crustal deformation rates in central and eastern u s inferred from gps analysis of continuous gps observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern united states suggests that the area is generally stable seven of the 62 stations show anomalous velocities but there is reason to suspect their monument stability assuming the remaining 55 stations are stable with respect to interior north america we have found the north america itrf97 euler vector 1 88 1 04 n 77 67 0 39 w 0 201 0 004 myr 1 that minimizes the rms station velocity referred to fixed north america all of these velocities are less than 3 2 mm yr 1 motion of several stations suggests the mississippi embayment may be moving southward away from the rest of the continent at a rate of 1 7 0 9 mm yr 1 the motion of the embayment produces a large gradient in velocity which in turn implies the highest seismic moment accumulation rate that we found although the highest rate is only marginally significant the fact that it occurs near new madrid where earthquake risk is thought to be high argues that the anomaly may be real nevertheless the identification of the anomaly remains tentative

detecting hazardous new zealand faults at depth using seismic velocity gradients abstract many large damaging earthquakes occur along previously unmapped faults because it is difficult to locate active faults that have slow average slip rates long recurrence intervals and weak surface expression we use recently collected seismic wave velocity data from new zealand to test whether there is a strong correlation between seismic velocity gradients deep in the earth s crust known active faults and large shallow historical earthquakes the correlation with active faults is significant at the 99 confidence level suggesting that seismic velocity gradients at depth can pinpoint active and in some cases unmapped faults that may reactivate and rupture in infrequent earthquakes in addition all eight of the post 1840 m w 7 upper crustal earthquakes in new zealand within the region of good tomographic coverage are spatially correlated with mid crustal seismic velocity gradients and ruptured faults that intersect them many of the seismic velocity gradients coincide with the faulted edges of strong blocks within basement rocks consistent with these marking preferred sites for fault reactivation owing to inherited strength contrasts we propose that seismic velocity gradients provide a means to map potentially hazardous undiscovered faults at mid crustal depths in advance of their activation in future damaging earthquakes

quaternary deformation along the meeman shelby fault near memphis tennessee imaged by high resolution marine and land seismic reflection profiles 1 a series of high resolution seismic reflection surveys was carried out in 2008 2010 and 2011 providing a total of five new seismic profiles constraining the location and character of the meeman shelby fault msf about 9 km west of memphis tennessee in the central u s the msf is the best documented fault closest to memphis yet discovered and shows a recurrent fault history the fault as imaged by the reflection profiles is 45 km long strikes n25 e and dips west northwest 83 exhibiting an up to the west sense of motion with a possible right lateral strike slip component the data show that on average the msf offsets the paleozoic unit 77 m and folds the top of the cretaceous unit and the paleocene eocene wilcox group 44 and 25 m respectively one seismic profile acquired along the mississippi river images the bottom of the quaternary alluvium warped up 28 m indicating recent activity of the msf calculated vertical slip rates of the msf during the deposition of the upper cretaceous paleocene eocene and quaternary sediments are 0 0022 0 0010 0 0004 and 0 2154 mm yr respectively suggesting an increase in fault activity during the quaternary consistent with the present stress field and the deformation of the new madrid seismic zone fault system we interpret the msf as a p shear fault in the context of a left stepping right lateral constraining strike slip fault system under a nearly east west oriented compressional stress field source scaling estimates indicate that the msf is capable of generating a m6 9 earthquake if rupturing in one event

identification of possible quaternary deformation in the northeastern mississippi embayment using quantitative geomorphic analysis of drainage basin asymmetry to investigate neotectonism in the mississippi embayment east of the new madrid seismic zone we identified geomorphic domains that show evidence of ground tilting during quaternary time transverse basin profiles were converted to two dimensional vectors that denote channel position with respect to basin divides these basin asymmetry vectors record the net direction and degree of lateral migration of trunk streams more than 2500 vectors were measured and spatially averaged within 400 km 2 bins this field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting the timing of stream migration was interpreted using across valley distributions of quaternary alluvial terraces comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults late quaternary activity is suggested for two northeast striking faults of the southeastern reelfoot rift margin we acquired two seismic profiles showing near surface faulting beneath scarps that follow the domain boundary associated with one of these northeast striking faults big creek fault zone reelfoot thrust seismicity ends on the south against this fault suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall our vector field also suggests late quaternary movement on the reelfoot thrust and on two other northwest striking faults here termed the hatchie river fault and the wolf river fault several other weak domains may imply minor elements of neotectonism our results demonstrate that morphometric analysis of drainage basin asymmetry can be an effective reconnaissance tool within neotectonic settings

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

evidence for holocene displacements on the bootheel fault lineament in southeastern missouri seismotectonic implications for the new madrid region the 135 km long bootheel lineament is a zone of en echelon narrow linear bands of sand blows oriented n24 e in southeast missouri and northeast arkansas within the epicentral area of the 1811 1812 new madrid earthquakes holocene faulting along the central part of the lineament vertically displaced a 10 2 ka old pleistocene braid stream sand 3 m and dextrally displaced a ca 2 4 ka old holocene paleochannel at least 13 m the fault zone is less than 8 m wide where studied in detail these observations suggest that the bootheel lineament is a fault and we therefore suggest that it be renamed the bootheel fault the area east of the bootheel fault in our study area may have been uplifted 3 m during at least three holocene events perhaps by a compressional pop up at a 1 5 km wide left step restraining offset south of the study site the very low level of instrumental seismicity recorded near the bootheel fault suggests that it is either locked because of structural complexity or it is currently inactive though the source zones are poorly known great earthquake sequences in a d 1811 1812 a d 1450 and a d 900 have been identified in the new madrid seismic zone using the historical record and paleoseismology tuttle et al 2002 1 based on the estimated 13 m of horizontal paleochannel displacement an approximate 2 4 ka paleochannel age and a mean great earthquake recurrence interval of 500 yr cramer 2001 2 tuttle et al 2002 1 the local mean horizontal slip rate is estimated to be 3 5 m per event when displacement does occur on the bootheel fault it may subsequently load other faults accounting for past earthquake sequences in the new madrid region 1 ref 56 2 ref 7

carbon flows in the biosphere present and future the atmosphere biosphere and ocean surface layers contain approximately equal amounts of carbon the deep ocean contains over 50 times as much the flux of carbon between these pools is dominated by the process of photosynthesis which is itself influenced by the co 2 concentration of the atmosphere over the last 200 years deforestation and now fossil fuel combustion have added co 2 to the atmosphere to increase the concentration by 27 half the increase occurred over the last 30 years the resulting greenhouse effect has been accompanied by an increase in the global average temperature of about 0 5 other 9greenhouse gases9 n 2 o 1 o 3 cfcs ch 4 are also contributing to the warming present uncertainties with estimating carbon flows result from the disputed contribution of deforestation the level of increased plant productivity and carbon storage due to co 2 fertilization and problems with estimating net primary production uncertainties in estimating future carbon balances arise from the extent of fossil fuel use especially by usa ussr and china the degree of control of greenhouse gas emissions the co 2 fertilization effect on plant productivity and vegetation responses including moisture availability and the rate of change of the climatic factors resulting from changing carbon fluxes

the emergence of seismic cycles from stress feedback between intra plate faulting and far field tectonic loading abstract using numerical modeling we show the emergence of cyclic slip behavior of faults from stress feedback through an idealized fault its surrounding plates and far field tectonic stress the tectonic stress is exerted on the fault through a force applied along an idealized plate margin acting on the fault resulting from the interactions of viscous embedding and external plates we find that in such coupled system the interaction of plates results into feedback with periodic deformation slip along the fault and episodic plate margin motions the viscosity of the embedding and loading plates primarily control the stress loading time and hence the slip recurrence interval for an earth like range of lithospheric viscosities we derive a power law with negative exponent 0 99 to 0 5 scaling the recurrence period with loading rate providing an explanation for the observables from paleoseismology and geodesy the feedback between single fault and far field stress that arises from interactions of deforming plates provides a context to understand the earthquake cycle within continents while reconciling the short term seismic deformation to the long term plate tectonics frame

seismic reflection profiling studies of a buried precambrian rift beneath the wabash valley fault zone sixty eight kilometers of 12 fold seismic reflection data were collected in the wabash river valley of southwestern indiana and southeastern illinois to investigate the configuration of a basement structure inferred from regional gravity and magnetic anomaly data the seismic profiles were also positioned to cross faults of the wabash valley fault system in a number of locations interpretation of the seismic reflection profiles and detailed gravity and magnetic profile data provides evidence for a series of northeasterly trending grabens in the basement these grabens are filled with pre mt simon layered rocks and are overlain by paleozoic sedimentary rocks of the illinois basin beneath the wabash river near grayville illinois an interpreted graben the grayville graben is approximately 15 km wide and contains about 3 km of fill individual boundary faults for the graben cut prominent reflectors within pre mt simon rocks and display offsets of up to 500 m the interpreted configuration of basement

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

the repeat time of the 1811 and 1812 new madrid earthquakes a geological perspective abstract the great new madrid earthquakes of 1811 and 1812 were accompanied by extensive liquefaction within the meizoseismal zone we examined tens of kilometers of freshly excavated ditch banks within the southern limb of the new madrid seismic zone for evidence of prehistoric liquefaction events radiocarbon dates indicate that the exposures studied provide a record of the last 5000 to 10 000 years analyses of the statistics of historical seismicity imply a relatively short 550 to 1100 yr repeat time for 1811 to 1812 type earthquakes in contrast our search did not reveal definitive evidence of widespread paleoliquefaction events and hence provides no independent support for the relatively short 550 to 1100 yr return time implied by statistics of historical seismicity

long aftershock sequences within continents and implications for earthquake hazard assessment one of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries plate tectonics gives no insight however into where and when earthquakes will occur within plates because the interiors of ideal plates should not deform as a result within plate interiors assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes here however we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago we present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries these predictions are in accord with observations so the common practice of treating continental earthquakes as steady state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere

toward a consistent model for strain accrual and release for the new madrid seismic zone central united states 1 at the heart of the conundrum of seismogenesis in the new madrid seismic zone is the apparently substantial discrepancy between low strain rate and high recent seismic moment release in this study we revisit the magnitudes of the four principal 1811 1812 earthquakes using intensity values determined from individual assessments from four experts using these values and the grid search method of bakun and wentworth 1997 we estimate magnitudes around 7 0 for all four events values that are significantly lower than previously published magnitude estimates based on macroseismic intensities we further show that the strain rate predicted from postglacial rebound is sufficient to produce a sequence with the moment release of one mmax6 8 every 500 years a rate that is much lower than previous estimates of late holocene moment release however mw6 8 is at the low end of the uncertainty range inferred from analysis of intensities for the largest 1811 1812 event we show that mw6 8 is also a reasonable value for the largest main shock given a plausible rupture scenario one can also construct a range of consistent models that permit a somewhat higher mmax with a longer average recurrence rate it is thus possible to reconcile predicted strain and seismic moment release rates with alternative models one in which 1811 1812 sequences occur every 500 years with the largest events being mmax 6 8 or one in which sequences occur on average less frequently with mmax of 7 0 both models predict that the late holocene rate of activity will continue for the next few to 10 thousand years

comment on why earthquake hazard maps often fail and what to do about it by s stein r geller and m liu stein et al 2012 contends that the occurrence of some recent destructive earthquakes in areas mapped as low hazard in some probabilistic seismic hazard maps illustrates limitations of earthquake hazard mapping this statement is fundamentally incorrect these instances illustrate that short term observations such as recent seismicity do not characterize the hazard from faults with long recurrence time earthquakes this is not an inherent limitation in the methodology of probabilistic seismic hazard assessment psha they repeat arguments made in their previous articles one of them recent stein et al 2011 and others on the new madrid region of the central united states that were published and commented on several years ago e g frankel 2003 2004 stein et al 2003 stein et al 2012 makes three major points 1 the inputs to seismic hazard maps should include long term geologic data in addition to historical and instrumental seismicity 2 uncertainties in hazard values should be estimated and communicated to users and 3 seismic hazard maps need to be objectively tested the first two points have long been recognized and practiced in the seismic hazard mapping community in the united states and elsewhere the third point has also been the subject of substantial work e g stirling and petersen 2006 this comment points out problems

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

global finite element model makes a small contribution to intraplate seismic hazard estimation seismic hazard estimates require merging datasets from seismology geodesy and geology that have different footprints which works best when there is a global model that relates them the rigid plate model serves this purpose for plate boundary hazard estimation but fails for intraplate hazard the global thin shell finite element model of the lithosphere by bird 1998 is a first attempt at a model with realistic intraplate regions it is based on stress equilibrium and assumed flow laws for the lithosphere incorporates topographic and geothermal variations and plate boundary faults and predicts long term anelastic strain rates in all plate interiors for comparison the historical seismic catalog jissig utsu 1996 and the instrumental catalog cmt dziewonski et al 1997 are converted to seismic strain rates in intraplate regions corresponding to the finite elements spatial correlations are tested between the logarithms of strain rates in order to reduce the dominance of the greatest earthquakes the finite element model has correlations of 0 391 with jissig and 0 338 with cmt neither of which is as high as the correlation of jissig with cmt 0 476 this may mean that the model is defective or that intraplate seismicity contains a large fraction of aftershocks and other triggered events if we take the cmt dataset as representative of the short term intraplate seismicity that we might try to forecast then multiple regression shows that this is best correlated 0 504 with a 56 44 mixture of the jissig and finite element model strain rates the contribution of the finite element model though small is significant with 99 9 confidence

distribution and formation of okhotsk sea intermediate water an analysis of isopycnal climatological data 1 in order to clarify the distribution and formation of okhotsk sea intermediate water osiw an isopycnal climatological data set based on all of the available historical observations is developed and examined the isopycnal maps clearly show that there are two direct ventilation sources for osiw dense shelf water dsw with cold and fresh properties influenced by sea ice formation in the northwest shelf region and forerunner of soya warm current water fscw which has warm and saline properties originating in the japan sea the cold and fresh water extends southward from the northwest shelf to the shelf slope off sakhalin island it suggests that dsw is transported southward by the east sakhalin current the dsw enters the kuril basin and mixes with fscw and western subarctic water wsaw originating from the north pacific to form osiw the annual mean production rate of dsw estimated from the total volume of dsw over the shelf in spring and summer is 0 67 sv 1 sv 106 m3 s the annual mean volume transport of fscw is estimated to be 0 08 sv on the basis of its cross section area and the current speed assumption of isopycnal mixing yields a mixing ratio of 1 1 0 1 among dsw wsaw and fscw to form osiw we estimate the annual production rate of osiw to be 1 4 sv the corresponding osiw s renewal time is 7 years continued assumption of isopycnal mixing yields a mixing ratio of 0 6 0 4 between wsaw and osiw to form oyashio intermediate water oyiw

seismology tectonic strain in plate interiors reply the independent analyses of gama global positioning system gps array in mid america data by calais 1 demonstrate the difficulties in determining patterns of rational deformation within otherwise rigid plates we are a long way from incorporating this type of information into seismic hazard analysis and we agree that longer time spans and improved spatial coverage with geodetic quality data are required in order to gather the observations necessary to start modelling and understanding this enigmatic region

steady contemporary deformation of the central basin and range province western united states we use data from western u s gps networks to estimate the rate pattern and style of tectonic deformation of the central basin and range province brp previous geodetic investigations have found the crust of eastern nevada and western utah to act as a rigid microplate with zero deformation rates to within measurement uncertainty observed transients in gps time series have led others to propose a megadetachment model predicting that the central brp behaves as a microplate but with time varying translation here we reassess these hypotheses benefiting from a significant increase in gps stations and time span and innovations in analysis techniques our results show that the brp crust deforms everywhere and all the time in a group of 24 stations between longitude 113 5 and 116 8 we find strain rates of 1 9 0 2 10 9 yr 1 extension directed n55 w and 2 2 0 2 10 9 yr 1 contraction directed n35 e inconsistent with microplate behavior the linearity of time series of strain from gps station triplets is inconsistent with episodic translation of quasi rigid domains one exception is station egan that exhibits nonlinear motion not found in adjacent stations the dominant signal in nevada is distributed shear consistent with pacific north america relative plate motion suggesting that stresses are transmitted through the lithosphere at least 800 km from the plate boundary the observed active extension is consistent with earthquake focal mechanisms and is in agreement with integrated rates estimated from earthquake geology our results do not support the proposed megadetachment in the brp

strong vertical mixing in the urup strait 1 microstructure measurements were conducted in one of the kuril straits in the summer of 2007 over the course of 1 day of repeated observations across the pacific side of the steep sill of the urup strait extremely strong mixing was observed during periods of pacific ward down sill flows and during the transition from pacific ward to okhotsk ward up sill flows with a turbulent energy dissipation rate of 10 6 to 10 5 w kg 1 and vertical diffusivity of 10 1 to 5 10 1 m2 s 1 during the period of strong mixing we observed homogeneous layers with a thickness of 300 600 m and potential density of 26 6 26 7 occupying the entire water column in one case high values of within this layer indicate the injection of diapycnal flows from the upper and lower layers possibly contributing to southward intrusion of intermediate water into the subtropical gyre

strain accumulation in the new madrid and wabash valley seismic zones from 14 years of continuous gps observation the mechanical behavior and hence earthquake potential of faults in continental interiors is an issue of critical importance for the resultant seismic hazard but no consensus has yet been reached on this controversial topic the debate has focused on the central and eastern united states in particular the new madrid seismic zone struck by four magnitude 7 or greater earthquakes in 1811 1812 and to a lesser extent the wabash valley seismic zone just to the north a key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults a quantity that remains debated here we address this issue with an analysis of up to 14 6 years of continuous gps data from a network of 200 sites in the central united states centered on the new madrid and wabash valley seismic zones we find that the high quality sites in these regions show motions that are consistently within the 95 confidence limit of zero deformation these results place an upper bound on strain accrual on faults of 0 2 mm yr and 0 6 mm yr in the new madrid and wabash valley seismic zones respectively for the new madrid region where a paleoseismic record is available for the past 5000 years we argue that strain accrual if any does not permit the 500 900 year repeat time of paleo earthquakes observed in the upper mississippi embayment these results together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicate that either tectonic loading rates or fault properties vary with time in the new madrid seismic zone and possibly plate wide

neotectonics of the southeastern reelfoot rift zone margin central united states and implications for regional strain accommodation the northeast striking new madrid fault system of central north america has been described as a right lateral strike slip system with a left stepping restraining bend thrust the fault system has one of the highest rates of seismic energy release in an intraplate setting and it has been regarded as a zone of significant earthquake hazard the new madrid fault system is the central part of the wider reelfoot rift fault system a northeast striking basement fault zone although component faults of the new madrid system are well defined by microseismicity recent geodetic surveys suggest that little if any strain is accumulating on the principal southern strike slip arm of the fault system seismicity and geologic data show that the restraining bend thrust continues past the southern strike slip arm to the southeastern reelfoot rift margin thus we suggest that earthquakes defining the southern arm of the new madrid fault system are primarily aftershocks of an earthquake on that arm during the last sequence of great earthquakes a d 1811 1812 and it is the southeastern rift margin fault system that is currently accommodating right lateral strain along the boundary of the thrust block this interpretation is consistent with recent geodetic results the southeastern rift margin coincides with a 150 km long linear topographic scarp from near memphis to the tennessee kentucky line and s wave reflection profiles auger data and a trench excavation reveal late wisconsin early holocene surface faulting and late holocene liquefaction associated with this fault line scarp variation in sense of throw along strike and flower structure geometry suggest that this is a strike slip fault recognition of this rift margin as an important element of active tectonism in the mississippi embayment has broad implications for assessment of the seismic hazard of this and similar intraplate settings temporal shifts in strain accommodation may give rise to short term seismicity patterns and or geodetic velocities that do not reveal long term tectonic patterns

spatiotemporal complexity of continental intraplate seismicity insights from geodynamic modeling and implications for seismic hazard estimation continental intraplate seismicity seems often episodic clustered and mi grating the observed seismicity shows both spatial clustering in seismic zones and scattering across large plate interiors temporal clustering followed by long periods of quiescence and migration of seismicity from one seismic zone to another here we explore the complex spatiotemporal patterns of intraplate seismicity using a 3d visco elasto plastic finite element model the model simulates tectonic loading crustal failure in earthquakes and coseismic and postseismic stress evolution for a later ally homogeneous lithosphere with randomly prespecified perturbations of crustal strength the model predicts various spatiotemporal patterns of seismicity at different timescales spatial clustering in narrow belts and scattering across large regions over hundreds of years connected seismic belts over thousands of years and widely scat tered seismicity over tens of thousands of years the orientation of seismic belts coincides with the optimal failure directions associated with the assumed tectonic loading stress triggering and migration cause spatiotemporal clustering of earth quakes when weak zones are included in the model the predicted seismicity initiates within the weak zones but then extends far beyond them if a fault zone is weakened following a large earthquake repeated large earthquakes can occur on the same fault zone even in the absence of strong tectonic loading these complex spatiotemporal patterns of intraplate seismicity predicted in this simple model suggest that assessment of earthquake hazard based on the limited historic record may be biased toward over estimating the hazard in regions of recent large earthquakes and underestimating the hazard where seismicity has been low during the historic record

fault slip rates in the modern new madrid seismic zone structural and geomorphic analysis of late holocene sediments in the lake county region of the new madrid seismic zone indicates that they are deformed by fault related folding above the blind reelfoot thrust fault the widths of narrow kink bands exposed in trenches were used to model the reelfoot scarp as a forelimb on a fault bend fold this coupled with the age of folded sediment yields a slip rate on the blind thrust of 6 1 0 7 mm year for the past 2300 100 years an alternative method used structural relief across the scarp and the estimated dip of the underlying blind thrust to calculate a slip rate of 4 8 0 2 mm year geometric relations suggest that the right lateral slip rate on the new madrid seismic zone is 1 8 to 2 0 mm year

sinking mafic body in a reactivated lower crust a mechanism for stress concentration at the new madrid seismic zone we propose a geodynamic model for stress concentration in the new madrid seismic zone nmsz the model postulates that a high density mafic body situated in the deep crust directly beneath the most seismically active part of the nmsz began sinking several thousands of years ago when the lower crust was suddenly weakened based on the fact that deformation rates in the nmsz have accelerated over the past 9 k y we envision the source of this perturbation to be related to the last north american deglaciation excess mass of the mafic body exerts a downward pull on the elastic upper crust leading to a cycle of primary thrust faulting with secondary strike slip faulting after which continued sinking of the mafic body reloads the upper crust and renews the process this model is consistent with the youth of activity the generation of a sequence of earthquakes and the velocity evolution during interseismic periods which depend upon the density contrast of the mafic body with respect to the surrounding crust its volume and the viscosity of the lower crust

space geodetic evidence for rapid strain rates in the new madrid seismic zone of central usa a series of large earthquakes centred on the town of new madrid in the mississippi valley in the winter of 1811 12 still reverberates in the world of seismology the controversy relates to their origin over 2 000 km from the nearest plate boundary and their relevance to earthquake hazard today the population of new madrid in the early nineteenth century was tiny a similar event today would have much more serious consequences new evidence based on gps data points to the existence of rapid strain rates in the area comparable in magnitude to those across active plate boundaries and consistent with known active faults in the region in the winter of 1811 1812 near the town of new madrid in the central united states and more than 2 000 km from the nearest plate boundary three earthquakes within three months shook the entire eastern half of the country and liquefied the ground over distances far greater than any historic earthquake in north america1 2 the origin and modern significance of these earthquakes however is highly contentious3 geological evidence demonstrates that liquefaction due to strong ground shaking similar in scale to that generated by the new madrid earthquakes has occurred at least three and possibly four times in the past 2 000 years refs 4 6 consistent with recurrence statistics derived from regional seismicity7 here we show direct evidence for rapid strain rates in the area determined from a continuously operated global positioning system gps network rates of strain are of the order of 10 7 per year comparable in magnitude to those across active plate boundaries and are consistent with known active faults within the region these results have significant implications for the definition of seismic hazard and for processes that drive intraplate seismicity

fine and microstructure observations in the urup strait kuril islands during august 2006 1 for the first time we performed continuous observations of turbulent mixing upon the sill of the urup strait kuril islands for a period of 1 day during august of 2006 time series of velocity profiles water properties and isopycnal depths show variability with a period of about 1 day however the water mass variability is not explained by simple water exchange between the sea of okhotsk and the north pacific empirical orthogonal function eof analysis of isopycnal coordinates extracted variability presumed to represent tidal flows as major eofs in profiles of the residual flow after subtracting the mean flow and major eofs we detected phase propagations consistent with internal gravity waves with an approximate period of 9 1 11 4 h the turbulent energy dissipation rate and vertical diffusivity k ranged from 1 10 9 to 3 10 8 w kg 1 and from 3 10 5 to 2 10 3 m2s 1 respectively occurrences of high dissipation rates generally corresponded to either strong shear or weak stratification a significant contribution of shear s to the dissipation rate was indicated with a relationship of s1 4 s1 8 probably related to propagating internal waves a strong mixing event was observed within the water column with extremely weak stratification and a richardson number below the critical value of 0 25 when the flow direction changed from up sill to down sill

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

global review of human induced earthquakes the human induced earthquake database hiquake is a comprehensive record of earthquake sequences postulated to be induced by anthropogenic activity it contains over 700 cases spanning the period 1868 2016 activities that have been proposed to induce earthquakes include the impoundment of water reservoirs erecting tall buildings coastal engineering quarrying extraction of groundwater coal minerals gas oil and geothermal fluids excavation of tunnels and adding material to the subsurface by allowing abandoned mines to flood and injecting fluid for waste disposal enhanced oil recovery hydrofracturing gas storage and carbon sequestration nuclear explosions induce earthquakes but evidence for chemical explosions doing so is weak because it is currently impossible to determine with 100 certainty which earthquakes are induced and which not hiquake includes all earthquake sequences proposed on scientific grounds to have been human induced regardless of credibility challenges to constructing hiquake include under reporting which is 30 of m 4 events 60 of m 3 events and 90 of m 2 events the amount of stress released in an induced earthquake is not necessarily the same as the anthropogenic stress added because pre existing tectonic stress may also be released thus earthquakes disproportionately large compared with the associated industrial activity may be induced knowledge of the magnitude of the largest earthquake that might be induced by a project mmax is important for hazard reduction observed mmax correlates positively with the scale of associated industrial projects fluid injection pressure and rate and the yield of nuclear devices it correlates negatively with calculated inducing stress change likely because the latter correlates inversely with project scale the largest earthquake reported to date to be induced by fluid injection is the 2016 m 5 8 pawnee oklahoma earthquake by water reservoir impoundment the 2008 m 8 wenchuan people s republic of china earthquake and by mass removal the 1976 m 7 3 gazli uzbekistan earthquake the minimum amount of anthropogenic stress needed to induce an earthquake is an unsound concept since earthquakes occur in the absence of industrial activity the minimum amount of stress observed to modulate earthquake activity is a few hundredths of a megapascal and possibly as little as a few thousandths equivalent to a few tens of centimeters of water table depth faults near to failure are pervasive in the continental crust and induced earthquakes may thus occur essentially anywhere in intraplate regions neither infrastructure nor populations may be prepared for earthquakes human induced earthquakes that cause nuisance are rare but in some cases may be a significant problem e g in the hydrocarbon producing areas of oklahoma usa as the size of projects and density of populations increase the potential nuisance of induced earthquakes is also increasing and effective management strategies are needed

in situ evidence for dextral active motion at the arabia india plate boundary the arabia india plate boundary also called theowen fracture zone is perhaps the least known boundary among large tectonic plates1 6 although it was identified early on as an example of a transform fault converting the divergent motion along the carlsberg ridge to convergent motion in the himalayas7 its structure and rate of motion remains poorly constrained here we present the first direct evidence for active dextral strike slip motion along this fault based on seafloor multibeam mapping of the arabia india somalia triple junction in the northwest indian ocean there is evidence for 12km of apparent strike slip motion along the mapped segment of the owen fracture zone which is terminated to the south by a 50 km wide pull apart basin bounded by active faults by evaluating these new constraints within the context of geodetic models of global plate motions we determine a robust angular velocity for the arabian plate relative to the indian plate that predicts 2 4mmyr 1 dextral motion along the owen fracture zone this transformfault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions8 11 which induced a change in configuration of the triple junction infrequent earthquakes of magnitude 7 and greater may occur along the arabia india plate boundary unless deformation is in the formof aseismic creep

lithospheric velocity structure of the new madrid seismic zone a joint teleseismic and local p tomographic study 1 the enigmatic seismicity in the new madrid seismic zone nmsz has been attributed to some abnormal lithospheric structure including the presence of dense mafic intrusions and a low viscosity lower crust however the area s detailed lithospheric structure remains unclear here we invert 2 056 teleseismic p and 12 226 local p first arrival times from a recent nine year dataset to infer the lithospheric velocity structure beneath the nmsz our results show that the seismically active zone is associated with a local ne sw trending low velocity anomaly in the lower crust and upper mantle instead of high velocity intrusive bodies proposed in previous studies the low velocity anomaly is on the edge of a high velocity lithospheric block consistent with the notion of stress concentration near rheological boundaries this lithospheric weak zone may shift stress to the upper crust when loaded thus leading to repeated shallow earthquakes

geometry numerical models and revised slip rate for the reelfoot fault and trishear fault propagation fold new madrid seismic zone abstract the geometry and structural relief of late holocene sediments folded across the reelfoot scarp are characterized with trench excavations shallow borings a digital elevation model dem of topography and reelfoot lake rl bathymetry results suggest the scarp forms by heterogeneous shear in the forelimb of a fault propagation fold seismic data and the accompanying structural analysis support the argument that the reelfoot fault does not offset the surface and that the reelfoot scarp is a fold limb structural relief measured across the reelfoot scarp is slightly higher than previous determinations and varies from 7 to 11 m along the western shoreline of rl numerical models based on trishear kinematics constrain growth of the reelfoot monocline and indicate that the underlying reelfoot thrust fault is steeply dipping the shallowest portion of the central reelfoot thrust segment dips 75 where the fault tip has propagated upward from 911 m to its current location 465 m beneath the surface the models indicate that the shallowest section of the southern thrust segment in the reelfoot thrust system dips even more steeply at 80 but has propagated upward only a few tens of meters to its present location 1016 m beneath the surface the thrust is flatter at deeper levels based on the location of earthquake hypocenters strain across the reelfoot scarp is partitioned into two or three separate fold scarps that collectively record a late holocene fault slip rate of 3 9 0 1 mm yr the slip rate is based on 9 m of structural relief the 2290 60 ybp age of folded sediment and a 75 dip for the fault this implies a rate of horizontal contraction in the seismic zone of 1 0 mm yr this rate is strongly dependent on the dip of the thrust calculated by the structural analysis the numerical models argue for reactivation of faults that previously offset paleozoic strata

displacement history and slip rate on the reelfoot fault of the new madrid seismic zone abstract a displacement history and slip rates were determined for the reelfoot fault in the new madrid seismic zone from a seismic reflection profile and trench data based on calculations from the seismic reflection line the average slip rate over the last 80 million years is 0 0009 mm year 1 slip rate during the late cretaceous was 0 0007 mm year 1 0 002 mm year 1 during the paleocene midway group 0 001 mm year 1 during paleocene eocene wilcox formation time 0 0003 mm year 1 during the post wilcox pre holocene period and a holocene slip rate of 1 8 mm year 1 based on trench data slip rate on the reelfoot fault has been 4 4 mm year 1 over the last 2400 years and a maximum of 6 2 mm year 1 during the two most recent earthquake cycles between ad 900 and ad 1812 the holocene slip rate is at least four orders of magnitude higher than the average late cretaceous and cenozoic slip rates for the reelfoot fault it would appear that there has been a quaternary change in the stress field in the central united states or the reelfoot fault is experiencing a short lived burst of seismic activity

a record of stable continental region earthquakes from western australia spanning the late pleistocene insights for contemporary seismicity abstract in plate boundary regions moderate to large earthquakes are often sufficiently frequent that fundamental seismic parameters such as the recurrence intervals of large earthquakes and maximum credible earthquake mmax can be estimated with some degree of confidence the same is not true for the stable continental regions scrs of the world large earthquakes are so infrequent that the data distributions upon which recurrence and mmax estimates are based are heavily skewed towards magnitudes below m w 5 0 and so require significant extrapolation up to magnitudes for which the most damaging ground shaking might be expected the rarity of validating evidence from surface rupturing palaeo earthquakes typically limits the confidence with which these extrapolated statistical parameters may be applied herein we present a new earthquake catalogue containing in addition to the historic record of seismicity 150 palaeo earthquakes derived from 60 palaeo earthquake features spanning the last 100 ka of the history of the precambrian shield and fringing extended margin of southwest western australia from this combined dataset we show that mmax in non extended scr is m7 25 0 1 and in extended scr is m7 65 0 1 we also demonstrate that in the 230 000 km 2 area of non extended scr crust the rate of seismic activity required to build these scarps is one tenth of the contemporary seismicity in the area consistent with episodic or clustered models describing scr earthquake recurrence a dominance in the landscape of earthquake scarps reflecting multiple events suggests that the largest earthquakes are likely to occur on pre existing faults we expect these results might apply to most areas of non extended scr worldwide

post seismic crustal deformation and strain rate in bhuj region western india after the 2001 january 26 earthquake summary the mw 7 6 bhuj earthquake in gujarat western india which occurred on 2001 january 26 was a major intraplate event in the indian subcontinent to study the characteristics of transient post seismic deformation at the earth s surface to elucidate the distribution of strain accumulation rate and so understand the earthquake recurrence process five gps campaigns were conducted at 14 sites in bhuj region during 2001 2002 the daily variations in the site position coordinates and the baselines during the early after shock period i e for 21 d starting from 2001 february 10 march 2 showed no short term post seismic crustal deformation neither logarithmic nor exponential function could be well fitted to any of the components of the time series of the position co coordinates indicating no discernable contribution from viscoelastic relaxation poroelastic rebound or afterslip mechanisms the estimated velocity field in itrf2000 spanning five epochs during 2001 2002 has an average of 50 mm yr 1 in north northeast direction to obtain a better perspective of post seismic deformation in the epicentral track the residual velocity field has been expressed in an india fixed reference frame the residual velocity of 11 62 mm yr 1 in a north northwest direction and 5 24 mm yr 1 towards the south seen at sites south and north of the epicentre respectively indicates localized ongoing convergence in the epicentral region at sites away from the epicentre no significant deformation took place the estimated principal strain from the velocity field gives average compression and extension rates of 0 07 and 0 04 micro strain yr 1 respectively a zone of maximum compressive strain rate of 0 30 micro strain yr 1 with azimuth of 11 delineated north of the epicentral region shows good agreement with seismic deformation along the blind fault derived from earthquake focal mechanisms these results suggest ongoing transpressional deformation across the area with a blocked structure embedded between the north wagad fault and south wagad fault this deformation may be related to the present neo tectonic compressive stress regime of the indian plate due to its nne movement against the collision front in the north and its proximity to the triple junction in the western continental margin of the study area

multiple late holocene earthquakes along the reelfoot fault central new madrid seismic zone the reelfoot fault is an east vergent reverse fault underlying the lake county uplift a low amplitude late holocene anticline bordered on the east by the 32 km long reelfoot scarp fluvial deposits across the scarp define an 8 m high east facing monocline most near surface deformation along the scarp is accommodated via folding rather than faulting we interpret the scarp as a fault propagation fold developed over a wcst dipping reverse fault interpreted from shallow seismic reflection data trench exposurcs provide evidence for three episodes of deformation along the reelfoot fault within thc past approximately 2400 years between a d 780 and 1000 between a d 1260 and 1650 and during a d 1812 our best estimate of the average recurrence interval for deformation along the scarp is 400 500 years each episode of deformation had a slightly different style the third most recent event produced a small graben a few tens of centimeters deep in the hanging wall of the reverse fault the second most recent earthquake produced about 1 3 m of throw in the graben as well as folding along the updip projection of the reverse fault and development of the scarp thesc relations suggest that graben development increased through time concomitant with growth of the monocline or that the events are of different magnitude the 1811 1812 episode of deformation produced abundant liquefaction prominent folding of fluvial strata along the scarp and minor faulting in the graben

a physical basis for time clustering of large earthquakes we develop a theory that links stress interaction between earthquakes and the occurrence of temporal clustering coseismic static stress change in the vicinity 50 km of large earthquakes suggests that perturbations of 0 1 to 1 bars may affect the occurrence of other earthquakes at larger distances interactions also seem to exist four m 8 earthquakes have occurred in mongolia on distant faults 400 km during the last century also paleoseismic observations documenting much longer time periods display a time clustering of major events we demonstrate with simple mechanical concepts that postseismic stress relaxation magnifies the coseismic stress change and has a major effect on fault interaction during the seismic cycle in the simple case where two distant faults are coupled the probabilistic occurrence of triggered earthquakes may increase dramatically due to long range postseismic coupling

the 6 june 2003 bardwell kentucky earthquake sequence evidence for a locally perturbed stress field in the mississippi embayment this article describes an unusually well behaved unusually well documented central and eastern united states ceus earthquake sequence detailed analysis of regional and local waveform data from the 6 june 2003 bardwell kentucky earthquake indicates that the mainshock has the seismic moment of m 0 1 3 0 5 10 15 n m m w 4 0 and occurred at a depth of about 2 1 km on a near vertical fault plane a temporary seismic network recorded 85 aftershocks that delineate an east trending fault approximately 1 km in length the hypocenters illuminate a vertical plane between 2 0 and 2 7 km depth the centroid of the aftershock distribution is at 36 875 n 89 010 w and a depth of 2 4 km the aftershock cluster is interpreted as a circular fault area with a radius of 0 44 0 03 km this source radius yields a static stress drop 67 14 bars for the mainshock the focal mechanism for the mainshock has strike 90 dip 89 and rake 165 with a subhorizontal p axis trending 135 a formal stress inversion based on the focal mechanisms of the mainshock and ten aftershocks indicates the maximum compressive stress trends 104 with a plunge of 5 the local stress field near bardwell is therefore rotated about 40 clockwise relative to 65 for eastern north america as a whole the bardwell earthquakes have the opposite sense of slip to earthquakes with east trending nodal planes that occur near new madrid missouri this requires a significant local rotation of the stress field over a distance of 60 km

pleistocene slip rates on the bocono fault along the north andean block plate boundary venezuela the bocono fault is a strike slip fault lying between the north andean block and the south american plate which has triggered at least five mw 7 historical earthquakes in venezuela the north andean block is moving toward nne with respect to a stable south american plate this relative displacement at 12 mm yr 1 in venezuela within the maracaibo block was measured by geodesy but until now the distribution and rates of quaternary deformation have remained partially unclear we used two alluvial fans offset by the bocono fault yaracuy valley to quantify slip rates by combining 10be cosmogenic dating with measurements of tectonic displacements on high resolution satellite images pleiades based upon a fan dated at 79 ka and offset by 1350 1580 m and a second fan dated at 120 273 ka and offset by 1236 1500 m we obtained two pleistocene rates of 5 0 11 2 and 20 0 mm yr 1 consistent with the regional geodesy this indicates that the bocono fault in the yaracuy valley accommodates 40 to 100 of the deformation between the south american plate and the maracaibo block as no aseismic deformation was shown by insar analysis we can assume that the fault is locked since the 1812 event this implies that there is a slip deficit in the yaracuy valley since the last earthquake ranging from 1 to 4 m corresponding to a mw 7 7 6 earthquake this magnitude is comparable to the 1812 earthquake and to other historical events along the bocono fault

reconciling short recurrence intervals with minor deformation in the new madrid seismic zone at least three great earthquakes occurred in the new madrid seismic zone in 1811 and 1812 estimates of present day strain rates suggest that such events may have a repeat time of 1000 years or less paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years however pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed this suggests that the seismic zone is a young feature possibly as young as several tens of thousands of years old and no more than a few million years old

tectonic stress within the new madrid seismic zone refraction data indicate a significant high density rift pillow beneath the new madrid seismic zone we present results of linear and nonlinear viscoelastic finite element modeling to determine whether support of the rift pillow may contribute significantly to the total present day stress field and we consider the implications for intraplate seismicity these models were run for a loading time of 100 m y to account for relaxation and transfer of stress since the last reactivation of the rift in the mid mesozoic results indicate that the nonlinear viscoelastic model with rheological stratification based on composition and temperature agrees well with the observed deformation within the seismic zone and with estimates of regional stress magnitudes the model predicts a maximum compression of 30 40 mpa above the rift pillow in the center of the rift axis if the magnitude of local compression predicted by the nonlinear model produces the inferred clockwise rotation of the order of 10 30 in the direction of shmax maximum horizontal compression near the rift axis the magnitude of regional compression is a factor of 1 to 2 times the magnitude of local compression and consistent with an origin due to ridge push forces the addition of the local stress associated with the rift pillow however results in an approximately 30 reduction in the resolved maximum horizontal shear stress thus while the stress associated with the rift pillow can rotate the stress field into an orientation favorable for failure reduction in the resolved shear stress requires a separate mechanism for strength reduction results of the modeling indicate that stresses from the load of the rift pillow may still be present in the upper crust even after 100 m y and may still play a role in present day deformation and seismicity of the new madrid seismic zone local stress fields of significant tectonic magnitudes may also occur around other ancient rift pillows and help explain the observed correlation between intraplate seismicity and failed rift zones

a seismic hazard uncertainty analysis for the new madrid seismic zone abstract a review of the scientific issues relevant to characterizing earthquake sources in the new madrid seismic zone has led to the development of a logic tree of possible alternative parameters a variability analysis using monte carlo sampling of this consensus logic tree is presented and discussed the analysis shows that for 2 exceedence in 50 year hazard the best estimate seismic hazard map is similar to previously published seismic hazard maps for the area for peak ground acceleration pga and spectral acceleration at 0 2 and 1 0 s 0 2 and 1 0 s sa the coefficient of variation cov representing the knowledge based uncertainty in seismic hazard can exceed 0 6 over the new madrid seismic zone and diminishes to about 0 1 away from areas of seismic activity sensitivity analyses show that the largest contributor to pga 0 2 and 1 0 s sa seismic hazard variability is the uncertainty in the location of future 1811 1812 new madrid sized earthquakes this is followed by the variability due to the choice of ground motion attenuation relation the magnitude for the 1811 1812 new madrid earthquakes and the recurrence interval for m 6 5 events seismic hazard is not very sensitive to the variability in seismogenic width and length

seismic structure of the central us crust and shallow upper mantle uniqueness of the reelfoot rift abstract using seismic surface waves recorded with earthscope s transportable array we apply surface wave imaging to determine 3d seismic velocity in the crust and uppermost mantle our images span several proterozoic and early cambrian rift zones mid continent rift rough creek graben rome trough birmingham trough southern oklahoma aulacogen and reelfoot rift while ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences the reelfoot rift is unique in its association with low mantle seismic velocity its mantle low velocity zone lvz is exceptionally pronounced and extends down to at least 200 km depth this lvz is of variable width being relatively narrow 50 km wide within the northern reelfoot rift which hosts the new madrid seismic zone nmsz we hypothesize that this mantle volume is weaker than its surroundings and that the reelfoot rift consequently has relatively low elastic plate thickness which would tend to concentrate tectonic stress within this zone no other intraplate ancient rift zone is known to be associated with such a deep mantle low velocity anomaly which suggests that the nmsz is more susceptible to external stress perturbations than other ancient rift zones

state of stress and intraplate earthquakes in the united states recently compiled data on the state of stress have been used to define stress provinces in the conterminous united states in which the orientation and relative magnitude of the horizontal principal stresses are fairly uniform the observed pattems of stress constrain mechanisms for generating intraplate lithospheric stresses coupled with new information on geologic structure and tectonism in seismically active areas of the midcontinent and east these data help to define some characteristics common to these areas and to identify key questions regarding why certain faults seem to be seismically active

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

chlorofluorocarbons in the sea of okhotsk ventilation of the intermediate water 1 ventilation of the intermediate layer in the sea of okhotsk is studied with regard to the ventilation of north pacific intermediate water npiw measurements of chlorofluorocarbons cfcs from 1998 to 2000 reveal that the okhotsk intermediate water is ventilated in two ways the first consists of dense water formation in the polynyas that form on the northern shelves during winter measurements show that on the northwestern shelf because of atmospheric cooling and brine rejection the cold water that forms is dense enough to enter the intermediate layer the cfc concentration in this dense shelf water dsw is high and almost saturated with respect to atmospheric cfcs indicating that the dsw experiences active air water gas exchange during its formation away from the shelves the cfc distribution shows that the dsw directly ventilates the upper level of the okhotsk sea intermediate water osiw the second ventilation process is driven by the strong tidal mixing around the bussol strait the observed distribution of cfcs at the 27 4 level suggest that diapycnal mixing around the strait transports cfcs from the surface to this deeper layer ventilating the osiw combination of both processes means that the osiw is more ventilated than pacific water at the same density levels

on the modified mercalli intensities and magnitudes of the 1811 1812 new madrid earthquakes we reexamine original felt reports from the 1811 1812 new madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks in many cases we interpret lower values than those assigned by earlier studies in some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues additionally earlier studies had assigned modified mercalli intensity mmi values of v vii to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high we investigate several approaches to contouring the mmi values using both analytical and subjective methods for the first mainshock on 02 15 lt december 16 1811 our preferred contouring yields m 7 2 7 3 using the area moment regressions of johnston 1996 for the 08 00 lt on january 23 1812 and 03 45 lt on february 7 1812 mainshocks we obtain m 7 0 and m 7 4 7 5 respectively our magnitude for the february mainshock is consistent with the established geometry of the reelfoot fault which all evidence suggests to have been the causative structure for this event we note that the inference of lower magnitudes for the new madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern united states we also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811 1812 sequence

seismic moment assessment of earthquakes in stable continental regions iii new madrid 1811 1812 charleston 1886 and lisbon 1755 summary the sizes of three major or great historical earthquakes are reassessed using the isoseismal area regression tools developed in parts i and ii of this study of stable continental region scr seismicity the earthquakes are 1811 new madrid central united states and its following sequence 1886 charleston coastal south carolina and 1755 lisbon oceanic intraplate off the continental shelf of portugal the analysis confirms the large size of these events and for the first time places constraints on the uncertainty of their seismic moment release because of the exceptionally low seismic wave attenuation of eastern north america ena a separate north american regression of seismic moment on isoseismal area was developed additionally the unknown western extents of the new madrid isoseismal areas were calibrated with the patterns of the m 6 3 6 6 1843 and 1895 earthquakes application of part ii analysis procedures with these corrections yields new madrid size estimates expressed as moment magnitude of m 8 1 0 31 for the 1811 december 16 m 7 8 0 33 for the 1812 january 23 and m 8 0 0 33 for the 1812 february 7 principal events the charleston earthquake s magnitude decreases from m 7 4 to m 7 3 0 26 after compensation for the effect of coastal plain sediments on its inner isoseismals intensity regressions for lisbon are calibrated against the isoseismal pattern of the nearly co located m 7 8 1969 st vincent earthquake which in this case increases the predicted size of lisbon from m 8 4 to m 8 7 0 39 these size estimates are supported by data from independent phenomena extent and severity of liquefaction the maximum distance of induced landslides and for lisbon tsunami wave amplitudes estimated source parameters are controlled by crustal or lithospheric temperature which governs the depth extent of brittle faulting using estimated continental and oceanic geotherms viable fault lengths are 30 80 km for charleston 120 180 km for 1811 new madrid and 180 280 km for lisbon for average displacements of 2 4 m 8 11 m and 10 14 m respectively and for average static stress and strain drops at the estimated seismic moments of this study the 1811 new madrid and the 1755 lisbon events are respectively the largest known scr and oceanic lithosphere earthquakes

microseismic activity and basement controls on an active intraplate strike slip fault ceres tulbagh south africa earthquakes far from plate boundaries are poorly understood because of few well studied examples and uncertainty of what controls the location of these events in 1969 a damaging local magnitude m l 6 3 strike slip earthquake with no surface expression occurred in the ceres tulbagh region in the south african stable continental interior here we present a microseismic study of the ceres tulbagh area conducted over three months in 2012 in which 172 events recorded on at least three stations follow a gutenberg richter relationship for 1 5 m l 0 5 the events delineate a 5 km wide subvertical zone that is microseismically active to a depth of 15 km this fault zone is subparallel to the 1969 aftershock zone and at low angle to the regionally inferred greatest horizontal stress we argue that the microseismically active zone is guided by inherited structures in the basement geology this and similar structures may represent significant earthquake hazard in plate interiors online material tables of station and event parameters and p and s wave arrival times

the origin of the north pacific intermediate water possible source regions of the north pacific intermediate water npiw were investigated with synoptic conductivity temperature depth surveys in the okhotsk sea kuril basin a pycnostad referred to as the okhotsk sea mode water osmw was found in the density range of 26 6 27 the pycnostad is not seen in the western subarctic gyre wsag thus it is an indicative water peculiar to the okhotsk sea the maximum thickness is at 26 7 26 9 centered at 26 8 which coincides with the npiw density range in the north pacific subtropical gyre in the oyashio area east of the southern kuril islands and hokkaido waters that have intermediate temperature salinity and potential vorticity between the osmw and the wsag water were distributed suggesting a following transport route of the npiw source water the thick thus low q q is potential vorticity and low salinity water mass outflowing from the okhotsk sea mixes with the relatively warm saline and high q wsag water to form the oyashio water a coastal part of the oyashio water flows southwestward along the east coast of the southern kuril islands and hokkaido retaining the pycnostad q minimum a large part of the low q oyashio water flows further southward and merges with the kuroshio extension and then flows eastward forming new npiw in this process a salinity minimum develops and the q minimum disappears because of the mixing with a saline kuroshio water old npiw without a pycnostad in the npiw density range these results suggest that the origin of npiw is the water mass in the okhotsk sea osmw and the density of the water mass primarily determines the npiw density centered at around 26 8

earthquake supercycles and long term fault memory abstract long records often show large earthquakes occurring in supercycles sequences of temporal clusters of seismicity cumulative displacement and cumulative strain release separated by less active intervals supercycles and associated earthquake clusters are only partly characterized via the traditionally used aperiodicity which measures the extent that a sequence differs from perfectly periodic supercycles are not well described by commonly used models of earthquake recurrence in the poisson model the probability of a large earthquake is constant with time so the fault has no memory in a seismic cycle renewal model the probability is quasi periodic dropping to zero after a large earthquake then increasing with time so the probability of a large earthquake depends only on the time since the past one and the fault has only short term memory we describe supercycles with a long term fault memory ltfm model where the probability of a large earthquake reflects the accumulated strain rather than elapsed time the probability increases with accumulated strain and time until an earthquake happens after which it decreases but not necessarily to zero hence the probability of an earthquake can depend on the earthquake history over multiple prior cycles we use ltfm to simulate paleoseismic records from plate boundaries and intraplate areas simulations suggest that over timescales corresponding to the duration of paleoseismic records the distribution of earthquake recurrence times can appear strongly periodic weakly periodic poissonian or bursty thus a given paleoseismic window may not capture long term trends in seismicity this effect is significant for earthquake hazard assessment because whether an earthquake history is assumed to contain clusters can be more important than the probability density function chosen to describe the recurrence times in such cases probability estimates of the next earthquake will depend crucially on whether the cluster is treated as ongoing or over

intrusions and anomalous vp vs ratios associated with the new madrid seismic zone 1 detailed p wave velocity vp and s wave velocity vs models and vp vs ratios were determined for a major portion of the new madrid seismic zone using arrival times recorded by the new madrid seismic network and portable array for numerical data acquisition panda stations we performed a simultaneous inversion for p and s wave velocities and hypocentral locations yielding the most detailed tomographic image of the upper portion of the crust to date low vp and high vs anomalies resulted in low vp vs ratios that correspond to the major arms of seismicity north of the intersection of the cottonwood grove blytheville arch cg ba fault with the reelfoot fault the unusual low vp vs values can be attributed to the presence of quartz rich rocks two regions contain anomalous vp and vs values and vp vs ratios that cannot be attributed to variations in rock composition and are probably produced by overpressured fluids one region is located on the hanging wall of the northern portion of the reelfoot fault and is aseismic the other region corresponds to a portion of the southern reelfoot fault that experiences swarm activity a distinct velocity contrast exists across the cg ba fault at depths exceeding 4 65 km basement rocks southeast of the fault have vp values that are 4 6 slower than values for rocks located to the northwest the most logical explanation is that the fault follows a preexisting structural feature or lithologic change in basement rocks

intraplate deformation of the indian subcontinent 1 while deformation at the earth s surface primarily occurs along tectonic plate boundaries major earthquakes have shaken regions deep within continental interiors three of the largest m 7 5 historic intraplate earthquakes occurred within the indian subcontinent suggesting the possibility of significant intraplate deformation we consider surface velocities determined from new gps data collected at 29 continuous gps stations and 41 survey mode gps stations in india between 1995 and 2007 to find a north south shortening rate of 0 3 0 05 nanostrain yr 1 which may be accommodated by 2 1 mm yr of more localized convergence across central india southward motions at 4 7 mm yr of sites on the shillong plateau in northeast india reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau the width and magnitude of the elastic strain accumulation field across the himalaya varies little from 76 90 longitude but the strain is more broadly distributed and convergence rates are higher along the eastern 200 km of the range

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

global tectonics and space geodesy much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries m 1 to 60 kilometers wide nonetheless many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide wide plate boundary zones cover m 15 percent of earth s surface area space geodesy which includes very long baseline radio interferometry satellite laser ranging and the global positioning system is providing the accurate long distance measurements needed to estimate the present motion across and within wide plate boundary zones space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years

three dimensional geometry of the reelfoot blind thrust implications for moment release and earthquake magnitude in the new madrid seismic zone mapping of the reelfoot blind thrust using portable array for numerical data acquisition panda seismicity suggests that it is a complex fault that changes its geometry along strike the thrust appears to be bounded to the north by an east trending strike slip fault the southern end of the thrust is defined by seismicity and does not terminate at a known transverse fault the northern portion of the thrust steepens at shallow levels forming a listric concave upward shape in cross section the southern segment of the thrust is interpreted to flatten near the top of the precambrian basement although some segmentation of the blind thrust is observed from the mapping of 3 km wide strips of seismicity oriented perpendicular to the fault it does not appear to be significant enough to prevent rupture along its entire length the area of the blind thrust 1301 km 2 coupled with several estimates of displacement in the 7 february 1812 event is used to determine the moment released during the event the values of m 0 range from 6 8 10 26 to 1 4 10 27 dyne cm with preferred values between 6 8 10 26 and 8 7 10 26 dyne cm similar calculations for an earthquake in a d 1450 yield a moment release of 1 0 10 27 dyne cm computed moment magnitude for the 7 february 1812 event ranges from m w 7 2 to 7 4 with preferred values between m w 7 2 and 7 3 the moment magnitude for the a d 1450 event is computed as m w 7 3 these values for the magnitude of the 1812 earthquake are lower than previous estimates based on historical records of shaking however this does not imply a lowered seismic risk in the new madrid seismic zone as site effects in the mississippi embayment may significantly amplify the ground motion caused by earthquakes of a given magnitude

fossil strain from the 1811 1812 new madrid earthquakes observations of postseismic deformation generally suggest that the effects of postseismic viscoelastic relaxation may persist for many decades after an earthquake in particular strain effects from the three great earthquakes that occurred in the new madrid seismic zone in 1811 1812 may influence present day measurements of ground deformation in this active seismic region of the central united states forward calculations using an earth rheology that may be appropriate for a continental intraplate region and a simple fault model for the 1811 1812 sequence suggest that postseismic relaxation may be an important factor in driving the unexpectedly high rate of shear deformation recently observed in the southern new madrid seismic zone

northeast oriented transpression structure in the northern new madrid seismic zone extension of a shear zone across the reelfoot fault stepover arm high resolution seismic reflection profiles recently acquired 12 km northeast of the new madrid seismic zone s reelfoot thrust and along the central axis of the reelfoot rift imaged steeply dipping n30 e striking faults that have uplifted and arched post paleozoic sediments in a manner consistent with a dextral strike slip component of displacement the subparallel fault strands have been traced 1 4 km between reflection profiles in order to evaluate the structure s potential regional scale the strike was projected northeast 22 km to its intersection with a nearby industry profile at the intersection this lower resolution profile exhibits a discrete 0 75 km wide structure with style and offset similar to the high resolution lines the high resolution images indicate the deformation extends above paleozoic bedrock affecting the late cretaceous and eocene mississippi embayment sediments as well as the base of the quaternary the paleozoic and cretaceous horizons show as much as 75 and 50 m of relief respectively with the middle eocene and basal quaternary disrupted 25 and 15 m respectively geologic and geophysical logs from a borehole adjacent to the seismic lines constrain the depth velocity and stratigraphic interpretations we interpret the faults as a minimum 34 km northeast extension of the axial fault zone from a throughgoing intersection with the left stepover reelfoot thrust

slow deformation and lower seismic hazard at the new madrid seismic zone global positioning system gps measurements across the new madrid seismic zone nmsz in the central united states show little if any motion these data are consistent with platewide continuous gps data away from the nmsz which show no motion within uncertainties both these data and the frequency magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8 their recurrence interval should well exceed 2500 years longer than has been assumed alternatively the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed hence the hazard posed by great earthquakes in the nmsz appears to be overestimated

some ecological implications of palaeoatmospheric variations the past composition of the atmosphere is gradually being elucidated with increasing precision but advances in the understanding of the ecological and evolutionary implications of atmospheric changes are not keeping pace a graphic model is presented here to indicate the complexity of interacting forces resulting from a change in atmospheric carbon dioxide level and it can be seen that any resultant ecological outcome will be influenced by a series of sometimes opposing factors this is particularly true of the hydrological consequences of atmospheric change and hydrology will undoubtedly prove a major influence on vegetation changes in the levels of both atmospheric carbon dioxide and oxygen have had profound effects on the evolution of plant life by modifying the selective pressures favouring alternative systems of carbon assimilation these photosynthetic strategies are also closely related to local hydrology more ecological and physiological information is clearly needed before the biological consequences of variations in the atmosphere of the past can be appreciated

mid continental earthquakes spatiotemporal occurrences causes and hazards abstract large earthquakes in north china australia northwestern europe central and eastern united states and other mid continents show complex spatiotemporal patterns that do not fit existing earthquake models individual faults or fault zones tend to fall into long term thousands of years or longer dormancy after a cluster of ruptures whereas large earthquakes seem to roam between widespread faults these behaviors are characteristic of complex dynamic systems of interacting faults in such systems widespread faults collectively accommodate slow tectonic loading and a major fault rupture both transfers stress to the neighboring faults and perturbs loading conditions on distant faults because of the slow tectonic loading local stress variations from fault interaction or nontectonic processes or changes of fault strength could trigger mid continental earthquakes the precise spatiotemporal occurrence of large mid continental earthquakes may be unknowable an intrinsic limitation of complex dynamic systems but their qualitative system behavior may be understood by a system approach this approach would render some commonly used concepts such as seismic cycles recurrence intervals characteristic earthquakes and seismic gaps inadequate or irrelevant in mid continents and calls for rethinking of the probability estimates based on these concepts it requires a better understanding of fault interactions on multiple spatial and temporal scales rather than focusing solely on the balance of tectonic loading and yield strength of individual faults or fault segments it also indicates the need for paleoseismic and geodetic studies extending beyond areas where recent large earthquakes occurred and for hazard assessments to reduce the biasing influence of the most recent large earthquakes that tend to dominate the short and incomplete earthquake records

uncertainty assessment for the seismic hazard map of spain abstract the uncertainty assessment for the development of the new seismic hazard maps of spain is explained in this work a detailed description of how uncertainties are considered in the different phases followed for the probabilistic seismic hazard assessment study is presented special emphasis is given to the characterization of the uncertainty of earthquake size parameters contained in the catalog and their propagation to subsequent phases of the analysis such as catalog homogenization completeness and declustering aleatory and epistemic uncertainties are examined and assessed using monte carlo simulations and a logic tree respectively the final impact of uncertainty in hazard estimates is evaluated through coefficient of variation maps showing the areas where larger and lower variability is obtained the hazard maps developed in this work are intended to be the basis for the future revision of the spanish seismic code

significant motions between gps sites in the new madrid region implications for seismic hazard position time series from global positioning system gps stations in the new madrid region were differenced to determine the relative motions between sta tions uncertainties in rates were estimated using a three component noise model con sisting of white flicker and random walk noise following the methodology of langbein 2004 significant motions of 0 37 0 07 one standard error mm yr were found between sites ptgvand stle for which the baseline crosses the inferred deep portion of the reelfoot fault baselines between stle and three other sites also show significant motion site mcty adjacent to stle also exhibits significant motion with respect to ptgv these motions are consistent with a model of interseismic slip of about 4 mm yr on the reelfoot fault at depths between 12 and 20 km if constant over time this rate of slip produces sufficient slip for an m 7 3 earthquake on the shallow portion of the reelfoot fault using the geologically derived recurrence time of 500 years this model assumes that the shallow portion of the fault has been pre viously loaded by the intraplate stress a gps site near little rock arkansas shows significant southward motion of 0 3 0 4 mm yr 0 08 mm yr relative to three sites to the north indicating strain consistent with focal mechanisms of earthquake swarms in northern arkansas

dense lower crust elevates long term earthquake rates in the new madrid seismic zone knowledge of the local state of stress is critical in appraising intraplate seismic hazard inverting earthquake moment tensors we demonstrate that principal stress directions in the new madrid seismic zone nmsz differ significantly from those in the surrounding region faults in the nmsz that are incompatible with slip in the regional stress field are favorably oriented relative to local stress we jointly analyze seismic velocity gravity and topography to develop a 3 d crustal and upper mantle density model revealing uniquely dense lower crust beneath the nmsz finite element simulations then estimate the stress tensor due to gravitational body forces which sums with regional stress the anomalous lower crust both elevates gravity derived stress at seismogenic depths in the nmsz and rotates it to interfere more constructively with far field stress producing a regionally maximal deviatoric stress coincident with the highest concentration of modern seismicity moreover predicted principal stress directions mirror variations observed independently in moment tensors at the nmsz and across the region

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

tectonic development of the new madrid rift complex mississippi embayment north america abstract geological and geophysical studies of the new madrid seismic zone have revealed a buried late precambrian rift beneath the upper mississippi embayment area the rift has influenced the tectonics and geologic history of the area since late precambrian time and is presently associated with the contemporary earthquake activity of the new madrid seismic zone the rift formed during late precambrian to earliest cambrian time as a result of continental breakup and has been reactivated by compressional or tensional stresses related to plate tectonic interactions the configuration of the buried rift is interpreted from gravity magnetic seismic refraction seismic reflection and stratigraphic studies the increased mass of the crust in the rift zone which is reflected by regional positive gravity anomalies over the upper mississippi embayment area has resulted in periodic subsidence and control of sedimentation and river drainage in this cratonic region since formation of the rift complex the correlation of the buried rift with contemporary earthquake activity suggests that the earthquakes result from slippage along zones of weakness associated with the ancient rift structures the slippage is due to reactivation of the structure by the contemporary nearly e w regional compressive stress which is the result of plate motions

relationship between observed upper mantle structures and recent tectonic activity across the southeastern united states the lithospheric structure of the southeastern united states is a product of earlier episodes of continental collision and breakup the region is located in the interior of the north american plate away from active plate margins however there is ongoing tectonism in the region with multiple zones of seismicity uplifting arches and cenozoic intraplate volcanism the mechanisms controlling this activity and the state of stress remain enigmatic two important factors are plate strength and preexisting inherited structures here we present new tomographic images of the upper mantle beneath the southeastern united states revealing large scale structural variations in the upper mantle examples include the relatively thick lithospheric mantle of stable north america that abruptly thins beneath the paleozoic appalachian orogeny and the slow upper mantle of the proterozoic reelfoot rift our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering this provides a viable explanation for seismicity uplifting and young intraplate volcanism we postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere we propose that piecemeal delamination has occurred beneath the region throughout the cenozoic removing a significant amount of reworked deformed mantle lithosphere ongoing lithospheric foundering beneath the eastern margin of stable north america explains significant variations in thickness of lithospheric mantle across the former grenville deformation front

seismology tectonic strain in plate interiors arising from r smalley jr m a ellis j paul r b van arsdale nature 435 1088 1090 2005 r smalley et al reply it is not fully understood how or why the inner areas of tectonic plates deform leading to large although infrequent earthquakes smalley et al 1 offer a potential breakthrough by suggesting that surface deformation in the central united states accumulates at rates comparable to those across plate boundaries however we find no statistically significant deformation in three independent analyses of the data set used by smalley et al and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

rupture characteristics of clustered microearthquakes and variations in fault properties in the new madrid seismic zone seismic waveforms from the portable array for numerical data acquisition panda network were used to relocate 45 events occurring in four spatial clusters in the northern new madrid seismic zone nmsz source time functions of the larger ml 2 5 events were obtained and yield estimates of rupture radii between 130 and 175 m and static stress drops at or below the megapascal level there is a tendency for closely located events within 200 m from one another to occur within short time intervals of minutes to days available focal mechanism solutions reveal that some of the clustered events have diverse slip directions indicating that the ruptures occur on adjacent fault patches rather than being repetitive over the same patch on the basis of this and a previous study of events farther south we infer that the properties of the faulting system in the nmsz are laterally heterogeneous and are subject to effects of some temporally and spatially localized processes that drive the faults toward seismic failure comparison of this observation with that in the san andreas fault near parkfield reveals that event clustering occurs in both fault systems on similarly short spatial and temporal scales the inferred localized processes may occur in both fault systems despite their different tectonic environment far field loading rate and geometric style of deformation on the other hand in the nmsz we have not observed any quasiperiodic and repetitive ruptures that have been observed near parkfield this is consistent with a slower or absent aseismic creeping in the nmsz

quaternary deformation and fault structure in the northern mississippi embayment as imaged by near surface seismic reflection data seismicity in the new madrid seismic zone nmsz in the central united states constrains the location of present deformation at depth along four main distinct arms while the surface expression of the ongoing deformation is still unclear to better constrain the surface deformation in the nmsz we integrate existing seismic reflection data with a new 300 km long high resolution seismic reflection profile acquired along the mississippi river from cape girardeau mo to caruthersville mo based on the data we interpret the reelfoot thrust and the new markham fault as upward splays of a blind master fault defined by the seismicity and extending at depth farther north to the south two faults the axial fault and the cottonwood grove fault are imaged above the southern arm of the nmsz both fault display deformation of the paleozoic through the tertiary sediments and a relief of 20 25 m at the base of the quaternary alluvium which we interpret as the result of strike slip motion along a complex fault plane geometry we propose two alternative interpretations for the relationship between the shallow faults and the seismicity in this area 1 the faults merge at depth and are presently both active and 2 the faults are distinct at depth and were active during the quaternary and only the axial fault is presently deforming geological structures mapped at the surface as part of this study show that quaternary deformation is accommodated along a fault network that is more complex than the simple four arm system illuminated by the seismicity a behavior predicted by analog and computer models

earth science new madrid in motion a new network of geodetic field stations has greatly improved monitoring of relative motion across a seismic zone in the central united states it seems that rapid deformation is occurring across this fault system a series of large earthquakes centred on the town of new madrid in the mississippi valley in the winter of 1811 12 still reverberates in the world of seismology the controversy relates to their origin over 2 000 km from the nearest plate boundary and their relevance to earthquake hazard today the population of new madrid in the early nineteenth century was tiny a similar event today would have much more serious consequences new evidence based on gps data points to the existence of rapid strain rates in the area comparable in magnitude to those across active plate boundaries and consistent with known active faults in the region

crustal structure beneath the wabash valley seismic zone from the joint inversion of receiver functions and surface wave dispersion implications for continental rifts and intraplate seismicity

paleoseismology of the southeastern reelfoot rift in western tennessee and implications for intraplate fault zone evolution 1 the southeastern reelfoot rift margin is expressed as a series of collinear scarps across western tennessee and shallow s wave reflection profiles coring and trenches show late quaternary faulting along this lineament at the north end our seismic profile and coring suggest 1 5 m of wisconsin down to the nw faulting coring and trenches across the central lineament show 3 m of up to the nw and 8 15 m of right lateral late wisconsin holocene faulting averaged late quaternary right lateral slip has been 0 85 0 37 mm yr on one fault plane at this locality suggesting that total slip across all southeast rift margin fault planes may accommodate much of the regional strain our seismic profile at this site shows up to the west faulting of eocene strata folded down to the west indicating structural inversion seismic profiles electrical surveys coring and a trench across the southern lineament segment show holocene faulting trenching exposed a vertical fault with 0 5 m of late holocene down to the nw displacement nearby coring and electrical surveys show 0 5 m of late holocene up to the nw faulting we conclude the southeastern reelfoot rift margin is a right lateral system with high angle faults showing both up to the nw and down to the nw separations age constraints permit an earthquake circa 2500 to 2000 years b p on the southwestern central segment of this fault system that ruptured 80 km we suggest the northeastern segment of the southeastern rift margin turned off in holocene when the reelfoot step over thrust turned on

high resolution 3 d p wave attenuation structure of the new madrid seismic zone using local earthquake tomography a three dimensional 3 d high resolution p wave seismic attenuation model for the new madrid seismic zone nmsz is determined using p wave path attenuation t values of small magnitude earthquakes md 3 9 events were recorded at 89 broadband and short period seismometers of the cooperative new madrid seismic zone network and 40 short period seismometers of the portable array for numerical data acquisition experiment the amplitude spectra of all the earthquakes are simultaneously inverted for source path t and site parameters the t values are inverted for qp using local earthquake tomography methods and a known 3 d p wave velocity model for the region the four major seismicity arms of the nmsz exhibit reduced qp higher attenuation than the surrounding crust the highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid rich fractures along the southeast extension of the reelfoot fault the qp results are consistent with previous attenuation studies in the region which showed that active fault zones and fractured crust in the nmsz are highly attenuating

how rigid is the stable interior of the north american plate we analyze data from eight permanent gps stations broadly distributed through the interior of the north american plate and use the resulting velocities to estimate an euler vector describing motion of stable north america as a single rigid plate the site velocities fit the single plate model with a mean residual of 1 3 mm yr the residuals do not appear to reflect post glacial rebound and tests for differential motion between eastern and western north america at the new madrid seismic zone show no resolvable motion within uncertainties the residuals likely reflect observational error and thus our estimate of the stability of the plate interior is likely an upper bound