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

is the central piedmont suture a low angle normal fault in the crystalline southern appalachians the carolina are terrane is in fault contact with the piedmont terrane along a seismically reflective surface dipping toward the hinterland and called the central piedmont suture the central piedmont suture may be interpreted as a thrust but existing data also support a silurian devonian normal slip origin 1 there are lower grade rocks in the hanging wall than in the footwall 2 a normal fault solution allows simultaneous metamorphism of the piedmont terrane and carolina terrane prior to their juxtaposition along the central piedmont suture 3 mineral ages in the piedmont terrane are older in the west than in the east consistent with an eastward progressive unroofing 4 along the western edge of the carolina terrane a linear belt of devonian subalkalic to alkalic granitoids and gabbro norites with low initial 87sr 86sr ratios may represent mantle derived magmas along the axis of rifting that are contemporary with major crustal extension the westernmost piedmont terrane includes the chauga belt the chauga belt comprises metavolcanic and metaplutonic units similar in rock type and age to those of the western carolina terrane chauga belt rocks are interpreted to be the westernmost exposures of the carolina terrane translated west on the lower plate by extension the piedmont and carolina terranes may thus compose a single lithotectonic element the piedmont terrane would represent the basement on which the arc was constructed the terrane was uplifted during extension along a major low angle normal fault recognized today as the central piedmont suture

assessment of earthquake hazard in the tokyo area japan abstract the probability of occurrence of an inland earthquake originating beneath the tokyo area is evaluated for a 10 year period from 1991 on the basis of an earthquake catalogue containing some 40 earthquakes which caused some damage to edo now tokyo over a period of 400 years the parameters of the weibull and lognormal probability distributions applied to recurrence interval statistics are estimated with these parameters it is concluded that an earthquake directly beneath the capital the magnitude of which is equal to or greater than 6 0 occurs with a probability of 0 40 for the period in question when the magnitude threshold is assumed as 6 4 and 7 0 the probabilities become 0 17 and 0 049 respectively these probability evaluations are extended to those for the seismic intensity at typical sites in the area although no accurate evaluation is possible because the exact focal depths of historical earthquakes are not known on the assumption that these earthquakes occur near the upper surface of the down going philippine sea plate however a typical depth of 30 km or so is suggested should an earthquake having a mean magnitude of 6 4 say and at a mean location of past earthquakes occur the probability of seismic intensity at typical sites in the capital area exceeding 5 on the japan meteorological agency jma scale would amount to 0 17 the possibility of having a highly damaging earthquake of intensity 6 on the jma scale also cannot be ruled out judging from earthquake disasters in the past although the probability does become lower to summarize it may be said that the probability of japan s capital area being hit by a damaging earthquake in the foreseeable future is not particularly low

a probabilistic assessment of earthquake hazard parameters in nw himalaya and the adjoining regions the maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of nw himalaya and the adjoining regions for this purpose we have prepared a reliable homogeneous and complete earthquake catalogue during the period 1500 2010 the technique used here allows the data to contain either historical or instrumental era or even a combination of the both in this study the earthquake hazard parameters which include maximum regional magnitude mmax mean seismic activity rate the parameter b or b log e of gutenberg richter g r frequency magnitude relationship the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900 2010 the uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters the earthquake hazard in the whole nw himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level tectonics and focal mechanism the annual probability of exceedance of earthquake activity rate of certain magnitude is also calculated for all seismogenic source zones the obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters it is observed that seismic hazard level is high in quetta kirthar sulaiman region in pakistan hindukush pamir himalaya region and uttarkashi chamoli region in himalayan frontal thrust belt the source zones that are expected to have maximum regional magnitude mmax of more than 8 0 are quetta southern pamir caucasus and kashmir himanchal pradesh which have experienced such magnitude of earthquakes in the past it is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity

earthquakes recurrence and interoccurrence times the purpose of this paper is to discuss the statistical distributions of recurrence times of earthquakes recurrence times are the time intervals between successive earthquakes at a specified location on a specified fault although a number of statistical distributions have been proposed for recurrence times we argue in favor of the weibull distribution the weibull distribution is the only distribution that has a scale invariant hazard function we consider three sets of characteristic earthquakes on the san andreas fault 1 the parkfield earthquakes 2 the sequence of earthquakes identified by paleoseismic studies at the wrightwood site and 3 an example of a sequence of micro repeating earthquakes at a site near san juan bautista in each case we make a comparison with the applicable weibull distribution the number of earthquakes in each of these sequences is too small to make definitive conclusions to overcome this difficulty we consider a sequence of earthquakes obtained from a one million year virtual california simulation of san andreas earthquakes very good agreement with a weibull distribution is found we also obtain recurrence statistics for two other model studies the first is a modified forest fire model and the second is a slider block model in both cases good agreements with weibull distributions are obtained our conclusion is that the weibull distribution is the preferred distribution for estimating the risk of future earthquakes on the san andreas fault and elsewhere

history of the west african neoproterozoic ocean key to the geotectonic history of circum atlantic peri gondwana adrar souttouf massif moroccan sahara abstract bordered by the archaean basement of the reguibat shield to the e and s the adrar souttouf massif is located in the southern regions of the moroccan sahara and represents the northern part of the mauritanide belt the central areas of this massif comprise the dayet lawda and sebkha matallah units that are mainly composed of mafic rocks ten samples taken from these rocks yielded 531 zircon grains that were analysed with respect to their morphology u th pb and lu hf isotope composition additionally 155 apatite grains from six samples were also dated by the u th pb method mostly well rounded zircon grains commonly showed bright cathodoluminescent cl overgrowth domains and leaching zones indicating metamorphic overprint around unaffected oscillatory zoned core areas all samples but one yielded two significant zircon age populations 605 ma and 634 ma with some inherited grains in the range of 650 740 ma and very scarcely up to 1190 ma for six samples the hf isotope composition suggests a major contribution of neoproterozoic juvenile magmas from depleted mantle source the zircon hf data for the remaining samples points to a predominant recycling of older archaean to palaeoproterozoic crust based on the geochemical composition of the rocks an island arc setting is assumed at the periphery of the west african craton close to the cryogenian ediacaran boundary subsequent metamorphism during accretion and partial obduction onto the basement rocks took place at about 605 ma a minor variscan overprint could be demonstrated for only one sample this case study exemplifies the great potential of the widely occurring metamorphosed mafic and ultramafic rocks along the western margin of the west african craton for palaeogeographic and geodynamic reconstructions including the peri gondwanan terranes during the late neoproterozoic

new insights into the origin of two contrasting himalayan granite belts the two parallel belts of miocene granite that extend along much of the himalaya differ in age petrogenesis and emplacement style we suggest that their origin is linked to shear heating on a continuously active decollement that cuts through previously metamorphosed indian supracrustal rocks that were transformed into basement during the initial stages of the indian asian collision numerical simulations assuming a shear stress of 30 mpa indicate that initiation of slip on the himalayan thrust at 24 ma could trigger discontinuous melting reactions leading to formation of the high himalayan granite chain from 24 to 20 ma and the north himalayan belt from 18 to 12 ma this model result agrees well with observation as do model predictions regarding emplacement style and location

plutonism in three orogenic pulses eastern blue ridge province southern appalachians department of geological sciences university of north carolina mitchell hall chapel hill nc 27599 3315

probabilistic assessment of earthquake hazards in the north east indian peninsula and hindukush regions the himalayan region is one of the most seismic prone areas of the world the north east ne indian peninsula and the hindukush regions mark the zone of collision of the indian and eurasian plates the probability of the occurrence of great earthquakes with magnitude greater than 7 0 during a specified interval of time has been estimated on the basis of four probabilistic models namely weibull gamma lognormal and exponential for the ne indian peninsula and hindukush regions the model parameters have been estimated by the method of maximum likelihood estimates mle and the method of moments mom the cumulative probability is estimated for a period of 40 years from 1964 and is ranging between 0 881 to 0 995 by the year 1995 using all four models for the ne indian peninsula the conditional probability is also estimated and it is concluded that the ne indian peninsula would expect a great earthquake at any time in the remaining years of the present century for the hindukush region the cumulative probability has already crossed its highest value but no earthquake of magnitude greater than 7 0 has occurred after 1974 in this area it may attribute to the occurrence of frequent shocks of moderate size as seventeen earthquakes of magnitude greater than 6 0 including four greater than 6 4 have been reported until 1994 from this region

probabilistic assessment of tsunami recurrence in the indian ocean the indian ocean is one of the most tsunamigenic regions of the world and recently experienced a mega tsunami in the sumatra region on 26 december 2004 m w 9 2 earthquake with tsunami intensity i soloviev imamura intensity scale equal to 4 5 causing heavy destruction of lives and property in the indian ocean rim countries in this study probabilities of occurrences of large tsunamis with tsunami intensities i 2 0 and i 3 0 average wave heights h 2 83 m and h 5 66 m respectively during a specified time interval were calculated using three stochastic models namely weibull gamma and lognormal tsunami recurrence was calculated for the whole indian ocean and the special case of the andaman sumatra java asj region excluding the 1945 makran event from the main data set for this purpose a reliable homogeneous and complete tsunami catalogue with i 2 0 during the period 1797 2006 was used the tsunami hazard parameters were estimated using the method of maximum likelihood the logarithm of likelihood function ln l was estimated and used to test the suitability of models in the examined region the weibull model was observed to be the most suitable model to estimate tsunami recurrence in the region the sample mean intervals of occurrences of tsunamis with intensity i 2 0 and i 3 0 were calculated for the observed data as well as for the weibull gamma and lognormal models the estimated cumulative and conditional probabilities in the whole indian ocean region show recurrence periods of about 27 30 years 2033 2036 and 35 36 years 2039 2040 for tsunami intensities i 2 0 and i 3 0 respectively while it is about 31 35 years 2037 2041 and 41 42 years 2045 2046 for a tsunami of intensity i 2 0 and i 3 0 respectively in the asj region a high probability 0 9 of occurrence of large tsunamis with i 2 0 in the next 30 40 years in the indian ocean region was revealed

crustal structure beneath the southern appalachians nonuniqueness of gravity modeling gravity models computed for a profile across the long wavelength paired negative positive bouguer anomalies of the southern appalachian mountains show that the large negative anomaly can be explained by a crustal root zone whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries a suture zone a mantle upwarp or a shallow body seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly the presence of outcropping mafic and ultramafic rocks in the southern appalachians and the inferred tectonic history of the appalachian orogen are most consistent with the suture zone model crust similar to continental crust probably exists beneath the coastal plain and inner continental shelf where the gravity anomalies return to near zero values

deep in the heart of dixie pre alleghanian eclogite and hp granulite metamorphism in the carolina terrane south carolina usa the central part of the carolina terrane in western south carolina comprises a 30 to 40 km wide zone of high grade gneisses that are distinct from greenschist facies metavolcanic rocks of the carolina slate belt to the se and amphibolite facies metavolcanic and metaplutonic rocks of the charlotte belt to the nw this region termed the silverstreet domain is characterized by penetratively deformed felsic gneisses granitic gneisses and amphibolites mineral assemblages and textures suggest that these rocks formed under high pressure metamorphic conditions ranging from eclogite facies through high p granulite to upper amphibolite facies mafic rocks occur as amphibolite dykes as metre scale blocks of coarse grained garnet clinopyroxene amphibolite in felsic gneiss and as residual boulders in deeply weathered felsic gneiss inferred omphacite has been replaced by a vermicular symplectite of sodic plagioclase in diopside consistent with decompression at moderate to high temperatures and a change from eclogite to granulite facies con ditions all samples have been partially or wholly retrograded to amphibolite assemblages we infer the following p t t history 1 eclogite facies p t conditions at 1 4 gpa 650 730 c 2 high p granulite facies p t conditions at 1 2 1 5 gpa 700 800 c 3 retrograde amphibolite facies p t conditions at 0 9 1 2 gpa and 720 660 c this metamorphic evolution must predate intrusion of the 415 ma newberry granite and must postdate formation of the charlotte belt and slate belt arcs 620 to 550 ma comparison with other medium temperature eclogites and high pressure granulites suggests that these assemblages are most likely to form during collisional orogenesis eclogite and high p granulite facies metamorphism in the silverstreet domain may coincide with a 570 535 ma event documented in the western charlotte belt or to a late ordovician early silurian event the occurrence of these high p assemblages within the carolina terrane implies that prior to this event the western carolina terrane charlotte belt and the eastern carolina terrane carolina slate belt formed separate terranes the collisional event represented by these high pressure assemblages implies amalgamation of these formerly separate terranes into a single composite terrane prior to its accretion to laurentia

reinterpretation of adcoh and cocorp seismic reflection data with constraints from detailed forward modeling of potential field data implications for laurentia peri gondwana suture abstract to better constrain the structure of the laurentian peri gondwana suture zone maps and a 2 dimensional regional cross section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields the central piedmont suture cps the boundary between the laurentian inner piedmont and the peri gondwanan carolina terrane is a low angle thrust fault 30 ramping up from an alleghanian mid crustal detachment at depths of about 12 km adcoh and cocorp seismic data image anticlinal structures in the footwalls of the hayesville thrust and the cps above the alleghanian decollement the footwall rocks have previously been interpreted as paleozoic shelf strata on the basis of sub horizontal seismic reflectors however the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of grenvillian basement the appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the carolina terrane toward the appalachian core a change in lower crustal density is not required so that grenville basement rocks may extend farther to the southeast than previously thought the 5 to 10 km of alleghanian uplift and exhumation predicted by p t crystallization data compiled in this paper can be easily accommodated by thrusting on four major low angle thrust systems great smoky mountain thrust gsmt hayesville brevard and cps unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation alleghanian collision along the southeastern appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter clockwise rotation of gondwanan west africa creating head on collision in the southern appalachians and at least 370 km of shortening

crustal evolution across the southern appalachians initial results from the sesame broadband array 1 receiver functions from the earthscope southeastern suture of the appalachian margin experiment broadband deployment and u s transportable array were analyzed to constrain average crustal thickness and composition across the southern appalachians low vp vs ratios 1 69 1 72 across the carolina terrane and parts of the inner piedmont indicate that the crust has a felsic average composition the results are consistent with models of thin skinned thrusting of carolina arc fragments over laurentian basement whereas arc collision models require significant crustal modification to explain the low vp vs new crustal thickness estimates provide constraints on the extent of the blue ridge crustal root the present root may be a remnant of a broader structure formed by alleghanian thrust loading root preservation is attributed to mesozoic heating and thinning of the lower crust beneath outboard terranes leaving colder blue ridge crust largely intact however thickened crust 50 55 km across the region may also be inherited from continental collision during the proterozoic grenville orogeny

wide angle three component seismic reflection profiling of the crust along the east coast gravity high southern appalachians using quarry blasts inversion of refraction wide angle reflection travel times for two dimensional velocity structure along the axis of the east coast gravity high in the carolina terrane of georgia indicates much higher crustal p wave velocities than previously modeled thirty nine timed quarry blasts recorded with a 20 element array of three component recorders at 330 m spacings provide reversed and overlapping coverage along the profile which crosses consortium for continental reflection profiling georgia line 5 ray paths are concentrated in high grade rocks of the charlotte and kiokee belts shot gathers show strong first arrivals moho reflections and numerous reflections from within the crust shear wave arrivals are particularly strong with prominent direct arrivals sg and reflections from the moho sms observed for all quarries three alternative models show average crustal p wave velocities of 6 5 6 6 km s and moho depths between 37 and 39 km p wave velocities increase from 6 0 6 2 km s at 1 km depth to 6 7 6 8 km s at a first order discontinuity at a depth of 24 26 km alternative models for the lower crust feature both a slight increase in velocity and velocity reversals at the 25 km discontinuity with velocities steadily increasing to between 6 9 and 7 5 km s at the base of the crust low average v p v s ratios for the crust 1 70 1 75 estimated from travel time ratios for sms and pmp reflections suggest that the high compressional wave velocities derived by inversion are associated with rocks of high metamorphic grade and granitic to intermediate not mafic average composition over most of the crust the low average ratios can also be explained in part by the presence of a layer of low p wave velocity in the midcrust possibly associated with a package of quartz rich platform and rift basin sediments overthrust late in the alleghanian orogeny by the carolina terrane allochthon as suggested by earlier workers crustal models incorporating the new estimate for crustal thickness beneath the carolina terrane show that the long wavelength component of the gravity gradient in georgia can be explained in terms of crustal thickness variations aeromagnetic data indicate that density variations responsible for local steepening of the gradient are confined largely to the lower half of the crust

simulation based distributions of earthquake recurrence times on the san andreas fault system earthquakes on a specified fault or fault segment with magnitudes greater than a specified value have a statistical distribution of recurrence times the mean recurrence time can be related to the rate of strain accumulation and the strength of the fault very few faults have a recorded history of earthquakes that define a distribution well for hazard assessment in general a statistical distribution of recurrence times is assumed along with parameter values assumed distributions include the weibull stretched exponential distribution the lognormal distribution and the brownian passage time inverse gaussian distribution the distribution of earthquake waiting times is the conditional probability that an earthquake will occur at a time in the future if it has not occurred for a specified time in the past the distribution of waiting times is very sensitive to the distribution of recurrence times an exponential distribution of recurrence times is poissonian so there is no memory of the last event the distribution of recurrence times must be thinner than the exponential if the mean waiting time is to decrease as the time since the last earthquake increases neither the lognormal or the brownian passage time distribution satisfies this requirement we use the virtual california model for earthquake occurrence on the san andreas fault system to produce a synthetic distribution of earthquake recurrence times on various faults in the san andreas system we find that the synthetic data are well represented by weibull distributions we also show that the weibull distribution follows from both damage mechanics and statistical physics

crustal thickness variations across the blue ridge mountains southern appalachians an alternative procedure for migrating wide angle reflection data abstract migration of wide angle reflections generated by quarry blasts suggests that crustal thickness increases from 38 km beneath the carolina terrane to 47 51 km along the southeastern flank of the blue ridge the migration algorithm developed for generating single fold images from explosions and earthquakes recorded with isolated short aperture arrays uses the localized slant stack as an intermediate data set in contrast with other methods it includes an interpretive step that is based on the assumption that all coherent p wave energy consists of reflections from planar interfaces each sample in the slant stack is mapped into a planar dipping segment with a length that is determined by the recording aperture migrated sections from within the blue ridge show increases in reflectivity at depths of 20 and 40 km high apparent reflectivity from 40 to 50 55 km suggests a layered zone in the lower crust that is similar to models proposed for the cumberland plateau in tennessee and the adirondacks the migration results are consistent with regional gravity data and with the occurrence of crustal roots beneath the urals another paleozoic orogen

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

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

evolution of the murphy synclinorium southern appalachian blue ridge usa abstract the western blue ridge allochthon of the southern appalachians is dominated by the 180 km long murphy synclinorium paired with anticlinoria to the northwest these are first generation northwest overturned doubly plunging large amplitude and wavelength 10 km isoclinal folds contemporaneous with peak neo acadian orogeny visian 335 345 ma regional metamorphism the synclinorium folds a regional unconformity separating neoproterozoic rift and lower paleozoic drift sequences from a younger successor basin sequence strain analysis of metaconglomerates from lithologic groups above and below the unconformity indicates coaxial low to moderate oblate to nearly plane strain in both groups the synclinorium evolved via nnw sse crustal shortening 32 combined with orthogonal nne ssw sub horizontal flow stretching 35 45 sub parallel to the developing fold axes differences in metamorphic grade and paleodepth 10 17 km of the exposed synclinorium had essentially no effect on strain magnitudes retrodeformation of the embedded regional unconformity reveals a very broad synclinal warping of the rift and drift facies units predating superposition of the murphy synclinorium suggesting tectonic inheritance in the latter structure s origin the earlier mild deformation is post early cambrian and may represent the only vestige of the dynamic effects of the middle ordovician taconic orogeny to be found in this region

whole rock pb and sm nd isotopic constraints on the growth of southeastern laurentia during grenvillian orogenesis the conventional view that the basement of the southern and central appalachians represents juvenile mesoproterozoic crust the final stage of growth of laurentia prior to grenville collision has recently been challenged new whole rock pb and sm nd isotopic data are presented from mesoproterozoic basement in the southern and central appalachians and the granite rhyolite province as well as one new u pb zircon age from the granite rhyolite province these data combined with existing data from mesoproterozoic terranes throughout southeastern laurentia further substantiate recent suggestions that the southern and central appalachian basement is exotic with respect to laurentia sm nd isotopic compositions of most rocks from the southern and central appalachian basement are consistent with progressive growth through reworking of the adjacent granite rhyolite province however pb isotopic data including new analyses from important regions not sampled in previous studies do not correspond with pb isotopic compositions of any adjacent crust the most distinct ages and isotopic compositions in the southern and central appalachian basement come from the roan mountain area eastern tennessee western north carolina the data set indicates u pb zircon ages up to 1 8 ga for igneous rocks inherited and detrital zircon ages 2 0 ga sm nd depleted mantle model t dm ages 2 0 ga and the most elevated 207 pb 204 pb observed in southeastern laurentia the combined u pb geochronologic and sm nd and pb isotopic data preclude derivation of southern and central appalachian basement from any nearby crustal material and demonstrate that grenville age crust in southeastern laurentia is exotic and probably was transferred during collision and assembly of rodinia these new data better define the boundary between the exotic southern and central appalachian basement and adjacent laurentian granite rhyolite province

geochemical and ndsrpb isotopic composition of alleghanian granites of the southern appalachians origin tectonic setting and source characterization abstract we report major element trace element and nd and sr isotopic ratios for 35 samples of late mississippian early permian alleghanian granites that intrude the carolina terrane eastern slate belt inner piedmont and kiokee belt of the southern appalachians major element compositions indicate that most plutons are high potassium k 2 o 4 metaluminous granites initial e nd depleted mantle model ages and initial 87 sr 86 sr ratios respectively of the plutons range from 8 2 to 3 4 940 1020 ma and 0 70642 0 72798 for the inner piedmont 2 3 to 2 0 660 1130 ma and 0 70421 0 71035 for the kiokee belt 2 7 to 2 4 660 870 ma and 0 70353 0 70816 for the eastern slate belt and 6 7 to 1 9 690 1140 ma and 0 70391 0 70739 for the carolina terrane the chemical and isotopic data are most consistent with formation of the granites by anatexis of continental crust rather than derivation from a depleted mantle source rocks of the carolina terrane have e nd 300 ma values and pb isotopic ratios indistinguishable from those of most alleghanian granites suggesting it is a likely source some alleghanian granites within the carolina terrane require a more evolved source than exposed carolina terrane rocks suggesting that evolved crust possibly grenville basement occurs structurally below or within the terrane the chemical and isotopic compositions of granites intruding the kiokee belt eastern slate belt and carolina terrane are similar suggesting that these terranes are geochemically similar in contrast alleghanian granites within the inner piedmont have higher initial 87 sr 86 sr and lower 143 nd 144 nd ratios indicating that their sources are isotopically more evolved the virtual absence of alleghanian plutons with mafic intermediate compositions and the lack of geographic trends in chemical and isotopic composition across the orogen makes a subduction origin for the granites unlikely the consistency of the geochemical data with a crustal anatectic origin of the granites together with the observation that they intruded synchronously with alleghanian thrusting in the valley and ridge province suggests strongly that they are collisional in origin the crustal heating events that produced the granites might have been caused by delamination of mantle lithosphere during collision of laurentia with gondwana 1 2 alternatively adequate heating may have occurred by crustal thickening during emplacement of thrust sheets 3

global risk from extreme geophysical events threat identification and assessment in an increasingly interconnected world any single geophysical hazard is capable of having consequences far beyond the range of immediate physical effects most recently this was demonstrated by the 2004 asian tsunami which took the lives of citizens from 57 different nations and by hurricane katrina in august 2005 which raised fuel prices worldwide and contributed to a record uk trade deficit in the month following the devastation of new orleans on an altogether wider scale global geophysical events gges are natural phenomena capable of having wholesale deleterious consequences for the world s environment economy and society these may arise i due to a global physical effect such as an episode of severe planetary cooling in response to a volcanic super eruption or large comet or asteroid impact or ii as a result of subsidiary ramifications for the global economy and social fabric of a cataclysmic regional event such as an atlantic or pacific wide mega tsunami or a more spatially confined event at a strategically sensitive location for example the awaited major tokyo earthquake while very infrequent the wide ranging and potentially ruinous consequences of a gge for the well being of the international community make it essential that they are seriously considered within any comprehensive assessment of natural threats

fault displacement rates on a range of timescales abstract displacements on tectonic faults primarily accrue during earthquakes at rates that vary through time to examine the processes that underlie the temporal changes in fault displacement rates we analyse displacements and displacement rates for time periods from the present to 5 10 20 300 500 1000 and 5000 kyr for 261 active reverse or normal faults from a worldwide dataset displacement rates depart from million year average rates by up to three orders of magnitude with the size of these departures inversely related to the duration of the sample period and to fault length short term 20 kyr displacement rates generally span a greater range on small faults than large a feature which suggests more variable growth on smaller faults simple earthquake slip modeling shows that variations in displacement rates require changes in both recurrence interval and slip per event and do not support the characteristic slip earthquake model as long as fault system strain rates are uniform displacement rates generally become constant over time periods between 20 and 300 kyr with the length of time required to reach stability being inversely related to the regional basin wide strain rates stable long term displacement rates and fluctuations in earthquake recurrence intervals and slip arise in part due to fault interactions

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

fully coupled formulation of surface flow with 2 phase subsurface flow for hydrological simulation with the aim of realizing a surface subsurface coupled fluid flow simulation the authors discuss surface flow models that can be used in the framework of the 2 phase subsurface numerical simulation system in this paper three surface flow models i e a kinematic wave model kw a diffusion wave model dw and a linearized diffusion wave model ldw are explained by approximating the momentum equation and are transformed into a set of nonlinear functions which can be solved simultaneously with the 2 phase subsurface flow by incorporating these into a 2 phase numerical simulation system comparison studies are carried out using experimental data and a field scale model so far as the results of the study are concerned it is concluded that the dw model gives reasonable performance for any case the ldw model provides mostly identical results with the dw model with some restrictions while the kw model is not applicable for the physical modelling of continuous flow through multiple slopes with different angles copyright 2000 john wiley sons ltd

probabilistic assessment of earthquake hazards in the indian subcontinent the indian subcontinent is one of the most seismic prone areas of the world the himalayan mountains in the north mid oceanic ridges in the south and earthquake belts surrounding the indian plate all show that the subcontinent has undergone extensive geological and tectonic processes in the past the probability of the occurrence of earthquakes with magnitude 6 m b 7 during a specified interval of time has been estimated on the basis of four probabilistic models namely lognormal weibull gamma and exponential distribution for the indian subcontinent the seismicity map has been prepared using the earthquake catalogue from the period 1963 1994 and six different zones have been identified on the basis of clustering of events the model parameters have been estimated by the method of maximum likelihood estimates mle and method of moments mom a computer program package has been developed for all four models which represents the distributions of time intervals fairly well the logarithmic of likelihood ln l is estimated for testing the models and different models have been found to be plausible the probability of different magnitude thresholds has been evaluated using the gutenberg richter formula log n a bm for magnitude distribution the constants a and b have been computed for each region and found to be varying between 5 46 8 53 and 0 87 1 34 respectively

a probabilistic estimate of the most perceptible earthquake magnitudes in the nw himalaya and adjoining regions nw himalaya and its neighboring region 25 40 n and 65 85 e is one of the most seismically hazardous regions in the indian subcontinent a region that has historically experienced large to great damaging earthquakes in the present study the most perceptible earthquake magnitudes mp are estimated for intensity i vii horizontal peak ground acceleration a 300 cm s2 and horizontal peak ground velocity v 10 cm s in 28 seismogenic zones using the two earthquake recurrence models of kijko and sellevoll bulletin of the seismological society of america 82 1 120 134 1992 and gumbel s third asymptotic distribution of extremes giii both methods deal with maximum magnitudes the earthquake perceptibility is calculated by combining earthquake recurrence models with ground motion attenuation relations at a particular level of intensity acceleration and velocity the estimated results reveal that the values of mp for velocity v 10 cm s show higher estimates than corresponding values for intensity i vii and acceleration a 300 cm s2 it is also observed that differences in perceptible magnitudes calculated by the kijko sellevoll method and giii statistics show significantly high values up to 0 7 0 6 and 1 7 for intensity acceleration and velocity respectively revealing the importance of earthquake recurrence model selection the estimated most perceptible earthquake magnitudes mp in the present study vary from mw 5 1 to 7 7 in the entire zone of the study area results of perceptible magnitudes are also represented in the form of spatial maps in 28 seismogenic zones for the aforementioned threshold levels of intensity acceleration and velocity estimated from two recurrence models the spatial maps show that the quetta of pakistan the hindukush pamir himalaya the caucasus mountain belt and the himalayan frontal thrust belt kashmir kangra uttarkashi chamoli regions exhibit higher values of the most perceptible earthquake magnitudes mw 6 0 these spatially distributed values indicate good agreement with high seismic hazard zones in previously published hazard maps based on seismicity maximum expected earthquake magnitudes during specific time intervals and maximum expected acceleration these maps have useful implications in preparing earthquake selection criteria for the anti seismic design of non critical structures in the study region

impact of fault parameter uncertainties on earthquake recurrence probability examined by monte carlo simulation an example in central taiwan abstract the region around taiwan is well known for its unique geological setting which has resulted in a high seismicity the central geological survey taiwan cgst has launched a series of investigation on characterizing the active faults on the island the cgst revealed that there are 33 active faults and their fault parameters are suggested in the latest publication in 2010 however the uncertainties of return period and earthquake magnitude are not provided the main objective of the paper is to study the impact of unspecified parameter uncertainties on recurrence earthquake probabilities in addition a numerical approach involving the use of monte carlo simulation was proposed to estimate the exceedance probabilities in which the parameter uncertainties were taken into account the meishan fault in central taiwan with the best estimate return period of 162 years and earthquake magnitude of 7 1 was used as an example the analyses verified the impact of parameter uncertainties on the exceedance probability in fault induced earthquake recurrence when uncertainty is high the exceedance probability associated with large magnitudes is high it was also observed that the probabilistic analysis in this study can generate a realistic continuous distribution of exceedance probabilities that cannot be obtained by a deterministic approach the best estimate distribution of exceedance probability was established by enveloping the curves estimated by both deterministic and probabilistic approaches accordingly the best estimate exceedance probability for a 7 5 magnitude earthquake recurring in 2011 2060 induced by the meishan fault in central taiwan was estimated as 11

geophysical anomalies along strike of the southern appalachian piedmont bouguer gravity anomalies and aeromagnetic anomalies display a northward increase of values in the charlotte and carolina slate belts from georgia to virginia analysis of these data with constraints imposed by seismic reflection seismic refraction conductivity measurements and surface geology imply that this increase is due to a corresponding increase in the percentage of mafic rocks in the upper crust a regional trend in the bouguer field is determined for an observed eastward decrease in crustal thickness based on seismic refraction measurements a comparison of the calculated regional with surface boundaries shows that in places the crustal thinning occurs more than 50 kilometers west of the inner piedmont charlotte belt transition the comparison also shows that the crustal thinning may take place west of exposed grenville basement the evidence thus indicates that the southern appalachian gravity gradient is not likely related to a crustal or lithospheric suture the evidence further indicates that because the upper crustal and deep crust upper mantle variations are independent in terms of spatial position the upper crust of the charlotte slate belts is decoupled from the lower crust perhaps at subhorizontal boundaries seen on reflection data

modeling earthquake recurrence in the himalayan seismic belt using time dependent stochastic models implications for future seismic hazards interest in and pertinent studies related to the seismic hazard in the himalayan region have increased significantly since the instrumental era and each damaging earthquake encourages its reestimation in the work presented herein the non poissonian probabilities of exceedance of magnitudes in a specified time in the future were investigated for different elapsed times based on the recurrence time intervals of past earthquakes in the himalaya using the weibull log normal gamma and inverse gaussian stochastic models the whole himalayan arc is divided into four seismogenic source zones viz the northwestern himalayas zone 1 the central seismic gap region zone 2 the eastern nepal and sikkim zone 3 and the eastern himalayas zone 4 by considering approximately 380 years of seismological data the suitability of each stochastic model for each zone was estimated using the kolmogorov smirnov k s test to describe the different physical processes responsible for earthquake occurrence the results show that the gamma inverse gaussian log normal and inverse gaussian models were most suitable for zones 1 4 respectively for m 6 0 the cumulative probability of recurrence intervals reaches up to 90 in 30 years for zones 1 and 2 49 years for zone 3 and 41 years for zone 4 the estimated conditional probability reaches 90 in 30 years in zone 1 35 years in zone 2 and 50 years in zones 3 and 4 the most suitable models for m 7 0 were found to be the log normal for zones 1 2 and 3 and gamma for zone 4 the cumulative probability for m 7 0 reaches 90 in 85 years in zone 1 86 years in zone 2 93 years in zone 3 and 148 years in zone 4 the estimated conditional probabilities reach 90 in 80 years in zone 1 90 years in both zone 2 and 3 and 150 years in zone 4 it is strongly recommended that model suitability be evaluated in complex regions such as the himalaya before proceeding with seismic hazard assessments the heterogeneous and complex tectonics of the himalayas differentiated plate motions different stress release patterns spatially and temporally and locking unlocking of faults thrusts are some of the reasons responsible for the different probabilistic models describing the earthquake occurrence phenomena in these four zones

formation of high pressure metabasites in the southern appalachian blue ridge via taconic continental subduction beneath the laurentian margin 1 tectonic models that account for the occurrence of eclogite retrograde eclogite peridotite and migmatitic basement gneisses in the southern blue ridge invoke closure of a small ocean basin between the eastern blue ridge ebr and western blue ridge wbr in this obducted ophiolite model franciscan type eastward subduction of oceanic crust beneath the piedmont arc occurred prior to obduction of the arc onto the laurentian margin the discovery of kilometer scale eclogite bodies near the ebr wbr boundary are cited as evidence for obducted ophiolite accreted island arc models however thermobarometric estimates based on mineral chemistry from hp metabasites of the western central and eastern blue ridge indicate that eclogites and granulites are medium temperature type 550 900 c inconsistent with the obducted ophiolite model mid ocean ridge basalt subducted beneath continental margins and island arcs rarely reaches temperatures in excess of 550 c thermobarometric comparisons of the present study and a reexamination of deep seismic profiles from the blue ridge allow for a model of westward subduction of continental material beneath laurentia during the taconic orogeny that produced a megamelange now preserved in the central and eastern blue ridge tectonic provinces p t paths determined from blue ridge hp metabasites are similar to p t paths determined previously from caledonian and variscan eclogites thermobarometric similarities imply a common tectonic history of continental collision subduction of continental crust to depths of 50 65 km followed by rapid eduction

estimates of long term probabilities for future great earthquakes in the aleutians we compute probabilities for future great earthquakes in the aleutian arc probability distributions are fitted to recurrence periods of great aleutian evens m sub w or 7 8 since 1788 given a probability distribution and data of the last grat earthquake in each arc segment time dependent conditional probabilities are determined for future periods of interest we obtain for the next two decades high probabilities 99 to 30 for great earthquakes in the shumagin yakataga unalaska and kommandorski seismic gaps these probabilities are higher than for any other assessed region of the u s believed to be capable of great earthquakes low probabilities 17 to 9 are found for segments that ruptured most recently in 1965 1964 and 1957 recurrence periods for great earthquakes measure on average about 80 years but vary substantially whether recurrence periods for great aleutian earthquakes follow a normal log normal or any other probability distribution is not resolved because in most arc segments the known seismic record embraces at best one or two recurrences the resulting uncertainty affects the magnitude of estimated probabilities especially in seismic gaps that have not ruptured for a long time in some instances a normal distribution yields a three times higher probability than the correspondingmore log normal distribution less

newly discovered eclogite in the southern appalachian orogen northwestern north carolina abstract recent detailed geologic mapping in the blue ridge belt of northwestern north carolina has revealed the first reported eclogite sensu stricto in the southern appalachian orogen the eclogite occurs at the base of the ashe metamorphic suite within a shear zone that separates the spruce pine thrust sheet from the underlying grenville age basement rocks this contact juxtaposes rocks of apparent oceanic affinities predominantly metapelite metabasite and meta ultramafic rocks with rocks of the ancient north american craton the primary metamorphic assemblage in the eclogite is garnet omphacite quartz rutile hornblende and plagioclase occur only as retrograde amphibolite facies phases in the eclogite pressure temperature estimates for the primary eclogite assemblage are consistent with minimum pressures of 13 17 kbar at 625 790 c while the retrograde amphibolite facies assemblage suggests conditions of 8 5 12 kbar and 650 730 c ultramafic blocks also occur within the shear zone containing the eclogite the presence of high pressure metamorphic rocks associated with ultramafic rocks and pelitic schists within a shear zone separating continental rocks from oceanic rocks is strong evidence for an ancient subduction event and indicates that at least part of the ashe metamorphic suite is a subduction related accretionary melange

resolving the timing of orogenesis in the western blue ridge southern appalachians via in situ id tims monazite geochronology both taconian ca 450 ma and acadian ca 380 ma ages of high grade deformation and metamorphism have been advocated for the western blue ridge southern appalachians united states to resolve this debate metamorphic monazite from the great smoky mountains was dated via in situ microsampling plus isotope dilution thermal ionization mass spectrometry id tims u pb ages are 450 5 ma 2 error and mean 207 pb 206 pb ages are 453 10 ma these data indicate that peak metamorphism and high grade deformation occurred during the taconian orogeny although they do allow for a low grade sub amphibolite facies acadian overprint unresolved issues remain regarding the comparability of u pb tims ages with those obtained via other methods

probabilistic assessment of earthquake hazard in gujarat and adjoining region of india the gujarat and adjoining region falls under all four seismic zones v iv iii and ii of the seismic zoning map of india and is one of the most seismically prone intracontinental regions of the world it has experienced two large earthquakes of magnitude m w 7 8 and 7 7 in 1819 and 2001 respectively and several moderate earthquakes during the past two centuries in the present study the probability of occurrence of earthquakes of m 5 0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely weibull gamma and lognormal a complete earthquake catalogue has been used covering the time interval of 1819 to 2006 the whole region has been divided into three major seismic regions saurashtra mainland gujarat and kachchh on the basis of seismotectonics and geomorphology of the region the earthquake hazard parameters have been estimated using the method of maximum likelihood the logarithmic of likelihood function ln l is estimated and used to test the suitability of models in three different regions it was found that the weibull model fits well with the actual data in saurashtra and kachchh regions whereas lognormal model fits well in mainland gujarat the mean intervals of occurrence of earthquakes are estimated as 40 455 20 249 and 13 338 years in the saurashtra mainland gujarat and kachchh region respectively the estimated cumulative probability probability that the next earthquake will occur at a time later than some specific time from the last earthquake for the earthquakes of m 5 0 reaches 0 9 after about 64 years from the last earthquake 1993 in saurashtra about 49 years from the last earthquake 1969 in mainland gujarat and about 29 years from the last earthquake 2006 in the kachchh region the conditional probability probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake is also estimated and it reaches about 0 8 to 0 9 during the time interval of about 57 to 66 years from the last earthquake 1993 in saurashtra region 31 to 51 years from the last earthquake 1969 in mainland gujarat and about 21 to 28 years from the last earthquake 2006 in kachchh region

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

probabilistic assessment of earthquake recurrence in northeast india and adjoining regions northeast india and adjoining regions 20 32 n and 87 100 e are highly vulnerable to earthquake hazard in the indian sub continent which fall under seismic zones v iv and iii in the seismic zoning map of india with magnitudes m exceeding 8 7 and 6 respectively it has experienced two devastating earthquakes namely the shillong plateau earthquake of june 12 1897 mw 8 1 and the assam earthquake of august 15 1950 mw 8 5 that caused huge loss of lives and property in the indian sub continent in the present study the probabilities of the occurrences of earthquakes with magnitude m 7 0 during a specified interval of time has been estimated on the basis of three probabilistic models namely weibull gamma and lognormal with the help of the earthquake catalogue spanning the period 1846 to 1995 the method of maximum likelihood has been used to estimate the earthquake hazard parameters the logarithmic probability of likelihood function ln l is estimated and used to compare the suitability of models and it was found that the gamma model fits best with the actual data the sample mean interval of occurrence of such earthquakes is estimated as 7 82 years in the northeast india region and the expected mean values for weibull gamma and lognormal distributions are estimated as 7 837 7 820 and 8 269 years respectively the estimated cumulative probability for an earthquake m 7 0 reaches 0 8 after about 15 16 2010 2011 years and 0 9 after about 18 20 2013 2015 years from the occurrence of the last earthquake 1995 in the region the estimated conditional probability also reaches 0 8 to 0 9 after about 13 17 2008 2012 years in the considered region for an earthquake m 7 0 when the elapsed time is zero years however the conditional probability reaches 0 8 to 0 9 after about 9 13 2018 2022 years for earthquake m 7 0 when the elapsed time is 14 years i e 2009

recurrence time and frequency slip statistics of slip events on the creeping section of the san andreas fault in central california summary an important question in seismic hazard assessments is the frequency size and recurrence interval statistics at a point on a fault does a point on a fault obey the same statistics as earthquakes in a region do this is a difficult question to answer because the number of repetitive earthquakes on a particular fault that have been observed is small in order to overcome this difficulty we consider slip events on the creeping section of the san andreas fault in central california sequences of up to 100 events are obtained from creepmeter records we compare the statistical distribution of recurrence times with the brownian passage time lognormal and weibull distributions and using goodness of fit tests find that the weibull is the preferred distribution we also consider the frequency amplitude distribution of slip events we find that the data clearly do not obey a gutenberg richter distribution instead there is a uniform distribution of event sizes for a large fraction of events

paleozoic and grenvillian structures in the southern appalachians extended interpretation of seismic reflection data interpretive reprocessing of seismic reflection data has elucidated paleozoic and grenvillian structures in the southern appalachians the seismic data include a 7500 km grid of adcoh seisdata and cocorp reflection profiles that traverse the blue ridge and inner picdmont geologic provinces of north carolina south carolina and georgia surface geology and potential field data were used to constrain the interpretation the reprocessed seismic reflection data have delineated the internal and external geometry of the crystalline blue ridge inner piedmont allochthon including the locations of the blue ridge master decollement haycsville fault and brevard fault zone on the basis of the reprocessed data all of the major faults within the allochthonous upper crust sole in the blue ridge master decollement reflections extending to the southeast from beneath the surface location of the hayesville fault to the blue ridge thrust might be the seismic signature of a high strain zone this implies that internal deformation of the blue ridge allochthon associated with the alleghanian orogeny might have occurred farther to the west than has been previously documented from field studies relative amplitude seismic data enabled the discrimination between blue ridge inner piedmont crystalline rocks and underlying lower paleozoic shelf strata thereby delineating the blue ridge thrust the interpreted geometry constrains the top of the shelf sequence beneath the blue ridge to depths of less than 3 km this relatively shallow depth of the shelf strata together with the presence of duplex structures and bright spots that are imaged within the sequence might imply favorable conditions for hydrocarbon exploration beneath the blue ridge midcrustal reflections from within the upper to iower crust are interpreted to originate from preserved grenvillian structures that were reactivated at the basement surface during late proterozoic early cambrian extension reflection continuity is occasionally disrupted by interpreted post grenvillian pre early cambrian low density intrusions topography at the basement surface possibly caused by the intrusions is interpreted to have controlled the formation of some of the structures within the overlying allochthon including blue ridge and brevard fault zone ramps correlation of seismic time structure contour maps with available gravity data and two dimensional gravity modeling suggest that anomalies in the gravity field can be attributed to low density sources within the autochthonous crust discontinuous reflection packages from depths of 36 42 km are interpreted to originate from the mohorovi i discontinuity the reflectors trend about n15 e with a true dip of approximately 15 nw

redistribution and export of contaminated sediment within eastern fukushima prefecture due to typhoon flooding tropical cyclones expose river basins to heavy rainfall and flooding and cause substantial soil erosion and sediment transport there is heightened interest in the effects of typhoon floods on river basins in northeast japan as the migration of radiocaesium bearing soils contaminated by the fukushima daiichi nuclear power plant fdnpp accident will affect future radiation levels the five main catchments surrounding fdnpp are the odaka ukedo maeda kuma and tomioka basins but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins here we address this issue and report catchment scale modelling of the five basins using the getflows simulation code the three dimensional 3d models of the basins incorporated details of the geology soil type land cover and used data from meteorological records as inputs the simulation results were checked against field monitoring data for water flow rates suspended sediment concentrations and accumulated sediment erosion and deposition the results show that the majority of annual sediment migration in the basins occurs over storm periods thus making typhoons the main vectors for redistribution the ukedo and tomioka basins are the most important basins in the region in terms of overall sediment transport followed by the other three basins each with similar discharge amounts erosion is strongly correlated with the underlying geology and the surface topography in the study area a low permeability pliocene dainenji formation in the coastal area causes high surface water flow rates and soil erosion conversely erosion is lower in an area with high permeability granite basement rocks between the hatagawa and futaba faults in the centre of the study area land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east the largest sediment depositions occur in the ogaki and takigawa dams at the confluence of the takase and ukedo rivers and at the ukedo river mouth having clarified the sediment redistribution patterns and controlling processes these results can assist the ongoing task of monitoring radioactive caesium redistribution within fukushima prefecture and contribute to the design and implementation of measures to protect health and the environment copyright 2016 john wiley sons ltd

the south western branch of the variscan belt evidence from morocco abstract this work is based on the compilation and re evaluation of the most significant data either personal or from the literature concerning the moroccan variscides the latter constitute the only moderately disturbed or even undisturbed part of the south western branch of the variscan belt facing directly nw gondwana they include two orogenic segments namely the northern mauritanides and the meseta domain exposed in the saharan and atlas meseta regions respectively and a foreland belt cropping out essentially in the anti atlas the eastward thrust units of saharan morocco oulad dlim mostly originate from the west african craton wac border in an area of thin palaeozoic sedimentation thin skinned fold thrust foreland arcs develop progressively northward zemmour at the expense of the increasingly thick palaeozoic series whereas thick skinned deformation characterizes the inverted proximal paleomargin in the anti atlas domain as suggested by the meseta and anti atlas stratigraphic similarities the meseta domain corresponds to a collage of moderately displaced thinned crustal blocks from the distal gondwana paleomargin variscan deformation is dominated by nw verging thrusts and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth the meseta anti atlas boundary is a major ene trending transpressional dextral fault referred to as the south meseta fault smf discussing the correlations between the variscan segments of morocco and sw iberia allows us to suggest that a latitudinal transform zone similar to the smf separated these segments during the late palaeozoic subduction of the rheic ocean crust would have been directed se ward along both the iberian and moroccan meseta and nw ward south of the smf i e along the wac

shallow mantle velocities beneath the southern appalachians from pn phases to constrain mantle structure that might contribute to the topography of the southern appalachian mountains pn phases from regional earthquakes recorded in northern georgia by earthscope southeastern suture of the appalachian margin experiment and transportable array stations were used to solve for shallow mantle p wave velocities mantle velocities vary laterally with values of 7 6 7 8 km s beneath the higher elevations of the blue ridge terrane and northwestern flank of the inner piedmont terranes and values of 8 3 8 5 km s farther south where elevation is lower the zone of low velocity mantle could represent a source of buoyancy that helps to support the higher elevations in addition to the root of thickened crust that also exists beneath the mountains

basement beneath the blue ridge and inner piedmont in northeastern georgia and the carolinas a preserved late proterozoic rifted continental margin seismic reflection magnetic and gravity data from the blue ridge and inner piedmont of georgia north carolina and south carolina indicate that southern appalachian basement contains two sets of steeply dipping normal faults that bound rotated and tilted blocks the predominant faults strike about n35 e subparallel to the axis of the orogen whereas the oblique set strikes about n10 w vertical offsets of as much as 1 3 km across individual n10 w striking faults have been observed on seismic profiles regionally the pattern is probably similar to normal faults in precambrian rocks exposed in the adiron dacks or along other rifted margins the initial age of faulting was late proterozoic 570 m y or older inferred from comparison of seismic reflectors in the eastern blue ridge and inner piedmont with stratigraphy along the great smoky thrust basement beneath the western portion of the inner piedmont in south carolina and northeastern georgia has been stable at least since the middle triassic and did not reactivate during the mesozoic breakup of pangea based on the absence of crosscutting relationships between basement faults and the brevard zone reflection basement structure related to rifting may partially explain the focal mechanisms of regional earthquakes the oblique fault set is consistent with well constrained north south striking subvertical nodal planes obtained for many basement earthquakes in the valley and ridge of eastern tennessee valley and ridge earthquakes in southwestern virginia are consistent with reactivation of the faults that strike parallel to the orogen we suggest that the basement structures survived phanerozoic orogeny because alleghanian continental collision was interpreted in the southern appalachians so that convergence between laurentia and gondwana stopped about the time their respective lithospheres came into contact

breakup of pangaea and plate kinematics of the central atlantic and atlas regions summary a new central pangaea fit type a is proposed for the late ladinian 230 ma together with a plate motions model for the subsequent phases of rifting continental breakup and initial spreading in the central atlantic this model is based on 1 a reinterpretation of the process of formation of the east coast magnetic anomaly along the eastern margin of north america and the corresponding magnetic anomalies at the conjugate margins of northwest africa and the moroccan meseta 2 an analysis of major rifting events in the central atlantic atlas and central mediterranean and 3 a crustal balancing of the stretched margins of north america moroccan meseta and northwest africa the process of fragmentation of central pangaea can be described by three major phases spanning the time interval from the late ladinian 230 ma to the tithonian 147 7 ma during the first phase from the late ladinian 230 ma to the latest rhaetian 200 ma rifting proceeded along the eastern margin of north america the northwest african margin and the high saharan and tunisian atlas determining the formation of a separate moroccan microplate at the interface between gondwana and laurasia during the second phase from the latest rhaetian 200 ma to the late pliensbachian 185 ma oceanic crust started forming between the east coast and blake spur magnetic anomalies whereas the morrocan meseta simply continued to rift away from north america during this time interval the atlas rift reached its maximum extent finally the third phase encompassing the time interval from the late pliensbachian 185 ma to chron m21 147 7 ma was triggered by the northward jump of the main plate boundary connecting the central atlantic with the tethys area therefore as soon as rifting in the atlas zone ceased plate motion started along complex fault systems between morocco and iberia whereas a rift drift transition occurred in the northern segment of the central atlantic between morocco and the conjugate margin of nova scotia the inversion of the atlas rift and the subsequent formation of the atlas mountain belt occurred during the oligocene early miocene time interval in the central atlantic this event was associated with higher spreading rates of the ridge segments north of the atlantis fz an estimate of 170 km of dextral offset of morocco relative to northwest africa in the central atlantic is required by an analysis of marine magnetic anomalies five plate tectonic reconstructions and a computer animation are proposed to illustrate the late triassic and jurassic process of breakup of pangaea in the central atlantic and atlas regions

modeling of contaminants mobility in underground domains with multiple free porous interfaces 1 existing simulation techniques for subsurface water quality management remain inadequate despite the phenomenal progress made in the computing capabilities in the past 2 decades one major lacunas found in mathematical models for groundwater hydrodynamics in combined free flow zones zones that are devoid of porous materials and porous domains e g soil water regions in the subsurface is that these models impose continuity of all flow transport parameters to describe the flow behavior at the intermediate surfaces between the two zones prescription of such interfacial conditions cannot always be physically justified and in general result in ill posed mathematical formulations the present paper aims to remove the above limitations of the mathematical models by imposing well posed mathematical formulations of mass and momentum transfer across the boundaries between free and porous zones underground for simulating subsurface flow the possibility of the existence of a multiple number of pervious boundaries in the domain across which water may flow is considered in this work as it represents the most realistic scenario for the subsurface transport processes the hydrodynamics of coupled fluid flow and behavior of contaminants transport are described combined effects of darcy and reynolds numbers on the subsurface transport of contaminants are discussed sensitivity of the flow variables to a coefficient of the permeability and porosity of interfacial boundary which is determined by its structural properties is also considered

computer modelling of the water resurge at a marine impact the lockne crater sweden abstract when a cosmic impact occurs at sea the resulting crater can form completely in the water mass or extend into the seafloor at intermediate to great water depths the collapse of the water cavity generates a forceful resurge of water along the seafloor towards the central part of the crater the erosive effects as well as certain conspicuous deposits from resurge flows are known from several craters this study uses numerical modelling to estimate the magnitude of the resurge in the case of the 455 myr old marine target lockne impact crater sweden the water depth at the lockne target site was at least 200 m possibly even as great as 1 km field evidence show that the resurge was strong enough to erode gullies hundreds of metres wide tens of metres deep and kilometres long with computer modelling we studied the behaviour of the flow to get a notion of its magnitude the calculations required simplification of the reality we used a fixed seafloor topography and pure water a rim in the water mass is expected but was neglected in the calculations the simplification likely led to underestimation of the magnitude of the resurge the effect of different target water depths was studied at 200 m target water depth about 1 2 10 11 m 3 of water were needed to fill the lockne crater including the water cavity this took about 2200 s it has been suggested that the main gully formation occurs when the resurge passes the inner rim of the crater that phase lasts for about 700 s with a 500 m target water depth these processes are 3 4 times faster the erosive force of the flow i e unit stream power is 1 9 10 5 wm 2 in the 200 m water depth model this is of the same magnitude as the lake missoula flood the greatest catastrophic flooding known on earth at 500 m target water the unit stream power is a magnitude greater

bouguer gravity in northeastern georgia a buried suture a surface suture and granites a bouguer gravity map of an area of northeastern georgia encompassing parts of the inner piedmont charlotte belt and carolina slate belt has been constructed from gravity stations spaced 2 km apart anomalies in the charlotte carolina slate belts are due to metamorphosed mafic rocks in the upper crust depth extent

structural analysis of the carolina inner piedmont terrane boundary implications for the age and kinematics of the central piedmont suture a terrane boundary that records paleozoic laurentia gondwana interactions new field mapping along the carolina inner piedmont terrane boundary in south carolina and eastern georgia reveals preaccretionary synaccretionary and postaccretionary faults the dextral strike slip lowndesville shear zone is adjacent to a 50 km long segment of the terrane boundary however the lowndesville shear zone is correlated eastward with the dextral strike slip beaver creek shear zone which is within the carolina terrane and predates 415 ma the lowndesville shear zone is overprinted by a dextral strike slip phyllonite zone named the deal creek shear zone the deal creek shear zone is correlated eastward with the gold hill silver hill shear zone which is also within the carolina terrane and records dextral strike slip motion between 400 and 325 ma the cross anchor and mulberry creek faults both truncate the lowndesville and the deal creek shear zones and form the terrane boundary the mulberry creek fault probably of triassic jurassic age juxtaposes the lowndesville shear zone adjacent to the carolina inner piedmont terrane boundary west of waterloo south carolina the cross anchor fault is the terrane boundary east of waterloo south carolina and forms the southeastern boundary of the whitmire reentrant crosscutting relationships indicate that the cross anchor fault is the oldest fault which juxtaposes the carolina and inner piedmont terranes in the study area these structural interpretations and available geochronological data indicate that the cross anchor fault is a 325 ma thrust fault and may be the central piedmont suture an early alleghanian suture resolves the problem of inserting the carolina terrane into the western iapetus ocean

variable late neogene exhumation of the central european alps low temperature thermochronology from the aar massif switzerland and the lepontine dome italy 1 several recent studies proposed an important increase in exhumation rate in the western european alps since circa 5 4 ma in order to assess potential spatial differences in exhumation histories we present new apatite fission track aft and apatite u th he ahe ages from the central aar massif guttannen area switzerland and the western lepontine dome formazza area italy internal u th zoning in apatites explains alpha ejection corrected ahe ages that are older than the corresponding aft ages in this study a qualitative interpretation of aft and ahe age elevation relationships suggests a two phase 9 7 and 5 3 ma exhumation scenario affecting the central alps with a stronger expression of the pliocene signal in the formazza area however a quantitative evaluation of exhumation scenarios using the 3 d heat equation solver pecube highlights the existence of several other likely scenarios casting doubt on the validity of a qualitative interpretation of the age elevation relationships in formazza scenarios suggested by quantitative modeling include continuous denudation at a rate of 750 m ma and a one step exhumation rate change from 300 to 1000 m ma at 5 ma in guttannen they include continuous denudation at a rate of 400 m ma with valley deepening and two periods of higher exhumation rate increasing from 300 to 700 m ma repeatedly at 9 7 and at 5 3 ma contingent upon further flexural isostatic modeling the magnitude of exhumation recorded in the axial region of the alps since circa 5 ma does not appear sufficient to solely explain the denudation recorded in the north alpine foreland basin

reprocessing and enhanced interpretation of the initial cocorp southern appalachians traverse abstract reprocessing of the 1978 1980 cocorp southern appalachian seismic reflection data has produced improved images of structures related to the emplacement of the blue ridge inner piedmont allochthon the results enhance and extend the interpretation presented previously that the blue ridge and inner piedmont are allochthonous above a shallow and shallow dipping detachment that can be followed from outcrop at the blue ridge valley and ridge transition to at least beneath the carolina terrane the continuity of reflections in the new images supports the interpretation that the southern appalachian detachment is not rooted on the east side of the inner piedmont but rather projects as a low angle detachment or zone of decoupling to beneath the coastal plain an implication of this geometry is that terranes such as the carolina terrane between autochthonous north america and the alleghanian suture beneath the coastal plain are detached thin flakes