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The Steens Mountain (Oregon) geomagnetic polarity transition, 2. Field intensity variations and discussion of reversal models The Steens Mountain (Oregon) geomagnetic polarity transition, 2. Field intensity variations and discussion of reversal models

We carried out an extensive paleointensity study of the 15.5±0.3 m.y. Miocene reversed‐to‐normal polarity transition recorded in lava flows from Steens Mountain (south central Oregon). One hundred eighty‐five samples from the collection whose paleodirectional study is reported by Mankinen et al. (this issue) were chosen for paleointensity investigations because of their low viscosity...
Authors
M. Prevot, Edward A. Mankinen, Robert S. Coe, C. Sherman Gromme

Description and preliminary testing of the CDSN Seismic Sensor Systems Description and preliminary testing of the CDSN Seismic Sensor Systems

The China Digital Seismograph Network (CDSN) is being designed and installed to provide the People's Republic of China with the facilities needed to create a national digital database for earthquake research. The CDSN, which is being developed jointly by the PRC State Seismological Bureau and the U.S. Geological Survey, will consist initially of nine digitally-recording seismograph...
Authors
Jon Peterson, Edwin E. Tilgner

Coupling of ocean bottom seismometers to sediment: Results of tests with the U.S. Geological Survey ocean bottom seismometer Coupling of ocean bottom seismometers to sediment: Results of tests with the U.S. Geological Survey ocean bottom seismometer

The response of an ocean bottom seismometer (OBS) to a transient pull that excites the natural OBS-sediment coupling resonance can be modeled as a mass-spring-dashpot system in which the resonant frequency and damping are functions of instrument mass and bearing radius and of the physical properties of the sediment (primarily the shear modulus). For the very soft sediments sometimes...
Authors
Anne M. Trehu

A note on the effect of bottom currents on an ocean bottom seismometer A note on the effect of bottom currents on an ocean bottom seismometer

Two three-component ocean bottom seismometers and a current meter were deployed a few hundred meters apart on the southern Blake Plateau off the United States eastern coast to study the effect of near-bottom currents on the background noise level of seismometers. Although analysis of the data is limited somewhat by instrumental problems, the increase in current speed, which ranged from 2...
Authors
Anne M. Trehu

A seismic-refraction profile across the San Andreas, Sargent, and Calaveras faults, west-central California A seismic-refraction profile across the San Andreas, Sargent, and Calaveras faults, west-central California

In 1981, the United States Geological Survey recorded a seismic-refraction profile across the southern Santa Cruz Mountains in west-central California to examine the shallow velocity structure of this seismogenic region. This 40-km-long profile, which consisted of three shotpoints, extended northeastward from near Watsonville, California, to Coyote Lake, crossing the San Andreas, Sargent...
Authors
Walter D. Mooney, Robert H. Colburn

Use of strontium isotopes to constrain the timing and mode of dolomitization of upper Cenozoic sediments in a core from San Salvador, Bahamas Use of strontium isotopes to constrain the timing and mode of dolomitization of upper Cenozoic sediments in a core from San Salvador, Bahamas

The 87Sr/86Sr ratios and the activity ratios of 234U/238U and 230Th/238U have been measured in dolomites from a 168-m-deep core taken on the island of San Salvador, Bahamas. These data suggest two periods of dolomitization. The first episode dolomitized Miocene age sediments during the latest Miocene, and the second dolomitized the Pliocene portion of the core and was still active as...
Authors
Peter K. Swart, Joaquin Ruiz, Charles W. Holmes
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