// BEGIN editorial data var i = 0; var earthquakes = new Array(); earthquakes.ID = "earthquakes"; earthquakes.ID_WB = 4865348; earthquakes.sPubDate = "4/29/2004 10:17:21 PM GMT"; earthquakes.mainsectionID = "" earthquakes.navsectionID = "3033054" earthquakes.appFmt = 2; earthquakes.itemsPerPage = 1; earthquakes.appWidth = 460; earthquakes.appHeader = "Q & A| Earthquakes"; earthquakes.appDeck = "MSNBC's interactive guide to earthquakes, from
fault lines to seismographs to damage estimations."; earthquakes.appFooter = "Sources: U.S. Geological Survey, National Earthquake Information Center, Federal Emergency Management Agency"; earthquakes.appNavStyle = 1; earthquakes.appLayout = 1; earthquakes.copyHeight = 150; earthquakes.copyMargin = 9; earthquakes[i++] = new Array("","What are earthquakes?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "An earthquake is caused by a sudden slip on a fault and it occurs when plates grind and scrape against each other. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake."; earthquakes[i++] = new Array("","What is a fault?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "A fault is a thin zone of crushed rock between two blocks of rock, and can be any length, from centimeters to thousands of kilometers. It is a fracture in the crust of the earth along which rocks on one side have moved relative to those on the other side. Most faults are the result of repeated displacements over a long period of time."; earthquakes[i++] = new Array("","What are the basic types of earthquakes?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The two basic types:
  • A strike-slip earthquake occurs on an approximately vertical fault plane as the rock on one side of the fault slides horizontally past the other.
  • In a dip-slip earthquake the fault is at an angle to the surface of the earth and the movement of the rock is up or down."; earthquakes[i++] = new Array("","Are earthquakes really on the increase?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "Not necessarily. Earthquakes of magnitude 7.0 or greater have remained fairly constant throughout this century and according to records have actually seemed to decrease in recent years.
    In the last 20 years more earthquakes are noticed yearly because of the increase in the number of seismograph stations in the world and improved global communications. This increase has helped seismological centers to locate many small earthquakes which were undetected in earlier years.     "; earthquakes[i++] = new Array("","What is the hypocenter?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The hypocenter is the point where the earthquake rupture begins, usually deep down on the fault."; earthquakes[i++] = new Array("","What is the epicenter?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The epicenter is the point on the surface directly above the hypocenter."; earthquakes[i++] = new Array("","How many earthquakes are reported yearly?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The National Earthquake Information Center now locates about 12,000 to 14,000 earthquakes worldwide each year, or 35 a day on average."; earthquakes[i++] = new Array("","Earthquake frequency worldwide:","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "
    Frequency of Earthquakes Worldwide
    DescriptionMagnitudeAnnual Average
    Great8 or higher1
    Major 7 - 7.918
    Strong6 - 6.9120
    Moderate5 - 5.9800
    Light4 - 4.96,200
    Minor3 - 3.949,000
    Very Minor1 - 39,000 (daily)
    "; earthquakes[i++] = new Array("","What is the Richter Scale?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The Richter Scale is used to measure the magnitude of earthquakes, as determined by seismograph measurements of the height of ground oscillations during an earthquake.
    Because the scale is based on a logarithm, every whole-number step in the scale represents about 31 times more energy than the amount represented by the preceding whole number value. The Richter scale has no upper limit; the largest known earthquakes have magnitudes in the 8.8 to 8.9 range.    "; earthquakes[i++] = new Array("","What is the Modified Mercalli Scale?","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "The Modified Mercalli Scale measures the intensity of an earthquake; in other words, the effect of the earthquake on the Earth's surface. This scale is composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, and is designated by Roman numerals. The scale does not have a mathematical basis; instead it is an arbitrary ranking based on observed effects."; earthquakes[i++] = new Array("","Damage of recent earthquakes in the U.S.:","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", ""); earthquakes[i-1].body = "Northridge, California (20 miles from Los Angeles)
  • January 17, 1994 at 4:31 a.m.
  • Magnitude: 6.7
  • Deaths: 57
  • Injuries: 9,000
  • Property Damage: $15 billion

    Loma Prieta Earthquake (south of San Francisco)

  • October 17, 1989 at 5:04 p.m.
  • Magnitude: 7.1
  • Deaths: 62
  • Injuries: 3,757
  • Property Damage: More than $6 billion"; // END editorial data