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1.
Weiping Qin 《地震科学（英文版）》1992,5(1):177-185
This paper gives a complete commentary on some popular gradings which based on the 2×2 contingency table, for one—dimensional seismologic prediction. It contains:
- In view of the statistical correlation, the Wallen gradingV=√QS is the most equitable one amomg all gradings.
- Each one of the three gradings: Zhenchao Gu gradingS, Obuhov gradingQ and Shaoxie Xu gradingR, has its own inadequacy although they are so easy for use.
- A set of gradings can be derived fromV. The harmonic mean ofS andQ, H(S,Q) and the Hedike gradingS H are the members of this set. The order of some popular gradings are given in Theorem 5. 3.
- In view of the measure of the overlapping part a gradingW is introduced. Another set of gradings may be derived from it. The index of efficiencyh is the severest one among this set.
2.
Microearthquake digital data collected at Campi Flegrei during the recent (1982–1985) ground uplift episode have been analyzed in order to infer source and medium seismic properties. The main results obtained from these analyses are:
- Hypocenter distribution and the size of the seismic zone do not change with time and do not depend on the ground uplift rate. Events occurred clustered in time with no simple causal relations between the cluster occurrences and their energy.
- Anelastic attenuation does not depend strongly on frequency, showing a constant pattern at high frequencies. The observed values of low and high frequency attenuation, due to the short source receiver distances, do not seriously affect the spectral content of signals radiated by the sources.
- A constant Brune stress drop pattern (～4–5 bars) as a function of seismic moment is observed. This indicates that the manner of fracturing is almost independent on magnitude of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic processes in a prefractured medium can explain the observed small stress drop values.
- Focal mechanisms from moment tensor estimates show that radiation patterns are mostly well interpreted in terms of double couple source models.
- The scaling of peak ground motion parameters (A max andV max vs seismic moment) can be explained by an ω2 source model (constant stress drop) multiplied by an exponential function with a small decay parameter, which takes into account the measured attenuation.
3.
The various useful source-parameter relations between seismic moment and common use magnitude lg(M 0) andM s,M L,m b; between magnitudesMs andM L,M s andm b,M L andm b; and between magnitudeM s and lg(L) (fault length), lg (W) (fault width), lg(S) (fault area), lg(D) (average dislocation);M L and lg(f c) (corner frequency) have been derived from the scaling law which is based on an “average” two-dimensional faulting model of a rectangular fault. A set of source-parameters can be estimated from only one magnitude by using these relations. The average rupture velocity of the faultV r=2.65 km/s, the total time of ruptureT(s)=0.35L (km) and the average dislocation slip rateD=11.4 m/s are also obtained. There are four strong points to measure earthquake size with the seismic moment magnitudeM w.
- The seismic moment magnitude shows the strain and rupture size. It is the best scale for the measurement of earthquake size.
- It is a quantity of absolute mechanics, and has clear physical meaning. Any size of earthquake can be measured. There is no saturation. It can be used to quantify both shallow and deep earthquakes on the basis of the waves radiated.
- It can link up the previous magnitude scales.
- It is a uniform scale of measurement of earthquake size. It is suitable for statistics covering a broad range of magnitudes. So the seismic moment magnitude is a promising magnitude and worth popularization.
4.
For most previous geomagnetic surveys, the time variations of the observatory closest to the site of observation have been used for reduction. The accuracy of repeat station measurements depends upon the distance between the station and the observatory. Nowadays, the requirements for the accuracy of repeat station measurements are much higher, especially with respect to local secular variation anomalies. On the other hand, transportable variograph stations are available, by means of which time variations can be recorded closer to the station site. The reduction steps for this method are: - the stability of the base-line values of the variographs; - the question as to what degree a quiet night value represents the normal value at that time (e.g. influence of aD st field and/or other fields). A repeat station survey of the Federal Republic of Germany was carried out in 1982. During the same time, eleven stations recorded the time variations in that area. We discuss the aforementioned aspects by way of an example taken from this survey. 相似文献
- Reduction of measured values to the base-line of the nearby variograph station;
- Computation of the nearest quiet night value using the baseline of the variograph;
- Computation of the difference between this value and the corresponding one at the observatory.
5.
A modified formula of the cumulative frequency-magnitude relation has been formulated and tested in a previous paper by the authors of this study. Based on the modified relationship, the following reoccurrence formulas have been obtained.
- For the ‘T-years period’ larger earthquake magnitude,M T $$M_T = \frac{1}{{A_3 }}ln\frac{{A_2 }}{{(1/T) + A_1 }}.$$
- For the value of the maximum earthquake magnitude, which is exceeded with probabilityP inT-years period,M PT $$M_{PT} = \frac{{ln(A_2 .T)}}{{A_3 }} - \frac{{ln[A_1 .T - ln(1 - P)]}}{{A_3 }}.$$
- For the probability of occurrence of an earthquake of magnitudeM in aT-years period,P MT $$P_{MT} = 1 - \exp [ - T[ - A_1 + A_2 \exp ( - A_3 M)]].$$
6.
Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by
- Total gas contents increasing south to north from 0.003 to 0.05 mole fraction;
- Constant CO2 (95±2 percent); near constant H2S (1.6±0.8), N2 (1.2±0.8), H2 (2±1), CH4 (1.2±1), and no O2 in the dry gas;
- Presence of numerous, straight chain and branched C2 to C6 hydrocarbons plus benzene in amounts independent of CH4 contents with highest concentrations in the deeper wells;
- Oxygen-18 contents of steam increasing south to north from ?5.0‰ to ?0.4‰ with little change in deuterium (?42±2‰).
- Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production;
- Synthesis of CH4 from H2 and CO2 with CO2 and H2 produced by thermal metamorphism and rock-water reactions;
- Extraction of C2 to C6 hydrocarbons from rock organic matter;
- Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ～220°C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south.
7.
Some recent calc-alkaline andesites and dacites from southern and central Martinique contain basic xenoliths belonging to two main petrographic types: The most frequent one has a hyalodoleritic texture (« H type ») with hornblende + plagioclase + Fe-Ti oxides, set in an abundant glassy and vacuolar groundmass. The other one exhibits a typical porphyritic basaltic texture (« B type ») and mineralogy (olivine + plagioclase + orthopyroxene + clinopyroxene + Fe-Ti oxides and scarce, or absent hornblende). Gradual textural and mineralogical transitions occur between these two types (« I type ») with the progressive development of hornblende at the expense of olivine and pyroxenes. Mineralogical and chemical studies show no primary compositional correlations between the basaltic xenoliths and their host lavas, thus demonstrating that the former are not cognate inclusions; they are remnants of basaltic liquids intruded into andesitic to dacitic magma chambers. This interpretation is strengthened by the typical calc-alkaline basaltic composition of the xenoliths, whatever their petrographic type (« H », « I » or « B »). The intrusion of partly liquid, hot basaltic magma into colder water-saturated andesitic to dacitic bodies leads to drastic changes in physical conditions. The two components; the basaltic xenoliths are quenched and homogeneized with their host lavas with respect to To;fO2 andpH2O conditions. « H type » xenoliths represent original mostly liquid basalts in which such physical changes lead to the formation of hornblende and the development of a vacuolar and hyalodoleritic texture. The temperature increase of the acid magma depends on the amount of the intruding basalt and on the thermal contrast between the two components. The textural diversity which characterizes the xenoliths reflects the cooling rate of the basaltic fragments and/or their position relative to the basaltic bodies (chilled margins or inner, more crystallized, portions). In addition to physical equilibration (T, fO2) between the magmas, mixing involves: mechanical transfer of phenocrysts from one component to another, in both directions; volatile transfer to the basaltic xenoliths, with chemical exchanges. It is here demonstrated that a short period of time (some ten hours to a few days) separates the mixing event from the eruption, outlining the importance of magma mixing in the triggering of eruption. The common occurrence of basaltic xenoliths (generally of « H » type) in calc-alkaline lavas is emphasized, showing that this mechanism is of first importance in calc-alkaline magma petrogenesis. 相似文献
8.
Four volcanic units have been distinguished on the islanf of Fayal. In order of decreasing age, these are: the eastern rift, and products of the activity preceding the collapse of the caldera visible at the summit of the stratovolcano, characterized by an alkaline series: basalt-hawaiite-mugearite-trachyte; the products of the explosive and postcaldera activity where only evolved lavas occur (benmoreites and trachytes); the recent basaltic activity of the Horta region; the western fissural activity — recent and historical. The two last units are characterized by exclusively basaltic, frequently picritic, eruptions. The lava groups cannot be distinguished by chemical criteria and have thus been treated as a single suite. Ninety samples have been analysed by X-ray fluorescence, and the mineralogy of 6 representative specimens has been determined by microprobe. The data were used to work out the evolution of the lava. The series is shown to have been produced by crystal fractionation under moderate water pressure from an alkali basalt. Moderate fractionation of amphibole during the last stages allow the liquids to remain weakly undersaturated from initial basalts until final trachytes. Mineralogical and chemical diversity between the most evolved lavas, benmoreites and trachytes, is an evidence of the strong influence ofpH2O and/orfO2 on the composition of such residua. 相似文献
9.
F. G. Piccinelli M. Mucciarelli P. Federici D. Albarello 《Pure and Applied Geophysics》1995,145(1):97-108
The Ridracoli Dam has been operating since 1981. Around the reservoir ISMES installed and operated for 10 years a seismic network, now reduced to a 3-D station. Earthquakes were recorded with completeness from magnitude 0.8 onwards. In the same period, all the parameters relevant to the dam and the environment were measured. This provided a complete data base for RIS studies, unique in its kind in Italy. The main findings of the analyses performed are the following:
- The filling of the reservoir has not influenced the seismicity of the area for most significant events (M L>3.5).
- Lesser seismicity around the reservoir seems to be correlated with water level in the reservoir, but also shows to be dependent on regional seismicity.
- b value shows a slight increase with time. This may indicate an increase in rock fracturing, which is known to precede the disappearing of Type II RIS.
10.
T. B. Yanovskaya 《Pure and Applied Geophysics》1996,148(1-2):319-336
A method of estimating the lateral velocity variations in the 2D case using the data on deviations of wave paths from straight lines (or great circle paths in the spherical case) is proposed. The method is designed for interpretation of azimuthal anomalies of surface waves which contain information on lateral variations of phase velocities supplementary to that obtained from travel-time data in traditional surface wave tomography. In the particular 2D case, when the starting velocity is constant (c 0) and velocity perturbations δc(x,y) are sufficiently smooth, a relationship between azimuthal anomaly δα and velocity perturbations δc(x,y) can be obtained by approximate integration of the ray tracing system, which leads to the following functional: $$\delta \alpha = \int_0^L {\frac{{s(\nabla m,n_0 )}}{L}} ds,$$ wherem(x,y)=δc(x,y)/c 0,L is the length of the ray,n 0 is a unit vector perpendicular to the ray in the starting model, integration being performed from the source to the receiver. This formula is valid for both plane and spherical cases. Numerical testing proves that for a velocity perturbation which does not exceed 10%, this approximation is fairly good. Lateral variations of surface wave velocities satisfy these assumptions. Therefore this functional may be used in surface wave tomography. For the determination ofm(x,y) from a set ofδα k corresponding to different wave paths, the solution is represented as a series in basis functions, which are constructed using the criterion of smoothness of the solution proposed byTarantola andNersessian (1984) for time-delay tomography problems. Numerical testing demonstrates the efficiency of the tomography method. The method is applied to the reconstruction of lateral variations of Rayleigh wave phase velocities in the Carpathian-Balkan region. The variations of phase velocities obtained from data on azimuthal anomalies are found to be correlated with group-velocity variations obtained from travel-time data. 相似文献
11.
12.
S. M. Spottiswoode 《Pure and Applied Geophysics》1989,129(3-4):673-680
This paper summarizes seismic and rockburst research activities related to South African deep-level gold mines over the period 1983 to 1987. It covers continued research in directions that were considered in the Seismicity in Mines Symposium in 1982 as well as in several new areas of research. Five broad areas are identified:
- Seismic data acquisition and processing. Improved seismic systems are being developed. Velocity models related to known stratigraphy are being used to provide more accurate estimates of seismic locations.
- Source mechanisms and near-source effects on seismic wave transmission. This work provides fundamental insights into seismicity and rock behaviour and is being applied in rockburst prediction research.
- Mine layouts. Excess shear stress is being investigated as a design parameter by analyzing mining configurations and resultant seismicity. In addition, better understanding of the behaviour of highly stressed remnants and pillars is also being obtained from seismic studies.
- Strong ground motion studies. Evaluation of the performance of support elements, including recently developed backfill materials, requires better knowledge of ground motion around underground excavations during seismic events and rockbursts.
- Rockburst prediction and control. Rockburst prediction research continues with some reported success. In addition, the feasibility of actively triggering fault slip or conditioning the rock ahead of the stope face to ameliorate the rockburst hazard is currently being investigated.
13.
László Szarka 《Surveys in Geophysics》1987,9(3-4):287-318
The paper gives a summary of geophysical aspects of man-made electromagnetic noise in the Earth as follows: - EM distortion effects of man-made constructions below and over the Earth's surface defined as ‘passive-noise’, - field observation of EM disturbances due to ‘active’ man-made sources, - EM source mechanism of some important active sources from a geophysical point of view, - efforts in order to improve the signal-to noise ratio by instrumental, methodological and dataprocessing ways, - application of man-made EM noise for geophysical prospecting. The paper is based on world-wide EM noise survey studies published mainly in geophysical journals. 相似文献
14.
Liparitic volcanism is a typical feature of the orogenic phase giving rise to the Kazakhstan, Middle Asia and Caucasus folded systems. The main characteristics of the liparitic volcanism common to these three regions are the following:
- Geo-structural zonation of the volcanic structures.
- Dismembered Moho surface within the volcanic structures.
- Synchronous, yet independent evolution of liparitic and andesitic volcanisms.
- Ignimbritic character of the liparitic volcanism.
- Lateral petrochemical zonation with some features common to the liparitic and andesitic rock series.
15.
J. Keller 《Bulletin of Volcanology》1969,33(3):942-959
Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km2. The rhyolites originated by melting of granitic crustal rocks. The petrological properties leading to this conclusion are as follows: -mineralogical composition of the pumice being 60 wt % of glass and 40 % of relictic granitic minerals (quartz, plagioclase, potash feldspar, biotite) in «phenocrysts» up to 1 cm Ø. -phenomena of strong corrosion, resorption and melting of all light colored «phenocrysts» in the rhyolitic pumice. -mineralogical and chemical identity between pumice and granitic xenolites found in great quantity in the pumice tuff. -structurally transitional types between pumice and the granites in different state of melting. -eutectic composition of the pumice glass for a pressure of 2 kb. 相似文献
16.
Geomagnetic solar and lunar daily variationsS andL, at Alibag, India are derived, by the well-known Chapman-Miller method, from the series of homogeneous mean hourly magnetic data of the years 1932 to 1972. The data for all the three elements — declinationD and horizontal and vertical intensitiesH andZ — are analysed, by dividing the data suitably for a study of the seasonal variations, the effect of the changes in the solar and magnetic activities onS andL, the oceanic dynamo contribution toL, and their interactions with each other. The main results are as follows.
- ForS the daily pattern and its seasonal progression conform to the type expected from a northern-hemisphere station. On the other hand, the amplitudes of all the four harmonics ofL systematically have higher values in winter, and inD andZ the harmonics show large phase differences between summer and winter. The pattern ofL in winter suggests that the lunar current system consists of a single set of vortices in the summer hemisphere rather than the conventional vortices, one set in each of the hemispheres.
- Solar-cycle modulation on the solar ranges as well as on the amplitudes of the first three harmonics ofS is greater than that expected solely from the increase in E-region conductivity, whereas the corresponding modulation onL is comparable to that on the E-region conductivity.
- With increasing magnetic activity the first harmonic ofS shows an increase, and the first three harmonics ofL indicate a general decrease, in amplitude.
- Of the variability inS 96%, but inL only 32%, is found to be accounted for by the combined effect of the variations in the solar and magnetic activities.
17.
Stacking velocity V C2, vertical velocity ratio γ 0, effective velocity ratio γ eff, and anisotropic parameter χ eff are correlated in the PS-converted-wave (PS-wave) anisotropic prestack Kirchhoff time migration (PKTM) velocity model and are thus difficult to independently determine. We extended the simplified two-parameter (stacking velocity V C2 and anisotropic parameter k eff) moveout equation from stacking velocity analysis to PKTM velocity model updating and formed a new four-parameter (stacking velocity V C2, vertical velocity ratio γ 0, effective velocity ratio γ eff, and anisotropic parameter k eff) PS-wave anisotropic PKTM velocity model updating and process flow based on the simplified two-parameter moveout equation. In the proposed method, first, the PS-wave two-parameter stacking velocity is analyzed to obtain the anisotropic PKTM initial velocity and anisotropic parameters; then, the velocity and anisotropic parameters are corrected by analyzing the residual moveout on common imaging point gathers after prestack time migration. The vertical velocity ratio γ 0 of the prestack time migration velocity model is obtained with an appropriate method utilizing the P- and PS-wave stacked sections after level calibration. The initial effective velocity ratio γ eff is calculated using the Thomsen (1999) equation in combination with the P-wave velocity analysis; ultimately, the final velocity model of the effective velocity ratio γ eff is obtained by percentage scanning migration. This method simplifies the PS-wave parameter estimation in high-quality imaging, reduces the uncertainty of multiparameter estimations, and obtains good imaging results in practice. 相似文献
18.
Presently available data on the reaction of SO2 with OH radicals (OH + SO2 + \(M\xrightarrow[{k_1 }]{}\) HSO3 +M) are critically reviewed in light of recent stratospheric sulfur budget calculations. These calculations impose that the net oxidation ratek of SO2 within the stratosphere should fall within the range 10?7≤k≤10?9, if the SO2 oxidation model for the stratospheric sulfate layer is assumed to be correct. The effective reaction rate constantk 1 * =k 1[M] at the stratospheric temperature is estimated as $$k_1^* = \frac{{(8.2 \pm 2.2) \times 10^{ - 13} \times [M]}}{{(0.79 \mp 0.34) \times 10^{ - 13} + [M]}}cm^3 /molecules sec$$ where [M] refers to the total number density (molecules/cm3). Using the above limiting values ofk 1 * , and the estimated OH density concentrations, the net oxidation rate is calculated as 3.6×10?7≤k≤1.3×10?8 at 17 km altitude. This indicates that the upper limit of thesek values exceeds the tolerable range imposed by the model by a factor of about four. Obviously the uncertainty of thek 1 * values and of the OH concentrations in the stratosphere is still too large to make definite conclusions on the validity of the SO2 model. 相似文献
19.
Federico Von Giovanoli André Lambert 《Aquatic Sciences - Research Across Boundaries》1985,47(2):159-178
Results obtained by means of an ultrasonic current meter in the plume of the Rhone river are summarized as follows:
- Currents of Rhone river water entering the lake were clearly discernible up to a distance of about 1 km from the river mouth. The interflow was observed at depth of 10 to 30 m.
- Interflow velocities decreased with increasing distance from the river mouth: from 40cm/s at a distance of 350 m to about 15 cm/s at 1 km.
- Short-term variations of current velocities and directions documented the highly turbulent nature of the interflow.
- The entering river water (inflow direction to the NNW) interfered with a persisting northeastward current of the lake water. At a distance of 1–2 km from the mouth the interflow gradually assumed the same direction, possibly due to deflection by Coriolis forces.
- Current velocities showed considerable variations within a time scale in the order of hours at the same measuring position. The reasons for these fluctuations remain unclear. Possible causes may be lateral oscillations of the entering river water or its deviation by river mouth bars during periods of reduced river discharge. Variations of the discharge alone cannot explain these current fluctuations.
20.