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101.
利用中法合作建立的微震数字地震台的资料研究了海原西断层松山附近地区的微震尾波的衰减特征.计算了170次地震的7个频带的尾波Qc值,得出该地区尾波衰减可用Qc=52f1.09表示,表明这个地区是构造活动水平较高的地区. 相似文献
102.
103.
Charles H. Estabrook Michael Weber Rainer Kind 《Geophysical Journal International》1997,130(2):349-364
We investigate large-amplitude phases arriving in the P -wave coda of broad-band seismograms from teleseisms recorded by the Gräfenberg array, the German Regional Seismic Network and the Global Seismic Network. The data set consists of all events m b≤ 5.6 from the Aleutian arc between 1977 and 1992. Earthquakes with large-amplitude coda waves correlate with the presence of oceanic crust in the source region. The amplitudes sometimes approach those of the P wave, much larger than predicted by theory. Modelling indicates that phases in the P -wave coda cannot be P -wave multiples beneath the source and receiver, or underside reflections, which precede PP , from upper-mantle discontinuities. Among the events, seismograms are very similar, where the arrival times of the unusual phases agree approximately with the predicted times of S -to- P conversions from the upper-mantle discontinuities under the source. Because the large-amplitude phases in the P -wave coda have little, if any, dependence on event depth and have predominantly an SV -wave radiation pattern towards the receiver, we suggest that they originate as SV and/or Rayleigh waves and are enhanced by lateral heterogeneity and multipathing from the subducting Aleutian slab. 相似文献
104.
For short-period near-earthquake records in eastern China, from the empirical attenuation formula of coda ground motion amplitudeA with timeτ: lgA=G−2. 235 lgτ, using the single scattering theory modified with epicentral distance, we obtain the curve family of corrected coda amplitudeA
c(r,t), andω/2Q
c values for each time interval of coda. From this,Q
c(f,h) values, which correspond to each observational average frequency and sampling depth, are calculated. The results substantially
agree with those observationalQ
c values in Yunnan, Beijing and central Asia. 相似文献
105.
AttenuationcharacteristicsofcodawavesandestimationofQcvaluesineasternChina黄才中,葛焕称,江铁鹰Cat-ZhongHUANG;Huan-ChengGEandTie-YingJI... 相似文献
106.
利用高精度的数字地震尾波记录来测定一定区域范围内或地震活动区内的介质品质因素Q,是一项非常有意义的工作。本文介绍了一套方法上较完备和相对规范化的尾波Q值计算软件,运用中国数字化地震台网(CDSN)记录给出计算实例。 相似文献
107.
Based on the single scattering model of seismic coda waves, we have calculated theQ-factor in Beijing and its surrounding regions by means of calculating the power density spectrum in frequency domain with
a fixed time window. The digital seismic data of 69 earthquakes from Beijing Telemetered Seismographic Network are used. These
earthquakes were recorded from January 1, 1989 to December 31, 1990 at 20 stations. This paper shows the variations of the
codaQ-factors in the studied region with different sites, frequency and lapse time, and the temporal change of the codaQ-factors in these two years. The results indicate that codaQ-factor depends strongly on the lapse time and frequency. It is assumed that whenQ
C=Q
0fη, for the three time windows of 15–30s, 30–60s and 60–90s, the average values ofQ
0 are 48, 115 and 217; and the average values ofη are 0. 89, 0.91 and 0.74, respectively.
Contribution No. 95A0009, Institute of Geophysics, SSB, China.
This work is a contract subject 85-04-01-02 of the State Seismological Bureau, China. 相似文献
108.
109.
110.
R. F. Mereu 《Pure and Applied Geophysics》1990,132(1-2):269-288
ThePmP wide-angle reflected signal from the Moho shows a wide variation in its characteristics when cornpared from region to region. If the earth's crust is simple and homogeneous and the Moho is a sharp discontinuity, supercriticalPmP wavelets are large and isolated in the 100 km to 300 km distance range when compared to the preceding signals on the seismic traces. If the crust itself has numerous short reflectors and the Moho transition zone is thick or badly disrupted from past tectonic disturbances, thenPmP is often poorly defined and difficult to identify in the coda of earlier arriving signals. These signals are poorly correlated because the reflectors themselves are in general not only discontinuous but tend to be distributed at various depths within the crust. The effect of the vertical velocity gradient in the crust is to make the reflective field for downgoing waves much greater than for upgoing waves. The large variations in reflection coefficients wiht angle of incidence has the effect of making the coda generated by a reflective machanism distance dependent. The reflected signals are also contaminated with scattered signals from smaller scale heterogeneities which may be distributed more uniformly within the crust.In conventional seismic inversion methods applied to crustal refraction experiments, emphasis is usually placed on obtaining a velocity model of the subsurface structure. These models are relatively simple and are limited in the amount of complexity which can be uniquely inferred from the data. The main problem arises because of the difficulties in the identification of the origin of the signals which are themselves often incoherent from trace to trace.In this paper it is shown how the conventional record section may be complemented with a normal moveout corrected intensity section which emphasizes areas of large signal complexities. Data from this intensity section is then used as input to obtain a quantitative measurement of a complexity parameter. These measurements may be used to infer or compare differences in crustal heterogeneity from one region to another. The discussion is illustrated with both numerical modeling data as well as data from recent crustal experiments which were conducted over the Canadian Shield. 相似文献