摘要:

Hugoniots of water, four dry tuffs, and two water‐saturated tuffs in the low‐stress region (σx>˜25 kb) were determined in gas gun experiments. Also states on the release adiabats of the dry tuff specimens were determined by shock reverberation techniques. The experimental water Hugoniot agreed well with a Hugoniot calculated from thermodynamic data. A comparison was also made between the experimental states in the tuff and states calculated from the assumptions that (1) volume changes due to shock heating are negligible; (2) the rigidity of the solid portion is responsible for the presence of the precursor and determines both its velocity and magnitude; and (3) a hydrodynamic, completely compacted state is achieved immediately and irreversibly once the Hugoniot elastic limit is exceeded. Calculated stress‐particle velocity states averaged about 30% in stress below the measured values for the dry specimens. This discrepancy indicates that compaction is not completed in the 1‐ to 2‐μsec duration of the experiments. Measured states were within experimental error of calculated states for the sat

ISSN:0148-0227    

DOI:10.1029/JB075i023p04375

年代:1970

数据来源: WILEY

摘要:

Heat flow was determined for deep boreholes at four sites on Amchitka Island, Alaska, and at one site near the northern central coast of Mindanao Island, the Philippines. Temperatures at all Amchitka sites were affected by vertical water movement, but portions of all temperature profiles were suitable for heat‐flow determinations. Measured heat flow increases with depth at Amchitka. If allowance is made for a post‐glacial increase in the mean surface temperature of the island, an equilibrium heat flow of 1.3 μcal/cm2sec results. At the Mindanao site, two independent determinations of heat flow over intervals of contrasting thermal conductivity agree, with a mean value of 1.1. Measurements of near‐surface radioactivity from both areas suggest that only a small fraction of the observed heat flux can be attributed to radioactive heat production in the

ISSN:0148-0227    

DOI:10.1029/JB075i023p04387

年代:1970

数据来源: WILEY

摘要:

Inclusions of granitic basement rocks, collected from the sparse ‘lava’ exposed at the 1.8‐km‐diameter Tenoumer crater, Mauritania, exhibit distinctive petrographic features considered indicative of shock‐wave action and diagnostic for meteorite impact. The observed effects include (1) distinctive planar features in quartz, oriented parallel toω{101¯3}and to other specific planes; (2) intense selective vesiculation of quartz and felspar grains; (3) presence of lechatelierite apparently formed by fusion of quartz grains; and (4) partial fusion and decomposition of biotite grains. These effects are quite distinct from those produced from conventional fusion of granitic xenoliths in lavas. The evidence from these inclusions supports the theory of a meteorite impact origin for the Tenoumer crater. The lava, which is chemically similar to the basement rocks and which has apparently been rapidly quenched, is interpreted as animpact meltformed by fusion of the basement rocks at the time of impact and injected into fractures in the crater wall, carrying with it highly shocked inclusions of basement rock. Values of Sr87/Sr86determined for the lava are approximately 0.720; they are almost identical with values determined for basement rock samples and are too high to represent primary melt derived from the mantle. Potassium‐argon age determinations on the melt rock establish the age of the Tenoumer crater a

ISSN:0148-0227    

DOI:10.1029/JB075i023p04396

年代:1970

数据来源: WILEY

摘要:

Repeated precision leveling across a fracture zone in southwest Iceland showed significant surface deformation over a period of three years, 1966 to 1969. Most of the observed deformation is assumed to have taken place during an earthquake swarm in September 1967, originating about 25 km to the southwest of the leveling profile. The observed deformation includes a dip‐slip displacement of about 6 mm on the fault Hrafnagjá, and subsidence of up to 8 mm of a narrow zone centered near the same fault. The rate of change of deformation away from the fault shows that the dip‐slip displacement is confined to a thin surface layer, probably less than 500 meters thick, and the subsidence can be explained as resulting from tensional displacement of about 7 mm in the fault zone between 400 and 3000 meters depth. During the year 1968 to 1969 the Hrafnagjá fault zone rose slightly, probably 1 to 2 mm, indicating a reversal of the subsidence observed during the previous two years. It is suggested that this uplift is due either to local heating caused by change of flow of ground water and associated thermal expansion or to lateral compression triggered by an earthquake of magnitude 6 that occurred on December 5, 1968, about 30 km east of the leveling pr

ISSN:0148-0227    

DOI:10.1029/JB075i023p04407

年代:1970

数据来源: WILEY

摘要:

This is the first of a series of reports on sound velocity, elasticity, and related properties of marine sediments from sedimentary environments associated with three major physiographic provinces in the North Pacific and adjacent areas: the continental terrace (shelf and slope), the deep‐water abyssal plain (turbidite), and the abyssal hill (pelagic). The following properties are listed in tables and illustrated in diagrams that interrelate various properties: grain size (mean diameter, percentages of sand, silt, and clay), bulk density, density of mineral grains, porosity, sound velocity, velocity ratio (velocity in sediment/velocity in sea water), impedance, and density × (velocity)2. Values are given for each sediment type within each environment. Significant differences in the density and porosity of the environments studied are caused by mineralogy, size and shape of grains, and sediment structure; presence of diatoms and clay mineralogy are particularly important. General equations and diagrams relating density and porosity to velocity should be abandoned in favor of entry into diagrams or equations for a single environment; velocity is then predictable within 1 to 2 per cent in most environments. Mean grain size has one of the best empirical relationships with velocity, which permits derivation of useful data from size analyses of dried cores. Porosity and density are excellent indices by which to determine values of impedance and density × (velocity)2. There is no usable, empirical relationship between sound velocity and shear strength (cohesion) as measured in soil mechanics tests. No anisotropic velocity relationships were measured in surficial sediments, and none is predicted for the upper few hundred meters in sea‐floor sedi

ISSN:0148-0227    

DOI:10.1029/JB075i023p04423

年代:1970

数据来源: WILEY

摘要:

Long geodimeter lines across the San Andreas, Hayward, and Calaveras faults in central California were compared with the measured creep rates of these faults. It was found that creep systematically accounted for only about one third of the long line changes. The residual line changes indicate an accumulating strain field having a principal compressive strain rate of −0.50×10−6yr−1at N11°E and a tensile strain rate of 0.50×10−6yr−1, or shear at a rate of 0.50×10−6yr−1. This rate is 25% less than if creep had not occurred, and it supports the conclusion that creep on these faults does not significantly release accumulating strain in this area. Alternatively, we explore the possibility that creep on other, secondary, faults in the area can explain the geodimeter data. We obtain an acceptable ad hoc model with creep on the Silver Creek, Calaveras, Sargent, and Paicines faults of 1.0, 0.6, 2.0, and 2.0 cm/yr, respectively. Measurements across all these faults must be made to answer the question of seismic risk in c

ISSN:0148-0227    

DOI:10.1029/JB075i023p04447

年代:1970

数据来源: WILEY

摘要:

In this study, unconfined samples of basalt, sintered and bonded perlite, insulating firebricks, and paraffin were subjected to thermal gradients ranging from 15°C/cm to 100°C/cm. Microshocks produced by thermoelastic stress relief were detected by means of miniature accelerometers. Histograms of microshock occurrences have similar shapes for all tests. Activity begins and increases abruptly following onset of heating or cooling of the sample. It reaches a maximum, and then decays hyperbolically, in approximate correlation with the time dependence of the thermal gradient. There are later swarms of activity apparently initiated by small thermal fluctuations in the sample. The log‐log plots of cumulative number of microshocks versus amplitude were constructed and show kinks or knees. The value of the negative slopebfor the linear approximations to these plots ranges from 1.2 to 2.7. These values are greater than those for normal earthquakes series and are similar to those observed for volcanicB‐type earthquakes. The effects of a cellular crack pattern, nonuniformity of stress due to the thermal gradient, and sample inhomogeneity may explain these re

ISSN:0148-0227    

DOI:10.1029/JB075i023p04455

年代:1970

数据来源: WILEY

摘要:

Two of the longest piston cores of deep‐sea sediment ever recovered were taken in the equatorial Pacific on the twelfth cruise of the research vesselRobert D. Conrad. The two cores, 26 and 28 meters in length, penetrate calcareous and siliceous ooze to sediments of Miocene age. Paleomagnetic measurements were made on samples partially demagnetized in a 60‐Hz alternating field of 50 oe. The sampling interval was every 10 cm between reversals and continuously across reversal boundaries. Similar paleomagnetic measurements were made at 10‐cm intervals on a siliceous ooze core 15 meters in length and on a red lutite core 8 meters in length. All four cores show a magnetic stratigraphy extending below the Gilbert polarity series/epoch 5 boundary. One of the long cores has an apparently continuous magnetic record back to an epoch we correlate with the sea‐floor‐spreading anomaly 5 at nine million years or older. For ease in correlation, this magnetic record has been subdivided into seven new magnetic epochs numbered from epoch 5 to epoch 11. The magnetic stratigraphy observed is in substantial agreement with the pattern of magnetic polarity epochs predicted by sea‐floo

ISSN:0148-0227    

DOI:10.1029/JB075i023p04465

年代:1970

数据来源: WILEY

摘要:

Subglacial rocks of Carboniferous age indicate that a vast ice cap once covered much of Gondwanaland, If the cap was comparable with that now covering Antarctica, it probably produced stresses sufficient to cause flow in the asthenosphere, to fracture the lithosphere, and to initiate the separation of the southern continents.

ISSN:0148-0227    

DOI:10.1029/JB075i023p04475

年代:1970

数据来源: WILEY

摘要:

The finite strain expressions, originally derived by F. Birch (1938), for the compressional and shear velocities in an isotropic solid under hydrostatic pressure, when rederived to be complete to first order in the strain, are functions of both the second‐ and third‐order elastic constants. The extra terms appearing in the complete first‐order theory for the velocities and their pressure derivatives are of the order of the ordinary elastic constants. There is no longer any discrepancy between first‐order finite strain theory and ultrasonic and seism

ISSN:0148-0227    

DOI:10.1029/JB075i023p04478

年代:1970

数据来源: WILEY