[1] The Hawaii-2 Observatory (H2O) is an excellent site for studying the source regions and propagation of microseisms since it is located far from shorelines and shallow water. During Leg 200 of the Ocean Drilling Program, the officers of the JOIDES Resolution took wind and wave measurements for comparison with double-frequency (DF) microseism data collected at nearby H2O. The DF microseism band can be divided into short-period and long-period bands, SPDF and LPDF, respectively. Comparison of the ship's weather log with the seismic data in the SPDF band from about 0.20 to 0.45 Hz shows a strong correlation of seismic amplitude with wind speed and direction, implying that the energy reaching the ocean floor is generated locally by ocean gravity waves. Nearshore land seismic stations see similar SPDF spectra, also generated locally by wind seas. At H2O, SPDF microseism amplitudes lag sustained changes in wind speed and direction by several hours, with the lag increasing with wave period. This lag may be associated with the time necessary for the development of opposing seas for DF microseism generation. Correlation of swell height above H2O with the LPDF band from 0.085 to 0.20 Hz is often poor, implying that a significant portion of this energy originates at distant locations. Correlation of the H2O seismic data with NOAA buoy data, with hindcast wave height data from the North Pacific, and with seismic data from mainland and island stations, defines likely source areas of the LPDF signals. Most of the LPDF energy at H2O appears to be generated by high-amplitude storm waves impacting long stretches of coastline nearly simultaneously, and the Hawaiian Islands appear to be a significant source of LPDF energy in the North Pacific when waves arrive from particular directions. The highest levels observed at mid-ocean site H2O occur in the SPDF band when two coincident nearby storm systems develop. Deep water, mid-ocean-generated DF microseisms are not observed at continental sites, indicating high attenuation of these signals. At near-coastal seismic stations, both SPDF and LPDF microseism levels are generally dominated by local generation at nearby shorelines.

[1] Comparison of the ambient noise data recorded at near-coastal ocean bottom and inland seismic stations at the Oregon coast with both offshore and nearshore buoy data shows that the near-coastal microseism spectrum results primarily from nearshore gravity wave activity. Low double-frequency (DF), microseism energy is observed at near-coastal locations when seas nearby are calm, even when very energetic seas are present at buoys 500 km offshore. At wave periods >8 s, shore reflection is the dominant source of opposing wave components for near-coastal DF microseism generation, with the variation of DF microseism levels poorly correlated with local wind speed. Near-coastal ocean bottom DF levels are consistently $20 dB higher than nearby DF levels on land, suggesting that Rayleigh/Stoneley waves with much of the mode energy propagating in the water column dominate the near-coastal ocean bottom microseism spectrum. Monitoring the southward propagation of swell from an extreme storm concentrated at the Oregon coast shows that near-coastal DF microseism levels are dominated by wave activity at the shoreline closest to the seismic station. Microseism attenuation estimates between on-land near-coastal stations and seismic stations $150 km inland indicate a zone of higher attenuation along the California coast between San Francisco and the Oregon border.

A three‐axis short‐period seismometer has been operating on the surface of Mars in the Utopia Planitia region since September 4, 1976. During the first 5 months of operation, approximately 640 hours of high‐quality data, uncontaminated by lander or wind noise, have been obtained. The detection threshold is estimated to be magnitude 3 to about 200 km and about 6.5 for the planet as a whole. No large events have been seen during this period, a result indicating that Mars is less seismically active than earth. Wind is the major source of noise during the day, although the noise level was at or below the sensitivity threshold of the seismometer for most of the night during the early part of the mission. Winds and therefore the seismic background started to intrude into the nighttime hours starting on sol 119 (a sol is a Martian day). The seismic background correlates well with wind velocity and is proportional to the square of the wind velocity, as is appropriate for turbulent flow. The seismic envelope power spectral density is proportional to frequency to the −0.66 to −0.90 power during windy periods. A possible local seismic event was detected on sol 80. No wind data were obtained at the time, so a wind disturbance cannot be ruled out. However, this event has some unusual characteristics and is similar to local events recorded on earth through a Viking seismometer system. If it is interpreted as a natural seismic event, it has a magnitude of 3 and a distance of 110 km. Preliminary interpretation of later arrivals in the signal suggest a crustal thickness of 15 km at the Utopia Planitia site which is within the range of crustal models derived from the gravity field. More events must be recorded before a firm interpretation can be made of seismicity or crustal structure. One firm conclusion is that the natural background noise on Mars is low and that the wind is the prime noise source. It will be possible to reduce this noise by a factor of 103 on future missions by removing the seismometer from the lander, operation of an extremely sensitive seismometer thus being possible on the surface.

Spreading center jumps identified west of the Galapagos Islands near 95°W occur in a pattern consistent with the propagating rift hypothesis. A new rift is gradually breaking through the Cocos plate. Each successive jump is slightly longer than the preceding jump. The new spreading center grows at a new azimuth toward the west as the old one dies. The jumps are a manifestation of rift propagation. We extend the analysis of propagating rifts to the case of continuous propagation and predict patterns of magnetic anomalies and bathymetry consistent with the observed patterns. In particular, we correctly predict the trends of fossil spreading centers and V patterns of magnetic anomaly offsets required by the propagating rift hypothesis. Similar V patterns have been observed on many other spreading centers and have been interpreted in various ways. The propagating rift hypothesis appears to offer a simple explanation, consistent with rigid plate tectonics, for each of these patterns. This hypothesis may also have important implications for continental rifting.

Seismometer operation for 21 days at Tranquillity Base revealed, among strong signals produced by the Apollo 11 lunar module descent stage, a small proportion of probable natural seismic signals. The latter are long-duration, emergent oscillations which lack the discrete phases and coherence of earthquake signals. From similarity with the impact signal of the Apollo 12 ascent stage, they are thought to be produced by meteoroid impacts or shallow moonquakes. This signal character may imply transmission with high Q and intense wave scattering, conditions which are mutually exclusive on earth. Natural background noise is very much smaller than on earth, and lunar tectonism may be very low.