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1.
Using the FLOWGO thermo-rheological model we have determined cooling-limited lengths of channel-fed (i.e. a) lava flows from Mauna Loa. We set up the program to run autonomously, starting lava flows from every 4th line and sample in a 30-m spatial-resolution SRTM DEM within regions corresponding to the NE and SW rift zones and the N flank of the volcano. We consider that each model run represents an effective effusion rate, which for an actual flow coincides with it reaching 90% of its total length. We ran the model at effective effusion rates ranging from 1 to 1,000 m3 s–1, and determined the cooling-limited channel length for each. Keeping in mind that most flows extend 1–2 km beyond the end of their well-developed channels and that our results are non-probabilistic in that they give all potential vent sites an equal likelihood to erupt, lava coverage results include the following: SW rift zone flows threaten almost all of Mauna Loas SW flanks, even at effective effusion rates as low as 50 m3 s–1 (the average effective effusion rate for SW rift zone eruptions since 1843 is close to 400 m3 s–1). N flank eruptions, although rare in the recent geologic record, have the potential to threaten much of the coastline S of Keauhou with effective effusion rates of 50–100 m3 s–1, and the coast near Anaehoomalu if effective effusion rates are 400–500 m3 s–1 (the 1859 a flow reached this coast with an effective effusion rate of 400 m3 s–1). If the NE rift zone continues to be active only at elevations >2,500 m, in order for a channel-fed flow to reach Hilo the effective effusion rate needs to be 400 m3 s–1 (the 1984 flow by comparison, had an effective effusion rate of 200 m3 s–1). Hilo could be threatened by NE rift zone channel-fed flows with lower effective effusion rates but only if they issue from vents at 2,000 m or lower. Populated areas on Mauna Loas SE flanks (e.g. Phala), could be threatened by SW rift zone eruptions with effective effusion rates of 100 m3 s–1.Editorial responsibility: J Donnelly-Nolan  相似文献   

2.
Thermal Anomalies and Earthquakes： Evidence from Wenchuan, China   总被引：1，自引：0，他引：1  
Earthquake prediction is a difficult problem in Earth sciences.Unsuccessful predictions one after another urged people to explore more synthetic and comprehensive methods for earthquake prediction.The Lithosphere-Atmosphere-Ionosphere(LAI)coupling theory pays great attention to the processes taking place within the near ground layer of atmosphere.It has achieved great results recently,and can enlighten us about the nature of an earthquake's precursor.Based on the NCEP reanalysis dataset,this paper attempts to track the anomalies of the surface's upward long wave radiation flux(ULWRF),the temperature at the depth of 10cm～20cm below ground surface layer(BGL)and the air temperature at 2 meters above ground surface(AIR)around the time of the strong Wenchuan earthquake.Thermal anomalies were observed before and after May 12,2008,the time of the Wenchuan earthquake.Perhaps the thermal anomaly that occurred prior to the earthquake can be taken as indicators of the earthquake,but in view of the complexity of the earthquake phenomena,using thermal anomaly as a precursor should be done with caution.  相似文献   

3.
《应用地球物理》2006,3(3):163-168
In multi-component seismic exploration, the horizontal and vertical components both contain P- and SV-waves. The P- and SV-wavefields in a seismic record can be separated by their horizontal and vertical displacements when upgoing P- and SV-waves arrive at the sea floor. If the sea floor P wave velocity, S wave velocity, and density are known, the separation can be achieved in ther-p domain. The separated wavefields are then transformed to the time domain. A method of separating P- and SV-wavefields is presented in this paper and used to effectively separate P- and SV-wavefields in synthetic and real data. The application to real data shows that this method is feasible and effective. It also can be used for free surface data.  相似文献   

4.
To determine the crustal structure in central Tibet, we used teleseismic waveform data recorded by 18 stations in the INDEPTH-Ⅲ seismic array across the central Tibet from the central Lhasa terrane to the central Qiangtang terrane. The S-wave velocity structures beneath stations are determined by inverting the stacked radial receiver function using the GA method. The first order features in the receiver function are modeled. Our results show that the Moho in Qiangtang is about 8 km shallower than that in Lhasa terrane along the INDEPTH-Ⅲ profile. It maybe suggests the northward subduction of the Lhasa mantle lid beneath the Qiangtang terrane is affected by the India-Asia collision. We conclude that there exist low velocity zone in the middle crust across the northern Lhasa and Qiangtang terrane, which can be related to the high temperature upper mantle beneath that.  相似文献   

5.
Introduction From the records of Wudalianchi volcanic group eruption in 1720~1721 obtained from the Man ethnic group files of Heilongjiang General Yamen in Qing Dynasty (WU, 1998; CHEN, WU, 2003), we have discovered the eruption time, state, material and scale of Laoheishan and Hu-oshaoshan volcanoes, as well as numerous seismic records. These historical materials are discov-ered for the first time although the study on Wudalianchi volcanic group has a long history. These earthquakes co…  相似文献   

6.
Cook Inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled. For the six events studied, mean emission rates for eruptions were ∼13,000 t/d CO2 and 5200 t/d SO2, but only ∼1200 t/d CO2 and 500 t/d SO2 for non-eruptive events (‘failed eruptions’). Statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t/d for CO2 and SO2, respectively. Emission rates greater than 4000 and 2000 t/d for CO2 and SO2, respectively, almost exclusively resulted during eruptive events (the only exception being two measurements at Fourpeaked). While this analysis could suggest that unerupted magmas have lower pre-eruptive volatile contents, we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions, or that magmas from failed eruptions experience less decompression such that the majority of H2O remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase (or both). In the majority of unrest and eruption sequences, increases in CO2 emission relative to SO2 emission were observed early in the sequence. With time, all events converged to a common molar value of C/S between 0.5 and 2. These geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice (i.e., from 20–35 to ∼4–6 km) and perhaps roughly similar initial volatile contents in all cases. Early elevated CO2 levels that we find at these high-latitude, andesitic arc volcanoes have also been observed at mid-latitude, relatively snow-free, basaltic volcanoes such as Stromboli and Etna. Typically such patterns are attributed to injection and decompression of deep (CO2-rich) magma into a shallower chamber and open system degassing prior to eruption. Here we argue that the C/S trends probably represent tapping of vapor-saturated regions with high C/S, and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface. At these volcanoes, however, C/S is often accentuated due to early preferential scrubbing of sulfur gases. The range of equilibrium degassing is consistent with the bulk degassing of a magma with initial CO2 and S of 0.6 and 0.2 wt.%, respectively, similar to what has been suggested for primitive Redoubt magmas.  相似文献   

7.
A distributed physically-based model describing coupled surface–subsurface flows is applied to an instrumented catchment to investigate the links between runoff generation processes and the dynamics of saturated areas. The spatial characterization of the system is obtained through geophysical measurements and in situ observations. The model is able to reproduce the dynamics of the system through the calibration of only few parameters with a clear physical interpretation, providing a solid basis for our numerical investigations. Such investigations demonstrate the important control exerted by surface topography on the time evolution of saturated area patterns, mainly mediated by topographic curvature, that dictates both the dominant streamflow generation process at the local scale and the connection-disconnection dynamics of saturated areas. The relation between hillslope water storage and streamflow, Q = f(V), is shown to be highly hysteretical and dependent on the mean saturation of the catchment: higher degrees of saturation tend to yield one-to-one relationships between streamflow and water storage. On the contrary, streamflow-water storage relations are importantly affected by the specific configuration of saturated areas connected to the outlet when the system is far from complete saturation. This observation contradicts common assumptions of a one-to-one relationship Q = f(V) often used to justify widely observed power-law Q vs. dQ/dt recession curves. Furthermore, even when Q = f(V) becomes unique at high degrees of saturation, no power-law form emerged in our runs, speculatively because of the small size of the catchment formed by a single incision and the corresponding hillslope.  相似文献   

8.
A simplified version of a kinetic–bioenergetic reaction model for anaerobic oxidation of methane (AOM) in marine sediments [Dale, A.W., Regnier, P., Van Cappellen, P., 2006. Bioenergetic controls on anaerobic oxidation of methane (AOM) in coastal marine sediments: a theoretical analysis. Am. J. Sci. 306, 246–294.] is used to assess the impact of transport processes on biomass distributions, AOM rates and methane release fluxes from the sea floor. The model explicitly represents the functional microbial groups and the kinetic and bioenergetic limitations of the microbial metabolic pathways involved in AOM. Model simulations illustrate the dominant control exerted by the transport regime on the activity and abundance of AOM communities. Upward fluid flow at active seep systems restricts AOM to a narrow subsurface reaction zone and sustains high rates of methane oxidation. In contrast, pore-water transport dominated by molecular diffusion leads to deeper and broader zones of AOM, characterized by much lower rates and biomasses. Under steady-state conditions, less than 1% of the upward dissolved methane flux reaches the water column, irrespective of the transport regime. However, a sudden increase in the advective flux of dissolved methane, for example as a result of the destabilization of methane hydrates, causes a transient efflux of methane from the sediment. The benthic efflux of dissolved methane is due to the slow growth kinetics of the AOM community and lasts on the order of 60 years. This time window is likely too short to allow for a significant escape of pore-water methane following a large scale gas hydrate dissolution event such as the one that may have accompanied the Paleocene/Eocene Thermal Maximum (PETM).  相似文献   

9.
This paper reviews the impacts of new satellite altimeter data sets and new technology on the production of satellite gravity. It considers the contribution of the increased data volume, the application of new altimeter acquisition technology and the potential for future developments. Satellite altimeter derived gravity has provided gravity maps of the world's seas since the 1980s, but, from 1995 to 2010, virtually all improvements were in the processing as there were no new satellite data with closely spaced tracks. In recent years, new data from CryoSat-2 (launched in 2010) and the geodetic mission of Jason-1 (2012–2013) have provided a wealth of additional coverage and new technology allows further improvements. The synthetic aperture radar mode of CryoSat-2 uses a scanning approach to limit the size of the altimeter sea surface footprint in the along-track direction. Tests indicate that this allows reliable data to be acquired closer to coastlines. The synthetic aperture radar interferometric mode of CryoSat-2 uses two altimeters to locate sea-surface reflection points laterally away from the satellite track. In a study to generate gravity for freshwater lakes, this mode is found to be valuable in extending the available satellite coverage. The AltiKa altimeter uses higher frequency radar to provide less noisy sea-surface signals and its new orbit mode gives potential for further improvements in satellite gravity. Future developments include the potential for swath mapping to provide further gravity improvements.  相似文献   

10.
As the joint project of IGBP (International Geo-sphere-Biosphere Programme) and IHDP (Interna-tional Human Dimensions Programme on Global En-vironmental Change), LUCC (Land Use/Land Cover Change) has been the focus of geographic studies, not only because it is one of the main contents of global environmental change studies, the linkage between physical and human sciences[1], but also because it has a close relationship with some elements’ cycles inside terrestrial ecosystem, such as…  相似文献   

11.
Tracing the sediment delivery from its source terrain to its ultimate sink envisage multiple factors that play a vital role in understanding present day erosional engine.To accomplish this,it is significant to distinguish the variable end-members contributing to the basin.The findings from the study of dryland coastal fluvial regime in Kachchh(Western India),which is one of the end members contributing to the Gulf of Kachchh coast(partial sink) and finally to the Arabian Sea(ultimate sink) have been presented here.Multi-proxy sediment provenance proxies such as grain-size,clay minerals,geochemistry and magnetic minerals have been employed to evaluate the provenance discriminating characteristics of the Kachchh dryland fluvial system and factors influencing them.The results of different proxies indicate that the provenance signatures of uplands are quite characteristic with magnetic susceptibility(χ) values of 20×10~(-7)m~3kg~(-1) and smectite(S)/kaolinite(K) ratio between 0.26 and 0.49.The middle reaches show marked increase in magnetic mineral concentration with χ values(140×10~(-7)m~3kg~(-1))and S/K ratio(4.92),while the estuarine tract shows χ values(80×10~(-7)m~3kg~(-1)),S/K ratio(1.90) and,characteristic heavy minerals(i.e.mica minerals),probably reflect the interplay between land and sea oscillations.Major sources of sediments within catchment scale were identified,viz.,upland sedimentary rocks(Juran and Bhuj Formation sandstone-shale) and middle reaches volcanic(Deccan Trap Formation basalt) rocks.The present study draw cautions in provenance of sediment discrimination in areas influenced by Deccan basalt that has the overwhelming sediment delivery and a comparatively subdued effects of other provenance signatures.The studied proxies of mineralogy of clays,magnetic minerals and geochemistry of heavy and major elements serve as the potential for fingerprint of sediment source regions and hence behold a strong position in source to sink studies globally.  相似文献   

12.
Mantle xenoliths brought up by Cenozoic volcanic rocks onto the earth‘s surface may provide direct information about the upper mantle beneath the volcanic region. This paper presents the study on mantle xenoliths collected from Haoti village, Dangchang County, Gansu Province, western China. The main purpose of the study is to gain an insight into the thermal structure and rbeology of the upper mantle beneath the region. The results show that the upper mantle of the region is composed mainly of spinel lherzolite at shallower depth (52-75km), and garnet iberzolite at greater depth (greater than 75km), instead of harzburgite and dunite as proposed by some previous studies. The upper mantle geotherm derived from the equilibrium temperatures and pressures of xenoliths from the region is lower than that of North China, and is somewhat closer to the Oceanic geotherm. The crust-mantle boundary is determined from the geotherm to be at about 52km, and the Moho seems to be the transition zone of lower crust material with spinel iberzolite. If we take 1280℃ as the temperature of the top of asthenosphere, then the fithospbere-asthenosphere boundary should be at about 120km depth. The differential stress of the upper mantle is determined by using recrystallized grain size piezometry, while the strain rate and equivalent viscosity are determined by using the high temperature flow law of peridotite. The differential stress, strain rate and viscosity profiles constructed on the basis of the obtained values indicate that asthenospberic diapir occurred in this region during the Cenozoic time, resulting in the corresponding thinning of the lithosphere. However, the scale and intensity of the diapir was significantly less than that occurring in the North China region. Moreover, numerous small-scale shear zones with localized deformation might occur in the iithospberic mantle, as evidenced by the extensive occurrence of xenoliths with tabular equigranular texture.  相似文献   

13.
Estimated Green’s function (EGF) between stations has been extracted from ambient seismic noise, direct surface wave and coda waves. It is also confirmed by laboratory experiments on ultrasonics and theoretical derivations assuming diffusive wave field, equi-partition of modes or random sources on an enclosed surface. This method provides a new approach to study the crust and mantle structure at regional scale, continental scale and global scale. Following the achievements with seismometer records, the reco...  相似文献   

14.
Microbial and molecular fossils from the Permian Zoophycos in South China   总被引：1，自引：0，他引：1  
The trace fossil Zoophycos was enriched in the lower part of the Guadalupian Maokou Formation of Permian in Laibin, Guangxi of South China, and characterized by observable lamellae within its spreiten. Associated with these lamellae are the prolific coccus- and spirillum-shaped microbe fossils. These microbes morphologically identified are 0.4―3.0 μm in diameter or length. Molecular fossils, including normal alkanes (dominated by C18, without an odd-over-even predominance), acyclic isoprenoids (such as pristane (Pr) and phytane (Ph)), extended tricyclic terpanes, pentacyclic triterpanes, steranes, al-kylcyclohexanes, dibenzothiophenes, benzonaphthothiophenes, benzobisbenzothiophenes, were in-strumentally identified in the wackestone characterized by the occurrence of abundant Zoophycos (composite ichnofabric indices are 4) and crowded microbial fossils. The value of the Pr/Ph ratio is less than 1, indicative of a dysoxic condition. The identification of abundant sulfur compounds (the thio-phene series) related to the contribution of reductive sulfur favors the occurrence of sulphate-reducing bacteria. The association of abundant microbial colonies with microbial molecular fossils within the spreiten suggests that trace fossils Zoophycos would be a multifunctional garden carefully constructed by the Zoophycos-producer, where different microbial colonies were orderly and carefully planted and cultured in different minor lamellae within spreiten. Hence, it is proposed that the Zoophycos-producer symbiosed with microbial colonies on the mutual basis of food supply and the redox conditions.  相似文献   

15.
Sponsored by the Chinese National Fundamental Research and Development Program in 2001,Guang-zhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS),through the Luzon Arc,to the Huatung Basin and the Gagua Ridge. Based on high-resolution seismic data from this survey,combined with gravimetric and magnetic modeling,a systematic effort is made to the study of the regional geodynamics offshore southern Taiwan. By focusing particularly on precollisional tectonic interactions between adjacent geological units and their tectonic affiliations,this study can help reveal early arc-continent collisional processes that formed the Taiwan orogen. The construction of the Manila accretionary prism and its eastward progressive deformation indicate that the subduction of SCS have experienced multiple phases of increased activity. Active precollisional crustal shortening within the Northern Luzon Trough resulted in tilting of sedimentary layers at angles between 6° and 13°. But the shortening induced by tilting accounts for only a tiny part of regional total crustal compression. The eastern flank of the Luzon Arc appears to be more active than the rest,evidenced by active faulting and folding in the intra-arc basins on the eastern flank. Magnetic modeling/inversion shows that the Luzon Arc may have experienced multiple phases of magmatic activities,causing lateral magnetic inhomogeneity. Bouguer gravity anomalies and gravity modeling indicate that the Huatung Basin has anomalously higher crustal and upper mantle densities than those of SCS and the Luzon Arc. In addition,there is a large bathymetric difference between the Huatung Basin and the northeastern part of SCS basin. These observations argue against early hypothesis that the Huatung Basin and the northeastern part of SCS basin may once have belonged to one single oceanic crust,in part or in whole. The Gagua Ridge,as a sliver of uplifted oceanic crust,may be related to a transient northwestward subduction of the western Philippine plate. All evidences point to the argument that the region offshore southern Taiwan is experiencing multiple terrain amalgamation,which is a classical model for continental growth.  相似文献   

16.
Estimation of Thomsen＇s anisotropic parameters is very important for accuratetime-to-depth conversion and depth migration data processing. Compared with othermethods, it is much easier and more reliable to estimate anisotropic parameters that arerequired for surface seismic depth imaging from vertical seismic profile （VSP） data, becausethe first arrivals of VSP data can be picked with much higher accuracy. In this study, wedeveloped a method for estimating Thomsen＇s P-wave anisotropic parameters in VTImedia using the first arrivals from walkaway VSP data. Model first-arrival travel times arecalculated on the basis of the near-offset normal moveout correction velocity in VTI mediaand ray tracing using Thomsen＇s P-wave velocity approximation. Then, the anisotropicparameters 0 and e are determined by minimizing the difference between the calculatedand observed travel times for the near and far offsets. Numerical forward modeling, usingthe proposed method indicates that errors between the estimated and measured anisotropicparameters are small. Using field data from an eight-azimuth walkaway VSP in TarimBasin, we estimated the parameters 0 and e and built an anisotropic depth-velocity modelfor prestack depth migration processing of surface 3D seismic data. The results showimprovement in imaging the carbonate reservoirs and minimizing the depth errors of thegeological targets.  相似文献   

17.
Abstract

This study deals with the Rimbaud catchment, a sub-catchment within the Réal Collobrier hydrological observatory in southeastern France, managed by Irstea since 1966. This observatory suffered a wildfire in 1990. Because of the dense network of streamgauges and raingauges available, this site provides a unique opportunity to test and compare two types of analysis, one based on paired catchments and the other a rainfall–runoff model, used to assess the hydrological impact of forest fire. In the present case, more than 20 years of pre-fire and post-fire data are available. We compare the ability of the two approaches to detect gradual changes at a daily time step. This case study illustrates how natural climatic variability (here a long drought which preceded the wildfire) can make the identification of hydrological changes extremely difficult.  相似文献   

18.
The North China craton (NCC) is distinctively dif-ferent from other Archean craton around the world due to violent construction-magmatic activity, ore deposi-tion and basin formation process and the deep dynam-ics could be probably related with lithospher…  相似文献   

19.
The mineralogical and geochemical characteristics of Fe-oxyhydroxide samples from one dredge station (long. 103°54.48′W, lat. 12°42.30′N, water depth 2655 m) on the East Pacific Rise near lat 13°N were analyzed by XRD, ICP-AES, and ICP-MS. Most Fe-oxyhydroxides are amorphous, with a few sphalerite microlites. In comparison with Fe-oxyhydroxides from other fields, the variable ranges in the chemical composition of Fe-oxyhydroxide samples are very narrow; their Fe, Si, and Mn contents were 39.90%, 8.92%, and 1.59%, respectively; they have high Cu (0.88%–1.85%) and Co (65×10−6−704×10−6) contents, and contain Co+Cu+Zn+Ni> 1.01%. The trace-element (As, Co, Ni, Cu, Zn, Ba, Sr) and major-element (Fe, Ca, Al, Mg) contents of these samples are in the range of hydrothermal sulfide from the East Pacific Rise near 13°N, reflecting that this type of Fe-oxyhydroxide constitutes a secondary oxidation product of hydrothermal sulfide. The Fe-oxyhydroxide samples from one dredge station on the East Pacific Rise near 13°N are lower in ΣREE (5.44×10−6–17.01×10−6), with a distinct negative Ce anomaly (0.12–0.28). The Fe-oxyhydroxide samples have similar chondrite-normalized rare-earth-element (REE) patterns to that of seawater, and they are very different from the REE composition characteristics of hydrothermal plume particles and hydrothermal fluids, showing that the REEs of Fe-oxyhydroxide are a major constituent of seawater and that the Fe-oxyhydroxides can become a sink of REE from seawater. The quick settling of hydrothermal plume particles resulted in the lower REE content and higher Mn content of these Fe-oxyhydroxides, which are captured in part of the V and P from seawater by adsorption. The Fe-oxyhydroxides from one dredge station on the East Pacific Rise near 13°N were formed by secondary oxidation in a low temperature, oxygenated environment. In comparison with the elemental (Zn, Cd, Pb, Fe, Co, Cu) average content of hydrothermal sulfide samples from the East Pacific Rise near 13°N, the Zn, Cd, and Pb contents of the Fe-oxyhydroxides are lower, and their Fe, Co, and Cu contents are higher. Supported in part by the Pilot Project of Knowledge Innovation Project, Chinese Academy of Sciences (Grant No. KZCX3-SW-223), and the Special Foundation for the Tenth Five Plan of COMRA (Grant No. DY105-01-03-1)  相似文献   

20.
The available literature on marine debris from Latin America and the Wider Caribbean Region was collected and linked, reviewing their methodologies and principal results (quantities, composition and spatial-temporal patterns). The study region comprises 52 coastal countries of which only 14 had registers of works on marine debris. A total of 70 works were available and 69 had their full contents accessed. Brazil dominated the available literature with 70% of the documents. Beaches were the most studied environment, and plastics the prevalent form of contamination in the whole region. The exposure of marine biota (species, type of contact, consequences) was highlighted. The studied region, although still little exploited by this sort of research, shows the same contamination patterns observed world-wide. We also contacted 40 researchers in the area, collecting scientific contributions, opinions and suggestions for improvement of this research field. Further advances and new (urgently needed) lines of research are also discussed.  相似文献   

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