昆仑山8.1级地震前中国大陆的构造应变背景

利用“网络工程”1998～2001年累积的1181个测站的GPS重复观测资料，采用双三次样条函数模型建立中国大陆水平运动模型速度场，用大地坐标在椭球面上计算各类应变场，详细分析了2001年昆仑山8．1级地震前中国大陆水平构造应变场空间分布特征。各类构造应变场的最高值都出现在喜马拉雅构造带与昆仑山地块内(地震断裂带南侧)，鲜水河—安宁河断裂带次之。分析表明，昆仑山8．1级地震正好发生在张性面膨胀应变率的高值区，第一、第二和最大剪应变率高值区边缘的突变区和最大、最小主应变率的高值区。     

洛坝铅锌矿床的构造演化分析

洛坝铅锌矿床位于黄诸关韧脆性变形带所波及的范围内,断裂、褶皱、劈理、节理等形态构造类型均很发育,经对小型构造的统计及应力场分析证明,矿区变形主要是在海西—印支期长期存在的南北向古应力场持续作用下形成的。     

昆仑山口大地震与地形变异常的讨论

针对昆仑山口大地震，总结了多种地形变（大地测量）手段所显示的异常变化及其时空分布，结果显示：8．1级大震前存在空间尺度大，时间尺度的地形变前兆异常，简要介绍了相关的异常图像，给出了初步解释，并对未来震情的发展进行了探讨，认为近期内强震活动向华北迁移的可能性不大。     

青藏块体东北缘地壳水平运动状态

应用青藏块体东北缘1999～2003年多期GPS观测资料，计算了不同时段GPS点水平运动速率。通过分析发现：甘青块体可分为东部块体和西部块体，东、西部块体的运动状态存在明显的差异；受2001年11月14日昆仑Ms8．1地震的影响，震后地壳运动状态发生了明显的改变。     

用素土桩挤密法处理陇东湿陷性黄土地基

素土桩挤密地基由桩间挤密土和回填素土夯实的桩体组成，它是一种人工“复合地基”。其作用是通过素土桩挤密法提高地基土的密实度，从而对湿陷性黄土达到消除浅部或深部的部分或全部湿陷性的作用，并改善地基承载能力，减少地基变形。本文通过现场单桩、群桩单元体轻便触探、小环刀深层取样、开剖取样等方法对场地地基土挤密前、后干重度和压实系数进行了对比分析，判定用素土桩挤密法处理陇东湿陷性黄土地基的可行性。     

Crustal motion and deformation in Greece from a decade of GPS measurements, 1993–2003

The Hellenic plate boundary region, located in the collision zone between the Nubian/Arabian and Eurasian lithospheric plates, is one of the seismo-tectonically most active areas of Europe. During the last 15 years, GPS measurements have been used to determine the crustal motion in the area of Greece with the aim to better understand the geodynamical processes of this region. An extended reoccupation network covering whole Greece has been measured periodically in numerous GPS campaigns since the late eighties, and a continuous GPS network has been operated in the region of the Ionian Sea since 1995. In this paper, we present a new detailed high-quality solution of continuous and campaign-type measurements acquired between 1993 and 2003. During the GPS processing, a special effort was made to obtain consistent results with highest possible accuracies and reliabilities. Data of 54 mainly European IGS and EUREF sites were included in the GPS processing in order to obtain results which are internally consistent with the European kinematic field and order to allow for a regional interpretation. After an overview of the results of the IGS/EUREF sites, the results from more than 80 stations in Greece are presented in terms of velocities, time series, trajectories and strain rates. Previous geodetic, geological and seismological findings are generally confirmed and substantially refined. New important results include the observation of deformation zones to the north and to the south of the North Aegean Trough and in the West Hellenic arc region, arc-parallel extension of about 19 mm/yr along the Hellenic arc, and compression between the Ionian islands and the Greek mainland. Due to continuous long-term observations of 4–8 years, it was possible to extract height changes from the GPS time series. In Greece, we observe a differential subsidence of the order of 2 mm/yr between the northern and central Ionian islands across the Kefalonia fault zone. The differential subsidence of the central Ionian islands with respect to the northwestern Greek mainland amounts to 4 mm/yr.     

High resolution paleoenvironmental and chronological investigations of Norse landnám at Tasiusaq, Eastern Settlement, Greenland

High-resolution paleoenvironmental data from a peat profile with a small pollen source area are used to reconstruct the impacts of landnám on vegetation and soils at a Norse farm complex (∅2 at Tasiusaq) comprising two farms in the Eastern Settlement of Greenland. Analyses include the AMS ¹⁴C dating of plant macrofossil samples and the use of Bayesian radiocarbon calibration to construct improved age-depth models for Norse cultural horizons. The onset of a regional landnám may be indicated by the clearance of Betula pubescens woodland immediately prior to local settlement. The latter is dated to AD 950-1020 (2σ) and is characterised by possible burning of Betula glandulosa scrub to provide grassland pasture for domestic stock. Clearance and grazing resulted in accelerated levels of soil erosion at a westerly farm. This was followed by an easterly migration of settlement and agriculture. Site constraints prevent an assessment of the demise of the easterly farm, but pressures of overgrazing and land degradation may have been the major factors responsible for the abandonment of the earlier farm.     

Morphological analysis of the drainage system in the Eastern Alps

We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben.     

Anthropogenic affects on lake sedimentation process: a case study from Lake Sapanca, NW Turkey

Lake Sapanca in NW Turkey is a fault originated freshwater basin fed by seasonally variable flows of 15 streams. Considerations of lake–river interaction, supported by statistical measures of 47 bottom samples, suggest that sediment transport and deposition within the lake is controlled by two types of human constructed structures in addition to natural factors: (1) the dykes constructed in the front of streams, which feed the lake by strong flows, to prevent the filling of lakebed by coarse-grained sediments; (2) the constructed regulator on the outflowing Çarksuyu stream results in a higher sedimentation rate of clay-sized material on the NE corner of the lake, which is extraordinary in the shelf environment.     

Evolution of subcontinental lithospheric mantle beneath eastern China: Re–Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts

The ages of subcontinental lithospheric mantle beneath the North China and South China cratons are less well-constrained than the overlying crust. We report Re–Os isotope systematics of mantle xenoliths entrained in Paleozoic kimberlites and Mesozoic basalts from eastern China. Peridotite xenoliths from the Fuxian and Mengyin Paleozoic diamondiferous kimberlites in the North China Craton give Archean Re depletion ages of 2.6–3.2 Ga and melt depletion ages of 2.9–3.4 Ga. No obvious differences in Re and Os abundances, Os isotopic ratios and model ages are observed between spinel-facies and garnet-facies peridotites from both kimberlite localities. The Re–Os isotopic data, together with the PGE concentrations, demonstrate that beneath the Archean continental crust of the eastern North China Craton, Archean lithospheric mantle of spinel- to diamond-facies existed without apparent compositional stratification during the Paleozoic. The Mesozoic and Cenozoic basalt-borne peridotite and pyroxenite xenoliths, on the other hand, show geochemical features indicating metasomatic enrichment, along with a large range of the Re–Os isotopic model ages from Proterozoic to Phanerozoic. These features indicate that lithospheric transformation or refertilization through melt-peridotite interaction could be the primary mechanism for compositional changes during the Phanerozoic, rather than delamination or thermal-mechanical erosion, despite the potential of these latter processes to play an important role for the loss of garnet-facies mantle. A fresh garnet lherzolite xenolith from the Yangtze Block has a Re depletion age of ∼1.04 Ga, much younger than overlying Archean crustal rocks but the same Re depletion ages as spinel lherzolite xenoliths from adjacent Mesozoic basalts, indicating Neoproterozoic resetting of the Re–Os system in the South China Craton.