liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

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

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

quaternary faulting in the southern mississippi embayment and implications for tectonics and seismicity in an intraplate setting the recently recognized saline river fault zone in the southwestern mississippi embayment strike 135 is characterized by moderate historic seismicity we document paleoseismicity possibly strong on the saline river fault zone that is outside the known region of neotectonism in the northern embayment six surface faults were excavated within the saline river fault zone and all faults displace marine eocene units and fluvial pliocene pleistocene units five show post wisconsin loess movement thermoluminescence tl age 23 6 3 ka and three deform middle to late holocene eolian silt tl age 5 1 0 6 ka and 3 6 0 5 ka as fault tip flexures along the principal excavated fault fault plane braiding and plunging drag folding suggest a strong component of left slip and subsidiary faults show both normal and reverse displacement 1m of pliocene pleistocene wisconsin and holocene units we interpret these faults as components of a left slip flower structure a shallow seismic reflection profile acquired across the principal fault and a subsidiary fault shows eocene stratigraphy separated in a reverse sense below 120 m depth and separated in a normal sense above 120 m supporting a strike slip interpretation in addition the only focal plane mechanism available in the area indicates left slip with a small reverse component we conclude that the saline river fault zone is a paleozoic mesozoic basement fault zone reactivated as a left slip system in a quaternary east west compressive stress field field evidence suggests that earthquakes with several meters of strike slip may be characteristic and the width of a liquefaction field on the saline river fault zone suggests an event of magnitude 5 5 6 considering a similarity of strike and sense of holocene movements of the meers fault of southern oklahoma and of the saline river fault zone there may be additional active fault zones that pose seismic hazards concealed by sediments in southern north america

rapid intraplate strain accumulation in the new madrid seismic zone remeasurement of a triangulation network in the southern part of the new madrid seismic zone with the global positioning system has revealed rapid crustal strain accumulation since the 1950s this area experienced three large moment magnitudes 8 earthquakes in 1811 to 1812 the orientation and sense of shear is consistent with right lateral strike slip motion along a northeast trending fault zone as indicated by current seismicity detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time

known and suggested quaternary faulting in the midcontinent united states abstract the midcontinent united states between the appalachian and rocky mountains contains 40 known faults or other potentially tectonic features for which published geologic information shows or suggests quaternary tectonic faulting we report results of a systematic evaluation of published and other publicly available geologic evidence of quaternary faulting these results benefit seismic hazard assessments by 1 providing some constraints on the recurrence intervals and magnitudes of large prehistoric earthquakes and 2 identifying features that warrant additional study for some features suggested quaternary tectonic faulting has been disproved whereas for others the suggested faulting remains questionable of the 40 features nine have clear geologic evidence of quaternary tectonic faulting associated with prehistoric earthquakes and another six features have evidence of nontectonic origins an additional 12 faults uplifts or historical seismic zones lack reported paleoseismological evidence of large quaternary earthquakes the remaining 13 features require further paleoseismological study to determine if they have had quaternary earthquakes that were larger than any known from local historical records seven of these 13 features are in or near urbanized areas where their study could affect urban hazard estimates these seven are 1 the belt of normal faults that rings the gulf of mexico from florida to texas 2 the northeast ohio seismic zone 3 the valmont and 4 goodpasture faults of colorado 5 the champlain lowlands normal faults of new york state and vermont and 6 the lexington and 7 kentucky river fault systems of eastern kentucky

geodetic constraints on the rigidity and relative motion of eurasia and north america gps observations in northeastern asia when combined with observations from the global network for the period 1992 1999 yield an angular rotation vector between eurasia and north america consistent with and a factor of two more precise than estimates derived using gps or vlbi data previously available from only western eurasia the new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the nuvel 1a global plate model suggesting a significant change in the relative motion of eurasia and north america over the past 3 myr the standard deviations of horizontal velocities from rigid plate motion for nineteen stations in eurasia and ten in north america are less than 1 mm yr the observations place an upper bound of 2 mm yr at 95 confidence for relative motion between western and eastern eurasia

geodetic constraints on glacial isostatic adjustment in europe 1 direct measurements of surface deformation due to glacial isostatic adjustment gia in europe have been so far mostly limited to the present day uplift area here we use permanent gps networks results to investigate the significance of gia effects in europe south of fennoscandia we show that uplift in fennoscandia is surrounded by subsidence reaching as far south as the alps with a maximum vertical rate of 1 5 mm yr between 50 5 53 n horizontal velocity gradients show shortening between fennoscandia and north central europe with strain rates of 10 9 yr 1 and principal compressional strain axis pointing to the gulf of bothnia in a radial pattern we find a very good quantitative agreement with the 3d surface displacement predicted by milne et al 2001 although the increase of misfit in far field of fennoscandia suggests that geodetic data outside of the uplift area may bring additional constraints to the rheological parameters used in gia models

the transition to topographic normal modes abstract the present note proposes an explanation of topographic normal modes that grow in a flow with a zonally symmetric mountain an issue of practical importance is whether one expects the maximum amplitude to occur poleward or equatorward of a mountain localized in the cross stream direction using a quasigeostrophic model it is shown that the occurrence of maximum amplitude to the south of the mountain occurs only for longer waves for a given wave of medium scale the amplitude is more likely to maximize to the south of the mountain for steeper slopes the transient behavior resulting from the sudden appearance of a mountain in the presence of an eady normal mode is discussed first the topographic correction to the eady mode quickly acquires a negative meridional tilt at the surface this tilted structure penetrates upward to the lid and advects basic state temperature because the phase tilt of the eady mode varies with zonal wavelength the phase of the topographic correction at the lid relativ

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

time variable deformation in the new madrid seismic zone new geodetic measurements show that the new madrid is currently deforming too slowly if at all to account for large earthquakes in the region over the past 5000 years this result together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicates that either tectonic loading rates or fault properties vary over a few thousand years

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

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

stratigraphic evidence for millennial scale temporal clustering of earthquakes on a continental interior fault holocene mississippi river floodplain deposits new madrid seismic zone usa abstract the earthquake cycles that characterize continental interior areas that are far from active plate boundaries have proven highly cryptic and difficult to resolve we used a novel paleoseismic proxy to address this issue namely we reconstructed holocene mississippi river channels from maps of floodplain strata in order to identify channel perturbations reflective of major displacement events on the high hazard and mid plate reelfoot thrust fault new madrid seismic zone u s a only three discrete slip events are currently documented for the reelfoot fault ad 900 ad 1450 and ad 1812 this study extends this record and thus illustrates the utility of stratigraphic proxies as paleoseismic tools we concurrently offer here some of the first quantified response times for tectonically induced channel pattern changes in large alluvial rivers we identified at least two cycles of pervasive meandering that were interrupted by channel straightening responses occurring upstream of the reelfoot fault scarp these straightening responses initiated at 2244 bc 269 to 1620 bc 220 and ad 900 respectively and each records initiation of a period of reelfoot fault slip after millennia of relative tectonic quiescence the second or new madrid straightening response was triggered by the previously known ad 900 fault slip event and this initial low sinuosity has been protracted until the modern day by the latter ad 1450 and ad 1812 events the first or bondurant straightening response began a period of several hundred to 1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the reelfoot fault these bondurant events predate the existing paleoseismic record for the reelfoot fault these data offer initial evidence that slip events on the reelfoot fault were temporally clustered on millennial scales and thus offers the first direct evidence for millennial scale clustering of earthquakes on a continental interior fault this carries additional ramifications namely faults that have been quiescent and non hazardous for millennia could re enter an enduring period of recurrent hazardous earthquakes with little warning likewise the reelfoot fault also reveals evidence of temporal clustering of earthquakes on short term cycles months as well as evidence for longer term reactivation cycles 10 4 10 6 years this introduces the possibility that temporal clustering could be hierarchical on some continental interior faults

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

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

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

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

paleoseismicity of two historically quiescent faults in australia implications for fault behavior in stable continental regions paleoseismic studies of two historically aseismic quaternary faults in australia confirm that cratonic faults in stable continental regions scr typically have a long term behavior characterized by episodes of activity separated by quiescent intervals of at least 10 000 and commonly 100 000 years or more studies of the approximately 30 km long roopena fault in south australia and the approximately 30 km long hyden fault in western australia document multiple quaternary surface faulting events that are unevenly spaced in time the episodic clustering of events on cratonic scr faults may be related to temporal fluctuations of fault zone fluid pore pressures in a volume of strained crust the long term slip rate on cratonic scr faults is extremely low so the geomorphic expression of many cratonic scr faults is subtle and scarps may be difficult to detect because they are poorly preserved both the roopena and hyden faults are in areas of limited or no significant seismicity these and other faults that we have studied indicate that many potentially hazardous scr faults cannot be recognized solely on the basis of instrumental data or historical earthquakes although cratonic scr faults may appear to be nonhazardous because they have been historically aseismic those that are favorably oriented for movement in the current stress field can and have produced unexpected damaging earthquakes paleoseismic studies of modern and prehistoric scr faulting events provide the basis for understanding of the long term behavior of these faults and ultimately contribute to better seismic hazard assessments

effect of microbial growth rate on temperature and metabolic water recorded in 18o 16o ratios of po4 in dna abstract it has been recently demonstrated that both temperature and intracellular metabolic water are recorded by the po4 moieties comprising the backbone of dna in microbial cells as well as in total microbial biomass po4 blake et al 2016 li et al 2016 temperature and intracellular water composition are reflected in the 18o 16o ratio of po4 18op in dna blake et al 2016 to determine whether the reported temperature recording by microbial dna po4 could be an artifact of variable microbial growth rate which may also vary as a function of temperature three strains of microorganisms having distinct and different growth rate patterns between 23 and 42 c pseudomonas fluorescens acinetobacter adp1 and marinobacter aquaeolei were cultured over a range of temperatures and growth rate patterns growth curve patterns for the different strains were distinct and growth rates increased with temperature however as we show here variations in 18op values of dna po4 did not correlate with changes in bacterial growth rates at a given temperature and o isotope fractionations i e partitioning of o isotopes between po4 in dna and o in water were not significantly different between strains

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction