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Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea

Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total...
Authors
W.G. Deuser, T.D. Jickells, Judith A. Commeau

Strain accumulation along the Laguna Salada Fault, Baja California, Mexico Strain accumulation along the Laguna Salada Fault, Baja California, Mexico

Strain accumulation observed over the 1978–1991 interval in a 30×100 km aperture trilateration network spanning the Laguna Salada fault is described by the principal strain rates 0.101±0.012 strain/yr N80°E±2° and −0.021±0.012 strain/yr N10°W±2°, extension reckoned positive. These strain accumulation rates have been corrected to remove coseismic effects of the nearby 1979 Imperial Valley...
Authors
James C. Savage, Michael Lisowski, N.E. King, W.K. Gross

Postseismic deformation following the 1989 (M = 7.1): Loma Prieta, California, earthquake Postseismic deformation following the 1989 (M = 7.1): Loma Prieta, California, earthquake

Postseismic deformation along a 90‐km profile bisecting the projected surface trace of the coseismic rupture of the 1989 Loma Prieta earthquake has been monitored by frequent GPS surveys for 3.3 years following the earthquake. In addition to the expected deformation associated with secular strain accumulation on the San Andreas and Calaveras faults, deformation associated with...
Authors
James C. Savage, Michael Lisowski, Jerry L. Svarc

Strain accumulation north of Los Angeles, California, as a function of time, 1977–1992 Strain accumulation north of Los Angeles, California, as a function of time, 1977–1992

No significant change in the rate of strain accumulation in a 40×120 km trilateration network spanning the San Gabriel mountains was observed from 1977.5 to 1991.8 despite an apparent increase in seismicity (ML > 4.5) beginning in late 1987 in the northern Los Angeles basin immediately to the south. The observed deformation (0.13±0.01 µstrain/yr right‐lateral shear across a vertical...
Authors
James C. Savage, Michael Lisowski

Estimates of site-dependent response spectra for design (methodology and justification) Estimates of site-dependent response spectra for design (methodology and justification)

Recent borehole-geotechnical data and strong-motion measurements constitute a new empirical basis to account for local geological conditions in earthquake-resistant design and site-dependent, building-code provisions. They provide new unambiguous definitions of site classes and rigorous empirical estimates of site-dependent amplification factors in terms of mean shear-wave velocity. A...
Authors
Roger D. Borcherdt

Venus cartography Venus cartography

The entire surface of the planet Venus is being mapped at global and regional scales (1:50,000,000 through 1:1,500,000) with synthetic aperture radar (SAR), radar altimeter, and radiometer measurements of physical properties from the Magellan spacecraft. The mapping includes SAR image mosaics, shaded relief maps, and topographic contour overlays made from altimetry data and by...
Authors
R. M. Batson, Randolph L. Kirk, Kathleen Edwards, H.F. Morgan
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