昆仑断裂带东段滑动速率梯度

欧亚大陆走滑断裂带是否实现对青藏地壳及岩石层的向东挤出,很大程度上取决于断层尾端变形的动力学机制。本文我们利用青藏高原北部昆仑断裂最东段千年尺度的地貌标志物提供一组最新的滑动速率测定结果。该断裂带是印度?亚欧碰撞带产生的最主要走滑断裂带之一,在西藏岩石层向东挤出的模型中扮演着主要的作用。曾有人争论在相当长的长度内该断裂显示出相同的滑动速率。黄河支流上的河流阶地位移以及阶地上物质的14C测年可以控制晚更新世至全新世断层以来的滑动速率。结果显示沿断裂东部约150km滑动速率从>10mm/a～<2mm/a自西向东系统地递减。这些数据向那些认为整条断裂滑动速率保持一致的观点提出质疑,相反揭示出位错的梯度性,这与那些在断层尾端预期的情形是类似的。另外,沿断层的滑动看起来在增厚的高原地壳内部终结,因此沿昆仑断裂的滑动导致的西藏岩石层的挤出都会被断裂尾端周围高原的内部变形所吸收。     

Role of wave–mean flow interaction in sun–climate connections: Historical overview and some new interpretations and results

Quasi-decadal variations in solar irradiance – termed the 11-year solar cycle (SC) – have been linked to variations in a variety of atmospheric circulation features, including the polar vortex, the Brewer–Dobson circulation, and the quasi-biennial oscillation. These features share an underlying commonality: they are all rooted in wave–mean flow interaction. The purpose of this paper is to provide a historical overview of the connection between the SC and wave–mean flow interaction and to propose a more complete theoretical framework for solar modulated wave–mean flow interaction that includes both zonal-mean and zonally asymmetric ozone as intermediaries for communicating variations in solar spectral irradiance to the climate system. We solve a quasi-geostrophic model using the WKB formalism to highlight the physics connecting the SC to planetary wave-drag. Numerical results show the importance of the zonally asymmetric ozone field in mediating the effects of solar variability to the wave-driven circulation in the middle atmosphere.     

Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china,and their geological significance

The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu–Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass ⁴⁰Ar/³⁹Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (⁸⁷Sr/⁸⁶Sr)_i ratio, a positive ε_Nd(t) values and high ²⁰⁶Pb/²⁰⁴Pb_t, ²⁰⁷Pb/²⁰⁴Pb_t and ²⁰⁸Pb/²⁰⁴Pb_t ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean.     

Community variations in population exposure to near-field tsunami hazards as a function of pedestrian travel time to safety

Efforts to characterize population exposure to near-field tsunami threats typically focus on quantifying the number and type of people in tsunami-hazard zones. To develop and prioritize effective risk-reduction strategies, emergency managers also need information on the potential for successful evacuations and how this evacuation potential varies among communities. To improve efforts to properly characterize and differentiate near-field tsunami threats among multiple communities, we assess community variations in population exposure to tsunamis as a function of pedestrian travel time to safety. We focus our efforts on the multiple coastal communities in Grays Harbor and Pacific Counties (State of Washington, USA), where a substantial resident and visitor population is threatened by near-field tsunamis related to a potential Cascadia subduction zone earthquake. Anisotropic, path distance modeling is conducted to estimate travel times to safety, and results are merged with various population data, including residents, employees, public venues, and dependent-care facilities. Results suggest that there is substantial variability among communities in the number of people that may have insufficient time to evacuate. Successful evacuations may be possible in some communities assuming slow walking speeds, are plausible in others if travel speeds are increased, and are unlikely in another set of communities given the large distances and short time horizon. Emergency managers can use these results to prioritize the location and determine the most appropriate type of tsunami risk-reduction strategies, such as education and training in areas where evacuations are plausible and vertical-evacuation structures in areas where they are not.     

Review: Regional groundwater flow modeling in heavily irrigated basins of selected states in the western United States

Water resources in agriculture-dominated basins of the arid western United States are stressed due to long-term impacts from pumping. A review of 88 regional groundwater-flow modeling applications from seven intensively irrigated western states (Arizona, California, Colorado, Idaho, Kansas, Nebraska and Texas) was conducted to provide hydrogeologists, modelers, water managers, and decision makers insight about past modeling studies that will aid future model development. Groundwater models were classified into three types: resource evaluation models (39 %), which quantify water budgets and act as preliminary models intended to be updated later, or constitute re-calibrations of older models; management/planning models (55 %), used to explore and identify management plans based on the response of the groundwater system to water-development or climate scenarios, sometimes under water-use constraints; and water rights models (7 %), used to make water administration decisions based on model output and to quantify water shortages incurred by water users or climate changes. Results for 27 model characteristics are summarized by state and model type, and important comparisons and contrasts are highlighted. Consideration of modeling uncertainty and the management focus toward sustainability, adaptive management and resilience are discussed, and future modeling recommendations, in light of the reviewed models and other published works, are presented.     

Vertical shaft collapse at the Jinchuan Nickel Mine, Gansu Province, China: analysis of contributing factors and causal mechanisms

In mining areas, vertical ventilating shafts are often threatened by ground movements induced by underground mining. In this paper, damage characteristics related to collapse of the vertical ventilating shaft at the No. 14 exploratory line in Jinchuan Nickel Mine, China are documented. The damage mechanism is then analyzed based on comprehensive consideration of geological conditions and distribution of underground excavations. The results indicate that the high dip angle of the ore body and fault/fissures were responsible for the damage of the shaft when ground movements occurred. Although the damaged shaft was repaired in a short time, its stability and safe usage are still threatened by potential future ground movements, because the shaft is located within a subsiding depression induced by underground mining. This case study indicates that when designing an underground mining operation, it is very important to locate a shaft outside of any area where future mining-induced subsidence may occur.     

A Typology of Catalyst Events for Collaborative Watershed Management in the United States

While much has been written about the benefits of collaborative watershed management to address nonpoint source pollution and other water quality concerns in the United States, few scholars have addressed the catalytic nature of events that generate these collective action responses. Further, because equivalent catalyst events in different communities do not always lead to collective action, it is critical to understand the interaction between a community's baseline conditions and the catalyst events that lead to collective action. This article presents a conceptual framework that illustrates the relationship between baseline conditions and events that lead to collective action. In this article a theoretical typology of catalyst events is presented that includes both intentional and nonintentional types of events. Understanding these types of catalyst events can help water quality advocates create and/or seize opportunities to nurture a collective action. This article concludes with a call for future research into catalyst events.     

Shifting sands on Mars: insights from tropical intra‐crater dunes

Evidence for sand motion is found in repeated observations of sand dunes at three sites in the Martian tropics by the High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. An eroding outcrop of layered sediments is identified as a possible source of the sand in Pasteur crater. Ancient layered sediments in Becquerel crater are actively being carved into flutes and yardangs by the blowing sands. Dunes in an un‐named crater in Meridiani near the Mars Exploration Rover Opportunity landing site advanced as much as 50 cm over an interval of one Martian year. Copyright © 2012 John Wiley & Sons, Ltd.     

Radiocarbon ages for the timing of debris avalanches at Mombacho Volcano, Nicaragua

Radiocarbon-dated lake sediments provide minimum-limiting ages for two major debris avalanches originating from Mombacho Volcano in Nicaragua. A basal age from Lake El Gancho indicates that the northeast debris avalanche (Las Isletas) occurred sometime before ～140 to 345 A.D. Basal ages from Lakes Blanca and Verde indicate that the southern (El Crater) debris avalanche occurred sometime before ～270 to 650 A.D. Both events therefore occurred in the space of a few centuries, yet there is strong evidence that the mechanisms varied for destabilization of each flank. Possibly, the influence of a developing hydrothermal system lead first to deeper structural failure in the substrata to produce the Las Isletas sector collapse, progressing to higher level destabilization within the edifice and the El Crater collapse.