摘要:

Helium isotope ratios (³He/4He) in Lassen Park and Yellowstone Park volcanic gases show large ³He enrichments relative to atmospheric and crustal helium indicating the presence of a dominant mantle‐helium component. The ratios in Lassen helium are 8 times atmospheric in acid hot spring gases, and about 3 times atmospheric in the gas phase in near‐neutral high‐temperature waters; the acid‐spring helium is thus isotopically similar to helium in island‐arc and other continental‐margin orogenic areas. At Yellowstone, however, the isotopic ratio in helium from the Mud Volcano area, in the eastern part of Yellowstone caldera, is 15.6 times atmospheric, similar to the ratio in helium from Kilauea and Iceland. These high ratios, 15 times atmospheric or greater, are probably distinctively associated with deep‐mantle plumes under hot‐spots, while ratios about 10 times atmospheric characterize mantle helium in basalt glasses at the crests of mid‐ocean rises. The presence of “Kilauea‐type” helium at Yellowstone indicates that at least in certain areas the continental crust is essentially transp

ISSN:0094-8276    

DOI:10.1029/GL005i011p00897

年代:1978

数据来源: WILEY

摘要:

During 1965 the University of San Agustin operated a net of 9 high‐sensitivity seismographs in southern Peru. Stable hypocenters for local earthquakes were determined by an interactive method utilizing both the P and the S arrival times. The hypocenters delineate a 30° dipping Benioff zone but also indicate considerable intraplate activity. Of particular interest is the existence of an aseismic wedge between the shallower earthquakes in the subducting lithosphere and those in the continental lithosphere. Investigations of other regions, e.g., the Aleutians and Japan, suggest that this may be a global phenomenon. We suggest that this aseismic wedge occurs because the compressive stress due to the interaction of the oceanic and continental plates is counterbalanced by tension caused by the downwarping of the continental lithosphere due to the drag of subduction. The unstressed zone (at depths less than 40 km) includes the coastal areas and explains the absence of large shallow earthquakes in that region. Further inland, beyond the region of downwarping, stresses are again adequate to cause large shallow earthquak

ISSN:0094-8276    

DOI:10.1029/GL005i011p00901

年代:1978

数据来源: WILEY

摘要:

Simple models for the interiors of the Galilean satellites and Titan involving metallic cores have been constructed. Then using a similarity law due to Busse possible surface equatorial dynamo magnetic fields of 2200, 800, 200, 60 and 100 nT have been estimated for Io through Titan, respectively.

ISSN:0094-8276    

DOI:10.1029/GL005i011p00905

年代:1978

数据来源: WILEY

摘要:

Ultraviolet absorption cross sections for gas‐phase HO2NO2have been measured from 190 to 330 nm at 269 K and 20 torr total pressure. The HO2NO2cross sections vary smoothly from 1.6 × 10−17cm² molecule−1at 190 nm to ˜2 × 10−20cm² molecule−1at 330 nm, and thus photolysis may be the major loss process for HO2NO2in the stratosphere. High resolution infrared absorptivities for HO2NO2were also determined in the present study since these data are needed for possible quantitative evaluation of HO2NO2stratospheric concentrations. The infrared cross sections for the 802.7 and 1304.2 cm−1Q‐branches of HO2NO2at 0.06 cm−1resolution are 2.1 × 10−18and 1.8 × 10−18cm

ISSN:0094-8276    

DOI:10.1029/GL005i011p00909

年代:1978

数据来源: WILEY

摘要:

Radiocarbon measurements on a 175‐year (A.D. 1800 to 1974) growth of the coral Montastrea annularis from The Rocks reef off the Florida Keys reveal the rate of local uptake of fossil fuel CO2and bomb14C by surface ocean waters of the Gulf Stream. In the nineteenth century, the pre‐bomb, pre‐industrial Δ14C value of surface ocean waters as seen in these corals of the Gulf Stream in the Florida Straits was −51 ± 2‰. By 1955, uptake of industrial CO2by these waters had lowered the Δ14C values to about −61‰. The results can be used to make predictions regarding anthropogenic CO2that can be expected to enter the oceans in future decades. Bomb‐produced14C is found to be present in the corals in comparable concentrations to that found in the dissolved inorganic carbon (DIOC) of the North Pacific and Nor

ISSN:0094-8276    

DOI:10.1029/GL005i011p00913

年代:1978

数据来源: WILEY

摘要:

Observations of the troposphere with a VHF radar using a large antenna for transmission and small spaced antennas for reception show that atmospheric velocities measured by the drifts method agree well with balloon winds. Many of the echoes from the middle troposphere appear to come from horizontally stratified layers. Studies of the irregularity structure by measurement of the spatial coherence of these echoes and of their angular spectra by interferometric techniques show that many echoes are caused essentially by specular reflection.

ISSN:0094-8276    

DOI:10.1029/GL005i011p00917

年代:1978

数据来源: WILEY

摘要:

Estimates of the ozone total columnar content, derived from Nimbus IV IRIS data, have been analyzed to estimate monthly averages of the total global atmospheric ozone. Over a 9‐month interval, the variation in this monthly average is approximately an order of magnitude greater than its associated uncertainty, and has characteristics in common with variations in the 10.7 cm solar flux, the Zurich sunspot number, and the total solar Lyman α flux. The highest correlation, 0.94, exists between the variation in the total Lyman α flux and the variation in the estimated total atmospheric.oz

ISSN:0094-8276    

DOI:10.1029/GL005i011p00921

年代:1978

数据来源: WILEY

摘要:

The total Thomson scatter cross‐section is considered in the presence of electron heating and as a function of the ratio of negative ion to electron number densities. For electron densities typical of the lower D region it is shown that the opposing factors of heating and negative ions lead to a local minimum of the cross‐section in the experimentally accessible range of 1.5 ≤ Te/Ti≤ 5. Electron heating is thus considered as a method for detecting negative ions and one early experiment may already have

ISSN:0094-8276    

DOI:10.1029/GL005i011p00925

年代:1978

数据来源: WILEY

摘要:

The largest change in apparent resistivity observed across a 3.3 km galvanic resistivity array during the first year of operation was 6%. This 6% decrease is strongly correlated with several months of continuous rain. Fluctuations in apparent resistivity appear to be larger after than before the rain. This is believed to be the result of a newly formed surface layer of high conductivity. No correlation is observed between local seismicity and resistivity.

ISSN:0094-8276    

DOI:10.1029/GL005i011p00928

年代:1978

数据来源: WILEY

摘要:

Surface roughness of nine radar backscatter units in the Askja Caldera region of Iceland was examined in computer‐enhanced like‐ and cross‐polarized radar images. A field survey of the caldera was then used to check the accuracy of the preliminary analysis. There was good agreement between predicted surface roughness of backscatter units and surface roughness observed in the field. In some cases, variations could be correlated with previously mapped geologic

ISSN:0094-8276    

DOI:10.1029/GL005i011p00931

年代:1978

数据来源: WILEY