Mexico,San Francisco,Los Angeles and Kobe: What Next?     

Lomnitz  Cinna 《Natural Hazards》1997,16(2-3):287-296

Some analogies in the distribution of damage in the 1985 Mexico, 1989 Loma Prieta, and 1995 Kobe earthquakes may be attributable to similarities in the history of reclamation of bayshore or lakeshore environments by emplacing artificial fill on soft mud. In all three cases, a transitional environment has generated similar soil types and analogous forms of human settlement. These similarities may translate into hazardous situations because of amplification of seismic waves in wedge-shaped low-velocity layers; nonlinearity of seismic wave propagation in soft water-saturated soils; transitions from solid-like to liquid-like behavior, including liquefaction and the emergence of prograde surface waves; and other unforeseen conditions arising from surface geology. Severe stability problems may arise in tall, top-heavy structures and in structures with horizontal spans of the order of the wavelength of surface waves. Effective strategies of hazard reduction include a recognition of the many unanticipated ways in which earthquake hazard may become an emergent property of complex nature-society systems.  相似文献   

Oil-generating coals of the San Juan Basin, New Mexico and Colorado, U.S.A.     

J.L. Clayton  D.D. Rice  G.E. Michael 《Organic Geochemistry》1991,17(6)

Coal beds of the Upper Cretaceous Fruitland Formation in the San Juan Basin of northwestern New Mexico and southwestern Colorado have significant liquid hydrocarbon generation potential as indicated by typical Rock-Eval Hydrogen Indexes in the range of 200–400 mg hydrocarbon/g organic carbon (type II and III organic matter). Small, non-commercial quantities of oil have been produced from the coal beds at several locations. The oils are characterized by high pristane/phytane (ca 4) and pristane/n-C₁₇ ratios (ca 1.2), abundant C₂₁₊ alkanes in the C₁₀₊ fraction with a slight predominance of odd carbon-numbered n-alkanes, abundant branched-chain alkanes in the C₁₅₊ region, and a predominance of methylcyclohexane in the C₄----C₁₀ fraction. The oils are indigenous to the Fruitland Formation coals and probably migrated at thermal maturities corresponding to vitrinite reflectance values in the range 0.7–0.8%. Although the oils found to date are not present in commercial amounts, these findings illustrate the potential of some coals to generate and expel oil under conditions of moderate thermal heating.  相似文献   

A prototype earthquake warning system for strike-slip earthquakes     

M. Nafi Toksöz  Anton M. Dainty  John T. Bullitt 《Pure and Applied Geophysics》1990,133(3):475-487

A prototype expert system has been developed to provide rapid warning of earthquakes while they are occurring. Warning times of up to 100 seconds will be possible. In the complete system, several accelerometers are distributed at intervals within a few kilometers of a known fault; data are telemetered to a central computer which implements the expert system. The expert system incorporates specific information about the type of fault to be monitored, and includes simple rules for estimating the fault slip, rupture length, and seismic moment, all in real time. If the seismic moment exceeds a preset value, an alarm may be issued. The prototype is designed for deployment on near-surface strike-slip faults such as the San Andreas and has been successfully tested with data from the 1979 Imperial Valley and 1984 Morgan Hill earthquakes. Crucial concepts have also been tested using synthetic data calculated for a model of the 1857 Fort Tejon earthquake. Parkfield, California, could be used as a test site.  相似文献   

Governing a city of unicorns: technology capital and the urban politics of San Francisco   总被引：1，自引：1，他引：0  

Donald McNeill 《Urban geography》2016,37(4):494-513

San Francisco is now widely considered to be the most important city in the world for the location of new technology start-up firms, especially high valuation “unicorns,” and is increasingly seen as both a locational and metaphorical extension of Silicon Valley. In this paper, I trace some of the political strategies and tensions that have accompanied the city’s prominence in this area, and in particular the distinctive role of technology and venture capital in the political economy of urban development. The paper has four empirical sections. It describes (1) the political machinations surrounding the 2011 and 2015 municipal elections, which saw the election of Ed Lee as Mayor with significant support from individual technology investors such as Ron Conway and Marc Benioff, and accompanied by various “tech-friendly” policy shifts; (2) the foundation of the “tech chamber of commerce” sf.citi as a means of enhancing the policy influence of the tech industry in San Francisco; (3) the introduction of a low taxation regime in the city’s Central Market area that has attracted technology companies such as Twitter as tenants; and (4) the urban policy tensions associated with the evolution of new “sharing economy” firms such as Uber and Airbnb, which have aggressively challenged municipal regulations in the taxi and property rental fields. Throughout these machinations, we can see a reshaping of capital fractions, with venture and angel capital increasingly involved in reengineering the labor, housing, and public transport markets of the city in order to circumvent the accumulation problems that tech investors had suffered in the earlier dot.com failures.  相似文献   

Biomarker responses in Macoma nasuta (Bivalvia) exposed to sediments from northern San Francisco Bay     

Ingeborg Werner  Swee J. Teh  Seema Datta  XiaoQiao Lu  Thomas M. Young 《Marine environmental research》2004,58(2-5):299

Our study investigates biomarker responses and survival of Macoma nasuta exposed to sediments collected from six locations in northern San Francisco Bay. Biomarkers analyzed were stress proteins (hsp70) in gill, mantle and digestive gland, lysosomal membrane damage and histopathologic lesions. Sediments and clam tissues were analyzed for a comprehensive suite of heavy metals and trace organic pollutants. Sediment grain size and organic carbon content were determined. Clams accumulated metals, polyaromatic hydrocarbons (PAHs) and organochlorine pesticides (aldrin and p,p^′-DDT and its metabolites p,p^′-DDD and p,p^′-DDE). Pearson and Spearman correlation analysis revealed that mortality, hsp70 in gill and histopathologic lesion scores in gonads, and lysosomal membrane damage were significantly correlated with tissue concentrations of DDT and/or its metabolites. Tissue concentrations of metals, in particular nickel, chromium, and copper, were associated with macrophage aggregates in digestive gland and germ cell necrosis. Cadmium was linked to mortality and lysosomal membrane damage.  相似文献   

Assessing 4D-VAR for dynamical mapping of coastal high-frequency radar in San Diego   总被引：1，自引：0，他引：1  

I. Hoteit  B. Cornuelle  S.Y. Kim  G. Forget  A. Khl  E. Terrill 《Dynamics of Atmospheres and Oceans》2009,48(1-3):175

The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm) with 1 km horizontal resolution and 40 vertical layers. The domain is centered on Point Loma, extending 117 km offshore and 120 km alongshore. The reference run (before adjustment) is initialized from a single profile of T and S and is forced with wind data from a single shore station and with zero heat and fresh water fluxes. The adjoint of the model is used to adjust initial temperature, salinity, and velocity, hourly temperature, salinity and horizontal velocities at the open boundaries, and hourly surface fluxes of momentum, heat and freshwater so that the model reproduces hourly HF radar radial velocity observations. Results from a small number of experiments suggest that the adjoint method can be successfully used over 10-day windows at coastal model resolution. It produces a dynamically consistent model run that fits HF radar data with errors near the specified uncertainties. In a test of the forecasting capability of the San Diego model after adjustment, the forecast skill was shown to exceed persistence for up to 20 h.  相似文献   

First vertebrate body remains from the Permian of Argentina (Elasmobranchii and Actinopterygii)     

Alberto Luis Cione  Soledad Gouiric-Cavalli 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(3):301-312

  相似文献   

Metamorphic evolution,partial melting and rapid exhumation above an ancient flat slab: insights from the San Emigdio Schist,southern California     

A. D. CHAPMAN  P. I. LUFFI  J. B. SALEEBY  S. PETERSEN 《Journal of Metamorphic Geology》2011,29(6):601-626

The San Emigdio and related Pelona, Orocopia, Rand and Sierra de Salinas schists of southern California were underplated beneath the southern Sierra Nevada batholith and adjacent southern California batholith along a shallow segment of the subducting Farallon plate in Late Cretaceous to early Tertiary time. These subduction accretion assemblages represent a regional, deeply exhumed, shallowly dipping domain from an ancient slab segmentation system and record the complete life cycle of the segmentation process from initial flattening and compression to final extensional collapse. An important unresolved question regarding shallow subduction zones concerns how the thermal structure evolves during the slab flattening process. New field relationships, thermobarometry, thermodynamic modelling and garnet diffusion modelling are presented that speak to this issue and elucidate the tectonics of underplating and exhumation of the San Emigdio Schist. We document an upsection increase in peak temperature (i.e. inverted metamorphism), from 590 to 700 °C, peak pressures ranging from 8.5 to 11.1 kbar, limited partial melting, microstructural evidence for large seismic events, rapid cooling (825–380 °C Myr^?1) from peak conditions and an ‘out and back’P–T path. While inverted metamorphism is a characteristic feature of southern California schists, the presence of partial melt and high temperatures (>650 °C) are restricted to exposures with maximum depositional ages between 80 and 90 Ma. Progressive cooling and tectonic underplating beneath an initially hot upper plate following the onset of shallow subduction provide a working hypothesis explaining high temperatures and partial melting in San Emigdio and Sierra de Salinas schists, inverted metamorphism in the schist as a whole, and the observed P–T trajectory calculated from the San Emigdio body. Lower temperatures in Pelona, Orocopia and Rand schists are likewise explained in the context of this overarching model. These results are consistent with an inferred tectonic evolution from shallow subduction beneath the then recently active Late Cretaceous arc to exhumation by rapid trench‐directed channelized extrusion in the subducted schist.  相似文献   

版纳勐养保护区鸟类及人为影响分析   总被引：1，自引：0，他引：1  

王直军  贾知行 《云南地理环境研究》1994,6(1):78-83

切实保护和利用好西双版纳现存热带森林，是急需处理的现实问题。本文通过勐养自然保护区鸟类调查结果，揭示了西双版纳保护区管理现状。多数地区实际上未管理起来，林区居民仍滥用自然资源，对鸟类的猎捕从未停止，有的地方颇为严重；从生物多样性着眼，环境质量在下降。现已管理起来的三岔河保护区，尽管旅游开放后尚存许多问题亟待探索和改进，但鸟类保护状况已明显改善，说明自然保护区旅游在科学管理下才是可行的。就此，本文分析、评价了勐养保护区鸟类受人为影响情况，对自然保护区管理工作提出建议。  相似文献   

Four-dimensional transform fault processes: progressive evolution of step-overs and bends     

John Wakabayashi  James V. Hengesh  Thomas L. Sawyer 《Tectonophysics》2004,392(1-4):279

Many bends or step-overs along strike–slip faults may evolve by propagation of the strike–slip fault on one side of the structure and progressive shut-off of the strike–slip fault on the other side. In such a process, new transverse structures form, and the bend or step-over region migrates with respect to materials that were once affected by it. This process is the progressive asymmetric development of a strike–slip duplex. Consequences of this type of step-over evolution include: (1) the amount of structural relief in the restraining step-over or bend region is less than expected; (2) pull-apart basin deposits are left outside of the active basin; and (3) local tectonic inversion occurs that is not linked to regional plate boundary kinematic changes. This type of evolution of step-overs and bends may be common along the dextral San Andreas fault system of California; we present evidence at different scales for the evolution of bends and step-overs along this fault system. Examples of pull-apart basin deposits related to migrating releasing (right) bends or step-overs are the Plio-Pleistocene Merced Formation (tens of km along strike), the Pleistocene Olema Creek Formation (several km along strike) along the San Andreas fault in the San Francisco Bay area, and an inverted colluvial graben exposed in a paleoseismic trench across the Miller Creek fault (meters to tens of meters along strike) in the eastern San Francisco Bay area. Examples of migrating restraining bends or step-overs include the transfer of slip from the Calaveras to Hayward fault, and the Greenville to the Concord fault (ten km or more along strike), the offshore San Gregorio fold and thrust belt (40 km along strike), and the progressive transfer of slip from the eastern faults of the San Andreas system to the migrating Mendocino triple junction (over 150 km along strike). Similar 4D evolution may characterize the evolution of other regions in the world, including the Dead Sea pull-apart, the Gulf of Paria pull-apart basin of northern Venezuela, and the Hanmer and Dagg basins of New Zealand.  相似文献