Final earthquake ppt.ppt
- 2. Elements of Engineering Seismology, Characterization of ground motion, Earthquake intensity and magnitude, Recording instruments and base line correction, Predominant period and amplification through soil, Earthquake spectra for elastic and inelastic systems, Response Spectrum, Indian Standard Codes on Earthquake Engineering, Seismic Zoning Map of India.
- 3. It is the study and application of seismology for engineering purposes. It generally applied to the branch of seismology that deals with the assessment of the seismic hazard of a site or region for the purposes of earthquake engineering It is the scientific study of earthquakes and the propagation of elastic waves through the Earth.
- 4. 1. Studying earthquake history and tectonics to assess the earthquakes that could occur in a region and their characteristics and frequency of occurrence 2. Studying strong ground motions generated by earthquakes to assess the expected shaking from future earthquakes with similar characteristics. These strong ground motions could either be observations from accelerometers or seismometers or those simulated by computers using various techniques
- 10. The shaking or trembling caused by the sudden release of energy Usually associated with faulting or breaking of rocks Continuing adjustment of position results in aftershocks
- 12. Foreshock ◦ Foreshocks are relatively smaller earthquakes that precede the largest earthquake in a series, which is termed the mainshock. Not all mainshocks have foreshocks. Mainshock ◦ The mainshock is the largest earthquake in a sequence, sometimes preceded by one or more foreshocks, and almost always followed by many aftershocks. Aftershock ◦ Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock. Aftershocks can continue over a period of weeks, months, or years.
- 13. Largest earthquake in a sequence Larger mainshocks strain larger volume of rock, have more aftershocks Foreshocks and aftershocks usually at least 1 magnitude unit smaller than mainshock
- 14. Smaller earthquakes that precede the mainshock ◦ often by just hours Few in number ◦ only half of mainshocks have even one foreshock Near mainshock hypocenter ◦ part of the nucleation process
- 15. smaller earthquakes following the largest earthquake of a sequence (the mainshock) near mainshock rupture zone ◦ follow almost all shallow earthquakes ◦ cover ruptured area ◦ can number in thousands ◦ can last for years or decades aftershocks of Northridge M 6.7 are still occurring ◦ The most predictable (and therefore well- studied) earthquakes
- 16. Every time there is an earthquake, the volume of rock around the rupture is strained, that is, twisted or squeezed. Sometimes, the strained rock breaks. Often, it takes a while for it to break, so the aftershocks may appear seconds to years after the causative quake. But we don’t know for sure why there is a delay. ◦ Static fatigue ◦ Visco-elastic relaxation ◦ Diffusion processes (fluids?)
- 18. Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs
- 19. Explains how energy is stored in rocks ◦ Rocks bend until the strength of the rock is exceeded ◦ Rupture occurs and the rocks quickly rebound to an undeformed shape ◦ Energy is released in waves that radiate outward from the fault
- 20. The Focus and Epicenter of an Earthquake • The point within Earth where faulting begins is the focus, or hypocenter • The point directly above the focus on the surface is the epicenter
- 21. ~80% of all earthquakes occur in the circum-Pacific belt ◦ most of these result from convergent margin activity ◦ ~15% occur in the Mediterranean-Asiatic belt ◦ remaining 5% occur in the interiors of plates and on spreading ridge centers ◦ more than 150,000 quakes strong enough to be felt are recorded each year
- 22. Seismic waves are caused by the sudden movement of materials within the Earth, such as slip along a fault during an earthquake. Volcanic eruptions, explosions, landslides, avalanches, and even rushing rivers can also cause seismic waves.
- 23. Seismic waves are caused by the sudden movement of materials within the Earth, such as slip along a fault during an earthquake. Volcanic eruptions, explosions, landslides, avalanches, and even rushing rivers can also cause seismic waves.
- 24. Compression wave Transverse Wave Seismic Wave ◦ Body Waves Primary or p-wave Compression wave Secondary or s-wave Transverse wave ◦ Surface Love wave Rayleigh wave
- 25. Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs. There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves.
- 27. Body waves ◦ P or primary waves fastest waves travel through solids, liquids, or gases compressional wave, material movement is in the same direction as wave movement ◦ S or secondary waves slower than P waves travel through solids only shear waves - move material perpendicular to wave movement
- 28. P Waves (Compression Wave) The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air.
- 29. D. Earthquake Waves 1. Primary Waves or P-Waves (Compressional Waves) a. Travel through solids, liquids and gases. b. They cause rock particles to vibrate in the same direction as the wave is traveling. c. They are the fastest traveling EQ waves.
- 30. S wave (transverse wave) The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock. This wave moves rock up and down, or side-to-side.
- 31. 2. Secondary Waves or S-Waves or Shear Waves a. Travel through solids, only. b. They cause rock particles to vibrate at right angles to the direction of travel of the wave. c. They travel slower than P-waves.
- 32. Surface Waves ◦ Travel just below or along the ground’s surface ◦ Slower than body waves; rolling and side-to-side movement ◦ Especially damaging to buildings
- 33. Love Waves The first kind of surface wave is called a Love wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side.
- 34. Rayleigh Waves The other kind of surface wave is the Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.
- 35. Seismic wave behavior ◦ P waves arrive first, then S waves, then L and R ◦ Average speeds for all these waves is known ◦ After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
- 37. 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
- 38. Modern Seismograph Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.
- 40. Seismic wave behavior ◦ P waves arrive first, then S waves, then L and R ◦ Average speeds for all these waves is known ◦ After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
- 41. Seismographs record earthquake events At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone
- 42. Damage in Oakland, CA, 1989 • Building collapse • Fire • Tsunami • Ground failure
- 43. Response of material to the arrival of energy fronts released by rupture Two types: ◦ Body waves P and S ◦ Surface waves R and L
- 44. Time-distance graph showing the average travel times for P- and S- waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves
- 45. Three seismograph stations are needed to locate the epicenter of an earthquake A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter
- 46. Intensity ◦ subjective measure of the kind of damage done and people’s reactions to it ◦ isoseismal lines identify areas of equal intensity
- 48. Awaran district, Balochistan region , Pakistan Awaran district, Balochistan region , Pakistan
- 49. • Modified Mercalli Intensity Map – 1994 Northridge, CA earthquake, magnitude 6.7
- 50. A seismograph is the the tool used to measure the strength of an earthquakes The seismograph prints out a seismogram that scientists read to determine the strength of the quake. The data from the seismogram is translated into a 1-10 rating on the Richter Scale. Each step in the scale represents a tenfold increase in the size of the quake!
- 51. Magnitude ◦ Richter scale measures total amount of energy released by an earthquake; independent of intensity ◦ Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open- ended logarithmic scale
- 52. Earthquake Precursors changes in elevation or tilting of land surface, fluctuations in groundwater levels, magnetic field, electrical resistance of the ground seismic dilatancy model seismic gaps
- 53. Earthquake Prediction Programs include laboratory and field studies of rocks before, during, and after earthquakes monitor activity along major faults produce risk assessments
- 54. Graph showing the relationship between the amount of waste injected into wells per month and the average number of Denver earthquakes per month Some have suggested that pumping fluids into seismic gaps will cause small earthquakes while preventing large ones