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1.
The 19 November 1923 earthquake in the Aran Valley (Central Pyrenees), with observed maximum intensityI max = VIII (MSK), has been studied through the compiling and reviewing of macroseismic information and collecting and processing early seismograms. Analysis of macroseismic data gives a focal depth ofh = 5 km and an anelastic attenuation coefficient 10–3 km–1. Analysis of early instrumental records allows the computation of estimate of magnitude (M L = 5.6) and seismic moment (M o = 1.1 × 1017 N × m) which are consistent with the values ofI o andh obtained from macroseismic data.  相似文献   

2.
Strong tectonic earthquakes within the crust always occur on already existing faults, and they have the property of a shear rupture. Such earthquakes with surface-wave magnitudes M < 7 obviously have a geometric similarity. Because of this similarity and the validity of the Gutenberg and Richter's energy—magnitude relation, the expression M = 2 log10 L + const., with L = focal length, is valid.The expression LmaxL* for the maximum focal length, is also valid if L* is the length of the rectilinear extent of the seismic line on which the maximum earthquake occurs. The bounds of L* may be given by sharp bends and/or by traversing deep faults. Thus the maximum imaginable earthquake on a seismic line with the length L* has the magnitude Mmax = 2 log10 L* + const.For the investigated region — the Alps and adjacent areas — from the data of recent and historical strong earthquakes, it follows that Mmax = 2 log10 L* + 1.7, if L* is measured in kilometres. These limiting values lie in the centre-field of the magnitude range for maximum earthquakes, published by Shebalin in 1970. By the aid of this equation it is also possible to assess the upper limiting value of the accompanying maximum scale intensity.  相似文献   

3.
Results from a recent earthquake in the Eastern Pyrenees are presented and the seismotectonics of the region is analyzed from the presently available data. On 26 September 1984 an earthquake (ML = 4.4) took place in the area of the historical destructive earthquake of 1428. Several portable stations installed in the epicentral area to record aftershocks permitted of defining a precise location at 42°19.2′N, 2°10.2′E and 5 km depth. A maximum felt intensity of V (MSK) is obtained from macroseismic data. The epicentral location lies within a block bounded by E-W-trending structures and the focal solution shows right-lateral shearing with a NW-SE pressure axis.The seismicity in the Eastern Pyrenees shows a complex pattern which can be associated with both E-W fractures and NE-SW fault systems. Focal solutions of another two recent earthquakes of ML ~ 4, with differences in horizontal pressure axis, are also discussed.  相似文献   

4.
A large earthquake of magnitude MW = 6.3 occurred on 14 August 2003 NW of the Lefkada Island, which is situated at the Ionian Sea (western Greece). The source parameters of this event are determined using body-wave modeling. The focal depth was found equal to 9 km, the constrained focal mechanism revealed dextral strike–slip motion (φ = 15°, Δ = 80° and λ = 170°), the duration of the source time function was 8 s and the seismic moment 2.9 × 1025 dyn cm. The earthquake occurred close to the northern end of the Kefallinia transform fault, where the 1994 moderate event and its aftershock sequence were also located. The epicentral distribution of the 2003 aftershock sequence revealed the existence of two clusters. The first one is located close to the epicentral area of the mainshock, while the second southern, close to the northwestern coast of the Kefallinia Island. A gap of seismicity is observed between the two clusters. The length of the activated zone is approximately 60 km. The analysis of data revealed that the northern cluster is directly related to the mainshock, while the southern one was triggered by stress transfer caused by the main event.  相似文献   

5.
This paper gives macroseismic and instrumental data on the 17 August 1983 Kamchatka earthquake which occurred in the center of the Kamchatka Gulf bend at a depth of 98 km with an epicentral intensity of VI–VII (MSK-64 scale), energy class 15, and magnitude MLH = 6.9. The focal mechanism represents a thrust along the inclined surface across the strike of the Kamchatka Gulf coastal line. The Primary-wave seismic moment M 0 is 6.3 × 1019 Nm, the Rayleigh wave M 0 is 1.6 × 1019 Nm, and the stress drop is 2.5 MPa. Copies of displacement and acceleration records are presented and the temporal and spatial distribution of the aftershocks is analyzed.  相似文献   

6.
F. Freund  D. Sornette   《Tectonophysics》2007,431(1-4):33
We propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic and electric phenomena which have been associated with earthquakes. The mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress. The electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice, called peroxy bonds or positive hole pairs (PHP), where a PHP represents an O3X/OO YO3 with X,Y = Si4+,Al3+,…, i.e. O− in a matrix of O2− of silicates. We propose that PHP are activated by plastic deformations during the slow cooperative build-up of stress and the increasingly correlated damage culminating in a large “critical” earthquake. Recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit. We conjecture that the intermittent and erratic occurrences of EM signals are a consequence of the progressive build-up of the battery charges in the Earth crust and of their release when crack networks percolate through the stressed rock volumes, providing a conductive pathway for the battery currents to discharge. EM signals are thus expected close to the rupture, either slightly before or after, that is, when percolation is most favored. The proposed mechanism should be relevant for the broader understanding of fractoemissions.  相似文献   

7.
Following a large-sized Bhuj earthquake (M s = 7.6) of January 26th, 2001, a small aperture 4-station temporary local network was deployed, in the epicentral area, for a period of about three weeks and resulted in the recording of more than 1800 aftershocks (-0.07 ≤M L <5.0). Preliminary locations of epicenters of 297 aftershocks (2.0 ≤M L <5.0) have brought out a dense cluster of aftershock activity, the center of which falls 20 km NW of Bhachau. Epicentral locations of after-shocks encompass a surface area of about 50 × 40 km2 that seems to indicate the surface projection of the rupture area associated with the earthquake. The distribution of aftershock activity above magnitude 3, shows that aftershocks are nonuniformly distributed and are aligned in the north, northwest and northeast directions. The epicenter of the mainshock falls on the southern edge of the delineated zone of aftershock activity and the maximum clustering of activity occurs in close proximity of the mainshock. Well-constrained focal depths of 122 aftershocks show that 89% of the aftershocks occurred at depths ranging between 6 and 25 km and only 7% and 4% aftershocks occur at depths less than 5 and more than 25 km respectively. The Gutenberg-Richter (GR) relationship, logN = 4.52 - 0.89ML, is fitted to the aftershock data (1.0<-M L<5.0) and theb-value of 0.89 has been estimated for the aftershock activity.  相似文献   

8.
On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofML = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ ML ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·1020 resp. 4·1018dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.  相似文献   

9.
Tokutaro Hatori 《GeoJournal》1996,38(3):313-319
The regional characteristics of tsunami magnitudes in the SE Asia region are discussed in relation to earthquake magnitudes during the period from 1960 to 1994. Tsunami magnitudes on the Imamura-Iida scale are investigated by the author's method (Hatori 1979, 1986) using the data of inundation heights near the source area and tide-gauge records observed in Japan. The magnitude values of the Taiwan tsunamis showed relatively to be small. On the contrary, the magnitudes of tsunamis in the vicinities of the Philippines and Indonesia exceed more than 1–2 grade (tsunami heights: 2–5 times) compared to earthquakes with similar size on the circum-Pacific zone. The relation between tsunami magnitude, m, and earthquake magnitude, M s, is expressed as m = 2.66 M s– 17.5 for these regions. For example, the magnitudes for the 1976 Mindanao tsunami (M s= 7.8, 3702 deaths) and the 1992 Flores tsunami (M s= 7.5, 1713 deaths) were determined to be m = 3 and m = 2.5, respectively. The focal depth of tsunamigenic earthquakes is shallower thand< 36 km, and the detectively of tsunamis is small for deep earthquakes being d > 40 km. For future tsunamis, it is indispensable to take precautions against shallow earthquakes having the magnitudes M s> 6.5.  相似文献   

10.
Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO4 solutions. Single-crystal XRD refinement with R1=0.0232 for the unique observed reflections (|Fo| > 4F) and wR2=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, Vo=160.11(4) cm3, and fractional positions for all atoms except the H in the H3O groups. The chemical composition of this sample is described by the formula (H3O)0.91Fe2.91(SO4)2[(OH)5.64(H2O)0.18]. The enthalpy of formation (Hof) is –3694.5 ± 4.6 kJ mol–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H2O, and -MgSO4. The entropy at standard temperature and pressure (So) is 438.9±0.7 J mol–1 K–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (Cp) data between 273 and 400 K were fitted to a Maier-Kelley polynomial Cp(T in K)=280.6 + 0.6149T–3199700T–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol–1. Speciation and activity calculations for Fe(III)–SO4 solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the Cp data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in Cp, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H3O)Fe3(SO4)2(OH)6 was estimated: Gof= –3226.4 ± 4.6 kJ mol–1, Hof=–3770.2 ± 4.6 kJ mol–1, So=448.2 ± 0.7 J mol–1 K–1, Cp (T in K)=287.2 + 0.6281T–3286000T–2 (between 273 and 400 K).  相似文献   

11.
We investigate background seismic activity of the Abruzzo region, a 5000 km2 area located within the Central Apennines of Italy, where in the past 600 years at least 5 large earthquakes (I = XI–X) have occurred.Between April 2003 and September 2004, a dense temporary seismic network composed of 30 digital three-component seismic stations recorded 850 earthquakes with 0.9 < ML < 3.7. We present earthquake locations and focal mechanisms obtained by standard procedures and an optimized velocity model computed with a search technique based on genetic algorithms.The seismicity occurs at a low and constant rate of  2.6 e− 04 events/daykm2 and is sparsely distributed within the first 15 km of the crust. Minor increases in the seismicity rate are related to the occurrence of small and localised seismic sequences that occur at the tip of major active normal faults along secondary structures.We observe that during the 16 months of study period, the Fucino fault system responsible for the 1915 Fucino earthquake (MS = 7.0), and the major normal faults of the area, did not produce significant seismic activity.Fault plane solutions evaluated using P-wave polarity data show the predominance of normal faulting mechanisms ( 55%) with NE-trending direction of extension coherent with the regional stress field active in this sector of the Apennines. Around 27% of the focal solutions have pure strike–slip mechanisms and the rest shows transtensional faulting mechanisms that mainly characterise the kinematics of the secondary structures activated by the small sequences.We hypothesize that the largest known NW-trending normal faults are presently locked and we propose that in the case of activation, the secondary structures located at their tips may act as transfer faults accommodating a minor part of the extensional deformation with strike–slip motion.  相似文献   

12.
The source parameters are determined for the Burma-India border earthquake of July 29, 1970, from body-wave spectra. We obtain seismic moment [ , ] · 1026 dyne cm, source dimension [ ] km, radiated energy [ , −ER (S) = 1.35] · 1020 ergs and the stress drop = 11 bars.  相似文献   

13.
Summary The crystal structure of scotlandite —a=4.505(2),b=5.333(2),c=6.405(6) Å, =106.24(3)o; space groupP21/m; cell content 2 {PbSO3} — was determined from singlecrystal X-ray diffractometer data. Scotlandite is isotypic with molybdomenite, PbSeO3. Lead is coordinated to nine oxygen atoms with Pb-Oav=2.75 Å, and possibly further to one sulphur atom with Pb–S=3.46 Å. The average S–O distance in the pyramidal SO3 group is 1.52 Å. The structural relationships to cerussite, PbCO3, are discussed.
Die Kristallstruktur des Scotlandits, PbSO3
Zusammenfassung Die Kristallstruktur des Scotlandits —a=4,505(2),b=5,333(2),c=6,405(6) Å, =106,24(3)o; RaumgruppeP21/m; Zellinhalt 2 {PbSO3} — wurde aus Einkristall-Röntgendiffraktometerdaten bestimmt. Scotlandit ist mit Molybdomenit, PbSeO3, isotyp. Blei wird von neun Sauerstoffatomen mit Pb–Oav=2,75 Å und möglicherweise zusätzlich von einem Schwefelatom mit Pb–S=3,46 Å koordiniert. Der durchschnittliche S–O-Abstand in der pyramidalen SO3-Gruppe mißt 1,52 Å. Die strukturellen Beziehungen zu Cerussit, PbCO3, werden diskutiert.

With 2 Figures  相似文献   

14.
Understanding the electromagnetic response to geodynamic processes occurring in the earth's upper crust, in particular pre-seismic and seismic processes, is a challenging task in modern geophysics. There is increasing evidence that seismo-electromagnetic (SEM) phenomena are difficult to describe quantitatively by “linear” models using “averaged” parameters of the medium, such as electrical and hydraulic conductivities. Because the upper crust is highly inhomogeneous (at all scales), porous, and can be fully or partially water-saturated, the most natural way to describe its parameters is via fractal-theoretic and percolation-theoretic models.Recent studies indicate that the electrokinetic effect is the most likely driving mechanism for the various types of SEM signals. Here we considered the hydraulic, electric, and electrokinetic conductances of a porous water-saturated medium as a function of porosity () and moisture content (θ), utilizing a percolation/fractal approach. We show that the electric conductivity and electrokinetic current in such a medium are both proportional to (–c)2 and (θ–θc)2, where c and θc are the critical values of porosity and moisture content, respectively. This behavior admits the possibility of a relatively large change in the respective electric and electrokinetic parameters due to a small change in the mechanical strain field. This is significant because it may account for the appearance of some types of SEM signals at large distances from the earthquake origin, which is the main deficiency of most models. Indeed, the anticipated strain changes related to pre-earthquake processes is usually very small except near the focal area. The expected ‘averaged’ electromagnetic response also would be very small, unless a local underground water system exists, not necessarily near the focal area, but which is close to critical point(s).We discuss the conditions under which electrotelluric and geomagnetic variations can accompany mechanical disturbances in the earth's crust.  相似文献   

15.
F. Di Luccio  E. Fukuyama  N.A. Pino   《Tectonophysics》2005,405(1-4):141-154
On October 31, 2002 a ML = 5.4 earthquake occurred in southern Italy, at the margin between the Apenninic thrust belt (to the west) and the Adriatic plate (to the east). In this area, neither historical event nor seismogenic fault is reported in the literature. In spite of its moderate magnitude, the earthquake caused severe damage in cities close to the epicenter and 27 people, out of a total of 29 casualties, were killed by the collapse of a primary school in S. Giuliano di Puglia. By inverting broadband regional waveforms, we computed moment tensor solutions for 15 events, as small as ML = 3.5 (Mw = 3.7). The obtained focal mechanisms show pure strike-slip geometry, mainly with focal planes oriented to NS (sinistral) and EW (dextral). In several solutions focal planes are rotated counterclockwise, in particular for later events, occurring west of the mainshock. From the relocated aftershock distribution, we found that the mainshock ruptured along an EW plane, and the fault mechanisms of some aftershocks were not consistent with the mainshock fault plane. The observed stress field, resulting from the stress tensor inversion, shows a maximum principal stress axis with an east–west trend (N83°W), whereas the minimum stress direction is almost N–S. Considering both the aftershock distribution and moment tensor solutions, it appears that several pre-existing faults were activated rather than a single planar fault associated with the mainshock. The finite fault analysis shows a very simple slip distribution with a slow rupture velocity of 1.1 km/s, that could explain the occurrence of a second mainshock about 30 h after. Finally, we attempt to interpret how the Molise sequence is related to the normal faulting system to the west (along the Apennines) and the dextral strike-slip Mattinata fault to the east.  相似文献   

16.
Yu.S. Tyupkin   《Tectonophysics》2007,431(1-4):73
The theory of an earthquake source nucleation is discussed. Based on the assumption that self organization of damage process takes place in the zone of an earthquake source nucleation the theory incorporates the damage rheology framework of Lyakhovsky et al. and the approach of phenomenology theory of second-order phase transition. Namely, the free energy governing the process of an earthquake source nucleation depends on two collective variables α and φ in addition to the strain tensor εij. The variable α quantifies the fracture of the medium and the variable φ quantifies the interaction effect of cracks. The region ΩS is associated with a potential source of an earthquake if the damage variable α exceeds the critical value αcr(1) inside ΩS. The important feature of a potential source is that interaction of fractures causes acceleration of damage process inside the region of potential source and the material should lose stability primarily in this region. Interaction of fractures results also in occurrence of a residual stress caused by nonuniformity of fracture density. The appearance and development of the potential source result in increase of intensity of damage process not only in the region of potential source but also in a certain neighborhood of the last. It is compatible with such observed effects as acceleration of seismic energy release and growth of correlation length of weak seismicity before large earthquake. Transition of potential source to the stage of avalanche-unstable fracturing is associated with instability generated by explosive increase of interaction of fractures when the damage variable α exceeds the second critical value αcr(2) inside ΩS.  相似文献   

17.
The aim of this study is to determine the isotopic composition (δ18O and δ2H) of interstitial water in bentonites. The study had been carried out from adsorbed vapour in homoionic bentonites. We have worked with the fraction <20 μm of a bentonite from Serrata de Níjar (Almería, Spain). Homoionic sodium and calcium bentonites were prepared as well as variable quantities of exchangeable Na/Ca (75Ca/25Na; 50Ca/50Na; 25Ca/75Na), by mixing pure sodium and calcium suspensions in the appropriate quantities. To carry out the hydration of the samples, every one of them was previously dried at 300 °C overnight, they were subjected to controlled saturation conditions in an atmosphere of different relative humidity and at a constant temperature of 20 °C, until equilibrium was achieved. The different vapour pressures were: P/Po = 0.05; P/Po = 0.078; P/Po = 0.15; P/Po = 0.32; P/Po = 0.45; P/Po = 0.63; P/Po = 0.8; P/Po = 1, obtained from the saturated solutions of different salts or sulphuric acid.The saturation water was extracted for isotopic analysis from an aliquot of a saturated sample. The technique used was vacuum extraction based on a modification of the one described by Araguás-Araguás et al. (1995).The differentiation between the isotopes of 18O and 2H from interstitial water in the bentonite samples, depending on the different relative humidity, may affect the ions diffusion in the interstitial solutions, since in those from low relative humidities, there could be a higher diffusion velocity as they are formed by molecules of light isotopes, versus interstitial solutions from higher relative humidities or those near saturation. This fact should be taken into account in studies on cation and solute transport from these solutions inside bentonite, even though it is important to continue studying and corroborating it with a larger number of solutions isotopically marked.  相似文献   

18.
In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy (Md max=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake (Io max=XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.  相似文献   

19.
M. Murru  R. Console  G. Falcone   《Tectonophysics》2009,470(3-4):214-223
We have applied an earthquake clustering epidemic model to real time data at the Italian Earthquake Data Center operated by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for short-term forecasting of moderate and large earthquakes in Italy. In this epidemic-type model every earthquake is regarded, at the same time, as being triggered by previous events and triggering following earthquakes. The model uses earthquake data only, with no explicit use of tectonic, geologic, or geodetic information. The forecasts are displayed as time-dependent maps showing both the expected rate density of Ml ≥ 4.0 earthquakes and the probability of ground shaking exceeding Modified Mercalli Intensity VI (PGA ≥ 0.01 g) in an area of 100 × 100 km2 around the zone of maximum expected rate density in the following 24 h. For testing purposes, the overall probability of occurrence of an Ml ≥ 4.5 earthquake in the same area of 100 × 100 km2 is also estimated. The whole procedure is tested in real time, for internal use only, at the INGV Earthquake Data Center.Forecast verification procedures have been carried out in forward-retrospective way on the 2006–2007 INGV data set, making use of statistical tools as the Relative Operating Characteristics (ROC) diagrams. These procedures show that the clustering epidemic model performs up to several hundred times better than a simple random forecasting hypothesis. The seismic hazard modeling approach so developed, after a suitable period of testing and refinement, is expected to provide a useful contribution to real time earthquake hazard assessment, even with a possible practical application for decision making and public information.  相似文献   

20.
We present the results of a systematic search for the identification of accelerating seismic crustal deformation in the broader northern Aegean area and in northwestern Turkey. We found that accelerating seismic deformation release, expressed by the generation of intermediate magnitude earthquakes, is currently observed in NW Turkey. On the basis of the critical earthquake model and by applying certain constraints which hold between the basic quantities involved in this phenomenon, it can be expected that this accelerating seismic activity may culminate in the generation of two strong earthquakes in this area during the next few years.The estimated epicenter coordinates of the larger of these probably impending earthquakes are 39.7°N–28.8°E, its magnitude is 7.0 and its occurrence time tc=2003.5. The second strong event is expected to occur at tc=2002.5 with a magnitude equal to 6.4 and epicenter coordinates 40.0°N–27.4°E. The uncertainties in the calculated focal parameters for these expected events are of the order of 100 km for the epicenter, ±0.5 for their magnitude and ±1.5 years for their occurrence time.  相似文献   

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