Interpretation Of Seismic Data Recorded By Earthquake Seismographs

17. Plot the earthquake data from the region associated with the Peru-Chile Trench from Table 1 on the right section of the graph paper, using a dot to represent each data point.

With our observation of the Shawangunk formation, we see a sedimentary rock formation containing a range of grain size. Such sizes range from pebbles (3cm-5cm), fine-grain sand, and medium-grain sand. There is some grading towards the bottom left of the outcrop known as a reverse grading with some small cross beds present (Figure 2). The grading occurs towards a slight part of the outcrop where we see the grading beginning as fine grain sediments and working up to coarser grain. With moderate sorting we see variations of degree of sorting per bed. As the degree of sorting varies as does the sphericity. The sediment bedding is well seen ranging in sizes of +/--20 cm to 40 cm. This outcrop has thick beds as one can see the basic units with cracks in between each (Figure 3). With mostly tabular beds consisting of sub-angular, and sub-rounded sediments, this outcrop also consists of some ventricular beds (Figure 4). When looking at figure 4, we have a small space of a ventricular bed present. This is because the bed comes in, pinches thicker bedding,

Structural Geology – When large bodies of rocks are formed these did not happen in one day. They have history within that can be studied. Structural Geology discovers this history to be able to tell what happened before, what kind of tectonic plate occurred. Structural Geology supports other Geology areas such as Petrology to discover natural gas or petroleum to say the least.

Determining the distance along the Earth's surface from a seismic station to the epicenter of an earthquake is based on the difference in arrival times between

The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada, an area of approximately 200,000 square miles. The ground motion caused by the earthquake source is recorded by instruments called seismographs. The zigzag trace made by a seismograph, called a "seismogram," reflects the changing amplitude and frequency content of the ground shaking beneath the instrument (usgs.gov). Using seismograms, scientists can determine the time, the epicenter, the depth, and the type of faulting of an earthquake as well as estimate how much energy was released by it.

Complete this week’s lab by filling in your responses to the questions from Geoscience Laboratory. Although you are only required to respond to the questions in this worksheet, you are encouraged to answer others from the text on your own.

Complete this week’s lab by filling in your responses to the questions from Geoscience Laboratory. Select answers are provided for you in red font to assist you with your lab work. Although you are only required to respond to the questions in this worksheet, you are encouraged to answer others from the text on your own.

Evaluate how Plate Tectonic Theory helps our Understanding of the Distribution of Seismic and Volcanic Events (40 marks)

To find out what had been happening below the surface, researchers created 3D images of the mantle portion of the North American Plate. Seismologists image the internal part of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground. The waves move faster through colder rocks and less quickly through warmer rocks. Rocks cool and harden as they become older, so the faster seismic waves, the older the rock.

The first are primary waves. These are very fast moving waves, travelling at between 1 and 8 kilometres per second. These particular waves can pass through solids, liquids and gases easily. Because they can travel through rock, as they pass the waves move tiny rock particles back and forth and pushing them apart and then back together. These waves typically arrive at the surface as an abrupt thud. The next type of waves are secondary waves. These move slower and can only pass through solids. These particular waves push rock particles outward. Since they only travel through solid materials, they get stopped at the liquid layer in the Earth's

❖ Found mostly near convergent tectonic plate boundaries where the P/T condition can be very high.

Anisotropy is the idea that the rocks properties vary with direction, so it is very important in which way that the rock was oriented compared to the load, or the compression, that is applied to the rock. This means that orientation of the bedding that varied between 0 degrees and 90 degrees was very important. The scientists used Thomsen’s parameters to quantify the elastic anisotropy. A few ways that the scientist recognized this was that when brittle shale was preceded by a change in the P wave anisotropy. This was because of the crack growth and mineral reorientation that was discussed earlier. Next, anisotropy variations were the largest for the shale that was deformed perpendicular to the bedding, so when the bedding angle was closer to 90 degrees. When the confining pressures were at the highest, the anisotropy variations were the largest, which makes a lot of sense when we know that the anisotropy is the idea that the properties of rocks vary with different orientation and it created anisotropy reversal at high confining pressures. The last information the scientists found was that the P wave anisotropy change was weak when the shale deformed parallel to the bedding, and this is because it could not take a lot of pressure because of the way it was

Despite more recent theories, this has not always been the case and early beliefs were generally based on religion not science. It is now common knowledge that the Earth’s interior consists of several layers, which include the upper mantle, the lower mantle, the outer core and the inner core. We are aware of changes in composition of the interior due to changes in states of matter, by using P and S seismic waves (P-waves being able to travel through both solids and liquids but S-waves only able to propagate through liquids as liquids do not resist shearing motion.) to monitor the depth at which waves are able to pass through. As density increases, seismic waves tend to decrease in speed but will travel faster through more rigid substances.

The earthquakes above give a brief glimpse into the importance of analyzing past and present fault configurations. If scientists could make a breakthrough in this area perhaps we could better predict earthquake activity and better prepare ourselves if it is deemed a potential disaster is looming.

At first, they thought the thick, old rocks could be remnants of ancient tectonic plates. But the shapes and locations of the thick and thin regions suggested a different explanation: through past rifting and accretion, areas of the North American Plate have become more dense and were pulled downward into the mantle through gravity. At certain times, the densest parts broke off from the plate and sank into the warm asthenosphere below. The asthenosphere, being lighter and more buoyant, surged in to fill the void created by the missing pieces of mantle, eventually cooling to become the thin, young rock in the images.