摘要:

K, Rb, and Sr concentrations and Sr isotopic composition are reported for hand‐picked fractions from the 175‐ to 1000‐μm Apollo 12 fines samples 12032 and 12070. In addition, two<1‐mm bulk fines samples, 14163,160 and 14259,21, from Apollo 14 were analyzed; these have model Rb‐Sr ages close to 4.6 b.y. The Apollo 14 data indicate the presence of a radiogenic component of 4.6‐b.y. model age like the Apollo 12 fines, confirming a very early geochemical differentiation of the moon. Progressively greater enrichment in K and Rb relative to the bulk fines is shown by microbreccia from both samples, ropy brown glass from 12032, and light‐grey lithic fragments from 12032. Model Rb‐Sr ages, based on a basaltic achondrite initial ratio, are generally close to 4.6 b.y. The microbreccias and ropy brown glass have model ages that are younger but indistinguishable from 4.6 b.y. within analytical error. Light grey lithic fragments from 12032 have a model age of 5.1 b.y. and must have had a multistage Rb/Sr evolution. The data are broadly compatible with two‐component mixing models of the Apollo 12 fines. On the basis of modal composition, the microbreccia is considered the major nonbasaltic constituent. A more complex model is necessary, since the light‐grey lithic fragments, at least, have a distinct Rb/Sr isotopic history. There is no compelling evidence that all the exotic material was introduc

ISSN:0148-0227    

DOI:10.1029/JB077i011p02007

年代:1972

数据来源: WILEY

摘要:

A method based on Sodano's inverse solution of geodesics for determining geodetic positions from hyperbolic navigation time differences is derived to an accuracy of 0.005 sec of arc. The inverse problem is also solved. Hyperbolic coordinates can be transformed directly to universal transverse Mercator coordinates by proper application of the universal transverse Mercator scale factor.

ISSN:0148-0227    

DOI:10.1029/JB077i011p02014

年代:1972

数据来源: WILEY

摘要:

A vibrating string accelerometer (VSA) sea gravity meter with electronics for digital readout has been assembled, tested, and used by the Woods Hole Oceanographic Institution. The VSA meter is installed in a portable van laboratory that also contains a digital computer for automatic logging of gravity, magnetic, and ship's velocity information. Two years of testing and use of the VSA gravity meter at sea are summarized. Tares and remaining sensitivity to variations in ambient temperature and supply voltage are inferred to be due primarily to the oscillator amplifiers. Improved oscillator amplifiers will be installed. During December 1969, the VSA meter, together with a gyrostabilized LaCoste and Romberg (L&R) sea gravity meter, were operated aboard the RVAtlantis 2. The values from the VSA and L&R gravity meters were both reduced using identical navigational information. Resulting profiles of free‐air anomalies derived from both meters differed by up to 15 mgal and led to the identification of a malfunction in the cross‐coupling circuitry of the L&R meter. Identical malfunctions have been subsequently identified in three other L&R sea gravity met

ISSN:0148-0227    

DOI:10.1029/JB077i011p02018

年代:1972

数据来源: WILEY

摘要:

An expression of stress components corresponding to a time‐dependent dislocation (discontinuity of displacement) is obtained for the case of a two‐dimensional longitudinal‐shear crack, on the basis of the Green function representation theorem of the elastic‐wave equation. This expression is used to examine various dislocations from the viewpoint of the boundary condition that should be satisfied on the fault plane. It is shown that the dislocation functions consistent with propagating cracks have quite different characteristics between the supersonic propagation with higher than shear‐wave velocity and the subsonic propagation with lower than shear‐wave velocity. For supersonic propagation, the source time function giving correct rupture propagation represents a step‐function type of change in the particle velocity, whereas the propagating cracks have a singularity similar to the static cracks at the edge in the case of subsonic propagation. The source time function proposed by J. N. Brune is applicable to supersonic propagation if a suitable correction is made, but this time function does not represent the correct behavior of the cracks propagating at a subsonic velocity. A source time function that is applicable to subsonic rupture propagation is also presented

ISSN:0148-0227    

DOI:10.1029/JB077i011p02034

年代:1972

数据来源: WILEY

摘要:

Short‐periodPwaves from five presumed explosions in eastern Kazakh with magnitudes mbranging from 5.3 to 5.7 are examined at five teleseismic arrays: Lasa, YKA, OONW, WRA, and GBA. Time domain transfer functions that convert the lower‐magnitude events to the largest event at the individual sensors of each array are calculated. These filters show that the observed source radiation of each event is space stationary over the aperture of each array but varies from array to array. At the Large‐Aperture Seismic Array (Lasa) these transfer functions qualitatively match theoretical transfer functions based on Blake's solution for the seismic radiation from a cavity excited by a step function in pressure, in which the cavity radius for each event is scaled according to the Lasa magnitude. When all the arrays are considered simultaneously, apparent anisotropic radiation is seen in two of the five events, where an amplitude variation up to a factor of 3 is observed between two array sites. Multisite estimation of the source parameters is attempted in the frequency domain, in which Haskell's explosion spectral model is fitted to each event spectrum after corrections for instrument response and attenuation are applied. At each array the attenuation that allows the fitted parameters to vary as dictated by the model is chosen as correct. With attenuation estimated at each array, the spectra observed at all arrays for a single event are simultaneously fitted to the three parameters of Haskell's source model. For most arrays the individual and simultaneous fitting schemes yield reasonable values for the source parameters. The assumed source model and the estimated attenuation parameter for central Asia to Lasa apparently explain why the spectral ratio of high‐ to low‐frequency energy in explosion sources increases as yield

ISSN:0148-0227    

DOI:10.1029/JB077i011p02045

年代:1972

数据来源: WILEY

摘要:

The earthquake focus is represented by a bilateral bidirectional fault model in which the final fault area is rectangular. The transfer functions for body waves for this fault model have been derived. The directivity functions for body waves are defined by taking the ratio of the transfer functions corresponding to two observation stations. The sensitivity of the directivity function forPwaves to the kinematic parameters and to the orientation of the fault plane is demonstrated. TheSwave directivity function appears to be relatively insensitive to the change in the kinematic parameters. A deep focus earthquake (H= 600 km,mb= 7.0) has been investigated and the kinematic parameters have been successfully recovered using the modulus of thePwave directivity function. The kinematic parameters are as follows: The fault plane is they‐znodal plane of the focal mechanism solution, the faulting is of the bilateral bidirectional type with total rupture along theyaxis of 75 km and total rupture along thezaxis of 29.5 km; the rupture speed along theyaxis is 3.97 km/sec and along thezaxis is 2.98 km/sec. The fault area is 2212 km2and the dislocation is estimated to be 26 c

ISSN:0148-0227    

DOI:10.1029/JB077i011p02062

年代:1972

数据来源: WILEY

摘要:

During the period from May 1969 to March 1970, seven moderate earthquakes occurred in the Delarof‐Andreanof Island region. The focal mechanisms of these earthquakes correspond to the motion that would be expected on the basis of plate tectonics. Of more particular significance, the motion in one of these shocks, located at intermediate depth in the Benioff zone, indicates horizontal tension parallel to the plate, corresponding to lateral extension as the plate descends under an arcuate structure convex to the plate motion. The spatial and temporal relation of these earthquakes and of their aftershock sequences to the over‐all activity of the arc and particularly to the seismicity of the Rat Islands during this period supports the hypothesis that the Aleutian Islands are active by independent blocks and that the boundaries of these blocks are permanent featu

ISSN:0148-0227    

DOI:10.1029/JB077i011p02072

年代:1972

数据来源: WILEY

摘要:

Microearthquakes in The Geysers area of northern California were recorded for 3 weeks with a radio‐telemetry array of eight seismograph stations in order to examine their distribution with respect to the area developed for geothermal power. Locations were determined for 53 earthquakes within about 10 km of The Geysers. Most epicenters lie in a zone about 4 km long and 1 km wide passing through the geothermal field along a principal fault zone. Focal depths in this trend range from near surface to about 4 km. A composite fault‐plane solution indicates dextral strike‐slip faulting on a NNW‐striking plane subparallel with the regional fault pattern. The results of this study suggest that accurate mapping of microearthquakes can be useful in the exploration for geothermal resources, if the earthquakes studied here are not somehow caused by development of th

ISSN:0148-0227    

DOI:10.1029/JB077i011p02081

年代:1972

数据来源: WILEY

摘要:

This study attempts to forecast likely locations for large shallow South American earthquakes in the near future by examining the past space‐time pattern of occurrence of large (M≥ 7.7) earthquakes, the lateral extent of their rupture zones, and, where possible, the direction of rupture propagation. Rupture zones of large shallow earthquakes generally abut and do not overlap. Patterns of rupture propagation appear to follow certain trends. These facts, plus the nonrandom behavior of the space‐time history of seismic activity, present consistencies that may permit prediction, in a gross sense, of future events. By mapping the rupture zones of large earthquakes (in contrast with plotting only epicenters), it is possible to identify segments of the shallow seismic zone that have not ruptured in many decades. Limited experience elsewhere indicates that these gaps between rupture zones tend to be filled by large‐magnitude earthquakes. In certain places it is possible to make approximate estimates of the time of occurrence of the next large earthquake. For at least 300 or 400 years, the entire fault segment near the Central Valley province of central and southern Chile (about 32°–46°S) has fractured about once each century from a generally N‐S progression of several large (M≥ 8) earthquakes. Large earthquakes in this region have almost always occurred to the south of a previous large earthquake. In addition, it is possible to infer a direction of rupturing for two large earthquakes in this century (1928 and 1960). Both these earthquakes fractured southward away from the rupture zone of an earlier earthquake. It would be consistent with these observations if a new series started about the end of this century near Valparaiso (33°S) and progressed southward. In other sections of South America there are several extensive segments of the active seismic belt that have not ruptured during this century. Northern Chile and southernmost Peru (about 17°–25°S) have been relatively aseismic for about 100 years. South of Lima (about 12.5°–14°S), between the rupture zones of the 1940 and 1942 Peruvian earthquakes, there is another significant gap in recent activity. Both these regions are probably areas of relatively high earthquake risk. The northern Peru and southern Ecuador region (about 9°–1°S) has also been relatively aseismic during this century. However, this region differs from the two previously mentioned gaps in that this coastal zone was a region of moderate seismicity during historic times. Perhaps aseismic creep is an unusually important factor in relieving tectonic strain along this particular segment of the shallow seismic zone. Another possibility is that large shallow earthquakes in this region have an extremely long recurrence time. Much of the shallow seismic zone of northern Ecuador and southwestern Colombia has ruptured twice during this century. During large earthquakes in this region, the rupturing tends to be directed toward the north or NE. The data for this region suggest that the area to the NE of the 1958 Colombian earthquake may be a region of rel

ISSN:0148-0227    

DOI:10.1029/JB077i011p02087

年代:1972

数据来源: WILEY

摘要:

Nearly 200 samples of single‐crystal quartz were broken in uniaxial compression. The quartz was observed to exhibit strong static fatigue, the mean fracture time 〈t〉 being related to stress σ, concentration of waterCH,O, and temperatureTby 〈t〉 =t0CH2O−;αexp [(u′/RT) − κ′σ]. Microfracturing associated with crack growth and spalling occurred continuously during the experiments. No creep strains could be detected. The rate of microfracturingnfollowed the expressionn=a0CH2Oαexp [(−u′/RT) + κ′σ]tγ. These and other results suggest that static fatigue of quartz is due to stress corrosion cracking. The most likely mechanism is a silica hydration reaction. Static fatigue is suggested as the mechanism of brittle creep of rocks and of time

ISSN:0148-0227    

DOI:10.1029/JB077i011p02104

年代:1972

数据来源: WILEY