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1.
《Applied Geochemistry》1997,12(4):429-436
Carbon dioxide emissions from the soil have been investigated along lines of equally spaced sampling points perpendicular to the Pernicana fault on Mt Etna. Anomalous values of soil CO2 have been found not only along the fault plane, but also along directions parallel to it, both to the N and to the S of the main fault. The acquired data seem to reveal a shallow step-like geometry of the Pernicana fault system with parallel faults being generally not deeper than the interface between Etna's volcanic cover and its sedimentary basement (a few hundred meters). The distribution of the anomalous CO2 emissions has also revealed that the Pernicana fault continues at least as far as the Ionian sea, in an area where only sedimentary rocks crop out. This finding would suggest that the main structure is deeper than the base of the volcanic cover, thus cutting at least the uppermost portion of Etna's sedimentary basement.Isotopic analyses of C carried out in samples from locations of high CO2, seem to indicate that the emitted CO2 is a mixture of an organic shallow component and a minor deeper magmatic one.Both chemical and isotopic data on soil gases emitted in the easternmost part of the studied area distinguished another tectonic structure which seems to be much deeper than the Pernicana fault and is roughly directed NNE-SSW, this direction being coincident with an important structural trend of eastern Sicily. 相似文献
2.
Maria Serafina Barbano Giovanna Pappalardo Claudia Pirrotta Simone Mineo 《Natural Hazards》2014,73(3):1587-1607
A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes. 相似文献
3.
Damage surrounding the core of faults is represented by deformation on a range of scales from microfracturing of the rock matrix to macroscopic fracture networks. The spatial distribution and geometric characterization of damage at various scales can help to predict fault growth processes, subsequent mechanics, bulk hydraulic and seismological properties of a fault zone. Within the excellently exposed Atacama fault system, northern Chile, micro- and macroscale fracture densities and orientation surrounding strike-slip faults with well-constrained displacements ranging over nearly 5 orders of magnitude (0.12 m–5000 m) have been analyzed. Faults have been studied that cut granodiorite and have been passively exhumed from 6 to 10 km depth. This allows direct comparison of the damage surrounding faults of different displacements. The faults consist of a fault core and associated damage zone. Macrofractures in the damage zone are predominantly shear fractures orientated at high angles to the faults studied. They have a reasonably well-defined exponential decrease with distance from the fault core. Microfractures are a combination of open, healed, partially healed and fluid inclusion planes (FIPs). FIPs are the earliest set of fractures and show an exponential decrease in fracture density with perpendicular distance from the fault core. Later microfractures do not show a clear relationship of microfracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement but appear to reach a maximum at a few km displacement. One fault, where damage was characterized on both sides of the fault core shows no damage asymmetry. All faults appear to have a critical microfracture density at the fault core/damage zone boundary that is independent of displacement. An empirical relationship for microfracture density distribution with displacement is presented. Preferred FIP orientations have a high angle to the fault close to the fault core and become more diffuse with distance. Models that predict off-fault damage such as a migrating process zone during fault formation, wear from geometrical irregularities and dynamic rupture are all consistent with our data. We conclude it is very difficult to distinguish between them on the basis of field data alone, at least within the limits of this study. 相似文献
4.
Jian-Cheng Lee Jacques Angelier Hao-Tsu Chu Jyr-Ching Hu Fu-Shu Jeng 《Comptes Rendus Geoscience》2005,337(13):1200-1207
In 1998 we installed five creepmeters across the Chihshang Fault, the active plate suture in eastern Taiwan. Daily creepmeter data indicated decreasing creeping rate from 1999 to 2003, suggesting increasing seismic hazard. The fault was ruptured by the Chengkung earthquake () on 10 December 2003. Through extrapolation of our earlier creep data of 1986–1991 and 1992–1997, we evaluate the minimum deficit in aseismic creep shortening as 106 or 46 mm (respectively) before this earthquake. The near-surface co-seismic shortening was limited, but the total shortening resulting from the earthquake, including post-seismic creep, was about 97 mm. This suggests that near the surface most of the detectable deficit has been absorbed by this earthquake and subsequent creep. We thus point out that creepmeter installation and monitoring bring a powerful tool in seismic hazard mitigation. To cite this article: J.-C. Lee et al., C. R. Geoscience 337 (2005). 相似文献
5.
Chester David K. Duncan Angus M. Dibben Christopher Guest John E. Lister Philip H. 《Natural Hazards》1999,19(1):29-46
The 1928 eruption of Etna, Sicily, although the largest such event this century, has not been studied in detail. In this paper the nature of the eruption, the destruction it caused – including the complete devastation of the town of Mascali (pre-eruption population 2,000) – and emergency responses of the authorities to it are reviewed in the context of fascist politics and planning priorities. It is contended that, although at one level the response to the 1928 eruption was successful, at another fascism merely continued and enhanced a reactive, propitiatory approach to hazard mitigation. We argue that this legacy was not successfully overcome until the middle of the nineteen eighties. Finally contemporary Italian moves towards a more proactive approach to disaster planning, both generally and in the context of Etna, are discussed. 相似文献
6.
A moderate-sized (Mw 5.3) earthquake occurred in the Dead Sea basin on February 11, 2004. A rigorous seismological analysis of the main shock and numerous aftershocks suggests that seismogenic structure was a secondary, antithetic fault within the Dead Sea fault system. The main shock is well located using all available regional seismic stations, and 43 aftershocks were precisely located relative to the main shock using a double difference algorithm. The first motion, focal mechanism for this earthquake demonstrates NNW–SSE and ENE–WSW striking nodal planes, and the aftershocks distribution is consistent with the latter — indicating a right-lateral sense of displacement. This orientation and sense of shear are consistent with similarly oriented geological faults around the Dead Sea basin — these structures are likely antithetic faults within the transform system. Although moderate in size, earthquakes that occur very close to the large Dead Sea fault system warrant consideration in the earthquake hazard assessment of the region: For example, owing to the proximity to the main fault, moderate earthquakes such as this may produce static changes in Coulomb stress along the main fault. 相似文献
7.
Tholeiitic basalt magmatism of Mount Etna and its relations with the alkaline series 总被引：1，自引：0，他引：1
J. C. Tanguy 《Contributions to Mineralogy and Petrology》1978,66(1):51-67
Mount Etna is composed for the most part of intermediate alkaline products, most of them porphyritic-the etnaïtes-, that may be defined as sodic trachybasalts or trachyandesites. The strato-volcanio itself overlies tholeiitic basalts (usually aphyric, except for olivine) belonging to three major types: olivine tholeiites (normative Ol+Hy; modal olivine and augite, titanomagnetite and ilmenite), pigeonite tholeiites (normative Hy+minor Ol or Qz; modal pigeonite and augite with minor olivine, ilmenite and titanomagnetite), transitional tholeiites, i.e. transitional between pigeonite tholeiites (aphyric) and alkali basaltic etnaïtes (porphyritic, with normative Ol+Ne or minor Hy; modal augite and olivine, titanomagnetite alone). An analcite basalt, chemically close to alkali basaltic etnaïtes, forms the small Cyclopean Islands, SE of Etna, and an alkali olivine basalt composes a neck at Paterno, SW foot of Etna.Both pigeonite tholeiites and alkali basaltic etnaïtes may be derived from a primitive olivine tholeiite magma by subtraction or addition of phases crystallized at moderate and low pressure (kaersutite±olivine, calcic plagioclase and clinopyroxene). The differentiation process implies crystal fractionation of the primitive olivine tholeiite magma at varying levels of the crust. The speed of ascent of the magma is thought to be the factor controlling the level at which differentiation may take place: in low velocity regimes, fractionation takes place at deeper levels of the crust. Slow ascent speeds would be the consequence of a developing crustal extension episode, induced by mantle diapirism that generated the olivine tholeiite magma below the Mount Etna area. 相似文献
8.
从20世纪80年代开始至今,河北平原出现了大量地裂缝,致使建筑物和道路交通遭受破坏,给当地人民生命财产带来了严重危害。断层蠕滑型地裂缝因其延伸长、深度大、破坏严重、防治难度大而更应引起重视,断层蠕滑型地裂缝对河北平原地裂缝的研究及防治具有重要意义。笔者在大量野外调查的基础上,从实地调查的800多条地裂缝中选取了两条典型断层蠕滑型地裂缝——隆尧地裂缝、辛-安-深-饶地裂缝,由物探、槽探等综合勘查手段作为验证,初步分析了该类型地裂缝的成因: 它们受控于断裂活动,区域内的深部构造活动为地裂缝的形成提供了动力基础。地下水、地表水的活动对地裂缝的地表开启及发展有重要的促进作用。 相似文献
9.
Prof. W. Schubert 《Rock Mechanics and Rock Engineering》1996,29(3):145-153
Summary In fault zones, excessive deformation during and after tunnel excavation is frequently encountered. Shoterete in combination with grouted rock bolts has successfully been used in many applications to control the deformation process. The magnitude of deformation frequently exceeds the deformability of the shotcrete lining. In the past, this problem has been solved by dividing the shotcrete lining into segments and leaving gaps between the segments to accommodate deformation without damage to the lining. The need for minimizing deformation in an extremely heterogeneous fault zone at the Galgenbergtunnel (Austria) led to the development of low cost yielding elements, installed between the shotcrete segments and the use of a new type of re-groutable brock bolts. New techniques in evaluating the results of displacement monitoring have improved the short term prediction. 相似文献
10.
11.
Michaela Ustaszewski Marco Herwegh Alastair F. McClymont O. Adrian Pfiffner Robyn Pickering Frank Preusser 《Journal of Structural Geology》2007,29(12):1943-1959
The Gemmi fault is a prominent NW–SE striking lineament that crosses the Gemmi Pass in the central Swiss Alps. A multidisciplinary investigation of this structure that included geological mapping, joint profiling, cathodoluminescence and scanning electron microscopy, stable isotope measurements, luminescence- and U-TH-dating, 3D ground penetrating radar (GPR) surveying and trenching reveals a history of fault movements from the Miocene to the Holocene. The main fault zone comprises a 0.5–3 m thick calcite cataclasite formed during several cycles of veining and brittle deformation. Displaced Cretaceous rock layers show an apparent dextral slip of 10 m along the fault.A detailed study of a small sediment-filled depression that crosses the fault provides evidence for a post-glacial reactivation of the fault. A trench excavated across the fault exposed a Late-Glacial-age loess layer and late Holocene colluvial-like slope-wash deposits that showed evidence for fault displacement of a few centimeters, indicating a recent strike-slip reactivation of the fault. Focal mechanisms of recent instrumentally recorded earthquakes are consistent with our findings that show that the fault at the Gemmi Pass, together with other parallel faults in this area, may be reactivated in today's stress field. Taking together all the observations of its ancient and recent activity, the Gemmi fault can be viewed as a window through geological space and time. 相似文献
12.
Surface deformations on the western flank of Mt Etna volcano, spanning 1980–2004, have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the S–SE Rift and faulting sensitivity. During this period, an accurate analysis of strain parameters, computed by inversion of SW electro‐optical distance data, suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly NE–SW buried fault crossing the area covered by this network, as supported by seismic observations of the 20–24 April 2001 swarm. Moreover, Coulomb stress change model analysis confirms that the displacement along this fault, heralding the July–August 2001 eruption 2 months earlier can be related to major stresses applied by a dike intrusion at depth along the S–SE Rift, as testified by the microseismicity occurring between November 2000 and 19 April 2001. 相似文献
13.
小江断裂带北段为白鹤滩水电站库区内规模最大的断裂构造,其几何展布特征与活动性对库区移民及其就近安置规划有明显的制约作用。通过对小江断裂北段大比例尺调查、断裂带石英形貌扫描以及现场氡气测量等综合研究,重新界定了小江断裂带北段展布,即北起宁南县华弹镇,沿金沙江左岸经永乐村,鲁吉、溜姑延伸至蒙姑以南,断裂带总体向西陡倾。石英微形貌统计分析与应力痕迹微形貌观察结果表明,断层强烈活动时间在晚更新世,同一石英颗粒表面具有代表两种滑动方式（蠕滑和黏滑) 的应力痕迹组合,应力痕迹的溶蚀程度、叠加和切割关系表明,断层在晚更新世的滑动至少有3个亚期次,早期为蠕滑,中晚期为黏滑。小江断裂北段的潜在地震危险性评估表明,其可能发生强震的最大震级约在MS6.8级~MS7.1级左右,为未来仍有可能再次活动的强震地区。 相似文献
14.
GIS and Volcanic Risk Management 总被引：7，自引：0，他引：7
Volcanic catastrophes constitute a majorproblem in many developing and developed countries. Inrecent years population growth and the expansion ofsettlements and basic supply lines (e.g., water, gas,etc.) have greatly increased the impact of volcanicdisasters. Correct land-use planning is fundamental inminimising both loss of life and damage to property.In this contribution Geographical Information Systems(GIS), linked with remote sensing technology andtelecommunications/warning systems, have emerged asone of the most promising tools to support thedecision-making process. Some GIS are presented fortwo volcanic areas in Italy, Mt. Etna and Vesuvius.GIS role in risk management is then discussed, keepingin mind the different volcanic scenarios of effusiveand explosive phenomena. Mt. Etna system covers alarge area (more than 1,000 km2) potentiallyaffected by effusive phenomena (lava flows) whichcause damage to both houses and properties in general.No risk to life is expected. The time-scales of lavaflows allow, at least in principle, modification ofthe lava path by the building of artificial barriers.Vesuvius shows typically an explosive behaviour. Inthe case of a medium size explosive eruption, 600,000people would potentially have to be evacuated from anarea of about 200 km2 around the Volcano, sincethey are exposed to ruinous, very fast phenomena likepyroclastic surges and flows, lahars, ash fallout,etc. Ash fallout and floods/lahars are also expectedin distal areas, between Vesuvius and Avellino,downwind of the volcano. GIS include digital elevationmodels, satellite images, volcanic hazard maps andvector data on natural and artificial features (energysupply lines, strategic buildings, roads, railways,etc.). The nature and the level of detail in the twodata bases are different, on the basis of thedifferent expected volcanic phenomena. The GIS havebeen planned: (a) for volcanic risk mitigation (hazard,value, vulnerability and risk map assessing), (b) toprovide suitable tools during an impending crisis, (c)to provide a basis for emergency plans. 相似文献
15.
Ying-Zhen Zhang 《Tectonophysics》1982,85(1-2)
A spatio-temporal analysis based on the data of eleven repeated levellings around the Tangshan region prior to the 1976 earthquake indicates that an uplift lasting for 2 years, from 1968 through 1969. with a magnitude of 50 mm, occurred in the epicentral area.Aseismic creep superimposed on the accumulated strain has been found in the vicinity of Tangshan and Baodi along both the Tangshan and the Jiyunhe faults.Assuming uniform strain accumulation and elastic dislocation, theoretical values of displacement at the various dislocation sites have been calculated and, using the least squares method, the optimal values of strain accumulation and the parameters of the creep faults in different years have been determined.The creep fault under Tangshan, a right-lateral normal fault, strikes N47°E and dips S87°E. and is 8 km long and 6 km wide. The upper boundary of the fault lies 2 km deep. The strike-slip and dip-slip offsets are, respectively, 104 cm and 8cm. The average rate of strain accumulation amounts to 0.9 × 10−7/yr. Creep at the fault amounted to 18.6 cm/yr and 1.4 cm/yr, respectively, in the strike and dip directions over the period 1969–1975. The Jiyunhe fault, although of smaller dimensions, has experienced a greater rate of creep than the Tangshan fault.A correlation of the above-mentioned uplift and creep with that of the Tangshan earthquake suggests that the uplift might have been a manifestation of the early development of the earthquake and that aseismic creep may be one of the precursory phenomena of shallow earthquakes. The sequence of processes preceding the Tangshan earthquake may be described as: strain accumulation-land upliftaseismic creep-inverse land deformation (or decrease in creep rate)-earthquake. 相似文献
16.
Fluid inclusions in San Carlos olivine stretch via plastic mechanisms when heat-treated at 1400° C and 0.1 MPa in controlled
atmospheres for several days. Measurable changes in both inclusion dimensions and fluid densities occur; densities decrease from 1.0 to 0.7 g/cc. Stretching is fastest along 100, and slower along 001 and 010. The dislocation microstructure around the inclusions suggests that creep mechanisms operate. Uncertainties in the experimental determinations of stretching rates result from optical resolution limits, errors inherent in measuring homogenization temperatures, uncertainties in the fluid equation of state, and changes in fluid chemistry during the heat-treatment. Inclusion stretching by dislocation creep can be treated using a model developed for hot isostatic pressing. In this model, we assume spherical symmetry of plastic flow, that the material yields by steady-state power-law creep, and that the parameters for the constitutive law and fluid equation of state are known. Stretching rates are predicted to depend on the difference between the fluid pressure and the external pressure, the temperature, the constitutive law governing power-law creep, and geometry. Predicted stretching rates show fair, but not exact, agreement with experimentally measured rates. The amount of stretching predicted by the model is in rough agreement with estimates based on dislocation microstructures around natural inclusions, if xenolith ascent rates are of the order of 1 cm/s or faster.Now at: L-201, Lawrence Livermore Laboratory, P.O. Box 808 Livermore, CA 94550, USA 相似文献
17.
A materials failure relation of accelerating creep as empirical description of damage accumulation 总被引：1，自引：0，他引：1
A general materials failure relation,
, describes accelerating creep of materials with rate coefficients andA, by relating rates of deformation,
, to changes in deformation rate,
(Voight, 1988). Time of failure can be extrapolated from inverse rate versus time data, and andA may be derived to permit one to calculate the failure time. The method is of value for quantitative hazard assessments.Mechanisms leading to damage accumulation during accelerating creep include creep fracture by stress corrosion and power law lattice deformation. These mechanisms are examined here as phenomenologically related to the materials failure relation. Apparently, both mechanisms favour , where is the parameter of the materials failure relation controlling the sensitivity to accelerating activity. For pure shear governed by power law creep of powerp, under constant load, =2.0 andA=p. Stress corrosion is widely described by Charles' equation, relating crack velocity to stress intensity during subcritical crack growth by the stress corrosion indexn. The relationship betweenn and is given by =(2n–2)/n. 相似文献
18.
Cinna Lomnitz 《Natural Hazards》1988,1(2):113-123
Numerical experiments on simulating ruptures of a one-dimensional plate boundary suggest that certain basic features of seismicity (including multiple ruptures and aftershock sequences) can be adequately reproduced if one assumes the existence of an elementary particle (or geon) of fault dynamics. Some general consequences of corpuscular assumptions in the earth sciences are discussed, with particular reference to the estimation of hazard. 相似文献
19.
Kahramanmaras and its surroundings are under the influence of East Anatolian and Dead Sea fault zones which have significance in the tectonics of Turkey. The long-term energy accumulation in these zones creates a very high risk level in terms of seismic hazard. In this study, the seismic hazard of Kahramanmaras Province and its vicinity was tried to be determined by using the probabilistic seismic hazard method approach. The earthquake catalog used in the study comprises 424 earthquakes equal or greater than M w ?=?4.0, covering a time period between 1 January 1900 and 1 January 2015. The earthquake data have been compiled from the catalogs of the International Seismological Center (ISC), Republic of Turkey Prime Ministry Disaster and Emergency Management Precidency (RTPMDEMP), Bogazici University Kandilli Observatory and Earthquake Research Institute. Seismic sources that could affect the study area have been identified according to the Earthquake Model of the Middle East (EMME). Seismic hazard parameters and peak horizontal acceleration values were obtained by using the selected attenuation relationships, and the results were given with iso-acceleration maps corresponding to a recurrence period of 475 years. The calculated peak horizontal acceleration values are generally varying between 0.21 and 0.41 in the study area. The result of this study shows that the southeastern parts of the study area have a greater seismic hazard compared with other parts. 相似文献
20.
Pathways to seismic hazard evaluation: Extreme and characteristic earthquakes in areas of low and high seismicity 总被引：4，自引：0，他引：4
Paul W. Burton 《Natural Hazards》1990,3(3):275-291
The general philosophy of seismic hazard evaluation described here is appropriate for selection of seismic input to regional earthquake engineering codes prior to detailed on-site inspections and geotechnical assessments. Some probabilistic seismic hazard methodologies which can be applied in areas of low and high seismicity, are briefly described to emphasise the main equations with specimen results. Three aspects of hazard assessment are explored by different pathways. These include the analysis of regional earthquake catalogues to obtain magnitude recurrence, particularly using Gumbel extreme value statistics. This is extended to assess ground shaking hazard which is usually sought by earthquake engineers. Thirdly, the concept of earthquake perceptibility is developed, leading to the identification of an earthquake magnitude or type which is characteristic of a region. This most perceptible earthquake is most likely to be felt at any site in a region and provides an earthquake selection criterion which can be used in aseismic design of noncritical structures. Because there are several methods of seismic hazard evaluation, the view is expressed that it is sensible for practical purposes to seek results from different methods or different pathways to the hazard evaluation.Paper presented at the Commission of the European Communities' School on Earthquake Hazard Evaluation, Athens, and at the 21st General Assembly of the European Seismological Commission, held in Sofia, 1988.Now at School of Environmental Sciences, University of East Anglia, University Plain, Norwich NR4 7TJ, U.K. 相似文献