基于水动力量化因子的岩溶强发育深度研究

地下水垂向循环水动力条件是岩溶发育深度的主要控制因素.为探求川东背斜构造岩溶区多级水流系统控制下的岩溶强发育深度,采用地理信息系统(GIS)技术,选取地形指数和水动力坡降构建岩溶水动力强弱的量化因子FHQ,并结合钻孔数据推求假角山背斜构造区地下岩溶强发育深度.研究显示:水动力因子FHQ与地形指数、水动力坡降在空间上呈明...     

The Earth's natural pulse electromagnetic fields for earthquake time–frequency characteristics: Insights from the EEMD–WVD method

Monitoring the Earth's natural pulse electromagnetic field (ENPEMF) signal is a geomagnetic detection approach for the Earth internal and external studies, and it provides a reference for earthquake prediction. In this paper, the Ensemble Empirical Mode Decomposition–Wigner Ville Distribution (EEMD–WVD) method is used to process the time sequences of the ENPEMF signal detected by GR‐01 receiving devices during the Lushan M_S7.0 earthquake (April 20th, 2013). By obtaining the intrinsic mode function (IMF), the time–frequency–amplitude joint distribution and the energy spectrum of the ENPEMF signal, the suspected anomalies before the earthquake could be shown. The results illustrate the ENPEMF signal before an earthquake and its time–frequency characteristics based on an EEMD–WVD algorithm, proving useful information about the anomalies around the time of the earthquake.     

Imaging shallow structure with active-source surface wave signal recorded by distributed acoustic sensing arrays

Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. To test the feasibility of DAS in shallow structure imaging, the PoroTomo team conducted a DAS experiment with the vibroseis truck T-Rex in Brady’s Hot Springs, Nevada, USA. The Rayleigh waves excited by the vertical mode of the vibroseis truck were analyzed with the Multichannel Analysis of Surface Waves (MASW) method. Phase velocities between 5 and 20 Hz were successfully extracted for one segment of cable and were employed to build a shear-wave velocity model for the top 50 meters. The dispersion curves obtained with DAS agree well with the ones extracted from co-located geophones data and from the passive source Noise Correlation Functions (NCF). Comparing to the co-located geophone array, the higher sensor density that DAS arrays provides help reducing aliasing in dispersion analysis, and separating different surface wave modes. This study demonstrates the feasibility and advantage of DAS in imaging shallow structure with surface waves.     

Finite difference calculation of traveltime on non-orthogonal grid

Finite difference methods have been widely employed in solving the eikonal equation so as to calculate traveltime of seismic phase. Most previous studies used regular orthogonal grid. However, much denser grid is required to sample the interfaces that are undulating in depth direction, such as the Moho and the 660 km discontinuity.Here we propose a new finite difference algorithm to solve the eikonal equation on non-orthogonal grid(irregular grid).To demonstrate its efficiency and accuracy, a test was conducted with a two-layer model. The test result suggests that the similar accuracy of a regular grid with ten times grids could achieve with our new algorithm, but the time cost is only about 0.1 times. A spherical earth model with an undulant660 km discontinuity was constructed to demonstrate the potential application of our new method. In that case, the traveltime curve fluctuation corresponds to topography. Our new algorithm is efficient in solving the first arrival times of waves associated with undulant interfaces.     

On the stability relationships between tidal asymmetry and morphologies of tidal basins and estuaries

Simple stability relationships are practically useful to provide a rapid assessment of coastal and estuarine landforms in response to human interventions and long‐term climate change. In this contribution, we review a variety of simple stability relationships which are based on the analysis of tidal asymmetry (TA). Most of the existing TA‐based stability relationships are derived using the one‐dimensional tidal flow equations assuming a certain regular shape of the tidal channel cross‐sections. To facilitate analytical solutions, specific assumptions inevitably need to be made, for example by linearizing the friction term and dropping some negligible terms in the tidal flow equations. We find that three major types of TA‐based stability relationships have been proposed between three non‐dimensional channel geometric ratios (represented by the ratio of channel widths, ratio of wet surface areas and ratio of storage volumes) and the tide‐related parameter a/h (i.e. the ratio between tidal amplitude and mean water depth). Based on established geometric relations, we use these non‐dimensional ratios to restate the existing relationships so that they are directly comparable. Available datasets are further extended to examine the utility of these TA‐based relationships. Although a certain agreement is shown for these relationships, we also observe a large scatter of data points which are collected in different types of landscape, hydrodynamic and sedimentological settings over the world. We discuss in detail the potential reasons for this large scatter and subsequently elaborate on the limited applicability of the various TA‐based stability relationships for practical use. We highlight the need to delve further into what constitutes equilibrium and what is needed to develop more robust measures to determine the morphological state of these systems. Copyright © 2018 John Wiley & Sons, Ltd.     

Adaptive multi-fidelity probabilistic collocation-based Kalman filter for subsurface flow data assimilation: numerical modeling and real-world experiment

Stochastic Environmental Research and Risk Assessment - The ensemble Kalman filter (EnKF) has received substantial attention in hydrologic data assimilation due to its ease of implementation. In...     

Antagonism between coral pathogen Vibrio coralliilyticus and other bacteria in the gastric cavity of scleractinian coral Galaxea fascicularis

Scleractinian corals host numerous microbial symbionts with different types of interactions. The gastric cavity of scleractinian coral, as a semiclosed subenvironment with distinct chemical characteristics(e.g., dissolved O2, pH, alkalinity, and nutrients), harbors a distinct microbial community and a diverse array of bacteria that can be pathogenic or beneficial. Galaxea fascicularis is one of the dominant massive scleractinian coral species on inshore fringing reefs in the northern South China Sea.Although the abundance of coral-associated bacteria has been investigated in G. fascicularis, less is known about the microorganisms in the gastric cavity. In this study, we specially isolated cultivable bacterial strains from the gastric cavity of G.fascicularis collected from Hainan Island using a noninvasive sampling approach. Among the 101 representative bacterial strains, one Vibrio coralliilyticus strain, SCSIO 43001, was found to be a temperature-dependent opportunistic pathogen of G.fascicularis. The antagonistic activity between the 100 strains and V. coralliilyticus SCSIO 43001 was tested using a modified Burkholder diffusion assay. Our results showed that V. coralliilyticus SCSIO 43001 inhibits the growth of Erythrobacter flavus and Sphingomonas yabuuchiae. Additionally, we found that three Pseudoalteromonas strains showed moderate to high antibacterial activity against V. coralliilyticus SCSIO 43001 and several other coral-associated Gram-negative bacterial strains.These results suggest that competition between the coral pathogen and other bacteria also occurs in the gastric cavity of coral, and Pseudoalteromonas strains in the gastric cavity of G. fascicularis may provide a protective role in the defense against coinhabiting coral pathogens at elevated temperature.     

Velocity anisotropy characteristics and pre-stack time migration imaging of the marine sedimentary strata in the South Yellow Sea Basin

The South Yellow Sea is a superimposed basin overlying Mesozoic-Cenozoic continental sediments, which in turn overlie Paleozoic-Mesozoic marine deposits that are now the target of hydrocarbon exploration. Strongly modified by multiple tectonic events, the marine sediments feature a large tectonic relief, with obvious horizontal anisotropy in seismic velocity, which significantly affects the seismic image quality. In this study, the sedimentary velocity anisotropy and its influence on image quality were analyzed using an analytical theory method, assuming transversely isotropic medium with vertical axis of symmetry (VTI), and using seismic and well-log data. Additionally, an anisotropic prestack time migration was used for the imaging of the field data. The results showed that the anisotropic pre-stack time migration processing could be used to significantly improve the accuracy of the seismic images in areas with distinct faults, offering clear images of accurately located fault planes and fault edges, thereby improving the lateral resolution of the seismic data and its signal-to-noise ratio.     

Seismology software: state of the practice

We analyzed the state of practice for software development in the seismology domain by comparing 30 software packages on four aspects: product, implementation, design, and process. We found room for improvement in most seismology software packages. The principal areas of concern include a lack of adequate requirements and design specification documents, a lack of test data to assess reliability, a lack of examples to get new users started, and a lack of technological tools to assist with managing the development process. To assist going forward, we provide recommendations for a document-driven development process that includes a problem statement, development plan, requirement specification, verification and validation (V&V) plan, design specification, code, V&V report, and a user manual. We also provide advice on tool use, including issue tracking, version control, code documentation, and testing tools.     

Bayesian Monitoring Design for Streambed Heat Tracing: Numerical Simulation and Sandbox Experiments

Heat tracing methods have been widely employed for subsurface characterization. Nevertheless, there were very few studies regarding the optimal monitoring design for heat tracing in heterogeneous streambeds. In this study, we addressed this issue by proposing an efficient optimal design framework to collect the most informative diurnal temperature signal for Bayesian estimation of streambed hydraulic conductivities. The data worth (DW) was measured by the expected relative entropy between the prior and posterior distributions of the conductivity field. An adaptively refined Gaussian process surrogate was employed to alleviate the computational burden, resulting in at least three orders of magnitude of speed-up. The applicability of the optimal experimental design framework was evaluated by both numerical and sandbox experimental cases. Results showed that the most informative locations centered in the transition zones among the main patterns of the hydraulic conductivity field, while the most informative times centered in a short period after the minimum/maximum temperature appeared. With the fixed number of measurements, extending the calibration period was more beneficial than increasing the monitoring frequency in improving the estimation results. To our best knowledge, this work is the first study on Bayesian monitoring design for streambed characterization with the heat tracing method. The method and results can provide guidance on selecting monitoring strategies under budget-limited conditions.