Geophysics
Geology 364
Introduction
Exploration Geophysics
Geology 364
An Introduction to Geophysical
Exploration
Kearey, Brooks, and Hill 3rd
Edition, 2002
What is Geophysics?
• A branch of experimental physics dealing
with the earth, including atmosphere,
hydrosphere, and lithosphere
Solid Earth Geophysics
• Physical properties of Earth
– Gross Structure (materials, heat, pressure)
• Redistribution of Global materials
– Plate Tectonics
• EarthScope
Exploration Geophysics
• Measures the physical properties of
materials below the earth’s surface to
detect or indicate the presence or location
of ore bodies or hydrocarbons and
geological structures
Environmental Geophysics
• Characterization of surface and ground
waters
• Organic and inorganic constituents
• Buried objects or voids
Shallow Subsurface Geophysics
• Void detection (karst, tunnels, etc.)
• Buried utilities
• Construction conditions
Borehole Geophysics
• Determination of materials and conditions
in proximity of a borehole (down hole
logging)
Divining for minerals
Early Attempts
• Chinese fortune tellers begin using loadstone to
construct their divining boards, eventually
leading to the first compasses. (Mentioned in
Wang Ch'ung's Discourses weighed in the
balance of 83 B.C.)
• Divining Rods to find more loadstone
• Magnetic compass used for iron prospecting as
early as 1640 (dip needle)
Brief Introduction to Geophysics
• Robert Fox discovered, in 1815, that certain minerals
exhibit spontaneous polarization and proposed an
exploration method.
• Conrad Schlumberger, 1912 used basic equipment to
map isopotential curves on family estate near Cean,
France.
• In 1913 he used spontaneous potential to locate a new
metallic sulfide deposit at Bor Yugoslavia.
– 26 ore bodies, some dating to 4,500 BC
– Source of copper for tools and bronze
Bor
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Type: High-sulphidation epithermal
massive-enargite (gold) sulphide deposits,
porphyry Cu-Mo and Mo deposits
Morphology:
Age of mineralization: Upper/Late
Cretaceous, 65 ± 4 Ma
Ore minerals: Enargite, pyrite, chalcopyrite,
bornite, chalcocite, covellite, molybdenite,
magnetite, pyrrhotite, galena, sphalerite,
grey copper
Alteration: Silicification, argillic alteration,
sericitization, chloritization, carbonatization
Host rocks: Andesite, volcaniclastic rocks,
pyroclastic rocks
Age of host rocks: Upper/Late Cretaceous,
Campanian, 78 ± 4 Ma
Host rock mineralogy: Quartz, andesite,
barite, pyrophyllite, diaspore, alunite,
anhydrite, sulphur
Mining: Surface and underground mining
Metals: Cu, Au, Ag
Conrad Schlumberger
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German geophysicist and petroleum
engineer noted for the invention, in
1927, of a method of continuous
electric logging of boreholes.
Beginning1912, Conrad Schlumberger
conceived the idea for electrical
measurements to map subsurface
rock bodies. He was joined by his
brother, Marcel, in 1919.
Schlumberger teams conducted
geophysical surveys in Romania,
Serbia, Canada, South Africa, Belgian
Congo and the U.S. Electrical
prospecting was used for the first time
to map a subsurface oil-bearing
structure - a salt dome in Romania. In
1927, the downhole electrical
resistivity log was recorded in a well in
Pechelbronn, France.
Born 2 Oct 1878; died 1936.
Brief Introduction to Geophysics
• Pierre Bouguer, 1735, noted the amount of plumb
deflection caused by particular peaks of the Andes.
• Sir George Everest, Surveyor-General of India, in the
1860s had a blown survey of a 365 mile-long, northsouth line. there was a difference of 550 feet between
the direct triangulation and astronomic methods. Error
caused by the mass of the Himalayas.
• 1915-1916 torsion balance used to delineate salt dome
oil field in Czechoslovakia. Employed in 1922 to locate
salt domes in the Gulf Coast Region. By 1929 all of the
piercement salt domes had been located by gravity
surveys.
Siesmics
Chang Heng, astronomer
royal to the Han Dynasty,
invented an accurate
seismograph in AD 132 – It
was a large bronze urn
With eight dragon heads
gazing outward in eight
directions. Each dragon
held a ball in his mouth.
Around the base of the urn,
under each dragon, sat a
frog with his mouth open.
Siesmics
• Rober Mallet, 1846, proposed to the Royal Irish
Academy a method of obtaining subsurface
information by artificial earthquakes
• In two years he developed a simple mercurybowl seismoscope and measured the P-wave
velocity of a granite by refraction.
• The First Principles of Observational Seismology
(1862)
Triode Vacuum Tube Amplifier
Basic Triode Vacuum Tubes
6L6 and 807
B9A
WWII - 1968
1907 - 1929
1930 - WWII
Siesmics
• In 1901, the Submarine Signal Company was formed and provided
underwater signaling devices to the United States Lighthouse
Service. In 1910, the brilliant Reginald Fessenden joined the
company. He invented an oscillator in 1911 that he steadily
improved. Within a few years, his massive 250kg transceiver went to
sea on the U.S. Coast Guard Cutter MIAMI, and on April 27, 1914
he was able to detect an iceberg over 20km away. While conducting
this experiment, Fessenden, who was quite seasick, and his coworkers, Robert F. Blake and William Gunn, serendipitously noted
an echo that returned about two seconds after the outgoing pulse.
This turned out to be a return from the bottom. "Thus, on just one
cruise.... Fessenden demonstrated that both horizontal and vertical
echoes could be generated within the sea..." (Bates et al. 1987).
Vines Branch Experiment, 1921
Basic Galvanometer 1905
• Analog Multimeter
Induction Coil
Basic Radio
• Simple Sparker
– All frequencies
• Lightning
• Sparker transmitters
• Early Wireless telegraphy
• Crystal Controlled
– Oscillator circuit (fixed frequency)
AM Radio Signal
Siesmics
• 1921 discovery of Orchard Dome, Texas
by fan shooting
• 1927 First successful reflection profile
• Seismics were developed in the 1920s
Refraction was most successful in
locating non-piercement salt domes during
the early 1920s.
• Reflection became routine in 1927.
Very Early Reflection Seismogram
Single Shot Analog Seismogram
(1930s)
Military and Early World War II
Developments
• Pendulum Gravimeters - U-Boat location
system with simple gravity map of Atlantic
Ocean.
• Magnetic Mines - disturbance of ambient
magnetic field.
• RADAR
– Magnetron Tube
• SONAR
The original Mark I Magnetic
Mine ('Type GA')
Proximity Fuze- miniature RF
transmitter-receiverprocessor.
Computers
• Naval Fire Direction computers
• Enigma German code
– host of top mathematicians and general
problem-solvers was recruited, and a bank of
early computers, known as 'bombes', was
built - to work out the vast number of
permutations in Enigma settings.
• Magic (Japanese code breaking)
Radar
• RAdio Detection And Ranging
• Magnatron Tube
– Ceramic and metal tube focus to produce a
beam
• Microwaves
– Wavelength << half the size of object!!!
– Reflection and Detection
Early Computers
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ORDVAC
ORDVAC was the first of two computers built under contract at the University of Illinois. ORDVAC
was delivered to US Army Aberdeen Proving Grounds in the spring of 1951 and checked out in
the summer. As part of the contract, funds were provided to the University of Illinois to build a
second identical computer known as ILLIAC I.
ILLIAC I
ILLIAC I was the first electronic computer in the United states built and owned by a university. It
was put on service on in 1952. It was built with 2,800 vacuum tubes. ILLIAC I had a 5k main
memory and 64k Drum memory..
ILLIAC II
The ILLIAC II was the first transistorized super computer. It was built by the University of Illinois.
At its inception in 1958 it was 100 times faster than competing machines of that day. It became
operational in 1962, two years later than expected.
ILLIAC II had 8192 words of core memory, backed up by 65,536 words of storage on magnetic
drums. The core memory access time was 1.8 to 2 µS. The magnetic drum access time was 7 µS.
A "fast buffer" was also provided for storage of short loops and intermediate results (similar in
concept to what is now called cache). The "fast buffer" access time was 0.25 µS.
The word size was 52 bits. Floating point numbers used a format with 7 bits of exponent (power of
4) and 45 bits the mantissa. Instructions were either 26 bits or 13 bits long, allowing packing of up
to 4 instructions per memory word.
Transister 1947
Tube vs Transistor Radios
Digital Computation
• Binary Byte is basic unit (1101)
• Right Justified
• Two Bytes (10110011) = 0 to F
Hexadecimal
• Two Bytes 1 to 256
• Four Bytes 1 to 65,536
Simple Integers in 2 byte (8 bits)
Range of Numbers
• Integers
• 16 bits (4 bytes) -32,768 to 32,767
• 32 bits (8 bytes) -2,147,483,687 to
2,147,483,686
• Floating Points
• Precision is size of gap between numbers
• 32 bits
• 22 bit mantissa, 9 bit exponent, 1 bit sign
Languages
• Assembly
• Compiler
– Operating Systems (DOS, OS1)
– Fortran, Basic, C, C++, Cobal, Pascal
• Application
Speed
• Integer calculations 200 to 2,000 times
faster than floating point
• Addition twice as fast as subtraction
• Multiplication 100-1,000 time faster than
division
• Transcendental functions real slow
• Many programs constrained by old
operating systems