west african proximity of the avalon terrane in the latest precambrian considerable debate surrounds the late neoproterozoic paleogeographic position of the avalon terrane specifically whether it was adjacent to west africa or amazonia new paleomagnetic results from upper neoproterozoic rocks in the avalon terrane challenge the latter position samples collected from the ca 580 570 ma marystown group in the southern part of the burin peninsula of newfoundland canada yield high temperature magnetic components including dual polarity directions which are considered to be primary on the basis of positive fold and agglomerate tests the resultant tilt corrected inclination is 538 representing a paleolatitude of deposition of 34 81 88 78 for the marystown group given the likelihood that amazonia and laurentia were still juxtaposed around 580 570 ma the marystown group results reveal that the paleolatitude of avalon is significantly lower than would be expected if it was part of amazonia in fact avalon was separated from northern amazonia by at least 1100 km at ca 580 ma if west africa was juxtaposed to amazonia opposite laurentia by this time these results place avalon at the same paleolatitude as the northern margin of the west african craton

provenance of upper devonian clastic meta sediments of the bollstein odenwald mid german crystalline zone variscides detrital zircons separated from paragneisses of the northern bollstein odenwald mid german crystalline zone variscides yielded cambrian to upper devonian u pb ages the age of the youngest detrital zircon population 371 3 ma and the lower carboniferous metamorphic overprint indicate an upper devonian depositional age of the paragneiss protolith the age spectra of detrital zircons suggest the latter to be derived from 1 ordovician igneous rocks of the saxothuringian zone 2 a late cadomian magmatic arc tepla barrandian unit and 3 a silurian devonian magmatic arc cadomian igneous activity is also documented by cambrian zircon cores in lower to middle devonian detrital zircons meso and paleoproterozoic detrital zircons which are typical for the old red continent and the rhenohercynian zone are entirely lacking the restricted palaeozoic detrital zircon age spectrum is attributed to a silurian devonian intra arc or trench setting both the lack of mesoproterozoic detrital zircons and the striking similarity of the u pb ages of the detrital zircon obtained from the bollstein odenwald with u pb ages from crystalline rocks of the saxothuringian basement rules out that the bollstein odenwald is forming a tectonic window rhenohercynian lower plate inside the mid german crystalline zone saxothuringian upper plate

proto avalonia a 1 2 1 0 ga tectonothermal event and constraints for the evolution of rodinia the neoproterozoic evolution of avalonia is thought to have been geodynamically linked to the amalgamation and dispersal of rodinia similar sm nd isotopic signatures for different periods of arc activity suggest that avalonian basement or proto avalonia was generated in a series of primitive oceanic island arcs between 1 2 and 1 0 ga because this interval coincides with the amalgamation of rodinia proto avalonia is inferred to have been located in a panthalassa like peri rodinian ocean an early 760 660 ma phase of avalonian arc activity is attributed to renewed subduction in the peri rodinian ocean following the breakup of rodinia which caused the accretion of avalonian terranes to the gondwanan margin by ca 650 ma further subduction along the margin occurred outboard of these terranes and resulted in the onset of main phase avalonian volcanism at 630 ma the diachronous cessation of arc magmatism is attributed to ridge trench collision and the generation of a continental transform the geodynamic link between avalonia and rodinia is analogous to that between the mesozoic dispersal of pangea and the tectonothermal evolution of western north america this event also resulted in the accretion of outboard terranes and in arc related magmatism that is currently being terminated in a diachronous manner by ridge collision and the generation of the san andreas transform the model implies that the neoproterozoic evolution of avalonia and other peri gondwanan terranes provide important constraints on the tectonic history of a large portion of the rodinian continental margin

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

late ediacaran paleogeography of avalonia and the cambrian assembly of west gondwana abstract the latest proterozoic tectonic evolution of avalonia one of the largest peri gondwanan terranes bears on the issue of gondwana amalgamation during the transition from rodinia to pangea new paleomagnetic results from mid late ediacaran strata in the newfoundland sector of avalonia confirm substantial apparent motion of that terrane between ca 590 and 560 ma consistent with a true polar wander interpretation for that interval when the avalonian poles are mapped onto complementary paleomagnetic records from west africa and laurentia the avalonia terrane may occupy any of four possible positions all of which are far removed from those cratons choosing the most kinematically parsimonious location leading toward gondwana assembly we find that avalonia was most likely proximal to amazonia during the ediacaran cambrian transition with a substantial 3000 km separation between amazonia and west africa at that time our results thus favor the existence of a wide clymene ocean and subsequent cambrian final assembly of west gondwana providing a key snapshot onto the evolving rodinia gondwana supercontinental transition

assessment of hirnantian synglacial eustacy and palaeogeography in a tectonically active setting the welsh basin uk the hirnantian stratigraphy of wales is critically assessed against the global evidence for two major hirnantian synglacial eustatic lowstands the evidence for two separate lowstands of relative sea level is locally suggestive in shelf sequences but generally only permissive in the basin nowhere can the possible candidate lowstands be separated biostratigraphically and thus basinwide correlation that might rule out local tectonic control is impossible to prove consistent with palaeolatitude evidence and a situation far removed from the gondwana margin there is no facies evidence e g dropstones for local glacial conditions and the diamictites are of mass flow origin sequence stratigraphic reasoning proves helpful in the correlation of the basinal succession in central wales with the shelf sequences along the tywi lineament and the variscan front and suggests that the first appearance of normalograptus persculptus in wales does not correspond with the base of the persculptus biozone extensive new palaeocurrent data and sedimentological restudy is combined with review of earlier knowledge to argue for significant revisions to previous palaeogeographic maps for generalized lowstand conditions notably along the bala lineament the variscan front and the central wales inliers

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

palynomorphs of the fezouata shale lower ordovician morocco age and environmental constraints of the fezouata biota abstract the present study documents new palynological investigations of the fezouata shale from the anti atlas morocco palynomorphs were extracted from samples collected from both outcrops and drill cuttings outcrop samples were taken near zagora and include some that were collected during excavation of stratigraphic horizons where exceptionally well preserved fossils of the fezouata lagerstatte occur subsurface samples were taken from the az 1 adrar zouggar mountain borehole which was extracted some 300 km to the southwest of zagora the palynological samples yielded acritarchs chitinozoans scolecodonts conodonts and fragments of graptolites the abundance and quality of preservation of palynomorphs varies greatly but rich and diverse assemblages were recovered from several samples the diversity and composition of the assemblages points to an open shelf environment generally mixed preservation states suggest resedimentation or differential transport histories the acritarchs can be assigned to the diagnostic messaoudensis trifidum acritarch assemblage which is typical of the tremadocian floian boundary interval of the gondwanan margin in high southern palaeolatitudes the acritarch taxa present in some of the lower parts of the fezouata shale including levels of exceptional preservation can be attributed to sub assemblages 1 2 of the messaoudensis trifidum assemblage and thus point to a late tremadocian age of the fezouata lagerstatte confirming biostratigraphic data provided by graptolites of the araneograptus murrayi graptolite biozone chitinozoans from the fezouata shale are from the e symmetrica and e brevis biozones and include various species that are well known from several localities on the gondwanan margin and from other palaeocontinents baltica laurentia and south china demarcating broad links between those regions the coincidence between index fossils of these three groups hitherto not all found in the same level suggests that the age assignments of chitinozoan biozones may be in need of revision

reconstructing the avalonia palaeocontinent in the cambrian a 519 ma caliche in south wales and transcontinental middle terreneuvian sandstones an early cambrian caliche on the st non9s formation emended is the base of the caerfai bay formation unit term changed at caerfai bay south wales subaerial exposure and the caliche mean the two formations were not genetically related units the st non9s is an older sand sheet likely tidalitic not delta related referred to avalonian depositional sequence ads 2 and the caerfai bay is a shallow mud basin unit refered to ads 4a the similar random formation upper ads 2 in north american avalonia has a basal age of c 528 ma and is unconformably overlain by red mudstones or sandstones in fault bounded basins on the avalonian inner platform coeval british sandstones lower hartshill wrekin st non9s brand hills are unconformably overlain by latest terreneuvian ads 3 or epoch 2 ads 4a units dates of 519 ma on caerfai bay ashes give an upper bracket on the late appearance of avalonian trilobites and suggest an ads 2 4a hiatus of several million years post st non9s and post random basin reorganization led to abundant caerfai bay formation volcanic ashes and sparse brigus formation ashes in newfoundland the broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that east and west avalonia formed one palaeocontinent the inner platform in southern britain was larger than the midlands craton a tectonically defined later palaeozoic area unrelated to terminal ediacaran early palaeozoic depositional belts the cool water successions of early palaeozoic avalonia were distant from coeval west gondwanan carbonate platforms

a rich ediacaran assemblage from eastern avalonia evidence of early widespread diversity in the deep ocean the avalon assemblage ediacaran late neoproterozoic provides some of the oldest evidence of diverse macroscopic life and underpins current understanding of the early evolution of epibenthic communities however its overall diversity and provincial variability are poorly constrained and are based largely on biotas preserved in newfoundland canada we report coeval high diversity biotas from charnwood forest uk which share at least 60 of their genera in common with ones in newfoundland this indicates that substantial taxonomic exchange took place between different regions of avalonia probably facilitated by ocean currents and suggests that a diverse deepwater biota may already have been widespread at the time contrasts in the relative abundance of prostrate versus erect taxa likely record differential sensitivity to physical environmental parameters hydrodynamic regime substrate and highlight their significance in controlling community structure

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

the armorica microplate fact or fiction critical review of the concept and contradictory palaeobiogeographical data abstract the problem of an armorica microplate detached from gondwana and having had during part of the palaeozoic an independent latitudinal evolution is reconsidered in terms of a critical review of the palaeomagnetic data that were the very roots of this concept and through an alternative approach based on palaeoclimatic and palaeobiogeographical data palaeomagnetic data for the silurian and the devonian of the south european regions supposedly constituting the armorica microplate remain rare and ambiguous those from gondwana are more numerous but contradictory enough to give rise to diverging models regarding the latitudinal evolution of this continent consequently the reality of an armorica microplate cannot be considered as established on the contrary lithological indicators of palaeoclimate and palaeobiogeographical data are in total harmony and indicate that in actual fact the southern european regions remained permanently closely connected with gondwana of which they composed the northern margin although repeatedly maintained for more than 20 years the concept of an armorica microplate can thus be considered a fiction this conclusion should lead to the dismissal of geodynamical models proposed for the variscan belt to which this concept was integrated and are contradicted by inescapable palaeobiogeographical constraints

origin of the rheic ocean rifting along a neoproterozoic suture the rheic ocean is widely believed to have formed in the late cambrian early ordovician as a result of the drift of peri gondwanan terranes such as avalonia and carolina from the northern margin of gondwana and to have been consumed in the devonian carboniferous by continent continent collision during the formation of pangea other peri gondwanan terranes e g armorica ossa morena northwest iberia saxo thuringia moldanubia remained along the gondwanan margin at the time of rheic ocean formation differences in the neoproterozoic histories of these peri gondwanan terranes suggest the location of the rheic ocean rift may have been inherited from neoproterozoic lithospheric structures formed by the accretion and dispersal of peri gondwanan terranes along the northern gondwanan margin prior to rheic ocean opening avalonia and carolina have sm nd isotopic characteristics indicative of recycling of a juvenile ca 1 ga source and they were accreted to the northern gondwanan margin prior to voluminous late neoproterozoic arc magmatism in contrast sm nd isotopic characteristics of most other peri gondwanan terranes closely match those of eburnian basement suggesting they reflect recycling of ancient 2 ga west african crust the basements of terranes initially rifted from gondwana to form the rheic ocean were those that had previously accreted during neoproterozoic orogenesis suggesting the rift was located near the suture between the accreted terranes and cratonic northern gondwana opening of the rheic ocean coincided with the onset of subduction beneath the laurentian margin in its predecessor the iapetus ocean suggesting geodynamic linkages between the destruction of the iapetus ocean and the creation of the rheic ocean

guzhangian mid cambrian trilobites from siliceous concretions of the valtorres formation iberian chains ne spain in the carbonate siliciclastic strata of west gondwana e g in the montagne noire france the aftermath of the mid languedocian mid cambrian regression is characterized by a late languedocian major turnover of trilobite families and a furongian early tremadocian radiation related to the stepwise immigration of trilobite invaders from east gondwana under persistent transgressive conditions the scarcity of upper languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the iberian chains spain where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions these have yielded the trilobites peronopsis cf insignis oidalagnostus trispinifer proampyx difformis proampyx aculeatus bailiaspis glabrata holocephalina agrauloides by ontogeny holasaphus cf centropyge and a paradoxidid gen et sp indet despite preservation and sampling biases the identification of this taphonomic window in offshore clayey substrates of west gondwana allows the recognition of a strong biogeographical link with baltica and the correlation of the global guzhangian stage and the solenopleura brachymetopa zone of scandinavia with part of the mediterranean upper languedocian substage less

silurian u pb zircon intrusive ages for the red river anorthosite northern cape breton island implications for the laurentia avalonia boundary in atlantic canada abstract current interpretations of the geology of cape breton island suggest that it exposes a complete cross section of the appalachians from laurentia across iapetan vestiges to avalonia crucial to this view is the presence of ca 1 ga plutons including anorthosites which have been regarded as correlatives of grenvillian basement a correlation that overlooks the fact that avalonia is also underlain by a ca 1 ga basement we analyzed zircons from the red river anorthosite blair river complex northwestern cape breton island previously dated as ca 1 1 ga they yielded 421 3 ma intrusive ages with older ages between 865 18 ma and 1044 20 ma inferred to be either xenocrysts derived from the country rock or from the source implications of these data suggest that the accompanying low pressure granulite amphibolite facies metamorphism of the blair river complex is either the root of a 440 410 ma magmatic belt produced during slab break off or relict ca 1 ga basement the blair river complex occurs in a nne ssw sinistral positive flower structure that progresses upwards from a neoproterozoic rifted arc through a low grade upper ordovician silurian overstep sequence to amphibolite facies fault slices capped by the low pressure granulite facies rocks blair river complex the correlation of neoproterozoic rifted arc units across most of cape breton island suggests it represents the deformed northwestern margin of avalonia intruded by a silurian lower devonian magmatic belt as the geological record in the blair river complex is similar to both grenvillian and avalonian basements its provenance is equivocal however pb isotopic data suggest the blair river complex has amazonian avalonia affinities thus cape breton island rather than representing a complete cross section of the appalachian orogen is part of pristine deformed avalonia with a positive flower structure exposing a cross section of avalonian crust

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

heterogeneous zircon cargo in voluminous late paleozoic rhyolites hf o isotope and zr hf records of plutonic to volcanic magma evolution voluminous rhyolitic lavas and ignimbrites c 34 000 km3 were formed in the ne german basin in a post collisional setting at c 295 ma trace elements ehf and 18o have been measured in dated magmatic and inherited rhyolitic zircons from three drill cores across the basin magmatic zircons crystallized in two stages the first stage in less differentiated and isotopically heterogeneous magmas and the second stage in more differentiated and isotopically homogeneous magmas the first and second stages can be related to the crystallization of zircons within a heterogeneous pluton and in an evolved silicic magma that was later erupted some zircons crystallized entirely during the evolved magma stage and provide good resolution for identifying and characterizing processes happening shortly before eruption the isotopic compositions of the magmatic zircons constrain the proportions of juvenile and reworked materials involved in the formation of voluminous silicic magmas in a post collisional tectonic setting the advantage of studying the volcanic rocks from the ne german basin is that their petrogenesis involved a relatively simple two source interaction during magma production which permits quantitative estimation of the amount of each source component afc modelling shows that the first stage zircons crystallized from magmas containing 5 80 of the juvenile component whereas the final rhyolitic magmas contained 30 40 of this material the inherited zircons have hf model ages of 1 9 2 2 ga suggesting that much of the local basement was initially derived from the mantle at that time and that it was subsequently reworked at around 1 5 ga similar model ages are a feature of baltica derived sediments and the implication is that such sediments underlie large areas of the ne german basin the lack of any record of avalonian basement in the ne german basin may indicate that both the sedimentary cover and the underlying basement are part of baltica

the 2008 may 29 earthquake doublet in sw iceland summary on 2008 may 29 an earthquake doublet shook the southwestern part of iceland the first main shock originated beneath mt ingolfsfjall located near the western margin of the south iceland seismic zone sisz approximately 40 km east of the capital reykjavik immediate aftershock activity was recorded by the sil seismic network operated by the icelandic meteorological office imo with both n s and e w structures illuminated over a broad area a continuous gps cgps network also operated by the imo recorded coseismic offsets with up to 200 mm of horizontal motion at the closest stations we estimate the coseismic surface deformation observed by campaign and continuous gps and satellite radar data insar we invert the geodetic data to find the optimal geometry location and slip on the main faults accounting for variation in the elastic parameters of the crust with depth our models indicate that most of the slip occurred on two n s structures spaced 5 km apart from a joint inversion of gps and insar data for variable slip models we find that most of the slip for the first ingolfsfjall event was concentrated at 2 4 km depth with a maximum of 1 9 m whereas the slip on the second kross fault was located deeper at 3 6 km depth with up to 1 4 m of motion the models give similar geodetic moments for the two main events equivalent to a moment magnitude of mw5 8 and mw5 9 for the first and second event respectively our estimated composite moment therefore equals a mw6 1 for the doublet smaller than the mw6 3 estimated from teleseismic data e g neic and harvard the geodetic data support rupture on two main faults and analysis of high rate 1 hz cgps data suggests that slip on the second fault initiated within 3 s of the first main shock static coulomb failure stress calculations indicate that the first event caused a stress increase in the area of the main asperity i e at the location of the largest slip patch on the second fault however we cannot rule out dynamic stress triggering due to the short time between the two main events the 2008 may 29 earthquake doublet appears to be a continuation of the earthquake sequence that started in 2000 june when two mw6 5 events struck the eastern and central part of the south iceland seismic zone in the span of 81 hr the 2000 june 2008 may sequence has released about half of the moment accumulated by plate motion since the previous earthquake sequence in 1896 1912 therefore continued earthquake activity with moderate size events rupturing n s faults in the sisz in the coming decades is likely

the cambrian to devonian odyssey of the brabant massif within avalonia a review with new zircon ages geochemistry sm nd isotopes stratigraphy and palaeogeography abstract this study provides an up to date and comprehensive review of the early palaeozoic evolution of the brabant massif belonging to the anglo brabant deformation belt situated at the southeastern side of avalonia microplate it is the only well known part of the northern passive margin of the rheic ocean the cambrian silurian sedimentary pile is 13 km thick with 9 km for the cambrian only the unraveling of this continuous registration reflects the successive rifting and drifting of avalonia from the gondwana mainland followed by soft collisional processes with baltica and finally the formation of laurussia based on recently established detailed stratigraphy sedimentology and basin development on u pb la icp ms analyses of igneous and detrital zircon grains along with geochemical data including sm nd isotopes a new geodynamic and palaeogeographic evolution is proposed brabant megasequence 1 lower cambrian to lowermost ordovician 9 km thick represents an embayment of the peri gondwanan rift from which the rheic ocean has evolved detrital zircon ages demonstrate that the brabant is a typical peri gondwanan terrane with a major pan african neoproterozoic age and a mixed west african and amazonian source palaeoproterozoic archaean and some mesoproterozoic age the transition towards the avalonia drifting is marked by an unconformity and a short volcanic episode the northward drift of avalonia towards baltica is recorded by the megasequence 2 middle to upper ordovician 1 3 km thick the source for mesoproterozoic zircons vanished as the result of the rheic ocean opening and the isolation from amazonian sources the transition to megasequence 3 is marked by a drastic change in palaeobathymetry and an important sub volcanic episode during a tectonic instability period 460 430 ma reflecting the avalonia baltica soft docking as also shown by the reappearance of mesoproterozoic detrital zircons typical of baltica unradiogenic nd isotope signature end 4 5 and tdm model ages 1 3 1 7 ga for brabant magmatic rocks indicate an old recycled component megasequence 3 uppermost ordovician to lowermost devonian 3 5 km thick includes the onset of a silurian foreland basin that reflects the tectonic inversion of the core of the massif brabantian orogeny in response to the baltica avalonia laurentia collision finally the comparison with the strikingly similar cambrian successions of the harlech dome wales avalonia and the meguma terrane nova scotia peri gondwana allows the construction of a new early cambrian palaeogeographic model for the whole avalonia microplate in which the meguma terrane is included

active faulting and natural hazards in armenia eastern turkey and northwestern iran active fault zones of armenia se turkey and nw iran present a diverse set of interrelated natural hazards three regional case studies in this cross border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster in northern armenia a combination of several natural and man made phenomena earthquakes landslides and unstable dams with toxic wastes along the pambak sevan sunik fault pssf zone lowers from 0 4 to 0 2 0 3g the maximum permissible level mpl of seismic hazard that may induce disastrous destruction and loss of life in the adjacent vanadzor depression in the ararat depression a large active fault bounded pull apart basin at the junction of borders of armenia turkey iran and azerbaijan an earthquake in 1840 was accompanied by an eruption of ararat volcano lahars landslides floods soil subsidence and liquefaction the case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact the north tabriz gailatu fault system poses a high seismic hazard to the border areas of nw iran eastern turkey nakhichevan azerbaijan and southern armenia right lateral strike slip motions along the north tabriz fault have given rise to strong earthquakes which threaten the city of tabriz with its population of 1 2 million the examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in armenia eastern turkey and nw iran this generally occurs across the junctions of international borders hence the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk

the october 1980 earthquake sequence near the new hebrides four large earthquakes occurred in 1980 in a seismic gap near the loyalty islands in the new hebrides at 3 25 ut on october 24 an event with m s 6 7 initiated the sequence three events m s 6 7 7 2 and 6 5 followed on the next day we investigated this sequence by using the seismicity first motion and waveform data and long period surface waves the first motion data constrain one of each pair of nodal planes with this constraint inversion of rayleigh and love wave spectra at 256 seconds determines the other nodal plane the mechanisms of all four events are almost pure thrust on a plane dipping about 20 degrees east and striking parallel to the local strike of the new hebrides trench the first day aftershocks indicate an initial rupture zone of about 2 000 km which is consistent with the estimated seismic moment of 3 10 27 dyne cm during the next two days the aftershock activity expanded to an area of 10 000 to 20 000 km in the directions both along and perpendicular to the trench within 5 hours after the third and largest event the initial rupture zone had become mostly quiescent modeling of waveforms suggests a body wave moment of between 0 5 and 1 0 10 27 dyne cm and a source process time of 11 seconds this pattern suggests that the initial rupture zone represents a zone of increased strength i e an asperity and the stress change due to failure of this asperity subsequently migrated outward during the two year period before the main event seismicity in the initial rupture zone was very low except near the point where the first mainshock initiated a very tight clustering of activity occurred there this pattern indicates gradual stress concentration near the asperity which finally failed during the mainshock sequence

marginal faunal belts and their structural implications with examples from the lower palaeozoic fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms on a global scale the identification of exterior oceanic biofacies may be of use in discriminating the course of former continental margins the isograptid graptolite biofacies early to middle ordovician can be distinguished from contemporary epicratonic graptolite biofacies its worldwide occurrence corresponds with continent margins reconstructed from other criteria hence a new isograptid record from irian jaya e new guinea although based on a small sample suggests that there may have been an ordovician oceanic site there on a continental scale the tectonic juxtaposition of different biofacies or of different stratigraphical packages contributes to an understanding of tectonics and can serve to quantify displacement the accretionary prism hypothesis for the southern uplands of scotland is supported and contrasted with the rearrangement of biofacies in the cambro ordovician cow head group of western newfoundland which reveals not only the original shelf margin slope topography now vanished but also provides an estimate of the movement involved in the emplacement of one taconic allochthon on a more local scale faunal evidence is used in assessing the original position of 9suspect9 marginal areas using the simplest possible model this shows for example that anglesey was not greatly separated from gondwana in the early ordovician but strike slip movement cannot be disproved local changes in relative sea level are determinable from sediments and faunas in marginal belts these may differ from the global eustatic curve and when this happens it is a measure of local tectonic activity particular sea level curves may serve to define structurally coherent units within mobile belts new sea level curves are contrasted for a segment of n wales north of the bala fault with that for central sw wales arenig llandovery the s welsh area mostly responded passively to the eustatic curve which can adequately account for shifts in facies and faunas while n wales had a curve often at odds with eustasy and reflecting its structural history

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

the margins of avalonia during cambrian and earliest ordovician times avalonia was an area forming an integral part of the huge gondwanan continent probably along the northern margin of amazonia until in early ordovician late arenig or llanvirn time it split off from gondwana leaving a widening rheic ocean to its south today its southern margin with gondwana extends northeast from east of cape cod massachusetts through nova scotia north of the meguma terrane and thence below sea level to the south of newfoundland on the eastern side of the present atlantic the southern margin may separate southwest portugal from the rest of the iberian peninsula it can be traced eastwards with more certainty from the south cornwall nappes to a line separating the northern phyllite belt on the southern margin of the rhenohercynian terrane and the mid german crystalline high there is no certain evidence of avalonian crust to the northeast of the elbe line the northern margin of avalonia extends westwards from south of denmark to the british isles where it merges with the iapetus ocean suture between scotland and england traced westwards it crosses ireland and reappears in northern newfoundland to the east of new world island where it may follow the trace of the dog bay line and the cape ray fault recent work suggests that the northern margin of avalonia may clip the northern tip of cape breton island in nova scotia and then enter the north american mainland at the bay of chaleur it may then be traced from north and west of the popelogan and bronson hill arcs to long island sound near newhaven connecticut the cambrian to devonian faunas reflect the history of avalonia initially they were purely gondwanan but as ordovician time proceeded more genera crossed firstly the tornquist ocean as it narrowed between avalonia and baltica to close in latest ordovician and early silurian times and secondly the iapetus ocean so that by the early silurian most of the benthic shelly faunas apart from the ostracods were the same round the adjacent margins of all three palaeocontinents

scaling relations of earthquake source parameter estimates with special focus on subduction environment abstract earthquake rupture length and width estimates are in demand in many seismological applications earthquake magnitude estimates are often available whereas the geometrical extensions of the rupture fault mostly are lacking therefore scaling relations are needed to derive length and width from magnitude most frequently used are the relationships of wells and coppersmith 1994 derived on the basis of a large dataset including all slip types with the exception of thrust faulting events in subduction environments however there are many applications dealing with earthquakes in subduction zones because of their high seismic and tsunamigenic potential there are no well established scaling relations for moment magnitude and length width for subduction events within this study we compiled a large database of source parameter estimates of 283 earthquakes all focal mechanisms are represented but special focus is set on large subduction zone events in particular scaling relations were fitted with linear least square as well as orthogonal regression and analyzed regarding the difference between continental and subduction zone oceanic relationships additionally the effect of technical progress in earthquake parameter estimation on scaling relations was tested as well as the influence of different fault mechanisms for a given moment magnitude we found shorter but wider rupture areas of thrust events compared to wells and coppersmith 1994 the thrust event relationships for pure continental and pure subduction zone rupture areas were found to be almost identical the scaling relations differ significantly for slip types the exclusion of events prior to 1964 when the worldwide standard seismic network was established resulted in a remarkable effect on strike slip scaling relations the data do not show any saturation of rupture width of strike slip earthquakes generally rupture area seems to scale with mean slip independent of magnitude the aspect ratio l w however depends on moment and differs for each slip type

reconstruction of ocean plate stratigraphy in the gwna group nw wales implications for the subduction accretion process of a latest proterozoic trench forearc abstract the gwna group in anglesey island and lleyn peninsula wales consists of a latest proterozoic volcano sedimentary trench melange which has a complicated accretionary structure and is poorly constrained by isotopic ages the melange contains oceanic trench rocks including pillow basalts cherts mudstones and sandstones which have not previously been interpreted as ocean plate stratigraphy ops we reconstructed imbricated ops at 5 localities in the coastal lleyn peninsula in order to constrain the depositional u pb age of the upper clastic sediments detrital zircons separated from 9 clastic sediments were analyzed with a nu attom single collector inductively coupled plasma mass spectrometer the ages indicate that there are two gwna groups maximum depositional ages of 1 at 608 601 ma and 2 at 564 539 ma that were deposited between the late neoproterozoic and the middle cambrian contemporaneously with dated calc alkaline arc magmatism and regional metamorphism in the anglesey lleyn complex the age spectra of the detrital zircons show a prominent peak at ca 650 600 ma and several proterozoic and archean ages to account for the older ages we integrated our new isotopic data with published radiometric and fossil ages and conclude that the clastic sediments at the top of the ops were deposited in a trench on the western active margin of avalonia when it was close to the amazonian craton and that the gwna group ops began to be incorporated into an accretionary wedge in an active subduction zone in the latest proterozoic

waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model summary in the inversion scheme of high frequency seismograms recorded by a local network we have developed the unconstrained moment tensor description to study weak events which are believed to reflect small scale complexities of the tectonic structure in order to allow the source mechanism to change with time each moment tensor component has its own time history in the inversion the measure of the similarity between the synthetic seismograms and the observed records is obtained by minimizing the norm l2 of their difference the initial synthetic seismograms are constructed by summing a set of time dependent functions named base functions these base functions are computed by normal mode summation for a discrete set of source depths and for two structural models considered to represent acceptable extremes for the region under study in the course of the inversion using a linear interpolation new base functions are computed for intermediate values of the starting depths and structures thereafter new synthetic seismograms are computed and compared with the observed records until the convergence is reached within some pre assigned threshold for the norm l2 the method has been tested by treating as observed records synthetic seismograms both displacement and velocity generated for instantaneous and finite duration sources the observed records have been computed for two structures one belonging to the structural range within which the base functions were computed the other lying outside this range random noise has been superimposed on the records when inverting synthetic records computed for a structure contained within the range of interpolation for the base functions the full moment tensor is retrieved satisfactorily provided that the noise level does not exceed about 20 per cent for records computed for a structure lying outside this range a spurious volumetric part of the moment tensor appears however if the volumetric part of the moment tensor is removed the source time function can be reconstructed satisfactorily and the source mechanism can be determined from the deviatoric part of the moment tensor the procedure has been applied to vertical component seismograms recorded in the friuli ne italy area for the ml 2 9 event of 1987 december 27 the retrieved source mechanism is in agreement with the distribution of the few first arrival polarities available and the source time function indicates a possible multiple rupture process

conodonts from the lower ordovician of morocco contributions to age and faunal diversity of the fezouata lagerstatte and peri gondwana biogeography this study documents conodont faunas of the fezouata formation recovered from the az 1 borehole at adrar zouggar mountain and from outcrops near zagora in south eastern morocco the fezouata formation was deposited on the peri gondwanan shelf near the south pole during early ordovician times it is composed of mostly fine grained siliciclastics and is well known for including beds displaying the exceptionally well preserved fezouata biota studies on different microfossil groups including conodonts increase the diversity recorded from this exceptional ecosystem strongly recrystallised conodont elements were extracted from the fine grained siliciclastic sediments by diluted hydrofluoric acid hf which was used for isolating palynomorphs the material is dominated by simple cone taxa such as parapaltodus semiacontiodus scolopodus scalpellodus drepanoistodus acodus paltodus and cornuodus in addition a few elements of early prioniodus are recovered this composition allows an estimation of uppermost tremadocian through basal floian ages for the fragmented elements because characteristic elements of younger assemblages including ramiform e g oepikodus baltoniodus or coniform e g tropodus protopanderodus apparatuses have not been recorded the association is devoid of any warm tropical and temperate water taxa and is typical for faunas in the cold water environments of the subpolar siliciclastic shelves during early ordovician times the new term of subpolar faunal domain is proposed for these conodont associations of low diversity that occur at high southern latitudes during the early ordovician ecological implications and palaeobiogeographical relationships of the conodont faunas are discussed

the ordovician history of the iapetus ocean in britain new palaeomagnetic constraints new late tremadoc early arenig palaeomagnetic results from sw wales imply that s britain part of eastern avalonia occupied a southerly latitude of c 60 s in early ordovician times when combined with scottish ordoviaan palaneomagnetic data which indicate a 15 s latitude the results indicate that the british sector of the iapetus ocean reached n latitudinal width of c 5000 km in tremadoc arenig times which was reduced to c 3000 km by llanvirn llandeilo mid ordovician times the new data resolve two previous controversies in palaeozoic palaeogeography first the high southerly palaeolatitude links avdonia to gondwana marginal to w africa thus reconciling codlicting reconstructions based upon either palaeomagnetic or faunal facies evidence alone second reliable llanvim palaeomagnetic data imply that avlonia had rifted northwards by arenig time whereas armorica remained proximal to northern africa throughout the ordovician the combined data therefore establish that avdonia and armorica formed separate micro continents when rifting from gondwana

coticules of the belgian type area stavelot venn massif limy turbidites within the nascent rheic oceanic basin abstract coticule is the name originating in belgium for a fine grained metasedimentary yellowish rock mainly composed of quartz spessartine and mica which is repeatedly interstratified in the hematite rich purple slates of the lower ordovician of the ardenne region it was described for the first time in the nineteenth century in the stavelot venn massif ardenne which is accordingly the type area for this peculiar lithology since then numerous occurrences were described all over the world in metamorphic rocks of various grades and ages the exact nature of the belgian coticule protolith remained hypothetical although intensively discussed for a long time in the literature after an extensive review of all the stratigraphical sedimentological and geochemical results and new field geochemical major and trace elements and nd isotopic investigations we propose a significantly improved and sustained genetic model the thin coticule layers were deposited offshore in a deep oceanic basin as limy mud turbidites during the early floian c 477 ma early ordovician density currents came from the north from the shelf which bordered the emergent brabant massif at that time and flowed down the slope to the deep basin plain the purple shales enclosing the coticule layers represent the normal pelagic sedimentation in the basin these shales are exceptionally rich in fe and mn because of the hydrothermal activity of the nearby and young rheic ocean ridge indeed the rheic ocean opened in the early ordovician c 482 ma during diagenesis the strongly oxidizing depositional environment favoured the mobility of mn 2 as opposed to fe 3 that remained insoluble and immobile this allowed for the migration of divalent manganese from the pelagic shales and for replacing calcium in the turbiditic carbonate fraction to form rhodochrosite later epizonal metamorphism transformed the clay quartz rhodochrosite paragenesis of the protolith into the muscovite quartz spessartine paragenesis of the coticule hence in the type area coticule genesis needed a peculiar environment including a continental shelf with limy mud deposits a continental slope generating periodical turbidites and a nearby oceanic ridge here the nascent rheic ocean delivering hydrothermal iron and manganese

automated moment tensor inversion to estimate source mechanisms of hydraulically induced micro seismicity in salt rock abstract two methods for an automated moment tensor inversion are investigated the first is a single source inversion using amplitude spectra of observed body wave phases and theoretical green functions and the second a relative moment tensor inversion using spectral moments of body wave phases an optional general dislocation source constraint is introduced to stabilize the inversions for sparse data both methods are successfully tested on synthetic data and are applied to hydraulically induced micro seismicity in salt rock the estimated moment tensors of 187 events show similar radiation patterns with a major double couple component and a small or zero isotropic component we explain the double couple component with failure on horizontal preexisting planes of weakness within the process zone of circular tension fractures

neoproterozoic palaeogeography of the cadomia and avalon terranes constraints from detrital zircon u pb ages detrital zircons from three neoproterozoic sandstone units from the cadomia terrane of northern france and the channel islands yield ages in three broad groups late neoproterozoic 650 600 ma early palaeoproterozoic 2 4 2 0 ga and archaean 2 5 ga the lack of mesoproterozoic zircon crystals combined with the high abundance of grains between 2 20 and 2 00 ga corresponds closely to the ages of exposed rocks in the west africa craton and thus it is suggested that cadomia was in close proximity to west africa by c 580 ma in contrast the main age groups of detrital zircon from the neoproterozoic avalon terrane are mesoproterozoic and there is a distinct gap of ages between 2 40 and 2 05 ga these significant differences suggest that the two terranes were in different locations relative to major gondwanan cratons in latest neoproterozoic time

microseismicity and seismotectonics of the north tabriz fault iran abstract we present the results of a microearthquake study conducted in 2004 with 31 portable stations around the city of tabriz which is crossed by an active fault and has experienced several destructive earthquakes in the recent history from april 24 until july 24 we recorded 80 earthquakes by more than 4 stations we complement these data with earthquakes recorded by the 8 permanent seismological stations of the tabriz network operated by institute of geophysics of the university of tehran from august 1995 until march 2008 among a total of 6377 events only 394 earthquakes were recorded by more than 5 stations and located with statistical uncertainties erz and erh less than 5 km and a gap less than 270 most of these earthquakes are located along the tabriz fault at a depth ranging from the surface to 20 km comparable to other studies conducted in central alborz we computed 22 focal mechanisms most of which show right lateral strike slip motion along east southeast planes consistent with the geologic evidence for quaternary slip we do not see any peculiar pattern near the tabriz pull apart basin or at both ends of the north tabriz fault where it terminates in ew trending reverse faults this suggests that the fault is simpler more mature at depth than at the surface

extension in nw iran driven by the motion of the south caspian basin contrasted tectonic styles occur in northern iran west of kopet dagh the south caspian basin is an aseismic and possibly rigid blockinvolved inthecollisionzonebetweeneurasiaandarabia tothenw largescalevelocityfield ofirangivenbyrecentrepeated gps surveys suggests 8 mm yr of right lateral displacement for the wnw ese faults in the tabriz region more surprisingly geodetic motion also suggests a prominent n 30 extension north to the tabriz fault where compression would be expected in order to quantify more precisely the right lateral movement of the tabriz region the extension of nw iran and the motion of the south caspian basin we deployed a dense gps network in nw iran from central iran to the turkish armenian and azerbaijan borders three repeated surveys from 2002 to 2004 assess that the tabriz fault concentrates entirely the 8 mm yr of right lateral movement observed in nw iran this rate is in good agreement with a recurrence interval time of 250 300 yr proposed from historical seismicity studies we found also two zones of extension one just north of the tabriz fault in the south of the talesh plateau and another close from the azerbaijan border north of the talesh plateau we suggest that the existence of a northward subduction of the south caspian basin could explain such an extension in the core of the arabia eurasia collision increasing evidences of quaternary extensional tectonics in the region from armenia to alborz may lead to significantly alter our understanding of the northern iran tectonics and challenge the traditional arabian indenter plate tectonics

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

rifting during separation of eastern avalonia from gondwana evidence from subsidence analysis subsidence curves for cambrian ordovician sequences from the anglo welsh segment of the paleocontinent of avalonia reveal two periods of regionally enhanced basement subsidence early cambrian 545 518 ma and late cambrian to early tremadocian 505 490 ma the earlier event may record transtension following the avalonian cadomian orogeny the second event may be a transtensional precursor to the late tremadocian volcanic arc on eastern avalonia however paleomagnetic faunal volcanic and sedimentary evidence suggests that the main separation of eastern avalonia from gondwana occurred after middle arenigian time rifting during separation is probably recorded by localized middle arenigian to llanvirnian 480 462 ma subsidence along the welsh basin margin but rifting must have occurred mainly on the now obscured southern margin of the avalonian continent pronounced caradocian 462 449 ma subsidence is associated with back arc rifting after separation from gondwana

ordovician palaeogeography with new palaeomagnetic data from the montagne noire southern france a joint palaeomagnetic and ar 40 ar 39 study has been performed on two olistolithic blocks from the cabrieres wildflysch in the montagne noire region of the massif central in france there andesitic volcanic and volcaniclastic rocks of llanvirn early caradoc age ca 470 458 ma occur despite extensive secondary alteration destruction of the dominant magnetic mineral phase and ar 40 ar 39 whole rock experiments that demonstrate that the volcanic rocks suffered significant argon loss a positive fold test and the presence of dual polarities suggest that a primary ordovician magnetisation has mostly survived this is one of the few documented cases where the argon system was substantially reset whilst a subordinate set of small relatively unaltered magnetite grains probably hosted in silicates still carry the original in this case ordovician remanence the new data show that the montagne noire region was located at high southerly latitudes 68degrees 19 15 during the mid ordovician this latitude represents the location for nw gondwana of which the massif central was a part palaeomagnetic data from all the central european massifs and terranes demonstrate a close link to the gondwana margin during the lower and middle ordovician

new detrital zircon age data reveal the location of the rheic suture in the mid german crystalline zone spessart and odenwald crystalline complexes new detrital zircon age data of metasedimentary rocks from the spessart and odenwald basement mid german crystalline zone variscides revealed results which are not compatible with current tectonic models the previously proposed existence of a tectonic window which includes lower plate rhenohercynian rocks within the upper plate saxothuringian zone in the spessart and odenwald basement does not agree with the results of this study this leads to a new course of the rheic suture and therefore a non coherence of the two major fault zones in these complexes the southern spessart crystalline complex accommodates the rheic suture which is most likely explained by a southward displacement of a whole segment of the mid german crystalline zone this displacement might extend over the ruhla crystalline complex a hitherto unknown age spectrum of a unit in the bollsteiner odenwald was found which might indicate a sliver of unidentified material in the variscan collision zone an unknown magmatic age of 350 ma is reported for igneous intrusions in the saxothuringian zone and can be used as an additional indicator to distinguish between laurussia and gondwana related rocks

a plate tectonic scenario for the iapetus and rheic oceans abstract the tectonics dynamics and biogeographic landscape of the early paleozoic were dominated by the opening and expansion of one large ocean the rheic and the diminution to terminal closure of another iapetus an understanding of the evolution of these oceans is thus central to an understanding of the early paleozoic but their chronicle also presents a rich temporal profile of the wilson cycle illustrating continental scale rifting microcontinent formation ocean basin development arc accretion and continent continent collision nevertheless contemporary paleogeographic models of the iapetus and rheic oceans remain mostly schematic or spatiotemporally disjointed which limits their utility and hinders their testing moreover many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios with the specific aim to resolve some of the uncertainties in the evolution of this early paleozoic domain and a broader aim to instigate the application of quantitative kinematic models to the early paleozoic i present a new plate tectonic model for the iapetus and rheic oceans the model has realistic tectonic plates which include oceanic lithosphere that are defined by explicit and rigorously managed plate boundaries the nature and kinematics of which are derived from geological evidence and plate tectonic principles accompanying the presentation and discussion of the plate model an extensive review of the underlying geological and paleogeographic data is also presented

deciphering the geology of some darriwilian sandbian ordovician ghost formations in the uk and north america using olistoliths in marine debris flows olistostromes with calcareous olistoliths are rare components in the ordovician successions in nw europe and north america having been described from only a small number of localities one of the best exposed but least known is in the garn formation in coastal outcrops in anglesey in northwestern wales here in the graptolite bearing shales of the garn formation there are numerous limestone olistoliths that are derived from an otherwise unknown ghost formation whose original depositional site remains an enigma these olistoliths contain a baltoscandian type of conodont fauna that is otherwise unknown in wales and england it represents the baltoniodus variabilis subzone of the amorphognathus tvaerensis zone similar but slightly older conodont faunas are recorded from olistoliths in the tweeddale member of the shinnel formation in southern scotland and in probable olistoliths of the cobbs arm limestone in northeasternmost newfoundland approximately coeval conodont faunas are present in calcareous olistoliths in the woods hollow shale of west texas and the womble shale in the ouachita mountains of arkansas usa lithological and conodont evidence indicates that the calcareous olistoliths were derived from carbonate sediments deposited in relatively shallow water it is concluded that the study of ghost formation olistoliths may provide otherwise unavailable but important data bearing on the marine depositional history of a particular region

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

early paleozoic avalon gondwana unity an obituary response to palaeontological evidence bearing on global ordovician silurian continental reconstructions by r a fortey and l r m cocks

cambrian and ordovician stratigraphy related to structure and seismic profiles in the western part of the english midlands in england the cambrian successions include relatively continuous dominantly argillaceous sequences nuneaton area 900 m thick and arenaceous successions punctuated by hiatuses malvern shropshire the tremadoc lower ordovician succeeds paraconformably it is widespread dominantly argillaceous and locally very thick 2000 m deposition of the lower tremadoc is thought to have been rapid uplift of regional extent occurred in early ordovician post tremadoc times and inversion of the basins such as the tremadoc worcester graben occurred during the variscan orogeny the disposition of the cambrian tremadoc beneath the upper llandovery unconformity is thought to reflect the arrangement of basins and highs at that time evidence from seismic profiles indicates deposition in half grabens in the welsh borderland evidence from outcrops and boreholes suggests that the st david s series middle cambrian is locally thickened against syn depositional faults the thinning and local absence of the st david s series across such faults is attributed to the influence of tilt block highs rifting and tilting allowed thick tremadoc to accumulate e g in a precursor worcester graben but evidence for the direction of thickening is masked by lack of seismic markers and by the effect of pre landovery erosion

earthquake doublet in kagoshima japan rupture of asperities in a stress shadow two shallow moderate m 6 earthquakes occurred in the northwestern part of kagoshima prefecture kyushu southern japan i discuss the effect of the stress change due to the first earthquake 26 march 1997 on the occurrence of the second earthquake 13 may 1997 the rupture characteristics of the two earthquakes are inferred in two steps to form the basis of the discussion i first invert strong ground motion data to construct kinematic source models and then estimate the distribution of static stress drop from the derived dislocation distributions the rupture process of the march event is simple and well described with rupture of a single asperity patch of high stress drop on the other hand multiple asperities on conjugate faults ruptured during the may event the maximum value of static stress drop for both earthquakes is about 4 mpa and seems lower than those of other japanese intraplate earthquakes the hypocenter and the largest asperity of the may earthquake are located in a stress shadow caused by the march earthquake thus the rupture history of the may earthquake is difficult to explain with a static stress change model other mechanisms such as fluid migration and dynamic stresses were also investigated but failed to explain the triggering i propose the coupled effect of static change in shear stress and normal stress under the rate and state dependent friction law as a possible mechanism

non double couple earthquakes of 1997 january in west bohemia czech republic evidence of tensile faulting summary a mixed family of double couple dc and non double couple non dc earthquakes was observed during the 1997 january earthquake swarm in west bohemia which is a geothermal region typical for the occurrence of earthquakes swarms the dc and non dc earthquakes occurred within a small area of less than 1 km 3 on faults of different orientations the stress in the area is determined from focal mechanisms and attains values plunge azimuth 1 33 156 2 48 20 3 23 262 with a shape ratio of r 0 69 0 15 the error in the stress directions plunge azimuth is up to 5 10 the absolute stress values were estimated to be 1 350 mpa 2 220 mpa and 3 162 mpa the lithostatic stress is 250 mpa the stress analysis shows that the dc earthquakes occurred on optimally oriented faults with high shear traction but the non dc earthquakes occurred on misoriented faults with low shear traction the percentage of the dc in earthquakes clearly correlates with the magnitude of shear traction high low dc is associated with high low shear traction this indicates that the type of faulting is probably controlled by tectonic stress and that the non dc earthquakes are not related to pure shear faulting but may combine shear and tensile faulting the tensile faulting is manifested by positive isotropic and compensated linear vector dipole components the tensile faulting is conditioned by high pore fluid pressure which was estimated to be approximately 244 mpa the fluid pressure is less than the lithostatic stress by 5 mpa the ratio of the fluid pressure to the maximum compressive stress is 0 7

twin surface ruptures of the march 2007 m 6 earthquake doublet on the sumatran fault although the 2000 km long sumatran fault is one of earth s longest and historically most active strike slip faults previous large historical ruptures have gone unmapped although some have been inferred from felt reports or from modeling of sparse geodetic data through field observation we documented twin surface ruptures associated with two m 6 earthquakes in march 2007 the first rupture broke a 22 km part of the 60 km long sumani segment southeast from a releasing stepover the second rupture occurred on a 22 5 km part of the 90 km long sianok segment northwest from the stepover dextral displacements on the two segments averaged 51 and 36 cm the earlier earthquake doublet in 1926 also straddled this stepover but also did not seem to have ruptured the entire fault segments thus using fault lengths between large stepovers to estimate earthquake magnitude will overestimate what is likely to occur online material photos of surface rupture and surface displacement measurements

the first furongian late cambrian echinoderm from the british isles furongian late cambrian echinoderms are extremely rare in the fossil record and only two previous reports have been described from the paibian stage worldwide here the third occurrence of an echinoderm from the paibian and the first ever reported in the furongian of britain is presented it is a primitive pelmatozoan which shows intermediate characteristics between eocrinoids with columnalbearing stems and primitive glyptocystitid rhombiferans the palaeobiogeographic affinities of cambrian echinoderm faunas from britain eastern avalonia are shown to be with gondwana

morphotectonic and geodetic evidence for a constant slip rate over the last 45 kyr along the tabriz fault iran iran is an active continental domain accommodating the convergence between the arabia and eurasia plates in northwestern iran deformation between the central iranian block and the caucasus domain is mainly accommodated by right lateral strike slip on the tabriz fault cities and villages including the city of tabriz have been destroyed by several strong historical earthquakes m similar to 7 in this study we compare the slip rates estimated from geodetic measurements radar interferometry and ups with those determined by dating a geomorphological offset of an alluvial fan along the tabriz fault the gps measurements along two profiles normal to the tabriz fault suggest a slip rate of 7 3 1 3 mm yr 1 the persistent scatterer radar interferometry analysis of envisat satellite archives from 2003 to 2010 shows a velocity gradient 6 3 mm yr 1 across the tabriz fault in agreement with gps results moreover it reveals that most of the area located south of the tabriz fault is affected by subsidence and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour west of tabriz morphotectonic investigations on an alluvial fan surface show a right lateral cumulative offset of 320 40 m luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 3 ka this yields a slip rate comprised between 6 5 and 7 3 mm yr 1 along this segment these results suggest that the late quaternary slip rate is in agreement with the present day slip rate estimated by geodetic measurements showing no slip rate changes during the past 45 000 yr short term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out but if they exist they do not affect the geodetic and the geomorphological estimates this study is in agreement with previous ones suggesting that long term slip rates i e averaged over several tens of seismic cycles are consistent with geodetic estimated slip rates i e extrapolated from few years of interseismic observations and suggests that perturbations of fault slip rates are related to variations over few seismic cycles

nw iran eastern turkey present day kinematics results from the iranian permanent gps network abstract a network of continuous gps stations has been installed in nw iran since 2005 to complement the survey gps network already existing in the region we present the 1999 2009 gps derived velocity field for this region based on the continuous and survey mode observations the results confirm a right lateral slip of 7 1 mm yr for the north tabriz fault in agreement with previous studies this rate is consistent with earthquakes of magnitude 7 7 3 and recurrence times of 250 300 yr the higher spatial coverage of the new network shows that deformation is localized in the vicinity of the chalderan south gailatu siah cheshmeh khoy fault and the north tabriz fault however the eastern end of the north tabriz fault appears to cross mount bozgush rather than following its southern foothills this new velocity field does not indicate the 8 mm yr of nne ssw extension suggested earlier for the region but rather shows lower extension of 1 2 1 mm yr across the eastern segment of the north tabriz fault and the talesh to the west the chalderan and the western north tabriz fault segment act like pure strike slip faults without significant extension or compression the denser network in the rudbar earthquake region ms 7 3 1992 shows no significant motion across the fault suggesting that the recurrence time of earthquakes like the rudbar event must be very long the lack of substantial compressive strain and the sharp azimuth change of the velocity vectors in the transition zone from arabia to lesser caucasus motion imply that processes other than extrusion possibly related to old subduction or delamination contribute to active deformation

the 2012 august 11 ahar earthquakes consequences for tectonics and earthquake hazard in the turkish iranian plateau we have examined the faulting in the 2012 august 11 mw 6 4 and 6 3 ahar nw iran earthquakes using a combination of field mapping remote sensing observations of tectonic geomorphology the cross correlation of optical satellite images and the inversion of seismic waveforms the first event was close to pure strike slip and the second was an oblique combination of thrust and strike slip motion mapped surface ruptures indicate at least one of these events accommodated mostly right lateral strike slip motion on an e w striking plane the occurrence of these earthquakes highlights the spatially distributed deformation in nw iran which has implications for both hazard assessment the ahar events killed over 300 people and injured over 3000 and also tectonic models of the region furthermore these earthquakes demonstrate that the tectonics of the ahar area is characterized by strike slip faulting and a component of shortening and not the previously suggested extension

early carboniferous extension in east avalonia 350 my record of lithospheric memory abstract despite reactivations during variscan and alpine orogenies and the opening of the northern atlantic avalonia is one of the few regions where the initial mid paleozoic basin structure is still recognisable largely intact and well studied its kinematics and dynamics remain however largely unknown in particular in view of the successive late paleozoic to recent evolution of the basin consequently the importance of the mid palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies in this paper we reassess the importance of mid palaeozoic tectonics on subsequent sedimentary basin evolution of north western europe to this end we analyse the dynamics of early variscan extension in avalonia based on the integration and re evaluation of available geophysical and geological data from lithosphere to basin scales based on a revised crustal map of the thor suture zone we present a new paleo tectonic reconstruction and tectonic scenario for the devonian carboniferous rifting these findings are key for a better understanding of long lived tectonic segmentation and post rifting deformation phases our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the north sea central graben were created in the early carboniferous consequently the main basement structuration of northwest europe was completed before the variscan orogeny and successive post variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups incorporation of the paleozoic structural grain allows for a consistent tectonic framework for the mesozoic contributing to fundamental understanding of basin evolution from our tectonic framework analysis avalonia therefore stands out as a fine example of long lived lithosphere memory spanning over 350 my of structural control in geodynamic evolution

the ahar varzeghan earthquake doublet mw 6 4 and 6 2 of 11 august 2012 regional seismic moment tensors and a seismotectonic interpretation abstract on 11 august 2012 an earthquake doublet m w 6 4 and 6 2 occurred near the city of ahar northwest iran both events were only 6 km and 11 minutes apart producing a surface rupture of about 12 km in length historical and modern seismicity has so far been sparse in this area spatially the region represents a transitional zone between different tectonic domains including compression in iran westward extrusion of the anatolian plate and thrusting beneath the caucasus in this study we inverted the surface waveforms of the two mainshocks and 11 aftershocks m w 4 3 to obtain regional seismic moment tensors the earthquakes analyzed can be grouped into pure strike slip including the first mainshock and oblique reverse mechanisms including the second mainshock the sequence provides information about faulting mechanisms at the spatial scale of the entire rock volume affected by the earthquake doublet including coinciding deformation on minor faults sub parallel to the main fault and riedel shears it occurred on a so far unknown fault structure which we call the ahar fault alongside the seismological data we used geological maps satellite images and digital elevation data to analyze the geomorphology of the region our analysis suggests that the adjacent north tabriz fault which accomodates up to 7 mm yr of right lateral strike slip faulting does not compensate the entire lateral shear strain and that part of it is compensated farther north combined our results suggest a temporally and spatially complex style of deformation reverse and strike slip overprinting older reverse deformation

active tectonics of the turkish iranian plateau 1 this paper examines how active faulting in the turkey iran caucasus region accommodates the arabia eurasia collision and the velocity field observed by gps the overall shortening across the zone is in general spatially separated partitioned into right lateral strike slip in the turkish iranian plateau and thrusting in the greater caucasus a band of counterclockwise rotating nw se right lateral strike slip faults accommodates a nw se gradient in ne directed velocity relative to eurasia between the black and caspian seas a nnw sse band of previously unrecognized oblique normal faults is present on the turkey iran border we estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 2 ma at present rates this implies a reorganization of deformation in the collision zone at that time after the initial collision at 12 ma probably in response to mantle induced dynamic uplift

circa 546 ma plume related dykes in the 1 ga novillo gneiss east central mexico evidence for the initial separation of avalonia abstract the 1 ga novillo gneiss exposed in an inlier in the front ranges of the laramide belt in east central mexico is cut by an unmetamorphosed ne trending mafic dyke swarm the gneiss represents the northernmost inlier of the oaxaquia terrane that underlies the backbone of mexico titanite and biotite from metasedimentary rocks yielded ages of 928 2 ma concordant u pb age and duplicate 40 ar 39 ar plateau ages of 697 7 and 697 10 ma which are inferred to represent cooling through 660 and 300 350 c respectively on the other hand hornblende from cross cutting ne trending mafic dykes yielded a 40 ar 39 ar plateau age of 546 5 ma which is inferred to closely post date the time of intrusion combined with published ages u pb zircon sm nd garnet k ar hornblende the data suggest that following granulite facies metamorphism at 982 6 ma 8 9 9 7 kbar and 730 775 c the novillo gneiss cooled at a rate of 1 45 c my if this latter rate is extrapolated it would place the rocks at the surface 30 c by 497 ma about 50 my after dyke emplacement geochemistry of the dykes indicates that they are fe rich tholeiites with i low mgo but high tio 2 and other hfse ii smooth mantle normalized incompatible trace element patterns peaking at nb and la and iii intraplate tectonic affinities these features are typical of enriched tholeiites associated with plumes current precambrian paleogeographic reconstructions place avalonia against oaxaquia and subsequently separate avalonia by way of ridge trench collision at 550 ma giving rise to the unique avalonian cambrian fauna and a rapid phase of early cambrian subsidence these events are contemporaneous with emplacement of the novillo mafic dykes suggesting that the plume related magmatism and separation of avalonia from oaxaquia are linked

biogeography and affinities of the bradoriid arthropods cosmopolitan microbenthos of the cambrian seas abstract this paper reviews the global biogeography and affinities of the bradoriida a group of cambrian early ordovician arthropods bradoriida appear in the fossil record during the early cambrian just prior to the earliest trilobite faunas seven families may form a natural monophyletic group of bradoriida sensu stricto comprising cambriidae kunmingellidae comptalutidae bradoriidae hipponicharionidae beyrichonidae and svealutidae amongst the bradoriida sensu lato some forms that lie outside these families have carapace designs that suggest an ostracod affinity particularly altajanella and vojbokalina bradoriida formed a major element of the cambrian evolutionary fauna and are components of the chengjiang burgess shale and buen formation lagerstatten bradoriida achieved global distribution from the atdabanian early cambrian their diversity peaked during the early and middle cambrian with highest diversity at the species and genus level amongst the palaeo tropical faunas of the south china 17 genera and east gondwana palaeocontinental regions 23 genera by contrast laurentian faunas were of much lower diversity 10 genera for the whole cambrian bradoriid diversity declined rapidly from the latest middle cambrian a trend that may be related to the major extinction of trilobites at the base of the late cambrian the youngest bradoriida comprise a few rare ordovician forms bradoriids appear to have occupied well oxygenated marine shelf facies the biogeographical patterns of early and middle cambrian bradoriida suggest climatic control on their distribution temperate and tropical faunas together with palaeogeographical constraints that also reflect trilobite provinciality kunmingellids and comptalutids were restricted to palaeo tropical subtropical sites but migrated between south china siberia and eastern gondwana palaeocontinents they are absent from the mid and high latitude faunas of the western gondwana avalonia and baltica palaeocontinental areas that were dominated by hipponicharionids beyrichonids and bradoriidae the laurentia palaeocontinent was isolated from the main zones of bradoriid diversity but its faunas include a number of early and middle cambrian bradoriidae indota bradoria walcottella and the region was colonised by cosmopolitan cambriids during the early cambrian and by supposed pelagic svealutids liangshanella and anabarochilina during the middle cambrian the genera walcottella dielymella and bullaluta were endemic to laurentia one species of anabarochilina that possibly dwelt near the sea surface achieved an equatorial to high southern latitude 70 s distribution during the late middle cambrian lejopyge laevigata biozone perhaps reflecting a reduced latitudinal temperature gradient for near surface ocean waters

the initiation and early tectonic significance of the outer hebrides fault zone scotland the outer hebrides fault zone is a major ese dipping detachment exposed within base ment gneisses of the archaean palaeoproterozoic lewisian complex northwest scotland the fault zone exhibits a long lived displacement history and was active during proterozoic end silurian carboniferous and mesozoic times the earliest deformation event preserved onshore was associated with top to the nw ductile thrusting a previous study proposed that thrust related protomylonitic and mylonitic fabrics are cross cut by amphibolites younger basics and laxfordian granite and pegmatite sheets this evidence was used to suggest that ductile thrusting occurred during the palaeoproterozoic inverian event at c 2500 ma our observations demonstrate however that mylonitic fabrics within the ductile thrust zone are superimposed on all components of the gneiss complex including amphibolites and laxfordian intrusions it therefore follows that the outer hebrides fault zone cannot be older than c 1685 ma the age of recently dated laxfordian granites in the outer hebrides geochronological studies have shown that the basement blocks of the northern outer hebrides and scottish mainland have different geological histories and were amalgamated dur ing proterozoic times at or after c 1700 ma we propose that early ductile thrusting along the outer hebrides fault zone formed part of this amalgamation process leading to burial and reheating of the footwall gneisses in lewis and north harris this would account for the c 1100 ma thermal event recorded by previous workers and implies that ductile thrusting along the outer hebrides fault zone is of grenvillian age

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

a new late ordovician hirnantia brachiopod fauna from nw turkey its biostratigraphical relationships and palaeogeographical setting late ordovician fossils including the distinctive hirnantia brachiopod fauna have been found in lower palaeozoic successions in istanbul and bolu yigilca western pontides nw turkey the middle ordovician sandbian faunas belong to the cooler water mediterranean province and they are followed by katian brachiopods including sulevorthis nicolella hesperorthis glyptorthis saukrodictya and kullervo and ostracods such as piretella eochilina and klimphores which represent deposition in warmer waters however the mediterranean province usually cooler water brachiopods drabovia and leptestiina also occur the pendik formation includes thin bryozoan rich limestones which probably represent the boda global warming event the overlying turbidites contain a hirnantia fauna developed within a brachiopod diplograptid association above them there are characteristic llandovery rhuddanian aeronian brachiopods such as leangella eoplectodonta stricklandia and hindella with the corals halysites paleofavosites and streptelasma in the bolu area katian brachiopods such as mcewanella dalmanella glyptorthis christiania oligorhynchia nicolella howellites and drabovinella also occur but there the overlying hirnantia fauna is developed within a hirnantia mucronaspis association the fauna and sediments indicate that the western pontides were not very cold during the latest ordovician despite turkey being placed in higher latitudes by previous authors it seems more probable that the pontides were at somewhat lower palaeolatitudes perhaps at about 40 s in those times however the precise palaeogeographical position of the terrane remains uncertain there are no hirnantian glaciogenic rocks there such as are found in the taurides of southern turkey

biogeographical significance of cambrian trilobites from the carolina slate belt abundant middle middle cambrian trilobites of the ptychagnostus atavus interval zone are described from the upper asbill pond formation informal name near batesburg south carolina the fauna containing at least nine species has strong affinities with cool water faunas of both armorica and baltica but little affinity with warm water shelf faunas of laurentia this is compatible with previous conclusions that the carolina slate belt is an exotic terrane that was accreted to north america during the early or middle paleozoic further evaluation however introduces an alternative possibility that the fauna could have lived in deep cool water environments along the periphery of laurentia and subsequent displacement need not necessarily have been great combined faunal and stratigraphic components of the carolina slate belt do not precisely match those of any known region but may be closest to those of bohemia although a southpolar location in proximity to armorica baltica and gondwana seems likely a definitive placement in a reconstruction of the cambrian world is not yet possible included in the trilobite fauna are the agnostoids hypagnostus mammillatus h parvifrons peronopsis fallax ptychagnostus sp and tomagnostus fissus the polymeroids include agraulos sp paradoxides cf polonicus paradoxides sp and skreiaspis sp

an earthquake doublet in ometepec guerrero mexico on june 7 1982 an earthquake doublet occurred in a gap near ometepec guerrero mexico which had been given a high seismic potential the two earthquakes first event m s 6 9 m b 6 0 16 3 n 98 4 w d 25 km second event m s 7 0 m b 6 3 16 4 n 98 5 w d 8 km of the doublet occurred within five hours of each other we determine the source parameters of these events by inverting surface wave data at a period of 256 s the results are for the first event strike 116 dip 77 slip 88 and seismic moment of 2 8 10 26 dyne cm and for the second event strike 116 dip 78 slip 89 and seismic moment of 2 8 10 26 dyne cm modeling of long period p waves suggests that the first event has a depth of 20 km and is represented by a single trapezoidal source time function with an effective duration of 6 s the second event is best modeled by two sources at depths of 15 and 10 km the combined effective source duration time for the two sources is about 10 s the ratio of the seismic moment obtained from body waves to that from surface waves is 0 5 for the first event and 1 for the second adding the seismic moment of the two events and considering the first week aftershock area 3200 km 2 the stress drop is 4 bars these results suggest that the first event that involved a deeper asperity caused an incremental stress change large enough to trigger the second event if the two events of the doublet broke distinct areas of the subduction zone the coseismic slip is 0 58 m and accounts for about 25 of the total plate motion between the cocos plate and the north america plate accumulated since the last large earthquake in the region other doublets similar to the ometepec doublet have occurred along the middle america trench during the past 70 years a regional distribution of comparable size asperities may be responsible for this relatively frequent occurrence of doublets and for the simplicity of earthquakes in the region the high convergence rate which produces rapid strain accumulation and short recurrence intervals for large earthquakes and the smooth sea floor subducted along the middle america trench may contribute to the homogeneous distribution of comparable size asperities we found a relation log t 1 3 log m 0 t is the average recurrence time and m 0 is the average seismic moment for large earthquakes along the subduction zone in the guerrero oaxaca region where the convergence rate and the properties of the subducted plate are considered relatively uniform a simple asperity model predicts this relation