ABSTRACT
A geophysical and geological survey conducted over the landward slope of the Middle America Trench offshore Guatemala has revealed lanward - dipping reflectors which are associated with high compressional wave velocities, large magnetic anomalies, and basic/ultrabasic rock. Multifold seismic reflection data reveal that the edge of the continental shelf is a structural high on which Cretaceous and younger sediments of the shelf basin onlap and pinch out. The upper part of the continental slope is covered in most places by a 0.5 to 1.0 km thick sediment apron with seismic velocities of 1.8 to 2.6 km/sec. Immediately beneath the sediment apron an irregular surface is the top of an interval with velocities of 4.3 to 4.7 km/sec. Within this interval landward - dipping reflections are traced to about 6 km below sea level. Above this zone of dipping reflectors two positive magnetic anomalies are observed as well as a positive gree - air gravity anomaly reported by other workers (AU)
Subject(s)
Geology , Earthquakes , Central AmericaABSTRACT
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.
ABSTRACT
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.
ABSTRACT
Seismic signals recorded from impacts of missiles at the White Sands Missile Range are radically different from the signal recorded from the Apollo 12 lunar module impact. This implies that lunar structure to depths of at least 10 to 20 kilometers is quite different from the typical structure of the earth's crust. Results obtained from this study can be used to predict seismic wave amplitudes from future man-made lunar impacts. Seismic energy and crater dimensions from impacts are compared with measurements from chemical explosions.
ABSTRACT
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.
