Search NASA⌕ Search

SEARCH · Search NASA

Results for “seismic modeling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Subducted slabs and the geoid - Constraints on mantle rheology and flow

The total geoid anomaly which is the result of a given density contrast in a convecting viscous earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries, as well as by the density contrast itself is discussed. If the internal density contrasts can be estimated, the depth and variation of viscosity with depth of the convecting system can be constrained. The observed long wavelength geoid is highly correlated with that predicted by a density model for seismically active subducted slabs. The amplitude of the correlation is explained if the density contrasts associated with subduction extend into the lower mantle or if subducted slabs exceeding 350 km in thickness are piled up over horizontal distances of thousands of km at the base of the upper mantle. Mantle wide convection in a mantle that has a viscosity increasing with depth provides the explanation of the long-wavelength geoid anomalies over subduction zones. Previously announced in STAR as N83-22874

Hager, B. H.↗
NASA NTRS1993

Optimism Experiment and Development of Space-qualified Seismometers in France

The OPTIMISM experiment will put two magnetometers and two seismometers on the Martian floor in 1995, within the framework of the Mars '94 mission. The seismometers are put within the two small surface stations. The seismometer sensitivity will be better than 10 exp -9 g at 1 Hz, 2 orders of magnitude higher than the Viking seismometer sensitivity. A priori waveform modeling for seismic signals on Mars shows that it will be sufficient to detect quakes with a seismic moment greater than 10 exp 15 Nm everywhere on Mars. Such events, according to the hypothesis of a thermoelastic cooling of the Martian lithosphere, are expected to occur at a rate close to one per week and may therefore be observed within the l-year lifetime of the experiment. Other aspects of the experiment are discussed.

Lognonne, P.↗
NASA NTRS1986

Finite difference simulations of seismic scattering Implications for the propagation of short-period seismic waves in the crust and models of crustal heterogeneity

Synthetic seismographs that were obtained by the finite difference method are presently applied to the study of elastic and acoustic wave scattering in two-dimensional media with random spatial variations in seismic velocity. The seismograms are analyzed to determine the variation in travel times and waveforms across arrays of receivers. The random media with Gaussian and exponential correlation functions considered differ in the spectral falloff of their velocity fluctuations at wavelengths smaller than 2pi times the correlation distance. It is found that alternative models of crustal heterogeneity can be tested by improved measurements of the frequency dependence of the crustal Q at frequencies greater than about 1 Hz, assuming that scattering is responsible for most of the attenuation at such frequencies.

Frankel, A.↗
NASA NTRS1984

Intraplate extensional tectonics of the eastern Basin-Range Inferencess on structural style from seismic reflection data, regional tectonics, and thermal-mechanical models of brittle-ductile deformation

Using 1500 km of industry-released seismic reflection data, surface geology, velocity models from refraction data, and earthquake data, the large extensional structures in the crust of the eastern Basin-Range and its transition into the Middle Rocky Mountains and Colorado Plateau have been studied. It is suggested that the close spatial correlation between normal faults and thrust fault segmentation along the Wasatch Front reflects major east-trending structural and lithological boundaries inherited from tectonic processes associated with the evolution of the cordilleran miogeocline, which began in the Precambrian.

Smith, R. B.↗
NASA NTRS2018

Impact-Seismic Investigations of the InSight Mission

Impact investigations will be an important aspect of the InSight mission. One of the scientific goals of the mission is a measurement of the current impact rate at Mars. Impacts will additionally inform the major goal of investigating the interior structure of Mars. In this paper, we review the current state of knowledge about seismic signals from impacts on the Earth, Moon, and laboratory experiments. We describe the generalized physical models that can be used to explain these signals. A discussion of the appropriate source time function for impacts is presented, along with spectral characteristics including the cutoff frequency and its dependence on impact momentum. Estimates of the seismic efficiency (ratio between seismic and impact energies) vary widely. Our preferred value for the seismic efficiency at Mars is 5 × 10−4, which we recommend using until we can measure it during the InSight mission, when seismic moments are not used directly. Effects of the material properties at the impact point and at the seismometer location are considered. We also discuss the processes by which airbursts and acoustic waves emanate from bolides, and the feasibility of detecting such signals. We then consider the case of impacts on Mars. A review is given of the current knowledge of present-day cratering on Mars: the current impact rate, characteristics of those impactors such as velocity and directions, and the morphologies of the craters those impactors create. Several methods of scaling crater size to impact energy are presented. The Martian atmosphere, although thin, will cause fragmentation of impactors, with implications for the resulting seismic signals. We also benchmark several different seismic modeling codes to be used in analysis of impact detections, and those codes are used to explore the seismic amplitude of impactinduced signals as a function of distance from the impact site. We predict a measurement of the current impact flux will be possible within the timeframe of the prime mission (one Mars year) with the detection of ∼ a few to several tens of impacts. However, the error bars on these predictions are large. Specific to the InSight mission, we list discriminators of seismic signals from impacts that will be used to distinguish them from marsquakes. We describe the role of the InSight Impacts Science Theme Group during mission operations, including a plan for possible night-time meteor imaging. The impacts detected by these methods during the InSight mission will be used to improve interior structure models, measure the seismic efficiency, and calculate the size frequency distribution of current impacts.

Ingrid Daubar↗
NASA NTRS1976

Computer simulation of earthquakes

Two computer simulation models of earthquakes were studied for the dependence of the pattern of events on the model assumptions and input parameters. Both models represent the seismically active region by mechanical blocks which are connected to one another and to a driving plate. The blocks slide on a friction surface. In the first model elastic forces were employed and time independent friction to simulate main shock events. The size, length, and time and place of event occurrence were influenced strongly by the magnitude and degree of homogeniety in the elastic and friction parameters of the fault region. Periodically reoccurring similar events were frequently observed in simulations with near homogeneous parameters along the fault, whereas, seismic gaps were a common feature of simulations employing large variations in the fault parameters. The second model incorporated viscoelastic forces and time-dependent friction to account for aftershock sequences. The periods between aftershock events increased with time and the aftershock region was confined to that which moved in the main event.

Cohen, S. C.↗
NASA NTRS1979

The Apollo passive seismic experiment

The completed data set obtained from the 4-station Apollo seismic network includes signals from approximately 11,800 events of various types. Four data sets for use by other investigators, through the NSSDC, are in preparation. Some refinement of the lunar model based on seismic data can be expected, but its gross features remain as presented two years ago. The existence of a small, molten core remains dependent upon the analysis of signals from a single, far-side impact. Analysis of secondary arrivals from other sources may eventually resolve this issue, as well as continued refinement of the magnetic field measurements. Evidence of considerable lateral heterogeneity within the moon continues to build. The mystery of the much meteoroid flux estimate derived from lunar seismic measurements, as compared with earth-based estimates, remains; although, significant correlations between terrestrial and lunar observations are beginning to emerge.

Latham, G. V.↗
NASA NTRS1985

Viscosity profile of the lower mantle

The viscosity of the earth's mantle is an important factor in studies of mantle convection and other problems in geodynamics. The present investigation is concerned with a determination of the variation of effective viscosity across the lower mantle from models of the Gibb's free energy of activation G(asterisk) and the adiabatic temperature profile. The variation of G(asterisk) with depth is calculated using both an elastic strain energy model, in which G(asterisk) is related to the seismic velocities, and a model which assumes G(asterisk) is proportional to the melting temperature.

Ellsworth, K.↗
NASA NTRS1999

Using a Genetic Algorithm to Model Broadband Regional Waveforms for Crustal Structure in the Western United States

In this study, we analyze regional seismograms to obtain the crustal structure in the eastern Great Basin and western Colorado plateau. Adopting a for- ward-modeling approach, we develop a genetic algorithm (GA) based parameter search technique to constrain the one-dimensional crustal structure in these regions. The data are broadband three-component seismograms recorded at the 1994-95 IRIS PASSCAL Colorado Plateau to Great Basin experiment (CPGB) stations and supplemented by data from U.S. National Seismic Network (USNSN) stations in Utah and Nevada. We use the southwestern Wyoming mine collapse event (M(sub b) = 5.2) that occurred on 3 February 1995 as the seismic source. We model the regional seismograms using a four-layer crustal model with constant layer parameters. Timing of teleseismic receiver functions at CPGB stations are added as an additional constraint in the modeling. GA allows us to efficiently search the model space. A carefully chosen fitness function and a windowing scheme are added to the algorithm to prevent search stagnation. The technique is tested with synthetic data, both with and without random Gaussian noise added to it. Several separate model searches are carried out to estimate the variability of the model parameters. The average Colorado plateau crustal structure is characterized by a 40-km-thick crust with velocity increases at depths of about 10 and 25 km and a fast lower crust while the Great Basin has approximately 35- km-thick crust and a 2.9-km-thick sedimentary layer.

Bhattacharyya, Joydeep↗
NASA NTRS1975

Seismically induced modification of lunar surface features

The formation of large impact craters and basins produced not only large volumes of ejecta but also catastrophic seismic waves. Theoretical models, extrapolation of terrestrial explosion data, and extrapolation of lunar impact data suggest surface displacements of 1-10 m at four crater radii from a Copernicus-size impact (4 x 10 to the 30th power ergs). Independent estimates of impact-generated stresses indicate that regions within 4 crater radii of an impact will receive shock waves with pressures exceeding 1 kbar. Greater areas also may receive shock effects as elastic waves following deep ray paths transform into shock waves near the surface. Additional seismic energy will be generated by impacts from secondary ejecta. The resulting large and long-lasting surface movement may contribute to the subdued appearance of the continuous ejecta blanket and secondary craters around large impact craters and to the degradation of small craters outside these zones.

Schultz, P. H.↗
NASA NTRS2008

Terrestrial Environment (Climatic) Criteria Guidelines for use in Aerospace Vehicle Development

This document provides guidelines for the terrestrial environment that are specifically applicable in the development of design requirements/specifications for NASA aerospace vehicles, payloads, and associated ground support equipment. The primary geographic areas encompassed are the John F. Kennedy Space Center, FL; Vandenberg AFB, CA; Edwards AFB, CA; Michoud Assembly Facility, New Orleans, LA; John C. Stennis Space Center, MS; Lyndon B. Johnson Space Center, Houston, TX; George C. Marshall Space Flight Center, Huntsville, AL; and the White Sands Missile Range, NM. This document presents the latest available information on the terrestrial environment applicable to the design and operations of aerospace vehicles and supersedes information presented in NASA-HDBK-1001 and TM X-64589, TM X-64757, TM-78118, TM-82473, and TM-4511. Information is included on winds, atmospheric thermodynamic models, radiation, humidity, precipitation, severe weather, sea state, lightning, atmospheric chemistry, seismic criteria, and a model to predict atmospheric dispersion of aerospace engine exhaust cloud rise and growth. In addition, a section has been included to provide information on the general distribution of natural environmental extremes in the conterminous United States, and world-wide, that may be needed to specify design criteria in the transportation of space vehicle subsystems and components. A section on atmospheric attenuation has been added since measurements by sensors on certain Earth orbital experiment missions are influenced by the Earth s atmosphere. There is also a section on mission analysis, prelaunch monitoring, and flight evaluation as related to the terrestrial environment inputs. The information in these guidelines is recommended for use in the development of aerospace vehicle and related equipment design and associated operational criteria, unless otherwise stated in contract work specifications. The terrestrial environmental data in these guidelines are primarily limited to information below 90 km altitude.

D L Johnson↗
NASA NTRS1993

Deformation of a weak subducted slab and variation of seismicity with depth

Numerical simulations of slab evolution are used here to show that a weak slab model is consistent with seismic observations. Assuming that earthquakes occur at a rate proportional to deformation rate, the observed variation with depth of seismicity rate and focal mechanisms is reproduced along with the cessation of seismicity at 670 km depth. Provided that sinking material encounters resistance at depth, the pattern of seismicity can be explained by any mechanism for deep earthquakes in which the rate of seismicity is proportional to strain rate in the slab.

Tao, Winston C.↗
NASA NTRS1975

On the composition of the lunar interior

There is now abundant geophysical and geochemical evidence suggesting that the moon has a thick plagioclase rich outer shell. This is most easily explained by early and extensive melting of a CaO and Al2O3 rich moon followed by fractional crystallization involving plagioclase flotation. Melilite is probably an important constituent of the interior. This model explains the seismic velocities, the mean density, and the moment of inertia of the moon. The moon is 73-88% high-temperature condensate.

Anderson, D. L.↗
NASA NTRS1978

Tidal stresses in the moon

The tidal stresses in a radially heterogeneous moon are calculated numerically as a function of time and location by using the latest moon model obtained from seismic data. Theoretical results are compared with the observed features of deep moonquakes and in particular with those of the most active A sub 1 hypocenter. The results show that (1) the magnitudes of tidal stresses are small, of the order of 1 bar and less, (2) they reach maxima in the seismically active depth range of 600-1200 km, (3) the geographic distribution of moonquake epicenters does not appear to be controlled solely by the highest tidal stresses, and the presence of heterogeneities and weak zones may be important in determining moonquake locations, (4) the occurrence times of moonquakes correlate with one or more of the tidal stress components, and (5) the presence of an ambient tectonic stress of about the same order of magnitude as the tidal stress is necessary to explain the observed reversal in polarity of the A sub 1 moonquakes.

Cheng, C. H.↗
NASA NTRS1983

Computational methods for estimation of parameters in hyperbolic systems

Approximation techniques for estimating spatially varying coefficients and unknown boundary parameters in second order hyperbolic systems are discussed. Methods for state approximation (cubic splines, tau-Legendre) and approximation of function space parameters (interpolatory splines) are outlined and numerical findings for use of the resulting schemes in model "one dimensional seismic inversion' problems are summarized.

Banks, H. T.↗
NASA NTRS2003

Satellite Detection of the Convection Generated Stresses in Earth

We review research developments on satellite detection of the convection generated stresses in the Earth for seismic hazard assessment and Earth resource survey. Particular emphasis is laid upon recent progress and results of stress calculations from which the origin and evolution of the tectonic features on Earth's surface can be scientifically addressed. An important aspect of the recent research development in tectonic stresses relative to earthquakes is the implications for earthquake forecasting and prediction. We have demonstrated that earthquakes occur on the ring of fire around the Pacific in response to the tectonic stresses induced by mantle convection. We propose a systematic global assessment of the seismic hazard based on variations of tectonic stresses in the Earth as observed by satellites. This space geodynamic approach for assessing the seismic hazard is unique in that it can pinpoint the triggering stresses for large earthquakes without ambiguities of geological structures, fault geometries, and other tectonic properties. Also, it is distinct from the probabilistic seismic hazard assessment models in the literature, which are based only on extrapolations of available earthquake data.

Liu, Han-Shou↗