new york alabama lineament a buried right slip fault bordering the appalachians and mid continent north america the new york alabama ny al lineament recognized in 1978 is a magnetic anomaly that delineates a fundamental though historically enigmatic crustal boundary in eastern north america that is deeply buried beneath the appalachian basin data not in the original aeromagnetic data set particularly the lack of any information available at the time to constrain the southern continuation of the anomaly southwest of tennessee left the source of the lineament open to conjecture we use modern digital aeromagnetic maps to fill in these data gaps and for the first time constrain the southern termination of the ny al lineament our analysis indicates that the lineament reflects a crustal scale right lateral strike slip fault that has displaced anomalies attributed to grenville orogenesis by 220 km palinspastic restoration of this displacement rearranges the trace of the grenville belt in southern rodinia and implies only passive influence on later formed appalachian structures the precise timing of dextral movement on the ny al structure is not resolvable from the existing data set but it must have occurred during one of or combinations of the following events 1 a late postcontractional post ottawan stage of the grenville orogeny 2 late neoproterozoic to cambrian rifting of laurentia or 3 right slip reactivation during the late neoproterozoic cambrian rifting of laurentia or during appalachian movements our palinspastic reconstruction also implies that the host rocks for modern earthquakes in the eastern tennessee seismic zone are metasedimentary gneisses and it provides an explanation for the spatial location and size of the seismic zone

deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

foraminifera from the irish sea glacigenic deposits at aberdaron western lleyn north wales palaeoenvironmental implications in a sequence of glacigenic sediments at aberdaron foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment all the diamict samples yielded remarkably uniform assemblages with similar numbers of benthic specimens and benthic species per unit weight of sediment similar planktic benthic ratios and similar ratios of clearly allochthonous to possibly autochthonous elements this is precisely as predicted by the terrestrial model of sedimentation where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the irish sea basin the results lend no support to a glacial marine model since no faunal responses to increasingly distal sedimentary environments are observed however the fauna is dominated by the foraminifera elphidium excavatum terquem forma clavata cushman which is commonly assumed to indicate glacial marine conditions the modern distribution of similar assemblages suggests that it is just as likely to represent the cold reduced salinity conditions that would have prevailed in the northern irish sea basin for much of the quaternary

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

the giles county virginia seismic zone a well defined seismic zone recently detected in virginia has an orientation that is not related to the surrounding geologic structures the orientation of the zone appears to be related to features below the appalachian overthrust belt a damaging earthquake that is important in evaluating seismic hazard in the southeastern united states may have occurred in the zone in 1897

lake charles louisiana earthquake of 16 october 1983 on 16 october 1983 at 19 40 utc a magnitude 3 8 earthquake occurred near lake charles in southwestern louisiana the earthquake was felt over an area of 2600 km2 and had a maximum modified mercalli intensity of v this was the first significant louisiana gulf coast earthquake to be recorded and located by nearby microseismic networks one possible foreshock and three aftershocks also were recorded and located using a velocity model developed for this study the focal mechanism of the earthquake was determined based on p wave first motions from 22 local and regional stations the solution indicates a predominantly east west trending southeast dipping normal fault with a small strike slip component the depth of this event 14 km provides the first significant evidence that normal faulting within the crystalline basement may control shallower growth faults along the gulf coast

mining related and tectonic seismicity in the east mountain area wasatch plateau utah u s a as part of a larger multi institutional seismic monitoring experiment during june august 1984 in the eastern wasatch plateau utah data from a subarray of 20 portable seismographs were used to investigate seismicity in the east mountain area an area of active underground coal mining and intense microseismicity eight stations of the subarray were concentrated on top of east mountain about 600 m above mine level at an average spacing of 2 to 3 km the primary objective was the accurate resolution of hypocenters and focal mechanisms for seismic events originating at submine levels data from high resolution seismic reflection profiles and drill hole sonic logs yielded a detailed velocity model this model features a strong velocity gradient in the uppermost 1 km which has a significant effect on takeoff angles for first arriving p waves from shallow seismic events two hundred epicenters located with a precision of 500 m cluster within an area about 5 km in diameter and show an evident spatial association with four sites of longwall mining during the study period a special set of foci rigorously tested for focal depth reliability indicates submine seismicity predominating within 500 m of mine level and extending at least to 1 km and perhaps to 2 km below mine level continuous monitoring for a 61 day period june 15 august 15 bracketed a 16 day mining shutdown july 7 22 during which significant seismicity comparable to that observed before the shutdown was observed ten focal mechanisms for seismic events originating at or down to 2 km below mine level nearly all imply reverse faulting consistent with previous results and the inferred tectonic stress field enigmatic events recorded with all dilatational first motions can be fit with double couple normal faulting solutions if they in fact occur above mine level perhaps reflecting overburden subsidence if these events are constrained to occur at mine level their first motion distributions are incompatible with a double couple source mechanism

the 9 december 2003 central virginia earthquake sequence a compound earthquake in the central virginia seismic zone the 9 december 2003 central virginia earthquake sequence was a compound earthquake consisting of two nearly identical events occurring about 12 sec apart the second event is separated by about 300 m from the first event along the azimuth of approximately 195 10 the source mechanism determined from regional waveform inversion indicates predominantly thrust faulting at a depth of approximately 10 2 km the sequence with two events attained the combined seismic moment of m 0 2 64 1 01 10 15 n m m w 4 3 the focal mechanism indicates a subhorizontal p axis trending 301 and plunging 19 a regional stress model for the central virginia seismic zone cvsz derived from the 9 december 2003 events and 11 previous earthquakes indicates a thrust faulting stress regime with 1 trending 133 12 and plunging 14 3 the least principal stress axis 3 trends 25 10 and plunges 52 3 the 1 axis is rotated approximately 68 clockwise relative to the average maximum horizontal compressional stress s hmax direction for eastern north america approximately 65 the 9 december 2003 earthquake sequence occurred among the systems of paleozoic and mesozoic faults above the southern appalachian decollement which is at depths from 12 to 19 km in the piedmont geologic province of central virginia

crustal velocity structure associated with the eastern tennessee seismic zone vp and vs images based upon local earthquake tomography we present three dimensional p and s wave velocity models for the active eastern tennessee seismic zone etsz using arrival time data from more than 1000 local earthquakes a nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters we image several velocity anomalies that persist through most of the inversion volume some anomalies support the presence of known features such as an ancient rift zone in northern tennessee other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies we image a narrow ne sw trending steeply dipping zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent new york alabama magnetic lineament the low velocity zone may have an apparent dip to the se at depths exceeding 15 km the low velocity zone is interpreted as a major basement fault juxtaposing granite rhyolite basement to the nw from grenville southern appalachian basement to the se relocated hypocenters align in near vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike slip fault we suggest that the etsz represents reactivation of an ancient shear zone established during formation of the super continent rodinia

seismotectonics of the southern appalachians abstract the southern appalachians of eastern tennessee and western north carolina is a region for which high quality instrumental seismic data have been very limited in this paper we report more than 100 new or relocated hypocenters obtained from the initial 2 1 2 yr of operation of the southern appalachian regional seismic network sarsn a 16 station four state telemetered network of short period vertical instruments these data provide a first order snapshot of southern appalachian seismicity that confirms some previous observations and adds new results for the region the most important new observations are well constrained focal depths and focal mechanisms for southern appalachian earthquakes the level of activity exceeds expectations and concentrates more heavily in the valley and ridge province of eastern tennessee as opposed to the blue ridge or inner piedmont than is evident in historical listings the large majority of these events lie between the new york alabama lineament and the clingman ocoee lineaments magnetic anomalies produced by deep seated basement structures an analysis of the uniqueness and stability of hypocentral depth yields reliable depths for 58 earthquakes and demonstrates that most southern appalachian seismic activity occurs beneath the decollement thus lending quantitative support to the argument that appalachian seismicity is unrelated to surficial geological or tectonic features several new focal mechanisms of a higher quality than previously available indicate that the basement of the valley and ridge is under ne sw compression and the principal mode of faulting is right lateral strike slip on nearly north south faults in both depth and type of faulting the seismogenic model we propose for the southern appalachians closely emulates the giles county zone to the north of our study area

magnetic properties of variably oxidized pillow basalt in our study of changes in magnetic properties during low temperature oxidation of oceanic pillows we were able to essentially eliminate variations in grain size which plagued many previous studies this was accomplished by keeping the cores parallel to the outer glassy margin of the pillow while drilling the variably oxidized portions of the basalt curie temperature tc measurements indicated a large range in the degree of low temperature oxidation although most were in the early stages of maghemitization tc 300 c in samples with hysteresis parameters showing pseudo single domain behavior the natural remanent magnetization jnrm and susceptibility both decreased substantially with low temperature oxidation thus the koenigsberger ratio jnrm jinduced did not change the reduction in jnrm was mirrored by comparable decreases in saturation magnetization and saturation remanence low temperature oxidation also increased the bulk coercivity and the coercivity of remanence in the oxidized basalt relative to the less oxidized these later results are consistent with the theory that low temperature oxidation generally stabilizes the remanent magnetization of seafloor pillow basalts the increase in coercivity with oxidation in these pillow basalts contrasts will synthetic samples which show an overall decrease the behavior of natural samples reflects processes which occur during low temperature oxidation that do not normally occur in synthetic samples specifically the loss of iron from the grain and perhaps grain cracking

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

fault plane solutions and relocations of recent earthquakes in middleton place summerville seismic zone near charleston south carolina the middleton place summerville seismic zone mpssz located about 20 km northwest of charleston is the most active seismic zone in south carolina between 1980 and 1991 58 events with md 0 8 to 3 3 were recorded in mpssz they lie in a diffuse area of 11 km by 14 km of which over two thirds are located in a narrow 5 km by 6 km zone the hypocentral depths range from 2 to 11 km with over 90 deeper than 4 km single fault plane solutions were obtained for 35 events based on the focal mechanisms the earthquakes were grouped into five subsets the mean p axis of all fault plane solutions is oriented n63 e in general agreement with the direction of shmax obtained from in situ stress measurements of the 35 events 18 are associated with reverse faulting on nw se striking and sw dipping fault planes these events were inferred to be associated with the ashley river fault zone which is not a planar feature but is composed of short segments of varying strikes n20 w to n70 w and dips 40 to 70 sw eleven events were associated with strike slip motion on nne ssw striking vertical faults and with thrust faulting on n s oriented faults dipping to the west respectively these two sets are identified as being parts of the woodstock fault zone the concentrated zone of seismicity included events associated with both the arf and wf zones suggesting that it is at the intersection of these two fault zones

shallow seismicity of arc continent collision near lae papua new guinea abstract in northeastern new guinea the narrow ramu markham valley rmv separates island arc rocks to the north from those of continental origin to the south and appears to be the western onland extension of the new britain trench to explore the tectonic processes at the leading edge of the island arc during collision we operated a portable seismic network for six weeks near the city of lae at the eastern end of the rmv we observed a narrow near vertical belt of seismicity between 10 and 30 km depth that we call the lae seismic zone lsz starting at the rmv in the southwest and trending northeasterly cutting across surface geologic structure the truncation of the lsz along a steep plane by the ramu markham fault zone rmfz and earthquake first motions suggest that the earthquakes occur in the hanging wall of a steep n dipping fault that crops out at the rmfz we also consider that the lsz is within the lower plate of a gently dipping thrust below 20 km depth the microearthquake zone is truncated by a gently ne dipping plane coinciding in depth and dip with nodal planes of recent large mb 5 6 and 6 0 thrust earthquakes we suggest that the huon peninsula is being emplaced onto the australian plate along a gently 25 dipping thrust fault that is 20 km deep beneath lae the rmfz may be a steeply dipping thrust fault that connects with this gently n dipping thrust but accommodates little convergence at present the lsz trends nearly perpendicular to an anticlinal range which appears to be sheared in a left lateral sense p wave first motions for earthquakes in the lsz with steep 70 to 90 dip nodal planes that strike parallel to the lsz suggest a component of south side up displacement also hence the crustal block south of the lsz may be rising relative to the huon peninsula and the rapid quaternary uplift rates estimated for the lae coastal region may be higher than the uplift rate of the huon peninsula as a whole we suggest that the lsz reveals a tear of small offset in the huon terrane but may be similar to a structure that produced a magnitude 7 earthquake near madang in 1970

interpreting iceberg deposits in the deep sea in their report millennial scale instability of the antarctic ice sheet during the last glaciation 9 june p 1815 s l kanfoush et al suggest that increases in ice rafted detritus ird observed in deep sea sediment records from the south atlantic ocean identify times of instability of

crustal and upper mantle velocity structure in the vicinity of the eastern tennessee seismic zone based upon radial p wave transfer functions teleseismic transfer function analysis is used to investigate crust and upper mantle velocity structure in the vicinity of the active eastern tennessee seismic zone etsz the etsz is associated with the new york alabama ny al magnetic lineament a prominent aeromagnetic anomaly indicative of grenville age basement structure radial component p wave transfer functions for 10 short period stations operated by the center for earthquake research and information are inverted for velocity structure velocity profiles are also determined for three broadband stations by converting the instrument response to that of an s 13 short period seismometer distinct differences in the velocity profiles are found for stations located on either side of the ny al magnetic lineament velocities west of the lineament are lower than velocities to the east of the lineament in the upper 10 km and in the depth range 30 to 50 km a gradational moho boundary is found beneath several stations located in the valley and ridge province a moho boundary is absent at four valley and ridge stations located east of the magnetic lineament and south of 35 5 n

group velocity tomography of the upper crust in the eastern tennessee seismic zone from ambient noise data abstract the eastern tennessee seismic zone etsz is the second most seismically active area in the central and eastern united states after the new madrid seismic zone but the relatively weak seismicity and the absence of correlation between the seismicity distribution and the surface geology make its seismogenic potential controversial in this work we investigate the structure of the upper crust in the etsz by means of group velocity tomography maps from seismic noise data results show that the seismic activity is associated with a relatively low velocity anomaly mainly located in one or more basement blocks these blocks bounded to the nw by the ny al lineament and to the se by the clingman lineaments are buried beneath low velocity strata consistent with the presence of a relatively thick sedimentary cover the imaged low velocity anomaly migrates towards the se at increasing periods suggesting a possible se dipping weak structure where most of the seismic activity takes place the correlation between the ny al magnetic signature and the position of the seismic velocity anomalies supports the interpretation of the low velocity zone as a major basement fault projected to the surface as the ny al magnetic lineaments the fault juxtaposes granite rhyolite basement to the nw with grenville southern appalachian basement to the se

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

focal mechanism analyses for eastern tennessee earthquakes 1981 1983 to investigate the neotectonic processes in the southern appalachians 10 single event focal mechanisms and 6 composite focal mechanisms were determined from 37 events that occurred in eastern tennessee between september 1981 and july 1983 both p wave polarities and sv p z amplitude ratios are input to a computer program that systematically searches the focal sphere for solutions acceptable within preset error limits hypocenter locations azimuth and departure angles are taken from locations obtained by the tennessee earthquake information center with a four layer velocity model a gradient velocity model developed to improve focal depth estimates and to provide continuously varying rather than discrete departure angles is used to relocate the seismic events for which single event focal mechanisms and composite focal mechanisms solutions are obtained the two different velocity models each produced focal mechanisms with similar nodal plane and p axis orientations indicating stable and reliable mechanism solutions the differences between average strike dip and rake angles of the two data sets range from 2 to 11 both single event focal mechanisms and composite focal mechanisms solutions exhibit predominantly strike slip motion along nearly vertical northerly right lateral or easterly left lateral oriented nodal planes standard deviations about the average strike dip and rake angles are generally less than 20 p axis trends average about n50 e with a nearly horizontal average plunge and both trend and plunge estimates have standard deviations of 25 or less

an analysis of earthquake focal depths in the southeastern u s seven years 1977 84 of seismic network monitoring in the southeastern u s have resulted in a catalog of 255 earthquakes 0 m 4 2 with erz 5 km focal depths from the valley ridge and blue ridge provinces mean depth 12 km were combined for analysis as were those for the piedmont and coastal plain provinces mean depth 8 km the mean focal depths between these two regions are shown to be statistically different the 90 depths of earthquakes are also very different between the regions implying a difference in the depth to the brittle ductile transition first order models of crustal rheology based on estimates of composition temperature and strain rate indicate that the observed differences in earthquake focal depths may reflect differences in strain rate and or composition

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

joint hypocenter velocity inversion for the eastern tennessee seismic zone a joint hypocenter velocity inversion for the eastern tennessee seismic zone etsz has resolved velocity features in basement rock below detached appalachian thrust sheets p and s wave arrival times from 492 earthquakes have been inverted for one 1 d and three dimensional 3 d velocity models to midcrustal depths the 3 d p and s wave velocity solutions are computed independly and are very similar in relation to the 1 d model velocity anomalies range from 8 to 16 in the first layer upper 5 km and between 7 in deeper layers prominent velocity anomalies parallel the seismic zone and are consistent from layer to layer the most persistent anomaly is a low velocity region that borders the seismic zone to the northwest and is flanked on either side by regions of anomalously high velocity the new york alabama ny al magnetic lineament coincides with or lies close to the southeast boundary of the prominent velocity low in both the p and s wave velocity images the spatial coincidence between velocity gravity and magnetic gradients suggests that major discontinuities are present in the basement relocation in the 3 d velocity model reduced the number of very deep earthquakes below 20 km and further accentuated differences in seismogenic properties on either side of the ny al lineament after relocation most earthquakes occur in a vertically bounded region roughly 30 km wide extending from 4 to 22 km in depth most earthquakes occur in regions characterized by either average velocity or small velocity anomalies

the 1984 southern yellow sea earthquake of eastern china source properties and seismotectonic implications for a stable continental area on 21 may 1984 a strong shock ms 6 3 mb 5 7 occurred in the southern yellow sea which shook the densely populated coastal area of eastern china about 1 min before the main shock a foreshock of mb 5 4 occurred because of interference from the foreshock no reliable p wave first motions or focal mechanisms have been obtained for the main shock from local seismic data in this paper long period teleseismic data have been used to investigate the source mechanism fault plane solutions determined from first motions as well as p and sh waveforms show a predominant strike slip motion with a small dip slip component on a steeply dipping plane the tectonic environment of this event supports the observation that margins of former rifts tend to be sites of midplate seismic source regions the yellow sea developed in a cratonic environment due to early cenozoic rifting the major graben faults strike nne ssw to ne sw and are intersected by second order faults trending wnw ese aftershock distribution suggests that the fault which generated the main shock probably strikes wnw ese the mechanism determined in this paper strikes 120 dips 88 and slips 28 this solution suggests that the earthquake ruptured along a secondary fault near the intersection of a more major nne ssw trending fault the epicentral area is subject to to an ene wsw compression and a nnw sse extension the seismic moment and focal depth are determined to be 1 09 1025 dyne cm and 12 4 km respectively relative hypocentral locations indicate that the focal depth of the foreshock is similar to that of the main shock and the hypocenter of the foreshock is located very close to the wnw ese striking nodal plane of the main shock mechanism and is about 20 km away from the main shock hypocenter source properties of the southern yellow sea earthquake have been compared with those of three major earthquakes of north china the stress drop of the yellow sea earthquake is determined to be about 42 bars this value is much lower than the stress drops computed for the 1966 hsingtai and the 1975 haicheng earthquakes of north china the southern yellow sea is characterized by short recurrence intervals while the hsingtai and haicheng areas have very long recurrence intervals the short recurrence intervals and low stress drop may reflect a lower material strength at the source region in the yellow sea

intraplate stresses and seismicity the role of topography and density heterogeneities abstract the stress induced by the topography and by density heterogeneities in the lithosphere has been computed for two different tectonic regions of the north american plate the lithosphere was assumed to consist of a two dimensional layered elastic slab over an inviscid fluid the calculations show that these stresses are locally comparable in magnitude to the regional tectonic stress 20 50 mpa two areas have been analyzed in greater detail the southeastern united states and the rio grande rift the stress in the southeastern united states is computed along a cross section perpendicular to the strike of the appalachian mountains the computed stress appears largest beneath the blue ridge and valley and ridge provinces where the appalachian seismicity is located the stress in the western united states is computed along a cross section perpendicular to the rio grande rift large stress is shown beneath the rift and the adjacent regions the stress induced by surface and internal loading is extensional in the rio grande rift and compressional in the colorado plateau and in the great plains

ice flow stages and glacial bedforms in north central ireland a record of rapid environmental change during the last glacial termination satellite imagery is a useful tool to assess large scale 10 3 km 2 geological patterns satellite imagery of north central ireland shows cross cut and overprinted subglacial bedform patterns bedform lineations supported by sedimentary evidence are used to reconstruct four ice flow stages named a d during the termination of the last devensian glaciation 22 000 13 000 radiocarbon 14 c years bp flow stage a relates to southwesterly flow of scottish ice across eastern ireland flow stage b during the last glacial maximum c 25 000 22 000 14 c years bp records southeasterly ice flow from dispersal centres in northern parts of ireland transverse subglacial ridges rogen moraines formed during stage b are the largest area of this ridge type in western europe flow stage c records erosional headcutting in the rogen moraine field and sediment streamlining drumlinization by ice streams drawn into the irish sea basin this flow stage is constrained by ams radiocarbon dates from marine microfaunas to around 14 500 14 c years bp flow stage d records drumlinization from an inland centre in the lough neagh basin overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity including millennial scale changes in amphi north atlantic climate field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems

seismodynamics of sweden deduced from earthquake focal mechanisms summary focal mechanisms from 18 major swedish earthquakes ml upp 3 reveal that 1 several of the studied earthquakes have focal mechanisms with significant extensional stresses which fit well to the idea of postglacial rebound as an important stress generator 2 in areas like south western sweden the north westerly trending compressional axes indicate that ridge push from the north atlantic ridge is also a considerable stress contributor 3 some local tectonic features like the skalderviken depression in kattegat are momentous for seismotectonic interpretations in addition to first p polarities full waveform modelling for frequencies up to 3 hz and epicentral distances up to 225 km provides rather robust focal mechanism determinations focal depths of seven events ranging from 11 to 37 km are well resolved within a few km by waveform modelling

short period surface wave dispersion and shallow crustal structure of central and eastern tennessee group velocity dispersion of explosion generated seismic surface waves with periods ranging from 0 2 to 1 5 sec is used to investigate shallow crustal structure of eastern and central tennessee several modes of both rayleigh and love waves can be identified and separated on the seismograms of seven sarsn regional network stations by zero phase digital filtering dispersion data for sinusoidal wave motion were based on digitized zero crossing times by forward modeling we find that a wave guide of at least two layers over a half space can adequately represent our particular multi mode narrow band observations in a layered section about 3 km thick lower velocities characterize outcropping clastic rocks of the cumberland plateau and higher velocities correspond to shallow carbonate rocks of the nashville dome half space shear velocities of about 3 9 km sec appear to represent lower paleozoic carbonate lithology deeper than 2 to 4 km on most of the observed paths our best data interpreted jointly with earlier data of oliver and ewing 1958 and of chen et al 1989 have a composite period range of 0 2 to 40 sec but they represent different appalachian paths group velocities over this broad spectrum are satisfied by a complex model with two low velocity layers the uniqueness of this model cannot be demonstrated but it represents important hypotheses concerning regional geologic features that can be tested more rigorously by improved surface wave dispersion data

landform modification by palaeo ice streams in east central ireland in eastern ireland subglacial bedforms including drumlins and rogen moraines were modified by headward erosion along two ice streams which had over lapping flow tracks the ice streams which hadtidewater termini are dated by geochrono metric and morphostratigraphic methods to 5 15 0 14 ckyr bp castleblaney ice stream and 13 8 14 ckyr bp armagh ice stream bedforms along ice stream tracks show a morphological continuum which reflects a down ice increase in the degree of modification by ice stream activity i e resulting in unmodified remoulded overprinted cross cut streamlined bedforms the down ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment transport mechanisms bedform and sedi mentary evidence suggest that discrete subglacial meltwater channels which developed up ice changed in a down ice direction to unchannelized flows which deepened towards the ice margin meltwater release from subglacial cavities and produced by strain heating at sheared ice stream margins probably helped support ice stream flow which ended as the volume of subglacial meltwater discharge decreased dated millennial scale cycles of ice activity may be related to instability at tidewater margins followed by complex thermal and hydraulic responses within the ice mass

intraplate seismicity and stress in the southeastern united states abstract the stress induced by topography and by density heterogeneities in the lithosphere has been computed for two seismic regions in the southeastern united states the southern appalachian mountains and the south carolina coastal plain the lithosphere was assumed to be a three dimensional layered elastic slab overlying an inviscid fluid the calculations indicate that the local stress is of the same magnitude as the tectonic stress tens of mpa but contradictory conclusions are suggested by the comparison of stress differences and principal directions with earthquake locations and focal mechanisms in the southern appalachians the seismicity correlates well with the stress maximum and focal mechanisms agree with the calculations where regional stress is combined with locally induced stress in south carolina a combination of regional and local stress can explain the orientation of focal mechanisms but stress does not concentrate in the region of charleston and thus other factors must play a role in the charleston seismicity

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

ams c 14 dating of deglacial events in the irish sea basin and other sectors of the british irish ice sheet sedimentary sequences deposited by the decaying marine margin of the british irish ice sheet biis record isostatic depression and successive ice sheet retreat towards centres of ice dispersion radiocarbon dating by accelerator mass spectrometry ams of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation enabling us to evaluate the dynamics of the bus and its response to north atlantic climate change here we use our radiocarbon dated stratigraphy to define six major glacial and sea level events since the last glacial maximum 1 initial deglaciation may have occurred 18 3 kyr c 14 bp along the northwestern irish coast in agreement with a deglacial age of similar to 22 cl 36 kyr bp for southwestern ireland ice retreated to inland centres and areas of transverse moraine began to form across the north irish lowlands 2 channels cut into glaciomarine deglacial sediments along the western irish sea coast are graded to below present sea level identifying a fall of relative sea level rsl in response to isostatic emergence of the coast 3 marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10 15 m similar to 16 7 c 14 kyr bp that flooded the irish sea coast and may have triggered deglaciation of a marine based margin in donegal bay 4 intertidal boulder pavements in dundalk bay indicate that rsl similar to 15 0 c 14 kyr bp was similar to present 5 a major readvance of all sectors of the biis occurred between 14 and 15 kyr 14 c bp which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins this event the killard point stadial indicates that the bus participated in heinrich event 1 6 subsequent deposition of marine muds on drumlins 12 7 c 14 kyr bp indicates isostatic depression and attendant high rsl resulting from the killard point readvance these events identify a dynamic biis during the last deglaciation as well as significant changes in rsl that reflect a combination of isostatic loading and eustatic changes in global sea level c 2005 elsevier ltd all rights reserved

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

the upper crust of the eastern tennessee seismic zone insights from potential fields inversion abstract the study investigates the crustal structure of the eastern tennessee seismic zone etsz by means of potential field inversion through the located euler deconvolution method inversion of magnetic field data shows that the top of the magnetic basement ranges between 6 and 12 km depth in the valley and ridge physiographic province while it is shallower

intertidal forms produced by floating ice in vestfirdir iceland forms produced by the action of intertidal ice in the fjord of kaldalon vestfirdir iceland are described and interpreted in terms of their morphogenetic environment isolated boulders resting on top of undisturbed fine sediments are interpreted as dropstones from floating intertidal ice following rockfall events boulder pavements and ridges which occur in the upper intertidal zone are related to the onshore movement of ice packing and bulldozing boulders together the occurrence of such ice formed features in kaldalon is attributed to their preservation within a low energy environment in spite of a limited ice climate the paucity of such forms preserved in the sedimentary record suggests that opportunities for burial and preservation are limited except where local infill is rapid

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

a local weakening of the brittle ductile transition can explain some intraplate seismic zones abstract a decrease in the strength of a localized area of the lower crust would decrease the depth to the brittle ductile transition and concentrate stress in the stronger elastic crust around and above the zone of decreased strength deformation within the zone of weakened lower crust would occur through viscous or dislocation creep in response to regional plate stress as well as by elastic failure in small earthquakes two dimensional finite element models of zones of weakness subjected to a regional plate stress predict stress amplification of 10 100 surrounding the local decrease in strength a finite element model for an irregular zone of weakness in the lower crust can generate stress directions and relative magnitudes that satisfy the focal mechanisms and seismicity of southeastern tennessee an analysis of the displacements and stresses in the central area of decreased crustal strength suggests that strike slip faulting should dominate above this zone the strike slip faulting should exhibit a strong thrust component the compression and extension of the crust surrounding the weakened zone at the level of the brittle ductile transition predicts that the dominant strike slip faulting should exhibit components of normal faulting on the edges of the weak zone which are near a line through the weak zone parallel to the regional stress and reverse faulting on the edges which are near a line transverse to the regional stress the seismicity of southeastern tennessee is diffused over a narrow elliptical zone trending ne the greatest concentration of activity is near the center the central zone is characterized by deep focus strike slip events with predominantly n or e striking nodal planes these events are responding directly to compression in the direction of the regional compressive stress and extension perpendicular to the regional compressive stress within the weak zone the area surrounding the central zone is characterized by focal mechanisms with larger components of reverse or normal fault movements events with normal components are dominant on the edges in line with the regional stress as predicted by the stress model for a weak central zone under stress the agreement between observed earthquake focal mechanisms in southeastern tennessee and models of crustal stress surrounding a zone of weakness suggests that these events may be caused by a zone of weakness in the lower crust

sea level change in the irish sea since the last glacial maximum constraints from isostatic modelling models of glacio hydroisostatic sea level change have been published for the british isles that are broadly consistent with the observational evidence as well as with glaciological constraints it has been argued however that the models fail to represent sea level change along the irish sea margins and in southern ireland for the post deglaciation period the argument rests on the interpretation of the depositional environment of the elevated irish sea drift on both sides of the irish sea whether this is terrestrial or glaciomarine the isostatic models for the british isles are consistent with the former interpretation in that sea levels on either side of the irish sea south of about the isle of man are not predicted to have risen above present sea level at any time since the deglaciation of the irish sea this implies that ice over both the irish sea and ireland was relatively thin ca 600 700 m over ireland if the glaciomarine interpretation of the elevated irish sea drift is correct then the maximum ice thickness over central and southern ireland would have to reach 2000 m exceeding that over scotland furthermore for the resulting sea level change to be consistent with the holocene evidence this thick ice sheet could not have extended to the eastern side of the irish sea nor could it have been very thick at its northern and western limits if such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the irish sea drift as terrestrial in origin copyright 2001 john wiley sons ltd

a late pleistocene intertidal boulder pavement from an isostatically emergent coast dundalk bay eastern ireland late pleistocene sequences around dundalk bay eastern ireland record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka sp a coastal exposure at cooley point consists of four major facies deposited outside this ice limit 1 a basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland it contains a well preserved arctic microfauna dominated by the foram elphidium clavatum and the ostracod roundstonia globulifera 2 a flat to undulating boulder facies pavement mostly one clast thick is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces pavement attributes are a result of intertidal activity in a cold climate the boulder source is due to rafting by ice flees from glacigenic debris deposited during an ice advance 3 laminated sand facies drape the pavement and are a result of variable current activity 4 the overlying gravel facies is separated from the sand facies by a marine erosion surface the gravel facies is subaqueous channelized and is overlain by late glacial raised beach ridges locally the gravels have been deformed by ice pressure from partially floating ice flees facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle the boulder pavement and deformed gravel facies suggest that ice flees and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought though they have a low preservation potential extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition this event may be related to a major meltwater event within the irish sea basin