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NASA NTRS1973

The velocity structure of the lunar crust.

Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (1) velocity increases from 100 to 300 m/sec in the upper 100 m to about 4 km/sec at 5 km depth, (2) a more gradual increase from about 4 km/sec to about 6 km/sec at 25 km depth,(3) a discontinuity at a depth of 25 km, and (4) a constant value of about 7 km/sec at depths from 25 km to about 60 km.

Kovach, R. L.↗

NASA NTRS1976

Numerical determination of the transmissibility characteristics of a squeeze film damped forced vibration system

Numerical solutions of the governing equations of motion of a liquid squeeze film damped forced vibration system were carried out to examine the feasibility of using a liquid squeeze film to cushion and protect large structures, such as buildings, located in areas of high seismic activity. The mathematical model used was that for a single degree of freedom squeeze film damped spring mass system. The input disturbance was simulated by curve fitting actual seismic data with an eleventh order Lagranging polynomial technique. Only the normal component of the seismic input was considered. The nonlinear, nonhomogeneous governing differential equation of motion was solved numerically to determine the transmissibility over a wide range of physical parameters using a fourth-order Runge-Kutta technique. It is determined that a liquid squeeze film used as a damping agent in a spring-mass system can significantly reduce the response amplitude for a seismic input disturbance.

Sutton, M. A.↗

NASA NTRS1978

Mantle convection pattern and subcrustal stress field under Asia

Satellite tracking and surface gravity data are used to model the subcrustal stress fields in the terrestrial mantle beneath Asia; the results permit interpretation of the tectonic and seismic systems in China. The east and west China blocks, together with five seismic zones, are identified and related to metallogenic domains on the Chinese mainland. In addition, it is shown that the subcrustal stresses beneath China are arranged perpendicularly to the major fault systems and seismic belts. Stress calculations indicate a notable zone of compression in north China, associated with the Shansi Graben, the Linfen Basin Systems and, possibly, the high seismicity of the region.

Liu, H.-S.↗

NASA NTRS1977

Internal friction quality-factor Q under confining pressure

It has been found in previous studies that small amounts of adsorbed volatiles can have a profound effect on the internal friction quality-factor Q of rocks and other porous media. Pandit and Tozer (1970) have suggested that the laboratory-measured Q of volatile-free rocks should be similar to the in situ seismic Q values of near-surface lunar rocks which according to Latham et al. (1970) are in the range of 3000-5000. Observations of dramatic increases in Q with outgassing up to values approaching 2000 in the seismic frequency range confirm this supposition. Measurements under confining pressures with the sample encapsulated under hard vacuum are reported to aid in the interpretation of seismic data obtained below the lunar surface. It has been possible to achieve in the experiments Q values just under 2000 at about 1 kbar for a terrestrial analog of lunar basalt. It was found that a well-outgassed sample maintains a high Q whereas one exposed to moisture maintains a low Q as the confining pressure is raised to 2.5 kbar. This result suggests that volatiles can indeed affect Q when cracks are partially closed and the high lunar seismic Q values reported are concomitant with very dry rock down to depths of at least 50 km.

Tittmann, B. R.↗

NASA NTRS1978

Lunar Seismology: the Internal Structure of the Moon

The direct P and S wave arrival times are the primary data set that can be measured on the seismograms of natural lunar seismic events. Polarization filtering techniques allow the enhancement of secondary body wave arrivals and record curves to identify the secondary phases and deduce structural information. Finally, shear wave amplitude vs. distance curves yield information on the location and magnitude of seismic velocity gradients in the interior. The results of these analyses show that the moon appears to have a two-layer crust at all four seismic stations: a 20 km upper crust that seems to be constant at all sites and a lower crust that is 40 km thick at stations 12 and 14 (mare), 55 + or - 10 km at station 16 (highland), and tentatively either 40 km or 70 km at station 15. The lower mantle extends from 480 km to at least 1100 km depth which is the maximum depth of penetration of all but a few seismic waves used as data. No definitive evidence for or against a lunar core exists.

Goins, N. R.↗

NASA NTRS1979

Planetary seismology and interiors

This report briefly summarizes knowledge gained in the area of planetary seismology in the period 1969-1979. Attention is given to the seismic instruments, the seismic environment (noise, characteristics of seismic wave propagation, etc.), and the seismicity of the moon and Mars as determined by the Apollo missions and Viking Lander experiments, respectively. The models of internal structures of the terrestrial planets are discussed, with the earth used for reference.

Toksoz, M. N.↗

NASA NTRS1980

Data User's Note: Apollo seismological investigations

Seismological objectives and equipment used in the passive seismic, active seismic, lunar seismic profiling, and the lunar gravimeter experiments conducted during Apollo 11, 12, 14, 15, 16, and 17 missions are described. The various formats in which the data form these investigations can be obtained are listed an an index showing the NSSDC identification number is provided. Tables show manned lunar landing missions, lunar seismic network statistics, lunar impact coordinate statistics, detonation masses and times of EP's, the ALSEP (Apollo 14) operational history; compressed scale playout tape availability, LSPE coverage for one lunation, and experimenter interpreted events types.

Vostreys, R. W.↗

NASA NTRS1981

Earthquakes - on the moon

Information obtained with the Apollo lunar seismic stations is discussed. The four types of natural seismic sources that have been identified are described, viz., thermal moonquakes, deep moonquakes, meteoroid impacts, and shallow moonquakes. It is suggested that: (1) the thermal quakes represent the slow cracking and movement of surface rocks; (2) the deep quakes are induced by the tide-generating force of the earth's gravity; (3) the meteoroids responsible for most of the observed impacts are in the mass range from 1 to 100 kg and are clustered in groups near the earth's orbit; and (4) the shallow quakes are similar to intraplate earthquakes and indicate that the moon is as seismically active as the interior regions of the earth's tectonic plates. The structure of the lunar interior as inferred from seismic signals due to both the last three natural sources and 'artificial' impacts of used spacecraft is examined in detail.

Nakamura, Y.↗

NASA NTRS1985

Mechanical Stress Regulation of Plant Growth and Development

Growth dynamics analysis was used to determine to what extent the seismic stress induced reduction in photosynthetic productivity in shaken soybeans was due to less photosynthetic surface, and to what extent to lower efficiency of assimulation. Seismic stress reduces shoot transpiration rate 17% and 15% during the first and second 45 minute periods following a given treatment. Shaken plants also had a 36% greater leaf water potential 30 minutes after treatment. Continuous measurement of whole plant photosynthetic rate shows that a decline in CO2 fixation began within seconds after the onset of shaking treatment and continued to decline to 16% less than that of controls 20 minutes after shaking, after which gradual recovery of photosynthesis begins. Photosynthetic assimilation recovered completely before the next treatment 5 hours later. The transitory decrease in photosynthetic rate was due entirely to a two fold increase in stomatal resistance to CO2 by the abaxial leaf surface. Mesophyll resistance was not significantly affected by periodic seismic treatment. Temporary stomatal aperture reduction and decreased CO2 fixation are responsible for the lower dry weight of seismic stressed plants growing in a controlled environment.

Mitchell, C. A.↗

NASA NTRS1984

Neotectonics of the Caribbean

Burke et al. (1980) have considered geologic and seismic data from Jamaica, while Mann et al. (1984) have examined data from Hispaniola. The present investigation is concerned with the neotectonics of the entire Caribbean region, taking into account the recent results in the northeastern Caribbean and a more comprehensive compilation of seismicity and neotectonic structures from other areas than has been available to most previous authors. It is hoped that this study will complement seismic network results in helping to pinpoint areas of seismic hazard. It is also intended to provide a framework for high-precision geodetic surveys of Caribbean plate motion using measurements from satellites and astronomical observations.

Mann, P.↗

NASA NTRS1987

Altimetry data and the elastic stress tensor of subduction zones

The maximum shear stress (mss) field due to mass anomalies is estimated in the Apennines, the Kermadec-Tonga Trench, and the Rio Grande Rift areas and the results for each area are compared to observed seismicity. A maximum mss of 420 bar was calculated in the Kermadec-Tonga Trench region at a depth of 28 km. Two additional zones with more than 300 bar mss were also observed in the Kermadec-Tonga Trench study. Comparison of the calculated mss field with the observed seismicity in the Kermadec-Tonga showed two zones of well correlated activity. The Rio Grande Rift results showed a maximum mss of 700 bar occurring east of the rift and at a depth of 6 km. Recorded seismicity in the region was primarily constrained to a depth of approximately 5 km, correlating well to the results of the stress calculations. Two areas of high mss are found in the Apennine region: 120 bar at a depth of 55 km, and 149 bar at the surface. Seismic events observed in the Apennine area compare favorably with the mss field calculated, exhibiting two zones of activity. The case of loading by seamounts and icecaps are also simulated. Results for this study show that the mss reaches a maximum of about 1/3 that of the applied surface stress for both cases, and is located at a depth related to the diameter of the surface mass anomaly.

Caputo, Michele↗

NASA NTRS1987

Distinct meteoroid families identified on the lunar seismograms

The meteoroid impact-seismic activity data recorded by the Apollo lunar seismic network is examined. The study investigates the difference in temporal distribution between large and small impacts, clustering of impacts in a two-dimensional space of the time of the year and the time of the month, and the relationship of these observations with terrestrial observations. Several distinct families of meteoroids impacting the moon are identified. Most meteoroids producing small impact-seismic events, including ones associated with cometary showers, appear to approach from retrograde heliocentric orbits. In contrast, most meteoroids associated with large impact-seismic events appear to approach from prograde orbits; the observation is consistent with a hypothesis that many of them represent stony asteroidal material. It is suggested that the previously reported discrepancy between lunar and terrestrial meteoroid-flux estimates may be due to the differences in lunar and terrestrial detection efficiency among various families of meteoroids.

Oberst, Jurgen↗

NASA NTRS1990

Age constraints for the present fault configuration in the Imperial Valley, California: Evidence for northwestward propagation of the Gulf of California rift system

Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault system, which includes the Mesquite Basin and Brawley Seismic Zone, is much younger than the 4 to 5 million year age of the valley itself. A minimum age of 3000 years is calculated for the northern segment of the Imperial fault from correlations between surface topography and geodetically observed seismic/interseismic vertical movements. Calculations of a maximum age of 80,000 years is based upon displacements in the crystalline basement along the Imperial fault, inferred from seismic refraction surveys. This young age supports recent interpretations of heat flow measurements, which also suggest that the current patterns of seismicity and faults in the Imperial Valley are not long lived. The current fault geometry and basement morphology suggest northwestward growth of the Imperial fault and migration of the Brawley Seismic Zone. It is suggested that this migration is a manifestation of the propagation of the Gulf of California rift system into the North American continent.

Larsen, Shawn↗

NASA NTRS1990

Assessing the nation's earthquakes

The basic purposes of this report are: (1) to make a convincing case for the intrinsic value of regional seismic networks; (2) to describe the seriousness of persistent problems in the current configuration and operation of these networks; (3) to outline recommendations for their modernization and future evolution, in particular, their short-term integration and long-term affiliation with the U.S. National Seismic Network. Important supplementary information is included in two appendices: a survey of regional seismic networks and implementation strategies for revitalization of regional seismic networks.

Source record↗

NASA NTRS1990

Continuous monitoring of the lunar or Martian subsurface using on-board pattern recognition and neural processing of Rover geophysical data

The ultimate goal is to create an extraterrestrial unmanned system for subsurface mapping and exploration. Neural networks are to be used to recognize anomalies in the profiles that correspond to potentially exploitable subsurface features. The ground penetrating radar (GPR) techniques are likewise identical. Hence, the preliminary research focus on GPR systems will be directly applicable to seismic systems once such systems can be designed for continuous operation. The original GPR profile may be very complex due to electrical behavior of the background, targets, and antennas, much as the seismic record is made complex by multiple reflections, ghosting, and ringing. Because the format of the GPR data is similar to the format of seismic data, seismic processing software may be applied to GPR data to help enhance the data. A neural network may then be trained to more accurately identify anomalies from the processed record than from the original record.

Mcgill, J. W.↗

NASA NTRS1991

Age constraints for the present fault configuration in the Imperial Valley, California - Evidence for northwestward propagation of the Gulf of California rift system

Larsen, Shawn↗

NASA NTRS1992

A test of present-day plate geometries for northeast Asia and Japan

Alternative geometries for the present-day configuration of plate boundaries in northeast Asia and Japan are tested using NUVEL-1 and 256 horizontal earthquake slip vectors from the Japan and northern Kuril trenches. Statistical analysis of the slip vectors is used to determine whether the North American, Eurasian, or Okhotsk plate overlies the trench. Along the northern Kuril trench, slip vectors are well-fit by the NUVEL-1 Pacific-North America Euler pole, but are poorly fit by the Pacific-Eurasia Euler pole. Results for the Japan trench are less conclusive, but suggest that much of Honshu and Hokkaido are also part of the North American plate. The simplest geometry consistent with the trench slip vectors is a geometry in which the North American plate extends south to 41 deg N, and possibly includes northern Honshu and southern Hokkaido. Although these results imply that the diffuse seismicity that connects the Lena River delta to Sakhalin Island and the eastern Sea of Japan records motion between Eurasia and North America, onshore geologic and seismic data define an additional belt of seismicity in Siberia that cannot be explained with this geometry. Assuming that these two seismic belts constitute evidence for an Okhotsk block, two published kinematic models for motion of the Okhotsk block are tested. The first model, which predicts motion of up to 15 mm/yr relative to North America, is rejected because Kuril and Japan trench slip vectors are fit more poorly than for the simpler geometry described above. The second model gives a good fit to the trench slip vectors, but only if Okhotsk-North America motion is slower than 5 mm/yr.

Demets, Charles↗

NASA NTRS2001

A Miniaturized Seismometer for Subsurface Probing on Mars

Seismology is one of the most powerful tools for investigating the subsurface structure of a planet. The mechanical structure information derived from seismic measurements is complementary to other methods of probing the subsurface (such as gravity and electromagnetics), both in terms of spatial and depth resolution and the relevant types of material properties being sensed. In the near-surface, the propagation of seismic waves is especially sensitive to density and degree of compaction. In addition, interfaces between layer with contrasting properties can be relatively easily delineated. The subsurface of Mars provides an obvious target for seismic investigations. Searching for the presence of water is among the highest priority goals of the Mars Exploration Program, but there are many other important science questions that could be addressed by a seismic profile of the upper layers of the crust. We have developed an extremely small, lightweight, low-power seismometer for planetary applications which is ideally suited for use on Mars. This instrument has previously been proposed and selected for use on a comet (on the Rosetta Lander, subsequently deselected for programmatic reasons) and Mars (on the NetLander mission, with an emphasis on global structure determination).

Banerdt, W. B.↗