Spectral content of Pamir-Hindu Kush intermediate depth earthquakes: Evidence for a high-Q zone in the upper mantle

Journal Article · Sun Jul 10 04:00:00 EDT 1977 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB082i020p02931· OSTI ID:7100280

Khalturin, V I; Rautian, T G; Molnar, P

Very high frequencies (5--10 Hz) are recorded at Garm, Tadzhikistan (..delta..approx.200 km), near Toktogul, Kirgizia (..delta..approx.600 km) and at other close stations from intermediate depth earthquakes in the Pamir-Hindu Kush region. The seismic phase, S/sub n/, is recorded with large amplitudes and high frequencies at stations in Pakistan and India from intermediate depth earthquakes. Such high frequencies require either extremely high average values of Q (several thousand) or very high stress drops of earthquakes (kilobars) or possibly both. Regardless of the stress drops, we infer that Qapproximately-greater-than1000 along paths through a portion of the mantle where Q is usually low. Thus these data indicate a discontinuity, or marked thinning, of the asthenosphere. Even if Q were infinite, the spectral content of the signals at Garm, in addition, could also be interpreted as evidence for relatively high stress drops for the intermediate depth earthquakes. If Q is equal to 3000, the highest calculated stress drops are for events with depths between about 50 and 180 km and range from several tens to several hundred bars.

• Research Organization: Institute of Physics of the Earth, Academy of Sciences, Moscow D-242
• OSTI ID: 7100280
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 82:20; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
AMPLITUDES
EARTH MANTLE
EARTHQUAKES
FREQUENCY RANGE
HZ RANGE
SEISMIC EVENTS
SEISMIC WAVES
STRESSES