Comparison of long-term and short-term uplift rates along an active blind reverse fault zone (Bajo Segura,Se Spain)

The seismic activity of the Guardamar-Torrevieja zone (Eastern Betic Cordillera, SE Spain) can be associated with the Bajo Segura fault zone, an E-W reverse blind fault with secondary NW-SE dextral faults. A high-precision levelling profile 30 kilometers long was set up and levelled in 1997 to monitor the vertical displacement of this active fault zone. This profile runs parallel to an older high-precision levelling line included in the Spanish first order levelling network measured by the Instituto Geográfico Nacional (IGN) in two different campaigns (1934 and 1976). The 1997 line was relevelled in 2003 and 10 new benchmarks were set up, both to increase benchmark density and to restore some of the 1997 benchmarks that had been destroyed. We have used the 1976 IGN and the 2003 measurement to construct a recent vertical movements profile with a significant time difference (27 years). This recent vertical movements profile shows that the vertical movements are very small, nearly equal to the error bars, with a 0.2 mm/year rise in the town of Guardamar, and a 0.2 mm/year subsidence of the southern part of the profile (Punta Prima) respect to the town of Torrevieja. These movements could be related to the activity of the Bajo Segura and the San Miguel faults respectively. Using geological markers we have deduced uplift rates of 0.1 mm/year during the last 3 million years. Therefore, these preliminary results indicate that geodetically (short-term deformation) determined uplift rates are similar to those estimated from geological markers (long term deformation).     

Multiple volcano deformation sources in a post-rifting period: 1989–2005 behaviour of Krafla,Iceland constrained by levelling,tilt and GPS observations

The Krafla rifting episode, which occurred in North Iceland in 1975–1984, was followed by inflation of a shallow magma chamber until 1989. At that time, gradual subsidence began above the magma chamber and has continued to the present at a declining rate. Pressure decrease in a shallow magma chamber is not the only source of deformation at Krafla, as other deformation processes are driven by exploitation of two geothermal fields, together with plate spreading. In addition, deep-seated magma accumulation appears to take place, with its centre ∼ 10 km north of the Krafla caldera. The relative strength of these sources has varied with time. New results from a levelling survey and GPS measurements in 2005 allow an updated view on the deformation field. Deformation rates spanning 2000–2005 are the lowest recorded in the 30-year history of geodetic studies at the volcano. The inferred rate of 2000–2005 subsidence related to processes in the shallow magma chamber is less than 0.3 cm/yr whereas it was ∼ 5 cm/yr in 1989–1992. Currently, the highest rate of subsidence takes place in the Leirbotnar area, within the Krafla caldera, and appears to be a result of geothermal exploitation.     

推算我国高精度和高分辨率似大地水准面的若干技术问题

讨论我国新一代高精度高分辨率似大地水准面的特点及其可能的精度和分辨率,列出了采用移去恢复法时的实用公式,介绍了计算斯托克司公式的严格方法和高程异常推估点的精度评定。     

海岸测量中GPS水准精度控制的探讨

简要介绍了高程系统的概念,分析了GPS水准拟合的基本数学模型,探讨了已知水准点极少时GPS水准拟合的精度控制问题,得出的一些结论可供海道测量工作者在海岸高程控制测量中参考.     

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精密工程测量数据处理综合系统讲座 第六讲 COSA_EREPS电子手簿及其应用

介绍了COSA_EREPS电子手簿的结构,详述了其水准测量、二三维控制测量、碎部测量、线路测设、工程放样等主要功能,总结了其应用特点。     

祁连山北缘断裂带的现代构造运动

本文依据现今区域水准测量资料及跨断层位移测量资料阐明祁连山北缘断裂带现今活动特点是以近南北—北东向的挤压并兼有右旋走滑的水平活动方式为主,在玉门一张掖段并伴有近似反对称的升降运动,最大垂直形变梯度R为0.2毫米/公里·年左右,跨断层基线测量的缩短速率为0.2—0.5毫米/年。在河西走廊内部,受次级构造运动的影响也存在有局部的隆起、拗陷的升降运动及断裂活动