Spectral analyses of high-frequency pn and sn phases observed at great distances in the Western pacific.

Both P(n), and S(n), phases recorded at distances greater than 3000 kilometers in the western Pacific have substantial amounts of energy at high frequencies, in sorne instances as high as 12 hertz for P(n) and 15 hertz for S(n), A comparison of P(n) and S(n) spectra reveals generally higher energy levels and higher proportions of high-frequency to low-frequency energy for S(n) than for P(n). Estimates of the effective quality factor, Q, indicate that the efficiency of S(n) propagation may be two or three times that of P(n). First arrivals of Pn and Sn have apparent velocities in agreement with values for the uppermost mantle, whereas maximum-energy arrivals have apparent velocities in agreement with values for the lower crust.

The viking seismic experiment.

A three-axis short-period seismometer is now operating on Mars in the Utopia Planitia region. The noise background correlates well with wind gusts. Although no quakes have been detected in the first 60 days of observation, it is premature to draw any conclusions about the seismicity of Mars. The instrument is expected to return data for at least 2 years.

Meteoroid storms detected on the moon.

Seismometers on the moon have detected several brief periods of enhanc ed meteoroid-impact activity, believed to represent encounters of the moon with "c louds" of objec ts in the kilogram range. The latest and most active encounter, in June 1975, is interpreted as a meteoroid c(loud of diameter 0.1 astronomical unit and total mass 10(l3) to 10(14) grams.

Seismic and bathymetric evidence of a fracture zone on gorda ridge.

Swarms of seaquakes have been located hydroacoustically on Gorda Ridge near 41.5 degrees N, 127.6 degrees W, where detailed bathymetric charts indicate a slight dextral offset of the rift valley in the center of the ridge. It is suggested that a fracture zone may be nascent in the area.