Physical properties (intrinsic and bulk densities, porosity, compressional and shear wave velocities, thermal diffusivity, and conductivity) are measured on 11 ordinary chondrites, one carbonaceous chondrite, and two achondritic clasts of a mesosiderite. With the previously reported results from Antarctic ordinary chondrites, the data are useful in clarifying the difference between H and L chondrites. For example, the intrinsic density of H chondrites (∼3800 kg/m3) is generally higher than that of L chondrites (∼3600 kg/m3). The sample porosity, less than 20%, strongly controls its elastic wave velocities, thermal diffusivity, and conductivity. The variations of elastic wave velocities and thermal properties with porosity show that as with lunar rocks, chondrites contain many cracks. These cracks are thought to be created on their parent bodies by the cumulative effects of many mutual collisions and impacts. Thermal properties are linear functions of elastic wave velocities for both H and L chondrites. The difference between H and L chondrites can be attributed to the content of metallic Fe‐Ni. Correlations between petrologic types, which roughly represent metamorphic temperature, and porosity are less obvious for L chondrites than for H chondrites. Since porosity is not changed significantly by impact events, it appears that the sintering process for L chondrites is independent of the metamorphic events represented by petrologic type.

No abstract

No abstract

Rayleigh wave phase velocities at periods 30-80 s in the Pacific Ocean are calculated by inverting phase and amplitude anomaly data using the paraxial ray approximation and the Gaussian beam method. The region is divided into 5"x 5" blocks, and approximately 200 source-receiver pairs from 18 well-studied events around the Pacific Ocean are used. First, we assume phase anomalies for the lithospheric age-dependent model. Next, conventional phase data inversions are conducted assuming great circle paths so that the phase discrepancies are reduced to less than T . This procedure is essential for later inversions using amplitude data. We then determine the residuals of both amplitude and phase terms by calculating ray-synthetic seismograms. Using the Born approximation for a 2-D wave equation, a nonlinear iterative inversion for phase velocities is performed with both residuals. FrBchet derivatives for the inversion consist primarily of two wavefields: (1) the wavefield at the model point from the source, and ( 2 ) the Green's function from the model point to the receiver. These wavefields are also calculated by the paraxial ray approximation and Gaussian beam methods. In the inverse formulations, the simple use of the conventional Backus-Gilbert approach yields undesirable results in the non-linear iterative case and an extra term is necessary to control the model perturbations in order to minimize departures from the a priori model. The use of this additional term guarantees that we are able to obtain a fairly reliable phase velocity model even in the present non-linear problem. In most cases residual variances are significantly reduced after two or three iterations as far as the starting model is fairly correct. Compared with the phase data inversions, this inverse scheme gives more reliable resolution and most of the inverted features in phase velocities are significantly larger than the uncertainty level while some features obtained by the great circle phase data Present address: Seismological Laboratory, California Institute of Technology, Pasadena, CA 9 11 25, USA. 6 162 K. Yomogida and K. Aki inversions are suspicious. The resulting model displays some interesting deviations from the lithospheric age-dependent model. For example, low velocity regions are correlated with the Hawaii, Samoa, French Polynesia and Gilbert Islands hotspots.

No abstract