Rainfall induced debris flows in pyroclastic deposits, Campania (southern Italy)   总被引：12，自引：0，他引：12  

Francesco Fiorillo  Raymond C. Wilson   《Engineering Geology》2004,75(3-4):263-289

A combination of empirical and physically based hydrological models has been used to analyze historical data on rainfall and debris-flow occurrence in western Campania, to examine the correlation between rainfall and debris-flow events.

Rainfall data from major storms recorded in recent decades in western Campania were compiled, including daily series from several rain gauges located inside landslide areas, supplemented by hourly rainfall data from some of the principal storms.

A two-phase approach is proposed. During phase 1, soil moisture levels have been modelled as the hydrological balance between precipitation and evapotranspiration, on a daily scale, using the method of Thornthwaite [Geograph. Rev. 38 (1948) 55].

Phase 2 is related to the accumulation of surplus moisture from intense rainfall, leading to the development of positive pore pressures. These interactions take place on an hourly time scale by the “leaky barrel” (LB) model described by Wilson and Wiezoreck [Env. Eng. Geoscience, 1 (1995) 11]. In combination with hourly rainfall records, the LB model has been used to compare hydrological effects of different storms. The critical level of retained rain water has been fixed by the timing of debris-flow activity, related to recorded storm events.

New rainfall intensity–duration thresholds for debris-flow initiation in western Campania are proposed. These thresholds are related to individual rain gauge and assume a previously satisfied field capacity condition. The new thresholds are somewhat higher than those plotted by previous authors, but are thought to be more accurate and thus need less conservatism.  相似文献   

Seismic activity at the MCT in Sikkim Himalaya     

Reena De  J.R. Kayal   《Tectonophysics》2004,386(3-4):243-248

A microearthquake survey in the Sikkim Himalaya raised a question whether the north–south segment of the Main Central Thrust (MCT) in this part of the Himalaya is seismically active(?). Fault-plane solution of a cluster of events occurred below this segment of the MCT shows right-lateral strike-slip motion. The seismic observations and the geological evidences suggest that a NNE–SSW trending strike-slip fault, beneath this segment, caused right lateral movement on the MCT, and is seismically active.  相似文献   

Bayesian inversion of 1994–1998 vertical displacements at Mt Etna: evidence for magma intrusion     

F. Obrizzo  F. Pingue  C. Troise  G. De Natale 《Geophysical Journal International》2004,157(2):935-946

  相似文献   

Ar / Ar dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction–exhumation cycle     

Laura Federico  Giovanni Capponi  Laura Crispini  Marco Scambelluri  Igor M. Villa   《Earth and Planetary Science Letters》2005,240(3-4):668-680

We present ³⁹Ar–⁴⁰Ar dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a ³⁹Ar–⁴⁰Ar age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction–exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene–Oligocene boundary.  相似文献   

Archaeoseismic record at the ancient Roman City of Baelo Claudia (Cádiz, south Spain)     

P.G. Silva  F. Borja  C. Zazo  J.L. Goy  T. Bardají  L. De Luque  J. Lario  C.J. Dabrio 《Tectonophysics》2005,408(1-4):129

This study represents the first paleoseismic approach in Spain in which archaeological remains are considered. The ancient Roman city of Baelo Claudia (1st–4th centuries AD), located at the axial zone of the Gibraltar Strait (Cadiz, south Spain), contains abundant disrupted architectural relics and ground collapses (i.e. landsliding, liquefacion) probably related to historic earthquake damage of intensity IX–X MSK. The archaeological stratigraphy of the city evidence two major episodes of abrupt city destruction bracketed in AD 40–60 and AD 350–395 separated by an intervening horizon of demolition for city rebuilding, otherwise characteristic for many earthquake-damaged archaeological sites in the Mediterranean. The second episode led the eventual city abandonment, and it is evidenced by good examples of column collapse, distortion, failure and breakdown of house and city walls, and pavement warping and disruptions documented during different archaeological excavations, which can be catalogued as secondary coseismic effects. Main damaged relicts observable today are the set of pop-up like arrays and warping developed in the ancient Roman pavement. Their analysis indicate an anomalous westwards ground displacement oblique to the main gentle southward slope of the topography, as also evidence failures, collapses and breakdown of walls and columns, suggesting that stress acted in a broad SW–NE/WSW–ENE orientation consistent whit the expectable motion along the largest NE–SW strike-slip faults of the zone, which in turn can be catalogued as seismic sources of moderate events (ca. 5 mb). Major disruptions and city abandonment were hesitantly related to relatively far strong earthquakes occurred during the late 4th century AD in the Mediterranean or western coast of Iberia by Menanteau et al. [Menanteau, L., Vanney, J.R., Zazo, C., 1983. Belo II : Belo et son environment (Detroit de Gibraltar), Etude physique d'un site antique. Pub. Casa de Velazquez, Serie Archeologie 4., Ed. Broccard, París.]. However, this study indicates that the occurrence of close moderate earthquakes jointly with the unstable character of the ground at the zone (site effect) is a more reliable hypothesis to explain the observed deformations.  相似文献   

Stochastic Modelling of the Impact of Flood Protection Measures Along the River Waal in the Netherlands     

Saskia Van Vuren  Huib J. De. Vriend  Sonja Ouwerkerk  Matthijs Kok 《Natural Hazards》2005,36(1-2):81-102

River flooding is a problem of international interest. In the past few years many countries suffered from severe floods. A large part of the Netherlands is below sea level and river levels. The Dutch flood defences along the river Rhine are designed for water levels with a probability of exceedance of 1/1250 per year. These water levels are computed with a hydrodynamic model using a deterministic bed level and a deterministic design discharge. Traditionally, the safety against flooding in the Netherlands is obtained by building and reinforcing dikes. Recently, a new policy was proposed to cope with increasing design discharges in the Rhine and Meuse rivers. This policy is known as the Room for the River (RfR) policy, in which a reduction of flood levels is achieved by measures creating space for the river, such as dike replacement, side channels and floodplain lowering. As compared with dike reinforcement, these measures may have a stronger impact on flow and sediment transport fields, probably leading to stronger morphological effects. As a result of the latter the flood conveyance capacity may decrease over time. An a priori judgement of safety against flooding on the basis of an increased conveyance capacity of the river can be quite misleading. Therefore, the determination of design water levels using a fixed-bed hydrodynamic model may not be justified and the use of a mobile-bed approach may be more appropriate. This problem is addressed in this paper, using a case study of the river Waal (one of the Rhine branches in the Netherlands). The morphological response of the river Waal to a flood protection measure (floodplain lowering in combination with summer levee removal) is analysed. The effect of this measure is subject to various sources of uncertainty. Monte Carlo simulations are applied to calculate the impact of uncertainties in the river discharge on the bed levels. The impact of the “uncertain” morphological response on design flood level predictions is analysed for three phenomena, viz. the impact of the spatial morphological variation over years, the impact of the seasonal morphological variation and the impact of the morphological variability around bifurcation points. The impact of seasonal morphological variations turns out to be negligible, but the other two phenomena appear to have each an appreciable impact (order of magnitude 0.05–0.1 m) on the computed design water levels. We have to note however, that other sources of uncertainty (e.g. uncertainty in hydraulic roughness predictor), which may be of influence, are not taken into consideration. In fact, the present investigation is limited to the sensitivity of the design water levels to uncertainties in the predicted bed level.  相似文献   

Test of a distributed modelling approach to predict flood flows in the karst Suoimuoi catchment in Vietnam     

Y. B. Liu  O. Batelaan  F. De. Smedt  N. T. Huong  V. T. Tam 《Environmental Geology》2005,48(7):931-940

The major obstacles for modelling flood processes in karst areas are a lack of understanding and model representations of the distinctive features and processes associated with runoff generation and often a paucity of field data. In this study, a distributed flood-modelling approach, WetSpa, is modified and applied to simulate the hydrological features and processes in the karst Suoimuoi catchment in northwest Vietnam. With input of topography, land use and soil types in a GIS format, the model is calibrated based on 15 months of hourly meteorological and hydrological data, and is used to simulate both fast surface and conduit flows, and groundwater discharges from karst and non-karst aquifers. Considerable variability in the simulation accuracy is found among storm events and within the catchment. The simulation results show that the model is able to represent reasonably well the stormflows generated by rainfall events in the study catchment.  相似文献   

GPS monitoring of vertical ground motion in northern Ardenne–Eifel: five campaigns (1999–2003) of the HARD project     

A. Demoulin  J. Campbell  A. De. Wulf  A. Muls  R. Arnould  B. Görres  D. Fischer  T. Kötter  M. Brondeel  D. Van. Damme  J. M. Jacqmotte 《International Journal of Earth Sciences》2005,94(4):515-524

We present the HARD project of GPS monitoring of vertical ground motion in NE Ardenne and Eifel (western Europe). Its main purposes are to get a better insight into the present-day rates of vertical ground motion in intraplate settings and to identify the various causes of these motions. Since 1999, we have carried out yearly campaigns of simultaneous GPS measurements at 12 sites situated so as to sample the different tectonic subunits of the study area and especially to record potential displacements across the seismogenic Hockai fault zone. Five campaigns (1999–2003) have been processed currently. Key issues of the data processing with the Gamit software are discussed and first results are presented. Though temporally consistent in many cases, the obtained vertical motion rates are spatially highly variable. They are also much too high (several mm/year) to support a tectonic interpretation, and a long-term influence of groundwater level variations is proposed to account for the observed motions. This influence should be distinguished from seasonal variations and from inter-survey variations linked to the varying degree of soil and subsoil drying off during the successive spring surveys.  相似文献   

Trace element compositions of submicroscopic inclusions in coated diamond: A tool for understanding diamond petrogenesis     

Emma Tomlinson  Isabel De Schrijver  Adrian P. Jones  Frank Vanhaecke 《Geochimica et cosmochimica acta》2005,69(19):4719-4732

Trace element compositions of submicroscopic inclusions in both the core and the coat of five coated diamonds from the Democratic Republic of Congo (DRC, formerly Zaire) have been analyzed by Laser Ablation Inductively Coupled Mass Plasma Spectrometry (LA-ICP-MS). Both the diamond core and coat inclusions show a general 2-4-fold enrichment in incompatible elements relative to major elements. This level of enrichment is unlikely to be explained by the entrapment of silicate mantle minerals (olivine, garnet, clinopyroxene, phlogopite) alone and thus submicroscopic fluid or glass inclusions are inferred in both the diamond coat and in the gem quality diamond core. The diamond core fluids have elevated High Field Strength Element (Ti, Ta, Zr, Nb) concentrations and are enriched in U relative to inclusions in the diamond coats and relative to chondrite. The core fluids are also moderately enriched in LILE (Ba, Sr, K). Therefore, we suggest that the diamond cores contain inclusions of silicate melt. However, the Ni content and Ni/Fe ratio of the trapped fluid are very high for a silicate melt in equilibrium with mantle minerals; high Ni and Co concentrations in the diamond cores are attributed to the presence of a sulfide phase coexisting with silicate melt in the diamond core inclusions. Inclusions in the diamond coat are enriched in LILE (U, Ba, Sr, K) and La over the diamond core fluids and to chondrite. The coats have incompatible element ratios similar to natural carbonatite (coat fluid: Na/Ba ≈0.66, La/Ta≈130). The coat fluid is also moderately enriched in HFSE (Ta, Nb, Zr) when normalized to chondritic Al. LILE and La enrichment is related to the presence of a carbonatitic fluid in the diamond coat inclusions, which is mixed with a HFSE-rich hydrous silicate fluid similar to that in the core. The composition of the coat fluid is consistent with a genetic link to group 1 kimberlite.  相似文献   

Exhumation patterns along shallow low‐angle normal faults: an example from the Altotiberina active fault system (Northern Apennines,Italy)          下载免费PDF全文

Chiara Caricchi  Luca Aldega  Massimiliano R. Barchi  Sveva Corrado  Domenico Grigo  Francesco Mirabella  Massimiliano Zattin 《地学学报》2015,27(4):312-321

A multi‐method approach (palaeothermal and thermochronological analyses; thermal modelling) is applied to reconstruct the exhumation history of the Altotiberina Fault (ATF), a representative example of crustal‐scale active low‐angle normal faulting in the Northern Apennines (Italy). Thermal maturity and thermochronological data yield similar burial histories but different exhumation patterns for the sedimentary successions in the hangingwall and the footwall of the ATF. Since 3.8 Ma, the ATF footwall has exhumed at rates of 0.90 mm a^?1. Exhumation led to bending and deactivation of the ATF uppermost portion as a result of tectonic unloading and isostatic adjustment, followed by migration of extension and the development of a set of domino‐like, east‐dipping normal faults, rooting on the buried portion of the ATF. ATF activity and isostatic rebound exhumed Triassic rock units from depths of about 4 km. We suggest that isostatic instability is accommodated at shallow crustal levels, in a similar way to what is observed on larger structures at mid‐low crustal levels.  相似文献