Some results of calibrating CG-2 gravimeters (sharpe) by the tilt method

am mam mauau m amaua aaum CG-2¶rt;u muna No; 174-G, 181-G u 228-G nuu m¶rt;a aa. mama mauau aum, m num mum mm 1. 10^–4 u n¶rt;um um a. a a¶rt;a ¶rt; a auum ama uum mauaum m mnam.     

Thermostat for the sharpe CG-2 gravimeter

Summary Gravimeters with a quartz system display a considerable temperature dependence. A simple thermostat for the Sharpe CG-2 gravimeter, eliminating this drawback, is described.Dedicated to Academician Alois Zátopek on His 65th Birthday     

欧洲绝对重力仪比对观测(ECGS'07)

介绍了2007年11月在欧洲卢森堡Walferdange举办的第二次绝对重力比对观测的概况及结果.有20台绝对重力仪参加了比对观测,在ECGS共15个测点上的比测结果标准偏差小于2.1×10~(-8)m·s~(-2).文章简述了数据处理方法以及结果分析,中国地震局地震研究所引进的FG5/232绝对重力仪参加了本次比对,为在中国大陆建立绝对重力基准提供了重要经验.     

Influence of atmospheric pressure variations on measurements made with Sharpe and Worden gravimeters

Summary The paper deals with the influence of the atmospheric pressure variations on Sharpe gravimeters CG 2 No. 226 and 280 and on the Worden gravimeter No. 978, equipped with a thermostat.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

Explanation of the internal air pressure effect on the worden gravity meter dial constant

Summary A model, explaining the effect of air pressure changes in the space of the measuring system on the fine dial counter constant of the Worden and similar gravity meters, is presented. It is based on the changes of the bellows volume with compensating the gravity changes. It is shown that the resetting the gravity meter in the whole range has practically no influence on the fine dial counter constant.

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Ways to improve metrological and operational characteristics of liquid gravimeters

A gas-liquid gravimeter of the manometric type with a drift-free elastic element, namely gas, proposed by the author is described. The possibility to implement an effective self-contained system allowing for complete compensation of the temperature and temperature gradient effects, as well as for actual elimination of the effect of a small inclination on the sensitive element of the gravimeter, is shown. Utilization of a float converter equipped with a capacitance transducer of displacements increases the measurement range up to ～10⁴ mGal, the calculation error in the entire range being ±1 μGal.     

The changes of sensitivity and drift rate of a worden gravimeter with time and temperature

Summary The analysis of the readings taken with aWorden gravimeter during fieldwork over a period of four years when compared with tests in a laboratory shows that its behaviour is not dependent on vibration and that the drift can be separated into two distinct parts; an isothermal drift and a thermal drift. The former is remarkably constant over short and long periods of time and is of the order of 0.01 mgal/hour. The latter is complicated and is dependent on the rate of change of the ambient temperature being different in size and sign, for quick and slow changes of temperature. The sensitivity changes slowly with time, 0.1% per year, and is only slightly affected by temperature. Tares or jumps in the readings are very rare. Modifications to the meter are suggested, consisting of the inclusion of a rheostat in the lighting circuit and the attachment of a thermometer to the outside of the instrument. In order to keep the correction for drift to a small size and to increase the accuracy, returns to a base station should be made according to changes in the ambient temperature rather than at fixed time intervals.

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Zusammenfassung Die Analyse der Lesungen einesWorden Gravimeters während einer vierjährigen Periode von Feldmessungen und deren Vergleichung mit den Resultaten einer Prüfung im Laboratorium zeigt, dass sein Verhalten nicht von Erschütterungen abhängt und dass sein Drift in zwei deutlich verschiedene Anteile gespalten werden kann, nämlich einen isothermalen und thermalen Drift. Der erstere Anteil ist bemerkenswert konstant über kurze und längere Perioden und seine Grössenordnung ist 0.01 mgal per Stunde. Der letztere ist kompliziert und hängt von der Schnelligkeit der Änderung der Temperatur der Umgebung ab und ist der Grösse und dem Vorzeichen nach verschieden für rasche und langsame Temperaturänderungen. Die Empfindlichkeit ändert sich langsam mit der Zeit, 0.1% per Jahr, und wird nur wenig durch die Temperatur beeinflusst. Sprünge in den Ablesungen sind sehr selten.Es werden zwei Modifikationen des Gravimeters vorgeschlagen, nämlich die Einschaltung eines Widerstandes im Beleuchtungskreis und die Anbringung eines Thermometers am Instrumentengehäuse. Um die Korrektion wegen Drift klein zu halten und die Genauigkeit zu erhöhen, wird empfohlen, dass das Wiederaufsuchen der Basisstation entsprechend der Änderung der Umgebungstemperatur und nicht in bestimmten, festgelegten Zeitintervallen erfolgen soll.

     

CG-5重力仪格值系数修正与应用研究

在地表重力观测过程中,CG-5重力仪的格值系数会随着时间推移而发生变化.选用河北测区内2015—2017年相对重力观测数据,基于重力差法对两台编号为C859、C873的CG-5相对重力仪进行格值系数的误差计算及修正,研究其变化特征,并对修正前后不同时间尺度的重力场变化进行对比分析.结果表明:两台CG-5相对重力仪的格值系数在3年内存在不同程度的变化,均呈现整体上升的趋势,累计变化量分别为0.028％,0.034％;采用修正后的格值系数可得到点值精度更高的平差结果;不同时间尺度上的重力场变化相比修正前也出现明显差异,2017年河北大城ML3.6级地震发生在格值系数修正后0.5 a期重力变化零值线附近,这些结果表明了对CG-5重力仪进行格值系数修正的正确性和必要性.     

Some results of observations of positive lightning discharges and relative phenomena in the east of Siberia

We have considered spatial distributions of positive lightning discharges in the east of Siberia for the summer seasons of 2003–2007 and properties of their electromagnetic signals with the ELF “slow tail”, which, as is known, can be accompanied by sprites. There are two main regions of positive discharges located in the south and west of Yakutsk. Two other “centers” (the northeastern and the eastern) are located in high-mountainous regions. In these regions the positive discharges intensity can exceed the negative discharge intensity.The electromagnetic signals in the ELF range (usually in the form of two half-cycles) were observed after the VLF atmospherics were recorded in the high-latitude regions. The delay of ELF pulses relative to the corresponding atmospherics was 0–7 ms. The long (up to 350 ms) events of quasi-periodic ELF oscillations with the period of about 7 ms (which corresponds to the quasi-period of ELF pulses) were revealed.     

Scientific achievements from the first phase (1997–2003) of the Global Geodynamics Project using a worldwide network of superconducting gravimeters

This paper aims to review the main scientific achievements which were obtained in the first phase (1997–2003) of the Global Geodynamics Project (GGP) consisting of a worldwide network of superconducting gravimeters (SG) of about 20 instruments. We show that the low noise levels reached by these instruments in various frequency bands allow us either to investigate new signals of very small amplitude or to better determine other signals previously seen. We first report new results in the long-period seismic band with special emphasis on the detection of the ₂S₁ normal mode and the splitting of the fundamental spheroidal mode ₂S₀ after the magnitude 8.4 Peru earthquake in 2001. We also discuss briefly the ‘hum’, which consists of a sequence of fundamental normal modes existing between 2 and 7 mHz even in the lack of any seismic excitation, and was first discovered on the Syowa (in Antarctica) instrument in 1998. We will comment on the search for the Slichter mode ₁S₁ of degree 1 which is associated with a translational motion of the inner core inside the liquid core. Atmospheric effects are reviewed from the local to the global scale and the improvement due to pressure loading computations on residual gravity signals is shown. An interesting study exhibiting the gravity consequence due to sudden rainfall and vertical mass motion in the atmosphere (without ground pressure change) is presented. The precision of the SGs leads to some convincing results in the tidal domain, concerning the fluid core resonance effect (free core nutation (FCN)) on diurnal tides or various loading effects (linear, non-linear) from the oceans. In particular, SGs gravity measurements are shown to be useful validating tools for ocean tides, especially if they are small and/or confined to coastal regions. The low instrumental drift of the SGs also permits to investigate non-tidal effects in time-varying gravity, especially of annual periodicity. Hydrology has also a signature which can be seen in SG measurements as shown by several recent studies. At even lower frequency, there is the Chandler motion of 435-day period which leads to observable gravity changes at the Earth's surface. We finally report on the progress done in the last years in the problem of calibrating/validating space satellite data with SG surface gravity measurements.     

利用重复测线校正海空重力仪格值及试验验证

通过分析海空重力测量系统误差的形成机理,我们发现海空重力仪格值标定误差是引起系统性测量偏差的主要因素之一.本文简要介绍了重力仪格值的标定方法,分析论证了格值标定的精度要求,提出了利用东西正反向重复测线检测校正海空重力仪格值的计算模型和补偿方法,分析讨论了该方法的校正精度及其适用条件,利用航空重力实际观测网数据对该方法的合理性和有效性进行了数值验证,证明该方法对消除海空重力测量系统性偏差具有显著作用.

     

The interdependence of seismic and volcanic phenomena: Some space — Time relationships in seismicity and volcanism

Research is described aimed at detecting significant relationships between patterns of earthquakes and volcanic eruptions. A large data file of seismic and volcanic events has been assembled on punched cards, and two computer programmes used to relate earthquakes to active or potentially active volcanic centres, and deep earthquakes to succeeding shallower ones and volcanic eruptions after the manner suggested byBlot. It is concluded that recognisable sequences occur in some areas, but that the process is neither universal nor invariable. The presence of random events or events due to other causes almost always obscures patterns of seismicity which seem to be related to volcanic eruptions. The «Blot process» appears to operate in some cases but is probably a second order phenomenon: primarily, correlated sequences of seismic and volcanic events result from periods of tectonic instability and perhaps increased tensional conditions which affect very wide areas of the Earth’s surface for periods of several months to several years at a time.     

Lunar transient phenomena (LTP): Manifestations,site distribution,correlations and possible causes

The author has been compiling a catalog of LTP reports (temporary changes observed on the moon). More than 1,400 of these observations, of which 1,353 have ancillary data, were analyzed in an attempt to determine the possible causes of LTP. There were 201 sites reported at least once; about $\text{1}\text{2}$ had two or more reports. One dozen sites contain 70% of all observations, and one site, Aristarchus, provides 30%. Of the dozen most reported sites, $\text{1}\text{2}$ are rayed and $\text{1}\text{2}$ are dark flat-floored craters. The distribution of sites strongly favors the borders of both the terra and marial sides of the maria. Many are within the maria, and a very few are inland; yet most of these are associated with dark flat areas.The phenomena manifest themselves in five categories, viz., Brightenings, or Darkenings, or as Gaseous, Reddish and Bluish events. Among the hypotheses proposed for their causes are tidal, low-illumination/thermoluminescence, magnetic-tail and solar-flare effects. Analyses were conducted to see if different phenomena had different causes. There is some suggestion that they do. As concerns the tidal effects. the strongest peaks are at 0.5 (apogee) for Gaseous and Darkenings phenomena, 0.6 for Reddish events, and 0.7 for Brightenings. Reddish LTP have the strongest correlation with sunrise, while Aristarchus, Plato, Ross D area, and Bluish phenomena have the strongest correlations with solar-flare activity that produced magnetic storms on earth. “All” observations, the ones labeled “Best” (probable true anomalies), and Aristarchus, showed minima in the first half and maxima in the last half of the anomalistic (tidal) period. Histograms of several individual sites, including neighboring ones, behave differently, e.g. Aristarchus and Herodotus. When observed data are compared with expected observations (assumed to be evenly distributed) there were various correlations. For the Best data, 12 and 10% of the LTP fall close to perigee and apogee, respectively, and 10% would be expected for each. Seventeen percent occur within one day after sunrise when 3% would be expected; 20% occur while the moon is in the earth's magnetopause where 14% would be expected, and 12% occurred the same day the earth had a magnetic storm where 3% would be expected.Charts of albedo vs. age of several points for ten features were constructed. From these the normal behavior of the features throughout a lunation period was obtained. Measures that depart 2 or more full steps in Elger's albedo scale, are considered to be anomalies. Several cases of anomalous measures show up; e.g., for points on the south wall of Eimmart an albedo of 3.5 was reported once at age 10 days while for age 9 days the average albedo was 8, as it was afterward at age 11 days. The 3.5 may have been an anomalous darkening but unnoticed by the observer. Most of the features remained stable. A few exceptions were found, with Dawes showing the most anomalies. These amounted to 12% by nights or 2% by individual measures. Thus, monitoring the moon may yield an LTP once in ten nights, or 50 observations.All hypotheses show correlations with some categories and some features. Sunrise correlation is the most frequent correlation. Few correlations involve as many as 50% of the observations. The distribution of all LTP sites is different from and unique compared with deep- and shallow-focus moonquake epicenters. Routine albedo measures reveal unobserved variations which amount to about 10% in nights of observation bu 2% of individual albedo measures.     

中国地震科学实验场:认识与实践

中国地震科学实验场提出的国家重大科技基础设施建议被列入《中华人民共和国国民经济和社会发展第十四个五年规划和2035年远景目标纲要》,不仅是实验场的一件大事,也是中国地震科技的一件大事.这一重大进展,是中国地震科学界近半个世纪的思考与尝试的结果.     

Landslide phenomena in the area of Pomarico (Basilicata–Italy): methods for modelling and monitoring

This paper takes into consideration landslide phenomena in the clayey slopes facing the built-up area of Pomarico which is situated in the southern part of the “Fossa Bradanica”, in Basilicata (Italy). Based on the great number of geologic, geomorphologic and historic informations a geotechnical model of the slope was built. Particular attention has been paid to define the geotechnical parameters of the soil and which mechanical models are to be used. The studies point out a correlation between the water level in the detritus cover and the stability condition of the slope showing that phenomena at first located at the foot of the slope spread quickly towards its summit as the piezometric height increases.     

Time series of superconducting gravimeters and water storage variations from the global hydrology model WGHM

The gravimetric time series achieved from the combination of superconducting and absolute gravimeters are characterized by highest precision and long-term stability. If the effects of Earth and ocean tides, atmosphere and polar motion are removed, the residual curve is dominated by hydrological mass variations. A major source of these variations is water storage changes in the vicinity of the sensor. However, global variations contribute to the signal significantly. For three stations of superconducting gravimeters, a comparison of the principal components obtained from the residual gravity curve on the one hand and continental water storage from the WaterGAP Global Hydrological Model (WGHM) on the other hand is carried out. The results demonstrate a coherence of seasonal variations but a difference in the contribution of the local zone at the individual stations, which point out the need for a careful and site-specific examination of local effects.