Earthquake.pptx
- 2. INTRODUCTION Earthquake ( also known as quake, tremor or temblor) is the phenomenon where there is a sudden release of extreme energy from the earth crust resulting in shaking and displacement of the ground along with the creation of seismic waves(detail is in coming sections) Earthquake shaking may cause lose of life and destruction of property. In strong Earthquake ground shake violently. Buildings may fall or sinks into the soil.
- 3. TERMS RELATED TO EARTHQUAKE Focus(Hypocenter): Focus is the point in the fault where rupture occurs and the location from which seismic waves are released. Epicenter: Epicenter is the point on the earth’s surface that is directly above the focus (the point where an earthquake or underground explosion originates) Fault: A fault is a fracture or zone of fractures between two blocks of rock.
- 4. TERMS RELATED TO EARTHQUAKE Fault line: A fault line is a surface trace of a fault, the line of intersection between the Earth’s surface. Fault scrap: A fault scrap is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults.
- 5. CAUSES OF EARTHQUAKE Primary cause of Earthquake is fault on crust of Earth. A fault is a fracture or zone of fractures between two blocks of rock in response to stress. Classification of Faults: 1.Normal Fault 2.Reverse Fault A normal fault is one in which the rocks above the fault plane, or hanging wall, move down relative to the rocks below the fault plane, or footwall A reverse fault is one in which the hanging wall moves up relative to the footwall.
- 6. 3.Strike slip Fault When rocks on either side of a nearly vertical fault plane move horizontally, the movement is called strike-slip.
- 7. OTHER CAUSES OF EARTHQUAKE Tectonic cause: There are seven major plates: African, Antarctic, Eurasian, Indo- Australian, North American, Pacific and South American The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.
- 8. Volcanic earthquakes Volcanic earthquakes are those that occur inside volcanoes or close to them. Earthquakes are produced by vibrations generated by the movement of magma or other fluids within the volcano. Pressure within the system increases and the surrounding rock fails, creating small earthquakes.
- 11. ARTIFICIAL INDUCTION Earthquakes are sometimes caused by human activities, including; •The injection of fluids into deep wells, •The detonation of large underground nuclear explosions, •The excavation of mines, and the filling of large reservoirs.
- 12. EFFECTS OF EARTHQUAKES Earthquakes have varied effects, including changes in geologic features, damage to man-made structures, and impact on human and animal life. Most of these effects occur on solid ground, but, since most earthquake foci are actually located under the ocean bottom, severe effects are often observed along the margins of oceans. Surface phenomena Earthquakes often cause dramatic geomorphological changes, including ground movements—either vertical or horizontal—along geologic fault traces; rising, dropping, and tilting of the ground surface; changes in the flow of groundwater; liquefaction of sandy ground; landslides; and mudflows.
- 13. Following certain earthquakes, very long- wavelength water waves in oceans or seas sweep inshore. More properly called seismic sea waves or tsunamis (tsunami is a Japanese word for “harbour wave”), they are commonly referred to as tidal waves, although the attractions of the Moon and Sun play no role in their formation. Tsunamis
- 14. Earthquake in Pakistan On October 8, 2005, a magnitude 7.6 earthquake shook the Kashmir region (a disputed territory controlled in part by Pakistan and India), along with sections of Pakistan, India and Afghanistan. More than 80,000 people perished as a result of the quake, while an estimated 4 million others were left homeless. The epicenter of this earthquake was located around Muzaffarabad, a city approximately 65 miles northeast of the Pakistani capital, Islamabad. The hypocenter was estimated to be 12 miles below the earth's surface. The duration of 60 seconds was twice that of an average earthquake.
- 15. The study of earthquake Seismic waves Seismic waves are waves that travel through or over Earth. They are usually generated by movements of the Earth's tectonic plates (earthquakes) but may also be caused by explosions, volcanoes and landslides. They can tell us much about the Earth's structure. Earthquakes generate four principal types of elastic waves; two, known as body waves, travel within the Earth, whereas the other two, called surface waves, travel along its surface.
- 16. P-Waves There are Four basic types of seismic waves •P-waves, •S-waves •Rayleigh Waves and •Love waves. P-waves and S-waves are collectively called body waves. TYPES OF SEISMIC WAVES P-waves, also known as primary waves or pressure waves, travel at the greatest velocity through the Earth. They propagate through a material by alternately compressing and expanding the medium.
- 17. P-Waves
- 18. S-Waves S-waves, also known as secondary waves, shear waves or shaking waves, are transverse waves that travel slower than P-waves. In this case, particle motion is perpendicular to the direction of wave propagation.
- 19. Love-Waves Love waves, named after the British seismologist A.E.H. Love, who first predicted their existence. They are propagated when the solid medium near the surface has varying vertical elastic properties. Displacement of the medium by the wave is entirely perpendicular to the direction of propagation and has no vertical or longitudinal components
- 20. Rayleigh waves Named after the British physicist Lord Rayleigh, who first mathematically demonstrated their existence. Rayleigh waves travel along the free surface of an elastic solid such as the Earth. Their motion is a combination of longitudinal compression and dilation that results in an elliptical motion of points on the surface. Of all seismic waves, Rayleigh waves spread out most in time, producing a long wave duration on seismographs.
- 21. After shocks Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault.
- 22. SEISMOGRAPH Seismographs are instruments used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network. A seismograph is securely mounted onto the surface of the earth so that when the earth shakes, the entire unit shakes with it EXCEPT for the mass on the spring, which has inertia and remains in the same place. The recording device on the mass records the relative motion between itself and the rest of the instrument, thus recording the ground motion.
- 23. SEISMOGRAM A seismogram is a graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time.
- 24. Magnitude Earthquake magnitude is a measure of the “size,” or amplitude, of the seismic waves generated by an earthquake source and recorded by seismographs. In 1935 the American seismologist Charles F. Richter set up a magnitude scale of earthquakes as the logarithm to base 10 of the maximum seismic wave amplitude (in thousandths of a millimetre) recorded on a standard seismograph (the Wood- Anderson torsion pendulum seismograph) at a distance of 100 km from the earthquake epicentre.
- 25. Richter scale of earthquake magnitude Magnitude level Category Effects Earthquakes per year less than 1.0 to 2.9 micro generally not felt by people, though recorded on local instruments more than 100,000 3.0–3.9 minor felt by many people; no damage 12,000–100,000 4.0–4.9 light felt by all; minor breakage of objects 2,000–12,000 5.0–5.9 moderate some damage to weak structures 200–2,000 6.0–6.9 strong moderate damage in populated areas 20–200 7.0–7.9 major serious damage over large areas; loss of life 3–20 8.0 and higher great severe destruction and loss of life over large areas fewer than 3