southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

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

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

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

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

a new analysis of the magnitude of the february 1663 earthquake at charlevoix quebec abstract this paper presents a new and comprehensive analysis of the magnitude of the 1663 charlevoix quebec earthquake based on a modified mercalli intensity scale mmi of about vi from reports of damage to chimneys and a masonry wall in roxbury and boston massachusetts the best estimate of the moment magnitude of this earthquake is m 7 3 to 7 9 from mmi attenuation relations using ground motion attenuation relations and the threshold for chimney and masonry damage from fragility curves for seventeenth and eighteenth century dwellings in boston the magnitude of the 1663 earthquake is at least m 6 9 if the damage occurred on very soft soil conditions and is m 7 3 to m 7 7 if the damage took place on firm soil or bedrock both the best estimate of a length of 73 km for the most active section of the charlevoix seismic zone and an estimated fault area of 73 km 25 km for the 1663 earthquake are consistent with an earthquake of m 7 3 to 7 6 based on scaling relationships also in the 1811 1812 new madrid earthquake sequence only the 7 february 1812 shock the largest of the sequence caused chimney damage beyond about 600 km the 7 february new madrid event is thought to have taken place on the reelfoot fault for which the length of the recent earthquake activity and of the suspected 1812 rupture is less than that of the active seismicity zone at charlevoix these observations suggest that the 1663 charlevoix earthquake was approximately comparable in magnitude to or even larger than the largest of the 1811 1812 new madrid earthquakes and therefore was at least m 6 8 when put together the several lines of analysis in this study indicate that the best estimate of the size of the 1663 earthquake is m 7 5 0 45

aeromagnetic gravity and differential interferometric synthetic aperture radar analyses reveal the causative fault of the 3 april 2017 m w 6 5 moiyabana botswana earthquake on april 3 2017 a mw 6 5 earthquake struck moiyabana botswana nucleating at 20 km focal depth within the paleoproterozoic limpopo shashe orogenic belt separating the archean zimbabwe and kaapvaal cratons we investigate the lithospheric structures associated with this earthquake using high resolution aeromagnetic and gravity data integrated with differential interferometric synthetic aperture radar dinsar analysis here we present the first results that provide insights into the tectonic framework of the earthquake the ruptured fault trace delineated by dinsar aligns with a distinct nw striking and ne dipping magnetic lineament within the precambrian basement the fault plane solution and numerical modeling indicate that the cause of the earthquake was 1 8 m displacement along a nw striking and ne dipping normal fault rupturing at 21 24 km depth we suggest that this seismic event was due to extensional reactivation of a crustal scale precambrian thrust splay within the limpopo shashe orogenic belt

constraining recent fault offsets with statistical and geometrical methods example from the jasneuf fault western alps france we propose two new approaches regarding recent fault offset measurements by studying the seismogenic potential of the jasneuf fault the ne trending right lateral strike slip jasneuf fault is the southwestern extension of the belledonne fault system in the vercors massif this fault which is located in an intraplate domain does not show strongly associated seismicity but displays morphological anomalies that are related to recent faulting right lateral offset of late cenozoic cliffs recent talwegs and post ganz scarps the two methods that we use to quantify fault slip are as follows 1 recursive measurements of stream offsets are conducted this analysis reveals that a stream network can display characteristic distances between streams that can be mistakenly interpreted as long term cumulative fault offsets a comparison of the apparent stream offset values and stream spacing values is necessary to identify the true offsets 2 we propose a new method that enables us to determine the fault offset and kinematics by using recursive measurements of topographic apparent offsets to counter the lack of morphologic features that are used to determine piercing points or lines this method enables us to define each possible slip vector for numerous artificial piercing points along a fault the slip vector that is shared by these piercing points is the true slip vector by applying these methodologies we determine that the jasneuf fault has accumulated slip since the messinian which corresponds to an average slip rate of 0 13 0 03 mm year the extension of the fault is poorly constrained nevertheless if we do not consider the potential aseismic creep slip component of the faulting we calculate that this fault could generate mw 5 7 earthquakes every similar to 500 years according to wells and coppersmith s scaling laws and by assuming that the faulting is limited to the sedimentary cover and the vercors plateau c 2016 elsevier b v all rights reserved

a multidisciplinary study of a slow slipping fault for seismic hazard assessment the example of the middle durance fault se france summary assessing seismic hazard in continental interiors is difficult because these regions are characterized by low strain rates and may be struck by infrequent destructive earthquakes in this paper we provide an example showing that interpretations of seismic cross sections combined with other kinds of studies such as analysis of microseismicity allow the whole seismogenic source area to be imaged in this type of region the middle durance fault mdf is an 80 km long fault system located southeastern france that has a moderate but regular seismicity and some palaeoseismic evidence for larger events it behaves as an oblique ramp with a left lateral reverse fault slip and has a low strain rate mdf is one of the rare slow active fault system monitored by a dedicated dense velocimetric short period network this study showed a fault system segmented in map and cross section views which consists of staircase basement faults topped by listric faults ramping off triassic evaporitic beds seismic sections allowed the construction of a 3 d structural model used for accurate location of microseismicity southern part of mdf is mainly active in the sedimentary cover in its northern part and in alpine foreland seismicity deeper than 8 km was also recorded meaning active faults within the crust cannot be excluded seismogenic potential of mdf was roughly assessed resulting source sizes and estimated slip rates imply that the magnitude upper limit ranges from 6 0 to 6 5 with a return period of a few thousand years the present study shows that the coupling between 3 d fault geometry imaging and accurate location of microseismicity provides a robust approach to analyse active fault sources and consequently a more refined seismic hazard assessment

impact of earthquake induced liquefaction and related ground failure on a mississippian archeological site in the new madrid seismic zone central usa an investigation of earthquake induced liquefaction features and related ground failure at the east archeological site 3po610 located near the southern end of the new madrid seismic zone was crucial to the identification of cultural features and horizons and interpretation of archeological data through the examination of stratigraphic and structural relations in the archeological excavation as well as in three nearby trenches it was determined that cultural horizons and features including the floor of a sweat lodge are tilted displaced downward and buried by a vented sand deposit known as a sand blow this sand blow is up to 1 m thick and is composed of four major depositional units suggesting that it formed during a sequence of large earthquakes the compound sand blow directly overlies cultural horizons and features indicating that the earthquakes occurred near the end of or soon after occupation on the basis of radiocarbon dating of samples collected above and below the sand blow the earthquakes are estimated to have occurred between a d 1300 and 1670 a new madrid earthquake sequence ca a d 1450 150 was the probable cause of liquefaction and ground failure at the site and may have led to cultural abandonment of the site ironically the earthquakes that may have led to abandonment of the site also helped to preserve it for posterity

sedimentary features influencing the occurrence and spatial variability of seismites late messinian gargano promontory southern italy abstract seventeen layers characterized by soft sediment deformation structures ssds were identified within the calcari di fiumicello an upper messinian miocene stratigraphic unit 30 m thick cropping out in the northern sector of the gargano promontory apulia southern italy facies analysis was performed on the whole outcrop and detailed sedimentological investigations were carried out on the deformed beds in order to interpret the deformation mechanism the driving mechanism and the possible trigger agent deformed layers occur in some thin bedded ooidal limestones skeletal calcarenite as well as in some pebble size conglomerate alternated with marls deposited in a protected embayment or barrier island lagoon system possibly characterized by high salinity and tidal influx ssds can be classified as load and slump slide structures the continuous exposures allow us to follow a single deformed layer along tens of meters hence several types of lateral variations were observed that can be summarised as follows 1 ssds disappear within a few meters with a decreasing pattern of their deformation or in an abrupt way 2 deformed layers laterally change in thickness and morphology and 3 a single deformed bed can laterally correspond to two deformed beds most of the soft sediment deformation features were identified as liquefaction and or fluidization features related to seismic shocks seismites seismites are often used as an indicator of seismic events especially along small outcrops trench excavation and core analysis this study highlights the value of the sedimentological analysis for paleoseismic investigations with the aim of improving criteria for identifying seismites in the sedimentary record and their suitability as marker of seismic events

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

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

empirical distance attenuation and the local magnitude scale for the central united states seismic waveform data from the cooperative new madrid seismic network cnmsn the u s national seismograph network usnsn and stations operated by the u s geological survey and the incorporated research institutions for seismology iu are corrected to the theoretical wood anderson response and the peak amplitudes are used to determine a local magnitude scale for the central united states the distance correction function can be expressed as graphic 1 with amplitude a in millimeters and hypocentral distance r in kilometers showing a weak attenuation with distance synthetic seismograms are calculated based on a detailed crustal model obtained from local well log acoustic data in the mississippi embayment to examine the effect of structure on station factors the results show that the mississippi embayment sediment as a whole may amplify seismic waves at some specific frequencies such as 0 5 and 5 0 6 0 hz with a factor less than 4 0 and may not amplify seismic waves in the frequency band from 0 5 to 9 9 hz on average even though the amplification factors do increase with the source magnitude estimations for b values and magnitudes of earthquakes with a return period of 500 yr in the central united states are performed based on the original new madrid catalog m d or m blg and the newly created m l catalog results show that the b value is smaller for the m l catalog 0 790 yielding one m 7 5 event every 500 yr a result that converges with the paleoearthquake estimate for the region on average the relation between m l and m d or m blg for 1 5 m d 5 0 can be expressed as m l 1 008 m d 0 0714 1 embed inline graphic 1 gif

characteristics of deuterium excess parameters for geothermal water in beijing this study investigates the characteristics of geothermal water in 10 geothermal fields in beijing the relationships between the deuterium excess parameter d and temperature depth age of geothermal groundwater groundwater flow field and eh were investigated using geothermal groundwater samples results showed that 1 the average d value of geothermal water is 5 4 whereas that of the groundwater in normal temperature is 6 04 the differences are induced by the oxygen isotope exchange during the water rock interaction which may be more easily completed in geothermal water than in cold groundwater 2 the d value increases remarkably with the age of the geothermal groundwater the d value increases from 11 2 to 14 6 when the age of the geothermal water is 12 760 130 a and 38 960 630 a respectively moreover the isotope heat exchange for composition of the hydrogen and oxygen isotopes in the geothermal groundwater proceeds sufficiently with time 3 the d value decreases from 5 72 to 3 03 when the depth increases from 125 13 to 3221 m generally in the same area the d value decreases with depth because the temperature is increasing 4 the d value of the groundwater gradually reduces from the northern recharge area to the southern discharge area the average d value is 7 31 in the northern recharge area and 5 68 in the middle beijing depression whereas the d value in the southern area of fengheying is 9 20 the larger difference in d values between the recharge and discharge areas is due to the slower velocity of underwater flow which induces longer time for oxygen exchange 5 the relationship between the d and eh is complex when eh is 200 mv the d value of the geothermal water decreases with the decrease in eh when eh is higher than 200 mv the d value increases slightly with the decrease in eh the study of the characteristics of deuterium excess parameters for geothermal water could provide a scientific isotopic evidence for assessment and exploitation measures in geothermal groundwater systems

including foreshocks and aftershocks in time independent probabilistic seismic hazard analyses time independent probabilistic seismic hazard analysis treats each source as being temporally and spatially independent hence foreshocks and aftershocks which are both spatially and temporally dependent on the mainshock are removed from earthquake catalogs yet intuitively these earthquakes should be considered part of the seismic hazard capable of producing damaging ground motions in this study i consider the mainshock and its dependents as a time independent cluster each cluster being temporally and spatially independent from any other the cluster has a recurrence time of the mainshock and by considering the earthquakes in the cluster as a union of events dependent events have an opportunity to contribute to seismic ground motions and hazard based on the methods of the u s geological survey for a high hazard site the inclusion of dependent events causes ground motions that are exceeded at probability levels of engineering interest to increase by about 10 but could be as high as 20 if variations in aftershock productivity can be accounted for reliably

a high frequency magnitude scale a high frequency magnitude scale m is proposed m 2 log a h f 3 where ahf is the high frequency level of the fourier amplitude spectrum of acceleration in cm sec average or random horizontal component at a hypocentral or closest fault distance of 10 km m can be determined from either instrumental data or the felt area of an earthquake the definition of m has been arranged such that m m moment magnitude for events of average stress drop in both eastern north america ena and california m provides a measure of the stress drop if m is also known the observed relationship between m and m indicates that the average stress drop is about 150 bars for ena earthquakes and about 70 bars for california earthquakes the variability of stress drop is much larger in ena than in california the chief justification for the m scale is its utility in the interpretation of the large preinstrumental earthquakes that are so important to seismic hazard estimation in eastern north america for such events m can be determined more reliably than can m or mn nuttli magnitude and forms a much better basis for estimating high frequency ground motions when used as a pair m and m provide a good index of ground motion over the entire engineering frequency band if both of these magnitudes can be defined for an earthquake then a ground motion model such as the stochastic model can be used to obtain reliable estimates of response spectra and peak ground motions

the great 1950 assam earthquake revisited field evidences of liquefaction and search for paleoseismic events abstract extensive field investigations were carried out for the first time in the meizoseismal area of the great 1950 assam earthquake aimed at exploring the paleoseismic history of the ne indian region through documentation of liquefaction features and radiocarbon 14c dating trenching at more than a dozen locations along the burhi dihing river valley and within the alluvial fans adjoining the brahmaputra and dibang rivers resulted in the identification of more than a dozen very prominent liquefaction features sand dykes sills sand blows etc as evidences of large to great earthquakes 14c dating of the organic material associated with some of the features indicates a paleoseismic record of about 500 yrs archived by the sediments in this region compelling geological evidence s of the great 1950 earthquake are well constrained by 14c dating out of the two historically reported seismic events 1548 ad and 1697 ad from this region 14c dating could constrain the 1548 ad event though not distinctly further studies using combined 14c and osl dating may better constrain the seismo chronology of the study region

liquefaction susceptibility mapping in the city of memphis and shelby county tennessee abstract earthquake induced sand dikes have been identified in cut banks of the wolf and loosahatchie rivers in the city of memphis and shelby county tennessee most of the dikes are near the mouths of these rivers within the city limits of memphis but one dike occurs 36 km upstream in the bank of the wolf river in collierville the dikes range in width from 1 to 50 cm and at some localities can be traced vertically as much as 4 m from their source bed to within 50 cm of the flood plain surface the age of the dikes is unknown but they are interpreted to be from the great 1811 1812 new madrid earthquakes because they are locally buried by historical sediments containing bricks the larger number of dikes and upstream extent of liquefaction along the wolf river suggests that liquefaction susceptibility is greater in the wolf river flood plain than in other flood plains in shelby county this greater liquefaction susceptibility of the wolf river flood plain appears to be due to the sand in its basal point bar sequence and a relatively thin overbank silt clay cap geologic and geologically based liquefaction susceptibility maps 1 24 000 were made of the memphis northwest and collierville 7 5 quadrangles of shelby county the liquefaction susceptibility maps show very high susceptibility for mississippi wolf and loosahatchie river flood plains high susceptibility in areas of artificial fill on these three flood plains moderate susceptibility along other flood plains and terraces in these quadrangles and low susceptibilities in the interfluve areas

simulation of earthquake ground motions in the eastern united states using deterministic physics based and site based stochastic approaches abstract earthquake ground motion recordings are scarce in the central and eastern united states ceus for large magnitude events and at close distances we use two different simulation approaches a deterministic physics based method and a site based stochastic method to simulate ground motions over a wide range of magnitudes drawing on previous results for the modeling of recordings from the 2011 m w 5 8 mineral virginia earthquake and using the 2001 m w 7 6 bhuj india earthquake as a tectonic analog for a large magnitude ceus event we are able to calibrate the two simulation methods over this magnitude range both models show a good fit to the mineral and bhuj observations from 0 1 to 10 hz model parameters are then adjusted to obtain simulations for m w 6 5 7 0 and 7 6 events in the ceus our simulations are compared with the 2014 u s geological survey weighted combination of existing ground motion prediction equations in the ceus the physics based simulations show comparable response spectral amplitudes and a fairly similar attenuation with distance the site based stochastic simulations suggest a slightly faster attenuation of the response spectral amplitudes with distance for larger magnitude events and as a result slightly lower amplitudes at distances greater than 200 km both models are plausible alternatives and given the few available data points in the ceus can be used to represent the epistemic uncertainty in modeling of postulated ceus large magnitude events

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

structural controls on localized intraplate deformation and seismicity in southern australia insights from local earthquake tomography of the flinders ranges data from an array of 24 seismometers are used to image the crust beneath the flinders ranges southeast australia with the goal of improving our understanding of crustal structure rheology and the mechanism responsible for the localized intraplate deformation that characterizes this region a subset of p and s wave traveltimes is inverted to jointly recover earthquake hypocenters p wave velocity structure and v p v s anomalies the p wave velocity model reveals a spatial correlation between major negative velocity perturbations and concentrations of seismicity in particular a cluster of seismicity is observed within a distinct low velocity region between the archean mesoproterozoic gawler craton and the palaeo mesoproterozoic curnamona province from 7 to 20km depth we postulate that this may be associated with a pre existing structural weakness in the crust that arises primarily from rifting between the curnamona province and the gawler craton another area characterized by a high level of seismicity overlies a major sequence of n s trending ross delamerian thrust faults which correspond to a band of low v p and particularly v p v s the lack of evidence for elevated heat flows in both of these seismogenic regions suggests that thermally induced weakness is unlikely to play a dominant role instead the dynamic behavior of this intraplate region appears to be caused by a serendipitously oriented regional stress field provided by far field forces that originate from the boundary between the pacific and australian plates which acts upon preexisting structural weaknesses in the lithosphere

late holocene liquefaction at sites of contemporary liquefaction during the 2010 2011 canterbury earthquake sequence new zealand abstract the 2010 2011 canterbury earthquake sequence ces caused up to 10 episodes of liquefaction at highly susceptible sites in eastern canterbury resulting in severe damage to land and infrastructure subsurface investigations at five sites over two study areas revealed ces dikes and sills that align with and crosscut pre ces liquefaction features including dikes a lateral sill a sandblister and a buried compound sandblow crosscutting relationships combined with carbon 14 14 c dating constrain the timing of the pre ces liquefaction features to likely post a d 1321 and pre 1960 in one study area pre ces features in the second study area likely formed in three distinct episodes post a d 1458 and possibly during the 1901 cheviot earthquake between a d 1297 and 1901 and pre a d 1458 the liquefaction potential of known active faults within the wider canterbury region are evaluated from back calculated magnitude bound curves and peak ground acceleration pga approximated using a new zealand specific ground motion prediction equation and compared with global liquefaction triggering thresholds analysis indicates that many active faults within north canterbury and offshore that are within 50 km of the study sites and capable of triggering m w 6 5 earthquakes have the potential to cause widespread liquefaction ruptures of these faults may have formed the pre ces liquefaction features combining the backcalculation approach with the modeled pga proves effective in determining the active faults capable of triggering liquefaction at the study sites and are therefore capable of triggering liquefaction in the future online material overview and further discussion of the probabilistic magnitude bound methodology framework and derivative curves description of sediment units and table of peak ground acceleration pga

strong ground motion inferred from liquefaction caused by the 1811 1812 new madrid missouri earthquakes peak ground accelerations pgas in the epicentral region of the 1811 1812 new madrid missouri earthquakes are inferred from liquefaction to have been no greater than 0 35 g pga is inferred in an 11 380 km2 area in the lower mississippi valley in arkansas and missouri where liquefaction was extensive in 1811 1812 pga was inferred by applying liquefaction probability curves which were originally developed for liquefaction hazard mapping to detailed maps of liquefaction by obermeier 1989 the low pga is inferred because both a shallow 1 5 m deep water table and a large moment magnitude m 7 7 earthquake were assumed in the analysis if a deep 5 0 m water table and a small magnitude m 6 8 earthquake are assumed the maximum inferred pga is 1 10 g both inferred pga values are based on an assumed and poorly constrained correction for sand aging if an aging correction is not assumed then the inferred pga is no greater than 0 22 g a low pga value may be explained by nonlinear site response soils in the study area have an average v s 30 of 220 15 m s a low inferred pga is consistent with pga values estimated from ground motion prediction equations that have been proposed for the new madrid seismic zone when these estimates are corrected for nonlinear soil site effects this application of liquefaction probability curves demonstrates their potential usefulness in paleoseismology

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

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

quantifying the uncertainty in site amplification modeling and its effects on site specific seismic hazard estimation in the upper mississippi embayment and adjacent areas the mississippi embayment located in the central united states and its thick deposits of sediments over 1 km in places have a large effect on earthquake ground motions several previous studies have addressed how these thick sediments might modify probabilistic seismic hazard maps the high seismic hazard associated with the new madrid seismic zone makes it particularly important to quantify the uncertainty in modeling site amplification to better represent earthquake hazard in seismic hazard maps the methodology of the memphis urban seismic hazard mapping project cramer et al 2004 is combined with the reference profile approach of toro and silva 2001 to better estimate seismic hazard in the mississippi embayment improvements over previous approaches include using the 2002 national seismic hazard model fully probabilistic hazard calculations calibration of site amplification with improved nonlinear soil response estimates and estimates of uncertainty comparisons are made with the results of several previous studies and estimates of uncertainty inherent in site amplification modeling for the upper mississippi embayment are developed i present new seismic hazard maps for the upper mississippi embayment with the effects of site geology incorporating these uncertainties

relocation of m 2 events of the 1989 dobi seismic sequence in afar evidence for earthquake migration the ethiopian side of central afar was struck in august 1989 by the largest seismic sequence three 6 1 ms 6 3 events 15 with ms or mb 5 0 since that of serdo in 1969 using the djibouti seismological network we relocated 297 of the events of that sequence as most of the large events took place outside the network we assessed the accuracy and stability of earthquake relocations by using three different velocity models and two relocation codes to try to relate individual shocks to distinct faults and surface breaks a majority of the events apparently occurred underneath the floor of the dobi graben an area about 45 km long and 15 km wide rupturing boundary and inner floor faults in agreement with the surface cracks and scarps that we mapped in the area the relocation shows that the principal events propagated about 50 km northwestwards along the graben in the first 40 hr a day and a half after the beginning of the sequence smaller events m 4 started to propagate more than 55 km eastwards towards asal lake using two three component stations installed near the ethiopian border we could determine reliable depths for 21 events the depths are compatible with a seismogenic crust about 14 km thick in the dobi and hanle graben area although the dobi sequence ruptured about 50 km of the fault array extending from serdo to asal where the regional stress was released by earthquakes in 1969 and 1978 respectively a seismic gap about 50 km long still subsists along the northern part of the gaggade region der ela half graben

stratigraphy and structure of the eocene memphis sand above the eastern margin of the reelfoot rift in tennessee mississippi and arkansas usa in total 1249 geophysical well logs were interpreted to map the stratigraphy and structure of the eocene memphis sand in west tennessee northwest mississippi and crittenden county arkansas where it overlies the southeastern margin of the reelfoot rift the memphis sand is a 300 m thick reworked fluvial sand deposited on a low relief subsiding plain with limited accommodation space the memphis sand has experienced syn and postdepositional faulting of four types in the region 1 west trending grabens were active during eocene claiborne deposition these grabens also appear to control modern drainage and thus may extend to the surface 2 the n33 e shelby faults pass through shelby county tennessee into northwest mississippi and extend to or near the surface they were right lateral normal faults during eocene memphis sand deposition but they became inverted reverse faults in the late eocene 3 the n67 e striking gibson faults are high angle normal and reverse faults with a component of right lateral strike slip these faults were active during memphis sand through lower cockfield deposition north of the hatchie graben and appear to be due to faulting above an outboard fault of the reelfoot rift 4 the n43 e striking lauderdale faults are high angle normal and reverse faults that reflect right lateral strike slip reactivation of the southeastern margin of the reelfoot rift the structure and stratigraphy revealed in this mapping indicate that the geology of the memphis sand is more complex than previously recognized faulting of the memphis sand and overlying sediments reveals potentially seismogenic faults in western tennessee eastern arkansas and northwestern mississippi this study provides fundamental data for future groundwater modeling and seismic hazard analysis

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

vented sediments and tsunami deposits in the puget lowland washington differentiating sedimentary processes the sandy deposits produced by tsunamis and liquefaction share many sedimentary features and distinctions between the two are important in seismically active coastal zones both types of deposits are present in the wetlands bordering puget sound where one or more earthquakes about 1100 years ago caused both tsunami flooding and sediment venting this co occurrence allows an examination of the resulting deposits and a comparison with tsunami and liquefaction features of modern events vented sediments occur at four of five wetland field localities and tsunami deposits at two in comparison with tsunami deposits vented sediments in this study and from other studies tend to be thicker although they can be thin vented sediments also have more variable thickness at both outcrop and map scale are associated with injected dykes and contain clasts derived from underlying deposits further vented sediments tend to contain a greater variety of sedimentary structures and these structures vary laterally over metres tsunami deposits compared with vented sediments are commonly thinner fine and thin landward more consistently have more uniform thickness on outcrop and map scales and have the potential of containing coarser clasts up to boulders for both tsunami deposits and vented sediments the availability and grain size of source material condition the characteristics of the deposit in the cases presented in this paper both foraminifera and diatom assemblages within tsunami deposits and vented sediments consisted of brackish and marine species and no distinction between processes could be made based on microfossils in summary this study indicates a need for more careful analysis and mapping of coastal sediments associated with earthquakes to avoid misidentification of processes and misevaluation of hazards

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

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

imaging the new madrid seismic zone using double difference tomography 1 three dimensional p and s wave velocity vp and vs models and high resolution earthquake relocations are determined for the new madrid seismic zone using double difference local earthquake tomography the data set consists of arrival times and differential times recorded by the cooperative new madrid seismic network cnmsn from 2000 to 2007 and the 1989 1992 portable array network and data acquisition deployment waveform cross correlation derived differential times for the cnmsn data are also incorporated the velocity solutions are compatible with previous solutions centered on the active arms of seismicity and cover a broader area including mafic intrusions along the margin of the reelfoot rift major features include elevated vp and vs associated with the mafic plutons and reduced vp and vs along and southeast of the axial fault af a major arm of seismicity trending along the rift axis low vp extends to a depth of at least 20 km along the portion of the af that extends south of the missouri bootheel a locally high vp vs anomaly imaged along the central portion of the reelfoot fault is spatially correlated with a significant change in fault trend and is interpreted as a region containing high pore pressure and or water filled microcracks

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

sensitivity analysis of seismic hazard for the northwestern portion of the state of gujarat india we test the sensitivity of seismic hazard to three fault source models for the northwestern portion of gujarat india the models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years these recurrence intervals imply that large earthquakes occur on one of these faults every 266 533 years similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the new madrid region in the central united states if one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults the peak ground accelerations pga horizontal and 1 hz spectral acceleration ground motions 5 damping are greater than 1 g over a broad region for a 2 probability of exceedance in 50 years hazard level these probabilistic pgas at this hazard level are similar to median deterministic ground motions the pgas for 10 in 50 years hazard level are considerably lower generally ranging between 0 2 g and 0 7 g across northwestern gujarat ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals these higher ground motions are mainly caused by the application of intraplate attenuation relations which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies for sites in bhuj and ahmedabad magnitude m 7 3 4 earthquakes contribute most to the pga and the 0 2 and 1 s spectral acceleration ground motion maps at the two considered hazard levels d 2004 elsevier b v all rights reserved

rare destructive earthquakes in europe the 1904 bulgaria event case abstract seismic hazard is difficult to assess in regions of low strain rates a major limitation often relates to the absence of large instrumentally recorded events precluding any comparison between seismological data and paleoseismic or morphotectonic informations we take advantage of the 1904 m s 7 1 earthquake that struck the southern edge of stable eurasia and investigate if morphotectonic and paleoseismic observations can provide a reliable estimate of the seismic potential of slow slipping faults we have conducted a paleoseismic study of the krupnik normal fault thought to be responsible for the event a section of the fault bearing remnants of a 2 m high scarp has been selected at the base of triangular facets the trenching site locates where the scarp cuts across colluviums washed from the bedrock facetted slopes we excavated two neighbouring trenches one across a well preserved portion of the scarp and one across a portion degraded by a landslide the excavations reveal a set of coarse colluvial units faulted against bedrock and affected by secondary fissures faulting appears to have resulted from a single event with normal throw greater than 1 3 m that occurred before the emplacement of the landslide accelerator mass spectrometry ams radiocarbon dates of charcoal samples are consistent with the interpretation that the krupnik fault slipped recently most probably in 1904 after a long lasting 10 ka period of quiescence the morphotectonic and paleoseismic observations yield seismic moment estimates compatible with the instrumental magnitude of the event and indicate that destructive and infrequent earthquakes typify the regional seismic behaviour

a bimodal hybrid model for time dependent probabilistic seismic hazard analysis the evaluation of evidence provided by geological studies and historical catalogs indicates that in some seismic regions and faults multiple large earthquakes occur in cluster then the occurrences of large earthquakes confront with quiescence and only the small to moderate earthquakes take place clustering of large earthquakes is the most distinguishable departure from the assumption of constant hazard of random occurrence of earthquakes in conventional seismic hazard analysis in the present study a time dependent recurrence model is proposed to consider a series of large earthquakes that occurs in clusters the model is flexible enough to better reflect the quasi periodic behavior of large earthquakes with long term clustering which can be used in time dependent probabilistic seismic hazard analysis with engineering purposes in this model the time dependent hazard results are estimated by a hazard function which comprises three parts a decreasing hazard of last large earthquake cluster and an increasing hazard of the next large earthquake cluster along with a constant hazard of random occurrence of small to moderate earthquakes in the final part of the paper the time dependent seismic hazard of the new madrid seismic zone at different time intervals has been calculated for illustrative purpose

major earthquakes recorded by speleothems in midwestern u s caves historic earthquakes generated by the new madrid seismic zone represent some of the largest recorded in the united states yet prehistoric events are recognized only through deformation in late wisconsin to holocene age near surface sediments liquefaction monoclinal folding and changes in river meanders in this article we show that speleothems in caves of southwestern illinois and southeastern missouri may constitute a previously unrecognized recorder of large earthquakes in the u s midcontinent region the timing of the initiation and regrowth of stalagmites in southwestern illinois and southeastern missouri caves is consistent with the historic and prehistoric record of several known seismic events in the u s midcontinent region we conclude that dating the initiation of original stalagmite growth and later postearthquake rejuvenation constitutes a new paleoseismic method that has the potential for being applied to any region around the world in the vicinity of major seismic zones where caves exist use of this technique could expand the geographical distribution of paleoseimic data document prehistoric earthquakes and help improve interpretations of paleoearthquakes

temporal clustering of major earthquakes along individual faults due to post seismic reloading palaeoseismic evidence suggests that earthquake recurrence intervals in some regions can be highly variable with clusters of multiple large events separated by much longer periods of quiescence because post seismic processes have a significant effect on the reloading rate of the coseismic fault we hypothesize that temporal variations in the amount of stress concentrated in the non seismogenic lithosphere can modulate large earthquake recurrence times we explore this hypothesis using simple analogue spring dashpot slider models we find that in the presence of small amounts of environmental noise post seismic stress transfer over timescales much longer than an earthquake cycle may be an important factor in generating clustering behaviour the propensity for the system to be clustered is a function of a non dimensional number that we call the wallace number w w is defined as the average earthquake stress drop divided by the product of the long term geologic strain rate across the fault and the effective viscosity of the system our results indicate that environments with relatively low strain rates and a relatively weak non seismogenic lithosphere are most susceptible to clustering driven by post seismic stress recycling mechanisms

evidence for episodic sand blow activity during the 1811 1812 new madrid missouri earthquake series four major earthquakes of the 1811 1812 new madrid series caused widespread ground disturbance mostly in the form of sand blows in the alluvial valley of the mississippi river although a recurrence interval of 600 700 yr has been estimated for major shocks recent excavations at an archeological site in northeastern arkansas revealed no evidence of ground disturbance for at least 1 3 ka prior to 1811 sand blows attributed to the new madrid series show that such features can have multiple episodes of sand extrusion through a single dike and vent

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

earthquakes in the eastern great lakes basin from a regional perspective abstract this paper presents a summary of the seismicity and its relation to stress and geologic structures in the eastern great lakes basin eglb and compares it with that of other regions in the central and eastern north america cena the earthquakes scattered throughout the eglb are occurring at a rate somewhat less than that of the appalachians and along the atlantic seaboard paleoseismology studies suggest that the lower seismicity rate may be characteristic of the eglb since the late wisconsin north of the eglb earthquakes have primarily thrust mechanisms while to the south of the eglb most earthquakes are strike slip throughout the region including the eglb the average p axes of the earthquakes are oriented ne sw and are aligned with the direction of the current plate driving stress on a regional basis earthquakes are centered primarily in the precambrian basement beneath the paleozoic cover many of the earthquakes in the eglb have occurred in areas of preexisting faults at least some of which may have been active during past episodes of continental rifting for individual faults that have been studied in some detail however it is not clear whether earthquakes represent reactivations of local preexisting structures or nucleation of new ruptures in or near the old fault zones

apparent late quaternary fault slip rate increase in the southern lower rhine graben central europe in regions of low strain long earthquake recurrence intervals 104 106 yrs and erosive processes limit preservation of quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates the lower rhine graben in the border region of germany the netherlands and belgium provides a unique opportunity to explore quaternary slip rate variations in a region of low strain using the basal 2 29 0 29 ma and surface 700 80 ka contacts of the regionally extensive main terrace hauptterrasse deposited by the rhine and maas rivers these surfaces are vertically offset 3 140 m and 0 68 m respectively across individual fault strands within a distributed network of northwest trending slow slipping 80 of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present which corresponds to a period of increased uplift of the nearby rhenish massif and regional volcanism however the apparent increase in slip rate could result in part from erosion of the footwall surface below the main terrace leading to an apparent displacement that is smaller than the total vertical offset since the start of the quaternary prior work focused on characterization of these faults as seismic sources in the lower rhine graben has preferentially relied on the average fault slip rate constrained using the base of the main terrace we suggest that average fault slip rates calculated using the 700 ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic hazard analysis electronic supplement 1 table of main terrace surface and basal contact offset measurements figure describing an unrealistic faulting scenario and a kml file with the fault trace mapping spanning the lower rhine graben 1 http www bssaonline org lookup suppl doi 10 1785 0120160197 dc1

geophysical surveys of earthquake induced liquefaction deposits in the new madrid seismic zone we explore the effectiveness and limitations of electrical and electromagnetic methods in imaging buried earthquake induced liquefaction deposits geophysical surveys conducted at liquefaction sites in the new madrid seismic zone nmsz in the central united states demonstrate that these subsurface imaging techniques can be useful tools in paleoseismology paleoseismological studies of liquefaction features provide one of the few means for estimating recurrence intervals of large earthquakes in the nmsz a region with widespread evidence of strong ground shaking but short instrumental record noninvasive geophysical methods minimize ground disturbance during these studies an attribute of particular importance when the studies are conducted at federally protected archaeological sites surveys such as those described here can be used to locate buried liquefaction deposits and to site trenches for detailed geologic studies

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

recurrent liquefaction induced by the 1989 loma prieta earthquake and 1990 and 1991 aftershocks implications for paleoseismicity studies sandblows formed in man made lake deposits near watsonville california resulted from the october 1989 m 7 1 loma prieta earthquake and its april 1990 m 5 5 aftershock and a march 1991 m 4 6 aftershock excavations in the dry bed of soda lake expose the subsurface structure of sandblows induced by the october and april events we also made surface observations three days after the march 1991 event lateral spread fissures developed in the lake sediment during the mainshock and the host deposits were vertically offset 3 to 6 5 cm liquefied sand erupted through the fissures onto the dry lake bed and formed sandblow cone deposits these deposits range from low angle conical structures 30 to 50 cm thick and 2 to 5 m in diameter to elongate deposits up to 35 m long sandblows associated with the april 1990 aftershock commonly reoccupied preexisting fissures but also formed new solitary vents sandblows developed during the march 1991 aftershock erupted only through preexisting vents sandblow vents reactivated in april 1990 contain sediment clasts of sandblow deposits formed in the october 1989 mainshock clasts of host sediment were also present in the sand dikes lamination in the sandblow cones and sand dikes shows that they were not formed in a single episode surface cones and feeder dikes composed of multiple laminated subunits represent the three generations of sandblows the subunits suggest that the cone deposits were formed by pulses of water and sediment expelled from the vent the pulses result from cyclic phases of local excess pore pressure and its release in the liquefied bed at depth the three generations of structures at soda lake formed six months to a year apart have distinct tonal and textural differences that may mimic liquefaction structures formed decades or centuries apart this study provides modern analogs for comparison to and interpretation of prehistoric liquefaction structures that are frequently partly eroded or poorly exposed

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

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

late holocene liquefaction features in the dominican republic a powerful tool for earthquake hazard assessment in the northeastern caribbean several generations of sand blows and sand dikes indicative of significant and recurrent liquefaction are preserved in the late holocene alluvial deposits of the cibao valley in northern dominican republic the cibao valley is structurally controlled by the septentrional fault an onshore section of the north american caribbean strike slip plate boundary the septentrional fault was previously studied in the central part of the valley where it sinistrally offsets holocene terrace risers and soil horizons in the eastern and western parts of the valley the septentrional fault is buried by holocene alluvial deposits making direct study of the structure difficult liquefaction features that formed in these holocene deposits as a result of strong ground shaking provide a record of earthquakes in these areas liquefaction features in the eastern cibao valley indicate that at least one historic earthquake probably the moment magnitude m 8 4 august 1946 event and two to four prehistoric earthquakes of m 7 to 8 struck this area during the past 1100 yr the prehistoric earthquakes appear to cluster in time and could have resulted from rupture of the central and eastern sections of the septentrional fault circa a d 1200 liquefaction features in the western cibao valley indicate that one historic earthquake probably the m 8 7 may 1842 event and two prehistoric earthquakes of m 7 8 struck this area during the past 1600 yr our findings suggest that rupture of the septentrional fault circa a d 1200 may have extended beyond the central cibao valley and generated an earthquake of m 8 additional information regarding the age and size distribution of liquefaction features is needed to reconstruct the prehistoric earthquake history of hispaniola and to define the long term behavior and earthquake potential of faults associated with the north american caribbean plate boundary manuscript received 6 september 2002

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

geoarchaeological evidence of strong prehistoric earthquakes in the new madrid missouri seismic zone sand blows and fissures that cover 10 500 km sup 2 in northeastern arkansas and southeastern missouri attest to the severity of the 1811 1812 earthquake series in the new madrid seismic zone however except for one occurence near new madrid missouri the region has been devoid of any evidence of other major shocks for at least 1 3 ka prior to 1811 and possibly for 9 ka stratigraphic relations and radiocarbon dating at a recently excavated archaeological site near east prairie missouri have revealed liquifaction phenomena attributable to a shock dated to within about 100 yr prior to a d 539 and a probable second one dated between about a d 539 and 991

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

new evidence for a large earthquake in the new madrid seismic zone between a d 1400 and 1670 in an integrated geological archaeological and geophysical study in the new madrid seismic zone of the southeastern united states we documented a prehistoric sand blow and related feeder dikes at an archaeological site near steele missouri archaeological analysis combined with radiocarbon dating suggest that the earthquake induced features formed between a d 1400 and 1670 this paleoseismic study provides the best evidence to date for a large earthquake occurring in the zone within 400 yr prior to the 1811 1812 new madrid earthquake sequence to determine an optimal location for excavating at the study site we mapped surficial artifact density and conducted geophysical surveys in doing so we were able to reveal critical relationships for constraining the age of the prehistoric earthquake with minimal impact to the archaeological site

polygenetic sand volcanoes on the features of liquefaction processes generated by a single event 2012 emilia romagna 5 9 mw earthquake italy one of the most important geological effects generated by the seismic events of emilia romagna italy 2012 was the liquefaction the first earthquake took place on 20th may 5 9 mw and generated liquefaction in the locality of san carlo mainly recorded as large fissure sand volcanoes detailed stratigraphic and sedimentology analyses of these sand bodies indicated the assemblage of rhythmic normal graded beds of sand for many individual sand volcanoes this is interpreted as repeated individual sand extrusions generating polygenetic sand blows for a single earthquake this original analysis made for first time in a case of extensive seismic liquefaction indicates that the different pulses sand extrusion occurred after seismic shaking and therefore no related to the cyclic seismic shearing stimulated by surface seismic waves underground liquefaction of shallow sandy layers and ground cracking assisted by relevant lateral spreading promoted water and sand ejections e w direction localised and repeated ground subsidence and bulging supported by the ejection of the underlying fluidized sediments feedback transient ground undulations and repeated sand ejections the unstable undulating behaviour of the ground reinforced and sustained the liquefaction process through time after the seismic shaking leading the occurrence of polygenetic sand volcanoes in summary the seismic liquefaction is the starting point of the process although only if these sand ejections could promote the instability of the ground since underground sand depletions feedback the liquefaction process through time the process stops when the hydrostatic balance is recovered in the affected zone

societal and observational problems in earthquake risk assessments and their delivery to those most at risk abstract losses from earthquakes continue to rise despite increasingly sophisticated methods to estimate seismic risk throughout the world this article discusses five specific reasons why this should be loss of life is most pronounced in the developing nations where three factors poverty corruption and ignorance conspire to reduce the effective application of seismic resistant codes a fourth reason is that in many developing nations the application of seismic resistant construction is inadvertently restricted to wealthy or civil segments of the community and is either unobtainable or irrelevant to the most vulnerable segment of the public the owner occupiers of substandard dwellings a fifth flaw in current seismic hazard studies is that sophisticated methodologies to evaluate risk are inappropriate in regions where strain rates are low and where historical data are short compared to the return time of damaging earthquakes the scientific community has remained largely unaware of the importance of these impediments to the development and application of appropriate seismic resistant code and is ill equipped to address them