dynamic earthquake rupture modelled with an unstructured 3 d spectral element method applied to the 2011 m9 tohoku earthquake an important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries to accomplish this we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes the 3 d open source code specfem3d and employ state of the art software for the generation of unstructured meshes of hexahedral elements these tools provide high flexibility in representing fault systems with complex geometries including faults with branches and non planar faults the domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field our implementation of dynamic rupture does not affect the parallel scalability of the code we verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults finally we present a preliminary dynamic rupture model of the 2011 m w 9 0 tohoku earthquake including a non planar plate interface with heterogeneous frictional properties and initial stresses our simulation reproduces qualitatively the depth dependent frequency content of the source and the large slip close to the trench observed for this earthquake

human impact overwhelms long term climate control of weathering and erosion in southwest china during the holocene there has been a gradual increase in the influence of humans on earth systems high resolution sedimentary records can help us to assess how erosion and weathering have evolved in response to recent climatic and anthropogenic disturbances here we present data from a high resolution similar to 75 cm k y sedimentary archive from the south china sea provenance data indicate that the sediment was derived from the red river and can be used to reconstruct the erosion and or weathering history in this river basin accelerator mass spectrometry c 14 dating provides direct age control and reveals coherent variations in clay mineralogy geochemistry and terrigenous flux indicative of strong chemical weathering and physical erosion during the mid holocene warm period 6400 4000 cal calibrated yr b p followed by weakening from ca 4000 1800 cal yr b p and renewed intensification since 1800 cal yr b p comparison with climatic records from china indicates that precipitation and temperature controlled both physical erosion and chemical weathering intensity before 1800 cal yr b p however weathering proxies in the offshore sediment indicate recent increased soil erosion we suggest that enhanced human activity deforestation cultivation and mining since the end of the chinese han dynasty 220 ce has overwhelmed the natural climatic controls on erosion in the red river

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

role of initial stress rotations in rupture dynamics and ground motion a case study with implications for the wenchuan earthquake 1 motivated by observations in the 2008 mw 7 9 wenchuan earthquake we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3 d finite element method based on anderson s theory of faulting we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault we find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion when a mismatch unfavorable for faulting between fault geometry and initial stress orientations is encountered rupture can spontaneously stop some first order features in the wenchuan event may be partially caused by rotations in the principal stress orientation along strike such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution these results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide

deep sea records of the continental weathering and erosion response to east asian monsoon intensification since 14 ka in the south china sea we analyzed sediment from ocean drilling program odp site 1144 in the northern south china sea to examine the weathering response of se asia to the strengthening of the east asian monsoon eam since 14 ka our high resolution record highlights the decoupling between continental chemical weathering physical erosion and summer monsoon intensity mass accumulation rates ti ca k rb hematite goethite and sr 87 sr 86 show sharp excursions from 11 to 8 ka peaking at 10 ka clay minerals show a shorter lived response with a higher kaolinite illite chlorite ratio at 10 7 9 5 ka however not all proxies show a clear response to environmental changes magnetic susceptibility rises sharply between 12 and 11 ka grain size becomes finer from 14 to 10 ka and then coarsens until similar to 7 ka but is probably controlled by bottom current flow and sealevel sr and nd isotopes show that material is dominantly eroded from taiwan with a lesser flux from luzon while clay mineralogy suggests that the primary sources during the early holocene were reworked via the shelf in the taiwan strait rather than directly from taiwan erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered pleistocene sediment largely from the now flooded taiwan strait which was transgressed by similar to 8 ka cutting off supply to the deep water slope none of the proxies shows an erosional response lasting until similar to 6 ka when speleothem oxygen isotope records indicate the start of monsoon weakening although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum lgm when the summer monsoon was weaker but the shelves were exposed c 2012 elsevier b v all rights reserved

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

3 d numerical simulations of earthquake ground motion in sedimentary basins testing accuracy through stringent models summary differences between 3 d numerical predictions of earthquake ground motion in the mygdonian basin near thessaloniki greece led us to define four canonical stringent models derived from the complex realistic 3 d model of the mygdonian basin sediments atop an elastic bedrock are modelled in the 1d sharp and 1d smooth models using three homogeneous layers and smooth velocity distribution respectively the 2d sharp and 2d smooth models are extensions of the 1 d models to an asymmetric sedimentary valley in all cases 3 d wavefields include strongly dispersive surface waves in the sediments we compared simulations by the fourier pseudo spectral method fpsm the legendre spectral element method sem and two formulations of the finite difference method fdm s and fdm c up to 4hz the accuracy of individual solutions and level of agreement between solutions vary with type of seismic waves and depend on the smoothness of the velocity model the level of accuracy is high for the body waves in all solutions however it strongly depends on the discrete representation of the material interfaces at which material parameters change discontinuously for the surface waves in the sharp models an improper discrete representation of the interfaces can cause inaccurate numerical modelling of surface waves for all the numerical methods considered except sem with mesh of elements following the interfaces a proper implementation of interfaces requires definition of an effective medium consistent with the interface boundary conditions an orthorhombic effective medium is shown to significantly improve accuracy and preserve the computational efficiency of modelling the conclusions drawn from the analysis of the results of the canonical cases greatly help to explain differences between numerical predictions of ground motion in realistic models of the mygdonian basin we recommend that any numerical method and code that is intended for numerical prediction of earthquake ground motion should be verified through stringent models that would make it possible to test the most important aspects of accuracy

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

upward flow of north pacific deep water in the northern south china sea as deduced from the occurrence of drift sediments 1 reflection seismic profiles show that drift sediments occur in the depth range of 1200 2800 m on the continental margin off southeast china these drift deposits were generated by upward flow near the dongsha islands of the north pacific deep water npdw which enters the south china sea via the bashi channel sill depth 2500 m this flow results in deposition of slope sediments resuspended off east and south taiwan on the slope southeast of the dongsha islands at 1200 m water depth this upward flow probably terminates and the npdw mixes with the surface water sediment ages from odp site 1144 southeast of the dongsha islands show that this process started at least 1 1 m y ago indications for mass wasting in the area of upslope water flow document the simultaneous occurrence of current and gravity controlled sedimentation processes however bottom current related drift sedimentation dominates

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

earthquake ruptures with strongly rate weakening friction and off fault plasticity part 1 planar faults abstract observations demonstrate that faults are fractal surfaces with deviations from planarity at all scales we study dynamic rupture propagation on self similar faults having root mean square rms height fluctuations of order 10 3 to 10 2 times the profile length our 2d plane strain models feature strongly rate weakening fault friction and off fault drucker prager viscoplasticity the latter bounds otherwise unreasonably large stress concentrations in the vicinity of bends our choice of a cohesionless yield function prevents tensile stress states and thus fault opening a consequence of strongly rate weakening friction is the existence of a critical background stress level above which self sustaining rupture propagation in the form of self healing slip pulses first becomes possible around this level at which natural faults are expected to operate ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity except for shallow inclinations of the maximum compressive stress to the fault less than about 20 the fluctuations are anticorrelated with the local fault slope these accelerations and decelerations of the rupture together with naturally emerging slip heterogeneity excite waves of all wavelengths and result in ground acceleration spectra that are flat at high frequency consistent with observed strong motion records

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

the three dimensional dynamics of dipping faults recent two dimensional dynamic simulations of dip slip faulting niel sen 1998 oglesby et al 1998 2000 shi et al 1998 have shown that the asym metric geometry of dip slip faults that intersect the free surface can have large effects on the dynamics of earthquake rupture the nonvertical dip angle of such faults leads to larger motion on the footwall than the hanging wall as well as much larger motion from thrust reverse faults than from normal faults with the same geometry and stress magnitudes in the present work we perform full three dimensional simulations of thrust reverse normal and strike slip faults and show that the same effects exist in three dimensions strike slip fault motion is either in between or lower than the motion of both dip slip faults additional three dimensional effects include strong rake rotation at the free surface the results confirm the findings of the previous studies and further elucidate the dynamic effects of the free surface on fault rupture slip and ground motion they are also borne out by early analyses of the 1999 chi chi taiwan thrust earthquake which displayed higher motion on the hanging wall than on the footwall and a strong oblique component of motion at the surface

rapid precipitation changes in the tropical west pacific linked to north atlantic climate forcing during the last deglaciation abstract the cause of rapid hydrological changes in the tropical west pacific during the last deglaciation remains controversial in order to test whether these changes were triggered by abrupt climate change events in the north atlantic ocean variations in precipitation during the last deglaciation 18 10 ka were extracted from proxy records of chemical weathering and terrigenous input in the western philippine sea wps the evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration cia elemental ratios k al toc tn and ti ca 13corg terrigenous fraction abundance and flux data from international marine global change study program images core md06 3054 collected on the upper continental slope of eastern luzon northern philippines sediment deposited during the last glacial maximum lgm shows weathering equal to or slightly greater than holocene sediment in the wps this unusual state of chemical weathering which is inconsistent with lower air temperatures and decreased precipitation in luzon during the lgm may be due to reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm sea level lowstand rapid changes in chemical weathering characterized by higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a were linked to rapid variations in precipitation in the wps during the last deglaciation the higher terrigenous inputs during the lgm relative to those of the holocene were controlled by sea level changes rather than precipitation the terrigenous inputs show a long term decline during the last deglaciation punctuated by brief spikes during the h1 and yd related to sea level rises and rapid precipitation changes in the wps respectively the proxy records of chemical weathering and terrigenous input from eastern luzon suggest high rainfall during the h1 and yd events consistent with inferred rainfall patterns based on fe ca records from offshore mindanao rapid precipitation changes in the wps did not coincide with migrations of the intertropical convergence zone itcz but rather were related to state shifts of the el nino southern oscillation enso during the last deglaciation based on proxy records and modeling results we argue that the atlantic meridional overturning circulation amoc controlled rapid precipitation changes in the tropical west pacific through zonal shifts of enso or meridional migration of the itcz during the last deglaciation our findings highlight the dominant role of the north atlantic ocean in the tropical hydrologic cycle during the last deglaciation

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

clay mineral variations in holocene terrestrial sediments from the indus basin abstract we employed x ray diffraction methods to quantify clay mineral assemblages in the indus delta and flood plains since 14 ka spanning a period of strong climatic change assemblages are dominated by smectite and illite with minor chlorite and kaolinite delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7 5 ka indicating stronger chemical weathering as the summer monsoon intensified changes in clay mineralogy postdate changes in climate by 5 3 ka reflecting the time needed for new clay minerals to form and be transported to the delta samples from the flood plains in punjab show evidence for increased chemical weathering towards the top of the sections 6

earthquake early warning system in southern italy methodologies and performance evaluation we investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity pgv from moderate to large earthquakes occurring in the southern apennines italy simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the pgv following an evolutionary probabilistic approach the system performance is measured through the effective lead time elt i e the time interval between the arrival of the first s wave and the time at which the probability to observe the true pgv value within one standard deviation becomes stationary and the probability of prediction error ppe which provides a measure of pgv prediction error the regional maps of elt and ppe show a significant variability around the fault up to large distances thus indicating that the system s capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault

spontaneous rupture processes on a bending fault 1 we simulated spontaneous rupture processes on a vertical bending strike slip fault in a three dimensional half space using a finite difference method rupture area and overall slip distribution on the fault vary with the initial stress field which depends on strike change at the bend rupture velocity and detailed slip distribution around the bend on the other hand are affected by time dependent normal stress change caused by rupture this dynamic stress change plays an important role in the rupture process ahead of the bend as well as in the resulting ground motion the numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models

rupture dynamics and ground motion from potential earthquakes around taiyuan china abstract using the curved grid finite difference method we develop dynamic spontaneous rupture models of earthquakes on the jiaocheng fault jf near taiyuan the capital and largest city of shanxi province in north china we then model the wave propagation and strong ground motion generated by these scenario earthquakes a map of the seismic hazard distribution for a potential m 7 5 earthquake is created based on dynamic rupture and true 3d modeling the tectonic initial stress fields derived from the inversion of focal mechanisms of historical earthquakes a nonplanar fault and a rough surface are considered in the dynamic rupture simulation based on the geological structure of the taiyuan basin normal faulting with a dipping angle of 60 is implemented for the scenario earthquake simulations the largest uncertainty of a potential earthquake in the jf zone is the hypocenter four cases are used to nucleate the earthquake at different locations using these dynamic rupture sources for the jf we further simulate and analyze both the seismic wave generated by the scenario earthquake and the strong ground motion it is found that the low velocity media of the taiyuan basin redistribute the ground motion well the effects of the regional stress fields on the dynamic rupture and hazard distribution are investigated and discussed further moreover a scenario earthquake which can cause great damage to the city of taiyuan is modeled and analyzed

impact of the east asian monsoon rainfall changes on the erosion of the mekong river basin over the past 25 000 yr abstract paleohydrological changes in the southern south china sea scs combined with clay mineralogy have been investigated along core md01 2393 recovered off the mekong river mouth in order to assess the impact of sea level and east asian monsoon rainfall intensity on erosion and weathering during the last 25 000 yr ssts and 18 o values determined on globigerinoides ruber were used to estimate past changes of local seawater oxygen isotope 18 o w the close position of the studied core to the mekong river mouth at sea level lowstand likely played a role in the 18 o w fluctuations resulting from changes of the monsoon rainfall and runoff into the mekong river basin the smectite illite chlorite and kaolinite illite chlorite ratios combined with the illite chemistry index during the holocene show higher chemical weathering of detrital material originating mainly from the lower reach of the mekong river at shorter time scales periods of strong monsoon rainfall are associated with an intensification of erosion of the mekong river lowland favoured by the development of incised valley systems inducing higher inputs of detrital material from the lower relative to the upper reach of the mekong river our findings imply a rapid response of erosion processes of the mekong river basin to the monsoon rainfall intensity changes

sedimentary processes on the mekong subaqueous delta clay mineral and geochemical analysis sedimentary processes on the inner mekong shelf were investigated by examining the characteristics of sediments sampled in gravity cores at 15 locations including grain size clay mineralogy sediment accumulation rates and the elemental and stable carbon isotopic composition of organic matter atomic c n ratios and delta c 13 deltaic deposits exhibit contrasting characteristics along different sides of the delta plain south china sea scs hereafter to the east and gulf of thailand got hereafter to the west as well as on and off the subaqueous deltaic system on one hand cores recovered from the subaqueous delta in the scs got are consisted of poorly well sorted sediments with similar different clay mineral assemblage with from mekong sediments excess pb 210 profiles supported by c 14 chronologies indicate either non steady scs side or rapid accumulation got side processes on the subaqueous delta the delta c 13 and c n ratio indicate a mixture of terrestrial and marine sourced organic matter in the deltaic sediment on the other hand cores recovered from areas with no deltaic deposits or seaward of the subaqueous delta show excess pb 210 profiles indicating steady state accumulation with a greater proportion of marine sourced organic matter core analysis s relevance with local depositional environment and previous acoustic profiling are discussed c 2012 elsevier ltd all rights reserved

fluid circulation in a complex volcano tectonic setting inferred from self potential and soil co2 flux surveys the santa maria cerro quemado zunil volcanoes and xela caldera northwestern guatemala the region encompassing santa maria cerro quemado and zunil volcanoes close to quetzaltenango the second largest city of guatemala is volcanically and tectonically complex in addition the huge xela caldera about 20 km in diameter crosses this area and links up to the important zunil fault zone located between the three volcanoes two highly active geothermal sites named zunil i and zunil ii are also located between these three volcanic edifices at the southeastern boundary of xela caldera in order to determine the permeability variations and the main structural discontinuities within this complex volcano tectonic setting self potential and soil co2 flux measurements have been coupled with a step of 20 m along a 16 880 km long profile crossing the entire area two shallow hydrothermal systems with maximum lateral extensions of 1 5 km in diameter are indicated by positive self potential elevation gradients below santa maria and cerro quemado volcanoes such small hydrothermal systems cannot explain the intense geothermal manifestations at zunil i and zunil ii another minor hydrothermal system is indicated by self potential measurements on the flank of santa maria along the edge of the xela caldera co2 flux measurements display slight variations inside the caldera and decreasing values crossing outside the caldera boundary we hypothesize the presence of a magmatic body inside the southeastern border of xela caldera to explain the deeper and more intense hydrothermal system manifested by the zunil i and the zunil ii geothermal fields this magmatic system may be independent from santa maria and cerro quemado volcanoes alternatively the hypothesized xela magmatic system could have a common magmatic origin with the cerro quemado dome complex consistent with previous findings on regional gas emissions sectors bordering the cerro quemado dome complex also have high amplitude minima short wavelength anomalies in self potential interpreted as preferential rain water infiltration along faults of major permeability probably related with the most recent stages of cerro quemado dome growth

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

the guatemala earthquake of 1816 on the chixoy polochic fault abstract forty historical documents have been found which describe a previously unknown very large earthquake on 22 july 1816 this event occurred along the strike slip boundary between the caribbean and north american plates in guatemala and southern mexico modified mercalli intensities are estimated from these accounts and a rough isoseismal map is constructed the damage pattern indicates that the causative fault was the left lateral chixoy polochic fault for which no damaging earthquake has previously been reported damage of modified mercalli intensity vii or greater covered an area of at least 13 000 km 2 extending over 340 km from alta verapaz province in guatemala westward to san cristobal ias casas in chiapas mexico the area of intensity vii indicates a moment of 1 10 28 dyne cm while the estimated length of the intensity vii isoseismal indicates a more likely figure of 3 5 10 27 dyne cm or an equivalent magnitude m w of 7 1 2 to 7 3 4 the reported aftershock sequence is compatible with an earthquake in this magnitude range these data demonstrate that the chixoy polochic fault is currently an active part of the caribbean north american plate boundary and is capable of producing very large earthquakes

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

the 1999 izmit turkey earthquake nonplanar fault structure dynamic rupture process and strong ground motion we simulated dynamic rupture propagation along various nonplanar fault models of the 1999 izmit turkey earthquake using a boundary integral equation method these models were inferred from geological and geodetic observations based on these results we modeled seismic wave propagation around the fault system using a finite difference method we focused on the effect of different fault geometries on the rupture process and seismic wave propagation numerical simulation results imply a rapid and continuous rupture propagation from the izmit sapanca lake segment to the sapanca akyazi segment the rupture under sapanca lake appears to have propagated not on a disconnected fault segment but along a smooth fault structure with a bend of only a few degrees the observational complexity of the surface breaks however can be best simulated by a highly segmented fault model this infers that fault geometric characters observed in the field reflect near surface structure and that seismological and geodetic features are controlled by global fault structure at depth then we investigated the effect of frictional parameters and the initial stress field in order to explain near field seismograms at station skr located a distance of a few kilometers from the fault we had to force the rupture to propagate at shallow depth close to the station in order to obtain this we had to introduce a finite cohesive force in the friction law that allows stress accumulation and release in the shallow crust the external stress field had to be large enough for the rupture to propagate at very rapid speed our simulation results show that it is important to include detailed fault geometry in the numerical simulation and to constrain frictional parameters and the initial stress field for understanding of the full dynamic process of an earthquake

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

cohesive strengthening of fault zones during the interseismic period an experimental study 1 there is widespread evidence indicating that faults regain a portion of their strength during the interseismic period here we present experiments designed to understand and quantify the interseismic cohesive strengthening resulting from fluid rock reactions in fault zones the triaxial experiments consisted of fracturing cores of fontainebleau sandstone under dry conditions forming a localized shear failure zone stage 1 the specimens were then reacted hydrothermally under isostatic conditions allowing the fault damage zone to compact consolidate and strengthen stage 2 following reaction the specimens were then reloaded to failure under nominally dry conditions so that the increase in cohesive strength of the fault could be measured stage 3 experiments show that cohesion increase is positively correlated to temperature and pore pressure during reaction after 6 hours of reaction at the highest temperatures 927 c and pore pressures 200 mpa cohesion increases by as much as 35 mpa microstructural examination of the specimens showed that the gouge particles within the fault compacted and cemented together exhibiting textures typical of pressure solution and that fractures in the surrounding damage zone had healed a theoretical treatment of the data was conducted using these experiments in combination with results on time dependent changes in fault cohesion presented by tenthorey et al 2003 we find that the rate controlling process in our experiments has an activation energy q of approximately 70 kj mol 1 we use this information to develop a model for time dependent cohesive strengthening in fault zones within the continental seismogenic regime we conclude that significant cohesive strengthening of fault zones can occur during the interseismic period of medium to large earthquakes given the presence of reactive pore fluids

effects of realistic surface topography on seismic ground motion in the yangminshan region of taiwan based upon the spectral element method and lidar dtm we combine light detection and ranging lidar digital terrain model dtm data and an improved mesh implementation to investigate the effects of high resolution surface topography on seismic ground motion based upon the spectral element method in general topography increases the amplitude of shaking at mountain tops and ridges whereas valleys usually have reduced ground motion as has been observed in both records from past earthquakes and numerical simulations however the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations especially the seismic response of the true ground surface here we use lidar dtm data which provide two meter reso lution at the free surface and a spectral element method to simulate three dimensional 3d seismic wave propagation in the yangminshan region in taiwan incorporating the effects of realistic topography a smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content the amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat topped hills experience lower levels of ground shaking interaction between small scale to pographic features and high frequency surface waves can produce unusually strong shaking we demonstrate that topographic variations can change peak ground accel eration pga values by 50 in mountainous areas and the relative change in pga between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response this suggests that high resolution realistic topographic features should be taken into account in seismic hazard analysis especially for densely populated moun tainous areas

structure and tectonic geomorphology of the qujiang fault at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system china abstract the northwest striking qujiang fault is located at the southeastern tip of the sichuan yunnan block which is bounded by the ailao shan red river fault and the xianshuihe xiaojiang fault system the qujiang fault is one of the most seismically active faults in western yunnan china and is considered to be the seismogenic fault of the 1970 ms 7 7 tonghai earthquake in this study we examine the geometry kinematics and geomorphology of this fault through field observations satellite images and dems it is a holocene active fault characterized by dextral strike slip movements with dip slip components it can be divided into northwest and southeast segments depending on different kinematics the northwest segment from baiyizhai to wujie shows right lateral strike slip with normal components whereas it is characterized by dextral movements with the northeast wall thrusting over the opposite in the southeast segment from wujie to miaobeishan the geophysical data combined with our investigations indicate that the fault dips steeply to the ne at depth while secondary faults with different dip directions developed at shallow surface owing to fault bifurcation during the tonghai earthquake a blind fault may have developed on the southwest wall resulting in aftershocks concentrated to the southwest of the surface raptures multiple tectonic landforms are developed along the fault the right lateral holocene slip rate was determined to be 2 84 3 27 mm year based on radiometrically dated offset gullies our analyses show that the present deformation at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system is partitioned into a shortening distributed over a region 150 km wide and a right lateral strike slip localized on the qujiang and jianshui faults since the late pleistocene the qujiang fault has been playing an important role in accommodating the ongoing se directed movements of the sichuan yunnan block creating strong earthquakes to release strain energy

increasing chemical weathering in the himalayan system since the last glacial maximum continental chemical weathering is central in earth s surface biogeochemical cycles as it redistributes elements across reservoirs such as the crust and the oceans however the evolution of weathering through time and its response to external forcing such as changes in climate remain poorly constrained in this work a composite sediment record from the bay of bengal is used to document the evolution of chemical weathering in the himalayan system himalayan range and indo gangetic floodplain the world largest sediment conveyor to the oceans since the last glacial maximum lgm the degree of weathering of the sediments is documented using mobile to immobile ratios such as k si and h2o si as well as detrital calcite abundance robust weathering proxies are derived by correcting the chemical composition of sediment for sorting effects that occur during transport and deposition the bay of bengal record is also further compared to the chemical composition of modern river sediments from the ganga and brahmaputra basin weathering proxies all indicate that the sediments exported by the ganga and brahmaputra rivers became increasingly weathered over the past 21 kyr whereas sr nd and major elements suggest a constant sediment provenance in the system over the last 21 kyr these changes in the degree of weathering of the sediments show that the weathering flux exported by the system to the indian ocean during the lgm was significantly lower than at present and demonstrate that chemical weathering in continental scale basins such as the ganga and brahmaputra responds to late quaternary climate changes

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

geochemical record of holocene to recent sedimentation on the western indus continental shelf arabian sea 1 we present a multiproxy geochemical analysis of two cores recovered from the indus shelf spanning the early holocene to recent 14 ka indus 23 is located close to the modern indus river while indus 10 is positioned 100 km further west the holocene transgression at indus 10 was over a surface that was strongly weathered during the last glacial sea level lowstand lower holocene sediments at indus 10 have higherendvalues compared to those at the river mouth indicating some sediment supply from the makran coast either during the deposition or via reworking of older sediments outcropping on the shelf sediment transport from makran occurred during transgressive intervals when sea level crossed the mid shelf the sediment flux from non indus sources to indus 10 peaked between 11 ka and 8 ka a hiatus at indus 23 from 8 ka until 1 3 ka indicates non deposition or erosion of existing indus shelf sequences higherendvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building holocene clinoforms chemical index of alteration cia mg al and sr isotopes are all affected by erosion of detrital carbonate which reduced through the holocene k al data suggest that silicate weathering peaked ca 4 6 ka and was higher at indus 10 compared to indus 23 fine grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain the indus shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

investigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang faultinvestigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang fault

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

extreme weathering erosion during the miocene climatic optimum evidence from sediment record in the south china sea investigating the interplay between continental weathering and erosion climate and atmospheric co 2 concentrations is significant in understanding the mechanisms that force the cenozoic global cooling and predicting the future climatic and environmental response to increasing temperature and co 2 levels the miocene represents an ideal test case as it encompasses two distinct extreme climate periods the miocene climatic optimum mco with the warmest time since 35 ma in earth s history and the transition to the late cenozoic icehouse mode with the establishment of the east antarctic ice sheet however the precise role of continental weathering during this period of major climate change is poorly understood here we show changes in the rates of miocene continental chemical weathering and physical erosion which we tracked using the chemical index of alteration cia and mass accumulation rate mar respectively from ocean drilling program odp site 1146 and 1148 in the south china sea we found significantly increased cia values and terrigenous mars during the mco ca 17 15 ma compared to earlier and later periods suggests extreme continental weathering and erosion at that time similar high rates were revealed in the early middle miocene of asia the european alps and offshore angola this suggests that rapid sedimentation during the mco was a global erosion event triggered by climate rather than regional tectonic activity the close coherence of our records with high temperature strong precipitation increased burial of organic carbon and elevated atmospheric co 2 concentration during the mco argues for long term close coupling between continental silicate weathering erosion climate and atmospheric co 2 during the miocene citation wan s w m kurschner p d clift a li and t li 2009 extreme weathering erosion during the miocene climatic optimum evidence from sediment record in the south china sea geophys res lett 36 l19706 doi 10 1029 2009gl040279

dynamic rupture of crosscutting faults a possible rupture process for the 2007 mw 6 6 niigata ken chuetsu oki earthquake 1 the 2007 mw 6 6 niigata ken chuetsu oki earthquake implies a complex fault mechanism several surveys suggest the possibility of two main segments crosscutting each other at their center i e a northern segment dipping to the northwest and a southern segment dipping to the southeast we modeled the dynamic rupture propagation numerically along the inferred segmented fault system using a boundary integral equation method biem the possibility of rupture transfer is numerically demonstrated and two rupture modes are described simultaneous rupture transfer along the overlapping part is possible only under a high stress load however this rupture mode yields an excessively high slip value otherwise where regional stress is relatively low but pore pressure is high enough to govern the rupture criterion described as the low frictional coefficient case in this study the rupture transfer to the other segment does not occur until rupture terminates on the first segment regardless of the crosscutting distance between the two segments in this case at the central crosscutting part a possible rupture scenario is that ruptures occur sequentially in different directions first a southbound rupture on the northwest dipping segment then a northbound rupture triggered on the southeast dipping segment a few seconds later the simulated rupture scenario on crosscutting faults can be strongly influenced by a preexisting fault structure determined by miocene rifting during an opening stage of the sea of japan and the subsequent shortening of the crust our results point to the importance of investigating earthquake rupture scenarios in complex fault systems based on existing geophysical and geological information and dynamic rupture mechanics

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

introduction to the river dominated shelf sediments of the east asian seas peter d clift1 jan harff2 3 jiaxue wu4 yan qiu5 department of geology and geophysics louisiana state university baton rouge la 70803 usa university of szczecin institute of marine and coastal sciences mickiewicza 18 pl 70 383 szczecin poland leibniz institute for baltic sea research seestrasse 15 d 18119 rostock warnemunde germany centre of coastal ocean science and technology sun yat sen university guangzhou 510275 china guangzhou marine geological survey china geological survey guangzhou 510760 china

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

the effect of fault geometry and minimum shear wavespeed on 3d ground motion simulations for an mw 6 5 hayward fault scenario earthquake san francisco bay area northern californiathe effect of fault geometry and minimum shear wavespeed on 3d ground motion simulations

rupture complexity of the 1970 tonghai and 1973 luhuo earthquakes china from p wave inversion and relationship to surface faulting the source processes of the 4 january 1970 tonghai earthquake m s 7 5 and the 6 february 1973 luhuo earthquake m s 7 5 in southwestern china were investigated using an inversion technique on the very complex body waves the two earthquakes were associated with 48 and 90 km of surficial strike slip rupture respectively and the distribution of displacement with distance along the fault was well documented by field studies of both events the source process for both earthquakes comprised three to four subevents with different moments and rupture durations these calculated parameters agree well with the field observations and aftershock distributions particularly in the total rupture length and in the amount and asymmetry of fault displacements relative to the locations of the main epicenters

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

stress rotations due to the m6 5 foreshock and m7 3 main shock in the 2016 kumamoto sw japan earthquake sequence a shallow m7 3 event with a m6 5 foreshock occurred along the futagawa hinagu fault zone in kyushu sw japan we investigated the spatiotemporal variation of the stress orientations in and around the source area of this 2016 kumamoto earthquake sequence by inverting 1 218 focal mechanisms the results show that the 3 axis in the vicinity of the fault plane significantly rotated counterclockwise after the m6 5 foreshock and rotated clockwise after the m7 3 mainshock in the hinagu fault segment this observation indicates that a significant portion of the shear stress was released both by the m6 5 foreshock and m7 3 mainshock it is estimated that the stress release by the m6 5 foreshock occurred in the shallower part of the hinagu fault segment which brought the stress concentration in its deeper part this might have caused the m7 3 mainshock rupture mainly along the deeper part of the hinagu fault segment after 28 hours

development of the east asian monsoon mineralogical and sedimentologic records in the northern south china sea since 20 ma we here reconstruct the past change of the east asian monsoon since 20 ma using samples from ocean drilling program odp site 1146 in the northern south china sea based on a multi proxy approach including a monomineralic quartz isolation procedure identification of clay minerals by x ray diffraction xrd and grain size analysis of isolated terrigenous materials terrigenous supply to odp site 1146 was dominated by changes in the strength of multiple sources and transport processes grain size data modeled by an end member modeling algorithm indicate that eolian dust from the and asian inland and fluvial input have contributed on average 20 and 80 of total terrigenous material to odp site 1146 respectively specifically about 40 53 of the total quartz feldspar and only 6 11 of the total clay is related to eolian supply at the study site detailed analysis of the sedimentary environment and clay minerals combined with previous studies shows that smectite originates mainly from luzon kaolinite from the pearl river and illite and chlorite from the pearl river taiwan and or the yangtze river the proportion and mass accumulation rate mar of the coarsest end member em1 interpreted as eolian dust ratios of illite chlorite smectite quartz feldspar and mean grain size of terrigenous materials at odp site 1146 were adopted as proxies for east asian monsoon evolution the consistent variation of these independent proxies since 20 ma shows three profound shifts in the intensity of east asian winter monsoon relative to summer monsoon as well as aridity of the asian continent occurred at similar to 15 ma similar to 8 ma and the youngest at about 3 ma in comparison the summer monsoon intensified contemporaneously with the winter monsoon at 3 ma the phased uplift of the himalaya tibetan plateau may have played a significant role in strengthening the asian monsoon at similar to 15 ma 8 ma and 3 ma c 2007 elsevier b v all rights reserved

an evolutionary model for the holocene formation of the pearl river delta china this paper reconstructs the evolutionary history of the pearl river delta over the last 9000 years and investigates land sea interaction in a large deltaic complex which formed under the influence

co evolution of monsoonal precipitation in east asia and the tropical pacific enso system since 2 36 ma new insights from high resolution clay mineral records in the west philippine sea clay mineralogical analysis and scanning electron microscope sem analysis were performed on deep sea sediments cored on the benham rise core md06 3050 in order to reconstruct long term evolution of east asian summer monsoon easm rainfall in the period since 2 36 ma clay mineralogical variations are due to changes in the ratios of smectite which derive from weathering of volcanic rocks in luzon island during intervals of intensive monsoon rainfall and illite and chlorite rich dusts which are transported from east asia by winds associated with the east asian winter monsoon eawm since luzon is the main source of smectite to the benham rise long term consistent variations in the smectite illite chlorite ratio in core md06 3050 as well as odp site 1146 in the northern south china sea suggest that minor contributions of eolian dust played a role in the variability of this mineralogical ratio and indicate strengthening easm precipitation in se asia during time intervals from 2360 to 1900 kyr 1200 to 600 kyr and after 200 kyr the easm rainfall record displays a 30 kyr periodicity suggesting the influence of el nino southern oscillation enso these intervals of rainfall intensification on luzon island are coeval with a reduction in precipitation over central china and an increase in zonal sst gradient in the equatorial pacific ocean implying a reinforcement of la nina like conditions in contrast periods of reduced rainfall on luzon island are associated with higher precipitation in central china and a weakening zonal sst gradient in the equatorial pacific ocean thereby suggesting the development of dominant el nino like conditions our study therefore highlights for the first time a long term temporal and spatial co evolution of monsoonal precipitation in east asia and of the tropical pacific enso system over the past 2 36 ma

paleoclimatic evolution of the sw and ne south china sea and its relationship with spectral reflectance data over various age scales abstract spectral analysis of sediment from international ocean discovery program iodp site u1433 in the south china sea can be used to constrain humidity and temperature through time by constructing hematite goethite records spanning the last 10 million years records in the southwest and northern parts of this basin show long term contrasting trends despite the fact that geochemical evidence for alteration is similar in both parts of the basin i e towards less alteration since 10 ma however contrasting clay mineral assemblages in the northern and southwestern areas do suggest long term changes in the relative climate of indochina and southern china we interpret this to reflect the northward migration of the itcz since the miocene resulting in a progressive drying of indochina and increasingly wet conditions in south china sediment believed to be supplied from the mekong river iodp site u1433 shows increasing chemical weathering at a time of long term drying of the climate this probably reflects increasing chemical weathering driven by slower transport and despite reduced rates of chemical alteration in the context of a colder drier climate since the miocene in general hematite goethite data are consistent with pollen constraints from the same drill site that show colder conditions with increasing hematite goethite since 3 ma and with a transition to apparently wetter conditions since the mid pleistocene transition mpt this implies that most of the sediment in the southwestern basin is weathered and eroded during warmer wetter interglacial phases at least since the mpt

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

clay mineral distribution in surface sediments of the northeastern south china sea and surrounding fluvial drainage basins source and transport clay mineralogy of surface samples throughout the northeastern south china sea scs and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine grained sediments three characteristic end members in clay mineral compositions were observed from three major provenances respectively major kaolinite and moderate illite and chlorite from the pearl river predominant illite and chlorite from taiwan and principal smectite from the luzon arc system the transport of four clay mineral species in the northeastern scs is influenced by various mechanisms smectite derived from the luzon arc system is transported mainly by surface current with significant influence of the kuroshio intrusion illite and chlorite from taiwan are mainly carried by deep water current while kaolinite from the pearl river is affected obviously by the westward guangdong coastal current and longshore current a westerly tongue shaped distribution of high contents of illite and chlorite mainly from taiwan on the eastern shelf may result from the westward guangdong coastal current during the winter the results suggest that clay mineral assemblages in the northeastern scs are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features the implication of clay minerals for proxies of the late quaternary east asian monsoon evolution is realized through both the provenance supply and current transport processes c 2010 elsevier b v all rights reserved

basin related effects on ground motion for earthquake scenarios in the lower rhine embayment summary the deterministic calculation of earthquake scenarios using complete waveform modelling plays an increasingly important role in estimating shaking hazard in seismically active regions here we apply 3 d numerical modelling of seismic wave propagation to m 6 earthquake scenarios in the area of the lower rhine embayment one of the seismically most active regions in central europe using a 3 d basin model derived from geology borehole information and seismic experiments we aim at demonstrating the strong dependence of ground shaking on hypocentre location and basin structure the simulations are carried out up to frequencies of ca 1 hz as expected the basin structure leads to strong lateral variations in peak ground motion amplification and shaking duration depending on source basin receiver geometry the effects correlate with basin depth and the slope of the basin flanks yet the basin also affects peak ground motion and estimated shaking hazard thereof outside the basin comparison with measured seismograms for one of the earthquakes shows that some of the main characteristics of the wave motion are reproduced cumulating the derived seismic intensities from the three modelled earthquake scenarios leads to a predominantly basin correlated intensity distribution for our study area

holocene evolution in weathering and erosion patterns in the pearl river delta sediments in the pearl river delta have the potential to record the weathering response of this river basin to climate change since 9 5 ka most notably weakening of the asian monsoon since the early holocene approximate to 8 ka cores from the pearl river delta show a clear temporal evolution of weathering intensity as measured by k al k rb and clay mineralogy that shows deposition of less weathered sediment at a time of weakening monsoon rainfall in the early mid holocene 6 0 2 5 ka this may reflect an immediate response to a less humid climate or more likely reduced reworking of older deposits from river terraces as the monsoon weakened human settlement of the pearl river basin may have had a major impact on landscape and erosion as a result of the establishment of widespread agriculture after around 2 5 ka weathering intensity sharply increased despite limited change in the monsoon but at a time when anthropogenic pollutants e g cu zn and pb increased and when the flora of the basin changed sr 87 sr 86 covaries with these other proxies but is also partly influenced by the presence of carbonate the sediments in the modern pearl river are even more weathered than the youngest material from the delta cores we infer that the spread of farming into the pearl river basin around 2 7 ka was followed by a widespread reworking of old weathered soils after 2 5 ka and large scale disruption of the river system that was advanced by 2 0 ka

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

orbital scale timing and mechanisms driving late pleistocene indo asian summer monsoons reinterpreting cave speleothem δ18o 1 southeast china cave 18o often interpreted as a pure east asian summer monsoon proxy lags maximum northern hemisphere summer insolation by 2 9 0 3 kyrs at the precession cycle the arabian sea summer monsoon stack lags by 8 1 kyr consistent with 13 other indian and east asian summer monsoon proxies from marine lake and terrestrial archives this 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology it requires reconciliation in the context of proxy interpretation both of these lags are incompatible with a direct response to northern hemisphere summer insolation implicating additional forcing mechanisms analysis of heterodynes in the cave 18o spectrum demonstrates that variance contained in the arabian sea summer monsoon proxies also resides in the cave 18o record this variance is subtracted from the cave 18o record yielding a residual that is highly coherent and in phase with precession minima reflecting the impact of winter temperature change on cave 18o meteorological precipitation under cold conditions thus we argue that the timing of light cave 18o peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone the 2 9 kyr precession band phase lag of cave 18o reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima this interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast china

asian summer monsoon influence on chemical weathering and sediment provenance determined by clay mineral analysis from the indus submarine canyon clay minerals from the indus canyon and eastern clinoform since 12 ka are uniformly rich in smectite and illite similar to those from the holocene indus flood plains a systematic enrichment of smectite in the proximal delta compared to the canyon and eastern clinoform argues for preferential capture of smectite close to the river mouth since 12 ka there is a rapid shift to a more smectite rich assemblage in the canyon and eastern clinoform after 5 ka this change is probably caused by a change in sediment source with less direct flux from the himalaya and more erosion of older weathered smectite rich sediment from the indus river flood plains driven by incision of the indus and its tributaries into the floodplain as summer monsoon rains weakened this influx of smectite is consistent with lower kaolinite smectite values since 5 ka the onset of large scale agricultural activities since 5 ka especially starting with the harappan civilization may also have enhanced incision and erosion of floodplain sediments over the same time period this study reports for the first time how monsoon strength variations since 12 ka affected the clay mineral assemblages and sediment provenance in a major submarine canyon

interseismic fault strengthening and earthquake slip instability friction or cohesion the slip instability of an earthquake and its abrupt energy release depend primarily on the intensity of strength drop during accelerated fault slip this process is typically attributed to changes of frictional resistance between two sliding blocks here we show that friction changes alone cannot explain observed strength variations of artificial fault zones sandstone samples with saw cut faults and gypsum gouge zones were subjected to many cycles of hold slide loading samples with water saturated gouge display 1 systematic time dependent increase of gouge strength 2 unstable failure of gouge with large stress drops and 3 lithification of gouge by crack sealing recrystallization porosity reduction and grain bonding all these features are absent in identical tests with dry gouge these observations indicate that gouge particles are cemented by chemical processes during hold periods and suggest that the cyclical strength variations are controlled by cohesion strengthening rather than by friction changes we further hypothesize that crustal fault zones could be lithified during the interseismic stage and this lithification would control earthquake slip instability

chemical indices cia and wip as proxies for integrated chemical weathering in china inferences from analysis of fluvial sediments abstract rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes how to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear the chemical index of alteration cia and the weathering index of parker wip have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles in this study concentrations of major oxides in the suspended particulate matter spm and fine grained floodplain sediments from 13 major rivers in china from north to south were analysed and compiled for the estimation of chemical weathering in china the gradual increase in cia and decrease in wip values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins a combined monsoon climate effect of temperature runoff and precipitation primarily controls the chemical weathering in china the provenance rock types and relief play minor roles in weathering whereas an active tectonic setting and typhoon events play key roles in the weathering process in taiwan the cia values of the finer spm samples within a given river are overall greater than those in the corresponding coarser floodplain sediments underscoring the effect of sediment grain size on cia values the irregular seasonal variation of the cia within a specific river further confirms the notion that the cia does not reflect the instantaneous chemical weathering on continents although it is impossible to build a general model for regulating the chemical weathering of continents this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can with careful application be quantitatively estimated using the proper geochemical proxies of river sediments

reconstruction of late quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of india abstract in order to reconstruct the variations in the intensity of summer monsoon precipitation during the late quaternary two sediment cores from the southwestern continental margin of india were studied for their clay mineral composition and grain size parameters kaolinite illite and gibbsite were dominant in a core off cochin illite with increasing kaolinite content towards the core top was found to dominate in a core from the continental slope off goa major sources of clays at both the core sites were from the hinterland rocks and soils careful evaluations of several factors that could complicate the clay distribution in marine environment indicate that the clay mineral parameters can be used as proxies for the intensity of summer monsoon precipitation in the past the relatively low values of humidity proxies kaolinite content k c and k i ratios and higher illite crystallinity with significant variations indicate that the summer monsoons in general were weaker during the late glaciation with distinct events of intensification at 28 000 and 22 000 yr bp the last deglaciation was characterised by an increased terrigenous input with high values of humidity proxies during 15 700 14 800 cal yr bp indicating an early strengthening of summer monsoon activity in the region the most remarkable increase in kaolinite content k c and k i ratios associated with much reduced values of chlorite and illite and illite crystallinity however occur between 8800 and 6400 cal yr bp it appears that the holocene precipitation maxima occurred after 9000 cal yr bp and lagged behind the precessional forcing the late holocene witnessed reduced rainfall activity and resultant decrease in hydrolysis starting at 5600 cal yr bp