1985 Vol. 7 No. 2
Abstract：
In the present paper, the authors discuss the different phases in DSS profile records obtained from Tangshan, and the methods of their interpretations. The DSS data of some profiles running through the Tangshan epicentral region show that the crustal structure in this region is characterized by some special features, which may bear some significant relations to the cause of the occurence of a great earthquake in continintal region.In this area, the earths crust are of three different types, each of which exhibits some peculiar features in velocity structure. An abrupt change of depth of Moho and hence a certain type of faulting usually occurs at or near the boundary between two areas of different types of crust. The difference between different crustal structures may be largely due to the difference in degree of vertical migration of-materials from the uppermost mantle into the crust. The crustal strusture of the epicentral region exhibits the highest degree of material migration from the uppermost mantle in to the lower crust. However, the present crustal structure is a collective fossil inherited from a long span of geological time. Therefore, it is still not very clear whether the migration processes which seem to have been very prominent in the past, are still working effectively at the present. A comparison has been made of the boundaries between different types of crustal structure with the geological map in which the Tertiary surface layer has been stripped off. If is striking that the boundary between different crustal structures is in coincidence with a certain ancient geological map. It is possible that in such an area as Beijing-Tianjing-Tangshan, which is not very far from the coast, different kinds of small ancient geological bodies have been brought together and cemented by ancient global tectonic processes. The main shock of Tangshan earthquake of 1976 occured in the crustal structure of type Ⅱ and near the boundary of the crustal structure of type Ⅱ and type Ⅲ. Therefore, either the occurence of Tang-shan earthquake is due to vertical migration of material from the uppermost mantle into the crust, or it is caused by the reactivation of the weak zone while the whole region is at present under the action of a certain tectonic force. However, it is quite certain that in the area with crustal structure of type Ⅱ, the middle crustal layer has negligible thickness or is totally absent. Since the upper part of the crust may be brittle, it will easily collapse under the action of present tectonic stress.
In the present paper, the authors discuss the different phases in DSS profile records obtained from Tangshan, and the methods of their interpretations. The DSS data of some profiles running through the Tangshan epicentral region show that the crustal structure in this region is characterized by some special features, which may bear some significant relations to the cause of the occurence of a great earthquake in continintal region.In this area, the earths crust are of three different types, each of which exhibits some peculiar features in velocity structure. An abrupt change of depth of Moho and hence a certain type of faulting usually occurs at or near the boundary between two areas of different types of crust. The difference between different crustal structures may be largely due to the difference in degree of vertical migration of-materials from the uppermost mantle into the crust. The crustal strusture of the epicentral region exhibits the highest degree of material migration from the uppermost mantle in to the lower crust. However, the present crustal structure is a collective fossil inherited from a long span of geological time. Therefore, it is still not very clear whether the migration processes which seem to have been very prominent in the past, are still working effectively at the present. A comparison has been made of the boundaries between different types of crustal structure with the geological map in which the Tertiary surface layer has been stripped off. If is striking that the boundary between different crustal structures is in coincidence with a certain ancient geological map. It is possible that in such an area as Beijing-Tianjing-Tangshan, which is not very far from the coast, different kinds of small ancient geological bodies have been brought together and cemented by ancient global tectonic processes. The main shock of Tangshan earthquake of 1976 occured in the crustal structure of type Ⅱ and near the boundary of the crustal structure of type Ⅱ and type Ⅲ. Therefore, either the occurence of Tang-shan earthquake is due to vertical migration of material from the uppermost mantle into the crust, or it is caused by the reactivation of the weak zone while the whole region is at present under the action of a certain tectonic force. However, it is quite certain that in the area with crustal structure of type Ⅱ, the middle crustal layer has negligible thickness or is totally absent. Since the upper part of the crust may be brittle, it will easily collapse under the action of present tectonic stress.
Abstract：
Based on 11 average Bouguer gravity anomalies of China three-dimensional gravity inversion for the whole country is carried out by Parker-Oldenburgs algorithm. The potential field formula of Parker (1973) is an exact mathematical expression and requires less computing time. In the present study, a great deal of current seismic data are utilized at control points and some improvements in the inversion are made to give reasonable results. The distribution of crustal thickness in China is obtained and the densities in the upper mantle down to a depth of 120 km are first presented as well.The results indicate that crustal thickness in China increases from 30-40 km for the eastern coast up to 68 km for most of the Tibetan Plateau, and changes smoothly in eastern China but appears more complicated in the West. There exist some correlations between the crustal thicknesses and geological structures. The upper mantle densities beneath the Tibetan Plateau and the western region of China are 3.40-3.65 g/cc in general, higher than 3.23-3.30 g/cc for the extensive east part of China. The eastern gravity gradient zone reflects the existence of a deep tectonic zone in the lower crust and the upper mantle beneath China, which may mean not only a crustal thickness gradient but also a higher density zone in the upper mantle. Isostatic adjustment is one of the reasons responsible for the uplift of the Tibetan Plateau.The author infers primarily that the upper mantle beneath China could be divided into three regions: the Tibetan plateau, the Middle-transition region and the Normal-east regions according to the lateral inhomogeneities, from which some geophysical phenomena are discussed.
Based on 11 average Bouguer gravity anomalies of China three-dimensional gravity inversion for the whole country is carried out by Parker-Oldenburgs algorithm. The potential field formula of Parker (1973) is an exact mathematical expression and requires less computing time. In the present study, a great deal of current seismic data are utilized at control points and some improvements in the inversion are made to give reasonable results. The distribution of crustal thickness in China is obtained and the densities in the upper mantle down to a depth of 120 km are first presented as well.The results indicate that crustal thickness in China increases from 30-40 km for the eastern coast up to 68 km for most of the Tibetan Plateau, and changes smoothly in eastern China but appears more complicated in the West. There exist some correlations between the crustal thicknesses and geological structures. The upper mantle densities beneath the Tibetan Plateau and the western region of China are 3.40-3.65 g/cc in general, higher than 3.23-3.30 g/cc for the extensive east part of China. The eastern gravity gradient zone reflects the existence of a deep tectonic zone in the lower crust and the upper mantle beneath China, which may mean not only a crustal thickness gradient but also a higher density zone in the upper mantle. Isostatic adjustment is one of the reasons responsible for the uplift of the Tibetan Plateau.The author infers primarily that the upper mantle beneath China could be divided into three regions: the Tibetan plateau, the Middle-transition region and the Normal-east regions according to the lateral inhomogeneities, from which some geophysical phenomena are discussed.
1985, 7(2): 158-170.
Abstract：
The synthetic calibration functions of body-wave magnitude for Chinese stations are formulated in terms of P and 8 wave travel times from earthquakes in the Chinese region and its corresponding velocity distribution model in the crust and mantle and absorption band Q model for the earth (abbreviated ABM-Q model), discussing the effects of geometrical spreading of seismic waves and absorption by the medium in the earth. The results obtained demonstrate:(1)A factor T1-a in the synthetic calibration function is introduced through the frequency-dependence of quality factor Q. That isf(△, h, T) = g(△, h) + a(△, h)/T1-aWhere the parameter a characterizes the degree of frequency-dependence of the quality factor Q in the ABM-Q model, but here it represents the period-dependence of the calibration functions. This is a theoretical improvement on the calibration functions of Gutenberg and Riehter (1956) and of Nortmann and Duda (1982).(2)The term a (A, h) characterizing effect of absorption has higher compensation obviously in the upper mantle and the bottom mantle in the new calibration functions, in comparison with Nortmann and Dudas (1982). This is consistent, so far as known with the tendency of Q distribution with depth.(3)The tendency of underestimating magnitude by Gutenberg and Riehter (1956) calibration functions in the short period range and by Nortmann and Duda (1982) calibration function in the long period range is improved in the preliminary practical tests, so that the magnitudes determinated from different seismic wave periods are basically consistent.(4)The new calibration functions can be used as basic data in formulating the calibration function of body-wave spectral magnitude.
The synthetic calibration functions of body-wave magnitude for Chinese stations are formulated in terms of P and 8 wave travel times from earthquakes in the Chinese region and its corresponding velocity distribution model in the crust and mantle and absorption band Q model for the earth (abbreviated ABM-Q model), discussing the effects of geometrical spreading of seismic waves and absorption by the medium in the earth. The results obtained demonstrate:(1)A factor T1-a in the synthetic calibration function is introduced through the frequency-dependence of quality factor Q. That isf(△, h, T) = g(△, h) + a(△, h)/T1-aWhere the parameter a characterizes the degree of frequency-dependence of the quality factor Q in the ABM-Q model, but here it represents the period-dependence of the calibration functions. This is a theoretical improvement on the calibration functions of Gutenberg and Riehter (1956) and of Nortmann and Duda (1982).(2)The term a (A, h) characterizing effect of absorption has higher compensation obviously in the upper mantle and the bottom mantle in the new calibration functions, in comparison with Nortmann and Dudas (1982). This is consistent, so far as known with the tendency of Q distribution with depth.(3)The tendency of underestimating magnitude by Gutenberg and Riehter (1956) calibration functions in the short period range and by Nortmann and Duda (1982) calibration function in the long period range is improved in the preliminary practical tests, so that the magnitudes determinated from different seismic wave periods are basically consistent.(4)The new calibration functions can be used as basic data in formulating the calibration function of body-wave spectral magnitude.
1985, 7(2): 190-201.
Abstract：
In recent years, ground fissures were found in ten prefectures or cities in the earthquake belt of Weihe River. There are 7 ground fissures in Xian city that total 26.3 km in length. They constitute a great threat to city construction. The auther has also found historical fissures of the Han, Tang and Ming Dynasties buried ibelow the ground surface in the cities of Xianyang, Xian and Woman. These newly discovered fissures, together with 18 fissures recorded in history, form four groups each with a period of 700-800 years that conform with earthquake periodicity.The result of the observations may provide a new -basis, for the prediction of ground fissures and earthquakes in the earthquake belt of the Weihe River.
In recent years, ground fissures were found in ten prefectures or cities in the earthquake belt of Weihe River. There are 7 ground fissures in Xian city that total 26.3 km in length. They constitute a great threat to city construction. The auther has also found historical fissures of the Han, Tang and Ming Dynasties buried ibelow the ground surface in the cities of Xianyang, Xian and Woman. These newly discovered fissures, together with 18 fissures recorded in history, form four groups each with a period of 700-800 years that conform with earthquake periodicity.The result of the observations may provide a new -basis, for the prediction of ground fissures and earthquakes in the earthquake belt of the Weihe River.
Abstract：
In this paper the attenuation characteristics of 8 recorded premonitory geo-sound signals of earthquakes in sand layer is measured, and the effect on the metabolic process of 5-hydroxytryptamine (5-HT) in the brains of mice is analysyed. The results are as follow:1.The forms of the attenuation characteristics of 8 geo-sound signals in sand layer are basically similar, showing that geo-sound signals have almost the same fundamental characteristics. The attenuation is obviously related to frequency within the frequency bands of 50-100 Hz and 250-630 Hz, but attenuation is relatively uniform in the dominant band of 100-250 Hz, that is, the absorption coefficient of a sand layer with a thickness of 20-30 cm is about 410-2- 610-2 dB/cm within this band.2.The relative attenuate rate of intensity level of geo-sound signals transmitted into a hole through a sand layer 30 cm thick shows some decrease as compared with attenuatim in sand of the same depth, and it is related to the fundamental characteristics of the geo-sound signal. Within the dominant band, single tumbling sound, continual sound of roasting beans and so on, and blast sound drop 4.40.8=, 3.50.3% and 3.00.2% respectively, but the drop in intensity of coninuous sound of snare drums is not obvious.3. Two groups of mice quiet adaptation of 48 hours are exposed for 30 minutes to random geo-sound signal noise of 105-85 dB and of 76-66 dB respectively. It was found that the accumulative volume of 5-hydroxyindole-3-acetie acid (5-HIAA), that is, the metabolite of 5-HT in the centre of both groups increases respectively 24.7% and 262.2% as compared with animals of the contsrol group.These results show that the spectrum characteristics of geo-sound with premonitory property transmitted into the ground is related to the absorption characteristics of the ground medium, and it is the stimulation by low frequency noise that makes the animals feel very uneasy. Though the dominant band of geo-sound transmitted into hole is obviously lower than the sensitivie band of hearing of mice. It may directly effect the metabolic process of 5-HT in the brains of mice. Moreover, acoustic effect of the hole may raise the ability of animals to distinguish sound signals above the noise background. It may be seen that geo-sound with premonitory property may be an important factor which causes the abnormal behavior of animals living in holes, eg. mice, prior to the occurrence of earthquakes.
In this paper the attenuation characteristics of 8 recorded premonitory geo-sound signals of earthquakes in sand layer is measured, and the effect on the metabolic process of 5-hydroxytryptamine (5-HT) in the brains of mice is analysyed. The results are as follow:1.The forms of the attenuation characteristics of 8 geo-sound signals in sand layer are basically similar, showing that geo-sound signals have almost the same fundamental characteristics. The attenuation is obviously related to frequency within the frequency bands of 50-100 Hz and 250-630 Hz, but attenuation is relatively uniform in the dominant band of 100-250 Hz, that is, the absorption coefficient of a sand layer with a thickness of 20-30 cm is about 410-2- 610-2 dB/cm within this band.2.The relative attenuate rate of intensity level of geo-sound signals transmitted into a hole through a sand layer 30 cm thick shows some decrease as compared with attenuatim in sand of the same depth, and it is related to the fundamental characteristics of the geo-sound signal. Within the dominant band, single tumbling sound, continual sound of roasting beans and so on, and blast sound drop 4.40.8=, 3.50.3% and 3.00.2% respectively, but the drop in intensity of coninuous sound of snare drums is not obvious.3. Two groups of mice quiet adaptation of 48 hours are exposed for 30 minutes to random geo-sound signal noise of 105-85 dB and of 76-66 dB respectively. It was found that the accumulative volume of 5-hydroxyindole-3-acetie acid (5-HIAA), that is, the metabolite of 5-HT in the centre of both groups increases respectively 24.7% and 262.2% as compared with animals of the contsrol group.These results show that the spectrum characteristics of geo-sound with premonitory property transmitted into the ground is related to the absorption characteristics of the ground medium, and it is the stimulation by low frequency noise that makes the animals feel very uneasy. Though the dominant band of geo-sound transmitted into hole is obviously lower than the sensitivie band of hearing of mice. It may directly effect the metabolic process of 5-HT in the brains of mice. Moreover, acoustic effect of the hole may raise the ability of animals to distinguish sound signals above the noise background. It may be seen that geo-sound with premonitory property may be an important factor which causes the abnormal behavior of animals living in holes, eg. mice, prior to the occurrence of earthquakes.
Abstract：
The step calibration signal has been widely used in seismograph calibration and check. Routine check is currently being made with step calibration signal at Standard Chinese Seismic Stations. However this check can only show qualitatively whether the instrument working state is normal and does not determine quantitative variations in the elementary constants of a seismograph. Therefore it is not effective in monitoring variations in instrument constants and thus the significance of impulse check is reduced.Some foregoing studies deal with the quantitativ relation between impulse check and instrument elementary constants, However they only discussed separately the effect of variations in period, damping constant, and magnification respectively on the response waveform. But in a practical observatory the variations in instrument elementary constants are. interrelated.In this paper the equation of motion for checking instrument by using the step calibration signal is derived and solved by Laplace transform. An analytic expression for instrument response is obtained. Then some cases of instrument parameter variations encountered in practice and their relation to instrument elementary constants are discussed. The instrument response waveforms of the above cases are calculated. The concept of characteristic parameters of response waveform is introduced for analyzing the relation between response waveform with instrument parameters and the interrelations between variations of elementary constants. The minimum variation range of characteristic parameters that can be identified on seismograms is given. Thus quantitative relations between elementary constant variations and the characteristic parameter variations of response waveform are established.At the end of this paper the variation ranges of elementary constants identified possibly in various variation cases and their reliablity are given.
The step calibration signal has been widely used in seismograph calibration and check. Routine check is currently being made with step calibration signal at Standard Chinese Seismic Stations. However this check can only show qualitatively whether the instrument working state is normal and does not determine quantitative variations in the elementary constants of a seismograph. Therefore it is not effective in monitoring variations in instrument constants and thus the significance of impulse check is reduced.Some foregoing studies deal with the quantitativ relation between impulse check and instrument elementary constants, However they only discussed separately the effect of variations in period, damping constant, and magnification respectively on the response waveform. But in a practical observatory the variations in instrument elementary constants are. interrelated.In this paper the equation of motion for checking instrument by using the step calibration signal is derived and solved by Laplace transform. An analytic expression for instrument response is obtained. Then some cases of instrument parameter variations encountered in practice and their relation to instrument elementary constants are discussed. The instrument response waveforms of the above cases are calculated. The concept of characteristic parameters of response waveform is introduced for analyzing the relation between response waveform with instrument parameters and the interrelations between variations of elementary constants. The minimum variation range of characteristic parameters that can be identified on seismograms is given. Thus quantitative relations between elementary constant variations and the characteristic parameter variations of response waveform are established.At the end of this paper the variation ranges of elementary constants identified possibly in various variation cases and their reliablity are given.
1985, 7(2): 226-230.
Abstract：
In this paper, a concise formula for a mantle structure with low velocity zone is presented, based on the works of Gerver and Markushevich, and McMechan. Although it is merely one of a large number of possible solutions, it is convenient for inverting the travel time data of the upper mantle when the information from LVZ is limited. The velocity structure of the upper-most mantle of the Beijing-Taiwan profile is given as an example.
In this paper, a concise formula for a mantle structure with low velocity zone is presented, based on the works of Gerver and Markushevich, and McMechan. Although it is merely one of a large number of possible solutions, it is convenient for inverting the travel time data of the upper mantle when the information from LVZ is limited. The velocity structure of the upper-most mantle of the Beijing-Taiwan profile is given as an example.
Abstract：
A method is introduced in this paper for precisely determining- wave velocity by means of a microcomputer-high speed data acquisition system. The accuracy of the wave velocity measurement is controlled by the travel-time determination. But this is currently done with a SYC-Ⅱ veloeimeter by determining the, position of a light sealer on its oscilloscope, resulting in a reading error well beyond 0.2 s. With the use of the system presented in this paper, this error can be greatly reduced. In the measurement, the tra-vel-time is recorded by a transient recorder with the highest sampling speed of 20 MHz (corresponding to a maximum reading error of 0.05s), and the data are transferred via a digital interface into a microcomputer which automatically determines the first wave arrival and immediately gives the results of travel-time as well as velocity.For the sample scales commonly adopted in the laboratory, the error in the velocity measurement by this method is within 0.7%. Thus the accuracy of velocity measurement is improved to a considerable extent .
A method is introduced in this paper for precisely determining- wave velocity by means of a microcomputer-high speed data acquisition system. The accuracy of the wave velocity measurement is controlled by the travel-time determination. But this is currently done with a SYC-Ⅱ veloeimeter by determining the, position of a light sealer on its oscilloscope, resulting in a reading error well beyond 0.2 s. With the use of the system presented in this paper, this error can be greatly reduced. In the measurement, the tra-vel-time is recorded by a transient recorder with the highest sampling speed of 20 MHz (corresponding to a maximum reading error of 0.05s), and the data are transferred via a digital interface into a microcomputer which automatically determines the first wave arrival and immediately gives the results of travel-time as well as velocity.For the sample scales commonly adopted in the laboratory, the error in the velocity measurement by this method is within 0.7%. Thus the accuracy of velocity measurement is improved to a considerable extent .
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