Pressure Instability of Magnetic Susceptibility of Pyrrhotite Bearing Rocks from the KTB Borehole

Experimental results of pressure-induced changes in mean magnetic susceptibility of rock samples from the main KTB borehole are reported. It was found that susceptibility values of rocks from depths between 5200 and 7000 m show unstable behaviour upon application of pressure, showing an increase in susceptibility of between 20 and 120%. This unstable behaviour was only detected in samples from the above mentioned depth interval, which contain both ferrimagnetic and antiferromagnetic phases of pyrrhotite. On the basis of thermomagnetic analysis, magnetic field treatment, optical microscopy and domain observations of undeformed and deformed samples, reasons for this instability are discussed and interpreted in relation to redistribution of internal stresses within the ferrimagnetic phase, resulting in changes in domain wall mobility.     

Comparison of in-situ Field Measurements of Soil Magnetic Susceptibility with Laboratory Data

Results of magnetic susceptibility mapping around a coal-burning power plant were used to verify the field in situ measurements with data acquired in laboratory on soil samples collected at approximately the same measurement grid sites at different distance from the source. This comparison enables quantifying the field data obtained using the Bartington MS2 meter and to relate them, at least approximately, to mass specific values. Moreover, it is shown that certain diversity in the grid points of field measurements and soil sampling can slightly bias the field measurements. However, this shift is of minor significance and Bartington field readings can be considered as reliable.     

Indices for Numerical Characterization of the Alteration Processes of Magnetic Minerals Taking Place During Investigation of Temperature Variation of Magnetic Susceptibility

The alteration of magnetic minerals taking place during the investigation of the temperature variation of bulk magnetic susceptibility is obvious from different courses of heating and cooling susceptibility vs. temperature curves. A set of indices is introduced to characterize these changes numerically. The A ₄₀ alteration index characterizes the change in susceptibility after executing the whole cycle of heating and cooling. The maximum difference between the heating and cooling curves is characterized by the A _max alteration index. The mean or average difference between the heating and cooling curves is characterized by the A _m alteration index. The situation whether the heating and cooling curves cross, is characterized by the A _cr alteration index. The technique of progressive repeated heating is proposed, together with the above indices, to locate the temperature intervals with weak and strong magnetic mineral changes induced by heating.     

Application of Wavelet Transform to Magnetic Data Due to Ruins of the Hittite,Civilization in Turkey

— In the recent years, geophysical methods have been applied successfully in archaeological studies. In this article we have studied the application of wavelet transform to magnetic data in order to estimate boundaries of various synthetic examples and real data. Enhanced Horizontal Derivative (EHD) method is also applied as an alternative method for boundary estimation. The performance of wavelet transform and the EHD method are evaluated using magnetic data of the Sarissa-Kusakli archaeological site. All boundary results are mutually compared. Based on these comparisons, we conclude that the wavelet transform provides reasonable results.This work was supported by the TUBITAK under Project YDABCAG-100Y021.Received: 23 October 2001     

Temporal (Un)correlations Between Coda <Emphasis Type="Italic">Q</Emphasis> and Seismicity: Multiscale Trend Analysis

This paper introduces a statistical technique, based on the recently developed Multiscale Trend Analysis (MTA), for quantifying correlations between non-stationary processes observed at irregular non-coincident time grids. We apply this technique to studying the temporal correlation between the dynamics of the ductile and brittle layers in the lithosphere. Our results confirm the previously reported strong positive correlation between the coda Q^–1 and seismicity and its drop before major earthquakes observed in California. The proposed technique has significant advantages over the conventional correlation analysis: (1) MTA allows one to work directly with non-coincident time series without preliminary resampling the data; (2) the correlation is defined via the stable objects—trends—rather than noisy individual observations, hence it is highly robust; (3) the correlations are quantified at different time scales. The suggested technique seems promising for the wide range of applied problems dealing with coupled time series.     

Magnetic Susceptibility and Heavy Metals Distribution from Risk‐cultivated Soil around the Iron–Steel Plant,China

Magnetic susceptibility is a non‐conventional way that can be used for evaluating proxy soil heavy metals pollution. The paper monitors available heavy metals (Cu, Fe, Zn, and Mn) present in cultivated soils around iron–steel plant by soil magnetic susceptibility. Our study was located in an area with high pollution with small grid density of 250 m in China. Results showed that low field magnetic susceptibility was significantly correlated with available Cu, Zn, and Mn. No clear association exists between magnetic susceptibility and available Fe, soil organic matter, pH. Frequency dependent susceptibility >5% suggests the possible presence of super‐paramagnetic particles, fly ashes produced during coal combustion.     

Magnetic Characteristics of Different Soil Types from Bulgaria

Magnetic studies of different soil types can provide valuable information about palaeoenvironmental conditions at the time they were formed. Results of investigations of rock-magnetism of genetically different soil types, which developed over varying time intervals (Meadow Chernozem - formed during the last 6000 years BP; Leached Cinnamonic soil - formed since the 3rd-2nd century BC and Pellic Vertisoil - the oldest, formed since the Late Pliocene) are presented. The soil profiles of the Leached Cinnamonic and Pellic Vertisoil are characterized by lower values of magnetic susceptibility, as compared to that of the parent materials. It is shown that using percentage frequency-dependent susceptibility (Xfd%) and viscous remanent magnetization (VRM), pedogenic alteration could be detected even in such circumstances. The variations of the parameters measured along the depth of the studied Meadow Chernozem soil profile are characterized by gradual smooth magnetic enhancement, pointing to the absence of secondary redistribution of pedogenic magnetites. In contrast to this case, the two other profiles (Leached Cinnamonic and Pellic Vertisoil) show magnetically enhanced lower (illuvial) horizons due to processes of acid destruction and re-precipitation of the original pedogenic ferromagnetic minerals down the profiles. These specific magnetic properties are of particular importance in using susceptibility variations as a palaeoclimatic proxy record.     

四川地区地震前跨断层数据异常分析

概述四川7.0级以上大震前观测场地的异常情况。在核实2个大震震前异常的基础上,将传统异常判别方法进行汇总。总结近年来针对跨断层监测数据进行分析进而识别异常的方法:原始数据反映的断层活动速率异常以及转折异常。在此基础上,引入小波分析的方法对大震前的异常进行判别。对小波分解得到的两个趋势项进行分析,发现了大震与小波分解项异常的对应性。最后,基于对原始数据和小波分解项的分析,提出利用跨断层数据分析大震前兆的参考意见,为以后的震前异常研究工作提供了基础。     

The Use of Field Dependence of Magnetic Susceptibility for Monitoring Variations in Titanomagnetite Composition - A Case Study on Basanites from the Vogelsberg 1996 Drillhole,Germany

In high Ti basanites from the Vogelsberg 1996 drillhole distinct variations in the field dependence of AC magnetic susceptibility correlate with compositional variations of titanomagnetite, as determined by temperature dependence of magnetic susceptibility. Curie temperatures for the basanites are in the range of 240 to 525°C. The field dependence reaches up to 20% for measurements in 30 A/m and 300 A/m AC field amplitude. It is demonstrated that two-field magnetic susceptibility measurements can prevail information about compositional changes of titanomagnetite and therefore support the interpretation of magnetic susceptibility logs from drillcores of basaltic rock suites.     

Rock Magnetic Investigation of Historical Lavas Used in Palaeointensity Studies

Five samples from historical lava flows on Mt. Etna, which had previously been used in a palaeointensity study, were examined using a combination of rock magnetic and microscopic techniques to elucidate the causes of failure of palaeointensity determination. The samples were characterised using a combination of low-temperature susceptibility (LT-), Bitter pattern imaging and scanning electron microscope (SEM). High-temperature susceptibility curves and hysteresis loops had been previously measured by Calvo et al. (2001). Of the five samples only one gave an accurate palaeointensity. This sample was deuterically oxidised and consisted of large exsolved ore grains. It was only possible to distinguish this sample either optically or magnetically from a similar sample by the LT- warming curves; the unsuccessful sample displayed alteration in the LT- warming curves, which was not readily observed in the high temperature susceptibility curves. It is proposed that the measurement of LT- curves before and after heating could be a more sensitive method of determining suitability for palaeointensity determination than previous rock magnetic pre-selection techniques.     

磁组构的分离与岩石构造变形分析

目前实验条件下获得的AMS（磁化率各向异性）是岩石内所有磁性矿物磁化率各向异性叠加的综合响应,详细的岩石磁学和构造地质学的综合分析表明常规AMS测试结果通常无法揭示岩石复杂的构造变形过程.本文综述了运用非磁滞剩磁各向异性（AARM）、低温AMS（LT-AMS）和高场AMS（HF-AMS）等实验方法对岩石AMS组分进行分离,可以定量获取不同磁性矿物的磁组构贡献,进而解释其不同的变形特征.在此基础上阐述了近年来针对不同磁性矿物组合的AMS分离方法的理论技术创新和进展及其在岩石构造变形特征分析中的应用前景,讨论了常见磁性矿物单晶的岩石磁学性质及各向异性度（P_j）与形状因子（T）在揭示岩石变形特征中的复杂性与局限性,最后举例并分析了磁组构分离技术在造山带岩石构造变形分析中的应用.

     

Effect of Stress on the Magnetic Memory of Induced Magnetic Anisotropy of Rocks and Its Mathematical Model

When re-heated to temperatures below the Curie temperature and subsequently cooled in a constant magnetic field (H _T), rock samples which contain magnetic minerals can acquire an induced magnetic anisotropy (IMA). As the result of acquiring the IMA, a constriction develops in the hysteresis loop of the magnetization of these rocks at the values of the magnetizing field close or equal to the HT. Thus the IMA is capable of retaining the information on the palaeointensity of the geomagnetic field, i.e., if IMA was created in a rock in the geomagnetic field in a past geological epoch, it preserves the information on the intensity of that field. Investigations have shown, that when IMA is created in a rock under external stress, the stress has an impact on the magnetic memory. Here we also deal with the issue of how stress affects the magnetic memory of IMA. A mathematical model for the effect of stress on magnetic memory phenomena related to induced magnetic anisotropy in rocks containing multidomain magnetite and titanomagnetite grains is proposed herewith. The effect of temperature on the magnetic memory of rocks is discussed also.     

小波分析方法在宁夏短水准资料分析中的应用

建立了小波分解模型,应用该模型将宁夏红果子形变台及苏峪口形变台短水准观测资料中的不同周期成分进行了有效分离。分离后的3阶近似及3阶细节部分所显示的异常变化能够更直观和显著地对应宁夏及周边地区发生的地震。     

Multiscale adaptive estimation of the conductivity field from head and tracer data

Large scale fluctuations in the conductivity field are regionalized and estimated via a maximum likelihood, adjoint-state methodology. Small-scale fluctuations within each region are estimated adaptively via a Kalman-like stochastic filter. The variance and integral scale within each region are assumed to control the small-scale fluctuations. A Monte Carlo technique is used to examine the distribution of large-scale conductivity estimates.     

Loess in the Czech Republic: Magnetic properties and paleoclimate

Summary We have studied 454 oriented samples from seven loess outcrops in the Czech Republic for comparison and correlation of the magnetic properties with those of the loess profiles in China and Central Asia. Three sections at Sedlec (Prague), Zeměchy and Dolní Věstonice cover the time span of the last glacial-interglacial cycle. Loess from the middle Pleistocene period including pedocomplexes V and VI was studied at Sedlešovice (Znojmo) and Karlštejn. Loess of uncertain — possibly lower to middle Pleistocene age — was sampled at Sedlec near Mikulov. At Červeny Kopec (Red Hill, Brno) we investigated the oldest loess near the Matuyama/Brunhes (M/B) boundary. The characteristic remanence (ChRM) determined after magnetic clearning is of normal polarity throughout all sections except at Červeny Kopec. There, two polarity changes from reversed to normal were found within two sections initially thought to represent two successive stratigraphic intervals. However, the marked similarities between lithological, susceptibility, declination and inclination profiles lead us to suggest that the two polarity changes are in fact one and the same. The two sections are therefore laterally equivalent and both have recorded the M/B field reversal. The susceptibility variations were used to mutually correlate the Czech sections and to construct a composite profile across the present day loess outcrops in the Czech Republic. They also serve as a paleoclimate proxy which can be compared and correlated with the paleoclimatic records observed in the Chinese and Central Asian loess. The origin of the low field susceptibility variations was studied by measuring the frequency dependence of susceptibility which revealed that the enhancement within the pedocomplexes is controlled by the amount of fine-grained ferromagnetic minerals present.     

Cyclostratigraphy of the Induan (Early Triassic) in West Pingdingshan Section, Chaohu, Anhui Province

The Induan sequence in the West Pingdingshan Section, Chaohu, Anhui Province, displays a series of superimposed mudstone/limestone cycles. The lithological character of the cycles, combined with power spectral and wavelet analysis of magnetic susceptibility readings, reveals 12 short eccentricity and 56 precession Milankovitch cycles - obliquity cycles are not apparent. The uniformity of cycle thicknesses indicates a stable depositional setting making this section ideal to perform various geo-logical studies. Accordingly, the Induan Stage is estimated to have lasted 1.1 Ma, and the depositional rate for this part of the section is about 3.7 cm/ka. This places the Induan-Olenekian boundary in the West Pingdingshan Section at about 251.5 Ma based on an age of 252.6 Ma for the Permian-Triassic boundary.     

广东省前兆台网数据跟踪分析情况概述

介绍了2014年6月份以来,广东前兆台网数据跟踪分析的开展情况,包括分析工作的推进,工作过程中存在过的问题及解决情况,事件分析的归类汇总和产出,典型事件记录的介绍和分析讨论。     

Magnetic fabric of bulgarian loess sediments derived by using various sampling techniques

Summary The anistropy of low field magnetic susceptibility has been studied for seven outcrops of loess sediments in North-Eastern Bulgaria. Different sampling methods were applied in order to choose the best technique for obtaining the primary magnetic fabric of such unconsolidated sediments. AMS results show significant changes in the petrofabric of samples collected by the first technique which disturbs the original sedimentary fabric. The second applied technique does not cause such a strong deformation but some disturbance of the magnetic fabric is probable. Typical sedimentary fabric is obtained from hand samples and it is therefore concluded that this represents the best method for obtaining reliable AMS results from soft sediments.     

Magnetic properties of the Tertiary red clay from Gansu

The study on magnetic properties of the red clay indicates that the red clay and loesspaleosol sequence have a common magnetic mineralogy, with magnetite, maghemite, hematite (and possibly goethite) contributing to the magnetic behavior. The red clay magnetic susceptibility is also found to have a positive relation with extrafine superparamagnetic grains. This suggests that, like the Quaternary loess-paleosols, an ultrafine ferrimagnetic component produced during pedogenesis in the red clay under humid conditions also plays an important role in susceptibility enhancement in the soil units. This is supported by the correlation between Rb/Sr ratio and magnetic susceptibility. This signifies that, like the above loess-paleosol sequence, the magnetic susceptibility of the red clay can be used as a general proxy paleoclimatic indicator, although whether its susceptibility in the red clay is comparable to pedogenesis intensity and requires further investigation. Magnetic susceptibility variation in the red clay thus also provides an eolian/pedogenic record of paleoclimatic evolution. Study of the background susceptibility indicates that, on average, the absolute scale of the paleoclimatic shift from red clay development to Quaternary loess deposition is similar to the climatic shift from stage 5 (S1) to stage 2–4 (L1). This may suggest that during the Quaternary there is an evident strengthening of the absolute wind intensity to bring more (about double) coarser and less weathered (non-SP fraction) eolian magnetic input from the source regions to the Loess Plateau than during the Pliocene. The presence of eolian red clay since 7.5 Ma BP in central-northern China implies an important environmental change from the underlying Cretaceous red sandstone. The red clay development was closely related to global drying and climate cooling since the Cretaceous and closely associated with the abrupt uplift of the Qinghai-Xizang Plateau at about that time. This uplift of the plateau intensified the East Asia monsoon system and started red clay deposition.     

Magnetic fabric of Plio-Pleistocene sediments from the Crotone fore-arc basin: Insights on the recent tectonic evolution of the Calabrian Arc (Italy)

Low-field anisotropy of magnetic susceptibility (AMS) analyses were performed on 532 samples collected in 36 (mostly lower Pliocene to lower Pleistocene) marine clay sites from the Crotone basin, a fore-arc basin located on top of the external Calabrian accretionary wedge. The Crotone basin formed since mid-late Miocene under a predominant extensional tectonic regime, but it was influenced thereafter by complex interactions with NW–SE left-lateral strike-faults bounding the basin, which also yielded post-1.2 Ma ∼30° counterclockwise block rotations. The basin is filled by continental to marine sediments yielding one of the thickest and best-exposed Neogene succession available worldwide. The deep-marine facies – represented by blue-grey marly clays gave the best results, as they both preserved a clear magnetic fabric, and provided accurate chronology based on previously published magnetostratigraphy and calcareous plankton (i.e. foraminifers and nannofossils) biostratigraphy. Magnetic susceptibility range and rock magnetic analyses both indicate that AMS reflects paramagnetic clay matrix crystal arrangement. The fabric is predominantly oblate to triaxial, the anisotropy degree low (<1.06), and the magnetic foliation mostly subparallel to bedding. Magnetic lineation is defined in 30 out of 36 sites (where the e12 angle is <35°). By also considering local structural analysis data, we find that magnetic fabric was generally acquired during the first tectonic phases occurring after sediment deposition, thus validating its use as temporally dependent strain proxy. Although most of the magnetic lineations trend NW–SE and are orthogonal to normal faults (as observed elsewhere in Calabria), few NE–SW compressive lineations show that the Neogene extensional regime of the Crotone basin was punctuated by compressive episodes. Finally, compressive lineations (prolate magnetic fabric) documented along the strike-slip fault bounding the basin to the south support the significance of Pleistocene strike-slip tectonics. Thus the Crotone basin shows a markedly different tectonics with respect to other internal and western basins of Calabria, as it yields a magnetic fabric still dominated by extensional tectonics but also revealing arc-normal shortening episodes and recent strike-slip fault activity. The tectonics documented in the Crotone basin is compatible with a continuous upper crustal structural reorganization occurring during the SE-migration of the Calabria terrane above the Ionian subduction system.