Coda Observed a NORSAR and NORESS.

Abstract
The purpose of this study was to determine the nature of the teleseismic P coda seen on short period seismograms, and specifically to separate it into a contribution from scattering near the source, if the source is in the crust, and scattering near the receiver. To accomplish this, digital data from NORSAR and NORESS were used in the frequency range 1-7 Hz and covering a time span of 20-200 sec after first P. The variation of the coda power spectrum of various types of events with time was examined and found to fit a simple exponential decay for all events, although the amplitude of the coda relative to first P was quite different for different types of events, being large for crustal earthquakes and lower for deep focus earthquakes and explosions. Data from NORESS were examined using frequency-wavenumber methods, particularly by determining the power as a function of wavenumber at a fixed frequency; this is equivalent to finding the power as a function of apparent velocity. Deep focus events had a coda dominated by low apparent velocities (3.5-4.5 km/sec), explosions a coda with equal power in high (10 km/sec) and low apparent velocities, crustal earthquakes a coda dominated by high apparent velocities. Keywords include: Teleseismic, Coda, NORSAR, NORESS, and f-k.

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