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The southern margin of the Ordos Basin is covered by thick loess sediments. This area is typically characterized by frequent geologic hazards and is rich in energy resources. Identifying the velocity structure of the loess layer is of great significance for geologic hazard prevention and resource explorations in this area. In this paper, we utilize Rayleigh-wave data for imaging the shear-wave velocity (vs) of the loess sediments in the Dongjiahe area, in the southern margin of the Ordos Basin. The data collected in the Dongjiahe area is dominated by the higher-order mode Rayleigh-wave; the dispersive energy of the fundamental mode Rayleigh-wave is weak and suppressed in some frequency bands. An improved frequency–wavenumber (F-K) transform method which can enhance the dispersive energy and expand the frequency range of the weaker fundamental (or higher) mode Rayleigh-wave is proposed in this paper. Numerically simulated data are first utilized to show the processes and effectiveness of the improved F-K transform method. Then, we utilize the improved F-K transform to generate multi-mode dispersive spectrums and extract dispersion curves of the real-world data collected in the Dongjiahe area. Dispersion curves are inverted for vs structure using the Levenberg–Marquardt method. The pattern of the two-dimensional vs section of the study area indicates that the loess sediments mainly distributes as approximate flat layers with vs gradually increasing as the depth increases. In addition, the results also reveal the bedrock depth of some parts of the survey line. [ABSTRACT FROM AUTHOR]

Aims: Although comammox have been discovered in a variety of ecosystems, there are few studies in urban lakes. This paper attempted to confirm whether this ammonia‐oxidizing microbe exists in urban lakes and to determine the factors influencing its existence. Methods and Results: This study investigated the diversity and abundance of comammox bacteria in sediments of a typical urban lake in China, and their ecological relationship with other ammonia‐oxidizing micro‐organisms. The phylogenetic analysis indicated that comammox clade A existed in the sediment of Lake Donghu, and the comammox bacteria co‐existed with ammonia‐oxidizing archaea (AOA), ammonia‐oxidizing bacteria (AOB) and anaerobic ammonia‐oxidizing (anammox) bacteria in the sediment of this lake. The abundances of the ammonia monooxygenase subunit A (amoA) genes for comammox, AOA, AOB and anammox 16S rRNA were 2·43 × 108, 1·07 × 108, 3·24 × 107 and 3·21 × 1011 copies per gram dry sediment respectively. Moreover, the amoA gene abundance of comammox was positively correlated with that of AOA and AOB. The redundancy analysis showed that the abundance of the comammox amoA gene was negatively correlated with the concentration of main indicators for nitrogen status in both the sediment and the water column, indicating that eutrophication may inhibit the growth of comammox bacteria. Conclusions: Comammox bacteria play an important ecological role in the nitrogen cycle of urban lake sediments. Significance and Impact of the Study: Our results indicated comammox bacteria were widespread in urban lakes and eutrophication may inhibit their growth. [ABSTRACT FROM AUTHOR]

Seismic characterisation of carbonate reservoirs is a challenging task because of special geological and geometrical properties of the reservoirs. This challenge is also due to the low signal-to-noise ratio and low resolution of seismic data. We improved the data quality by applying an inverse- Q filter to 3D seismic data, and in turn increased the accuracy of reservoir characterisation. We implemented the inverse- Q filter in a stabilised fashion so that we can compensate seismic amplitudes and correct for waveform phases simultaneously. We conducted the case study on 3D seismic data from the Ordovician carbonate reservoirs in the Tarim Basin, China, where the Ordovician sediment is buried very deep, with a depth larger than 5000 m, and has extremely strong heterogeneity either in the vertical or the horizontal direction. The stabilised inverse- Q filter improved the lateral continuity of seismic reflections, enhanced the spatial and vertical resolution, and strengthened weak signals in 3D seismic data. Therefore, we were able to characterise the interior details of the unconformity of the Ordovician sediment and to illustrate vug caves and fault fractures within the target carbonate reservoirs. [ABSTRACT FROM AUTHOR]

SUMMARY A composite Holocene sediment profile ∼5 m in length, constrained by both radiocarbon dating and magnetic susceptibility based correlation, was obtained from three Livingstone piston cores collected in ∼10-m water depth in the Huguangyan (HGY) maar lake, southern China. The homogeneous silty clay indicates stable and continuous deposition. The dominant magnetic carrier is magnetite in the pseudo-single-domain grain size range and thus is suitable for recording palaeomagnetic secular variations (PSV). Results show that the HGY PSV curves can be correlated faithfully to the counterparts at a regional scale. Therefore, the PSV data is a potential tool for stratigraphic correlation and for further refining the chronological framework of lake sediment sequences from Southern China. Further comparison of the HGY PSV records with the coeval European and North American counterparts confirms the existence of strong permanent magnetic flux lobes at the core-mantle boundary. The discrepancy in amplitude and out-phase pattern among the different regional records may be ascribed to the evolution of the magnetic flux lobes. [ABSTRACT FROM AUTHOR]

The Sichuan earthquake, Mw 7.9, struck the Longmen Shan (LMS) range front, China, on 2008 May 12, affecting an area of moderate historical seismicity where little active shortening has been previously reported. Recent studies based on space geodesy have succeeded in retrieving the far field surface displacements caused by the earthquake, but the near field (±25 km from the faults) coseismic surface displacement is still poorly constrained. Thus, shallow fault geometry and shallow coseismic slip are still poorly resolved. Here, for the first time for this earthquake, we combine C and L-band Synthetic Aperture Radar offsets data from ascending and descending tracks to invert for the 3-D surface displacement in the near coseismic field of the Sichuan earthquake. Our data, coupled with a simple elastic dislocation model, provide new results strongly suggesting the presence of a blind thrust striking along the range front and being active at depth during the earthquake. The presence of a rupture on a blind thrust brings new evidence for an out-of-sequence thrusting event and new elements for interpreting the tectonic strain partitioning in the LMS, which has important implications both for seismic hazard assessment and long-term evolution of the mountain belt. [ABSTRACT FROM AUTHOR]

Detailed palaeomagnetic investigations were carried out on two 23 m long sediment cores from Erlongwan maar lake, NE China. The sediment composition of both cores is nearly identical. Based on a macroscopical inspection of the cores 410 graded layers intercalated into the laminated sediments were identified. Measurements of the anisotropy of the magnetic susceptibility revealed that these layers have not disturbed the sediment structure in general, but only in intervals where their thicknesses exceeds 50 cm. The age model for Erlongwan is based on 15 AMS 14C-datings on bulk sediment, showing that the sediment profile spans the last 37 ka cal BP. Although one of the sediment cores has been slightly deformed during core recovery, similar inclination and declination records could be obtained by standard palaeomagnetic methods. The stacked inclination and declination records show both variations similar to those known from palaeosecular variation records from Eastern China and Japan. Therefore, the presented study is a contribution to the ongoing process of compiling a PSV mastercurve for East Asia. [ABSTRACT FROM AUTHOR]

Examines several loess sequences located east of the Liupan mountain region in China. Attainment of records of the Blake polarity event; Influence of regional variations in the sedimentary environment on the inconsistent recording of the Blake event; Occurrence of severe dust storms.