Long-Period Seismological Research Program
Abstract
During the first year of the subject contract, five high-gain, long- period (HGLP) seismograph stations were maintained and a sixth station was installed and maintained. Research completed under this contract included investigation into the characteristics of long-period earth noise, the detection capabilities of the high-gain stations, digital signal enhancement techniques, and new methods of distinguishing earthquakes from underground explosions, as well as several studies in general seismology using high-gain data. A detailed study of earth noise at all 11 HGLP sites found that the spectra of earth noise at each site is characterized by a minumum in the period range 25 to 45 seconds. The level of earth noise recorded by vertical seismographs is independent of local meteorological conditions, but at shallow sites, the earth noise levels recorded by horizontal seismographs exhibit a diurnal cycle associated with daily variations of atmospheric turbulence. The horizontal earth noise associated with atmospheric turbulence is attenuated by overburden to about 10% of the surface noise level at a depth of about 150 m. A new surface wave magnitude scale based on the amplitude of higher-mode Rayleigh waves was developed and applied to earthquakes and explosions in central Asia. In other investigations, surface waves were used to study the focal mechanism of small magnitude events, the pulse distortion of body waves travelling non-minimum time paths was computed, and the use of seismograph arrays in determining earth structure was examined.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 1976
- Accession Number
- ADA029667
Entities
People
- Donald W. Forsyth
- Lynn R. Sykes
Organizations
- Lamont–Doherty Earth Observatory