mass movements in tropical volcanic terrains the case of teziutlan mexico abstract during the last decade soil degradation coupled with global climate changes has increased hydrogeological hazards in mexico in tropical volcanic terrains alteration processes have enhanced the formation of clay minerals that promote water retention and result in soil rock weakness intense seasonal rainfall can trigger the liquefaction and remobilization of these low resistance terrains during the first week of october 1999 heavy rains affected eastern mexico including puebla state as a consequence approximately 3000 mass movements consisting of rock and soil slides and slips debris flows and avalanches were generated in this area in the town of teziutlan puebla which is located on volcanic deposits a single mass movement event caused approximately 150 deaths in the present work we identified two types of mass movements in the teziutlan area type 1 superficial erosion of an unwelded ignimbritic sequence forming small detrital fans and type 2 thin soil slide debris flow from the remobilization of a volcanic sequence composed of clay rich paleosols interbedded with ashfall horizons the clay rich volcanic paleosols favored the formation of perched water tables on a hydraulic aquiclude positive pore water pressures triggered the failure based on these results the principal human settlement in the teziutlan area may be threatened by future debris flows which could cause serious harm to the dense population and severe damage to its infrastructure it is necessary to prevent future deaths and damage by installation of mitigative measures based on detailed studies without any further study it will not be possible to prevent and mitigate a natural disaster with the same magnitude as the 1999 catastrophic hydrogeological phenomena

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

late cretaceous paleomagnetic results from southeastern china and their geological implication abstract a paleomagnetic study was carried out on late cretaceous red beds in central jiangxi province southeastern china stepwise thermal demagnetization was used to isolate the characteristic higher temperature component htc from the jishui d 355 7 i 34 8 95 6 3 and ganzhou d 15 6 i 35 6 95 5 5 areas respectively the htc direction from the jishui area passes enkin s fold test at 95 confidence level and indicates an 18 9 5 5 counter clockwise rotation relative to the referent pole of the stable south china block scb the htc direction from ganzhou passes both mcfadden s fold test at 95 confidence level and reversal test comparing these two new poles 81 0 n 322 2 e a95 5 8 from jishui and 74 4 n 225 1 e a95 5 2 from ganzhou with other coeval poles reported from south china these results demonstrate a significant difference in paleolatitude 9 9 4 1 between coastal and inland areas which might be either related to dextral shearing faulting between them or inclination shallowing conducted by sedimentation and or compaction however results obtained from both anisotropy of the isothermal remanence air method and corrected results of the elongation inclination model of tauxe and kent l tauxe d v kent a simplified statistical modal for the geomagnetic field and the detection of shallow bias in paleomagnetic inclinations was the ancient magnetic field dipolar in j e t channell d v kent w lowrie j meert eds timescales of the paleomagnetic field geophys monogr am geophys union 145 2004 101 115 indicate that a distinct inclination flattening occurred in our samples

new late cretaceous and paleogene paleomagnetic results from south china and their geodynamic implications 1 to better understand the tectonic evolution of south china block scb in response to the india asia collision we present new paleomagnetic results from late cretaceous and paleogene red bed formations of the hengyang basin of hunan province in the interior part of the scb stepwise thermal demagnetization of the rocks isolated a high temperature component the tilt corrected mean direction from the late cretaceous rocks is d 15 6 i 29 9 with a95 5 7 n 26 sites corresponding to a paleopole at 71 9 n 236 3 e with a95 4 7 which passes reversal tests the tilt corrected mean direction d 358 9 i 35 4 with a95 5 0 n 22 sites from the paleogene rock which passes the reversal test gives a pole at 82 6 n 300 6 e with a95 4 4 the low field anisotropy of magnetic susceptibility results suggest that the red beds have not experienced significant strain due to compaction or tectonic stress while the anisotropy of isothermal remanence results suggest that postdepositional compaction in these red beds produced no more than 3 4 of inclination shallowing these paleomagnetic and rock magnetic tests imply that the remanence is primary on the basis of paleomagnetic results obtained from coeval basalts in mongolia and siberia we suggest that no significant latitudinal motion has taken place between the scb and siberia since the late cretaceous the significant latitudinal discrepancy between the scb and european block could be due to nonrigid behavior of the eurasian plate since the late cretaceous a 16 7 5 0 clockwise rotation of the scb during the late cretaceous to the paleogene could be related to the collision of india and asia in the west and the subduction of the circum pacific plate to eastern asia in the east

cretaceous palaeomagnetic results from hainan island in south china supporting the extrusion model of southeast asia abstract we report the cretaceous palaeomagnetic results from hainan island south china in hainan island we collected the early cretaceous redbeds of the lumuwan formation at eleven sites we also describe the tectonic kinematics for and around hainan island since the cretaceous deduced from our and previous palaeomagnetic results the palaeolatitude of hainan island is 25 9 n 3 4 3 2 implying that hainan island was situated about 7 north from the present position during the cretaceous the palaeopole of hainan island latitude 77 7 n longitude 162 1 e k 65 6 and a95 4 4 suggests 4 0 5 8 counterclockwise rotation and 14 1 5 5 southward translation relative to the suspected coherent part of the south china block scb since the cretaceous the rotation and translation of similar sense 18 8 7 4 and 7 8 6 9 respectively are detected in the existing palaeomagnetic result from the xinlong formation in guangxi which is situated approximately 400 km north northwest from hainan island the southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the scb in a similar pattern to the indochina block which had resulted from the indentation of india into asia this sw part seems to have slightly rotated counterclockwise because its extrusion was probably smaller in scale than the indochina block and therefore it was dragged out by the indochina block this hypothesis is supported by the existence of a northwest southeast trending fault system parallel to the red river fault

eruption rates and compositional trends at los humeros volcanic center puebla mexico the los humeros volcanic center located 180 km east of mexico city is one of several pleistocene silicic centers in the back arc portion of the mexican neovolcanic belt the eruptive history at los humeros suggests that average eruptive rates increased with time and exceeded rates of regeneration of differentiated magma silicic volcanism began 0 47 ma ago with extrusion of high silica rhyolite domes shortly thereafter at 0 46 ma ago 115 km3 of magma zoned from high silica rhyolite to rhyodacite were erupted resulting in formation of the xaltipan ignimbrite and collapse of the 21 15 km los humeros caldera high silica rhyolite domes then erupted along the northwestern ring fracture zone of the caldera they are covered by the faby tuff a dominantly rhyodacitic sequence of plinian fall deposits erupted from the southeast quadrant of the los humeros caldera dated at 0 24 ma a second major caldera forming event occurred 0 1 ma ago with the eruption of the zaragoza tuff a nonwelded ignimbrite zoned from rhyodacite to andesite eruption of these 12 km3 of magma led to collapse of the 10 km diameter los potreros caldera which is nested within the older los humeros caldera between 0 04 and 0 03 ma ago an arc of andesitic scoria cones concentrated along the southern ring fracture zone of the los humeros caldera fed lavas that flowed southward from the volcanic center and andesite lavas built two small shields between the eastern rims of the two calderas approximately 6 km of andesitic magma were extruded during this stage activity continued up to 0 02 ma ago with eruption of 10 km3 of rhyodacitic to andesitic lava flows from centers near the northern margin of the los potreros caldera in the area between the eastern rims of the two calderas and within a broad band where the southern segments of the inferred los humeros and los potreros ring fracture zones nearly coincide simultaneous venting of rhyodacitic and andesitic tephra within this band led to formation of the 1 7 km diameter el xalapazco caldera minor fault bounded uplift of the southeastern quadrant of the los potreros caldera followed the latest stage of volcanic activity is represented by the eruption of 0 25 km3 of olivine basalt lavas along the southern ring fracture zone of the los humeros caldera and on the floors of the los potreros and el xalapazco calderas erupted magmas show an overall trend with time toward more mafic compositions volumetric eruptive rates increased from 0 06 km3 per thousand years 0 25 ma ago to 0 2 km3 per thousand years in the last 0 1 ma the increase in eruptive rate may have been the result of a progressive decrease in the structural integrity of the roof zone of the system as successive caldera forming eruptions reactivated old zones of weakness and created new ones an increasingly disrupted roof allowed mafic and intermediate magmas to reach the surface relatively rapidly decreasing their residence time in a high level chamber and thus the time available for their differentiation

determining rheological parameters of debris flow material abstract a 2 0 m diameter steel 30 inverted cone and plate viscometer rheometer was designed constructed and used to test the behaviour of coarse grained debris flow materials a 1 5 scale model machine was also constructed and used to test the internal flow dynamics of the viscometer rheometer and to obtain results for fluids grain fluid mixtures and debris flow fines for fluids and grain fluid mixes our results were similar to those obtained earlier using standard viscometric systems derived rheological parameters for debris flow materials and clay slurries agreed well with those determined from calculation direct measurement and field observation apparent viscosities were shear rate dependent extremely sensitive to water content and as high as 6000 pa s instantaneous stresses within shearing debris flow material varied over a wide range debris flow materials with bimodal grain size distributions had a dilatant plastic rheology those with a low content of coarse material and unimodal grain size distribution or exceptionally high fines content had a plastic or viscoplastic rheology

convective vigour and heat flow in chemically differentiated systems parametric models of planets used to study their thermal evolution are generally based on scaling laws for purely thermal convection however planetary mantles may be chemically highly differentiated due to partial melting which may form thick layers of depleted and dehydrated melting residue e g continental roots this results in inhomogeneity of density which affects the driving force of convection and viscosity through the water content which directly influences the dynamics of the system this work investigates the applicability of scaling laws developed for purely thermally convecting systems to chemically differentiated systems representative of planetary mantles the effects of depletion related buoyancy and melting related dehydration and particularly the stratified convection patterns which may result from these are considered two different strategies are applied to this end first a large number of numerical thermochemical convection experiments are performed of which the dynamics and heat flow characteristics are studied secondly theoretical approximations are developed from existing scaling laws to describe the heat flow of chemically stratified systems with separately convecting layers these are tested using numerical simulations the results show that the presence of a chemical stratification in the mantle may significantly alter heat flow patterns relative to a purely thermally convecting system by either influencing the thickness of the thermal boundary layer or dividing the convecting part of the system in vertically separate cells this is consistent with recent petrological findings although the chemical stratification may be inherently instable against remixing the present results suggest that the timescales of remixing may be much larger than those of thermal equilibration therefore it is important to consider chemical stratification in thermal evolution models for present day earth conditions and realistic rheological parameters the results predict that the lower parts of continental roots may be convecting separately from the underlying mantle the thick depleted layer which has been speculated to underly the martian crust may also have exhibited convection in the lower parts when convection takes place in the depleted zone mantle heat flow values are predicted to increase by a factor of 2 5 relative to non convecting depleted zones if this process acts for significant periods of time during planetary evolution it will strongly influence the planet s thermal evolution

paleomagnetic study of cretaceous rocks from pu er western yunnan china evidence of internal deformation of the indochina block abstract cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the jingxing and nanxin formation around pu er 23 0 n 101 0 e western part of yunnan province china in order to examine quantitative amount of tectonic deformation of the simao terrane due to collision of india with asia after stepwise thermal demagnetization the high temperature component magnetization with unblocking temperature of around 680 c is isolated positive field tests show that the high temperature component magnetization from 25 sites is primary for the cretaceous formations a tilt corrected mean direction is d 59 9 i 45 2 with 95 5 1 corresponding to a paleopole at 35 8 n 173 1 e with a 95 5 6 comparison with cretaceous paleomagnetic pole of the whole china block indicates that amount of clockwise rotation in the pu er area is evaluated to be 46 9 with respect to the whole china block which is consistent with large amount of rotation in the mengla and jinggu areas 47 and 66 in the central part of the simao terrane clockwise rotation of the central part is larger by more than 20 compared to the yunlong and yongping areas of northern part of the simao terrane suggesting that the simao terrane experienced internal deformation the southward displacement of the pu er area expected from inclination data is 7 5 6 6 with respect to the chuan dian fragment which is a similar estimate to other areas in the simao terrane and the indochina block while the simao terrane displaced southward by 800 km together with clockwise rotation of 30 as a whole further clockwise rotation occurred in the central part

tectonic evolution of the tancheng lujiang tan lu fault via middle triassic to early cenozoic paleomagnetic data the north striking tancheng lujiang tan lu fault is a conspicuous and controversial feature of the eastern asian landscape near the southeast extremity of the fault in anhui province we collected paleomagnetic samples at 17 middle triassic t2 and 10 upper cretaceous k2 to lower cenozoic e1 sites t2 remanent magnetizations are interpreted as primary in two of three areas the three areas are rotated 37 to 137 counterclockwise with respect to the south china block scb reference direction k2 e1 remanent magnetization directions pass regional fold and reversals tests and are not rotated with respect to surrounding areas counterclockwise rotation of t2 strata therefore ended before k2 and is attributed to left lateral shear acting along tan lu during the north china block ncb scb collision in shandong province 700 km north of the anhui sites four areas containing 33 upper jurassic j3 and cretaceous sites have negligible declination differences except for one which has dispersed directions the fold test is inconclusive for this latter area and positive for the other three regional concordance of the j3 e1 paleomagnetic data including paleolatitudes together with observed deformation patterns suggest that an extensional regime prevailed in the late cretaceous and cenozoic euler pole positions that constrain the north south china collision and account for tan lu motion suggest at least 500 km of sinistral shear took place along the fault and either 1 subduction and related ultrahigh pressure uhp metamorphism occurred near the present location of the qinling dabieshan and sulu uhp belts while tan lu acted as a transform fault that connected the two subduction zones or 2 tan lu and sulu were parts of the same transform fault system and no uhp rocks formed in situ at sulu in either case uhp rocks originally exhumed near dabieshan could have been transported by plate capture toward sulu along tan lu after north and south china impacted near dabieshan the tan lu fault grew within the scb as the dabieshan corner indented the scb causing folds in scb cover rocks to conform to the ncb margin late cretaceous to cenozoic reactivation of tan lu with both right lateral strike slip and normal fault motion occurred as the scb extruded east relative to the ncb under the influence of the india asia collision

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

hydro mechanical analysis of volcanic ash slopes during rainfall rainfall induced landslides in volcanic ashes represent a major natural hazard in many regions around the world due to their loose structure volcanic ash slopes are prone to rainfall induced landslides the paper presents a continuum modelling approach for the analysis of wetting induced instability phenomena at the onset of failure in loose volcanic ash slopes a numerical simulation of a landslide prone volcanic slope in costa rica is carried out with a 2d hydro mechanical finite element slope model a constitutive model based on the effective stress concept extended to partially saturated conditions is used to reproduce the volcanic ash hydro mechanical behaviour the model parameters were calibrated through a previous extensive laboratory testing campaign simulation results allow to anticipate the behaviour of the slope during rainfall infiltration and to analyze the development of the failure mechanism results of the coupled numerical model demonstrate the important role of wetting and drying cycles slope geometry and bedrock on the timely evolution of matric suctions and wetting induced deformations moreover it is observed that the pore collapse upon wetting enhances the development of a localised shear failure mechanism in unsaturated conditions

rain triggered lahar susceptibility using a shallow landslide and surface erosion model abstract lahars are mass flows containing variable concentrations of water and volcanic debris that can cause catastrophic impacts to life livelihoods and infrastructure downstream from their volcanic origin accurate and quantitative information on lahar hazards are essential for reducing the impact of these events lahar hazard assessments often focus on the use of numeric or empirical models to describe flow behaviour and inundation areas which rely on historic lahar events and expert elicitation to define model inputs this results in qualitative or semi quantitative estimates of hazard that do not account for the mechanics of lahar initiation or in the case of rain triggered lahars the dependence of rainfall intensity and duration on initiation here we develop a method for calculating rain triggered lahar susceptibility defined as the occurrence probability of a particular lahar initial volume at a specific location the model relies on terrain and deposit characteristics and a probabilistic measure of rainfall in the form of rainfall intensity frequency duration relationships results for a case study of the october 28 1995 lahar at mangatoetoenui stream ruapehu volcano new zealand indicate lahar volume is controlled by a characteristic timescale relating the deposit depth h to the hydraulic diffusivity d 0 in the ratio h 2 d 0 the timescale describes the transmission of positive pore pressures within the deposit leading to shallow failure as a consequence of this timescale rainfall duration is the most important factor determining initial lahar sediment volume rainfall intensity plays a minor role controlling the volume of water in the lahar mixture this observation is consistent with power law relationships used to determine lahar triggering rainfall thresholds the rain triggered lahar susceptibility approach developed here is anticipated to improve probabilistic lahar hazard assessments by providing quantitative reproducible estimates of initial lahar volumes

major natural hazards in a tropical volcanic island a review for mayotte island comoros archipelago indian ocean abstract mayotte is a french overseas territory of the comoros archipelago since the 1980 mayotte has developed quickly its population has multiplied by four in less than 30 years infrastructure expanded rapidly in lowlands and slums developed in steep areas through deforestation or close to riverbeds this development urgently required steps to ensure the safety of urban areas from 2002 to 2006 a major programme of natural hazards evaluation and zonation was conducted by the french geological survey in the 17 districts of mayotte the programme resulted in the publication of the first single hazard zonation maps for mayotte at 1 25 000 scale in rural areas and at 1 10 000 scale in urban areas hazard maps regarding landslides and rock falls stream floods seismic lithological and topographical amplification potential liquefaction potential and cyclonic marine submersion were produced for mayors and land planners these atlases also included prevention guidelines to minimize risks associated with land use or urbanization within hazard prone areas this article presents the main achievements of the programme whose main problems were the absence of archives of previous studies and the original volcanic geology of the island of mayotte the atlases highlight areas with numerous landslides zones susceptible to flash floods sectors likely to be submerged by storm surges and areas subject to seismic site effects due to thick volcanic weathered formations this programme emphasizes the fundamental role in such tropical volcanic islands of a good knowledge of the weathered formations for the assessment of most natural hazards this initial hazard mapping represented the first step to achieve specific regulatory risk prevention plans for an efficient land use risk mitigation and reduction policy in mayotte

paleomagnetism of late mesozoic granitic intrusions in hong kong implications for upper cretaceous reference pole of south china two late jurassic early cretaceous granite plutons in hong kong were sampled at 16 sites for paleomagnetic determination the two granites show differences in magnetic properties and mineralogy but similar natural remanent magnetization nrm directions multiple magnetizations and dual polarity have been detected in the samples isothermal remanent magnetism magnetic susceptibility and coercivity measurements reveal multidomain titanomagnetite as the principal magnetic carrier a rating of paleomagnetic results from individual sites was based on the number of specimens efficacy of the demagnetization procedures and within site variance of nrm directions the pole position from 12 high quality sample sites is 171 9 e 78 2 n a95 10 6 the dual polarity and cooling ages of the granites suggest a late cretaceous acquisition of the remanent magnetism based on four different studies the upper cretaceous reference pole of south china is located at 194 3 longitude 73 5 n latitude a95 10 4 paleomagnetic results from north china south china and eurasia show no large scale cenozoic relative movements among the three blocks but the small separation between the paleomagnetic poles of south china and eurasia probably implies a minor relative movement since the late cretaceous

the rain triggered atenquique volcaniclastic debris flow of october 16 1955 at nevado de colima volcano mexico abstract on october 16 1955 at 10 45 a m local time after three days of intense rain 140 mm that was twice the monthly average precipitation a devastating flood surge formed a volcaniclastic debris flow on the eastern slopes of nevado de colima volcano nearly simultaneous flood surges formed in the arroyo seco los platanos and dos volcanes ravines that coalesced with the larger flow in the atenquique ravine at each confluence with a tributary the flow was diluted the texture and structure of the preserved 1955 deposits near high water marks indicate that the downstream flow was mainly in the lower range of debris flow concentration 60 sediment concentration by weight downstream the tributaries the flood encountered a 0 06 10 6 m 3 water reservoir that failed significantly increasing the surge volume additional entrained sediment also increased the flow volume downstream the flood wave reached the town of atenquique as an 8 9 m catastrophic wave causing the death of more than 23 people the partial destruction of the town and losses of 13 000 000 pesos 1 million us dollars today to a paper mill and company facilities according to eyewitness accounts the flood wave had a peak discharge that lasted ca 10 to 15 minutes at atenquique deposits at the site and the high water marks observed from photographs of the town s church indicate that sediment concentration was ca 60 wt the flood continued for about 1 km to its junction with the tuxpan river where it was diluted by mixing with normal flood flow the deposits covered an area of 1 2 km 2 and had a minimum volume of 3 2 10 6 m 3 the main deposit consists of a single unit averaging 4 m in thickness with weak textural variations that suggest surging within the flood wave the deposit is heterolithologic and consists of boulders set in a matrix of sand size sediment with polymodal or bimodal distributions and normal grading varying with distance from source the town of atenquique has been reconstructed largely within the area inundated by the 1955 flood wave thus creating the conditions for a future disaster a rainfall intensity warning system and an educational program for inhabitants are strategies to mitigate this risk

spatial and temporal occurrence of rainfall induced shallow landslides of flow type a case of sarno quindici italy article i nfo rainfall induced shallow landslides of flow type provide unstable masses which often travel long run out distances with high velocities thus posing a high societal risk when they affect large areas therefore analysis of their spatial and temporal occurrence is relevant to landslide hazard assessment as the first step of the risk analysis in order to address this issue this paper outlines a multidisciplinary procedure that is applied to the may 1998 sarno quindici landslides southern italy whose spatial and temporal occurrence is not satisfactorily addressed in current literature the spatial occurrence of the landslides is analysed using heuristic models for both the source and propagation areas the temporal occurrence of the landslides is firstly compiled and then related to the cumulated rainfall stratigraphy and hydraulic boundary conditions finally the spatial and temporal occurrence of the main landslide triggering mechanism is modelled over the whole affected area by analysing the groundwater regime and slope stability conditions the obtained results show that the spatial and temporal occurrence is strongly related to stratigraphy and hydraulic boundary conditions at both the slope and massif scales they also highlight a suitable procedure for assessing the spatial and temporal occurrence of complex landslides over large areas

hydrological landslide triggering in ash covered slopes of manizales columbia abstract a study on hydrological landslide triggering was carried out on ash covered slopes near the city of manizales columbia the saturated hydraulic conductivity of the different soil types and the pressure head fluctuations in relation to rainfall were determined in order to detect saturated zones in the soil profile which form preferential zones for the development of slip surfaces of landslides tensiometer measurements revealed saturation in the topsoil as a result of infiltration of rainfall in the ashes as a result of a perched water table and at the soil bedrock contact as a result of a groundwater table the location of the saturated zones in the soil profile proved to be in accordance with the location of slip surfaces observed in the field three landslides were selected for back analysis to establish the pressure heads that could have triggered these landslides the pressure heas obtained by back analysis were compared with the measured pressure head ranges the back calculated pressure heads proved to support the conclusions of the hydrological study

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

clockwise rotation of the red river fault inferred from paleomagnetic study of cretaceous rocks in the shan thai malay block of western yunnan china more than 150 samples were collected at 23 sites from the lower cretaceous jingxing formation near the city of yongping 25 5 n 99 5 e which is located on the west side of the red river fault sixteen sites have characteristic directions with a high temperature component above 500 c the high temperature component of magnetization from twelve sites is of pre fold origin and reveals clockwise deflection in declination d 42 0 i 51 1 and 95 15 7 the easterly declination of more than 40 at yongping is consistent with the cretaceous paleomagnetic direction d 45 of chuxiong 25 n 101 5 e which is located on the east side of the red river fault both areas were subjected to about 25 clockwise rotation with respect to the eastern part of the yangtze block since cretaceous time we conclude that the red river fault was rotated through25 16 with respect to the eastern part of the yangtze block associated with rotation of the yongping and chuxiong areas removal of the rotation from the red river fault indicates that the latter and the jinsha suture formed a straight line along n55 w s55 e within the asian continent from vietnam to the tibetan plateau in the present coordinate system during the cretaceous the linear feature of the red river fault and jinsha suture was probably deformed to the present curved shape as a result of collision of the indian continent with the asian continent

paleomagnetic study of cretaceous rocks from the yangtze block central yunnan china implications for the india asia collision abstract more than 200 samples for this study were collected at 30 sites from the cretaceous matoushan and puchanghe formations around the city of chuxiong 25 n 101 5 e twenty four sites have characteristic directions with a high temperature component above 350 c paleomagnetic directions from 21 sites of the cretaceous formations reveal clockwise deflection in declination d 44 6 i 41 3 and 95 10 7 the reliability of the direction is ascertained through a positive fold test and the presence of normal and reversed polarities comparison with paleomagnetic data from other areas indicates that the chuxiong area was rotated clockwise through26 17 with respect to the eastern part of the yangtze block whereas it was subjected to more than 44 of clockwise rotation with respect to the neighboring blocks of lhasa 56 21 and western sichuan 44 16 since cretaceous time the clockwise rotation of chuxiong is a reflection of rotational motion of the large region including the southeastern qiangtang terrane and the jinsha suture red river fault paleomagnetic data and tectonic features suggest that the rotation occurred prior to the folding in the central yunnan province probably during the paleogene this large rotation is a spectacular example of the deformation in the southeastern part of the asian continent due to the collision of india

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

paleomagnetic constraints on the extent of the stable body of the south china block since the cretaceous new data from the yuanma basin china abstract we undertook a paleomagnetic investigation of cretaceous red sandstones at 30 sites within the yuanma basin in western hunan central south china block scb china the aim of this study is to further constrain the extent of the scb that has been stable since the cretaceous we isolated the characteristic directions of higher temperature components htcs with an unblocking temperature of 650 to 690 c by progressive thermal demagnetization and principal component analysis the optimal concentrations of global mean htc directions calculated using the direction correction tilt test were achieved at 92 7 59 1 87 9 25 0 and 93 3 19 7 untilting indistinguishable from 100 untilting for early cretaceous k1 13 sites late cretaceous k2 17 sites and k site groupings k1 k2 30 sites respectively this treatment yielded positive tilt tests and the htcs are considered to be primary magnetic components acquired before tilting of the sedimentary layers early k1 and late k2 cretaceous paleomagnetic poles calculated using the site mean directions untilted completely are located at similar positions this suggests the absence of local rotations linked to cretaceous strain within the study area the cretaceous k1 k2 mean paleomagnetic pole calculated using virtual geomagnetic poles from all sites is in agreement with previously reported cretaceous paleomagnetic poles from the eastern and western scb this indicates that the hunan region has been part of the stable body of the scb since the cretaceous and that the tectonic influence of the india asia collision did not extend to within the stable body of the scb the reference cretaceous pole position latitude 80 1 n longitude 204 1 e a 95 2 5 calculated using eight cretaceous poles from the stable body of the scb is similar to those determined from stable eurasia and the north china block ncb this result indicates that the india asia collision caused no relative motion as detected by paleomagnetic analysis among stable eurasia ncb and the stable body of the scb

weathering distribution in a steep slope of soft pyroclastic rocks as an indicator of slope instability abstract weathering of rocks on steep slopes influences slope instability and sometimes leads to slope failure during heavy rainfall to determine the weathering intensity of hillslope rocks and its inward change from the slope surface measurements of the penetrative hardness of rocks which correlates with their strength were made in some slopes composed of soft pyroclastic rocks on kyushu island japan a gradual reduction in hardness from the interior to the slope surface was recognized within slopes the hardness change was almost concordant with changes in other weathering indices such as rock color clay minerals and apparent grain size the weathered zone indicated by the reduction in hardness was 1 2 m thick at the foot of steep slopes which are frequently subjected to gullying and surface failures whereas the zone was 7 8 m thick at slope summits which are gentle and stable for a long period although the inward change in hardness was gradual on all parts of a slope the change was marked on the foot slope where the strength contrast between weathered and non weathered rock was greater the thickness of the weathered zone on the foot slope therefore controls the volume of failed materials when a failure occurs the difference in weathered thickness between the foot and the summit of a slope much affects the style of failure in general and consequently shapes the characteristic configuration of slopes in this region the estimated weathering rate on a slope surface based on hardness distribution was on the order of 10 2 to 100 cm year 1 assuming a constant rate this rate is far greater than that of other rocks therefore the frequent occurrence of slope failures in this region was attributed to this rapid weathering

paleomagnetism of cretaceous to lower tertiary rocks from southwestern sichuan a revisit abstract a re study has been carried out on the cretaceous to lower tertiary rocks from southwestern sichuan province on the south china block the characteristics remanent magnetization chrm resolved from the paleocene eocene leidashu formation is of dual polarity and very shallow inclination the anomalouslylow paleolatitude 6 9 6 3 n indicated by the inclination is not supported by geological evidence from this region and is probably due to inclination error related to depositional and or post depositional processes a positive fold test as well as the prevalence of normal polarity suggests that the chrm of the mid upper cretaceous xiaoba formation might be acquired during the cretaceous long normal superchron clns the tilt corrected mean direction of the xiaoba formation d i 8 1 38 8 95 6 6 n 18 sites is not significantly different from a preliminary result d i 357 6 31 6 95 8 6 n 12 samples we reported earlier for the collective xiaoba and leidashu formations the resultant paleopole 81 5 n 220 9 e a95 7 1 is coincident with other cretaceous poles for the chinese blocks comparison with the eurasian apparent polar wander path apwp indicates neither significant rotation nor latitudinal translation of the study area relative to eurasia the newly obtained mean direction for the xiaoba formation is believed to be more reliable than our earlier result since it is based on a larger sample size and is apparently free from effects of the shallow inclination observed in the leidashu formation and should supercede our previous preliminary result the paleopole derived from sevenentes of the lower cretaceous feitianshan formation 69 0 n 204 6 e a95 4 3 deviates from the track from the late jurassic to late cretaceous poles the deviation might be reduced by further sampling

structural and stratigraphic development of the newark extensional basin eastern north america evidence for the growth of the basin and its bounding structures the newark basin is a half graben bounded on its northwestern margin by a system of mostly normal slip faults many of which are reactivated paleozoic thrust faults and were active at least sporadically during the deposition of the entire basin fill as a result of along strike variations in displacement on the border fault system subsidence increased from the lateral edges toward the center of the basin and from the hinged margin toward the border fault system some intrabasinal faults also formed during the deposition of units currently preserved in their hanging walls along strike variations in the density of intrabasinal faults probably reflect changes in the dip angle of the border fault system variations in the amount of extension accommodated on these intrabasinal faults resulted in the formation of a transfer fault along strike variations in fault displacement probably produced the transverse folds in the hanging walls immediately adjacent to border faults and major intrabasinal normal faults some folds formed syndepositionally progressively younger strata onlap basement rocks along the hinged margin of the basin and younger splays of the border fault system propagated into the footwall the basin therefore grew deeper wider and longer through time

cretaceous and tertiary paleomagnetic results from southeast china and their tectonic implications abstract we report cretaceous and tertiary paleomagnetic data from fujian guangxi and guangdong provinces in south china in guangxi province we sampled early cretaceous redbeds of the xinlong formation at eight localities separated by up to 100 km the high temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test and implies 18 8 counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in sichuan province a tertiary basin lying in a southeast trending fault zone is also rotated counterclockwise by 40 8 both results can be explained very well by a simple block rotation model for the cenozoic tectonic evolution of western guangxi province that is driven by left lateral shear on southeast trending faults the timing and sense of shear are the same as for india asia collision models involving the extrusion of indochina along the red river fault zone which lies several hundred kilometers to the southwest but the magnitude of fault displacement in guangxi is much less in the coastal provinces of fujian and guangdong we find late cretaceous directions that are rotated clockwise with respect to sichuan province combined with similar clockwise rotations found by two other studies of coeval rocks from the same region the mean rotation for the coastal provinces is 12 8 this could indicate a coherent block rotation of the region driven by extrusion tectonics however the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum pacific tectonics

behavior of a loosely compacted unsaturated volcanic soil in this paper the stress strain relationsihp and volumetric behavior of a loosely compacted unsaturated decomposed volcanic soil fill were studied by conducting three series of triaxial stress path tests 1 consolidated undrained on the saturated fill 2 constant water content and 3 a reducing suction under constant deviator stress on the unsaturated fill the last two series of tests were designed to simulate the effects of undrained response and rainfall infiltration in initially unsaturated slopes respectively it was found that the saturated loose volcanic soil behaves like clay under isotropic compression but it resembles sand behavior when it was subjected to undrained shear for isotropically consolidated unsaturated specimens sheared under a constant water content a hardening stress strain and a nonlinear shear strength suction relationship are observed at relatively high suctions both angle of friction and apparent cohesion appear to be independent of suction volumetric contraction during shear is observed in this series of tests on the other hand anisotropically consolidated loose unsaturated specimens subjected to a reducing suction change from contractive to dilative behavior as the net mean stress increases this observed volumetric behavior unlike the shear strength is stress path dependent and cannot be explained by using the existing elastoplastic critical state theoretical framework extended for unsaturated soils

the october 16 2013 rainfall induced landslides and associated lahars at izu oshima volcano japan abstract intense rainfall related to the typhoon t1326 on october 15 16 2013 total 824 mm maximum hourly rainfall 118 5 mm triggered numerous landslides and associated lahars at izu oshima volcano the northernmost part of izu mariana volcanic arc japan the landslides were concentrated mainly in a 2 km 2 area located on the western slope of izu oshima volcano most of the landslides were shallow soil slips 4 m 3 km 2 based on debris volumes trapped by sediment retention dams the characteristics of rainfall induced landslides and associated lahars at izu oshima volcano in 2013 provide an important lesson about future non eruption related landslide and lahar hazards at tephra rich volcanoes

paleomagnetic study of middle cretaceous rocks from yunlong western yunnan china evidence of southward displacement of indochina middle cretaceous red sandstones and siltstones were collected at 20 sites for paleomagnetic study from the nanxin formation around yunlong 25 8 n 99 4 e western part of yunnan province china after stepwise thermal demagnetization high temperature component magnetization with unblocking temperature of about 675 c is isolated a positive fold test at the 99 confidence limit shows that the high temperature component magnetization is primary for the middle cretaceous nanxin formation a tilt corrected formation mean direction is d 40 2 i 49 9 with 95 3 9 corresponding to a paleopole at 54 6 n 171 8 e with a95 4 4 comparison with previously reported cretaceous paleomagnetic directions indicates that the yunlong area has been subjected to southward displacement by 11 9 7 5 corresponding to 1300 800 km with respect to the stable yangtze craton since cretaceous time as well as clockwise rotation through 36 3 13 6 this study elucidates that indochina was squeezed out of the asian continent due to collision of india accompanied with clockwise rotation

new mesozoic apparent polar wander path for south china tectonic consequences a new paleomagnetic study in the south sichuan basin south china block has been carried out on sediments of early triassic to middle jurassic age detailed stepwise thermal and alternating field demagnetizations allowed us to isolate two to three components a low temperature component component a falls close to the local present earth field direction a middle temperature component component b is found both in limestone and red beds of early triassic age in limestones of middle triassic age and finally in red beds of jurassic age the component b directions failed the fold test but show a significant increase of the ks kg ratio at 60 when a progressive stepwise unfolding is applied the directions obtained at 60 unfolding are grouped best and yield a pole position at 76 5 n 174 1 e a95 3 7 that is close to the late cretaceous pole of the south china block scb or the early tertiary pole of the eurasian plate characteristic directions are finally obtained component c for early triassic and early to middle jurassic sediments only both with reversal and fold tests they yield pole positions at 44 1 n and 217 2 e a95 4 9 and 79 n and 227 e a95 4 5 respectively the early triassic result well fits other data of the same age from the scb the revised late permian to cretaceous paleopole data provide a new mesozoic apparent polar wander path for south china the successive pole positions from late permian to early triassic indicate motion of the south china block as a whole rather than local rotations linked to important strain within the block the early to middle jurassic pole is statistically indistinguishable from the compiled north china block ncb poles and indicates that final suturation between the two blocks occurred by the end of the triassic which is coherent with the age of ultra high pressure metamorphism in the dabie sulu areas of eastern china the asian plate including the mongol central asian block ncb and scb however was probably separated from siberia by the mongol okhotsk ocean during jurassic time

cretaceous paleomagnetism of the eastern south china block establishment of the stable body of scb abstract a paleomagnetic investigation was performed on the cretaceous red sandstones collected at the eastern side of the south china block scb china and attempted to establish the stable part of the scb since the cretaceous paleomagnetic specimens were collected at 39 25 and 14 sites from three independent parts the northern central and southern regions of eastern scb respectively characteristic directions of higher temperature components htcs with an unblocking temperature of 680 c were isolated from 69 78 sites the optimal concentrations of global mean htc directions calculated using the direction correction tilt test were achieved at 79 19 95 27 71 37 and 117 98 untilting for the early cretaceous sites from the northern part late cretaceous sites from the northern central and southern parts respectively this treatment gives positive tilt tests or brings the optimal concentration not far from being indistinguishable from positive tilt tests although this observation can be due to imperfect separation of a primary component htc from a secondary one lower temperature component we adopted completely 100 untilted directions of the htcs as the paleomagnetic field directions during the cretaceous because the mean directions after complete untilting were almost equal to each mean direction after incomplete untilting showing the optimal concentration the mean paleomagnetic poles for three independent parts were located at almost the same positions and were indistinguishable from that for sichuan the western side of scb at the 95 confidence level this observation indicates that there is no relative movement between the eastern and western sides of scb and implies that a large part of the scb excluding a 400 km wide swath along the red river fault has behaved as its coherent stable body since the cretaceous the cretaceous paleomagnetic pole for the stable body of the scb latitude 80 0 n longitude 206 7 e a 95 2 5 is worth using as a reference cretaceous paleomagnetic pole of the scb and agrees strongly with the reference eurasian paleomagnetic pole during the cretaceous period

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

paleomagnetic results from cretaceous and jurassic rocks of south and southwest yunnan evidence for large clockwise rotations in the indochina and shan thai malay terranes abstract cretaceous and jurassic redbeds have been sampled from south and southwest yunnan china for paleomagnetic study the paleomagnetic directions resolved from the cretaceous rocks indicate that the xiaguan area which is located on the red river fault has not been rotated with respect to stable eurasia since at least late cretaceous times and that the jinggu mengla area 200 400 km farther south has been rotated by 46 65 clockwise the jurassic results reveal the same rotation pattern at face value the differences between the observed cretaceous paleolatitudes and those predicted from the eurasian apparent polar wander path apwp indicate a southward extrusion of the region but the amount of extrusion is not large enough to be resolved by paleomagnetic methods comparison with mesozoic paleomagnetic data from central yunnan northern thailand and northwestern borneo suggests that the red river fault is not a demarcation between unrotated and significantly rotated regions and that sundaland did not respond to the india asia collision as a single coherent unit the existing paleomagnetic data from east asia appear to indicate that the crust in central tibet and tien shan north of tarim directly in front of the indian indentor has been substantially shortened and thickened whereas the crust in the syntaxial areas has probably been largely squeezed out to further evaluate the relative importance of crustal thickening and extrusion in the tectonic evolution of the tibetan plateau paleomagnetic investigation should be intensified in the bounding zones to the indian indentor and be expanded into the cenozoic sedimentary rocks in tibet and surrounding regions

paleomagnetism of upper cretaceous rocks from south china paleomagnetic study of upper cretaceous redbeds from two areas in south china was undertaken in an effort to constrain better the history of tectonic movements in southeastern asia from the nanjing area 32 n l19 e high temperature characteristic directions which pass a fold test were obtained from ten sites 43 samples in the upper cretaceous puko and yanzijing formations the paleomagnetic pole position 76 3 n 172 6 e a95 10 3 agrees well with a late cretaceous reference pole for eurasia and thus confirms that this part of south china was fully sutured to eurasia by the end of the cretaceous with no paleomagnetically resolvable subsequent relative rotation in western sichuan 26 5 n 102 3 e high temperature characteristic directions of normal and reverse polarity were obtained from twelve samples 48 specimens in the upper cretaceous to lower paleocene xiaoba and leidashu formations a provisional paleomagnetic pole position 80 9 n 296 8 e a95 7 7 differs significantly from a late cretaceous eurasia reference pole in terms of apparent tectonic movement the difference in paleopole positions would indicate a 13 10 3 northward translation and 22 11 2 counterclockwise rotation of western sichuan relative to eurasia confirmation of this reconnaisance result which would suggest that western sichuan was pushed ahead of an impinging india is needed

new paleomagnetic constraints on the extrusion of indochina late cretaceous results from the song da terrane northern vietnam abstract samples were collected for paleomagnetic investigations from the upper cretaceous yen chau formation in the song da terrane 21 7 n 103 9 e bounded by the ailao shan red river fault system and song ma fault in an attempt to examine extrusion tectonics of east asia primary nature of the high temperature 600 690 c component of magnetization from 13 sites is supported by a positive fold test the tectonic corrected data provides the characteristic late cretaceous paleomagnetic direction for the song da terrane d 6 4 i 32 0 with 95 8 5 n 13 sites corresponding to a paleopole lying at 82 9 n 220 7 e a95 6 9 comparison with coeval paleomagnetic poles for the neighboring tectonic blocks indicates no latitudinal translation of the son da terrane with respect to the south china block whereas the shan thai block and the southern part of the indochina block revealed a southward displacement of 10 5 9 5 in latitude with respect to the song da terrane we conclude that the southeastern segment of the ailao shan red river fault system to the east of the dien bien phu fault is not a demarcation of the extruded indochina peninsula the indochina block extruded probably along some faults between the song da terrane and the khorat plateau

new palaeomagnetic data supporting the extent of the stable body of the south china block since the cretaceous and some implications on magnetization acquisition of red beds summary previous palaeomagnetic studies have demonstrated that a large part of the south china block scb has behaved as a stable body since the cretaceous we undertook a palaeomagnetic investigation of lower cretaceous red sandstones at 24 sites within the ganzhou and xingguo basins in southern jiangxi province in china the aim of this study was to further constrain the extent of the scb which has been stable since the cretaceous we isolated the characteristic directions of higher temperature components htcs with an unblocking temperature from 650 to 700 c by progressive thermal demagnetization and principal component analysis the optimal concentration of site mean htc directions calculated using the direction correction tilt test was achieved at 51 2 32 4 per cent untilting indicating syntilting magnetization suggesting that the remanences were not acquired immediately after sedimentation most cretaceous sedimentary basins on the eastern part of the scb were controlled by fault movement extensional basins most tilting in such an extensional basin is thought to have progressed contemporaneously with the structural and stratigraphic development of the basin we concluded that the remanence acquisition of red sandstones on the ganzhou and xingguo basins occurred during synsedimentary tilting we adopted 51 2 per cent untilted directions of the htcs as the palaeomagnetic field directions during the early cretaceous the mean palaeomagnetic pole 76 3 n 224 3 e 95 3 3 calculated using virtual geomagnetic poles from 23 sites excluding site 20 which has an insufficient number of samples showing a stable magnetic component is in good agreement with the late cretaceous palaeomagnetic poles from the same region and also with most of cretaceous poles previously reported from the stable body of the scb this agreement indicates that the jiangxi region has been part of the stable body of the scb since the cretaceous this result also demonstrates that the tectonic influence of the india asia collision did not destroy the rigidity of most of the scb the global mean pole position 78 8 n 214 4 e 95 2 6 calculated using sixteen cretaceous poles from the stable body of the scb is suitable for use as the reference cretaceous palaeomagnetic pole of the stable scb

hydrological factors affecting rainfall induced shallow landslides from the field monitoring to a simplified slope stability analysis abstract rainfall induced shallow landslides can seriously affect cultivations and infrastructures and cause human losses a continuous monitoring of unsaturated soil hydrological properties is needed to understand the effects of pore water pressure and water content on shallow landslides triggering and slope safety factor in this work the impact of water content pore water pressure and hydrological hysteresis on safety factor reconstruction is analyzed by applying two different models lu and godt s and slip models to a monitored slope located in oltrepo pavese northern italy a shallow landslide event in the studied slope during the monitoring allowed for identifying the triggering mechanism and modeling the safety factor changes the conditions of instability mechanism develop in periods with frequent rainfalls the uprising of a perched water table in the soil profile gets nil or positive pore water pressure which linked with the nil effective soil cohesion of some soil horizons allows for the shallow landslide triggering the safety factor trends correctly predicted unstable conditions safety factor 1 0 in correspondence of the shallow landslide triggering time on the basis of both water content and pore water pressure a better prediction gets when the safety factor is modeled considering the hysteresis effects modeling the safety factor on the basis of water content can make a good assessment of shallow failures triggering conditions only for failures in unsaturated soils and for completely saturated soils instead considering pore water pressure it is possible estimating safety factor changes linked with the development of positive pore water pressures which can be linked in some cases to shallow landslide development

modeling the october 2005 lahars at panabaj guatemala an extreme rainfall event in october of 2005 triggered two deadly lahars on the flanks of toliman volcano guatemala that caused many fatalities in the village of panabaj we mapped the deposits of these lahars then developed computer simulations of the lahars using the geologic data and compared simulated area inundated by the flows to mapped area inundated computer simulation of the two lahars was dramatically improved after calibration with geological data specifically detailed field measurements of flow inundation area flow thickness flow direction and velocity estimates collected after lahar emplacement were used to calibrate the rheological input parameters for the models including deposit volume yield strength sediment and water concentrations and manning roughness coefficients simulations of the two lahars with volumes of 240 200 55 400 and 126 000 29 000 m3 using the flo 2d computer program produced models of lahar runout within 3 of measured runouts and produced reasonable estimates of flow thickness and velocity along the lengths of the simulated flows we compare areas inundated using the jaccard fit model sensitivity and model precision metrics all related to bayes theorem these metrics show that false negatives areas inundated by the observed lahar where not simulated and false positives areas not inundated by the observed lahar where inundation was simulated are reduced using a model calibrated by rheology the metrics offer a procedure for tuning model performance that will enhance model accuracy and make numerical models a more robust tool for natural hazard reduction

new and revised set of cretaceous paleomagnetic poles from hong kong implications for the development of southeast china a paleomagnetic study of upper cretaceous 80 ma dikes from hong kong was conducted with the aim of better understanding the late cretaceous cenozoic kinematic history of southeast china twelve out of seventeen sites collected from four dikes revealed primary trms and yield a late cretaceous paleopole at 69 38n 211 28e where a95 8 98 and k 107 a synthesis of south china block cretaceous poles indicates that coastal southeast china which is bounded by the lianhuashan fault zone to the northwest and the changlenanao fault zone to the southeast has moved relative to inland central south china the discordant cretaceous paleopoles from the south china block suggest a moderate net clockwise rotation of the coastal southeast china relative to central south china since the late cretaceous this clockwise rotation is probably the result of micro blocks along the south china margin experiencing vertical axis rotations in response to the penetrative dextral shear along the se china margin during oblique subduction of the pacific plate beneath south china an alternative interpretation involves regional extension that displaced a raft block southeastwards of the margin generating apparent paleomagnetic records with no real block rotations q 2004 elsevier ltd all rights reserved

influence of grass roots on shear strength of pyroclastic soils this paper investigates the effects of indigenous vegetation on the shear strength of loose pyroclastic soils of the campania region southern italy these soils are frequently affected by shallow

spatio temporal patterns of historical shallow landslides in a volcanic area mt aso japan abstract the evaluation of spatially and temporally distributed records of translational shallow landslides in heterogeneous watersheds provides insights needed to understand disastrous processes recurrent slope instability events occurred between 1953 and 1998 in two watersheds of mt aso western japan this paper investigates 1 the spatio temporal characteristics of translational shallow landslides dimensions numbers densities and area subjected to failure observed at a particular location 2 dem based landform characteristics elevation slope angles curvatures and their control on landslide distribution and 3 rainfall characteristics the evaluation of the landslide history consequences and characteristics of spatially and temporally distributed landslides are based on the series of inventory maps for years 1954 1977 1990 and 1998 geologically the watersheds consist of pyroxene olivine andesite basalt lava pyroclastics deposits gravel sand and clay deposits originated from takadake nekodake and washigamine volcanoes during 45 years 1953 1998 a total of 619 and 976 numbers of shallow landslides have been recognized in the sakurakigawa and furuegawa watersheds respectively repeated sliding denuded a total surface area of 0 372 km 2 in the sakurakigawa watershed representing 35 of the watershed area similarly slides denuded a total of 0 534 km 2 in the furuegawa watershed representing 12 of the watershed area for example storm events of june 1953 and july 1990 with rainfall intensities of 49 and 61 mm h 1 respectively triggered numerous landslides about 25 and 47 of sakurakigawa and furuegawa watersheds respectively still bears the potential to produce landslides landslides were commonly observed where thick unconsolidated tephra layers and pyroclastics rocks overlain by thin tephra bed existed and for a slope inclination range of 30 35

rainfall induced landslides by deficit field matric suction in unsaturated soil slopes landslides are mainly triggered by decrease in the matric suction with deepening the wetting band by rainfall infiltrations this paper reports rainfall induced landslides in partially saturated soil slopes through a field study a comprehensive analysis on umyeonsan mt landslides in 2011 was highlighted the incident involves the collapse of unsaturated soil slopes under extreme rainfall event fundamental studies on the mechanism and the cause of landslides were carried out a number of technical findings are of interest including the failure mechanism of a depth of soil and effect of groundwater flow the downward movement of wetting band and the increase of groundwater level based on this an integrated analysis methodology for a rainfall induced landslide is proposed in this paper that incorporates the field matric suction for obtaining hydraulic parameters of unsaturated soil the field matric suction is shown to govern the rate of change in the water infiltration for the landslide analysis with respect to an antecedent rainfall special attention was given to a one dimensional infiltration model to determine the wetting band depth in the absence of the field matric suction the results indicate that landslide activities were primarily dependent on rainfall infiltration soil properties slope geometries vegetation and groundwater table positions the proposed methodology has clearly demonstrated both shallow and deep seated landslides and shows good agreement with the results of landslide investigations

the direction correction tilt test an all purpose tilt fold test for paleomagnetic studies abstract the tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting while several tilt test formulations have been proposed none fully satisfies the requirements of statistical validity applicability to all bedding geometries and ease of use this paper introduces the direction correction dc test which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections the dc test is similar to mcfadden s correlation test because both test whether or not the site directions contain information about the bedding tilts however the dc test gives greater weight to sites with greater counter bedding the dc test is similar to watson s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions however the dc test uses analytical rather than numerical methods graphical output aids the researcher in recognizing problem sites using both real and simulated data the dc test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries the simulations show that the power of the tilt test is inversely proportional to the 95 confidence interval 95 of the overall mean as a rule of thumb paleomagnetists should attempt to sample sufficient sites to obtain an 95 less than 1 6 of the bedding attitude difference