勘探地球物理專業(yè)術(shù)語匯編

1、勘探地球物理專業(yè)術(shù)語匯編（中英對照）前言 本匯編節(jié)選自地球物理學(xué)家R.E.Sheriff所著Encyclopendic Dictionary of Exploration Geophysics。內(nèi)容按地球物理中的主要方向分別編排為地震、電磁、重磁、測井及數(shù)據(jù)處理，涉及到主要術(shù)語近500個(gè)并配備了中文譯文?？勺鳛榭辈榧夹g(shù)與工程及地球物理學(xué)專業(yè)本科學(xué)生專業(yè)英語的輔助教材，也可供有關(guān)研究生或技術(shù)人員參考。限于譯者的水平和時(shí)間倉促，錯誤之處敬請批評指正。CONTENTS Gravity1 Magnetic11 Electrical21 Seismic31 Log78 Data precessing83

2、Gravity重力accuracy: 1. The degree of freedom from error; the total error compared to the true value. Compare precision, uncertainty, and sensitivity. 2. The capability of an instrument to follow a true value. Inaccuracy is the departure from the true value due to any instrument error such as lack of

3、repeatability, drift, temperature effects, or other causes.準(zhǔn)確度：1. 誤差的自由度；相對于真實(shí)值的總誤差。參照精度、不確定性和靈敏度。2. 儀器測量真實(shí)值的能力。不準(zhǔn)確度是由于儀器誤差如復(fù)測正確度、掉格、溫度影響或其它原因引起的偏離真實(shí)值的誤差。AGC: Automatic gain control.AGC：自動增益控制。Airy Hypothesis: A mode of compensation for isostasy in which topographically elevated areas are compensate

4、d by underlying “roots” of crustal material penetrating into the higher density subcrust.艾里假說：地殼均衡補(bǔ)償?shù)囊环N模式，認(rèn)為地形升高的區(qū)域可由它下面扎入更高密度地殼物質(zhì)形成的“根”來補(bǔ)償。alias: An ambiguity in the frequency represented by sampled data. Where there are fewer than two samples per cycle, an input signal at one frequency yields the

5、same sample values as (and hence appears to be ) another frequency at the output of the system. Half of the frequency of sampling is called the “folding” or “Nyquist” frequency fN; a frequency larger than this, fN+Y, appears to be the smaller frequency, fN-Y. The two frequencies, fN+Y and fN-Y are “

6、aliases” of each other. Thus , for a signal sampled every 4 msec, or 250 times per second, the Nyquist frequency is 125 hz; if, for example, 50 hz is within the passband, then 200 hz will also be passed if an alias filter has not been used and will appear in the output to have a 50 hz frequency. To

7、avoid aliasing, frequencies above the Nyquist frequency must be removed by an alias filter before the sampling. The passbands obtained by folding about the Nyquist frequency are called alias bands, side lobes, and secondary lobes. Aliasing is an inherent property of all sampling systems. It applies

8、to digital seismic recording, to the sampling which is done by the separate elements of geophone and shotpoint arrays, and to sampling such as done in gravity surveys where the potential field is determined only at discrete stations, etc.假頻：采樣數(shù)據(jù)所表現(xiàn)出的頻率的多值性。當(dāng)每周期少于兩個(gè)采樣點(diǎn)時(shí)，某一頻率的輸入信號與系統(tǒng)輸出端另一頻率的信號具有（看起來象是

9、）相同的采樣值。采樣頻率的一半叫作“折疊頻率”或“奈奎斯特頻率”fN；大于該頻率的頻率fN+Y與小于該頻率的頻率fN-Y看起來很象。這兩個(gè)頻率fN+Y 和 fN-Y相互“混疊”。因此，對于采樣間隔為4毫秒的信號，或者說每秒采樣250次的信號，其奈奎斯特頻率為125 hz；例如，設(shè)頻率為50 hz的信號在通頻帶內(nèi)，如果不用去假頻濾波器，則頻率為200 hz的信號在輸出端也會得到頻率為50 hz的輸出信號。為避免頻率混疊現(xiàn)象，在采樣之前必須用去假頻濾波器將高于奈奎斯特頻率的頻率成分濾除。由奈奎斯特頻率折疊得到的通頻帶叫作假頻通帶、旁瓣和副瓣?；殳B是所有采樣系統(tǒng)的固有特性。適用于數(shù)字地震記錄、檢波器

10、和炮點(diǎn)排列的單個(gè)元素采樣、和重力測量中大小僅取決于離散點(diǎn)位置的位場的采樣等等。amplitude spectrum: Amplitude-versus-frequency relationship such as is computed in a Fourier analysis. See Fourier transform.振幅譜：由傅立葉分析計(jì)算得到的振幅與頻率的關(guān)系曲線。見傅立葉變換。antiroots: Shallow high-density mantle material beneath thin portions of the relatively light crust. Ch

11、aracterized by shallow Moho. The effect is to bring topographically low areas (like ocean basins ) into isostatic equilibrium. 反山根：淺層高密度地幔物質(zhì)，它位于密度相對較輕的地殼細(xì)薄部分的下面。以淺層莫霍界面為標(biāo)志。其作用是對地形低的區(qū)域（如大洋盆地）進(jìn)行均衡補(bǔ)償。Bouguer anomaly: 1. The residual value obtained after latitude correction, elevation correction (includ

12、ing both free-air and Bouguer corrections), and terrain correction have been applied to gravity data. 2. Sometimes, a departure from smoothness in the contours on a map showing Bouguer gravity values (an anomaly in Bouguer anomaly values).布格異常：1. 重力資料經(jīng)緯度改正、高程改正（包括自由空間改正和布格改正）和地形改正后的剩余值。2. 有時(shí)指布格重力等值線

13、圖中偏離于平滑值的差值（布格異常值中的異常）。Bouguer correction: A correction to gravity data because of the attraction of the rock between the station and the elevation of the datum (often sea level) or, in the case of stations below the datum elevation, for the rock that is missing between the station and datum. The Bo

14、uguer correction is 0.4185 h mgal, where is the specific gravity of the intervening rock and h is the difference between the station and datum elevations in meters (or 0.01276 ph mgal if h is in feet). In surface ship gravity data, the Bouguer correction replaces the sea water with rock and in the p

15、receding expression is the difference in specific gravity of the rock and that of sea water (usually taken as 1.03).布格改正：由于測點(diǎn)與基準(zhǔn)面（通常為海平面）高程之間的巖石引力或因測點(diǎn)低于基準(zhǔn)面高程造成測點(diǎn)與基準(zhǔn)面之間沒有巖石存在等原因而對重力資料進(jìn)行的校正。布格改正表達(dá)式為0.4185 h毫伽，其中是中間層巖石密度，h為測點(diǎn)與基準(zhǔn)面之間的高程差，單位為米（或0.01276 ph毫伽，h的單位為英尺）。對于船上重力資料，布格改正以巖石代替海水，而前面所給表達(dá)式中的則為巖石比重與海

16、水比重之差（常?。?。continuation: Determining from a set of measurements of a potential field made over one surface what values the field will have over another surface (specifically at another elevation).延拓：由一個(gè)面上的一組位場測量值來確定該場在另一個(gè)面上的值（尤其是另一個(gè)高程面）。density: Mass per unit volume. Commonly measured in gm/cm3 = 103

17、kg/m3, often without the units being expressed explicitly.密度：單位體積上的質(zhì)量。一般用克/厘米3=103千克/米3來度量，通常沒有明確的表示單位。density contrast: The difference in density between two formations.密度差：兩巖層之間密度的差值。depth of compensation: The assumed depth at which the pressure due to the overlying crustal elements is constant an

18、d below which lateral density variations disappear. Involved in isostatic correction sometimes taken as the top of the asthenosphere. See also Pratt hypothesis.補(bǔ)償深度：一個(gè)假定深度，在此處上覆地殼成分產(chǎn)生的壓力為常數(shù)且該深度以下橫向密度變化消失。在均衡校正中有時(shí)將其作為軟流層的頂部。見普拉特假說。dot chart: A chart used to compute the theoretical gravity (or other p

19、otential) effect of a mass distribution. A dot chart is superimposed on a scale cross-section drawn through the mass; the number of dots which fall within the mass outline multiplied by the anomalous density is proportional to the gravity effect at the origin of the chart. The chart is then moved to

20、 a different position on the outline and the number of dots counted again to give the effect at another point, and so on for every point for which the gravity value is to be determined. Most charts assume that the mass distribution extends to infinity perpendicular to the plane of the chart and end

21、corrections have to be applied to remove this restriction. Also called graticule. 布點(diǎn)量板：用來計(jì)算某一質(zhì)量分布的理論重力（或其它位場）效應(yīng)的曲線圖。布點(diǎn)圖疊加在由質(zhì)量繪制而成的相似比例橫剖面上；落在質(zhì)量略圖內(nèi)的點(diǎn)的個(gè)數(shù)乘于異常密度正比于原圖中的重力效應(yīng)。然后移動布點(diǎn)圖在質(zhì)量略圖上的位置，重新計(jì)算點(diǎn)的個(gè)數(shù)給出另一點(diǎn)上的重力效應(yīng)，依此類推確定出每個(gè)點(diǎn)上的重力值。多數(shù)布點(diǎn)圖都假定質(zhì)量分布在垂直于圖形平面方向上無限延伸，因此必須進(jìn)行末端改正來去除這一限制。也叫格子量板。double Bouguer correction

22、: The Bouguer correction to sea level for measurements made on the ocean floor involves a correction to remove the upward attraction of the sea water above the meter and another correction to replace the sea water with the replacement density. Similar double corrections are required for measurements

23、 made in mines or in boreholes.雙重布格改正：海底測量數(shù)據(jù)到海平面的布格改正，包括去除重力計(jì)上面海水向上的引力以及用等效密度來替換海水密度。在礦井或鉆孔測量時(shí)也需要進(jìn)行類似的“雙重”校正。downward continuation: The process of determining from values measured at one level the value of a potential (e.g., gravitational) field at a lower level. The potential field is not continuou

24、s across the boundaries of anomalous masses; as the depth from which anomalies originate is approached, their potential field expression becomes sharper and tends to outline the mass better until the depth of the mass is reached, whereupon the field computed by continuation becomes erratic. Noise in

25、 the data often precludes successful application. See continuation.向下延拓：由某一平面上位場（如重力場）測量值來計(jì)算位場在更低一個(gè)平面上的值。異常質(zhì)量邊界處位場是不連續(xù)的；隨著深度向產(chǎn)生異常的位置靠近，位場表現(xiàn)的越來越明顯且質(zhì)量輪廓越來越好，直到達(dá)到質(zhì)量深度位置，因此由延拓計(jì)算得到的場變的沒有規(guī)律。資料中的噪聲通常會妨礙延拓的成功進(jìn)行。見延拓。elevation correction: l. The correction applied to reflection or refraction time values to re

26、duce observations to a common reference datum. 2. In gravity, the sum of the free air and Bouguer corrections. The elevation correction is obtained by multiplying the difference between station and reference elevation by the elevation correction factor (ecf).ecf = (0.0941-1 276) mgal/ft - 0.004185)

27、mgal/m,where = density.高程改正：l. 將反射或折射時(shí)間值還原到一個(gè)公共參考基準(zhǔn)面上的校正方法。2. 重力場中的自由空間改正和布格改正之和。高程改正可由測點(diǎn)高程與參考高程的差乘于高程改正因子（ecf）得到。ecf = (0.0941 - 0.01 276) 毫伽/英尺 - 0.004185) 毫伽/米其中為密度。field continuation: See continuation.位場延拓：見延拓。figure of the earth: Geoid.大地水準(zhǔn)面：重力平面。free-air anomaly: Gravity data which have been c

28、orrected for latitude and elevation (free-air correction) but not for the density of the rock between datum and the plane of measurement (Bouguer correction).自由空間異常：經(jīng)緯度改正和高程改正（自由空間改正）后的重力資料，但沒有進(jìn)行基準(zhǔn)面與測量面之間的巖石密度改正（布格改正）。free-air correction: 1. A correction for the elevation of a gravity measurement re

29、quired because the measurement was made at a different distance from the center of the earth than the datum. The first term of the mgal/m. 2. In Turam, normalizing a ratio of successive measurements by dividing by the ratio of the calculated free-space vertical magnetic field. Compare normal correct

30、ion.自由空間改正：1./米。2. 土拉姆法中，對連續(xù)測量率通過除于自由空間垂直磁場理論計(jì)算率進(jìn)行標(biāo)準(zhǔn)化。參照正常改正。free oscillation of the earth: A simple change-of-shape oscillation of the whole earth. The period is 53 minutes in the lowest mode. 地球自由震蕩：地球整體形狀變化的簡諧震蕩。最小振動周期為53分鐘。gal: A unit of acceleration, used in gravity measurements. One gal = l cm

31、/sec2 = l0-2 m/sec2. The earths nominal gravity is 980 gal.伽：加速度單位，用于重力測量。1伽=1厘米/秒2= l0-2米/秒2。地球正常重力為980伽。geodesy: The study of the earths form and gravitational field. Involves the location of points on the earth with respect to reference systems.大地測量學(xué)：研究地球形狀和重力場的一門學(xué)科。包括確定地球上的點(diǎn)相對于參照系的位置。geoid: The

32、sea-level equipotential surface to which the direction of gravity is everywhere perpendicular. An oblate ellipsoid of revolution (the spheroid) which approximates the geoid is the reference for geodetic latitude determinations.大地水準(zhǔn)面：重力方向處處鉛垂的海水等位面。近似地球體的一個(gè)旋轉(zhuǎn)橢球面，即大地緯度測定的一個(gè)參考面。gradiomanometer: A devic

33、e for determining the density of the wellbore fluid by measuring the pressure on two bellows and therefore the vertical pressure gradient 壓差密度計(jì)：通過測量兩個(gè)感壓箱的壓力和其垂直壓力梯度來測定井身流體密度的一種儀器。gradiometer: A device for measuring the gradient of a potential field. 1. An arrangement of two magnetometers, one above

34、the other, so that the difference in their readings is proportional to the vertical gradient of the magnetic field. 2. A three-arm torsion balance which is sensitive to gravity gradients but not to curvature.梯度儀：測量位場梯度的一種儀器。1. 兩個(gè)磁強(qiáng)計(jì)的排列，其中一個(gè)在另一個(gè)的上面，因此它們的讀數(shù)之差正比于磁場的垂直梯度。2. 對重力梯度反應(yīng)靈敏而對曲度反應(yīng)不靈敏的三臂扭秤。gravi

35、meter: An instrument for measuring variations in gravitational attraction; a gravity meter. Most present gravimeters are of the unstable or astatic type. The gravitational force on a mass in the meter is balanced by a spring arrangement, and a third force is provided which acts when the system is no

36、t in equilibrium. This third force intensifies the effect of changes of gravity and increases the sensitivity of the system. In the LaCoste-Romberg gravimeter , the main spring which balances out the gravitational pull on the weight is a zero-length spring inclined at an angle. A zero-length spring

37、has a stress-strain curve which passes through zero length when projected back to zero strain. (For example, a spring which requires an initial stress before the coils begin to separate.) Zero-length springs have very long periods and high sensitivity. The Worden gravimeter uses a horizontal torsion

38、 fiber or hinge as the main spring. This and the accessory measuring springs and supports are made of quartz and are very small and hence very light in weight. The Worden meter incorporates temperature-compensating features and is usually encased in a thermos bottle to further reduce its temperature

39、 sensitivity. See also shipboard gravimeter.重力儀：測量地球引力變化的一種儀器；重力儀。多數(shù)現(xiàn)有重力儀為不穩(wěn)定型或無方向型。重力儀本身質(zhì)量引起的重力可通過彈簧布罩來平衡，且當(dāng)系統(tǒng)處于不平衡狀態(tài)時(shí)，系統(tǒng)提供的第三種力將會起作用。該力增強(qiáng)了重力變化的影響，增加了系統(tǒng)的靈敏度。在拉考斯特-隆貝格重力儀中，平衡掉重量萬有引力的主彈簧是一個(gè)以某一角度傾斜的“零長式彈簧”。零長式彈簧的應(yīng)力-應(yīng)變曲線在零應(yīng)變上的投影通過零長。（例如，在簧圈開始分開之前需要一個(gè)初應(yīng)力。）零長式彈簧具有很長的壽命周期以及很高的靈敏度。渥爾登重力儀用一條水平扭絲或“鉸鏈”作為主彈簧。主

40、彈簧和附屬測量彈簧以及支架都是由石英制成的，尺寸很小，因此重量也很輕。渥爾登重力儀具有溫度補(bǔ)償性能，通常被封裝在一個(gè)保溫瓶中以進(jìn)一步減小它的溫度靈敏度。見船載重力儀。gravitational constant: The proportionality constant in Newtons Law of Universal Gravitation. The gravitational force F between two point masses m1 and m2 can be related to the distance r between them:F = mlm2/r2.10-1

41、1 newton m2/kg2. The gravitational acceleration g is the force per unit (face on the mass which is in the gravimeter):g = F/m1 = m2/r2.萬有引力常數(shù)：牛頓萬有引力定律中的比例常數(shù)。兩質(zhì)點(diǎn)m1 和 m2之間的萬有引力F與兩點(diǎn)之間的距離r有關(guān)：F = mlm2/r2.10-11牛頓米2/千克2。重力加速度g為單位質(zhì)量上的力（朝著重力儀質(zhì)量方向）：g = F/m1 = m2/r2.gravity: The force of attraction between bod

42、ies because of their mass. Usually measured as the acceleration of gravity. See gravitational constant.重力：物體之間因具有質(zhì)量而產(chǎn)生的引力。通常測量的是重力加速度。見萬有引力常數(shù)。gravity anomaly: 1. Bouguer anomaly. 2. The difference between the gravity which is observed and that expected from a model. 3. Residual gravity. 重力異常：1. 布格異常

43、。2. 重力觀測值與模型期望值之差。3. 剩余重力值。gravity meter: Gravimeter.比重計(jì)： 重力儀。gravity reduction: Applying Bouguer elevation, free-air, isostatic, latitude, or terrain corrections to gravity measurements.重力改正：將布格高程改正、自由空間改正、均衡改正、緯度改正、或地形改正應(yīng)用于重力測量。gravity survey: Measurements of the gravitational field at a series of

44、 different locations over an area of interest. The objective in exploration work is to associate variations with differences in the distribution of densities and hence of rock types. Occasionally the whole gravitational field is measured (as with a pendulum) or derivatives of the gravitational field

45、 (as with a torsion balance), but usually the difference between the gravity field at two points is measured (as with a gravimeter). Gravity data usually are displayed as Bouguer or free-air anomaly maps. 重力調(diào)查：在某一靶區(qū)上對一系列不同位置處的重力場所進(jìn)行的測量。調(diào)查工作的目的是將重力變化與密度分布以及巖石類型聯(lián)系起來。有時(shí)侯需測量絕對重力場（如通過單擺）或重力場的導(dǎo)數(shù)（如通過扭力平衡），

46、但通常所測的是兩點(diǎn)之間的重力差（如通過重力儀）。重力資料通常用布格或自由空間異常圖來顯示。gravity unit: A unit of gravitational acceleration, equal to 0.1 mgal or 10-6 m/sec2. Sometimes called G unit.重力單位-6米/秒2。有時(shí)也叫G單位。Gutenberg discontinuity: The boundary between the earths mantle and core.古登堡不連續(xù)面：地幔與地核的分界面。horizontal cylinder: A model used i

47、n calculating potential field effects. A horizontal cylinder infinitely long so that the ends of the cylinder do not produce any effects. The model is equivalent to a line whose mass is A per unit of length when is the density contrast and A is the cross-sectional area of the cylinder.水平圓柱體：用來計(jì)算位場效應(yīng)

48、的一個(gè)模型。水平圓柱無限長，因此圓柱體兩端不產(chǎn)生任何效應(yīng)。該模型可等效為一條單位長度上質(zhì)量為A的直線，其中為密度差，A為圓拄體的橫截面積。isostasy: The gravitational balance of large portions of the earths crust as though they were floating on a denser underlying layer (the asthenosphere); it thus accounts for major topography. The Pratt hypothesis assumes density va

49、riations so that areas of less-dense crust rise topographically above areas of more-dense crust. The Hayford modification of the Pratt hypothesis requires that the pressure be balanced at the depth of compensation. The Airy hypothesis varies the thickness of crustal blocks of constant density so tha

50、t the thicker parts ride higher; thus mountainous areas are compensated by deep roots and deep ocean basins by antiroots. Ocean basins thus may have antiroots at 6-8 km with the roots of mountains extending to 50-60 km. The Heiskanen modification permits density to vary but compensates 2/3 of the to

51、pography with roots. The Vening Meinesz hypothesis allows some of the balance to be accommodated laterally by the surrounding region rather than achieve balance in the vertical direction only; the radius of regionality is of the order of 200 km.地殼均衡說：地殼大部分處于重力均衡，它們好象是漂浮在下伏致密層（軟流層）上一樣；可用來對主要地形做出解釋。普拉

52、特 地殼均衡 假說假定地殼密度是變化的，因此認(rèn)為地殼密度低的地區(qū)的地勢比密度高的地區(qū)要高。普拉特假說的海福特修正則要求“均衡深度”處的壓力是均衡的。艾里假說則認(rèn)為密度為常數(shù)的地殼板塊的厚度是變化的，因此越厚的部分地勢越高；即高山地區(qū)具有很深的“山根”以達(dá)到均衡，而大洋盆地則有“反山根”。大洋盆地反山根在6-8千米深處，而高山地區(qū)的反山根可延深至50-60千米。海斯坎寧修正認(rèn)為密度是變化的，但用作補(bǔ)償?shù)纳礁鶠榈匦胃叨鹊?/3。韋寧邁內(nèi)茲假說認(rèn)為均衡可通過周圍區(qū)域進(jìn)行橫向調(diào)節(jié)而不是僅在垂直方向上達(dá)到均衡；“區(qū)域半徑”為200千米。isostatic correction: A correction

53、 to gravity data to compensate for lateral density or thickness variations between large blocks of the earths crust. The correction must assume a model and is made from elevation data and waterdepth data using zone charts.均衡改正：對重力資料所進(jìn)行的校正以補(bǔ)償?shù)貧ぶ写笮蛪K體之間的橫向密度或厚度變化。必須假定一個(gè)模型利用環(huán)帶量板得到高程和水深數(shù)據(jù)來進(jìn)行校正。latitude c

54、orrection: l. A correction of gravity data because of variation in centrifugal force resulting from the earths rotation as the distance to the earths axis varies with latitude and for variation of the earths radius because of polar flattening. The International Gravity Formula for such variation is0

55、52884 sin2 - 00059 sin22) mgal.The latitude correction amounts to 1.308 sin2 mgal/mile = 0.813 sin2 mgal/km. 2. A gyrocompass correction for the rotation of the horizontal north vector as a function of latitude. (The horizontal north vector is tangent to the earth and hence the rotation is the resul

56、t of earth curvature.)緯度改正：l. 由于地球旋轉(zhuǎn)而引起的離心力隨緯度到地軸距離的變化而變化以及由極向扁率引起的地球半徑的變化而對重力資料進(jìn)行的校正。該變化的國際正常重力公式為：052884 sin2 - 00059 sin22) 毫伽。而緯度改正等于1.308 sin2毫伽/英里= 0.813 sin2毫伽/千米。2. 對水平向北矢量以緯度為函數(shù)旋轉(zhuǎn)而做的回轉(zhuǎn)羅盤校正。（水平向北矢量與地面相切，因此矢量旋轉(zhuǎn)是由地球曲率引起的。）local gravity: Bouger value from which the regional has been subtracted;

57、 residual.局部重力值：扣除區(qū)域重力值后的布格重力值；剩余重力值。normal gravity: The value of gravity at sea level according to a theoretical formula which assumes the earth to have a simple regular ellipsoidal shape. See latitude correction.正常重力：假定地球?yàn)橐粋€(gè)簡單而規(guī)則的橢球體時(shí)，由理論公式得到的海平面處的重力值。見緯度改正。Poissons equation：In space where the sou

58、rce density is , the Laplacian of a potential U is2 U = 4K,where is the operator del and K is a constant (gravitational constant in case of mass and gravitational potential). The constant 4 is deleted in the mks system. In empty space where = 0, this becomes Laplaces equation.泊松方程：在源密度為的空間中，位場U的拉普拉斯

59、算子為：2 U = 4K,其中為del算子，K為常數(shù)（質(zhì)量的萬有引力常數(shù)和重力勢）。在米-千克-秒單位制中應(yīng)去掉常數(shù)4。真空中 = 0，則變成拉普拉斯方程。Pratt hypothesis: A model of compensation for isostasy in which topographically high areas are compensated by lower-density crustal material. The densities are so related to the surface elevations that pressures are everyw

60、here equal at a uniform depth of compensation. Compare Airy hypothesis.普拉特假說：認(rèn)為地形高的區(qū)域可由其地殼物質(zhì)的低密度來補(bǔ)償?shù)囊环N地殼均衡模型。密度與地面高程緊密相關(guān)使得在同一個(gè)均衡深度上的壓力處處相等。參照艾里假說。second-derivative map: A map of the second vertical derivative of a potential field, such as gravity. Such maps tend to emphasize local anomalies and isol