to be 0 16 0 06 m w e a 1 locally up to 0 43 m a 1 w e this corresponds to 15 33 of the local winter balance and 5 10 of the total winter balance measured since 1987

interannual variability of the eastward current in the western south china sea associated with the summer asian monsoon the interannual variability of the eastward current in the western south china sea scs during the summer of 1993 2012 is examined with satellite altimeter data and regional ocean modeling system roms model output it is found that the meridional location of the eastward current displays apparent interannual variability the core of the eastward current shifts between 10 7 n and 17 6 n with a standard deviation of 1 6 results from sverdrup theory and roms experiments demonstrate a close dynamic linkage between the north south migration of the eastward current and the scs summer monsoon anomaly on the interannual time scale when the summer monsoon has southwesterly northeasterly anomaly the eastward current moves southward northward with the southward northward shift of the eastward current the summer cold filament in the scs moves southward northward as well

superimposed ice regime of a high arctic glacier inferred using ground penetrating radar flow modeling and ice cores 1 a 900 mhz ground penetrating radar gpr profile collected along 1 7 km of the centerline of a high arctic glacier in svalbard is interpreted using shallow ice core data and thermomechanical flow modeling four distinct zones are visible in the image and correspond to areas of firn recent and older superimposed ice and ablation zone glacier ice on the ground the areas of firn and superimposed ice are characterized by relatively steeply and gently dipping internal reflecting horizons irh respectively in the radar image the irhs arise from permittivity contrasts due to density variations produced in firn by alternating firn and ice layers and in superimposed ice by varying air bubble content recently formed and older superimposed ice can be distinguished in the gpr image a three dimensional flow model is used to indicate the long term mass balance and flow history responsible for the spatial distribution and orientation of superimposed ice irhs in the radar image results indicate that the irh distribution can only be explained by invoking a down glacier shift in mean 30 year equilibrium line altitude ela by 20 30 m compared with measured mean 30 year ela they also suggest that many of the superimposed irhs are relict features produced 100 years b p when the ela was 100 150 lower than at present this work advocates combined gpr and flow modeling as a unique tool for validating mass balance measurements and or inferring the mass balance dynamic history of a glacier beyond a recent measurement period

mesoscale eddies cases study at xisha waters in the south china sea in 2009 2010 analyzing the observed currents at xisha 110 3899 degrees e 17 1038 degrees n during may 2009 to may 2010 it is found that the kinetic energy has significant mesoscale variability and each peak responds to large positive negative ocean surface current curl caused by mesoscale eddies compared the kinetic energy with the wind stress work and the pressure work it is also found that the barotropic pressure work which is mainly contributed by the sea surface height ssh corresponding to the mesoscale eddies behaves like the kinetic energy the contribution of the mesoscale eddies to the kinetic energy can be up to 90 sometimes and reach deep level every time using the satellite altimeter data the paths of mesoscale eddies contributing to the kinetic energy variability are traced back in the winter half of the year the mesoscale eddies propagating along the northern south china sea shelf or across the basin from the west of the philippines toward xisha arrive at xisha influencing the kinetic energy in the summer half of the year the mesoscale eddies are mainly from the south which were shed from the vietnam coast current and the cause for eddy shedding may be related to the relaxation of the ekman transport anomalies

interannual variability of the surface summertime eastward jet in the south china sea the summertime eastward jet sej located around 12 n 110 e 113 e as the offshore extension of the vietnam coastal current is an important feature of the south china sea scs surface circulation in boreal summer analysis of satellite derived sea level and sea surface wind data during 1992 2012 reveals pronounced interannual variations in its surface strength ssej and latitudinal position ysej in most of these years the jas july august and september mean ssej fluctuates between 0 17 and 0 55 m s 1 while ysej shifts between 10 7 n and 14 3 n these variations of the sej are predominantly contributed from the geostrophic current component that is linked to a meridional dipole pattern of sea level variations this sea level dipole pattern is primarily induced by local wind changes within the scs associated with the el nino southern oscillation enso enhanced weakened southwest monsoon at the developing decaying stage of an el nino event causes a stronger weaker sej located south north of its mean position remote wind forcing from the tropical pacific can also affect the sea level in the scs via energy transmission through the philippine archipelago but its effect on the sej is small the impact of the oceanic internal variability such as eddy current interaction is assessed using an ocean general circulation model ogcm such impact can lead to considerable year to year changes of sea level and the sej equivalent to 20 of the observed variation this implies the complexity and prediction difficulty of the upper ocean circulation in this region

interannual mode of sea level in the south china sea and the roles of el nino and el nino modoki 1 enso scale variation of the summer ocean circulation in the south china sea scs is investigated the interannual mode of ssh features a north south dipole pattern that modulates the cold jet off vietnam during the summers before and after the el nino the mode has opposite signs of extrema strengthened circulations couple with the cold sstas during the el nino developing summers weakened circulations accompany the warm sstas during the decaying summers heat advection by the basin circulation modulates the sst variation the impact of the 1997 el nino on the scs circulation contrasting that of 1994 and 2002 el nino modoki is assessed with moderate sst warming but further westward shift of the low level convergence of the atmosphere in the equatorial pacific the el nino modoki phenomenon enhanced the western north pacific summer monsoon inside the scs driving stronger circulations in both the summers of 1994 and 2002

multiphase formation of superimposed ice during a mass balance year at a maritime high arctic glacier meteorological and snow temperature data from midtre lovenbreen spitsbergen svalbard indicate two distinct annual phases of rapid snowpack warming and superimposed ice formation in 1998 99 short periods of positive air temperatures in early winter lasting up to 36 hours and often coinciding with rainfall caused rapid glacier wide melting percolating water froze to form superimposed ice on the lower half of the glacier and wetted refrozen snow and ice lenses at higher altitudes the second period of superimposed ice formation commenced in may june 1999 and continued for 5 weeks at low altitudes and throughout the summer at high altitudes these observations at midtre lovenbreen are typical of spitsbergen glaciers and reflect the unique climatology of the region they contrast with those from glaciers in more continental climatic settings where superimposed ice formation is confined to a single period during summer there are significant implications for glacier mass balance with superimposed ice locally comprising up to 20 of winter balances and accounting for 16 25 of the annual accumulation since projected climatic warming is greatest during the winter months in arctic regions superimposed ice may become an increasingly important component of the winter and potentially the net balance of spitsbergen glaciers

kuroshio intrusion and the circulation in the south china sea 1 the princeton ocean model is used to study the circulation in the south china sea scs and its seasonal transition kuroshio enters leaves the scs through the southern northern portion of the luzon strait the annually averaged net volume flux through the luzon strait is 2 sv into the scs with seasonal reversals the inflow season is from may to january with the maximum intrusion of kuroshio water reaching the western scs during fall in compensation of summertime surface offshore transport associated with coastal upwelling from february to april the net transport reverses from the scs to the pacific the intruded kuroshio often forms an anticyclonic current loop west of the luzon strait the current loop separates near the dongsha islands with the northward branch continuously feeding the south china sea warm current scswc near the shelf break and the westward branch becoming the south china sea branch of kuroshio on the slope which is most apparent in the fall the scswc appears from december to february on the seaward side of the shelf break flowing eastward against the prevailing wind diagnosis shows that the onshore ekman transport due to northeasterly monsoon generates upwelling when moving upslope and the particular distributions of the density and sea level associated with the cross shelf motion supports the scswc

regional dynamics of seasonal variability in the south china sea abstract dynamics of the seasonal cycle of sea surface height ssh in the south china sea scs are studied using observations as well as numerical and theoretical models seasonal variability of the scs is interpreted in light of large scale dynamics and rossby waves it is found that the seasonal cycle over most of the scs basin is determined predominantly by the regional ocean dynamics within the scs the ssh variability is shown to be forced mainly by surface wind curl on baroclinic rossby waves annual baroclinic rossby waves cross the basin in less than a few months leaving the upper ocean in a quasi steady sverdrup balance an anomalous cyclonic anticyclonic gyre is generated in winter summer by the anomalous cyclonic anticyclonic wind curl that is associated with the northeasterly southwesterly monsoon in addition surface heat flux acts to enhance the wind generated variability the winter surface cooling warming cools warms the mixed layer especially in the central scs reducing

reconstruction of the historical temperature trend from measurements in a medium length borehole on the lomonosovfonna plateau svalbard a medium length ice core was drilled at the ice divide on the lomonosovfonna plateau 1230 m a s l svalbard in may1997 as part of this project temperature measurements were performed in the 120 m deep borehole at this site the ice thickness based on radar measurements is 126 5 m and the mean annual accumulation rate is 380 kg m 3 the measurements over the 15 120 m depth interval show a nearly isothermal profile with a mean value of 2 8 c and a standard deviation of 0 2 c the measurements reveal a temperature minimum at approximately 70 m depth and a temperature gradient of 0 011 0 004 c m 1 near the bottom the temperature minimum and relatively low temperature gradient cannot be explained in terms of a steady state climate numerical calculations with a simple onedimensional diffusion advection model show that the temperature increased at a maximum rate of 0 02 0 025 k a 1 over the last 100 years the total temperature increase amounting to 2 0 3 0 k forcing the model with the observed record at svalbard airport revealed that in the 19th century the surface temperature was at most 2 5 k lower and that the instrumental observations started during a period with temperatures comparable to the end of the 19th century the data are of particular interest for historical simulations since often no other temperature data are available in polar areas

mesoscale eddies in the northern south china sea a fine grid resolution model with realistic bathymetry and forcing has been developed to study the characteristics of the mesoscale eddies for the northern south china sea scs the scs model derives its open boundary conditions from a larger scale model which minimizes errors related to the uncertainty of the kuroshio intrusion at the open boundaries the model results are consistent with previous observations model sea surface height anomaly demonstrates that the hydrography and circulation in the northern scs are modulated by westward propagating mesoscale eddies originating in the vicinity of the luzon strait this explains the observed intra seasonal fluctuations at the southeast asian time series study seats station the mesoscale eddies have the same propagation speed as baroclinic rossby waves 0 1 ms 1 the periods of eddy shedding estimated from strouhal number are around 40 50 days in december and 80 120 days in august respectively the seasonal variability of the kuroshio intrusion results in more eddies in winter than in summer r 2007 elsevier ltd all rights reserved

sources of backscatter at 5 3 ghz from a superimposed ice and firn area revealed by multi frequency gpr and cores we investigate the major sources of backscatter at 5 3 ghz within the superimposed ice and firn areas of a polythermal glacier two ground penetrating radar systems an 800 mhz impulse system and a polarimetric 5 3 ghz frequency modulated continuous wave system are used to acquire along glacier profiles in the accumulation area of kongsvegen svalbard the 800 mhz response is used to map reflection horizons in the glacier using cores from the superimposed ice and firn areas the causes of these reflection horizons in terms of snow firn and ice layers are investigated superimposing the reflection horizons on the co polarized and cross polarized 5 3 ghz profile we are able to determine how the 5 3 ghz frequency responds to the different media scattering at rough interfaces and volume scattering occur in the superimposed ice area and are apparently caused by air bubble number size and distribution in the firn the strongest return originates from below the previous summer surface consistent with previous findings at approximately the same depth strong incoherent scattering begins the rapid decrease in coherent reflections indicates the significance of scattering in the firn

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

styles of sedimentation beneath svalbard valley glaciers under changing dynamic and thermal regimes glacier beds provide crucial information concerning past and present ice dynamics and thermal regime in this paper we present structural and sedimentological data from four valley glaciers austre lovenbreen midtre lovenbreen vestre lovenbreen and austre broggerbreen on broggerhalvoya nw spitsbergen the main focus of this paper is midtre and austre lovenbreen two typical high arctic land based polythermal valley glaciers the former has a long record of documentation regarding its response to twentieth century climatic warming structural mapping on the glacier surface and analysis of sediments in the proglacial area of midtre lovenbreen indicate that the dynamic regime and thermal structure of the glacier have changed through time dynamically midtre lovenbreen was once heavily crevassed and relatively fast moving but now is virtually crevasse free and slow moving the sedimentary record indicates that extensive areas of this glacier were wet based when it was in a more advanced state probably at its neoglacial maximum late nineteenth early twentieth centuries during this advance a thin deforming layer of diamicton commonly fluted was draped over the existing morphology in the presently exposed proglacial area this morphology consisted of large streamlined ridges aligned parallel to ice flow erosion of the underlying bedrock appears to have been limited radio echo soundings of the glacier show that at present it is characterized by a polythermal basal thermal regime with wet based subglacial conditions only beneath its thicker parts modification of the bed is limited under this thermal regime and as a result the supraglacial environment dominates modern sedimentation comparative studies on austre lovenbreen which also is probably polythermal indicate similar sedimentary characteristics and facies associations although here there are much more extensive areas of striated bedrock indicative of former basal sliding in contrast both austre broggerbreen and by analogy vestre lovenbreen are known to be predominantly cold based collectively these four glaciers suggest a trend of glacier recession and thinning accompanied by a change in thermal regime from predominantly wet based through partly frozen to completely frozen this study suggests that svalbard valley glaciers have several dynamic modes and that glaciers switch between these modes largely as a reaction to changes in mass balance

in situ stress orientation near the san andreas fault preliminary results to 2 1 km depth from the cajon pass scientific drillhole stress induced wellbore breakouts were analyzed in the cajon pass scientific drillhole 4 3km ne of the san andreas fault to determine the orientation of the principal horizontal stresses using borehole televiewer digitized data in the depth interval 1750 2115 m the mean orientation of the maximum horizontal stress is 073 the scatter in the orientation of breakouts is as much as 37 and variations occur with wavelengths of few hundred meters in this interval reflecting either true changes in stress orientation with depth or the variability of rock anisotropy all the measured orientations however result in left lateral shear stress resolved onto planes parallel to the san andreas fault contrary to its post miocene right lateral slip of 300 km the stress orientation is consistent however with reported left lateral displacement across the cleghorn fault 3 km northeast of and possibly subparallel to the san andreas near cajon pass since the pleistocene the cajon pass stress orientation may reflect the current state of stress across the san andreas fault in which case it should change prior to right lateral slip on this fault or a shallow local perturbation to the san andreas stress field in which case it should rotate couterclockwise with depth determination of the stress orientations at greater depths in the cajon pass drillhole will better sample the near field of the san andreas fault and help resolve this question

overview of the multi layer circulation in the south china sea abstract the south china sea scs is a semi enclosed ocean basin with its sole deepwater renewal channel in the northeast the luzon strait connected to the northwestern pacific the circulation in the scs is endowed with a distinctive multi layer structure which is influenced by the seasonally reversing southeast asian monsoon at the surface modulated kuroshio intrusion in the upper layer and enhanced diapycnal mixing and persistent luzon strait deepwater overflow in the deep layer after being diapycnally mixed by energetic internal tides internal waves and mesoscale eddies waters entering the scs in the upper and deep layers through the luzon strait are returned to the northwestern pacific in the intermediate layer this inflow outflow inflow structure in vertical induces net inflows of potential vorticity in the upper and deep layers and a net outflow of potential vorticity in the intermediate layer of the luzon strait which are believed to be closely related with the circulation structure in the scs a sandwiched circulation in the scs namely anticyclonic in the intermediate layer and cyclonic in the upper and deeper layers was recently reported but controversial issues still remain on its spatial pattern and temporal variability to ascertain this sandwiched circulation and reveal its driving mechanism is of much scientific interest to the on going discussion on the scs circulation and its role in regional climate different from previous review articles focusing on eddies or circulation in a specific layer or area we overview the full depth circulation of the scs layer by layer and outline its possible forcing mechanisms and furthermore provide perspectives for further investigation

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

the stress heat flow paradox and thermal results from cajon pass conventional friction models predict a substantial thermal anomaly associated with active traces of strike slip faults but no such anomaly is observed from over 100 heat flow determinations along 1 000 km of the san andreas fault the cajon pass well is being drilled to bring deep heat flow and stress data to bear on this paradox preliminary heat flows to 1 7 km in the neighboring arkoma well indicated a positive anomaly of about 30 as would be expected if frictional resistance of the fault were 50 mpa or so but the pliocene and pleistocene history of the transverse ranges particularly high rates of uplift and erosion could also explain the anomaly preliminary stress results from cajon pass and a new interpretation of regional data by mark d zoback and colleagues suggests that the maximum compressive stress near the fault is almost normal to the trace and hence the resolved shear stress is low and the fault weak although this is consistent with long standing evidence from low heat flow vexing questions remain regarding the physics of strike slip faulting the heat flow data show large variability with depth probably from three dimensional structure and an overall decrease from over 90 mw m in the upper kilometer to less than 80 mw m in the lower 300 m with no evidence of advective heat transfer whether this decreasing trend is significant and whether it continues downward to the background value 70 mw m less the radiogenic heat from overlying rocks as expected for a weak fault must be verified with data from greater depth

controls on the distribution of surge type glaciers in svalbard we analyzed the possible controls on the distribution of surge type glaciers in svalbard using multivariate logit models including 504 glaciers and a large number of glacial and geological attributes specifically we examined the potential effect of geological boundaries mass balance conditions and thermal regime on surging it was found that long glaciers with relatively steep slopes overlying young fine grained sedimentary lithologies with orientations in a broad arc clockwise from northwest to southeast are most likely to be of surge type no relation between lithological boundaries and surge potential could be established possible explanations for length being conducive to surging are transport distance related substrate properties distance related attenuation of longitudinal stresses and the possible relation between thermal regime and glacier size analysis of glaciers with recorded radioecho sounding reveals that a polythermal regime accumulation area ratios close to balance and a large elevation span increase the surge potential the logit models also enabled us to detect 19 new surge type glaciers to reclassify six glaciers as normal and to identify unusual surge type glaciers our model results suggest that a polythermal regime and fine grained potentially deformable beds are conducive to the surge potential of svalbard glaciers

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

evidence for subglacial ponding across taylor glacier dry valleys antarctica hubbard alun lawson w anderson b hubbard b p 2004 evidence for subglacial ponding across taylor glacier dry valleys antarctica annals of glaciology 39 1 79 84 rae2008

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

the cajon pass scientific drilling experiment overview of phase 1 the cajon pass scientific drilling project is a broad interdisciplinary experiment involving over two dozen principal scientists phase i of drilling coring and downhole experimentation began dec 8 1986 and ended april 2 1987 with the hole at a depth of 2115 m 82 m of core recovered and a wide range of downhole experiments successfully completed in this paper we briefly outline the scientific motivation for the project and provide an overview of the scientific program we also indicate some of the varied research areas in the earth sciences where data obtained in this experiment will provide unique and important insight into active in situ processes regional geologic structure and rock and fluid composition and origin

from glacier facies to sar backscatter zones via gpr we present a comparison between data acquired with frequency modulated ground penetrating radar gpr and satellite synthetic aperture radar sar both radars are polarimetric and operate at a center frequency of 5 3 ghz the field site is the polythermal glacier kongsvegen svalbard along glacier gpr profiles cover the ablation area and the accumulation area where the latter consists of superimposed ice si and firn the glacier facies are clearly identifiable on the gpr profiles although we show that the copolarized response is better for distinguishing different ice zones whereas the si firn boundary is most obvious in the cross polarized response a calibrated backscatter coefficient is calculated for the gpr data and compared with the sar backscatter coefficient the sar zones are in very good agreement with the gpr derived glacier facies we show that in the ablation area the sar response is dominated by backscatter from the previous summer surface in the si and firn areas it is dominated by sources below the previous summer surface

velocity and stress fields in grounded glaciers a simple algorithm for including deviatoric stress gradients a new and efficient algorithm for computing the three dimensional stress and velocity fields in grounded glaciers includes the role of deviatoric stress gradients a consistent approximation of first order in the aspect of ratio of the ice mass gives a set of eight field equations for the five stress and three velocity components and the corresponding boundary conditions a coordinate transformation mapping the local ice thickness on to unity and approximating the derivatives in the horizontal direction by centred finite differences yields five ordinary differential and three algebraic equations this allows use of the method of lines starting the integration with prescribed stress and velocity components at the base and a simple iteration procedure converges rapidly the algorithm can lie used for a wide range of stress strain rate relations as long as strain only depends on deviatoric and shear stresses and on temperature sensitivity tests using synthetic and realistic ice geometries show the relevance of normal deviatoric stresses in the solutions for the velocity components even for ice sheets stress and velocity fields may deviate substantially from the widely used shallow ice approximation

englacial and proglacial glaciotectonic processes at the snout of a thermally complex glacier in svalbard many glaciers in svalbard which tend to be thermally complex with both warm and cold ice produced complex push moraines or thrust moraine complexes at the time of their maximum neoglacial advance and during their subsequent recession uv rsbreen which nearly reaches the coast of northwest spitsbergen has a push moraine 50 m high comprising gravel and sand of fluvial origin and diamicton derived from basal ice as well as thrust masses of dead ice the push moraine is almost entirely a product of the tectonic processes especially thrusting that occurred in the snout of the glacier and in the frozen sediments immediately in journal of quaternary science front thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed thrusting in the foreland is an extension of the same processes that occur within the ice itself and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface subsidiary near horizontal thrusts parallel to the bedding plane link thrusts dipping up glacier and result in local thickening of individual subglacial sedimentary units gravels incorporated in this way retain their integrity but sands are folded whereas uplifted debris rich basal ice is intensely folded the distinctive tectonic style of low dip bedding in gravels truncated by high angle 30 40 thrusts and only localised folding in less competent material differs from most descriptions of such ridges but may be typical of many push moraines composed principally of fluvial material

focal mechanisms and the state of stress on the san andreas fault in southern california focal mechanisms have been determined from p wave first motion polarities for 138 small to moderate 2 6 m 4 3 earthquakes that occurred within 10 km of the surface trace of the san andreas fault in southern california between 1978 and 1985 on the basis of these mechanisms the southern san andreas fault has been divided into five segments with different stress regimes earthquakes in the fort tejon segment show oblique reverse sup on east west and northwest striking faults the mojave segment has earthquakes with oblique reverse and right lateral strikesup motion on northwest strikes the san bernardino segment has normal faulting earthquakes on north south striking planes while the banning segment has reverse strike sup and normal faulting events all occurring in the same area the earthquakes in the indio segment show strike slip and oblique normal faulting on northwest to north south striking planes these focal mechanism data have been inverted to determine how the stresses acting on the san andreas fault in southern california vary with position along strike of the fault one of the principal stresses is vertical in all of the regions the vertical stress is the minimum principal stress in fort tejon and mojave the intermediate principal stress in banning and indio and the maximum principal stress in san bernardino the orientations of the horizontal principal stresses also vary between the regions the trend of the maximum horizontal stress rotates over 35 from n15 w at fort tejon to n20 at indio except for the san bernardino segment the trend of the maximum horizontal stress is at a constant angle of about 65 to the local strike of the san andreas fault implying a weak fault the largest change in the present stress state occurs at the end of the rupture zone of the 1857 fort tejon earthquake it appears that the 1857 rupture ended when it propagated into an area of low stress amplitude possibly caused by the 15 angle between the strikes of the san jacinto and san andreas faults the strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation

rupture mechanism and interface separation in foam rubber models of earthquakes a possible solution to the heat flow paradox and the paradox of large overthrusts abstract spontaneous stick slip along the interface between stressed foam rubber blocks is a simple analog of earthquake rupture and stick slip results from this model are used to elucidate the role of normal stress variations along the interface in the stick slip process observations indicate significant normal interface vibrations and separation during slip suggesting that dynamic changes in normal stress rather than a drop in the coefficient of friction may control stick slip as suggested for example by tolstoi oden and martins and brune and co workers observations of particle trajectories indicate that stick slip shear motion is associated with various degrees of fault separation for an asymmetric model the motion is consistent with slipping motion of the type suggested by schallamach and price for a symmetric model the motion is similar to that suggested by comninou and dundurs if interface waves of this type involving separation during slip occur in earthquakes they may be a solution to the heat flow paradox since a major part of the slip occurs during separation and during low normal stress thus frictional heat generation is reduced normal interface vibrations during stick slip may explain the high corner frequency of p wave spectra and the generally high levels of p wave spectra beyond the corner frequency schallamach comninou type waves are consistent with the partial stress drop abrupt locking self healing models of brune and heaton

the mechanical paradox of large overthrusts the mechanical paradox of large overthrusts originates with a fallacious assumption in the conceptual model upon which mechanical analyses of overthrust faulting have been based the notion that the maximum width of a sheet of rock that may be displaced along an overthrust fault can be determined by using the mohr coulomb failure criterion to compare the strength of the rocks with the stress required to overcome the total frictional resistance to slip and the total cohesion or adhesion over the entire fault surface tacitly assumes that slip is initiated and occurs simultaneously over the entire fault surface this unstated and untenable assumption which is incompatible with what is known about real faults is the real explanation for the mechanical paradox a realistic model for overthrust faulting must be compatible with the nature of real overthrust faults and particularly with the way in which displacements including earthquake displacements occur on real faults most large overthrusts are discrete shear surfaces within a coherent mass of rock that is physically continuous around their ends total displacement clearly varies from place to place over these discrete shear surfaces and moreover must be the cumulative result of many relatively small incremental displacements that also varied from place to place over the finite part of the fault surface on which they occurred each increment began as a local shear failure and propagated along the fault as a smeared out somigliana dislocation at a velocity that was small considering the time required for propagation over the total area of the fault during any individual displacement event whether a megathrust earthquake or a creep event only a small part of the fault surface was in relative motion at any one time fault displacements may appear to occur simultaneously across laboratory specimens that are very small relative to the velocity of propagation of displacement because the transit time is so short when the linear scale is expanded over six orders of magnitude to encompass an entire surface of a large overthrust fault however the transit time is much longer because the velocity of propagation is very small relative to the area of the fault surface and the displacement clearly involves only a very small part of the fault surface at any one time the shape and size of overthrust faults result from the propagation of dislocations and this process is controlled by the strength heterogeneity and anisotropy of the rock mass as well as by variations in the regional stress field but not by the frictional resistance to sliding integrated over the entire fault surface

comparison of a three dimensional model for glacier flow with field data from haut glacier d arolla switzerland a three dimensional finite difference model based on a first order solution of the ice flow equations is applied to haut glacier d arolla switzerland the numerical model successfully converges at horizontal resolutions down to 70 m so a number of detailed comparisons with field data can be made modelled surface velocities with no basal sliding component are compared with surface velocities observed on the glacier over four different time periods the best fit is achieved with over winter surface velocities r 2 0 75 using a rate factor a in glen s flow law of 0 063 a 1 bar 3 surface zones of maximum computed effective stress display a high level of coincidence with observed crevassing the orientation of which is successfully predicted by the direction of the tensile component of the computed principal surface stress comparison of the relative magnitude and direction of computed principal stresses with principal strains measured at the ice surface also correspond closely in an attempt to simulate the observed annual velocity distribution within a cross section of the glacier tongue we incorporate two basal motion patterns into the model by treating net annual ice motion as a time weighted composite of three separate flow situations normal sliding enhanced sliding and no sliding we are able to reproduce the key features of the observed cross sectional ice and basal slip velocity distributions these experiments indicate there may be substantial decoupling taking place along an elongated narrow zone at the bed of haut glacier d arolla and that this decoupling interacts in a complex manner with the englacial stress and strain field

modeling south china sea circulation response to seasonal forcing regimes 1 a three dimensional ocean model has been utilized to study circulation and its seasonal variation in the south china sea scs in response to the forcing of the asian monsoon and the kuroshio intrusion the scs ocean model has a resolution of approximately 10 km horizontal spacing and 30 vertical levels with a realistic bottom topography the model is forced with time dependent wind stress and heat flux from national center for environmental prediction reanalysis data as well as with lateral fluxes from a pacific ocean model of 40 km horizontal resolution this study reports on the analysis of the mean seasonal circulation and dynamic processes in response to monsoonal wind stress the kuroshio intrusion and other intrinsic forcing processes it is found that the seasonal circulation in the scs is mainly driven by the monsoonal wind stress and greatly influenced by the inflow from the kuroshio intrusion strong currents along the continental margin of the scs form mean basin wide cyclonic and anticyclonic circulations in the winter and summer respectively multiscale eddies are embedded in the general circulation across the basin while mainstream of the kuroshio passes through the luzon strait without intruding into the scs partial intrusion occurs in the upper 200 m near the shelf margin southwest of taiwan at times when winter dynamic conditions prevail in the north scs the intrusion of the kuroshio into the scs also occurs at depths in all seasons mainly along the continental slope the coastal current separation to the east off southern vietnam and the associated eddy formations characterize the circulation in the south scs the simulated results compare well with the corresponding observed fields dynamical processes involved in the forced flow fields are investigated by examination of the momentum balances the analyses reveal that the circulation in the scs is generally dominated by the geostrophic currents north of the luzon strait positive nonlinearity in the zonal direction is locally intensified which leads to the formation of centripetal acceleration for the mainstream of the kuroshio to turn eastward the kuroshio intrusion at depths is governed by the ageostrophic flows and highly associated with the net westward pressure gradient force coastal jet separation to the east off vietnam is mainly associated with the local wind stress field and with the shelf topography in the summer and winter respectively sensitivity study reveals that the weakening of the kuroshio markedly enhances kuroshio s intrusion and forms an anticyclonic eddy west of the luzon strait

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

dynamic stress drop and rupture dynamics of the october 15 1979 imperial valley california earthquake abstract a dynamic faulting model is constructed to determine the dynamic stress drop and relative strength distribution for the october 15 1989 imperial valley earthquake and to study the dynamics of rupture propagation for this event reproduction of the kinematic quantities of the strike slip rate strike slip final offset rupture time and rupture duration bu varying the dynamic parameters of dynamic stress drop and yield strength is attempted the fault plane is discretized in 1 5 km square grids the model incorporates first order corrections for the effect of the free surface and material property heterogeneity on the calculation of rupture at depth the strike slip particle velocities final offsets and rupture durations of the kinematic model are matched within about 40 everywhere below about 5 km except in the hypocentral region and in a high displacement region 20 km north of the epicenter the strike slip rate of the dynamic model is half and rupture duration double those of the kinematic model in the epicentral region the rupture durations and strike slip final offsets are two thirds those of the kinematic model in a high stress drop region beneath the el centro crossing array two slip concentrations correspond to stress drop concentrations one of about 80 bar at 20 km from the epicenter and at 8 km depth and the other of about 70 bar at 30 km from the epicenter and 10 km depth most of the dynamic stress drop occurs between the depths of 9 and 11 km averaging about 60 bar stress drops in the 7 9 km range vary between 25 and 35 bar while stress drops in the 5 7 km depth range vary between 10 and 15 bar this depth dependence of stress drop was a consistent feature across nearly 20 km of the fault stress drop appeared to be well correlated with rock type negative stress drop was found in the sediment regions and the regions at depth while positive stress drop was found in the metasediment regions between the depths of 5 and 11 km yield strength and rupture velocity are inversely related high yield strength is found in regions of low rupture velocity and vice versa rupture was found to terminate at the northern end of the fault by collision with a high strength barrier a region of supersonic rupture velocity was found to occur in a region of high stress drop and low fracture strength the kinematic rupture velocity at the northern end of the fault was found to be unreasonably low results show that this region reaches its peak stress before the kinematic break time yield strength increased with depth in the seismogenetic zone until the base of the zone was reached below which it tapered off slightly

kuroshio intrusion into the south china sea a review the kuroshio carrying the northwestern pacific water intrudes into the south china sea scs through the luzon strait significantly affecting the temperature salinity circulation and eddy generation in the scs thus the kuroshio intrusion makes important contributions to the momentum heat and salt budgets in the scs in the past decades much work has been done on the kuroshio intrusion this paper reviews past efforts and summarizes our current understanding of the kuroshio intruding processes from observational evidence laboratory results theoretical analyses and a range of numerical model simulations in addition discrepancies between results simulated by models as well as those between simulations and observations are presented specifically this paper addresses the following topics 1 different types of the kuroshio intrusion into the scs and their identification 2 vertical structure of the kuroshio in the luzon strait 3 an overview of the luzon strait transport resulting from observations and numerical model simulations 4 seasonal and interannual variations of the kuroshio intrusion as well as eddy generation due to the kuroshio path variation and 5 dynamical mechanisms e g wind forcing interbasin pressure gradient beta effect and hysteresis potential vorticity eddy activity controlling the kuroshio intrusion into the scs finally several future research topics for gaining a better understanding of the kuroshio intruding processes are suggested c 2014 the authors published by elsevier ltd

modelling glacier response to measured mass balance forcing measurements of summer and winter mass balances have been carried out over the past 53 years on storglaciaren northern sweden repeated surveys of the glacier have resulted in several maps of surface topography as well as a map of the bed topography a new time dependent ice flow model allows us to compare the observed surface evolution of the glacier with that computed by the model using measured mass balance maps as input the computed volume change compares well with the measured change the model replicates the distribution of surface elevation to within 10 m over 30 years of integration on the model side these deviations can be attributed to the low resolution discretization of the model domain as well as to the limited accuracy of the ice rheology and omitted basal sliding on the other hand the uncertainties of the topography and mass balance maps match the model uncertainties in this sense the experiments are a validation of both model and observations

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

summer upwelling in the south china sea and its role in regional climate variations seasonal and interannual variations of summer upwelling off the south vietnam coast and the offshore spread of cold water are investigated using a suite of new satellite measurements in summer as the southwesterly winds impinge on annam cordillera a north south running mountain range on the east coast of indochina a strong wind jet occurs at its southern tip offshore east of saigon resulting in strong wind curls that are important for ocean upwelling off the coast in july and august an anticyclonic ocean eddy develops to the southeast advecting the cold coastal water offshore into the open south china sea scs the center of this cold filament is located consistently north of the wind speed maximum indicating that open ocean upwelling helps to cool the ocean surface corroborating evidence for the cold filament is found in ocean color observations that reveal a collocated tongue of high chlorophyll concentration the development of this cold filament disrupts the summer warming of the scs and causes a pronounced semiannual cycle in sst moreover the cold filament is an important player in interannual variability in the summer scs in 1998 the cold filament and mid summer cooling never took place giving rise to a strong basin wide surface warming interannual sst variance has a local maximum over the climatological cold filament and is much greater than the variance over the adjacent indian and western pacific oceans a cold filament index is constructed which displays significant lagged correlation with sst in the eastern equatorial pacific and indian oceans indicative of a teleconnection from el nino

interdecadal variability of the eastward current in the south china sea associated with the summer asian monsoon abstract based on the simple ocean data assimilation soda dataset and three types of sverdrup streamfunction an interdecadal variability of the eastward current in the middle south china sea scs during summer is identified both the pattern and strength of the summer asian monsoon wind stress curl over the scs contribute to the interdecadal variability of this current from 1960 to 1979 the monsoon intensified and the zero wind stress curl line shifted southward both the core of positive wind stress curl in the northern scs and the negative curl in the southern scs moved southward and thus induced a southward shift of both the southern anticyclonic and northern cyclonic gyres resulting in a southward displacement of the eastward current associated with these two gyres in the meantime the southern northern scs anticyclonic cyclonic ocean gyre weakened strengthened and therefore also induced the southward shift of the eastward current near the intergyre boundary in contrast the eastward cu

hydraulic fracturing in situ stress measurements to 2 1 km depth at cajon pass california stress measurements to 2 1 km reveal stress changes with depth that cannot be explained by an elastic response to uniform crustal strain the data at about 1 km depth suggest that the stress is limited by the frictional strength of rock and is perturbed at greater depths by faults which intersect the borehole the stress data indicate that there is little or no right lateral shear stress acting on planes parallel to the san andreas fault

revealing the nature of radar reflections in ice dep based fdtd forward modeling 1 successful simulation of ground penetrating radar gpr traces in polar ice is achieved by numerical finite difference time domain fdtd forward modeling properties of the modeled medium are taken from high resolution dielectric profiling dep of the upper 100 m of an ice core from dronning maud land antarctica the gpr reference trace is calculated from stacking of a normal moveout corrected common midpoint survey carried out near the borehole location the excellent agreement of synthetic and gpr based results demonstrates the capability of fdtd models to reproduce radargrams from ice core properties for interpretation of radio echo sounding data and emphasizes the exploitation of radar data for improved interpretations of glaciological climate proxys in addition to presenting modeling results we perform sensitivity experiments to investigate the nature and origin of radar reflection in ice discuss reasons for the failure of modeling studies in the past and indicate new approaches

structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard hambrey michael murray t glasser n f hubbard a 2005 structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard journal of geophysical research 110 pp 1 19 rae2008

an exceptional anticyclonic eddy in the south china sea in 2010 the highest sea level near the xisha islands in recent 20 years occurred during august 2010 satellite altimeter data indicated that the extreme event was largely due to an anticyclonic eddy whose amplitude exceeded 20 cm and size exceeded 400 km on 11 august 2010 cruise observations showed the eddy raised the center temperature by 7 7 degrees c at 75 m and vertically extended to 500 m eddy tracking showed it had a life span of more than 8 months and propagated far from the south of xisha islands such strong and long lasting eddy that moved northward for such a long distance was observed for the first time in the south china sea scs observational data from ctd xbt and the reconstructed three dimensional temperature and salinity were used to explore the eddy s features and vertical structure our analyses show the 2010 summer monsoon and current in the western boundary of the scs were largely altered after the 09 10 el nino event from may onward the wind blew northward and strengthened over the northwestern scs such wind drove a strong northward current along the western boundary which carried the eddy northward by advection from may to july energy budget showed during the eddy northward propagation the boundary current passed energy to the eddy which led to the continuing growth of the eddy in both strength and size