NPS ARCHIVE 1969 IVEY, C. A GRAVITY SURVEY OF FORT ORD, CALIFORNIA by Clarence Gresham Ivey DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCWooi MONTEREY, 0, United States Naval Postgraduate School THESIS A Gravity Survey of Fort Ord, California by Clarence Gresham Ivey, Jr. October 1969 Tku document keu been apptovtd ^ofi pubtic *e- lzcu>£ and salt; i£t> dLti&Ubution lb tmturuXzd. Ti QQtxnn DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL MONTEREY, CA 93943-5101 A Gravity Survey of Fort Ord, California by Clarence Gresham^Ivey , Jr. Lieutenant Commander, United States Navy B.S.E., Princeton University, 1957 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL October 1969 ABSTRACT In April 1969, 50 different gravity stations on and around the perimeter of Fort Ord, California, were obtained using a LaCoste- Romberg Model G Geodetic Gravity Meter. The density of stations en- abled accurate location of 5-mgal contours of Simple Bouguer Anomaly. The major differences found between the new and previously published contours occurred in the west and southwest regions of Fort Ord. Five stations obtained by an earlier investigator were re- occupied during this study. The differences in observed gravity at these stations ranged from -0.37 mgal to -0.70 mgal . In an attempt to explain the differences, 11 additional stations were reoccupied in August 1969. Observed gravity differences for these stations ranged from -0.05 mgal to -0.58 mgal. The differences could not be fully explained nor could the earlier study be success- fully tied to this study. Fort Ord lies on a gravity low and is isostatically overcompen- sated. Further gravity readings are required on the Monterey Peninsula and in the Salinas Valley to adequately define the sub- structure of Fort Ord. TABLE OF CONTENTS I. INTRODUCTION , 5 II. THE SURVEY 5 A. SELECTION OF AREA 5 B. EQUIPMENT 6 C. DATA COLLECTION 8 III. GRAVITY CORRECTIONS 9 A. THEORETICAL GRAVITY 10 B. TIDAL CORRECTION 10 C. FREE AIR CORRECTION 11 D. BOUGUER CORRECTION 11 E. TERRAIN CORRECTION 12 F. CURVATURE CORRECTION 13 IV. GRAVITY ANOMALIES 13 A. FREE AIR ANOMALY (FAA) 14 B. SIMPLE BOUGUER ANOMALY (SBA) 14 C. COMPLETE BOUGUER ANOMALY (CBA) 14 V. DATA REDUCTION 14 VI. RESULTS 14 VII . CONCLUSIONS 44 VIII. RECOMMENDATIONS 44 APPENDI X A: . Deri vati on of the Free Ai r Correcti on 45 COMPUTER OUTPUT: Summary of Data 48 BIBLIOGRAPHY 52 INITIAL DISTRIBUTION LIST 53 FORM DD 1473 55 ACKNOWLEDGEMENTS The author wishes to express his appreciation to Dr. Joseph J. von Schwind who assisted in obtaining the first gravimeter and provided advice and a willing ear as this thesis took form. Mr. H.W. Oliver and Mr. S.L. Robbins, both of the United States Geological Survey, Menlo Park, California, provided instruments, maps, computer programs, and hours of counselling and instruction, all of which are greatly ap- preciated. Finally appreciation is expressed to Dr. R.H. Chapman of the California Division of Mines and Geology, San Francisco, California, who made available all the data that had been gathered previously in the area covered by the Santa Cruz Sheet. I INTRODUCTION Gravity measurements are made for a number of reasons. Some of these are scientific and some are commercial. The geophysicist uses gravity anomalies as an aid in interpreting the geological substructure of an area. The mining or petroleum geologist is looking particularly for promising structures for commercial exploitation. Geodesists use gravity anomalies as an aid in determining the shape of the earth. Gravity values, once ascertained, may be of future use to the Armed Forces as a means of precise positioning. The original purposes of this study were (1) to obtain practical experience in conducting a complete gravity survey of an area, (2) to reduce the data obtained to a standard usable form, and (3) to de- termine the geological substructure of the area surveyed. The first two objectives were successfully completed. The third purpose was not successfully concluded for the reasons explained in the final pages of this paper. II. THE SURVEY A. SELECTION OF AREA An unsurveyed area close to Monterey, California, was desired so that the survey could be conducted during weekends and half-days that were available. Two possible areas met the above criteria: (1) the northern end of the Santa Lucia Range located to the south of the Monterey Peninsula and (2) Fort Ord, California. The former area is roadless in the unsurveyed areas, Neither the time nor the resources required to conduct a horseback survey of the area was available to the author. The latter and smaller of the two areas was therefore chosen Fort Ord has roads covering most of its previously unsurveyed area and its proximity to the Naval Postgraduate School made three-hour field trips practical. Previous gravity surveys around the perimeter of Fort Ord indicated the existence of a local low Simple Bouguer Anomaly [Bishop and Chapman, 1967] , but no observations had been made on Fort Ord to accurately lo- cate the site of the low. Arrangements were made by the author to enter the firing range area to obtain stations which would help deline- ate this low. B. EQUIPMENT Two gravimeters were made available to the author by the U.S. Geological Survey (U.S.G.S.). A LaCoste and Romberg Model G Geodetic Gravity Meter, serial G58, was utilized for all observations made in April 1969. Serial number G143 was used for the August 1969 observa- tions. Both meters have a range greater than 7000 milligals (mgal), a reading accuracy of! 0.01 mgal, and a drift rate of less than 1.0 mgal per month. Model G meters are sealed to eliminate any effect from changes in atmospheric pressure and, as a safety precaution, are also internally pressure compensated. The gravity sensor is completely de- magnetized and enclosed with a magnetic shield. The entire meter is maintained at a constant temperature while in operation. A simplified diagram of the basic meter is shown in Fig. 1. The gravity response system consists of a weight on the end of a horizon- tal beam supported by a zero-length spring. The shock-eliminating springs form a floating pivot, thus eliminating any friction in the Connecting Links Lever Shock Eliminating Spring Fig, 1. Simplified Diagram of Meter moving system. The gravity response system is completely suspended by springs and will withstand any shock that does not damage its housing. The lever system and measuring screw shown in Fig. 1 are accurate ly calibrated over their entire range. Since the calibration factors depend only on the quality of the measuring screw and the lever system and not upon any type of auxiliary springs they do not change per- ceptibly with time [laCoste- Romberg] . Topographic maps at a scale of 1:24000 of the Fort Ord area were provided by U.S.G.S. to provide elevation control for the observations, Additional data was provided by the IKS. Army Corps of Engineers from their elevation control surveys conducted by the 663 Engineering Com- pany in April 1962 and by the Sacramento District Corps of Engineers in February and March 1969. C. DATA COLLECTION During the period 3-13 April 1969, 51 different stations were occupied on six separate days. For each set of runs the first and last station occupied was the California Division of Mines and Geo- logy Base Station No. 259 (CH259) located at the Monterey Airport,, Of the 51 stations, five were obtained and reported earlier [Sieck, 1964j , one was the base station and the remaining 44 stations were new. An attempt was made to locate and occupy all monumented bench marks around the perimeter of or on Fort Ord which were shown on the U.S.G.S. topographic maps. Six of 15 were recovered and oc- cupied. The remaining nine monumented bench marks were not found by the author. A few of these had obviously been destroyed by con- struction and others were most likely concealed by thick vegetation. 8 The remaining stations were located at non-monumented bench marks shown on the U.S.G.S. topographic maps, monumented bench marks, both permanent and temporary, established by the U.S. Army Corps of Eng- ineers and, in one case at the peak of a hill. This last station was the only one where the elevation was based on a spot elevation rather than a vertical control survey. At each station occupied the station number, meter reading, time of reading, height relative to the reference elevation, reference elevation, and description of the surrounding terrain were recorded. At the conclusion of each set of runs the two readings taken at the base station were corrected for tide effects and compared in order to check for tares and to compute drift corrections. The drift was assumed to be linear over the period of the observations. The maximum drift rate used was found to be 0.04 mgal/hr, This drift rate was applied over two stations on 3 August, During the original survey in April the drift rates ranged from 0.00 mgal/hr to 0.02 mgal/hr. One set of observations on 3 August was discarded due to an ap- parent tare of about 0.25 mgal , since the drift rate required to account for the change in observed values at the base station would have been 0.10 mgal/hr. III. GRAVITY CORRECTIONS Gravity observations must be corrected to reduce the measurements to the value which would be observed on a uniform spheroid fitted as closely as possible to sea level. This reference spheroid is competely smooth with the vertical distribution of density with depth horizontally uniform. A. THEORETICAL GRAVITY The reference spheroid is best approximated by a tri axial spheroid, which is an ellipsoid of revolution modified by depressions along the tvo 45°- latitude lines and by a flattening and bulging of the equator j^Dobrin, I960]] . The general form of the gravity variation to be expected on such a reference spheroid is given by: 9= 9o [l + C, sirr L - C2 sin2 2 l_] (1) o where g0 is the value of gravity at the equator at longitude 180 , C, and C2 are constants which give a measure of the earth's true shape and L is latitude.' The constants are determined by fitting world-wide pendulum measure- ments of gravity, which have been reduced to sea level, to the formula by the method of least squares. Since 1884 various investigators have determined the value of the constants using measurements available at the time. The 1930 International constants were used for this study, which when substituted into (1) gives the theoretical gravity (THG) in mgal at any latitude L: THG = 978049 [l + 0.0052884 sin2 L - 0.0000059 sin2 2L] (2) B. TIDAL CORRECTION Before the actual gravity values as read at each station were re- duced to sea level the effect of the orbiting moon was removed. The orbital parameters of the moon are well known and the tidal effect 10 can be predicted in advance. The tidal gravity corrections were de- termined by use of the tables and nomogram of the Service Hydrographique de la Marine and Compagnie Generale de Geophysique [1968]] . The tidal correction and instrument drift correction were combined and added to the measured value of gravity to obtain the observed gravity. C. FREE AIR CORRECTION The next correction that was made to the measured gravity was the free air correction (FAC). This correction assumes the existence of only air between the station and sea level and accounts only for the difference in elevation. The correction in mgal applied for this survey was: FAC = [0.09411549 - 0.000137789 sin2 L J E 0.0000000067E (3) where E = elevation in feet of station above sea level. [Scheibe and Howard, 1 964j (See Appendix 1 for a derivation of this correction. ) D. BOUGUER CORRECTION An adjustment must be made for the oversimplification of assuming only air exists between the station and sea level. This was done by assuming that a slab of density p , thickness E and extending infinite- ly in all horizontal directions exists between the station and sea level. The effect of this slab is called the Bouguer Correction (BC) and is given in mgal by: BC = 277T f E = 0.012774 p E (4) where p= density in g/cm-3 Y= univeral gravitational constant [_ Grant and West, 1965 and S. L. Robbins, personal communication] 11 E. TERRAIN CORRECTION Another correction was required to account for the fact that there is not a uniform slab, whose upper surface is the "Bouguer plane", but rather there is the actual topography of the land in the vicinity of the station Both the material extending above the hypothetical slab and the material missing from the slab due to the actual topo- graphy result in a reduction of the measured gravity values . Hills reduce the value because the mass opposes the attraction at the station due to the mass of the earth, and the valleys also cause a reduction because they were included in the Bouguer correction, but in fact are not there. These corrections are added to the observed gravity. In theory the volume and average density of each variation from the Bouguer plane must be calculated and its effect on the station as a function of distance must be determined. In practice a template is used which divides the area in the vicinity of the station into com- partments. The template consists of concentric circles with each annular ring divided into compartments. In general the number of com- partments in each ring increases with increasing radius. The average elevation in each compartment is determined by visual inspection. The absolute value of the difference in elevation between the com- partment and the station is used to enter a correction table which provides the applicable correction for a given assumed density. Hayford-Bowie templates were used throughout this survey through Zone F. For terrain corrections at distances between 2,29 km and 166.70 km from the station, the U.S.G.S. computerized Terrain Cor- rection Program was utilized. 12 The principle features of this program are that topography is digi- tized on a latitude and longitude grid, compartments are assembled on the basis of map boundaries and an exact tie to a circular inner boundary (the outer radius of zone F) is made. All terrain corrections (TC) were based on an assumed density of 3 2.67 gm/cm. F. CURVATURE CORRECTION A final correction was required to account for the curvature of the earth. The Bouguer correction assumes a flat earth which is a reason- able assumption for short distances, but is inaccurate for the greater distances utilized by the computerized Terrain Correction Program. Lambert [1930] developed the curvature correction (CC) to account for the fact that the earth is not flat. Although he computed the correction to four significant places in the first term, he utilized the value of 77* only to three significant places. U.S.G.S. has recom- puted the correction [S. L. Robbins, personal communication] and found it to be in mgal : CC = 0.0004462E - 3.282 x 10~ E2 + 1.27 x 10~' E3 (5) IV. GRAVITY ANOMALIES A gravity anomaly is the residue left after corrections have been applied to the observed gravity and the theoretical gravity has been subtracted from the result. There are different names for gravity anomalies, depending upon which corrections have been applied. 13 A. FREE AIR ANOMALY (FAA) This anomaly is given by: FAA - OG + FAC - THG (6) B. SIMPLE BOUGUER ANOMALY (SBA) The SBA is given by: SBA = OG + FAC - BC - THG (7) It is this anomaly that is normally used for comparative purposes and that which is plotted on Fig, 3 to Fig. 27. C. COMPLETE BOUGUER ANOMALY (CBA) When all corrections discussed above are included the result is the Complete Bouguer Anomaly: CBA = OG + FAC - BC + TC - CC - THG (8) V. DATA REDUCTION Manual corrections for tide, drift ana" terrain corrections through Hayford-Bowie Zone F were computed by the author. All other data re- duction was accomplished by existing U.S.GoS. Gravity Reduction Pro- grams on the U.S.G.S. IBM 360 Computer. The results are summarized beginning on page 48 . VI. RESULTS As shown in Fig. 2 to 27 a local Simple Bouguer Gravity low of -35 mgal exists in the extreme eastern portion of Fort Ord. This low decreases to the southwest, becoming zero at approximately the Monterey - Seaside line and continuing positive to the southwest. 14 On Fort Ord itself the SBA ranges from - 5.05 mgal to -35.59 mgal . A value of - 38.52 mgal was located on Reservation Road which runs between Salinas and Marina forming the eastern boundary of Fort Ord. The large number of stations in the relatively small area allowed the 5-mgal contours of SBA to be accurately located. The new contours agree well with the contours plotted by Bishop and Chapman D9671 in the eastern portion of Fort Ord. In the western and southwestern area there are major changes in the contour location. These changes are attributed to the greater saturation of stations made during this study. During April 1969, five stations were recovered which had been obtained previously and reported by Sieck [1964^1 . Table I compares the values of observed gravity at these five stations. An attempt was made to account for the observed differences, but no satisfactory explanation was evident. The first and most obvious explanation was that CA 879, CA 883 and CA 843 were obtained on one day and the remaining two stations were measured on another day. Ivey's data shows that CA 890 and CA 843 were surveyed on April 6, 1969, and the remaining three stations were occupied on April 3, 1969. Sieck's data does not include dates, but the numbers he assigned to the original stations suggest that CA 884 and CA 883 were surveyed on the same day, CA 879 and CA 890 on some other day and CA 843 on still another day. No correlation between observed gravity and the date of the measurement could be found. A portion of the observed differences may possibly be attributed to the fact that Sieck used Worden gravimeters provided by U.S.G.S. These meters can not be read to better than ±0.1 mgal and a figure 15 of ± 0.15 mgal is probably more realistic. Further, Seick established four base stations in the area for his use, and tied them to CH 176 (Wool lard Station WU-3) located at Stanford University. COMPARISON OF OBSERVED GRAVITY MEASURED AT FIVE STATIONS OBSERVED (+979800 GRAVITY mgal ) Station SIECK IVEY Difference CA 879 62.92 63.40 -0.48 CA 884 40.07 40.81 -0.64 CA 883 49.73 50.11 -0.38 CA 890 43.05 43.75 -0.70 CA 843 33.50 33.87 -0.37 TABLE I The calibration error for the U.S.G.S. Worden gravimeters has been determined to be one in six hundred. Thus for every six mgal difference in gravity between two stations the meter will introduce an error of 0.01 mgal. The difference in gravity between Stanford and Fort Ord is about 78 mgal which would produce an error of approximately 0.13 mgal. If both of the above errors are additive a possible error of about 0.33 mgal may exist in Sieck's data. To confirm this, during the period 1 - 3 August 1969, an additional 11 stations occupied by Sieck were recovered by Ivey. These 11 stations were those in Marina, Seaside, Spreckles and Salinas (west of US 101) Quad- rangles that could be found. Table II shows a comparison 16 of observed gravity as measured at these 11 stations. If the same errors are assumed to apply to Seick's data the differences range from + 0.38 mgal to - 0.25 mgal . COMPARISON OF OBSERVED GRAVITY AT 11 DIFFERENT STATIONS IN MONTEREY-SALINAS VICINITY OBSERVED GRAVITY ( + 979800 mgal ) Station SIECK IVEY Difference CA 845 58.30 58.25 0.05 CA 844 62.20 62.27 -0.07 CA 716 57.50 57.63 -0.13 CA 873 58.40 58.56 -0.16 CA 702 59.70 59.88 -0.18 CA 886 28.73 28.95 -0.22 CA 709 45.70 46.06 -0.36 CA 842 42.70 43,07 -0.37 CA 847 56.80 57.26 -0.46 CA 850 86.20 86,74 -0.54 CA 849 64.80 65.38 -0.58 TABLE II In addition to the above comparisons, two runs were made between CH 258 and CH 259 as a further check on the latter to eliminate a possible source of error due to an incorrect value of gravity being used for the base station. The average of the two runs showed a difference of observed gravity between the two stations of 0.01 mgal less than the value published by Chapman [1966] . 17 MONTEREY BAY _ .... t N 36 °3?3 YM / 3 / 00 w II III IV Note: i) Plate I covers entire area ii) Plates I la - Vf cover areas indicated Fig, 2 Diagram of Survey Area Showing Area Coverage by Photographic Plates OJOOOm £ ¥■ SCALE 1:2 o 1000 i— i i— i : 1000 2000 3000 UTM GRID AND 1947 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET CONTOUR INTERN, DASHED LINES REPRESEN" DATUM IS MEAN DEPTH CURVES AND SOUNDINGS IN FEET- SHORELINE SHOWN REPRESENTS THE APPI THE MEAN RANGE OF TIDE I! THIS MAP COMPLIES WITH NATION, FOR SALE BY U. S. GEOLOGICAL SURVEY, DENVf A FOLDER DESCRIBING TOPOGRAPHIC MAPS ) X *5 + Fig. 4. -Plate Ha 20 (MOSS L\ANDINQ> 1:24000 00 4000 — I 5000 6000 7000 FEET 1 KILOMETER :RVAL 20 FEET ENT 10-FOOT INTERVALS AN SEA LEVEL -IT-DATUM IS MEAN LOWER LOW WATER PPROXIMATE LINE OF MEAN HIGH WATER : IS APPROXIMATELY 5 FEET DNAL MAP ACCURACY STANDARDS JVER 25, COLORADO OR WASHINGTON 25, D. C. S AND SYMBOLS IS AVAILABLE ON REQUEST 1 MILE 3 W, (-:--. ; \ Sb . ■t Fig. 5. Plate lib 21 47'30" HOLLISTER (CALIF. 25) 27 Ml. CASTROVILLE I 5 1*1. Fig. 6. Plate lie 22 12H5'00" Fig. 7. Plate lid 23 Fig. 8. Plate He 24 woe Fig. 9. Plate Ilf 25 Av . -*. -V ■^ V *.. •< V , // m^gaa^r-jgaa^l^^fc ^ * \T^^^^flHr7/?— -^ "^ 1^ ^ Fig. 19. Plate IVd 35 Fig. 20. Plate IVe 36 **•*.. i / \ \ \ / < / i / V / I 'Vs JJ\ \ ^»>* \V» ^ ,n % *1_LA^O If DE i?#K« ^§A " Fig. 25. Plate Vd 41 K*5? «0 which can be written: gh= g0 + Ah + Bh2 + Ch3 + Dhy+ ... (c) where A, B, C, etc. correspond to the coefficients of the Taylor expansion. Hi rvonen [l96Cf| developed the potential differences u = u0 - uh in terms of a Taylor expansion along the normal and since M. = g and <)*" u _ h g ah1" ah his results can be applied here„ Then A = kM [z + e2 - m - 27_ me2 + e^ - sin2L(3 e2-5m-y — me2 2~ 14 a b and ■2e«J B = kM f3 - 5m + 2e2 - sin2" Lfi (9e2 - 15m)] 2~2 a b 2 2 where m= Q) a b kM 45 k = universal gravitational constant M = mass of earth a = equitorial radius of ellipsoid b ~ polar radius of ellipsoid L = latitude e = second eccentricity of international ellipsoid. When constants for the International ellipsoid are used a - 637838800 cm e2= 0.006722670022 m - 0.00344986385 cm3/gm - sec"2 kM = 1.541363543 x 10"6 sec"2 2 a b A = - (0.308777237 - 0.000452063 sin"2 L0 ) B = .07264891075 x 10~* - 0.00021230891 x 10"6 sin2 l_0 . Approximate the earth as a sphere of mass M and radius R, then considering only that part of the gravity due to the Newtonian at- traction g' = kM 2 R the vertical rate of change of g with respect to R is dg -2 Mi dR ~ R3 which corresponds to the main term of A. Differentiation of the above yields dag 6 kM 2 " 4 dR^ R which corresponds to the main term of EL Also a3g - 24 kM dR3 R5 46 At any point P0 on the earth's surface 9„ = M Ro2 and thus 3 (^Jo ■ -24 9o dR Ro3 When g0 = 980 gals R0 = 6371.2 km, *3 /_1\ = -9.094392 x 10"8 gals/km3 ldR3y° and C = - 1.515732 x 10~8 gals/km3 By the same procedure t 'dR i^l) = 120 _Jo = 0.71371096 x 10_1° gals/kmZ R0 and -10 4 D = 0.029737957 x 10 gals/km . Collecting terms and converting height to feet and gravity values to mgal : gh = g - (.0941154901 - .000137789 sin2 LQ)E - (.00674933167 x 10" - 0.0001972422 x 10" sirr |_ )E2 - 1.515732 x 10"8 E3 - ... (d) Truncating at 10 , the Free Air Correction is obtained from (d): FAC = (0.09411549 - 0.000137789 sin2 L)E - 0.0000000067 E2 47 COMPUTER OUTPUT: Summary of Data BASE STA CH2 59 CA879 CA884 CA883 IV 4 IV IV IV IV - CH259 LATITUDE 36 35.23 36 39 39 39 40 40 39 39 36 36 36 36 36 36 36 36 15 28 25 41 11 04 62 14 FORT G6V 979869 LONGITUDE 121 50.89 121 49.56 121 47.08 121 48.43 121 47.91 121 48.34 121 47.91 121 47.69 121 47.52 ORD, C .12 M ELEV 171.8 235.7 245.0 169. 1 129.0 107.6 118.4 183.9 240.9 ALIFCRNIA ETER G58 READING 32 96.04 3290.50 3268 3277 3277 3281 3279 3273 63 63 18 31 49 82 SURVEY READIN T+D 0.14 0.16 0.21 0.19 0.17 0.14 0.14 0.13 3270.13 0.12 G 3296 OBSV- 97986 97986 97984 97985 97984 97985 97985 97984 97984 .04 GRAV 9.12 3.4C 0.81 0.11 9.62 3.87 1.98 6.10 2.27 BASE STA CH259 IV 9 IV 10 IV 11 - CH259 LATITUDE 36 35.23 36 36.14 36 37.25 36 35.39 FORT ORD, CALIFORNIA GBV 972869.12 METER G58 LONGITUDE 121 50.89 121 47.34 121 48.35 121 46.31 ELEV 171.8 541.8 543.4 929.5 READING 3296.22 3253.30 3258.55 3231.84 SURVEY READING 3296.22 T+D OBSV-GRAV -0.01 979869.12 -0.02 979824.67 -0.03 979830.09 -0.02 979802.44 BASE STA CH259 IV 12 IV IV IV IV IV IV IV IV IV 13 14 15 16 17 18 19 20 21 CA89C IV 23 CA843 - CH259 LATITUDE 36 35.23 36 37 36 37 37 37 37 36 36 36 36 36 36 36 36 36 36 36 36 36 24 13 16 39 30 30 45 37.68 37.46 39.68 39.34 37.93 37.73 F GBV 97 LONGIT 121 50 121 121 121 121 121 121 121 121 121 121 121 121 121 43 44 44 45 45 46 48 47 46 45 43 42 41 ORT 0 9869. UDE .89 .68 .64 .76 .10 .75 .10 .15 .76 .77 .22 .34 .99 .56 RD, 12 ELEV 171. 673. 259. 569. 303. 453. 406. 439. 464. 499. 191. 131. 54. 208. CALIF METER RE 32 32 32 32 32 32 32 32 32 32 32 32 32 32 CRNIA G58 AOING 96.13 36 65 50 62 93 48 10 69 55.20 59.42 65.26 60.08 54.19 70.34 71.54 74.19 62.02 SURVEY READING T+D 0.C7 0.10 0.13 0.13 0.14 0.15 16 17 17 16 0.17 0.16 0.15 0.14 3296.13 OBSV-GRAV 979869.12 979807.90 979837.44 979821.52 979834.56 979826.82 979831.20 979837.25 979831.89 979825.78 979842.51 979843.75 979846.48 979833.87 bASE STA CH259 IV 25 IV IV IV IV 26 27 28 29 BAS STA CH259 IV 3C IV IV IV IV IV IV IV IV IV IV IV IV 31 32 33 34 35 36 37 38 39 4C 41 42 - CH259 LATITUDE 36 35.23 38.64 38.65 38.64 39.28 39. 17 FORT ORD, GBV 979869.12 36 36 36 36 36 - CH259 LATITUDE 36 35.23 36 36.17 36 36.89 36 37.32 36 37.80 36 37.50 36 36.74 36 35.79 36 35.59 36 35.48 36 35.15 36 35.23 36 35.06 36 34.87 LONGITUDE 121 50.89 48.75 43.33 47.93 48.03 48.64 121 121 121 121 121 FORT GBV 97986 LONGITUDE 121 50.89 49.37 49.22 48.98 47.44 44.46 44.68 44.97 45.02 45.07 45.40 45.84 46.24 46.89 121 121 121 121 121 121 121 121 121 121 121 121 121 ELEV 171.8 186.5 249.8 301.4 188.0 187.2 ORD, CAL 9.12 MET ELEV 171.8 264.5 315.7 330.5 435.7 197.6 333. 1 431.8 758.8 790.8 797.9 843.5 796.5 723.3 CALIFORNIA METER G58 READING 3296.12 3273.32 3272.51 3267.80 3274.98 3277. C7 IFCRNIA ER G58 READING 3296.10 3285.74 3273.99 3274.98 3259.90 3263.93 3262.30 3257.76 3239.11 3237.69 3238.20 3236.18 3239.68 3245.28 SURVEY READING 3296.12 T + D 0.08 0.09 0.11 0.10 0.10 0.11 SURVEY READING T+D 0.12 0.12 0.12 0.11 0.10 0.10 0.09 0.08 0.06 0.06 0.05 0.04 0.04 0.03 OBSV-GRAV 979869.12 979850.70 979844.70 979839.81 979847.25 979849.42 3296.10 OBSV-GRAV 979869.12 979853.39 979851.40 979847.24 979831.62 979840.97 979834.09 979829.38 979810.05 979808.58 979809.09 979806.99 979810.62 979816.41 48 APR 3 1969 T+D 0.14 Dl 2. 67 D2 2.60 THEO-GRAV FAA 8A1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 2.36 0.92 1.00 979882.60 2.97 -5.07 0.10 2.70 -2.47 -2.33 979887. 11 -23.25 -31.61 0.11 2.03 -29.63 -29.46 979887.06 -21.05 -26.82 0.07 2.13 -24.76 -24.67 979887.29 -25.54 -29.94 0.06 2.03 -27.97 -27.91 9 79888.30 -24.31 -27.98 0.05 2.0 2 -26.01 -25.97 979888.20 -25.08 -29.12 0.05 1.99 -27.18 -27.13 979887.60 -24.20 -30.4 7 0.08 2.33 -28.22 -28.12 979886.91 -21.97 APR 4 -30.19 1969 0.11 2.14 -28.15 -27.99 T+D -0.01 Dl 2. ,67 D2 2.60 THEO-GRAV FAA BA1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 2.36 0.92 1.00 979882.59 -6.Q6 -25.44 0.23 2.53 -23.09 -22.66 979884. 19 -2.98 -21.51 0.23 2.80 -18.95 -18.53 979881.51 8.36 APR 6 -23.34 1969 0.39 3.92 -19.80 -19.07 T+D 0.07 Dl 2, ,67 D2 2.60 THFO-GRAV FAA RA1 CC TC CBA1 CBA2 979881.28 4.00 -1.36 0.C8 2.86 0.92 1.00 979882.73 -11.06 -34.18 0.29 5.00 -29.47 -28.99 979884.01 -22.12 -30.99 0.11 3.06 -28.04 -27.88 979882.62 -7.51 -26.94 0.24 2.3 8 -24.30 -23.86 979884.39 -20.85 -31.36 0.13 2.75 -28.74 -28.54 979884.26 -14.81 -30.27 0.20 2.43 -27.98 -27.64 979884.26 -14.82 -28.69 0.18 2.25 -26.61 -26.30 979884.47 -5.84 -20.84 0.19 2.46 -18.58 -18.24 979884.80 -9.24 -25.08 0.20 2.43 -22.85 -22.49 979884.49 -11.74 -23.77 0.21 2.55 -26.43 -26.05 979887.68 -27.20 -33.72 0.08 1.83 -31.96 -31.84 979887. 19 -31.12 -35.59 0.06 1.92 -33.72 -33.66 979885.16 -33.60 -35.44 0.02 2.59 -32.88 -32.89 979884.83 -31.42 APR 8 -33.52 1969 0.09 2.39 -35.73 -35.61 T+D 0.08 Dl 2, ,67 D2 2.60 THEO-GRAV FAA BA1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 2.36 0.92 1.00 979886. 19 -17.94 -24.31 0.08 2.29 -22.09 -21.98 979886.20 -18.00 -26.52 0. 11 2.19 -24.44 -24.27 979886. 19 -18.02 -28.30 0.13 2.20 -26.24 -26.0 2 979887. 11 -22.17 -23.58 0.08 2.10 -26.56 -26.45 979886.95 -19.92 APR 12 -26.30 1969 0.08 2.24 -24.14 -24.03 T+D 0.12 Dl 2, .67 02 2.60 THEO-GRAV FAA 8A1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 2.36 0.92 1.00 979882.63 0.64 -8.38 0.12 2.5 8 -5.92 -5.75 979883.67 -2.57 -13.34 0.14 2.60 -10.87 -10.66 979884.29 -5.96 -17.23 0.14 2.55 -14.82 -14.59 979884.98 -12.38 -27.24 0.19 2.52 -24.90 -24.58 979884.55 -24.99 -31.73 0.09 2.49 -29.32 -29.21 979883.45 -18.03 -29.39 0. 14 2.3 8 -26.66 -26.43 979882.93 -12.94 -27.67 0.19 2.94 -24.91 -24.60 979881.80 -0.38 -26.26 0.32 3.29 -23.29 -22.69 979881.64 1.32 -25.65 0.33 3.27 -22.71 -22.08 979881. 16 2.98 -24.23 0.34 2.93 -21.64 -21.00 979881.28 5.05 -23.71 0.35 3.27 -20.81 -20.13 979881.03 4.50 -22.66 0.33 3.15 -19.85 -19.21 97988C.76 4. 15 -20.69 0.31 2.96 -18.03 -17.45 49 FGRT ORD, CALIFORNIA SURVEY BASE - CH259 G8V 979869 .12 METER G58 READING 3296.14 STA LATITUDE LONGITUDE ELEV READING T+D OBSV-GRAV CH259 36 35.23 121 50.89 171.8 3296. 14 0.12 979869.12 IV 43 36 34.83 121 47.28 704.5 3247.78 0.12 979819.04 IV 44 36 34.70 121 47.66 572.5 3257.00 0.13 979828.60 IV 45 36 34.65 121 48.05 429.1 3267.43 0.14 979839.41 IV 46 36 34.62 121 48.44 349.4 3272.95 0.14 979845.13 IV 47 36 35.01 121 48.92 230.9 3284.00 0.15 979856.58 IV 48 36 35.38 121 49.43 162.3 3291.47 0.15 979864.31 IV 49 36 35.62 121 49.8 7 139.3 3294.92 0.15 979867.89 IV 5C 36 35.93 121 49.6 7 243.6 3289.83 0.16 979862.63 BASE - CH259 STA LATITUDE CH259 36 35.23 CH258 36 40.43 BASI STA CH259 CA850 CA873 CA8 86 CA842 CA7C9 CH258 CA702 CA716 CA844 CA845 BASE STA CH259 CA847 CA840 - CH259 LATITUDE 36 35.23 36 36.00 36 30.10 36 32.30 36 36.44 36 38.67 36 40.43 36 41.77 36 41.58 36 43.95 36 42.88 - CH259 LATITUDE 36 35.23 36 39.68 36 37.80 FGRT ORD, CALIFORNIA GBV 979869.12 METER 143 LONGITUDE ELEV REAOING 121 50.39 171.8 3432.61 121 39.36 50.0 3421.44 FORT ORD, GBV 979369.12 LONGITUDE ELEV 121 50.89 171. 121 52.40 16. 121 45.35 243. 121 43.46 505. 121 38.69 55. 121 39.78 47. 121 39.36 50. 121 41.96 34. 121 44.03 26. 121 46.76 26. 121 47.47 56. CALIFCRNIA METER 143 REAOING 8 3432.69 0 3449.54 2 3422.63 5 3394.33 5 3407.81 0 3410.66 0 3421.40 0 3423.85 0 3421.69 0 3426.12 0 3422.27 FORT ORD, CALIFORNIA GBV 979869.12 METER 143 LONGITUDE ELEV READING 121 50.89 171.8 3432.83 121 48.97 86.6 3421.52 121 50.10 90.0 3429.30 SURVEY READING 3432.61 T+D OBSV-GRAV 0.12 979869.12 0.09 979857.40 SURVEY READING T+D 0.07 0.05 0.C4 0.04 0.06 0.07 0.07 0.08 0.C9 0.10 0.11 3432.69 OBSV-GRAV 979869.12 979886.74 979858.56 979828.95 979843.07 979846.06 979857.30 979859.88 979857.63 979862.27 979858.25 SURVEY READING 3432.83 T+D OBSV-GRAV 0.10 979869.12 0.08 979857.26 0.05 979865.38 NOTES •CH» BA •CA» GR • IV« SH GBV = T+D = 06SV- THEO- FAA = BA1 = CC = TC = CBA1 CBA2 CALIFORNIA OIVISION OF MINES AND GEOLOGY NEW STATIONS ON THE SANTA CRUZ GRAVITY STATIONS ARE SE STATIONS. STATIONS ARE RECOVERED STATIONS ON THE SANTA CRUZ AVITY SHEET. STATIONS ARE EET. GRAVITY BASE VALUE TIDE PLUS DRIFT CORRECTION GRAV = OBSERVED GRAVITY GRAV = THEORETICAL GRAVITY FREE AIR ANOMALY SIMPLE BOUGUER ANOMALY FOR CURVATURE CORRECTION TERRAIN CORRECTION = COMPLETE BOUGUER ANOMALY FOR = COMPLETE BOUGUER ANOMALY FOR DENSITY 2.67 DENSITY DENSITY 2.67 2.60 50 APR 13 1969 T+D 0.12 01 2, ,67 02 2.60 THFO-GRAV FAA BA1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 c.oa 2.86 0.92 1.00 979880.70 4.61 -19.42 0.30 3.45 -16.27 -15.72 97988C.52 1.93 -17.59 0.24 3.04 -14.80 -14.36 979880.45 -0.67 -15.31 0.19 3.01 -12.48 -12.17 979880.40 -2.41 -14.33 0.15 2.85 -11.63 -11.39 979880.96 -2.66 -10.54 0.10 2.75 -7.89 -7.75 979881.50 -1.91 -7.45 0.07 2.78 -4.73 -4.66 979881.84 -0.85 -5.60 0.06 3.32 -2.34 -2.30 979882.29 3.25 AUG 1 -5.05 1969 0.11 2.34 -2.33 -2. 18 T+D 0.12 01 2, ,67 02 2.60 THEO-GRAV FAA 8A1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 979888.76 -26.66 AUG 2 -28.36 1969 0.02 T+D 0.07 01 2. ,67 02 2.60 THEO-GRAV FAA 3A1 CC TC CBA1 CBA2 979881.23 4.00 -1.86 0.08 — - — — — — 979882.39 5.85 5.31 0.01 9 79873.90 7.53 -0.76 0.11 979877.07 -0.57 -17.81 0.22 - — — - — - 979883.02 -34.73 -36.62 0.02 - — - - — — 979886.23 -35.74 -37.35 0.02 979888.76 -26.76 -28.46 0.02 979890.69 -27.62 -28.77 0.02 979890.42 -30.34 -31.23 0.01 - — — — — — 979893.83 -29.11 -30.00 0.01 979892.29 -28.77 AUG 3 -30.68 1969 0.02 T+D 0.10 01 2. 67 02 2.60 THEO-GRAV FAA BA1 CC TC CBA1 CBA2 979881.28 4.00 -1.86 0.08 — — — — — — 979887.68 -22.27 -25.23 0.04 - - — — — — 979884.98 -11.14 -14.20 0.04 51 BIBLIOGRAPHY Bishop, C. C. and R, H Chapman. 1967. Bouguer Gravity Map of Cali- fornia (Santa Cruz Sheet), The California Division of Mines and Geology, San Francisco. Chapman, R. H„ 1966. The California Division of Mines and Geology Base Station Network (Supplement to Special Report 90). California Division of Mines and Geology, San Francisco, 4 p., Dobrin, M. B. 1960. Introduction to Geophysical Prospecting. McGraw- Hill Book Company, Inc., New York. 446 p. Grant, F. S. and G. F. West. 1965. Interpretation Theory in Applied Geophysics. McGraw-Hill, Inc., San Francisco. 583 p. Hirvonen, R. A. 1960. New Theory of the Gravimetric Geodesy. Ann. Acad. Sci. Fennicae, A., 111(56), Helsinki, 50 p. LaCoste-Romberg, Instruction Manual for LaCoste and Romberg, Inc., Model G Geodetic Gravity Meter No. 58, LaCoste and Romberg, Inc., Austin, Texas, Lambert, W. D. 1930. The Reduction of Observed Value of Gravity to Sea Level. Bulletin Geodesique. 26:107 - 181. Scheibe, D. M. and H. W. Howard. 1964. Classical Methods for Reduction of Gravity Observations; ACIC Reference Publication No 12, Aero- nautical Chart and Information Center, St. Louis, Mo, 65 p. Service Hydrographique de la Marine and Compagnie Generale de Geo- physique. 1968. Tidal Gravity Corrections for 1969, Geophysical Prospecting, Supplement 1. 16: 53 p. Sieck, H. C. 1964. A Gravity Investigation of the Monterey - Salinas Area. Unpublished Student Research Project. Stanford University, Palo Alto, California. 52 INITIAL DISTRIBUTION LIST No. Copies 1. Defense Documentation Center 20 Cameron Station Alexandria, Virginia 22314 2. Library, Code 0212 Naval Postgraduate School 2 Monterey, California 93940 3. Oceanographer of the Navy The Madison Building 732 N. Washington Street 1 Alexandria, Virginia 22314 4. Assoc. Professor J. J. von Schwind Code 58 Vs 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 5. Asst Professor R. S. Andrews Code 58 Ad 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 6. Mr. H. W. Oliver 1 U. S. Geological Survey 345 Middlefield Road Menlo Park, California 94025 7. Dr. R. H. Chapman California Division of Mines and Geology 1 Ferry Building San Francisco, California 94111 8. LCDR C. G. Ivey, Jr. 1 USS Tang (SS 563) FP0 San Francisco, California 96601 9. Professor R. J. Smith Code 58 Sj 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 53 Unclassified Security Classification DOCUMENT CONTROL DATA -R&D (Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified) originating ACTIVITY (Corporate author) Naval Postgraduate School Monterey, California 93940 2a. REPORT SECURITY CLASSIFICATION Unclassified 2b. GROUP 3. REPORT TITLE A Gravity Survey of Fort Ord, California 4. DESCRIPTIVE NO T E S ( Type of report and, inclusive dates) Master's Thesis; October 1969 5. AUTHOR(S) (First name, middle initial, last name) Clarence Gresham Ivey, Jr. «. REPORT DATE October 1969 la. TOTAL NO. OF PAGES 55 76. NO. OF REFS 10 8a. CONTRACT OR GRANT NO. b. PROJEC T NO. 9a. ORIGINATOR'S REPORT NUMBER(S) 9b. OTHER REPORT NOISI (Any other numbers that may be assigned this report) 10. DISTRIBUTION STATEMENT This document has been approved for public release and sale; its distribution is unlimited. II. SUPPLEMENTARY NOTES 12. SPONSORING MILI TARY ACTIVITY Naval Postgraduate School Monterey, California 93940 13. ABSTRACT In April 1969, 50 different gravity stations on and around the perimeter of Fort Ord, California, were obtained using a LaCoste-Romberg Model G Geodetic Gravity Meter. The density of stations enabled accurate location of 5-mgal con- tours of Simple Bouguer Anomaly. The major differences found between the new and previously published contours occurred in the west and southwest regions of Fort Ord. Five stations obtained by an earlier investigator were reoccupied during this study. The differences in observed gravity at these stations ranged from -0.37 mgal to -0.70 mgal . In an attempt to explain the differences, 11 additional stations were re- occupied in August 1969. Observed gravity differences for these stations ranged from -0.05 mgal to -0.58 mgal. The differences could not be fully explained nor could the earlier study be successfully tied to this study. Fort Ord lies on a gravity low and is isostatically overcompensated. Further gravity readings are required on the Monterey Peninsula and in the Salinas Valley to adequately define the substructure of Fort Ord. DD FORM I47O 1 NOV «5 I *T / W S/N 0101 -807-681 1 (PAGE 1) 55 Unclassified Security Classification A-S1408 Unclassified Security Classification KEY WO R OS Gravity Survey Fort Ord, California Simple Bouguer Anomaly DD ,^..1473 «"<* S/N 0101-807-6821 ROLE WT ROLE W T ROLE W T 56 Unclassified Security Classification A-31 409 thesl95 A gravity survey of Fort Ord, California 3 2768 002 10199 0 DUDLEY KNOX LIBRARY