| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
INSTITUTE OF GEOPHYSICS AND PLANETARY PHYSICS SCRIPPS INSTITUTION OF OCEANOGRAPHY UNIVERSITY OF CALIFORNIA-SAN DIEGO, LA JOLLA, CALIFORNIA 92093
Abstract
Ambient noise conditions at four IRIS/IDA sites in the USSR are characterized from 0.01 to 100 Hz as part of a study to ascertain the utility of broadband three-component seismic stations in monitoring regional Eurasian seismicity. Estimates of the power spectral density of noise levels were computed for a 5-day period in two seasons (winter and summer), at two times of the day. Of these periods, lower noise conditions were found at night in the summer. In general, at 1 Hz and above, noise levels and their variations correlate predictably with the soundness of vault construction and the proximity of the station to civilization. Absolute noise levels at the IRIS/IDA/USSR sites range from a high of about –120 dB to a low of –155 dB relative to (1 m/s2)2/Hz, between 1 and 5 Hz. A time-of-day variation in noise was observed at all sites, with noise levels during the work day ranging from 7 to 14 dB higher than night levels, depending on the site. This effect was observed only for frequencies above about 1 Hz. Observed seasonal variations (winter versus summer) are highly station dependent, although the seasonal effect is restricted to frequencies below 1 Hz and is in general centered on the microseism peak (0.1 to 0.2 Hz). Below 0.1 Hz, noise levels are influenced by the thermal and barometric isolation of the site. Low-frequency levels were not studied below 0.01 Hz. Minimum detectable magnitudes are estimated for the IRIS/IDA stations using the observed noise levels over 1 Hz. In general, a magnitude 3 event should be detectable at 1,000 km by all stations under night noise conditions if the dominant signal frequency is 1 Hz; the magnitude estimates increase with increasing frequency. These detectability estimates assume a conservative signal-to-noise ratio of 6.
High-frequency data recorded by independent equipment co-located with the IRIS/IDA system during a 2-week experiment allow estimation of noise levels at the sites up to 100 Hz. Borehole versus surface noise levels recorded during the high-frequency experiment showed significant noise reduction (20 dB) can be achieved by borehole deployment at sites with exposed surface vaults. With well-isolated surface vaults, borehole noise reduction is about a factor of 2. Absolute noise levels between 1 to 10 Hz observed at IRIS/IDA/USSR sites are systematically higher than average NORESS noise by about 7 dB to 25 dB, depending on the station.
This article has been cited by other articles:
|
|
 |
|
  Broadband Seismic Background Noise at Temporary Seismic Stations Observed on a Regional Scale in the Southwestern United States Bulletin of the Seismological Society of America, December 1, 2002; 92(8): 3335 - 3342.
|
|
|
|
|
|
C. J. Young, E. P. Chael, M. M. Withers, and R. C. Aster A comparison of the high-frequency (>1 Hz) surface and subsurface noise environment at three sites in the United States Bulletin of the Seismological Society of America, October 1, 1996; 86(5): 1516 - 1528. [Abstract] [PDF]
|
|
|
|
|
|
C. J. Young, E. P. Chael, D. A. Zagar, and J. A. Carter Variations in noise and signal levels in a pair of deep boreholes near Amarillo, Texas Bulletin of the Seismological Society of America, October 1, 1994; 84(5): 1593 - 1607. [Abstract] [PDF]
|
|
|
|
|
|
T. C. BACHE, S. R. BRATT, H. J. SWANGER, G. W. BEALL, and F. K. DASHIELL Knowledge-based interpretation of seismic data in the Intelligent Monitoring System Bulletin of the Seismological Society of America, October 1, 1993; 83(5): 1507 - 1526. [Abstract] [PDF]
|
|
|
|
|
|
H. K. GIVEN and J.-F. FELS Site characteristics and ambient ground noise at IRIS/IDA stations AAK (Ala-Archa, Kyrgyzstan) and TLY (Talaya, Russia) Bulletin of the Seismological Society of America, June 1, 1993; 83(3): 945 - 953. [PDF]
|
|
|
|
|
|
A. LEVSHIN, L. RATNIKOVA, and J. BERGER Peculiarities of surface-wave propagation across central Eurasia Bulletin of the Seismological Society of America, December 1, 1992; 82(6): 2464 - 2493. [Abstract] [PDF]
|
|
|
|
|
|
F. RIVIERE-BARBIER, A. SUTEAU-HENSON, V. Z. RYABOY, and J. A. CARTER Analysis of three-component data from IRIS/IDA stations in the USSR Bulletin of the Seismological Society of America, February 1, 1992; 82(1): 192 - 220. [Abstract] [PDF]
|
|
|
|
|
|
A. SUTEAU-HENSON Three-component analysis of regional phases at NORESS and ARCESS: Polarization and phase identification Bulletin of the Seismological Society of America, December 1, 1991; 81(6): 2419 - 2440. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
