Operation Ivy, Pacific Proving Grounds, Report to the Scientific Director: Underwater Pressures of Seismic Waves

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Report to the Scientific Director UNDERWATER PRESSURES OF SEISMIC WAVES Appovcd fer public tde~~f3: Serippe lnatltutlon 02 Ooeanography La Jolla, Cal mla f Ita contents In

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Xhderwaterpressure8 from the seismic waves of tie Ivy Test shots were recorded in a I- to 12-cps ham& with the equipment used In the seismic survey carried out concurrently with the teat. Mike shot wan received on US3 Lipan, 48 km easterly from Ground Zero, with a hydrophore swpended at 200 ft deptb. Peak preesure of 10 millibars and mean pressure amplitude of 0 zdllbare were recorded. King shot was recorded on a hydrophone suapeixied In the Paxq Island test drill hole. Peak pressures were off ecale, but the mean preaeure of the initial seismic-wave group was estimated to be 2 millibar& From intewity measurements of aeirrmic refracted waves made during the Bikini Survey of 1050, it ia eMmated that these pressure levels correqond to TNT ehote, fired above ground or water, of charge eke 5 megaton8 and 0.5 megaton, reepectively, with a probable error of a factor of 10. ‘i 1

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Oscillograms of First Arrivals of Sefemfc Waver FrwJencp Response, Mike Shot, 1 November 1952 Frequency Responee, King Shot, 16 November 1952 . Seiamic-wave Inteneitiee As t Functf.~r of Dlstance at Bikini

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PRESSURES OF SEiSMiC WAVES During the oebmic refraction ehzdh of Eniwetok Atoll,* made in,conjunction with the Ivy Testa, seismic wave0 from Mike and Ring ehota were recorded with the same recording equipment used.in the llei6mic survey. These obeervatione are of interest for. a number of reasons, among which are the followtag: 1. Measurement of the preaaure levels gives the magnitude8of the selemic-wave intenritfe8 in the 5- to lO-cps frequency range. 2. Comparieon with TNT shots made at similar diatancer enable8 rough estimates of the TNT equivalent weight required to produce the observed wave intensities. , We ehot was received on USB Lipan (ATF-85) at eetimated poeltion 1134.4 north latitude, 162098.3’ east longitude. This ia 48 km (25 8ea milee) from Ground Zero. The Lipan wa8 underway at about 2 knots, towing 8 small dry dock. The receivtng hydrophore was towed at ; depth of 200 ft, about 100 yd astern. Firing in&ant ~88 picked up WIa photocell from a light meter furnished by Loris Gardner of Task Unit 8, Technical Photography Unit, Task Group King Ehot was recetved at the Parry bland drill hole,* which ia at coordinate position (10 sea milee) from the nomlnai target Ground Zero at coordtitea 108,150 It north, 124,130 it ea8t. The receiving hydrophone was lowered to a depth of 250 ft into the drill hole. The firing instant, a8 in Mike ehot, wan picked up on a light-meter photocell. The recorded wave6 for both Mike and Ring shots are illustrated in Fig. 1. The record of Ktng rhot rhows the amplified output of the light meter which recorded the light wave. The pips meaeured on a recording from the nero line to a peak or trough, and “lnteneity measurements of the refracted eefemic wave8” refer6 to the pressure level expressed in decibels relative to pressure ampiitude” is the average of the pressure amplitudes for the fir& four eucceeaive peaks and trough6 following the wave arrival, beginning with the firet trough (pressure minimum). For example, if the’departures from the zero line were 2 bars for the first trough, 4 barr for the first peak, 6 bara for the second trough, and 8 bar8 for the second peak, the mean pressure amplittxie would be 5 bars.

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rhom between the If&t-wave and ground-wave tracee were recorded from a break-clrcult r . . chronometer andxxxur at l-eec intervals. Before and after each ehot, the chronometer was . calfbrated by recording the radio time signals from WWV. The drift curves of chronometer err& were linear within 0.01 ret, which is the order of the error of reading the record. Hence, it ir eotimated that the time of firfng is known (with respect to WWVtime) to about 0.02 sec. Ffrfng in&ante, in the MarshaLI If&m& time, were 0714: 59.18 f 0.02 8ec for Wke shot and 1129: 59.77 + 0.02 aec for King shot. Travel time8 of the ground waves were 13.00 and 5.31 eec, Fb. 2-FrWency mepmm Mike ehot. 1 November 1952. For each shot, after the level of eefemic wave8 had dropped to background level, the receiving system was calibrated for eeneitivity as a function of frquency by the standard procedure of 4eMng eignale of known voltage and frequency across a calibrated reeialor placed in &eerie8with the piezoelectric crystal in the hydrophone. Since the hydrophone had been previowly callbrated In a preeeure chamber, the preeeure sensitivity was known in term6 of equivalent voltage input to the calibration resistor. From theee caUbratione the over-all pree8ure sen6itivitiee aa a function of frequency were determined for each of the two setup8 and are plotted in Figs. 2 and 3. In order to indicate the magnftuds of the pressure level, the amplitude expected for eignals of lQ* bar amplitude of the dominant frequejrcy of 5 cpe for M&e shot and of iCrs bar amplitude and 8 cp dominant frequency for King shot irl drawn on the respective oscillograme. The peak recorded amplitude for Mike shot wa8 10 millibare. The mean amptitude, defined aa the mean of four wcceeeive peake and trough8 of predleure starting with the first trough, was 6 millibars.

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141.16 set afbr tke firtng inatan~. The atr wave from Xlng shot a88 r&h etrongk and wae . Wed UP W the hydm@mm and also by the light meter. Ita travel Ume was 46.74 sec. There are very few ~Urhecl dita 011the pre88ure8 produced ia overlying water by seismic Furtherxnore, maay of these record8 are un8uitable for tnbn8tty measurements becwble the sity mea6uremant. Fortunately, however, there were wallable 8ome unpublbhed measurement8 made at Blkinl In the cour8e of the selamic survey at B&II& in 1950, which are directly pertinent. These conaW of mean pre88ure measurement8 a8 a function of frequency for a proffle extending 8outherly from a point just lnrlde the lagoon in the Ehyu C&annel att to a di8tPnCe af

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. them cmdltio~ and rtth frequescy rcrpohser comparable to thoee &own 00 P&s. 2 and 2, the scatter fs observed, but oo the average the Latensity decrea8es eystematfcally wlth range at a rat8 betwe1311the inverse third and fourth power of the range. The scatter is typlcll of meanurementaof thf8 kind andU&rate8 that a single inten8ity measurement can be expected to fndfcate merely a rougJt order of mq@tude of the 8ource energy, even when the avernge tran8mUMon loss is well established by many meanuremente. 3910extrapolation of the dahk of Flg. 4 can be te8ted by comparison with data from the Bellgoliud binst of 18 Aprtl lQ41 (in which 4000 ton8 of high exploaloes wa8 fired in rock wa8 gtven. From Fig. 4, the average level of 8 l-lb ahot at 53 km b about -10 db, or 0.3 microbar. Hence for 4000 too8 tb8 predicted mean pressure amplitwle t8 800 mlcrobvre. The agreement with the observed peak prersure of 1200 microbars le mpeh better than could be espected, and it giver 8ome coaftdence that extrapolatim to greater charge she would be Th8 greated rem&big uncertainties ue (1) the allowance to be made for shote placed above uls groaad or seasurfaceinstead of well beneath the surface a8 ln the ubaeturrttoas of tbe re8pon8e in the cued hole in the ground a8 compared with the refqxmse of the Byrne hydropbam ewpended in water pbore the ground. Both these C~8iderPtiUU3 tiive considerable practtcal import&s and deserve theoretical work, which, a8 far 26 the author ts aware, ha8 not been undertaken Rough c8timatee of tbeee effecte cun be obtafned from obeei-vatlone by tbs aatbor that (1) 50-Xb shots give 10 to 20 db lower level of refracted ground wave when fired 8t the water’8 8urface tban when fired at a 200-n depth sod (2) sigh received cm a bydroplxme

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La tha.EIugelab ihnd drill hole in the eeiszic survey’ were about 10 db below those tecelred ou the same hydrophone tu water at comparable ranges. . . From the above camideration8, taking the level at 48 km In Fig. 4 to be -10 db, it is estimated that,the Intensity from Mike shot correspcnde to approximately 4 x lo” lb of TNT fired underwater or undergmGnd or to between 4 X 10’ and 4 x 1O’olb If fired aboveground. Simikarly, taking the level at 18.5 km ln Fig. 4 to be 0 db, King shot equivalent is estimated to be between 4 x lo’ and 4 x 10’ lb lf fired aboveground 1. Rubaell W. R&t, Subsurface Structure of Eniwetok Atoll from Seiemic Refraction Cbservations, Etoport on Ivy Project 11.4, 1953. on Eniwetok Atoll, Marshall Ielands, Bull. Am. rlsaoc. Petroleum Ceol., 37: 2251-2280 (1953). Sylvania Guyot, U. 9. Ceol. Survey Profess. Paper 280 (in press). 4. P. L. Willmore, Seiamtc Experiments on the North German Explosions, 1948 to 1947, Trans. Roy. Sac. London, 242A: 123-151 (1949).

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The ~rmaster General, CBB, Lieiaon Officer. Reseuxh and Development MI.. Chief, Army Field Forces. Ft. Monroe, Vs. President, Board ti. OChFF, Ft. Blfse. Tex. Commandsxt. Corn& and General Staff College, Ft. Leavenworth, Kan., Commandant. The M&GM Branch, Tbe hrtlllery School. Ft. Bliss, Tex. Comme&ng General. Medical Fleld Service S&xl, Bmoke Army Medical Center, Commaadant, Army MedicJ. 8ervice Gruk8t.e Ecbool, Walter Beed Army Medical Commuulud, Cbemtcal Corpe Bcbool, Cbemtcti Corps Training Command. Commandin2 General. Reaeu%h and Engtneerlng Commutd. Army Chemical Center, Commending General. The Engtaeer Center, Ft. Behotr. Va., ATM Asst. Comm~dant. Commanding Offleer. Engtneer Research end Development Laboratory. Ft. Belvoir, Va., Commaudfng Officer, Army Medlcd Research Laboratory, Ft. Knox, Ky. Cornmating Officer. Chemical Corps Chemical end Radiological L&oratory. Army Cbemfcal Center, Md., ATTN: Tech. Library

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Dwector, Armed Forcea hutbIte of Pathology, 7th aad rndepenwe Averme. S.W.. Director, Operattoae Reseuch otllce, Jotie Hopktns Unlverrlty, 6410 Connecticut Chief, Eareau of Ysctlcinc aad Surgery, D/34,WeeMn@e 25, D. C., Cmdlng Offker, U. 8. Neal Dewge Control Tmhlng Center, Naval Base. PhiluJelpbt8 24, Pa, ATTN: ABC Defense Cavm Coma Offtcer, 0.8. Naval Ualt, Cbemtcrl Corps &bool, Army Chemicel Compunder. U. 8. Naval Ordnurce JdxwUory. BIlver Sprtag 19, Yd., ATFN: EH Cm Offker. U. 8. Naval Bediological Defeeee Labatory, Commrader. U.S. Naval Air DerelopmewtCeder. Johnevllle, Pe Commmdbg Offlcer and Dhctor, U. 9. NaveI Eagineering Experim& Steiioa,

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ATTN: war Plsar Dtv, Ccnnmedsr. BtrJegLc Air Cocnmsnd, Offutt Air Force Base. Omeh, Neht., Ccmmoader, Tecticicrl A& Cammrsd, Lsqley APB, VC.. ATTN: Documd Security Brsncb Commsnder, hit Defense Commsed. ILd APB, Cola. Comaauder, Air &Ueriel Ccunmuni, Wright-PUteaYionAFB. Dayton. 0.. Commander, Air Ttuaing Command, Bcoct AFB, Bellevllle, EL. Commander, Atr University, Yurrll AFB. Ah. Caumwier. Flylq Ttainfq hfr Farce, Waco, Tu.. ATI% Director of Coauuuulet. ka&wrtars. Technk-rl Trsinbg Air Force, Gulfpost. Miss.. Commrodmnt, Air Fome S&no1of Atiationkdicine, RandolphAFB, Tex, Commaader, Wright Air Development Cc&r, Wright-Patterson AFB, Dqton. 0.. Commmdar, Aft Fotce Cudarid@ Reaeatch Center, 230 Altsny Street, Cuabrldge 38, Xaaa,. ATTN: CRW,,Abmlc Wtirre Dltectomte Commander, AIt Fome Cmbrl~ Reseuth Center, 230 Albany Street. C-r, Lwty AFB, Denver. Cdo.. ATTN: Doparhent of Armament Tnintng TbB RAND corponllon, 1700 Man meet, arlta Monlcs, calif., ATI’N: Nuclear Eactgy Mvisloa

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Commudant, Armed Forcer Stat! Collcgn, Wehi% 11. VR. ATTN: Secretmy Cammwltng Cenerrl, Field Command, Arm4 Imm Spe~Irl Weapons Project, i PO Bar 6100, Altaqueque, N. Mex. La6 Alamos Sclentitle Laboratoy, Report Ll*rul. PO Box l&h LOS Alamos. Uaivqraity of c8Uhma ltaauoo Laborrbry. FD Bx 808, Livennore, Cdif., ATTN: Xargaret Fddea

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