residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

localized seismic deformation in the upper mantle revealed by dense seismic arrays seismicity along continental transform faults is usually confined to the upper half of the crust but the newport inglewood fault nif a major fault traversing the los angeles basin is seismically active down to the upper mantle we use seismic array analysis to illuminate the seismogenic root of the nif beneath long beach california and identify seismicity in an actively deforming localized zone penetrating the lithospheric mantle deep earthquakes which are spatially correlated with geochemical evidence of a fluid pathway from the mantle as well as with a sharp vertical offset in the lithosphere asthenosphere boundary exhibit narrow size distribution and weak temporal clustering we attribute these characteristics to a transition from strong to weak interaction regimes in a system of seismic asperities embedded in a ductile fault zone matrix

crustal thicknesses in se brazilian shield by receiver function analysis implications for isostatic compensation hypothesis are proposed to explain the data 1 a lower density by 30 40 kg m 3 i n the lithospheric mantle under the archean block of the sao francisco craton relative to the proterozoic lithosphere is responsible for maintaining the high elevations in the plateau area relatively low density and high p wave velocity are compatible with a depleted low feo composition for the archean lithosphere 2 alternatively if the density contrasts between archean and proterozoic lithospheres are smaller than the values above then the crust beneath the paranabasin must be more dense than that of the craton higher crustal density and high poisson s ratio would be consistent with magmatic underplating in the lower crust beneath the paranabasin as inferred from other studies index terms 7205 seismology continental crust 1242 9360 information related to geographic region south america 7218 seismology lithosphere and upper mantle keywords crust upper mantle brazil parana basin san francisco craton

locally and remotely triggered aseismic slip on the central san jacinto fault near anza ca from joint inversion of seismicity and strainmeter data we study deep aseismic slip along the central section of the san jacinto fault near the anza seismic gap in southern california elevated strain rates following the remote m w7 2 4 april 2010 el mayor cucapah and the local m w5 4 7 july 2010 collins valley earthquakes were recorded by plate boundary observatory borehole strainmeters near anza and were accompanied by vigorous aftershock sequences we introduce a method to infer the distribution of triggered aseismic slip from combined seismicity and geodetic data based on a rate and state friction model that maps observed changes in seismicity rates into stress changes we invert for the cumulative slip in the 10 day period following each main shock synthetic tests show that the effect of aftershock interactions on the inferred slip distribution is negligible the joint data set is more consistent with a model in which aseismic slip on a principal fault triggers seismicity on adjacent faults than with one in which aseismic slip and seismicity are coplanar our results indicate that aseismic slip primarily occurs along the rim of two seismicity clusters adjacent to anza gap as well as beneath the anza gap itself at depths larger than 10 km the triggered aseismic slip generated by the two main shocks has little overlap a pattern also found in sequences of large earthquakes occurring on a same fault stresses inferred from seismic activity leading to the collins valley main shock suggest that this earthquake was triggered by stresses imposed by the el mayor cucapah remote triggered aseismic slip which persisted for more than 2 months

earthquakes in the western alpine mantle wedge abstract the assessment of seismic activity in the shallow continental mantle has long been hindered by the low resolution of both seismic imaging and earthquake locations in young collision zones here we combine the most recent and high resolution image of the lithospheric structure of the western alps with a high quality dataset of anomalously deep earthquakes recorded in the same area in the past 25 yrs we show that these earthquakes are aligned on an active lithospheric strike slip fault and we provide evidence that this fault is located in the mantle wedge beneath the adriatic moho our results i provide direct evidence that deep material can be seismogenic or not depending on the lithology ii confirm the role of serpentinization in favoring the aseismic creep of mantle rocks and iii demonstrate that the upper mantle can be stiff and seismogenic not only in cold cratons but also in young orogenic belts

very high strains recorded in mylonites along the alpine fault new zealand implications for the deep structure of plate boundary faults abstract oblique displacement on the alpine fault which forms the principal structure along the australian pacific plate boundary in south island new zealand has resulted in exhumation of a kilometre wide mylonite zone in the hanging wall adjacent to the current brittle fault trace the mylonites formed under amphibolite facies conditions at depths of ca 25 km and have been uplifted during the past 5 ma a suite of 65 70 ma pegmatite veins in the hanging wall alpine schists has been progressively deformed within the mylonite zone and sheared out over a strike length of ca 100 km measurements of the thickness distribution of the pegmatite veins within the non mylonitised schists and at three localities within the progressively strained mylonites have been used to estimate strain values within the mylonites the thicknesses approximate a log normal distribution with a mean value that is progressively reduced through the protomylonites mylonites and ultramylonites by assuming that the thickness distribution currently observed in the schists was the same for the pegmatites within the mylonites before strain a model of deformation incorporating simple shear and simultaneous pure shear is used to strain the undeformed veins until a fit is obtained with the strained distributions shear strains calculated range from 12 to 22 for the protomylonites 120 to 200 for the mylonites and 180 to 300 for the ultramylonites corresponding to pure shear values of 1 3 in each case these values are compatible with the strains predicted if most of the surface displacement on the fault over the past 5 ma were accommodated within a 1 2 km wide mylonite zone through the middle and lower crusts the results suggest that processes such as erosional focussing of deformation and thermal weakening may cause intense strain localisation within the lower crust with plate boundary deformation restricted to narrow zones rather than becoming increasingly distributed over a widening shear zone with depth

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

relative contributions of crustal temperature and composition to controlling the depth of earthquakes in southern california 1 control of the 13 km range of the maximum depth of earthquakes in southern california has been attributed previously to lateral variations in either crustal temperature or crustal rock composition here i compare heat flow a proxy for crustal temperature local maximum depths of earthquakes d95 and best guess crustal rock compositions plotting heat flow versus d95 produces distinct trends for each rock composition with each trend representing an isotherm marking the onset of plastic behavior offsets between the trends measure the differences in the plastic behavior temperatures of each rock composition these offsets are comparable to the d95 variations with heat flow thus crustal temperature and composition contribute about equally to the control of the maximum depths of earthquakes the observed isotherm slopes imply vertical variations in crustal composition in addition to the lateral variations

sea ice response to atmospheric and oceanic forcing in the bering sea abstract a coupled sea ice ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the bering sea over the period 1970 2008 the model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature sst and the basic features of the upper ocean circulation in the bering sea model results suggest that tides affect the spatial redistribution of ice mass by up to 0 1 m or 15 in the central eastern bering sea by modifying ice motion and deformation and ocean flows the considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during january may ranging from 0 9 1012 m3 in 1996 to 1 8 1012 m3 in 1976 and averaging 1 4 1012 m3 which is almost twice the january may mean total ice volume in the bering sea the large scale southward ice mass advection is constrained by warm surface waters in the south that melt 1 5 1012 m3 of ice in mainly t

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

a detailed image of the continent borderland transition beneath long beach california new crustal images beneath long beach california show the region of the inner borderland to continent transition the cross sections are obtained from stacked autocorrelations of virtual sources generated from oil industry data recorded in the city of long beach ca they show that the moho is dipping at 65 and obliquely truncates an 10 km thick flat lying lower crustal fabric the moho appears to be fault controlled and an integral part of the extrusion of the catalina schist that underlays the inner borderland the basement interface has significant offsets of up to 2 km none of which correspond to the mapped trace of the newport inglewood fault

seismic studies of the brasilia fold belt at the western border of the sao francisco craton central brazil using receiver function surface wave dispersion and teleseismic tomography abstract the tocantins province in central brazil is composed of a series of ssw nne trending terranes of mainly proterozoic ages which stabilized in the neoproterozoic in the final collision between the amazon and sao francisco cratons no previous information on crustal seismic properties was available for this region several broadband stations were used to study the regional patterns of crustal and upper mantle structure extending the results of a recent e w seismic refraction profile receiver functions and surface wave dispersion showed a thin crust 33 37 km in the neoproterozoic magmatic arc terrane high average crustal vp vs ratios 1 74 1 76 were consistently observed in this unit the foreland domain of the brasilia foldbelt on the other hand is characterized by thicker crust 42 43 km low vp vs ratios 1 70 1 72 were observed in the low grade foreland fold and thrust zone of the brasilia belt adjacent to the sao francisco craton teleseismic p wave tomography shows that the lithospheric upper mantle has lower velocities beneath the magmatic arc and goias massif compared with the foreland zone of the belt and sao francisco craton the variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile the integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the goias massif and the foreland domain of the brasilia belt whereas little variation was found across the foldbelt craton surface boundary these results support the hypothesis that the brasilia foreland domain and the sao francisco craton were part of a larger sao francisco congo continental plate in the final collision with the amazon plate

paradoxical pseudotachylyte fault melt outside the seismogenic zone abstract fault generated melt pseudotachylyte is an established indicator of palaeoseismic faulting the existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime central to this issue is whether all pseudotachylyte originates as pressure dependent frictional melt along slip surfaces or if pressure independent processes have roles in its formation propagation of high velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone pseudotachylyte from the minas fault zone nova scotia canada is used to demonstrate the formation and preservation of fault related melt under lower crustal conditions microstructures retain evidence of intense dislocation glide with minimal climb and ductile disaggregation of the host the latter are consistent with intracrystalline deformation in the peierls stress controlled glide regime it remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high velocity slip or is itself responsible for both instability and the thermal transient there are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts tremor that emphasize the mechanistic complexity of deep faulting and the need to extend consideration beyond that of a simple brittle ductile response the occurrence of tremor bursts fall within the depth range of paradoxical pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination

the mara rosa arch in the tocantins province further evidence for neoproterozoic crustal accretion in central brazil the mara rosa volcano sedimentary sequence consists of several nne trending belts of metavolcanic metabasalts to metarhyolites and metasedimentary rocks micaschists quartzites cherts exposed over large areas of the tocantins province a neoproterozoic brasiliano orogenic region in the central part of brazil the supracrustal belts are separated by terrains dominated by metatonalites and metadiorites and intruded by several post orogenic granitic and dioritic bodies these volcano sedimentary and associated metaplutonic rock associations have been previously interpreted as a typical granite greenstone terrain of the archaean basement in this paper we present geochronological and isotopic data for rocks of the metavolcanic metaplutonic rock association samples of a felsic metavolcanic rock from the posse gold mine and a metatonalite yielded u pb zircon ages of 862 8 ma and 856 7 13 ma respectively these are interpreted as crystallization ages of the igneous protoliths titanites from the same metavolcanic rock sample yielded a concordant recrystallization age of 632 4 ma sm nd isotopes for these rocks indicate primitive compositions with nd t of 4 6 and 3 7 and tdm model ages of 1 0 ga a syn tectonic dioritic intrusion has an u pb crystallization age of 630 6 ma and nd t of 1 9 and tdm of 1 0 ga additional sm nd analyses on metasedimentary rocks and post orogenic granites of the mara rosa region yield tdm ages between 1 2 and 1 0 ga the isotopic data combined with preliminary trace element results suggest that the protoliths of the metavolcanic and metaplutonic rocks investigated were formed in an island arc system off the coast of the sao francisco congo continent at around 860 ma recrystallization and deformational ages of 630 ma may represent the timing of final ocean closure and continental collision the rock associations structural pattern geochronological and isotopic characteristics of the rocks from the mara rosa region are very similar to those of neoproterozoic arc terrains exposed 300 km to the southwest in the arenspolis area proving the regional importance of the neoproterozoic crustal accretion event in the central part of brazil

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

late cenozoic tectonic evolution of the los angeles basin and inner california borderland a model for core complex like crustal extension we propose that the los angeles basin inner california borderland lab ib and the southern borderland off baja california formed by large magnitude crustal extension beginning in latest oligocene earliest miocene time and that these regions represent major late cenozoic rifts the southern borderland is analogous to the gulf of california rift but the onset of rifting in this region may have preceded the opening of the gulf by as much as 15 to 20 m y the lab ib rift is more complex than the southern borderland because it formed in the wake of the rotating western transverse ranges wtr a large crustal block that has undergone more than 90 of neogene clockwise rotation total extension in both rifted regions is estimated to be in excess of 200 km or comparable to the magnitude of late cenozoic crustal extension now estimated for the basin and range province also like the basin and range the crustal floors of the basins in these highly extended domains are characterized by metamorphic core complexes and detachment faults voluminous miocene volcanic rocks and hanging wall fragments of pre rift strata and basement rocks stranded atop detachments during extension in support of this model we synthesize a wide variety of existing geologic data and present interpretations of new geophysical data seismic reflection profiles these profiles image features that we infer are detachment faults and overlying remnants of fragmented and rifted hanging wall rocks we also suggest that a similar but slightly earlier onset of crustal extension affected the santa maria basin and adjacent regions in central california and that the southern margin of this santa maria basin rift was overridden during neogene clockwise rotation of the wtr

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

bering strait throughflow and the thermohaline circulation received 25 august 2005 revised 10 november 2005 accepted 14 november 2005 published 21 december 2005 1 in this study we employ a global coupled climate model to show that the bering strait is important to the variations of the thermohaline circulation three experiments are analyzed a present day control run and two freshwater hosing runs results show that as the thermohaline circulation weakens due to freshwater forcing in the northern north atlantic the bering strait throughflow weakens and even reverses its direction and the export of the arctic freshwater into the northern north atlantic is reduced or the arctic even takes freshwater from the latter thus helping the thermohaline circulation to recover relatively quickly after the end of the freshwater hosing citation hu a and g a meehl 2005 bering strait throughflow and the thermohaline circulation geophys res lett 32 l24610 doi 10 1029 2005gl024424

imaging widespread seismicity at midlower crustal depths beneath long beach ca with a dense seismic array evidence for a depth dependent earthquake size distribution we use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in long beach california poor signal to noise ratio due to anthropogenic activity is mitigated via downward continuation of the recorded wavefield the downward continued data are continuously back projected to search for coherent arrivals from sources beneath the array which reveals numerous previously undetected events the spatial distribution of seismicity is uncorrelated with the mapped fault traces or with activity in the nearby oil fields many events are located at depths larger than 20 km well below the commonly accepted seismogenic depth for that area the seismicity exhibits temporal clustering consistent with omori s law and its size distribution obeys the gutenberg richter relation above 20 km but falls off exponentially at larger depths the dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area because the event size distribution above 20 km depth obeys a power law whose exponent is near one this improvement yields a hundred fold decrease in the time needed for effective characterization of seismicity in long beach

investigating microearthquake finite source attributes with iris community wavefield demonstration experiment in oklahoma author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 1072 1087 doi 10 1093 gji ggy203

magnitudes and moment duration scaling of low frequency earthquakes beneath southern vancouver island we employ 130 low frequency earthquake lfe templates representing tremor sources on the plate boundary below southern vancouver island to examine lfe magnitudes each template is assembled from hundreds to thousands of individual lfes representing over 269 000 independent detections from major episodic tremor and slip ets events between 2003 and 2013 template displacement waveforms for direct p and s waves at near epicentral distances are remarkably simple at many stations approaching the zero phase single pulse expected for a point dislocation source in a homogeneous medium high spatiotemporal precision of template match filtered detections facilitates precise alignment of individual lfe detections and analysis of waveforms upon correction for 1 d geometrical spreading attenuation free surface magnification and radiation pattern we solve a large sparse linear system for 3 d path corrections and lfe magnitudes for all detections corresponding to a single ets template the spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12 24 h of lfe activity during an ets episode when tidal sensitivity is low the remainder is released in bursts over several days particularly as spatially extensive rapid tremor reversals rtrs during which tidal sensitivity is high rtrs are characterized by large magnitude lfes and are most strongly expressed in the updip portions of the ets transition zone and less organized at downdip levels lfe magnitude frequency relations are better described by power law than exponential distributions although they exhibit very high b values 5 we examine lfe moment duration scaling by generating templates using detections for limiting magnitude ranges mw 1 5 mw 2 0 lfe duration displays a weaker dependence upon moment than expected for self similarity suggesting that lfe asperities are limited in fault dimension and that moment variation is dominated by slip this behavior implies that lfes exhibit a scaling distinct from both large scale slow earthquakes and regular seismicity

reconstruction and analysis of the chukchi sea circulation in 1990 1991 1 the chukchi sea cs circulation reconstructed for september 1990 to october 1991 from sea ice and ocean data is presented and analyzed the core of the observational data used in this study comprises the records from 12 moorings deployed in 1990 and 1991 in u s and russian waters and two hydrographic surveys conducted in the region in the fall of 1990 and 1991 the observations are processed by a two step data assimilation procedure involving the pan arctic ice ocean modeling and assimilation system employing a nudging algorithm for sea ice data assimilation and the semi implicit ocean model utilizing a conventional four dimensional variational 4d var assimilation technique the reconstructed cs circulation is studied to identify pathways and assess residence times of pacific water in the region quantify the balances of volume freshwater and heat content and determine the leading dynamical factors configuring the cs circulation it is found that in 1990 1991 high ao index and a cyclonic circulation regime pacific water transiting the cs toward the canada basin followed two major pathways namely via herald canyon herald branch of circulation 0 23 sv and between herald shoal and cape lisburne central branch of circulation and alaskan coastal current 0 32 sv the annual mean flow through long strait was negligible 0 01 sv typical residence time of pacific water in the region varied between 150 days for waters entering the cs in september and 270 days for waters entering in february march momentum balance analysis reveals that geostrophic balance between barotropic pressure gradient and coriolis force dominated for most of the year baroclinic effects were important for circulation only in the regions with large horizontal salinity gradients associated with the fresh alaskan and siberian coastal currents and the cape lisburne and great siberian polynyas in the polynyas the baroclinic effects were due to strong salinification and convection processes associated with sea ice formation

the role of fluid pressure on frictional behavior at the base of the seismogenic zone to characterize stress and deformation style at the base of the seismogenic zone we investigate how the mechanical properties of fluid rock systems respond to variations in temperature and strain rate the role of fluids on the processes responsible for the brittle ductile transition in quartz rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the earth our initial analysis of this competition suggests that the effective stress law for sliding friction should not work as efficiently near the brittle ductile transition as it does at shallow conditions

geodetic slip rates in the southern san andreas fault system effects of elastic heterogeneity and fault geometry 1 we use high resolution interferometric synthetic aperture radar and gps measurements of crustal motion across the southern san andreas fault system to investigate the effects of elastic heterogeneity and fault geometry on inferred slip rates and locking depths geodetically measured strain rates are asymmetric with respect to the mapped traces of both the southern san andreas and san jacinto faults two possibilities have been proposed to explain this observation large contrasts in crustal rigidity across the faults or an alternate fault geometry such as a dipping san andreas fault or a blind segment of the san jacinto fault we evaluate these possibilities using a two dimensional elastic model accounting for heterogeneous structure computed from the southern california earthquake center crustal velocity model cvm h 6 3 the results demonstrate that moderate variations in elastic properties of the crust do not produce a significant strain rate asymmetry and have only a minor effect on the inferred slip rates however we find that small changes in the location of faults at depth can strongly impact the results our preferred model includes a san andreas fault dipping northeast at 60 and two active branches of the san jacinto fault zone in this case we infer nearly equal slip rates of 18 1 and 19 2mm yr for the san andreas and san jacinto fault zones respectively these values are in good agreement with geologic measurements representing average slip rates over the last 10 10 years implying steady long term motion on these faults

using a time based subarray method to extract and invert noise derived body waves at long beach california the reconstruction of body waves from the cross correlation of random wavefields has recently emerged as a promising approach to probe the fine scale structure of the earth however because of the nature of the ambient noise field the retrieval of body waves from seismic noise recordings is highly challenging and has only been successful in a few cases here we use seismic noise data from a 5 200 node oil company survey to reconstruct body waves and determine the velocity structure beneath long beach california to isolate the body wave energy from the ambient noise field we divide the entire survey into small aperture subarrays and apply a modified double beamforming scheme to enhance coherent arrivals within the cross correlated waveforms the resulting beamed traces allow us to identify clear refracted p waves traveling between different subarray pairs which we then use to construct a high resolution 3d velocity model of the region the inverted velocity model reveals velocity variations of the order of 3 and strong lateral discontinuities caused by the presence of sharp geologic structures such as the newport inglewood fault nif additionally we show that the resolution that is achieved through the use of high frequency body waves allows us to illuminate small geometric variations of the nif that were previously unresolved with traditional passive imaging methods

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

analysis of teleseismic p waves with a 5200 station array in long beach california evidence for an abrupt boundary to inner borderland rifting we analyze teleseismic p waves from four mw 6 5 earthquakes recorded by a petroleum industry survey in long beach california the survey used a 2 d array with up to 5200 seismometers 120 m mean spacing and 7 10 km aperture at frequencies near 1 hz p wave travel times and amplitudes exhibit coherent lateral variations over scales as short as 400 m including locally delayed travel times and increased amplitudes at the crest of the long beach anticline deeper heterogeneity is indicated by p wave phase velocities that deviate from reference model predictions for events from southwestern azimuths we postulate that a sharp northeastward increase in moho depth from the inner borderland ib to mainland southern california causes the anomalous phase velocities elastic forward modeling finds the travel times are fit well by a moho that dips 65 to the northeast and flattens 10 km southwest of the newport inglewood fault zone constraining the felsic thickness of mainland crust to 28 km requires an 8 km thick layer with a p velocity of 7 km s beneath it which could result from basal accretion of former farallon ocean crust or magmatic underplating during miocene volcanism forward models with a 65 moho dip predict a p to s conversion with a phase velocity of 5 km s deconvolution of the array s mean p wave signal isolates a similar later arriving phase the steep crust thickness transition supports a locally abrupt boundary to ib rifting our results highlight the utility of dense short period arrays for passive imaging at near surface to uppermost mantle depths

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

seismotectonics of the newport inglewood fault zone in the los angeles basin southern california the newport inglewood fault zone nif strikes northwest along the western margin of the los angeles basin in southern california the seismicity 1973 to 1985 of m l 2 5 that occurred within a 20 km wide rectangle centered on the nif extending from the santa monica fault in the north to newport beach in the south is analyzed a simultaneous full inversion scheme velest is used to invert for hypocentral parameters two velocity models and a set of station delays arrival time data from three quarry blasts are included to stabilize the inversion the first velocity model applies to stations located along the rim and outside the los angeles basin and is well resolved it is almost identical to the starting model which is the model routinely used by the cit usgs southern california seismic network for locating local earthquakes the second velocity model applies to stations located within the los angeles basin it shows significantly lower velocities down to depths of 12 to 16 km which is consistent with basement of catalina schist below the sediments in the western los angeles basin the distribution of relocated hypocenters shows an improved correspondence to mapped surface traces of late quaternary fault segments of the nif a diffuse trend of seismicity is observed along the inglewood fault from the dominguez hills across the baldwin hills to the santa monica fault in the north the seismicity adjacent to long beach however is offset 4 to 5 km to the east near the trace of the subsurface los alamitos fault the depth distribution of earthquakes along the nif shows clustering from 6 to 11 km depth which is similar to average seismogenic depths in southern california thirty nine single event focal mechanisms of small earthquakes 1977 to 1985 show mostly strike slip faulting with some reverse faulting along the north segment north of dominguez hills and some normal faulting along the south segment south of dominguez hills to newport beach the results of an inversion of the focal mechanism data for orientations of the principal stress axes and their relative magnitudes indicate that the minimum principal stress is vertical along the north segment while the intermediate stress is vertical along the south segment the maximum principal stress axis is oriented 10 to 25 east of north reverse faulting along the north segment indicates that a transition zone of mostly compressive deformation exists between the los angeles block and the central transverse ranges

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere 1 faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults oceanic detachment faults subduction zones and continental rifts however few data exist that directly explore the frictional properties of peridotite rocks improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere furthermore our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes it has been hypothesized and some experimental data indicate that plastic yielding by dislocation glide low temperature plasticity determines the direct effect in the rate and state frictional constitutive formulation plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and or displacement dependent friction evolution effect and frictional healing we present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas medium deformation apparatus in the temperature range of 400 1000 c with 100 mpa confining pressure we conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability we also conducted slide hold slide experiments to investigate the time and temperature dependence of fault zone restrengthening frictional healing the mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding the data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts we explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

earthquake cycle simulations with rate and state friction and power law viscoelasticity abstract we simulate earthquake cycles with rate and state fault friction and off fault power law viscoelasticity for the classic 2d antiplane shear problem of a vertical strike slip plate boundary fault we investigate the interaction between fault slip and bulk viscous flow with experimentally based flow laws for quartz diorite and olivine for the crust and mantle respectively simulations using three linear geotherms dt dz 20 25 and 30 k km produce different deformation styles at depth ranging from significant interseismic fault creep to purely bulk viscous flow however they have almost identical earthquake recurrence interval nucleation depth and down dip coseismic slip limit despite these similarities variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations additionally in the 25 and 30 k km simulations the crust drags the mantle the 20 k km simulation also predicts this except within 10 km of the fault where the reverse occurs however basal tractions play a minor role in the overall force balance of the lithosphere at least for the flow laws used in our study therefore the depth integrated stress on the fault is balanced primarily by shear stress on vertical fault parallel planes because strain rates are higher directly below the fault than far from it stresses are also higher thus the upper crust far from the fault bears a substantial part of the tectonic load resulting in unrealistically high stresses in the real earth this might lead to distributed plastic deformation or formation of subparallel faults alternatively fault pore pressures in excess of hydrostatic and or weakening mechanisms such as grain size reduction and thermo mechanical coupling could lower the strength of the ductile fault root in the lower crust and concomitantly off fault upper crustal stresses

generic dependence of the frequency size distribution of earthquakes on depth and its relation to the strength profile of the crust 1 we explore the idea that the relative size distribution of earthquakes quantified using the so called b value is negatively correlated with differential stress because the maximum possible differential stress increases linearly in the brittle upper crust we expect to find a decrease of b with depth we test this expectation for seven continental areas around the world each of which is described by a regional earthquake catalog we find a monotonic decrease in b value between 5 and 15 km depth the decrease stops near the brittle ductile transition we specifically focus on the high quality catalogs of earthquakes in california to perform a sensitivity test with respect to depth uncertainty we also estimate the probability depth gradient for the occurrence of a target magnitude event and study the behavior of b with depth in near and off fault zones we also translate the observed b depth gradients into b differential stress gradients our findings suggest that b values are negatively correlated with differential stress and hus have the potential to act as stress meters in the earth s crust

layered crustal anisotropy around the san andreas fault near parkfield california the rheology of the earth s crust controls the long term and short term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials in this paper we examine the seismic structure and anisotropy of the crust around the san andreas fault saf near parkfield california using teleseismic receiver functions these data indicate that the crust is characterized by spatially variable and strongly anisotropic upper and middle crustal layers with a moho at 35 km depth the upper layer is 5 10 km thick and is characterized by strong 30 anisotropy with a slow axis of hexagonal symmetry where the plane of fast velocity has a strike parallel to that of the saf and a dip of 40 we interpret this layer as pervasive fluid filled microcracks within the brittle deformation regime the 10 15 km thick midcrustal layer is also characterized by a weak axis of hexagonal symmetry with 20 anisotropy but the dip direction of the plane of fast velocity is reversed the midcrustal anisotropic layer is more prominent to the northeast of the san andreas fault we interpret the mid crustal anisotropic layer as fossilized fabric within fluid rich foliated mica schists when combined with various other geophysical observations our results suggest that fault creep behavior around parkfield is favored by intrinsically weak and overpressured crustal fabric

control of bering strait transport by the meridional overturning circulation author s cessi paola abstract abstractit is well established that the mean transport through bering strait is balanced by a sea level difference between the north pacific and the arctic ocean but no mechanism has been proposed to explain this sea level difference it is argued that the sea level difference across bering strait which geostrophically balances the northward throughflow is associated with the sea level difference between the north pacific and the north atlantic arctic in turn the latter difference is caused by deeper middepth isopycnals in the indo pacific than in the atlantic especially in the northern high latitudes because there is deep water formation in the atlantic but not in the pacific because the depth of the middepth isopycnals is associated with the dynamics of the upper branch of the meridional overturning circulation moc a model is formulated that quantitatively relates the sea level difference between the north pacific and the arctic north atlantic with the wind stress in the antarctic circumpolar region since this forcing powers the moc and with the outcropping isopycnals shared between the northern hemisphere and the antarctic circumpolar region since this controls the location of deep water formation this implies that if the sinking associated with the moc were to occur in the north pacific rather than the north atlantic then the bering strait flow would reverse these predictions formalized in a theoretical box model are confirmed by a series of numerical experiments in a simplified geometry of the world ocean forced by steady surface wind stress temperature and freshwater flux

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

seismic imaging of source region in the 1976 ms 7 8 tangshan earthquake sequence and its implications for the seismogenesis of intraplate earthquakes

intraplate seismicity in se brazil stress concentration in lithospheric thin spots summary intraplate seismicity has generally poor correlation with surface geological patterns except for major extensional features such as aborted continental rifts which may act as weak zones it is usually difficult to find simple geology based models to explain differences in seismic activity in stable continental regions seismicity in brazil is clearly not uniform and a few areas of higher activity have been identified however the seismic areas show almost no correlation with the main geological provinces which is typical of other intraplate settings a recent uppermantle tomography study in se and central brazil using approximately 8500 p wave and 2000 pkp wave arrivals recorded in 59 sites since 1992 has mapped p wave velocity anomalies from lithospheric depths down to 1300 km in this region higher seismic activity occurs preferentially in areas with low p wave velocities at 150 250 km depth the low p wave velocities are interpreted as shallower asthenosphere in such areas a hotter geotherm will reduce the strength of the lithospheric upper mantle causing most of the intraplate forces to be concentrated in the brittle upper crust the low velocity anomalies coincide with late cretaceous provinces of alkaline intrusions the proposed ponding of the trindade plume head beneath lithospheric thin spots is consistent with our tomography results suggesting that plume effects may have helped to preserve lithosphere asthenosphere topography although other factors are also important the present data show that stress concentrations resulting from lithosphere asthenosphere topography should play an important role in explaining the intraplate seismicity in the brazilian platform

a 15 year catalog of more than 1 million low frequency earthquakes tracking tremor and slip along the deep san andreas fault low frequency earthquakes lfes are small rapidly recurring slip events that occur on the deep extensions of some major faults their collective activation is often observed as a semicontinuous signal known as tectonic or nonvolcanic tremor this manuscript presents a catalog of more than 1 million lfes detected along the central san andreas fault from 2001 to 2016 these events have been detected via a multichannel matched filter search cross correlating waveform templates representing 88 different lfe families with continuous seismic data together these source locations span nearly 150 km along the central san andreas fault ranging in depth from 16 to 30 km this accumulating catalog has been the source for numerous studies examining the behavior of these lfe sources and the inferred slip behavior of the deep fault the relatively high temporal and spatial resolutions of the catalog have provided new insights into properties such as tremor migration recurrence and triggering by static and dynamic stress perturbations collectively these characteristics are inferred to reflect a very weak fault likely under near lithostatic fluid pressure yet the physical processes controlling the stuttering rupture observed as tremor and lfe signals remain poorly understood this paper aims to document the lfe catalog assembly process and associated caveats while also updating earlier observations and inferred physical constraints the catalog itself accompanies this manuscript as part of the electronic supplement with the goal of providing a useful resource for continued future investigations

interbasin transport of the meridional overturning circulation abstractthe meridional overturning circulation moc is studied in an idealized domain with two basins connected by a circumpolar channel in the southernmost region flow is forced at the surface by longitude independent wind stress freshwater flux and fast temperature relaxation to prescribed profiles the only longitudinal asymmetry is that one basin is twice as wide as the other two states a preferred one with sinking in the narrow basin and an asymmetrically forced one with sinking in the wide basin are compared in both cases sinking is compensated by upwelling everywhere else including the passive basin despite the greater area of the wide basin the residual overturning transport is the same regardless of the location of sinking the two basins exchange flow at their southern edge by a geostrophic transport balanced by the difference in the depth of isopycnals at the eastern boundaries of each basin gnanadesikan s model for the upper branch of the moc is extended to include two basins conn

anomalously deep crustal earthquakes in the ventura basin southern california earthquakes at depths of 20 30 km occur beneath the ventura basin in southern california the epicentral distribution of deep seismicity outlines an east trending ellipse which corresponds closely with the mapped santa clara syncline the main structural element of the ventura basin with 15 km thickness of sediments clear pn and pg phases are seen for even the deepest earthquakes which demonstrate that these earthquakes are occurring within the crust travel time curves from shallow and deep earthquakes in the western transverse ranges require that the depth to the moho under the ventura basin must be depressed by 7 10 km relative to the surrounding area indicating crustal thickening of 20 35 other researchers have shown that the ventura basin has the lowest heat flow in western california thus low heat flow exceptionally thick 15 km sediments rapid shortening of the crust the deep earthquakes and a depressed moho all coincide within a small area strongly suggesting a common cause for all five phenomena the confinement of the deep earthquakes and depressed moho to the ventura region suggests that the rapid shortening of the ventura basin is anomalous and not representative of the rate of shortening across all of the western transverse ranges

a family of repeating low frequency earthquakes at the downdip edge of tremor and slip we analyze an isolated low frequency earthquake lfe family located at the downdip edge of the main episodic tremor and slip ets zone beneath western washington state the 9000 individual lfes from this repeating family cluster into 198 swarms that recur roughly every week cumulative lfe seismic moment for each swarm correlates strongly with the time until the next swarm suggesting that these lfe swarms are time predictable precise double difference relative locations for 700 individual lfes within this family show a distribution that is approximately 2 km long and 500 m wide elongated parallel to the relative plate convergence direction the distribution of locations 300 m vertical spread lies within a few hundred meters of two different plate interface models and has a similar dip peak to peak lfe s wave amplitudes range from 0 2 to 18 nm individual lfes exhibit a trend of increasing magnitude during swarms with smaller events at the beginning and the largest events toward the end the largest lfes cluster in a small area 300 m radius coincident with maximum lfe density we propose that the less concentrated smaller lfes act to unlock this patch core allowing it to fully rupture in the largest lfes usually toward the end of a swarm we interpret the patch responsible for producing these lfes as a subducted seamount on the downgoing juan de fuca jdf plate lfe locking efficiency slip estimated during 5 years from summing lfe seismic moment divided by plate rate determined slip is at most 20 and is highly concentrated in two 50 m radius locations in the larger patch core estimated individual lfe stress drops range from 1 to 20 kpa but could also be significantly larger

attenuation models qp and qs in three dimensions of the southern california crust inferred fluid saturation at seismogenic depths we analyze high dynamic range waveform spectra to determine t values for both p and s waves from earthquakes in southern california we invert the t values for three dimensional 3 d frequency independent q p and q s regional models of the crust the models have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth and extend from the u s mexico border to the coast ranges in the south and sierra nevada in the north in general qp and qs increase rapidly with depth consistent with crustal densities and velocities the 3 d q p and q s models image the major tectonic structures and to a much lesser extent the thermal structure of the southern california crust the near surface low q p and q s zones coincide with major sedimentary basins such as the san bernardino chino san gabriel valley los angeles ventura and santa maria basins and the salton trough in contrast at shallow depths beneath the peninsular ranges southern mojave desert and southern sierras we image high q p and q s zones which correspond to the dense and high velocity rocks of the mountain ranges several clear transition zones of rapidly varying q p and q s coincide with major late quaternary faults and connect regions of high and low q p and q s at midcrustal depths the q p and q s exhibit modest variation in slightly higher and lower qp or qs zones which is consistent with reported crustal reflectivity in general for the southern california crust q s q p is greater than 1 0 suggesting partially fluid saturated crust a few limited regions of q s q p less than 1 0 correspond to areas mostly outside the major sedimentary basins including areas around the san jacinto fault suggesting a larger reduction in the shear modulus compared to the bulk modulus or almost complete fluid saturation

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

a theory of the interhemispheric meridional overturning circulation and associated stratification abstracta quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem it relies on a matching among three regions the circumpolar channel at high southern latitudes a region of isopycnal outcrop at high northern latitudes and the ocean basin between the theory describes both the middepth and abyssal cells of a circulation representing north atlantic deep water and antarctic bottom water it suggests that although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel middepth stratification results from a balance between the wind driven upwelling in the channel and deep water formation at high northern latitudes d

scaling relationship between the duration and the amplitude of non volcanic deep low frequency tremors 1 we investigate a duration amplitude relation of non volcanic deep low frequency dlf tremors in the tokai region southwest japan to constrain the source process of the tremors we apply two models to the distribution one is an exponential model as a scale bound distribution and the other a power law model as a scale invariant distribution the exponential model shows a better fit to the duration amplitude distribution of the tremors than a power law model implying that the dlf tremors are caused by a scale bound source process the source process of the dlf tremors therefore differs from those for earthquakes we suggest that the non volcanic dlf tremor is possibly caused by a fixed source dimension with variable excess pressure of fluid or variable stress drop

deep seismic refraction and gravity crustal model and tectonic deformation in tocantins province central brazil abstract interpretation of seismic refraction data in the central sector of tocantins province central brazil has produced a seismic crustal model with well defined upper intermediate and lower crust layers having smooth velocity gradient in each layer the depths to moho vary from 32 to 43 km and mean crustal p velocity varies from 6 3 km s beneath goias magmatic arc on the western side to 6 4 km s below goias massif in the central portion and the foreland fold and thrust belt on the eastern side the behaviour of the lower crust layer allows an improved understanding of regional gravimetric features of the central and northern sectors of tocantins province and suggests subduction of the amazon plate in central brazil in the southeastern sector the refraction experiment resulted in the detection of a thinner crust 38 km below brasilia fold belt and a thicker crust 41 km below parana basin and sao francisco craton 42 km the upper crust beneath parana basin is around 20 km thick whereas it is less than 10 km thick below the craton these results bring new insights into the geological history of the central and southeastern sectors of tocantins province gravimetric measurements in the central sector of tocantins province delineate a high and a low anomaly separated by a steep gradient with a ne direction the axis of the gradient seems to bend still further to ne in the northern sector of that province whereas the gravimetric high continues northwards defining a separation between them this suggests that those features belong to different tectonic processes that occurred during tocantins province orogenesis the gravimetric model which incorporates seismically resolved structure beneath tocantins province better matches the observed gravimetric data although tectonic movements have only been monitored with high precision gps for short time interval 1999 2001 the results suggest observable deformations the main seismicity of central brazil the goias tocantins seismic belt seems to be spatially associated with the large gravimetric high anomaly and with the observed tectonic deformation

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

nd isotopic study of the neoproterozoic mara rosa arc central brazil implications for the evolution of the brasilia belt abstract the goias magmatic arc is a 0 9 0 64 ga island arc underlying large areas of the western part of the brasilia belt in central brazil it is exposed in two separate sections known as the arenopolis arc in the south and the mara rosa arc in the north it is made of island arc volcanic sedimentary sequences forming narrow nne to nnw belts separated from each other by tonalitic granodioritic granitic orthogneisses all rocks are metamorphosed under upper greenschist to amphibolite facies conditions but have kept major geochemical and isotopic features indicating the juvenile nature of the igneous protoliths the meta igneous and metasedimentary rocks are intruded by a number of late to post orogenic granites e nd 850 ranging from 1 5 to 4 6 with t dm values between 1 0 and 1 1 ga metasedimentary rocks in the mara rosa supracrustal belts display geochemical features suggesting that they represent first cycle immature sediments which preserve chemical characteristics of their igneous sources their nd isotopic characteristics support this interpretation t dm model ages for detrital metasediments are mostly in the interval between 0 9 and 1 2 ga indicating that they are a product of erosion of the arc rocks the absence of older contributions to these sediments seems to indicate an intraoceanic setting this is also suggested by the nd isotopic composition of the 0 8 ga old tholeiitic amphibolites which display positive initial e nd 4 9 indicating derivation from a depleted mantle source syn orogenic deformed granites forming small intrusions within the supracrustal belts have t dm ages ranging from 0 77 to 2 54 ga the older model age values indicate the presence of hidden fragments of ancient crust which were probably tectonically interleaved with younger rocks during accretion of the arc the post orogenic granites are moderately peraluminous and the nd model ages between 1 0 and 1 3 ga indicate that their parental magmas were predominantly re melts of the arc rocks their peraluminous nature reflects the incorporation of substantial amounts of arc sediments in the original magma garnet whole rock sm nd ages for the metasediments may be interpreted to refer to two metamorphic events an older event at 0 76 0 73 ga and a younger event at 604 610 ma mineral chemistry indicate that the older episode was characterized by higher p t and the younger by lower p t the older metamorphic event is interpreted preliminarily as the result of the accretion of island arc terranes to the western edge of the orogen and the younger event as a result of final ocean closure and continental collision between the amazon and sao francisco continents the goias arc formation and accretion is partially coeval with rodinia break up suggesting that the western margin of the sao francisco congo was peripheral in that supercontinent and faced a wide oceanic basin during most of the neoproterozoic

pushing the limit of earthquake detection with distributed acoustic sensing and template matching a case study at the brady geothermal field template matching has been widely applied in the detection of earthquakes and other seismic events due to its power in detecting weak signals recent studies using synthetics have shown that application of template matching to large n arrays can potentially detect earthquakes substantially below the noise level here we apply template matching to the distributed acoustic sensing das data recorded in the brady hot springs geothermal field nevada using 5 catalogued events we detect 116 events and find 68 of them well below the noise level we confirm 112 events are true earthquakes by examining the patterns of their sensor to sensor cross correlation sections this demonstrates that the combination of das and template matching has capability to detect microseismicity below the noise level which is unusual for conventional seismic arrays and methods with the updated catalogue we observe a surge of earthquakes during the shutdown of a geothermal power plant nearby in addition the rapid increases in the downhole pressure record coincide with intense swarms of earthquakes these observations show a strong correlation between the seismicity frequencies and the downhole pressure changes finally we investigate several factors that may affect the detection performance and compare different strategies for spatial down sampling in order to provide helpful insights for future large n design and data processing

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

crustal geophysics and seismicity in southern california the geographical distribution of the 1981 2005 seismicity in southern california forms a 150 km broad zone adjacent to the pacific north america plate boundary ranging from depths of 1 30 km with the bulk of the focal depths in the range of 2 12 km the distribution of the seismicity that includes both mainshock aftershock sequences and background events is affected by both static and kinematic geophysical parameters of the crust the static parameters include heat flow topography crustal density v p v s ratio hypocentral fault distance and crustal thickness from receiver functions the tectonic loading is represented by kinematic parameters such as the crustal shear strain rate field and the dilatational strain rate field in our analysis we normalize the seismicity relative to the areal density of the range of values of each of the parameters most of the seismicity occurs in areas of average heat flow low to intermediate topography average vp vs and high late quaternary fault density and forms seismogenic zones that extend through the brittle crust the location of late quaternary faults often described as zones of weakness influences the geographical distribution of seismicity more than any other parameter although above or below average crustal properties such as high heat flow thin crust or very low v p v s values exist these properties only influence the spatial distribution of seismicity in a minor way as an example the salton trough area of low topography high heat flow high v p v s high shear strain rate and thin crust has distributed seismicity within a thin seismogenic zone also somewhat surprisingly areas of high topography low heat flow low v p v s low shear strain rate and thick crust have low seismicity rates but a thin seismogenic zone we determine an empirical relationship between heat flow and crustal thickness to show how the 400 c temperature isotherm gradually deepens with crustal thickness and forms the base of the seismogenic zone for crustal thicknesses from 22 to 37 km for crustal thickness ranging from 37 to 43 km the 250 c isotherm forms the base of the seismogenic zone suggesting that seismic faulting in these regions is confined to the top of the upper crust 12 14 km and thus does not accommodate plate motion

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

the effect of southern ocean surface buoyancy loss on the deep ocean circulation and stratification abstractthe deep ocean circulation and stratification have likely undergone major changes during past climates which may have played an important role in the modulation of atmospheric co2 concentrations the mechanisms by which the deep ocean circulation changed however are still poorly understood and represent a major challenge to the understanding of past and future climates this study highlights the importance of the integrated buoyancy loss rate around antarctica in modulating the abyssal circulation and stratification theoretical arguments and idealized numerical simulations suggest that enhanced buoyancy loss around antarctica leads to a strong increase in the abyssal stratification consistent with proxy observations for the last glacial maximum enhanced buoyancy loss moreover leads to a contraction of the middepth overturning cell and thus upward shift of north atlantic deep water nadw the abyssal overturning cell initially expands to fill the void however if the buoyancy loss rate furt

structure of the los angeles basin from ambient noise and receiver functions a velocity v s and structure model is derived for the los angeles basin california based on ambient noise surface wave and receiver function analysis using data from a low cost short duration dense broad band survey lassie deployed across the basin the shear wave velocities show lateral variations at the compton los alamitos and the whittier faults the basement beneath the puente hills san gabriel valley shows an unusually high velocity 4 0 km s 1 and indicates the presence of schist the structure of the model shows that the basin is a maximum of 8 km deep along the profile and that the moho rises to a depth of 17 km under the basin the basin has a stretch factor of 2 6 in the centre grading to 1 3 at the edges and is in approximate isostatic equilibrium

crustal scale shear zones and heterogeneous structure beneath the north anatolian fault zone turkey revealed by a high density seismometer array continental scale deformation is often localised along strike slip faults constituting considerable seismic hazard in many locations nonetheless the depth extent and precise geometry of such faults key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard are poorly constrained in the mid to lower crust using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 izmit earthquake we map previously unknown small scale structure in the crust and upper mantle along this part of the north anatolian fault zone nafz we show that lithological and structural variations exist in the upper mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle the surface expression of the nafz in this region comprises two major branches both are shown to continue at depth with differences in dip depth extent and possibly width we interpret a 10 km zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the moho layers of anomalously low velocity in the mid crust 20 25 km depth and high velocity in the lower crust extending from depths of 28 30 km to the moho are best developed in the armutlu almacik block between the two shear zones a mafic lower crust possibly resulting from ophiolitic obduction or magmatic intrusion can best explain the coherent lower crustal structure of this block our images show that strain has developed in the lower crust beneath both northern and southern strands of the north anatolian fault our new high resolution images provide new insights into the structure and evolution of the nafz and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km

paleoseismicity of the north branch of the newport inglewood fault zone in huntington beach california from cone penetrometer test data abstract application of cone penetrometer testing cpt is a promising method for studying subsurface fault zones in stratified unconsolidated sediment where trenching is not feasible analysis of data from 72 cpts spaced 7 5 to 30 0 m apart and 9 borings indicates that the north branch fault the active strand of the newport inglewood fault zone nifz in huntington beach has generated at least three and most likely five recognizable surface ruptures in the past 11 7 0 7 ka additional smaller earthquakes similar to the m w 6 4 1933 long beach earthquake may also have occurred but would not be recognizable with this method the minimum right lateral holocene slip rate of the nifz in the study area is estimated to be 0 34 to 0 55 mm yr the actual slip rate may be significantly higher

seismic velocity anomalies beneath se brazil from p and s wave travel time inversions 1 we present the result from teleseismic travel time inversions for p and s wave data mainly recorded at portable broadband stations in se brazil the stations were deployed at 45 sites within an area 1000 1700 km during the years 1992 1999 more than 10 000 relative p and s wave arrival times including core phases were obtained from the waveforms using a new coherence functional these p and s relative phase times are independently inverted for slowness perturbations earthquake relocations and station corrections the final models represent the least amount of structure required to explain the residuals within a defined standard error the robust and consistent features in the velocity anomaly models are interpreted and their resolution is tested with synthetic case inversions we confirm the existence of a cylindrical low velocity anomaly beneath the parana basin which has been interpreted by vandecar et al 1995 as the fossil conduit through which the initial tristan da cunha plume head traveled to generate the parana etendeka flood basalts about 130 ma we now show that this low velocity cylindrical structure seems to be confined to the upper mantle beneath the upper mantle the velocity anomalies show a n s oriented pattern which we interpret as due to the nazca plate subducted slab at lithospheric depths the archean southern part of the sao francisco craton shows high velocities down to 200 300 km all areas with late cretaceous postrift alkaline intrusions are characterized by low velocities at lithospheric depths

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events

two stage red sea rifting inferred from mantle earthquakes in neoproterozoic lithosphere abstract we use earthquake geothermometry measured heat flow and structural constraints from p wave receiver functions to model the thermal evolution of the lithosphere beneath harrat lunayyir we suggest that the lithosphere thinned to its present 60 km thickness in a second stage of lithospheric thinning at 15 12 ma following initial red sea extension at 27 ma harrat lunayyir is an active volcanic field located in the arabian shield 150 km east of the red sea rift axis in the lithospheric mantle beneath harrat lunayyir we locate 64 high frequency earthquakes at depths of 42 48 km all with m l 2 5 these brittle failure earthquakes must have nucleated at relatively low temperatures based upon global maximum nucleation depths and temperature dependent deformation experimental results therefore the mantle earthquakes show that the upper mantle lithosphere is not in thermal equilibrium with the shallow 60 km underlying asthenosphere our thermal modeling indicates that the lithosphere beneath harrat lunayyir thinned to its current 60 km thickness at 12 2 ma as constrained by thermal modeling of 1 surface heat flow 2 the depth to the mid crustal brittle ductile transition and 3 the depth to the upper mantle brittle ductile transition