evolution of mesozoic sandstone compositions southern junggar northern tarim and western turpan basins northwest china a detrital record of the ancestral tian shan abstract sandstone compositional data can be a powerful tool in the interpretation of tectonic and climatologic influences on sedimentary basin fill in addition to yielding important information about porosity in sandstone petroleum reservoirs in order to explore these relationships a modified gazzi dickinson point counting technique was used to analyze the composition of 143 mesozoic sandstone samples from the southern junggar northern tarim and western turpan basins of northwestern china results indicate that a mesozoic ancestral version of the tian shan physiographically separated the junggar and tarim basins and provided sand of very different composition to each basin mesozoic sandstone from the northern tarim basin is diverse in composition and lithic rich qm41f14l45 qp42lvm26lsm32 is locally micaceous and contains common radiolarian chert grains and few dense accessory minerals inferred source rocks include upper paleozoic alkali granite and metamorphic complexes thick silurian bedded chert sequences and lower paleozoic strata of a passive continental margin in contrast sandstone from the southern junggar and western turpan basins is uniformly volcanic rich qm21f21lt58 qp13lvm68lsm19 and contains abundant dense accessory minerals and only local radiolarian chert and mica inferred principal source rocks are devonian carboniferous andesitic arc volcanics the effect of sampling scale on sandstone composition outweighs that of plate tectonic setting samples were derived mostly from medium and coarse grained fluvial systems that likely drained only portions of the ancestral tian shan and hence preserve local source rock signatures rather than an integrated compositional signal that can be directly compared to plate tectonic petrofacies models in addition though mesozoic basins of western china were most akin to broken foreland basins mesozoic sandstone is considerably more compositionally diverse and lithic rich than that of modern or ancient broken foreland basins because of the variety of accreted terranes constituting the ancestral tian shan temporal changes in sandstone composition are consistent with episodes of mesozoic deformation in the tian shan each deformational episode increased physiographic relief of the ancestral range produced renewed downcutting and erosion of source rocks and resulted in the deposition of compositionally very immature sandstone in adjacent basins although a regional early mesozoic megamonsoon and an early cretaceous rain shadow cast across the northern tarim basin are interpreted from regional facies and paleontologic data neither paleoclimatic phenomenon appears to have significantly modified sandstone composition in the study area calculations of intergranular volume porosity cement indicate that porosity in sandstone from the tarim and junggar basin depocenters was reduced principally by burial compaction and that the rate of porosity reduction was highest for lithic rich samples

carbon dioxide and radon gas hazard in the alban hills area central italy abstract the sudden and catastrophic or slow and continuous release at surface of naturally occurring toxic gases like co 2 h 2 s and rn poses a serious health risk to people living in geologically active regions in general this problem receives little attention from local governments although public concern is raised periodically when anomalous toxic gas concentrations suddenly kill humans or livestock for example elevated co 2 concentrations have been linked to the death of at least 10 people in the central italian region of lazio over the last 20 years while it was the co 2 asphyxiation of 30 cows in a heavily populated area near rome in 1999 which prompted the present soil gas study into the distribution of the local health risk a detailed geochemical survey was carried out in an area of about 4 km 2 in the ciampino and marino districts whereby a total of 274 soil gas samples were collected and analysed for more than 10 major and trace gas species data were then processed using both statistical and geostatistical methods and the resulting maps were examined in order to highlight areas of elevated risk general trends of elevated co 2 and rn concentrations imply the presence of preferential pathways i e faults and fractures along which deep gases are able to migrate towards the surface the co 2 and rn anomalous trends often correspond to and are usually elongated parallel to the apennine mountain range the controlling structural feature in central italy because of this fundamental anisotropy in the factors controlling the soil gas distribution it was found that a geostatistical approach using variogram analysis allowed for a better interpretation of the data with regard to the health risk to local inhabitants it was found that although some high risk areas had been zoned as parkland others had been heavily developed for residential purposes for example many new houses were found to have been built on ground which has soil gas co 2 concentrations of more than 70 and radon values of more than 250 kbq m 3 it is recommended that land use planners incorporate soil gas and or gas flux measurements in environmental assessments in areas of possible risk i e volcanic or structurally active areas

evolution of the canadas edifice and its implications for the origin of the canadas caldera tenerife canary islands the volcano stratigraphic and geochronologic data presented in this work show that the tenerife central zone has been occupied during the last 3 ma by shield or central composite volcanoes which reached more than 3000 m in height the last volcanic system the presently active teide pico viejo complex began to form approximately 150 ka ago the first canadas edifice ce volcanic activity took place between about 3 5 ma and 2 7 ma the ce i is formed mainly by basalts trachybasalts and trachytes the remains of this phase outcrop in the canadas wall cw sectors of la angostura 3 5 3 0 ma and 3 0 2 7 ma boca de tauce 3 0 ma and in the bottom of some external radial ravines 3 5 ma the position of its main emission center was located in the central part of the cc the volcano could have reached 3000 m in height this edifice underwent a partial destruction by failure and flank collapse forming debris avalanches during the 2 6 2 3 ma period the debris avalanche deposits can be seen in the most distal zones in the n flank of the ce i tigaiga breccia a new volcanic phase whose deposits overlie the remains of ce i and the former debris avalanche deposits constituted a new volcanic edifice the ce ii the dyke directions analysis and the morphological reconstruction suggest that the ce ii center was situated somewhat westward of the ce i reaching some 3200 m in height the ce ii formations are well exposed on the cw especially at the el cedro 2 3 2 00 ma sector they are also frequent in the s flank of the edifice 2 25 1 89 ma in tejina 2 5 1 87 ma as well as in the tigaiga massif to the n 2 23 ma during the last periods of activity of ce ii important explosive eruptions took place forming ignimbrites pyroclastic flows and fall deposits of trachytic composition their ages vary between 1 5 and 1 6 ma adeje ignimbrites to the w in the cw the upper ucanca phonolitic unit 1 4 ma could be the last main episode of the ce ii afterwards the can adas iii phase began it is well represented in the cw sectors of tigaiga 1 1 ma 0 27 ma las pilas 1 03 ma 0 78 ma diego hernandez 0 54 ma 0 17 ma and guajara 1 1 ma 0 7 ma the materials of this edifice are also found in the se flank these materials are trachybasaltic lava flows and abundant phonolitic lava and pyroclastic flows 0 6 ma 0 5 ma associated with abundant plinian falls the ce iii was essentially built between 0 9 and 0 2 ma a period when the volcanic activity was also intense in the dorsal edifice situated in the easterly wing of tenerife the so called valleys of la orotava and gu imar transversals to the ridge axis also formed during this period in the central part of tenerife the ce iii completed its evolution with an explosive deposit resting on the top of the ce for which ages from 0 173 to 0 13 ma have been obtained the cc age must be younger due to the fact that the present caldera scarp cuts these deposits on the controversial origin of the cc central vertical collapse vs repeated flank failure and lateral collapse of mature volcanic edifices the data discussed in this paper favor the second hypothesis clearly several debris avalanche type events exist in the history of the volcano but most of the deposits are now under the sea the caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent teide pico viejo volcanoes

sinkholes in hypogene versus epigene karst systems illustrated with the hypogene gypsum karst of the sant miquel de campmajor valley ne spain abstract the garrotxa banyoles artesian aquifer system in ne spain includes zones with epigene and hypogene evaporite karst and sinkhole development the sinkhole fields related to hypogene evaporite dissolution are associated with the discharge zones of the aquifer where groundwater from a confined limestone rises traversing an overlying gypsum formation capped by thick marls this work analyses the sinkhole field developed in the sant miquel de campmajor valley smcv a discharge area of the aquifer where a cartographic inventory including 94 sinkholes has been produced sinkholes in this hypogene gypsum karst are mainly large caprock collapse sinkholes rooted in deep seated cavities generated by interstratal hypogene karstification as corroborated by an electrical resistivity imaging eri survey they show a non clustered distribution within the sinkhole field and the variations in size and density across the area are mainly controlled by the thickness of the marl caprock the magnitude and frequency relationships of the sinkholes can be modelled with a high goodness of fit with a log normal function like in other regions of the world however in this deep seated hypogene system the depressions show much larger dimensions potential differences between the sinkholes developed in hypogene and epigene karst environments are discussed including their distribution with respect to the groundwater flow system their spatial patterns and dimensions

lyttelton volcano banks peninsula new zealand primary volcanic landforms and eruptive centre identification abstract lyttelton volcano banks peninsula new zealand has historically been viewed as a simple volcanic cone this paper uses digital terrain models dtm and primary volcanic landforms to reinterpret lyttelton volcano as having multiple eruptive centres primary volcanic landforms are features produced during active volcanism classified as constructional hypabyssal and erosional volcanic features constructional volcanic features are lava flows scoria cones and domes hypabyssal volcanic features are dykes and sills and erosional volcanic features are valley and ridge patterns and orientations lava flow trends are recognised from aerial photograph analysis and supported by field observations highlighting radiating lava trends around specific locations within lyttelton harbour scoria cones and domes occur on the outer flanks of volcanic cones and are used as such in the identification of remnant cone surfaces dyke orientations are plotted and then projected to the interior of the volcano defining 13 zones of convergence the projected arrays of these orientations highlight defined regions along the erosional crater rim each indicating a radial dyke swarm from which the projected trends of the associated dykes indicate an eruptive centre valley and ridge orientations are projected from the longest valley or ridge segment towards the inner harbour radiating erosive patterns are incepted during the growth and degradation of a volcanic cone with the resulting trends orienting to the summit zones of convergence eruptive centres are identified from lava flow orientations onlapping lava sequences scoria cones and intrusive locations the summit of a volcanic edifice can be identified from the orientations of valleys and ridges while radial dyke systems determine whether this summit was a volcanic centre or simply a local topographic high volcanic landforms are used to identify cone sectors the preserved sector associated with a particular eruptive centre cone sector limits are defined by a basal footprint and an erosional crater rim with similar arcuate features remnant cone features being exposed in the interior of the volcano lyttelton volcano comprises fifteen volcanic cones with vent locations controlled by underlying fault lineaments the growth and erosion of each volcanic cone is reflected in primary volcanic landforms with the preserved features of cones confined to cone sectors and cone artefacts

a new model for the dynamic evolution of chinese lithosphere continental roots plume tectonics abstract chinese continental lithosphere comprises three tectonic domains 1 eastern china a region characterized by rifting extensional basins and voluminous basaltic volcanism 2 central china a plexus of cratonic terrains with low heat flow 40 50 mw m2 including the tarim erdos and yangtze blocks welded by pre cenozoic orogenic belts and 3 western china a region comprising the qinghai tibet himalaya orogen the relatively thin crust 35 km and lithosphere 70 km of eastern china is believed to reflect mantle upwelling while near normal crust 45 km and thickened lithosphere 200 km in central china suggest a mantle lithosphere root resembling those inferred for the kaapvaal and siberian cratons thickened crust 70 km and lithosphere 150 km in western china reflect the advanced development of an orogen root the lower density and relative buoyancy of central cratonic mantle roots appear to have contributed to the long term tectonic stability of the central chinese lithospheric blocks in contrast gravitational instability produced by thickening of the denser western chinese lithosphere and the resulting subsidence and eventual delamination of orogenic roots are believed to have led to postorogenic extensional collapse although the geological relationships suggest compressional forces caused both mountain building and orogen root development extensional stress resulting from gravitational collapse is believed to have induced lithospheric and crustal thinning with concomitant reduction of topography the term continental roots plume tectonics has been adopted to describe the configuration and dynamic condition of subcontinental lithosphere and upper mantle beneath china accordingly it is proposed that supracrustal tectonic forms represent the surface expressions of and responses to deep continental roots plume tectonics while the prevailing view is that the western orogenic belt is not genetically related to eastern continental rifting such a relationship is inherent to the continental roots plume tectonics model it is further proposed that the formation of orogenic lithosphere roots triggered eastward extrusion of the asthenosphere along the 400 km depth mantle interface and in response to subduction at the eastern margin produces plume like upwelling beneath eastern china we suggest that processes involved in continental roots plume tectonics are directly responsible for the formation and evolution of the eurasian supercontinent

large landslides associated with a diapiric fold in canelles reservoir spanish pyrenees detailed geological geomorphological mapping trenching and electrical resistivity imaging abstract detailed geomorphological geological mapping in canelles reservoir the spanish pyrenees reveals the presence of several large landslides overlooked in previous cartographic works one of the slope movements designated as the canelles landslide corresponds to a 40 10 6 m 3 translational landslide reactivated in 2006 by a severe decline in the reservoir water level the geomorphic features mapped in the upper part of the canelles landslide including surface ruptures corroborated by electrical resistivity imaging and trenching indicate multiple displacement episodes previous to the 2006 human induced event consistently the stratigraphic and structural relationships observed in a trench record at least two displacement events older and larger in magnitude than the 2006 reactivation the oldest recorded event occurred in the 6th to 7th centuries and the second in 1262 1679 yr ad this latter episode might be correlative to the 1373 ribagorza earthquake m w 6 2 which caused the reactivation of a landslide and the consequent destruction of a village in the adjacent valley the available data indicate that over more than one millennium the kinematics of the landslide has been characterised by discrete small displacement episodes these data together with the available literature on rapid rockslides do not concur with the acceleration predicted by modelling in a previous investigation which foresees a speed of 16 m s 1 despite the low average dip of the sliding surface 9 10 this case study illustrates that the trenching technique may provide valuable practical information on the past behaviour of landslides covering a much broader time span than instrumental and historical records

lithospheric structure of tibet and western north america mechanisms of uplift and a comparative study we seek to determine the mantle lid thickness of the lithosphere and to constrain the mechanisms that are responsible for the cenozoic uplift of the tibetan plateau located behind the himalaya collision zone and the western united states located behind the san andreas transform convergent plate boundary selected first p arrivals of international seismological centre isc data at distances less than 22 are analyzed by the two station method to constrain the upper mantle structure of the basin and range br colorado plateau cp great plains gp and tibetan plateau tp the data are presented as plots of apparent velocity versus distance to the second station we show that these observations of apparent velocities versus distance as well as those that concern the attenuation of sn provide estimates of the mantle lid thicknesses we obtain the following mantle lid thicknesses br 20 40 km cp 35 50 km gp 150 195 km and tp 135 180 km sn is not observed for paths beneath the br and cp while sn efficiently propagates beneath the gp sn is also observed beneath most of tibet except in the north central part of the tp a possible interpretation of our observations is that indian continental lithosphere underthrusts only about the southern 2 3 of tibet

volcanic complexes in the eastern ridge of the canary islands the miocene activity of the island of fuerteventura abstract fuerteventura has been since early stages of its growth the result of three different adjacent large volcanic complexes southern central and northern the definition of these volcanic complexes and their respective growing episodes is based on volcano stratigraphic morphological and structural criteria particularly radial dyke swarms each complex has its own prolonged history that might be longer than 10 m y during that time several periods of activity alternating with gaps accompanied by important erosion took place the evolution of each volcanic complex has been partially independent but all the three are affected by at least three miocene tectonic phases that controlled considerably their activity the volcanic complexes are deeply eroded and partially submerged in the core of the northern and the central volcanic complexes there is a set of submarine and plutonic rocks intensely traversed by a dyke swarm known as the basal complex the basal complex has been interpreted in different ways but all previous authors have considered it to be prior to the subaerial shield stage of the island here we advance the idea that the basal complex represent the submarine growing stage of the volcanic complexes and the hypabyssal roots plutons and dykes of their successive subaerial growing episodes two seamounts situated nearby southwest of the island might be interpreted as remains of two other major volcanoes these two volcanoes together with those forming the present emerged island of fuerteventura and finally those of famara and los ajaches situated further north on lanzarote constitute a chain of volcanoes located along a lineation which is subparallel to the northwestern african coastline and which may relate to early atlantic spreading trends in the area

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

dem based reconstruction of southern basse terre volcanoes guadeloupe archipelago fwi contribution to the lesser antilles arc construction rates and magma production abstract we combine radiometric ages and geomorphologic investigations to quantify the relief creation of well preserved volcanic surfaces applied to the volcanoes of southern basse terre guadeloupe lesser antilles arc the last 650 ka volcanic evolution of this island has been modeled using ten main stages constrained by k ar ages previously obtained on lava flows and domes from the volcanic massifs of the axial chain 1000 435 ka and from the grande decouverte volcanic complex 250 ka present based on the construction of a 250 000 point database inferred from the analysis of the guadeloupe digital elevation model 3d reconstructions of the successive volcanic stage landforms were calculated and the correlated geochronological maps drawn using arcgis software volumes and rates of construction were computed for each time span separating these ten stages the average construction rates calculated here are 2 4 0 3 10 4 km 3 yr for the last million years 0 9 0 3 10 4 km 3 yr for the last 100 ka and 0 9 0 2 10 4 km 3 yr for the last 15 ka although basse terre volcanism is characterized by a marked dominance of effusive products our estimates should be considered as minimum values because the material that went into the sea during explosive events was not taken into account however we note that a relatively high construction rate of 4 5 1 3 10 4 km 3 yr has been obtained for the icaques volcano which was emplaced during the 630 600 ka time interval within the depression formed by the first large scale flank collapse having affected southern basse terre the sudden release of the lithostatic load induced by this mass wasting event could explain this value which is significantly higher than the average value of 0 8 0 1 10 4 km 3 yr obtained for the last 650 ka finally the comparison with other analogous volcanic massifs from islands and continental arcs points to a relatively low magmatic production for southern basse terre which could be tentatively related to the relatively slow subduction rate of the atlantic plate

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

growth after collapse the volcanic and magmatic history of the neostromboli lava cone island of stromboli italy this study focuses on the holocene neostromboli lava cone which is part of the stromboli volcano aeolian islands italy it represents an important example of the structure and behaviour of lava cone re growth shortly after a large scale volcano sector collapse neostromboli s eruptive style is dominated by extrusion of sheet like a a lava flows and associated autoclastic breccias the lava cone developed during five phases of activity phases a to e representing discrete episodes of lava effusion characterised by rapid changes in magma composition spatial development of the feeder system and physical properties of erupted lavas through time although they all belong to the potassic series ks with sio2 49 55 wt and mgo 2 50 6 25 wt the neostromboli lavas have distinct petrogenetic characteristics ranging from leucite free and low sr shoshonitic basalts phases a and b to leucite bearing shoshonitic basalts with high phase c and intermediate phase d sr contents and to leucite free biotite bearing shoshonites phase e three different batches of mantle derived relatively primitive basic magmas fed the activity of phases a c and d the evolution phases a to b is inferred to have occurred in a continuously replenished tapped and crystallizing rtf magma chamber whereas phase e products were dominantly generated by fractional crystallization from phase d magmas the neostromboli cone shows summit flank and satellite vents and sheet intrusions with different geometry and location through time reflecting the interplay of regional tectonics precursory instability processes and volcano load

high resolution imaging of the high agri valley basin southern italy with electrical resistivity tomography abstract the first high resolution images of the fault controlled high agri valley basin obtained with the electrical resistivity tomography are presented the agri valley is one of the more complex components of the quaternary fault network of the apennine chain the geometry of the pre quaternary bedrock the location and dip of the master fault and the tectonic evolution of the basin are still a subject of debate therefore deep electrical resistivity tomography integrated with stratigraphic analyses has been carried out to improve knowledge of the geological setting of the basin the high resolution electrical images allow us to reconstruct the complex geometry of the basin the electrical imaging highlights the irregular shape of the basin which is bordered by shallow faults and filled with pleistocene alluvial deposits in longitudinal cross section the basin appears as a mosaic of fault bounded blocks forming three different depocenters separated by intrabasinal highs in transverse cross section the basin is an irregular graben locally asymmetric to the northeast and with secondary grabens due to antithetic faults

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

neotectonics and late holocene paleoseismic evidence in the plio quaternary daroca half graben iberian chain ne spain implications for fault source characterization this work has been supported by project cgl2017 85045 p ministerio de economia industria y competitividad gobierno de espana

from source terrains of the eastern alps to the molasse basin detrital record of non steady state exhumation fission track cooling ages of detrital apatite aft in the east alpine molasse basin display age groups corresponding to geodynamic events in the orogen since jurassic times these age groups are typical of certain thermotectonic units which formed a patchwork in the swiss and eastern alps by a combination of petrographic and thermochronologic data progressive erosion of source terrains is monitored in different catchments since the oligocene the aft cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed after termination of tectonic exhumation lag times of debris derived from the core complexes increased neither on the scale of the entire eastern alps or on the scale of individual catchments steady state exhumation is observed due to the highly dynamic changes of exhumation rates since late eocene collision d 2005 elsevier b v all rights reserved

dynamic fluvial systems and gravel progradation in the himalayan foreland although the large scale stratigraphy of many terrestrial foreland basins is punctuated by major episodes of gravel progradation the relationships of such facies to hinterland tectonism and climate change are often unclear structural reentrants provide windows into older and more proximal parts of the foreland than are usually exposed and thus provide key insights to earlier phases of foreland evolution our magnetostratigraphic studies show that although the major lithofacies preserved within the himachal pradesh structural reentrant in northwestern india resemble neogene facies in pakistan they have a much greater temporal and spatial variability from 11 5 to 7 ma major facies boundaries in himachal pradesh vary by as much as 2 3 m y across distances of 20 30 km and are controlled by the interference between a major southeastward flowing axial river and a major southwestward flowing transverse river a thick but highly confined middle to late miocene conglomerate facies includes the oldest extensive siwalik conglomerates yet dated 10 ma and implies the development of significant erosional topography along the main boundary thrust prior to 11 ma our studies document extensive syntectonic gravel progradation with conglomerates extending tens of kilometers into the undeformed foreland during a period of increased subsidence rate and within 1 2 m y of major thrust initiation overall gravel progradation is modulated by the interplay among subsidence sediment supply and the proportion of gravels in rivers entering the foreland

identification of latent faults using a radon test abstract this paper discusses the use of 222rn concentrations in water of natural springs as a geomorphological method to identify latent faults in low mid term activity areas the identification of this type of active fault may be crucial in hazard analysis structural geomorphology and in landscape evolution analysis the test used to identify these faults is based on the measuring of 222rn concentrations in water of springs linked to faults and comparison with those obtained from springs which although exactly the same lithological context are not linked with faults reference values if the difference between the measured value and the reference value is positive then an anomaly is identified and that measurement indicates a spring linked to a latent fault the test was applied and validated in springs linked to faults with a latent behaviour in cantabria northern spain these faults have shown an intermittent movement over the last 50 000 years and have contributed towards landslide processes playing a significant role in landscape evolution of the area

sinkholes and caves related to evaporite dissolution in a stratigraphically and structurally complex setting fluvia valley eastern spanish pyrenees geological geomorphological and environmental implications abstract evaporite karst and sinkhole development is analysed in a geologically complex area of ne spain including four evaporite units with different characteristics and affected by compressional and extensional tectonic structures the exposed paleosinkholes including remarkable early pleistocene paleontological sites provide valuable information on the subsidence mechanisms and reveal the significant role played by interstratal karstification in the area these gravitational deformation structures including hectometre scale bending folds and oversteepened normal faults strongly suggest that the present day compressional regime inferred in previous studies may be largely based on the analysis of non tectonic structures two gypsum caves ca 1 km long show that passages with restricted cross sectional area may produce large breccia pipes and sinkholes thanks to the removal of breakdown boulders by high competence episodic floods moreover the upward progression of cave ceilings by paragenesis and condensation dissolution contributes to increase the probability of sinkhole occurrence an inventory of 135 sinkholes together with their geological and geomorphological context has been developed this data base has been used to infer several properties of the sinkholes with practical implications a magnitude and frequency scaling relationship spatial distribution patterns dominant controlling factors and risk implications

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

late jurassic early cretaceous continental convergence and intracontinental orogenesis in east asia a synthesis of the yanshan revolution abstract the basic tectonic framework of continental east asia was produced by a series of nearly contemporaneous orogenic events in the late middle jurassic to early cretaceous commonly the late mesozoic orogenic processes were characterized by continent continent collision large scale thrusting strike slip faulting and intense crustal shortening crustal thickening regional anatexis and metamorphism followed by large scale lithospheric extension rifting and magmatism to better understand the geological processes this paper reviews and synthesizes existing multi disciplinary geologic data related to sedimentation tectonics magmatism metamorphism and geochemistry and proposes a two stage tectono thermal evolutionary history of east asia during the late middle jurassic to early cretaceous ca 170 120 ma in the first stage three orogenic belts along the continental margins were formed coevally at ca 170 135 ma i e the north mongol okhotsk orogen the east paleo pacific coastal orogen and the west bangong nujiang orogen tectonism related to the coastal orogen caused extensive intracontinental folding and thrusting that resulted in a depositional hiatus in the late jurassic as well as crustal anatexis that generated syn kinematic granites adakites and migmatites the lithosphere of the east asian continent was thickened reaching a maximum during the latest jurassic or the earliest cretaceous in the second stage ca 135 120 ma delamination of the thickened lithosphere resulted in a remarkable 120 km lithospheric thinning and the development of mantle derived magmatism mineralization metamorphic core complexes and rift basins the middle jurassic early cretaceous subduction of oceanic plates paleo pacific meso tethys and mongol okhotsk and continent continent collision e g lhasa and qiangtang along the east asian continental margins produced broad coastal and intracontinental orogens these significant tectonic activities marked by widespread intracontinental orogeny and continental reconstruction are commonly termed the yanshan revolution movement in the chinese literature

geometric and temporal evolution of an extensional detachment fault hohhot metamorphic core complex inner mongolia china the early cretaceous hohhot metamorphic core complex and its master hohhot detachment fault are 400 km west of beijing in the daqing shan mountains of inner mongolia the complex developed across the east trending yinshan fold and thrust belt within 4 m y following cessation of thrusting ca 125 ma see note added in proof in main text postcontractional extension was initiated within a mid crustal zone of mylonitic and ductile shear that was in part controlled by carboniferous strata sandwiched between its proterozoic and archean crystalline basement and an overlying thrust sheet of similar crystalline rocks the hohhot detachment fault appears to have rooted into deep kinematically active levels of the mid crustal shear zone higher inactive levels of the mylonitic section were transected by the fault and carried upward in its footwall geometries of the footwall mylonitic rocks indicate localized ramp flat geometries of the fault within and across them the crosscut top of the mylonitic sequence defines a mylonitic front that departs from the gently south dipping detachment fault and dips northward into its footwall early cretaceous extension was widespread elsewhere in northern china and was particularly pronounced in the yunmeng shan core complex north of beijing the gravitational collapse of orogenically thickened crust acting in concert with localized centers of deep seated plutonism appear to have led to the development of isolated metamorphic core complexes within a broad region of more distributed extensional deformation

constructive and destructive episodes in the building of a young oceanic island la palma canary islands and genesis of the caldera de taburiente the results of new field observations 23 new k ar determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of la palma after the seamount activity represented by the materials of the basal complex an eruptive phase between 2 0 and 1 3 ma formed a large shield a period of volcanic quiescence followed until around 1 ma during which a large lateral collapse partly destroyed the former edifice between 1 05 and 0 7 ma activity was renewed in the shield and a n s ridge was built in the southern part of the island around 0 7 ma two new large lateral collapses affected the western part of both edifices and they were followed by eruptions between 0 71 and 0 65 ma which built a new edifice that partly filled the depressions thus created the caldera de taburiente constitutes the eroded remnants of the depression formed in the northern shield from 0 65 ma to present activity has been restricted to the n s ridge which has continued to grow southwards there was a general n s migration of volcanic activity with time but in the shield the trend was northwest to southeast eruptive rates seem to have been fairly constant during the different eruptive phases considered between 0 15 and 0 37 km3 ka a very similar succession of constructive and destructive episodes has been obtained for the neighboring island of hierro but in this case the activity started around 0 8 ma and eruptive rates were about 0 5 km3 ka

dike swarms key to the reconstruction of major volcanic edifices the basic dikes of la gomera canary islands the detailed study of the age and distribution of the basic dikes of la gomera canary islands has allowed us to reconstruct the evolution of its main volcanic edifice the dikes of the oldest unit the basal complex have a n70 80 dominant direction at regional scale on the other hand the dikes of the post basal complex subaerial units are the result of local stress fields the oldest swarm is composed of sills dated at 10 2 9 3 ma four younger radial dike swarms have been identified s1 s2 s3 and s4 with ages of 9 1 8 4 ma 8 2 6 7 ma 5 5 4 4 ma and 5 3 4 0 ma respectively the reconstruction of the magmatic focus location using these swarms shows a migration southwards with an average speed of 1 6 mm year this temporal sequence of parallel swarms sills and radial swarms is a pattern frequently repeated during the building of large insular volcanic edifices in the canary islands as well as in other archipelagos

tectonics of the dabieshan eastern china and possible exhumation mechanism of ultra high pressure rocks the dabieshan is divided into three tectonic domains the southern dabieshan is a stack of allochtons from top to bottom i unmetamorphosed cambrian early triassic series unconformably covered by jurassic sandstone ii weakly metamorphosed proterozoic slate iii hp rocks mostly retrogressed into greenschist facies iv uhp allochton v uhp free gneisses these units exhibit a nw se lineation and top to the nw shearing reworked by s verging folds the central dabieshan is a migmatitic dome superimposed on uhp metamorphism and bounded by a detachement fault responsible for the exhumation of the uhp unit during its retrogression into amphibolite facies in the northern dabieshan early foliation and n s trending compressional lineation are deformed by n verging folds coeval to the syn exhumation ductile structures of the central dabieshan a geodynamic model involving coeval thrusting and normal faulting is discussed

geomorphology and geochronology of sackung features uphill facing scarps in the central spanish pyrenees abstract the paper analyses uphill facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central spanish pyrenees previous studies of sackung landforms in the pyrenees have argued for deglacial unloading as the genetic mechanism but this causal and temporal relationship has not been proved due to the lack of chronological data the antislope scarps in the two studied locations vallibierna and estos are developed in palaeozoic metasedimentary rocks parallel to the contour lines and the structural grain occur in the intermediate sector of the hillslope and are up to 0 5 km long and several meters high a trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis charcoal from the lowermost unit in vallibierna provided an age of 5 9 cal ka for the sackung and extrapolation of the three dates obtained in estos indicates that the trough formed ca 7 6 7 8 cal ka deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka the time lag of 5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development but did not initiate the movement seismic shaking is proposed as a probable triggering factor this hypothesis although supported by the sudden deformation event recorded by a failure plane exposed in vallibierna trench and by the seismic and neotectonic activity of the area cannot be proved due to the lack of chronological information about paleoearthquakes

a late holocene deep seated landslide in the northern french pyrenees abstract a very large deep seated landslide dsl in the northern pyrenees with over 1 4 10 9 m 3 was mapped and dated based on sedimentation rates and 10 be terrestrial cosmogenic radionuclide surface exposure cre dating our analysis on the landslide reveals the role of inherited structures in the landslide process and highlighted typical gravitational morpho structures and a small lake trapped at the toe of the landslide head scarp the rate of lake sedimentation 0 86 0 57 mm yr 1 also provided us with the approximate age of the landslide 1106 540 yr the cre dating result highlights two main slope destabilization phases then we discussed the history of dsl activity and its controlling factors information related to historic markers and the absence of particular climate markers and changes during the medieval dark ages point to a single event in ad 1380 due to a major seismic event lavedan earthquake

volcano structural analysis of la garrotxa volcanic field ne iberia implications for the plumbing system abstract the garrotxa volcanic field is related to the neogene quaternary european rift system and is the youngest representation of monogenetic volcanism in the iberian peninsula it encompasses over 50 eruptive vents most of them well preserved cones in an area of about 600 km2 lying between the cities of olot and girona ne spain in this paper we investigate the relationship between the neogene extensional tectonics and the spatial distribution of the volcanoes in the area the analysis includes the distribution of faults fissures and vents as well as morphostructural lineaments and the morphometrical analysis of volcanic cones and craters in addition we use the location of the regional seismicity recorded since 1978 and the sites of freshwater springs and mantle derived gases as indicators of active faults and open fractures finally we consider the location of ultramafic xenoliths within volcanic deposits as a way of identifying the deepest fractures in the zone and estimating magma ascent velocities the results obtained show that this volcanic area consists of an extensional basin delimited by two principal nw se faults that favoured the ascent of magma from either the source region or from shallower reservoirs located at the base of the crust towards the upper part of the crust magma transport was captured by shallow secondary extensional nnw sse striking faults whose formation is linked to the slight transtensional movement of the main bounding faults our study provides evidence of how the local stress field and contrasts in substrate stratigraphy could have controlled magma migration which suggests that precise knowledge of the stress configuration substrate geology and structural discontinuities in such regions is crucial in the forecasting of monogenetic volcanism

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

tectonics of an ultrahigh pressure metamorphic terrane the dabie shan tongbai shan orogen china ultrahigh pressure metamorphic rocks with coesite and diamond form a tectonic slice over 20 km thick called the eclogite zone within the dabie shan complex in the qinling orogen in central china the orogen separates the sino korean block in the north from the yangtze block in the south the dabie shan complex is a composite terrane made up of eclogite facies and amphibolite facies gneiss slices and represents fragments of the lower continental crust of the yangtze block the dabie shan complex is bounded in the south by a triassic foreland fold thrust belt and in the north by a greenschist facies metaclastic unit the foziling group which probably represents the passive continental apron deposits of the yangtze block farther north is a granulite facies gneiss complex the qinling group which has ultramafic slivers and includes the remnants of an island arc with two bounding suture zones north of the qinling group are early paleozoic active margin deposits of the sino korean block the eclogite zone in the dabie shan complex is sandwiched between amphibolite facies gneiss slices dating by sm nd rb sr and ar ar of two eclogite samples from the eclogite zone gives early to middle triassic ages 236 246 ma the initial end values indicate reworking of a 2 11 and 1 55 ga continental crust a himalayan type tectonic evolution is envisaged for the qinling orogen with the creation of a 100 km thick crustal thrust wedge through continuous underplating during the subduction of the yangtze continental lithosphere exhumation of the ultrahigh pressure metamorphic rocks was chiefly achieved by the southward propagation of the thrust planes thereby isostatically uplifting and eroding the earlier deeply subducted parts of the orogen a total of 680 km of southward thrusting in front of dabie shan is inferred based on the abrupt termination of the tanlu fault normal faulting possibly caused by gravitational collapse probably also had a role in the exhumation process

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

integrated geophysics and soil gas profiles as a tool to characterize active faults the amer fault example pyrenees ne spain the combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions in this study we carried out geochemical soil gas sampling 222rn 220rn and co2 electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of amer in the spanish pyrenees where the presence of recent fractures is evident in the field data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that 1 endogene gases radon 222rn and carbon dioxide co2 are released from the meta sedimentary basement rocks across the main fractured zones with higher permeability values while lower cenozoic detrital sedimentary formations act as an impervious boundary 2 sites with highest radon concentrations 52 kbq m 3 coincide with the zones in the amer fault showing more recent geomorphic evidence of activity and more specifically with those areas covered by thinner surficial formations 3 the lowest 222rn values 0 2 0 4 kbq m 3 were recorded just on the master active fault plane this pattern could be explained by a dilution effect resulting from high rates of soil co2 efflux 267 g m 2 day 1 4 soil thoron 220rn activity is maximum 143 kbq m 3 in areas with high surficial fracturing 5 groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases the agreement between the different data geochemical geophysical and hydrogeological and field observations geology and geomorphology leads us to propose a preliminary tectonic gravitational model for the study area

the application of gpr and eri in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation this work illustrates the practicality of investigating sinkholes integrating data gathered by ground penetrating radar gpr electrical resistivity imaging eri and trenching or direct logging of the subsidence affected sediments in combination with retrodeformation analysis this mutidisciplinary approach has been tested in a large paleosinkhole developed during the deposition of a quaternary terrace on salt bearing evaporites the subsidence structure exposed in an artificial excavation is located next to puilatos a village that was abandoned in the 1970s due to severe subsidence damage detailed logging of the exposure revealed that the subsidence structure corresponds to an asymmetric sagging and collapse paleosinkhole with no clear evidence of recent activity the sedimentological and structural relationships together with the retrodeformation analysis indicate that synsedimentary subsidence controlled channel location the development of a palustrine environment and local changes in the channel pattern gpr profiles were acquired using an array of systems with different antenna frequencies including some recently developed shielded antennas with improved vertical resolution and penetration depth although radargrams imaged the faulted sagging structure and provided valuable data on fault throw they did not satisfactorily image the complex architecture of the fluvial deposit eri showed lower resolution but higher penetration depth when compared to gpr roughly capturing the subsidence structure and yielding information on the thickness of the high resistivity alluvium and the nature of the underlying low resistivity karstic residue developed on top of the halite bearing evaporitic bedrock data comparison allows the assessment of the advantages and limitations of these complementary techniques highly useful for site specific sinkhole risk management this article is protected by copyright all rights reserved

geomorphological study of long term erosion on a tropical volcanic ocean island tahiti nui french polynesia abstract a quantitative geomorphological study has been made on 27 river basins in tahiti nui volcanic island french polynesia to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall tahiti nui is composed of a main shield volcano cut by two huge landslides on each side of a main e w rift zone the northern landslide depression was rapidly buried by the construction of a second shield the late activity of which overflowed the crest and then filled the southern landslide depression the island is now volcanically inactive and is deeply dissected by erosion the present geometries of the river basins are first compared using dimensionless parameters derived from a digital elevation model the original volcanic surfaces are then reconstructed to estimate the volumes removed by erosion and determine the average rates of long term erosion the basins developed on the flanks of the main shield are wider shallower and gentler than the basins incising the post landslide second shield indicating a higher degree of evolution rainfall concentration on the windward eastern side of the island also contributed to increase the vertical lowering of the volcanic relief and the enlargement of the valleys the magnitude of erosion however is neither directly linked with the age of the units incised nor with the differential amounts of rainfall erosion rates determined over the last 1 myr range between 10 3 km 3 kyr 1 and 0 25 km 3 kyr 1 the highest values occur in the basins incising the main e w rift zone and or the lateral rims of the northern and southern landslide depressions long term dissection has thus been enhanced along the geological discontinuities of the eruptive system deep erosion was first constrained along the axis of the main e w rift zone where numerous dykes compartmentalize the volcanic structure into large unstable blocks dykes most probably acted as mechanical discontinuities along which shallow gravitational landslides recurrently occurred such mass wasting episodes produced significant amounts of debris partly preserved as highly indurated sedimentary breccias of various ages exposed at various locations subsequent dissection of tahiti nui was enhanced to the north and to the south leading to the rapid evolution of the papenoo and taharuu drainage systems over the last 500 kyr long term dissection on tahiti nui has been responsible for the removal of at least 350 km 3 of volcanic material from the surface and for the partial exhumation of a shallow intrusive complex partly composed of coarse grained plutonic rocks gabbros and syenites in the central part of the eruptive system structurally controlled erosion is thus a key component of landscape evolution on such high relief oceanic tropical islands

soil gas profiles as a tool to characterise active tectonic areas the jaut pass example pyrenees france a new method to investigate active tectonic structures using soil gas composition at faults suggests relevant information about regional stress conditions which can be obtained rapidly and at relatively low cost in 1995 we carried out geochemical profiles around the epicentre of the m 5 1 1980 earthquake near arudy in the french pyrenees where the presence of minor fractures is evident in the field and confirmed using satellite spot imagery fractures are conduits facilitating fluid migrations in the crust and are also pathways for the release of deep seated gases to the atmosphere in order to investigate the implication of these fractures in the present deformation i e if they are connected to the hercynian substratum at a depth of about 1800 m soil gases were measured along four traverses crossing the observed structures gases determined were 222rn co2 and 4he each of them for their characteristic source 222rn has essentially a shallow origin due to its short half life whereas co2 is the major soil gas component with a mainly surficial biogenic source however there could additionally be co2 from crustal or mantle degassing which would also be the principal sources of he data analysis clearly reveals anomalous values for each gas at specific positions along the traverses two sets of fractures corresponding to different observed trends are distinguished the one characterised by he anomalies accompanied by other gases and the second with few identified he anomalies the agreement between the geochemical data and the field observations leads us to propose a deformation model for the area studied analogous to a pull apart system located in a right lateral shear zone

ground water radon anomaly before the kobe earthquake in japan radon concentration in ground water increased for several months before the 1995 southern hyogo prefecture kobe earthquake on 17 january 1995 from late october 1994 the beginning of the observation to the end of december 1994 radon concentration increased about fourfold on 8 january 9 days before the earthquake the radon concentration reached a peak of more than 10 times that at the beginning of the observation before starting to decrease these radon changes are likely to be precursory phenomena of the disastrous earthquake

localization and characterization of an active fault in an urbanized area in central guatemala by means of geoelectrical imaging article i nfo article history the polochic and motagua faults define the active plate boundary between the north american and caribbean plates in central guatemala a splay of the polochic fault traverses the rapidly growing city of san miguel uspantan that is periodically affected by destructive earthquakes this fault splay was located using a 2d electrical resistivity tomography ert survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built ert images show the fault as a 50 m wide near vertical low resistivity anomaly bounded within a few meters by high resistivity anomalies forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location geometry and internal structure of the fault zone as well as the affected lithologies our results indicate that the city is constructed on a 20 m thick surficial layer consisting of poorly consolidated highly porous water logged pumice this soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking the electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might at least in part be fed by water rising along the fault therefore the potential threat posed by this fault splay may not be limited to its seismic activity per se but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments the results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of san miguel uspantan and illustrate the potential of ert surveying for paleoseismic studies

resistivity imaging technique to delineate shallow subsurface cavities associated with old coal working a numerical study subsidence is an environmental hazard due to subsurface cavities associated with abandoned coal workings in the eastern indian coalfields these cavities pose danger to coal mining of deeper coal seams most of these subsurface cavities are unapproachable as no mine plans are available here an attempt has been made to detect and possible delineation of air and as well as water filled cavities applying electrical resistivity imaging eri technique using dipole dipole pole dipole and wenner schlumberger arrays models are simulated with a reasonable resistivity value of formations considering board and pillar mining environment in multilayer earth the inverted resistivity section corresponding to water filled cavities without a barrier could be able to detect three cavities for dipole dipole and wenner schlumberger arrays whereas pole dipole array could detect all four cavities later on with inclusion of 1 m coal as a barrier in the model the dipole dipole array could be able to bring the signature of cavities whereas pole dipole and wenner schlumberger configuration is unable to provide any signature similar resistivity responses are noticed for air filled cavities with and without barrier conditions when all three arrays data are jointly inverted there is a significant improvement in resistivity response which enables the detection of water filled as well as air filled cavities with and without a barrier

evaluating quaternary activity versus inactivity on faults and folds using geomorphological mapping and trenching seismic hazard implications abstract the incorporation of active faults in seismic hazard analyses may have a significant impact on the feasibility design and cost of major engineering projects e g nuclear facilities dams especially when located in the site vicinity the regulatory definition of active versus inactive fault is generally based on whether the fault has ruptured or not after a specific chronological bound i e fault recency this work presents a methodology mainly based on geomorphological mapping and trenching for determining whether specific faults can be considered as active or inactive the approach is illustrated through the analysis of several faults located in the spanish pyrenees loiti leyre la trinidad ruesta faults the 29 km long loiti thrust was included in the neotectonic map of spain as a probable neotectonic structure previous works based on geomorphological investigations incorporated the 28 km long leyre thrust as a significant seismic source in a probabilistic seismic hazard analysis which challenged the seismic design of nearby large dams the production of detailed geomorphological strip maps along the faults allowed the recognition of specific sites where the faults are covered by quaternary deposits the establishment of chronosequences pediments terrace sequences and the available geochronological data helped identifying the most adequate morpho stratigraphic units for satisfactorily evaluating fault activity vs inactivity the excavation of trenches at the selected sites provided unambiguous information on the presence or lack of deformation in the quaternary cover overlying the fault and the origin of scarps tectonic versus erosional trenches were also useful for collecting samples and reliably measuring the relative height of terraces overlain by thick colluvium the evidence gathered by these methods were complemented with the numerical dating of non deformed slope deposits covering a fault the analysis of the longitudinal profiles of old pediment surfaces located in the proximity of a fault the examination of a cave situated next to a fault searching for speleoseismological evidence and regional geodetic and seismotectonic data gps measurements earthquake focal mechanisms the integration of all the data and especially the trenches dug in non deformed old terrace deposits 100 ka truncating the faults indicates that the analysed faults can be considered inactive and that previous neotectonic postulations were based on non valid geomorphological interpretations

differentiating between gravitational and tectonic faults by means of geomorphological mapping trenching and geophysical surveys the case of the zenzano fault iberian chain n spain abstract the zenzano fault scarp has been developed on the top of a 475 m high erosional escarpment underlain by an upper brittle sequence and a lower halite bearing evaporitic formation the 1850 m long fault with a maximum displacement of 45 m and parallel to the escarpment has offset the back of a dip slope generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages defeated streams both gravitational and tectonic interpretations were previously proposed for this active surface rupture the fault scarp has been investigated by detailed geological and geomorphological mapping geophysical surveys gpr and ert and two trenches excavated across the fault in disrupted drainages the geophysical profiles clearly imaged the fault helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block although the maximum displacement to length ratio dmax l of the fault fall within the range of tectonic faults of similar length according to the world database the geological and geomorphological context together with several parameters reveal that this structure corresponds to a gravitational failure 1 anomalously high vertical displacement per event 1 4 m 2 high apparent vertical slip rate 0 6 mm year and 3 short recurrence interval of faulting events the negligible horizontal displacement component on the dip slip fault as well as the presence of very large caprock collapse sinkholes and saline springs strongly suggest that interstratal karstification of the halite bearing evaporites has played a primary role in the development of the gravitational failure the formation of this morphostructure has been favoured by pre existing tectonic faults erosional unloading related to the removal of an overburden ca 800 m thick and enhanced groundwater recharge due to the blockage of the drainage this work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin

construction and destruction of mont pelee volcano volumes and rates constrained from a geomorphological model of evolution this study presents long term volumes and construction rates for the mont conil mont pelee volcano and rate estimates at which volcanic activity creates relief an algorithm shapevolc is used to numerically model topographic surfaces volcano morphology is analyzed using current digital elevation model in combination with mapped geology to produce 10 paleotopographies at the end of four constructional stages and three destructional events volumes of each constructional stage were estimated at about 35 2 km3 26 2 km3 8 3 km3 and 2 5 km3 for a total cumulative erupted volume of 72 2 km3 we estimate that mont pelee accounted for about 10 of the lesser antilles arc production in the last 100 kyr the volcano has been built at an average rate of 0 13 km3 kyr during the last 550 kyr during that time construction rates varied by a factor of 15 from 0 04 km3 kyr in early stages up to 0 52 km3 kyr after the second flank collapse volumes displaced by each flank collapse were estimated at 14 7 km3 8 8 km3 and 3 5 km3 thus about 37 of the total constructed volume integrated over the volcano s lifetime the rate at which flank collapses removed material off the island is 0 15 km3 kyr in contrast long term erosion rates outside collapsed areas are estimated at about 0 05 0 7 km3 kyr or 11 km3 of material removed this latter rate is not negligible which strengthens the importance of taking into account recurrent small erosional events on the geomorphological evolution of a volcanic island in a tropical context

electrical resistivity imaging for aquifer mapping over chikotra basin kolhapur district maharashtra electrical resistivity study assumes a special significance for mapping aquifers in hard rock areas a two dimensional 2d resistivity survey of chikotra basin southern part of kolhapur district in the deccan volcanic province of maharashtra was conducted the aim of this work was to determine the aquifer zones of the study area using electrical resistivity imaging technique the hydro geological section derived from the available dug well borehole lithology suggests that the top layer comprises red bole laterite or black soil followed by weathered fractured rock grading into compact basalts the sources of groundwater appear to be available in weathered and fractured basalt trapped between weathered overburden and hard rock results from the 2d inverted models of resistivity variation with depth suggest the occurrence of aquifers mostly in weathered fractured zones within the traps or beneath it the resistivity models suggest that the northern part of the study area represents a promising aquifer zone with reasonable thickness of weathered basement the models further indicate that there are several locations throughout the basin for possible groundwater exploration as it exhibited strong water bearing potential in the subsurface rocks

fracture related wavefield polarization and seismic anisotropy across the greendale fault we investigate seismic signatures of fracturing in a newly ruptured strike slip fault by determining the wavefield polarization in the new zealand canterbury plains area and across the greendale fault which was responsible for the 3 september 2010 darfield mw 7 1 earthquake previous studies suggested that fractured rocks in fault damage zones cause directional amplification and ground motion polarization in the fracture perpendicular direction as an effect of stiffness anisotropy and cause velocity anisotropy with shear wave velocity larger in the fracture parallel component an array of 14 stations was installed following the darfield earthquake we assess polarization both in the frequency and time domains through the individual station horizontal to vertical spectral ratio and covariance matrix analysis respectively and compare the results to previously reported anisotropy measurements from shear wave splitting stations installed in the canterbury plains have an amplification peak between 0 1 and 0 3 hz for both earthquakes and ambient noise we relate the amplification to the resonance of a considerable thickness c 1 km of soft sediments lying over the metamorphic bedrock analysis of seismic events revealed the existence of another peak in amplification between 2 and 5 hz at two on fault stations which was not visible in the noise analysis in contrast to the lower frequency peak the ones between 2 and 5 hz are more strongly anisotropic attaining amplitudes up to a factor of 4 in the n52 direction to interpret this effect we model the fracture pattern in the fault damage zone produced by the fault kinematics we conclude that the horizontal polarization is orthogonal to extensional fractures which predominate in the shallow layers 2 km expected in n101 direction on the basis of the model thus different fracture distribution at different depths may explain different results for amplification compared to anisotropy we propose polarization amplification analysis as a complementary method to s wave splitting analysis polarization analysis is rapidly computed and robust and it can be applied to either earthquakes or ambient noise recordings giving useful information about the predominant fracture patterns at various depths

metamorphic core complexes vs synkinematic plutons in continental extension setting insights from key structures shandong province eastern china abstract continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust though a metamorphic core complex mcc reveals a much stronger crustal extension than a synkinematic pluton the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations in eastern asia a major continental extensional event occurred during mesozoic and early cenozoic times the resulting various extensional events described in previous studies consist in large intracontinental basins important volcanism emplacement of plutons in the upper crust and exhumation of mccs an efficient description of mccs and plutons in eastern asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations in that way an integrated structural and geophysical study has been realized to precisely discriminate the structure in the jiaodong peninsula shandong province eastern china previously regarded as simple sheared plutons a succession of three main stages have been identified all pertaining to a nw se extensional setting 1 the exhumation of the late jurassic early cretaceous linglong mcc below the se dipping linglong detachment fault 2 the emplacement of the guojialing syntectonic pluton below the n dipping extensional guojialing intracrustal shear zone 130 124 ma and 3 a penetrative brittle normal faulting associated with gold mineralizations 120 ma as a result the maximum amount of extension in jiaodong peninsula characterized by partially melted lower to middle crust upward into the linglong mcc should be revised to late jurassic early cretaceous period

the structural and tectonic relationships of the major fault systems of the tan lu fault zone with a focus on the segments within the north china region abstract the jiashan lujiang yishu and bohai segments have been the most tectonically active parts of the tan lu fault system since the mesozoic any analysis of faulting processes in the tan lu system is highly dependent on the relationships among the three segments here we divide the tan lu system into three styles of faulting strike slip faulting regional extensional faulting and listric normal faulting on the basis of emap data seismic profiles and geological evidence we suggest that 1 the strike slip faults which formed in the late jurassic include mainly the jiashan lujiang fault the deep parts of the chihe taihu fault and the guhe sanbing fault these three faults have had the most dramatic effect on the jiashan lujiang segment the strike slip style of faulting produced a huge positive flower structure that extends between the deep section of the chihe taihu fault and the guhe sanbing fault and overlaps with the position of the zhangbaling ductile shear zone 2 the regional extensional style of faulting whose characteristics are reflected best in the yishu fault zone is composed of the changyi dadian anqiu quxian yishui yangtou and tangwu gegou faults all of which were active during the early cretaceous these extension dominated faults extend southwards to the jiashan and hefei basins and die out in front of the dabie mountains to the north the faults penetrate the deeper parts of the weibei depression where they controlled cretaceous deposition in graben horst graben structures 3 the listric normal faults which were initiated in the paleogene generally occur around the bohai bay basin and include a series of ne trending faults in the weibei depression such as the tandong and tanxi faults these listric faults differ from the regional extensional faults in their localized occurrence and association with basin formation our study indicates that these three styles of faulting varied not only in timing and mechanical properties but developed at different levels at different locations resulting in different tectonic relationships and the formation of different geologic features in the different segments of the tan lu master system

subsurface initiation of tafoni in granite terrains geophysical evidence from ne spain geomorphological implications abstract granite cavities in the north east of spain which developed below the weathering front are reported these cavities up to 3 m across and probably filled with water saturated weathered granite have been detected by electrical resistivity tomography ert as low resistivity anomalies enclosed in high resistivity media corresponding to unweathered granite rock the caverns appear as hyperbolic reflections in a radargram obtained by ground penetrating radar gpr and show similar shape and size to the tafoni found in the surrounding granite outcrops data gathered in this study support a subterranean origin of some of the tafoni a new conceptual model for the initiation and growth of granite cavities under subsurface conditions is proposed groundwater flow through vertical and sheet fractures triggers preferential weathering at points where meter sized spheroidal pockets of weathered granite develop erosion of the rock mass leads to the exposure of these pockets evolving under subaerial conditions as typical tafoni

motion of kilauea volcano during sustained eruption from the puu oo and kupaianaha vents 1983 1991 kilauea erupted almost continuously from january 1983 through 1991 although the summit began subsiding during the rift zone dike intrusion that initiated this eruption remarkably steady ground surface motions began in late 1983 after a magnitude 6 6 earthquake beneath the slopes of nearby mauna loa volcano and continued until the onset of brief upper east rift zone earthquake swarms in late 1990 during these 7 years the summit and upper rift zones subsided up to 10 11 and 4 8 cm yr 1 respectively and summit baselines contracted up to 6 cm yr 1 baselines directed northward from the summit to stations on mauna loa extended at rates up to 7 cm yr 1 and a baseline from south of the summit to mauna loa extended 4 cm yr 1 much of this extension is inconsistent with deformation caused solely by summit magma reservoir collapse and more likely reflects rifting as the south flank of the volcano moved seaward from the summit and rift zones farther from the summit baselines crossing the south flank extended up to 2 cm yr 1 and a south flank tide gauge rose 2 cm yr 1 the lower east rift zone 40 50 km from the summit subsided about 2 cm yr 1 motion on kilauea then is broadly consistent with slip along low angle south flank faults generating subsidence that is focused at the summit and along the rift system behind the faulting and uplift along the coastal south flank ahead of it dislocation models that combine these elements show that much of kilauea s edifice migrated seaward producing ground surface motions along the south flank of up to about 6 cm yr 1 the magnitude 6 1 earthquake of 1989 punctuated these motions along the eastern south flank producing more than 25 cm of seaward displacement and 15 km east of the epicenter up to 24 cm of subsidence south of the lower east rift zone unlike the magnitude 7 2 south flank earthquake of 1975 the 1989 event was preceded neither by summit magma reservoir inflation nor by rift zone dike intrusions and accompanying compression of the south flank deformation was probably caused by the weight of the volcanic overburden and by ongoing dilation and slip within the rift system

sedimentary record and tectonic implications of mesozoic rifting in southeast mongolia the east gobi basin of mongolia is a poorly described late jurassic early cretaceous extensional province that holds great importance for reconstructions of mesozoic tectonics and paleogeography of eastern asia extension is especially well recorded in the structure and stratigraphy of the unegt and zuunbayan subbasins southwest of saynshand mongolia where outcrop and subsurface relationships permit recognition of prerift synrift and postrift mesozoic stratigraphic megasequences within the synrift megasequence three sequences developed in response to climatic and rift related structural controls on sedimentation where best exposed along the northern margin of the unegt subbasin each of the synrift sequences is bounded by unconformities and generally fines upward from basal alluvial and fluvial conglomerate to fluvial and lacustrine sandstone and mudstone resedimented ashes and basalt flows punctuate the synrift megasequence rifting began in the unegt subbasin prior to 155 ma with coarse alluvial filling of local fault depressions subsidence generally outstripped sediment supply and fresh to saline lacustrine environments expanding southward with time dominated the unegt zuunbayan landscape for much of latest jurassic early cretaceous time episodic faulting and volcanism characterized the basin system for the balance of the early cretaceous a brief period of compressional and or transpressional basin inversion occurred at the end of the early cretaceous prior to deposition of a widespread upper cretaceous overlap sequence the driver s of late jurassic early cretaceous extension remain uncertain because southeast mongolia occupied an intraplate position by the beginning of the cretaceous extension in the east gobi basin was coeval with collapse and extension of early mesozoic contractional orogenic belts along the northern and southern borders of mongolia and probably was a linked phenomenon strike slip faulting associated with collisions on the southern asian and mongol okhotsk margins likely also played a role in late mesozoic deformation of the east gobi region perhaps partitioning the gobi from apparently coeval large magnitude contractional deformation in the yinshan yanshan orogenic belt south of the study area in inner mongolia

dem based morphometry as a tool for reconstructing primary volcanic landforms examples from the borzsony mountains hungary a complex application of digital elevation model dem derivatives is presented for a highly degraded volcanic area the miocene borzsony mountains hungary we propose unconventional geometrical and mathematical transformations of the original dem data in order to enhance the topographic features of the volcanic relief that stem from the primary landforms it is the actual ridges that represent the least degraded surfaces of an original hypothetical volcanic cone therefore the statistical dem properties such as ridge pattern 1 slope angle distribution 2 and higher order slope derivatives 3 should be strongly correlated with the paleosurface automated creation of a ridge pattern image is based on the local histogram of the dem and helps to outline the original surface remnants a local slope angle histogram may point out structurally coherent parts of the original cone for instance tectonic displacements or large scale sector slumping does not affect the slope angle histogram of the original relief evaluating the ridge maps and slope aspect maps of the borzsony mountains allows various cone sectors to be identified and connected to the original volcano structural elements finally the polar coordinate transformed pct image 4 centered on a hypothesized eruptive vent enhances the original radial valley pattern in the case of multiple eruptive centers and or post eruptive tectonic modifications the radial pattern is changed which may be evidenced in the pct image in fact the pct image analysis for the borzsony mountains suggests a complex post eruptive tectonic scenario the presented methods can be recommended to infer the original configuration of highly degraded volcanic structures with poorly known tectonic and erosional history

geological and geomorphological evolution of the etna volcano ne flank and relationships between lava flow invasions and erosional processes in the alcantara valley italy abstract in this paper the interrelationships between volcanic activity and fluvial events in the alcantara valley are investigated based on the correlation between the stratigraphy of the ne flank of mt etna and subsurface data the geological and geomorphological evolutions of the valley are reconstructed new 1 10 000 scale geological mapping shows that the bulk of this sector of the volcano is made up of the ellittico volcano lava flows though they are widely covered by the products of the eruptive activity of the last 15 ka the present day morphological setting of the alcantara valley is the result of two main evolutionary phases initiated during the activity of the ellittico volcano only one lava flow invasion of the valley floor occurred in the first phase this phenomenon was followed by a long period of erosional processes leading to the entrenchment of the drainage pattern and the erosion of the ellittico lava flow about 20 25 ka ago an important change in the frequency of the lava flow invasions into the valley occurred associated with the final stage of the ellittico volcano activity marking the beginning of the second phase during this phase volcanic processes became predominant with respect to other morphogenetic processes in the alcantara valley lava flows coming from the ne flank of the ellittico volcano caused a radical modification of the morphological setting of this area even though only one lava flow emitted by an eruptive fissure located within the valley partially filled the riverbed during the eruptive activity of the last 15 ka the complete filling of the alcantara valley floor occurred in particular between 15 and 7 ka a lava flow originated from the mt moio scoria cone filled the valley floor for a distance of about 9 km following a short period of erosion an eruptive fissure located within the valley generated a 20 21 km long lava flow that was channelled along the full extent of the alcantara valley and stretches for about 3 km offshore in the ionian sea in the last 7 ka lava flows originating from the ne rift zone produced only temporary damming of the riverbed without any important contribution to the filling of the alcantara valley

erosion calderas origins processes structural and climatic control the origin and development of erosion modified erosion transformed and erosion induced depressions in volcanic terrains are reviewed and systematized a proposed classification addressing terminology issues considers structural geomorphic and climatic factors that contribute to the topographic modification of summit or flank depressions on volcanoes breaching of a closed crater or caldera generated by volcanic or non volcanic processes results in an outlet valley under climates with up to 2000 2500 mm annual rainfall craters and calderas are commonly drained by a single outlet the outlet valley can maintain its dominant downcutting position because it quickly enlarges its drainage basin by capturing the area of the primary depression multi drained volcanic depressions can form if special factors e g high rate geological processes such as faulting or glaciation suppress fluvial erosion normal fluvial erosion modified volcanic depressions the circular rim of which is derived from the original rim are termed erosion craters or erosion calderas depending on the pre existing depression the resulting landform should be classed as an erosion induced volcanic depression if the degradation of a cluster of craters produces a single drained irregular shaped basin or if flank erosion results in a quasi closed depression under humid climates craters and calderas degrade at a faster rate mostly at subtropical and tropical ocean island and island arc volcanoes their erosion results in so called amphitheater valleys that develop under heavy rainfall 2500 mm year rainstorms and high elevation differences structural and lithological control and groundwater in ocean islands may in turn preform and guide development of high energy valleys through rockfalls landsliding mudflows and mass wasting given the intense erosion amphitheater valleys are able to breach a primary depression from several directions and degrade the summit region at a high rate occasionally amphitheater valleys may create summit depressions without a pre existing crater or caldera the resulting negative landforms which may drain in several directions and the primary origin of which is commonly unrecognizable should be included in erosion transformed volcanic depressions

chronology and processes of late quaternary hillslope sedimentation in the eastern south island new zealand optical and radiocarbon dating of loessic hillslope sediments in new zealand s south island is used to constrain the timing of prehistoric rockfalls and associated seismic events and quantify spatial and temporal patterns of hillslope sedimentation including responses to seismic and anthropogenic forcing trenches adjacent to prehistoric boulders enable stratigraphic analysis of loess and loess colluvium pre and post dating boulder emplacement respectively luminescence ages from loessic sediments constrain the timing of boulder emplacement to between 3 0 and 12 5 ka well before the arrival of polynesians ca ad 1280 and europeans ca ad 1800 in new zealand and suggest loess accumulation was continuing at the study site until 12 13 ka large 5 m3 prehistoric rockfall boulders preserve an important record of holocene hillslope sedimentation by creating local traps i e accommodation space for sediment aggradation i e colluvial wedges and upbuilding soil formation sediment accumulation rates increased considerably 10 factor increase following human arrival and associated anthropogenic burning of hillslope vegetation our study presents new numerical ages to place the evolution of loess mantled hillslopes in new zealand s south island into a longer temporal framework and highlights the roles of earthquakes and humans on hillslope surface process

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

pseudo 3d imaging of a low slip rate active normal fault using shallow geophysical methods the geleen fault in the belgian maas river valley in a detailed site survey for paleoseismic trenching we applied shallow geophysical prospecting techniques including ground penetrating radar gpr electric resistivity tomography ert and resistivity mapping to identify locate and visualize in 3d the geleen fault an active normal fault bordering the roer valley graben in northeast belgium because of a low slip rate the geomorphic expression of this fault is very faint in the relatively young deposits of the maas river valley ert profiles show the fault as a broad near vertical anomaly characterized by sharp lateral resistivity contrasts with an associated vertical offset of sediment layers we observed offsets of 15 m and 5 m for the base and top respectively of a middle late pleistocene fluvial gravel layer shallow ert and gpr profiles indicate that younger sediments are also affected by faulting but the amount and sense of offset appear to be conflicting ert profiles show a near surface high resistivity layer with an apparent rever

radon emanation from giant landslides of koefels tyrol austria and langtang himal nepal the identification of extremely high indoor radon concentrations in the village umhausen tyrol austria initiated a scientific program to get information about the source and distribution of this noble gas the high concentrations can not be related to u anomalies or large scale fault zones the nearby giant landslide of koefels with its highly fractured and crushed orthogneisses are the only possible source of radon despite the fact that the u and ra content of the rocks is by no means exceptional the reasons for the high emanation rates from the landslide are discussed and compared to results gained from a similar examination of the giant landslide of langtang himal nepal the exceptional geologic situation in both cases as well as the spatial distribution of different concentration levels indicate that both landslides must be considered as the production sites of radon independent of the u and ra contents of the rocks the most important factors producing high emanation rates are the production of a high active surface area and circulation pathways for rn enriched soil air by brittle deformation due to the impact of the landslidemass

the 2010 2011 canterbury earthquake sequence environmental effects seismic triggering thresholds and geologic legacy abstract seismic shaking and tectonic deformation during strong earthquakes can trigger widespread environmental effects the severity and extent of a given effect relates to the characteristics of the causative earthquake and the intrinsic properties of the affected media documentation of earthquake environmental effects in well instrumented historical earthquakes can enable seismologic triggering thresholds to be estimated across a spectrum of geologic topographic and hydrologic site conditions and implemented into seismic hazard assessments geotechnical engineering designs palaeoseismic interpretations and forecasts of the impacts of future earthquakes the 2010 2011 canterbury earthquake sequence ces including the moment magnitude m w 7 1 darfield earthquake and m w 6 2 6 0 5 9 and 5 8 aftershocks occurred on a suite of previously unidentified primarily blind active faults in the eastern south island of new zealand the ces is one of earth s best recorded historical earthquake sequences the location of the ces proximal to and beneath a major urban centre enabled rapid and detailed collection of vast amounts of field geospatial geotechnical hydrologic biologic and seismologic data and allowed incremental and cumulative environmental responses to seismic forcing to be documented throughout a protracted earthquake sequence the ces caused multiple instances of tectonic surface deformation 3 events surface manifestations of liquefaction 11 events lateral spreading 6 events rockfall 6 events cliff collapse 3 events subsidence 4 events and hydrological 10s of events and biological shifts 3 events the terrestrial area affected by strong shaking e g peak ground acceleration pga 0 1 0 3 g and the maximum distances between earthquake rupture and environmental response r rup both generally increased with increased earthquake m w but were also influenced by earthquake location and source characteristics however the severity of a given environmental response at any given site related predominantly to ground shaking characteristics pga peak ground velocities and site conditions water table depth soil type geomorphic and topographic setting rather than earthquake m w in most cases the most severe liquefaction rockfall cliff collapse subsidence flooding tree damage and biologic habitat changes were triggered by proximal moderate magnitude m w 6 2 earthquakes on blind faults ces environmental effects will be incompletely preserved in the geologic record and variably diagnostic of spatial and temporal earthquake clustering liquefaction feeder dikes in areas of severe and recurrent liquefaction will provide the best preserved and potentially most diagnostic ces features rockfall talus deposits and boulders will be well preserved and potentially diagnostic of the strong intensity of ces shaking but challenging to decipher in terms of single versus multiple events most other phenomena will be transient e g distal groundwater responses not uniquely diagnostic of earthquakes e g flooding or more ambiguous e g biologic changes preliminary palaeoseismic investigations in the ces region indicate recurrence of liquefaction in susceptible sediments of 100 to 300 yr recurrence of severe rockfall event s of ca 6000 to 8000 yr and recurrence of surface rupturing on the largest ces source fault of ca 20 000 to 30 000 yr these data highlight the importance of utilising multiple proxy datasets in palaeoearthquake studies the severity of environmental effects triggered during the strongest ces earthquakes was as great as or equivalent to any historic or prehistoric effects recorded in the geologic record we suggest that the shaking caused by rupture of local blind faults in the ces comprised a worst case seismic shaking scenario for parts of the christchurch urban area moderate m w blind fault earthquakes may contribute the highest proportion of seismic hazard be the most important drivers of landscape evolution and dominate the palaeoseismic record in some locations on earth including locations distal from any identified active faults a high scientific priority should be placed on improving the spatial extent and quality of off fault shaking records of strong earthquakes particularly near major urban centres