白光连续谱与模型大气

本文依据白光耀斑连续发射谱的一般观测事实,通过对一系列模型大气的非局部热动平衡计算,从半经验角度探讨了白光连续发射与模型大气的关系。结果表明:光球深层的温度增加或者过渡区存在平台结构均可解释观测到的白光辐射增强。对如何从理论上来解释这些大气结构本文也提出了一些看法。     

The mitigation of the vibration effects caused by tunnel blasts in urban areas: a case study in Istanbul

Ground vibrations generated by commercial explosives in tunnel construction may cause structural damage in urban areas. Therefore, suppressing the vibration effects and mitigating the possible hazard after blasting is important. We present a new method of controlled blasting that is environmentally friendly, and easy to utilize for tunnel construction. Small charges in this method are detonated sequentially to produce minimum side effects. The efficiency of the charges may be increased based on the previously monitored shots. This method is utilized in a tunnel construction in Istanbul with five experimental shots. In these experiments, the duration and also the quantity of explosives were carefully controlled. We were able to obtain better results with short durations (480 ms) instead of long durations (9,000 ms) although the vibration levels defined as peak particle velocity (PPV) became bigger while the quantity of the explosive charge increased from 3.088 to 9.264 kg.     

Ichnology of Bhuban and Boka Bil Formations,oligocene-miocene deposits of Manipur Western Hill,Northeast India

Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm), Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone (Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong energy condition, subtidal to lower intertidal environment, rich in organic nutrients.     

Geomorphic characteristics of a bedrock river inferred from drainage quantification,longitudinal profile,knickzone identification and concavity analysis: a DEM-based study

An examination of river channels has ability to provide substantial information regarding the geomorphic characteristics, control of lithology, tectonic uplift and geomorphic evolution during the geological past of an area. In this paper, a detailed study of geomorphic and structural investigation has been carried out for Pravara basin, Maharashtra, with the help of 90-m resolution SRTM DEM and geospatial techniques. Drainage network analysis performed in this paper demonstrates the general geomorphic characteristics, while the analysis of longitudinal profile synthesises lithological control over Pravara basin. Pravara is a 6th order drainage basin, encompassing an area of 2637 km². Bifurcation ratio reveals low to moderate structural control. Due to the hard rock lithology, the drainage density and stream frequency are low, and it indicates higher permeability in the sub-surface layers. The shape parameters denote that Pravara is highly elongated and it is easier to control floods in this basin. Relief parameters show very steep slope and higher vulnerability to the slope failure in some areas. Upstream of Pravara river has shown that series of breaks and knickzones indicate active erosion and acute lithological control on the channel. Major breaks are observed only in the main channel whereas in two major tributaries, no such breaks found, instead these tributaries are characterised by several knickzones which indicate regional variation in the lithological physiognomies. Different lithological stages on knickpoint and channel incision substantiate rejuvenation of Pravara river in several phases during geological past. The geospatial methodology carried out in this study can be pragmatic elsewhere around this world to recognise the geomorphic appearances and lithological control of a drainage basin.     

Seismic profile analysis of the Kangra and Dehradun re-entrant of NW Himalayan Foreland thrust belt,India: A new approach to delineate subsurface geometry

In the NW Sub-Himalayan frontal thrust belt in India, seismic interpretation of subsurface geometry of the Kangra and Dehradun re-entrant mismatch with the previously proposed models. These procedures lack direct quantitative measurement on the seismic profile required for subsurface structural architecture. Here we use a predictive angular function for establishing quantitative geometric relationships between fault and fold shapes with ‘Distance–displacement method’ (D–d method). It is a prognostic straightforward mechanism to probe the possible structural network from a seismic profile. Two seismic profiles Kangra-2 and Kangra-4 of Kangra re-entrant, Himachal Pradesh (India), are investigated for the fault-related folds associated with the Balh and Paror anticlines. For Paror anticline, the final cut-off angle \(\beta =35{^{\circ }}\) was obtained by transforming the seismic time profile into depth profile to corroborate the interpreted structures. Also, the estimated shortening along the Jawalamukhi Thrust and Jhor Fault, lying between the Himalayan Frontal Thrust (HFT) and the Main Boundary Thrust (MBT) in the frontal fold-thrust belt, were found to be 6.06 and 0.25 km, respectively. Lastly, the geometric method of fold-fault relationship has been exercised to document the existence of a fault-bend fold above the Himalayan Frontal Thrust (HFT). Measurement of shortening along the fault plane is employed as an ancillary tool to prove the multi-bending geometry of the blind thrust of the Dehradun re-entrant.     

Experimental study on the instability mechanism of the major-defect fractured rock

Based on calculations of rock fracture surface and angle, incremental-load creep experiments were conducted on two groups of major-defect fractured rock specimens in an RLW-2000 rheology test system. The research investigated the fracture type and the creep properties of major-defect fractured rock and analyzed the relationships between failure load and horizontal or vertical projection distance, and between each of theme and fracture area or angle. The results showed that rock fracture was divided into three types according to the distribution, including I, II, and III types. I, II, and III types were respectively an internal fracture running through neither the upper nor lower end, one through the upper or lower end and one through both upper and lower ends, and a III type was further sub-divided into III_I and III_II types. The instantaneous strain was larger than the creep strain under the same creep loading stage. As the creep loading increased on two groups of major-defect fractured rock, the instantaneous strain decreased abruptly and then increased abruptly, while the creep strain decreased rapidly at first and later increased near-linearly. When the failure angle was larger than the friction angle, failure load was positively correlated with failure angle yet was negatively correlated with vertical projection distance. Vertical projection distance and fracture angle, which decided fracture type, controlled rock failure load. Failure load increased in turn from I type to III type, and low-type fracture determined mainly failure load in multiply-fracture specimen.     

Wavefield analysis of crosswell seismic data

Despite the numerous advantages of crosswell seismic data over surface seismic data, crosswell seismic geophysics is still underutilized and underdeveloped. The factors limiting the full utilization of crosswell data include the lack of standardized methods for processing and imaging the data. This is because crosswell data is not completely understood. To improve the understanding of crosswell data, we performed acoustic and elastic modeling of a west Texas carbonate oilfield data using finite difference methods and crosswell geometry. To account for the different wave modes in the field data, we decomposed the full data into its constituent wave modes. Results of the forward modeling show that elastic synthetic data is a better representation of crosswell field data than the popular acoustic synthetic data. Wavefield decomposition gave insight into the time-space kinematics behavior of the different wave modes that constitute the full data. Overall, the study improved our understanding of crosswell field data. The learning from this study has been utilized to perform data-driven reflection enhancement processing where the discerned characteristic of different seismic arrival is utilize to suppress unwanted and enhanced the desired wave modes. The processing reduced the complex data to only up-going P-P reflections that can be imaged to reveal the subtle geological structures of the oilfield.     

Towards a Digital Earth: using archetypes to enable knowledge interoperability within geo-observational sensor systems design

Earth System Science (ESS) observational data are often inadequately semantically enriched by geo-observational information systems to capture the true meaning of the associated data sets. Data models underpinning these information systems are often too rigid in their data representation to allow for the ever-changing and evolving nature of ESS domain concepts. This impoverished approach to observational data representation reduces the ability of multi-disciplinary practitioners to share information in a computable way. Object oriented techniques that are typically employed to model data in a complex domain (with evolving domain concepts) can unnecessarily exclude domain specialists from the design process, invariably leading to a mismatch between the needs of the domain specialists, and how the concepts are modelled. In many cases, an over simplification of the domain concept is captured by the computer scientist. This paper proposes that two-level modelling methodologies developed by health informaticians to tackle problems of domain specific use-case knowledge modelling can be re-used within ESS informatics. A translational approach to enable a two-level modelling process within geo-observational sensor systems design is described. We show how the Open Geospatial Consortium’s (OGC) Observations & Measurements (O&M) standard can act as a pragmatic solution for a stable reference-model (necessary for two-level modelling), and upon which more volatile domain specific concepts can be defined and managed using archetypes. A rudimentary use-case is presented, followed by a worked example showing the implementation methodology and considerations leading to an O&M based, two-level modelling design approach, to realise semantically rich and interoperable Earth System Science based geo-observational sensor systems.     

Dipole tilt controls bow shock location and flaring angle

The dipole tilt angle has been found to affect Earth’s bow shock. This work presents a quantitative relationship between the dipole tilt angle and the bow shock location and flaring angle. We collected a large data set of bow shock crossings from four different satellites (IMP 8, Geotail, Magion 4, and Cluster), including some recent crossings obtained during 2012–2013. The results from a statistical analysis demonstrate that: (1) the subsolar standoff distance increases but the flaring angle decreases with increasing dipole tilt angle; (2) when the dipole tilt angle changes sign from negative to positive, the dayside bow shock moves toward Earth and the shift can be as much as 2.29 R _E, during which the flaring angle increases; and (3) the shape of bow shock in the northern and southern hemispheres differs. For the northern hemisphere bow shock, with increasing positive/negative dipole tilt angle, the flaring angle increases/decreases. While for the southern hemisphere, the trend is the opposite; with increasing positive/negative dipole tilt angle, the flaring angle decreases/increases. These results are helpful for future bow shock modeling that needs to include the effects of dipole tilt angle.