SEISMOLOGY AND SEISMIC DRILLING
Seismologist departement is responsible for drilling a hole shot point and planting explosives properly. Drilling carried out before recoording implemented. During drilling operations,drilling on bullet point with the depth of tolerance that has been determined by the counter party. After the hole is filled with explosive, then tamping. Results of drilling holes in the field is ready to fire. Output from a drilling depth is another form of data charging explosives, and the number of explosives that are used on every hole. In addition,drilling must also provide data on the shot point offset or compensation. The lithology is very influential on the productivity of drilling. In lithologic hard drilling productivity will decline. Another obstacle is often found in sandy areas that can cause the drill pipe stuck. In the area of coral often fell apart when the pipe drill holes unplugged. Drilling will also be hampered in areas that are difficult to find water.
Seismology
From Wikipedia, the free encyclopedia
Seismology (
/saɪzˈmɒlədʒi/) is the scientific study of
earthquakes and the propagation of
elastic waves through the
Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as
tsunamis as well as diverse
seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A related field that uses
geology to infer information regarding past earthquakes is
paleoseismology. A recording of earth motion as a function of time is called a
seismogram. A seismologist is a scientist who does research in seismology.
Highlights of the history of seismology
Some milestones in the development of seismology are:
[1]
Early speculations on the natural causes of earthquakes in the writings of
Thales of Miletos (ca. 585 B.C.E.),
Anaximenes of Miletos (ca. 550 B.C.E.),
Aristotle (ca. 340 B.C.E.) and
Zhang Heng (132 C.E.).
In 132 C.E.,
Zhang Heng of China's
Han dynasty designed the first known seismoscope.
In 1664
Athanasius Kircher argued that eathquakes were caused by the movement of fire within a system of channels inside the Earth.
In 1703
Martin Lister (1638 to 1712) and
Nicolas Lemery (1645 to 1715) proposed that earthquakes were caused by chemical explosions within the earth.
The
Lisbon earthquake of 1755,
coinciding with the general flowering of science in Europe, set in
motion intensified scientific attempts to understand the behaviour and
causation of earthquakes. The earliest responses include work by
John Bevis (1757) and
John Michell
(1761). Michell determined that earthquakes originate within the Earth
and were waves of movement caused by "shifting masses of rock miles
below the surface".
From 1857
Robert Mallet laid the foundation of instrumental seismology and he carried out seismological experiments using explosives.
In 1897,
Emil Wiechert's theoretical calculations led him to conclude that the
Earth's interior consists of a mantle of silicates, surrounding a core of iron.
In 1906
Richard Dixon Oldham
identified the separate arrival of P-waves, S-waves and surface waves
on seismograms and found the first clear evidence that the Earth has a
central core.
[2]
In 1910, after studying the 1906 San Francisco earthquake,
Harry Fielding Reid put forward the "
elastic rebound theory"
which remains the foundation for modern tectonic studies. The
development of this theory depended on the considerable progress of
earlier independent streams of work on the behaviour of elastic
materials and in mathematics.
In 1926
Harold Jeffreys was the first to claim, based on his study of earthquake waves, that below the crust, the core of the Earth is liquid.
In 1937
Inge Lehmann determined that within the earth's liquid outer core there is a solid
inner core.
By the 1960s earth science had developed to the point where a
comprehensive theory of the causation of seismic events had come
together in the now well-established theory of
plate tectonics.
Types of seismic wave
Main article:
Seismic wave
Seismogram records showing the three components of ground motion. The
red line marks the first arrival of P-waves; the green line, the later
arrival of S-waves.
Seismic waves are
elastic waves that propagate in solid or fluid materials. They can be divided into
body waves that travel through the interior of the materials;
surface waves that travel along surfaces or interfaces between materials; and
normal modes, a form of standing wave.
Body waves
There are two types of body wave,
P-waves and
S-waves (both body waves). Pressure waves or Primary waves (
P-waves), are
longitudinal waves that involve
compression and
rarefaction
(expansion) in the direction that the wave is traveling. P-waves are
the fastest waves in solids and are therefore the first waves to appear
on a
seismogram.
S-waves, also called shear or secondary waves, are
transverse waves
that involve motion perpendicular to the direction of propagation.
S-waves appear later than P-waves on a seismogram. Fluids cannot support
this perpendicular motion, or
shear, so S-waves only travel in solids. P-waves travel in both solids and fluids.
[3]
Surface waves
The two main kinds of surface wave are the
Rayleigh wave,which has some compressional motion, and the
Love wave,
which does not. Such waves can be theoretically explained in terms of
interacting P- and/or S-waves. Surface waves travel more slowly than
P-waves and S-waves, but because they are guided by the surface of the
Earth (and their energy is thus trapped near the Earth's surface) they
can be much larger in amplitude than body waves, and can be the largest
signals seen in earthquake seismograms. They are particularly strongly
excited when their source is close to the surface of the Earth, as in a
shallow earthquake or explosion.
[3]
Normal modes
The above waves are traveling waves. Large earthquakes can also make the Earth "ring" like a bell. This ringing is a mixture of
normal modes
with discrete frequencies and periods of an hour or longer. Motion
caused by a large earthquake can be observed for up to a month after the
event.
[3]
The first observations of normal modes were made in the 1960s as the
advent of higher fidelity instruments coincided with two of the largest
earthquakes of the 20th century - the
1960 Great Chilean Earthquake and the
1964 Great Alaskan Earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.
Earthquakes
One of the first attempts at the scientific study of earthquakes followed the
1755 Lisbon earthquake. Other especially notable earthquakes that spurred major developments in the science of seismology include the
1857 Basilicata earthquake,
1906 San Francisco earthquake, the
1964 Alaska earthquake, the 2004
Sumatra-Andaman earthquake, and the 2011
Great East Japan earthquake. An extensive list of famous earthquakes can be found on the
List of earthquakes page.
Controlled seismic sources
Seismic waves produced by
explosions or vibrating controlled sources are one of the primary methods of
underground exploration in geophysics (in addition to many different
electromagnetic methods such as
induced polarization and
magnetotellurics). Controlled-source seismology has been used to map
salt domes, faults, anticlines and other geologic traps in
petroleum-bearing
rocks,
geological faults, rock types, and long-buried giant
meteor craters. For example, the
Chicxulub Crater, which was caused by an impact that has been
implicated in the extinction of the
dinosaurs, was localized to Central America by analyzing ejecta in the
Cretaceous–Paleogene boundary, and then physically proven to exist using seismic maps from
oil exploration.
[4]
Detection of seismic waves
Seismometers
are sensors that sense and record the motion of the Earth arising from
elastic waves. Seismometers may be deployed at Earth's surface, in
shallow vaults, in boreholes, or
underwater. A complete instrument package that records seismic signals is called a
seismograph.
Networks of seismographs continuously record ground motions around the
world to facilitate the monitoring and analysis of global earthquakes
and other seismic sources. Rapid location of earthquakes makes
tsunami
warnings possible because seismic waves travel considerably faster than
tsunami waves. Seismometers also record signals from non-earthquake
sources ranging from explosions (nuclear and chemical), to local noise
from wind or anthropogenic activities, to incessant signals generated at
the ocean floor and coasts induced by ocean waves (the global
microseism), to
cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes with energies as high as 4.2 × 10
13 J
(equivalent to that released by an explosion of ten kilotons of TNT)
have been recorded by seismographs, as have a number of industrial
accidents and terrorist bombs and events (a field of study referred to
as
forensic seismology). A major long-term motivation for the global seismographic monitoring has been for the detection and study of
nuclear testing.
Mapping the earth's interior
Seismic velocities and boundaries in the interior of the
Earth sampled by seismic waves
Because seismic waves commonly propagate efficiently and interact
with internal structure, they provide high-resolution noninvasive
methods for studying Earth's interior. One of the earliest important
discoveries (suggested by
Richard Dixon Oldham in 1906 and definitively shown by
Harold Jeffreys in 1926) was that the
outer core
of the earth is liquid. Since S-waves do not pass through liquids, the
liquid core causes a "shadow" on the side of the planet opposite of the
earthquake where no direct S-waves are observed. In addition, P-waves
travel much slower through the outer core than the mantle.
Processing readings from many seismometers using
seismic tomography,
seismologists have mapped the mantle of the earth to a resolution of
several hundred kilometers. This has enabled scientists to identify
convection cells and other large-scale features such as Ultra Low Velocity Zones near the
core–mantle boundary.
[5]
Seismology and society
Earthquake prediction
Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called
earthquake prediction.
Various attempts have been made by seismologists and others to create
effective systems for precise earthquake predictions, including the
VAN method.
Most seismologists do not believe that a system to provide timely
warnings for individual earthquakes has yet been developed, and many
believe that such a system would be unlikely to give significant warning
of impending seismic events. However, more general forecasts routinely
predict
seismic hazard.
Such forecasts estimate the probability of an earthquake of a
particular size affecting a particular location within a particular
time-span, and they are routinely used in
earthquake engineering.
Public controversy over earthquake prediction erupted after Italian authorities
indicted six seismologists and one government official for
manslaughter in connection with
a magnitude 6.3 earthquake in L'Aquila, Italy on April 5, 2009. The indictment has been widely perceived
[by whom?] as an indictment for failing to predict the earthquake and has drawn condemnation from the
American Association for the Advancement of Science and the
American Geophysical Union.
The indictment claims that, at a special meeting in L'Aquila the week
before the earthquake occurred, scientists and officials were more
interested in pacifying the population than providing adequate
information about earthquake risk and preparedness.
[6]
Tools
Seismological instruments can generate large amounts of data. Systems for processing such data include:
Notable seismologists
- Aki, Keiiti
- Don L. Anderson
- Bolt, Bruce
- Claerbout, Jon
- Dziewonski, Adam Marian
- Ewing, Maurice
- Galitzine, Boris Borisovich
- Gamburtsev, Grigory A.
- Gutenberg, Beno
- Hough, Susan
- Jeffreys, Harold
- Jones, Lucy
- Kanamori, Hiroo
- Keilis-Borok, Vladimir
- Knopoff, Leon
- Lehmann, Inge
- Mallet, Robert
- Mercalli, Giuseppe
- Milne, John
- Mohorovičić, Andrija
- Oldham, Richard Dixon
- Fusakichi Omori
- Sebastião de Melo, Marquis of Pombal
- Press, Frank
- Richards, Paul G.
- Richter, Charles Francis
- Sekiya, Seikei
- Sieh, Kerry
- Paul G. Silver
- Tucker, Brian
- Vidale, John
- Wen, Lianxing
- Winthrop, John
- Zhang Heng
See also
