238 resultados para periodicity fluctuation
Resumo:
The effects of fresh thalli and culture medium filtrates from two species of marine macroalgae, Ulva pertusa Kjellm (Chlorophyta) and Gracilaria lemaneiformis (Bory) Dawson (Rhodophyta), on growth of marine microalgae were investigated in co-culture under controlled laboratory conditions. A selection of microalgal species were used, all, being identified as bloom-forming dinoflagellates: Prorocentrum donghaiense Lu sp., Alexandrium tamarense (Lebour) Balech, Amphidinium carterae Hulburt and Scrippsiella trochoide (Stein) Loeblich III. Results showed that the fresh thalli of either U. pertusa or G. lemaneiformis significantly inhibited the microalgal growth, or caused mortality at the end of the experiment. However, the overall effects of the macroalgal culture filtrates on the growth of the dinoflagellates were species-specific (inhibitory, stimulatory or none) for different microalgal species. Results indicated an allelopathic effect of macroalga on the co-cultured dinoflagellate. We then took P. donghaiense as an example to further assess this hypothesis. The present study was carried out under controlled conditions, thereby excluded the fluctuation in light and temperature. Nutrient assays showed that nitrate and phosphate were almost exhausted in G. lemaneiformis co-culture. but remained at enough high levels in U pertusa co-culture, which were well above the nutrient limitation for the microalgal growth, when all cells of P. donghaiense were killed in the co-culture. Daily f/2 medium enrichment greatly alleviated the growth inhibition on P. donghaiense in G. lemaneiformis co-culture, but could not eliminate it. Other environmental factors, such as carbonate limitation, bacterial presence and the change of pH were also not necessary for the results. We thus concluded that allelopathy was the most possible reason leading to the negative effect of U. pertusa on P. donghaiense, and the combined roles of allelopathy and nutrient competition were essential for the effect of G. lemaneiformis on P. donghaiense. (c) 2006 Elsevier B.V. All rights reserved.
Resumo:
Prolonged floral longevity and bumblebees as dominate pollinators in alpine ecosystem have been suggested to overcome pollination limitation of alpine plants arising from the decrease of pollinator activity with increasing altitude. However, this conclusion has never been examined in the Qinghai-Tibetan Plateau (QTP), the highest and largest plateau in the world. In this study, we intended to test year-to-year correlations between floral longevity, visiting frequency and pollen limitation of this species between two populations (at 3200 m and 4000 m) of Gentiana straminea in this plateau. Pollinator exclusion elongated both male and female phases greatly at both sites, and durations of both male and female phases in natural condition varied greatly over three years. The visiting frequency of bumblebees varied greatly at the higher altitude, but seemed to be stable at the lower altitude. Seed production was pollination limited in both populations in most studied years. The floral durations, pollinator frequency and pollination limitation showed no significant and consistent variations with the increase of altitude. The previous hypothesis that the prolonged floral longevity of alpine plants can compensate for low levels of pollinator visitation therefore could not be confirmed, and our results further suggested that in the QTP platform, the altitude shows no consistent effect on the reproductive performance of this species, despite that the fluctuation of visit frequency intensified at the higher altitude.
Resumo:
1. Complete sequences of 1140 base pair of the cytochrome b gene from 133 specimens were obtained from nine localities including the inflow drainage system, isolated lakes and outflow drainage system in Qinghai-Tibetan Plateau to assess genetic diversity and to infer population histories of the freshwater fish Schizopygopsis pylzovi.2. Nucleotide diversities (pi) were moderate (0.0024-0.0045) in populations from the outflow drainage system and Tuosuo Lake, but low (0.0018-0.0021) in populations from Qiadam Basin. It is probable that the low intra-population variability is related with the paleoenvironmental fluctuation in Qiadam Basin, suggesting that the populations from Qiadam Basin have experienced severe bottleneck events in history.3. Phylogenetic tree topologies indicate that the individuals from different populations did not form reciprocal monophyly, but the populations from the adjacent drainages cluster geographically. Most population pairwise F-ST tests were significant, with non-significant pairwise tests between Tuosu Lake and Tuosuo Lake in the north-west of the Qinghai-Tibetan Plateau. Analysis of molecular variance (AMOVA) indicates that the significant genetic variation was explained at the levels of catchments within and among, not among specific boundaries or inflow and outflow drainage systems.4. The nested clade phylogeographical analysis indicates that historical processes are very important in the observed geographical structuring of S. pylzovi, and the contemporary population structure and differentiation of S. pylzovi may be consistent with the historical tectonic events occurred in the course of uplifts of the Qinghai-Tibetan Plateau. Fluctuations of the ecogeographical environment and major hydrographic formation might have promoted contiguous range expansion of freshwater fish populations, whereas the geological barriers among drainages have resulted in the fragmentation of population and restricted the gene flow among populations.5. The significantly large negative F-s-value (-24.91, P < 0.01) of Fu's F-s-test and the unimodal mismatch distribution indicate that the species S. pylzovi underwent a sudden population expansion after the historical tectonic event of the Gonghe Movement.6. The results of this study indicate that each population from the Qinghai-Tibetan Plateau should be managed and conserved separately and that efforts should be directed towards preserving the genetic integrity of each group.
Resumo:
A study was carried out to examine the effect of dynamic photosynthetically active photon flux density (PPFD) on photoinhibition and energy use in three herbaceous species, prostrate Saussurea superba, erect-leaved S. katochaete, and half-erect-leaved Gentiana straminea, from the Qinghai-Tibet Plateau. Chlorophyll fluorescence response was measured under each of three sets of high-low PPFD combinations: 1700-0, 1400-300, and 1200-500 mu mol m(-2) s(-1), illuminating in four dynamic frequencies: 1, 5, 15, and 60 cycles per 2 h. The total light exposure time was 2h and the integrated PPFD was the same in all treatments. The highest frequency of PPFD fluctuation resulted in the lowest photochemical activity, the highest level of non-photochemical quenching, and the greatest decrease of F-v/F-m (maximal photochemical efficiency of PSII). The 5 and 15 cycles per 2h treatments resulted in higher photochemical activity than the 1 cycle per 2h treatment. The 1700-0 PPFD combination led to the lowest photochemical activity and more serious photoinhibition in all species. S. superba usually exhibited the highest photochemical activity and CO2 uptake rate, the lowest reduction of F-v/F-m,F- and the smallest fraction of energy in thermal dissipation. With similar fractions of thermal dissipation, S. katochaete had relatively less photoinhibition than G. straminea owing to effective F-o quenching. The results suggest that high frequency of fluctuating PPFD generally results in photoinhibition, which is more serious under periods of irradiation with high light intensity. (c) 2005 Elsevier B.V. All rights reserved.
Resumo:
To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau, CO2 flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons. CO2 flux dynamics was distinct between the two seasons. During the growing season from May to September, the ecosystem exhibited net CO2 uptake from 08:00 to 19:00 (Beijing Standard Time), but net CO2 emission from 19:00 to 08:00. Maximum CO2 uptake appeared around 12:00 with values of 0.71, 1,19, 1.46 and 0.67 g CO2 m(-2) h(-1) for June, July, August and September, respectively. Diurnal fluctuation Of CO2 flux showed higher correlation with photosynthetic photon flux density than temperature. The maximum net CO2 influx occurred in August with a value of 247 g CO2 m(-2). The total CO2 uptake by the ecosystem was up to 583 g CO2 m(-2) for the growing season. During the non-growing season from January to April and from October to December, CO2 flux showed small fluctuation with the largest net CO2 efflux of 0.30 g CO2 m(-2) h(-1) in April. The diurnal CO2 flux was close to zero during most time of the day, but showed a small net CO2 eff lux from 11:00 to 18:00. Diurnal CO2 flux, is significantly correlated to diurnal temperature in the non-growing season. The maximum monthly net CO2 eff lux appeared in April, with a value of 105 g CO2 m(-2). The total net CO2 eff lux for the whole non-growing season was 356 g CO2 m(-2).
Resumo:
基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用有限元软件ANSYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯塑料压力管道热板焊接过程。并对焊接接头的应力分布进行有限元分析,得到了环向、轴向及径向瞬态应力分布规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本吻合。
Resumo:
研究了非线性控制理论中的近似线性化方法在移动机器人控制上的应用问题。针对机器人控制领域中多输入多输出(MIMO)仿射非线性系统,研究了一种基于平衡流形的近似线性化算法,并用此算法解决了一类完整约束正交轮式全方位移动机器人(WMR)的镇定问题。仿真分析表明,此方法不仅能够实现系统的镇定,而且降低了因平衡工作点变动给系统稳定性带来的影响,同时也大大地简化了对非线性系统的综合设计过程,具有良好的控制效果和实用性。
Resumo:
针对机器人控制领域中一类多输入多输出(MIMO)仿射非线性系统,提出了一种基于平衡流形的近似线性化状态反馈镇定算法,并用此算法解决了一类完整约束轮式移动机器人(WMR)的镇定问题.仿真分析表明,此方法不仅能够实现系统的镇定,而且降低了因平衡工作点变动给系统稳定性带来的影响,同时也大大地简化了对非线性系统的综合设计过程,具有良好的控制效果和实用性.
Resumo:
基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用AN SYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯(HDPE)塑料压力管道热板焊接过程,并对焊接接头的应力分布进行有限元分析,得到了环向、轴向以及径向瞬态应力分布的基本规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本符合
Resumo:
The Indian monsoon, an integral part of the global climate system, has been extensively investigated during the past decades. Most of the proxy records are derived from marine sediments and focused on time periods of the late Miocene and Pleistocene. The Pliocene represents a period when Earth’s boundary conditions underwent dramatic changes. However, variations of the Indian monsoon during the Pliocene and its forcing mechanisms have remained unclear. The Yuanmou Basin, located in the region of the Indian monsoon, provides an ideal target for understanding the Pliocene history of Indian monsoon variations. Detailed investigations on the lithostratigraphy, magnetostratigraphy and limnology of a 650-m-thick fluvio-lacustrine sedimentary sequence from the basin are carried out in the present study. The clay and clay-plus-fine-silt fractions of the sediments are referred to the midlake-facies components, and changes in the percentages of both fractions generally reflect changes in the water level of the lakes developed in the basin closely related to variations in the intensity of the Indian monsoon. Whereas the greenish-gray lacustrine mud beds represent the environment of deep-water lakes, and the frequency of individual lacustrine mud beds is considered to indicate the frequency of the deep-water lakes developed in the basin associated with the variability of the Indian monsoon. The proxy data suggest that the Indian monsoon experienced abrupt shifts at 3.53, 3.14, 2.78 and 2.42 Ma, respectivey. 1) Since 3.53 Ma, the midlake-facies components displayed a general trend of increase in the concentrations, accompanied by an increase in the sedimentation rate from an average ~10 to 25 cm ka–1. The data suggest that high stands of the lakes in the basin rose progressively, implying a gradual intensification of the Indian monsoon since that time. This shift occurred coeval with the accelerated uplift of the northern Tibetan Plateau, denoting a close link between the Indian monsoon strengthening and the Tibetan Plateau uplifting. 2) 2.78 Ma ago, the concentrations of the midlake-facies components decreased abruptly and the dominant fraction of the sediments turned to fluvial sands. The data indicate that lakes in the basin disappeared, reflecting a dramatic decline in the intensity of the Indian monsoon at that time. This shift coincided with the formation of extensive Northern Hemisphere ice sheets, implying a quick response of the low-latitude monsoon regime to the high-latitude glaciation. 3) At 3.14 Ma, the initial appearance of blackish-grey mud beds with long durations and occasional occurrences of lacustrine mud beds indicate that the basin was overall dominated by shallow lakes, implying a shift to decreased variability of the Indian monsoon at that time. At 2.42 Ma, an increase in the frequency and a decrease in the duration of the lacustrine mud beds suggest that deep-water lakes were frequently developed in the basin, denoting a shift to increased variability of the Indian monsoon at that time. The former shift coincides with the onset of large-scale glaciation in the circum Atlantic region and the latter corresponds to the inception of predominance of the 41 ka periodicity in Northern Hemisphere ice-sheet cover fluctuations, presumably suggesting a physical link between the Indian monsoon system and the high-latitude ice sheets in the Northern Hemisphere.
Resumo:
Petroleum and natural gas is an important strategic resources. The short of the reserves will block the development of economy and threaten the safety of nation, along with the main oil fields of our country coming to the height of power and splendor of the exploitation and exploration. Therefore, it makes a great sense to inaugurate new explorative field and increase the reserves of petroleum and natural gas. Magnetic exploration is a main method of geophysics exploration. the developing observation apparatus and the perfect processing method provide wide space for magnetic exploration in these years. The method of magnetic bright spot is an application of magnetic exploration. The vertical migration of the hydrocarbon changes physical and chemical environment above the hydrocarbon reservoir, the new environment make tervalent iron translate into bivalent iron, that produce small scale magnetic anomaly, that is magnetic bright spot. The method of magnetic bright spot explores oil and gas field by the relation between the hydrocarbon and magnetic anomaly. This paper systemically research to pick-up and identify magnetic bright spot combining an oil field item, then point out advantaged area. In order to test the result, the author use the seismic information to superpose the magnetic bright spot, that prove the magnetic bright spot is reliable. then, the author complete a software to pick and identify the magnetic bright spot. The magnetic basement is very important to research forming and evolvement of the basin, especially, it is a crucial parameter of exploring residual basin in the research on pre-Cenozoic residual. This paper put forward a new method to inverse the interface of the magnetic layer on the basis of previous work, that is the method of separation of magnetic field step by step. The theory of this method is to translate the result of magnetic layer fluctuation to the result of magnetization density change, and the magnetic layer is flat, the paper choose thickness of magnetic layer as unit thickness, and define magnetic layer as a unit-thickness layer in order to convenient calculation, at the same time, define the variational magnetization density as equivalent magnetic density. Then we translate the relation between magnetic field and layer fluctuation to the relation between magnetic field and equivalent magnetic density, then, we can obtain the layer fluctuation through calculating equivalent magnetic density. Contrast to conventional parker method, model experimentation and example checkout prove this method is effective. The merit of this method is to avoid flat result in a strongly fluctuant area because of using a uniform average depth, the result of this method is closer to the fact, and this method is to inverse equivalent magnetic density, then translate equivalent magnetic density to layer fluctuation, this lays a foundation to inverse variational magnetic density in the landscape orientation and portrait.
Resumo:
Application of long-term exploration for oil and gas shows that the reservoir technology of prediction is one of the most valuable methods. Quantitative analysis of reservoir complexity is also a key technology of reservoir prediction. The current reservoir technologies of prediction are based on the linear assumption of various physical relationships. Therefore, these technologies cannot handle complex reservoirs with thin sands, high heterogeneities in lithological composition and strong varieties in petrophysical properties. Based on the above-mentioned complex reservoir, this paper conducts a series of researches. Both the comprehending and the quantitative analysis of reservoir heterogeneities have been implemented using statistical and non-linear theories of geophysics. At the beginning, the research of random media theories about reservoir heterogeneities was researched in this thesis. One-dimensional (1-D) and two-dimensional (2-D) random medium models were constructed. The autocorrelation lengths of random medium described the mean scale of heterogeneous anomaly in horizontal and deep directions, respectively. The characteristic of random medium models were analyzed. We also studied the corresponding relationship between the reservoir heterogeneities and autocorrelation lengths. Because heterogeneity of reservoir has fractal nature, we described heterogeneity of reservoir by fractal theory based on analyzing of the one-dimensional (1-D) and two-dimensional (2-D) random medium models. We simulated two-dimensional (2-D) random fluctuation medium in different parameters. From the simulated results, we can know that the main features of the two-dimensional (2-D) random medium mode. With autocorrelation lengths becoming larger, scales of heterogeneous geologic bodies in models became bigger. In addition, with the autocorrelation lengths becoming very larger, the layer characteristic of the models is very obvious. It would be difficult to identify sandstone such as gritstone, clay, dense sandstone and gas sandstone and so on in the reservoir with traditional impedance inversion. According to the obvious difference between different lithologic and petrophysical impedance, we studied multi-scale reservoir heterogeneities and developed new technologies. The distribution features of reservoir lithological and petrophysical heterogeneities along vertical and transverse directions were described quantitatively using multi-scale power spectrum and heterogeneity spectrum methods in this paper. Power spectrum (P spectrum) describes the manner of the vertical distribution of reservoir lithologic and petrophysical parameters and the large-scale and small-scale heterogeneities along vertical direction. Heterogeneity spectrum (H spectrum) describes the structure of the reservoir lithologic and petrophysical parameters mainly, that is to say, proportional composition of each lithological and petrophysical heterogeneities are calculated in this formation. The method is more reasonable to describe the degree of transverse multi-scale heterogeneities in reservoir lithological and petrophysical parameters. Using information of sonic logs in Sulige oil field, two spectral methods have been applied to the oil field, and good analytic results have been obtained. In order to contrast the former researches, the last part is the multi-scale character analysis of reservoir based on the transmission character of wave using the wavelet transform. We discussed the method applied to demarcate sequence stratigraphy and also analyzed the reservoir interlayer heterogeneity.
Resumo:
This thesis is based on the research project of Study on the Geological Characteristics and Remaining Oil Distribution Law of Neogene Reservoirs in Liunan Area, which is one of the key research projects set by PetroChina Jidong Oilfield Company in 2006. The determination of remaining oil distribution and its saturation changes are the most important research contents for the development and production modification of oilfields in high water-cut phases. Liunan oilfield, located in Tangshan of Hebei Province geographically and in Gaoliu structural belt of Nanpu sag in Bohai Bay Basin structurally, is one of the earliest fields put into production of Jidong oilfield. Focusing on the development problems encountered during the production of the field, this thesis establishes the fine geological reservoir model through the study of reservoir properties such as fine beds correlation, sedimentary facies, micro structures, micro reservoir architecture, flow units and fluid properties. Using routine method of reservoir engineering and technology of reservoir numerical modeling, remaining oil distribution in the target beds of Liunan area is predicted successfully, while the controling factors of remaining oil distribution are illustrated, and the model of remaining oil distribution for fault-block structure reservoirs is established. Using staged-subdivision reservoir correlation and FZI study, the Strata in Liunan Area is subdivided step by step; oil sand body data-list is recompiled; diagram databases are established; plane and section configuration of monolayer sandstone body, and combination pattern of sandstone bodys are summarized. The study of multi-level staged subdivision for sedimentary micro-facies shows that the Lower member of Minghuazhen formation and the whole Guantao formation in Liunan Area belong to meandering river and braided river sedimentary facies respectively, including 8 micro facies such as after point bar, channel bar, channel, natural levee, crevasse splay, abandoned channel, flood plain and flood basin. Fine 3D geological modeling is performed through the application of advanced software and integration of geological, seismic logging and reservoir engineering data. High resolution numerical simulation is performed with a reserve fitting error less than 3%, an average pressure fitting fluctuation range lower than 2Mpa and an accumulate water cut fitting error less than 5%. In this way, the distribution law of the target reservoir in the study area is basically recognized. Eight major remaining oil distribution models are established after analysis of production status and production features in different blocks and different layers. In addition, fuzzy mathematics method is used to the integreted evaluation and prediction of abundant remaining oil accumulation area in major production beds and key sedimentary time units of the shallow strata in Liunan Area and corresponding modification comments are put forward. In summary, the establishment of fine reservoir geological model, reservoir numerical simulation and distribution prediction of remaining oil make a sound foundation for further stimulation of oilfield development performance.
Resumo:
The Jinchuan Nickel Mine is the largest underground mine with cut-and-fill mining in China. It is very difficult to be exploited for very low safety stability of rock mass caused by complex geological conditions, developed faults, cracked rock mass and high stress. In this paper, the laws of rock mass movement、mechanics of shaft deformation and destroy were analyzed based on the collection of date, the detailed field engineering investigations, ground movement monitoring by GPS, theoretical analysis and numerical simulation. According to the GPS monitoring result of ground surface movement, there are different ground movement characteristics among the three Mine area of Jinchuan Nickel Mine. In No. 2 Mine area, the ground movement funnel with apparent asymmetry is developing, the influence scope is larger in the up faulted block than in the down faulted block, and the centre of ground movement is moving along the up faulted block direction with increasing depth of mining. Moreover, the tunnels in the corresponding area with the centre of ground movement are damaged seriously. In Longshou Mine area, the ground movement funnel is also developing, but the moving path and the nonlinear characters are more sophisticated because of the long-term effects of open excavating and the effects of underground mining together. In No. 3 Mine area, the underground mining impact on surface is not serious for the time of mining activity is not for long, but the ground movement funnel is also forming now. The underground mining has caused widespread land subsidence in Jinchuan Nickel Mine area, but the phenomena of surface raise appeared in some partial areas of Longshou Mine area and No. 3 Mine area. Analysis proved that the reason for the open pit bottom raise is the slope deformation activation caused by the excavation from open pit into underground mine; and that the raise of surface in No.3 Mine area is caused by the effect of elastic foundation due to underground mining. Although the GPS Monitoring results show the amount of subsidence is increasing constantly, the subsidence rate has a descending tendency with fluctuation in Jinchuan No. 2 Mine area. The subsidence rate curve is a time function and exists an extreme point, the rate increasing before extreme point and decreasing after the extreme point ,but the scale of decreasing rate will be very small after the rate decreasing up to a certain degree, moreover, the characteristics is different among different areas, which have some relation with the distance to the mining section and the dip of the ore body. ArcView is GIS software, which we adopted as a development platform, and made secondary development by its development language “avenue”, through which we developed a ground movement analysis and forecast System for Jinchuan Nickel Mine, which contain three modules : management of ground movement information; analysis and evaluation of ground movement; and ground movement forecast. In the module of evaluation, using the technique of MATLAB6.5 program with VB6.0, the system can achieve the ANN prediction model for GPS monitoring data, data preparation results analysis and model integrated was realized by Avenue programming. Finally, the author analyzed the mechanical of deformation and destroy of the No. 14 shaft, and its repair and artificial-support effectiveness also given detailed demonstration in various aspect. The result showed that the reason for the destroy of No. 14 shaft is underground mining, and being the case, the destroy of the shaft also has its special features, which mainly contains forked stress contour for mining steep ore and fault effect caused by mining activities. The repair and artificial-support played some restrictions on the rock mass movement and deformation, but did not show a strong or marked effect. With the increasing of mining depth and large-scale, the closure rock of the shaft will still deformed, even be destroyed.
Resumo:
Petroleum and Natural Gas is an important strategic resources. The reserves of Petroleum and Natural Gas can’t meet the need of our country, which also blocks the development of economy and threatens the safety of national. Therefore, it makes a great sense to bring “the second round of oil & gas exploration” into effect and study the exploration of oil and gas of Pre-Cenozoic residual basins in China. The integrated geophysical exploration is the main way to research the Pre-Cenozoic residual basins. Gravity exploration is one of the most important exploration methods, which has played an important role in oil and gas prospecting, such as compartmentalizing geotectonic elements, delineating the distribution range of sedimentary basins, searching oil and gas structure, abstracting oil and gas information, and so on, from its naissance. The isostatic gravity anomalies is significant for exploration, which can help us research deep crustal structure, the equilibrium state of earth, the geologic structure of shallow crust, the basement shape of sedimentary basins and the genetic evolution of sedimentary basins. In the paper, we stress the implication and physical meanings systemically, and discuss the calculation theory. On the basis of previous work, we test different isostatic compensation models and parameters to find out their influences to the result of isostatic gravity anomalies. In addition, we improve the method of isostatic gravity anomalies calculation and give a system of isostatic gravity anomalies calculation which is proved has satisfying effect. From the research above, we find that the results of Platt model and Airy model are consistent, which have similar form and almost the same value. However, by contrast, the Airy model is proved has better adaptability than Platt model. The two main parameters——crust thickness and density difference of crust and mantle, both have influence to the isostatic gravity anomalies, but the latter have more. Finally, we adopt the regional field extending edge method to make the result more of actual geologic condition. On the methods above, we calculate the isostatic gravity anomalies field in Yellow Sea area from the Bouguer gravity anomalies and the water depth and altitude data. And then the isostatic gravity anomalies character is analyzed and the integrated geological-geophysical interpretation is made on the basis of summarizing the previous research result systemically and analyzing other geophysical data and geological information. From the research, we find that the Yellow Sea area belongs to continental type crust equilibrium regions, where the isostatic gravity anomalies field is placid and has less fluctuation values, which implies that the area is in equilibrium state to different extends.