late cenozoic transpressional ductile deformation north of the nazca south america antarctica triple junction abstract the southern andes plate boundary zone records a protracted history of bulk transpressional deformation during the cenozoic which has been causally related to either oblique subduction or ridge collision however few structural and chronological studies of regional deformation are available to support one hypothesis or the other we address along and across strike variations in the nature and timing of plate boundary deformation to better understand the cenozoic tectonics of the southern andes two east west structural transects were mapped at puyuhuapi and aysen immediately north of the nazca south america antarctica triple junction at puyuhuapi 44 s north south striking high angle contractional and strike slip ductile shear zones developed from plutons coexist with moderately dipping dextral oblique shear zones in the wallrocks in aysen 45 46 top to the southwest oblique thrusting predominates to the west of the cenozoic magmatic arc whereas dextral strike slip shear zones develop within it new 40ar 39ar data from mylonites and undeformed rocks from the two transects suggest that dextral strike slip oblique slip and contractional deformation occurred at nearly the same time but within different structural domains along and across the orogen similar ages were obtained on both high strain pelitic schists with dextral strike slip kinematics 4 4 0 3 ma laser on muscovite biotite aggregates aysen transect 45 s and on mylonitic plutonic rocks with contractional deformation 3 8 0 2 to 4 2 0 2 ma fine grained recrystallized biotite puyuhuapi transect oblique slip dextral reverse kinematics of uncertain age is documented at the canal costa shear zone 45 s and at the queulat shear zone at 44 s published dates for the undeformed protholiths suggest both shear zones are likely late miocene or pliocene coeval with contractional and strike slip shear zones farther north coeval strike slip oblique slip and contractional deformation on ductile shear zones of the southern andes suggest different degrees of along and across strike deformation partitioning of bulk transpressional deformation the long term dextral transpressional regime appears to be driven by oblique subduction the short term deformation is in turn controlled by ridge collision from 6 ma to present day this is indicated by most deformation ages and by a southward increase in the contractional component of deformation oblique slip to contractional shear zones at both western and eastern margins of the miocene belt of the patagonian batholith define a large scale pop up structure by which deeper levels of the crust have been differentially exhumed since the pliocene at a rate in excess of 1 7 mm year

crustal attenuation in the southern andean retroarc 38 39 30 s determined from tectonic and gravimetric studies the lonco luan asthenospheric anomaly abstract the western retroarc of the southern andes between 38 and 40 s is formed by a nnw elongated ridge not associated with stacked thrust sheets on the contrary during the last 4 3 ma this ridge was affected by extensional deformation regional uplift and related folding on a very broad scale receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust expected crustal thickness at these latitudes is around 38 km whereas in this part of the retroarc the thickness is less than 32 km the causes for such attenuation have been linked to a moderate steepening of the subducted nazca plate beneath the south american plate which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 ma gravimetric studies show that the upper plate did not react homogeneously to slab steepening but ancient sutures and lithospheric discontinuities deeply buried under mesozoic to cenozoic sequences in the retroarc were locally reactivated these processes resulted in an asthenospheric anomaly that correlates at the surface with the area of pliocene to quaternary doming widespread extension and three radial troughs two of the troughs have accommodated substantial amounts of extension but the third was probably aborted at an early stage moreover the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly and their age distribution may indicate minor migration of the asthenospheric anomaly between 4 and 2 ma through the western south american plate

strong ground motion and damage in the taipei basin from the moho reflected seismic waves during the march 31 2002 hualien taiwan earthquake 1 the march 31 2002 hualien offshore earthquake ml6 8 mw7 0 caused minor damage near its epicenter but significant damage in taipei about 110 km from the epicenter the recorded pga values around the taipei basin vary in a factor of 5 the high pga values in the southeastern part of the basin correspond to the most significant damage area during the earthquake strong ground motion recordings from this event recorded at stations around the taipei basin exhibit several distinct large amplitude seismic arrivals that can be interpreted as the pmp smp and sms phases the largest amplitude of the critically reflected s wave from the moho sms and the amplification of soft shallow sediments unique for each site are responsible for the maximum peak ground motion and the significant damage in the taipei basin during the hualien offshore earthquake

mechanisms of basin contraction and reactivation in the basement involved malargue fold and thrust belt central andes 34 36 s we have conducted a structural study of both the basement involved malargue fold and thrust belt mftb and the active san rafael block srb which are located in the central andes at latitude 34 36 s based on several field examples located both in the inner and frontal part of belt and from the distal foreland zone we focus on the relationships between basement and cover deformation with respect to the known palaeogeography and structural inheritance in several zones we point out similarities in the structural and sedimentary responses to andean shortening the recent morphologic response has also been investigated through the analysis of active deformation along the eastern border of the srb we show that these structural and sedimentary processes are continuous in time and space since they can be applied in the various parts of the fold belt and also at different stages of fold and thrust belt building as well finally we propose the illustration of those mechanisms by complete cross section along the rio grande valley and a possible kinematic scenario of deformation propagation

bidirectional visible nir and biconical ft ir reflectance spectra of almahata sitta meteorite samples abstract bidirectional visible and near infrared and off axis biconical fourier transform infrared reflectance spectra of almahata sitta meteorite stone samples fragments of asteroid 2008 tc3 have been measured these meteorites represent the first freshly fallen polymict ureilites available for such studies although the chip samples show varying degrees of terrestrial weathering depending on their environment on earth many of them are much fresher than other ureilites known to date the majority of the almahata sitta chips studied here show only a weak near uv absorption a flat spectrum at visible and near ir wavelengths and varying depths of the 1 and 2 m pyroxene and olivine bands the astronomical reflectance observations of the asteroid 2008 tc3 over the range 0 55 1 0 m provide a constraint on what a combination of the measured spectra can represent in the surface reflectance of the asteroid over the 0 32 2 55 m range measured in this study most of the recovered samples of almahata sitta have textures and albedos similar to stones 27 largest recovered fragment 4 and 47 results of linear least square fits of the asteroid 2008 tc3 spectrum with two sets of the meteorite spectra suggest that the asteroid had 10 12 albedo and no fine regolith on its surface we note that other lithologies may be at the surface of other fragments of the asteroid family from which 2008 tc3 originated in that case reflectance spectra could vary significantly among family members

reflectance spectra of the elephant moraine a79001 meteorite implications for remote sensing of planetary bodies abstract eeta 79001 a shergottite meteorite includes a pair of nonbrecciated basaltic lithologies joined along a planar igneous contact these two lithologies a and b are examples of the type of basaltic contacts likely to occur on the surfaces of many planetary bodies as such eeta 79001 offers a unique opportunity to compare analysis techniques available in situ with those available remotely for comparison to petrologic and geochemical studies reflectance spectra of lithologies a and b are obtained and analyzed with the modified gaussian model mgm this modeling leads to the unambiguous identification of two pyroxene phases in each lithology all spectral features including an absorption near 1 2 m often attributed to plagioclase are found to be due solely to the presence of two pyroxenes this ambiguity between pyroxene and plagioclase absorptions suggest that caution be used in interpretation of remote spectra results from the mgm analysis of spectra of eeta 79001 are also used to provide estimates on the major element composition of the pyroxene phases in the two lithologies in addition based solely on spectral analyses lithology b is shown to have 11 17 more high calcium pyroxene relative to low calcium pyroxene than lithology a each of the results derived independently with the mgm are shown to compare favorably within 5 10 to those obtained from more traditional geochemical and petrographic methods the compositional inferences that were derived from modeling the spectra of eeta 79001 with the mgm are examples of the type of information available from remotely acquired spectral data by providing a method for determining changes in relative composition and abundance of pyroxenes in neighboring units the mgm offers an opportunity to add compositional information to geologic and morphologic data and thus greatly enhance the science return on studies of surfaces throughout the solar system

a magnetotelluric study in the southern chilean andes long period magnetotelluric investigations were carried out along two transects traversing the southern chilean andes from the pacific ocean until the argentinian border near latitude 39 s to study the mid and deep crustal distribution of electrical conductivity dimensionality analysis showed that the mt data may be regarded as 2 d with the exception of areas in the longitudinal valley and the region east of the volcanic chain a subsequent multi site decomposition of magnetotelluric impedances yielded approx n s regional strike directions for most parts of the two profiles first 2 d inversion revealed a zone of moderately high conductivities approx 0 1 s m in the deep crust below the active volcanic arc extending eastwards to the argentinian border inversion results of both profiles are very similar except of a good mid crustal conductor in the longitudinal valley which only appears in the north and may image a fault zone running obliquely to the main south andean structures

gravity isostasy and andean crustal shortening between latitudes 30 and 35 s we started the work by analyzing an e w crustal section at 33 s latitude which extends from the western chilean trench crosses the andean belt and goes inland into argentina a two layer gravity seismic model was prepared here it provided a maximum moho depth of 62 km beneath the andean axis this model is consistent with a one layer standard crustal model with normal thickness t 33 km and densities of 2 9 g cm3 and 3 3 g cm3 for the crust and the upper mantle respectively then we analyzed the andean isostatic behaviour on four andean gravimetric sections at latitudes of 30 32 33 and 35 s based on one layer simple models these results show antiroots near the chilean trench and crustal thickenings beneath the andean belt which locate the moho discontinuity at depths of 70 km at 30 s 65 km at 32 and 33 s and 57 km at 35 s from the crustal gravimetric models the following provisional charts for the sector were prepared and compared 1 topography 2 bouguer gravity 3 isostatic corrections 4 moho contours these charts are consistent with each other and they point out that the compensation of the andean belt trends approximately to isostasy in the airy concept other results also confirm this 1 the remarkable decrease of the isostatic anomalies in each of the analyzed sections as regards the bouguer anomalies and 2 the relationships between the exceeding areas and the corresponding crustal root areas which are consistent with the airy numerical relations as to the perfect isostatic equilibrium thus the bouguer anomalies are mainly controlled by the m discontinuity finally shortenings in the andean sector were fixed based on the crustal thicknesses found from gravity inversion these are 150 km at 30 s decreasing southwards and reaching only 90 km at 35 s these shortenings explain the cenozoic andean uplift without requiring other mechanisms such as magmatic intrusions

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

petrologic insights from the spectra of the unbrecciated eucrites implications for vesta and basaltic asteroids we investigate the relationship between the petrology and visible near infrared spectra of the unbrecciated eucrites and synthetic pyroxene plagioclase mixtures to determine how spectra obtained by the dawn mission could distinguish between several models that have been suggested for the petrogenesis of vesta s crust e g partial melting and magma ocean here we study the spectra of petrologically characterized unbrecciated eucrites to establish spectral observables which can be used to yield mineral abundances and compositions consistent with petrologic observations no information about plagioclase could be extracted from the eucrite spectra in contrast pyroxene dominates the spectra of the eucrites and absorption band modeling provides a good estimate of the relative proportions of low and high ca pyroxene present cr is a compatible element in eucrite pyroxene and is enriched in samples from primitive melts an absorption at 0 6 lm resulting from cr 3 in the pyroxene structure can be used to distinguish these primitive eucrites the spectral differences present among the eucrites may allow dawn to distinguish between the two main competing models proposed for the petrogenesis of vesta magma ocean and partial melting these models predict different crustal structures and scales of heterogeneity which can be observed spectrally the formation of eucrite allan hills alh a81001 which is primitive cr rich and relatively unmetamorphosed is hard to explain in the magma ocean model it could only have been formed as a quench crust if the magma ocean model is correct then alha81001 like material should be abundant on the surface of vesta and the vestoids

imaging shallow crustal structure in the upper mississippi embayment using local earthquake waveform data a 1d normal moveout nmo corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary p and s wave coda and on sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure 5 km in the upper mississippi embayment acoustic well log data were used to constrain the p wave velocity in the upper 5 km events at close distances and with clear p and s arrivals were selected to ensure reliable nmo correction for reflections and transmissions the observed reflections and transmissions are important controlling factors on modeling waveforms we analyzed local earthquake data recorded at all broadband and one short period station of the cooperative new madrid seismic network despite polarity differences among p s and sp waveforms consistent reflectors in the sedimentary section can be imaged across the three wave types correlation with a basement penetrating well indicates that reflectors at the base of the upper cretaceous holocene mississippi embayment supergroup the base of the cambrian ordovician knox group and the high velocity lower upper cambrian bonneterre formation are shown in pseudoprofiles among stations in the upper mississippi embayment our study finds that a one layer homogeneous velocity model of sediments in the ranges of 1 95 2 42 km s for v p and 0 60 0 73 km s for v s overlying a half space of paleozoic rocks with velocities in the ranges of 6 0 6 2 km s for v p and 3 26 3 6 km s for v s can represent shallow crustal structure in the upper mississippi embayment differential times of p ppphp and s ssshs appear linearly proportional to sediment thicknesses which best fits a one layer sediment structure with average v p 2 042 0 041 km s and v s 0 709 0 051 km s in the least squares sense predicted by the wave propagation effects online material figures illustrating seismograms process procedure imaged reflectors and resolved velocity structure for six broadband stations and one short period station

role of viscous plate coupling in the late tertiary andean tectonics 1 plate coupling between oceanic and continental plates in convergent margins of andean type is analyzed from the continuum mechanics approach we postulate a simple mechanism that accounts for the compressive regime in andean type environments in this mechanism deformation in the continental lithosphere is split into two distinctive domains the forearc domain and the arc foreland domain the forearc deformation is controlled by the balance between buoyancy forces associated with the trench and continental slope relief and the stress transferred from the convergence velocity through the age and velocity dependent slip zone the arc foreland deformation is controlled by the absolute plate velocity of the continental plate and the resistance at the slip zone strength of the coupling zone is determined by analyzing the dynamic trench topography along the active margin of south america between 0 and 55 s using this approach we found strength values in the range of 20 95 mpa in strong direct correlation with the age of the subducting plate the slip layer strength observation has been successfully tested against a thermal and strain rate dependent rheological model from this theoretical result we define an empirical relationship between strength of the slip zone and the age and convergence velocity applying this plate coupling model we reproduce shortening rates in the order of 1 10 km myr in agreement with those reported for the late tertiary evolution of the andes model results reproduce some first order features of the geological evolution of the margin such as the shape of the trench the overall andes relief the altiplano buildup and block rotation patterns in addition the model provides a mechanism to explain the evolution of the central depression the inversion of tertiary basins under slow convergence rates during the miocene and the segmentation of the margins tectonic erosion

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

geomorphologic evidence for plio quaternary shortening in the southern neuquen basin 40 s argentina a morphostructural analysis of a pliocene flood basalt formation in the southern neuquen basin 40 s shows evidence of contractional deformation less than 3 5ma ago this formation exhibits a general dip towards the south east with relict outcrops located 100m higher than the main source volcano which suggests a local tilting of the lava flow this tilt has been brought about by plio quaternary reactivation of the eastern border of the sanico massif along two thrusts that offset the lava flow another long wavelength bulge in the southern part of the lava flow unit indicates a possible pliocene uplift of the north patagonian massif these results provide new evidence of continuing shortening in the neuquen basin during the plio quaternary challenging thehypothesis that an extensional regime has existed since the end of the miocene in this basin

tectonic development of the north patagonian andes and their related miocene foreland basin 41 30 43 s 1 the northern patagonian andes have been constructed through multiple mechanisms that range from tectonic inversion of extensional structures of early to middle jurassic age in the main andes to oligocene in the precordilleran region these have acted during two distinctive orogenic stages first in late early cretaceous and later in miocene times late oligocene extension separates these two contractional periods and is recorded by half grabens developed in the retroarc region the last contractional stage coexists with an eastward foreland expansion of the late miocene arc whose roots are presently exposed as minor granitic stocks and volcanic piles subordinately in the main andes east of the present arc as a consequence of this orogenic stage a foreland basin has developed having progressed from 18 ma in the main north patagonian andes where the mountain front was flooded by a marine transgression corresponding to the base of the nirihuau formation to 11 ma in the foreland area cannibalization of this foreland basin occurred initially in the hinterland and then progressed to the foreland zone blind structures formed a broken foreland at the frontal zone inferred from growth strata geometries during pliocene to quaternary times most of the contractional deformation was dissipated in the orogenic wedge at the time when the arc front retracted to its present position

late cenozoic geomorphic and tectonic evolution of the patagonian andes between latitudes 42 s and 46 s an appraisal based on fission track results from the transpressional intra arc liquine ofqui fault zone fission track ft thermochronology has been applied to investigate the low temperature cooling and denudation history of the patagonian andes along the southern part of the intra arc transpressional liquine ofqui fault zone between 42 and 46 s the liquine ofqui fault is shown to have been the focus of enhanced cooling and denudation initiated between ca 16 and 10 ma several fault blocks with different cooling histories are identified these are separated by major oblique or reverse slip faults proposed to form the eastern part of a major crustal scale dextral transpression zone local very fast rates of cooling and denudation between ca 7 and 2 ma were coeval with collision of the chile rise an active mid oceanic ridge with the peru chile trench between 47 and 48 s this location is close to the southern termination of the liquine ofqui fault implying that the collision of the ridge was a major force driving late cenozoic transpression the lack of significant cooling and denudation before ca 16 ma is indicative of pure strike slip or transtensional movement along the liquine ofqui fault before the collision of the ridge digital landscape analysis supports glacial and periglacial erosion as the main contributor to denudation since ca 7 ma leading to restriction of topographic development the combination of transpression induced rock uplift and glacial erosion is shown to be very effective at causing localized denudation anomalously young ft ages along the liquine ofqui fault are attributed to the existence of a late cenozoic localized heat flow anomaly along the fault

the southern andes between 36 and 40 s latitude seismicity and average seismic velocities abstract the project issa 2000 integrated seismological experiment in the southern andes consists of a temporary seismological network and a seismic refraction profile a network of 62 seismological stations was deployed across the southern andes at 38 s three hundred thirty three local seismic events were observed in a 3 month period p and s arrival times of a subset of high quality data were inverted simultaneously for 1 d velocity structure hypocentral coordinates and station delays seismic refraction data along a transect at 39 s provide further constraints on the crustal structure low crustal velocities beneath the forearc may be either due to subducted trench sediments or serpentinized mantle material of the continental lithosphere the continental moho is not clearly observed in this region average velocities of the crust beneath the arc are higher than those beneath the forearc crustal thickness is about 40 km crustal seismicity concentrates in the forearc region along the bio bio and gastre fault zones the area between these two prominent fault zones seems to be nearly devoid of crustal seismicity but shows highest uplift and topography in the forearc region benioff seismicity is observed down to 150 km depth resulting in the first accurate image of the benioff zone in the southern andes a maximum of seismicity at 60 km depth may be caused by dehydration embrittlement

recognition of minor constituents in reflectance spectra of allan hills 84001 chips and the importance for remote sensing on mars reflectance spectra of splits 92 and 271 from the martian meteorite allan hills alh 84001 are presented and analyzed in this paper although the visible and infrared spectra of both chips show that the dominant mineralogy is low ca pyroxene the focus here is on identification of the minor constituents infrared spectra measured at multiple spots along the surface of chips 92 and 271 show subtle spectroscopic variations due to changes in the low ca pyroxene texture and composition and to the presence of secondary minerals absorption bands observed near 0 93 and 1 95 m are characteristic of low ca pyroxene strong mid infrared reststrahlen bands are observed near 9 and 19 5 m in all surface spectra and additional bands near 7 10 5 11 4 17 8 20 5 and 23 m are variable depending on the low ca pyroxene texture and the presence of secondary minerals selected spectra exhibit carbonate features near 4 6 4 7 1 and 11 3 m detailed analysis of these carbonate features indicates the presence of mg fe carbonate which is consistent with petrographic studies many of these spectra with strong carbonate features exhibit a magnetite feature near 17 9 m and a shoulder near 20 5 m that cannot be uniquely ascribed to one mineral spectroscopic identification of the minor carbonate and magnetite minerals in this probable piece of mars indicates that detection of small amounts of these minerals of possible biological significance will be possible using infrared hyperspectral analyses of the martian surface also of importance for remote sensing on mars is the result that mg fe and mg fe carbonates in a low ca pyroxene matrix should be distinguishable from one another in the spectral region measured by the thermal emmitance spectrometer tes

using the modified gaussian model to extract quantitative data from lunar soils 1 the lunar soil characterization consortium lscc has examined and characterized a suite of lunar soils with a wide range of compositions and maturities the purpose of this study is to compare the vis nir spectral properties of these lunar soils with their petrologic and chemical compositions using the modified gaussian model mgm to obtain quantitative data about the character of relatively weak near infrared absorption bands useful compositional information can be extracted from high quality soil spectra using the mgm the model had some difficulty fitting absorption bands in the 2 mm region of the lunar spectrum but bands in the 1 and 1 2 mm regions provided physically realistic results the model was able to distinguish high ca and low ca pyroxenes in the lscc suite of lunar soils in the appropriate relative abundance in addition unexpected insights into the nature and causes of absorption bands in lunar soils were identified for example at least two distinct absorption bands are required in the 1 2 mm region of the spectrum and neither of these bands can be attributed to plagioclase or agglutinates but are found instead to be largely due to pyroxene

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

near infrared reflectance spectra from bulk samples of the two martian meteorites zagami and nakhla abstract zagami and nakhla are achondrites and belong to the shergotty nakhla chassigny snc meteorite group it is generally accepted that mars is their parent body mineralogical and chemical analyses have revealed that the major mineral phases of these two meteorites are pyroxene olivine maskelynite and plagioclase in this work near infrared biconical reflectance measurements were performed on sawed surfaces of chips from zagami and nakhla spectra obtained with an analytical spot diameter on the order of the mineral grain size reflect the heterogeneous distribution of different mineral phases the characteristic absorption bands of the pyroxenes are numerically evaluated in terms of the modified gaussian model spectra with overlapping absorption features are resolved into the basic absorption bands from these results it can be estimated what kind of clinopyroxenes belong to the investigated mineral assemblages as a result the major clinopyroxene phase in nakhla is ca rich augite whereas in zagami both ca rich and ca poor pyroxenes are present by means of such a procedure laboratory spectra of minerals become more informative and may help in discussing martian remote sensing data in the near infrared region

on the modified mercalli intensities and magnitudes of the 1811 1812 new madrid earthquakes we reexamine original felt reports from the 1811 1812 new madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks in many cases we interpret lower values than those assigned by earlier studies in some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues additionally earlier studies had assigned modified mercalli intensity mmi values of v vii to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high we investigate several approaches to contouring the mmi values using both analytical and subjective methods for the first mainshock on 02 15 lt december 16 1811 our preferred contouring yields m 7 2 7 3 using the area moment regressions of johnston 1996 for the 08 00 lt on january 23 1812 and 03 45 lt on february 7 1812 mainshocks we obtain m 7 0 and m 7 4 7 5 respectively our magnitude for the february mainshock is consistent with the established geometry of the reelfoot fault which all evidence suggests to have been the causative structure for this event we note that the inference of lower magnitudes for the new madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern united states we also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811 1812 sequence

candidates source regions of martian meteorites as identified by omega mex abstract the objective of this study is to identify and map spectral analogues of some key martian meteorites basaltic shergottites los angeles shergotty que 94201 lherzolitic shergottite alh a77005 nakhla chassigny and the orthopyroxenite alh 84001 in order to localize terrain candidates for their source regions we develop a best fit procedure to reproduce the near infrared nir spectral properties of the martian surface as seen by the hyperspectral imaging spectrometer omega mex from the nir spectra of the martian meteorites the fitting process is tested and validated and root mean square rms global maps for each meteorite are obtained it is found that basaltic shergottites have nir spectral properties the most representative of the martian surface with the best spectral analogues found in early hesperian volcanic provinces sites with spectral properties similar to those of alh a77005 are scarce they are mainly localized in olivine bearing regions such as nili fossae and small noachian early hesperian terrains the only plausible source region candidate for chassigny is the nili patera caldera dated to 1 6 ga widespread spectral analogues for the alh 84001 meteorite are found northeast of syrtis major and northwest of the hellas basin while this distribution is in agreement with the low calcium pyroxene rich composition and old age 4 1 ga of this meteorite the modal mineralogy of these candidates is not consistent with that of this meteorite no convincing spectral analogue is found for the amazonian aged nakhla meteorite suggesting that its olivine high calcium pyroxene rich composition could be representative of the amazonian terrains buried under dust finally some young rayed craters are proposed as possible candidates for source craters of the studied martian meteorites

spectroscopic analysis of martian meteorite allan hills 84001 powder and applications for spectral identification of minerals and other soil components on mars spectroscopic measurement and analysis of martian meteorites provide important information about the mineralogy of mars as well as necessary ground truths for deconvolving remote sensing spectra of the martian surface rocks the spectroscopic properties of particulate alh 84001 from 0 3 to 25 m correctly identify low ca pyroxene as the dominant mineralogy absorption bands due to electronic transitions of ferrous iron are observed at 0 94 and 1 97 m that are typical for low ca pyroxene a strong broad water band is observed near 3 m that is characteristic of the water band typically associated with pyroxenes weaker features near 4 8 5 2 and 6 2 m are characteristic of particulate low ca pyroxene and can be distinguished readily from the features due to high ca pyroxene and other silicate minerals the reflectance minimum occurs near 8 6 m for the alh 84001 powder which is more consistent with high ca pyroxene and augite than low ca pyroxene the dominant mid infrared ir spectral features for the alh 84001 powder are observed near 9 and 19 5 m however there are multiple features in this region these mid ir features are generally characteristic of low ca pyroxene but cannot be explained by low ca pyroxene alone spectral features from 2 5 5 m are typically associated with water organics and carbonates and have been studied in spectra of the alh 84001 split 92 powder and alh 84001 splits 92 and 271 chip surfaces weak features have been identified near 3 5 and 4 m that are assigned to organic material and carbonates another feature is observed at 4 27 m in many surface spots and in the powder but has not yet been uniquely identified spectroscopic identification of minor organic and carbonate components in this probable piece of mars suggests that detection of small amounts of organics and carbonates in the martian surface regolith would also be possible using visible infrared hyperspectral analyses laboratory spectroscopic analysis of martian meteorites provides a unique opportunity to identify the spectral features of minerals and other components while they are embedded in their natural medium

experimental petrology of the mars pathfinder rock composition constraints on the interpretation of martian reflectance spectra 1 experiments to determine the crystallization sequence of the mars pathfinder mpf rock composition have been carried out to explore the range of possible mineral assemblages in this sio2 rich 57 4 wt martian igneous rock recent mars global surveyor thermal emission spectrometer observations have suggested the presence of large volumes of andesitic lava covering the northern hemisphere of mars but this interpretation has been called into question experimentally produced mineral assemblages can be used to infer spectral characteristics that would exist in andesitic lavas similar in composition to the mpf rock the inferred spectra could then be used with remotely sensed data to further constrain the identity of surface rock types on mars we performed a series of experiments at 0 1 mpa at the quartz fayalite magnetite and iron quartz fayalite oxygen buffers and 100 mpa at the ni nio oxygen buffer using the calculated soil free mpf composition potential mineralogies for a lava with the mpf composition would be sio2 57 wt feo 18 wt rich glass plagioclase quartz augite and fe ti oxides a contoured pyroxene quadrilateral with band i and ii minima was used to predict pyroxene composition on the basis of reflectance spectra using the quadrilateral in reverse the augite produced in the experimental series should have band i and ii minima at 0 97 m and 2 15 m respectively the absence of the 1 m minima in the imager for mars pathfinder imp spectra could be due to masking phases possibly the fe ti oxides produced in our experiments at 1000 c

quantifying seismic vulnerability dynamical shear strain and liquefaction of the quaternary deposits in the doon valley near the main boundary thrust in the northwest himalaya india abstract erosion and deposition are two conjugate surface dynamical processes that affect differently to the soft soil site characteristics of quaternary deposits in the doon valley and at its northern topographic transition zone near the main boundary thrust mbt during an impending large magnitude earthquake what would be the seismic vulnerability and liquefaction susceptibility of the soft soil at both the regions we quantified seismic vulnerability index effective dynamical shear strain and the expected ground deformation in the valley soft soil through h v site characteristics using seismic ambient noise data at the in accessible topographic transition zone near the mbt site effects were studied using moderate and light magnitude earthquakes recorded by three broad band seismographs bbs results show unique dual peak mean resonant frequencies 1 11 and 1 38 hz and amplification factors 1 69 and 1 51 at the topographic transition zone which highlights a bimodal distribution of site effects where the top soil formation is influenced by erosion and deposition due to topographic slope instability apart from fluvial re working here relatively compact oldest doon gravel is present in the foothill terraces with the re worked fluvial deposition of the youngest doon gravel however in the valley and its terraces the soft soil formed under fluvial environ is relatively thick 10 to 2 and mean resonant frequency of 1 1 hz the spot resonant frequencies increases from 1 hz to more than 6 hz from the hft region to the mbt while the amplification factor decreases from 14 to 1 in general the valley soft soil is susceptible for liquefaction because the estimated dynamical shear strain is 15 25 millistrains under medium 2 2 m s 2 225 years and long 4 6 m s 2 2500 years term strong motion conditions which is much higher than the soil plasticity limit of ten millistrains that lead to liquefaction dynamical shear strain distribution with depth at eight boreholes in the valley indicate 20 m is the liquefaction potential depth where the pore pressure induced peak shear strain exceeds the threshold shear strain of 0 01 during the passage of seismic waves isolated locations in the valley like that at dharmawala h1 where all site parameters are very high and would be hazardously vulnerable to liquefaction however near the mbt the liquefaction possibility of soft soil is less but would experience ground deformation of more than 50 cm

consistency of geologic and geodetic displacements during andean orogenesis displacement and convergence rates inferred from gps and marine magnetic data suggest that this trend may be continuing at present hence an increasing fraction of convergence is being absorbed by mountain building this change may reflect increased plate coupling due to decreased sediment supply younger subducting lithosphere or increased normal stress at the interface from the effects of uplift index terms 8102 tectonophysics continental contract orogenic belts 8157 evolution of the earth plate motions past 3040 8158 evolution of the earth plate motions present and recent 3040 8099 structural geology general or miscellaneous

the loma prieta earthquake ground motion and damage in oakland treasure island and san francisco abstract the basis of this study is the acceleration velocity and displacement wave forms of the loma prieta earthquake 18 october 1989 m 7 0 at two rock sites in san francisco a rock site on yerba buena island an artificial fill site on treasure island and three sites in oakland underlain by thick sections of poorly consolidated pleistocene sediments the waveforms at the three rock sites display a strong coherence as do the three sedimentary sites in oakland the duration of strong motion at the rock sites is very brief suggestive of an unusually short source duration for an earthquake of this size while the records in oakland show strong amplification effects due to site geology the s wave group at treasure island is phase coherent with the oakland records but at somewhat diminished amplitudes until the steps in acceleration at approximately 15 sec apparently signaling the onset of liquefaction all seven records clearly show shear wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances 95 3 km from an earthquake of this magnitude while the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them we have had some difficulty in making such relationships quantitative or even just clear the three oakland records from sites that form a nearly equilateral triangle about the cypress street viaduct collapse are dominated by a long period resonance 1 1 2 sec period far removed from the natural frequency of the structure to transverse motion 2 5 hz or from high frequency amplification bands observed in aftershock studies a spectral ratio arbiter of this discrepancy confuses it further the failure of the east bay crossing of the san francisco oakland bay bridge cannot be attributed to relative displacements of the abutments in oakland and yerba buena island but the motions of the bay bridge causing failure remain unknown the steps in acceleration at treasure island present unusual strong motion accelerogram processing problems and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps a variety of coincidences suggests that the treasure island accelerogram is the most likely strong motion surrogate for the filled areas of the marina district for which no mainshock records are available but the relative contributions of bad ground poor construction and truly strong ground motion to damage in the marina district will never by known in any quantitative way the principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes our understanding of the very complex relationships between strong ground motion and earthquake damage will in general remain rudimentary imprecise and vague

tectonostratigraphic evolution of a mesozoic graben border system the chachil depocentre southern neuquen basin argentina the chachil depocentre is one of a number of early mesozoic extensional basins that form the early depocentres of the southern neuquen basin in argentina the synrift volcanic fill is composed of andesites rhyolites and volcaniclastic deposits coarse grained non marine facies dominate the sedimentary fill mainly in the form of sediment gravity flow deposits stream flow deposits and minor non marine carbonates are also locally present the evolution of the graben border system was mainly controlled by subsidence along the main boundary fault the chihuido bayo fault system and recurrent volcanic activity marked changes in the thickness of the synrift megasequence indicate that episodic normal faulting in the hanging wall was also important the integration of structural magmatic and sedimentary data from the study area has led to the definition of three stages in the evolution of the synrift succession the early rift stage is defined by the interplay between bimodal volcanism and gravity driven sedimentation the mid rift stage is marked by the transition to acidic magmatism rhyolitic and pyroclastic flows also associated with coarse grained non marine deposition the late rift stage is dominated by fine grained turbidites and pyroclastic falls related to the first marine sedimentation in the neuquen basin

spectral reflectance of martian meteorites spectral signatures as a template for locating source region on mars we report the spectral reflectance of martian meteorites from 0 3 2 6 microns for the purpose of cataloguing spectra and the association of their spectral properties with mineralogy and petrology we fit the spectra to a series of overlapping modified gaussian absorptions using least squares fitting the results are validated against established relationships between photon interactions with mineral chemistry and the band parameters these resultant band parameters can be used to constrain interpretations of martian reflectance spectra in the search for the source region of meteorites from mars the limitations of the fitting method are discussed

localized damage caused by topographic amplification during the 2010 m 7 0 haiti earthquake microzonation maps use local geological conditions to characterize seismic hazard but do not generally consider topography ground motions during the haiti earthquake are found to have been significantly amplified along a high topographic ridge which caused substantial structural damage indicating that topography can play an important role in seismic hazard local geological conditions including both near surface sedimentary layers1 2 3 4 and topographic features5 6 7 8 9 are known to significantly influence ground motions caused by earthquakes microzonation maps use local geological conditions to characterize seismic hazard but commonly incorporate the effect of only sedimentary layers10 11 12 microzonation does not take into account local topography because significant topographic amplification is assumed to be rare here we show that although the extent of structural damage in the 2010 haiti earthquake was primarily due to poor construction topographic amplification contributed significantly to damage in the district of petionville south of central port au prince a large number of substantial relatively well built structures situated along a foothill ridge in this district sustained serious damage or collapse using recordings of aftershocks we calculate the ground motion response at two seismic stations along the topographic ridge and at two stations in the adjacent valley ground motions on the ridge are amplified relative to both sites in the valley and a hard rock reference site and thus cannot be explained by sediment induced amplification instead the amplitude and predominant frequencies of ground motion indicate the amplification of seismic waves by a narrow steep ridge we suggest that microzonation maps can potentially be significantly improved by incorporation of topographic effects

aptian to recent compressional deformation foothills of the neuquen basin argentina abstract the neuquen basin lies in north western patagonia on the eastern foreland of the andes it formed as a rift basin in the early mesozoic and contains some 5000 m of triassic to aptian sediment mainly marine as a result of andean orogeny the western edge of the basin now forms part of the foothills we describe some of the main compressional structures drawing on surface and sub surface data we argue that regional eastward dips are due to west verging thrust displacements on the andacollo loncopue fault system during a late cretaceous peruvian phase aptian to campanian continental sediment accumulated in a retro arc foreland basin which was mainly of flexural origin nevertheless more than 1500 m of late cretaceous sediment accumulated in the footwall of the east verging agua amarga thrust the peruvian phase was responsible also for transpressional reactivation of a rift transfer zone the huincul arch the incaic phase eocene was responsible for north westerly trending folds and thrusts reactivation of cretaceous thrusts abundant andesitic lavas and high level intrusions and a swarm of north easterly trending bitumen dykes the quechua phase miocene to recent produced northerly trending folds and thrusts and a miocene foreland basin containing some 1000 m of basalt lava flows structures that formed during the incaic and quechua phases are broadly compatible with the history of convergence at the pacific margin of south america as deduced from plate reconstructions

seismic site amplification factors in campi flegrei southern italy the method of spectral ratios of s waves from local small earthquakes recorded at various sites in the campi flegrei volcanic area southern italy has been used to evaluate the seismic site response in the frequency range 1 15 hz the spectra of the s wave trains recorded at the short period seismic stations are corrected for attenuation using attenuation parameters quality factor q previously determined for the area using the coda method a reference station has been used selected on the basis of the highest number of recorded earthquakes and not on geological considerations the relative uniformity of the geological conditions and the absence of hard rock sites conditioned such choice the method has been checked using the coda wave method to estimate the spectral site response and similar results were obtained the results show a relative peak of the spectral ratio pattern centred at low frequency 2 3 hz and a minimum of 0 2 at 8 hz for two stations located on yellow tuff such results are interpreted as being caused by a filtering effect produced by selective attenuation such a pattern could be of interest for seismic engineering purposes in view of the abundance of tuff over a wide area in this densely inhabited region

coupling of south american and african plate motion and plate deformation although the african plate s northeastward absolute motion slowed abruptly 30 million years ago the south atlantic s spreading velocity has remained roughly constant over the past 80 million years thus requiring a simultaneous westward acceleration of the south american plate this plate velocity correlation occurs because the two plates are coupled to general mantle circulation the deceleration of the african plate due to its collision with the eurasian plate diverts mantle flow westward increasing the net basal driving torque and westward velocity of the south american plate one result of south america s higher plate velocity is the increased cordilleran activity along its western edge beginning at about 30 million years ago

tectonic shortening and crustal thickness in the central andes how good is the correlation exceptional thickening of continental crust beneath the central andes is believed to be mainly a result of tectonic shortening of the south american plate in neogene time this shortening has been estimated to have contributed as much as 70 80 of the present crustal volume a compilation of published shortening values and our own estimates based on balanced cross sections from the central andes between lat 3 s and 40 s suggest that 70 80 is a maximum rather than an average value for this part of the andes tectonic shortening and the crustal cross section area are only loosely correlated variations in tectonic shortening are more abrupt than those of crustal areas particularly near the northern and southern ends of the altiplano puna high plateau where thick crust is associated with relatively small amounts of shortening shortening there may account for no more than about 30 of the present crustal cross section area the processes that created the remaining crustal area are not clear but are likely to involve poorly constrained pre neogene tectonic shortening moderate magmatic additions to the crust tectonic underplating of material derived from the forearc and possible flow of ductile lower crust along strike

local site effects during the orkney earthquake of 5 august 2014 site response analysis is conducted at 37 seismic stations located in the gauteng north west and free state provinces in south africa using the nakamura h v spectral ratio technique on records of the orkney 5 august 2014 earthquake the earthquake of magnitude ml 5 5 led to the unfortunate death of one person and damage of more than 600 houses intensity data collected soon after the event showed that the effects of the earthquake appeared to vary significantly across the region this motivated the authors to conduct a more detailed investigation of the effects of site conditions on seismic station records in the region resonance frequency values obtained from the h v ratios were observed to vary strongly across the region and also within seismic station clusters similar behaviour was observed with the peak amplitude of the ratios at the resonance frequency except for the johannesburg area whose results showed a relatively simple shape of the ratios implying less complex velocity structure all the h v ratios exhibit dominant peaks at resonant frequencies that varied between 0 5 and 35 hz the average observed resonant frequency was f 7 9 hz the amplitude of the dominant peaks also varied strongly from 1 66 to 11 69 with only two sites exhibiting maximum peaks with amplitude smaller than 2 these results serve as a strong motivation or justification for the on going microzonation studies in south africa where a detailed study of the velocity structure will be used to obtain reliable information on site amplification and resonance

a site effect study in acapulco guerrero mexico comparison of results from strong motion and microtremor data abstract the city of acapulco is located near or above the mature seismic gap of guerrero along the mexican subduction zone with the purpose of studying the character of strong ground motion on soft sites four digital accelerographs have been installed in the city on such sites these instruments have been in operation since 1988 two additional instruments part of the guerrero accelerograph array are located on hard sites in the area one of these vnta has been in operation since 1985 and the other acan since 1989 these stations have recorded several earthquakes we use data from eight events 4 2 m 6 9 to study spectral amplification of seismic waves at the soft sites with respect to vnta the s waves are amplified by a factor of 6 to 25 at the soft sites in a fairly broad range of frequencies both the amplification and the frequency band over which it occurs depend upon the site although the largest earthquake in our data set m 6 9 gave rise to a peak horizontal acceleration exceeding 0 3 g at one of the soft sites no clear evidence of nonlinear behavior of the subsoil is found spectral amplifications of s wave coda are very similar to those of s waves we also measured microtremors at the strong motion sites the microtremor spectra were interpreted using reasonable assumptions to test the feasibility of this technique in reproducing the spectral amplifications observed during earthquakes our results show that only a rough estimate of site response can be obtained from this technique at least in acapulco caution is warranted in its use elsewhere

the late jurassic to present evolution of the andean margin drivers and the geological record 1 uncommonly long lived subduction and variable plate geometry along the south american andean plate margin resulted in diverse relationships between magmatic flux and extensional and contractional deformation as recorded by the overriding continental plate convergence velocities absolute overriding plate velocities and subducting slab ages were resolved along the trench from 170 ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions deformation style and magmatic features in the overriding plate key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors extensional back arc basins involving mafic oceanic crust developed only when the overriding plate velocity of south america was directed away from the trench and the modeled age of the subducting slab was older than 50 myr the development of fold and thrust belts and uplift of major plateaus was accompanied by trench normal convergence velocities in excess of 4 cm yr parameters investigated in this study revealed no correlation with the timing of major magmatic events nor was any correlation observed with the structural style of fold and thrust belts

in situ compositions of martian volcanics implications for the mantle the primary objective of this analysis is to determine the mineralogic composition of relatively pristine terrains exposed on the surface of mars this analysis is conducted using imaging spectrometer data acquired in 1989 by the imaging spectrometer for mars ism instrument that was onboard the phobos ii spacecraft the ism instrument acquired some of the highest spectral 64 channels between 0 77 and 3 14 m and spatial resolution 22 km pixel observations to date of mars focused on the equatorial region relatively unaltered surfaces were identified in these data on the basis of their spectral properties low albedo weak spectral slope absence of ferric absorptions and were found in volcanic terrains of syrtis major valles marineris ophir planum and sinus meridiani oxia palus spectra representative of the diversity among terrains were extracted for detailed analysis using the modified gaussian model to determine the primary mafic mineralogy it was determined that the mafic mineralogy of the regions investigated is dominated by low calcium and high calcium pyroxene lcp hcp and that there was homogeneity within a given region but some heterogeneity between regions in the relative abundance of lcp to hcp the two pyroxene mineralogy is consistent with the mineralogies of the basaltic snc meteorites believed to have originated on mars two pyroxene volcanic mineralogies are indicative of large degrees of partial melting e g komatiites or a mantle source depleted in aluminum integration of these findings with previous studies of mars and the snc meteorites indicates that 1 the snc mineralogies are representative of large volcanic regions of mars with surface ages as old as 2 3 ga 2 the martian mantle was depleted in aluminum at least as long ago as the oldest terrain analyzed ophir planum and 3 there has been little evolution in the composition of mantle source regions as the 180 ma snc mineralogies are comparable to those of the oldest terrains analyzed

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

inversion of an oligocene volcano tectonic basin and uplifting of its superimposed miocene magmatic arc in the chilean central andes first seismic and gravity evidences abstract a new structural model is presented for the cenozoic part of the main range east of santiago a chain made up of thick miocene ignimbrites and andesitic lavas overlying primitive oligocene volcanoclastics deposited on a thin continental crust because the latter coya machali formation locally show tight folding close to the margins of the miocene volcanics they had previously been described as deformed prior to construction of the arc our field observations analysed along two profiles at 33 and 34 15 s however support the conclusion hinted at by ongoing geochronological and geochemical studies deformation of both formations is synchronous and related to late miocene inversion of the coya machali intra arc basin uplift of the rigid arc rocks and part of its volcanoclastic basement took place mainly along two northward shallowing boundary structures that seem to share a lower decollement the eastern fierro out of sequence thrust and a series of western back thrusts that resemble triangle zones seismic data obtained from el teniente porphyry copper mine 34 s rockbursts and two gravimetric profiles at the western end of the southern profile are compatible with a decollement located at that locality 2 3 km under the surface

tertiary tectonics of the patagonian andes retro arc area between 38 15 and 40 s latitude the structure and tectonics of the retro arc area of the andes between 38 degrees 30 and 40 degrees s remains poorly understood because of the scarcity of previous structural studies this paper analyzes the styles distribution and timing of the deformation in the eastern flank of the andes between these latitudes with focus in the tertiary tectonics of the area this andean section can be divided into an internal and an external domain based on its distinctive structural evolution the boundary between them coincides with the bio bio and alumine valleys which separate sectors of the fold and thrust belt with opposite vergence and different structural styles structures developed in the external domain during the andean cycle are associated with a west verging fold and thrust belt which was controlled geometrically by pre existing normal faults of the mesozoic rift phase we also differentiate three segments along the external domain of the inner retro arc zone at these latitudes each segment is associated with a tertiary depocenter related to the western border of a structural high copahue pino hachado block and cordilleras de catan lil and chachil which constitutes an outstanding feature within the study area the recognition and interpretation of the main structures and the spatial and temporal distribution of the tertiary sequences allowed us to establish a tectonic model in which the uplift of this nnw trending block during upper miocene times originated a series of intermontane depocenters well represented between 38 and 40 degrees s as a result of that syntectonic and synorogenic deposits accumulated in a compressive regime these depocenters can be integrated in a narrow deposition zone associated with the western slope of the copahue pino hachado block and its southward prolongation in the cordillera de catan lil and cordillera del chachil on the basis of tectonostratigraphic controls we define the last andean contractional phase of the inner retro arc area at these latitudes between 11 and 5 67 ma for the northern segment between 10 and 6 2 ma for the central segment and between 13 to 8 and 43 ma for the southern segment after this short lived compressional stage deformation migrated to the west associated with the onset of the liquine ofqui strike slip fault zone along the intra arc zone c 2010 elsevier b v all rights reserved

cenozoic climate change as a possible cause for the rise of the andes causal links between the rise of a large mountain range and climate have often been considered to work in one direction with significant uplift provoking climate change here we propose a mechanism by which cenozoic climate change could have caused the rise of the andes based on considerations of the force balance in the south american lithosphere we suggest that the height of and tectonics in the andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands and shear stresses in the subduction zone depend on the amount of subducted sediments we propose that the dynamics of subduction and mountain building in this region are controlled by the processes of erosion and sediment deposition and ultimately climate in central south america climate controlled sediment starvation would then cause high shear stress focusing the plate boundary stresses that support the high andes

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

compressional and transpressional stress pattern for pliocene and quaternary brittle deformation in fore arc and intra arc zones andes of central and southern chile kinematic analysis of fault slip data for stress determination was carried out on late miocene to quaternary rocks from the fore arc and intra arc regions of the chilean andes between 33 and 46 south latitudes studies of neogene and quaternary infilling the central depression as well as plutonic rocks of the north patagonian batholith along the liquine ofqui fault zone have revealed various compressional and or transpressional states of stress in the pliocene the maximum compressional stress 1 was generally oriented east west during the quaternary the deformation was partitioned into two coeval distinctive states of stress in the fore arc zone the state of stress was compressional with 1 oriented in a n s to nne ssw direction in the intra arc zone the state of stress was transpressional with 1 striking ne sw along the coast in one site 37 30 s the quaternary strain deformation is extensional with an e w direction which can be explained by a co seismic crustal bending readjustment

late miocene earliest pliocene glaciation in southern argentina implications for global ice sheet history abstract in south america at latitude 47 s till was deposited sometime between 7 m y and 4 6 m y ago at a time when the local climate was colder than today s during this same interval glaciers extended to sea level in southeast alaska and widespread cooling of the ocean surface in middle latitudes worldwide marine regression and change in the oxygen isotopic composition of ocean water occurred from the last three events major late miocene expansion of the antarctic ice sheet has been inferred on the assumption that the history of north atlantic ice rafting precludes the existence of northern hemisphere ice sheets until 3 m y ago this is disputed first because precipitation in antarctica would probably have decreased at temperatures below today s second because the antarctic ice sheet cannot expand appreciably until buildup of northern hemisphere ice sheets has lowered sea level third because virtually no late miocene sediments are present at the labrador sea dsdp sites that are critical to the reconstruction of north atlantic ice rafting history and fourth because the scale of late miocene glaciation in alaska is at least permissive for simultaneous buildup of ice at similar latitudes further east if global ice sheet volume at the end of the miocene was greater than it is today by an amount that would have lowered sea level by several tens of meters the excess ice did not accumulate in antarctica but in the northern hemisphere chiefly in north america away from the atlantic coast

high calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites our analyses of high quality spectra of several s type asteroids 17 thetis 847 agnia 808 merxia and members of the agnia and merxia families reveal that they include both low and highcalcium pyroxene with minor amounts of olivine 0 4 high calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies the silicate mineralogy inferred for thetis and the merxia and agnia family members requires that these asteroids experienced igneous differentiation producing broadly basaltic surface lithologies together with 4 vesta and its smaller vestoid family members and the main belt asteroid 1489 magnya these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies based on this analysis of a small subset of the near infrared asteroid spectra taken to date with spex at the nasa irtf we expect that the number of known differentiated asteroids will increase consistent with the large number of parent bodies inferred from studies of iron meteorites

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

implications of deep marine miocene deposits on the evolution of the north patagonian andes abstractthe north patagonian andes 38 43 30 s present topographic and geologic characteristics distinct from those of the central andes to the north including a lower altitude a predominance of plutonic rocks and the presence of a major n s trending dextral strike slip intra arc discontinuity known as the liquine ofqui fault zone lofz the timing for the uplift of the north patagonian andes remains poorly constrained principally because high exhumation rates resulted in the erosion of most of its volcano sedimentary cover during the late cenozoic the strongly deformed cenozoic marine deposits ascribed to the ayacara formation which crop out on the western flank of this range at 42 s can provide for a better understanding of the recent geologic evolution of this range to discern this formation s age and sedimentary environment we have integrated sedimentology ichnology foraminiferal paleontology and geochronology our results indicate that this unit was deposited in a deep marine environ

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

the compositional diversity of non vesta basaltic asteroids abstract we present near infrared 0 78 2 45 m reflectance spectra for nine middle and outer main belt a 2 5 au basaltic asteroids three of these objects are spectrally distinct from all classifications in the bus demeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type the remainder of the sample are classified as v or r type all of these asteroids are dynamically detached from the vesta collisional family but are too small to be intact differentiated parent bodies implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system the 1 and 2 m band centers of all objects determined using the modified gaussian model mgm were compared to those of 47 vestoids and fifteen hed meteorites of known composition the heds enabled us to determine formulas relating band 1 and band 2 centers to pyroxene ferrosilite fs compositions using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids we also conduct a careful error analysis of the mgm derived band centers for implementation in future analyses the six outer belt v and r type asteroids show more dispersion in parameter space than the vestoids reflecting greater compositional diversity than vesta and its associated bodies the objects analyzed have fs numbers which are on average between five and ten molar percent lower than those of the vestoids however identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result given the gradient in oxidation state which existed within the solar nebula these results tentatively suggest that these objects formed at either a different time or location than 4 vesta

extension and basin formation in the southern andes caused by increased convergence rate a mid cenozoic trigger for the andes the southern andes between 33 and 45 s latitude are characterized by a series of complex basins that spanned the contemporaneous active continental margin which itself was characterized by volcanic activity the basins are filled with thick up to 3000 m accumulations of interbedded sedimentary and volcanic strata of late oligocene early miocene age we interpret that these basins developed during a phase of moderate extension within the plate margin system triggered by an increased rate of convergence of the farallon nazca and south american plates between 28 and 26 ma this history is inconsistent with models of convergence that link high rates of convergence of a continental margin and an oceanic plate to strong compressional coupling although extensional basins of this age are only well described in the southern andes the convergence history and volcanic chronology are similar farther north in the central andes 18 33 s leading to the speculation that extension may have characterized the late oligocene early miocene interval regionally we hypothesize that this extension was a necessary condition to subsequent building of the modern andes mountains

u pb geochronology and magnetostratigraphy of a north patagonian syn orogenic miocene succession tectono stratigraphic implications for the foreland system configuration abstract the syn orogenic miocene deposits of the patagonian foreland system were the focus of numerous works in the latest years due to their central role in the comprehension of the tectono stratigraphy and tectonic evolution related to the patagonian andean growth in this work we present a chronostratigraphic scheme based on magnetostratigraphy and u pb geochronology for one of the syn orogenic successions of the patagonian foreland system the paso del sapo basin the sequence is constrained to an age of 14 9 to 14 9 14 6 ma for the basal alluvial systems of la pava formation with mean sedimentation rates of 4 2 cm kyr of 14 6 to 12 8 12 7 ma for the lacustrine deltaic environments of the lower collon cura formation with sedimentation rates ranging from 1 6 to 26 0 cm kyr and of 12 8 12 7 to 14 9 to

attenuation assessment of blast induced vibrations derived from an underground mine abstract attenuation assessment of vibration induced by underground explosions is a source of concern due to its associated with damage analyses of underground facilities and ground structures based on the blast events at different levels of ore have different impacts on ground structures to understand the attenuation rule of vertical propagation is essential for the safe design of mining blasts in a new built underground mine eight seismographs were installed with different depths to monitor the blast vibrations and 236 events included 24 events on the ground were recorded during mining production over a period of eight months certainly the blasting design propagating medium and its mechanical parameters were also carefully investigated in the light of the collected data various prediction equations are employed to establish a suitable relationship for describing the attenuations of peak particle velocity ppv and frequency the charge weight effect on the frequency attenuation of the induced ground motion is also discussed moreover the effect of surface soil overburden has also been analyzed based on a supplementary monitoring work the results indicate that scaled distance sd with cube root scaling for the explosive quantity can properly perform the far field vibration irrespective of how much the item of charge weight represents its simplified form still makes the oldest equation still be widely used the average frequency af and its modified frequency equation perform well in the rock mass the soil overburden has a low impact on the ground motion while the influence of charge weight per delay on ground wave frequency has diminished

miocene block uplift and basin formation in the patagonian foreland the gastre basin argentina abstract the intraplate fault block mountains and intermontane deposits of the gastre basin which are recorded more than 550 km east of the andean trench in central patagonia argentina are analyzed the gastre basin is one of the largest patagonian intermontane basins limited by uplifted blocks strongly oblique to the andean chain it was originated by reverse faulting and inversion of pre existing normal faults associated with a mesozoic rift basin and defined by older crustal heterogeneities the deformational event occurred during the middle miocene related to a short contractional episode 16 1 14 86 ma probably in response to an eastward migration of the andean fold and thrust belt during pliocene to quaternary times neither younger fault block uplifts nor reconfigurations of the basin occurred similarities between the study area and other parts of the patagonian foreland such as the presence of miocene reverse or inversion tectonics as well as the accommodation of the miocene sedimentary successions suggest that the gastre basin is part of a major late early to middle miocene broken foreland system i e the patagonian broken foreland that exhumed discrete fault block mountains and generated contemporary basins along more than 950 km parallel to the andean trench i e between 40 00 and 48 00 south latitude based on recent studies on the southern andean margin this continental scale contractional episode may be the result of a flat slab subduction segment nevertheless such a hypothesis is very difficult to support when analyzing such a large flat subduction segment along the entire patagonian trench this suggests the need to consider alternative flat slab trigger mechanisms or other factors in the generation of broken foreland systems

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard