利用FG5绝对重力仪观测数据确定重力垂直梯度          下载免费PDF全文

宛家宽  罗志才  赵珞成 《地球物理学报》2018,61(1):119-126

本文建立了利用FG5实测数据求解重力垂直梯度的数据处理模型与算法.通过对多次自由落体实验的下落距离拟合残差叠加求均值，发现下落距离观测量中存在明显的有色噪声.通过对有色噪声的建模，并以剩余残差为依据选取可靠的下落时段，解算测站点的重力垂直梯度.利用本文所提出的数据处理方法分别对FG5-214绝对重力仪在两个测站上的观测数据进行处理，以相对重力仪测量的重力垂直梯度结果为参考值，本文处理得到的重力垂直梯度结果相比于未考虑有色噪声并依据经验选取下落时段的解算方法得到了显著改善.  相似文献   

基于密集台阵的青藏高原东北缘地壳精细结构及九寨沟地震震源区结构特征分析   总被引：8，自引：2，他引：6       下载免费PDF全文

李敏娟  沈旭章  张元生  刘旭宙  梅秀苹 《地球物理学报》2018,61(5):2075-2087

基于青藏高原东北缘密集宽频带野外流动观测台阵以及固定台站资料，利用双差层析成像方法对地震位置和研究区的地壳速度结构进行了反演.最终用于联合反演的地震事件合计9644个.结果显示青藏高原东北缘速度结构具有明显的横向不均匀性.从整体上看，青藏高原地区表现为低速异常，鄂尔多斯表现为高速异常，而扬子地块亦表现为高速异常.不同深度处速度结构表现不一致，同一深度处P波速度结构和S波速度结构也有明显差异.由西秦岭北缘断裂带、临潭-宕昌断裂以及礼县-罗家堡断裂围限的地震活动强烈的区域中，P波速度结构由深度0 km时呈现的低速异常，逐渐过渡到5 km时高低速相间分布的特征；而S波速度结构在此区域中，由近地表0 km时高低速相间分布的特征，逐渐过渡到30 km时几乎表现为低速异常.2017年8月8日九寨沟7级地震所在的塔藏断裂、岷江断裂和雪山断裂围限区域，在深度20 km处的P波速度结构和周围存在明显差异，九寨沟地震处于高速异常与低速异常的过渡带内.此外，2013年7月22日发生在青藏高原东北缘的岷漳县6.6级地震，震源区所在的临潭-宕昌断裂附近的P波速度结构在15 km深度处也有明显特征，震源位置所在区域也处于高低速过渡带.该区域这种地壳内部高低速过渡带可能是应力比较容易积累而发生中强地震的一个重要场所.  相似文献   

3D P-WAVE VELOCITY STRUCTURE AT THE NORTHEASTERN MARGIN OF ORDOS BLOCK     

HAN Xiao-ming  Liu Fang  ZHANG Fan  CHEN Li-feng  LI Juan  LI Shuan-hu  YANG Hong-ying 《地震地质》2018,40(1):215-231

Using the 7 100 absolute first arrivals of P waves and 91 513 relative P arrival times of 726 events at the northeastern margin of the Ordos block since 2009, the 3D fine structure of P wave velocity within the depth of 15km in the crust was inverted by the double difference seismic tomography method. The results show that there exist obvious high-speed continuous bodies in the northwest of the study area, and their lateral areas increase gradually with depth, while the velocity of east and south is relatively low. The velocity inhomogeneity exists and differs at different depths. The lateral differences of velocity are related to seismicity and faults. The 5~15km depth profile shows that earthquakes tend to occur in the area with relatively high velocity or high speed transition zones, which to some extent reflects the fragility of regional crustal media and the strong differential movement of faults in vertical and horizontal directions where the crust body is easy to absorb and store strain energy and generate major earthquakes. A "Y"-shape low-velocity channel is present in the lower crust around Liangcheng, corresponding to the NW-trending Heilaoyao-Shahukou fault set, which may reveal the migration path of the Late Tertiary-Quaternary basalt eruption. The Helingeer M6.2 earthquake in 1976 was related to the formation of the locking section of the thermal welding in this area. The three-dimensional fine structure of P wave velocity presented in this paper provides intuitive seismological evidence for physical and chemical properties of crustal media and the deep tectonic environment of earthquake preparation.  相似文献   

天津港“8·12”爆炸事件记录波形分析          下载免费PDF全文

王晨辰  张盛中  杨晓瑜  张冰  李世鑫  刘敏 《地震工程学报》2018,40(1):130-138

利用天津地震台网23个短周期地震仪记录到的2015年8月12日天津港爆炸事件波形数据,对事件进行初步分析和研究。分别使用能量包络线法和波形匹配法,共识别出4次爆炸事件,并结合波形互相关的主事件定位法对爆炸事件进行定位。分析结果表明:第一次爆炸发生的时间为2015年8月12日23时34分4秒,1.77s后发生了规模更大的二号爆炸事件;34.11s后又发生了最强的三号爆炸事件;86.33s再一次发生了能量较弱的四号爆炸事件,其中二号与三号爆炸事件相距65~70m,二号与四号事件相距160~170m。此外,通过选用爆破、矿塌、核爆和天然地震等不同类型事件的波形数据,从时间域和频率域分别对这些事件进行对比分析,发现其震相特征表现出明显差异。  相似文献   

逆时偏移在声反射成像测井中的应用方法研究          下载免费PDF全文

李雨生  李宁  武宏亮  王克文  冯周  刘鹏 《地球物理学报》2020,63(4):1705-1714

声反射成像测井中常用的基于射线理论的Kirchhoff积分偏移算法和基于单程波理论的F-K偏移算法均可实现井旁缝洞反射体的快速偏移成像,但其仅适用于地层垂向变化较弱的速度场和高陡角裂缝的偏移成像,无法实现低角度反射体的准确偏移归位,产生偏移假象误导测井解释.逆时偏移基于全波动方程,可适应强垂向变化速度场,实现近似水平反射体的偏移成像.本文详细分析了将逆时偏移应用于声反射成像测井时存在的数据准备、时间采样间隔匹配和成像条件改进等若干问题,通过设置多组理论模型来说明算法对井旁不同反射体的识别能力.模拟资料和实际资料处理结果证实,较F-K偏移算法,逆时偏移算法成像精度更高、收敛性更好,可有效实现近似水平构造偏移归位.改进的归一化互相关成像条件可解决深部地层的远井壁成像衰减问题,降低测井解释的多解性.逆时偏移将成为声反射成像测井高精度偏移技术的发展方向.  相似文献   

Using visibility analysis to improve point density and processing time of SfM-MVS techniques for 3D reconstruction of landforms     

Álvaro Gómez-Gutiérrez  Trent Biggs  Napoleon Gudino-Elizondo  Paz Errea  Esteban Alonso-González  Estela Nadal Romero  José Juan de Sanjosé Blasco 《地球表面变化过程与地形》2020,45(11):2524-2539

Image network geometry, including the number and orientation of images, impacts the error, coverage, and processing time of 3D terrain mapping performed using structure-from-motion and multiview-stereo (SfM-MVS). Few studies have quantified trade-offs in error and processing time or ways to optimize image acquisition in diverse topographic conditions. Here, we determine suitable camera locations for image acquisition by minimizing the occlusion produced by topography. Viewshed analysis is used to select the suitable images, which requires a preliminary digital elevation model (DEM), potential camera locations, and sensor parameters. One aerial and two ground-based image collections were used to analyse differences between SfM-MVS models produced using: (1) all available images (ALL); (2) images selected using conventional methods (CON); and (3) images selected using the viewshed analysis (VIEW). The resulting models were compared with benchmark point clouds acquired by a terrestrial laser scanner (TLS) and TLS-derived DEMs. The VIEW datasets produced denser point clouds (28–32% more points) and DEMs with up to 66% reduction in error compared with CON datasets due to reduction of gaps in the DEM. VIEW datasets reduced processing time by 37–76% compared with ALL, with no reduction in coverage or increase in error. DEMs produced with ALL and VIEW datasets had similar slope and roughness, while slight differences that may be locally important were observed for the CON dataset. The new method helps optimize SfM-MVS image collection strategies that significantly reduce the number of images required with minimal loss in coverage or accuracy over complex surfaces. © 2020 John Wiley & Sons, Ltd.  相似文献   

Water transport and tracer mixing in volcanic ash soils at a tropical hillslope: A wet layered sloping sponge     

Giovanny M. Mosquera  Patricio Crespo  Lutz Breuer  Jan Feyen  David Windhorst 《水文研究》2020,34(9):2032-2047

Andosol soils formed in volcanic ash provide key hydrological services in montane environments. To unravel the subsurface water transport and tracer mixing in these soils we conducted a detailed characterization of soil properties and analyzed a 3-year data set of sub-hourly hydrometric and weekly stable isotope data collected at three locations along a steep hillslope. A weakly developed (52–61 cm depth), highly organic andic (Ah) horizon overlaying a mineral (C) horizon was identified, both showing relatively similar properties and subsurface flow dynamics along the hillslope. Soil moisture observations in the Ah horizon showed a fast responding (few hours) “rooted” layer to a depth of 15 cm, overlying a “perched” layer that remained near saturated year-round. The formation of the latter results from the high organic matter (33–42%) and clay (29–31%) content of the Ah horizon and an abrupt hydraulic conductivity reduction in this layer with respect to the rooted layer above. Isotopic signatures revealed that water resides within this soil horizon for short periods, both at the rooted (2 weeks) and perched (4 weeks) layer. A fast soil moisture reaction during rainfall events was also observed in the C horizon, with response times similar to those in the rooted layer. These results indicate that despite the perched layer, which helps sustain the water storage of the soil, a fast vertical mobilization of water through the entire soil profile occurs during rainfall events. The latter being the result of the fast transmissivity of hydraulic potentials through the porous matrix of the Andosols, as evidenced by the exponential shape of the water retention curves of the subsequent horizons. These findings demonstrate that the hydrological behavior of volcanic ash soils resembles that of a “layered sponge,” in which vertical flow paths dominate.  相似文献   

Quick Phase Identification for Dense Seismic Array with Aid from Long Term Phase Records of Co-located Sparse Permanent Stations     

CHEN Yini  LI Jun  WANG Zhenjie  ZHAO Mengqi  YU Tiehong  LI Danning  YU Junyi  WANG Weitao 《中国地震研究》2020,34(3):328-342

The phase identification and travel time picking are critical for seismic tomography, yet it will be challenging when the numbers of stations and earthquakes are huge. We here present a method to quickly obtain P and S travel times of pre-determined earthquakes from mobile dense array with the aid from long term phase records from co-located permanent stations. The records for 1 768 M ≥ 2.0 events from 2011 to 2013 recorded by 350 ChinArray stations deployed in Yunnan Province are processed with an improved AR-AIC method utilizing cumulative envelope and rectilinearity. The reference arrivals are predicted based on phase records from 88 permanent stations with similar spatial coverage, which are further refined with AR-AIC. Totally, 718 573 P picks and 512 035 S picks are obtained from mobile stations, which are 28 and 22 times of those from permanent stations, respectively. By comparing the automatic picks with manual picks from 88 permanent stations, for M ≥ 3.0 events, 81.5% of the P-pick errors are smaller than 0.5 second and 70.5% of S-pick errors are smaller than 1 second. For events with a lower magnitude, 76.5% P-pick errors fall into 0.5 second and 69.5% S-pick errors are smaller than 1 second. Moreover, the Pn and Sn phases are easily discriminated from directly P/S, indicating the necessity of combining traditional auto picking and integrating machine learning method.  相似文献   

Semantic and syntactic interoperability in online processing of big Earth observation data     

Martin Sudmanns  Dirk Tiede  Stefan Lang  Andrea Baraldi 《International Journal of Digital Earth》2018,11(1):95-112

ABSTRACT

The challenge of enabling syntactic and semantic interoperability for comprehensive and reproducible online processing of big Earth observation (EO) data is still unsolved. Supporting both types of interoperability is one of the requirements to efficiently extract valuable information from the large amount of available multi-temporal gridded data sets. The proposed system wraps world models, (semantic interoperability) into OGC Web Processing Services (syntactic interoperability) for semantic online analyses. World models describe spatio-temporal entities and their relationships in a formal way. The proposed system serves as enabler for (1) technical interoperability using a standardised interface to be used by all types of clients and (2) allowing experts from different domains to develop complex analyses together as collaborative effort. Users are connecting the world models online to the data, which are maintained in a centralised storage as 3D spatio-temporal data cubes. It allows also non-experts to extract valuable information from EO data because data management, low-level interactions or specific software issues can be ignored. We discuss the concept of the proposed system, provide a technical implementation example and describe three use cases for extracting changes from EO images and demonstrate the usability also for non-EO, gridded, multi-temporal data sets (CORINE land cover).  相似文献   

Mapping cropland fallow areas in myanmar to scale up sustainable intensification of pulse crops in the farming system     

Murali Krishna Gumma  Prasad S Thenkabail  Kumara Charyulu Deevi  Irshad A Mohammed  Pardhasaradhi Teluguntla  Adam Oliphant 《地理信息系统科学与遥感》2018,55(6):926-949

Cropland fallows are the next best-bet for intensification and extensification, leading to increased food production and adding to the nutritional basket. The agronomical suitability of these lands can decide the extent of usage of these lands. Myanmar’s agricultural land (over 13.8 Mha) has the potential to expand by another 50% into additional fallow areas. These areas may be used to grow short-duration pulses, which are economically important and nutritionally rich, and constitute the diets of millions of people as well as provide an important source of livestock feed throughout Asia. Intensifying rice fallows will not only improve the productivity of the land but also increase the income of the smallholder farmers. The enhanced cultivation of pulses will help improve nutritional security in Myanmar and also help conserve natural resources and reduce environmental degradation. The objectives of this study was to use remote sensing methods to identify croplands in Myanmar and cropland fallow areas in two important agro-ecological regions, delta and coastal region and the dry zone. The study used moderate-resolution imaging spectroradiometer (MODIS) 250-m, 16-day normalized difference vegetation index (NDVI) maximum value composite (MVC), and land surface water index (LSWI) for one 1 year (1 June 2012–31 May 2013) along with seasonal field-plot level information and spectral matching techniques to derive croplands versus cropland fallows for each of the three seasons: the monsoon period between June and October; winter period between November and February; and summer period between March and May. The study showed that Myanmar had total net cropland area (TNCA) of 13.8 Mha. Cropland fallows during the monsoon season account for a meagre 2.4% of TNCA. However, in the winter season, 56.5% of TNCA (or 7.8 Mha) were classified as cropland fallows and during the summer season, 82.7% of TNCA (11.4 Mha) were cropland fallows. The producer’s accuracy of the cropland fallow class varied between 92 and 98% (errors of omission of 2 to 8%) and user’s accuracy varied between 82 and 92% (errors of commission of 8 to 18%) for winter and summer, respectively. Overall, the study estimated 19.2 Mha cropland fallows from the two major seasons (winter and summer). Out of this, 10.08 Mha has sufficient moisture (either from rainfall or stored soil water content) to grow short-season pulse crops. This potential with an estimated income of US$ 300 per hectare, if exploited sustainably, is estimated to bring an additional net income of about US$ 1.5 billion to Myanmar per year if at least half (5.04 Mha) of the total cropland fallows (10.08 Mha) is covered with short season pulses.  相似文献