What is a seismologist?

1- Principal functions
Seismologists are Earth scientists, specialized in geophysics, who study the genesis and the propagation of seismic waves in geological materials. These geological materials can range from a laboratory sample to the Earth as a whole, from its surface to its core. Their research aims at interpreting the geological composition and structures of the Earth. In the case of earthquakes, seismologists evaluate the potential dangers and seek to minimize their impact through the improvement of construction standards. The vast majority of seismologists work in petroleum exploration, where the seismic waves come from controlled sources (explosions, vibrations caused by trucks). The generated seismic waves make it possible to locate the geological structures at depth. At the Geological Survey of Canada, the Seismology and Electromagnetism Section carries out such research. Other seismologists study the seismic waves generated by much more powerful sources: natural, like earthquakes and mining events, or artificial, like underground nuclear tests. The fundamental work of a seismologist is to locate the source, the nature, and the size (magnitude) of these seismic events. In Canada, this work is mainly carried out by the seismologists of Earthquakes Canada. Within the study of earthquakes, several specialities exist. Certain seismologists study the relation between faults, stress and seismicity (i.e. seismo-tectonics), others interpret the mechanisms of rupture from seismic wave data (focal mechanisms), others integrate geoscientific information in order to define zones of seismicity (seismic zoning), and finally others, collaborate with engineers in an attempt to minimize the damage caused to structures (earthquake engineering). Seismologists work in multidisciplinary ms composed of Earth scientists, technicians and professionals from the fields of computers, physics, electronics, telecommunications and civil engineering. Contacts with emergency organizations are often necessary.

2- Tools of the seismologist
There is no seismology without seismographs! Seismographs are the key tool of seismologists since they make it possible to collect and to record the vibrations of the Earth. Traditionally, seismographs recorded on paper (analogue recorders). This type of apparatus is becoming much less popular. Nowadays, digital instruments are preferred since they allow better definition of ground vibrations and make readings much more precise. During field surveys, sometimes made following large seismic events, portable seismographs are deployed in order to increase the number of seismographs in the area of study. If the survey is carried out in remote locations, seismologists may use trucks, planes, or helicopters. The seismologists might even have to sleep under tents! At all times, the seismologists use computers. These make it possible to record and visualize the movements of the Earth. Specialized software, sometimes developed by the seismologists themselves, makes it possible to interpret the seismological data.

3- Interests
As with any Earth scientist, curiosity and a thirst for knowledge are essential to the seismologist. Moreover, a meticulous nature, an interest in computer science, and in certain cases, in outdoor activities, are necessary. Though often called upon to work alone, the seismologist must also be able to work within teams to solve problems. Well developed written and oral communication skills are important in order to communicate the results of their research.

4- Studies
Depending on their field of interest, seismologists can come from following the fields: geology, geophysics, physics or applied mathematics. A university undergraduate degree is necessary, and Masters studies or Doctoral work are significant assets for more advanced research. Though several Canadian universities offer degrees in Earth sciences (geology, geological engineering, geophysics), none offer programs dealing with the seismology of earthquakes. Specialization can be done at the Graduate level (Masters, Doctorate) after a first degree in the disciplines mentioned above.

5- Prospects for employment
In Canada, seismologists interested in the study of earthquakes number only a few dozen. The prospects for employment are thus relatively restricted. However, the possibility of recruitment increases according to the level of gen_infoation of the candidates. In Canada, one finds the majority of seismologists at the Geological Survey of Canada, as well as at universities and with several engineering firms.

Plate Boundaries

At the same time, some of the oldest ocean crust occurs in deep sea trenches, which run parallel to continental mountain ranges. A lot of very large earthquakes have been plotted along deep ocean trenches, suggesting that these are seismically active areas (meaning the crust is moving). Scientists put two and two together, noting that the youngest oceanic crust was along the mid-ocean ridges and the oldest ocean crust was along the very bottoms of deep sea trenches. That neatly defined the edges of the tectonic plates and showed the direction of their movement. Where the deep sea trenches were found converging boundaries.
A Converging Boundary is the opposite of a spreading boundary. Typically you will see a converging boundary on a tectonic plate that is on the opposite side of a spreading boundary. As a plate moves in one direction it collides with the adjacent plate on its "front" end in a deep sea trench, while the trailing end of the plate is being pulled and stretched (spreading) from the plate on the other end at a mid-ocean ridge. For example, look at the Pacific plate (click to enlarge the plate tectonics map). The entire plate is moving north and westward as the top edge converges with the North American and European plates. You can see the left side of the Pacific plate is converging with the Indian plate. Then if you look at the bottom and right edges of the plate you can see it's spreading apart from the Antarctic and Nazca plates.
Sometimes you'll see volcanic activity at converging boundaries where plates are crashing into each other. When one plate (usually the lighter continental crust) rides up over the top of the other it's called a subduction zone - because one plate margin is being subducted under the other.
A good example of this type of plate margin is where the Nazca and South American plates are crashing into each other. The lighter continental South American plate is riding up over the heavier oceanic Nazca plate. Deep down where the leading edge of the Nazca plate is diving down under the South American plate it's making contact with the molten magma of the earth's mantle. The long cordillera, or chord-like chain of volcanic mountains known as the Andes, are a result of the rumpling of the South American plate where the Nazca plate crashes into it, and the volcanoes that have formed from the increased seismic activity on the Nazca plate margin deep down.
In other converging boundaries, there is no volcanic activity because the tectonic plates are both continental plates, weighing the same. No subduction happens along these margins, just massive deformation of the edges of the plates. A good example of this is the Himalayan Mountains where the European and Indian plates meet. The two plates have continued ramming into each other, causing the crust to buckle, wrinkle, and uplift into the highest mountain range on earth.
The few transverse boundaries are places where the two plates are just sliding past each other. In many of these boundaries there is a lot of tension and strain where the two plates are sliding and scraping past each other. The resulting strain from the sliding action of the plates causes cracks in the crust called faults. As the larger plates move past each other some chunks of crust and overlying rock are broken into fault blocks. When there is a big enough movement along the cracks or faults in the earth's crust we feel it in the form of earthquakes. One of the most famous faults is the San Andreas, which runs along the west coast of California. It's famous for generating many of the larger quakes in California, including the world-renowned San Francisco earthquake of 1906. Funny thing is, the 1906 earthquake itself didn't do nearly as much damage as the fires that burned the

Volcanoes

What are volcanoes?

A Volcano is a gap in the earth where molten rock and other materials come to the earth's surface. Some volcanoes are just cracks in the earth's crusts. Others are weak places in the earth's crust, which occur on places where magma bubbles up through the crust and comes to the earth's surface. Magma is molten rock that occurs by partial melting of the crust and the mantle by high temperatures deep down in the ground. Once magma comes to the earth's surface it is called lava.
Active and non-active volcanoesThere are volcanoes in different phases of activity:Active volcanoes, which are likely to erupt at any moment, dormant volcanoes, which lie dormant for centuries, but then erupt suddenly and violently, and extinct volcanoes - ones no longer likely to erupt.

Types of Volcanoes

This article was contributed by Charles W. Finkl, Jr., Professor of Geology, Florida Atlantic University; Director, Coastal Education and Research Foundation; Editor, Journal of Coastal Research.

Volcanoes are usually classified by shape and size. These are determined by such factors as the volume and type of volcanic material ejected, the sequence and variety of eruptions, and the environment. Among the most common types are shield volcanoes, stratovolcanoes, and cinder cones.

Shield volcanoes have a low, broad profile created by highly fluid basalt flows that spread over wide areas. The fluid basalt cannot build up a cone with sides much steeper than 7 degrees. Over thousands of years, however, these cones can reach massive size. The Hawaiian Islands are composed of shield volcanoes that have built up from the sea floor to the surface some 3 miles (5 kilometers) above. Peaks such as Mauna Loa and Mauna Kea rise to more than 13,600 feet (4,145 meters) above sea level. Hawaii is the largest lava structure in the world, while Mauna Loa, if measured from the sea floor, is the world's largest mountain in terms of both height and volume.

Stratovolcanoes are the most common volcanic form. They are composed of alternating layers of lava and pyroclastic material. When a quiet lava flow ends, it creates a seal of solidified lava within the conduit of the volcano. Pressure gradually builds up below, setting the stage for a violent blast of pyroclastic material. These alternating cycles repeat themselves, giving stratovolcanoes a violent reputation.
A cinder cone is a conical hill of mostly cinder-sized pyroclastics. The profile of the cone is determined by the angle of repose, that is, the steepest angle at which debris remains stable and does not slide downhill. Larger cinder fragments, which fall near the summit, can form slopes exceeding 30 degrees. Finer particles are carried farther from the vent and form gentle slopes of about 10 degrees at the base of the cone. These volcanoes tend to be explosive but may also extrude some lava. Cinder cones are numerous, occur in all sizes, and tend to rise steeply above the surrounding area. Those occurring on the flanks of larger volcanoes are called parasitic cones.
Volcanic activity typically alternates between short active periods and much longer dormant periods. An extinct volcano is one that is not erupting and is not likely to erupt in the future. A dormant volcano, while currently inactive, has erupted within historic times and is likely to do so in the future. An inactive volcano is one that has not been known to erupt within historic times. Such classification is arbitrary, however, since almost any volcano is capable of erupting again.
In the late stages of volcanic activity, magma can heat circulating groundwater, producing hot springs and geysers (see Geyser and Fumarole). A geyser is a hot-water fountain that spouts intermittently with great force. One of the best-known examples is Old Faithful in Yellowstone National Park. Fumaroles are vents that emit gas fumes or steam.
Volcanoes occur along belts of tension, where continental plates diverge, and along belts of compression, where the plates converge. Styles of eruption and types of lava are associated with different kinds of plate boundaries. Most lavas that issue from vents in oceanic divergence zones and from midoceanic volcanoes are basaltic. Where ocean plates collide, the rock types basalt and andesite predominate. Near the zone where an ocean plate and continental margin converge, consolidated ash flows are found.
Nearly 1,900 volcanoes are active today or known to have been active in historical times. Of these, almost 90 percent are situated in the Pacific Ring of Fire. This belt partly coincides with the young mountain ranges of western North and South America, and the volcanic island arcs fringing the north and western sides of the Pacific basin. The Mediterranean-Asian orogenic belt has few volcanoes, except for Indonesia and the Mediterranean where they are more numerous. Oceanic volcanoes are strung along the world's oceanic ridges, while the remaining active volcanoes are associated with the African rift valleys.

FOLD

Compositional or metamorphic layers of rocks may bend during ductile deformation to produce folds. Folds commonly form during regional horizontal shortening in orogenic (mountain building) belts at microscopic to regional scales in all rock types (given suitable deformation conditions). Even rocks that at Earth's surface may be brittle and shatter when rapidly deformed, may fold during the application of regional, tectonic stresses over a long period of time at depth. Such a change in rock rheology is due to elevated temperature and confining pressure and the presence of fluids at deeper levels of the crust.
Upright layers (where young beds overlie older beds) that are arched upward are called anticlines. If the direction of younging (facing) is not known, such folds are called antiforms. Layers that are bent downward are called synclines (where beds are upright) or synforms where facing is not known. Cylindrical folds show the same profile in sections normal to their axes at any position along the axis. Folds where profiles vary from section to section and layers describe part of a cone are called conical folds. Folds are also classified according to the orientation of their hinge line or fold axis (the axis of curvature) and of their axial surface (the surface that bisects fold limbs and passes through the fold axis). The angle the fold hinge makes with the horizontal is called the plunge of a fold. Folds plunge gently when this angle is 10–30°, moderately between 30–60°, steeply between 60–90°, and are vertical when axes plunge 90°. Folds are upright where the axial surface is steeply dipping, inclined where the axial surface is moderately dipping, overturned where the axial surface is shallowly dipping and one limb is inverted, and recumbent where the axial surface is horizontal. In parallel folds, the layer thickness measured normal to the layer is constant around the fold. In similar folds, layer thicknesses measured parallel to the axial plane are constant. In describing folds, it is also important to note the inter-limb angle and whether fold hinges are rounded or angular.
Strong (competent) layers interlayered with more ductile (incompetent) layers buckle during layer-parallel shortening. The wavelength of the resulting folds depends on both the layer thickness and the viscosity (competence) contrast between layers. Larger wavelength folds develop in thick or competent layers. Folds may also develop during ductile flow in high-grade metamorphic rocks and in incompetent, lower-grade rocks. Irregular and often highly contorted syn-sedimentary folds can form during deposition of sedimentary rocks within slumps (which may be triggered by earthquakes).
When rocks that have already been folded are subjected to further shortening, early-formed folds may be refolded. Different fold interference patterns develop depending on the relative orientations of axes and axial surfaces for both generations of folds. A "dome and basin" (or, "egg carton") pattern results from the interference between two sets of upright folds whose axial surfaces are at a large angle to each other. A mushroom-shaped interference pattern results where folds with horizontal or shallowly dipping axial surfaces are folded by upright folds. A "hook" interference pattern occurs where fold axes are of similar orientation, but where axial surfaces are at a high angle to each other.
Folds may also form during regional crustal extension, such as in sedimentary basins. Roll-over antiforms develop over curved extensional (normal) faults in the upper, brittle crust or ductile shear zones in the middle to lower crust. Synforms are formed above areas where the underlying fault or ductile shear zone changes from shallowly to steeply dipping. Folds may also form during back-rotation of layers between two extensional faults or ductile shear zones. In high-grade rocks, folds may also form in surrounding layers when a competent layer pinches and swells or separates into barrel-shaped fragments (boudins) during layer-parallel extension.
Folds control the formation and localization of some petroleum and mineral deposits. Many oil and gas traps are created by regional-scale antiforms or domes formed by fold superposition, in wrench zones, or on the margins of salt diapirs. Some gold deposits are also controlled by folds. Differences in fold style of adjacent beds may lead to parting of beds along fold hinges. Quartz and, if chemical conditions are favorable, gold, may be deposited from fluids that migrate to such dilatational sites forming saddle reefs. In higher-grade rocks, rare metal pegmatites may intrude dilatational sites along fold hinges. Folds also provide geologists with valuable information about the orientation of stresses in Earth's crust at the time of their formation, helping them to unravel regional geological history.

Sediment is deposited in horizontal layers, called "beds". The oldest sediment is on the bottom and the youngest is on the top (unless the beds are overturned). After deposition, compressional stress applied to a rock will cause it to fold. There are two main types of folds. An anticline is a fold that bends downward, creating a hill-like structure. A syncline is a fold that bends upward in the shape of a "U".

Anticline Syncline

Folds are considered either cylindrical or non-cylindrical. If you were to slice a cylindrical fold (like bread), the sections would appear similar. If you could to take a pencil, without lifting it from the surface of the fold, and bring it from one limb to the other, the fold is cylindrical. Looking at the diagram of the non-cylindrical fold, it is evident that the pencil could not remain on the surface.

The plunge of a structure is measured as an angle with respect to its position from the horizontal. Folds can be plunging or non-plunging, according to the inclination of its fold axis. (see below diagrams)

The above photograph represents a fold that occurs in Unit 2. Strikes and dips were taken on both limbs and the data was plotted on a stereonet in order to determine the orientation of the fold axis.