摘要:

The seismic crustal structure of the moon is known in the region of Oceanus Procellarum from the analysis of artificial impact data. To extend this knowledge we have used data from natural lunar seismic events to search for secondary seismic wave arrivals in the form of peg‐leg multiples caused by reflections at crustal interfaces and converted arrivals caused by refractions at crustal interfaces. A polarization filter has been applied to the data to enhance the rectilinear particle motion expected for the onset of these body wave arrivals in the scattered coda of lunar seismograms. The results of this work tentatively indicate that the highland site at station 16 has a 75 km thick crust with an intermediate 20 km interface, compared to the 60 km crust and 20 km interface in Oceanus Procellarum, a mare region. Since the 20 km upper crust appears to exist at both highland and mare sites, it probably does not represent a mare basalt layer but rather a more general feature of the crust. Crustal thickness may partially control elevation by isostas

ISSN:0094-8276    

DOI:10.1029/GL008i001p00029

年代:1981

数据来源: WILEY

摘要:

The crustal thickness and uppermost mantle P wave velocity at several seismic stations in Northwestern Turkey were estimated using the established travel time‐distance relation method. The data suggest a flat layered crust of average thickness 28.4 ± 3.45 km with an average uppermost mantle P wave velocity of 8.05 ± 0.17 km/s. This is similar to results obtained for the North Aegean Sea and suggests a close structural link between the two ar

ISSN:0094-8276    

DOI:10.1029/GL008i001p00033

年代:1981

数据来源: WILEY

摘要:

Measurements of the specific dissipation factor, Q−1, have been made in saturated rock as a function of effective pressure. The measurements were made at two different frequencies, one in the range of 100 to 250 Hz and the other in the range of 7 to 9 kHz, using the resonant bar method. In saturated rock, Q−1is lower at the lower frequency, and the difference between the values of Q−1measured at the high and low frequencies decreases as effective pressure increases. At effective pressures greater than 200 bars, the Q−1of saturated Berea sandstone measured at 200 Hz approaches that of dry Berea sandstone measured a

ISSN:0094-8276    

DOI:10.1029/GL008i001p00036

年代:1981

数据来源: WILEY

摘要:

Static and dynamic bulk moduli (Ksand Kd) are measured as continuous functions of pressure from zero to 2‐3 kilobars for two sandstones, a tuff, limestone, granite, and oil shale. Results for the sandstones and granite are in good agreement with previously reported data with Ks/Kdvarying from about 0.5 at atmospheric pressure to close to unity at pressures 2 kilobars and above. For rocks behaving elastically under static loading, the Ks/Kdratio is inversely related to the microcrack density. For the limestone, time dependent deformation associated with pore collapse results in Ks/Kdratios approaching 0.1 at high pressure. Upon unloading, while initially high ( ∼ 1.0) at high pressures, Ks/Kdbecomes lower than values obtained during loading at low pressures (<1 kilobar) due to opening of microcracks generated during pore collapse. For the oil shale, in which few microcracks exist, Ks/Kdremains relatively constant with pressure at a value of about

ISSN:0094-8276    

DOI:10.1029/GL008i001p00039

年代:1981

数据来源: WILEY

摘要:

Rheological properties of three recent mudflows at Mount St. Helens were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits. Calculated yield strengths of 1100, 1000, and 400 Pa, maximum flow velocities of 10 to 31 m/s, volumetric flow rates of 300 to 3400 m³/s, and plastic viscosities of 20 to 320 Pa‐s all compare favorably with measured and estimated values cited in the literature. A method for determining likely sites of future mudflow initiation based on these data is outlin

ISSN:0094-8276    

DOI:10.1029/GL008i001p00043

年代:1981

数据来源: WILEY

摘要:

The existence of an 8 fathom (15 m) shoal charted near 23°N, 86°W, a deep water position which is in the vicinity of the Yucatan Current's historical axis, was investigated usingin situand remotely sensed data. Satellite visible data (0.4 µm ‐ 0.7 µm) were used to search for bottom reflections as well as topographically induced sea surface reflection patterns; no evidence was found in either technique. Satellite infrared data (10.5 µm ‐ 12.5 µm) and shipboard bathythermograph data were used to search for a thermal manifestation of turbulence downstream of 23°N, 86°W; again no evidence was found. The satellite infrared data were also used to identify water masses in the bathymetric survey area for the purpose of defining echo sounding correction zones. Corrected echo soundings in the vicinity of 23°N, 86°W vary about 2% in cross‐line comparisons but show no soundings

ISSN:0094-8276    

DOI:10.1029/GL008i001p00047

年代:1981

数据来源: WILEY

摘要:

On the basis of the thermodynamic stability of hydrates of SO2, H2S and CO2, it is suggested that those compounds may be found in some terrestrial volcanic environments. Hydrates of SO2and H2S may be found in low‐temperature fumaroles, especially where surrounding rocks are below 0°C. Such situations could occur at high altitudes and/or high latitudes. Hydrates of H2S, SO2, and CO2may be found on grain surfaces and in pore spaces of pyroclastic or other material overlying gas sources where proper conditions prevail, such as pore pressure equal to overburden pressure. For H2S, such deposits can occur with mean surface temperatures as high as 20°C. Submarine volcanism could give rise to stable submerged hydrate occurrences analogous to both the above occurren

ISSN:0094-8276    

DOI:10.1029/GL008i001p00051

年代:1981

数据来源: WILEY

摘要:

Deformation experiments on Hale albite rock have produced faults at 5 to 15 kb confining pressure and 700° to 1125°C, when hydrolytic weakening is suppressed by either the absence of water or by low pressure. The faults are characterized by: 1) an angle of about 45° to σ1, 2) very little gouge, and 3) several percent permanent strain before failure. Temperature dependent friction is believed to allow frictional sliding and faulting at stresses below those predicted by the Coulomb failure criterion, but above those of hydrolytically weakened crystal plastic flow. High confining pressure, low friction and reduced tensile stress concentrations may allow the fault to propagate as a shear rather than a tensile cr

ISSN:0094-8276    

DOI:10.1029/GL008i001p00055

年代:1981

数据来源: WILEY

摘要:

Sixty radiocarbon measurements were performed on aragonite from annually banded corals collected from three sites in the Galápagos Islands. Preanthropogenic Δ14C values of coral that grew around A.D. 1930 averaged −70‰. This is substantially lower than average values previously reported (−51‰) for corals from Florida and Belize in the western North Atlantic Ocean. A decrease of 6‰ was noticed in coral that grew from 1930 to 1954. This decrease could be interpreted as a Suess effect in surface ocean water. The 100‰ increase in Δ14C for coral that grew from 1954 to 1973 is the result of bomb‐produced14C that was introduced to the surface ocean waters. The14C levels in corals that grew during El Niño years were considerably higher than those for normal years. These higher values are attributed to the absence of up welling at the equator duri

ISSN:0094-8276    

DOI:10.1029/GL008i001p00059

年代:1981

数据来源: WILEY

摘要:

We report lidar measurements of the aerosol content of the atmosphere for the first two months following the volcanic eruption of Mt. St. Helen. The measurements were taken near L'Aquila (Italy) with a lidar system utilizing a 50cm diameter telescope. The measurements are compared to similar data for the previous quiescent period and show a large increase of the backscattering ratio in the stratosphere and upper troposphere. Layers have been observed at various altitudes. A strong layer at 10‐14Km has been observed only initially. Layers between 14‐25Km have been observed continually. These features show a considerable day to day variabil

ISSN:0094-8276    

DOI:10.1029/GL008i001p00063

年代:1981

数据来源: WILEY