摘要:

Natural seismic events have been detected by the long‐period seismometers at Apollo stations 16, 14, 15, and 12 at annual rates of 3300, 1700, 800, and 700, respectively, with peak activity at 13‐ to 14‐day intervals. Repetitive moonquakes from 41 hypocenters produce seismograms characteristic of each. About 90% of the long‐period signals are from these and other numerous, less active hypocenters, and meteoroid impact signals account for the remainder. At each hypocenter, moonquakes occur only within an active period of a few days during a characteristic phase of the monthly lunar tidal cycle. An episode of activity may contain up to four quakes from one hypocenter. Nearly equal numbers of hypocenters are active at opposite phases of the monthly cycle, accounting for the 14‐day peaks in total lunar seismic activity. A period of about 206 days in the seismic activity of several of the hypocenters is superimposed on a strong one‐to two‐year trend where the signal amplitudes decrease to the instrumental detection threshold. A 206‐day period with no secular decrease in amplitude is also observed in the total lunar seismic activity, suggesting that the total number of active hypocenters does not vary appreciably with time. Moonquake magnitudes range between 0.5 and 1.3 on the Richter scale with a total energy release estimated to be about 1011ergs annually. With several possible exceptions, the moonquake foci located to date occur in two narrow belts on the near side of the moon. Both belts are 100–300 km wide, about 2000 km long, and 800–1000 km deep, and they lie along great‐circle arcs. Seismic data from a far‐side focus and a large far‐side meteoroid impact define the base of the lunar lithosphere at a depth of about 1000 km. In our present model the rigid lithosphere overlies an asthenosphere of reduced rigidity in which present‐day partial melting is probable. Tidal deformation presumably leads to critical stress concentrations at the base of the lithosphere, where moonquakes are found to occur. The striking tidal periodicities in the pattern of moonquake occurrence and energy release suggest that tidal energy is the dominant source of energy released as moonquakes. Thus, tidal energy is dissipated by moonquakes in the lithosphere and probably by inelastic processes in the asthenosphere. The low level of seismicity and the absence of shallow seismicity implies that the moon is neither expanding nor contracting at an appreciable rate. The secular accumulation of strain implied by the uniform polarities of moonquake signals may result from weak convection in the asthenosphere or from secular recession

ISSN:8755-1209    

DOI:10.1029/RG012i001p00001

年代:1974

数据来源: WILEY

摘要:

The principal magnetic results of the Apollo program are the demonstration of the natural remanent magnetization (NRM) of returned lunar samples, the discovery of local remanent fields at the Apollo 12, 14, 15, and 16 sites, and the detection with the 15 and 16 subsatellites of magnetic anomalies whose size suggests sources of homogeneous remanent magnetization with a scale size of at least tens of kilometers. The predominant ferromagnetic constituent of the Apollo sample is metallic iron, alloyed sometimes with a few percent of nickel and cobalt. The soils and breccias contain a few tenths to 1% by weight of iron, whereas mare basalts contain about one‐tenth as much. The iron in the mare basalts is typically fine and single domain. Excess iron in the form of superparamagnetic and single‐domain spherules in impact‐generated glass is found in the soil and unannealed breccias. In contrast, in well‐annealed breccias the iron is somewhat coarser and multidomain. A NRM of between 10−3and 10−7gauss cm³ g−1has been reported in the samples. Certain breccias carry the strongest and most stable NRM. The NRM has three major sources: contamination, secondary magnetization acquired on the lunar surface, and primary magnetization associated with the origin of the rock. Some rocks appear to carry primary NRM. Two Thellier‐Thellier intensity determinations have yielded values of 2100±80 and 1.6 Oe for the ancient lunar fields in which NRM was acquired. There are other indications of a large spread in field values, but more determinations are badly needed. The fields observed with the Apollo surface magnetometers have ranged from a few gammas to hundreds of gammas. They are remanent fields due to near‐surface magnetized material. Highland sites exhibit stronger fields than do the mare sites. The sources of the fields have been interpreted as homogeneously magnetized plates that have been disturbed by later impact demagnetization. The anomalies detected by the subsatellites are relatively localized and strong on the farside of the moon, having dimensions comparable with those of the larger craters. The most spectacular feature is near the Van de Graaff crater. On the nearside, subdued magnetic relief predominates. The origin of lunar magnetism remains a puzzle. Numerous suggestions have been made. Although some of them can already be eliminated as being unfeasible, there remain an embarrassingly large numb

ISSN:8755-1209    

DOI:10.1029/RG012i001p00023

年代:1974

数据来源: WILEY

摘要:

The extreme antiquity and lack of evidence for significant chemical processing of the chondritic meteorites since they were formed suggest the possibility that their chemistry and mineralogy may have been established during the condensation of the solar system. By using equilibrium thermodynamics, the sequence of condensation of mineral phases from a cooling nebula of solar composition has been calculated. Applying the predictions of these theoretical models suggests that (1) the chemistry and mineralogy of Ca‐Al‐rich inclusions in C2 and C3 chondrites were established during condensation at temperatures>1300°K; (2) fractionation of such inclusions is necessary to account for the refractory element depletions of ordinary and enstatite chondrites relative to the carbonaceous chondrites; (3) the metal‐silicate fractionation in ordinary chondrites took place in the nebula atT<1000°K andPtot∼ 10−5atm; (4) the volatile element depletion of C2 and C3 chondrites relative to C1 chondrites took place during chondrule formation; (5) the most volatile elements are depleted in ordinary chondrites because they accreted before these elements were totally condensed; and (6) many chemical features of planetary rare gases and organic material in carbonaceous chondrites could have been established during condensation. Chemical fractionation during condensation may also be responsible for the heterogeneous accumulation of the earth, the refractory element enrichment of the moon, and the varying Fe/Si ratios of the terrestr

ISSN:8755-1209    

DOI:10.1029/RG012i001p00071

年代:1974

数据来源: WILEY

摘要:

This paper is concerned with applying Green's function techniques to the theory of the tides. It is shown that by making certain assumptions about the analytic properties of the tidal Green's function, one can obtain an expression for it in terms of the Siegert states of the ocean. A similar expression can also be obtained by assuming that Laplace's tidal equations adequately describe the tide. Relationships between the mathematics of the Green's function and the physics of the ocean are developed, and the Green's function is then used to formally solve the tidal equation. By making assumptions about the smoothness of a related quantity, the response function, one can obtain a simple equation for tidal prediction. The equation may be of some practical use, for example, in superseding the Admiralty method of tidal prediction.

ISSN:8755-1209    

DOI:10.1029/RG012i001p00103

年代:1974

数据来源: WILEY

摘要:

Recent measurements of solar particles in the energy interval between hundreds of keV and a few MeV have shown that a direct connection exists between a portion of the high‐latitude geomagnetic field and the interplanetary magnetic field. The access window for 300‐keV solar protons that reach the center of the polar cap may be as near as 150REin the downstream magnetotail. Solar protons that precipitate into the atmosphere at latitudes near the geomagnetic cutoff enter through the flanks of the magnetosphere and the nearby neutral sheet, possibly within 30REof the earth. Comparison of the patterns of auroral particle precipitation with the zones of access of energetic solar electrons and protons indicates that a substantial fraction of the aurora originates on field lines connected to the interplanetary fi

ISSN:8755-1209    

DOI:10.1029/RG012i001p00117

年代:1974

数据来源: WILEY

摘要:

Variable concentrations of different‐sized water insoluble particles were found in single raindrops and bulk precipitation water and in single snowflakes and hailstones collected in different parts of the world. The experimental evidence shows that aerosol particles are of extreme importance in the formation of the liquid and solid phases of precipitation. A fraction of particles in the 0.2‐ to 2‐µm‐diameter size range acts as cloud condensation nuclei. Condensation of water vapor creates an aerosol cloud that now consists of a population whose size distribution differs from that of the aerosol in the surrounding air and that consists on a mass basis largely of water. Very large particles create conditions for aerodynamic capture of different‐sized cloud particles with subsequent growth of precipitation elements. Those particles are sea‐salt particles in maritime clouds, ice crystals and ice pellets in storms, and deka‐ and hecto‐µm soil particles in severe hailstorms. The ice phase in clouds is initiated on ice‐forming nuclei that are derived from the aerosol population. The ice phase is formed through three basic mechanisms. Contact nucleation takes place when a supercooled water droplet collides with an aerosol particle at the temperature at which that particle can nucleate ice. If the supercooled waterdrop is warmer than the ice nucleation temperature of the colliding aerosol particles, the latter may be captured and become a hydrosol particle. Upon further supercooling the hydrosol particle will act as a freezing nucleus and nucleate ice. The temperature of a freezing waterdrop (liquid ice system) is 0°C, and the released water vapor during freezing produces in the wake of the drop a region of water vapor supersaturation with respect to liquid water at the temperature of the environment. Some of the aerosol particles exposed to that supersaturation will nucleate ice through condensation followed by freezing. Ice‐forming nuclei in snow crystals vary from 0.1 to 13 µm. The majority of particles present in snow crystals are scavenged. Soil particles from arid regions play an important role as ice‐forming nuclei during the northwest monsoon season in Japan. The majority of particles in cirrus clouds are of terrestrial origin but particles of extraterrestrial origin were found in large numbers on certain occasions. Preferential transfer of magnetic particles from air into the ice phase of clouds seems to be evident. The heat and water vapor exchange during phase transitions affect the aerosol population present between cloud particles. Thermophoresis and diffusiophoresis are both active in the transfer of 0.02‐ to 2‐µm‐diameter aerosol particles into precipitation elements. Particles smaller than 0.02 µm are transferred by Brownian diffusion and those larger than 2 µm by impaction. Determination of a lifetime of an aerosol particle within a cloud, or in other words determination of the rate of an aerosol particle transfer into a liquid or solid phase of a cloud, depends on the sizes of interacting particles and their physica

ISSN:8755-1209    

DOI:10.1029/RG012i001p00129

年代:1974

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG012i001p00135

年代:1974

数据来源: WILEY