BUREAU OF MINERAL RESOURCES GEOLOGY AND GEOPHYSICS

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1 reic5(.(3^ Copy for Ohio?: Geophy, loaz, COMMONWEALTH OF AUSTRALA DEPARTMENT OF NATONAL DEVELOPMENT BUREAU OF MNERAL RESOURCES GEOLOGY AND GEOPHYSCS RECORDS: 1965/66 BUREAU OF MNERAL RESOURCES GEOPHYSCAL LBRARY Ref 6 ^(4 ^ THE EFFWT AT RABAUL OF SSMC SEA WAVES GENTRATED BY THE.GREAT.ALASKAN EARTHQUAKE OF, 28TWMARCH, 1964 by C.D. Branch The information contained in this report has been obtained by the Department of National Development, as part of the policy of the Commonwealth Government, to assist in the exploration and development of mineral resources. t may not be published in any form or used in a company prospectus without the permission in writing of the Director, Bureau of Mineral Resources, Geology and Geophysics.

2 THE EFFECT AT RABAUL OF SESMC SEA WAVES GENERATED BY THE GREAT ALASKAN EARTHQUAKE OF 28TH MARCH 1964 by C.D. Branch^BUREAU OF MNERAL RESOURCES GEOPHYSCAL LBRAil Records No. 1965/66 Ref^... CONTENTS Page SUMMARY 1 EARTHQUAKE AND WARNNG DATA 1 EFFECT OF SESMC SEA WAVES AT RABAUL 1 ANALYSS OF TDE GAUGE RECORD 2 TRAVEL TME AND OCEAN DEPTH 2 RECOMMENDATONS 3 LLUSTRATON PLATE 1: Tide gauge record at Rabaul of Seismic sea waves generated by the great Alaskan earthquake of 28th March,1964. The information contained in this report has been obtained by the Department of Yational Development, as part oof the policy of the Commonwealth Government^tsiassist in the exploration and development of mineralresources. t may not be published in any form or used in a company prospectus without the permission in writing of the Dirootor, Bureau of Mineral Resources, Geology and Geophysics. 2

3 SUMMARY A seismic sea wave generated by the great Alaskan earthquake of 28th March, 1964, arrived in Rabaul at 0125 L.T. on the 29th.^Theinitial wave height was four inches.^a possible second seismic sea wave arrived at 0723 and a wave at 0933 had a crest to trough height of 16 inches.^a maximum double amplitude of 24 inches was recorded at 1330, possibly caused by oscillations from the first and second seismic sea wave groups coming in phase. Oscillations of sea level due to this earthquake lasted four days.^the velocity of the first seismic sea wave was calculated to be 444 miles per hour, and the average ocean depth between Alaska and Rabaul is 9000 feet. EARTHQUAKE AND WARNNG DATA At G.M.T. on the 28th March, 1964, an earthquake of magnitude,8.5 (CGS) occurred at latitude 61.1 N and longitude 147.6'W, at a depth of 20 kilometres. A seismic sea wave was generated which caused extensive damage throughout the Gulf of Alaska, along the west coast of North America, and in Hawaii: A telegraphic bulletin advising that a seismic sea wave had been generated was issued from the Honolulu Magnetic Observatory to all stations in their seismic sea wave warning network in the Pacific.^The bulletin also advised the expected arrival time of the wave at the various stations.^rabaul is not in the warning network, but the bulletin was overheard by the duty officer at the Overseas Telecommunications Station, Rabaul, and passed to the Vulcanologist at 2000 L.T. (1000 G.M.T.). ^The Rabaul harbour master was also notified, and on his own initiative advised all boats to move into mid-stream. The first warning bulletin gave the expected arrival time of the wave at Guam as 1315 G.M.T. and at Samoa as 1430 G.M.T.. Later bulletins told of wave heights between 8 and 16 feet at Hawaii. ^The wave arrived half an hour later then expected at Guam and succeeding arrival times were changed accordingly. An arrival time at Rabaul between 1430 and 1600 G.M.T. was calculated.^attempts to contact outlying Administration centres by radio, particularly Kavieng and Lorengau, to warn them of a possibly seismic sea wave and to receive details of the wave should it arrive so that appropriate precautions could be taken at Rabaul, were unsuccessful because no radio schejule is maintained at night. t was thought unwise to broadcast warning of the wave over the A.B.C. and Administration radio stations because of the unwarranted panic it may have caused. EFFECT OF SESMC SEA WAVES AT RABAUL The first wave arrived at 1525 G.M.T. (0125 L.T.). No withdrawal of water preceeded the wave, and it boiled in over mud flats around the head of Simpson Harbour. A wave height of four inches was recorded on the tide gauge at the Main Wharf (Pl.l).^Succeeding waves arrived at 30 to 35 minute intervals and the fourth wave at 0315 L.T. had a trough to crest height of 10i inches. t was concluded that a destructive wave wol!ld not arrive at Rabaul and warning of the seismic sea wave wn.r withdrawn.

4 2. ANALYSS OF TDE GAUGE RECORD Wave activity due to the first seismic sea waves was recorded from 0125 L.T. until 0645 L.T. and forms the first seismic aea wave group (P1.1). ^At 0723 L.T. wave activity recommenced with a sudden withdrawal of three inches and at 0805 L.T. the ensuing smooth pattern of wave oscillations was abruptly disrupted.^t is thought that one or other of these two times represents the first arrival of a second seismic sea wave group, generated by an aftershock of the main Alaskan.earthquake.^The recorded trace of following waves is irregular, indicating inter- ^. ference between the first and second seismic sea wave groups. Possibly because of the interference the amplitude of some waves was increased, and at Rabaul a maximum crest to trough height of 16 inches was recorded at 0933 L.T. The second seismip sea wave group caused noticeable effects at Tabar sland (02'50'S., E) where a rise and fall of sea level of about 12 inches commenced at 0830 L.T, and continued with a peril of 15 mingtes for some hours;^numundo Plantation (05 32'S., E) reported that at 0845 L.T. the sea level rose about 12 inches and took about 15 minutes to fall to normal. This phenomenon occurred a further four times during the day. About 12 noon on the 29th.the wave motions due to the first and second seismic sea wave groups appear to have come in phase.^a series of symmetrical oscillations were recorded, with a period of 30 to 33 minutes, which increased in double amplitude from 13 inches at 1220 L.T. to a maximum of 24" at 1330 L.T., then decreased in amplitude and became increasingly irregular during the next six hours. A rise in sea level of four feet was reported from Cape Gloucester (western end of New Britain) about 1400 hours. rregular, small oscillations caused by the seismic sea waves continued until about 1600 L.T. on 1st April. TRAVEL TME AND OCEAN DEPTH Assuming that the first seismic sea wave group was generated at the same time as the earthquake, it means that the wave took 12 hours to travel the 5550 miles from Alaska to Rabaul.^This is an average velocity of 444 miles per hour. The average ocean depth between Alaska and Rabaul may be calculated using the following formula. h V 2 where h. average depth of ocean. V = velocity of way, g. acceleration due to gravity. Therefore, the average ocean depth between Alaska and Rabaul is 9000 feet.

5 t is of great importance to know the travel times for seismic sea waves so that if waves are generated by future earthquakes in the same area, their arrival time may be calculated reasonably accurately. ^This is particularly so for the Alaskan area which le highly seismic and from where more seismic sea waves must be expected. n the case of the March 1964 earthquake it was impossible to predict the arrival time of the wave within one or two hours, but with the data presented here, future predictions will be far more precise. The Chilean area is another from which seismic sea waves may be expected.^earthquakes in that area in May 1960 generated seismic sea waves which reached Rabaul. For reference and comparison, the data calculated by Taylor & Barrie (1960) are included here: velocity of wave 385 m.p.h., and an average ocean depth of 6790 feet along the wave path. RECOMMENDATONS t is considered vital for the safety of the sea board population in the Territory that adequate warning of seismic sea waves be received at the major centres, and that radio channels be maintained to disseminate the information to outlying centres.^at present, the receipt of warning from the Honolulu Magnetic Observatory, which maintains a seismic sea wave warning network, is haphazard because no centre in the Territory is a station in the warning network.^to overcome this, a submission has been sent to tbe Administrator requesting that application be made to join the network, and for some responsible authority in the Territory to receive and disseminate the warning bulletins. REFERENCE TAYLOR, G.A. & BARRE, J., Tsunamis in the Territory of New Guinea from South American earthq6akes May Bur.Min.Resour.Aust.Rec., 1960/65 (unpubl.).

6 ^ TDE^GAUGE^RECORD GENERATED^BY T H E^GREAT AT^RABAUL^0S^SESMC^SEA WAVES^Plate 1 ALASKAN^EARTHQUAKE^OF 28TH MARCH 1964^. NCREASED^AMPLTUDE^DUE^ ste t! ONSET^SECOND^SE.ts m(c. SEA WAVE GRouP OR. 2.1 _..ri 2'6" / LocAL TME! HOURS^01^. ONSET FRST SESMC SEA WAVE GlzouP 0125 HR-S ^ z 9 TN MARCH 1964 ORG K TME of EARTHQUAKE. : 1336 (9.AB. LocAL TNAE) 28Th taarch.^(0336 G. si.t) ^^^ o3^o4^05^06^07.^08 ^ 09 10^11 NOTCEABLE EFFECTS^AT TA BAR. S^(Ca So'S, E), NUMUND 0^PN^(05 32' 5, SO or^e) RSE N SEA LEVEL CAPE GLOUCESTER ABOUT 1400 HouR.S 1^ ^15 of 44 AT (os 28' S, E) FR.ST AND second WAVE 6,RouPS ARRVtKG^114.PHASE g LAST^NOTCEABLE EFFECT DuE To SESMC SEA WAVES^ABOUT.^---> WS^1ST APRL^ % ^1^1 15^16^17^18 ^^ 1^1 19^2.o^21^22^ ^^^ 02^03^04^05^06 30TH KAARCH 1964 Comp (Zed on..c/ cleau.w7 4.. C.D. ap cinch, Yalca n lop ca 101 s erwatory,, to.6 az d. Bureau of Mineral Resources, Geology and Geophysics To accompany Record /965/ /A2127

COMMONWEALTH OF AUSTRALIA DEPARTMENT OF NATIONAL DEVELOPMENT. RECORD No. 1964/160. BUREAU OF Inv:AL It. ireoropn GECCIKICAL LIMY

ic14.41-(1(-0 eopy 3 COMMONWEALTH OF AUSTRALIA DEPARTMENT OF NATIONAL DEVELOPMENT BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS RECORD No. 1964/160 BUREAU OF Inv:AL It. ireoropn GECCIKICAL LIMY EeL^S.*.