High-resolution sedimentary record of lead in the coastal mud of the East China Sea in the past one hundred and fifty years

In the East China Sea （ECS）, there are some mud areas, including the south coastal mud area, the north coastal mud area, and the mud area to the southwest of Cheju Island. X-ray fluorescence （XRF） techniques and Thermal Ionization Mass Spectrometry （TIMS） were used to study the high-resolution sedimentary record of Pb concentrations and Pb stable isotopic compositions in the past one hundred and fifty years in the coastal mud of the ECS. Pb concentrations of a ^210Pb dating S5 core in the study area have increased rapidly since 1980, and reached the maximal value with 65.08 μg/g in 2000, corresponding to the fast economic development of China since the implementation of the ＂Reform and Open Policy＂ in 1978; ^206Pb/^207Pb ratios generally had stabilized at 1.195 from 1860 to 1966, and decreased gradually from 1966 to 2000, indicating that the anthropogenic source Pb contribution to the ECS has increased gradually since 1966, especially since 1980. Pb concentrations decreased distinctly from 2000 to 2003 and ^206Pb/^207Pb ratios increased from 2001 to 2003, corresponding closely to the ban of lead gasoline from 2000 in China. From 1950 to 2003, there occurred four distinct decrease events of ^206Pb/^207Pb, possibly responding to the Changjiang River （Yangtze River） catastrophic floods in 1998, 1991, 1981 and 1954; from 1860 to 1966, there were two decrease periods of ^206Pb/^207Pb, which may respond to the catastrophic floods of Changjiang River in 1931 and 1935, and 1870. As a result of the erosion and drowning by the catastrophic floods, the anthropogenic lead accumulated in soil and water environments over a long period of time was brought into the Changjiang River, then part of them was finally transported into the ECS, which leads to changes in Pb stable isotopic composition.     

A pronounced dry event recorded around 4.2 ka in brine sediments from the northern Red Sea

Partly laminated sediments were sampled from the brine-filled, anoxic Shaban Deep basin in the northern Red Sea. At about 4200 cal yr BP more than two millennia of anoxic sedimentation is replaced by a sub-oxic facies strongly suggesting the episodic absence of the brine. At the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase (within less than 100 yr) pointing to a strong positive salinity anomaly at the sea surface. This major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small Shaban Deep basin. The timing and strength of the reconstructed environmental changes around 4200 cal yr BP suggest that this event is the regional expression of a major drought event, which is widely observed in the neighboring regions, and which strongly affected Middle East agricultural civilizations.     

A laboratory experiment to monitor the contact state of a fault by transmission waves

We performed a series of laboratory experiments in which elastic waves were transmitted across a simulated fault. Two types of experiments were carried out: (1) Normal Stress Holding Test (NSHT): normal stress was kept constant for about 3 h without shear stress and transmission waves were observed. (2) Shear Stress Increasing Test (SSIT): shear stress was gradually increased until a stick-slip event occurred. Transmission waves were continuously observed throughout the process of stress accumulation. We focused on the change in transmission waves during the application of shear stress and especially during precursory slips.It was found in NSHT that the amplitude of transmission waves linearly increased with the logarithm of stationary contact time. The increase amounted to a few percent after about 3 h. Creep at asperity contacts is responsible for this phenomenon. From a theoretical consideration, it was concluded that the real contact area increased with the logarithm of stationary contact time.We observed in SSIT a significant increase in wave amplitude with shear stress application. This phenomenon cannot be attributed to the time effect observed in NSHT. Instead, it can be explained by the mechanism of “junction growth” proposed by Tabor. Junction growth yields an increase in real contact area. It is required for junction growth to occur that the material in contact is already plastic under a purely normal loading condition. A computer simulation confirmed that this requirement was satisfied in our experiments. We also found that the rate at which the amplitude increased was slightly reduced prior to a stick-slip event. The onset time of the reduction well coincides with the onset of precursory slip. The cause of the reduction is attributed to the reset of stationary contact time due to displacement. This interpretation is supported by the result of NSHT. Taking the time of stationary contact in SSIT into account, we may expect the change in wave amplitude to be, at most, only a few percent. The observed slight reduction in increasing rate is, in this sense, reasonable. The static stiffness of the fault also decreases with precursory slip. It was also found that low frequency waves are a better indicator of precursory slip than high frequency waves. This might suggest that low frequency waves with longer wavelength are a better indicator of average behavior of faults. The problem, however, merits a further investigation. The shifts in phase were also found to be a good indicator of the change in contact state of the fault. The changes in both amplitude and phase of transmission waves are unifyingly understood through the theory of transmission coefficient presented by Pyrak-Nolte et al. Rough surfaces have a tendency to give larger stick-slips than smooth surfaces. The amount of precursory slip is larger for rough surfaces than for smooth surfaces. Although it was confirmed by a computer simulation that rough surfaces have larger contact diameters than smooth surfaces, the rigorous relationship between the surface roughness (contact diameter) and the amount of precursory slips was not established.     

Deep structure of the Nojima Fault, southwest Japan, estimated from borehole observations of fault-zone trapped waves

To estimate the deep structure of the southern part of the Nojima Fault, southwest Japan without the influence of near-surface structures, we analyzed the Love-wave-type fault-zone trapped waves (LTWs) recorded by a borehole seismometer at 1800 m depth. We examined the polarization, dispersion, and dominant frequency of the wavetrain following the direct S-wave in each seismogram to identify the LTW. We selected eight candidates for typical LTWs from 462 records. Because the duration of the LTW increases with hypocentral distance, we infer that the low velocity fault-zone of the Nojima Fault continues towards the seismogenic depth. In addition, since the duration of the LTW increases nonlinearly with hypocentral distance, we infer that the S-wave velocity of the fault-zone increases with depth. The location of events showing the LTW indicates that the fault-zone dips to the southeast at 75° and continues to a depth of approximately 10 km. We assumed a uniform low-velocity waveguide to estimate the average structure of the fault-zone. We estimated the average width, S-wave velocity, and Q_s of the fault-zone by comparing an analytical solution of the LTW with measured data. The average width, S-wave velocity, and Q_s of the fault-zone are 150 to 290 m, 2.5 to 3.2 km/s, and 40 to 90, respectively. Hence the fault-zone structure with a larger width and smaller velocity reduction than the fault-zone model estimated by previous surface observation is more suitable to represent the average fault-zone structure of the Nojima fault. The present study also indicated that the shallow layers and/or a shallow fault-zone structure drastically changes the characteristics of the LTW recorded at the surface, and therefore cause a discrepancy in the fault-zone model between the borehole observation and surface observation.     

Geophysical methods applied to fault characterization and earthquake potential assessment in the Lower Tagus Valley, Portugal

The study region is located in the Lower Tagus Valley, central Portugal, and includes a large portion of the densely populated area of Lisbon. It is characterized by a moderate seismicity with a diffuse pattern, with historical earthquakes causing many casualties, serious damage and economic losses. Occurrence of earthquakes in the area indicates the presence of seismogenic structures at depth that are deficiently known due to a thick Cenozoic sedimentary cover. The hidden character of many of the faults in the Lower Tagus Valley requires the use of indirect methodologies for their study. This paper focuses on the application of high-resolution seismic reflection method for the detection of near-surface faulting on two major tectonic structures that are hidden under the recent alluvial cover of the Tagus Valley, and that have been recognized on deep oil-industry seismic reflection profiles and/or inferred from the surface geology. These are a WNW–ESE-trending fault zone located within the Lower Tagus Cenozoic basin, across the Tagus River estuary (Porto Alto fault), and a NNE–SSW-trending reverse fault zone that borders the Cenozoic Basin at the W (Vila Franca de Xira–Lisbon fault). Vertical electrical soundings were also acquired over the seismic profiles and the refraction interpretation of the reflection data was carried out. According to the interpretation of the collected data, a complex fault pattern disrupts the near surface (first 400 m) at Porto Alto, affecting the Upper Neogene and (at least for one fault) the Quaternary, with a normal offset component. The consistency with the previous oil-industry profiles interpretation supports the location and geometry of this fault zone. Concerning the second structure, two major faults were detected north of Vila Franca de Xira, supporting the extension of the Vila Franca de Xira–Lisbon fault zone northwards. One of these faults presents a reverse geometry apparently displacing Holocene alluvium. Vertical offsets of the Holocene sediments detected in the studied geophysical data of Porto Alto and Vila Franca de Xira–Lisbon faults imply minimum slip rates of 0.15–0.30 mm/year, three times larger than previously inferred for active faults in the Lower Tagus Valley and maximum estimates of average return periods of 2000–5000 years for M 6.5–7 co-seismic ruptures.     

A way to synchronize models with seismic faults for earthquake forecasting: Insights from a simple stochastic model

Numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks. Their final goal would be to forecast future large earthquakes. In order to use them for this task, it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates (just as, for example, meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them). However, lithospheric dynamics is largely unobservable: important parameters cannot (or can rarely) be measured in Nature. Earthquakes, though, provide indirect but measurable clues of the stress and strain status in the lithosphere, which should be helpful for the synchronization of the models.The rupture area is one of the measurable parameters of earthquakes. Here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes. Our purpose here is to forecast synthetic earthquakes in a simple but stochastic (random) fault model. By imposing the rupture area of the synthetic earthquakes of this model on other models, the latter become partially synchronized with the first one. We use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model. This forecasting strategy outperforms others that only take into account the earthquake series. Our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults. This hypothesis could be tested in the future with more detailed models and actual seismic data.     

Two-stage metamorphic evolution of the Bemarivo Belt of northern Madagascar: constraints from reaction textures and in situ monazite dating

New results on the pressure–temperature–time evolution, deduced from conventional geothermobarometry and in situ U‐Th‐total Pb dating of monazite, are presented for the Bemarivo Belt in northern Madagascar. The belt is subdivided into a northern part consisting of low‐grade metamorphic epicontinental series and a southern part made up of granulite facies metapelites. The prograde metamorphic stage of the latter unit is preserved by kyanite inclusions in garnet, which is in agreement with results of the garnet (core)‐alumosilicate‐quartz‐plagioclase (inclusions in garnet; GASP) equilibrium. The peak metamorphic stage is characterized by ultrahigh temperatures of ～900–950 °C and pressures of ～9 kbar, deduced from GASP equilibria and feldspar thermometry. In proximity to charnockite bodies, garnet‐sillimanite‐bearing metapelites contain aluminous orthopyroxene (max. 8.0 wt% Al₂O₃) pointing to even higher temperatures of ～970 °C. Peak metamorphism is followed by near‐isothermal decompression to pressures of 5–7 kbar and subsequent near‐isobaric cooling, which is demonstrated by the extensive late‐stage formation of cordierite around garnet. Internal textures and differences in chemistry of metapelitic monazite point to a polyphasic growth history. Monazite with magmatically zoned cores is rarely preserved, and gives an age of c. 737 ± 19 Ma, interpreted as the maximum age of sedimentation. Two metamorphic stages are dated: M1 monazite cores range from 563 ± 28 Ma to 532 ± 23 Ma, representing the collisional event, and M2 monazite rims (521 ± 25 Ma to 513 ± 14 Ma), interpreted as grown during peak metamorphic temperatures. These are among the youngest ages reported for high‐grade metamorphism in Madagascar, and are supposed to reflect the Pan‐African attachment of the Bemarivo Belt to the Gondwana supercontinent during its final amalgamation stage. In the course of this, the southern Bemarivo Belt was buried to a depth of >25 km. Approximately 25–30 Myr later, the rocks underwent heating, interpreted to be due to magmatic underplating, and uplift. Presumably, the northern part of the belt was also affected by this tectonism, but buried to a lower depth, and therefore metamorphosed to lower grades.     

Heavy metals in freshly deposited sediments of the river Subernarekha, India: an example of lithogenic and anthropogenic effects

Heavy metal distribution patterns in river sediments aid in understanding the exogenic cycling of elements as well as in assessing the effect of anthropogenic influences. In India, the Subernarekha river flows over the Precambrian terrain of the Singhbhum craton in eastern India. The rocks are of an iron ore series and the primary rock types are schist and quartzite. One main tributary, the Kharkhai, flows through granite rocks and subsequently flows through the schist and quartzite layers. The Subernarekha flows through the East Singhbhum district, which is one of India’s industrialised areas known for ore mining, steel production, power generation, cement production and other related activities. Freshly deposited river sediments were collected upstream and downstream the industrial zone. Samples were collected from four locations and analysed in <63-μm sediment fraction for heavy metals including Zn, Pb, Cd and Cu by anodic stripping voltammetry. Enrichment of these elements over and above the local natural concentration level has been calculated and reported. Sediments of the present study are classified by Muller’s geo-accumulation index (I _geo) and vary from element to element and with climatic seasons. During pre-monsoon period the maximum I _geo value for Zn is moderately to highly polluted and for Cu and Pb is moderately polluted, respectively, based on the Muller’s standard. Anthropogenic, lithogenic or cumulative effects of both components are the main reasons for such variations in I _geo values. The basic igneous rock layer through which the river flows or a seasonal rivulet that joins with the main river may be the primary source for lithogenic components.     

Deep seismic reflection study over the Vindhyans of Rajasthan: Implications for geophysical setting of the basin

This paper presents results of high-resolution deep seismic reflection profiling of the Proterozoic Vindhyan basin of the Rajasthan area along the Chandli-Bundi-Kota-Kunjer profile. Seismic images have been used to estimate the thickness of Vindhyan strata as well as to understand the tectonic framework of the basin. The results are constrained by gravity, magnetic and magnetotelluric data. The study reveals gentle SE-dipping reflection bands representing the Vindhyan strata. The seismic sections depict gradual thickening of the Vindhyan succession towards southeast from Bundi. The velocities of the upper and lower Vindhyans are identified as 4.6-4.8 km/s and 5.1-5.3 km/s. The NW limit of the Vindhyan basin is demarcated by the Great Boundary Fault (GBF) that manifests as a 30 km wide NW dipping thrust fault extending to a depth of 30 km.     

Erratum “Boundary” in ancient Persian tradition of statehood: an introduction to the origins of the concept of boundary in pre-modern history

Erratum to: GeoJournal 62: 51–58 DOI 10.1007/s10708-005-8562-2 The erroneous version of this article was originally published in GeoJournal 62: 51–58. This amended version corrects the formatting errors which are evident in the original version.Abstract It is universally accepted that the need for defining precise lines of separation and points of contacts between states is the byproduct of the emergence of nation-states and ‘world economy’ in the nineteenth century Europe. Nevertheless, it is hard to overlook the fact that these modern notions are rooted in periods prior to the emergence in Europe of nation-states. There are indications that ancient civilizations were familiar with the notion of ‘state’ in connection with the concepts of territory and boundary. Ancient texts reveal that this basic principle existed in ancient Persian literature in respect of matters of state, territory, and boundary. Similarly, the likelihood exists that these Persian notions could have influenced Roman civilization. It is widely believed that a combination of ancient Greco-Roman and Persian civilizations is a major contributor to what culturally constitutes ‘West’. Later in the Sassanid period the inter-linked notions of state, territory, and boundary developed substantially, coming quite close to their contemporary forms. On the other hand, considering that ‘justice’ was the corner stone of ancient Persian Political philosophy, the idea that ancient␣Iranian spatial arrangement might have contributed to the evolution of the concept of democracy in the West may not be too difficult to contemplate.The online version of the original article can be found at