a high resolution record of the last deglaciation in the central mediterranean sea palaeovegetation and palaeohydrological evolution abstract a high resolution palynological and stratigraphical record of a marine deep sea core in the adriatic sea documents marine and continental palaeoenvironmental changes in the basin during the last deglaciation and early holocene a chronology is derived from the oxygen isotope stratigraphy three periods of aridity marked by the development of a semi desert rich in artemisia occurred between 18 5 and 16 kyr between 14 4 and 12 7 kyr and between 11 1 and 9 7 kyr consistent with the last glacial maximum the oldest dryas and the younger dryas they are correlated with increases in productivity and intensification of the levantine water formation in the eastern mediterranean basin during the warmer bolling allerod 12 7 11 1 kyr the presence of the cold temperate dinocyst bitectatodinium tepikiense is interpreted as indicating the establishment of a strong seasonal thermal gradient probably linked to seasonal cold freshwater runoff from the po river attested by the unique presence of pollen of freshwater plants the expansion of forest and the development of the warmer dinocysts start with termination ib during the holocene three tree phases are recognized and are contemporaneous with the preboreal boreal and atlantic chronozones of europe the two phases of sapropel deposition are marked by higher pollen and dinocyst concentrations and a high representation of brigantedinium spp which indicate higher preservation of organic material and or freshwater runoff of the po river

irregular recurrence of paleoearthquakes along the central garlock fault near el paso peaks california 1 new investigations at the el paso peaks paleoseismic site have refined and extended the record of paleoearthquakes for the central garlock fault event evidence in the form of buried fissures scarps folds and upward terminations has allowed us to identify six well resolved earthquakes designated as events w u r q k and f within the last 7000 years the exposures that we excavated did not reveal additional evidence for three poorly resolved events reported by mcgill and rockwell 1998 evidence for event y identified in the previous study was reexamined and found not to be a paleoearthquake radiocarbon dates of detrital charcoal combined with a method of interpolating the event ages with revised sedimentation rates provide our preferred constraints on the timing of faulting events the most recent surface rupturing earthquake event w occurred between a d 1450 and 1640 the penultimate event u occurred between a d 675 and 950 event r which was unrecognized in the previous study occurred between a d 250 and 475 event q occurred relatively shortly before event r between a d 25 and 275 event k occurred between 3340 and 2930 b c the oldest identified paleoearthquake event f occurred between 5300 and 4670 b c the event ages indicate that earthquake recurrence is highly irregular at the el paso peaks site with individual preferred intervals ranging from as little as 215 years to as many as 3300 years the irregular recurrence of surface rupturing earthquakes along the central garlock fault may be related to temporal and spatial clustering of earthquakes proposed for faults in the eastern california shear zone

origin of high mountains in the continents the southern sierra nevada active and passive seismic experiments show that the southern sierra despite standing 1 8 to 2 8 kilometers above its surroundings is underlain by crust of similar seismic thickness about 30 to 40 kilometers thermobarometry of xenolith suites and magnetotelluric profiles indicate that the upper mantle is eclogitic to depths of 60 kilometers beneath the western and central parts of the range but little subcrustal lithosphere is present beneath the eastern high sierra and adjacent basin and range these and other data imply the crust of both the high sierra and basin and range thinned by a factor of 2 since 20 million years ago at odds with purported late cenozoic regional uplift of some 2 kilometers

seismic and aseismic deformation associated with the 1952 kern county california earthquake and relationship to the quaternary history of the white wolf fault synthesis of geodetic geologic and seismic data from the white wolf fault california indicates that the fault separates an area of late quaternary and continuing rapid uplift in the tehachapi mountains and transverse ranges from even more rapid subsidence in the southern san joaquin valley on july 21 1952 rupture of the white wolf fault produced the ml 7 2 kern county earthquake we used the aftershock zone to delimit the size of the faulted slip surface and applied constraints imposed by the known 1952 1953 horizontal shear strains to model the measured coseismic vertical displacements with an elastic dislocation model a curved fault trace with decreasing fault depth 27 to 10 km from the surface vertically to the base slip 3 to 1 m and dip 75 to 20 from the 1952 epicenter at the southwest end of the fault toward the northeast provides the fit most consistent with the geodetic record the measured seismic moment the fault plane solution and the pattern of surface rupture two short releveled lines near the 1952 epicenter tilted 4 and 17 rad down to the north from 5 10 years before the earthquake the preseismic tilts differ significantly from ten other surveys of these lines left lateral fault crossing shear strain from 0 2 20 years before the quake was two times greater than both preseismic off fault strains and the post seismic fault crossing strains during the first seven years after the earthquake aseismic deformation was negligible from 1959 to 1972 uplift reached 160 mm over an area larger than the aftershock zone rising first in the epicentral region and then at the northeast end of the fault this was unaccompanied by any surface fault slip reconstruction of the vertical separation on the white wolf fault from late quaternary and late miocene stratigraphic marker beds shows that the rate of reverse fault slip increased forty fold from 0 1 0 2 mm yr to 3 9 mm yr between the past 10 15 m y and the most recent 0 6 1 2 m y we estimate a 170 to 450 yr average recurrence interval for earthquakes on the white wolf fault with slip equivalent to that in 1952 the 1952 earthquake appears to be characteristic of the quaternary record of fault displacement in the increase in white wolf slip toward the san andreas fault the ratio of reverse to lateral slip 1 3 1 and the ratio of vertical fault slip to emergence of the hanging wall block 3 1 the 8500 m deep sedimentary basin on the down thrown block cannot be explained by repeated slip of the white wolf fault in an elastic medium

three dimensional crustal structure of the southern sierra nevada from seismic fan profiles and gravity modeling traveltime data from the 1993 southern sierra nevada continental dynamics seismic refraction experiment reveal low crustal velocities in the southern sierra nevada and basin and range province of california 6 0 to 6 6 km s as well as low upper mantle velocities 7 6 to 7 8 km s the crust thickens from southeast to northwest along the axis of the sierra nevada from 27 km in the mojave desert to 43 km near fresno california a crustal welt is present beneath the sierra nevada but the deepest moho is found under the western slopes not beneath the highest topography a density model directly derived from the crustal velocity model but with constant mantle density satisfies the pronounced negative bouguer anomaly associated with the sierra nevada but shows large discrepancies of 50 mgal in the great valley and in the basin and range province matching the observed gravity with anomalies in the crust alone is not possible with geologically reasonable densities we require a contribution from the upper mantle either by lateral density variations or by a thinning of the lithosphere under the sierra nevada and the basin and range province such a model is consistent with the interpretation that the uplift of the present sierra nevada is caused and dynamically supported by asthenospheric upwelling or lithospheric thinning under the basin and range province and eastern sierra nevada

the phytoplankton bloom in the northwestern arabian sea during the southwest monsoon of 1979 the biological variability of the northwestern arabian sea during the 1979 southwest monsoon has been investigated by the synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets and the results of wind driven modeling of upper ocean circulation the phytoplankton bloom in the northwestern arabian sea peaked during august september extended from the oman coast to about 65 e and lagged the development of open sea upwelling by at least 1 month in total the pigment distributions hydrographic data and model results all suggest that the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the arabian coast was limited to the continental shelf in the promotion of high concentrations of phytoplankton upward ekman pumping to the northwest of the somali jet axis stimulated the development of a broad open sea phytoplankton bloom oceanward of the oman shelf vertical mixing during the 1979 southwest monsoon was apparently not a primary cause of the regional scale phytoplankton bloom

the structure of near inertial waves during ocean storms abstract current meter data from two sites were analyzed for near inertial motions generated by storm during the ten month period of the ocean storms experiment in the northeast pacific ocean the most striking feature of the inertial wave response to storms was the almost instantaneous generation of waves in the mixed layer followed by a gradual propagation into the thermocline that often lasted many days after the initiation of the storm the propagation of near inertial waves generated by three storms in october january and march was studied by using group propagation theory based on the wkb approximation it was found that wave frequencies were slightly superinertial with inertial shifts 1 3 in october and march and around 1 in january the phase of near inertial currents propagated upward below the mixed layer confirming the downward radiation of energy by these waves the average downward energy flux during the storm periods was between 0 5 and 2 8 mw m 2 the vertical wavelengths indicated

paleoproductivity in the equatorial indian ocean for the last 260 000 yr a transfer function based on planktonic foraminifera a principal component analysis pca of planktonic foraminifera in surface sediment of the northern equatorial indian ocean defines two major assemblages the first one dominated by globigerinoides sacculifer g ruber globigerinella aequilateralis and globoquadrina conglomerata characterizes non upwelling areas the second dominated by globigerina bulloides g falconensis and globigerinita glutinata characterizes upwelling areas the distribution of planktonic foraminiferal species in the area is mainly related to primary production pp the pca applied to core md 900963 samples defines an alternation of the two assemblages through time a non upwelling one similar to that present in the core tops and an upwelling assemblage which contains in addition neogloboquadrina dutertrei globorotalia menardii and g crassaformis equatorial indian ocean core top samples are introduced as additional rows in the pca calculated on core md 900963 samples and a transfer function is constructed correlating factorial coordinates of core tops within the range of changes occurring in core md 900963 with estimated pp values applied to the last 260 000 yr the transfer function indicates that the precession is the major orbital forcing on equatorial productivity changes and that annual pp increases by about 85 from interglacial to glacial interstadials these results are in agreement with an independent productivity index based on coccoliths direct impact of insolation on equatorial productivity could be explained by the link between southern oscillation and intensity of zonal winds which seem to lead the productivity of surface waters at the location of core md 900963

a solar irradiance trigger for millennial scale abrupt changes in the southwest monsoon 1 marine sedimentary records of the last glacial from tropical monsoon latitudes indicate climate fluctuations comparable to rapid changes in 18o recorded in greenland synchronizing two high resolution sedimentary records from the oman and pakistan margins we resolve millennial scale reversals in sea surface temperature sst gradient sst across the arabian sea which directly correspond with the majority of dansgaard oeschger d o events for the last 65 kyr the relative amplitude of individual monsoon and d o events appears comparable suggesting coupled and at least hemispheric forcing to explore this quasi cyclic forcing we compare alkenone based geologic data with modern satellite derived sst estimates between sites interstadial conditions fall within the range of monsoons during the holocene but stadial conditions have no analogs following published associations between eurasian winter snow cover ewsc and monsoon rainfall and el nino southern oscillation enso events and anomalous ewsc we find a good correlation between the southern oscillation index soi and arabian sea sst throughout the modern data set an apparent 11 year cyclicity in the soi reveals an association between the monsoon soi and solar output variability the soi primarily tracks solar total irradiance but the soi monsoon linkage becomes nonlinear during excursions of the soi associated with el nino events strong el ninos coincide precisely with minimum solar irradiance during the solar cycle which we attribute to threshold behavior in tropical pacific ssts and associated trade wind strength we propose that both short term interannual decadal and long term centennial millennial changes in solar output are consistent with records of enso variability monsoon intensity and d o event timing

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

geochemical implications of the lipid composition of thioploca spp from the peru upwelling region 15 s thioploca a genus of colorless sulphur oxidizing filamentous bacteria constitutes as much as 80 of the biomass in dysaerobic surface sediments o2 0 1 ml l bottom water in the coastal upwelling regimes of peru and chile the lipid composition of thioploca collected from sediments from the oxygen minimum zone in the peru upwelling region near 15 s is presented here and we provide the first assessment of the influence of thioploca on organic compound distributions in upwelling regime sediments since marine species of thioploca have been found only in dysaerobic surface sediments of upwelling regimes biomarkers for this organism may be useful in identifying similar depositional conditions in the sedimentary record thioploca dry was found to be 3 8 4 1 wt lipid three fatty acids cis 16 1 9 16 0 and cis 18 1 11 accounted for 69 72 of this lipid hydroxy fatty acids hopanoids and hydrocarbons were conspicuously absent from the thioploca the thioploca was found to contain cyclolaudenol a c31 sterol with an unusual structure diagenetic alteration products of this sterol may serve as markers for thioploca input to sedimentary organic matter and hence as markers for paleo upwelling depositional environments in the sedimentary record

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

tropical sea surface temperatures during the last glacial period a view based on alkenones in indian ocean sediments abstract the quantification of tropical temperatures during the last glacial cycle 0 150 kyr bp is a controversial issue since different proxies seem to provide conflicting informations to obtain a complementary point of view we use the alkenone method to estimate sea surface temperatures and focus our work on deep sea sediments recovered from the tropical indian ocean we present alkenone data obtained in two cores which cover in detail the last deglaciation and in about twenty cores distributed between 20 s and 20 n that were chosen to evaluate the temperature contrast of the last glacial interglacial transition our results indicate that indian ocean tropical temperatures remained an average within 1 5 2 5 c of their present values during the last glaciation at 10 n the last deglaciation is characterized by two warming steps which is similar to the classical deglacial chronology observed in the north atlantic area at 20 s the deglacial warming occurred at ca 15 cal kyr bp lagging significantly 5 4 kyr behind the antarctic warming but in phase with northern hemisphere time series

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

coulomb stress models for the 2019 ridgecrest california earthquake sequence abstract we present a coulomb stress analysis for the july 4th mw 6 4 and july 5th mw 7 1 earthquakes of the 2019 ridgecrest california earthquake sequence we find that the coulomb stress on the mw 6 4 rupture plane was increased by the 1872 owens valley earthquake and slightly increased by the 1952 kern county earthquake like wise the rupture plane of the july 5th mw 7 1 earthquake was promoted by both the owens valley and kern county earthquakes as well as being promoted slightly by the 1992 landers earthquake and the 1999 hector mine earthquake to investigate the regional coulomb stress change from the ridgecrest earthquake sequence we calculate coulomb stress change on nearby faults from both the mw 6 4 and mw 7 1 earthquakes we find that the mw 6 4 earthquake promoted failure at the epicen ter of the mw 7 1 earthquake which struck 34 h later furthermore the mw 6 4 and mw 7 1 ridgecrest earthquakes increased coulomb stress on the garlock fault to the west of the rupture and decreased coulomb stress to the east the panamint valley fault was relaxed by the ridgecrest earthquakes the most significant stress change is an increase of coulomb stress to the south of the ridgecrest sequence on the nearby blackwater fault the blackwater fault situated between the lan ders and ridgecrest earthquakes was loaded significantly by the mw 7 1 ridgecrest earthquake up to 0 12 mpa and by lesser amounts by the landers and hector mine earthquakes of the known active faults in the region including the garlock fault the blackwater fault appears to have been loaded the most by the ridgecrest earth quakes

impact of oceanic reorganizations on the ocean carbon cycle and atmospheric carbon dioxide content a zonally averaged circulation biogeochemical ocean model is used to explore how the distribution of po4 and 13c in the major basins and the atmospheric pco2 respond to rapid changes in the thermohaline circulation thc different evolutions of the atlantic thc are simulated by applying surface freshwater pulses typical for example of heinrich events and the last deglaciation in the model when the thc completely collapses po4 increases 0 5 mmol m 3 and 13c decreases 1 because of a longer residence time of waters at the surface these surface anomalies are propagated to the bottom north atlantic when the thc resumes when the thermohaline overturning is only partly reduced and at shallower depths changes in bottom waters are accompanied by a po4 decrease and 13c increase at intermediate levels in the mid latitude atlantic this results in enhanced vertical gradients of these properties consistent with chemical and isotopic reconstructions for the last glacial maximum finally the atmospheric pco2 increases during the cold period in the north atlantic when the thc is reduced with an amplitude 7 30 atm and timescale 10 to 1 2 10 yr depending on the intensity of the thc change this is qualitatively consistent with recent data from an antarctic ice core documenting a pco2 increase during the younger dryas and after heinrich events 4 and 5

source parameters for the 1952 kern county earthquake california a joint inversion of leveling and triangulation observations coseismic leveling and triangulation observations are used to determine the faulting geometry and slip distribution of the july 21 1952 mw 7 3 kern county earthquake on the white wolf fault a singular value decomposition inversion is used to assess the ability of the geodetic network to resolve slip along a multisegment fault and shows that the network is sufficient to resolve slip along the surface rupture to a depth of 10 km below 10 km the network can only resolve dip slip near the fault ends the preferred source model is a two segment right stepping fault with a strike of 51 and a dip of 75 sw the epicentral patch has deep 6 27 km left lateral oblique slip while the northeastern patch has shallow 1 12 5 km reverse slip there is nearly uniform reverse slip epicentral 1 6 m northeast 1 9 m with 3 6 m of left lateral strike slip limited to the epicentral patch the seismic moment is m0 9 2 0 5 1019 n m mw 7 2 the signal to noise ratio of the leveling and triangulation data is reduced by 96 and 49 respectively the slip distribution from the preferred model matches regional geomorphic features and may provide a driving mechanism for regional shortening across the comanche thrust and structural continuity with the scodie seismic lineament to the northeast

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

deep sea corals off brazil verify a poorly ventilated southern pacific ocean during h2 h1 and the younger dryas abstract simultaneous 14 c and th u dating of deep sea corals are useful for reconstructing the intensity of deep ocean circulation in the past as they deliver the time between the gas exchange of the water with the atmosphere and the incorporation of the 14 c in the carbonates adkins and boyle 1997 adkins et al 1998 mangini et al 1998 th u ages of deep sea corals sampled in sediment cores from locations off the coast of brazil bathed by antarctic intermediate water at depths between 600 and 800 m group close to heinrich events h2 h1 and the younger dryas the 14 c of the water bathing the corals starts to decrease approximately 2 kyr before the heinrich events and decreases to values 400 lower than the corresponding back tracked atmospheric values the timing and the magnitude of the decrease is similar to that observed in intermediate water in the n pacific off baja california marchitto et al 2007 and in the eastern pacific stott et al 2009 high ventilation ages partly exceeding 4000 years are an unambiguous indication for a reduction of north atlantic deep water formation during h2 h1 and the yd as deduced from higher 231 pa 230 th activity ratios and from end in n atlantic ocean sediments mcmanus et al 2004 pahnke et al 2008 yu et al 1996 they also could indicate a poorly oxygenated southern pacific ocean at the end of the heinrich events

on the sources formation and circulation of red sea deep water red sea deep water is renewed from sources in the far north of the red sea upwelling of deep water throughout the basin maintains the sharp pycnocline with its base near the depth of the sill at bab el mandeb before now deep water renewal was thought to occur mainly by means of convective deep water formation in the north which renews the bottom water and gives rise to a southward flowing bottom current carbon 14 and 3he data from the geosecs indian ocean expedition lead to the identification of an additional volumetrically larger mode of northern deep water formation in which new deep water is injected immediately beneath the pycnocline this mode of deep water formation to be called the isopycnal mode also gives rise to a southward flowing current in this case at the top of the deep water mass geosecs data also demonstrate the existence at intermediate depths in the deep water of a return flow to the north the surface history in the nuclear era of the 14c in the deep water source region was reconstructed by direct radiocarbon measurements on annual growth bands of corals calculation then shows that new deep water forms in the convective mode at a rate of 0 05 0 01 sverdrup sv expressed as if the flow were continuous and is due principally to processes occurring in the mouth of the gulf of suez the injection beneath the pycnocline of new deep water formed in the isopycnal mode is 0 11 0 02 sv this new deep water appears to originate mainly in the extreme open northern red sea the gulf of aqaba makes a modest but significant contribution to both modes the total deep water renewal rate is about 0 16 sv yielding a bulk deep water residence time of about 36 years oxygen consumption in the deep water shows approximately exponential decrease of consumption rate with depth as expected on geological and geophysical grounds hydrographically significant fluxes of heat and salt from the sea floor into the red sea deep water are discernible in the hydrography helium 3 flux from the sea floor into the deep water is about 69 1 stp year

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

deep circulation change linked to heinrich event 1 and younger dryas in a middepth north atlantic core a core from the mid atlantic ridge at 43 5 n and 3 km water depth shows distinct evidence of the deglacial events known as heinrich event 1 probably the marine equivalent of oldest dryas cooling in europe and the younger dryas the heinrich event dated at three levels to between 14 3 and 15 0 ka is marked by a minimum in foraminifera per gram by maxima in rates of sedimentation ice rafted debris per gram and relative abundance of n pachyderma s and by a 18o minimum in planktonic foraminifera the younger dryas event is marked by peak abundance of n pachyderma s and a planktonic 18o maximum benthic foraminiferal 13c reaches minimum values during both the heinrich event and the younger dryas our data indicate pronounced changes in surface water properties were coupled with reduced production of north atlantic deep water at each of these times

foreshock migration preceding the 2016 mw 7 0 kumamoto earthquake japan we investigated the spatiotemporal evolution of an earthquake sequence following a series of large shallow intraplate earthquakes including a mw 6 2 foreshock and mw 7 0 main shock in the kumamoto area of kyushu sw japan to more precisely characterize the evolution of the earthquake sequences we applied a matched filter technique to continuous waveform data using template events obtained via a double difference relocation algorithm migrations of seismicity fronts along the directions of fault strike and dip are clearly seen starting immediately after the mw 6 2 foreshock these migrations are interpreted to result from aseismic slip triggered by the foreshock propagating toward the nucleation point of the subsequent mw 7 0 main shock rupture when combined with static stress changes induced by the mw 6 2 foreshock it is likely that stress transfer from both aseismic and seismic slip during the foreshock sequence loaded stress onto the main shock rupture faults bringing them closer to failure

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

sedimentary pigments and nature of organic matter within the oxygen minimum zone omz of the eastern arabian sea indian margin abstract sedimentary pigments carbon and nitrogen content and their stable isotopes were studied in three short cores collected from the oxygen minimum zone omz of the eastern arabian sea eas nine pigments including chlorophyll a and their degradation products were quantified using high performance liquid chromatography hplc astaxanthin followed by canthaxanthin and zeaxanthin were the major carotenoids detected in these cores the total pigment concentration was high in the core collected from 500 m water depth 6 5 gg 1 followed by 800 m 1 7 gg 1 and 1100 m 1 1 gg 1 depths respectively the organic carbon did not have considerable control on sedimentary pigments preservation pigment degradation was comparatively high in the core collected from the 800 m site which depended not only the bottom dissolved oxygen levels but also on the faunal activity as reported earlier the bottom water dissolved oxygen and presence of fauna have good control on the organic carbon accumulation and preservation at indian margin omz sediments the c n ratios and 13 c values for all the cores conclude the marine origin of organic matter and 15 n profiles revealed signature of upwelling associated denitrification within the water column

coulomb stress evolution in a diffuse plate boundary 1400 years of earthquakes in eastern california and western nevada usa diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates these characteristics make it difficult to understand the spatial and temporal distribution of seismicity the area east of the sierra nevada between longitudes 121 degrees w and 116 degrees w is part of a diffuse plate boundary at least 17 major surface rupturing earthquakes have happened here in the last 1400 years our purpose is to determine whether these events influence each other or whether they are randomly distributed in time and space we model the evolution of coseismic and postseismic coulomb failure stress changes delta cfs produced by these earthquakes and we also model interseismic stresses on the entire fault network our results show that 80 of the earthquake ruptures are located in areas of combined coseismic and postseismic delta cfs 0 2 bar this relationship is robust as shown by the control tests that we carried out using random earthquake sequences we also show that the fish lake valley pyramid lake and honey lake faults have accumulated 45 37 and 27 bars respectively of total delta cfs i e coseismic postseismic interseismic in the last 1400 years such values are comparable to the average stress drop in a major earthquake and these three faults may be therefore close to failure

sampling the oxygen minimum zone off pakistan glacial interglacial variations of anoxia and productivity preliminary results sonne 90 cruise during cruise sonne 90 the well developed oxygen minimum zone omz in the northeastern arabian sea was sampled in great detail to study surface ocean productivity and organic carbon accumulation preservation during the last hundred to hundred thousands of years nearly anoxic conditions on and below the seafloor are indicated by the lack of macrobenthos and nekton absence of bioturbation high marine organic carbon accumulation and preservation of laminated sediments between about 300 and 1000 m water depth on the steep continental slope this pattern approximately coincides with the zone of extremely low o2 concentrations presently observed in the water column accumulation of organic material on the deeper slope near the lower boundary of the omz is enhanced by downslope transport downcore we observe a complex alternation of dark colored laminated and light colored homogeneous facies in general laminated organic carbon rich intervals were deposited under suboxic bottom water and enhanced productivity conditions mainly during warm stages e g bolling allerod and holocene from 8000 yrs b p to recent the homogeneous bioturbated intervals indicate normal bottom water oxygen levels and reduced productivity during or just after cold stages e g terminations ia and b and younger dryas the striking facies similarities of the sedimentary record in cores collected from different areas and water depths suggest a unique pattern of late pleistocene corg accumulation in the northeastern arabian sea which depends mainly on regional surface ocean productivity and intermediate water oxygenation however the sedimentary record is also influenced by variations in sediment supply from the makran and karachi shelf and from indus river discharge during rapid sea level changes

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

in the shadow of 1857 the effect of the great ft tejon earthquake on subsequent earthquakes in southern california the great 1857 fort tejon earthquake is the largest earthquake to have hit southern california during the historic period we investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake when post 1857 earthquakes with unknown focal mechanisms were assigned strike slip mechanisms with strike and rake determined by the nearest active fault 13 of the 13 southern california m 5 5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture when post 1857 earthquakes in the transverse ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike slip 11 of the 13 earthquakes were encouraged by the 1857 earthquake these results show significant correlations between static stress changes and seismicity patterns the correlation disappears around 1907 suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century

inception of the eastern california shear zone and evolution of the pacific north american plate boundary from kinematics to geodynamics 1 the san andreas fault saf is the transform boundary between the pacific and the north american plates yet up to 25 of the relative plate motion is now accommodated by the eastern california shear zone ecsz here we investigate the inception of the ecsz and its geodynamic interactions with the saf using a 3 d viscoelastoplastic finite element model for a given fault configuration of the plate boundary zone the model simulates long term slip on the faults and plastic strain outside the faults our results show that the formation of the big bend of the saf around 5 12 ma impeded fault slip and localized strain along the ecsz causing its inception development of the ecsz was further enhanced by the activation of the garlock fault gf and lithospheric weakening caused by the encroachment of the basin and range extension similarly the san jacinto fault sjf in southern california developed along a belt of localized strain which resulted from the formation of the restraining bend along the san bernardino mountains segment of the saf 2 myr ago once activated the sjf reduced slip on both the southern saf and the ecsz across the mojave desert these results indicate causative relationship between the saf and the ecsz the inception of the ecsz and other young faults is the consequence of the evolving saf plate boundary zone that continuously adjusts itself to accommodate the relative plate motion

refining the shallow slip deficit geodetic slip inversions for three major m w 7 strike slip earthquakes 1992 landers 1999 hector mine and 2010 el mayor cucapah show a 15 60 per cent reduction in slip near the surface depth 2 km relative to the slip at deeper depths 4 6 km this significant difference between surface coseismic slip and slip at depth has been termed the shallow slip deficit ssd the large magnitude of this deficit has been an enigma since it cannot be explained by shallow creep during the interseismic period or by triggered slip from nearby earthquakes one potential explanation for the ssd is that the previous geodetic inversions lack data coverage close to surface rupture such that the shallow portions of the slip models are poorly resolved and generally underestimated in this study we improve the static coseismic slip inversion for these three earthquakes especially at shallow depths by 1 including data capturing the near fault deformation from optical imagery and sar azimuth offsets 2 refining the interferometric synthetic aperture radar processing with non boxcar phase filtering model dependent range corrections more complete phase unwrapping by snaphu statistical non linear approach for phase unwrapping assuming a maximum discontinuity and an on fault correlation mask 3 using more detailed geologically constrained fault geometries and 4 incorporating additional campaign global positioning system gps data the refined slip models result in much smaller ssds of 3 19 per cent we suspect that the remaining minor ssd for these earthquakes likely reflects a combination of our elastic model s inability to fully account for near surface deformation which will render our estimates of shallow slip minima and potentially small amounts of interseismic fault creep or triggered slip which could make up a small percentages of the coseismic ssd during the interseismic period our results indicate that it is imperative that slip inversions include accurate measurements of near fault surface deformation to reliably constrain spatial patterns of slip during major strike slip earthquakes

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

geochemical evidence for anoxic deep water in the arabian sea during the last glaciation various paleoceanographic studies have indicated that the deep ocean was probably depleted in dissolved oxygen during the last glacial period approximately 18 kyr b p delta sup 18 o stage 2 compared to present time however direct evidence of low oxygen content in the deep waters has been lacking here the authors report geochemical evidence of near anoxic conditions in the deep arabian sea during the entire last glacial cycle delta sup 18 o stages 2 3 and 4 anoxia is inferred from the concomitant enrichment of organic carbon and authigenic uranium in the glacial sections of a core from the deep eastern arabian sea the anoxic conditions during the last glacial period probably caused by a change in deep water circulation evidently enhanced preservation of organic matter and simultaneous removal of uranium from seawater 57 refs 3 figs 2 tabs

rock magnetic and geochemical record in a sediment core from the eastern arabian sea diagenetic and environmental implications during the late quaternary abstract rock magnetic concentration grain size and mineralogy parameters together with organic carbon calcium carbonate redox sensitive elements 18 o of globigerinoides ruber and radiocarbon dating were carried out on a 445 cm long sediment core collected at 1380 m depth off mangalore southwestern margin of india the top 290 cm sediments of the core correspond to the last 18 kabp the 18 o and magnetic records exhibit major events at 16 kabp 14 5 kabp 11 5 kabp and 9 8 8 6 kabp related to start and intensity of the summer monsoon and climate change and are synchronous with that of the western arabian sea and north atlantic the sediments with high magnetic susceptibility correlate with high sedimentation rates the sediments are dominated by fine grained magnetite but intervals of 1 2 3 8 kabp and 10 13 5 kabp were subjected to diagenetic changes resulting in the dissolution of fine grained magnetites and enrichment of redox sensitive trace elements cu ni zn v mo and u the sediments between 290 cm and 445 cm correspond to 18 27 kabp and are characterized by distinct decrease in magnetic concentration grain size and mineralogy parameters high organic carbon low concentrations of redox sensitive trace elements and abundant pyritized tubules the reductive diagenetic conditions indicated by rock magnetic properties are in contrast with the weak sub oxic conditions revealed by low concentrations of trace elements in the sediments the seasonal organic matter flux produced during the winter monsoon and moderate sedimentation rates favoured reductive diagenesis in the sediments at and below the last glacial maximum lgm intermittent bioturbation however allowed oxidants to penetrate into the sediments remobilized redox sensitive trace elements into the water column and modified the primary geochemical signal of the sedimentary environment

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

variations of the monsoon regime during the upper quaternary evidence from carbon isotopic record of organic matter in north indian ocean sediment cores abstract the 13 c 12 c ratios and contents of organic carbon in deep sea sediment cores of the north indian ocean have been compared for the different climatic stages as determined by oxygen isotope stratigraphy using the differences in the 13 c values between marine and terrestrial organic matter the terrestrial contribution to the eastern gulf of bengal and the andaman sea has been determined for modern and glacial times the geographical distribution of the terrestrial organic carbon linked to sea surface circulation shows that during the last glacial period the ne monsoon circulation was the dominant feature the organic carbon abundance within the sediment which is related to local productivity was greater during glacial times in the areas where production depends on the ne monsoon strength coast of north india in the arabian sea and andaman sea suggesting its reinforcement

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

the lycopane c31 n alkane ratio as a proxy to assess palaeoxicity during sediment deposition abstract recently two of us schulte et al earth planet sci lett 173 1999 205 221 advocated the use of the c 35 c 31 n alkane ratio to reconstruct past variations in the intensity of the oxygen minimum zone omz in the northeastern arabian sea new analyses of arabian sea surface sediments and re analysis of previously investigated sediments indicate however that the marked increase of the c 35 c 31 n alkane ratio in surface sediments from within the omz is due to enhanced preservation of lycopane which on some stationary phases in gas chromatography co elutes with the n c 35 alkane under anoxic conditions re examination of published data farrington et al org geochem 13 1988 607 617 on surface sediments from the peru upwelling region also revealed a marked preservation of lycopane and thus a higher abundance relative to terrestrial n alkanes under anoxic conditions within the omz thus the lycopane c 31 n alkane ratio can be interpreted as an oxicity proxy an overview of literature data indicates that lycopane is indeed often abundant in sediments which were deposited under anoxic conditions the carbon isotopic composition of lycopane and its response to the perturbation of the global carbon cycle during the cenomanian turonian oceanic anoxic event suggests that lycopane is derived from a marine photoautotroph although its biological source has yet to be identified

refining the southern extent of the 1872 owens valley earthquake rupture through paleoseismic investigations in the haiwee area southeastern california recent upward revision of the 1872 owens valley earthquake from mw 7 4 7 5 to 7 7 7 9 implies either additional unrecognized rupture length or anoma louslystronggroundmotionsassociatedwiththisevent weinvestigatethefirstpossibility through paleoseismic trenching south of the mapped surface rupture in the haiwee area where historical accounts suggest significant surface deformation following the earth quake trenching focused on a prominent north striking scarp herein termed the sage flat fault expressed in pleistocene alluvial fans east of haiwee reservoir surficial map ping and ground based light detection and ranging lidar surveying suggest that this faultaccommodateseast downnormalmotion andpossiblyacomparableamountofdex tralslip trenchingandluminescencedatingbracketsthetimingofthemostrecentsurface rupturing earthquake between 25 7 and 30 1 ka and provides evidence for an earlier event predating this time in combination with scarp profiling these dates also suggest am aximum rate of normal dip slip fault motion up to 0 1 mm yr over this period although we discovered no evidence for recent surface rupture on the sage flat fault a series of subvertical fractures and fissures cut across young trench stratigraphy consis tentwithsecondarydeformationassociatedwithseismicshaking assuch wesuggestthat possible ground disturbance in the haiwee area during the 1872 event primarily reflected ground shaking or liquefaction related deformation rather than triggered slip in addition we infer a structural and kinematic connection between the owens valley fault and oblique dextral faults north of lower cactus flat in the northwestern coso range rather thanawest stepintonorthernorwesternrosevalley considerationofthesestructuresin the total extent of the owens valley fault suggests a length of 140 km of which at least 113 km ruptured during the 1872 event online material procedural details and expanded results from the osl sample analyses as well as high resolution paleoseismic trench logs

variations of oxygen minimum and primary productivity recorded in sediments of the arabian sea abstract two deep sea sediment cores from the northeastern and the southeastern arabian sea were studied in order to reconstruct the palaeoenvironments of the past glacial cycles core 136kl was recovered from the high productivity area off pakistan within the modern oxygen minimum zone omz by contrast modern primary productivity at the site of md900963 close to maldives is moderate and bottom waters are today well oxygenated for both cores we reconstructed the changes in palaeoproductivity using a set of biomarkers alkenones dinosterol and brassicasterol the main result is that primary productivity is enhanced during glacial stages and lowered during interstadials the proxies associated with productivity show a 23 kyr cyclicity corresponding to the precession related insolation cycle palaeoredox conditions were studied in both cores using a new organic geochemical parameter c35 c31 n alkane ratio developed by analysing surface sediments from a transect across the omz off pakistan the value of this ratio in core 136kl shows many variations during the last 65 kyr indicating that the omz was not stable during this time it disappeared completely during heinrich and the younger dryas events pointing to a connection between global oceanic circulation and the stability of the omz the c35 c31 ratio determined in sediments of core md900963 shows that bottom waters remained rather well oxygenated over the last 330 kyr which is confirmed by comparison with authigenic metal concentrations in the same sediments a zonally averaged circulation biogeochemical ocean model was used to explore how the intermediate indian ocean responds to a freshwater flux anomaly at the surface of the north atlantic as suggested by the geochemical time series both the abundance of southern ocean water and the oxygen concentration are significantly increased in response to this freshwater perturbation

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

organic matter preservation on the pakistan continental margin as revealed by biomarker geochemistry in order to assess whether the oxygen minimum zone omz in the arabian sea has an eaect on the preservation and composition of organic matter in surface sediments we investigated samples from three diaerent transects on the pakistan continental margin across the omz in addition to determining the total amount of organic carbon toc we analyzed the extractable lipids by gas chromatography combined gas chromatography mass spectrometry and compound specific stable carbon isotope measurements the extractable lipids are dominated by marine organic matter as indicated by the abundance of lipids typical of marine biota and by the bulk and molecular isotopic composition sediments from within the omz are enriched in organic carbon and in several extractable lipids i e phytol n alcohols total sterols n c35 alkane relative to stations above and below this zone other lipid concentrations such as those of total n fatty acids and total n alkanes fail to show any relation to the omz only a weak correlation of toc with mineral surface area was found in sediments deposited within the omz in contrast sediments from outside the omz do not show any relationship between toc and surface area among the extractable lipids only the n alkane concentration is highly correlated with surface area in sediments from the hab and makran transects in sediments from outside the omz the phytol and sterol concentrations are also weakly correlated with mineral surface area the depositional environment of the indus fan oaers the best conditions for an enhanced preservation of organic matter the omz together with the undisturbed sedimentation at moderate rates seems to be mainly responsible for the high toc values in this area overall the type of organic matter and its lability toward oxic degradation the mineral surface area the mineral composition and possibly the secondary productivity by sedimentary bacteria also appear to have an influence on organic matter accumulation and composition 2000 elsevier science ltd all rights reserved

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal mg ca in the southeastern arabian sea over the past 450 ka comparison between globigerinoides ruber and globigerinoides sacculifer 1 the influence of supralysoclinal calcite dissolution on the mg ca thermometer over the last 450 ka is assessed using globigerinoides ruber and globigerinoides sacculifer from a core site in the eastern arabian sea the studied site is characterized by precession cycled paleoproductivity changes that have induced calcite dissolution in the sediments although the core still contains 40 80 caco3 during high productivity periods the narrow sized test weights of both foraminiferal species tend to decrease with increasing mn ca ratio indicating corrosive pore water conditions scanning electron microscope observations show that g sacculifer maintains a better preserved test ultrastructure than g ruber microprobe mapping reveals that mg rich bands in g ruber chamber walls are preserved despite reduced ca content assuming that the low test weight and offset in mg ca temperature between g sacculifer and g ruber are exclusively produced by calcite dissolution the bias in mg ca temperature determination can be estimated at around 1 c comparable to uncertainty of this thermometry despite the evidence for test dissolution foraminiferal mg ca seems to preserve initial temperature signals under the studied conditions

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

suppression of large earthquakes by stress shadows a comparison of coulomb and rate and state failure stress shadows generated by california s two most recent great earthquakes 1857 fort tejon and 1906 san francisco substantially modified 19th and 20th century earthquake history in the los angeles basin and in the san francisco bay area simple coulomb failure calculations which assume that earthquakes can be modeled as static dislocations in an elastic half space have done quite well at approximating how long the stress shadows or relaxing effects should last and at predicting where subsequent large earthquakes will not occur there has however been at least one apparent exception to the predictions of such simple models the 1911 m 6 0 earthquake near morgan hill california occurred at a relaxed site on the calaveras fault we examine how the more complex rate and state friction formalism based on laboratory experiments might have allowed the 1911 earthquake rate and state time to failure calculations are consistent with the occurrence of the 1911 event just 5 years after 1906 if the calaveras fault was already close to failure before the effects of 1906 we also examine the likelihood that the entire 78 years of relative quiet only four m 6 earthquakes in the bay area after 1906 is consistent with rate and state assumptions given that the previous 7 decades produced 18 m 6 earthquakes combinations of rate and state variables can be found that are consistent with this pattern of large bay area earthquakes assuming that the rate of earthquakes in the 7 decades before 1906 would have continued had 1906 not occurred these results demonstrate that rate and state offers a consistent explanation for the 78 year quiescence and the 1911 anomaly although they do not rule out several alternate explanations

sea surface temperatures of southern midlatitudes 0 160 kyr b p 1 late quaternary climate fluctuated between extremes of glaciations lasting 90 kyr on average and interglacial episodes lasting 10 kyr still largely unknown are the spatial and temporal evolution of these global climate states with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations though it is widely believed that the southern hemisphere oceans play a central role in global climate changes few paleoclimate records exist from there here we present three new alkenone derived sst records from the midlatitude southern hemisphere spanning the last 160 kyr a full glacial interglacial cycle our subtropical sst records from the last glacial period are characterized by 1 warming 47 23 kyr b p when high latitudes in both hemispheres cooled and 2 milder temperatures during the penultimate glacial period than during the last glacial interval these sst features are found to be of tropical to subtropical wide extent implying increased thermal gradients at times of high latitude ice sheet growth this has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

static stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 m 7 1 hector mine earthquake southern california the proximity in time 7 years and space 20 km between the 1992 m 7 3 landers earthquake and the 1999 m 7 1 hector mine event suggests a possible link between the quakes we thus calculated the static stress changes following the 1992 joshua tree landers big bear earthquake sequence on the 1999 m 7 1 hector mine rupture plane in southern california resolving the stress tensor into rake parallel and fault normal components and comparing with changes in the post landers seismicity rate allows us to estimate a coefficient of friction on the hector mine plane seismicity following the 1992 sequence increased at hector mine where the fault was unclamped this increase occurred despite a calculated reduction in right lateral shear stress the dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction 0 8 we calculated the coulomb stress change using 0 8 and found that the hector mine hypocenter was mildly encouraged 0 5 bars by the 1992 earthquake sequence in addition the region of peak slip during the hector mine quake occurred where coulomb stress is calculated to have increased by 0 5 1 5 bars in general slip was more limited where coulomb stress was reduced though there was some slip where the strongest stress decrease was calculated interestingly many smaller earthquakes nucleated at or near the 1999 hector mine hypocenter after 1992 but only in 1999 did an event spread to become a m 7 1 earthquake

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

a critical evaluation of depositional parameters controlling the variability of organic carbon in arabian sea sediments abstract organic carbon distribution in the surficial sediments of the arabian sea to some extent mirrors the surface productivity being both high in the peripheral portions and low in the central region suggesting that the productivity is a primary source of organic matter however a critical examination reveals that the organic enrichment on the slope of the indian margin is two to four higher max 16 71 than on the slope of the arabian peninsula max 7 54 while the productivity in the former region is three to four times lower than the latter this observation suggests that the influence of productivity on organic enrichment is of secondary importance high concentrations 4 of organic carbon exactly coincide with the oxygen minimum zone 150 1500 m water depth evidently reflecting the crucial role played by the anoxic bottom waters in the preservation of organic carbon incidently the organic rich band along the western indian slope is wide long and highly concentrated as compared to that of the slope of the arabian peninsula and no organic enrichment is found on other continental slopes of the arabian sea although an equally intense oxygen minima impinge on the floor of the slope such a variability of organic carbon on the slopes is attributed to various geological parameters such as texture of sediments rates of fine terrigenous sediment deposition shelf width slope gradient bottom currents and adsorption capacity of individual clay minerals all these observations suggest that the productivity is not an ultimate control for the organic enrichment of bottom sediments but it is the bottom water anoxia in conjunction with various depositional parameters which determine the degree of preservation

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

two phase westward encroachment of basin and range extension into the northern sierra nevada 1 structural geophysical and thermochronological data from the transition zone between the sierra nevada and the basin and range province at latitude 39 n suggest 100 km westward encroachment of basin and range extensional deformation since the middle miocene extension accommodated primarily by east dipping normal faults that bound west tilted range forming fault blocks varies in magnitude from 150 in the wassuk and singatse ranges to the east geological and apatite fission track data from exhumed upper crustal sections in the wassuk and singatse ranges point to rapid footwall cooling related to large magnitude extension starting at 14 15 ma farther to the west geological and thermochronological data indicate a younger period of extension in the previously unextended pine nut mountains the carson range and the tahoe truckee depression initiated between 10 ma and 3 ma and incipient post 0 5 ma faulting to the west of the tahoe truckee area these data imply the presence of an extensional breakaway zone between the singatse range and the pine nut mountains at 14 15 ma forming the boundary between the sierra nevada and basin and range at that time in addition fission track data imply a miocene preextensional geothermal gradient of 27 5 c km 1 in the central wassuk range and 20 5 c km 1 in the singatse range much higher than the estimated early tertiary gradient of 10 5 c km 1 for the sierra nevada batholith this might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting apatite fission track geophysical and geological constraints across the sierra nevada basin and range transition zone indicate a two stage coupled structural and thermal westward encroachment of the basin and range province into the sierra nevada since the middle miocene

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

evaluating models of coulomb stress transfer is variable fault geometry important to determine the importance of receiver fault geometry in coulomb stress calculations a new methodology is presented to model faults with variable geometry although most models use planar faults it is known that these are inaccurate representations of faults observed in the field the central italian apennines are chosen as a straightforward tectonic system with well exposed normal faults to investigate the effect of variable geometry it is shown that the static coulomb stress transfer is most sensitive to changes in strike of the receiver faults rather than changes in dip and rake therefore a novel methodology to generate strike variable faults composed of discrete rectangular patches is developed using the 2009 l aquila earthquake mw 6 3 the calculated stress transferred to planar versus variable faults is assessed the stress transferred to variable faults is sufficiently different when compared to planar cases to merit other earthquake sequences being reassessed with available fault geometry

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed