a teleseismic analysis of the new brunswick earthquake of january 9 1982 the analysis of the new brunswick earthquake of january 9 1982 has important implications for the evaluation of seismic hazards in eastern north america although moderate in size mb 5 7 it was well recorded teleseismically source characteristics of this earthquake have been determined from analysis of data that were digitally recorded by the global digital seismograph network from broadband displacement and velocity records of p waves we have obtained a dynamic description of the rupture process as well as conventional static properties of the source the depth of the hypocenter is estimated to be 9 km from depth phases the focal mechanism determined from the broadband data corresponds to predominantly thrust faulting from the variation in the waveforms the direction of slip is inferred to be updip on a west dipping nne striking fault plane the steep dip of the inferred fault plane suggests that the earthquake occurred on a preexisting fault that was at one time a normal fault from an inversion of bodywave pulse durations the estimated rupture length is 5 5 km average properties of the rupture process were examined by a moment tensor analysis of long period p and sh body waves the long period moment of this earthquake was 5 3 1024 dyne cm the static and dynamic stress drops are 41 and 65 bars respectively similar to those of many earthquakes with similar moment in regions that are more seismically active the joint epicenter determination algorithm was used to locate relative to the mainshock the three teleseismically recorded aftershocks that occurred through march 31 1982 the relocated hypocenters of the aftershocks are significantly different from each other and from that of the mainshock they provide additional support for the source dimensions inferred from the waveform analysis

regional warming pliocene 3 ma paleoclimate of europe and the mediterranean the paleoclimate of the middle pliocene ca 3 ma was generally warmer than present particularly at middle to high latitudes it has been suggested that this period may represent an analogue for future climate change mechanisms that have been proposed to account for this warming are enhanced thermohaline circulation and or greater concentrations of co 2 in the atmosphere we present new climate model simulations supported by geological data that suggest that in the european and mediterranean region the climate was warmer by 5 c wetter by 400 1000 mm yr and less seasonal than present modeling results suggest that an intensification of the icelandic low pressure system and the azores high pressure system occurred during the middle pliocene as a direct result of higher annual sea surface temperatures and reduced ice cover in the northern hemisphere this change increased the surface pressure gradient over the region and strengthened annual westerly wind velocity by 4 m s 1 associated increases in wind stress by 20 n m 2 over the north atlantic ocean may have enhanced the flow of surface currents such as the gulf stream and north atlantic current which in turn would have sustained the higher sea surface temperatures these changes to the regional climate system would have driven greater atmospheric and oceanic transport of heat from equatorial regions to the north atlantic ocean particularly during winter such conditions are proposed as a likely cause of the warming indicated for europe and the mediterranean ca 3 ma

broad band deconvolution of gdsn data summary advances in the theory of wave propagation and source mechanism have coincided with the recent deployment of a global network of digitally recording seismographs the gdsn global digital seismograph network we demonstrate that broad band records of body wave ground displacement and velocity with spectral information from several hertz to tens of seconds can be obtained by the simultaneous deconvolution of the long and short period components of the gdsn seismographs frequency dependent effects in body waves that may arise from source complexity or from propagation through the earth are much more apparent and measurable in the broad band records than in the original seismograms

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

enhanced airborne dispersal of silicic tephras during the onset of northern hemisphere glaciations from 6 to 0 ma records of explosive volcanism and climate change in the subpolar north atlantic a 6 m y long composite marine record of explosive silicic volcanism from five ocean drilling program sites in the subpolar north atlantic was compared with several marine records of global and local paleoclimate proxies benthic d 18 o and ice rafted debris records coarsening and high frequency of occurrence of icelandic tephras were recorded in 3 6 3 ma sediments suggesting that these tephras were dispersed farther from the source by enhanced westerly winds over the subpolar north atlantic the 40 ar 39 ar ages were determined by laser probe on k feldspar and biotite phenocrysts of tephras that were erupted from the jan mayen volcanic system compared to the tuned paleomagnetic age model the 40 ar 39 ar dating 0 618 6 0 007 ma to 4 90 6 0 05 ma yields a new age model that postdates by 155 k y the inception of ice rafting on the iceland plateau during the cold marine isotope stage m2 i e 3 3 3 14 ma

seismic imaging of major tectonic features in the crust of phanerozoic eastern australia abstract crustal architecture can be recognised from seismic fabric characteristics and velocity information across phanerozoic eastern australia three major crustal sub divisions are identified from data in southern queensland they occur under west to east the nebine ridge taroom trough and new england fold belt with each crustal sub division having its own internal architecture but separated by major bounding structures geosutures these features are assessed against evolutionary models for the region the significant conclusions are as follows 1 1 the nebine ridge forms the southeastern part of the thomson fold belt but has a crustal architecture distinctly different from that under the central part of the fold belt tentatively supporting an evolutionary model involving fragmentation and eastward stretching and thinning of a precambrian australian craton the ridge crust has possibly been considerably altered by carboniferous plutonism and compressional events 2 2 between the nebine ridge and the crust under the taroom trough of the bowen basin there is a major low angle 5 10 geosuture the foyleview geosuture which extends from upper to lower crustal levels along a series of prominent horizons it was probably active during the major carboniferous tectonism which severely structured devonian basins west of the nebine ridge the geosuture forms the southeastern boundary of the thomson fold belt 3 3 the crustal architecture under the taroom trough has little obvious structure above an outstanding moho transition zone however the prominent meandarra gravity ridge striking along the trough axis highlights the possibility of high density mafic volcanics within the crust and the probability of a rift model being appropriate early in the trough s history the sedimentary basin architecture supports the concept of an early extensional history for the crust within a poorly defined n s trending strike slip regime 4 4 between the taroom trough and the new england fold belt we interpret a high angle geosuture extending through the crust the burunga mooki geosuture reactivation during late palaeozoic early mesozoic times produced a series of reverse faults along the uplifted eastern margin of the trough some of these structures are tentatively considered to be positive flower structures above deeper faults with strike slip movement the geosuture separates regions with distinctly different seismic fabrics and played an important role in the formation of the bowen gunne dah sydney basin system 5 5 within the new england fold belt crustal domains can be recognized associated with late palaeozoic oroclinal bending and early mesozoic trans tensional basins major oroclinal bending of the upper crust in the west of the fold belt is interpreted above a mid crustal detachment the texas detachment in the central part of the fold belt the seismic data support a trans tensional mechanism for the formation of triassic basins with steeply dipping bounding faults under the east of the fold belt an imbricate thrust stack accretionary wedge is clearly imaged above a mid crustal horizon the brisbane mid crustal detachment upper crustal deformation appears to have occurred above this detachment 6 6 from the nebine ridge to the coast the moho is clearly defined below a 3 km thick moho transition zone hast of the thomson fold belt the moho level is identified as a gently undulating feature at 36 38 km depth and probably re established after the major late palaeozoic tectonic events which formed the crust under the taroom trough and new england fold belt this contrasts with the middle palaeozoic lower crustal moho features which appear to be preserved under the thomson fold belt 7 7 the thickest crust under the nebine ridge about 44 km appears to be associated with lower crustal wedging from the east there is an apparent thinning of the non sedimentary crust under the deepest basin taroom trough of about 30 compared with the crust to the west and east no crustal thickening is evident in the region of oroclinal bending within the new england fold belt

growth of an intermittent ice sheet in iceland during the late pliocene and early pleistocene abstract deep sea paleoclimatic records show that the quaternary climate around iceland was and probably still is very sensitive to rapid shifts in north atlantic oceanic circulation studies of several key sections in iceland indicate that similar oscillations are reflected in the late pliocene and early pleistocene terrestrial stratigraphy correlations between six rock sequences in western northern eastern and southern iceland show a fairly distinct trend during the pliocene pleistocene transition indicating the progressive growth of an ice sheet from southeast toward the north and west the correlations are based on k ar dates and paleomagnetic studies a total of 11 glacial horizons are recorded in a stratigraphic column from eastern iceland extending back 6 5 myr in western iceland 7 glacial horizons are preserved in a rock section dated from 7 0 to 1 8 myr and in northern iceland 14 glacial horizons are identified in a section that extends back to 9 0 myr well over 20 glacial horizons have been identified in the stratigraphic column in iceland full scale glacial interglacial cyclicity with regional ice cover is indicated at approximately 2 6 myr a further amplification leading to islandwide glaciations is identified at 2 2 2 1 myr these results show that changes in the ice cover in iceland correlate with the deep sea oxygen isotope records from benthic and planktonic foraminifera as well as ird studies from the north atlantic

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

evolution of iceberg melting biological productivity and the record of icelandic volcanism in the irminger basin since 630 ka abstract planktic 18 o and 13 c records and point count records of biogenic volcanic and nonvolcanic terrigenous ice rafted debris ird sediment components from hole 919a in the irminger basin northern north atlantic provide a comprehensive dataset from which a paleoceanographic reconstruction for the last 630 kyr has been developed the paleoceanographic evolution of the irminger basin during this time contains both long term patterns and significant developmental steps one long term pattern observed is the persistent deposition of hematite stained ice rafted debris this record suggests that the modern and late pleistocene discharges of icebergs from northern redbed regions to the irminger sea lie in the low end of the range observed over the last 630 kyr in addition arctic front fluctuations appear to have been the main controlling factor on the long term accumulation patterns of ird and planktic biogenic groups the hole 919a sediment record also contains a long term association between felsic volcanic ash abundances and light 18 o excursions in both interglacial and glacial stages which suggests a causal link between deglaciations and explosive icelandic eruptions a significant developmental step in the paleoceanographic reconstruction based on benthic evidence was for diminished supply of denmark strait overflow water dsow beginning at 380 ka possibly initiated by the influx of meltwater from broad scale iceberg discharges along the east greenland coast there is also planktic evidence of a two step cooling of sea surface conditions in the irminger basin first at 338 309 ka and later at 211 190 ka after which both glacials and interglacials were colder as the arctic front migrated southeast of site 919 in addition to offering these findings this reconstruction provides a longer term geologic context for the interpretation of more recent paleoceanographic events and patterns of deposition from this region

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

geophysical differences in the lithosphere between phanerozoic and precambrian australia abstract cannikin atomic bomb recordings indicate that there are differences in travel times from the aleutian islands test site to phanerozoic and precambrian provinces in australia of up to 1 1 s explosion seismic studies in central and southeastern australia enable travel time corrections for crustal and upper mantle structure to be made to recordings of such teleseismic events structure in the upper 60 km can account for at most about 0 2 s of the residual difference but attempts to constrain the remaining residual time to the region above the lehmann discontinuity at about 200 km depth are difficult to reconcile with explosion seismic models regional differences in seismic velocity structure between phanerozoic and precambrian australia therefore appear to exist at depths greater than 200 km electrical conductivities within the mantle have been investigated using two methods long period electromagnetic depth sounding using magnetometer arrays demonstrates that conductivities increase at about 200 km under phanerozoic australia but not until about 500 km depth under precambrian australia shorter period magnetotelluric measurements can only resolve shallower structures these too indicate a similar trend but with sub crustal conductivities increasing at less than 100 km under phanerozoic australia magma at these depths and shallower may be the source for cainozoic volcanism in eastern australia under precambrian central and northern australia magnetotelluric investigations indicate that pronounced conductivity increases do not occur until depths of 150 200 km are reached oceanic magnetic observations indicate that the australian lithospheric plate as a whole is separating from antarctica at a rate of about 7 cm yr the seismic and conductivity structures under the continental region of this plate indicate that lateral inhomogeneities possibly extend to depths as great as 500 km and are probably caused by the passage of eastern australia over a hot spot hawaiian studies indicate that hot spots are not local features but result from large scale disturbances in the mantle conductivity increases commencing in the depth range 100 250 km may give an indication of uppermost zones within which the palaeozoic lithospherc has been substantially modified resulting in elevated surface heat flow volcanism and seismic travel time anomalies

north atlantic deep sea sedimentation of late quaternary tephra from the iceland hotspot piston cores recovered from the north atlantic were used to study the sedimentation of holocene and pleistocene volcanic ash in the irminger and iceland basins ash zones 1 11 100 yr b p 2 55 000 yr b p and 3 305 000 yr b p were identified from their major element glass composition the silicic and alkalic ash zones 1 and 2 originate from the southeastern volcanic zone of iceland where they correlate with the solheimar ignimbrite from katla volcano and the thorsmork ignimbrite from tindfjallajokull volcano respectively the low alkali composition of silicic ash zone 3 indicates a source from one of the silicic centers in the active rift system ash zones 2 and 3 occur in the irminger basin as dispersed glass shards over a depth interval of several tens of centimeters their compositional and granulometric characteristics reflect an initial fallout on pack ice north of iceland followed by ice rafting sedimentation in the denmark strait prior to bioturbation 18o stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval at the time when seas north of iceland were ice covered sedimentary features indicate that turbidity currents were also involved in the dispersal of ash zones 1 and 2 south of iceland the initiation of these gravity currents from the shelf can be attributed to either glacier bursts jokulhlaups carrying tephra or the entrance of pyroclastic flows into the ocean

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

influence of convective sedimentation on the formation of widespread tephra fall layers in the deep sea the formation of widespread volcanic ash fall layers in deep sea sediments was investigated experimentally to examine the settling behavior of tephra 20 180 m diameter as it travels from the atmosphere into water using a fallout mass flux rate that was constrained by measurements of distal fallout from the 1980 eruption of mount st helens 0 2 g cm 2 hr the experiments show that particle settling in the water column is dramatically accelerated by the formation of diffuse vertical gravity currents the currents form as a result of convective instabilities that develop in a surface boundary layer when the local particle concentration becomes large at the air water interface the settling velocity of particles drops abruptly and the concentration of particles increases because of the differential in mass flux above and below the fluid surface the implication of the experiments is that deposition of distal tephra fall layers in deep sea sediments may be dominantly controlled by diffuse vertical gravity currents as opposed to passive settling of individual particles through the water column this process greatly reduces the residence time of fine ash in the ocean and diminishes the role of ocean currents in influencing the distribution patterns of individual tephra layers support for this mechanism comes from observations of greatly accelerated tephra settling rates in the south china sea following the 1991 eruption of mount pinatubo in the philippines

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

rapid onset of glacial conditions in the subarctic north pacific region at 2 67 ma clues to causality north pacific deep sea sediments recovered by ocean drilling leg 145 constrain the timing of the late pliocene major intensification of northern hemisphere continental glaciation a change in sediment character from nonglacial to glacial specifically abrupt increases in the amount of terrigenous clastic sediment and ice rafted debris occurred all across the north pacific at about 2 67 ma this change occurred very rapidly perhaps within 2000 yr too quickly to be a direct response to either tectonic or orbital forcing as the number and thickness of volcanic ash layers increased 10 fold at this same time we suggest that rapid intensification of glaciation may be associated with the widespread episode of explosive volcanism that began then

explosive silicic volcanism in iceland and the jan mayen area during the last 6 ma sources and timing of major eruptions abstract fifty three major explosive eruptions on iceland and jan mayen island were identified in 0 6 ma old sediments of the north atlantic and arctic oceans by the age and the chemical composition of silicic tephra the depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6 ma and paleoclimatic proxies 18 o ice rafted debris for the last 1 ma major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off rift volcanic zones in iceland and to the jan mayen volcanic system the tholeiitic central volcanoes along the iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4 9 ma they were the source of at least 26 eruptions of dominant rhyolitic magma composition including the late pleistocene explosive eruption of krafla volcano of the eastern rift zone at about 201 ka the central volcanoes along the off rift volcanic zones in iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition with three distinct episodes recorded at 4 6 5 3 3 5 3 6 and 0 1 8 ma the longest and last episode recorded 11 pleistocene major events including the two explosive eruptions of tindfjallajokull volcano thorsmork ca 54 5 ka and katla volcano solheimar ca 11 9 ka of the southeastern transgressive zone eight major explosive eruptions from the jan mayen volcanic system are recorded in terms of the distinctive grain size mineralogy and chemistry of the tephra the tephra contain k rich glasses k 2 o sio 2 0 06 ranging from trachytic to alkali rhyolitic composition their normative trends ab q or and their depleted concentrations of ba eu and heavy ree reflect fractional crystallisation of k feldspar biotite and hornblende in contrast their enrichment in highly incompatible and water mobile trace elements such as rb th nb and ta most likely reflect crustal contamination one late pleistocene tephra from jan mayen was recorded in the marine sequence its age estimated between 617 and 620 ka and its composition support a common source with the borga pumice formation at sor jan in the south of the island

seismic evidence of increased tectonothermal activity near the oberpfalz deep continental drilling location se germany the success of ultradeep drilling projects as e g within the german continental deep drilling programme kontinentales tiefbohrprogramm ktb in the oberpfalz strongly depends on the thermal and geological tectonic environment of the well in the present paper we apply the correlation of elevated temperatures and seismic reflectivity of the lower continental crust to the deep seismic network of the oberpfalz the results together with the correlation to other geoscientific data indicate increased temperatures in the area of the ktb location these temperatures are most probably related to influences of the eger graben and possibly are not yet measured at the surface using heat flow determinations

identification of a mis 6 age c 180 ka icelandic tephra within ne atlantic sediments a new potential chronostratigraphic marker the incidence of volcanic ash tephra within marine sediments serves as a useful stratigraphic marker and tool for correlation in addition where an independent age estimate exists tephra layers can provide a means of dating the sediments themselves here we present a geochemically characterized size sorted tephra layer within marine isotope stage mis 6 most likely resulting from primary air fall from an icelandic volcanic source this tephra layer is tentatively correlated to the kerlingarfjoll volcanic system using major element geochemistry the ash layer has an interpolated age of 181 6 ka based on the age model for md04 2822 we briefly review the occurrence of silicic tephra in the north atlantic region from mis 7 to mis 5e inclusive and find potential correlatives to the md04 2822 mis 6 ash layer in the norway basin and irminger sea

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

single station fault plane solutions abstract fault plane solutions are derived from systematic trial and error grid testing of three component body waveform data from a single station modeling p and sh waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between p and sh waveforms is sufficient to discriminate between fault type e g strike slip versus dip slip and often agrees with well constrained first motion studies events studied are the 9 april 1968 borrego mountain california 20 june 1978 thessaloniki greece 13 august 1978 santa barbara california 20 may 1979 alaska and 6 august 1979 coyote lake california earthquakes it is also shown using data from the 27 july 1980 sharpsburg kentucky earthquake that inclusion of pp p and sp p polarity and amplitude information to an otherwise unconstrained first motion study can significantly improve the quality of the fault plane solution although there are many potential problems source multiplicity directivity etc which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable the results of this study suggest that sparse high quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first motion studies at a minimum they should be performed together as a consistency check this procedure would be most useful in the common situation where only a few receivers are available for a particular event

source mechanism study of the 1982 new brunswick canada earthquake sequence using combined surface wave methods abstract a combined phase matched filtering and narrow bandpass filtering method and a surface wave love to rayleigh spectral amplitude ratio method are used to analyze the 1982 new brunswick earthquake sequence the analysis was carried out on the long period fundamental mode surface wave signals 10 to 50 sec for the main shock and its four largest aftershocks recorded at three gdsn stations scp lon and alq in north america estimates of source mechanism parameters focal depth dip rake and strike obtained for the 9 january 1982 main shock and the largest aftershock on 11 january 1982 are consistent with wetmiller et al 9s 1984 results for these events using local and regional body wave observations source mechanism parameters were also obtained for the 9 january 1982 the 31 march 1982 and the 16 june 1982 aftershocks which do not have independent estimates since these three events have low signal to noise ratios s n at some frequencies the source parameter estimates are not as well constrained as those of the main shock and the 11 january aftershock the inferred principal stress orientations are in all cases consistent with the prevailing ene maximum compressive stress characteristic of most areas in eastern north america among the principal aftershocks the most reliable source parameter estimates were for the 11 january aftershock because of its consistently high s n seismograms this aftershock consisted of thrusting on a fault plane conjugate to the main shock fault plane with dip of 40 to 55 to the northeast rake of 60 to 80 strike of 337 to 342 and a depth of 6 km this result also supports wetmiller et al 9s 1984 findings for this event the 9 january aftershock has a source mechanism similar to that of the main shock but a shallower depth of 6 km versus 7 km for the main shock the 31 march aftershock is associated with the upper portion of the main shock rupture with a much shallower depth of approximately 3 km the result for the 16 june aftershock is not as dependable but it appears to have a deeper depth of 8 km or more which suggests extension of the rupture zone to greater depth the results of this study indicate that surface wave data from only a few three component far field stations can be used to infer source parameters including depth for events as small as about m b 4 5 to the extent that eastern north america is typical of other continental interiors in terms of crustal structure and attenuation similar capabilities are anticipated for such areas

quasi dynamic models of simple earthquakes application to an aftershock of the 1975 oroville california earthquake a class of kinematic rupture models for simple earthquakes is proposed these models incorporate results from both theoretical and numerical solutions to the mixed boundary value problem of a three dimensional frictional rupture the analytic form for the slip velocity is divided into two phases the rupture growth during which the slip distribution is self similar kostrov 1964 and the healing during which the slip velocity decreases monotonically to zero the arrival of a p wave stopping phase propagating into the interior of the rupture area from the fault perimeter initiates the healing the duration of healing may be varied to produce a gradual or abrupt stopping of the rupture which permits modeling a wide range of high frequency spectral behavior these models are used to generate synthetics which are fit to the velocity and the velocity squared pulse shapes obtained from strong motion accelerograms of the 0103 aftershock of the 1975 oroville california earthquake the aftershock ml 4 6 has a moment of 1 8 1023 dyne cm and a total radiated energy of 2 7 1019 dyne cm the fitted source model propagates updip with a rupture velocity of 0 85 and a dynamic stress drop of 210 bars the arrival times of five stopping phases correlated across the suite of accelerograms are used to determine the relative locations of the hypocenter and five stopping events the description of rupture determined from these stopping events both corroborates the source model obtained from the waveform modeling and establishes an important counterpoint to the model by providing a dynamic interpretation of the unmodeled complexity of the waveforms

seismic imaging of extended crust with emphasis on the western united states understanding of the crust has improved dramatically following the application of seismic reflection and refraction techniques to studies of the deep crust this is particularly true in areas where the last tectonic event was extensional such as the basin and range province of the western united states and much of western europe in these regions a characteristic reflective pattern has emerged whereby the lower crust is highly reflective and the upper crust and upper mantle are either poorly reflective or strikingly nonreflective in the metamorphic core complex belt in the western united states where extension can be as much as an order of magnitude greater than in the more classic continental rift zones the lower crustal reflectivity thickens and rises yielding a picture of a crust that is reflective throughout synthetic seismic studies have documented that the reflectivity in these regions can be modeled by numerous laminae tens of meters thick and hundreds of meters across characterized by inter layered high and low velocities two geologic factors are interpreted as contributing to this layered character ductile strain responding to stress in the thermally weakened middle and lower crust and intrusive layering corresponding to injection of subhorizontal sheets of mantle derived magmas these two processes yield a variety of geologic structures including transposed compositional layering mylonitic ductile shear zones and intrusive mafic sheets all of which occur at the proper scales to cause the prominent reflectivity observed if metamorphic core complexes are representative of extended continental crust world wide then these results suggest that magmatism and ductile flow have also contributed to the evolution of the middle and lower crust in many other areas around the world

seismic evidence for a low viscosity lower crust beneath the continental deep drilling location oberpfalz germany abstract a network of six deep seismic reflection profiles was recorded in the oberpfalz as part of the pre site investigations for the german deep drilling programme in addition this network is crossed by a longer regional profile a striking observation is the highly variable reflectivity of the lower crystalline crust based on the relationship between temperature dependent viscosity and crustal reflectivity it seems possible to relate the changes encountered here to the tectono thermal regime we propose that processes forming the eger graben also thermally influence the crust beneath the oberpfalz these mechanisms should have a considerable impact on the maximum depth of the deep borehole the results of the pilot hole give strong support to our interpretation the temperatures are higher than the maximum estimates from near surface heat flow determinations and the maximum depth for the borehole has been reduced from 14 to 10 km

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

seasonal sea ice cover during the warm pliocene evidence from the iceland sea odp site 907 abstract sea ice is a critical component in the arctic and global climate system yet little is known about its extent and variability during past warm intervals such as the pliocene 5 33 2 58 ma here we present the first multi proxy ip25 sterols alkenones palynology sea ice reconstructions for the late pliocene iceland sea odp site 907 our interpretation of a seasonal sea ice cover with occasional ice free intervals between 3 50 3 00 ma is supported by reconstructed alkenone based summer sea surface temperatures as evidenced from brassicasterol and dinosterol primary productivity was low between 3 50 and 3 00 ma and the site experienced generally oligotrophic conditions the east greenland current and east icelandic current may have transported sea ice into the iceland sea and or brought cooler and fresher waters favoring local sea ice formation between 3 00 and 2 40 ma the iceland sea is mainly sea ice free but seasonal sea ice occurred between 2 81 and 2 74 ma sea ice extending into the iceland sea at this time may have acted as a positive feedback for the build up of the greenland ice sheet gis which underwent a major expansion 2 75 ma thereafter most likely a stable sea ice edge developed close to greenland possibly changing together with the expansion and retreat of the gis and affecting the productivity in the iceland sea

late pliocene millennial scale climate variability in the northern north atlantic prior to and after the onset of northern hemisphere glaciation 1 sediments recovered at ocean drilling program site 984 on the reykjanes ridge provided multicentennial scale records of late pliocene climate change over the onset of northern hemisphere glaciation nhg 2 95 2 82 ma short term climate variations prior to and after the onset of continent wide glaciation were compared to test the hypothesis of whether dansgaard oeschger do cycles may have been triggered by continental ice breakouts during two selected interglacial stages prior to and after nhg g15 and g1 climate variability resembled that found in the holocene and the mid pliocene warm period in contrast do like periodicities of 1470 2900 and 4400 years indeed only occurred in glacial stages after the onset of nhg g14 g6 and 104 but not in stage g20 prior to the onset these results suggest a causal link between do cycles and the late pliocene onset of major nhg and ice breakouts in the north atlantic

aftershock sequences of the 1982 miramichi new brunswick earthquakes the mb 5 7 miramichi new brunswick earthquake of 9 january 1982 was located by comparison to the aftershock distribution in central new brunswick canada at 47 00 n 66 60 w with a focal depth of 7 km and an uncertainty of 3 km on each of the spatial coordinates the main shock was followed by a long and complex aftershock sequence with four events m 4 5 and more than 800 events m 1 0 until 30 june 1982 the aftershocks were studied by three temporary field networks set up in the epicentral areas from 10 to 20 january 2 to 7 april and 17 to 23 june 1982 and by the permanent canadian seismograph networks the aftershock activity was concentrated in a volume approximately 6 km ns 6 km ew 8 km deep and arranged in a north trending conjugate v pattern the miramichi earthquakes were predominatly thrust earthquakes occurring on north trending mid to high angle faults in the upper 8 km of the crust in the presence of an east west compressive horizontal regional stress field detailed field surveys have not yet been able to associate the earthquakes with any known preexisting faults the main shock had a moment of 2 2 0 7 1024 dyne cm and a stress drop of 35 to 70 bars the rupture started at 7 km depth on a plane striking 195 dipping 50 down to the west and propagated up to the east with a rake angle of 120 aftershocks deeper than 3 5 km had composite mechanisms very similar to the main shock s but shallower events took place on more steeply dipping planes up to 78 dip the rupture planes of the main shock and its principal aftershocks may have been similarly curved the magnitude frequency relationship b 0 8 of the aftershocks was comparable to the regional one the aftershock activity decayed as t 0 8 and had the highest rate of activity following the principal aftershock on 11 january that aftershock mb 5 4 appears to have ruptured the east dipping plane conjugate to the main shock s plane two other principal aftershocks mb 5 1 on 9 january and mb 5 0 on 31 march were associated with the main shock rupture plane while the fourth large event mb 4 7 on 16 june occurred 30 km west of the other activity and was seemingly unrelated however all the earthquakes were apparently associated with the same granitic terrain the miramichi earthquakes did not produce any significant surface faulting one small 25 mm surface displacement was found but it was identified as a secondary stress induced movement along a preexisting joint