geophysical and geological evidence of neotectonic deformation along the hovey lake fault lower wabash valley fault system central united states high resolution seismic shear wave reflection profiles were collected over a segment of the hovey lake fault a known paleozoic fault within a system of faults in the southernmost wabash river valley of the central united states although the fault zone called the wabash valley fault system lies in an area of recognized prehistoric and contemporary seismicity the seismogenic potential of this system remains poorly defined consequently the objectives of this study are to assess the hovey lake fault one of the more prominent fault strands in the system for neotectonic reactivation and if present collect sediment samples for dateable material from the disrupted horizons to provide an age constraint for the movement the resultant stacked profiles show high angle deformation extending above the paleozoic bedrock and into upper quaternary sediment time displacement calculations from the data show approximately 10 5 m of offset on the top of bedrock horizon and 2 m of inverted displacement along the earliest arriving quaternary soil reflector preliminary correlative coring and carbon 14 age dating of a disrupted soil horizon located 7 7 m below ground surface suggest fault movement at this site as late as approximately 37 000 years before present

upper crust beneath the central illinois basin united states newly available industry seismic reflection data provide critical information for understanding the structure and origin of the upper crust 0 12 km depth beneath the central illinois basin and the seismic tectonic framework north of the new madrid seismic zone in the central mississippi valley mapping of reflector sequences furnishes the first broad three dimensional perspective of the structure of precambrian basement beneath the central united states midcontinent the highly coherent basement reflectivity is expressed as a synformal wedge of dipping and subhorizontal reflections situated beneath the center of the illinois basin that thickens and deepens to the northeast e g 0 to 3 km thickness along a 123 km south to north line the thickening trend of the wedge qualitatively mimics the northward thickening of the late cambrian mt simon sandstone however other paleozoic units in the illinois basin generally thicken southward into the basin center the seismic data also reveal an anomalous subsequence defined by a spoon shaped distribution of disrupted reflections located along the southern margin of the wedge the boundaries of this subsequence are marked by distinct steeply dipping reflections possible thrust faults that continue or project up to antiformal disruptions of lower paleozoic marker reflectors suggesting paleozoic or possibly later tectonic reactivation of precambrian structure the areal extent of the subsequence appears to roughly correspond to an anomalous concentration of larger magnitude upper to middle crustal earthquakes there are multiple hypotheses for the origin of the precambrian reflectivity including basaltic flows or sills interlayered with clastic sediments and or emplaced within felsic igneous rocks such explanations are analogous to nearby keweenawan rift related volcanism and sedimentation which initiated during proterozoic rifting and were followed eventually by reverse faulting along the rift margins caused by grenville compression

seismic structure of the crust and uppermost mantle of north america and adjacent oceanic basins a synthesis we present a new set of contour maps of the seismic structure of north america and the surrounding ocean basins these maps include the crustal thickness whole crustal average p wave and s wave velocity and seismic velocity of the up permost mantle that is pn and sn we found the following 1 the average thickness of the crust under north america is 36 7 km standard deviation s d 8 4 km which is 2 5 km thinner than the world average of 39 2 km s d 8 5 for continental crust 2 histograms of whole crustal p and s wave velocities for the north amer ican crust are bimodal with the lower peak occurring for crust without a high velocity 6 9 7 3 km sec lower crustal layer 3 regions with anomalously high average crustal p wave velocities correlate with precambrian and paleozoic orogens low average crustal velocities are correlated with modern extensional regimes 4 the average pn velocity beneath north america is 8 03 km sec s d 0 19 km sec 5 the well known thin crust beneath the western united states extends into north west canada 6 the average p wave velocity of layer 3 of oceanic crust is 6 61 km sec s d 0 47 km sec however the average crustal p wave velocity under the eastern pacific seafloor is higher than the western atlantic seafloor due to the thicker sediment layer on the older atlantic seafloor

eudaemonema webbi sp nov mammalia mixodectidae from the late paleocene of western canada the youngest known mixodectid mixodectidae mammalia archonta are an unusual poorly known family of dermopteran like mammals that have been discovered at several north american localities of primarily early paleocene age among the three or four recognized mixodectid genera eudaemonema simpson is perhaps one of the least understood being known from only a few localities of late torrejonian and earliest tiffanian age this paper reports on a new species of eudaemonema from the late paleocene of alberta canada that significantly extends the geographic and stratigraphic ranges of the genus eudaemonema webbi sp nov is known from middle and late tiffanian localities in central and south central alberta and it represents the youngest and northernmost species of eudaemonema so far discovered e webbi differs from the genotypic species e cuspidata in being larger and in having a suite of dental characters e g molariform posterior premolars enlarged molar protocone and hypocone development of a second grinding platform on the

deep structure of northern mississippi embayment in september 1980 the u s geological survey conducted a seismic refraction investigation of the northern mississippi embayment during the investigation 34 shots from nine shotpoints were recorded along a series of profiles the profiles were parallel to and across an inferred precambrian rift zone which is outlined by a series of magnetic anomalies and covers an area at least 200 km 125 mi long and 70 km 45 mi wide along the northeast southwest trending axis of the rift a 0 7 to 1 1 km 2 297 to 3 609 ft thick 1 8 km sec layer representing the unconsolidated tertiary and cretaceous sediments overlies a 2 km 6 562 ft thick 5 95 km sec layer representing a paleozoic carbonate sequence beneath the carbonates is a 3 km 9 843 ft thick low velocity layer which probably consists of late precambrian clastics the presence of this low velocity layer is indicated on the seismic profiles by an abrupt cutoff of the 5 95 km sec arrivals at about 20 km 12 mi from the shotpoints this cutoff is followed by a 30 to 40 km 20 to 25 mi long zone of no arrivals beyond which are seen delayed arrivals from a 6 2 km sec crystalline basement the 11 km 6 8 mi thick 6 2 km sec basement overlies a lower crus composed of a 6 6 km sec layer whose thickness decreases to the northeast owing to its replacement by an anomalous high velocity 7 3 km sec basal layer the base of the crust ranges from a 39 km 24 mi depth at the southern end of the profile to a 46 km 29 mi depth at the northern end where the 7 3 km sec layer is 20 km 12 mi thick below the base of the crust moho the upper mantle has a velocity of 8 0 km sec the velocity structure beneath the west flank of the embayment is simpler than that of the axis 5 95 6 2 6 6 7 3 and 8 0 km sec the low velocity layer is absent and the anomalous 7 3 km sec layer is thinner than along the axial profile the profiles perpendicular to the rift show that the low velocity layer is restricted to the axial zone and that the anomalous 7 3 km sec basal crustal layer reaches maximum thickness there the tectonic model proposed to explain the origin of this embayment velocity structure includes a late precambrian mantle plume that intruded the lower crust of the northern embayment causing uplift and or crustal stretching and subsequent rifting of the axial area this was followed by erosion subsidence and subsequent deposition of sediments in the resulting trough

site amplification scattering and intrinsic attenuation in the mississippi embayment from coda waves we estimate site amplification intrinsic q q i and scattering q q s values from three component coda of broadband data recorded by cooperative new madrid sesimic network stations for center frequencies 0 2 0 5 1 0 2 0 and 5 0 hz near 0 5 and 1 0 hz site amplification factors for the transverse component recorded by stations in the mississippi embayment are between 1 7 and 18 compared with stations outside the embayment the amplification factor becomes smaller at frequencies lower than 0 5 hz and higher at those greater than 1 0 hz the radial component shows a similar amplification however the vertical component shows relatively less amplification q i and q s are estimated from coda using an energy flux model for two time windows after the direct s wave and at 0 5 and 1 0 hz center frequencies the two time windows include coda up to and after twice the s wave travel time at each station coda parameters change with the time window and are attributed to a mixture of incoherent coda with coherent s wave reverberations directly after the s wave q i and q s inferred from stations outside of the embayment have higher values than those from stations within the embayment a plane wave model qualitatively explains the lack of coda amplification at high frequencies compared with a low frequency without recourse to anelastic attenuation arguments however the plane wave model cannot explain the very large observed coda amplifications at 1 and 0 5 hz seen in the data suggesting that other wave scattering effects must be occurring in the embayment velocity structure this is consistent with the relatively low q s values inferred from the energy flux model for stations within the embayment in addition to coda amplification we performed a synoptic noise study that revealed that pre event ambient background noise behaves in a similar manner to the coda for stations within and outside of the embayment the presence of large lateral velocity heterogeneities in the embayment may cause q s values to be low there

three dimensional crustal structure of eastern north america extracted from ambient noise 1 group velocity dispersion curves of surface waves extracted from ambient seismic noise are inverted to find 3 d shear wave structure of the crust beneath eastern north america the 3 d model consists of one sediment layer and another six layers with fixed depths at 5 7 5 10 15 25 and 43 km velocities of the seven layers together with the thickness of the sediment layer are determined by the simulated annealing method we found that almost all failed ancient rifting events e g the reelfoot rift ouachita triple junction and the midcontinent rift and rifting related events e g the ozark uplift and the nashville dome are associated with high velocity bodies in the middle and lower crust our results also suggest the existence of a triple junction like high velocity body centered around the new madrid and the wabash valley seismic zones with the reelfoot rift the ozark uplift and the nashville dome being on its southwestern northwestern and southeastern arms respectively we also found that the western limb of the midcontinent rift mcr extends southwestward to western oklahoma and texas and the eastern limb of the mcr extends southeastward into western ohio the appalachian mountains are characterized by high velocity upper crust underlain with relatively low velocity middle and lower crust all major seismic zones are associated with either divergent or convergent events the new madrid seismic zone and wabash valley seismic zone are clearly associated with the failed reelfoot rift both the eastern tennessee seismic zone and ouachita orogen seismic zone are located along convergent boundaries

the vertical component p wave receiver function the vertical component p wave receiver function is an important source of data in studies of the crust mantle transfer function for determining earth structure under isolated receivers or under receiver arrays this waveform illuminates a missing aspect of the wave propagation in receiver function studies that employ only the horizontal components of motion and yields complementary constraints on near receiver heterogeneity and p wave propagation the vertical component p wave receiver function is formed using an array estimate for the effective teleseismic source function that is then deconvolved from all the vertical and horizontal components of ground motion at each station in the array one dimensional three dimensional and stochastic wave propagation models are used to test the robustness of the technique breakdown of single station receiver function deconvolution occurs because of high levels of noncorrelated noise between the ground motion components receiver functions for stations of the southern california terrascope array are investigated using the array technique vertical receiver functions for stations in the los angeles basin and long valley caldera show high amplitude secondary arrivals that cannot be explained by simple 1d structures but probably reflect wave propagation in 3d basin structures three component receiver functions from the station at mammoth lakes california show pathological behavior where the horizontal components of ground motion exceed the amplitude of the vertical components suggesting extreme topographic and 3d velocity heterogeneity use of all three components of the receiver function in modern passive array experiments is encouraged to reduce the problems of nonuniqueness in determining earth models

lithology and shear wave velocity in memphis tennessee we have derived a new three dimensional model of the lithologic struc ture beneath the city of memphis tennessee and examined its correlation with measured shear wave velocity profiles the correlation is sufficiently high that the better constrained lithologic model may be used as a proxy for shear wave velocities which are required to calculate site amplification for new seismic hazard maps for memphis the lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs some sampling to 500 m depth and a moving least squares algorithm seventy six new shear wave velocity profiles have been measured and used for this study most sampling to 30 m depth or less all log and velocity observations are publicly available via new web sites

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

ground motion simulations of 1811 1812 new madrid earthquakes central united states we performed a suite of numerical simulations based on the 1811 1812 new madrid seismic zone nmsz earthquakes which demonstrate the importance of 3d geologic structure and rupture directivity on the ground motion response throughout a broad region of the central united states cus for these events our simulation set consists of 20 hypothetical earthquakes located along two faults associated with the current seismicity trends in the nmsz the hypothetical scenarios range in magnitude from m 7 0 to 7 7 and consider various epicenters slip distributions and rupture characterization approaches the low frequency component of our simulations was computed deterministically up to a frequency of 1 hz using a regional 3d seismic velocity model and was combined with higher frequency motions calculated for a 1d medium to generate broadband synthetics 0 40 hz in some cases for strike slip earthquakes located on the southwest northeast striking nmsz axial arm of seismicity our simulations show 2 10 s period energy channeling along the trend of the reelfoot rift and focusing strong shaking northeast toward paducah kentucky and evansville indiana and southwest toward little rock arkansas these waveguide effects are further accentuated by rupture directivity such that an event with a western epicenter creates strong amplification toward the northeast whereas an eastern epicenter creates strong amplification toward the southwest these effects are not as prevalent for simulations on the reverse mechanism reelfoot fault and large peak ground velocities 40 cm s are typically confined to the near source region along the up dip projection of the fault nonetheless these basin response and rupture directivity effects have a significant impact on the pattern and level of the estimated intensities which leads to additional uncertainty not previously considered in magnitude estimates of the 1811 1812 sequence based only on historical reports the region covered by our simulation domain encompasses a large portion of the cus centered on the nmsz including several major metropolitan areas based on our simulations more than eight million people living and working near the nmsz would experience potentially damaging ground motion and modified mercalli intensities ranging from vi to viii if a repeat of the 1811 1812 earthquakes occurred today moreover the duration of strong ground shaking in the greater memphis metropolitan area could last from 30 to more than 60 s depending on the magnitude and epicenter online material tables of 1d velocity models used to generate the high frequency synthetics and figures of source models and peak ground motion synthetics

liquefaction related ground failure a case study in the new madrid seismic zone central united states large curvilinear sand blows resulting from earthquake induced liquefaction commonly occur along the margins of fine grained channel fill deposits in the st francis basin of the new madrid seismic zone one such example identified on aerial photographs and satellite images was studied in detail by examining relations of sedimentary deposits and liquefaction features in the field and by compiling borehole data previously collected by the army corps of engineers ground failure in this example included liquefaction of subsurface sandy deposits development of en echelon fissures in the overlying channel fill deposit forceful venting of sandbearing water to the ground surface resulting in the formation of sand dikes and sand blows and differential ground subsidence across the sand dikes a combination of mechanisms including the development of a water rich zone below the clayey surficial deposits may have contributed to the failure at the study site located in southeastern missouri the near surface sedimentary geology can be described as a two layered system with a sandy channel deposit below and a less permeable clayey overbank deposit above the contact between the two layers is roughly horizontal except where embedded by a channel fill deposit the basal contact of the channel fill deposit is inclined along its margin and extends below the base of the overbank deposits sand blows are abundant in the overbank deposits which are about 6 m thick in contrast sand blows rarely occur within the 18 m thick channel fill deposit except along its margin here feeder dikes of the sand blows are concentrated within 15 m of and arranged in an en echelon pattern subparallel to the margins of the channel fill deposit on the side of the feeder dikes toward the edge of the channel fill deposit the ground surface is displaced downward as much as 1 2 m large ground displacements often pose the greatest threat to the integrity of engineered structures as demonstrated in this case study the spatial relations of sedimentary deposits as well as their permeability and thickness appear to influence both the location and mode of ground failure a better understanding of factors contributing to liquefaction related ground failures can help to identify sites that may be prone to large ground displacements and thus to mitigate the hazard posed by earthquakes in this region

sequence stratigraphy and relative sea level history of the middle and upper ordovician of the nashville dome tennessee abstract eleven depositional sequences are present in the middle and upper ordovician of the nashville dome all but one lack lowstand systems tracts and many display evidence of subaerial exposure such as paleokarst or regional erosional truncation at their sequence boundaries which are combined with transgressive surfaces features formed during the transgression such as hardgrounds are more prominent at most sequence boundaries than are those features related to subaerial exposure all sequences have maximum flooding zones with aggradational stacking rather than discrete maximum flooding surfaces condensation features are much more common at transgressive surfaces than within the maximum flooding zone the expression of these parasequences and sequences changes with the onset of the taconic orogeny although parasequences from equivalent depositional environments can be recognized before and after the onset of the orogeny their facies composition changes completely sequences following the orogeny display fewer paleokarst features more pyritized and iron stained hardgrounds at flooding surfaces and transgressive surfaces and more phosphatic lags and mineralization at transgressive surfaces than those preceding the orogeny a relative sea level curve for the nashville dome has a long term 5 m y component presumably dominated by subsidence and a short term 1 3 m y component consisting of 10 50 m fluctuations that is primarily the result of eustasy

seismic reflection imaging of tertiary faulting and related post eocene deformation 20 km north of memphis tennessee abstract other than the crittenden county fault zone ccfz little is known about the seismic hazard from earthquake faults within 50 km of memphis tennessee a city that contains a large inventory of older buildings that are vulnerable to moderate and strong earthquake ground shaking to address this lack of knowledge about faulting near memphis we acquired a 4 5 km long mini sosie seismic reflection profile across the boundary between the loess covered bluffs and modern mississippi river flood plain in meeman shelby forest state park north of memphis we imaged a previously unknown reverse thrust fault that displaces paleozoic and cretaceous rocks and upwarps tertiary deposits on the floodplain portion of the profile about 25 km north of downtown memphis the paleozoic and cretaceous rocks are vertically faulted about 70 and 40 m respectively in an up to the west sense of displacement the fault displacement apparently terminates in the basal portion of the paleocene section and causes only an upwarping of the overlying deposits the overlying paleocene and eocene deposits which are probably the youngest deposits imaged are upwarped about 50 60 m with the same sense of displacement as the underlying older units the sense of displacement amplitude and appearance of the fault in the seismic data are very similar to that observed in the seismic reflection images of the ccfz 15 km west of this profile although we have imaged this new fault in only one location its proximity to memphis and similarities to the ccfz leads us to speculate that it may be a parallel structure to the ccfz and thus warrants further study

joint local and teleseismic tomography in the central united states exploring the mantle below the upper mississippi embayment and the illinois basin three dimensional high resolution crustal and upper mantle p and s wave velocity vp and vs models are presented for the central united states the study utilizes local and teleseismic data reco

wave field continuation and decomposition for passive seismic imaging under deep unconsolidated sediments abstract the coastal plains of the central and eastern united states contain deep sections of unconsolidated to poorly consolidated sediments these sediments mask deeper crustal and upper mantle converted phases in teleseismic receiver functions through large amplitude near surface reverberations thick sediments also amplify ambient noise levels to generally reduce data signal to noise ratios removing shallow sediment wave propagation effects is critical for imaging deep lithospheric structures a propagator matrix formalism is used to downward continue the wave field for teleseismic p waves into the midcrust and then to separate the upgoing s wave field from the total teleseismic response of the p wave to expose deep sp conversions this method requires that the earth model from the surface to the reference depth be known teleseismic p wave data for the memphis tennessee station mph are analyzed using a reference station deconvolution technique to produce vertical and radial p wave transfer functions these transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion the inverted earth model is incorporated into the wave field continuation and decomposition technique to estimate the upgoing s wave field at 10 km depth in the crust moho and possible deeper ps conversions are identified with this process

three dimensional geologic map of the hayward fault northern california correlation of rock units with variations in seismicity creep rate and fault dip in order to better understand mechanisms of active faults we studied relationships between fault behavior and rock units along the hayward fault using a three dimensional geologic map the three dimensional map constructed from hypocenters potential field data and surface map data provided a geologic map of each fault surface showing rock units on either side of the fault truncated by the fault the two fault surface maps were superimposed to create a rock rock juxtaposition map the three maps were compared with seismicity including aseismic patches surface creep and fault dip along the fault by using visualization software to explore three dimensional relationships fault behavior appears to be correlated to the fault surface maps but not to the rock rock juxtaposition map suggesting that properties of individual wall rock units including rock strength play an important role in fault behavior although preliminary these results suggest that any attempt to understand the detailed distribution of earthquakes or creep along a fault should include consideration of the rock types that abut the fault surface including the incorporation of observations of physical properties of the rock bodies that intersect the fault at depth

diatoms as quantitative paleodepth indicators in coastal areas of the southeastern beaufort sea arctic ocean abstract surface sediment diatom assemblages in depth profiles along the southeastern beaufort sea coasts canada were analysed to describe the relationship between species distribution and water depth of deposition the 74 coastal stations sampled were distributed in several sedimentary environments from salt marshes to the inner shelf the relationship between diatom species distribution and water depth was examined using canonical correspondence analysis cca and partial cca the water depth accounted for 9 7 of the variance in the data set the diatom water depth relationship is believed to be controlled by the shoreface circulation which results in a shift in the relative abundance of the epipsammon epipelon and plankton along the water depth gradient upper shoreface assemblages are dominated mainly by epipelic species and a few number of epipsammic taxa whereas deeper environments are dominated by planktonic species a transfer function was derived using weighted averaging regression and calibration to reconstruct the water depth of deposition over the coastal interval from mean sea level to a maximum of 14 m depth on the coastal shelf of the southeastern beaufort sea the transfer function allows relative sea level to be predicted from fossil diatom assemblages with a root mean square error of 1 43 m this model is likely to produce reliable water depth inferences along the southeastern beaufort sea coasts and in other shallow sandy microtidal environments dominated by low energy waves and influenced by freshwater discharge the transfer function was used to provide quantitative paleodepth inferences for late holocene sediments from the atkinson point area based on fossil diatom assemblages

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

a revision of the late cretaceous paleocene eutherian mammal cimolestes marsh 1889 cimolestes marsh is a north american eutherian mammal primarily known from latest cretaceous deposits in alberta wyoming saskatchewan and montana at present five species of cimolestes are considered valid all lancian in age they include one of the largest north american late cretaceous therian mammals as well as one of the smallest a size range far exceeding that within other genera of tribosphenic therians contemporary with cimolestes such as the leptictoid eutherian gypsonictops simpson or genera of alphadontid or pediomyid marsupials moreover the species of cimolestes display a disparity of dental morphology in addition to size well in excess of interspecific differences within these genera given these considerations cimolestes is clearly a grade taxon uniting species sharing an adaptively subzalambdodont dentition but showing divergent specializations within this pattern that are inconsistent with monophyly of its presently included species to correct these imbalances this paper limit

aceroryctes dulcis a new palaeoryctid mammalia eutheria from the early eocene of the wasatch formation of southwestern wyoming usa the palaeoryctidae are a group of small bodied likely insectivorous mammals known principally from the paleocene and early eocene from approximately 65 to 53 ma of north america here we report on a new palaeoryctid from the early eocene early wasatchian wa3 north american land mammal age main body of the wasatch formation washakie basin near bitter creek station in southwestern wyoming usa acerorcytes dulcis gen et sp nov is unique among palaeoryctids in having a double rooted p2 with a small anterior cusp p3 with pronounced para and metastylar cusps and a reduced but conspicuous metacone p4 with a weakly developed metacone and an anteroposteriorly compressed protocone and m1 2 with deep ectoflexus and a sharp metastylar blade a phylogenetic analysis based on 32 dental characters of the nine known north american palaeoryctid species including aceroryctes dulcis recovered eight equally parsimonious cladograms similar to prior studies the analysis suggests that the genus palaeoryctes

subsurface structure of the petit spot volcanoes on the northwestern pacific plate 1 a seismic reflection survey was conducted in the northwestern pacific to investigate subsurface structure of small volcanoes considered to be formed by the newly discovered petit spot intra plate volcanism in contrast with an acoustically transparent sedimentary layer in the ambient northwestern pacific sedimentary layers are acoustically opaque with interbedded strong reflections beneath the volcanoes these reflections are possibly caused by inhomogeneous structure due to intrusion of central vent subhorizontal strong reflections at base of the sedimentary layer identified in the vicinity of volcanoes are probably reflections from sills of dense lavas flowing out within the sedimentary layer these volcanoes could be monogenetic volcanoes produced by small amount of magma intrusion 1 km3 in volume although such small volcanoes have never been discovered unless through a high resolution bathymetric mapping the invisible intra plate volcanism affects successive evolution modification of the crustal architecture of old age oceanic plates

crustal structure of the appalachian highlands in tennessee abstract crustal structure of the southern appalachians and adjacent interior low plateaus in tennessee is derived from seismic refraction measurements observed by the u s geological survey in 1965 along reversed lines normal nw se and parallel ne sw to the structure of the appalachian highlands major geologic divisions its easternmost part is located approximately 80 km southwest of the westernmost part of the cocorp seismic reflection traverse within the blue ridge province the velocity depth models derived for both observational directions consist of three crustal layers with surprisingly high velocities being about 6 1 6 2 km s in the upper crust down to 7 10 km depth 6 7 6 8 km s for the middle crust between about 17 and 34 km and varying from 7 1 to 7 4 km s for the lower crust at about 40 47 km depth the boundaries between the three crustal layers as well as the crust mantle boundary are transition zones of up to 11 km thickness similar to old orogens in other parts of the earth the main result is a thick crust at places in excess of 50 km with high average velocity and a broad crust mantle transition zone

late cretaceous and cenozoic geology of the new madrid seismic zone structure contour maps constructed from well seismic reflection and outcrop data of the tops of the paleozoic section upper cretaceous section paleocene midway group and eocene section illustrate the post paleozoic structure of the new madrid seismic zone region isopach maps of the late cretaceous section midway group and eocene section help constrain the timing of the structural events these maps which encompass much of the northern mississippi embayment reveal reactivation of the underlying late precambrian cambrian reelfoot rift during midway group deposition but no reactivation during late cretaceous or eocene deposition the structure contour maps also indicate a subtle south plunging depression on the tops of the paleozoic upper cretaceous and midway group along the axis of the northern mississippi embayment that we have called a trench this trench is 50 km wide has a maximum depth of 100 m and appears to have formed during the eocene the trench s western boundary coincides with the blytheville arch lake county uplift and its southeastern margin underlies memphis tennessee the blytheville arch lake county uplift is the structure responsible for the new madrid seismic zone and thus it is possible that the southeastern margin of the trench is also a fault zone northern mississippi embayment post paleozoic stratigraphy consists of sands silts and clays that thicken from 477 m at new madrid missouri to 987 m near memphis tennessee the uniformity of these sediments indicates their elastic properties and therefore seismic velocities are very similar however variations in cementation and unconformities within the section may influence seismic wave propagation manuscript received 17 june 1999

a new type of intra plate volcanism young alkali basalts discovered from the subducting pacific plate northern japan trench alkali pillow basalts were collected from the toe of the oceanward slope of the northern japan trench these alkali basalts formed as a result of a low degree of partial melting of pacific ocean mantle and rapid rise of the magma no fractionation in shallow magma chambers reconstructing pacific plate motion based on 40ar 39ar age dates of 5 95 0 31 ma for these basalts indicates that they erupted outboard of outer swell or forebulge of the japan trench in the nw pacific we suggest that these alkali basalts represent a new form of intra plate volcanism whereby magmatic activity occurs off the forebulge of the downgoing pacific slab perhaps using conduits related to fracturing of the slab during bending prior to subduction

microtremor observations of deep sediment resonance in metropolitan memphis tennessee we measured site resonance periods throughout metropolitan memphis tennessee the site resonance was derived from recordings of ambient microtremor and is a direct measurement of seismic ground shaking in the memphis metropolitan area the period t0 in s is predicted by the empirical relation t0 0 39899 7 8922 10 3h 3 0634 10 6h2 350 h 1100 m where h is the thickness in m of the unconsolidated sediments that overly hard paleozoic rocks assuming that a quarter wavelength relationship governs the relationship between resonant period sediment thickness and average shear wave speed we estimate the average shear wave speed of unconsolidated sediments as a function of sediment thicknesses vs 521 15 0 37459h 350 h 1100 m the scatter in the observations and discordance with earlier work suggests that caution is warranted in applying these values of wave speed indiscriminately to sites in the absence of further detailed work

a cocorp deep reflection profile across the buried reelfoot rift south central united states abstract a cocorp deep reflection survey across the northern mississippi embayment reveals essential features of the late precambrian early paleozoic reelfoot rift stratified reflections delineating the sedimentary fill of the rift basin are of variable thickness the base ranging from 2 0 to a maximum of 3 5 s twt 4 to 8 km depth in contrast the base of phanerozoic the sedimentary section immediately east of the rift is at 1 4 s 2 8 km depth correlation with a basement penetrating well indicates that the base of the upper cretaceous holocene mississippi embayment supergroup base of the cambrian ordovician knox group and the lower upper cambrian bonneterre formation are basin wide seismic stratigraphic markers clastic sedimentary strata of the lamotte formation which immediately overlie precambrian basement show clear angular discordance with the overlying subhorizontal bonneterre formation indicating that the base of the bonneterre marks the transition from active extension to passive subsidence within the reelfoot rift palinspastic restoration of the basement suggests relatively modest extension associated with rift formation 17 the blytheville arch an axial antiformal feature as well as a number of lesser structures indicative of multiple episodes of fault reactivation are also evident on the cocorp profile the crystalline basement beneath the reelfoot rift is relatively devoid of reflections down to 5 0 s 12 15 km depth beyond which it passes gradationally into a complexly reflective diffractive middle and lower crust the lower crust however does not exhibit the distinctly laminated character commonly observed in mesozoic cenozoic extensional provinces the crust mantle transition beneath the rift is characterized by a gradational downward cessation of crustal reflectivity at 12 13 s 40 km depth followed by an unreflective zone which in turn is followed by a distinct horizontal reflection at 14 5 s the latter is not observed on existing profiles outside the rift at present it is not possible to determine strictly whether the deep horizon represents moho or alternatively a discrete feature sill within the uppermost mantle however its spatial association with the reelfoot rift suggests that the two are genetically related regional relations together with the existence of dipping fabric in the deep crust beneath the rift suggest the possibility that the reelfoot rift formed along the southern extension of the circa 1 ga grenville front

the relocation of microearthquakes in the northern mississippi embayment three component seismograms recorded by a small array of digital instruments in the northern mississippi embayment consistently show a high amplitude phase on the vertical component that arrives approximately 0 8 s before the shear wave on the basis of its timing and apparent velocity this phase is identified as an s p conversion from the boundary between the unconsolidated cenozoic sediments and the underlying paleozoic rocks synthetic models of ground motion in the mississippi embayment indicate that vertical displacement amplitudes are higher for s p conversions than for transmitted shear waves at all angles of incidence the models and their agreement with observations of the three component seismograms suggest that true shear waves cannot be reliably identified from vertical component seismograms recorded in this area the travel times of converted phases are used together with crustal velocity models derived from a recent seismic refraction survey to relocate approximately 500 microearthquakes recorded by the central mississippi valley regional seismic network since the network data are recorded by vertical component seismographs we assume that the s phases observed at the stations sited on unconsolidated sediments are s p conversions this assumption significantly reduces the average rms residual and provides well constrained hypocentral locations for 350 earthquakes the relocated microearthquakes cluster tightly along previously identified epicentral trends focal depths range from 0 5 to 22 km but events deeper than 14 km are rare and events shallower than 3 km are confined almost exclusively to the area between ridgely tennessee and new madrid missouri focal mechanisms are generally consistent with the results of previous studies the axial seismicity trend which extends from caruthersville missouri to marked tree arkansas is characterized by right lateral strike slip motion on a northeast trending nearly vertical fault plane the events between ridgely tennessee and new madrid missouri commonly show strike slip focal mechanisms with minor components of both normal and reverse dip slip

diversity and climate change in the middle late wasatchian early eocene willwood formation central bighorn basin wyoming abstract densely distributed mammal samples from the willwood formation in the central part of wyoming s bighorn basin span episodes of major climate change previous work has focused on dramatic short term 0 5 myr during a 1 myr period of relatively static cool temperatures and a subsequent 1 myr period of warming that begins with the biohorizon b event and ends with the early eocene climatic optimum eeco in which the earth reached the hottest temperatures of the cenozoic geographic information systems is used to create spatially constrained subsamples to limit and explore the effects of the species area relationship on multiple aspects of diversity including the alpha average locality and beta locality differentiation components of species richness and the evenness and relative dominance of species abundance distributions results demonstrate previously unrecognized spatial bias in the upper levels of the section that complicate the interpretation of faunal response to the eeco evenness is strongly related to alpha richness whereas beta richness and dominance vary independently evenness increases significantly and richness becomes significantly more variable during warming richness also increases but the rise in alpha richness is not significant and the rise in beta richness is equivocal the dominance of the fauna by two abundant lineages escalates consistently regardless of changes in temperature diversity is not obviously affected across the biohorizon b event indicating that further study is necessary

late wisconsin to holocene deformation in the new madrid seismic zone the new madrid earthquakes of 1811 1812 produced regional deformation in northwestern tennessee southeastern missouri and northeastern arkansas landforms such as the lake county uplift reelfoot lake and the sunklands of northeast arkansas either formed or were reactivated during these great earthquakes two hundred and fifty three cores were used to construct a structure contour map of the unconformity between the eocene strata and the overlying quaternary mississippi river alluvium in the new madrid seismic zone this map reveals relief that mirrors the surface deformation and provides additional data on the distribution of regional deformation we interpret the structure contour map as a representation of the late wisconsin to the present strain field of the new madrid seismic zone this map provides constraints for future kinematic analyses of late quaternary new madrid faulting and allows forecasting of future coseismic deformation

evaluation of deep sediment velocity structure in the new madrid seismic zone detailed knowledge of the physical properties of the sediments filling the mississippi embayment has proven critical to both unravel the tectonic frame work operating in the region and assess the seismic hazards posed by the new madrid seismic zone in this article we show that independent geotechnical estimates for p and s wave velocities are compatible with a sedimentary model of k feldspar clasts embeded in water and we test its validity by modeling receiver functions at a number of broadband stations by constraining the bulk sediment thicknesses beneath each station from independent reflection profiling estimates we have been able to recover the depth to the top of the cretaceous from the receiver function data at individual stations our receiver function modeling thus provides confidence in the velocity and density structures extrapolated from in situ geotechnical measurements in the upper mississippi embayment

the 18 june 2002 caborn indiana earthquake reactivation of ancient rift in the wabash valley seismic zone the 18 june 2002 caborn indiana earthquake m w 4 6 occurred on a steeply dipping fault at a depth of about 18 km regional and teleseismic waveform data were used to obtain an accurate hypocenter with uncertainties better than about 2 km in both vertical and horizontal directions the source mechanism determined from regional waveform analysis is predominantly strike slip along near vertical nodal planes dips 82 and 84 striking 28 and 297 the nearly horizontal p axis trends 252 and plunges 10 the close proximity of the epicenter to the trace of the compound caborn fault and good agreement between the strike and dip of that fault and the source mechanism of the 2002 event suggests that the earthquake may have occurred on that fault most of the wabash valley faults as mapped from the shallow subsurface data extend into the precambrian basement to at least 7 km depth without significantly changing their orientation the june 2002 event at 18 km depth and the south central illinois earthquake on 9 november 1968 m w 5 3 which occurred at 25 km depth suggest that the seismogenic depth in the wabash valley seismic zone extends down to at least 18 km depth this earthquake is unique because it is the largest instrumented event to date that is clearly located within the area spanned by the wabash valley fault system its focal mechanism vertical strike slip faulting at depth may suggest that buried faults associated with a possible precambrian rift system are being reactivated by the contemporary east east northeast trending regional horizontal compressive stress

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

contour mapping of relic structures in the precambrian basement of the reelfoot rift north american midcontinent a new contour map of the basement of the reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features the major features are two asymmetric intrarift basins bounded by three structural highs and the rift margins the basins are oriented normal to the northeast trend of the rift two of the highs appear to be ridges of undetermined width that extend across the rift the third high is an isolated dome or platform located between the basins the minor features are three linear structures of low relief oriented subparallel to the trend of the rift two of these located within the rift basins may divide the rift basins into paired subbasins these mapped features may be the remnants of initial extensional rifting half graben faulting and basement subsidence the rift basins are interpreted as having formed as opposing half graben and the structural highs are interpreted as having formed as associated accommodation zones some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime a detailed knowledge of the geometries of the reelfoot rift s basement features therefore is essential when evaluating their seismic risk potential

modifications to existing ground motion prediction equations in light of new data we compare our recent ground motion prediction equations gmpes for western north america wna boore and atkinson 2008 ba08 and eastern north america ena atkinson and boore 2006 ab06 atkinson 2008 a08 to newly available ground motion data based on these comparisons we suggest revisions to our gmpes for both wna and ena the revisions for wna affect only those events with m 5 75 while those for ena affect all magnitudes these are simple modi fications to the existing gmpes that bring them into significantly better agreement with data the wealth of new data clearly demonstrates that these modifications are warranted we therefore recommend the use of the updated equations for seismic hazard analyses and other applications more detailed studies are under way by many investigators including ourselves to develop a new generation of ground motion models in both wna and ena from scratch through a comprehensive reevaluation of source path site and modeling issues in time those more complete models will replace those proposed in this study however as the new models will be several years in development we recommend using the modified models proposed herein labeled ba08 for wna ab06 for ena and a08 for ena to replace a08 as interim updates to our existing models the proposed models are in demonstrable agreement with a rich database of ground motions for moderate magnitude earthquakes in both wna and ena and are constrained at larger magnitudes by the ba08 magnitude and distance scaling

seismic hazard map of southeast missouri and likely magnitude of the february 1812 new madrid earthquake abstract the new madrid seismic zone lies beneath the upper mississippi embayment straddling the border between southeastern missouri and northwestern tennessee in late 1811 and early 1812 it produced five earthquakes of magnitudes 6 5 violently shaking the central and eastern united states ceus its magnitude and recurrence are of concern to today s central united states regions by considering the effects of local geology deterministic scenario maps m w 7 3 and 7 7 were produced for ground motions intended to simulate the 7 february 1812 event nm3 which was the largest felt these maps include spatial estimates of peak ground acceleration and of 0 2 s and 1 0 s spectral acceleration sa compared with the isoseismic map of modified mercalli intensities mmis in southeast missouri the mmis converted from 0 2 s sa suggest that m w 7 7 is a plausible scenario for nm3 to better constrain its magnitude other ceus sites shaken during nm3 were also examined local site conditions were studied and evaluated before calculating the threshold magnitude for the reported mmis these results indicate that the magnitude of nm3 was at least m w 7 6 which validates our estimated size of m w 7 7 for southeastern missouri

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

receiver function and gravity constraints on crustal structure and vertical movements of the upper mississippi embayment and ozark uplift the upper mississippi embayment ume where the seismically active new madrid seismic zone resides experienced two phases of subsidence commencing in the late precambrian and cretaceous respectively to provide new constraints on models proposed for the mechanisms responsible for the subsidence we computed and stacked p to s receiver functions recorded by 49 usarray and other seismic stations located in the ume and the adjacent ozark uplift and modeled bouguer gravity anomaly data the inferred thickness density and vp vs of the upper and lower crustal layers suggest that the ume is characterized by a mafic and high density upper crustal layer of 30 km thickness which is underlain by a higher density lower crustal layer of up to 15 km those measurements in the background of previously published geological observations on the subsidence and uplift history of the ume are in agreement with the model that the cretaceous subsidence which was suggested to be preceded by an approximately 2 km uplift was the consequence of the passage of a previously proposed thermal plume the thermo elastic effects of the plume would have induced wide spread intrusion of mafic mantle material into the weak ume crust fractured by precambrian rifting and increased its density resulting in renewed subsidence after the thermal source was removed in contrast the ozark uplift has crustal density thickness and vp vs measurements that are comparable to those observed on cratonic areas suggesting an overall normal crust without significant modification by the proposed plume probably owing to the relatively strong and thick lithosphere

rift structure of the northern mississippi embayment from the analysis of gravity and magnetic data gravity and magnetic data have been simultaneously inverted to derive a crustal model of the northern mississippi embayment which is compatible with geologic and seismic refraction data the results indicate that this region is a site of a late precambrian early paleozoic rift system an anomalously dense layer is present at the base of the crust and thickens beneath a broad northeast trending graben that formed during the initial phases of rifting the thickest part of anomalous crust occurs beneath the region of greatest seismic activity which lies within the geographic limits of the graben it is suggested from this correlation that strain accumulates within the anomalous crust layer which acts as an inhomogeneity in a relatively homogeneous lithosphere based on the results of this study and previous geophysical studies the complex tectonic evolution of the upper mississippi embayment since late precambrian time is rift formation possibly along a pre existing shear zone graben development in cambrian time reactivations in permian and cretaceous time and subsequent formation of the present mississippi embayment and fault zones with large influences from rift structures

assessing uncertainties in high resolution multifrequency receiver function inversion a comparison with borehole data we use teleseismic p to s converted waves from a permanent station to estimate the uncertainties in a 1d elastic model of the shallow crust 0 7 km depth obtained from the inversion of receiver function rf data our earth model consists of layers with constant s wave velocity vs and p to s wave velocity ratio vp vs we apply a bayesian formulation and transdimensional monte carlo sampling to compute posterior uncertainties of the earth model the model uncertainties rely on a realistic representation of the data uncertainties and we estimate directly from the stacking of the teleseismic data a full error covariance matrix to explore the effect of the number of teleseismic events and of the rf frequency 9 content we compare the results of inverting a single rf computed for a cut off filter frequency of 4 hz to the joint inversion of four rfs computed from independent ensembles in a larger pool of events for cut off frequencies of 0 5 1 2 and 4 hz the inversion results are compared to the li

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

determination of shallow shear wave attenuation in the mississippi embayment using vertical seismic profiling data abstract we used vertical seismic profiling vsp data collected in four shallow boreholes about 40 to 60 m deep to study the shear wave attenuation in the mississippi embayment in southwestern tennessee the source was an air powered hammer that produces repeatable sh waves that were recorded by monitor geophones deployed on the surface very close to the source the spectral ratio method was used to estimate the shear wave quality factor q s the method assumes that the amplitudes of the seismic waves decay exponentially in the frequency domain the spectral ratio was computed using a vsp trace at a certain depth and the corresponding monitor trace using the source monitor trace as reference eliminates possible artifacts that may be introduced by changes in the source ground coupling the slope of a least square line fitted to the logarithm of the spectral ratio versus frequency gives the attenuation coefficient z for that depth then a straight line is fitted to z as a function of z and the slope of this line is used to estimate an average value of q s for the four sites shelby farms covington brownsville and jackson the q s values are 25 3 2 6 18 6 3 4 18 4 7 6 and 16 4 2 6 respectively to assess the reliability of these results synthetic vsp data were generated from the first cycles of the monitor traces recorded in the four sites and these q s values except for brownsville good matches with correlation coefficients equal to 96 99 were obtained between the synthetic vsps and the actual vsps indicating that the q s values we obtained are reliable in addition these values are also consistent with recent results obtained by others using seismic data generated by small earthquakes recorded by the japanese strong motion network kiban kyoshin kik net

in situ measurement of seismic shear wave absorption in the san francisco holocene bay mud by the pulse broadening method by the pulse broadening method seismic absorption of san francisco holocene bay mud has been determined with the use of an impulsive shear wave source at the surface two receivers embedded in clay holocene bay mud and digital seismic recording the seismic anelastic quality factor is determined from 20 measurements to be 16 0 with a random error of 0 9 three sources of systematic error are examined the fractional systematic error on the anelastic quality factor is estimated to be 11 details of experimental arrangement and error analysis are given

source and site response study of the 2008 mount carmel illinois earthquake abstract two separate inversions are performed using the ground motion data from the 2008 mount carmel illinois earthquake one uses aftershocks as empirical green s functions to determine a finite fault slip distribution the second uses mainshock ground motion spectra to calculate source path and site response parameters the slip inversion reveals a prominent asperity at the hypocenter with an area of approximately 6 km 2 moment of m w 5 20 and stress drop of about 100 bars considering all major and minor slip the total moment is m w 5 45 the rupture velocity is not resolvable due to the small source area after fixing the geometric spreading the source path and site parameter inversion yields a similar moment of m w 5 26 and a corner frequency of 0 89 hz which also give a stress drop of approximately 100 bars our combined geometric and anelastic attenuation function q f r b 1137 f 0 12 r 0 94 fits the regional spectral amplitudes where the data is more plentiful as well as previously derived attenuation relationships site response spectra show prominent resonant frequencies that correlate with the thickness of mississippi river sediments and mississippi embayment deposits in addition higher frequency resonance peaks are observed that most likely represent higher mode resonances and resonances from shallower structure

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

major proterozoic basement features of the eastern midcontinent of north america revealed by recent cocorp profiling cocorp profiling in the eastern midcontinent of north america has 1 traced an extensive sequence of precambrian layered rocks beneath southern illinois indiana and western ohio 2 detected a broad zone of east dipping basement reflectors associated with the grenville front beneath western ohio and 3 discovered a wide region of west dipping reflectors penetrating most of the crust beneath eastern ohio the precambrian layered assemblage may be as much as 11 km thick beneath southern illinois extends at least 170 km in an east west direction and contains several strong reflectors that have a lateral continuity of 80 km or more industry seismic data indicate that the layering is extensive in a north south direction as well possible explanations for the layering include the silicic igneous rocks of the ca 1 48 ga eastern granite rhyolite province which are penetrated by basement drill holes throughout the region perhaps intermixed or underlain by mafic igneous or sedimentary rocks the 40 50 km wide zone of strong east dipping 25 30 reflectors beneath west central ohio corresponds to the position of the grenville front as determined from potential field and drill hole data these dipping reflectors in the upper and middle crust are interpreted to result from ductile deformation zones mylonites like those exposed at the grenville front in canada and imaged on the glimpce seismic reflection lines in lake huron both the cocorp and glimpce lines show a remarkably similar reflection geometry despite the more than 500 km separating the two profiles easternmost ohio appears to be underlain by pronounced west dipping 40 reflectors in the middle and lower crust which are also interpreted as marking a region of pervasive ductile deformation 80 km or more in width analogy with similar reflection packages elsewhere suggests that these reflections may mark a major collision zone the west dipping reflectors may be correlative with similar reflectors imaged on another cocorp survey in northern alabama the correlations suggested by these new results though tentative imply that the eastern midcontinent is composed of a relatively simple assemblage of crustal blocks

crust and upper mantle structure of the new madrid seismic zone insight into intraplate earthquakes we determine a 3 d p wave velocity model of the crust and upper mantle down to 400 km depth to investigate structural heterogeneity and its influences on the generation of intraplate earthquakes in the new madrid seismic zone we used 4871 high quality arrival times from 187 local earthquakes and 30 846 precise travel time residuals from 1041 teleseismic events recorded by the earthscope usarray transportable array our results show that beneath the reelfoot rift a significant low velocity low v zone exists in the upper mantle down to 200 km depth with a large volume of 200 x 200 x 150 km 3 the origin of the low v zone may be related to the passage of the bermuda hotspot and the stalled ancient farallon slab materials foundering in the mantle transition zone this low v zone may have relatively low shear strength and act as a viscously weak zone embedded in the lithosphere being apt to concentrate tectonic stress and transfer stress to the seismogenic faults in the upper crust leading to the large intraplate earthquakes in the new madrid seismic zone c 2014 elsevier b v all rights reserved

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

regional variations in near surface shear wave velocity in the greater memphis area abstract site specific and regional analyses were conducted for an area that includes southwestern tennessee eastern arkansas and northwestern mississippi to establish characteristic shear wave velocity vs profiles based on measured profiles compiled from several researchers site specific studies were conducted at two locations near memphis tennessee to determine the uncertainty and randomness in measuring vs due to test related factors and local variability the result of this analysis was subsequently used as a criterion for establishing the range of variability for the characteristic vs profiles measured vs profiles were aggregated based on the age and type of geologic deposits in the memphis area to obtain characteristic profiles holocene alluvial deposits were found to have a fairly uniform shear wave velocity profile in the mississippi river floodplain pleistocene deposits characterized by a surficial layer of loess in the terrace regions of mississippi and tennessee were found to be more variable the average shear wave velocity in the upper 30 m was calculated for each measured profile based on the recommendations of the 1997 national earthquake hazards reduction program nehrp provisions to assess the susceptibility of a deposit to ground motion amplification the lowest and highest average near surface shear wave velocities were identified in the mississippi river alluvium and the pleistocene deposits respectively based on the nehrp site classes all deposits may be classified as d stiff soil however due to the thickness of soft soil deposits in the alluvial plain these deposits may be classified as e more than 3 m of soft clay based on the site class description rather than the shear wave velocity therefore a re evaluation of the nehrp site classes is proposed for the central us to more accurately represent the actual site conditions

a three dimensional simulation of seismic waves in the santa clara valley california from a loma prieta aftershock abstract the finite difference method is used to propagate elastic waves through a 3 d model of the santa clara valley an alluvium filled basin that underlies the city of san jose california the model was based on depth to bedrock information from water wells in the area the simulation corresponded to a region 30 east west by 22 north south by 6 depth km and contained about 4 million grid points synthetic seismograms from the simulation are accurate at frequencies up to 1 hz motions from a magnitude 4 4 aftershock of the loma prieta earthquake were modeled snapshots of ground motion and synthetic seismograms from the simulation are presented the simulation illustrates s to surface wave conversion at the edges of the basin and the large amplitude and long duration of ground motion in the basin compared to the surrounding rock love waves produced at the edge of the basin are the largest arrivals in the transverse synthetics because of the slow group velocity of the love waves sites near the center of the basin have longer durations of significant motions than basin sites near the valley edges sites near the center of the basin also show larger peak amplitudes on the transverse component array analysis of the synthetic seismograms indicates that love waves tend to propagate parallel to the eastern and western edges of the valley rayleigh waves are produced along the southern margin of the basin from incident s waves large radial motions occur where a rayleigh wave impinges on the northeast margin of the valley some rayleigh waves travel westward across the basin after being scattered from the eastern edge of the valley synthetic seismograms from the simulation have similar peak amplitudes as seismograms recorded by the sunnyvale dense array for this aftershock although the duration of the tranverse component is not matched by the synthetic seismogram using this basin model the simulation indicates that the love waves observed on the actual seismograms were produced by conversion of incident s waves at the southern margin of the santa clara valley 2 d simulations show how the s to love wave conversion is affected by the angle of incidence of the s wave and the sharpness of the velocity transition between the alluvium and bedrock as more accurate basin models are developed 3 d simulations should become valuable for predicting ground motions in sedimentary basins for future large earthquakes

upper mississippi embayment shallow seismic velocities measured in situ abstract vertical seismic compressional and shear wave p and s wave profiles were collected from three shallow boreholes in sediment of the upper mississippi embayment the site of the 60 m hole at shelby forest tennessee is on bluffs forming the eastern edge of the mississippi alluvial plain the bluffs are composed of pleistocene loess pliocene pleistocene alluvial clay and sand deposits and tertiary deltaic marine sediment the 36 m hole at marked tree arkansas and the 27 m hole at risco missouri are in holocene mississippi river floodplain sand silt and gravel deposits at each site impulsive p and s waves were generated by man made sources at the surface while a three component geophone was locked downhole at 0 91 m intervals consistent with their very similar geology the two floodplain locations have nearly identical s wave velocity vs profiles the lowest vs values are about 130 m s 1 and the highest values are about 300 m s 1 at these sites the shear wave velocity profile at shelby forest is very similar within the pleistocene loess 12 m thick in deeper older material vs exceeds 400 m s 1 at marked tree and at risco the compressional wave velocity vp values above the water table are as low as about 230 m s 1 and rise to about 1 9 km s 1 below the water table at shelby forest vp values in the unsaturated loess are as low as 302 m s 1 vp values below the water table are about 1 8 km s 1 for the two floodplain sites the vp vs ratio increases rapidly across the water table depth for the shelby forest site the largest increase in the vp vs ratio occurs at 20 m depth the boundary between the pliocene pleistocene clay and sand deposits and the eocene shallow marine clay and silt deposits until recently seismic velocity data for the embayment basin came from eartquake studies crustal scale seismic refraction and reflection profiles sonic logs and from analysis of dispersed earthquake surface waves since 1991 seismic data for shallow sediment obtained from reflection refraction crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin the present borehole data however are measured from sites representative of large areas in the mississippi embayment therefore they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking

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

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

three dimensional p wave velocity structure in the new madrid seismic zone a three dimensional p wave velocity model for the new madrid seismic zone nmsz has been developed using a nonlinear travel time tomography method the inversion involved 709 earthquakes recorded by digital three component portable array for numerical data acquisition stations deployed in the nmsz over the time period 1989 through 1992 analysis of ray coverage and inversion of a synthetic data set showed that the model has high resolution to a depth of 11 km low velocity anomalies correlate with the prominent northwest and northeast trending arms of seismicity lowest velocity anomalies 8 occur at the intersection of these arms and are associated with shallow seismicity and a high swarm rate these low velocity regions are interpreted to be the result of increased fluid pressure associated with structurally disrupted rocks beneath the blytheville pascola arch complex small regions of high velocity limited to the upper few km of the crust correlate with gravity and magnetic anomalies and are interpreted to be igneous intrusions high velocity anomalies also parallel the edges of the reelfoot rift margin and probably are associated with crystalline precambrian rocks that form the margin of the reelfoot rift graben most earthquakes are associated with low velocity regions and avoid regions of high velocity

velocity structure of the northern mississippi embayment sediments part ii inversion of teleseismic p wave transfer functions abstract detailed shear and compressional gradient velocity structure for the unconsolidated sediments of the mississippi embayment me have been obtained through simultaneous inversion of radial and vertical teleseismic transfer functions for 60 broadband stations inside the me transfer functions were calculated by deconvolving a vertical array beam from the radial and vertical displacement at each station inside the embayment the vertical array beam was constructed by stacking all the vertical components of motions for stations on the bedrock and outside the embayment to reduce the effect of incoherent scattering improving estimates of the source time function and stabilizing the deconvolution a bounded variable least squares inversion technique was applied to invert for velocity nodes on the top and bottom of the sediment layer p wave velocity changes from 1 0 km s near the surface and increases with depth from 3 5 to 4 km s in deeper parts s wave velocity varies from 0 3 km s and increases to 1 6 km s in deeper sections to the south electronic supplement gradient velocity structure of the northern mississippi embayment sediments for 60 broadband stations

orogeny and stratigraphy numerical models of the paleozoic in the eastern interior of north america a computer model is used to estimate patterns of lithospheric deformation caused by obduction and removal of loads within orogenic belts regions of lithospheric downwarp become sedimentary depocenters and regions of lithospheric upwarp suffer erosion by following the deposition and erosion of sedimentary packages through a number of model time steps it is possible to calculate a synthetic stratigraphy for a given study area this model is applied to the post early ordovician stratigraphy of the eastern interior region of north america the loading that drives lithospheric deformation is associated with the development of the appalachian and ouachita orogens and the independent development of the michigan and illinois intracratonic basins model results are shown to be consistent with presently observed stratigraphy lithology and cumulative erosion and are then used to estimate the configuration of given sediment packages at discrete intervals following their deposition these estimates are presented in the form of isopach maps stratigraphic cross sections and time stratigraphic diagrams as a function of time over the last 470 ma by tracking the burial and erosion history of sedimentary units we are able to establish a cause and effect relationship between particular tectonic events and the extent of preservation of sedimentary units in particular we suggest that the pennsylvanian permian alleghanian orogeny produced major sediment cover over much of the study area

the origin of crowley s ridge northeastern arkansas erosional remnant or tectonic uplift the geomorphology of crowley s ridge apparent quaternary reactivation of the ridge bounding faults and orientation of the faults to the present stress field suggest that the faults bounding crowley s ridge and the western margin of the reelfoot rift may be seismogenic fifteen high resolution seismic reflection lines were acquired across and adjacent to the margins of crowley s ridge to test the hypothesis that corwley s ridge is fault bounded eleven of the reflection lines were 24 channel mini sosie data with 1 sec record length and four lines were 24 channel shotgun source data with 0 25 sec record length nine lines traversed the margins and adjacent areas of the northern segment of the ridge near jonesboro arkansas and the other six were located south of jonesboro on the southern segment the reflection data show that paleozoic through eocene wilcox sections have been uplifted beneath crowley s ridge from 60 to 30 m across ridge bounding faults however eocene or pliocene pleistocene near surface strata appear to be displaced a maximum of 7 5 m based on reflection and geomorphologic data we believe that reactivation of the bounding faults of crowley s ridge occurred concurrently with and strongly influenced wisconsin denudation of the mississippi valley

nehrp soil classifications for estimating site dependent seismic coefficients in the upper mississippi embayment abstract local soil conditions have a profound influence on the characteristics of ground shaking during an earthquake exceptionally deep soil deposits on the order of 100 1000 m deep are found in the upper mississippi embayment of the central united states shear waves sh from earthquakes in the new madrid seismic zone are expected to be strongly affected by the sharp impedance contrasts at the bedrock sediment interface attenuation of seismic waves in the soil column and the sh wave velocities of the more poorly consolidated near surface 50 m soils sh wave velocities of the near surface soils at nearly 400 sites in the upper mississippi embayment were determined using conventional seismic sh wave refraction and reflection techniques based on the average sh wave velocities of the upper 30 m of the soils sites in the mississippi river floodplain portion of the study area are predominantly classified as site class d 180 360 m s in accordance with the 1997 nehrp provisions sites away from the active floodplains in western kentucky and western tennessee the sh wave velocities of the upper 30 m of soils typically ranged from mid 200 to mid 300 m s several sites in western kentucky had averaged sh wave velocities greater than 360 m s thereby qualifying them as site class c 360 760 m s in accordance with the 1997 nehrp provisions one dimensional site effects including amplification and dynamic site period were calculated for a representative suite of sites across the upper mississippi embayment at latitude 38 5 although seismic attenuation is greater in the mississippi river floodplain i e thicker lower velocity material the site effects tend to be greater than in the uplands of western tennessee because of larger impedance contrasts within the near surface soils

sedimentary basins investigation using teleseismic p wave time delays abstract passive seismic methods have been proven successful in recent years at retrieving information about the large scale structure of a sedimentary basin these methods are based on ambient noise recordings and local and distant teleseismic earthquake data in particular it has been previously observed that the arrival time of teleseismic p waves recorded inside a sedimentary basin shows time delays and polarization that both strongly depend on the basin properties and structure in this paper we present a new methodology for determining seismic p wave velocity in a sedimentary basin based on the time delay of a teleseismic p wave travelling through the low velocity basin infill with respect to a teleseismic wave recorded outside the basin the new methodology is developed in a bayesian framework and thus it includes estimates of the uncertainties of the p wave velocities for this study we exploit synchronous recordings of teleseismic p wave arrivals at a dense linear array of broadband seismic stations using data from two teleseismic events coming from two different incoming angles the results obtained by the new proposed methodology are successfully compared to classical cross correlation measurements and are used to infer properties of a sedimentary basin such as the basin bounding fault s geometry and the average p wave velocity of the sedimentary basin fill

geochronology and mammalian biostratigraphy of middle and upper paleocene continental strata bighorn basin wyoming the bighorn basin of northwestern wyoming preserves one of the most complete records of middle paleocene to lower eocene continental biota the geochronology of this important interval depends partly on numerical calibration of the geomagnetic polarity time scale gpts but the middle and late paleocene parts of the gpts have been poorly constrained radioisotopically a new volcanic ash from the northern bighorn basin provides the first radioisotopic age for upper middle paleocene strata upper selandian and is an important calibration point for the base of polarity chron c26n and the selandian thanetian stage boundary in the gpts sanidine from the ash has a weighted mean age of 59 00 0 30 2 ma based on twenty three 40 ar 39 ar bulk laser fusion analyses the ash corroborates the revised age estimate for the base of chron c26n in the most recent geomagnetic polarity time scale gpts 04 and confirms that c26n is older than depicted in the 1995 gpts we place paleocene mammalian biozones in the bighorn basin into a refined geochronologic framework these biozones are the primary basis for biostratigraphic correlation of middle and upper paleocene continental deposits in north america new paleomagnetic data provide synchronous tie points for correlation among three stratigraphic sections in the northern bighorn basin and to the gpts paleomagnetic correlation study of new fossil material review of known faunas and refined stratigra phy enable us to reevaluate several biozones we define three new zones based on first occurrences of taxa the phenacolemur ti 4b probathyopsis ti 5a revised and copecion cf 3 revised zones the phenacolemur zone includes some faunas previously placed in the plesiadapis churchilli and plesiadapis fodinatus zones ti 4 and ti 5a respectively the probathyopsis zone replaces the p fodinatus zone and the copecion zone replaces the phenacodus ectocion acme zone cf 3 seven of the biozones considered here are subdivisions of the tiffanian land mammalage thetiffanianwasoriginallytypifiedbythemasonpocketfaunainsouthwest ern colorado but it is now much better known from faunas in the northern bighorn basin biostratigraphic evidence and new paleomagnetic data from the bighorn basin indicate that mason pocket is considerably older than was previously recognized and occurs in chron c26r rather than c25r the geochronologic framework presented here helps to constrain the temporal ranges of species that occur in the middle and late tiffanian and it allows the bighorn basin record to be better compared to other faunal floral and paleoclimate records both regionally and globally

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

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

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

regional wave propagation from mexican subduction zone earthquakes the attenuation functions for interplate and inslab events the seismic waves from subduction zone earthquakes are significantly affected by the presence of 3d variation in crust and upper mantle structure around the source area these heterogeneous structures also profoundly modify the character of seismic waves as they propagate from the source area to regional distances this is illustrated by studying shallow interplate earthquakes along the mexican subduction zone and deeper inslab normal faulting earthquakes in the subducted cocos plate beneath mexican mainland the strong motion recordings of these earthquakes are used to evaluate the character of wave propagation along the path between the source region and mexico city we compare the wavefield from two large earthquakes of different source type during the shallow h 17 km interplate 1995 guerrero earthquake m w 7 3 the lg phase is the most prominent feature at regional distances of about 150 to a few hundred kilometers from the source the presence of a lateral velocity gradient in the crust caused by the subduction of the cocos plate enhances the lg wave amplitude which is then amplified further in the mexican volcanic belt by amplification in the low velocity volcanic rocks both effects lead to very large ground motions along the path from the coast to the mexican inland in the frequency band from 0 2 to 4 hz however for the deeper h 40 km inslab normal faulting 1999 oaxaca earthquake m w 7 5 the amplitude of the lg phase is too small to produce the abnormal wave propagation and the direct s wave and its multiple sms reflections between the free surface and moho show a simple attenuation with increasing distance we compare these observations with numerical simulations of seismic wave propagation using the fourier spectral method the results provide a key to the understanding of seismic wave field generated by shallow interplate and deeper inslab earthquakes in a realistic 3d heterogeneous structure

array observations of microseismic noise and the nature of h v in the mississippi embayment abstract ambient ground motion data were collected using phased seismic arrays in fall 2002 and spring 2007 within the mississippi embayment and at a single station external to the embayment these data allowed us to determine the wave field composition of ambient noise for understanding wave propagation mechanisms giving rise to spectral peaks using nakamura s h v technique ambient ground motions in the frequency band of 0 1 0 33 hz 10 3 sec period were dominated by spatially localized rayleigh and love wave microseisms generated by high ocean waves along the north american seaboard in the time periods of analysis seismic waves important in forming the h v peak near 4 sec period are composed of relatively high phase velocity rayleigh and love waves that convert to propagating homogeneous shear waves in the thick unconsolidated sediments of the embayment the h v resonant period is controlled by both constructive and destructive interference of these shear waves a simple relationship for the h v peak is given using a propagator matrix formulation that predicts the resonance frequency of a layered medium for surface wave motion at the base of the system the amplitude of the observed h v peak however does not give an accurate estimate of shear wave amplification because it depends on the slowness of the incident wave the inconsistency in estimated average shear wave velocities using the h v method and differential travel times of local earthquake sp phases in the mississippi embayment may be explained by misidentification of sp wave conversion points from deeper interfaces

on the use of high resolution topographic data as a proxy for seismic site conditions vs30 an alternative method has recently been proposed for evaluating global seismic site conditions or the average shear velocity to 30 m depth v s 30 from the shuttle radar topography mission srtm 30 arcsec digital elevation models dems the basic premise of the method is that the topographic slope can be used as a reliable proxy for v s 30 in the absence of geologically and geotechnically based site condition maps through correlations between v s 30 measurements and topographic gradient here we evaluate the use of higher resolution 3 and 9 arcsec dems to examine whether we are able to resolve v s 30 in more detail than can be achieved using the lower resolution srtm data high quality dems at resolutions greater than 30 arcsec are not uniformly available at the global scale however in many regions where such data exist they may be employed to resolve finer scale variations in topographic gradient and consequently v s 30 we use the u s geological survey earth resources observation and science eros data center s national elevation dataset ned to investigate the use of high resolution dems for estimating v s 30 in several regions across the united states including the san francisco bay area in california los angeles california and st louis missouri we compare these results with an example from taipei taiwan that uses 9 arcsec srtm data which are globally available the use of higher resolution ned data recovers finer scale variations in topographic gradient which better correlate to geological and geomorphic features in particular at the transition between hills and basins warranting their use over 30 arcsec srtm data where available however statistical analyses indicate little to no improvement over lower resolution topography when compared to v s 30 measurements suggesting that some topographic smoothing may provide more stable v s 30 estimates furthermore we find that elevation variability in canopy based srtm measurements at resolutions greater than 30 arcsec are too large to resolve reliable slopes particularly in low gradient sedimentary basins

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

velocity structure of the northern mississippi embayment sediments part i teleseismic p wave spectral ratios analysis abstract the mississippi embayment overlies the new madrid seismic zone in the central united states and consists of a thick succession of unconsolidated sediments that covers the paleozoic basement rock the high velocity contrast at the basement sediment interface and the near vertical ray paths of teleseismic p waves generate very large p to s conversions on the radial component and large p reverberations on the vertical component this characteristic of p wave propagation is used to study p and s wave resonance in the sedimentary layer horizontal to vertical h v and vertical to horizontal v h power spectral ratios are calculated for a time window around the teleseismic p wave arrivals at broadband stations of the usarray transportable array northern embayment lithosphere experiment and the new madrid cooperative seismic network in the embayment using a map of sediment thickness we developed models for average p and s wave velocity versus sediment thickness the resulting shear wave velocity model matches very well with the model obtained from an h v ambient noise study in the region the shear wave velocity model shows low velocity near the edges of the embayment with average velocities increasing with increasing sediment thickness consistent with increased sediment compaction fundamental resonance frequency for s waves ranges from 0 2 to 0 4 hz for the embayment sediments electronic supplement two figures showing the synthetic test results and a table that includes peak resonance frequency and average v p and v s

faulting parameters of earthquakes in the new madrid missouri region abstract the advent of high resolution digital seismic recording and advances in computer technology enable the combination of traditional regional seismic network observations with direct seismogram modeling to improve estimates of small earthquake faulting geometry depth and size we illustrate a combined modeling approach using observations from three earthquakes that occurred within the environs of the new madrid seismic zone two missouri earthquakes from september 26 1990 and may 4 1991 and the southern illinois earthquake of february 5 1994 we also re examine the faulting geometry for two events from the 1960s that are inconsistent with the current estimate of the regional stress field based on direct modeling of the long period seismograms associated with these events we revise earlier estimates of the earthquake parameters for the march 3 1963 and july 21 1967 missouri earthquakes comparing the new and revised results with existing earthquake mechanisms in the region we find that tension axes are generally aligned in a n s to nw se direction while the compression axes trend in a ne to e direction an interesting exception to this pattern are the march 3 1963 and two nearby earthquakes that lie within a well defined 30 km long left step in seismicity near new madrid

broadband microtremor observation of basin resonance in the mississippi embayment central us we report systematic variations in the fundamental period of seismic site resonance within the mississippi embayment the resonance periods are revealed by peaks in horizontal to vertical h v spectral ratios of microtremor measurements and increase with the depth to the sediment basement interface the sediment depth varies slowly enough spatially that at any site it can be modeled as a one dimensional problem revealing structural details of the sedimentary column the strong impedance contrast and gentle dip of the base of the embayment sediments may trap seismic energy within the soft sediments increasing durations and amplitudes of strong ground motions broadband recordings of microtremor within the mississippi embayment provide a simple method to study the seismic response of the basin

mapping p wave azimuthal anisotropy of the new madrid seismic zone abstract we determine a detailed tomographic model of 3 d p wave azimuthal anisotropy in the crust and upper mantle beneath the new madrid seismic zone nmsz using a large number of high quality arrival time data of 877 local earthquakes and relative travel time data of 1511 teleseismic events recorded at 62 usarray stations the tomographic inversion is conducted by using a limited memory broyden fletcher goldfarb shanno algorithm for bound constrained optimization because damping regularization is not required in this inversion scheme the obtained results are less affected by human subjectivity a prominent low velocity zone with ne sw fast velocity directions of azimuthal anisotropy down to 160 km depth beneath the nmsz is imaged which may reflect upwelling mantle materials probably triggered by passage of the bermuda hotspot from the southwest of the mississippi embayment our results also reveal a subhorizontal high velocity anomaly around the moho discontinuity with a width of 150 200 km confirming the existence and defining the geometry of a lens shaped high density rift pillow near the moho which may result from the mantle upwelling nw se fast velocity directions of azimuthal anisotropy appear in the lower crust beneath the mississippi embayment this result may reflect recent weakening of a detachment fault above the rift pillow which drives recurrently sinking of the rift pillow and as a consequence causing large repeating intraplate earthquakes in the nmsz

fault plane determination of the 18 april 2008 mount carmel illinois earthquake by detecting and relocating aftershocks we developed a sliding window cross correlation scc detection technique and applied the technique to continuous waveforms recorded by the cooperative new madrid seismic network stations following the 18 april 2008 illinois earthquake the technique detected more than 120 aftershocks down to m l 1 0 in the 2 week time window following the mainshock which is three times more than the number of aftershocks reported by the seismic network most aftershocks happened within 24 hrs of the mainshock we then relocated all events by the double difference relocation algorithm accurate p and s wave differential arrival times between events were obtained by waveform cross correlation after relocation we used the l1 norm to fit all located events by a plane to determine the mainshock fault plane the best fit plane has a strike of 292 11 and dips 81 7 to the northeast this plane agrees well with the focal mechanism solutions of the mainshock and four largest aftershocks by combining the aftershock locations and focal mechanism solutions we conclude that the 18 april earthquake occurred on a nearly vertical left lateral strike slip fault orienting in the west northwest east southeast direction the fault coincides with the proposed left stepping divide accommodation zone in the la salle deformation belt and indicates reactivation of old deformation zone by contemporary stresses in the midcontinent

ground motion modeling of the 1906 san francisco earthquake part i validation using the 1989 loma prieta earthquake we compute ground motions for the beroza 1991 and wald et al 1991 source models of the 1989 magnitude 6 9 loma prieta earthquake using four different wave propagation codes and recently developed 3d geologic and seismic velocity models in preparation for modeling the 1906 san francisco earthquake we use this well recorded earthquake to characterize how well our ground motion simulations reproduce the observed shaking intensities and amplitude and durations of recorded motions throughout the san francisco bay area all of the simulations generate ground motions consistent with the large scale spatial variations in shaking associated with rupture directivity and the geologic structure we attribute the small variations among the synthetics to the minimum shear wave speed permitted in the simulations and how they accommodate topography our long period simulations on average under predict shaking intensities by about one half modified mercalli inten sity mmi units 25 35 in peak velocity while our broadband simulations on average under predict the shaking intensities by one fourth mmi units 16 in peak velocity discrepancies with observations arise due to errors in the source models and geologic structure the consistency in the synthetic waveforms across the wave propagation codes for a given source model suggests the uncertainty in the source parameters tends to exceed the uncertainty in the seismic velocity structure in agree ment with earlier studies we find that a source model with slip more evenly distributed northwest and southeast of the hypocenter would be preferable to both the beroza and wald source models although the new 3d seismic velocity model improves upon previous velocity models we identify two areas needing improvement nevertheless we find that the seismic velocity model and the wave propagation codes are suitable for modeling the 1906 earthquake and scenario events in the san francisco bay area online material modified mercalli intensities and velocity waveforms and a movie of simulated wave propagation