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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A study of tectonic activity in the Basin-Range Province and on the San Andreas Fault. No. 3: Kinematics of Great Basin intraplate extension from earthquake, geodetic and geologic information

Strain rates assessed from brittle fracture, associated with earthquakes, and total brittle-ductile deformation measured from geodetic data were compared to paleostrain from Quaternary geology for the intraplate Great Basin of the western United States. These data provide an assessment of the kinematics and mode of lithospheric extension that the western U.S. Cordillera has experienced in the last 5 to 10 million years. Strain and deformation rates were determined by the seismic moment tensor method using historic seismicity and fault plane solutions. Contemporary deformation of the Great Basin occurs principally along the active seismic zones. The earthquake related strain shows that the Great Basin is characterized by regional E-W extension at 8.4 mm/a in the north that diminishes to NW-SE extension of 3.5 mm/a in the south. Zones of maximum extension correspond to belts of shallow crust, high heat flow, and Quaternary basaltic volcanism, suggesting that these parameters are related through an effect such as a stress relaxation allowing bouyant uplift and ascension of magmas.

Eddington, P. K.↗
NASA NTRS1985

Thermoelastic stress - How important as a cause of earthquakes in young oceanic lithosphere?

Thermoelastic or thermal stress is a potentially important contributor to the state of stress in the oceanic lithosphere. The present paper provides several simple models for the state of thermoelastic stress in a young oceanic lithosphere, taking into account a comparison of the predictions of these models with the characteristics of near-ridge earthquakes. Attention is given to the characteristics of near-ridge earthquakes, sources of stress in an oceanic lithosphere, previous models of thermal stress, the calculation of thermal stress, and thermal stress models. A test is conducted of the hypothesis that thermoelastic stress is a significant component of the stress field in a young oceanic lithosphere. The considered models support the hypothesis that thermoelastic stress is a significant component of the stress field in a young oceanic lithosphere.

Bratt, S. R.↗
NASA NTRS1984

Modeling of the surface static displacements and fault plane slip for the 1979 Imperial Valley earthquake

Three-dimensional finite element modeling techniques are used to synthesize geodetic and seismological results for 1979 Imperial Valley earthquake. The strategy pursued consists of two principal steps. In the first step, the seismologically-derived coseismic fault slip is taken as a function of position in the fault plane and is applied directly to the three-dimensional dislocation model. In the second step, a physical model of stresses and constitutive parameters is perturbed so as to reproduce the observed fault slip. Hence, the principal features of the coseismic slip pattern are explained by a stress-driven fault model in which: (1) a spatially unresolved asperity is found equivalent to a stress drop of 18 MPa averaged over an area of 15 sq km, and (2) driving stress is essentially absent on the fault segment overlapping the 1940 earthquake rupture zone.

Slade, M. A.↗
NASA NTRS1987

Disruption of the Mauna Loa magma system by the 1868 Hawaiian earthquake - Geochemical evidence

To test whether a catastrophic earthquake could affect an active magma system, mean abundances (adjusted for 'olivine control') of titanium, potassium, phosphorus, strontium, zirconium, and niobium of historic lavas erupted from Mauna Loa Volcano, Hawaii, after 1868 were analyzed and were found to decrease sharply relative to lavas erupted before 1868. This abrupt change in lava chemistry, accompanied by a halved lava-production rate for Mauna Loa after 1877, is interpreted to reflect the disruptive effects of a magnitude 7.5 earthquake in 1868. This interpretation represents a documentable case of changes in magmatic chemical variations initiated or accelerated by a major tectonic event.

Tilling, Robert I.↗
NASA NTRS1987

Earthquake source mechanisms and transform fault tectonics in the Gulf of California

The source parameters of 19 earthquakes in the Gulf of California were determined from an inversion of long-period P and SH waveforms. The inversion procedure is described and the estimated precision of the derived source parameters is examined, with particular attention given to source complexity, the resolution of slip vector azimuth, and the resolution of centroid depth. The implications of these earthquake source characteristics for the tectonic evolution of the gulf are discussed.

Goff, John A.↗
NASA NTRS1987

Crustal deformation in Great California Earthquake cycles

A model in which coupling is described approximately through a generalized Elsasser model is proposed for computation of the periodic crustal deformation associated with repeated strike-slip earthquakes. The model is found to provide a more realistic physical description of tectonic loading than do simpler kinematic models. Parameters are chosen to model the 1857 and 1906 San Andreas ruptures, and predictions are found to be consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces. Results indicate that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps the crust-mantle transition zone.

Li, Victor C.↗
NASA NTRS1989

Properties of earthquakes generated by fault dynamics

A model for fault dynamics consisting of a uniform chain of blocks and springs pulled slowly across a rough surface is presented. The only nonlinear element of the model is a slip-stick friction force between the blocks and the surface. It is found that this model gives rise to events of all sizes. The numerical evaluation of the distribution of earthquake magnitudes results in a power-law spectrum similar to what is observed in nature. Like certain other dissipative dynamical systems, the observed large fluctuations in earthquake magnitude persist because the system is in a state of marginal stability.

Carlson, J. M.↗
NASA NTRS1990

The global geodynamic effect of the Macquarie Ridge earthquake

The coseismic effect of the Macquarie Ridge earthquake on the earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are compared. It is found that this earthquake should have caused the length-of-day to decrease by 0.06, the position of the mean rotation pole to shift 0.11 milliarcsec towards 323 E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10 to the 13th.

Gross, Richard S.↗
NASA NTRS1990

Geodetic measurement of deformation in the Loma Prieta, California earthquake with very long baseline interferometry

VLBI measurements were conducted immediately after the Loma Prieta earthquake and compared with VLBI gathered at Monterey, San Francisco, and Point Reyes since 1983 to obtain preearthquake deformation rates with respect to a North American reference frame. The estimated displacements at Monterey and San Francisco are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the northern segment of the fault rupture. Cartesian positions are presented at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the earthquake's vicinity.

Clark, T. A.↗
NASA NTRS1991

GPS measurements of deformation associated with the 1987 Superstition Hills earthquake: Evidence for conjugate faulting

Large station displacements observed from Imperial Valley Global Positioning System (GPS) campaigns are attributed to the November 24, 1987 Superstition Hills earthquake sequence. Thirty sites from a 42 station GPS network established in 1986 were reoccupied during 1988 and/or 1990. Displacements at three sites within 3 kilometers of the surface rupture approach 0.5 m. Eight additional stations within 20 km of the seismic zone are displaced at least 10 cm. This is the first occurrence of a large earthquake (M(sub S) 6.6) within a preexisting GPS network. Best-fitting uniform slip models of rectangular dislocations in an elastic half-space indicate 130 + or - 8 cm right-lateral displacement along the northwest-trending Superstition Hills fault and 30 + or - 10 cm left-lateral displacement along the conjugate northeast-trending Elmore Ranch fault. The geodetic moments are 9.4 x 10(exp 25) dyne-cm and 2.3 x 10(exp 25) dyne-cm for the Superstition Hills and Elmore Ranch faults, respectively, consistent with teleseismic source parameters. The data also suggest the post seismic slip along the Superstition Hills fault is concentrated at shallow depths. Distributed slip solutions using Singular Value Decomposition indicate near uniform displacement along the Elmore Ranch fault and concentrated slip to the northwest and southeast along the Superstition Hills fault. A significant component of non-seismic displacement is observed across the Imperial Valley, which is attributed in part to interseismic plate-boundary deformation.

Larsen, Shawn↗
NASA NTRS1991

Earthquakes and sea level - Space and terrestrial metrology on a changing planet

A review is presented of the stability and scale of crustal deformation metrology which has particular relevance to monitoring deformation associated with sea level and earthquakes. Developments in space geodesy and crustal deformation metrology in the last two decades have the potential to acquire a homogeneous global data set for monitoring relative horizontal and vertical motions of the earth's surface to within several millimeters. New tools discussed for forecasting sea level rise and damaging earthquakes include: very long baseline interferometry, satellite laser ranging, the principles of GPS geodesy, and new sea level sensors. Space geodesy permits a unified global basis for future metrology of the earth, and the continued availability of the GPS is currently fundamental to this unification.

Bilham, Roger↗
NASA NTRS1991

Earthquake prediction

The state of the art in earthquake prediction is discussed. Short-term prediction based on seismic precursors, changes in the ratio of compressional velocity to shear velocity, tilt and strain precursors, electromagnetic precursors, hydrologic phenomena, chemical monitors, and animal behavior is examined. Seismic hazard assessment is addressed, and the applications of dynamical systems to earthquake prediction are discussed.

Turcotte, Donald L.↗
NASA NTRS1992

Patterns of seismic activity preceding large earthquakes

A mechanical model of seismic faults is employed to investigate the seismic activities that occur prior to major events. The block-and-spring model dynamically generates a statistical distribution of smaller slipping events that precede large events, and the results satisfy the Gutenberg-Richter law. The scaling behavior during a loading cycle suggests small but systematic variations in space and time with maximum activity acceleration near the future epicenter. Activity patterns inferred from data on seismicity in California demonstrate a regional aspect; increased activity in certain areas are found to precede major earthquake events. One example is given regarding the Loma Prieta earthquake of 1989 which is located near a fault section associated with increased activity levels.

Shaw, Bruce E.↗
NASA NTRS1992

Global positioning system measurements of deformations associated with the 1987 Superstition Hills earthquake - Evidence for conjugate faulting

Large station displacements observed from Imperial Valley Global Positioning System (GPS) compaigns are attributed to the November 24, 1987 Superstition Hills earthquake sequence. Thirty sites from a 42 station GPS network established in 1986 were reoccupied during 1988 and/or 1990. Displacements at three sites within 3 kilometers of the surface rupture approach 0.5 m. Eight additional stations within 20 km of the seismic zone are displaced at least 10 cm. This is the first occurrence of a large earthquake (M(sub S) 6.6) within a preexisting GPS network. Best-fitting uniform slip models of rectangular dislocations in an elastic half-space indicate 130 + or - 8 cm right-lateral displacement along the northwest-trending Superstition Hills fault and 30 + or - 10 cm left-lateral displacement along the conjugate northeast-trending Elmore Ranch fault. The geodetic moments are 9.4 x 10 (exp 25) dyne-cm and 2.3 x 10 (exp 25) dyne-cm for the Superstition Hills and Elmore Ranch faults, respectively, consistent with teleseismic source parameters. The data also suggest the post seismic slip along the Superstition Hills fault is concentrated at shallow depths. Distributed slip solutions using Singular Value Decomposition indicate near uniform displacement along the Elmore Ranch fault and concentrated slip to the northwest and southeast along the Superstition Hills fault. A significant component of non-seismic displacement is observed across the Imperial Valley, which is attributed in part to interseismic plate-boundary deformation.

Larsen, Shawn↗
NASA NTRS1992

An application of synthetic seismicity in earthquake statistics - The Middle America Trench

The way in which seismicity calculations which are based on the concept of fault segmentation incorporate the physics of faulting through static dislocation theory can improve earthquake recurrence statistics and hone the probabilities of hazard is shown. For the Middle America Trench, the spread parameters of the best-fitting lognormal or Weibull distributions (about 0.75) are much larger than the 0.21 intrinsic spread proposed in the Nishenko Buland (1987) hypothesis. Stress interaction between fault segments disrupts time or slip predictability and causes earthquake recurrence to be far more aperiodic than has been suggested.

Ward, Steven N.↗
NASA NTRS1993

DSS-14 subreflector actuator dynamics during the Landers earthquake

The 28 Jun. 1992 Landers earthquake ground motion records at the Echo site (DSS-12 antenna) were adjusted to provide a better match with spectra from the measured Mars site (DSS-14 antenna) instrument tower response. A finite-element model of the antenna structural system was analyzed for response to this ground motion. Dynamic forces and displacements were computed in the locality of components that had failed during the earthquake. Calculated forces in the range of 30,000 to 35,000 lb on failed Y-axis actuator U-joints were consistent with laboratory load tests. The load capacity of these joints was found to be below the range of 34,000 to 42,000 lb. Dynamic amplification factors of from 6 to 16 were computed for the quadripod apex accelerations with respect to the ground accelerations. The largest factor--25--was found at the outboard end of the X-actuator.

Levy, R.↗
NASA NTRS1991

Concept for the subresolution measurement of earthquake strain fields using SPOT panchromatic imagery

The use of satellite-derived imagery for measuring subresolution horizontal terrain displacments associated with present-day earthquakes is discussed with reference to data from the French SPOT satellite whose sensor array provides 10-m panchromatic imagery. The measured terrain displacements can be up to several meters, but usually no more than 6-8 m even for major earthquakes. The general approach is to spatially match the after image to the before image at each point on a half-kilometer grid by iteratively interpolating one and testing its correlation with the other. The discussion covers the basic algorithm, results of initial tests, error types and limitations, and future work.

Crippen, Robert E.↗
NASA NTRS1993

Absolute far-field displacements from the 28 June 1992 Landers earthquake sequence

Displacements observed for the Landers earthquake indicate that the depth of the bottom of the rupture is shallower towards the northern end. Displacements were dominantly symmetric and the rupture extended farther south on the Johnson Valley fault than has been mapped on the basis of surface ground offsets. The combined geodetic moment for the Landers and Big Bear earthquakes agrees well with teleseismic estimates.

Blewitt, Geoffrey↗