V

Several methods were used to estimate Vs30 from site profiles with borehole depths of about 20 m for the strong-motion stations located in Southwest China. The methods implemented include extrapolation (constant and gradient), Geomatrix Site Classification correlation with shear-wave velocity, and remote sensing (terrain and topography). The gradient extrapolation is the preferred choice of this study for sites with shear-wave velocity profile data. However, it is noted that the coefficients derived from the California data set are not applicable to sites in Southwest China. Due to the scarcity of borehole profiles data with depth of more than 30 m in Southwest China, 73 Kiknet profiles were used to generate new coefficients for gradient extrapolation. Fortunately, these coefficients provide a reasonable estimate of Vs30 for sites in Southwest China. This study showed Vs30 could be estimated by the time-average shear-wave velocity (average slowness) of only 10 meters of depth. Furthermore, a median Vs30 estimate based upon Geomatrix Classification is derived from the results of the gradient extrapolation using a regional calibration of the Geomatrix Classification with Vs30. The results of this study can be applied to assign Vs30 to the sites without borehole data in Southwest China

Whole Earth Telescope observations of BPM 37093 : a seismological test of crystallization theory in white dwarfs

BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~1.1 Mʘ) to theoretically crystallize while still inside the ZZ Ceti instability strip (Teff ~ 12 000 K). As a consequence, this star represents our first opportunity to test crystallization theory directly. If the core is substantially crystallized, then the inner boundary for each pulsation mode will be located at the top of the solid core rather than at the center of the star, affecting mainly the average period spacing. This is distinct from the “mode trapping” caused by the stratified surface layers, which modifies the pulsation periods more selectively. In this paper we report on Whole Earth Telescope observations of BPM 37093 obtained in 1998 and 1999. Based on a simple analysis of the average period spacing we conclude that a large fraction of the total stellar mass is likely to be crystallized

Whole Earth Telescope observations of BPM 37093 : a seismological test of crystallization theory in white dwarfs

BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~1.1 Mʘ) to theoretically crystallize while still inside the ZZ Ceti instability strip (Teff ~ 12 000 K). As a consequence, this star represents our first opportunity to test crystallization theory directly. If the core is substantially crystallized, then the inner boundary for each pulsation mode will be located at the top of the solid core rather than at the center of the star, affecting mainly the average period spacing. This is distinct from the “mode trapping” caused by the stratified surface layers, which modifies the pulsation periods more selectively. In this paper we report on Whole Earth Telescope observations of BPM 37093 obtained in 1998 and 1999. Based on a simple analysis of the average period spacing we conclude that a large fraction of the total stellar mass is likely to be crystallized