Interference between P and p P (or P,, and pP,,) in a seismic signal causes the spectrum of the combined wave train to be scalloped with a period equal to the depth-phase delay time T. Determination of the null frequency interval ( A f = l /~) , together with a knowledge of the overburden compressional velocity, permits an estimate of the source depth to be made. Scalloping produced by reverberations at the recording station can be reduced by forming the average of a suite of individual station spectra. The spectral bandwidth available for analysis can be broadened by removing instrument response. To determine objectively the periodicities in the average spectrum, the cepstrum and pseudo-autocorrelation are computed. This depth determination method combining spectral, pseudoautocorrelation, and cepstral analysis is applied successfully to Pn or P data sets for three underground explosions whose depths are known a priori.
r Mnd PKP codA cltaractori•tic• aro dotormlnod (or oarthquakoa fro• 15 aala•lc raaion• at recorded •t 17 World Wido Standard Soitmoaraph Stations (WWSSS), In dotormlnlna tho coda characterittlca for an event, amplitude moaturumonta, scaled relative to tho larae•t excursion in the coda, aro ••do In tuccoaaivo tlmo wlndow1 1 and tho codM onvolopo obtained by connoctlna tuccottive obtorvatlont. Tho Individual cod• ovoraao coda and 1tandard iloviatlona about tho avoraao cod• a1 ~ function of tiMe into tho coda jln unit• of ~~J aro alvon for oach tot or moature•ent•• Thu coda for event• In a atvon roalon rocordo at a alvon d atanco are found to ho very timllar to tho coda for ovont• fro• another • ro111on rocordod ot tho 11mo dlltanco. That ll, coda charac~rlltlca aro dottrlllnod pr111art ly by tho urlv•J tlmu and •mplitudo of •~aniflcant 1oco11dary phut "-1)1•urther, tho coda ch'ra~torlltlet dotormlnod for lorao ovonta (6,0 mh~7.0) appear ~r,pllcablo t~~m•ller ovent1 (5,0 •~ 6,0) 11 well. llalna d11ta In tho rrrnao 45"<11<80", tho lo~rtorm ••coda daca~ ~n•tant l ror ehp10 tl••• aroaur than four minutu 11 ,0017 per ucond (o•), In tho ranae II •c clos•, the deuy conltant ll 1011owh•t hr11or, heinll on tho or•Jor of ,0037 por tocond, \ \ ' ' a ICI V ~011101 k
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