The Study of Earthquake Waves to Interpret the Earth's Internal Structure and Composition
Studying the different waves that are given off in an eathquake can
identify the internal composition and structure of the earth. There
are three types of wave Primary or 'push' waves (P-waves), Secondary
or 'shock' waves (S-waves) and Longitudal or 'long' waves (L-waves).
The waves that must be studied to interpret the earth's internal
structure and composition are 'Body Waves' Body waves are another name
for P or S waves.
Earthquakes occur most commonly in seismic zones; these zones are
related with oceanic ridges, young fold mountains and island arcs.
Earthquake foci are located at depths under the surface up to a
maximum of approximately 700km. They are grouped into shallow
(0-70km), Intermediate (70-300km) and Deep (300-700km). The zone in
which earthquake foci are found is called the Benioff zone.
The focus of any earthquake cannot be found any deeper than about
700km, this suggests that the composition of the earth below this
depth is different from above it and so is not adequate for earthquake
foci to be located and therefore it must change from a rock that can
be easily fractured to a less easily fracturable rock.
When an earthquake occurs, it produces waves that radiate out from the
epicentre (The point on the surface directly above the focus). The
body waves that are produced go into the earth. P-waves travel fastest
with S-waves coming second, at half the speed.
P and S-waves need dense, rigid rock to travel fastest in, as the rock
gets less dense, the body waves slow down and when the rock turns to a
liquid form, the S-waves cannot travel through and the P-waves are
greatly decreased in velocity and refracted. As body waves travel into
the earth, they enter the Moho, this area of crust is very dense and
rigid and so both waves speed up rapidly. At approximately 50km, the
waves suffer a slight decrease in velocity, before beginning to
increase in velocity again after about 50km. This shows that there
Quartzite is a non-foliated metamorphic rock. This rock is intrusive and forms when exposed to extreme amounts of heat and pressure. Over a billion years ago, there was an ocean where Kamiak Butte is. This ocean floor was made of sand, as time went on oceans receded and the exposed sand underwent processes that turned it into sandstone – or as we learned in class the process of lithification. Years later, this sandstone would morph into the quartzite that is present now.2
This sedimentary rock has hardened over the many years with sand shells, small pebbles, grains of sand and rocks of various sizes. In comparison to our 4.5 billion year old Earth, these sand shells might as well be brand new, when in reality they could be up to 1,000 years old. If the sandstone were to be replaced with calcite it would completely change the subclass of rock, it would then be chemical & organic limestone. The variation in sand stone is due to different rates of deposition and change in patterns of the sediment movement (Mc Knight, p. 384). These tightly compacted varying stones and shells will be weathered away by wind and waves over time and could eventually be reduced to a rock the size of your hand.
There are many pro’s for attempting to forecast an earthquake or volcano. Forecasting an earthquake or eruption saves lives and property, mainly by preparation, as there is no way to prevent these events with today technology.
hard rock is eroded, it can cause an island of hard rock left of the
On Earthquakes An earthquake is a shaking or trembling of the crust of the earth caused by underground volcanic action or by the breaking and shifting of rock beneath the surface. The volcanic action and shifting rocks create strain which continues to build to a sudden release of pressure resulting in a shock wave. The vibrations produced in the crust can vary from barely noticeable to enormously destructive. Shock waves can be classified into two broad categories. Waves that send particles oscillating back and forth in the same direction as the waves are traveling are called primary.
The plate tectonic theory is a theory that geologists use to help explain the Earth’s surface processes and events. It explains that the sliding of these plates are either away from each other, sliding past each other, or sliding into each other and causing one of the plates to slide beneath the other. There are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries. A divergent boundary occurs when two tectonic plates move away from each other. Magma then flows up from the mantle to fill in the space between the plates, forming a raised ridge called a mid-ocean ridge. The magma also spreads in the exterior, forming new ocean floor and new oceanic crust. A convergent boundary occurs when two plates
eddies, slightly spinning, then all of a sudden, it slaps into a rock or gets sucked beneath the water by a small whirlpool. After doing this enough times one will realize
There were two main ways scientists learned about Earth’s interior. One way scientists learned about Earth’s interior was through rock samples. Scientists drilled rocks underneath Earth’s surface, and compared them to the ones on Earth’s surface. Another way scientists learned about Earth’s interior was through seismic waves. With seismic waves, scientists study how they traveled through Earth, and their speed and path. These are the two main ways how scientists learned about Earth’s interior.
Beno Gutenberg was the foremost observational seismologist of the twentieth century. He combined exquisite analysis of seismic records with powerful analytical, interpretive, and modeling skills to contribute many important discoveries of the structure of the solid Earth and its atmosphere. Perhaps his best known contribution was the precise location of the core of the Earth and the identification of its elastic properties. Other major contributions include the travel-time curves; the discovery of very long-period seismic waves with large amplitudes that circle the Earth; the identification of differences in crustal structure between continents and oceans, including the discovery of a significantly thin crust in the Pacific; the discovery of a low-velocity layer in the mantle (which he interpreted as the zone of decoupling of horizontal motions of the surficial parts from the deeper parts of the Earth); the creation of the magnitude scale for earthquakes; the relation between magnitudes and energies for earthquakes; the famous universal magnitude-frequency relation for earthquake distributions; the first density distribution for the mantle; the study of the temperature distribution in the Earth; the understanding of microseisms; and the structure of the atmosphere.
7. Refer to Figure 22-6. What name is given to the core of the modern-day North American continent that formed in the Proterozoic?
There are two main ways scientists learned about Earth’s interior. During earthquakes, seismic waves form, in which scientists use. For example, seismic waves travel through earth by speed and path that travel through earth. They study how seismic waves travel through Earth by how fast and which path it goes. The second main way is the rock samples are very useful that are drilled and scientists looked at rocks that came to the surface. An example of this is that they drilled into the earth and found rocks that came to the surface. In conclusion, scientists study about the earth’s interior by using two main ways.
Coastal Erosion operates at different rates and different times. Limestone rock is eroded slower than sedimentary rock. The cliff at Muriwai made of sedimentary rock was eroded back to expose 'Fisherman's Rock' - the shore platform which, made of limestone -- tended to erode back slower than the cliff.
The formation of Earth’s crust began during the Hadean eon, shortly after the Chaotian interval of core formation and solidification of the magma ocean (Allegre et al., 2008; Elkins-Tanton, 2008; Rudge et al., 2010). This process initiated with the differentiation of the crust-mantle zones from a bulk silicate Earth (BSE) reservoir, which is thought to have also produced the first continuous terrestrial crust (Allegre et al., 2008). However, whole rock signatures from original Hadean crust have not been preserved in the known geologic record and can only be inferred by isotopic analysis (Tessalina et al., 2010; Rizo et al., 2012). The one continuous trace of this early crust comes in rare detrital zircon grains within sandstone units (Jack Hills) of the Yilgarn Craton in Western Australia (Compston and Pidgeon, 1986; Kemp et al., 2010). Intensive study has surrounded the Jack Hills zircon and has produced various geodynamic models for the early Earth, as well as controversial observations and interpretations (Valley et al., 2002; Harrison et al., 2008). For these reasons, research of the Late Archean igneous complexes has become a primary interest for crustal evolution insight from the Earth’s interior that is otherwise unavailable for study (Smithies et al., 2005; Nebel et al., 2013).
The definition of the term thin bed involves the concept of the resolving power (Widess, 1973) thus seismics is impacted by resolution. Most geological structures have a smaller vertical dimension than a horizontal one (Chang et al, 1996), thus, the ratio of the vertical dimensions plays a very important role in seismic resolution. As the dimension ratio decreases, the difficulty in identifying geological events increases and become more challenging (Chang et al, 1916). Sheriff, (1991) defines Seismic resolution as the ability to separate two features that are very close together; the minimum separation of the bodies before their identifies are lost. It is seen as the minimum distance between two events that can be seen
An acoustic wave can simply be described as a longitudinal wave. A longitudinal wave is a wave that vibrates and moves in the direction of its propagation. This means the medium is either in the same or opposite direction of the way the wave travels. Acoustic waves are a form of Mechanical longitudinal waves; these waves are otherwise known as compression waves or compressional waves. Compressional waves obviously produce compression, decompression, and rarefaction to travel.