首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
The paper presents the current state of magnitude estimation for Koyna earthquakes exceeding magnitude 3.0. We estimate coda duration magnitude from analogue seismograms recorded on the short period vertical (SPZ) seismometer at Hyderabad seismic observatory HYB and determine moment magnitude using very broad-band (VBB) data from the Geoscope station (HYB)and short period digital data from the local seismic network of NationalGeophysical Research Institute (NGRI) around the Koyna and Warna reservoirs.Firstly, the seismograms of 97 Koyna earthquakes exceeding magnitude 4.0 havebeen used to establish a new empirical coda duration magnitude scale which includes the higher order terms of log10, where is the coda length in seconds. Four background noise levels (1, 2, 6 and 10 mm) areconsidered to estimate the coda duration. We found that the duration magnitudes for 1 mm background level are more stable than those for 2, 6 and 10 mm. The new coda duration magnitude (Mdnew) scale, for 1 mmlevel, is:Mdnew = –0.594 + 2.04 log10 – 0.0435 (log10)2The estimated Mdnew are compatible with the reported MS values of the NGRI observatory and the mb values of the United States Geological Survey (USGS). These magnitudes can be obtained within the standard deviation of ± 0.26 units of MS (NGRI). A new relatively homogeneous catalog for Koyna earthquakes of Mdnew 4.0 is obtained. The momentmagnitudes for 34 Koyna-Warna events of Mdnew ranging from 3.0 to 5.4 have been estimated using two techniques. The first utilizes amplitudes of band-pass filtered (between 15 and 30 sec) velocity traces of moderate Koyna-Warna earthquakes of MW} 4.4 to 5.4, we abbreviate the magnitude using MA. The second is based on the S-wave spectrum of short period seismograms of local earthquakes (MW < 3.8). Moment magnitudes estimated by spectral analysis mainly depend on the estimation of event's long-period spectral level and appears to saturate for moderate Koyna-Warnaearthquakes (MW > 3.8). We recommend the use of both techniques whenever possible. The estimated moment magnitudes and Mdnew show an almost linear relationship with a standard deviation of ± 0.05.  相似文献   

2.
Summary Using the fromulae given byGutenberg andRichter, the writer has computed the magnitude and energy of 1804 earthquakes which occurred in Turkey during the period 1850–1960. For drawing the Isenerget, the formula =log10 S has been used in accordance with the definitions given byToperczer andTrapp, whereS=e i/F·p represents the energy in erg/m2 h corresponding to the surface element of 0.5° Lat. x 0.5° Long. Also the relationship between the seismicity and the tectonics of Turkey has been studied by drawing the maps of the epicenters, the focus-depths and the frequences of the earthquakes with various intensities.  相似文献   

3.
The vertical velocity, , and the diabatic heating were computed at 800, 600, 400 and 200 mb surfaces using the Omega equation. The highest contribution to is from the diabatic heating produced by condensation associated with the precipitations appearing to be the main source of diabatic heating. The net radiative cooling and the thermal advection in the upper troposphere over the warm anticyclone result in diabatic cooling over the eastern part of the Bay of Bengal and adjoining northern and eastern regions.List of Symbols Used C p Heat capacity at constant pressure - f Coriolis parameter - g Acceleration due to gravity - P Atmospheric pressure - Q Diabatic heating rate per unit mass - R Gas constant of air - S Static stability parameter - t Time - U, V Zonal and meridional wind components - Specific volume - Relative vorticity - Absolute vorticity - Potential temperature - Geopotential - Vertical velocity (dP/dt) - 1 Adiabatic vertical velocity - 2 Vertical velocity due to certain forcing - 3 Diabatic vertical velocity - Isobaric gradient operator - 2 Laplacian operator - J(A, B) Jacobian operator  相似文献   

4.
A formula to determine the local magnitude (ML) following Richters original definition was empirically derived for the Korean Peninsula. A total of 1,644 digital seismograms from 142 Korean earthquakes that occurred from 1997 to 2000 were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response to be appropriate for the original definition of ML. Then, the zero-to-peak amplitude was measured in millimeters on the synthetic Wood-Anderson seismogram. Multiple regression analysis was conducted to determine distance and station correction terms for the measured peak amplitudes. The best-fit solution for ML yielded the following formula for the Korean Peninsula:where A() and S denote the peak amplitude on the synthetic Wood-Anderson seismogram at distance and the station correction term, respectively. Note that the second term, distance correction, was adjusted with Richters ML, taking into consideration attenuation differences between the Korean Peninsula and southern California, where Richter originally introduced ML. On average, the magnitudes determined in this study are nearly the same as those determined by the Korea Institute of Geoscience and Mineral Resources (KIGAM), but are larger than those of the Korea Meteorological Administration (KMA) by as much as 0.36.  相似文献   

5.
We consider a general stochastic branching process,which is relevant to earthquakes as well as to many other systems, and we study the distributions of the total number of offsprings (direct and indirect aftershocks in seismicity) and of the total number of generations before extinction. We apply our results to a branching model of triggered seismicity, the ETAS (epidemic-type aftershock sequence) model. The ETAS model assumes that each earthquake can trigger other earthquakes (aftershocks). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake (fertility), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime in which the distribution of fertilities is characterized by a power law ~1/1+. For earthquakes we expect such a power-distribution of fertilities with =b/ based on the Gutenberg-Richter magnitude distribution ~ 10–bm and on the increase ~ 10–m of the number of aftershocks with the mainshock magnitude m. We derive the asymptotic distributions pr(r) and pg(g) of the total number r of offsprings and of the total number g of generations until extinction following a mainshock. In the regime < 2 for which the distribution of fertilities has an infinite variance, we find This should be compared with the distributions obtained for standard branching processes with finite variance. These predictions are checked by numerical simulations. Our results apply directly to the ETAS model whose preferred values =0.8–1 and b=1 puts it in the regime where the distribution of fertilities has an infinite variance. More generally, our results apply to any stochastic branching process with a power-law distribution of offsprings per mother  相似文献   

6.
We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment isM o =3.4×1020 Nm, which is consistent with the value determined from long-period surface waves,M o =3.7×1020 Nm. The average rise time of dislocation is determined to be 10 s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault widthW=50 km, we obtained the dislocationD=1.3 m. From andD the dislocation velocity isD=D/0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop =1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2E s /M o , where andE s are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than . The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion.  相似文献   

7.
We describe slip-rate dependent friction laws based on the Coulomb failure criteria. Frictional rate dependence is attributed to a rate dependence of cohesionc and friction angle . We show that differences in the stress states developed during sliding result in different Coulomb friction laws for distributed shear within a thick gouge layer versus localized shear within a narrow shear band or between bare rock surfaces. For shear within gouge, shear strength is given by =c cos + n sin, whereas for shear between bare rock surfaces the shear strength is =c cos + n tan, where and n are shear and normal stress, respectively. In the context of rate-dependent Coulomb friction laws, these differences mean that for a given material and rate dependence of the Coulomb parameters, pervasive shear may exhibit velocity strengthening frictional behavior while localized shear exhibits velocity weakening behavior. We derive from experimental data the slip-rate dependence and evolution ofc and for distributed and localized shear. The data show a positive rate dependence for distributed shear and a negative rate dependence for localized shear, indicating that the rate dependence ofc and are not the same for distributed and localized shear, even after accounting for differences in stress state. Our analysis is consistent with the well-known association of instability with shear localization in simulated fault gouge and the observation that bare rock surfaces exhibit predominantly velocity weakening frictional behavior whereas simulated fault gouge exhibits velocity strengthening followed by a transition to velocity weakening with increasing displacement. Natural faults also exhibit displacement dependent frictional behavior and thus the results may prove useful in understanding the seismic evolution of faulting.  相似文献   

8.
Summary The distribution of radioactive(Th, U, K), major and selected trace(Rb, Sr, Ba, Y, Zr, V, Cr, Ni) elements of granulites from the Saxonian Granulite Complex was studied. Similarly to the South Bohemian granulites, the Saxonian granulites can be divided according to the contents of their major and trace elements into two main groups, groupA containing mostly acid and subacid granulites (K 2 O>2.5%, SiO 2 >68%), and groupB containing mostly intermediate and basic granulites (K 2 O<2.5%, SiO 2 <68%). Statistically significant differences between groupsA andB were found for all major oxides and several trace elements(Rb, V, Cr, Ni). The Saxonian granulites follow the same calc-alkaline trend as the South Bohemian, granulitesA being placed mostly in the rhyolite field and granulitesB mostly in the dacite, andesite and basalt fields of this trend. The investigated granulites are characterized by a considerable scatter ofTh andU contents accompanied by very variableTh/U ratios; theTh andU concentrations of granulitesA are substantially lower than is usual for rocks of corresponding acidity.
¶rt;a an¶rt;u a¶rt;uamu(Th, U, K) u ua ¶rt;u(Rb, Sr, Ba, Y, Zr, V, Cr, Ni) m aum n¶rt;a aaum na. naa, m u¶rt;aum n uu aam n aaum u ¶rt;u am aua, u u uu. aum n u uu ma a¶rt;um ¶rt; ¶rt;nn; nnA nua¶rt;ama a au¶rt; u au¶rt;aum (K 2 O>2,5%, Si O 2 >68%), nnB ¶rt;u u aum (K 2 O<2,5%, SiO 2 <68%). ¶rt; muunnau mm mamumuu m au ¶rt; a u u ¶rt; m ¶rt;u m(Rb, V, Cr, Ni). auaum n¶rt;¶rt;m um- m¶rt; a u -uaum;aumA a¶rt;ma a uum n, uaumB a a ¶rt;aum, a¶rt;um u aam n m m¶rt;a. ¶rt;aum — u unnA — aamum uu ¶rt;au da¶rt;uamu mTh uU.
  相似文献   

9.
The effect of randomly distributed cracks on the attenuation and dispersion ofSH waves is theoretically studied. If earthquake ruptures are caused by sudden coalescence of preexisting cracks, it will be crucial for earthquake prediction to monitor the temporal variation of the crack distribution. Our aim is to investigate how the property of crack distribution is reflected in the attenuation and dispersion of elastic waves.We introduce the stochastic property, in the mathematical analysis, for the distributions of crack location, crack size and crack orientation. The crack size distribution is assumed to be described by a power law probability density (p(a) a – fora minaa max according to recent seismological and experimental knowledge, wherea is a half crack length and the range 13 is assumed. The distribution of crack location is assumed to be homogeneous for the sake of mathematical simplicity, and a low crack density is assumed. The stochastic property of each crack is assumed to be independent of that of the other cracks. We assume two models, that is, the aligned crack model and the randomly oriented crack model, for the distribution of crack orientation. All cracks are assumed to be aligned in the former model. The orientation of each crack is assumed to be random in the latter model, and the homogeneous distribution is assumed for the crack orientation. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.We observe the following features common to both the aligned crack model and the randomly oriented crack model. The attenuation coefficientQ –1 decays in proportion tok –1 in the high frequency range and its growth is proportional tok 2 in the low frequency range, wherek is the intrinsic wave number. This asymptotic behavior is parameter-independent, too. The attenuation coefficientQ –1 has a broader peak as increases and/ora min/a max decreases. The nondimensional peak wave numberk p a max at whichQ –1 takes the peak value is almost independent ofa min/a max for =1 and 2 while it considerably depends ona min/a max for =3. The phase velocity is almost independent ofk in the rangeka max<1 and increases monotonically ask increases in the rangeka max>1. While the magnitude ofQ –1 and the phase velocity considerably depend on the orientation of the crack in the aligned crack model, the above feature does not depend on the crack orientation.The accumulation of seismological measurements suggests thatQ –1 ofS waves has a peak at around 0.5 Hz. If this observation is combined with our theoretical results onk p a max, the probable range ofa max of the crack distribution in the earth can be estimated for =1 or 2. If we assume 4 km/sec as theS wave velocity of the matrix medium,a max is estimated to range from 2 to 5 km. We cannot estimatea max in a narrow range for =3.  相似文献   

10.
Lunar and solar atmospheric tidal oscillations have been determined with reasonable accuracy from a ten-year record of hourly mercury-barometer readings, corrected to mean-sea-level, at Rarotonga (Cook Islands), 21.2°S. For the lunar semidiurnal tide, the annual determination shows an amplitude (56 b) slightly lower and a phase (51°) much smaller than the values (58 b, 72°) that would be derived, for the position of Rarotonga, from the spherical harmonic analysis given byHaurwitz andCowley (1969). The seasonal variation of this oscillation, as given by the monthly and J, E, D values, shows most of the characteristic features found in world-wide determinations. In particular, the near equality of the J, D amplitudes at Rarotonga tends to support theHaurwitz andCowley (1969) suggestion of negative J-D values in southern middle latitudes. For the solar tides, the semidiurnal and terdiurnal oscillations at Rarotonga are similar to those found at other stations in the south-west Pacific region. However, for the diurnal oscillation, the annual amplitude (232 b) is only about half the value (465 b) indicated for the position of Rarotonga by the world maps of theS 1(p) annual harmonic coefficients given byHaurwitz (1965). It thus seems likely that the relatively small area of lowS 1(p) annual amplitude in the eastern part of the south Pacific, as indicated by these maps, is much more extensive than formerly supposed.  相似文献   

11.
Riassunto L'A. mostra corne dal metodo più semplice di misura di rcsistività d'un suolo del polo singolo, si possano dedurrc tutti gli altri (Wenner, Schlumberger, ecc). CiÒ dà la possibilità di risalire immediatamente dai grafici s di un dispositivo a quelli di un altro. L'A., dopo rettificato recenti valutazioni del metodo dei due punti, rimuove la pretesa da altri formulata di porre gerarchie nei dispositivi di misure s .
Summary The Author shows how departing from simplest method of the ground resistivity measurement with the single pole can be deduced all another methods (Wenner, Schlumberger, etc.). That gives the practical possibility to pass immediately the s graphics of one arrangement to these of other types of arrangement. After having rectified recently mades evaluations about the two points method, the Author removes the requirements made from other side to graduate the s measuring arrangements.
Zusammenfassung Der Verfasser zeigt wie man von der einfachsten Methode der Widerstandsmessung eines Bodens mit Einzelpol alle anderen Methoden (Wenner, Schlumberger, usw.) ableiten kann. Dadurch hat man die praktische Möglichkeit, von den s Diagrammen einer Anordnung sofort auf jene anderer Anordnungen überzugehen. Nach Richtigstellung von kürzlich geäusserten Ansichten über die Zweipunktmethode, beseitigt der Verfasser die von Anderen gestellten Ansprüche, die s Messanordnungen vermeintlichen Vorzügen nach staffeln zu wollen.

Relazion e presentata il 5 Aprile 1956 alla Quarta Assemblea Generale dcllaSocietà Italiana di Geofisica e Meteorologia (Genova: 5–8 Aprile 1956).  相似文献   

12.
Summary The primary scattering of atmospheric haze is computed by modification of an approximative method evolved byde Bary, basing on skylight measurements carried out on the Musalla, a mountain of 3000 m height in Bulgaria, at various altitudes of the sun and in different horizontal circles at a wavelength of 450 nm. This measured total radiation is reduced by the radiation induced by the scattering at molecules as well as by secondary or multiple scattering at turbidity aerosol. The single scattering of the atmospheric haze thus computed is discussed for various assumed Linke turbidity factors.The concluding deductions relate to a comparison of haze scattering functions with theoretical scattering functions, the results attained agreeing closely with superimposed logarithmic Gaussian distributions and only partly with the scattering functions computed byBullrich. These deductions prove optically the increase of larger particles (r 00.64 m) during forenoon. The analysis of the scattering functions conductes to a shortage of particles withr 0=0.2 m in agreement with other investigations.
Zusammenfassung In Abwandlung einer vonde Bary angegebenen Approximationsmethode wird die Primärstreuung des atmosphärischen Dunstes berechnet. Zugrundegelegt werden Himmelsllichtmessungen, die auf dem etwa 3000 m hohen Mus Alla in Bulgarien bei verschiedenen Sonnenhöhen und in verschiedenen Horizontalkreisen bei einer Wellenlänge von 450 nm durchgeführt wurden. Von dieser gemessenen Gesamtstrahlung werden die Anteile substrahiert, die durch Streuung an Molekülen sowie durch zwei-oder mehrfache Streuung an Trübungsaerosol hervorgerufen werden. Die so berechnete Einfachstreuung des atmosphärischen Dunstes wird für verschiednee angenommene Linke'sche Trübungsfaktoren diskutiert.Abschließend werden die Dunststreufunktionen mit theoretischen Streufunktionen verglichen, wobei eine gute Übereinstimmung mit überlagerten logarithmischen Gauß-Verteilungen und nur teilweise mit vonBullrich berechneten Streufunktionen erzielt wurde. Es kann dabei optisch die Zunahme großer Teilchen (r 00,64 m) im Laufe des Vormittags gezeigt werden. Die Analyse der Streufunktionen führt zu einem Fehlen von Teilchen mitr 0=0,2 m in Übereinstimmung mit anderen Untersuchungen.
  相似文献   

13.
Summary Measuring, with the aid of two filters, the instantaneous intensity of the solar radiation in two wave lengths ( B = 0.44 , R = 0.64 ) by means of a sun photometer designed byVolz, we carried out determinations of the decadic turbidity coefficientB (=0.5 ) and the wave length exponent of the haze extinction for Mexico City. Observations were made for almost two and a half years (1960 to 1962 period). A seasonal size distribution in both parameters was found. Although the data thus obtained are provenient of a contaminated atmosphere, comparison of our data is made with those found for higher latitudes ofÅngström, Schüepp andVolz. The height of the homogeneous haze layerH D was calculated showing pronounced variations for a given wind direction. The maximum and minimum values ofB enable us to get, by the first approximation, the aerosol size distribution ofJunge for our latitudes. However, for exceptional very clear days having maximum actinometric intensity of the solar radiation the sensitivity of the microamperimeter in theVolz sun photometer fails.  相似文献   

14.
A theoretical model is presented which allows computing the efficiency with which aerosol particles of radius 0.1r10 m are collected by simple ice crystal plates of radius 50a c 640 m in air of various relative humidities, temperatures and pressures. Particle capture due to thermophoresis, diffusiophoresis and inertial impaction are considered. It is shown that the capture efficiency of an ice crystal in considerably affected by phoretic effects in the range 0.1r1 m. For aerosol particles ofr>1 m the efficiency is strongly controlled by the flow field around the crystal and the density of the aerosol material. Trajectory analysis also predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretica results are found to agree satisfactorily with the laboratory studies presently available. Comparison shows that for the same pressure, temperature and relative humidity of the ambient air ice crystal plates are better aerosol particle scavengers than water drops.  相似文献   

15.
Simple models are discussed to evaluate reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating. By comparing various single well and doublet production schemes, it is shown that reinjection of heat depleted water greatly enhances heat recovery and reservoir lifetime, and can be optimized for maximum heat production. It is concluded that geothermal aquifer production should be unitized, as is already done in oil and gas reservoirs.Nomenclature a distance between doublets in multi-doublet patterns, meters - A area of aquifer at base temperature, m2 drainage area of individual doublets in multidoublet patterns, m2 - D distance between doublet wells, meters - h aquifer thickness, meters - H water head, meters - Q production rate, m3/sec. - r e aquifer radius, meters - r w well radius, meters - R g heat recovery factor, fraction - S water level drawdown, meters - t producing time, sec. - T aquifer transmissivity, m2/sec. - v stream-channel water velocity, m/sec. - actual temperature change, °C - theoretical temperature change, °C - water temperature, °C - heat conductivity, W/m/°C - r rock heat conductivity, W/m/°C - aCa aquifer heat capacity, J/m3/°C - aCr rock heat capacity, J/m3/°C - WCW water heat capacity, J/m3/°C - aquifer porosity, fraction  相似文献   

16.
Faulting and seismicity in the upper continental crust require considerable differential stresses. Application of experimentally developed friction, fracture and flow laws shows that high differential stresses can only exist in the uppermost crust. Direct hydraulic fracturing measurements in deep boreholes seem to support this rock mechanics conclusion. The experimental data base presently consists of approximately 500 hydrofrac tests conducted in about 100 boreholes at about 30 different geographical locations. To illustrate the variation of measured stresses with depth, the data are expressed as dimensionless horizontal stresses in the formS H,h/Sv=(/z)+, whereS v=gz Extrapolation of the experimental data to greater depth shows that the minor horizontal stress approaches the valueS h/Sv=0.5 which limits friction on wet faults, and that the major horizontal stress approaches a value close toS H/Sv=1 at rather shallow depth (5 to 10 km.). This limits faulting and seismicity in most of the upper crust to either strike-slip or normal faults. The lower boundary for seismicity is mainly dependent on tectonic strain accumulation and rock creep at the environmental conditions at depth.  相似文献   

17.
In a previous paper (Makropoulos andBurton, 1983) the seismic risk of the circum-Pacific belt was examined using a whole process technique reduced to three representative parameters related to the physical release of strain energy, these are:M 1, the annual modal magnitude determined using the Gutenberg-Richter relationship;M 2, the magnitude equivalent to the total strain energy release rate per annum, andM 3, the upper bound magnitude equivalent to the maximum strain energy release in a region.The risk analysis is extended here using the part process statistical model of Gumbel's IIIrd asymptotic distribution of extreme values. The circum-Pacific is chosen being a complete earthquake data set, and the stability postulate on which asymptotic distributions of extremes are deduced to give similar results to those obtained from whole process or exact distributions of extremes is successfully checked. Additionally, when Gumbel III asymptotic distribution curve fitting is compared with Gumbel I using reduced chi-squared it is seen to be preferable in all cases and it also allows extensions to an upper-bounded range of magnitude occurrences. Examining the regional seismicity generates several seismic risk results, for example, the annual mode for all regions is greater thanm(1)=7.0, with the maximum being in the Japan, Kurile, Kamchatka region atm(1)=7.6. Overall, the most hazardous areas are situated in this northwestern region and also diagonally opposite in the southeastern circum-Pacific. Relationships are established between the Gumbel III parameters and quantitiesm 1(1),X 2 and , quantities notionally similar toM 1,M 2 andM 3 although is shown to be systematically larger thanM; thereby giving a physical link through strain energy release to seismic risk statistics. Inall regions of the circum-Pacific similar results are obtained forM 1,M 2 andM 3 and the notionally corresponding statistical quantitiesm 1(1),X 2 and , demonstrating that the relationships obtained are valid over a wide range of seismotectonic enviroments.  相似文献   

18.
The Drude law (molecular refraction) for the temperature radiation in a monoatomic model of the Earth's mantle is derived. The considerations are based on the Lorentz electron theory of solids. The characteristic frequency (or eigenfrequency) of independent electron oscillators (in energy units, ) is identified with the band gapE G of a solid. The only assumption is that solid material related to the Earth's mantle has the mean atomic weight A21 g/mole, and its energy gap (E G) is about 9 eV. In this case the value of molecular refraction (in cm3/g) is (n 2–1)/=0.5160.52, where andn are the density and the refractive index at wavelength D=0.5893 m (sodium light), respectively. The average molecular refraction of important silicate and oxide minerals with A21, obtained byAnderson andSchreiber (1965) from laboratory data, is , where denotes the mean arithmetic value calculated from three principal refractive indices of crystal. For the rock-forming minerals with 19A<24 g/mole the new relation was found byAnderson (1975).  相似文献   

19.
Aftershocks or swarms indicate increase of the flow intensity in the vicinity of the initial earthquakes. By normalizing their number according to the dynamic range of the standard frequency magnitude distribution the increase or positive aftereffect property of the initial earthquakes can be compared for different magnitude intervals, periods of time or regions. After applying accurate formal algorithm of aftershock identification it is possible to study negative aftereffect of the main events (nonaftershocks) in the catalog.Negative aftereffect means decrease of the probability of successive events in a time-space vicinity of the main event, when the aftershocks are over. The negative effect is the most important part of the seismic cycle and seismic gaps approach. Global statistical test give high confidence level for the relative decrease in intensity of the flow of the events withM7 in the first 20–25 years after the events withM8 in their 1o-vicinities in the total time period under study of approximately 60 years. The decrease approximates 32% of the undisturbed intensity of the flow ofM>7 events in the vicinities.Self-similar negative aftereffect was observed 3–7 years after 6M<7 events, it totals approximately 18% of the undisturbed intensity. Another type of self-similarity of seismic regime, with respect to the negative aftereffect, is the decrease of probabilities of aftershocks with large magnitudes in aftershock sequences. When we have adequate dynamic range in the catalog for the study of this property, for example, for main events withM7 in the catalog with low cut-off limitM=4, the statistical significance of the negative aftereffect is clear. However, the absolute value of the effect is also rather small, about 10%, which means that in 90% of the cases the aftershock sequences do not experience lack of energy due to the main shock energy release and follow a standard magnitude distribution for earthquakes in the entire catalog.The small values of the negative aftereffect apparently indicate partial stress relase by earthquakes and may explain short recurrence time intervals after major earthquakes observed periodically in different places.  相似文献   

20.
Summary The accuracy of wave field extrapolation is studied with respect to the discretization of field data and integral extrapolator. Assuming a far-field approximation of the Rayleigh-Sommerfeld solution for a two-dimensional scalar wave equation, the minimum and the maximum transmitted frequency are expressed as functions of the sampling intervals t, x, and the half-width x0 and angle a of the migration aperture. The theoretical limitation of the transmitted frequency band is tested on numerical examples.
aamuam mm manuu auumu m ¶rt;umuauu n u uma manu nama. ¶rt; u uma u -¶rt;a ¶rt; ¶rt; a au, ¶rt; nuuuu ¶rt;a n mu ¶rt; uua u aua n¶rt;aa amm a uu m a -nmam ¶rt;umuauu t u , nuu 0 u a a uau anm. mu n¶rt;u amm ¶rt;uanaa mmua a u nua.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号