中国第一批大地热流数据

本文叙述了观测大地热流的方法和仪器, 其中包括在钻孔中测定温度的半导体热敏电阻井温仪和在室内测定岩芯标本热导率的装置.给出了最近几年在华北地区11个地点的16个钻孔中取得的温度和热导率数据以及计算热流值的结果.初步讨论了热流值分布与本区复杂地质条件之间的关系, 如中国北部及东部地区热流值与世界同类型地质单元相比较具有较高值和较大分散性的可能解释.      

Short-term and imminent anomalies of earthquake of load and unload response ratio of the well level to earth tides

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The effect of water on stress relaxation of faulted and unfaulted sandstone

A series of stress relaxation experiments have been carried out on faulted and intact Tennessee sandstone to explore the influence of pore water on strength at different strain rates. Temperatures employed were 20, 300 and 400°C, effective confining pressure was 1.5 kb and strain rates as low as 10^–10 sec^–1 were achieved. Most samples were prefaulted at 2.5 kb confining pressure and room temperature. This is thought to have secured a reproducible initial microstructure.The strength of the dry rock was almost totally insensitive to strain rate in the range 10^–4 to 10^–10 sec^–1. In contrast, the strength of the wet rock decreased rapidly with strain rate at rates less than 10^–6 sec^–1. Brittle fracture of the quartz grains which constitute this rock is the most characteristic mode of failure under the test conditions used.The experimental data are discussed in terms of the possible deformation rate controlling processes, and it is suggested that in the wet experiments at intermediate to high strain rates (10^–7 to 10^–4 sec^–1) the observed deformation rate is controlled by the kinetics of water assisted stress corrosion, whilst deformation at low strain rates (ca. 10^–9 sec^–1) is controlled by a pressure solution process.The results have implications for the rheology of fault rocks at depths of perhaps 10 to 15 km in sialic crust.     

Possible strain events reflected in water levels in wells along San Jacinto fault zone,southern California

Water levels have been monitored in wells along the San Jacinto fault zone since 1977. The three largest earthquakes to occur within 30 km of the segment of the San Jacinto fault zone being monitored with continuous recorders showed magnitudesM of 4.5, 4.8, and 5.5. Two wells in Borrego Valley, 31 to 32 km southeast of theM=5.5 earthquake on 25 February 1980, showed anomalous spikes recording a probable strain event 88 hours before the earthquake. Two other wells 12 km northwest of the epicenter showed no water-level anomalies. No water-level anomalies preceded theM=4.8 earthquake near Anza on 15 June 1982. Anomalous water-level fluctuations occurred in a well near Ocotillo Wells, 13 km northeast of theM=4.5 earthquake on 22 March 1982, 19 to 23 days prior to the earthquake. Similar fluctuations in other wells have not been followed by sizable earthquakes. A simultaneous drop in water level occurred in four wells on 8 September 1982; this possible strain event was not associated with a sizable earthquake. The presumed strain events occur only in wells that show earth tides and may have been the result of creep on strands of the San Jacinto fault zone. Although water-level anomalies have occurred in only one or two wells prior to two out of three moderate (M=4.5–5.5) earthquakes, the simultaneous drop in water level on 8 September 1982 and the spikes in two wells before theM=5.5 earthquake on 25 February 1980 suggest that wells responsive to earth tides may detect strain events.     

Lunar seismicity and tectonics

Seismic signals from 300–700 deep moonquakes and about four shallow moonquakes are detected by the long-period seismometers of two or more of the Apollo seismic stations annually. Deep-moonquake activity detected by the Apollo seismic network displays tidal periodicities of 0.5 and 1 month, 206 d and 6 a. Repetitive moonquakes from 60 hypocenters produce seismograms characteristic of each. At each hypocenter, moonquakes occur only within an active period of a few days during a characteristic phase of the monthly lunar tidal cycle. An episode of activity may contain up to four quakes from one hypocenter. Nearly equal numbers of hypocenters are active at opposite phases of the monthly cycle, accounting for the 0.5-month periodicity. The 0.5- and 1-month activity peaks occur near times of extreme latitudinal and longitudinal librations and earth-moon separation (EMS). The 206-d and 6-a periodicities in moonquake occurrence and energy release characteristics are associated with the phase variations between the librations and EMS. Because of the exact relationship between tidal phases and the occurrence of deep moonquakes from a particular hypocenter, it is possible to predict not only the occurrence times from month to month, often to within several hours, but also the magnitudes of the moonquakes from that hypocenter. The predicted occurrence of large A₁ moonquakes in 1975, following a 3-a hiatus, confirms the correlation between A₁-moonquake activity and the 6-a lunar tidal cycle and implies a similar resurgence for all of the deep moonquakes. Because no matching shallow moonquake signals have been identified to date, tidal periodicities cannot be identified for the individual sources. However, shallow moonquakes generally occur near the times of extreme librations and EMS and often near the same tidal phase as the closest deep moonquake epicenters. With several possible exceptations, the deep-moonquake foci located to date occur in three narrow belts on the nearside of the moon. The belts are 100–300 km wide, 1,000–2,500 km long and 800–1,000 km deep and define a global fracture system that intersects in central Oceanus Procellarum. A fourth active, although poorly defined, zone is indicated. The locations of 17 shallow-moonquake foci, although not as accurate as the deep foci, show fair agreement with the deep-moonquake belts. Focal depths calculated for the shallow moonquakes range from 0–200 km. Deep-moonquake magnitudes range from 0.5 to 1.3 on the Richter scale with a total energy release estimated to be about 10¹¹ erg annually. The largest shallow moonquakes have magnitudes of 4–5 and release about 10¹⁵–10¹⁸ erg each. Tidal deformation of a rigid lunar lithosphere overlying a reduced-rigidity asthenosphere leads to stress and strain concentrations near the base of the lithosphere at the level of the deep moonquakes. Although tidal strain energy can account for the deep moonquakes in this model, it cannot account for the shallow moonquakes. The tidal stresses within the lunar lithosphere range from about 0.1 to 1 bar and are insufficient to generate moonquakes in unfractured rock, suggesting that lunar tides act as a triggering mechanism. The largest deep moonquakes of each belt usually occur near the same characteristic tidal phases corresponding to near minimum or maximum tidal stress, increasing tidal stress, and alignments of tidal shear stresses that correspond to thrust faulting along planes parallel to the moonquake belts and dipping 30–40°. With few exceptions, the shallow moonquakes occur at times of near minimum tidal stress conditions and increasing tidal stress that also suggest thrust faulting. The secular accumulation of strain energy required for the shallow moonquakes and implied by the uniform polarities of the deep moonquake signals probably results from weak convection. A convective mechanism would explain the close association between moonquake locations and the distribution of filled mare basins and thin lunar crust, the earth-side topographic bulge, and the ancient lunar magnetic field. The low level of lunar seismic activity and the occurrence of thrust faulting both at shallow and great depths implies that the moon is presently cooling and contracting at a slow rate.     

压容式钻孔应变仪的初步试验结果

本文介绍一种应变灵敏度达到110-11的压容式钻孔应变仪,该仪器在软地层中接收到了地震波和固体潮波,至少对于周期从0.3秒到数天的频段所收到的信号中包含着地层应变变化的真实信息。      

Vertical variation of apparent and palaeoclimatically corrected heat flow densities in the central baltic shield

The vertical variation of heat-flow density in the Central Baltic Shield was studied in 17 drill holes (389–1060 m deep). Apparent heat-flow densities calculated in 100 m depth sections, with typical determination errors smaller than 2 mW/m², showed a variation of up to 15 mW/m² in single holes. A palaeoclimatic correction for surface temperature variations during the last million years was calculated as a function of depth for each hole with a homogeneous half-space conduction model. If the bedrock temperatures are controlled only by conduction of heat, and the temperature history is accurately known, the palaeoclimatically corrected heat-flow densities should have the same (steady-state) value at all depths throughout a drill hole. In practice, the quality of the correction is indicated by decrease or increase in the standard errors of the drill-hole means of heat-flow density. When the corrections were applied to the measured data, the standard errors decreased in only eight drill holes, and the vertical variation in palaeoclimatically corrected values ranged from a few mW/m² to 10 mW/m². In some of the holes, this variation can be attributed to heat-flow refraction at inclined conductivity interfaces, resulting in local heat-flow anomalies. However, the most important cause of the variation seems to be groundwater flow in bedrock, i.e., heat transfer disturbing the conductive regime. This notion is supported by heat-flow density-depth plots and temperature-depth plots and the decrease in observed heat-flow variation below 500 m depth, which is the typical depth of rapidly changing fresh groundwater, below which more saline (and stagnant) groudwaters are usually encountered. The present results indicate the following: 1) Groundwater flow can be fairly common in the upper parts of bedrock in the Baltic Shield, and purely conductive circumstances do not necessarily prevail everywhere; 2) palaeoclimatically corrected heat-flow values must be used with great precaution, especially when signs of groundwater flow are present in the data; 3) the palaeoclimatic correction can be applied to study groundwater flow in bedrock indirectly and to test whether a conductive regime prevails or not.     

Multicomponent observation of crustal activity in the DPRI 800 m borehole close to the Nojima Fault

Abstract An 800 m borehole was drilled near the Nojima Fault, on which a strike–slip larger then 1 m occurred during the 1995 Hyogo-ken Nanbu earthquake ( M = 7.2). Crustal activity near the fault has been observed since May 1996 using a multicomponent instrument installed at the bottom of the borehole. Data of three components of strain, two components of tilt and temperature observed from May 1996 to December 1998 were analyzed. Long-term changes of strain and tilt show a north-east–south-west extension and southwards subsidence. As for the Earth tides and atmospheric effect, orientation of the principal axis of strain was mainly east-west and orientation of the maximum subsidence was mainly north-south. The observational data of strain had variations corresponding to a change in temperature at a depth of 800 m. The thermal expansion coefficient of the crust was calculated to be approximately 2.0 × 10⁻⁶/°K.     

上海佘山压容式钻孔应变仪观测资料的调和分析

对安装在上海佘山地震台的YRZ-2型压容式钻孔应变仪的观测资料分别进行了未经海潮改正和经过海潮改正的调和分析计算。结果表明:(1)各主要半日波的勒甫数l2与根据Gutenberg-Bullen地球模型A计算而得到的结果接近;(2)各主要日波的勒甫数l2较半日波明显地小,这可能是传感器和井壁之间的耦合状况以及整个观测系统的频响特征所致;(3)在上海,海潮负荷引起的应变效应在数值上与起潮力直接引起的应变效应相当,经海潮改正后,计算结果的精度有显著提高。      

加卸载响应比在体应变固体潮中的应用

从岩石的应变与应力的非线性响应分析了体应变固体潮加卸载响应比的物理机理, 给出了体应变固体潮加卸载响应比的计算方法,并以昌平和峰峰台的体应变观测值为例,计算了二台的体应变固体潮加卸载响应比。结果表明,在中强地震前存在增大变化。     

A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan

We have installed a laser strainmeter system in a deep tunnel about 1,000 m below the ground surface at Kamioka, Gifu, Japan. The system consists of three types of independent interferometers: (1) an EW linear strainmeter of the Michelson type with unequal arms, (2) an NS-EW differential strainmeter of the Michelson type with equal arms and (3) a NS absolute strainmeter of the Fabry–Perot type. These are configured in L-shaped vacuum pipes, each of which has a length of 100 m. (1) and (2) are highly sensitive (order of 10⁻¹³ strain) and have wide dynamical range (10⁻¹³–10⁻⁶). Observations with strainmeters (1) and (2) started on June 11, 2003. (3) is a new device for absolute-length measurements of the order of 10⁻⁹ of a long-baseline (100 m) Fabry–Perot cavity by the use of phase-modulated light. This third strainmeter will be ready for operation before the end of 2004. The laser source of strainmeters (1) and (2) is a frequency-doubled YAG laser with a wavelength of 532 nm. The laser frequency is locked onto an iodine absorption line and a stability of 2 × 10⁻¹³ is attained. The light paths of the laser strainmeter system are enclosed in SUS304 stainless steel pipes. The inside pressure is kept to be 10⁻⁴ Pa. Consequently, quantitative measurement of crustal strains of the order of 10⁻¹³ can be attained by employing the laser strainmeter system of (1) and (2) at Kamioka. This resolving power corresponds to that of a superconducting gravimeter. Using the laser strainmeter system, we expect to determine parameters related to fluid core resonance, core modes and core undertone as well as other geodynamic signals such as slow strain changes caused by silent earthquakes or slow earthquakes.     

Radiated seismic energy and strain energy release in laboratory dynamic tensile fracture

Tensile dynamic fractures were propagated under two experimental congifurations for the purpose of assessing the relative amount of strain energy release that is consumed as fracture energy and radiated as seismic waves. The configurations used were (1) application of localized thermal stresses to 2.29 mm-thick plates of soda-lime glass and (2) double cantilever beam (DCB) experiments in 12.7 mm-thick glass plates, in which a fracture is propagated from a notch at one end of the specimen by application of a transverse load. Fracture propagation velocities of 0.35–2 mm/s were obtained for fractures in the first configuration. A capacitance transducer with a point-like probe was used for measuring the seismic displacement waveforms from propagating fracture sources. This transducer is capable of measuring absolute surface displacements with a resolution of 0.01 nm. It has a flat frequency response in the range 10 kHz to 6 MHz. Measured seismic efficiencies, or the ratio of radiated seismic energy to strain energy released, are in the range 10^–5 to 10^–3.     

High precision tilt observation at Mt. Etna Volcano,Italy

In 2007–2008, we installed on Mt. Etna two deep tilt stations using high resolution, self-leveling instruments. These installations are a result of accurate instrument tests, site selection, drilling and sensor positioning that has allowed detecting variations related to the principal diurnal and semidiurnal tides for first time on Mt. Etna using tilt data.     

A low magnitude seismic sequence near Isernia (Molise,Central Italy) in January 1986

Following the increase in seismic activity which occurred near Isernia (Molise, Central Italy) in January 1986, a digital seismic network of four stations with three-component, short-period seismometers, was installed in the area by the Osservatorio Vesuviano. The temporary network had an average station spacing of about 8–10 km and, in combination with permanent local seismic stations, allowed the accurate determination of earthquake locations during an operating period of about one month. Among the 1517 detected earthquakes, 170 events were selected with standard errors on epicentre and depth not greater than respectively 0.5 and 1.5 km. The most frequent focal depths ranged between 4 and 8 km, while the epicentres distribution covered a small area NE of Isernia of about 10 km². A main rupture zone could not be clearly identified from the spatial distribution of the earthquakes, suggesting a rupture mechanism involving heterogeneous materials. The activity was characterized by low energy levels, the largest earthquake, on January 18, 1986, havingM _D =4.0. The time sequence of events and pattern of seismic energy release revealed a strong temporal clustering of events, similar to the behaviour commonly associated with seismic swarms.     

Measurements of tidal gravity and load deformations on Unst (Shetlands)

Summary The tidal gravimetric factor due to the elastic yielding of the Earth has been determined by gravimetric measurements on Unst (Shetland Islands), extending over the time of one month. Its corrected value isG=1.205±0.03. The influence of applying different methods of harmonic analysis, and the effects of ambient temperature and pressures and of the sea tides on the gravimetric results are discussed. No significant difference inG for semi-diurnal and diurnal tides remains after the necessary corrections have been made. The amplitude of the semidiurnal load depression is about 2 cm and it is shown that the more distant North Atlantic tides have a greater effect than the regional tides near the Shetlands. An approximate calculation gives 4.3×10¹¹ CGS-units as the mean rigidity of the part of the Earth's crust yielding to the maritime loading differences in this region.     

Finite strain theories and comparisons with seismological data

All the finite strain equations that we are aware of that are worth considering in connection with the interior of the Earth are given, with the assumptions on which they are based and corresponding relationships for incompressibility and its pressure derivatives in terms of density. In several cases, equations which have been presented as new or independent are shown to be particular examples of more general equations that are already familiar. Relationships for deriving finite strain equations from atomic potential functions or vice versa are given and, in particular it is pointed out that the Birch-Murnaghan formulation implies a sum of power law potentials with even powers. All the equations that survive simple plausibility tests are fitted to the lower mantle and outer core data for the PEM earth model. For this purpose the model data are extrapolated to zero temperature, using the Mie-Grüneisen equation to subtract the thermal pressure (at fixed density) and the pressure derivative of this equation to substract the thermal component of incompressibility. Fitting of finite strain equations to such zero temperature data is less ambiguous than fitting raw earth model data and leads immediately to estimates of the low temperature zero pressure parameters of earth materials. On this basis, using the best fitting equations and constraining core temperature to give an extrapolated incompressibilityK ₀=1.6×10¹¹Pa, compatible with a plausible iron alloy, the following numerical data are obtained: Core-mantle boundary temperature 3770 K Zero pressure, zero temperature densities: lower mantle 4190 kg m^–3 outer core (solidified) 7500 kg m^–3 Zero pressure, zero temperature incompressibility of the lower mantle 2.36×10¹¹PaHowever, an inconsistency is apparent betweenP() andK() data, indicating that, even in the PEM model, in which the lower mantle is represented by a single set of parameters, it is not perfectly homogeneous with respect to composition and phase.     

Analysis of observations with dual sensor superconducting gravimeters

Among the 21 superconducting gravimeters presently operating worldwide four instruments exist that are equipped with two vertically aligned sensor units. Three of the instruments are installed in Germany (Bad Homburg, Moxa, Wettzell) and one in South Africa (Sutherland). Comparisons of the data sets obtained with the dual sensor systems yield information on instrumental effects and sensitivity as well as on the efficiency of reductions of environmental effects applied to the data. The latter is an important constraint when looking for small geodynamic signals like Slichter and core modes or aperiodic variations.From analyses of the two data sets of each instrument a small but significant difference of 1-3% in the response of the sensor units on barometric pressure variations is found. Likewise, the records of lower and upper sensor vary slightly but not systematically with regard to the noise levels in the different frequency ranges. The tidal analyses yield an agreement of the tidal parameters generally well within the standard deviations determined from the least squares adjustment in the tidal analysis. The deviations are in the range between 0×10⁻⁴ and 3×10⁻⁴ for the amplitude factor and the phases differ between 0.0005° and 0.01° for the four main tidal constituents O1, K1, M2, and S2.The comparison of the gravity residuals of the two sensors with each other as well as with their sum and difference in the time and frequency domain shows the existence of identical signals in the records of the two sensors in the whole range of observation. This probably means that either the environmental reductions applied are not sufficient or there are additional disturbing effects in the data which have not been taken care of yet. From the study it emerges that it is not possible to get entirely rid of the tidal signals in the data. This is probably also due to the fact that despite reductions the data sets contain additional signals and slightly different noise at tidal frequencies which affect the result of the tidal analysis.     

广东中山晚更新世最早海侵层与水动型海平面变化

中山市珠海格力商业大厦场址钻孔表明，距今（４５１２０±９１０）ａ海水已经侵入珠江三角洲地区，当时海平面约在－３４．７ｍ。沉积剖面及其比较研究表明，场区从晚更新世海侵以来是连续的滨海相沉积；场区还是晚更新世海侵以来差异构造运动显著的珠江三角洲（乃至东南沿海）地区地壳的一块“稳定小岛”。其晚更新世以来的滨海相沉积反映了渐进上升的实际水动型海平面变化     

Observation of recent tectonic movements by extensometers in the Pannonian Basin

In Hungary four extensometric observatories were established in the last two decades. The extensometers were installed primarily for observations of Earth tides. A 15-year continuous data series (1991–2005) was recorded at the Sopronbánfalva station and a 7-year record (1993–1999) was obtained at the Pécs station. The length of the measured continuous data series at the two other stations (Bakonya and Budapest) is only a few years. The long-term data records were also applied to the investigation of long-periodic deformations caused by recent tectonic movements. To get an insight into the present day tectonic processes on the margin of the Pannonian Basin, the measurement results of two additional stations (Vyhne in Slovakia and Beregovo in Ukraine) were also included into the investigations. The seasonal variations in the long data series due to temperature and air pressure effects were eliminated. The residual curve – after the correction of the seasonal effects and filtering the “high frequency” components (e.g. earthquakes, Earth tides, etc.) – contains the instrumental drift. It is impossible to determine this curve mathematically. It can be diminished by special instrumental solutions and by regular calibration of the instruments. This paper shows methods and possible solutions how the instrumental drift was investigated and eliminated in order to get the most reliable data for studying recent tectonic movements. The reliability of the extensometric measurements was tested by the tidal evaluation of the data series. The results of the observations show that the Pannonian Basin is under compressive stress. The strain rates measured by extensometers on the margin of the basin are about three orders of magnitude higher than the intra-plate strains obtained by GPS measurements. The reason for this large difference arises from the interaction between the plate boundary and intra-plate forces and from the different measurement techniques. Investigations showed that the rate of the tectonic movements varies, and depends on the local geographical and topographical conditions.