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GRAVITY PROGRAM S c i e n t i s t Making a Gravimeter Survey on Blue G l a c i e r
GRAVITY PROGRAM Page A. Organization of Technical Panel on Seismology & Gravity 237 B. Summary of Panel Actions 238 C. Proje c t Objectives and Results 238 5.1 A n t a r c t i c Gravity Personnel 239 5.2 A n t a r c t i c Gravimeter 239 5.4 A n t a r c t i c Gravimeters 239 5.6 Reduction of Traverse Gravity Data 240 5.7 Pendulum Measurements of Gravity 241 5.8 Gravimeter Measurements 243 5.10 Marine Gravity Measurements 244 5.12 Mean R i g i d i t y of the Earth-Earth Tide Observations 246 5.16 A n t a r c t i c Pendulum Measurements 249 5.18 Reduction of Pendulum and Gravimeter Data 250 5.19 Reduction of Marine Gravity Measurements 251 236
GRAVITY A. Organization of Technical Panel on Seismology and Gravity 1. Establishment of the Panel. I n December 1954, earth s c i e n t i s t s were i n v i t e d to p a r t i c i p a t e i n the work of the U.S. National Committee f o r the IGY by serving as mem- bers of the Technical Panel on Seismology and Gravity. At the f i r s t meeting of the Panel, J.B. Macelwane was elected chairman, Maurice Ewing, v i c e chairman, and Howard E. T a t e l , secretary. Upon the death of Prof. Macelwane i n 1956, Perry Byerly was elected chairman of the Panel. The IGY Technical Panel on Glaciology had been assigned the r e s p o n s i b i l i t y f o r a n t a r c t i c traverses on which seismic and g r a v i t y as w e l l as g l a c i o l o g i c a l measurements were made. W i l l i a m 0. F i e l d , chairman of the Glaciology Panel, was i n v i t e d to be a member of the Panel on Seismology & Gravity, e s p e c i a l l y to provide l i a i s o n between the two panels; he remained a member of the Seismology & Gravity Panel u n t i l the spring of 1958. 2. Composition of the Panel. ( A f f i l i a t i o n at time of appointment.) a. Panel Members Robert F. Beers Hugo Benioff Perry Byerly (Chairman from 1956) A.P. Crary Dean S. Carder Maurice Ewing W i l l i a m 0. F i e l d ( U n t i l A p r i l 1958) J.B. Macelwane (Died 1956) Donald R. Rice Howard E. T a t e l (Died Nov. 1957) Merle A. Tuve George P. Woo Hard J. Lamar Worzel b. Consultants Carl 0. Alexis J.N. Adkins H.S. Haskell C a l i f o r n i a I n s t i t u t e of Technology U n i v e r s i t y of C a l i f o r n i a Geophysics Research D i r e c t o r a t e (AFCRL) U.S. Coast and Geodetic Survey Lamont Geological Observatory American Geographical Society St. Louis U n i v e r s i t y U.S. Coast and Geodetic Survey Department of T e r r e s t r i a l Magnetism, Carnegie I n s t i t u t i o n of Washington Department of T e r r e s t r i a l Magnetism, Carnegie I n s t i t u t i o n of Washington U n i v e r s i t y of Wisconsin Lamont Geological Observatory O f f i c e of Naval Research O f f i c e of Naval Research Geophysics Research Di r e c t o r a t e (AFCRL) c. Secretariat (IGY S t a f f ) John Hanessian, J r . (Jan. 1955 - Feb. 1956, A p r i l 1957 Stanley Ruttenberg (February 1956 - A p r i l 1957) Pembroke J. Hart (From May 1958) 3. Panel Meetings. There were eight meetings of the Panel. F i r s t Meeting Second Meeting Thi r d Meeting Fourth Meeting F i f t h Meeting May 1958) January 25, 1955 Washington, D.C. February 2, 1956 Washington, D.C. November 17, 1956 Washington, D.C. A p r i l 27, 1957 Washington, D.C. November 2, 1957 Washington, D.C. 237
GRAVITY Si x t h Meeting May 2, 1958 Washington, D.C. Seventh Meeting November 29, 1958 Berkeley, C a l i f o r n i a Eighth Meeting A p r i l 2, 1959 Tucson, Arizona B. Sunnnary of Panel Actions 1. Development of Program. I n a d d i t i o n to considering the task of working out an IGY program i n seismology and g r a v i t y which would be of appropriate s c i e n t i f i c value, the Panel l a i d great stress on the fundamental c r i t e r i a established by CSAGI, espe- c i a l l y these: that the programs be e i t h e r synoptic or i n t e r n a t i o n a l i n scope or char- acter. This was considered e s s e n t i a l since much of the most s i g n i f i c a n t c u r r e n t research i n these f i e l d s d i d not f a l l w i t h i n CSAGI d e f i n i t i o n s , e.g. seismic model studies. The IGY g r a v i t y program e a r l y envisioned by the Panel included: a. Gravity programs on the oversnow traverses I n the A n t a r c t i c b. Pendulum and gravimeter networks. Including a n t a r c t i c gravimeter s t a t i o n s c. Submarine g r a v i t y measurements d. Data reduction and p u b l i c a t i o n The o r i g i n a l program was subsequently expanded to include e a r t h t i d e studies made at an i n t e r n a t i o n a l network of s t a t i o n s and the expansion of the g r a v i t y measurements at sea to Include the newly developed sea-surface Graf gravimeter. Several a d d i t i o n a l p r o j e c t s of great I n t e r e s t to the Panel that were proposed a f - t e r the e a r l y formulation of the IGY program were not possible to include i n the f i n a l program, p a r t l y as a r e s u l t of l i m i t e d funds and p a r t l y because they were marginal i n r e l a t i o n to the CSAGI p r i o r i t i e s regardless of t h e i r s c i e n t i f i c m e r i t . For the IGC-59 program, the Panel s p e c i f i c a l l y urged the co n t i n u a t i o n of the pen- dulums and gravimeter network observations and the sea-surface gravimeter measurements. C. Project Objectives and Results 1. Summary of Program. The g r a v i t y program consisted of research a c t i v i t i e s i n : a) pendulum and gravimeter measurements, b) submarine pendulum g r a v i t y measurements and c) earth t i d e studies. Projects provided f o r the procurement, i n s t a l l a t i o n and operation of gravlmeters at several new s t a t i o n s and on oversnow traverses. Other p r o j e c t s were established f o r the c o l l e c t i o n , reduction, analysis and p u b l i c a t i o n of data. 2. Order of Project Description. The pr o j e c t s that are described i n the f o l l o w i n g pages are i n numerical order to correspond w i t h the o r i g i n a l f o rmulation of the pro- gram. For convenience, the p r o j e c t s are grouped below to r e f l e c t s i m i l a r i t y of pur- pose. A n t a r c t i c Gravity Personnel 5.1 A n t a r c t i c Equipment-Gravimeter 5.2, 5.4 Reduction of Gravity Data 5.6, 5.18, 5.19 Pendulum Measurements of Gravity 5.7, 5.16 Gravimeter Measurements 5.8 Marine Gravity Measurements 5.10 Earth Tides 5.12 3. Cancelled P r o j e c t s . Former p r o j e c t s bearing the f o l l o w i n g numbers were e l i m i n - ated from the program or combined w i t h other p r o j e c t s : 5.3, 5.5, 5.9, 5.11, 5.13, 5.14, 5.15, 5.17. 238
GRAVITY Project 5.1 - A n t a r c t i c Gravity Personnel 1. Objectives. This p r o j e c t , administered by the A r c t i c I n s t i t u t e of North America, provided f o r the h i r i n g of personnel to make g r a v i t y measurements during the g l a c i o - l o g i c a l -geophysical traverses and f o r observations at the various a n t a r c t i c s t a t i o n s . 2. Operations. Personnel were selected and screened through the several research groups t h a t were responsible f o r organizing the traverse operations, and through the G l a c i o l o g i c a l Headquarters O f f i c e (see p r o j e c t 4.9). Men who were selected were h i r e d through t h i s p r o j e c t , given i n d o c t r i n a t i o n t r a i n i n g , and supplied w i t h a n t a r c t i c c l o t h - i n g , through cooperation w i t h the U.S. Navy Task Force 43 and the U.S. Army Quartermas- t e r Corps. Insurance and medical expenses were covered out o f t h i s p r o j e c t . S c i e n t i f i c instruments and supplies were provided through other p r o j e c t s , as were the traverse operations. A f t e r the operations were over, the s c i e n t i f i c personnel were supported under other p r o j e c t s to analyze t h e i r data. 3. Personnel. The a d m i n i s t r a t i v e supervision of t h i s p r o j e c t was given by W.A. Wood, AINA. Eight s c i e n t i s t s were employed under t h i s grant during the two operating sea- sons of IGY. Project 5.2 - A n t a r c t i c Gravimeter 1. Objectives. This p r o j e c t , at the Lament Geological Observatory, Columbia Univer- s i t y provided f o r the purchase of a portable gravimeter f o r use on the oversnow t r a - verses. The instrument was used by personnel employed under p r o j e c t 5.1; data were analyzed under p r o j e c t 5.6. 2. Operations. A Worden gravimeter was purchased and packed f o r shipment to Antarc- t i c a ; insurance was provided under t h i s p r o j e c t . 3. Personnel. The equipment was purchased under the supervision of Maurice Ewing. Project 5.4 - A n t a r c t i c Gravimeters 1. Objectives. This p r o j e c t of the U n i v e r s i t y of Wisconsin provided f o r the purchase of portable gravimeters f o r use on the oversnow traverses. The instruments were used by personnel employed under p r o j e c t 5.1; data were analyzed under p r o j e c t 5.6. 2. Operations. Several used gravimeters were purchased and reconditioned and modi- f i e d i n the shops at the U n i v e r s i t y . Three gravimeters were borrowed and modified. Insurance was provided f o r the borrowed gravimeters. 3. Personnel. The equipment was purchased and reconditioned under the supervision of George P. Uoollard. 239
GRAVITY Project 5.6 - Reduction of Traverse Gravity Data 1. Obiectives. This p r o j e c t at the U n i v e r s i t y of Wisconsin provided f o r the reduction and p u b l i c a t i o n of g r a v i t y data taken during the oversnow traverses i n A n t a r c t i c a car- r i e d out from L i t t l e America, Byrd and E l l s w o r t h Stations during the a n t a r c t i c summers of 1957-58 and 1958-59. 2. Operations. Raw instrument readings were taken at 3 to 5-mile i n t e r v a l s on a l l the oversnow traverses and reduced to obtain values of g r a v i t y . T h e o r e t i c a l g r a v i t y values were computed, considering the e l e v a t i o n above sea l e v e l and the l a t i t u d e cor- r e c t i o n , and anomalies were then derived f o r f r e e - a i r and Bouguer anomalies from com- parisons of the observed and computed values. The i n t e r p r e t a t i o n of the data was int e g r a t e d w i t h the i n t e r p r e t a t i o n of the seismic data (see p r o j e c t 11.7), since these data are i n t i m a t e l y r e l a t e d and the seismic data are e s s e n t i a l f o r i n t e r p r e t i n g the g r a v i t y data. 3. Personnel. George P. Woollard was p r o j e c t d i r e c t o r , s c i e n t i s t s who p a r t i c i p a t e d i n the work were Edward T h i e l , Ned Ostenso, John Behrendt, Edwin Robinson, James Sparkman, Hugh Bennett, John Weihaupt, Forrest Dowling, Thomas Landon and Perry Parks. 4. Results. See p r o j e c t 11.7 f o r discussion of a n t a r c t i c bedrock surface and c r u s t a l s t r u c t u r e as deduced from the traverses. The g r a v i t y data are published i n part i n a monograph (see below) and i n part i n the series of A n t a r c t i c G l a c i o l o g i c a l IGY Report of the American Geographical Society. 5. Bibliography. J.C. Behrendt: "IGY A n t a r c t i c Oversnow Traverse Program, 1957-58." IGY Glac. Rept.. Series No. 1, Amer. Geogr. Soc, 1958. E.G. T h i e l , C.R. Bentley, N.A. Ostenso and J.C. Behrendt: "Oversnow Traverse Programs Byrd and E l l s w o r t h Stations, A n t a r c t i c a , 1957-59, Seismology, Gravit y , and Magnetism." IGY Glac. Rept.. Series No. 2, Amer. Geogr. Soc, 1959. E.G. T h i e l and N.A. Ostenso: "The Contact of the Ross Ice Shelf w i t h the Continental Ice Shelf, A n t a r c t i c a . " Jour. G l a c . v o l . 3, no. 29, pp. 823-32, 1961. J.G. Weinhaupt: "Geophysical Studies i n V i c t o r i a Land, A n t a r c t i c a . " Res. Rept. Series No. 1, Univ. of Wisconsin, 123 pp., 1961. G.P. Woollard and J.C. Rose: " I n t e r n a t i o n a l Gravity Measurements." Soc.. Explor. Geophysicists. 518 pp., 1963. 240
GRAVITY Project 5.7 - Pendulum Measurements of Gravity 1. Objectives. This p r o j e c t , c a r r i e d out i n cooperation w i t h the Woods Hole Oceano- graphic I n s t i t u t i o n and Cambridge U n i v e r s i t y , England, was established i n order to com- pl e t e a series of world l i n e s of f i r s t - o r d e r pendulum g r a v i t y s t a t i o n s , along meridians extending between the two polar regions. These measurements would serve as standardi- zation ranges (over changes 6f 5000 mgals) f o r the c a l i b r a t i o n of geodetic gravimeters to w i t h i n 1 mgal, and as i n t e r n a t i o n a l c o n t r o l points f o r the i n t e g r a t i o n of g l o b a l g r a v i t y data. 2. Operations. Teams of s c i e n t i s t s made several t r i p s , f l y i n g MATS and commercial a i r l i n e s , to e s t a b l i s h four meridian l i n e s of observations, taking advantage of pre- v i o u s l y occupied l o c a t i o n s , where possible, and making t i e s between the l i n e s so as to provide one reference datum. The Un i v e r s i t y of Wisconsin Gulf quartz pendulums and the Invar pendulums of Cambridge U n i v e r s i t y , England, were used i n order to check on possible systematic e r r o r s between d i f f e r e n t sets o f instruments. I n general, obser- vations took only 36-48 hours at each l o c a t i o n . The locations of observations were as follows: Line A: Alaska to Chile Pt. Barrow, Alaska Fairbanks, Alaska Whitehorse, Yukon, Canada Edmonton, Alberta, Canada Great F a l l s , Montana Denver, Colorado Houston, Texas Monterrey, Mexico Mexico D.F., Mexico Balboa, Canal Zone Bogota, Colombia Quito, Ecuador Lima, Peru La Paz, B o l i v i a Antofagasta, Chile Santiago, Chile Punta Arenas, Chile Line B: Canada to Argentina Ottawa, Ontario, Canada Woods Hole, Massachusetts Palisades, New York Washington, D.C. Charleston, South Carolina Miami, F l o r i d a Key West, F l o r i d a Caracas, Venezuela Belem, B r a z i l Rio de Janeiro, B r a z i l Buenos Aires, Argentina Note: Line B t i e d to Line A by d i r e c t connections: Washington, D.C. - Madison, Wisconsin - San Francisco, C a l i f o r n i a Balboa, Canal Zone - Caracas, Venezuela Santiago, Chile - Buenos A i r e s , Argentina Line C: Norway to East A f r i c a Hammerfest, Norway Oslo, Norway Copenhagen, Denmark Bad Harzburg, West Germany Teddington, England Frankfurt a/M., West Germany Rome, I t a l y T r i p o l i , Libya Cairo, UAR (Egypt) Khartoum, Sudan Asmara, Ethiopia Nair o b i , Kenya Line D- Japan to A n t a r c t i c a Chitose, Japan Kyoto, Japan Tokyo, Japan Okinawa Clark AFB (Manila) P h i l i p p i n e s Hong Kong Singapore, Malaya Darwin, A u s t r a l i a Cairns, A u s t r a l i a Townsville, A u s t r a l i a Brisbane, A u s t r a l i a Sydney, A u s t r a l i a 241
GRAVITY Lusaka, No. Rhodesia V i c t o r i a F a l l s , So. Rhodesia Johannesburg, Republic of S. A f r i c a Capetown, Republic of S. A f r i c a Melbourne, A u s t r a l i a Hastings, New Zealand Wellington, New Zealand Christchurch, New Zealand Dunedln, New Zealand Ross Is l a n d (McMurdo), A n t a r c t i c a Mawson, A n t a r c t i c a Mirny, A n t a r c t i c a Note: Line D t i e d to Line A from: Tokyo, Japan - Clark AFB, P h i l i p p i n e s and Christchurch, New Zealand v i a Honolulu, Hawaii and San Francisco, C a l i f , to Denver, Colorado Line A t i e d to Line C from: Denver, Colorado v i a Madison, Wisconsin and Washington, D.C. to Teddlngton, England European - West Coast of A f r i c a Teddlngton, England Paris, France Lisbon, Portugal Dakar, F. West A f r i c a Accra, Ghana L e o p o l d v i l l e , Congo Mid-Contlnent North America Huron, South Dakota B e l o l t , Kansas Tulsa, Oklahoma Houston, Texas 3. Personnel. This p r o j e c t was under the supervision of G.P. Woollard. Associated w i t h him were John Rose, Robert Iverson, Thomas Landon, Ned Ostenso, Oscar S t r i c k l a n d and Richard L o n g f i e l d of the U n i v e r s i t y of Wisconsin and B.C. Browne and J.M. Jackson of Cambridge U n i v e r s i t y , England. 4. Data. Data from these observations have been published i n a recent compilation of g r a v i t y measurements, l i s t e d below. 5. Results. The o r i g i n a l o b j e c t i v e of providing a world-wide network of f i r s t - o r d e r g r a v i t y s t a t i o n s was accomplished, and r e c e n t l y i t was also possible t o use the same i-nstrumencs to observe at Potsdam, the i n t e r n a t i o n a l g r a v i t y datum, thus t y i n g the e n t i r e g l o b a l system together. 5. Bibliography. G.P. Woollard and J.C. Rose: " I n t e r n a t i o n a l Gravity Measurements." Soc. Explor. Geophyslcists. 518 pp., 1963. G.P. Woollard: "An Evaluation of the Potsdam Datum." Hawaii I n s t i t u t e of Geophysics, S c i e n t i f i c Report No. 1, September 1963. 242
GRAVITY Project 5.8 - Gravimeter Measurements 1. Objectives. This p r o j e c t at the U n i v e r s i t y of Wisconsin was undertaken to provide: a. A network of g r a v i t y c o n t r o l bases on an i n t e r n a t i o n a l basis; b. Regional networks of g r a v i t y observations (10 to 20 mile spacing) along w i t h traverses i n areas where there were no e x i s t i n g data, i n cooperation w i t h l o c a l geo- p h y s i c i s t s ; and c. Ties between pendulum g r a v i t y base points and connections to l o c a l a i r p o r t g r a v i t y s i t e s used I n world g r a v i t y network. 2. Operations. Teams of observers, using modified geodetic gravimeters t h a t had been selected f o r s t a b i l i t y and r e l i a b l e d r i f t r a t e s , v i s i t e d remote s i t e s and, using MATS and commercial a i r c r a f t , occupied s t a t i o n s i n Central and South America, Europe, Af- r i c a , A u s t r a l i a and i n the A r c t i c and A n t a r c t i c , and also along the m e r i d i a l l i n e s of the pendulum observations (see p r o j e c t 5.7). Connections were made between the var- ious a n t a r c t i c s t a t i o n s and New Zealand. A gravimeter was loaned to the B r i t i s h Trans- A n t a r c t i c Expedition, where g r a v i t y observations were made approximately every 15 miles across A n t a r c t i c a and to the C a l i f o r n i a Exploration Co. who established bases i n Cen- t r a l and South America f o r interconnecting o i l company surveys i n these areas. Routes followed by the gravimeter teams followed c l o s e l y c i r c u i t s so tha t d r i f t rates could be checked upon closure of a loop of s t a t i o n s . 3. Personnel. This work was under the supervision of G.P. Woollard. Associated w i t h him were James Weinman, James Sparkman, Edward T h i e l , Robert Iverson, Thomas S. Landon, John C. Behrendt, Richard L o n g f l e l d , J u l i o Monges Caldera and Geoffrey Oldham. 4. Data. Gravity values f o r the p r i n c i p a l I n t e r n a t i o n a l bases established under t h i s program were published i n a recent volume by Woollard (see below). 5. Results. The comparative studies c a r r i e d out through m u l t i p l e connections between widely separated points having much the same value of g r a v i t y as Rome and New York, L i s - bon and Buenos A i r e s , Rome and Capetown, i n d i c a t e that the i n t e r n a t i o n a l network of gravimeter bases has a r e l i a b i l i t y of about 10.3 mgal. This represents about an order of magnitude improvement i n the q u a l i t y of the c o n t r o l t h a t existed previously. 6. Bibliography. "Results f o r a Gravity Control Network a t A i r p o r t s I n the United States." Geophysics, v o l . 23, no. 3, 1958, pp. 520-55. J.C. Behrendt and G.P. Woollard: "An Evaluation o f the Gravity Control Network i n North America." Geophysics, v o l . 26, no. 1, 1961, pp. 57-76. G.P. Woollard and J.C. Rose: " I n t e r n a t i o n a l G r avity Measurements." Soc. Explor. Geophyslcists. 518 pp. 1963. G.P. Woollard and J u l i o Monges Caldera: "Gravity Control i n Central and South America." ( I n press.) 243
GRAVITY Project 5.10 - Marine Gravity Measurements 1. Objectives. This p r o j e c t at the Lamont Geological Observatory, Columbia Univer- s i t y , was established to make possible extended measurements of the earth's g r a v i t a t i o n f i e l d at sea, m order to f u r t h e r geodetic e f f o r t s at determination of the geoid, and to study the geological processes underlying the r e l a t i o n of continents and ocean ba- sins and the earthquake epicenter b e l t s of the earth. The p r o j e c t provided f o r the purchase of a Graf sea surface gravimeter, and i t s m o d i f i c a t i o n , and f o r the construc- t i o n of the more conventional Vening Meinesz pendulum gravimeters f o r use on submarines. 2. Operations. The Graf gravimeter was mounted on a g y r o - s t a b i l i z e d p l a t f o r m and used successfully to obtain g r a v i t y observations i n the open sea on board the USS COM PASS ISLAND. Some submarine time was also obtained f o r use of the Vening Meinesz ap- paratus, through the cooperation of the navies of South A f r i c a , A u s t r a l i a , and Great B r i t a i n . The i n i t i a l t e s t s on the COMPASS ISLAND were made several hundred miles southeast of New York, moving from the deep ocean basin across the c o n t i n e n t a l slope and onto the c o n t i n e n t a l s h e l f . The readings, which were reduced very q u i c k l y as com- pared w i t h submarine data, compared favorably w i t h g r a v i t y observations taken w i t h pendulums on board the submarine USS TUSK ten years e a r l i e r . One Vening Meinesz pendulum apparatus was constructed and assembled completely. Parts f o r two others were constructed but have not been assembled. 3. Personnel. J. Lamar Worzel was p r o j e c t d i r e c t o r ; associated w i t h him were Matthew Smith, Robert Wall, Hugh Traphagen, Mark Langseth, and Manik Taiwan!. 4. Results. During the IGY, the comparative t e s t s between the Graf sea gravimeter and the Vening Meinesz pendulums were made aboard the same submarine. These t e s t s showed s t a t i s t i c a l l y that the Graf sea gravimeter gave r e s u l t s i n e x c e l l e n t agreement w i t h the pendulum measurements. I t was concluded t h a t i t was also l i k e l y t h a t sur- face ship measurement could be made w i t h the Graf sea gravimeter mounted on a s t a b i l - ized p l a t f o r m . Tests were made on USS COMPASS ISLAND, an 800 ton f i n - s t a b i l i z e d Naval a u x i l i a r y , w i t h the Graf sea gravimeter mounted on a g y r o - s t a b i l i z e d p l a t f o r m . The r e s u l t s were ex c e l l e n t and showed th a t observations were possible on a surface vessel f o r a much larger p r o p o r t i o n of time than was expected. The main problems l i m i t i n g the accuracy were those r e l a t e d t o the navigation of the ship and the determination of the speed over the ground. Continuous records of g r a v i t y were obtained on 6000 miles of tr a c k over such features as a c o n t i n e n t a l margin, oceanic basins, the M i d - A t l a n t i c Ridge, seamounts, and the S t r a i t of G i b r a l t a r . A temporary stable p l a t f o r m was i n s t a l l e d on R.V. VEMA, a 200 f t . , 500 ton a u x i l - i a r y schooner. Gravity measurements were made about 15 per cent of the time on VEMA cruise 15 which circumnavigated the South American continent. Especially notable were continuous p r o f i l e s across the Middle America Trench and across the trench and i s l a n d arc s t r u c t u r e of the Windward Caribbean i s l a n d s . I n cooperation w i t h the A u s t r a l i a n s , pendulum measurements were made aboard the B r i t i s h submarine HMS TELEMACHUS across the Tasman Sea, between the islands of New Zealand, on several crossings of the Tonga Trench, and on the F i j i p l a tform. I n cooperation w i t h the Republic of South A f r i c a pendulum measurements were made on a delayed cruise on the B r i t i s h submarine HMS ACHERON i n the v i c i n i t y of the Repub- l i c of South A f r i c a and from Durban to Mombasa to Karachi. 244
GRAVITY Bibliography. a. Papers Presented at Meetings. J. Lamar Worzel "Tests of Graf Sea Gravimeter." Paper Presented at the AGU Meetings i n Washington, D.C, A p r i l 29-May 2, 1957. J Lamar Worzel: "Gravity Measurements on a Surface Ship With the Graf Sea Gravimeter." Paper Presented at AGU Meeting i n Washingtbn, D.C, May 5-8, 1958. J. Lamar Worzel "Continuous Gravity Measurements on a Surface Ship With the Graf Sea Gravimeter." Paper Presented at the 28th Annual Meeting of the Society of Exploration Geophysicists i n San Antonio, Texas, October 13-18, 1958. Manik Talwani, J. Lamar Worzel and Maurice Ewing: "Gravity Anomalies and Crust a l Section Across the Tonga Trench." Paper Presented at the 40th Annual Meeting of AGU i n Washington, D.C, May 4-7, 1959. J. Lamar Worzel: "Continuous Gravity Measurements on a Surface Ship With the Graf Sea Gravimeter." Paper Presented O r a l l y at the Pans Meeting of the I n t e r n a t i o n a l Gravimetric Commission, September 14-20, 1959. b. Published Papers. J. Lamar Worzel and A. Graf: "Comparison of the Graf Sea Gravimeter With the Vening Meinesz Apparatus on Board the Submarine USS BBCUNA." B u l l . Geod., no. 45, 1957, pp. 38-53, " F i r s t Sea Surface Gravimeter." IGY B u l l . . no. 8, February 1958. J. Lamar Worzel: "Continuous Gravity Measurements on a Surface Ship With the Graf Sea Gravimeter." J. Geophys. Res., v o l . 64, no. 9, Sept. 1959, pp. 1299-1315. 245
GRAVITY Project 5.12 - Mean R i g i d i t y of the Earth - Earth Tide Observations 1. Obiectives. This p r o j e c t at the I n s t i t u t e of Geophysics, U n i v e r s i t y of C a l i f o r n i a , Los Angeles, provided earth t i d e observations w i t h h i g h l y s e n s i t i v e automatically r e - cording gravimeters at twelve s t a t i o n s d i s t r i b u t e d around the earth. Seven of the l o - cations were on oceanic i s l a n d s , f i v e ( i n c l u d i n g Saigon) were c o n t i n e n t a l s t a t i o n s . The objectives were the determination of improved values of the r i g i d i t y of the earth at t i d a l periods of approximately 12 and 24 hours, i n v e s t i g a t i o n of the dependence of the observations upon geographic p o s i t i o n , and the measurement, i f possible, of phase lags associated w i t h the components of t i d a l response of the s o l i d earth. 2. Operations. At each of the t h i r t e e n s t a t i o n s occupied, observations were taken throughout u s e f u l i n t e r v a l s of 33 to 40 days w i t h a LaCoste-Romberg earth t i d e g r a v i - meter. I n order to allow the instruments to s e t t l e down to a slow rate of d r i f t before s t a r t i n g the observations proper, several days of a d d i t i o n a l i n i t i a l recordings were taken at each s t a t i o n . Observations were successfully completed a t : Glendora, C a l i f . , Honolulu, Hawaii; Wake I s l a n d , Baguio C i t y , P h i l i p p i n e s ; Saigon, Vietnam, New D e l h i , I n d i a ; Bermuda; Bukavu, Congo; and Bunia, Congo; T r i e s t e , I t a l y ; and Winsford and Bids- ton, England. At the Azores, excessive microseismic disturbances during the passage of a deep barometric depression ruined the record. Unfortunately, i t was necessary to abandon the observation planned at I s t a n b u l because of damage to one of the i n s t r u - ments. Arrangements f o r these observations were made by the IGY Committees of the countries concerned. Transportation and shipping were furnished by MATS through the cooperation of ONR. The f i e l d work was divided between E.A. Kraut and R.F.S. Forbes, operating independently w i t h d i f f e r e n t gravimeters. The graphical records were read at half-hour i n t e r v a l s , w i t h a least read-out count of 1/2 microgal, by an automatic reader (the Benson-Lehner Corp. OSCAR) which recorded the readings on punched cards. A t a b u l a t i o n machine was used to make t y p e w r i t t e n cop- ies f o r the data c o l l e c t i n g centers of the IGY. The punched cards can also be repro- duced f o r any organization p r e f e r r i n g the information i n t h i s form. Reduction of the observations i s more adequately described i n the l a s t reference c i t e d , (Harrison, Ness, Longman, Forbes, Kraut, S l i c h t e r , 1963). 3. Personnel. This p r o j e c t was under the d i r e c t i o n of L.B. S l i c h t e r , J.T. P e t t i t , Glen L. Brown, Alan Day, J.C. Harrison, E.A. Kraut, R.F.S. Forbes, N.F. Ness, I.M. Longman, and A. Lachenbruch p a r t i c i p a t e d i n the observations or data reduction. 4. Data. The earth t i d e data were tabulated according to the CSAGI recommendation and forwarded to the World Data Center f o r Earth Tides, Observatoire Royal de Belglque, Brussels, Belgium; they are also a v a i l a b l e at UCLA. 5. Results. The r a t i o of the measured amplitude of a t i d a l c o n s t i t u e n t to i t s theo- r e t i c a l amplitude on a r i g i d e a r t h i s c a l l e d the gravimetric f a c t o r f o r that c o n s t i - tuent. The constituents f o r which the observations were s i g n i f i c a n t are the two major semi-diurnal c o n s t i t u e n t s M2, S2K2. and the two major d i u r n a l c o n s t i t u e n t s Oj^P^Kj^. The gravimetric f a c t o r s f o r each of these four constituents as observed at each of twelve s t a t i o n s are p l o t t e d m Figure 1. The e r r o r l i m i t s are also i n d i c a t e d i n F i g - ure 1. These r e s u l t s , e s p e c i a l l y f o r the case of the large M2 component, show v a r i - ations w i t h geographic p o s i t i o n which are s i g n i f i c a n t l y beyond l i m i t s of observational e r r o r . The M2 gravimetric f a c t o r at New Delhi i s s i g n i f i c a n t l y low, and the average f a c t o r f o r the seven i s l a n d s t a t i o n s i s larger than that f o r the f i v e Continental Sta- t i o n s , New D e l h i , Saigon, Bunia, T r i e s t e , Lwiro--(Saigon i s regarded as c o n t i n e n t a l because of the extensive shallow seas and Island masses i n i t s neighborhood and the large distances to the deep ocean.) 246
GRAVITY MEAN AND STATIC SULLEN B STATIC BULLEN B 0. COMPONENT P, K, COMPONENT MEAN MEAN 12-HOUR BULLEN B 12-HOUR BULLEN B Mj, COMPONENT $2 K2 COMPONENT Figure 1. Gravimetric f a c t o r s w i t h e r r o r l i m i t s i n comparison w i t h t h e i r mean values and computed values f o r the Bullen B earth model. Points are p l o t t e d i n the order of Honolulu Glendora, Wake, Manila, Saigon, New De l h i , Bunia, T r i e s t e , Bidston, Bermuda. Lwiro. WlTiBrni-H ' 7 Lwiro, Winsford. 247
GRAVITY E f f o r t s to determine s i g n i f i c a n t phase lags i n each of these t i d a l components were made. The large M2 component i s best suited f o r t h i s purpose. The mean M2 phase lag was small, only 0.8°, but the average scatter of i n d i v i d u a l observations without r e - gard to sign from t h i s mean was large, 2.8°. The determination of phase i s c e r t a i n l y not of s a t i s f a c t o r y p r e c i s i o n . The geographic di f f e r e n c e s i n the t i d a l y i e l d i n g deserve f u r t h e r study. These differences may reveal a mosaic-like s t r u c t u r e f o r t i d a l deformations, i n which the cru s t tends to y i e l d i n large i n d i v i d u a l blocks, w i t h the displacements concentrated along the bounding surfaces of adjacent blocks. 6. Bibliography. (The l i s t e d papers were generally reported at AGU, or lUGG, or other meetings, p r i o r to p u b l i c a t i o n . ) H. Benioff, J.C Harrison, L.H. LaCoste, W.H. Munk, L.B. S l i c h t e r : "Searching f o r the Earth's Free O s c i l l a t i o n s . " J. Geophys. Res., v o l . 64, no. 9, pp. 1334-37, 1959. J.T. P e t t i t , L.B. S l i c h t e r , and L. LaCoste: "Earth Tides." Trans.. AGU. v o l . 34, no. 2, 1953, pp. 174-184. J.T. P e t t i t : "Tables f o r the Computation of the T i d a l Accelerations of the Sun and Moon." Trans. AGU. 35, 1954. I . M. Longman: "Formulas f o r Computing the T i d a l Accelerations Due to the Moon and the Sun." J. Geophys. Res., v o l . 64, 1959, pp. 2351-2355. I.M. Longman: "The I n t e r p o l a t i o n of Ea r t h - t i d e Records." J. Geophys. Res., v o l . 65, 1960, pp. 3801-3803. L.B. S l i c h t e r , M. Caputo: "Deformation of an Earth Model by Surface Pressures." J. Geophys. Res., v o l . 65, no. 12, I960, p. 4151. L.B. S l i c h t e r : " E a r t h - t i d e s . " McGraw-Hill Encyclopedia of Science and Technology. 4, 1960, pp. 346-351. L.B. S l i c h t e r , "Gravity Tide Measurements." Trans. AGU. v o l . 41, no. 2, pp. 1960-61. M. Caputo: "Deformation of a Layered Earth by an A x i a l l y Symmetric Surface Mass D i s t r i b u t i o n . " J. Geophys. Res.. v o l . 66, no. 5, 1961, p. 1479. I.M. Longman: "A Green's Function f o r Determining the Deformation of the Earth Under Surface Mass Loads, 1, Theory." J. Geophys. Res.. v o l . 67, 1962, pp. 845-850. M. Caputo. "Tables f o r the Deformation of an Earth Model by Surface Mass D i s t r i b u t i o n s . " Geophys. Res., v o l . 67, no. 4, 1962, p. 1611. J.C. Harrison, N.F. Ness, I.M. Longman, R.F.S. Forbes, E.A. Kraut, and L.B. S l i c h t e r : "Earth-tide Observations Made During the I n t e r n a t i o n a l Geo- physical Year." J. Geophys. Res., v o l . 68, no. 5, 1963, pp. 1497-1516. L.B. S l i c h t e r : "Secular E f f e c t s of T i d a l F r i c t i o n Upon the Earth's Rotation." J. Geophys. Res., v o l . 68, no. 14, 1963, p. 4281. 248
GRAVITY Project 5.16 - A n t a r c t i c Pendulum Measurements 1. Ob.iectives. This p r o j e c t at the U n i v e r s i t y of Wisconsin, Department of Geology, provided f o r pendulum measurements of g r a v i t y at McMurdo Sound, Mawson and Mirny, A n t a r c t i c a , where i t was possible to transport the heavy equipment. The prime objec- t i v e was to set one or more r e l i a b l e pendulum g r a v i t y bases f o r c o n t r o l purposes. 2. Operations. Using the compound quartz pendulums and an u l t r a high-range Worden geodetic gravimeter, the f i r s t connection involved observations at Madison, Wisconsin, San Francisco, C a l i f . ; Hastings, N.Z.; Wellington, N.Z.; McMurdo Sound, A n t a r c t i c a ; Melbourne, A u s t r a l i a ; Christchurch, N.Z., Dunedin, N.Z.; Honolulu, Hawaii, San Fran- cisco, C a l i f . , and back to Madison. The second connection involved measurements at Madison, Wis., San Francisco, C a l i f . , Melbourne, A u s t r a l i a , Mirny, Mawson, A n t a r c t i c a ; Melbourne, A u s t r a l i a , San Francisco, C a l i f . , and back to Madison. A brass marker was set i n the concrete slab poured at McMurdo Sound i n the b u i l d - ing i n which the observations were made. The marker gives a p r e l i m i n a r y value of 982.992 gals. The s i t e was t i e d by gravimeter to Hydrographic O f f i c e marks, "South," "Hut," and "Fortress Rocks," and also to Cape Evans (Scott's Hut), the McMurdo Church- yard and the a i r operations-meteorology b u i l d i n g . The Cape Evans s i t e was the same as that used f o r a pendulum observation by the Scott Expedition. As t h i s expedition also observed at Christchurch and Wellington, N.Z., three t i e s were made to previous observations. The only previous connection under the U.S. program to eastern Antarc- t i c a had been a gravimeter connection to Mirny en route from McMurdo to Melbourne. 3. Personnel. The p r o j e c t was under the d i r e c t i o n of G.P. Woollard; observations were made on the f i r s t connection by John Rose and Robert Iverson and on the second connection by Oscar Strickholm. 4. Bibliography. G.P. Woollard: "Pendulum and Gravimetric Measurements of the Earth's Gravity." IGY B u l l . , no. 17,1958, pp. 5-11. G.P. Woollard and J.C. Rose: " I n t e r n a t i o n a l Gravity Measurements." Soc. Explor. Geophysicists. 518 pp., 1963. 249
GRAVITY Project 5.18 - Reduction of Pendulum and Gravlmeter Data 1. Obiectives. This p r o j e c t at the U n i v e r s i t y of Wisconsin, Department of Geology, provided f o r the reduction of data obtained under p r o j e c t s 5.7, 5.8, and 5.16 mentioned e a r l i e r . 2. Operations. Approximately 150 pendulum observations were analyzed and g r a v i t y da- t a derived. Some 2000 gravimeter readings were reduced and g r a v i t y value and many thousand observations were reduced and in t e g r a t e d m connection w i t h the r e g i o n a l studies. 3. Personnel. This work was under the d i r e c t i o n of G.P. Woollard, w i t h the a s s i s t - ance of John Rose, Robert Iverson, E.G. T h i e l , Ned Ostenso, Hugh Bennett, John Beh- rendt, Edwin Robinson, James Sparkman, Forrest Dowling, Charles Bentley, L. McGinnis, Thomas Landon, John Weinhaupt, Oscar Strickholm, and D e l i a Lavin. 4. Data. The data as f i n a l l y derived from the IGY observations were published as l i s t e d below. 5. Bibliography. E.G. T h i e l , N.A. Ostenso, H.F. Bennett, E.S. Robinson and J.C. Behrendt: "IGY A n t a r c t i c Oversnow Traverse Program, 1957-58." IGY Glac. Rept.. Series No. 1, Amer. Geogr. Soc, 1959. E.G. T h i e l , C.R. Bentley, N.A. Ostenso, and J.C. Behrendt: "Oversnow Traverse Programs, Byrd and E l l s w o r t h Stations, A n t a r c t i c a , 1957-1958, Seismology, Gravity and Magnetism." IGY Glac. Rept.. Series No. 2, Am. Geogr. Soc, 1959. J.G. Weinhaupt: "Geophysical Studies i n V i c t o r i a Land, A n t a r c t i c a . " Res. Rept.. Series No. 1, Univ. of Wisconsin, 123 pp. 1961. G.P. Woollard: "Pendulum and Gravimetric Measurements of the Earth's Gravity." IGY B u l l . , no. 17, 1958, pp. 5-11. G.P. Woollard and J.C. Rose: " I n t e r n a t i o n a l Gravity Measurements." Soc. Explor. Geophysicists. 518 pp. 1963. 250
GRAVITY Project 5.19 - Reduction of Marine Gravity Measurements 1. Obiective. This p r o j e c t at the Lamont Geological Observatory, Columbia U n i v e r s i t y , provided f o r the reduction of g r a v i t y data taken at sea under p r o j e c t 5.10. 2. Operations. Pendulum g r a v i t y data obtained during cruises of HMS TELEMACHUS and HMS ACHERON were reduced. These data were then i n t e r p r e t e d m terms of the v a r i a t i o n s of c r u s t a l s t r u c t u r e and the r e s u l t s published. The continuous Graf meter data were reduced and g r a v i t y values obtained. 3. Personnel. This p r o j e c t was supervised by J. Lamar Worzel, w i t h the assistance of Capt. V.R. S i n c l a i r , Mrs. R. Skinner and Robert Wall. 4. Bibliography. A. T u r k e l i : "Analysis of a Continuous Gravity P r o f i l e from the Madeira Abyssal P l a i n Through the S t r a i t of G i b r a l t a r to Alboran Basin." Columbia Un i v e r s i t y Master's D i s s e r t a t i o n , 1963. M. Talwani: "Gravity Measurements on HMS ACHERON i n South A t l a n t i c and Indian Oceans, B u l l . Geol. Soc. Amer.. v o l . 73, 1962, pp. 1171-1182. M. Talwani, J.L. Worzel, and M. Ewing: "Gravity Anomalies and Crustal Section Across the Tonga Trench." J. Geophys. Res., v o l . 66, pp. 1265-1278. 251
