摘要:

An effective solution to the problem of the detection and identification of low‐yield coupled and fully decoupled underground nuclear explosions appears available via use of high‐frequency seismic data ranging up to 30 or 40 Hz. In order to evaluate detection‐identification capabilities when using such data, it is necessary to estimate (1) spectral characteristics and relative amplitudes of bothPandSwaves from explosions and earthquakes over the frequency band from 5 to 40 Hz, (2) signal transmission characteristics over this band through pertinent types of earth structure, and (3) recording system and ground noise characteristics over this frequency band. In this study, each of these topics is considered in turn as they relate to detection and discrimination of the signals from low‐yield coupled and decoupled explosions in the regional and teleseismic distance ranges. Estimates of the capabilities of specific hypothetical networks to detect and identify (insofar as signal‐to‐noise ratio is an important factor in identification) explosions within the USSR are then considered. These estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability. Following the assessment of detection capabilities, the problem of identification of small events is considered, with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal‐to‐noise ratio. The principal results and conclusions of this study are as follows: (1) seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30–40 Hz when using presently available hardware; (2) average amplitudes of high‐frequency noise in a variety of geological environments are very low and change little with time or season; (3) transmission of high‐frequencyPandSwave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 Hz, with effectiveQfactors in shield areas being about 9000 and 4000 for high‐frequencyPnandSn, respectively, while the effectiveQforPnwaves in tectonic areas is about 1000; (4) a properly designed and deployed network of 25 simple three‐component nonarray stations internal to the USSR and 15 similar stations surrounding the USSR is predicted to be capable of multistation detection at high signal‐to‐noise ratio of fully decoupled 1‐kt explosions located at all potential decoupling sites within the USSR; (5) by inference from the quantitative agreement of empirical observations and theoretical predictions, when using lower‐frequency data over a great range of explosion yields, we conclude that procedures based on the use of both detectablePandSwaves will serve to identify explosion‐generated seismic signals at least as small as those expected fr

ISSN:8755-1209    

DOI:10.1029/RG024i002p00143

年代:1986

数据来源: WILEY

摘要:

Clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones. Based on a critical appraisal of the geophysical and geological literature, 26 parameters are estimated for each of 39 modern subduction zones. To isolate causal relationships among these parameters, multivariate analysis is applied to this data set. This analysis yields empirical quantitative relations that predict strain regime and strike‐slip faulting in the overriding plate, maximum earthquake magnitude, Benioff zone length, slab dip, arc‐trench gap, and maximum trench depth. Excellent correlation is found between length of the Benioff zone and the product of convergence rate and age of the downgoing slab. This relationship is consistent with the conductive heating model of Molnar et al. (1979), if the model is modified in one respect. The rate of heating of the slab is not constant; it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate. The structural style in the overriding plate is determined by its stress state. Though the stress state of overriding plates cannot be quantified, one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional (class 1, back‐arc spreading) to strongly compressional (class 7, active folding and thrusting). This analysis indicates that strain class is probably determined by a linear combination of convergence rate, slab age, and shallow slab dip. Interplate coupling, controlled by convergence rate and slab age, is an important control on strain regime and the primary control on earthquake magnitude. Arc‐parallel strike‐slip faulting is a common feature of convergent margins, forming a forearc sliver between the strike‐slip fault and trench. Optimum conditions for the development of forearc slivers are oblique convergence, a compressional environment, and a continental overriding plate. The primary factor controlling presence of strike‐slip faulting is coupling; strongly oblique convergence is not required. The rate of strike‐slip faulting is affected by both convergence obliquity and convergence rate. Maximum trench depth is a response to flexure of the underthrusting plate. The amount of flexural deflection at the trench depends on the vertical component of slab pull force, which is very sensitive to slab age and shallow slab dip. Shallow slab dip conforms to the cross‐sectional shape of the overriding plate, which is controlled by width of the accretionary prism and duration of subduction. Deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow. Much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike‐slip faulting and strain regime. Empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology

ISSN:8755-1209    

DOI:10.1029/RG024i002p00217

年代:1986

数据来源: WILEY

摘要:

The possibility of El Niño being a result of the random superposition of stochastically forced equatorial Kelvin waves is investigated, with the help of the theory of statistics of extremes, which provides us with the tools to evaluate the threshold crossing statistics of the sea level (SL) and sea surface temperature (SST) anomaly fields. Knowledge of the probability density function and the power spectrum of a random process allows one to compute the threshold crossing statistics of the process (e.g;, the mean rate of crossings of some level, the mean time or distance between successive crossings, or the mean time or distance it stays above some level after each crossing). A linear, stratified, equatorial β plane Kelvin wave ocean model is forced by stochastic zonal winds. The zonal velocity field is used to advect mean zonal temperature gradients to produce SST anomalies. Solutions are obtained in terms of the zonal wave number‐frequency spectra of SL and SST. These spectra are used to compute the threshold crossing statistics of the respective fields. The results are sensitive to some of the assumptions (e.g., spectral shape of forcing and values of spectral cutoffs). The time and space scales for the SL and SST excursions above 2 standard deviations are found to be small, when compared with observed El Niño scales. The stochastic assumption is reinterpreted as a possible triggering mechanism, rather than as a full explanation, for El Niño occurrences. Better knowledge of the wind stress forcing spectrum (zonal wave number and frequency) is needed in order to test the plausibility of the stochastic argument in a more conclusiv

ISSN:8755-1209    

DOI:10.1029/RG024i002p00285

年代:1986

数据来源: WILEY

摘要:

A review is provided of multiple scattering theory associated with radiative transfer problems in planetary atmospheres. The radiative transfer equation pertaining to a scattering, absorbing, and emitting medium is considered. Analytic solutions are presented and computational aspects are discussed for plane parallel atmospheres. These computationally efficient and reliable solutions can be used to attack a multitude of radiative transfer problems in realistic atmospheres. Computational illustration is provided, a discussion of certain applications of the theory is presented, and some remaining theoretical problems are pointed out.

ISSN:8755-1209    

DOI:10.1029/RG024i002p00299

年代:1986

数据来源: WILEY

摘要:

The geochemical reservoirs and cycles of the earth are discussed. Models involving the isotopic evolution of the enriched continental crustal reservoir and the complementary depleted mantle reservoir are considered. Analytic solutions for the fractionation factorsfand isotope ratios ε are obtained using consistent approximations. The results are applied to data on the samarium‐neodymium, rubidium‐strontium, and thorium‐uranium‐lead systems. Using a model for instantaneous crustal differentiation, data on young rocks provide constraints on the mean age of the continental crust and on the mass of the depleted mantle reservoir. Although there are a variety of uncertainties, we favor a mean continental age of τc=2.1±0.7 Ga. A mass balance based on samarium‐neodymium and rubidium‐strontium data favors a mass for the depleted layer near the mass of the upper mantle. Mass balances for argon and helium, isotope correlations between strontium and neodymium and between thorium and uranium, and the substantial quantities of primordial helium and argon found in ocean island basalts (OIB) from Hawaii and Iceland favor the existence of a sizable near‐primitive reservoir. We conclude that the isotope data favor a near‐primitive lower mantle with a barrier to mantle convection at a depth of 650 km. Thus the isotope data favor layered mantle convection rather than whole mantle convection. Isotope data on older rocks provide information on the time evolution of the continents. An important question is whether significant volumes of continental crust are recycled back into the mantle. Isotope data on old continental rocks that can be associated with the depleted mantle appear to favor significant volumes of crustal recycling. We have also studied the implications of preferential recycling of either parent or daughter isotopes. Recycling of either isotope increases the age of the continental crust inferred from isotope data. Studies of lead isotopes in mid‐ocean ridge basalts (MORB) and OIB show that they evolved in uranium rich environments for several billion years. This is the “missing lead” paradox; we associate the missing lead with the lower continental crust. We conclude that the radiogenic lead evolved either in the depleted mantle reservoir or in the radiogenic upper crust. The isotopic heterogeneities of OIB are also considered; these are attributed to (1) entrainment of near‐primitive lower mantle rock and (2) inclusion of recently subducted and delaminated co

ISSN:8755-1209    

DOI:10.1029/RG024i002p00311

年代:1986

数据来源: WILEY

摘要:

The extensive body of investigations of apparent correlations between solar wind/IMF disturbances and subsequent changes in the vorticity of the winter troposphere, which we designate as SV, is reviewed as representative of the search for sun‐weather relationships. Research on aspects of SV has for more than a decade been a dominant and controversial thrust in the search for links between short‐term solar variations and associated changes in the lower atmosphere. In particular, correlations identified between IMF sector boundary passages and subsequent decreases in the tropospheric vorticity, while not ubiquitous, continue to be perceived as one of the more credible sets of evidence for possible sun‐weather responses. We identify uncertainties in this research, which appear to have contributed inappropriate biases on both sides of the issue of the credibility of the SV response. Analyses leading to either positive or negative conclusions have generally concentrated upon the statistical procedures and have typically not addressed either the choice of parameters or the selective factors involved in the physical relationships existing between parameters. Thus we find that investigations of SV have characteristically lacked sufficient rigor for substantial conclusions to be drawn. Nonetheless, throughout the investigations on the subject a thread of observational evidence persists, suggestive of the possible associations between external forcing and atmospheric change. The obvious significance of such a possibility in our view clearly encourages further investigation. However, we strongly recommend that the research be conducted in a more interdisciplinary manner, emphasizing the variable physical relationships and the secular change in these relationships, selective factors which are known to exist between the variables believed critical to the pr

ISSN:8755-1209    

DOI:10.1029/RG024i002p00329

年代:1986

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG024i002p00349

年代:1986

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG024i002p00350

年代:1986

数据来源: WILEY

摘要:

Studies of the earth's radiation budget now form a major part of climate research using measurements made from earth‐orbiting and geostationary satellites. However, there has been considerable interest in this topic well before the development of space observing systems. In this paper we provide the historical perspective to radiation of budget studies and describe the early studies from the beginning of this century until the 1960

ISSN:8755-1209    

DOI:10.1029/RG024i002p00351

年代:1986

数据来源: WILEY

摘要:

We review here the history of satellite missions and their measurements of the earth radiation budget from the beginning of the space age until the present time. The survey emphasizes the early struggle to develop instrument systems to monitor reflected shortwave and emitted long‐wave exitances from the earth and the problems associated with the interpretation of these observations from space. In some instances, valuable data sets were developed from satellite measurements whose instruments were not specifically designed for earth radiation budget observations. The effort of understanding the earth radiation budget has been the work of many people from different countries of the world, an effort of proud accomplishmen

ISSN:8755-1209    

DOI:10.1029/RG024i002p00357

年代:1986

数据来源: WILEY