P.A. Friberg | Geology Reports

USGS2011

U.S. Geological Survey Near Real-Time Dst Index

The operational version of the United States Geological Survey one-minute Dst index (a global geomagnetic disturbance-intensity index for scientific studies and definition of space-weather effects) uses either four- or three-station input (including Honolulu, Hawaii; San Juan, Puerto Rico; Hermanus, South Africa; and Kakioka, Japan; or Honolulu, San Juan and Guam) and a method based on the U.S. Geological Survey definitive Dst index, in which Dst is more rigorously calculated. The method uses a combination of time-domain techniques and frequency-space filtering to produce the disturbance time series at an individual observatory. The operational output is compared to the U.S. Geological Survey one-minute Dst index (definitive version) and to the Kyoto (Japan) Final Dst to show that the U.S. Geological Survey operational output matches both definitive indices well.

Open-File Report↗

USGS1990

Ground motion

No abstract available.

California↗

USGS1990

Sediment-induced amplification and the collapse of the Nimitz Freeway

The amplification of ground motion by low-seismic-velocity surface sediments is an important factor in determining the seismic hazard specific to a given site. The M s = 7.1 Loma Prieta earthquake of 17 October 1989 was the largest event in the contiguous United States in 37 years, and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence 1 . These data can be used to image the seismic source, to study detailed Earth structure, and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface. Near the edge of San Francisco Bay, site conditions vary considerably on scales of hundreds of metres. The collapsed section of the two-tiered Nimitz Freeway in Oakland was built on San Francisco Bay mud, whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse. Here we analyse high-quality, digital aftershock recordings from several sites near the Nimitz Freeway, and conclude that soil conditions and resulting ground-motion amplification may have contributed significantly to the failure of the structure.

California↗