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.

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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.

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Distinctive ruptures of the surface faulting which generated the destructive 1995 Hyogoken-Nanbu Earthquake (Ms=7.2) appeared along the Nojima fault, an active fault on the northwestern coast of Awaji island, Japan. The surface fault ruptures in Awaji island extend southwestward continuously for about 9km from Easki near the epicenter to Toshima in Hokudan town, and caused prominent right-latearl offsets of 1.9m at maximum on roads, paddy dikes with vertical displacement of 1.2m at maximum, while no large surface faulting has been reported in Kobe where major damage and casualties have appeared. Most of the surface ruptures follow along the pre-existing active fault traces of the Nojima fault. The ruptures are generally arranged in left-stepping echelon, and local extensional and compressional jog forms such as trenches, mole tracks, buldges are sometimes related to changes in fault strikes. The earthquake fault seems to have propagated bilaterally northeastward and southwestward from the hypocenter in the Straits of Akashi near the major jog of the earthquake fault system. The source process of the earthquake deduced from the slip distribution along the earthquake fault in Awaji island well explains near-field P-waveforms of broad-band seismometers for early part in about 4 seconds. The later part of much larger amplitude should attribute to the northeast fault ruptures toward Kobe.

S U M M A R YUsing the boundary integral method to simulate SH waves numerically in 2-D homogeneous full-or half-space media with randomly distributed cavities, we compare the amplitude attenuation of direct waves with the temporal decay of the coda. The boundary integral method includes the effect of any degree of multiply scattered waves for a wide frequency range, up to wavelengths smaller than the size of the cavities. We consider seismograms on the free surface so that heterogeneities exist only on one side of the receivers, a situation that resembles actual seismic observations. Seismograms are computed for a vertically incident plane wave and for an isotropic line source. In both cases, the value of Q-' as a function of kd, where k is the wavenumber and d is the cavity diameter, peaks around kd = 2 for the direct wave, which is consistent with some single-scattering models. Coda Q-' determined by the temporal decay of the coda envelope agrees well with Q-' for the direct wave for models with a root-meansquare fluctuation of velocity, Q, of about 10 per cent in a half-space. On the other hand, the coda Q-' is systematically larger than the direct wave Q-' in full-space models, that is, without the inclusion of the reflection at the free surface. When the cavity density is doubled (a>20 per cent), the coda energy increases rapidly and its temporal decay decreases, so that coda Q-' becomes smaller than the direct wave Q-', even for full-space models. With a smaller value of cr (about 5 per cent), the coda decays rapidly and the relation between the two types of Q-' is reversed: the coda Q-' becomes larger than the direct wave Q-'. By comparing results from seismograms composed only of singly scattered waves with those that include multiply scattered waves, we can compare the relative contribution of each singly and multiply scattered wavefield to the two measures of Q. Single scattering mainly determines both the direct wave Q-' and the coda Q-' for the smallest value of a, while the values of both kinds of attenuation, particularly the direct wave Q-', are strongly affected by multiple scattering when a is large. Our results imply that a reasonable estimate of scattering attenuation can be obtained by measuring the temporal decay of the coda, if the scattering character of the Earth is similar to our models with a Q of around 10 per cent, where the single scattering is found to be dominant.