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1.
Summary Distribution of compressional-wave velocities in the mantle is determined fromdT/d measurements using the Uppsala seismograph array station (UPSAS). Short-period vertical-component seismograms from 181 events in the epicentral distance range 16°–100° have been used. The velocity distribution shows anomalous variations at depths of 750, 1500, 1800, 2300 and 2550 km. Evidence of lateral heterogeneity beneath the northern part of the Asian continent, in the depth range 1700–2300 km, is discussed. Computed travel times, based on this velocity-depth relation, are tested by an examination of travel-time residuals from the Long Shot and Milrow explosions on Amchitka, Aleutian Islands.  相似文献   

2.
Summary Relative arrival times at the Uppsala tripartite seismograph array station are used to determinedT/d and ray azimuth for some 200 compressional phases. Corrections, although very small, are applied for station elevations, telephonic transmission delays and array geometry. The computeddT/d and ray azimuths are further corrected to remove the effect of lateral heterogeneity immediately beneath the array station. Errors indT/d and azimuth are considered from a partly theoretical, partly empirical approach. They amount to about 0.18 sec/deg indT/d and 1.6° in azimuth. Standard deviations in epicentral locations are empirically determined to be about 2° due to slowness error and less than 1.5° due to azimutherror; or about 250 km overall. These figures compare favourably with other, more costly, arrays.  相似文献   

3.
Summary The average dependence of the calibration function q and the travel-time residuals t on the depth and distance of the source has been derived for individual branches of PKP waves using earthquakes from the SW Pacific Ocean (distance interval 147°–159°, depths 0–700 km). The analysis of very distant shocks of all depths according to the regional PKP travel time tables can be completed by the magnitude determination.  相似文献   

4.
Radial velocity anomalies in the lower mantle that give rise to triplications in the travel-time curve for short-periodP waves will produce arrivals havingdT/d values that differe by roughly 0.2–0.5 s/deg. The first two arrivals associated with such triplications will be separated by less than one second over a distance range of 4°–10° they may not, therefore, be separable visually on single seismograms, so that their presence can only be inferred from some measurable property that depends on their mutual interference. If there are lateral variations in the regions of anomalous velocity gradients, the interfering signals will also have different azimuths of arrival. Using two synthetic wavelets we have investigated the effect of interference on bothdT/d and azimuth measurements at the Yellowknife Array. We found that if the interfering pulses have a dominant frequencyv, there is a range of time separations (0.30/v0.55/v) over which the measureddT/d and azimuth values may fluctuate by much more than the differences indT/d and azimuth between the interfering signals. We have evaluated the following empirically defined functions for three different primary signals, and for three different relative amplitudes of the interfering signals:f (t), the drift function, which expresses how the measured slownesses,p, and azimuths, , differ from the slownesses and azimuths of the primary wavelets; f(), the range function, which describes the behaviour of the upper and lower bounds ofp and as a function of the difference in arrival times of the signals, andf , studied the properties of these functions, and have outlined how these properties provide criteria based on the numerical and statistical characteristics of the arrival vectors, and on the waveform of the signal that will enable small radial velocity anomalies to be more clearly delineated.Contribution No. 863 from the Earth Physics Branch.  相似文献   

5.
The arrival at the Yellowknife Array (YKA) of closely-spaced P-waves having slightly different values ofdT/d, azimuth, and amplitude has been simulated using synthetic 1 Hz wavelets. Adaptive-processing determinations of apparent slowness and azimuth show a remarkable pattern of fluctuations with time for varying separations of the interfering pulses. In the critical separation range 0.30 to 0.55 s, these fluctuations greatly exceed the differences in arrival vectors of the primary wavelets themselves. Observation of characteristic interference patterns on real array seismograms might permit the identification of triplications associated with radial velocity anomalies in the lower mantle. Processed YKA seismograms for three events at distances close to 90° are presented, which, despite apparently simple P onsets illustrate the pattern of drift indT/d expected for such a triplication.Contribution from the Earth Physics Branch No. 648.  相似文献   

6.
Summary Among various trial models ofP-wave travel times, there exists at least one model which best predicts the times of first arrivals from a certain region at a set of recording stations even if no attempt is made to correct the travel-time standards against known station errors and source bias. In teleseismic distance range (25°100°) and surface-focus case, the possibility of statistically establishing which of the twoP models, viz. Jeffreys-Bullen and Herrin, is more appropriate for each of the four source regions, viz. Southern Nevada, Aleutian Islands, Eastern Kazakh and Novaya Zemlya, is discussed in this paper. Data corresponding to a set of underground explosions from these regions form the basis of such an analysis. The Herrin model is found to be better applied to Aleutian Islands region while the Jeffreys-Bullen model seems more appropriate for each of the remaining three regions.As a result of the study of the travel-time models, numerical estimates of space and time corrections pertaining to the above mentioned regions, based on the most appropriate model and directly applicable to the computed source parameters, are obtained. On applying these corrections, the size of source location error ellipse and the source-time error reduce to very small representative values, viz. 4 km×6 km (area 75 km2) and ±0.2 sec respectively.  相似文献   

7.
Summary Numerous observations of teleseismicPn phases have been made on short-period seismograph records in Sweden. The observations now cover the distance range of 2360 to 4670 km, that is about six times the distance range reported in an earlier paper. The propagation paths are exclusively confined to the Russian platform, which means that a very homogeneous structure is required for the propagation ofPn to large distances. The relation between travel-timet (sec) and distance along the earth's surface (km) ist=: (8.20±0.12)+(0±6), based on 30 observations. The real velocity ofPn (underneath Moho) is 8.15±0.12 km/sec and the corresponding Poisson's ratio, obtained by combination with the teleseismicSn velocity (4.72 km/sec), is 0.248. These are averages for the Russian platform. The problem of the relative occurrence ofPn andSn in teleseismic records is briefly discussed.  相似文献   

8.
Summary About 360 seismic events from almost all directions recorded at 13 seismological observatories in Sweden and Finland have been investigated. The depths of these events vary from the surface to 650 km and the epicentral distances from 9° to 119° with fairly even coverage. The two most separated stations in this array are about 15° apart (Karlskrona in Sweden and Kevo in Finland). Comparison of observed travel-time curves and their slope with those ofJeffreys-Bullen andHerrin are made. Generally, the observed travel times are earlier than theJeffreys-Bullen times and later than theHerrin ones. Path and depth effects on residuals with respect to the two given tables are studied, and station corrections and source corrections are estimated. Global and regional travel-time tables of theP-wave have been constructed for this network of stations.On leave from Geophysical Institute, Tehran University, Tehran, Iran  相似文献   

9.
Summary Mean directions of magnetization (29 normal and 31 reversed) were recorded for 60 magmatic localities of middle Miocene age from the Börzsöny Mountains (Hungary). The overall mean direction of RM, irrespective of polarity, isD=0,9°;I=59,8°; withk=8,3 and 95=6,8°. The coordinates of the corresponding geomagnetic north pole are =82,7°, A=193,8 with p=7,7° and m=10,2°.  相似文献   

10.
Summary This paper is an attempt towards determination of station adjustments for Shillong and Delly Observatories from considerations of a large number ofP n residuals. Station adjustments toJeffreys-Bullen travel time tables for Shillong comes to about 4 seconds and for Delhi 2 seconds respectively for 20°.  相似文献   

11.
The active faults near Tehran are capable of producing Mw magnitudes of 6.62?C7.23; at epicentral distances of 25?km from the active faults, and Mw?=?7.23, the peak ground horizontal acceleration, PGH, is between 386 and 730?cm/s2 and peak ground vertical acceleration, PGV, is between 192 and 261?cm/s2; the historic earthquake of the fourth century BC, Mw?=?7.16 produced the highest estimated PGH acceleration in Tehran, between 254 and 479?cm/s2 and PGV acceleration between 127 and 173?cm/s2. Earthquakes from 1909 to 2008, within 300?km from Tehran, are used for calculation of magnitude frequency relation, and results are applied to estimate PGH and PGV accelerations as a function of magnitudes for a set of fixed epicentral distance and site conditions; also as a function of epicentral distances for a set of fixed magnitudes and site conditions. Poisson??s distribution is used for probability calculation of PGH and PGV accelerations for several exposure times, site conditions and epicentral distances; accelerations with very high probability, near 1, are presented. At an epicentral distance of 10?km and exposure time of 450?years, in the northern part of Tehran, close to Mosha and the Northern Tehran faults, PGH acceleration is 800?C420?cm/s2 and PGV is 400?C220?cm/s2 with high probability. At an epicentral distance of 25?km and 1,000?years exposure time, PGH is 610?C320?cm/s2 and PGV is 310?C160?cm/s2 with high probability, where larger values are for soft soil and smaller values are for hard rock.  相似文献   

12.
The main shock of the West-Bohemian earthquake swarm, Czechoslovakia, (magnitudem=4.5, depthh=10 km) exhibits an irregular areal distribution of macroseismic intensities 6° to 7° MSK-64. Four lobes of the 6° isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre. This distribution can be explained by the energy flux of the directS wave generated by a circular source, the hypocentral location and focal mechanism of which are taken from independent instrumental studies. The theoretical intensity, which is assumed to be logarithmically proportional to the integrated squared ground-motion velocity (i.e.,I=const+log v 2 (t)dt), fits the observed intensity with an overall root-mean-square error less than 0.5°. It is important that the present intensity data can also be equally well explained by the isotropic source. The fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region. The results encourage a broader application of the simple modelling technique used.  相似文献   

13.
The January 17, 1994 Northridge earthquake (Mw = 6.7, 34.213° N, 118.537° W, depth = 18.4 km) was recorded extensively in the immediate source region by strong, ground motion accelerometers. The resulting seismograms show complex S wave patterns. Nevertheless, visual correlations of the strong-ground-motion velocity and displacement time-histories clearly identify two significant wave pulses: a secondary S pulse (called S2) arriving 3–5 seconds after the initial S wave pulse (called S1). A plausible assumption is that these phases are generated at areas on the rupturing thrust fault that experienced especially large slip. Conventional travel-time computations, relating the relative arrival times between the onsets of the primary S1 and secondary S2 phases, yield a hypocenter of the initiation point, constrained to a independently etimated fault plane, of the secondary wave source (called H2) at 34.26°N, 118.54° W, with a depth of 14.1 km; the 68% confidence error in depth is 1.3 km. This location is about 6 km up-dip and north from the estimated hypocenter, on the fault plane of the initial principal seismic source (called H1). The seismic moment for both the initial H1 and secondary source H2 was estimated from the SH displacement pulse. Values averaged over eight stations were 8.61 ± 9.56 × 1024 dyne-cm and 2.49 ± 2.31 × 1025 dyne-cm respectively. Reasons why the sum of the two seismic moments is smaller than the total estimated seismic moment of 1.2 × 1026 dyne-cm for the Northridge earthquake are discussed. The location of the initiation point of a second source H2 in the Northridge thrust faulting is consistent with independent computations of the fault slip pattern. The estimated stress drop for the initial and secondary sources are 1 = 150 ± 15 bars and 2 = 110 ± 11 bars, respectively.  相似文献   

14.
Summary Regional variations have been indicated in the slope of theP travel-time curve in the shadow zone of the earth's core. Further study is needed since the uncertainties of the slope are large, especially for the observations from North American stations. There is no significant difference between themean slope of theP travel-time curve in the 95°102.9 range and those obtained byJeffreys, andJeffreys andBullen. However, there is a significant difference between themean slope in the 103° to 135° range as obtained in this study, and those obtained byJeffreys andBullen, and in a later revision byJeffreys. Themean travel-time curve ofP in the shadow zone of the earth's core should be lowered. A trial travel-time table is given with amean slope of 4.41 sec/deg. This table is in close agreement with the times obtained byGutenberg andRichter, and with the trial travel-times ofLehmann. Under the assumption of diffraction the longitudinal wave velocity has been determined to be 13.7 km/sec at the core-mantle boundary.This paper was presented at the Annual Meeting of the Seismological Society of America Reno, Nevada, 1966.  相似文献   

15.
Zusammenfassung In einer früheren Mitteilung wurde berichtet, daß in der astronomischen Navigation alle Höhendifferenzen (h) eines bestimmten Koppelortes einen Kreis beschreiben (Löhr, Dt. Hydrogr. Z. Bd. 11, Heft 1, 35, 1958).Im folgenden wird dieser geometrische Ort näher untersucht und h-Kreis benannt. Seine wesentliche Eigenschaft besteht darin, daß jede Sehne des Kreises, die vom Koppelort aus unter einem bestimmten Azimutwinkel gezogen wird, die Höhendifferenz des Gestirnes darstellt, das im Zeitpunkt der Beobachtung sich auf dem entsprechenden Azimutgroßkreis befand.Da die Längen- und Breitendifferenz ebenfalls Höhendifferenzen von Gestirnen — die einen Azimut von 90° (270°) und 0° (180°) nachweisen — darstellen, so ergibt sich daraus, daß die durch Konstruktion des h-Kreises entstandenen Schnittpunkte mit dem Meridian und Breitenparallel des Koppelortes die wahre Länge und Breite des Ortes des Beobachters angeben.
The h-circle and its practical use in determining the longitude and latitude of a point of observation
Summary An earlier report (Löhr, Dt. Hydrogr. Z., Vol. 11, Issue 1, p. 35, 1958) dealing with astronomical navigation, establishes that all altitude differences (h) from any given dead reckoning describe a circle.The following report examines this locus which is termed the h-Circle. The h-circle is characterized by the fact that any chord drawn from the dead reckoning at a certain azimuthal angle will represent the difference in altitude of that celestial body which at the time of observation was located in the corresponding azimuthal great circle.The longitude and latitude differences also represent the altitude differences of celestial bodies with azimuth 90° (270°) and 0° (180°). Hence, it follows that the true longitude and latitude of the observer's position are indicated by the points where the meridian and the latitude parallel of the dead reckoning are intersected by the h-circle.
Le h-cercle et sa mise en pratique pour la détermination de la longitude et de la latitude du lieu d'observation
Résumé Dans une communication précédente il a été rapporté qu'en navigation astronomique toutes les différences d'hauteur (h) d'un certain point estimé font un cercle (Löhr, Dt. Hydrogr. Z. Bd. 11, Heft 1, 35, 1958).Ci-après ce lieu géométrique sera examiné plus près et sera nommé le cercle h. Sa qualité essentielle réside dans le fait que chaque corde du cercle, tirée du point estimé sous un angle azimutal déterminé, constitue la différence d'hauteur de l'étoile, qui au moment de l'observation se trouva au grand cercle azimutal correspondant.Vu que des différences en longitude et en latitude forment également des différences d'hauteur des étoiles- qui indiquent un azimut de 90° (270°) et 0° (180°)-, il en ressort, que les points d'intersection entre les coordonnées géographiques du point estimé et le h-cercle, indiquent la vraie longitude et latitude du lieu de l'observateur.
  相似文献   

16.
Summary The method of the automated computation of the gravimetric deflections of the vertical and of the geoidal heights for the European region is described. The work was carried out during the period 1986–1988 by the Topographic Service of the Czechoslovak Army. The computation applies to 20 sheets of the international map 1:1 000 000 (total area of =16c, =30c - see Fig. 1). The mean values of the free-air anomalies for each surface element =5, =7.5, approximately 9 × 9 km, were used with radius of integration of 300 km.  相似文献   

17.
From the events synthesized from the one-dimensional dynamical mass-spring model proposed byBurridge andKnopoff (1967), the relation between rupture length and earthquake momentM is studied for various model parameters. The earthquake moment is defined to be the total displacement of a connected set of mass elements which slide during an event. A parameter stiffness ratios is defined as the ratio of the spring constant between the two mass elements to that between one mass element and the moving plate. The velocity-dependent friction law (including weakening and hardening processes) is taken to control the sliding of a mass element. The distribution of the breaking strengths over the system is considered to be a fractal function. The cases for severals values and different velocity-dependent friction laws with different decreasing ratesr w of the frictional force with sliding velocity are studied numerically. The weakening process of the frictional force from the static one to the dynamic one obviously affects theM– relation. Meanwhile, a rapid weakening process rather than a slow weakening process can result in aM– relation, which is comparable to the observed one. Although an increase in thes value can yield an increase in the upper bound of the value and the number of events with largeM and values, the scaling of theM– relation is not affected by the change of thes value. For the cases in this study, the theoretical –M relations for small events withM<1 are almost in the form: M 1/2, while those for large events withM>1 have a scaling exponent less than but close to 1. In addition, the fractal dimension, the friction drop ratio and the roughness of the distribution of the breaking strengths over the fault surface are the minor parameters influencing the –M relation. A comparison between the theoreticalM– relation and the observed one for strike-slip earthquakes shows that for large events the theoreticalM– relation is quite consistent with the observed one, while for small events there is a one-order difference in the two relations. For the one-dimensional model, the decreasing rate of the dynamic frictional force with velocity is the main factor in affecting the characteristic value of the earthquake moment, at which the scaling of theM– relation changes.  相似文献   

18.
The static displacement field of the Athens 1999 earthquake has been numerically modeled by a BEM method and analysed from SAR interferometry images with compatible results: (a) for a fault that reaches the surface the subsidence field coincides with the hangingwall domain of the Fili neotectonic normal fault with maximum amplitude, d max, 5.5–7 cm, which is consistent with the possibly co-seismic displacement of 6–10 cm observed in the field, the average fault dislocation of 5–8 cm found by the application of circular source models, and the displacement up to 6 cm predicted by empirical relations between magnitude and displacement; the field of uplift covers the footwall domain of the fault with d max1.5 cm;d gradually decreases with distance from the fault at a gradient of 0.4 cm/km, (b) for a blind fault d max is only 1.8 and 0.3 cm in the hangingwall and footwall, respectively, and the decay gradient becomes 0.15 cm/km, (c) the total deformation area is 15 km × 15 km and the Fili fault, with a preferred mean dip of 60°, constitutes the natural boundary between the subsidence and uplift areas. The macroseismic field pattern is similar with that of the static ground deformation. The majority of intensity values VI (MM and EMS-98 scales), are distributed within the hangingwall of the Fili fault, while the highest intensities (VIII and IX) concentrate very close to the Fili fault within its hangingwall domain. A gradual decrease of the intensities with the distance from the Fili fault is evident. Because of the similarity between the intensity distribution pattern and the static ground deformation pattern, we make the hypothesis that the latter predicts well enough the main characteristics of the former although the ground displacement is dominated by relatively low frequency as compared to the ground acceleration.  相似文献   

19.
Maximum amplitude observations of local and regional seismic phases(S g and L g, with 800 km) recorded by stations of the I.N.G.National Seismological Network in the period 1994–1999 have beenused to investigate the attenuation of such phases in Italy. The propagationmodel adopted herein accounts for both geometrical spreading, with a termdepending on a given power of distance, and inelastic absorption of themedium, with a term depending exponentially on the distance. Fitting theparameters of the model with experimental data, we considered two cases:assuming a quality factor Q proportional to the frequency f orindependent of f. We compared our results with the values tabled byRichter in 1935, which are still used for the local magnitude estimate in theI.N.G. bulletins. The values found in this study are different than thosegiven by Richter. This suggests that these new values should be used insteadto compute the local magnitude in Italy.  相似文献   

20.
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   

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