摘要:

We present a correction to a paper by Okal and Anderson (1975) about multiple ScS travel‐time anomalies. We have reanalyzed data for ScS2surface bounces in the South Atlantic Ocean. From these data an ScS2‐S residual of 23.6 seconds was found by Okal and Anderson (1975). This corresponded to an ScS2surface bounce point under Trindade island and was inferred to be due to very slow upper mantle associated with the Trindade hot spot. The analysis we present here invalidates this conclusion. The nature of the upper mantle under Trindade is an open is

ISSN:0094-8276    

DOI:10.1029/GL008i010p01027

年代:1981

数据来源: WILEY

摘要:

A simple model has been developed to study the thermal consequences of ridge subduction. The geological process is modeled as a flat plate moving over a finite line heat source. Effects of plate velocity, ridge length and the oblique angle between ridge and trench axes have been investigated. Calculated results indicate that the depth of thermal perturbation of a ridge is inversely proportional to plate velocity. Thermal effects will penetrate deeper into a plate for longer ridges if the ridge axis is parallel to the direction of plate motion. However, depth of thermal disturbance is found to be independent of ridge length if ridge axis is normal to plate motion direction.

ISSN:0094-8276    

DOI:10.1029/GL008i010p01031

年代:1981

数据来源: WILEY

摘要:

Increased abundances were measured for several trace atmospheric gases in the decade 1970‐1980. The equilibrium greenhouse warming for the measured increments of CH4, chlorofluorocarbons and N2O is between 50% and 100% of the equilibrium warming for the measured increase of atmospheric CO2during the same 10 years. The combined warming of CO2and trace gases should exceed natural global temperature variability in the 1980's and cause the global mean temperature to rise above the maximum of the late 1930'

ISSN:0094-8276    

DOI:10.1029/GL008i010p01035

年代:1981

数据来源: WILEY

摘要:

The very close correlation observed on Venus between topography and gravity on a regional scale is clearly related to the isostatic compensation of the topographic loads. Observed gravity anomalies over topographic features of moderate lateral extent, located in the equatorial region (0° to 40° N latitude and 10° W to 60° E longitude) are somewhat larger than those computed with a model of local isostatic compensation (of Airy type). They may rather be explained by a model of compensation including elastic forces within the lithosphere which contribute to support topographic loads through elastic stresses. We have applied the theory of lithospheric flexure : to explain in wavelength and in amplitude the observed gravity anomalies, a flexural rigidity of ∼ 4 × 1028dyne cm has been estimated for the Venus lithosphere in the rolling plains province. This value is very low compared to the oceanic terrestrial lithosphere (ranging from ∼ 1028dyne cm near ridge crests to ∼ 2 × 1031dyne cm near subduction zones). The corresponding thickness of the elastic upper layer able to maintain elastic stresses for long time duration is ∼ 7.5 km. This value may not be representative of the entire Venu

ISSN:0094-8276    

DOI:10.1029/GL008i010p01039

年代:1981

数据来源: WILEY

摘要:

An active source electrical conductivity sounding was carried out near the East Pacific Rise at 21°N. The average electrical conductivity from 2 km beneath the seafloor into the upper mantle was found to be about 0.004 S/m. There is no evidence of fully molten magma at a distance of 7 km from the spreading axis. The inferred conductivity with depth of the crustal rock is consistent with Brace’s model of connected, seawater filled pores in rocks heated from benea

ISSN:0094-8276    

DOI:10.1029/GL008i010p01043

年代:1981

数据来源: WILEY

摘要:

Revisions in the dates of reported geomagnetic excursions during the Brunhes Epoch are proposed in light of possible correlations between a section at Gioia Tauro, Italy, deep‐sea cores, a core from Lake Biwa, Japan, and some lava flows. The anomalously long, double Blake Event reported at Gioia Tauro is here correlated with the Blake Event (∼110 kyr) and the Biwa 1 event (180 ± 5 kyr); an hiatus may be present in the section between these two events. The α event at Gioia Tauro is correlated with the Biwa 2 event at about 295 kyr; the β event with the "Biwa 3" event at about 400 kyr; the γ event with the Snake River event at 480 ± 50; and the δ event, not recorded elsewhere, is estimated to have occurred at ∼620 kyr. These proposed refinements in the age estimates of the excursions suggest an approximately 100 kyr cyclicity. If the events are real and the revised dating is correct, the timing of the geomagnetic events seems to coincide with times of peak eccentricity of the earth's orbit, suggesting a causal

ISSN:0094-8276    

DOI:10.1029/GL008i010p01047

年代:1981

数据来源: WILEY

摘要:

The axial (Brunhes) magnetic anomaly over the Galapagos spreading center shows consistent short‐wavelength anomalies that are not consistent with a uniformly magnetized layer. We interpret this anomaly to confirm the presence of the Emperor reversed event at 0.49 ± 0.05 mybp, with a duration about 0.01 m.y. Further, this anomaly is consistent with a two‐layer magnetic source, with the lower layer having very broad transition zones, offset away from the axis from those of the upper layer by about 1

ISSN:0094-8276    

DOI:10.1029/GL008i010p01051

年代:1981

数据来源: WILEY

摘要:

K‐Ar and paleomagnetic data from cores through a sequence of basalt flows in the eastern Snake River Plain provide evidence for a brief (0.005 to 0.01 m.y.) reversal of the geomagnetic field 0.46 ± 0.05 m.y. ago. This reversed polarity event has also been found in sea‐floor magnetic anomalies and in sediment cores and is probably the Emperor event of Ryan [1

ISSN:0094-8276    

DOI:10.1029/GL008i010p01055

年代:1981

数据来源: WILEY

摘要:

The 616−523rotational transition at 22.2 GHz has been used to measure the H2O vertical profile in the upper stratosphere and mesosphere. Observations were made during January, April, July, and September 1980 and, except in April, theaverageprofile was characterized by a 10 ppmv layer between 60 and 70 km and a decrease in concentration to less than 1 ppmv above 80 k

ISSN:0094-8276    

DOI:10.1029/GL008i010p01059

年代:1981

数据来源: WILEY

摘要:

Atmospheric observations spanning the past three years show that methane increased at 1.2 (±0.3)% per year at Cape Grim in Tasmania (41°S). This rate of increase can be compared to the 1.9 (±0.4)% per year observed at Cape Meares in Oregon (45°N) over the past two years. Over the corresponding period the concentration at Cape Grim increased by 1.4 (±0.4)% per year. The southern hemisphere data also suggest seasonal variations with minimum concentrations in March and maximum in September. These results are based on 26 large volume, stable air samples collected cryogenically in stainless steel flasks and 75 smaller volume air samples collected in glass flasks, all analyzed by a gas chromatograph using a flame ionization dete

ISSN:0094-8276    

DOI:10.1029/GL008i010p01063

年代:1981

数据来源: WILEY