the somali current in autumn 1984 before the onset of the north east monsoon the somali current undergoes vigorous variations during the course of the south west monsoon although the initial phases of this response were fairly intensively studied during the fgge indian ocean experiment index in 19791 2 relatively little is known about what happens in the late summer monsoon and the transition to the winter monsoon in october 1984 we carried out measurements in the somali current regime with a shipboard acoustic doppler current profiler which showed that a continuous somali current did not exist at this time instead the cross equatorial flow with a transport of 12 l06 m3 s 1 in the upper 100 m identified by relatively low surface salinities was found to turn offshore south of 2 n between 6 and 11 n a large closed anticyclonic gyre marked by relatively high surface salinities was found with a transport of 32 106 m3 s 1 in the upper 250 m which is significantly greater than previously estimated from geostrophic calculations

free surface effects on the propagation of dynamic rupture dynamic rupture of reverse and normal fault intersecting the surface are investigated in the case of a normal fault nucleating at depth and propagating upwards coupling of rupture radiated stress and free boundary conditions at the surface may induce a shallow secondary nucleation anticipating up to a few seconds the arrival of the main rupture front indeed the free surface induces normal stress fluctuations modifying the fault frictional strength no significant effect on rupture velocity is observed in the case of reverse faulting these incidences are explained by a stress analysis and illustrated by some numerical simulations in the case of dynamic normal faulting in a homogeneous half space the described effects could explain some observations of high frequency radiation close to the surface in documented shallow earthquakes like in kalamata 1986 bouin 1994

deep crustal reflections from a vibroseis survey in northern switzerland abstract in 1982 a vibroseis survey comprising 180 km of reflection profiles was run in northern switzerland in order to investigate the suitability of the crystalline basement for the deposition of highly radioactive waste a configuration was chosen with 144 channels 25 m of geophone spacing 20 s sweeps ranging from 11 to 61 hz and stacking of 4 or 8 sweeps of 3 simultaneous vibrators at twice the geophone spacing the listening time was generally 4 s and at 4 sites it was extended to 11s for the detection of deeper crustal reflectors this survey unravelled the complicated fault and thrust system beneath the swiss folded jura mountains the stack from 4 s to 11 s reveals clearly a strong sloping reflector between 3 0 and 3 5 s which is strong evidence for a pronounced differentiation in the upper crust a series of reflections is observed between 5 8 and 7 2 s the top of which can be correlated with the conrad discontinuity a strong layered signal between 9 0 and 9 5 s is interpreted as reflections from the m discontinuity the main features are compatible with results from nearby refraction surveys in the southern rhinegraben rift system which show a distinct velocity increase of about 0 5 km s in the lower crust at a depth ranging from 15 to 20 km followed by an inversion zone or a laminated structure before reaching the moho at about 27 km depth the correlation of the field recordings with the first 10 s of the up sweep only shows some loss of resolution in the uppermost 3 s because of the lower frequency content of the signal however the lower parts of the sections are nearly identical the fact that the deeper reflectors in the sections can consistently be traced laterally is a strong argument for using this processing technique thus high coverage vibroseis surveys utilizing up sweep can be processed for deep crustal reflections even if the recording time is restricted to the standard 4 s provided the surface static corrections are carried out with high precision

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

development of the flow field during the onset of the somali current 1979 abstract during the spring and summer of 1979 a multi ship survey studied the changes in currents along the east african coast in response to the transition from the northeast to the southwest monsoon the somali current in late april and early may flowed southwestward along the coast from northern somalia to about the equator surface currents were 50 100 cm s 1 and the transport was 3 106 m3 s 1 south of the equator the east african coast current eacc flowed northward the two currents met in the vicinity of the equator and turned offshore to the southeast surface velocities in the eacc were about 200 cm s 1 and its transport in the top 100 m was 15 106 m3 s 1 with the initial onset of southerly winds in early may the somali current reversed by mid may at 3 n surface speeds of 200 cm s 1 were observed the flow did not continue up the coast but turned offshore by 4 n the second onset of the monsoon took place in mid june shortly after this surface currents 350 cm s 1 were observed at the tur

temperature dependence of oxygen isotope fractionation in coccolith calcite a culture and core top calibration of the genus calcidiscus abstract reconstructions of seawater temperature based on measurement of oxygen isotopes in carbonates mostly derive from analyses of bulk sediment samples or manually picked foraminifera the temperature dependence of 18 o fractionation in biogenic calcite was first established in the 1950s and the objective of the present study is to re evaluate this temperature dependence in coccolith calcite with a view to developing a robust proxy for reconstructing vital effect free 18 o values coccoliths the micron sized calcite scales produced by haptophyte algae that inhabit surface mixed layer waters are a dominant component of pelagic sediments despite their small size recent methodological developments allow species specific separation and thus isotopic analysis of coccoliths from bulk sediments this is especially the case for calcidiscus spp coccoliths that are relatively easy to separate out from other sedimentary carbonate grains including other coccolith taxa three strains of coccolithophores belonging to the genus calcidiscus and characterised by distinct cell and coccolith diameters were grown in the laboratory under controlled temperature conditions over a range from 15 to 26 c the linear relationship that relates 18 o fractionation to the temperature of calcification is here calibrated by the equation t c 5 83 18 o calcidiscus 18 o medium 4 83 r 0 98 the slope of the regression is offset of 1 1 from that of equilibrium calcite this offset corresponds to the physiologically induced isotopic effect or vital effect the direction of fractionation towards light isotopic values is coherent with previous reports but the intensity of fractionation in our dilute batch cultures was significantly closer to equilibrium compared to previously reported offset values no significant isotopic difference was found between the three calcidiscus coccolithophores ruling out a control of the cell geometry on oxygen isotope fractionation within species of this genus this also indicates that our culture calibration may be applied to all calcidiscus coccoliths found in the sediment we compared the culture calibration to 18 o measured from near monogeneric calcidiscus fractions separated out from core top sediments we found concordant 18 o fractionation factors for the core top calibration with a good linear coefficient r 0 94 the near monogeneric calcidiscus assemblages seem however to record slightly heaviest 18 o values compared to the data of culture study this discrepancy may be due to a possible seasonality effect on the production of calcidiscus coccoliths the uncertainty of the calibration is of similar magnitude to those of other proxies used for sst reconstruction such as foraminiferal 18 o or the alkenone undersaturation index this confirms that coccoliths can be used as a complementary or alternative substrate to foraminiferal shells for isotopic analyses comparing 18 o of coccoliths to these other sst proxies or developing an interspecific comparison of coccolith geochemistry may give insights into the carbonate chemistry of seawater through key periods of the geological record

synthetic seismograms for a complex crustal model the algorithm of the original reflectivity method has been vectorized and implemented on a cdc cyber 205 computer calculation times are shortened by a factor of 20 to 30 compared with a general purpose computer with a capacity of several million floating point operations per second mflop the rapid calculation of synthetic seismograms for complex models high frequency sources and all offset ranges is a provision for modeling not only particular phases but the whole observed wavefield as an example we model refraction data of the black forest southwest germany and are able to derive rather tight constraints on the physical properties of the lower crust

influence of dip and velocity heterogeneity on reverse and normal faulting rupture dynamics and near fault ground motions we investigate the influence of fault dip 35 60 and crustal velocity heterogeneity on rupture dynamics and near fault ground motions from normal and reverse faulting the same initial conditions were used except for the direction of initial shear stress in each dynamic rupture calculation we used two 3d elastic finite element approaches that employ split nodes for the computations in homogeneous and weakly heterogeneous half spaces with faults dipping 50 maximum fault normal peak velocities occurred on the hanging wall however for fault dips 50 maximum fault normal peak velocities occurred on the footwall bilateral and unilateral rupture simulations in weakly heterogeneous media found that reverse faulting slip velocities frequency band 1 3 5 hz were on average 39 larger than those during normal faulting however on average reverse faulting slip velocities were only 16 larger than normal faulting slip velocities for frequencies 50

processing of wide angle vibroseis data in 1984 seismic wide angle vibroseis experiments across the rhine graben in eastern france southwest germany were carried out as a joint french german venture signals generated by french vibrators were recorded at the eastern flank of the graben in the black forest with a 200 channel array spread along 16 km group spacing 80 m data were recorded at offsets between 66 and 82 km the data are characterized by a low signal to noise ratio s n and distortions of seismic phases caused by strong topographic variations for wide angle records conventional static corrections based on the assumption of vertical travelpaths are no longer appropriate ray parameter dependent time delays should be used in order to correctly eliminate topographic and near surface influences on the data in addition delineation of reflector segments requires an increase in s n a two dimensional filter based on forward and inverse slant stacking was designed to handle the time delay and s n problems simultaneously stacking al

summer monsoon response of the northern somali current 1995 preliminary results on the development of the northern somali current regime and great whirl during the summer monsoon of 1995 are reported they are based on the water mass and current profiling observations from three shipboard surveys of r v meteor and on the time series from a moored current meter and adcp array the monsoon response of the gw was deep reaching to more than 1000m involving large deep transports the northern somali current was found to be disconnected from the interior arabian sea in latitude range 4 n 12 n in both water mass properties and current fields instead communication dominantly occurs through the passages between socotra and the african continent from moored stations in the main passage a northward throughflow from the somali current to the gulf of aden of about 5 sv was determined for the summer monsoon of 1995

linked 3 d modelling of megathrust earthquake tsunami events from subduction to tsunami run up e h m t u and a a g acknowledge additional support by the german research foundation dfg projects no ga 2465 2 1 ga 2465 3 1 by bacatec project no a4 and baylat by konwihr the bavarian competence network for technical and scientific high performance computing project newwave by kaust crg gast grant no ors 2016 crg5 3027 and fragen grant no ors 2017 crg6 3389 02 by the european union s horizon 2020 research and innovation program exahype grant no 671698 cheese grant no 823844 and tear grant no 852992

the three dimensional dynamics of dipping faults recent two dimensional dynamic simulations of dip slip faulting niel sen 1998 oglesby et al 1998 2000 shi et al 1998 have shown that the asym metric geometry of dip slip faults that intersect the free surface can have large effects on the dynamics of earthquake rupture the nonvertical dip angle of such faults leads to larger motion on the footwall than the hanging wall as well as much larger motion from thrust reverse faults than from normal faults with the same geometry and stress magnitudes in the present work we perform full three dimensional simulations of thrust reverse normal and strike slip faults and show that the same effects exist in three dimensions strike slip fault motion is either in between or lower than the motion of both dip slip faults additional three dimensional effects include strong rake rotation at the free surface the results confirm the findings of the previous studies and further elucidate the dynamic effects of the free surface on fault rupture slip and ground motion they are also borne out by early analyses of the 1999 chi chi taiwan thrust earthquake which displayed higher motion on the hanging wall than on the footwall and a strong oblique component of motion at the surface

structural and rheological implications of lower crustal earthquakes below northern switzerland abstract a detailed study of the recent seismicity in the northern alpine foreland of switzerland reveals that earthquakes with magnitudes between 0 9 and 4 2 occur not only in the upper part of the crust but contrary to observations in most other intracontinental settings seismicity extends down to depths of about 30 km in the lower crust observed p wave velocities in the focal region of even the deepest earthquakes are less than 6 3 km s 1 the average value of poisson s ratio for the entire focal depth range 6 30 km lies between 0 23 and 0 24 focal mechanisms are mostly a combination of strike slip and normal faults with consistent orientations of p and t axes but without any systematic dependence on focal depth from geological observations regional strain rates are of the order of 10 13 s 1 two dimensional temperature modelling indicates that temperatures in the lower crustal seismogenic zone are well above 450 c under the assumption of a dry environment the observed p wave velocities and poisson s ratios imply either a granitic or quartz rich gneissic composition or possibly a gabbroic quartz free granulite the deformation would be governed either by the rheology of quartz or of plagioclase the onset of ductility observed in laboratory studies lies around 300 c for quartz and around 450 c for plagioclase thus conditions in the lower crust beneath northern switzerland appear to be incompatible with the occurrence of either brittle failure or plastic instabilities as is implied by the existence of earthquakes alternatively lower crustal earthquakes could be a manifestation of the presence of fluids in the lower crust fluids under near lithostatic pressure either evolved in situ from metamorphic reactions or from infiltration from the mantle would tend to decrease the effective stress on pre existing faults and thus allow brittle friction failure to occur at depths where under dry conditions or low fluid pressures only ductile deformation would be expected

shattered rock and precarious rock evidence for strong asymmetry in ground motions during thrust faulting recent thrust faulting models both physical and numerical have indicated very high ground motions on the hanging wall and relatively low motions on the footwall of thrust faults in this article recent field evidence supporting this strong asymmetry is described earlier field observations of objects thrown in the air also suggest that ground motions must have exceeded 1 g and 100 cm sec new shattered rock evidence on the hanging wall of thrust faults in southern california supports the occurrence of intense ground motions on the other hand the lack of shattered rock and the presence of precariously balanced rocks on the footwall of two thrust faults in southern california indicate relatively low ground motions thus indicating strong asymmetry in ground motions near the fault trace for thrust faults some current ground motion attenuation curves and hazard maps may give too low values on the hanging wall and too high values on the footwall this could be of critical importance to estimating earthquake hazard from potentially large thrust fault earthquakes in the los angeles basin and elsewhere in the world the new evidence also supports the idea that dynamic inertial detachment of the hanging wall from the footwall occurs in nature in the manner suggested by some recent physical and numerical models if such detachment occurs it could also have important implications for understanding thrust fault rupture mechanics for example the paradox of large overthrusts and the heat flow paradox for thrusts

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

the importance of the dynamic source effects on strong ground motion during the 1999 chi chi taiwan earthquake brief interpretation of the damage distribution on buildings the 1999 chi chi taiwan earthquake that originated on a low angle reverse fault showed complexity and uncommon characteristics the records show that the hanging wall side is characterized by larger particle motions than the foot wall and the ground motion is stronger in the northern part than in the southern part of the causative fault although the strongest ground motion occurred near the north ern part of the trace structural damage was heavier in the southern part in order to get a better understanding of the complex damage distribution caused by this earth quake the dynamic rupture process was numerically simulated because of the dif ferences between the observed features of the rupture process in the northern and southern parts of the fault each part was modeled independently by using a 2d discrete element model dem the principal results of the simulation show that the velocity ground motions in the northern part in the frequency range of 0 5 2 hz natural frequency range of standard structures are small near the surface break thus light structural damage might be predicted near the surface rupture moreover in the northern part the fault rupture propagation reaches the surface with a very slow velocity about 1 2 km sec however in the southern part the rupture propa gation reaches the surface with higher velocity about 3 0 km sec these differences between the models could explain why the ground motion near the surface rupture in the northern part caused less damage in structures than the ground motion in the southern part

tracer signals of the intermediate layer of the arabian sea in 1995 hydrographic and chlorofluorocarbon cfcs components f11 f12 measurements were carried out in the gulf of aden in the gulf of oman and in the arabian sea in the gulf of oman the f12 concentrations in the persian gulf outflow pgw at about 300m depth were significantly higher than in ambient surface water with saturations reaching 270 these high values could not be caused by air sea gas exchange the outflow was probably contaminated with oil and the lipophilic character of the cfcs could then lead to the observed supersaturations the intermediate f12 maximum decreased rapidly further east and south at the strait of bab el mandeb in the gulf of aden the red sea outflow rsw was saturated with f12 to about 65 at 400m depth and decreased to 50 while descending to 800m depth the low saturation is not surprising because the outflow contains deep and intermediate water masses from the red sea which were isolated from the surface for some time the tracer contributions to the arabian sea for indian central water icw and pgw are about equal while below 500m depth the rsw contribution greatly exceeds icw modeling the cfc budget of the arabian sea the inflow of icw north of 12 degrees n is estimated to be 1 6 sv depending mainly on the strength of the flow of red sea water into the arabian sea

seismic structure of gneissic granitic upper crust geological and petrophysical evidence from the strona ceneri zone northern italy and implications for crustal seismic exploration summary we present a stochastic seismic model of gneissic granitic upper crust by estimating the amplitude probability distribution and the autocorrelation function of the inferred seismic velocity field of the strona ceneri zone northern italy unlike previous investigations of the adjacent ivrea zone and the lewisian gneiss complex scotland the lithologies mapped in the strona ceneri zone cannot be directly correlated with laboratory measured seismic velocities the amplitude probability distribution of the extensive petrophysical database and the relatively uniform mineralogical composition of the lithologies indicate that the velocity distribution in the strona ceneri zone can be approximated as being continuous and gaussian based on this assumption and using the spatial autocorrelation function measured from a digitized geological cross section we have modelled the fine scale structure of the strona ceneri zone as a self affine medium with a fractal dimension of 2 50 0 15 and horizontal and vertical characteristic scales of 2 6 0 4 km and 1 4 0 3 km respectively on near offset shot gather seismic data strona ceneri type upper crustal heterogeneity produces a reflected field with the appearance of incoherent scattered noise characteristic of non reflective transparent upper crust found in extended phanerozoic provinces this type of heterogeneity has a considerable effect on seismic imaging of underlying reflective lower crust individual reflection segments are disrupted and shifted in time by up to several tenths of a second and the boundaries of the reflective zone become distorted and blurred at far offsets seismic scattering from heterogeneity of this type reproduces the commonly observed rapid decay and scattered distribution of pg amplitudes comparable amplitude decay patterns result from layered deterministic upper crustal velocity structures with velocity inversions

the netherlands indian ocean expedition 1992 1993 first results and an introduction the netherlands indian ocean programme was carried out with the rv tyro in the nw indian ocean the arabian sea and off kenya and the seychelles during 1992 1993 with the objective to study the effect on both spatial and temporal scales of the monsoon on the climate system in the northern indian ocean the programme included five research foci studied in different projects project a was directed towards the effects of the seasonally reversing monsoonal system on the coastal ecosystems in kenya especially to gain a clear understanding of the physical chemical and biological processes occurring in the coastal zone this includes the development of the marine flora and fauna in response to the changing conditions in the coastal zone the second project b aimed at a study of the dynamics of the pelagic system including a quantification of the carbon flux and biogeographical studies with the emphasis on distribution and taxonomy of plankton part of this project was designed as pilot project for the jgofs northwest indian ocean study carried out in 1994 95 covering most of the jgofs core measurements these studies were planned in close cooperation with the geological project c tracing a seasonal upwelling system aimed at determining the spatial and temporal variability of biological chemical and geological parameters that define an upwelling system and recognizing these in the sedimentary record as proxies for upwelling in the waters off somalia and yemen project d concentrated on two main issues the first was the late quaternary productivity and the dynamics of the oxygen minimum zone in the northeast arabian sea the second was the depositional architecture and sediment facies of the middle and lower indus fan the biology of oceanic reef systems of the seychelles formed the last project e within the netherlands indian ocean programme and was mainly directed towards biogeographical taxonomical and ecological studies of the reefs the studies comprised within these projects were and are being carried out at a range of different institutes and preliminary results were discussed at an arabian sea workshop held at nioz texel the netherlands from 13 16 february 1995 the papers in this special form the first group of results from the progamme and as a consequence the articles have a strongly variable character the first paper by kromkamp et al describes temporal and spatial variability of primary production along the kenyan coast and their relationship to the development of the cyanobacterium trichodesmium

gulf of aden eddies and their impact on red sea water 0 5 m s 1 while the equally energetic anticyclone appeared to be decoupled from the surface circulation all three eddies reached nearly to the 1000 2000 m deep sea floor with speeds as high as 0 2 0 3 m s 1 extending through the depth range of rsw comparison of salinity and direct velocity measurements indicates that the eddies advect and stir rsw through the gulf of aden anomalous water properties in the center of the anticyclonic eddy point to a possible formation site in the somali current system index terms 4520 oceanography physical eddies and mesoscale processes 4536 oceanography physical hydrography 4512 oceanography physical currents citation bower a s d m fratantoni w e johns and h peters gulf of aden eddies and their impact on red sea water geophys res lett 29 21 2025 doi 10 1029 2002gl015342 2002

evidence for the variation of stress drop between normal and thrust faulting earthquakes in italy the horizontal components of 45 strong motion accelerograms recorded in friuli italy from may to september 1976 have been analyzed in order to estimate the stress drop of eight thrust faulting earthquakes two different stress parameters the brune stress drop and the apparent stress a have been considered the friuli main shock has a strong stress drop 800 bars while the aftershocks have stress drops which range from 250 to 400 bars five accelerograms written by the montenegro yugoslavia earthquake of april 1979 have also been analyzed this thrust faulting earthquake had a stress drop of 900 bars the stress drops of these thrust faulting earthquakes are compared to the stress drops determined by rovelli et al 1988a for nine normal faulting earthquakes which occurred in the apennines region from 1979 to 1984 the radiated energies and apparent stresses have also been calculated for the set of apennine earthquakes the thrust faulting earthquakes in the alpine dynaride region exhibit higher values for both the brune and the apparent stress than the normal faulting earthquakes in the apennines region excluding the friuli and montenegro main shocks the brune stress drops of the thrust faults are approximately 3 times those of the normal faults while the apparent stresses are twice as large this difference is statistically significant at a confidence level of 95 the same difference also emerges from the scaling of the peak ground motions recorded in these two regions suggesting an enhanced severity of the seismic input in the alpine dynaride environment compared with the apennines

the great whirl observations of its seasonal development and interannual variability 1 in situ measurements are used together with sea surface height data to study the development and variability of the great whirl gw a large quasi stationary anticyclone that appears off the coast of somalia during the southwest monsoon season we find that anticyclonic circulation indicative of the gw appears on average in april almost two months before the onset of the southwest monsoon winds this early initiation is coincident with the arrival of annual rossby waves at the western boundary with the onset of the monsoon winds in early june the gw proper intensifies quickly remaining at its peak throughout july august and september and dissipating about one month after the winds have died the gw is present for an average 166 30 days per year and the position of its northern flank close to 9 n coincides with the latitude of zero wind stress curl the intraseasonal variability of the gw is intense as a result of mutual advection with one to three flanking cyclones which accompany the gw 70 of the time and tend to circulate clockwise around it there is no consistent seasonal pattern for the development or dissipation of the gw although movement to the southwest is common toward the end of the season the gw of 1995 deepened from 200 m in june to over 1000 m in september and strengthened from a swirl transport of 10 to 60 sv cool waters in its core resulted from advection via the somali current and some local vertical mixing

the complexity of the crust and moho under the southeastern superior and grenville provinces of the canadian shield from seismic refraction wide angle reflection data the major features of the individual velocity models poisson s ratio values and crustal complexity derived from the interpretation of seismic data sets from four long range seismic refraction wide angle reflection experiments are summarized the experiments were conducted from 1982 92 in the southeastern portion of the canadian shield in the conventional analysis of seismic refraction wide angle reflection data only the onset times and amplitudes of the major arrival phases are used to derive seismic velocity models of the region under study these models are over smoothed have a number of intermediate discontinuities are unable to explain the pg coda and bear very little resemblance to the models derived from the analysis of near vertical seismic reflection data in this paper some of the differences between seismic models derived from near vertical reflection analysis and those from refraction analysis are reconciled from an analysis of the wide angle reflection fields of the crustal coda wav

dynamic geometrical effects on strong ground motion in a normal fault model we report results of measurement of particle motion in a foam rubber model of normal faulting and compare the results with similar results for a strike slip geometry standard computer modeling of strong ground motion from normal fault earthquakes has used dislocation theory in which slip along the shallow part of the fault is prescribed by assuming particular time functions for fault slip unfortunately in the case of normal faults there are essentially no near fault data from large earthquakes to constrain the modeling in an extensional faulting regime the static normal and shear stresses along the fault must approach zero at the surface and thus the upper few kilometers of the fault have inherently less stored strain energy than the maximum possible for strike slip faults in addition there are dynamic effects from geometry and drop in fault normal stress which affect the fault motion physical models of faulting such as foam rubber modeling are guaranteed to obey static and dynamic mechanical laws and thus can be used to gain insight into the physical processes involved in this study we compare surface accelerations from normal fault and strike slip geometries the data show surface accelerations near the normal fault trace that are systematically lower by anmore average factor of about 0 1 compared to the accelerations at the side sensors which represent strike slip motion these results suggest that kinematic modeling of ground motion using classical dislocation techniques is inappropriate on the shallow part of the fault the results of this study are qualitatively similar to those obtained for numerical models such as a dynamic lattice model ital shi ital et al 1997 and a finite element model ital oglesby ital et al 1998 lending support to the probability that similar effects take place in the real earth copyright 1999 american geophysical union less

synoptic interpretation of seismic reflection and refraction data summary the structure of the upper lithosphere beneath southern germany northern switzerland and west central utah u s a has been investigated in detail by various geophysical methods a synoptic interpretation of travel time and amplitude data obtained in seismic refraction and wide angle reflection surveys combined with near normal incidence reflection observations now permits the elucidation of the fine structure in a more quantitative and unified manner with this scheme it is possible to unambiguously identify low velocity zones and to deduce velocity gradients if reliable amplitude information is included in the inversion process

development of near surface flow pattern and water mass distribution in the somali basin in response to the southwest monsoon of 1979 abstract near surface observations of temperature salinity and current are used to describe the seasonal reversal of the somali current during 1979 in response to the onset of the southwest monsoon winds during april prior to the reversal of the winds north of the equator the northward flowing east african coastal current eacc and the southward flowing somali current sc converged near the equator the eacc was characterized by surface waters with salinities less than 35 1 and the sc by salinities greater than 35 3 the winds reversed north of the equator during the first week of may and the boundary current intruded in the form of an anticyclonic gyre to 2 5 n most of the low salinity water was recirculated back south of the equator by the offshore limb of the gyre it did not flow continuously at the surface into the eastward equatorial jet which was present farther offshore during may and june that current was fed by high salinity water from the region to the north of the low latitude gy

defining fault avoidance zones and associated geotechnical properties using masw a case study on the springfield fault new zealand abstract the springfield thrust fault at dalethorpe west canterbury new zealand provides a test case to explore the correlation between shear wave velocities at a range of scales and direct field observations of distributed deformation and outcrop properties the springfield fault ruptures to the surface through hard torlesse greywacke overlain on a flight of late quaternary glacio fluvial terraces by 5 m of gravel fault slip has displaced all but the lowest terraces revealing the geometry and location of faulting we used multi channel analysis of surface waves and meter scale cross hole measurements to map shear wave velocities below the lowest apparently undisplaced terrace we correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory both field and laboratory results indicate that the shear wave velocity of torlesse greywacke declines sharply with increasing fracture density field surveys further indicate that relatively unweathered high velocity greywacke is being exhumed in a bivergent wedge between two opposite facing thrusts the fracturing and low shear wave velocities are focused in a wide low velocity damage zone that has developed in the hanging wall of the main thrust and a smaller but similar feature in the hanging wall of the backthrust this is consistent with the geomorphology of the site our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain this type of analysis has utility for land use planning on or close to active faults especially where they are obscured by fluvial deposits

a study of the circulation and salinity budget of the arabian sea with an isopycnic coordinate ocean model abstract the evolution of surface circulation and salinity budget are studied with the open boundary version of the miami isopycnic coordinate ocean model micom that uses a global micom simulation as a boundary condition under climatological wind and thermodynamic forcing the model develops solutions that are in good agreement with the climatologically forced global micom results and with observations when the observed winds force the model interannual variability of the surface fields increases significantly however coalescence of the two large eddies off somalia in the end of the summer monsoon suggested in earlier observations does not occur in the model to identify what processes facilitate or restrict the merger a series of experiments was performed with modified model parameters and forcing fields the eddies coalesced when half slip rather than no slip boundary conditions were used in this case less positive vorticity was produced at the coast resulting in reduced blocking effect on the propagation of the southern eddy the socotra island which is submerged in the standard model hinders a northward movement of the great whirl leading to a stronger interaction between the eddies which results in their subsequent merging a more realistic coalescence occurs in an experiment where winds are held constant after reaching the peak summer value freshwater fluxes from the east and south are important for the salinity budget in the arabian sea where evaporation exceeds precipitation the only significant cross equatorial transport of low salinity water occurs in the upper 400 m in the model most of this water is advected below the surface mixed layer at the western boundary the strongest interaction between the mixed layer and the oceanic interior occurs during the summer in the coastal upwelling regions off somalia almost half of all upwelled water comes from depths between 100 and 200 m thus signifying the importance of mid depth circulation and water mass distribution for the surface processes

the dynamics of thrust and normal faults over multiple earthquake cycles effects of dipping fault geometry we perform dynamic simulations of thrust and normal faults over multiple earthquake cycles our goal is to explore effects of asymmetric fault geometry on the long term seismicity and dynamics of dipping faults a dynamic finite element method is used to model the interseismic and coseismic processes with a dynamic relaxation technique for the former the faults are loaded by stable sliding along the downward continuation of the faults the asymmetric fault geometry of dipping faults with respect to the free surface cause changes in normal stress during the interseismic and coseismic periods these changes are of opposite sign in the two periods resulting in a stabilization of the normal and shear stresses over many earthquake cycles both faults develop relatively stable event patterns in which a large event that ruptures the entire fault is preceded by a number of small events with various rupture lengths a strong asymmetry in fault and ground motion exists between thrust and normal faults and between the hanging wall and the footwall of both faults on faults dipping less than 70 in both normal and thrust faults the horizontal component of ground motion dominates on the footwall while the vertical component dominates on the hanging wall the above results may have implications in seismic hazard analysis and building design in regions where dip slip faults predominate

a 90 kyr upwelling record from the northwestern indian ocean using a novel long chain diol index abstract presently upwelling is of major importance for driving primary productivity in the arabian sea but its intensity in the past is not well constrained here we used long chain 1 14 alkane diols specific lipids of diatoms of the genus proboscia as new proxies to reconstruct upwelling conditions in the arabian sea variations in the seasonal lipid fluxes were determined using sediment traps in the somalia upwelling system deployed 80 km off the coast on the somali continental slope niop 905 10 45 444 n 51 56 655 e at 1265 m water depth 268 m above the sea floor and 270 km off the coast in the deep somali basin south of socotra niop 915 10 43 068 n 53 34 422 e at 3047 m depth 1000 m above the sea floor highest fluxes of c 28 and c 30 1 14 diols up to almost 600 g m 2 day 1 were only observed during nutricline shoaling at the onset of the southwest monsoon swm prior to massive upwelling by contrast fluxes of c 30 1 15 diols derived from as yet undefined biological sources only increased marginally during the swm and also during the northeast monsoon nem when instead of upwelling enhanced vertical mixing led to a second productivity pulse sediment core niop 905 taken at the continental slope site showed strong fluctuations in relative concentrations of long chain 1 14 and 1 15 diols with time which we quantified as the summed concentrations of c 28 and c 30 1 14 diols divided by the summed concentrations of c 28 and c 30 1 14 diols and c 30 1 15 diols this diol index follows the same trend as other upwelling intensity records from the arabian sea that are based on sea surface temperature reconstructions organic carbon content barium aluminium ratios and abundance and stable isotope composition of specific foraminiferal species the diol index was relatively high during the holocene ca 0 7 but much lower during the late glacial maximum ca 0 2 it was generally low during the last glacial but elevated values were found during the first half of marine isotope stage 3 between 60 and 45 ka and at the end of marine isotope stage 5 1 approximately 80 ka suggesting intensified glacial upwelling our data shows that long chain diols are suitable proxies to reconstruct past upwelling intensities in the arabian sea

the conrad discontinuity and the top of the reflective lower crust do they coincide abstract in order to investigate an often quoted coincidence of an intracrustal velocity jump the conrad discontinuity and lower crustal reflections found in tectonothermally young areas 54 reflection seismic profiles have been analysed and combined with 50 refraction seismic profiles adjacent to the reflection lines such a relationship is however contradicted by the observation that in some places a reflective lower crust is found while a velocity discontinuity is missing most of the compared data sets clearly demonstrate that the velocity jump if present is found more than 2 km below the uppermost reflections from the lower crust it is thus concluded that the two phenomena are not related occasionally both a reflective lower crust rlc and a conrad discontinuity can be observed in this case the differences in depth between the two can be explained by the structure of the velocity increase as in the example of the kapuskasing uplift in canada due to the overall depth dependent increase of seismic velocity a genetic correlation of high velocity and reflectivity is negligible this conclusion is supported by the observed highly reflective lower crust of the urach low velocity body by explaining the rlc with thermorheological arguments the upper limit of reflections simply appears as a thermal boundary depending only on temperature material and fluid content the theological models presented are explaining a rlc with and without the presence of a velocity discontinuity

currents and transports of the great whirl socotra gyre system during the summer monsoon august 1993 from august 11 to 22 1993 a conductivity temperature depth acoustic doppler current profiler survey was carried out in the somali socotra region to investigate currents and transports associated with the great whirl and socotra gyre circulation during the height of the summer monsoon the monsoon circulation was confined to the upper 300 m depth with intense surface currents up to 2 2 m s 1 in the great whirl and up to 1 4 m s 1 in the socotra gyre deeper reaching flow was found in the northwestern part of the somali basin and in the passage between the shelf of somalia and abd al kuri the great whirl transport was 58 sv of which nearly 25 were due to ageostrophic flow components the northern part of the great whirl thereby appeared as a closed circulation cell in which the offshore transport was balanced by a southward transport of the same magnitude upwelled water was advected from the cold wedge of the upwelling regime at the somali coast along the edge of the gyre the water in the center of the gyre had the characteristics of indian equatorial water iew the socotra gyre carried 23 sv of modified arabian sea water asw with the transports in the two anticyclonic gyres nearly balanced the exchange of water masses between the somali basin west of the carlsberg ridge and the arabian sea occurred in two areas about 16 sv of warm and saline surface water of southern offshore origin entered the northern somali basin within a 120 km wide swift current between the great whirl and the socotra gyre the other key region for the exchange of water masses was the passage between somalia and abd al kuri there the total northward transport was 13 sv with contributions of iew of upwelled water close to the surface and asw underneath

coupling between sw monsoon related surface and deep ocean processes as discerned from continuous particle flux measurements and correlated satellite data particle flux data obtained by time series sediment traps deployed at water depths of approximately 3000 m in the western central and eastern arabian sea since 1986 were compared with wind speeds derived from measurements made by microwave radiometer flying on polar orbiting satellites and sea surface temperatures ssts provided by the physical oceanography distributed active archive center at jet propulsion laboratory this comparison has allowed us to trace the link between the oceanographic and biological processes related to the development of the sw monsoon with the pattern and interannual variability of particle fluxes to the interior of the arabian sea we could recognize the well known upwelling systems along the coasts of somalia and oman as well as open ocean upwelling at the beginning of the sw monsoon both open ocean upwelling and coastal upwelling off oman cause a cooling of surface waters at our western and central arabian sea stations when ssts fall below their long term average an increase in fluxes which are dominated by coccolithophorid derived carbonates occurs the timing of this increase is determined by the rate of surface water cooling further intensification of upwelling as the sw monsoon progresses causes additional increases in biogenic opal fluxes denoting diatom blooms in the overlying waters the total fluxes during this period are the highest measured in the open arabian sea at the central arabian sea location the fluxes are only randomly affected by these blooms the particle flux in the eastern arabian sea is as high as in the central arabian sea but is influenced by a weaker upwelling system along the indian coast the observed interannual variability in the pattern of particle fluxes during the sw monsoons is most pronounced in the western arabian sea this is controlled by the intensity of the upwelling systems on the one hand and the transport of cold nutrient poor south equatorial water into the oman region on the other the latter effect which is strongest during the sw monsoon with highest recorded wind speeds reduces the influence of upwelling and the related particle fluxes at the western arabian sea station where highest fluxes occur during sw monsoons with moderate wind speeds thus coastal and open ocean upwelling are most effective in transferring biogenic matter to the deep sea during the sw monsoons of intermediate strength

settling dissolution and burial of biogenic silica in the sediments off somalia northwestern indian ocean abstract particle fluxes of biogenic silica through the water column silica burial fluxes into the sediments and the flux of dissolved silica across the sediment water interface estimated from pore water profiles are used to assess the behaviour of biogenic silica at two stations 80 and 270 km offshore along a transect off the somali coast in the northwestern indian ocean particulate biogenic silica fluxes varied from 0 3 mmol m 2 day 1 in the non upwelling season to 6 mmol m 2 day 1 during upwelling on the somali slope fluxes were lower in the somali basin from 0 2 to 2 3 mmol m 2 day 1 evaluation of the dissolution curves derived by wet chemical leaching in sediment trap and sediment samples shows that the km values the apparent reactivity rates in alkaline medium are higher for the shallow sediment traps than for deep trap and boxcore sediments modelling of pore water profiles shows that in the sediment most dissolution occurs in the top halfcentimetre and pore water effluxes are in close agreement with those from in situ benthic incubations our results show that less than 10 of the biogenic silica arriving on the somali margin is buried in the sediments giving a burial efficiency lower than the approximately 20 reported from the open arabian sea

the volume transport of the somali current during the 1995 southwest monsoon abstract during the summer monsoon of 1995 two hydrographic and direct velocity sections were occupied over the continental shelf and slope off the coast of somalia in order to capture the flux of the western boundary current the first section was in early june just after the onset of the monsoon winds when no current was observed instead there was an anticyclonic eddy at the boundary with a small net northward transport of 3 5 1 5 sv the second section was occupied in mid september when a strong somali current was evident the resulting snapshot represents the only direct velocity section of the jet structure as it flows along the western boundary the strength of the somali current was 37 5 sv this is in general agreement with previous observations given the temporal variability of the current and represents a peak value according to contemporary model simulations the somali current of september extended far into shallow coastal waters of less than 200 m depth with speeds over 150 cm s 1 resulting in a considerable transport of 14 sv over the shelf northward flow of more than 10 cm s 1 penetrated to over 2000 m depth along the continental slope so that the subthermocline flux contributes another 13 sv to the total volume transport model simulations and satellite images of sea surface height illustrate that the somali current system exhibits large spatial variability on short timescales and thus differences in measured transports owe as much maybe more to the changing path of the current as to variability in its strength

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

abyssal circulation in the somali basin the bottom and deep circulation in the somali basin are investigated on the basis of hydrographic and direct velocity profiles from three shipboard surveys carried out during the southwest monsoon in 1995 and of velocity time series from the woce mooring array icm7 the inflow of bottom water into the somali basin through the amirante passage drives a thermohaline circulation which may be modulated by the monsoon wind forcing details of the abyssal circulation have been discussed controversially deep velocity records from the mooring array in the northern somali basin are dominated by fluctuations with periods of 30 50 days and amplitudes above full size image 1 k despite this strong variability annual record averages indicate the existence of a deep western boundary current dwbc below full size image 1 k at the base of the continental slope south of socotra island as part of a cyclonic bottom circulation the southwestward dwbc transport off socotra island is estimated to full size image 1 k the bottom and deep water exchange between the somali and arabian basin north of 7 n is estimated from two cross basin geostrophic velocity sections referenced by vertically averaged ladcp currents for the bottom water an eastward transport into the arabian basin of full size image 1 k and full size image 1 k was determined in june and august respectively while for the deep water layer above full size image 1 k eastward transports of full size image 1 k in june and full size image 1 k in august were obtained

effects of fault dip and slip rake angles on near source ground motions why rupture directivity was minimal in the 1999 chi chi taiwan earthquake we study how the fault dip and slip rake angles affect near source ground velocities and displacements as faulting transitions from strike slip motion on a vertical fault to thrust motion on a shallow dipping fault ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip the nature of the shear wave directivity is the key factor in determining the size and distribution of the peak velocities and displacements strong shear wave directivity requires that 1 the observer is located in the direction of rupture propagation and 2 the rupture propagates parallel to the direction of the fault slip vector we show that predominantly along strike rupture of a thrust fault geometry similar in the chi chi earthquake minimizes the area subjected to large amplitude velocity pulses associated with rupture directivity because the rupture propagates perpendicular to the slip vector that is the rupture propagates in the direction of a node in the shear wave radiation pattern in our simulations with a shallow hypocenter the maximum peak to peak horizontal velocities exceed 1 5 m sec over an area of only 200 km 2 for the 30 dipping fault geometry similar to the chi chi earthquake whereas for the 60 and 75 dipping faults this velocity is exceeded over an area of 2700 km 2 these simulations indicate that the area subjected to large amplitude long period ground motions would be larger for events of the same size as chi chi that have different styles of faulting or a deeper hypocenter

fault structure control on fault slip and ground motion during the 1999 rupture of the chelungpu fault taiwan the chelungpu fault taiwan ruptured in a mw 7 6 earthquake on 21 september 1999 producing a 90 km long surface rupture analysis of core from two holes drilled through the fault zone combined with geologic mapping and detailed investigation from three outcrops define the fault geometry and physical properties of the chelungpu fault in its northern and southern regions in the northern region the fault dips 45 60 east parallel to bedding in both the hanging wall and footwall and consists of a narrow 1 20 cm core of dark gray sheared clay gouge the gouge is located at the base of a 30 to 50 m zone of increased fracture density confined asymmetrically to the hanging wall microstructural analysis of the fault gouge in dicates the presence of extremely narrow clay zones 50 300 lm thick that are interpreted as the fault rupture surfaces few shear indicators are observed outside of the fault gouge implying that slip was localized within the gouge zone slip localization along a bed parallel surface resulted in a narrow gouge zone that pro duced less high frequency ground motion and larger displacements average 8 m during the earthquake than in the southern region displacement in the southern region averaged only 2 m but ground shaking consisted of large amounts of high frequency ground motion the fault in the southern region dips 20 30 at the surface and consists of a wide 20 70 m thick zone of sheared foliated shale with numerous gouge zones these data demonstrate a potential correlation between fault structure i e gouge width geometry and earthquake characteristics such as displacement and ground motion i e acceleration

monitoring the variations of the socotra upwelling system during the last 250 kyr a biogenic and geochemical approach abstract a combination of changes in the species composition of the radiolarian populations and in the sediment chemical composition content and mass accumulation rates of carbonate organic carbon and selected major and trace elements with special attention paid to ba is used to reconstruct the variations in upwelling activity over the last 250 kyr in the socotra gyre area somali socotra upwelling system nw indian ocean in the socotra gyre core md 962073 at 10 n the variations in upwelling intensity are reconstructed by the upwelling radiolarian index uri while the thermocline surface radiolarian index tsri testifies to productivity variations during non upwelling intervals despite an origin related both to marine and terrigenous inputs the geochemical records of organic carbon silica and trace elements ba p cu and zn normalized to al are controlled by the variations in surface paleoproductivity the data indicate a continuous increase in upwelling intensity during the last 250 kyr with a maximum activity within the mis 3 while high productivity periods in between the upwelling seasons occurred both during glacial and interglacial intervals a comparison of our data with published observations from another gyre of the somalian upwelling area located at 5 n in the somali gyre area shows differences regarding periods of upwelling activity and their geochemical imprint three hypotheses are proposed to explain these differences 1 changes in the planktonic community resulting in more silica rich deposits in the socotra gyre and more carbonate rich deposits in the somali gyre that are controlled by differences in the source water of the upwelling 2 a more important terrigenous input in the southern gyre and 3 a different location of the sites relative to the geographic distribution of the upwelling gyres and hydrologic fronts

dynamic rupture modeling of the m7 2 2010 el mayor cucapah earthquake comparison with a geodetic model author s kyriakopoulos c oglesby dd funning gj ryan kj abstract 2017 american geophysical union all rights reserved the 2010 mw 7 2 el mayor cucapah earthquake is the largest event recorded in the broader southern california baja california region in the last 18nyears here we try to analyze primary features of this type of event by using dynamic rupture simulations based on a multifault interface and later compare our results with space geodetic models our results show that starting from homogeneous prestress conditions slip heterogeneity can be achieved as a result of variable dip angle along strike and the modulation imposed by step over segments we also considered effects from a topographic free surface and find that although this does not produce significant first order effects for this earthquake even a low topographic dome such as the cucapah range can affect the rupture front pattern and fault slip rate finally we inverted available interferometric synthetic aperture radar data using the same geometry as the dynamic rupture model and retrieved the space geodetic slip distribution that serves to constrain the dynamic rupture models the one to one comparison of the final fault slip pattern generated with dynamic rupture models and the space geodetic inversion show good agreement our results lead us to the following conclusion in a possible multifault rupture scenario and if we have first order geometry constraints dynamic rupture models can be very efficient in predicting large scale slip heterogeneities that are important for the correct assessment of seismic hazard and the magnitude of future events our work contributes to understanding the complex nature of multifault systems

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

somali current rings in the eastern gulf of aden 1 new satellite based observations reveal that westward translating anticyclonic rings are generated as a portion of the somali current accelerates northward through the socotra passage near the mouth of the gulf of aden rings thus formed exhibit azimuthal geostrophic velocities exceeding 50 cm s are comparable in overall diameter to the width of the gulf of aden 250 km and translate westward into the gulf at 5 8 cm s ring generation is most notable in satellite ocean color imagery in november immediately following the transition between southwest boreal summer and northeast winter monsoon regimes the observed rings contain anomalous fluid within their core which reflects their origin in the equator crossing somali current system estimates of socotra passage flow variability derived from satellite altimetry provide evidence for a similar ring generation process in may following the winter to summer monsoon transition cyclonic recirculation eddies are observed to spin up on the eastern flank of newly formed rings with the resulting vortex pair translating westward together recent shipboard and lagrangian observations indicate that vortices of both sign have substantial vertical extent and may dominate the lateral circulation at all depths in the eastern gulf of aden

ground displacements around the fault of the september 20th 1999 chi chi taiwan earthquake ground displacements in the meizoseismal area of the september 20 1999 chi chi earthquake are derived from accelerograms at 39 stations on the hanging wall side a maximum horizontal nw directed motion of 8 meters and a vertical rise of 3 7 meters are found near the northern end of the n s trending surface trace of the fault on the footwall side and next to the fault a maximum horizontal motion of 1 3 meters and a maximum downward vertical motion of 1 meter are observed the displacement field describes the source as a thrust fault with left lateral motion the displacements increase from south to north along the fault and so does the left lateral component of the fault motion from about 10 to 60 of the total horizontal displacement the recorded motions especially ground velocities and accelerations are noticeably stronger on the hanging wall side than on the footwall side

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

effects of the hanging wall and footwall on ground motions recorded during the northridge earthquake abstract systematic differences in ground motion on the hanging wall and footwall during the northridge earthquake are evaluated using empirical data an empirical model for the hanging wall effect is developed for the northridge earthquake this empirical model results in up to a 50 increase in peak horizontal accelerations on the hanging wall over the distance range of 10 to 20 km relative to the median attenuation for the northridge earthquake in contrast the peak accelerations on the footwall are not significantly different from the median attenuation over this distance range recordings from other reverse events show a similar trend of an increase in the peak accelerations on the hanging wall indicating that this systematic difference in hanging wall peak accelerations is likely to be observed in future reverse events

intraseasonal variability in the southwestern arabian sea and its relation to the seasonal circulation an analysis of topex poseidon altimeter data and in situ current and temperature data obtained between april 1995 and october 1996 from a moored array shows strong intraseasonal fluctuations in the southwestern arabian sea an oceanic region where the great whirl gw a predominantly wind generated very energetic anticyclone is present during the southwest monsoon fluctuation periods between 30 and 50 days up to 100 days during some years are observed in the 8 year altimetric dataset mostly during late summer and fall these fluctuations are largest in a 1000 km wide region off the somali omani and yemeni coasts north of 5 n suggesting a local generation mechanism the in situ data at different moorings show strong and coherent fluctuations that are characterized by southwestward phase propagation and northward energy propagation their periods range from 30 to 60 days and increase steadily from july 1995 to january 1996 in the first stage these periods are at and below the cut off period of freely propagating first baroclinic mode rossby waves but approach this theoretical limit later in the year instabilities of the flow in the transition region between the southern gyre and the gw are likely sources of these fluctuations

interpretation of subhorizontal crustal reflections by metamorphic and rheologic effects in the eastern part of the pannonian basin summary the geologic origin of subhorizontal reflections often observed in crustal seismic sections was investigated by establishing metamorphic facies and strength of rocks in depth and correlating these properties to seismic reflection sections from eastern hungary estimation of the depths of metamorphic mineral stability zones utilized the principles developed by fyfe et al and known geothermal data of the area the strength versus depth profile was derived by relating local seismic p wave interval velocities to meissner et al s activation energy the results show that the series of subhorizontal reflections observed in the pannonian basin are a consequence of combined metamorphic and rheologic changes in depths the synthesis of the integrated data set suggests that the retrograde alteration of the pre tertiary basement above the percolation threshold was made possible by the softening effect of shear zones and their water conducting capacity the subhorizontal reflections of highest energy of the consolidated crust below the percolation threshold originate in the depths of greenschist amphibolite and granulite metamorphic mineral facies which were formed in geothermal and pressure conditions similar to those existing today these results imply the overprint of earlier variscan metamorphic sequences of the crust by more recent retrograde metamorphic processes

multicycle dynamics of nonplanar strike slip faults 1 we perform two dimensional dynamic models of strike slip faults with a change in strike a bend over multiple earthquake cycles to examine the long term effects of nonplanar fault geometry a viscoelastic model a proxy for off fault deformation and tectonic loading is introduced for the interseismic process to avoid pathological stress buildup around the bend a finite element method with an elastodynamic model is used to simulate dynamic earthquake ruptures we find that stresses near the bend differ strongly from the regional stress field and that the fault develops a relatively steady state in which the stress level and the event pattern on the fault are stable reduced normal stress on the dilatational side and increased normal stress on the compressive side of the bend during dynamic ruptures result in the bend serving as an initiation and or a termination point s for rupture typical events on such a fault consist of two classes unilateral events that rupture only the favorable segment and bilateral events that rupture the favorable segment and part of or the entire unfavorable segment in the latter class of events a time delay in rupture around the bend results from a high yield stress on the compressive side of the bend other effects of the bent fault geometry include higher displacement on the inward wall than on the outward wall higher slip on the more favorable segment than on the less favorable segment and a large slip velocity on the compressive side of the bend

a lithospheric cross section through the swiss alps ii constraints on the mechanical structure of a continent continent collision zone summary the calculation of strength profiles along the european geotraverse egt through the swiss alps yields constraints on the large scale vertical and lateral mechanical structure through the alpine continent continent collision zone strength profiles are evaluated for different assumptions on petrological stratification and strain rate and are based on temperature depth profiles derived from transient thermo kinematic modelling of the neoalpine orogeny the main contribution to the total strength results from the mantle lithosphere which is strongly controlled by temperature in contrast the crustal contribution is mainly determined by variations in petrological stratification a direct correlation between surface heat flow and the total strength of the crust the mantle lithosphere and the entire lithosphere crust and mantle lithosphere is not observed our results demonstrate that in tectonically active areas a transient thermal model along with detailed knowledge of the deep structure and petrology is necessary to evaluate lithospheric strength envelopes inside the collision zone strain rate has a strong control on the bottom of the mechanically strong crust whereas outside the collision zone the effect is less significant the cut off depth of seismicity along the profile which correlates largely with the bottom of the mechanically strong crust deviates from the 300 400 c isotherm the inferred effective elastic thickness for the molasse basin north of the alps is in agreement with flexural modelling results whereas for the southern alps the predictions deviate

earthquake nucleation on dip slip faults with depth dependent frictional properties 1 previous research has indicated that for dip slip faults embedded in a half space the nonvertical asymmetric fault geometry can have a significant effect on the seismic nucleation process using quasi static simulation methods and a slip weakening friction law we investigate the coupled effects of asymmetric fault geometry and depth dependent frictional properties on seismic nucleation on dip slip faults as a first order approximation to the depth dependent parameters in the earth we assume that the normal stress tapers to a small value near the free surface and we assume that the drop in frictional coefficient decreases with depth we find that these depth dependent properties have an important effect on the nucleation process of these faults compared to models with homogeneous frictional properties the nucleation point moves down dip the time to unstable slip nucleation decreases and the amount of preseismic surface slip increases significantly however these effects do not dominate the effects of the asymmetric dipping geometry of these faults on the nucleation process thrust faults nucleate farther up dip than normal faults and nucleate earlier as well normal faults have a larger amount of preseismic surface slip than thrust faults the results indicate that both geometrical and frictional heterogeneity can have important effects on nucleation and that both sources of complexity must be taken into account to produce accurate models of the seismic nucleation process

applying wedge theory to dynamic rupture modeling of fault junctions wedges such as accretionary prisms and thin skinned fold and thrust belts occur frequently in nature and can be the site of devastating earthquakes critical wedge theory can be applied to these settings but this steady state description of wedge deformation is at odds with the periodic occurrence of earthquakes we discuss how critical wedge theory applies to the seismic cycle and we use elastic wedge theory to constrain realistic stress states our goal is to determine the rupture behavior of an earthquake in a wedge if rupture initiates on the basal sliding surface will it stay confined to the basal surface or will it propagate onto a fault branch interior to the wedge this information can significantly alter the seismic hazard in areas where fault intersections occur we answer this question using numerical models of dynamic rupture propagation through branched geometries for which the stress state is a pivotal input parameter we apply wedge theory to constrain the stress state but inherent to this theory is the assumption of a weak basal fault we investigate the role of this assumption and determine that rupture is unlikely to propagate from a weak basal fault onto a strong branch fault without the aid of a physical process such as pore fluid migration along the branch this framework is applied to the rupture of the 2008 wenchuan earthquake we find that we are able to reproduce the behavior at some fault intersections but our 2d model is not able to reproduce all the behaviors possibly due to the oblique nature of this event

fault geometry and the dynamics of the 1999 chi chi taiwan earthquake the 1999 m 7 6 chi chi taiwan earthquake produced a data set of unparalleled size and quality particularly in the near source region where data have been previously quite scarce the large amount of near source data allows the verification of many predictions of thrust fault behavior for faults that intersect the surface of the earth through rigorous three dimensional dynamic models of the chi chi earthquake it can be shown that many aspects of the observed near source ground motion in this event are direct effects of the asymmetrical dipping fault geometry these effects include the hanging wall moving more than the footwall with strongly peaked velocities right at the fault trace and a transition from predominantly thrust motion in the south of the fault to largely left lateral motion in the north building on the work of oglesby and day 2001 the current work helps to delineate the effects of fault geometry nonuniform prestress and dynamic waves on the physics of the chi chi earthquake and dip slip faults in general in particular we find that a completely homogeneous prestress pattern still fits the gross features of the near source ground motion quite well additionally the strike slip component of motion near the fault trace is seen to be a combination of dynamic and static effects finally dynamic overshoot is seen to be much larger for dip slip faults than for otherwise identical vertical faults the results emphasize the necessity of rigorous models that correctly account for both the effects of fault geometry and dynamic waves in the rupture and slip processes manuscript received 31 july 2000

uplift history of thrust belts an approach based on fission track data and thermal modelization abstract a tentative method to reconstruct the uplift history in thrust belts from fission tracks ft data is proposed as it is well established that the thermal gradient varies considerably both with time and depth in the evolution of mountains a time dependent thermal model is used to infer the temperature time history of sampled rocks given parameters such as the thrust thickness 7 t and the erosion v t randomly chosen in an acceptable range among a great number of trials monte carlo simulation this technique is applied to the corsican island which is a good example of alpine thrust belt the most striking result is that a large range of different possible erosion histories can explain the same set of ft data and that further geological constraints are required to give reasonable bounds in the case of corsica information on the minimum eroded thickness and on the relative amplitude of erosion phases gives sufficient constraints on the erosion uplift history since thrusting

on the inference of absolute stress levels from seismic radiation abstract spudich p k p 1992 on the inference of absolute stress levels from seismic radiation in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 99 106 this paper determines the conditions under which it is possible to learn the absolute stress level at a subset of points on a fault from observation of the fault kinematics specifically the points on a rupturing fault can be divided into two groups those points at which the rake rotates during the rupture process and those points at which the rake does not rotate if it is true that sliding frictional traction is collinear with the instantaneous velocity of one side of a fault then at the former group of points having rotating rakes there is a unique absolute stress consistent with the motion while at the latter group of points having rakes that do not rotate the absolute stress is unspecified by the motion published dislocation solutions for the 1979 imperial valley 1986 north palm springs 1987 whittier narrows and 1989 loma prieta california earthquakes are examined for evidence of temporal rotations of rake at the hypocenters and largest asperities the 1986 north palm springs earthquake shows evidence of a possible rake rotation at the hypocenter this may imply a low absolute stress level

mesoscale eddies coastal upwelling and the upper ocean heat budget in the arabian sea estimation of the terms in the upper ocean heat budget from a moored array in the central arabian sea shows periods when a rough balance between the temperature trend and the horizontal advection of heat exists altimetry and sea surface temperature imagery are used to demonstrate that these episodes of strong horizontal advection are associated with mesoscale features during the wintertime northeast ne monsoon these are capped off mesoscale eddy features generated during the previous summertime southwest sw monsoon and have little horizontal transport of heat within the mixed layer during the sw monsoon the major contribution is strong offshore export of coastally upwelled water in a filament with a strong surface presence temperature and salinity properties from the moored array and a seasoar survey during the formation of the coastal filament confirm the offshore transport of the upwelled water mass to the site of the moored array more than 600 km offshore estimates of the filament section heat flux are several percent of the total estimated heat flux due to upwelling along the arabian peninsula and remote sensing data show that similar mesoscale variability along the coast is enhanced during the sw monsoon this points to the importance of mesoscale modulated transports in not only the observed heat budget at the moored array but in the overall upper ocean heat budget in the arabian sea

vorticity and vertical circulation at an ocean front abstract density and velocity data with 4 km horizontal resolution from a survey of a front during fasinex frontal air sea interaction experiment are combined to describe the structure of the top 300 m of the ocean the geostrophic velocity field is derived and is used to examine the relative importance of stratification relative vorticity and twisting terms in ertel s potential vorticity q tenfold isopycnic changes in q are found across a horizontal scale of only 10 km these changes are confined to isopycnals that outcrop from the seasonal thermocline into the mixed layer the ageostrophic velocity field is quantified by solution of the omega equation and vertical velocities of up to 40 m day 1 are found small 40 km surface trapped top 200 m eddies are found to play a crucial role in the transport and effective diffusion of properties across the thermocline out of the mixed layer

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

sea surface temperatures during the sw and ne monsoon seasons in the western arabian sea over the past 20 000 years abstract the western arabian sea is influenced by the seasonal southwest and northeast monsoon wind systems in the modern day sw monsoon induced upwelling of cold water leads to lowest ssts in summer while in glacial periods weakened upwelling and increased cooling by ne monsoon winds may have resulted in lowest sst in winter in order to reconstruct the western arabian sea seasonal sea surface temperature sst evolution during the monsoons over the past 20 000 years a novel proxy is used that captures the contrast in seasonal ssts the presented proxy concerns the difference in 18o between two shallow dwelling species of planktonic foraminifera globigerinoides ruber which calcifies throughout the year and globigerina bulloides which mainly calcifies during sw monsoon driven upwelling we convert this 18o difference to the difference in calcification temperature tcrub bul and use it in combination with mg ca derived temperatures to reconstruct seasonal ssts we present the monsoon evolution record of core niop929 located nw of the island of socotra based on our results we distinguish three distinct modes i a glacial monsoon mode 20 13 ka bp characterised by weakly negative tcrub bul values and sw monsoon ssts tsw that are 2 c higher than ne monsoon ssts tne this pattern is indicative for a weak sw monsoon and stronger cooling by glacial ne monsoon winds compared to the modern situation ii a transitional mode 13 8 ka bp characterised by tcrub bul values around 0 and thus a reduced difference between tsw and tne iii the modern monsoon mode which started at 8 ka bp with the main shift toward low summer ssts and high winter ssts the modern mode is characterised by tcrub bul values around 4 c indicative of a strong sw monsoon associated with strong upwelling and weak influence of the ne monsoon on sst we propose that measuring mg ca on both species will improve the accuracy of the sst estimates

rupture dynamics on a bimaterial interface for dipping faults dip slip faulting may juxtapose different geologic materials with differ ent properties such that a strong material contrast will naturally tend to form both the material contrast across a fault and dip slip motion on a nonvertical fault lead to normal stress variations during earthquake rupture this normal stress variation will significantly affect dynamic rupture propagation to demonstrate this we model dynamic rupture propagation on two dimensional 2d reverse and normal faults 30 45 and 60 dipping with 20 material contrasts for predominantly up dip rupture propagation we find that normal stress variations due to the free surface and material contrast can either reinforce or counteract each other depending on the configuration for reverse faults we find a larger strength drop for a more com pliant hanging wall and a lower strength drop for a more compliant footwall for normal faults we find a larger strength drop for a more compliant footwall and a lower strength drop for a more compliant hanging wall for both reverse and normal faults ground motion will be more symmetric between the hanging wall and footwall with compliant material on the footwall and more asymmetric if more compliant materials are on the hanging wall our results have important implications for the dynamics of crustal and perhaps subduction zone earthquake faulting where strong bimaterial contrasts across dipping faults are possible in continental settings reverse faulting will tend to advect rigid materials from greater depth onto the hanging wall such that the effects of fault dip and material contrast will counteract one another in subduction zones the hanging wall is likely to be more compliant and hence the material and geometric effects may reinforce one another

the fate of upwelled waters in the great whirl august 1995 abstract the great whirl is a large anticyclonic gyre that develops off the northern somali coast during the southwest monsoon in august 1995 the noaa ship malcolm baldrige surveyed the seaward edge of the upwelling zone associated with this gyre the fate of recently upwelled water was followed by mapping surface property distributions along a cool surface feature that extended seaward along the northern edge of the great whirl surface properties t s and chlorophyll a surface velocity adcp and xbt and ctd casts were interpreted in relation to the trajectories of three instrumented surface drifters deployed in the feature cool surface waters correspond in space to the shoaling of the upper thermocline and offshore advection from the coast surface chlorophyll a concentrations decreased from 2 to 3 g l 1 in the upwelling zone to 0 5 1 5 g l 1 in the surface feature and contiguous waters maximum surface velocities in the great whirl were 250 cm s 1 with velocities 100 cm s 1 along the northern perimeter of the gyre decorrelation time scales for u and v velocity components and chlorophyll a fluorescence from the drifters were on the order of 4 to 7 days these times are comparable to those over which the drifters were ejected from the great whirl into the socotra gyre decorrelation times for sea surface temperature were somewhat longer 10 days all three platforms passed between the somali coast and socotra within a week of their deployment and then traveled east into the northern arabian sea

sedimentation in the western arabian sea the role of coastal and open ocean upwelling monsoon induced coastal and open ocean upwelling explain 84 of the variations of the organic carbon fluxes measured in the deep western arabian sea in this paper sea level measurements satellite derived wind speeds sea surface temperatures and nutrient profiles are used to discern the relative importance of these factors on fluxes measured during nine years of continuous sediment trap deployments this exercise shows i the increase in fluxes observed during the initial stages of the sw monsoons are caused by open ocean upwelling which develops faster than the coastal upwelling ii coastal upwelling triggers diatom blooms from nutrients from subsurface water and sediment resuspension and more importantly by injecting resting stages of diatoms back into the euphotic zone iii silica depletion resulting from diatom blooms in laterally advecting water masses leads to a replacement of diatoms by other nitrate limited organisms iv organic carbon fluxes to the deep arabian sea increase in response to an intensification of both coastal and open ocean upwelling weak coastal upwelling and strong open ocean upwelling also increase organic carbon fluxes the varying dominance of their influence is reflected in the timing and the composition of the peak fluxes v the link between organic carbon flux and monsoon strength is non linear probably due to changes in the surface currents and to vigorous turbulence in the surface water during strong sw monsoons these processes could reduce the organic carbon flux in the western arabian sea by about 65

ten year recurrence time between two major earthquakes affecting the same fault segment earthquake ruptures stop when they encounter barriers impeding further propagation these barriers can theoretically originate from changes of geometry or nature of the seismic faults or from a strong lowering of the tectonic stresses typically due to the occurrence of a recent major earthquake we show here that this latter mechanism can be ineffective at stopping rupture expansion the 17 november 2013 magnitude 7 8 scotia sea earthquake has propagated into a 100 km long zone already ruptured 10 years ago by a magnitude 7 6 earthquake given the plate velocities between scotia and antarctic plates 8 9 mm yr simple recurrence models would have predicted that the segment affected by the 2003 earthquake could not be reruptured by a major earthquake during several hundreds of years this earthquake pair indicates that the variations of the tectonic stress during the seismic history of the fault are small compared to the stresses dynamically generated by a large earthquake

mesoscale dynamics in the arabian sea and a focus on the great whirl life cycle a numerical investigation using roms the great whirl gw is a persistent anticyclonic mesoscale eddy that is observed seasonally in the arabian sea during a period embedding the 3 months of the southwest monsoon june july august at a quasi steady location its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean realistic regional numerical experiments using roms are performed to investigate the life cycle of the gw which is not well resolved by sparse available in situ measurements in the region using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties including position radius depth and vorticity we i confirm the role of basin scale downwelling rossby waves in the gw generation ii clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization and iii suggest a connection between basin scale rossby wave dynamics and gw collapse

the first world catalog of earthquake rotated objects eros part ii statistical analyses and related interpretations the article presents the results of the quantitative statistical analyses of the first world catalog of earthquake rotated objects eros presented in part i of the study cucci et al 2016 we searched for possible relations between the epicentral distance of eros occurrence and a number of customary seismological observables such as magnitude intensity focal mechanism etc the reliability of results is quantitatively checked by means of some suitable statistical tests we found strong evidence of a clear log linear dependence of the epicentral distance to which an ero can be observed on the magnitude m w of the source event we note that the probability of observing eros near the epicentral area d 10 km inversely decreases with the earthquake magnitude and that for large earthquakes m w 8 this probability remains significant around 30 beyond 100 km from the epicenter unexpectedly we did not find significant relations between eros occurrence and epicentral intensity possibly because of high dispersion of intensity values the data analyzed in the present study identifies intensity 6 as the lowest intensity for rotation occurrence this is different from the main macroseismic scales which indicate the eros as a diagnostic of larger intensity degrees this outcome could suggest the need for revision and for updating the diagnostics indicated in the intensity scales as for the focal mechanisms of the seismic events we found higher probabilities of observing rotations beyond 10 km distance from the epicenter of a thrust faulting earthquake than for a normal faulting earthquake this probability reverses beyond 50 km distance especially for high magnitude seismic events our results indicate interesting insights to potential end users of the eros catalog in the fields of historical seismology and earthquake engineering

dynamics of thrust faulting 2d lattice model particle motions in a foam rubber model of shallow angle thrust faulting show many features different from those commonly assumed in dislocation models of subduction thrusts brune 1996 as a complement to a physical foam rubber experiment we have carried out dynamic simulation using a 2d lattice numerical model the model is constructed as a triangular block sliding over a rectangular elastic block it consists of a 2d set of particles interacting with each other by nonlinear hooke s forces and obeying newton s equations of motion rough surfaces are introduced on the contact plane of the two blocks to simulate realistic friction the numerical simulations demonstrate several key features of thrust faulting including stick slip fault opening and strong breakout and shaking at the hanging wall toe the wedge shaped tip of the outcropping hanging wall block of the thrust fault all consistent with the foam rubber experiments the stick slip motion shows an approximate time and slip repeatable behavior each slip event is characterized by a self healing pulse associated with fault opening and frictional locking the rupture pulse propagates steadily along the fault when rupture reaches the toe of the fault outcrop the hanging wall breaks away from the foot wall and creates a large opening vibration of the hanging wall the peak acceleration observed at the hanging wall toe of the fault outcrop is about 3 to 4 times the peak acceleration in the center part of the fault and about 2 to 3 times the motion of the foot wall such a large increase in peak acceleration at the toe is caused mainly by multiply reflecting stress waves trapped in the wedge shaped hanging wall of the fault the strong asymmetry of the particle velocity between the hanging wall and foot wall is an important feature of the results consistent with the foam rubber model but different from standard dislocation models this dynamic result illustrates the important effects of thrust faulting geometry on fault slip and ground motion

calibration of stable isotope composition of thoracosphaera heimii dinoflagellate calcite for reconstructing paleotemperatures in the intermediate photic zone in this study we investigate the temperature dependence of oxygen isotope ratios preserved in calcite formed by the dinoflagellate thoracosphaera heimii focusing primarily on the development of a geological proxy geochemical analysis of the calcite shells produced by this species represents a valuable proxy for reconstructing environmental conditions in the intermediate photic zone calibration is based on isotopic analysis from culture experiments performed in very dilute batch conditions as well as from near monospecific t heimii assemblages separated from core top sediments results are similar for both approaches and indicate that t heimii shells have oxygen isotope compositions close to equilibrium values predicted for inorganic calcite precipitation this calibration of the isotopic composition of dinoflagellate calcite indicates that monospecific assemblages of t heimii can be used to unravel paleotemperatures in the intermediate photic zone by applying isotopic transfer functions for equilibrium calcite in culture however a 18 o offset of a1 is observed at temperatures 17 c which falls below the natural temperature range of this species culture analyses also reveal a relationship between temperature and carbon isotope composition of calcite the mechanisms behind this relationship remain to be explored but their identification may provide a better understanding of carbon isotope systematics from both biogeochemical and geological perspectives comparison of the oxygen isotope composition of t heimii shells with that of shallower dwelling organisms such as the coccolithophores represents a valuable proxy for determining temperature gradients within the photic zone and may enable reconstruction of the evolution of the depth of the thermocline

the three dimensional dynamics of a nonplanar thrust fault advances in computational methodology have made it possible to ex plore the dynamics of earthquake rupture on nonplanar faults using a method that allows geometrical flexibility we simulate in three dimensions the dynamics of a fault that has an abrupt change in dip with depth using a homogeneous prestress on both fault segments we find that while the resultant final stress field is strongly influenced by the fault bend the fault slip and low frequency ground motion are relatively insensitive to the pure dynamic effects of the nonplanar fault the ground velocity from the nonplanar fault is qualitatively quite similar to that of a planar fault with the same dip angle as the nonplanar fault s shallow segment as the effects of multiple earthquakes accumulate on this fault stress concentrations at the fault bend are compounded but the effect of the free surface on the stress appears to approach a steady state the results of this study imply that for the prediction of peak ground motion from faults that intersect the surface of the earth a bend in the fault at depth may not be a significant factor the very long term effects of the fault bend are not fully determined but could lead to complexity in the rupture and slip process in future events