Lunar seismic profiling experiment natural activity study

The Lunar Seismic Experiment Natural Activity Study has provided a unique opportunity to study the high frequency (4-20 Hz) portion to the seismic spectrum on the moon. The data obtained from the LSPE was studied to evaluate the origin and importance of the process that generates thermal moonquakes and the characteristics of the seismic scattering zone at the lunar surface. The detection of thermal moonquakes by the LSPE array made it possible to locate the sources of many events and determine that they are definitely not generated by astronaut activities but are the result of a natural process on the moon. The propagation of seismic waves in the near-surface layers was studied in a qualitative manner. In the absence of an adequate theoretical model for the propagation of seismic waves in the moon, it is not possible to assign a depth for the scattering layer. The LSPE data does define several parameters which must be satisfied by any model developed in the future

Results from the Apollo passive seismic experiment

Recent results from the Apollo seismic network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km; and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. The best model for the zone of original differentiation appears to be a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro; overlying an ultramafic cumulate (olivine-pyroxene) about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals has recently been identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes

Results from the Apollo passive seismic experiment

Recent results from the Apollo Seismic Network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. It was shown that the best model for the zone of original differentiation is a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro, and overlying an ultramafic cumulate about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals recently were identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes

Scientific Rationale and Requirements for a Global Seismic Network on Mars

Following a brief overview of the mission concepts for a Mars Global Network Mission as of the time of the workshop, we present the principal scientific objectives to be achieved by a Mars seismic network. We review the lessons for extraterrestrial seismology gained from experience to date on the Moon and on Mars. An important unknown on Mars is the expected rate of seismicity, but theoretical expectations and extrapolation from lunar experience both support the view that seismicity rates, wave propagation characteristics, and signal-to-noise ratios are favorable to the collection of a scientifically rich dataset during the multiyear operation of a global seismic experiment. We discuss how particular types of seismic waves will provide the most useful information to address each of the scientific objectives, and this discussion provides the basis for a strategy for station siting. Finally, we define the necessary technical requirements for the seismic stations

The Viking seismometry

Efforts were made to determine the seismicity of Mars as well as define its internal structure by detecting vibrations generated by marsquakes and meteoroid impacts. The lack of marsquakes recognized in the Viking data made it impossible to make any direct inferences about the interior of Mars and only allowed the setting of upper bounds on the seismic activity of the planet. After obtaining more than 2100 hours worth of data during the quite periods at rates of one sample per second or higher, the Viking 2 seismometer was turned off as a consequence of a landing system failure. During the periods when adequate data were obtained, one event of possible seismic or meteoroid impact origin was recognized; however, there is a significant probability that this event was generated by a wind gust

Seismology on Mars

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 five months of operation approx. 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 indicating that Mars is less seismically active than Earth

Seismic and Acoustic Signals Detected at Loihi Seamount by the Hawaii Undersea Geo-Observatory

The Hawai\u27i Undersea Geo-Observatory (HUGO) is an ocean bottom observatory located on the summit of Lo\u27ihi seamount, Hawai\u27i. An electro-optical cable connects the HUGO junction box to a shore station on the Big Island of Hawaii, thereby enabling the first real-time monitoring of a submarine volcano. HUGO was active for 3 months in 1998, collecting nearly continuous, real-time data on a high-rate hydrophone. Signals detected during that time include local as well as teleseismic earthquakes, T phases from Pacific-wide earthquakes, landslides on the submarine flank of Kilauea, and eruption sounds from the current Kilauea eruption. The data do not indicate a Lo\u27ihi eruption during the time that HUGO was active. The variety and quality of signals detected by the HUGO hydrophone confirms that a real-time observatory can serve a valuable role in studies of oceanic acoustics, local and teleseismic earthquakes, and submarine eruption mechanics

Origin of Intraplate Volcanoes from Guyot Heights and Oceanic Paleodepth

The height of a guyot as measured from the surrounding regional sea floor to the volcano\u27s slope break records the water depth at the time the guyot submerged. Thus guyot heights may be used as indicators of the paleodepth of the surrounding ocean floor. We compile data on the heights of 68 intraplate guyots and atolls in the Pacific Ocean as well as 46 volcanic islands in the Pacific, Atlantic, and Indian Oceans. We find that guyot heights generally increase with the age of the lithosphere upon which they were emplaced, although there is a large amount of scatter. In nearly all cases, seamount height, and thus seafloor paleodepth, is less than expected of normal seafloor. These results suggest that most of the volcanoes in this study formed on anomalously shallow seafloor, consistent with formation at hotspots. To characterize thermal anomalies associated with these hotspot swells, we model guyot heights by calculating the isostatic uplift predicted for normal lithosphere that has been partly reheated and is underlain by anomalously hot mantle. This model is able to explain the anomalous water depth at most of the seamounts with hotspot thermal anomalies of 100°–300°C. The heights of a few volcanic chains, however, are not anomalously low, suggesting that these volcanoes are not associated with hotspots. In addition, the observed trend of Hawaiian-Emperor guyot heights as well as the subdued morphology and gravity signature of the oldest Emperor seamounts supports our hypothesis that Cretaceous age Meiji seamount may have formed on or near a spreading center

Hydroacoustic Detection of Submarine Landslides on Kilauea Volcano

Landslides produced at the site where lava flows into the ocean at Kilauea volcano have been detected hydroacoustically. Up to 10 landslides per day were detected by a hydrophone on the Hawaii Undersea Geo-Observatory (HUGO), located 50 km south of the entry site. The largest of these landslides, partly subaerial events known as bench collapses, were detected by a network of hydrophones in the eastern Pacific, 5000–7000 km away from the source. The landslides display a characteristic spectral signature easily recognizable among other signals such as earthquake T-phases and anthropogenic noises. The fact that signals are detected at great distances suggests that hydroacoustic detection of landslides could be a powerful tool in tsunami monitoring and modeling efforts

Elastic properties of the lunar surface from Surveyor spacecraft data Final report

Elastic properties of lunar surface from Surveyor spacecraft dat