on the geologic structure at the epicenter of the 1886 charleston south carolina earthquake the study focuses on evidence of cenozoic faulting in the epicentral area of the 1886 charleston south carolina earthquake and its connection with mesozoic structure the seismic data consist of several reflection profiles collected near summerville south carolina in the period 1975 1983 reprocessing of the data reveals an extensive early mesozoic extensional basin approximately 20 km in width between summerville and charleston the basin is delineated by the geometry of reflections that image early mesozoic volcanic and sedimentary rocks and by positive magnetic and gravity anomalies cenozoic compressional reactivation of mesozoic extensional faults is imaged in the interior of the basin the northwestern boundary of the basin is marked by a sharp gradient in the magnetic field folded cretaceous and tertiary atlantic coastal plain sediments in association with diffractions and truncated reflections from the early mesozoic section at four locations along this magnetic gradient indicate that the northwestern basin boundary is faulted instrumentally located earthquakes are clustered at the location of the faults imaged in the interior of the basin and in proximity to the northwestern basin margin modeling of magnetic and gravity data indicates that the upper crust beneath the seismically imaged structural basin is composed largely of mafic rocks to a depth of at least 4 km we propose that the charleston earthquake occurred due to compressional reactivation of a mesozoic fault in a localized zone of intense early mesozoic continental rifting

lisbon 1755 a case of triggered onshore rupture it has been widely recognized both in classical and in modern studies that the lisbon earthquake of 1755 was a multiple event composed of three shocks separated by a few minutes see e g reid 1914 attempts to constrain the location of the source have led to a diversity of proposals reflecting apparent contradictions in the data the tsunami and damage along the south and southwest iberian coast and in morocco favor an offshore source whereas the presence of an additional zone of strong shaking in the lower tagus valley ltv near lisbon favors a more northerly location by combining the contemporary accounts with intensity data from other earthquakes we favor a compound source with a large distance between the faults we propose that although the mainshock was offshore the resulting stress changes induced the rupture of the ltv fault at a distance on the order of 350 km but subject to large uncertainty in the offshore location a few minutes after the mainshock we favor this model rather than site effects causing high intensities in the lisbon area because the highest intensities show a negative correlation to soft soil several other phenomena described in the eyewitness accounts can also be explained by the local rupture now proposed such as a tsunamilike wave in the tagus river ground deformation affecting the course of the tagus river and the spatial pattern of damaging aftershocks recognition of this missing episode of rupture on the ltv fault significantly changes the hazard estimate for the lisbon area

implications of felt area magnitude relations for earthquake scaling and the average frequency of perceptible ground motion abstract observed relations between felt area and moment magnitude m for stable continental regions scr and california earthquakes can be explained by a simple model with geometrical spreading attenuation q 1 and earthquake stress drops that remain constant from m 4 to 8 differences in the slopes of the observed felt area m relations between scr and california earthquakes are consistent with differences in q between these tectonic settings fitting the felt area m data to the model yields an estimate of f q where f is the average frequency of minimum perceptible ground motion using fits to the data and instrumentally derived values of q i find that f is between about 2 and 4 hz i present an estimate of the spectral acceleration level associated with the lower limit of perceptibility

a threshold based earthquake early warning system for offshore events in southern iberia the south of the iberian peninsula is situated at the convergence of the eurasian and african plates this region experiences large earthquakes with long separation in time the best known of which was the great 1755 lisbon earthquake which occurred sw of san vicente cape sw iberian peninsula the high risk of damaging earthquakes has recently led carranzaet al geophys res lett 40 2013 to investigate the feasibility of an eews in this region analysis of the geometry for the iberian seismic networks and the san vicente cape area led the authors to conclude that a threshold based approach which would not require real time location of the earthquake might be the best option for an eews in sw iberia in this work we investigate this hypothesis and propose a new eew approach that extends standard p wave threshold based single station analysis to the whole network the proposed method enables real time estimation of the potential damage at stations that are triggered by p waves and those which are not triggered with the advantage of greater lead times for release of alerts results of tests made with synthetic data mimicking the scenario of the great 1755 lisbon earthquake and those conducted by applying the new approach to available recordings indicate that an eew estimation of the potential damage associated with an event in the san vicente cape area can be obtained for a very large part of the iberian peninsula

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

synthetic pn and sn phases and the frequency dependence of q of oceanic lithosphere the oceanic lithosphere is an extremely efficient waveguide for high frequency seismic energy in particular the propagation of the regional to teleseismic oceanic pn and sn phases is largely controlled by properties of the oceanic plates the shallow velocity gradient in the sub moho lithosphere results in a nearly linear travel time curve for these oceanic phases and an onset velocity near the material velocity of the uppermost mantle the confinement of pn sn to the lithosphere imposes a constraint on the maximum range that a normally refracted wave can be observed the rapid disappearance of sn and the discontinuous drop in pn sn group velocity beyond a critical distance dependent upon the local thickness of the lithosphere are interpreted as a shadowing effect of the low q asthenosphere wave number integration was used to compute complete synthetic seismograms for a model of oceanic lithosphere the results were compared to data collected during the 1983 ngendei seismic experiment in the southwest pacific the pn sn coda is successfully modeled as a sum of leaky organ pipe modes in the sediment layer and oceanic water column while scattering is present to some degree it is not required to explain the long duration and complicated nature of the pn sn wave trains the presence of extremely high frequencies in pn sn phases and the greater efficiency of sn than pn propagation are interpreted in terms of an absorption band rheology a shorter high frequency relaxation time for p waves than for s waves results in a rheology with the property that q q at low frequency while q q at high frequency consistent with the teleseismic pn sn observations the absorption band model is to viewed as only an approximation to the true frequency dependence of q in the oceanic lithosphere for which analytic expressions for the material dispersion have been developed

an empirical estimate of near source ground motion for a major mb 6 8 earthquake in the eastern united states abstract three empirical techniques are used to estimate ground motion amplitudes in the near source region of a major earthquake hypothesized to occur along the east coast of the united states these techniques include the estimation of strong motion parameters from the statistical analysis of selected strong motion records from empirical and theoretical attenuation relations and from modified mercalli intensity source parameters for the hypothesized earthquake were selected to be similar to those inferred for the 1886 charleston south carolina earthquake the epicentral region is characterized by a modified mercalli intensity of x from which magnitudes of m b 6 8 m s 7 2 and m 7 2 were estimated inferred fault mechanisms for the hypothesized event vary from strike slip on a vertical fault to reverse or reverse oblique slip on a fault dipping as shallow as 45 the median estimate of peak horizontal acceleration for a point located 15 km from the surface projection of fault rupture is 0 30 g independent of site geology corresponding estimates of peak horizontal velocity are 35 cm sec for soil and soft sedimentary rock sites and 18 cm sec for crystalline basement rock sites strong motion parameters for a point located 15 km from the epicenter corresponding to a point located directly above the rupture zone of the hypothesized earthquake are estimated to be approximately 80 per cent higher than these estimates or about 0 55 g for peak acceleration and about 63 and 33 cm sec for peak velocity on soil soft rock and crystalline rock respectively corresponding velocity acceleration ratios are 115 cm sec g for soil soft rock sites and 60 cm sec g for crystalline rock sites standard deviations associated with the natural logarithm of peak horizontal acceleration and velocity are estimated to be 0 5 and 0 7 respectively representing an 84th percentile estimate or equivalently an upper 68 per cent confidence limit that is approximately 65 per cent higher than the median for acceleration and 100 per cent higher than the median for velocity while these strong motion values are generally higher than those currently used in the seismic design of most structures in the eastern united states their impact on the seismic safety of specific sites in the region will depend on an assessment of the probability of occurrence of an earthquake of this size within the near source region of these sites

assessment of liquefaction hazards in charleston quadrangle south carolina abstract in this paper an improved method for evaluation of liquefaction hazard is presented the liquefaction potential index developed by iwasaki and his co workers is modified using the concept of probability the modified liquefaction potential index is then calibrated with field observation data which yields an empirical equation for the probability of liquefaction induced ground failure the method and procedure is then employed to study the ground shaking level of the 1886 charleston south carolina earthquake based on an analysis of liquefaction hazard in the charleston peninsula the results show that the ground shaking level of the 1886 event may be represented with moment magnitude mw 6 9 and peak ground surface acceleration amax 0 2 g finally the liquefaction hazard in the charleston quadrangle is evaluated and mapped using the ground motion that corresponds to the 475 year return period details of this assessment including limitation of the results are presented

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

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

magnitudes and locations of the 1811 1812 new madrid missouri and the 1886 charleston south carolina earthquakes we estimate locations and moment magnitudes m and their uncertainties for the three largest events in the 1811 1812 sequence near new madrid missouri and for the 1 september 1886 event near charleston south carolina the intensity magnitude m i our preferred estimate of m is 7 6 for the 16 december 1811 event that occurred in the new madrid seismic zone nmsz on the bootheel lineament or on the blytheville seismic zone m i is 7 5 for the 23 january 1812 event for a location on the new madrid north zone of the nmsz and 7 8 for the 7 february 1812 event that occurred on the reelfoot blind thrust of the nmsz our preferred locations for these events are located on those nmsz segments preferred by johnston and schweig 1996 our estimates of m are 0 1 0 4 m units less than those of johnston 1996b and 0 3 0 5 m units greater than those of hough et al 2000 m i is 6 9 for the 1 september 1886 event for a location at the summerville middleton place cluster of recent small earthquakes located about 30 km northwest of charleston

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

helium isotopes as a tool for detecting concealed active faults 1 a magnitude mj 7 3 crustal earthquake occurred in the western tottori area southwest japan on 6 october 2000 however there was no obvious prefaulting indication at surface of a fault corresponding to the western tottori earthquake in 2000 this study was undertaken to elucidate the geographic distribution of 3he 4he ratios around the seismic source region using helium isotope data obtained from groundwater samples from drinking water wells the maximum 3he 4he ratio observed was from the water well nearest to the epicenter of the main shock in addition there appears to be a clear trend of decreasing 3he 4he ratios with distance away from the main trace of the probable fault segments the observations provide significant evidence that the source fault of the earthquake in 2000 is associated with leakage of mantle volatiles through the crust to the earth s surface we suggest that helium isotopes can be regarded as a tool for investigating and or mapping concealed active faults with no surface expression

intraplate earthquakes and the state of stress in oceanic lithosphere abstract the sources of stress responsible for oceanic intraplate earthquakes and their usefulness for inferring the tectonic stress field are investigated through a synthesis of the source mechanisms of 58 of the largest such events determined by inversion of long period p and sh waveforms further constraints are provided by the global distribution of oceanic intraplate seismicity and a calculation of the seismic moment release per unit volume of seismogenic lithosphere as a function of lithosphere age although frequently associated with relict tectonic features large oceanic intraplate earthquakes are generally reliable indicators of the state of stress in the source region most oceanic intraplate seismicity occurs in young lithosphere

appropriate boundary conditions for modeling very long earthquakes and physical consequences we have studied two sets of models to find appropriate boundary conditions for the theoretical modeling of very long earthquakes i e those for which the length l is much larger than the width w of the rectangular aftershock area and the resulting physical consequences in the first set we study the conventional rectangular crack model for l w 2 and 4 i e the stress drop is confined to a rectangular region and there is no rupture outside this region w model in the second set of models which is suggested by geologic data we constrain the stress drop to a rectangular zone seismogenic layer but we do not have any constraint on the rupture above and below this layer the applied stress in this region above and below the seismogenic layer is taken to be exactly equal to the yield stress of the material so that no stress drop occurs when it yields this implies that the material on either side of the seismogenic layer is shearing aseismically just before the earthquake occurs and also implies that the material in these regions is purely plastic the major conclusion of our work is that the second set of models the rupture propagates dynamically for some distance into these nonbrittle zones above and below the seismogenic layer this result is supported by geological evidence and also by recent seismic evidence that moments of some large earthquakes increase with increasing wavelength at very long periods the slip in large parts of these zones is found to be nonnegligible the slip is still confined to a finite width which may be considered as an effective width but this width is larger than the width of the seismogenic brittle layer this effective width increases as the length of the region of stress drop increases and may be larger than this length for long faults thus for the second set of models the aftershock area would underestimate the actual rupture area the moment and the slip at the center for the second set of models are larger than for the first set for the same l w ratio of the stress drop region even if we assume that there is no radiated energy from the regions above and below the seismogenic zone for l w 2 the duration of slip at interior points on the fault for the two models are the same but for l w 4 the duration of slip at a given interior point is much larger for the second set of models however the particle velocity during this added time of slip for the second class of models is small and almost constant so that at least for l w up to 4 this difference may not be significant for strong ground motion near such a fault the rise times and slips at any interior point of the fault is mainly width controlled for the first set of models and mainly controlled by the length of the elastic region or the effective width for the latter set since longer faults are observed to have larger slips than shorter ones of the same width the first set of models would predict that stress drops increase with rupture length for the same fault width however this observation can be explained by the second set of models even for constant stress drops for the second set of models we find that a fault twice the length of another has much less than double the slip for the same average stress drop we suggest that both classes of models studied are realistic models of earthquake sources but for different cases

the 16 may 1909 northern great plains earthquake abstract the largest historical earthquake in the northern great plains occurred on 16 may 1909 our analysis of intensity assignments places the earthquake location 48 81 n 105 38 w close to the montana saskatchewan border with an intensity magnitude m i of 5 3 5 4 observations from two seismic observatories in europe give an average m s value of 5 3 the 1909 earthquake is near an alignment of epicenters of small earthquakes in montana and saskatchewan and on strike with the mapped hinsdale fault in montana thus the 1909 earthquake may have occurred on a 300 km long seismically active fault which could have seismic hazard implications for the region particularly for the hydraulically emplaced earth filled fort peck dam constructed in the 1930s on the missouri river in northeast montana

strong ground motions in north america from the bolivia earthquake of june 9 1994 mw 8 3 the bolivia earthquake was remarkable for being felt in north america as far as 8680 km from the epicenter this paper examines the characteristics of ground motions in north america from the perspective of strong motion seismology data on ground motions is mostly from high gain stations but we also have two strong motion accelerograms the largest accelerations and highest frequencies are associated with the p and pcp phases which also correlate with the felt reports in several instances felt locations are associated with a combination of favorable factors most are in a distance range where p wave amplitudes tend to be relatively high as observed in the empirical correction factors for body wave magnitude and in regions with relatively high values of q in the lithosphere in addition site effects structural amplification or both seem to contribute to the selective detection of the earthquake in the regions where some people noticed it motions were far below design spectra for earthquake resistant design and far below levels likely to be associated with damage

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

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

a comparison of earthquake damage areas as a function of magnitude across the united states this study investigates the relationship between earthquake magnitude and the size of damage areas in the eastern and western united states to quantify damage area as a function of moment magnitude m 149 mmi vi and vii areas for 109 earthquakes 88 in the western united states 21 in the eastern united states and canada were measured regression of isoseismal areas versus m indicated that areas in the east were larger than those in the west at both intensity levels by an average 5 in the m 4 5 to 7 5 range in terms of radii for circles of equivalent area these results indicate that damaging ground motion from shocks of the same magnitude extend 2 the epicentral distance in eastern north america compared to the west to determine source and site parameters consistent with the above results response spectral levels for eastern north america were stochastically simulated and compared with response spectral ordinates derived from recorded strong ground motion data in the western united states stress drop values of 200 bars combined with a surficial 2 km thick low velocity sedimentary layer over rock basement produced results that are compatible with the intensity observations i e similar response spectral levels in the east at approximately twice their epicentral distance in the western u s distance these results suggest that ground motion modeling in eastern north america may need to incorporate source and site parameters different from those presently in general use the results are also of importance to eastern u s hazard assessments as they require allowance for the larger damage areas in preparedness and mitigation programs

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

tectonic deformation in the new madrid seismic zone inferences from map view and cross sectional boundary element models the lack of instrumental recordings and obvious fault scarps associated with the 1811 1812 new madrid earthquakes necessitates examination of more subtle indicators of the geometry and type of faulting associated with these events morphologic and geologic features and the distribution of modern seismicity are used to infer the slip distribution and type of faulting strike or dip slip number strike length and width of the major faults in the new madrid seismic zone nmsz this is accomplished through two dimensional boundary element modeling of the strain field arising from slip on hypothetical faults that is driven by either coseismic or uniform regional strains tectonic deformation is reflected in 1 the seismicity 2 the lake county uplift 3 reelfoot lake 4 the fractured rocks of the blytheville arch and 5 the st francis sunk lands many of these features can be qualitatively explained as resulting from tectonic deformation due to slip on two left stepping right lateral strike slip faults that are coincident with the northeast trending zones of seismicity and the blytheville arch the morphology appears to be at least in part a consequence of major earthquakes that rupture these faults the locations of the 1811 1812 and largest post 1812 earthquakes and the models are consistent with a process in which the 1811 1812 earthquakes relieved accumulated regional shear strain causing the greatest post 1812 shear strains to exist at the ends of the fault zone modeling results also suggest that the numerous small earthquakes in the nmsz are not aftershocks of the 1811 1812 earthquakes but instead represent continuous localized adjustments to a uniform regional strain field the bootheel lineament does not appear to be significant in shaping the morphology geologic structure and pattern of seismicity in the nmsz the absence of fault scarps and coherence of shallow reflectors overlying the blytheville arch suggests that the major nmsz faults may not have ruptured to the surface during the 1811 1812 earthquakes the inferred lengths of the 1811 1812 earthquake ruptures also suggest that their sizes may have been overestimated model predicted subsidence within the st francis sunk lands indicates that tectonic deformation also may have influenced alluvial processes in the nmsz

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

estimating locations and magnitudes of earthquakes in eastern north america from modified mercalli intensities we use 28 calibration events 3 7 m 7 3 from texas to the grand banks newfoundland to develop a modified mercalli intensity mmi model and associated site corrections for estimating source parameters of historical earthquakes in eastern north america the model batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm mmi 1 41 1 68 times mathbf m 0 00345 times delta 2 08 mathrm log delta end document where is the distance in kilometers from the epicenter and m is moment magnitude provides unbiased estimates of m and its uncertainty and if site corrections are used of source location the model can be used for the analysis of historical earthquakes with only a few mmi assignments we use this model mmi site corrections and bakun and wentworth s 1997 technique to estimate m and the epicenter for three important historical earthquakes the intensity magnitude m i is 6 1 for the 18 november 1755 earthquake near cape ann massachusetts 6 0 for the 5 january 1843 earthquake near marked tree arkansas and 6 0 for the 31 october 1895 earthquake the 1895 event probably occurred in southern illinois about 100 km north of the site of significant ground failure effects near charleston missouri manuscript received 14 march 2002

imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres application to the azores western mediterranean region abstract the matching between linear trends of hypocentres and fault planes indicated by focal mechanisms fms is frequently used to infer the location and geometry of active faults this practice works well in regions of fast lithospheric deformation where earthquake patterns are clear and major structures accommodate the bulk of deformation but typically fails in regions of slow and distributed deformation we present a new joint fm and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and fms even in regions of distributed deformation we apply the method to the azores western mediterranean region with particular emphasis on western iberia the analysis relies on a compilation of hypocentres and fms taken from regional and global earthquake catalogues academic theses and technical reports complemented by new fms for western iberia the joint clustering algorithm images both well known and new seismo tectonic features the azores triple junction is characterised by fms with vertical pressure p axes in good agreement with the divergent setting and the iberian domain is characterised by nw se oriented p axes indicating a response of the lithosphere to the ongoing oblique convergence between nubia and eurasia several earthquakes remain unclustered in the western mediterranean domain which may indicate a response to local stresses the major regions of consistent faulting that we identify are the mid atlantic ridge the terceira rift the trans alboran shear zone and the north coast of algeria in addition other smaller earthquake clusters present a good match between epicentre lineations and fm fault planes these clusters may signal single active faults or wide zones of distributed but consistent faulting mainland portugal is dominated by strike slip earthquakes with fault planes coincident with the predominant nne ssw and wnw ese oriented earthquake lineations clusters offshore sw iberia are predominantly strike slip or reverse confirming previous suggestions of slip partitioning

evidence of possible tectonic upwarping along the south carolina coastal plain from an examination of river morphology and elevation data although the fault s responsible for the 1886 charleston south carolina earthquake have not yet been identified primarily because of the lack of surface rupture evaluation of landsat imagery aerial photography and topographic maps have revealed an 200 km long 15 km wide north northeast trending zone composed of subtle topographic highs and morphologic changes in rivers that may be associated with tectonic activity river anomalies observed within this zone include river bends that are convex toward the north northeast incised channels changes in river patterns and convex upward longitudinal profiles analyses of geologic and geophysical data further indicate that these surface features may be the result of ongoing tectonic uplift along a north northeast trending fault zone possibly associated with recent seismicity near charleston

common features of the excitation and propagation of strong ground motion for north american earthquakes the central matter of this investigation is the commonly held belief that eastern north america ena earthquakes are felt to much greater distances at all levels of intensity than their western u s wus counterparts of the same source strength by comparing the areas enclosed by modified mercalli intensities i to iii felt iv v vi and vii for ena and wus earthquakes at the same source strength we find that this proposition is mostly false at damaging levels of ground motion intensities vi to vii and greater for m 7 neither should such differences exist if strong ground motion is confined to r 150 km and arrives principally as body waves and if ena and wus earthquakes share the same average stress drop in fact observable differences in the areas enclosed by intensity vi a vi for ena and wus earthquakes at the same m point to slight but significant differences in stress drop the ena earthquakes having stress drops a factor of about 2 higher only for the largest earthquakes m 7 as the 1811 to 1812 new madrid and 1886 charleston earthquakes seem to be can strong ground motion propagate to much greater distances as low loss higher mode surface waves in ena relative to wus the strong dependence of high frequency strong ground motion on stress drop and its weak dependence on m admit the possibility that the 1811 to 1812 events and the 1886 charleston earthquakes are no larger than m 6 to 7 provided that their stress drops are higher than average by a factor of 2 or so

the 26 january 2001 m 7 6 bhuj india earthquake observed and predicted ground motions although local and regional instrumental recordings of the devastating 26 january 2001 bhuj earthquake are sparse the distribution of macroseismic effects can provide important constraints on the mainshock ground motions we compiled available news accounts describing damage and other effects and interpreted them to obtain modified mercalli intensities mmis at 200 locations throughout the indian subcontinent these values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method although preliminary the maps reveal several interesting features within the kachchh region the most heavily damaged villages are concentrated toward the western edge of the inferred fault consistent with western directivity significant sediment induced amplification is also suggested at a number of locations around the gulf of kachchh to the south of the epicenter away from the kachchh region intensities were clearly amplified significantly in areas that are along rivers within deltas or on coastal alluvium such as mudflats and salt pans in addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0 1000 km we then convert the predicted hard rock ground motion parameters to mmi by using a relationship derived from internet based intensity surveys that assigns mmi based on the average effects in a region the predicted mmis are typically lower by 1 3 units than those estimated from news accounts although they do predict near field ground motions of approximately 80 g and potentially damaging ground motions on hard rock sites to distances of approximately 300 km for the most part this discrepancy is consistent with the expected effect of sediment response but it could also reflect other factors such as unusually high building vulnerability in the bhuj region and a tendency for media accounts to focus on the most dramatic damage rather than the average effects the discrepancy may also be partly attributable to the inadequacy of the empirical relationship between mmi and peak ground acceleration pga when applied to india the mmi pga relationship was developed using data from california earthquakes which might have a systematically different stress drop and therefore a different frequency content than intraplate events when a relationship between response spectra and mmi is used we obtain larger predicted mmi values in better agreement with the observations

earthquakes and rock deformation in crustal fault zones the physical origin of earthquakes lies ultimately in the geological structure of fault zones and the deformation processes that occur therein in response to tectonic stress although the possibility now exists that the nucleation regions for large earthquakes at depths of 10 km may shortly become directly accessible by deep drilling our present knowledge of fault structure and the shallow earthquake source is derived largely from a variety of indirect sources these include seismological studies surface studies of fault zones and earthquake ruptures geodetic information on modes of fault slip geophysical constraints on fault zone structure and rheology and information garnered from materials science and experi mental rock deformation studies of fault zone structure and the rock products of faulting provide complementary information on deformation processes at depth in fault zones although descriptions of fault rocks are widespread in the geological literature e g spry 1969 higgins 1971 it is only in the past decade that they have begun to be interpreted in the context of the physical conditions and processes prevalent in seismically active fault zones at different crustal depths sibs on 1977 watts williams 1979 anderson et a11983 wise et ai 1984 such interpretations are still at an early stage but the deformation textures and structural associations of fault rocks have already been shown to have the potential to yield information on such diverse topics as shear stress levels power dissipation and seismic efficiency during earthquake faulting on fluid pressure levels and episodic fluid flow accompanying

ce anomalies in the textural components of upper cretaceous karst bauxites from the apulian carbonate platform southern italy the chemical and mineralogical composition of upper cretaceous apulian karst bauxites southern italy and their textural components i e ooids and matrix has been studied the bulk samples are composed of boehmite hematite anatase and kaolinite the samples collected along a vertical profile show a downward enrichment for the elements rb sr ba ni and cr a similar distribution is observed in deposits bauxitized in situ at the expense of matrix like material collected in the karst zone the ooids consist mainly of hematite with minor boehmite and anatase whereas in the matrix boehmite prevails on hematite kaolinite and anatase in the void fillings in the matrix there is a ca fluorocarbonate having a ce ce of 5 8 the ooids with the exception of ce are enriched in ree and show a higher la yb ch ratio relative to the matrix the matrix exhibits a large positive ce anomaly whereas the ooids have negative ce anomaly the ce fractionation between the textural components can be explained assuming 1 ce oxidation and cerianite precipitation in the uppermost part of the deposits 2 scavenging of ree from ce depleted percolating solutions by the iron oxide inducing both ree enrichment and ce negative anomalies in ooids 3 remobilization of cerium as fluoride complex as a consequence of more acidic conditions in the uppermost part of the deposit and precipitation of ce3 as fluorocarbonate mineral toward the carbonate bedrock barrier at alkaline ph alternatively the cerium remobilization possibly as a carbonate fluoride complex could be due to an eh decrease favoured by a rise of the groundwater level

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

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

instrumental magnitudes of historical earthquakes 1892 to 1898 in the 1890s of the dawn of instrumental seismology a variety of primitive but sophisticated seismographs were erected in europe the quality varies greatly from instrument to instrument in use of those records the instrument magnification needs to be calibrated with extreme caution because of the lack of damping from comparison of the trace amplitudes measured by such instruments with those by reliable instruments the effective gain for surface wave maxima of distant shocks is determined here for each of the vertical or horizontal pendulums that were operated at catania rocca di papa ischia roma padua nicolajew charkow strassburg and shide the effective gain is found to be greatly different from the static magnification the period of surface wave maxima is on average 17 sec the results are applied to reported amplitudes for determining the surface wave magnitude of 53 major earthquakes recorded from 1892 to 1898 the magnitude of the destructive tsunami earthquake that occurred off northeastern honshu japan on 15 june 1896 is determined to be 7 2 the great assam india earthquake of 12 june 1897 has a magnitude of 8 0 the present study demonstrates that despite various difficulties historical records if properly interpreted provide invaluable information

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

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

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

re evaluation of seismic intensities and relocation of 1969 saint vincent cape seismic sequence a comparison with the 1755 lisbon earthquake seismic intensity for the february 28 1969 mw 7 8 earthquake have been re evaluated using original documents in local archives such as contemporary newspapers council minutes monographic studies among other sources for spain portugal and morocco and answers to macroseismic questionnaires for morocco this information is used to plot a new intensity map for the whole region affected by the earthquake portugal spain and morocco the intensity values vary from viii to ix in the e w coast of algarve southern portugal to ii iii furthermore we have relocated the hypocentres for main shock and 24 aftershocks using a new 3d crustal velocity model for the gulf of cadiz region and a non linear probabilistic location methodology most of them previously lacking a depth estimate the new locations show an e w distribution of epicenters with focus located in the uppermost mantle most of them with depths between 30 and 50 km no earthquakes have been located at depths shallower than 30 km a comparison between peak ground accelerations pgas estimated from the observed intensities for the 1969 and the lisbon 1755 earthquakes and synthetic pga values generated assuming two different scenarios using the 1969 and 2009 earthquakes for the 1755 lisbon event shows that the observed damage produced by the 1755 earthquake may be better explained assuming a reverse dip slip mechanism oriented in ne sw direction similar to that of the 2009 earthquake rather than assuming focal mechanism similar to that of the 1969 earthquake

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

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