Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small <Emphasis Type="Italic">δ</Emphasis> Spot

In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows, which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear. Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex β δ sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude that shear flows are a common phenomenon in complex active regions and δ spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric shear flows along the magnetic neutral line are not related to any change of the local magnetic shear. We present high-resolution observations of NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO). Time series of speckle-reconstructed white-light images and two-dimensional spectroscopic data were combined to study the temporal evolution of the three-dimensional vector flow field in the β δ sunspot group. An hour-long data set of consistent high quality was obtained, which had a cadence of better than 30 seconds and subarcsecond spatial resolution.     

Role of fluvial and structural processes in the formation of the Wahiba Sands, Oman: A remote sensing perspective

The Wahiba Sands in northeastern Oman are bordered on the north, south and west by highlands. Remote sensing data are used to characterize the region between 19–23.5°N and 56.5–60°E by mapping surface and near-surface drainage, faults and fractures and aeolian features. It is suggested that the sands were originally deposited with surface runoff from the principal wadis and fluvially reworked fault zones, which define the northeastern and southwestern margins. These fluvial processes resulted in the accumulation of the vast groundwater resources now stored there. During dry climates, wind became the principal modification regime and it began to sort and shape the sediments into the dune forms that characterize today's Wahiba region. The thickness of the sands reflects the depth of the basin in which they lie. The center of the basin is filled with the thickest sand (the High Sands) and contains the highest groundwater concentrations. Presently, aeolian reworking dominates in the Wahiba region, although the Low and the Peripheral Sands continue to experience some fluvial action from occasional, seasonal rainfall. Even though dry conditions dominate today, it is clear that similar to the Sahara of North Africa, the surface sands of the Wahiba basin are indicators of groundwater occurrence.     

The 2003 Mw 7.2 Fiordland subduction earthquake, New Zealand: aftershock distribution, main shock fault plane and static stress changes on the overlying Alpine Fault

The 2003 August 21 Fiordland earthquake ( M _L7.0, M _W7.2) was the largest earthquake to occur in New Zealand for 35 yr and the fifth of M6+ associated with shallow subduction in Fiordland in the last 15 yr. The aftershocks are diffuse and do not distinguish between the two possible main shock fault planes implied by the Harvard CMT solution, one corresponding to subduction interface thrusting and the other corresponding to steeply seaward dipping thrusting. The distinction is important for calculating the induced stress changes on the overlying Alpine Fault which has a history of very large earthquakes, the last possibly in 1717. We have relocated the aftershocks, using data from temporary seismographs in the epicentral region and the double difference technique. We then use the correlation between aftershock hypocentres and regions of positive changes in Coulomb Failure Stress (CFS) due to various candidate main shock fault planes to argue for concentrated slip on the shallow landward dipping subduction interface. Average changes in CFS on the offshore segments of the Alpine Fault are then negative, retarding any future large events. In our models the change in CFS is evaluated on faults of optimal orientation in the regional stress field as determined by inversion of P -wave polarities.     

山东招平断裂带大磨曲家金矿床流体包裹体初步研究

The Damoqujia gold deposit,discovered recently and located in the north of Zhaoping fault zone,is a large altered rock type deposit.In this paper,we report the preliminary research results of the fluid inclusions and discuss its metallogenic implications. The homogenization temperatures of fluid inclusions fall into four ranges:310～350℃,230～270℃,160～200℃and 110～150℃; corresponding to the four stages of hydrothermal ore-forming processes:coarse grain pyrite-milk white quartz stage(Ⅰ),smoky gray Au-bearing quartz-fine grain pyrite stage(Ⅱ),Au-bearing polymetallic sulfide-quartz stage(Ⅲ),and quartz-carbonate stage(Ⅳ). Ore-forming fluid is with low salinity and low density,ranging from 1.4 Wt_(NaCl)% to 13.6 Wt_(NaCl)% and from 0.48g/cm~3 to 1.03g/cm~3 respectively.The inclusions are dominated by H_2O and CO_2 in gaseous compositions,and Na~ and K~ in positive ions,SO_4~(2-)and Cl~- in negative ions of liquid compositions.Au-S complex is the major form for transportation of gold.The pressure varied from 260MPa to 340MPa during the formation of CO_2-bearing inclusions at the early mineralization;the fluids are rich in SO_4~(2-)and Na~ .The pressure is 26-49×10~5 Pa during the formation of the aqueous salt inclusions in late mineralization,the inclusions are rich in CI~-(F~-), Na~ .δ~(18)O_(qurrtz)is 10.64～12.68%o,and the correspondingδ~(18)O_(H_2)O andδD is-5.44～6.47‰and-95.52～-106.48‰respectively.Based on the studies about compositions and hydrogen and oxygen isotopes of inclusions,it is evidenced that ore-forming fluid is magmatic hydrothermal fluid in early period,but affected by meteoric water in late.     

Highland Boundary Fault Zone: Tectonic implications of the Aberfoyle earthquake sequence of 2003

The Highland Boundary Fault Zone (HBFZ) is one of the major faulted tectonic boundaries in Great Britain. Historically, seismicity has occurred in this zone around the town of Comrie. But an earthquake sequence that occurred in 2003 near the village of Aberfoyle (M_L 1.3–3.2) was the first significant activity to be recorded in the HBFZ since the installation of modern seismograph networks in the 1970s. This study describes detailed analysis of these data. The waveform signals of the events were almost identical and by applying a cross-correlation technique combined with multiple event location, the alignment of the events was found to be WSW–ENE. This alignment matches one of the nodal planes determined by joint focal mechanism analysis. The fault plane dips to the northwest, and shows oblique sinistral strike–slip with normal movement. The orientation of the event alignment matches the direction and orientation of observed features in the HBFZ. Hence, it is concluded that the WSW–ENE striking nodal plane was the causative fault that is associated with the HBFZ. The orientation of maximum compressional stress is rotated from the regional average expected due to the Mid-Atlantic ridge-push force. This rotation is possibly explained by stresses due to postglacial rebound. Smaller events in the sequence were used as empirical Green's functions and deconvolved from the larger events to determine source time functions. The corresponding corner frequencies matched results from spectral fitting, showing that the events were of relatively low stress drop.     

论浙江东部早白垩世中期断陷事件和断陷岩套

早白垩世中期中国东南部发生过一次断陷事件,并形成一事件地层单元——断陷岩套。叙述了断陷岩套的形成机理、特征和类型,并利用事件地层单元同时性原理,论证了建组剖面"塘上组"的层位与永康群下部馆头组相同,而非高居永康群之上的"新构造亚层";也论证了嵊县三界一带的所谓"大爽组二段"应为馆头组。这两个断陷岩套中所含生物群证实:事件地层学原理所得的关于其层位与时代的结论是正确的。     

S和S-L型构造岩的显微组构与渗透性能的声学识别

为了解断裂与流体渗透的动态关系,针对S和S-L型构造岩及其原岩,采用超声波实验方法测算岩石的波速和衰减,经过与孔隙度等微孔隙结构参数的对比和相关分析,研究认为:S-构造岩和(S-L)-构造岩具有明显的各向异性,在平行面理方向上,波速和品质因子较大,渗透性最强,是最佳的流体运移方向;在垂直面理方向上,波速和品质因子较小且通常小于原岩的,封闭性最强,是最佳的封闭流体方向。波速和品质因子分别与孔隙度具有负线性关系,与气柱高度、突破压力等表征岩石封闭性能的参数具有正相关关系。张性角砾岩的波速和品质因子小于原岩的,而渗透性增强,并无明显的各向异性。     

U–Pb zircon dating of post-obduction volcanic-arc granitoids and a granulite-facies xenolith from New Caledonia. Inference on Southwest Pacific geodynamic models

In New Caledonia, the occurrence of one of the World’s largest and best-exposed subduction/obduction complex is a key point for the understanding of the geodynamic evolution of the whole Southwest Pacific region. Within the ophiolite, pre-and post-obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes. At 27.4 Ma, a new East-dipping subduction generated the active margin magmatism along the western coast of the island (Saint-Louis massif). At 24.3 Ma, the eastward shift of the magma activity and slightly different geochemical features (Koum-Borindi massif) was either related to the older slab break-off; or alternatively, due to the eastward migration of the mantle wedge following the collision of the eastern margin of the Low Howe rise. Finally, the occurrence of a granulite-facies xenolith in the Koum-Borindi massif with comparable 24.5 Ma U–Pb zircon age and isotopic features (initial ε_Nd = 5.1) suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness. Geochronological evidence for continuous convergence during the Oligocene infers an East-dipping Eocene-Oligocene subduction/obduction system to have existed in the Southwest Pacific from the d’Entrecasteaux zone to the North Island of New Zealand.     

A fault zone cause of large amplification and damage in Avcılar (west of Istanbul) during 1999 Izmit earthquake

Twenty seven buildings collapsed and 2076 buildings were heavily damaged during 17 August 1999 Izmit Earthquake in Avc?lar (west of Istanbul), which is nearly 100 km from the epicenter of the earthquake. The geology of Avc?lar consists of Upper Miocene poorly bounded conglomerate and sandstone (Çukurçe?me formation), claystone with sandstone and limestone interbedding (Güngören member) and limestone with sandstone and claystone interbedding (Bak?rköy formation). Lithological and geotechnical parameters of these formations in Avc?lar are not different from non damaged parts of the western Istanbul such as Zeytinburnu, Bak?rköy and Beylikdüzü, but these formations were cut by several faults in the damaged area. Collapsed and damaged buildings are located on this fault zone. Thus, cause of large amplification and damage in Avc?lar might be related with this fault zone because the fault zone behaves as a waveguide trapping seismic energy.     

The Magellan mound province in the Porcupine Basin

The Magellan mound province is one of the three known provinces of carbonate mounds or cold-water coral banks in the Porcupine Seabight, west of Ireland. It has been studied in detail using a large and varied data set: 2D and 3D seismic data, sidescan sonar imagery and video data collected during ROV deployment have been used to describe the mounds in terms of origin, growth processes and burial. The aim of this paper is to present the Magellan mounds and their setting in an integrated, holistic way. More than 1,000 densely spaced and mainly buried mounds have been identified in the area. They all seem to be rooted on one seismic reflection, suggesting a sudden mound start-up. Their size and spatial distribution characteristics are presented, together with the present-day appearance of the few mounds that reach the seabed. The underlying geology has been studied by means of fault analysis and numerical basin modelling in an attempt to identify possible hydrocarbon migration pathways below or in the surroundings of the Magellan mounds. Although conclusive evidence concerning the processes of mound initiation proves to be elusive, the results of both fault analysis and 2D numerical modelling failed to identify, with confidence, any direct pathways for focused hydrocarbon flow to the Magellan province. Diffuse seepage however may have taken place, as drainage area modelling suggests a possible link between mound position and structural features in the Hovland-Magellan area. During mound development and growth, the interplay of currents and sedimentation seems to have been the most important control. Mounds which could not keep pace with the sedimentation rates were buried, and on the few mounds which maintained growth, only a few corals survive at present.