a new attenuation relation for strong ground motion in japan based on recorded data following the 1995 hyogo ken nanbu kobe earthquake the japanese government in an effort to prevent future earthquake disasters installed networks consisting of a large number of strong motion observation stations further national seismic hazard maps were made available to the public on an internet website in march 2005 by the headquarters for earthquake research promotion however these maps indicate only the local seismic intensity for japan as empirically con verted from predicted peak velocity in consolidated soils for various applications other strong motion indexes such as the response spectral acceleration are required in this study a database of whole japanese strong ground motion records between 1963 and 2003 is established in order to identify a new standard attenuation relation for japan for response acceleration as well as peak value it is usually very difficult to determine a suitable model form due to the large variability of strong motion data and correlation among the model variables because the strong coupling of variables in an attenuation model and the statistical power of the data is often not large enough to determine the necessity of these parameters therefore in this study our model has only three variables earthquake magnitude shortest distance to the seismic fault plane and focal depth to improve predictions given by the model site correction terms are adopted and additional terms for correcting regional anomalous seismic intensity with respect to the base model are determined the good fit between the model and observed strong motion records suggests that the new model is reasonably robust

cambro ordovician anatexis and magmatic recycling at the thinned gondwana margin new constraints from the kouřim unit bohemian massif the kou im unit represents one of the largest pre variscan meta igneous complexes in the bohemian massif and a geochronological whole rock geochemical and sr nd isotopic study was conducted to better understand the magmatic evolution of the early paleozoic gondwana margin five orthogneisses yield u pb zircon ages ranging from 492 4 to 484 2 ma two leucogranites give u pb zircon ages of 500 4 and 485 2 ma interpreted to be inherited from their orthogneiss host rock two samples from the metasedimentary host rock are dominated by neoproterozoic cambrian detrital zircons the abundance of zircon inheritance in the orthogneisses and whole rock sr nd isotopic composition imply an origin from relatively mature continental crustal material the subalkaline subaluminous slightly peraluminous and high k calc alkaline arc like geochemical signature of the orthogneisses is interpreted as inherited from the recycled cadomian metasedimentary source and both the magmatic and metasedimentary rocks are correlated with similar occurrences in the adjacent moldanubicum and tepla barrandian unit the late cambrian early ordovician magmatic activity is linked to crustal anatexis which was probably initiated by thermal and gravitational relaxation of the thickened cadomian arc type crust followed by lithospheric thinning assisted by far field forces the extensional event led to the formation of a passive margin associated with the opening of the rheic ocean supplementary material analytical methods petrographic descriptions with photographs of studied samples collections of cl images of representative zircon grains results of la icp ms u pb analyses of zircons and an additional geochemical diagram are available at https doi org 10 6084 m9 figshare c 4649255

geometry and regional significance of neoproterozoic cadomian structures of the narcea antiform nw spain the narcea antiform is located at the hinterland to foreland transition of the variscan belt in the nw of the iberian massif it consists of an antiformal stack of fault propagation folds that developed in the hanging wall of allochthonous thrust sheets during the first variscan deformation event in the palaeozoic rocks the neoproterozoic narcea slates formation cropping out in the core of the narcea antiform records a cadomian deformation event that formed large asymmetric nw vergent folds with related axial planar cleavage developed in the lower greenschist facies these folds are truncated by the lower cambrian angular unconformity lower cambrian conglomerates contain pebbles with predepositional microstructures that are widespread in the underlying neoproterozoic rocks the narcea antiform provides valuable information concerning major tectonic cadomian events the large scale near recumbent cadomian folds developed between 560 and 540 ma top to the nw kinematics can be deduced for the cadomian plate convergence transverse to the variscan convergence in present coordinates it was followed shortly afterwards by large displacements along the northern gondwana margin that resulted in its accretion alongside the essentially undeformed neoproterozoic rocks of the central iberian zone before early cambrian times

deformation of the oceanic crust between the north american and south american plates fracture zone trends and magnetic anomalies in the atlantic ocean indicate that the north american plate must have moved with respect to the south american plate during the opening of the atlantic a comparison of plate tectonic flow lines with fracture zones identified from geosat and seasat altimeter data suggests that the north american south american plate boundary migrated northward from die guinea demarara shear margin to the vema fracture zone before chron 34 84 ma to north of the doldrums fracture zone before chron 22 51 9 ma and to north of the mercurius fracture zone between chron 32 72 5 ma and chron 13 35 5 ma the paleoridge offset through time identified from magnetic anomalies and the computed cumulative strike slip motion in the plate boundary area indicate that the triple junction may have been located between the mercurius and the fifteen twenty fracture zones after 67 ma chron 30 plate reconstructions indicate a late cretaceous phase of transtension followed by transpression in the tertiary for the tiburon barracuda ridge area south of the fifteen twenty fracture zone the ocean floor in this area is characterized by a series of ridges and troughs with large bouguer gravity anomalies up to 135 mgal we use smoothing spline estimation to invert bouguer anomalies for crustal layer structure our model results suggest that the moho is uplifted 2 4 km over short wavelengths 70 km at the barracuda and tiburon ridges and imply large anelastic strains the severely thinned crust at the two ridges implies that crustal extension must have taken place before they were uplifted we propose that the north south american plate boundary migrated to the latitude of the tiburon ridge bounded by the vema and marathon fracture zones before chron 34 84 ma post chron 34 crustal thinning during a transtensional tectonic regime may have been localized at preexisting structural weaknesses such as the vema marathon mercurius and fifteen twenty fracture zone troughs but reaching the fifteen twenty fracture zone and future barracuda ridge area only after chron 32 72 5 ma this interpretation concurs with our crustal structural model which shows stronger crustal thinning underneath the tiburon ridge than at the barracuda ridge subsequent transpression may have continued along the existing zones of weakness in the tertiary creating the presently observed crustal deformation and uplift of the moho accompanied by anelastic failure of the crust middle eocene upper oligocene turbidites on the slope of the tiburon ridge now located 800 m above the abyssal plain suggest that most of its uplift occurred at post oligocene times the unusually shallow moho underneath the tiburon and barracuda ridges represents an unstable density distribution which may indicate that compressive stresses are still present to maintain these anomalies and that the north american south american plate boundary may still be located in this area

review of geochemical variation in lower palaeozoic metabasites from the ne bohemian massif intracratonic rifting and plume ridge interaction

empirical ground motion relations for subduction zone earthquakes and their application to cascadia and other regions ground motion relations for earthquakes that occur in subduction zones are an important input to seismic hazard analyses in many parts of the world in the cascadia region washington oregon northern california and british columbia for example there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab these hazards are in addition to the hazard from shallow earthquakes in the overlying crust we have compiled a response spectra database from thousands of strong motion record ings from events of moment magnitude m 5 8 3 occurring in subduction zones around the world including both interface and in slab events the 2001 m 6 8 nis qually and 1999 m 5 9 satsop earthquakes are included in the database as are many records from subduction zones in japan kyoshin net data mexico guerrero data and central america the size of the database is four times larger than that available for previous empirical regressions to determine ground motion relations for subduc tion zone earthquakes the large dataset enables improved determination of attenu ation parameters and magnitude scaling for both interface and in slab events soil response parameters are also better determined by the data we use the database to develop global ground motion relations for interface and in slab earthquakes using a maximum likelihood regression method we analyze regional variability of ground motion amplitudes across the global database and find that there are significant regional differences in particular amplitudes in cascadia differ by more than a factor of 2 from those in japan for the same magnitude distance event type and national earthquake hazards reduction program nehrp soil class this is believed to be due to regional differences in the depth of the soil profile which are not captured by the nehrp site classification scheme regional correction factors to account for these differences are proposed for cascadia and japan the results of this study differ significantly from previous analyses based on more limited data and have important implications for seismic hazard analysis the ground motion relations predict that a great megathrust earthquake m 8 at a fault distance of about 100 km would produce pseudoacceleration psa 5 damped horizontal component on soil sites of about 110 cm sec 2 at 0 5 hz 660 cm sec 2 at 2 5 hz and 410 cm sec 2 at 5 hz with a peak ground acceleration of about 180 cm sec 2 these damaging levels of motion would be experienced over a very large area corresponding to a rectangular area about 300 km wide by 500 km long large in slab events m 7 5 would produce even higher psa values within 100 km of the fault but the in slab motions attenuate much more rapidly with distance thus the hazard posed by moderate to large in slab events such as the 2001 nisqually earth quake is modest compared to that of a cascadia megathrust earthquake of m 8 in terms of the area that would experience damaging levels of ground motion

early palaeozoic rift related magmatism in variscan europe fragmentation of the armorican terrane assemblage early palaeozoic bimodal rift related magmatism is widespread throughout much of the variscides of europe it is traceable from the polish sudetes to nw iberia granitic plutonism generally predates cambro ordovician bimodal magmatism in the n bohemian massif this early palaeozoic granitic plutonism was generated by partial melting of cadomian basement whereas contemporaneous alkali granites with a mantle component are typical of the nw iberian massif silurian devonian mafic magmatism in the n bohemian massif massif central and nw iberian massif is partly preserved as obducted ophiolites compositional diversity displayed by cambro ordovician mafic magmatism can be accounted for by interaction between a spreading centre and an upwelling mantle plume this indicates that combined tensional forces and mantle plume convection assisted the early palaeozoic dispersal of terranes from the n gondwana margin continued fragmentation resulted in development of an archipelago of related terranes separated by a network of seaways and formation of oceanic crust

slow subduction of old lithosphere in the lesser antilles abstract the lesser antilles subduction zone is an extreme case of the subduction of old 90 m y lithosphere at a slow 2 cm y convergence rate focal mechanisms of the largest earthquakes in the area have been obtained using body and surface wave data during the time period 1950 1978 studied the subduction seismicity appears to represent primarily intraplate rather than interplate deformation all three large magnitude seven earthquakes were from intraplate normal faults no large thrust faulting earthquakes and few small ones occurred these observations suggest that the plate boundary is largely decoupled that subduction is at least partially aseismic and that the downgoing slab is in a state of extension

high pressure metamorphism in the early variscan subduction complex of the sw iberian massif abstract several units exposed in the boundary area of the ossa morena zone omz and the south portuguese zone spz preserve petrographic and thermobarometric evidence for an early metamorphic episode m1 developed under a high p low to intermediate t gradient related to early variscan subduction in the sw iberian massif in the omz these are the cubito moura unit p min 9 2 kbar and t 395 45 c blueschists from its basal melange p min 12 4 kbar and t 310 11 c and the underlying fuenteheridos group p 10 9 0 4 kbar and t 449 31 c the equivalent units in the spz are the la minilla formation p 8 7 0 4 kbar and t 388 16 c and the lawsonite pseudomorphs bearing pulo do lobo formation all these units formed part of an approximately ne verging orogenic wedge present coordinates developed by the accretion of subducted slabs of the outermost margin of gondwana and other elements of the rheic ocean realm from at least the middle devonian to the lowermost tournaisian high pressure rocks were subsequently emplaced on more internal zones of the omz that only experienced a younger high t low to intermediate p metamorphism m2 this high t event was coeval with magmatic activity from the uppermost devonian to the middle mississippian probably as a consequence of transtensional lithospheric thinning and or delamination of the lower crust and mantle lithosphere of the gondwana margin pre late devonian synorogenic sedimentation in forearc and back arc basins of the subduction complex evolved to a late devonian middle mississippian foreland basin system in early collisional stages finally a new middle late mississippian fold and thrust belt with opposite sw vergence and new foreland basins developed during late collisional stages

historical seismicity of the southeastern caribbean and tectonic implications we have relocated the twenty eight largest magnitude 4 3 ms 7 3 historical 1922 1963 earthquakes of the southeastern caribbean we also present new focal mechanisms for seven of these events the relocations are based on reported issp ands arrival times that we analyzed using generalized linear inversion techniques the new focal mechanisms were constrained by first motionp polarities as reported by the iss and as picked by us where records were available and by the polarities and ratios ofsh andssh andsv andssv arrivals that we determined from seismograms the results of the relocations are commensurate with the distribution of seismicity observed in the recent era hypocenters are shallow and intermediate in depth 0 200 km and the events occur almost exclusively in areas known to be currently seismic the frequent seismic activity in the vicinity of the paria peninsula venezuela is clearly a persistent feature of the regional earthquake pattern intermediate depth earthquakes indicative of subduction beneath the caribbean plate occur here and along the lesser antilles arc the grenadines seismic gap is confirmed as an area of low seismic moment release throughout the historical era trinidad and the eastern gulf of paria were also largely quiescent

p wave velocity tomography of the venezuelan region from local arrival times arrival times from the local seismological network of venezuela were used to estimate a three dimensional p wave velocity model for the region between longitude 60 74 w and latitude 6 14 n to a depth of more than 80 km the inversion was carried out by damped least squares describing the media by homogeneous velocity blocks the resolved lateral velocity variations in the first layer 0 30 km depth showed a correlation with the main stratigraphic features of the area while second layer 30 50 km depth showed the influence of moho depth variations through the region generating a pattern well correlated to the bouguer anomaly map lithospheric seismic velocities below the moho appear to be influenced by the major crustal fault systems an important low velocity zone is present below the triple junction of the fault systems of oca bocono and moron in northwestern venezuela farther south a similar low velocity zone is present below the junction of the bocono and the santa marta fault systems those are the two continental corners of the triangular maracaibo block below 80 km depth the fourth layer the low velocity zones show a connected pattern that follows or is adjacent to the crustal fault zones the presence of subducted atlantic lithosphere below the eastern venezuelan basin could explain the high velocity zone at this location a similar interpretation emerges from the tectonic wedging model previously proposed to explain the pronounced minimum of the gravity anomaly

cambrian ensialic rift related magmatism in the ossa morena zone evora aracena metamorphic belt sw iberian massif sm nd isotopes and shrimp zircon u th pb geochronology abstract the late ediacaran c 560 550 ma serie negra sediments of the evora aracena metamorphic belt ossa morena zone sw iberian massif preserve a record of the erosion of an avalonian cadomian magmatic arc and subsequent related turbiditic sedimentation detrital zircon from the serie negra is characterized by predominantly ediacaran and cryogenian ages with few paleoproterozoic and archean cores and a marked lack of grenvillian ages these features when combined with the metasediments enrichment in lree la yb 14 negative eu anomalies low 147 sm 144 nd values 0 121 and negative e nd 550 5 5 indicate that the protolith serie negra sediments were derived from a continental magmatic arc a period of late cadomian ca 560 540 ma tectonism was followed by an extended episode of widespread bimodal magmatism related to cambrian ca 540 500 ma rifting this tectonic inversion is expressed in the geological record by a regional early cambrian unconformity shrimp zircon u th pb ages from four felsic orthogneisses from the evora massif record cambrian 527 10 ma 522 5 ma 517 6 ma and 505 5 ma crystallization ages for their igneous protoliths this confirms the existence of widespread lower paleozoic igneous activity in the ossa morena zone i a lower cambrian ca 535 515 ma igneous felsic dominated sedimentary complex with calc alkaline signature and associated carbonate and siliciclastic deposition and ii a middle cambrian ordovician ca 515 490 ma igneous bimodal sedimentary complex with calc alkaline and tholeiitic signatures and associated dominant siliciclastic deposition but also carbonate sediments the cambrian felsic magmatism was characterized by negative eu anomalies la lu n 0 8 11 147 sm 144 nd 0 1289 0 1447 and e nd 500 ranging from 1 5 to 0 8 a tendency towards peraluminous compositions suggests late fractionation low degrees of partial melting or the mixing of crustal and mantle derived material in the magma source region some felsic rocks possibly represent the last residual melts of high temperature zircon undersaturated mafic magmas later affected by crustal contamination while others indicate partial melting of crustal metasediments variably contaminated by basaltic liquids the transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic n e morb products th n ta n 147 sm 144 nd 0 1478 0 1797 and e nd 500 values ranging from 6 4 to 7 3 while the n morb amphibolites have 147 sm 144 nd 0 1818 0 1979 and e nd 500 values of 5 8 and 7 0 reaching a maximum of 9 1 in contrast other amphibolites have a negative ta anomaly 1 35 n ta n 147 sm 144 nd values ranging from 0 1639 to 0 1946 and e nd 500 values of 3 5 to 5 2 suggesting derivation by crustal assimilation processes the sub alkaline igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling these results strengthen the proposed geodynamic scenarios for the sw iberian massif by which cadomian accretion gave rise to an ensialic rift that developed into a proto oceanic basin and incipient spreading opening of the rheic ocean a similar transition from a convergent to a divergent plate boundary during the ediacaran to cambrian ordovician has also been reported in other segments of the northern gondwana margin

strain and strain rate in a synkinematic trondhjemitic dike evidence for melt induced strain softening during shearing bohemian massif czech republic abstract emplacement related deformation of a cambrian trondhjemitic dike located at the western border of the tepla barrandian unit central european variscides is studied in detail the trondhjemitic melt was emplaced at t 750 c into an active low temperature ca 350 c east northeast trending dextral transcurrent shear zone thermal modelling indicates that the rheologically critical melt fraction and the solidus of the dike were achieved after 1 and 3 days of cooling respectively the major part of the shearing occurred within 8 days after the melt emplaced the zonation of the dike in strain magnitude mineralogy and geochemistry can be explained by the laterally varying rheology from margin to centre during cooling and shearing the deformation was volume constant and the strain data plot in the apparent constrictional field the unusually high value of the calculated longitudinal strain rate 2 8 10 6 s 1 equivalent to a displacement rate of 2 cm h 1 is probably related to the intruding melt that lubricated the shear zone and thus enhanced its displacement velocity consequently melts that intrude as dikes into active transcurrent shear zones may significantly weaken the strength of the middle and upper continental crust

a preliminary paleomagnetic pole for mid cretaceous rocks from tobago further evidence for large clockwise rotations in the caribbean south american plate boundary zone abstract the island of tobago occupies the eastern end of the central igneous belt of the caribbean south american plate boundary zone volcaniclastic sediment of the albian 100 ma tobago volcanic group and dikes of similar age within it were sampled in two homoclinal sections with different attitudes the mean of virtual geomagnetic poles for 12 sites 25 4 n 24 1 e a95 4 2 is well defined pre tilting and apparently reliable yet is far removed from a similar age reference pole for south america five other paleomagnetic studies of cretaceous rocks from widely separated localities farther west in the plate boundary zone yield pole positions that are remarkably similar to the tobago pole poles obtained from the guajira peninsula of colombia the islands of aruba and bonaire and the caribbean mountains of venezuela are among those that agree with the tobago result the paleolatitudes for study areas within the plate boundary zone are consistent with an origin on or near south america yet the poles throughout the zone are rotated roughly 90 dextral relative motion between the caribbean and south american plates was probably responsible for the rotation

gondwana break up and the northern margin of the saxothuringian belt variscides of central europe at the northwestern edge of the hercynian bohemian massif saxothuringian belt new u pb zircon age data from rift related magmatic rocks indicate that the initiation of gondwana break up in this area started during the middle to upper cambrian magmatic rocks from a bimodal morb to within plate volcanic sequence in the vesser area are dated between ca 517 and 501 ma the volcaniclastic sequences analysed exhibit basal layers of conglomerates and mature sandstones which can be correlated with a widespread gondwana derived onlap horizon of an uppermost cambrian tremadocian age that links the vesser area with the saxothuringian continental basin the association of the vesser rocks with the saxothuringian terrane as part of the armorican terrane assemblage is further demonstrated by a coeval magmatic development and by identical detrital components which are derived from a common cadomian basement white mica with a ca 539 ma k ar minimum age and inherited zircon signatures the vesser unit situated between the nw margin of the saxothuringian zone and the mid german crystalline zone probably represents a n facing remnant of an ocean continent transition of the or within the armorican terrane assemblage and involves sections of the early break up process at the peri gondwanan shelf south of the rheic ocean

velocity field across the southern caribbean plate boundary and estimates of caribbean south american plate motion using gps geodesy 1994 2000 global positioning system gps observations between 1994 and 2000 at twenty two sites in the lesser antilles and northern south america indicate that the caribbean plate along its southern boundary slips at a rate of 20 5 2 mm a with an azimuth of n 84 2 e at 65 w relative to the south american plate east of 68 w 80 of the dextral slip is contained within a 80 km wide shear zone centered on the el pilar san sebastian fault system west of 68 w the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending bocono fault 9 11 mm a in western venezuelan and an offshore system near the northern coast

seismic hazard maps of mexico the caribbean and central and south america abstract the growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures due to an insufficient knowledge of existing seismic hazard and or economic constraints minimization of the loss of life property damage and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard we have produced a suite of seismic hazard estimates for mexico the caribbean and central and south america one of the preliminary maps in this suite served as the basis for the caribbean and central and south america portion of the global seismic hazard map gshm published in 1999 which depicted peak ground acceleration pga with a 10 chance of exceedance in 50 years for rock sites herein we present maps depicting pga and 0 2 and 1 0 s spectral accelerations sa with 50 10 and 2 chances of exceedance in 50 years for rock sites the seismicity catalog used in the generation of these maps adds 3 more years of data to those used to calculate the gsh map different attenuation functions consistent with those used to calculate the u s and canadian maps were used as well these nine maps are designed to assist in global risk mitigation by providing a general seismic hazard framework and serving as a resource for any national or regional agency to help focus further detailed studies required for regional local needs the largest seismic hazard values in mexico the caribbean and central and south america generally occur in areas that have been or are likely to be the sites of the largest plate boundary earthquakes high hazard values occur in areas where shallow to intermediate seismicity occurs frequently

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

structure and deformation history of the northern range of trinidad and adjacent areas conflicting models have been proposed for both the evolution of northern south america and the neotectonics of the south caribbean plate boundary zone the trinidadian portion of the margin is particularly controversial but surprisingly it has been little studied we present a structural analysis of trinidad s northern range pertinent updates of the island s stratigraphy and sedimentology and new zircon fission track age determinations and use them to constrain trinidad s geologic history and to better understand the controlling tectonic processes in our interpretation trinidad s three e ene striking ranges which are separated by late neogene recent depocenters expose 1 the northern range group generally greenschist metamorphosed upper jurassic to cretaceous north facing continental slope sediments of the northern range deposited on the northern south american passive margin 200 400 km to the wnw and 2 the trinidad group cretaceous paleogene shelf slope sediments of the central and southern trinidad deposited less than 100 km wnw of their present location a small allochthon composing the sans souci group cretaceous tholeiitic volcaniclastic basaltic and gabbroic rocks sans souci formation and sediments toco formation now in the northeastern northern range has been transported hundreds of kilometers from the west with the caribbean plate despite earlier references to cretaceous orogenesis all deformation in trinidad is of cenozoic age the first deformation in the northern range d1 formed north vergent nappes and induced greenschist metamorphism probably in the late eocene or oligocene the nappes developed either by the underthrusting of the proto caribbean crust beneath south america due to convergence between north and south america or as gravity slides caused by oversteepening induced by this convergence and or the passage of the caribbean plate s peripheral bulge and arrival of its foredeep northern range d2 deformation is south vergent and represents the incorporation of northern range metasediments into the caribbean accretionary prism the transition to d3 brittle transpressive right lateral strike slip faulting is interpreted to be due to the uplift and east southeastward transpressive emplacement of northern range caribbean prism rocks onto the south american stepped shelf this emplacement formed the miocene transpressive thrust belts and foreland basin in central and southern trinidad in the final phase of northern range deformation d4 e w normal faults and shear zones and conjugate nnw sse and ne sw normal faults developed and displacement on preexisting e w right lateral strike slip faults continued the 11 ma northern range zircon fission track ages suggest rapid uplift from the late miocene to recent late miocene subsidence of the tobago platform immediately to the north of the northern range and greater than 3 km of normal down to the north displacement indicated for the north coast fault zone separating the northern range and tobago platform leads us to postulate that the rapid uplift of the northern range was in response to the northward detachment of the tobago platform from above the northern range along the north dipping transtensional north coast fault zone this late miocene change in deformation style can be explained by a change from caribbean south american right lateral transpression to right lateral strike slip generally striking 080 this has generally induced a component of extension on pre existing faults striking at greater than 080 and a component of compression on faults striking at less than 080

probabilistic seismic hazard assessment at the eastern caribbean islands a probabilistic seismic hazard analysis has been performed to compute probabilistic seismic hazard maps for the eastern caribbean region 10 n 19 n 59 w 64 w which includes in the north the leeward islands from anguilla to dominica and in the south the windward islands from martinique to grenada barbados trinidad and tobago the analysis has been conducted using a standard logic tree approach that allowed systematically taking into account the model based i e epistemic uncertainty and its influence on the computed ground motion param eters hazard computations have been performed using a grid of sites with a space resolution of 0 025 degrees covering the territory of the considered islands two different computation methodologies have been adopted the standard cornell mcguire approach cornell 1968 mcguire 1976 based on the definition of appropriate seismogenic zones sz and the zone free approach developed by woo 1996 which overcomes the ambiguities related with the definition of seis mic sources the interplay and complexities between shallow crustal intraplate and interface subduction seismicity of the caribbean region have been thoroughly investigated by merging all available databases a comprehensive and updated earthquake catalog for the region has been compiled also a thorough investigation has been undertaken to identify the most suitable ground motion prediction equa tions to be used in the analyses uniform hazard spectra have been calculated for the horizontal component of ground motion rock and level site conditions 4 return periods rp 95 475 975 and 2475 yr and 22 spectral accelerations sa with structural periods ranging from 0 to 3 s sas at 0 2 and 1 0 s for 2475 yr rp have been calculated to allow the definition of seismic hazard in the region of study according to the international building code ibc international code council icc 2009

long term earthquake prediction in central america and caribbean sea based on the time and magnitude predictable model abstract instrumental and historical information on strong mainshocks for 12 seismogenic sources in central america and caribbean sea has been used to show that the interevent time t t in years between two strong earthquakes and the magnitude m f of the following mainshock are given by the relations log t t 0 30 m m i n 0 48 m p 0 69 log m 0 13 70 m f 0 98 m m i n 0 31 m p 0 28 log m 0 4 55 where m min is the surface wave magnitude of the smallest mainshock considered m p the magnitude of the preceding mainshock and m 0 the moment rate per year in each source on the basis of these relations the probability of the occurrence of a mainshock during the decade 1993 to 2002 as well as the magnitude of this expected mainshock in each seismogenic source has been calculated the highest probability p 10 0 67 was estimated for the seismogenic source of el salvador a 1 for the occurrence of a large earthquake with expected magnitude m f 7 5 and high probabilities p 10 0 55 were estimated for the seismogenic sources of jamaica c 3 and puerto rico c 5 for earthquakes with expected magnitudes m f 7 5 in both sources

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

comprehensive probabilistic seismic hazard analysis of the andaman nicobar regions an updated catalog of earthquakes has been prepared for the andaman nicobar and adjoining regions the catalog was homogenized to a unified magnitude scale and declustering of the catalog was performed to remove aftershocks and foreshocks eleven regional source zones were identified in the study area to account for local variability in seismicity characteristics the seismicity parameters were estimated for each of these source zones and the seismic hazard evaluation of the andaman nicobar region has been performed using different source models and attenuation relations probabilistic seismic hazard analysis has been performed with currently available data and their best possible scientific interpretation using an appropriate instrument such as the logic tree to explicitly account for epistemic uncertainty by considering alternative models source models maximum magnitude and attenuation relationships the hazard maps for different periods have been produced for horizontal ground motion on the bedrock level

tectonic evolution of the boundary between the central iberian and ossa morena zones variscan belt southwest spain three tectonometamorphic units can be differentiated in the boundary between the central iberian and ossa morena zones of the iberian massif variscan belt the three units have been named the northern unit central unit and southern unit the northern unit corresponds to the border of the central iberian zone it evolved at low temperature and intermediate or low pressure metamorphic conditions and was affected by top to the se ductile shearing the central unit placed under the northern unit preserves high pressure silurian eclogitic assemblages retrograded by high to medium temperature and finally low temperature ductile shearing with top to the nw sense of movement oblique left lateral the central unit is superposed on the southern unit the latter corresponds to the border of the ossa morena zone and underwent low pressure intermediate temperature metamorphism synchronous with right lateral top to the se ductile shearing the envisaged tectonic evolution is as follows after a stage of lower paleozoic rifting subduction of the central unit under the northern unit took place in silurian times as a result of the crustal thickening a gravitational instability developed giving way to left lateral extensional shearing that affected the entire central unit the combined action of oblique thrusting at the front of the wedge and oblique extensional shearing at the rear caused the exhumation of the high pressure rocks of the central unit this tectonic evolution reveals that the boundary between the central iberian and ossa morena zones is a suture of the variscan belt

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

segmentation of the lesser antilles subduction zone abstract precise hypocentral locations of earthquakes recorded on local seismic networks from 1978 to 1984 have established the configuration of the benioff zone beneath the lesser antilles island arc there are two distinct segments to the zone one to the north of martinique which trends nnw and one to the south of st lucia which trends nne the northern zone dips at 60 50 the southern zone has a dip of 50 45 in the north but is vertical in the south pleistocene volcanoes are aligned in distinct segments which closely mirror the kink in the benioff zone mid miocene swarms of dykes in martinique and st lucia have nw and ne azimuthal modes respectively we interpret this to mean that this kink in the subduction zone existed as long ago as the miocene the kink may represent the deformation of a single subducting plate or two separate north and south american plates subducting beneath the caribbean plate with a triple junction in the region of martinique st lucia

metamorphic and deformational imprint of cambrian lower ordovician rifting in the ossa morena zone iberian massif spain abstract the high temperature metamorphism recorded in the valuengo and monesterio areas constitutes a rare occurrence in the ossa morena zone of southwest iberia where low grade metamorphism dominates the metamorphism of the valuengo area has been previously considered either cadomian or variscan in age whereas that of monesterio has been interpreted as a cadomian imprint however these areas share important metamorphic and structural features that point towards a common tectonometamorphic evolution the metamorphism of the valuengo and monesterio areas affects late proterozoic and early cambrian rocks and is syn kinematic with a top to the north mylonitic foliation which was subsequently deformed by early variscan folds and thrusts the u pb zircon age 480 7 ma we have obtained for an undeformed granite of the valuengo area is consistent with our geological observations constraining the age of the metamorphism we propose that this high temperature metamorphic imprint along a nw se ductile extensional shear zone is related to the crustal extension that occurred in the ossa morena zone during the cambro ordovician rifting in the same way the tectonothermal effect of the preorogenic rifting stage may have been wrongly attributed to orogenic processes in other regions as well as in this one

a hybrid inversion technique for the evaluation of source path and site effects employing s wave spectra for subduction and upper crustal earthquakes in el salvador we propose a hybrid inversion analysis hia technique aimed at incorporating earthquakes from different seismogenic sources in one single inversion scheme the application of this technique provides estimations of the source path and site effects at 23 strong motion stations in el salvador central america the strong motion dataset comprises 404 triaxial accelerograms corresponding to 63 subduction and upper crustal earthquakes with m s magnitudes between 3 0 and 7 8 application of the hia technique reveals 1 good matching of the estimated source spectra with those derived from the 2 point source model 2 rapid and low attenuation patterns characterizing the upper crustal volcanic belt and subduction zone respectively and 3 soil transfer functions characterized by amplification ratios larger than those derived from spectral ratio techniques by a factor of two reference site dependent techniques yield similar soil transfer functions at all stations whereas the horizontal to vertical spectral ratio technique yields similar results at sites characterized by clearly predominant peaks

crystallographic preferred orientations and microstructure of a variscan marble mylonite in the ossa morena zone sw iberia the mylonitic marbles of the cherneca shear zone a variscan sinistral strike slip structure developed in the ossa morena zone sw iberia related to the emplacement of the santa olalla igneous complex were studied in detail different mylonites from protomylonites to ultramylonites were analyzed by electron back scattering diffraction ebsd in order to determine the crystallographic preferred orientation cpo of calcite the cpos show very good agreement with experimental torsion work giving suitable interpretations of the operative slip systems and strain quantifications thus the obtained natural cpos validate the experimental approaches a wide range of observed textures and microstructures are mainly controlled by the amount of shear strain the presence of secondary phases and the development of antithetic subsidiary shears the effect of secondary phases and the nucleation of antithetic shear bands on texture development are discussed

age constraints to the relationships between magmatism metamorphism and tectonism in the aracena metamorphic belt southern spain the aracena metamorphic belt amb southwest iberian peninsula is characterized by the following geological elements a a high temperature low pressure ht lp metamorphic belt a few kilometres wide and more than 200 km long b a linear belt of oceanic amphibolites with a low pressure inverted metamorphic gradient c crustal scale ductile shear zones and d mafic noritic intrusions of high mg andesite boninite composition the relationships between these elements led to the proposal of a model of ridge subduction for this sector of the hercynian belt of europe this interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously the results of a geochronological study ar ar rb sr and sm nd clearly support a late paleozoic tectonic evolution at an active continental margin the time evolution of the metamorphism in the oceanic domain ranging from 342 6 0 6 ma in the west to 328 4 1 2 ma in the east over a distance of 70 km along the metamorphic belt support a tectonic model of triple junction migration responsible for the creation at depth of a slab free window with decisive consequences for the thermal evolution of the region the origin of the linear metamorphic belt of ht lp regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple junction at the continental margin

supergene enrichment of precious metals by natural amalgamation in the las cruces weathering profile iberian pyrite belt sw spain abstract natural au ag hg alloys occur in the las cruces ore deposit in the eastern part of the iberian pyrite belt they are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene cu rich mineralization drill core analyses show a heterogeneous distribution of au ag and hg within the weathering profile with mean values of 5 1 ppm 155 ppm and 52 ppm respectively in general the absolute tenures increase towards the bottom of the weathered profile mineralogical studies conducted on samples from the active mine workings indicate that hg and precious metals occur mainly as au ag hg alloys these associations constitute the best potential resource for precious metals at the las cruces deposit this paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes combining paragenetic information mineral chemistry and the data pertaining to the solubilities of au ag and hg in a weathering profile we suggest a two stage genetic model for the formation of the las cruces au ag hg mineralization 1 release of au ag and hg from the massive sulfide deposit by weathering processes during the gossan formation at ph 0 9 v conditions au ag and hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental au halides oxides and sulfates and 2 remobilization of hg ag and au in the gossan after the deposit was buried beneath the neogene carbonate rich sedimentary cover the buffering capacity of the percolating fluids due to their interaction with the carbonate rich sedimentary pile leads to significant mineralogical and geochemical changes at near neutral conditions ph 6 7 eh 0 v hg ag and au are newly remobilized as thiosulfate sulfate and hydroxide complexes and newly fixed by sorption during ferric hydroxide formation and as sulfates several cycles of dissolution precipitation of au ag and hg near the redox front occur by oscillations in the water table and changes in the ph eh conditions the interaction of downward migrating fluids with high reductant lithologies black shales and massive sulfides seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar ag sulfides and sulfosalts as well as the precipitation of au ag hg amalgams

tectonics of the beja acebuches ophiolite a major suture in the iberian variscan foldbelt the beja acebuches ophiolitic complex baoc south portugal spain corresponds to a high grade metamorphic belt along the boundary between ossa morena and the south portuguese zones and comprises a lithostratigraphic sequence including from top to bottom metabasalts metamorphosed multiple dyke intrusions in gabbro flasergabbros and metaserpentinites it is affected by three deformation phases d1 affects the ophiolite lower stratigraphic units and is represented by a mylonitic cleavage with a stretching lineation where shear criteria indicates the sense of shear to be towards the north north east this deformation event can be related to the ophiolite emplacement above the crystalline footwall of the serpa antiform affecting precambrian basement and cambrian cover rocks the obduction polarity ist north eastwards similar to the subduction polarity that generates the beja gabbroic complex bgc implying a flake geometry the second deformation phase d2 is represented by an intense wnw ese sinistral shear event which is responsible for the shattered appearance of the suture d2 is reactivated later by a more brittle d3 event involving thrusting to the south west again with a sinistral component 40ar 39ar isotopic ages were obtained for metamorphosed multiple dyke intrusions in the baoc s gabbro 342 6 1 4 ma for metagabbroic cumulates 340 7 1 9 ma and for the undeformed unmetamorphosed bgc 341 1 1 3 ma occurring to the north of the ophiolitic suture these ages reflect a last regional cooling event in the area which post dates the ophiolite emplacement and the intrusion of the bgc through this oceanic sequence

u pb age constraints on variscan magmatism and ni cu pge metallogeny in the ossa morena zone sw iberia new u pb zircon ages from the santa olalla igneous complex have been obtained which improve the knowledge of the precise timing of variscan magmatism in the ossa morena zone sw iberia this complex has a special relevance as it hosts the most important ni cu platinum group element pge mineralization in europe the aguablanca deposit u pb zircon ages have been obtained for seven samples belonging to the santa olalla igneous complex and spatially related granites with the exception of the cala granite 352 4 ma which represents an older intrusion the bulk of samples yield ages that cluster around 340 3 ma the santa olalla tonalite 341 5 3 ma the sultana hornblende tonalite 341 3 ma a mingling area at the contact between the aguablanca and santa olalla stocks 341 1 5 ma the garrote granite 339 3 ma the teuler granite 338 2 ma and dioritic dykes from the aguablanca stock 338 6 0 8 ma the bodonal cala porphyry which has also been dated 530 3 ma comprises a group of sub volcanic rhyolitic intrusions belonging to the bodonal cala volcano sedimentary complex which hosts the igneous rocks the knowledge that emplacement of the aguablanca deposit was related to episodic transtensional tectonic stages during the variscan orogeny will be fundamental in future mineral exploration in the ossa morena zone

kernel estimation methods for seismic hazard area source modeling in probabilistic seismic hazard analysis the representation of seismic sources by area zones is a standard means of data reduction however where the association between seismicity and geology is complex as it is in many tectonic regimes the construction of zone geometry may become contentiously subjective and ambiguities may end up being resolved through appeal to the nonscientific rule of conservatism or pragmatism although consideration of alternative zonations within a logic tree framework provides a channel for some of the uncertainty it does not address the fundamental validity of the zonation procedure itself in particular neither the minimal assumption of uniform seismicity within a zone nor the euclidean geometry of a zone accord with the fractal spatial distribution of seismicity and the magnitude insensitivity of zonation ignores the spatial extent and correlations of different sized earthquakes an alternative procedure for area source modeling avoids euclidean zones and is based statistically on kernel estimation of the activity rate density inferred from the regional earthquake catalog the form of kernel is governed by the concepts of fractal geometry and self organized criticality with the bandwidth scaling according to magnitude in contrast with zonal models for intraplate regions the kernel estimation methodology makes provision for moderate earthquakes to cluster spatially while larger events may migrate over sizeable distances

variscan intracontinental deformation the coimbra cordoba shear zone sw iberian peninsula the coimbra cordoba shear zone is a major lineament roughly parallel to the nw se variscan structures of the southern iberian peninsula inside the shear zone evidence for a non coaxial strain path exists from structural microstructural and lattice preferred orientation data on quartz plane strain is suggested by the study of microstructures in the xy and yz sections in all formations occurring in the shear zone with increasing strain a mylonitic series develops the deformation contemporaneous with epizonal to mesozonal metamorphism is responsible for 1 1 the regional subvertical foliation oblique to the shear zone 2 2 the well defined subhorizontal lineation striking nw se 3 3 the discrete planes of shear roughly parallel to the shear zone the data are interpreted as resulting from a left lateral slip motion with a displacement of at least 72 km in the light of plate tectonics it is inferred that the coimbra cordoba lineament could have been a suture zone which evolved into an intracontinental left lateral shear zone during the variscan orogeny of the ibero armorican arc

a gps estimate of relative motion between north and south america gps velocity data are used to estimate the euler vector describing rigid body motion of north america relative to south america assuming the boundary between the north and south american plates is located near the fifteen twenty fracture zone in the equatorial atlantic the euler vector predicts extension across the royal trough up to 1 mm yr and convergence across the barracuda ridge at about 2 mm yr in agreement with geological estimates averaged over tens of millions of years further west convergence between north and south america at rates up to 8 mm yr may contribute to deformation of the caribbean plate along its southwest boundary with south america

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

melt enhanced deformation a major tectonic process convergent tectonics between continental crustal blocks result in deep burial and anatexis of supracrustal rocks anatectic and or mantle derived melts combine to form a melt weakened zone in the thickened lower crust the accumulation of melt eventually leads to crustal failure along melt lubricated shear zones rapid 1 mm yr vertical component movements of large crustal blocks result we refer to these crustal displacements as tectonic surges the melt lubricated shears are characterized by the close association of sheared country rocks with foliated or massive igneous sills and plutons rocks that formed at different crustal levels are juxtaposed across these shear zones one result of surges with large lateral component of movement is metamorphic inversion with high pressure and high temperature metamorphic rocks structurally over lower pressure and temperature assemblages large and rapid vertical surges may displace crust containing abundant melt and may result in high t p including granulite facies metamorphism and preservation of metamorphic textures caused by rapid decompression

ediacaran palaeozoic tectonic evolution of the ossa morena and central iberian zones sw iberia as revealed by sm nd isotope systematics abstract sm nd isotopic analyses of palaeozoic sedimentary and igneous rocks in the southwest iberian massif western end of the european variscan belt are presented in order to unravel its complex poly orogenic evolution during the closure of the rheic ocean and the amalgamation of pangea the gondwanan margin in southwest iberia sw iberia is subdivided into the ossa morena and central iberian zones separated by the badajoz cordoba shear zone which represents a cryptic suture zone between these terranes the relationships between these terranes and between units preserved within the suture zone e g the sierra albarrana group during the palaeozoic and neoproterozoic are controversial sm nd isotopic studies of representative sedimentary sequences covering the entire pre variscan record of the ossa morena and central iberian zones show very similar characteristics from the uppermost ediacaran onwards these data indicate that their accretion to one another must have been completed by the late neoproterozoic ediacarin that time an event assigned to cadomian orogeny and that they never separated substantially from each other since that time the sm nd isotopic composition of the sierra albarrana group metasedimentary rocks is similar to that of the pre cadomian sequences of the ossa morena zone serie negra suggesting derivation from a common source the common provenance of the palaeozoic sequences in the two zones is identical to that of the pre cadomian serie negra of the ossa morena zone which in accordance with the data presented herein and published u pb zircon data indicates a west african affinity

tectonic setting of the north gondwana margin during the early ordovician a comparison of the ollo de sapo and famatina magmatic events abstract this paper presents a comparison of compiled geochronological and geochemical data from the ollo de sapo and famatina magmatic events the ollo de sapo magmatic sequence is located in northwest iberia and was emplaced during the early ordovician from 495 to 474 ma the famatina complex is a magmatic sequence located in northern argentina that was emplaced during the early to mid ordovician from 483 to 463 ma these magmatic events are currently interpreted to have been emplaced in different tectonic settings despite both having occurred along the north gondwana margin geochronological data indicates that these magmatic events occurred contemporaneously over at least 9 m y and therefore can provide a snapshot of the northern gondwana margin during the mid ordovician major element data indicates that both magmatic suites are calc alkaline to alkali calcic and trace element and ree data show magmatic signatures that are indistinguishable this study highlights the similarity between the ollo de sapo and the famatina magmatic suites and discusses alternative models for their emplacement based on paleomagnetic and paleobiogeographical data these data indicate that the ollo de sapo was likely emplaced in a subduction zone setting while the famatina magmatic suite may be of parautochthonous origin to gondwana implying that the pampeanan margin may not have been active during the early to mid ordovician

early paleozoic rifting and bimodal volcanism in the ossa morena zone of south west spain lower paleozoic volcanic members have been investigated by geological petrographical and geochemical means in a traverse across the ossa morena zone omz in south west spain

thermal modelling in low pressure high temperature metamorphic belts abstract low pressure high temperature metamorphic belts occur throughout the world they display a characteristic metamorphic style which has remained unchanged with time they are found in disparate tectonic settings including magmatic arcs regions of extension regions of thickened crust in continent continent collision zones and accretionary wedges they are commonly characterized by an abundance of granitoid plutons pressures of metamorphism are primarily less than or equal to that of the aluminosilicate triple point approximately 4 kbar while temperatures are in the range 500 750 c with rare exceptions inferred ptt paths are nearly isobaric and recrystallization was rapid and prograde metamorphic thermal gradients are commonly in the range 60 150 c km these conditions necessitate the presence of a large component of advective heat transfer and or anomalously high basal heat flow during metamorphism the large magmatic fluxes associated with the formation of magmatic arcs provide an adequate heat source for low pressure metamorphism lpm lithospheric extension is likely to produce lpm only if the degree of thinning is large 3 and there is additional heat from magmas the generation of lpm by crustal thickening requires either a large component of advective heating by magmas anomalously high basal heat flow or pre thickening lithospheric extension lpm in this environment must necessarily be accompanied by plutonic activity advection of heat by aqueous fluids may provide a significant contribution to the thermal budget but acting along is unlikely to produce lpm regional lpm induced by advective sources rarely occurs along a geotherm which increases monotonically with depth or synchronously across the region at a given depth it occurs over time as a series of overlapping temporally separate and spatially localized thermal events

magma emplacement in transpression the santa olalla igneous complex ossa morena zone sw iberia the santa olalla igneous complex a late variscan group of intrusions located in the ossa morena zone sw iberia has been the focus of a gravity and structural study the structure outlined by the foliation map is complex showing two different structural domains one characterized by vertical and the other by horizontal magmatic foliations the vertical fabrics are restricted to the ne half of the complex which is in direct contact with a variscan sinistral strike slip fault cherneca fault whereas the horizontal fabrics are developed in the sw half of the complex which is characterized by a horizontal tabular geometry gravity modeling indicates that the deeper floor of the plutons is closely related to the ne margin and the cherneca fault an emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results 1 magma ascent was favored by releasing bends in the trace of the cherneca fault 2 when magma reached the present level it intruded to the sw with a horizontal sheet geometry generating the subhorizontal foliation domain 3 after emplacement the ne half of the complex suffered the external tectonic stress field provoked by sinistral motion along the cherneca fault subsequently generating the subvertical magmatic foliation domain

space and time in the tectonic evolution of the northwestern iberian massif implications for the variscan belt recent advances in geochemical studies of igneous rocks isotopic age data for magmatism and metamorphism quantitative pressure temperature p t estimates of metamorphic evolution and structural geology in the northwestern iberian massif are integrated into a synthesis of the tectonic evolution that places the autochthonous

relocated aftershocks of the march 10 1988 trinidad earthquake normal faulting slab detachment and extension at upper mantle depths abstract we relocated aftershocks of the march 10 1988 earthquake off the east coast of trinidad in order to determine the fault plane for the main shock and to understand this anomalous earthquake series the march 10 main shock m w 6 6 was the first significant instrumentally recorded earthquake to occur in the epicentral region east of trinidad the reported depth of the main shock 53 km by the international seismological centre isc is unusual but is consistent with observations of pp p times the main shock harvard centroid moment tensor cmt solution nearly pure normal faulting on nodal planes striking ene is also unusual given the depths of the seisms and the rarity of extensional faulting at these depths using p arrival times tabulated by the isc we relocated the aftershocks using the joint hypocentral determination method to find new locations relative to the main shock in map view the relocated epicenters form a tight elliptical cluster with major axis trending wnw ese and minor axis nne ssw virtually all the seisms in the earthquake series occurred at depths ranging from 30 to 60 km deeper than normal crustal earthquakes in an area previously not considered a locus of subducting lithosphere the aftershocks define a distinct plane dipping 34 nw this dip is consistent with the harvard cmt focal mechanism of the main shock one cmt nodal plane dips 38 n and strikes ene very close to our estimate of the active fault plane thus the march 10 aftershocks are consistent with slip on the north dipping plane of the main shock because the earthquake series occurred 100 km se of oceanic south american slab subducting beneath the caribbean plate at a depth generally inconsistent with shallow normal faulting outside of slabs we interpret the main shock as having occurred deep 50 km in south american lithosphere currently moving nw into the subduction zone the occurrence of this earthquake indicates an extensional stress applied to the lithosphere of the south american plate likely related to a combination of slab pull to the nw as the slab subducts beneath the caribbean plate and to detachment of the subducting lithosphere from buoyant continental south america

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

a large eddy simulation study of a quasi steady stably stratified atmospheric boundary layer abstract using the large eddy simulation les technique the authors study a clear air stably stratified atmospheric boundary layer abl as it approaches a quasi steady state the beaufort sea arctic stratus experiment base dataset is used to impose initial and boundary conditions the authors explore the parameter space of the boundary layer by varying latitude surface cooling rate geostrophic wind inversion strength and surface roughness recognizing the critical dependence of the results of les on the subgrid scale sgs model they test and use a nonlinear sgs model which is capable of reproducing the effects of backscatter of turbulent kinetic energy tke and of the sgs anisotropies characteristic for shear driven flows in order to conduct a long term les so that an abl can reach a quasi steady state a parallel computer code is developed and simulations with a spatial domain of up to 963 grid points are performed the authors analyze the evolution of the mean wind potential temperature

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

oblique collision and tectonic wedging of the south american continent and caribbean terranes our studies of the surface structures seismicity and gravity anomalies of the caribbean south american plate boundary zone of northeast venezuela and trinidad show that the crustal and upper lithospheric structure and kinematics of this zone are complex and differ markedly along strike we propose a model of the zone9s lateral transition from near trinidad west to caracas emphasizing three concepts 1 the steepening detachment and then sinking away of atlantic oceanic lithosphere that is was attached to the northern edge of continental south america 2 the wedging seaward and imbricate thickening of the northern margin of the continent in the region of the detaching atlantic slab the continental wedge overrides the slab and is overridden by terranes attached to the caribbean plate and 3 that the structural and kinematic transitions are a consequence of the progressive oblique collision between continental south america and the overriding caribbean terranes

cadomian vs variscan evolution of the ossa morena zone sw iberia field and 40ar 39ar mineral age constraints abstract six hornblende and ten muscovite concentrates have been dated from three contrasting tectonic units exposed within the ossa morena zone of the iberian massif these include 1 the obejo valsequillo domain north of the badajoz cordoba shear zone 2 the sierra albarrana structural unit immediately south of the badajoz cordoba shear zone and 3 the thermal some exposed within the olivenza monesterio antiform zafra monesterio domain hornblende from foliated amphibolite in the obejo valsequillo domain siera negra unit displays internally discordant 40ar 39ar age spectra as a result of both intracrystalline contamination with extraneous argon and slight rejuvenation 36ar 40ar vs 39ar 40ar isotope correlations are generally well defined and yield ages of c 550 560 ma these are interpreted to date cooling following late precambrian early paleozoic cadomian tectonothermal activity this was followed by slight variscan rejuvenation at c 375 400 ma muscovite from this unit displays internally discordant age spectra which reflect more extensive variscan rejuvenation of intracrystalline argon systems which had initially cooled below appropriate blocking temperatures at c 560 ma hornblende and muscovite from the sierra albarrana domain sierra albarrana group record 40ar 39ar plateau and isotope correlation ages which range between c 392 ma and 351 ma these results indicate that complete variscan rejuvenation was followed by relatively rapid post metamorphic cooling hornblende separated from various lithologie elements exposed in the olivenza monesterio antiform yield variable results hornblende within a mafic xenolith in the monesterio granodiorite records an isotope correlation age of c 553 ma which is interpreted to date the last cooling through appropriate argon retention temperatures hornblende within amphibolite of the montemolin series lower serie negra records internally discordant age spectra which reflect extensive variscan c 390 400 ma rejuvenation of intracrystalline argon systems which had initially recorded ages c 500 ma muscovite was concentrated from several lithologie elements in this area including 1 mylonitic monesterio granodiorite 2 metasedimentary rocks of the montemolin succession displaying high grade sillimanite potassium feldspar bearing assemblages and 3 migmatitic schist of the siere negra group these muscovite concentrates display similarly discordant 40ar 39ar age spectra which suggest significant but incomplete variscan rejuvenation occurred at c 400 ma this appears to have affected intracrystalline argon systems which had initially cooled through appropriate closure temperatures sometime prior to c 450 ma following an initial high grade cadomian metamorphism the 40ar 39ar results clearly reflect a variable complex and polymetamorphic evolution for the ossa morena zone internal consistency of data within each regional tectonic unit compared with marked contrast between the units provides evidence of the extremely heterogeneous variscan tectonothermal overprint the results demonstrate that the present tectonic architecture of the ossa morena zone was not solely the result of late variscan wrench tectonics but instead a consequence of processes active since at least the lower middle devonian juxtaposition of regional structural units with contrasting tectonothermal histories and recording variable rates and extents of uplift are consistent with maintainence of an overall transpressional variscan tectonic regime

the structure of a major suture zone in the sw iberian massif the ossa morena central iberian contact abstract we have investigated the stratigraphy structure and metamorphism of the boundary between the ossa morena zone omz and the central iberian zone ciz two significant continental portions of the variscan iberian massif the omz ciz contact is marked by a strongly deformed and metamorphosed nw se trending narrow band namely the central unit in which partially retrogressed eclogites are included during the middle late devonian the ciz overthrust the omz and in the footwall km scale recumbent folds and thrusts developed with decoupling and underplating of the lower crust at the same time in the hanging wall there took place intense though localized back folding and back shearing in the early carboniferous a transtensional tectonic regime sank the overthrust block resulting in the exhumation of eclogites these eclogites probably came from the underthrust omz lower crust and they are at present included in the suture zone central unit of this continental collision the extension is responsible for the origin of a basin and bimodal magmatism on the southern border of the ciz a late episode of folding and fracturing significantly contributed to the final complex picture of this suture boundary

u pb zircon ages and structural development of metagranitoids of the tepla crystalline complex evidence for pervasive cambrian plutonism within the bohemian massif czech republic u pb zircon dating of three metagranitoids situated within a tilted crustal section at the northwestern border of the tepla barrandian unit tepla crystalline complex tcc yields similar cambrian ages the u pb data of zircons of the tepla orthogneiss define an upper intercept age of 513 7 6 ma the 207pb 206pb ages of 516 10 and 511 10 ma of nearly concordant zircons of the hanov orthogneiss and the lestkov granite are interpreted to be close to the formation age of the granitoid protolith similar to the cambrian granitoids of the southwestern part of the tepla barrandian unit doma lice crystalline complex dcc the middle cambrian emplacement of the tcc granitoids postdates cadomian deformation and metamorphism of the upper proterozoic country rocks but predates variscan tectonometamorphic imprints structural data as well as sedimentological criteria suggest a dextral transtensional setting during the cambrian plutonism related to the early paleozoic break up of northern gondwana due to strong variscan crustal tilting the degree of variscan tectonometamorphic overprint is strikingly different in the dated granitoids it is lowest in the weakly or undeformed lestkov granite located in the greenschist facies domain the tepla orthogneiss in the north underwent pervasive top to nw mylonitic shearing under amphibolite facies conditions there is no indication for a resetting of the u pb isotopic system of the tepla orthogneiss zircons that could be attributed to this imprint radiation damages accumulated until recent have probably caused lead loss

transition and equilibration of neutral atmospheric boundary layer flow in one way nested large eddy simulations using the weather research and forecasting model abstractthe weather research and forecasting model permits finescale large eddy simulations les to be nested within coarser simulations an approach that can generate more accurate turbulence statistics and improve other aspects of simulated flows however errors are introduced into the finer domain from the nesting methodology comparing nested domain flat terrain simulations of the neutral atmospheric boundary layer with single domain simulations using the same mesh but instead using periodic lateral boundary conditions reveals the errors contributed to the nested solution from the parent domain and nest interfaces comparison of velocity spectra shows good agreement among higher frequencies but greater power predicted on the nested domain at lower frequencies profiles of mean wind speed show significant near surface deficits near the inflow boundaries but equilibrate to improved values with distance profiles of the vertical flux of x momentum show significant underprediction by the nested dom

metamorphic degassing of carbonates in the contact aureole of the aguablanca cu ni pge deposit spain analysis of magmatic and sedimentary rocks of several large igneous provinces has demonstrated that the release of gas during plutonic metamorphic processes may be linked to global climate change and mass extinctions aguablanca one of the largest cu ni pge deposits in europe formed during the variscan orogeny when a mafic magma intruded limestones and shales creating a contact aureole composed of marble skarn and hornfels our petrological and geochemical investigation of the aureole provides evidence that a combination of the two processes led to the formation of the ore deposit the assimilation of terrigenous sediments supplied s to the magma while the assimilation of carbonates changed the oxygen fugacity and decreased the solubility of sulfur in the magma the metamorphic assemblages in the contact aureole are directly related to heterogeneity of the protolith and particularly to the original proportions of calcite and clay we modeled carbon dioxide degassing during contact metamorphism and showed that pure limestone is relatively unproductive because of its high reaction temperature the presence of clay however leads to the formation of calc silicates and significantly enhances co2 degassing our estimations suggest that degassing of the aguablanca contact aureole released about 74 8 mt of co2 a relatively low volume that we attribute to the composition of the host rock mainly a pure limestone a far larger volume of carbon dioxide was emitted by the contact metamorphism of dolostones in the contact aureole of panzhihua part of emeishan large igneous province sw china we propose that the level of emission of carbon dioxide depends strongly on the nature of the protolith and has to be considered when predicting environmental impact during the emplacement of large igneous provinces

3d gravity modelling of the aguablanca stock tectonic control and emplacement of a variscan gabbronorite bearing a ni cu pge ore sw iberia the aguablanca stock is a variscan mafic pluton located in the ossa morena zone southern iberian massif hosting an unusual ni cu pge mineralization associated with magmatic breccia pipes which intruded its northern part the emplacement of the aguablanca stock and the mineralized breccia pipes are related to the activity of the cherneca ductile shear zone a variscan sinistral shear zone that favoured magma ascent through the upper crust a detailed gravity study has been carried out in order to investigate the 3d geometry of the aguablanca intrusion and to get insights about the emplacement mechanism and tectonic controls of the mineralization the three dimensional gravity modelling shows that the stock has an inverted drop geometry with a feeder zone in contact with the cherneca ductile shear zone the inferred orientation of the feeder zone suggests that the emplacement probably took place along an open tensional crack formed within the strain field of the adjacent cherneca ductile shear zone the modelling of the breccia pipes hosting the ni cu pge ore shows that they are included inside the feeder zone thus their emplacement is probably controlled by successive opening events of this tensional crack

seismicity and tectonics of the southeastern caribbean we present 33 new focal mechanisms for se caribbean earthquakes 1963 1988 we use these mechanisms in conjunction with 28 previously available mechanisms to distinguish between two models of plate boundary zone interaction in the se caribbean the trench trench transform and hinge faulting model and the right oblique collision model shallow 0 70 km and intermediate 70 200 km depth earthquakes occur in the study region we focus on the tectonic causes of these events and the motions they delineate the shallow earthquakes are in a broad linear zone which trends ne from the paria peninsula of venezuela towards barbados intermediate depth earthquakes cluster beneath and nw of the peninsula and deepen to the nw perpendicular to the ne trending shallow events the vertical distribution of the earthquakes suggests a slab with steep nw dip shallow dextral strike slip on e striking faults is restricted to a 60 km wide linear zone between the gulf of cariaco and the western margin of the gulf of paria dextral strike slip is active only as far east as the gulf of paria and not within or east of trinidad shallow thrust events with ene striking planes distributed between the araya peninsula and the gulf of paria indicate collision at crustal levels between south america and caribbean and that folding and thrusting are still active over a 60 km interval south of the araya paria isthmus active thrusting in venezuela corroborates predictions of transpression between caribbean and south america and discounts transtensional motions between the two plates in the se caribbean the conjunction of shallow thrust strike slip and normal earthquakes in the gulf of paria at around 62 3 may be the expression of unpartitioned oblique compressive deformation in the plate boundary zone intermediate 165 km h 70 km depth thrust and dip slip events within the nw dipping slab indicate that oceanic lithosphere probably originally attached to south america subducts to the nw beneath the caribbean plate shallow normal faulting events e and ne of trinidad are expressions of plate bending about near horizontal axes parallel to the lesser antilles subduction zone we conclude that the earthquake mechanisms provide strong support for the right oblique collision model of caribbean south american plate interaction

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

on the earthquake hazards of puerto rico and the virgin islands abstract puerto rico and the virgin islands are located near the northeastern corner of the caribbean seismic zone numerous large earthquakes have struck these islands some with disastrous results the 400 yr long earthquake record of puerto rico describes shocks affecting nearly all portions of the island the last destructive shock in 1918 7 5 m s did not occur along the main seismic zone but rather on an intraplate fault near mona canyon off the northwest coast a possible great earthquake in 1787 8 to 8 25 m s appears to have occurred along the main seismic zone near the puerto rico trench to the north of the island but data for the event are scarce a disastrous earthquake in the virgin islands 1867 7 5 m s also occurred on an intraplate fault this fault is one of a series that bound the anegada trough separating saint croix from the main chain of the virgin islands seafloor morphology microearthquakes and the record of historic earthquakes define a zone of deformation extending from the puerto rico trench northeast of the virgin islands trending southwest along the anegada trough and then westerly along the muertos trough the muertos trough is the locus of convergence between the floor of the caribbean sea and puerto rico maximum dimensions of future large earthquakes are inferred from sizes of blocks in the anegada and muertos troughs as well as mona canyon shocks as large as 7 5 can occur on these intraplate faults although strain rates on these faults may be an order of magnitude less than on faults in the puerto rico trench the large number of potential sources suggest that damaging earthquakes in this part of the caribbean can come from either the puerto rico trench or the intraplate faults with nearly equal probability

structure of the entrainment zone capping the convective atmospheric boundary layer the authors use large eddy simulation les to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer pbl over a range of bulk richardson numbers ri the les code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer extensive flow visualization is used to examine the structure of the inversion layer and to illustrate the temporal and spatial interaction of a thermal plume and the overlying inversion it is found that coherent structures in the convective pbl that is thermal plumes are primary instigators of entrainment in the ri range 13 6 ri 43 8 at ri 5 13 6 strong horizontal and downward velocities are generated near the inversion layer because of the plume interface interaction this leads to folding of the interface and hence entrainment of warm inversion air at the plume s edge at ri 5 34 5 the inversion s strong stability prevents folding of the interface but strong horizontal and downward motions near the plume s edge pull down pockets of warm air below the nominal inversion height these pockets of warm air are then scoured off by turbulent motions and entrained into the pbl the structure of the inversion interface from les is in good visual agreement with lidar measurements in the pbl obtained during the lidars in flat terrain field experiment a quadrant analysis of the buoyancy flux shows that net entrainment flux or average minimum buoyancy flux wu min is identified with quadrant iv w2u1 0 motions that is warm air moving downward plumes generate both large negative quadrant ii w1u2 0 and positive quadrant iii w2u2 0 buoyancy fluxes that tend to cancel the maximum vertical gradient in potential temperature at every x y grid point is used to define a local pbl height zi x y a statistical analysis of zi shows that skewness of zi depends on the inversion strength spectra of zi exhibit a sensitivity to grid resolution the normalized entrainment rate we w where we and w are entrainment and convective velocities varies as ari21 with a 0 2 in the range 13 6 ri 43 8 and is in good agreement with convection tank measurements for a clear convective pbl the authors found that the finite thickness of the inversion layer needs to be considered in an entrainment rate parameterization derived from a jump condition

large eddy simulations of real world episodes in complex terrain based on era reanalysis and validated by ground based remote sensing data abstracta computationally efficient and inexpensive approach for using the capabilities of large eddy simulations les to model small scale local weather phenomena is presented the setup uses the

peridotite xenoliths in silica rich potassic latite from the transition zone of the colorado plateau in north central arizona potassic latite in the transition zone of the colorado plateau near chino valley arizona contains abundant eclogite and amphibolite xenoliths and minor websterite and pyroxenite xenoliths one unit contains peridotite xenoliths analyzed samples have mg ratios of 68 and 71 58 and 63 wt sio2 and are enriched in potassium and other large ion lithophile lil elements rare earth element ree patterns are light ree enriched with la greater than 100 times chondritic abundance the peridotite xenoliths are partly to totally altered but contain remnant olivine orthopyroxene and clinopyroxene one harzburgite nodule also contains spinel mineral compositions from the xenoliths are relatively refractory and similar to those in other spinel peridotite xenoliths from the colorado plateau geothermometry on olivine spinel and two pyroxene pairs indicates equilibration temperatures of less than 800 c for the peridotite nodules the relatively low temperatures calculated from mineral equilibria are consistent with temperature estimates for other mantle nodules from under the colorado plateau

ground motion attenuation relationships for subduction zone earthquakes in northeastern taiwan subduction zone earthquakes have not been taken into special consid eration in most previous probabilistic seismic hazard analyses psha in taiwan however they may be critical to properly analyze the earthquake hazard in metro politan taipei so they need to be studied strong motion data from subduction zone earthquakes of both interface and intraslab types obtained by the tsmip and smart1 arrays in northeastern taiwan are used to establish the attenuation equa tions for peak ground acceleration pga and response spectral acceleration sa the resultant pga and sa attenuation equations include two site classes and two earth quake source types the ground motion values predicted by these attenuation equa tions are higher than those obtained from the crustal earthquake attenuation equations previously used in taiwan but are lower than those predicted by the attenuation equa tions for worldwide subduction zone earthquakes

the impact of valley geometry on daytime thermally driven flows and vertical transport processes the influence of valley geometry on thermally driven flows is studied by means of high resolution simulations an idealized valley plain topography and a spatially constant but time dependent surface sensible heat flux are used to generate upslope upvalley and plain to mountain winds a systematic variation of valley depth width and length induces differences in the cross and along valley flow field and thermal structure of the boundary layer the deeper the valley the stronger the upvalley winds and the more favoured the formation of vertically stacked circulation cells and an elevated valley inversion layer upvalley winds become weaker for wide valleys the development of plain to mountain circulations increases vertical exchange processes between the boundary layer and the free atmosphere considerably compared with vertical transport processes over a plain the analysis of mass flux budgets and forward trajectories indicates that mass is transported three to four times more effectively from the surface to the free atmosphere over valleys than over flat terrain vertical transport processes are strongest for deep and narrow valleys

neotectonics of puerto rico and the virgin islands northeastern caribbean from gps geodesy the boundary between the north american and caribbean plates is characterized primarily by left lateral motion along predominantly east west striking faults seismicity and marine geophysical survey data are consistent with at least two and possibly three microplates in the diffuse boundary zone in the northeastern caribbean 1 the gonave 2 the hispaniola and 3 the puerto rico northern virgin islands prvi we discuss results from gps geodetic measurements acquired since 1994 to test the microplate hypothesis define prvi translation and rotation within the boundary zone and constrain prvi neotectonics gps derived velocities are analyzed with respect to both north american and caribbean plate reference frames integrated displacements across prvi are limited to a few millimeters per year consistent with a rigid prvi and permitting calculation of an average velocity for prvi the motions of prvi relative to north america and the caribbean are 16 9 1 1 mm yr toward n68 e 3 1 and 2 4 1 4 mm yr toward s79 w 26 1 respectively in contrast with some recent models ongoing rotation of prvi about a nearby 25 distant vertical axis is not supported by the geodetic data in addition we argue against eastward tectonic escape of prvi and favor a simple progressive increase in velocity across the plate boundary zone requiring that the summed magnitude of strike slip fault slip rates will equal the total plate motion rate between the caribbean and north america gps data are consistent with components of left lateral strike slip faulting along the muertos trough south of puerto rico and shortening across the puerto rico trench comparison of gps velocities for prvi with respect to north america with total north america caribbean relative motion suggests up to 85 of north american caribbean plate motion is accommodated by the puerto rico trench and offshore faults north of puerto rico differences in gps derived velocities from hispaniola and prvi yield east west extension across the n s trending mona rift of a few millimeters per year when estimated elastic strain accumulation effects along the north hispaniola deformed belt and the septentrional fault zone are considered the opening rate implies an age of the mona rift of 2 3 million years agreeing with marine geophysical data that support a young age for the structure

arc parallel extension and localization of volcanic complexes in guadeloupe lesser antilles 1 subduction of atlantic seafloor under the caribbean plate causes shallow earthquakes within the lesser antilles volcanic arc such earthquakes above the subduction interface show strike slip or normal fault plane solutions the latter with e w striking nodal planes to better assess seismic hazard and the coupling between volcanism and tectonics we investigated faulting related to overriding plate deformation in the guadeloupe archipelago using aerial photographs satellite spot images and topographic maps 1 25000 scale we mapped active and middle to late pleistocene fissures and normal fault systems that cut the uplifted coral platforms grande terre and marie galante and the volcanic rocks of basse terre the available marine geophysical data show that the faults extend offshore to bound submarine rifts the e w striking 1500 m deep v shaped marie galante rift separates the two islands of marie galante and grande terre normal faults in the north of grande terre appear to mark the similarly v shaped western termination of the 5000 m deep n 50e to n130 e striking desirade graben three shallow m 5 5 earthquakes 6 may 1851 29 april 1897 3 august 1992 appear to have ruptured segments of the marie galante rift boundary faults the young la grande decouverte volcanic complex of basse terre including the 1440 a d soufriere dome lies within the western termination of the marie galante rift the ancient volcanic shoulders of the rift buttress the active dome to the north and south which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the caribbean sea or southeastward into the atlantic ocean the marie galante rift is typical of other troughs transverse to the northeastern edge of the caribbean plate we interpret such troughs which are roughly orthogonal to the arc to result from slip partitioning and extension perpendicular to plate convergence that they disappear southward implies that they result from interaction between the caribbean and north american plates

resolved turbulence characteristics in large eddy simulations nested within mesoscale simulations using the weather research and forecasting model abstractone way concurrent nesting within the weather research and forecasting model wrf is examined for conducting large eddy simulations les nested within mesoscale simulations wind speed spectra and resolved turbulent stresses and turbulence kinetic energy from the nested les are compared with data from nonnested simulations using periodic lateral boundary conditions six different subfilter scale sfs stress models are evaluated using two different nesting strategies under geostrophically forced flow over both flat and hilly terrain neutral and weakly convective conditions are examined for neutral flow over flat terrain turbulence appears on the nested les domains only when using the two dynamic sfs stress models the addition of small hills and valleys wavelengths of 2 4 km and maximum slopes of 10 yields small improvements with all six models producing some turbulence on nested domains weak convection surface heat fluxes of 10 w m 2 further accelerates the development of turbulen