The Six Modified Mercalli Intensity Scale

The effect of an earthquake on the Earth’s surface is called the intensity. The intensity scale consists of a series of certain key responses such as people awakening, movement of furniture, damage to chimneys, and finally – total destruction. Although numerous intensity scales have been developed over the last several hundred years to evaluate the effects of earthquakes, the one currently used in the United States is the Modified Mercalli (MM) Intensity Scale. It was developed in 1931 by the American seismologists Harry Wood and Frank Neumann. This scale, composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. It does not have a mathematical basis; instead it is an arbitrary ranking based on observed effects.

The Modified Mercalli Intensity value assigned to a specific site after an earthquake has a more meaningful measure of severity to the nonscientist than the magnitude because intensity refers to the effects actually experienced at that place.

The lower numbers of the intensity scale generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage. Structural engineers usually contribute information for assigning intensity values of VIII or above.

Top 6 modified scale

1.) 1976 Moro Gulf Earthquake and Tsunami – up to 8,000 deaths

  • Date: August 16, 1976
  • Magnitude: 8.0 moment magnitude scale
  • Epicenter: Celebes Sea
  • Damages: Not accounted
  • Affected areas: Mindanao and Borneo

2.) 1645 Luzon Earthquake – 600 deaths (Spaniards only)

  • Date: November 30, 1645 at about 08:00 PM
  • Magnitude: 7.5
  • Epicenter: Nueva Ecija
  • Damages: Hundreds of buildings and houses were destroyed
  • Affected areas: Central Luzon, Manila

3.) 1990 Luzon Earthquake – 1,621 deaths

  • Date: July 16, 1990, at 4:26 PM
  • Magnitude: 7.8
  • Epicenter: 15° 42′ N and 121° 7′ E near Rizal, Nueva Ecija
  • Damages: Scores of buildings collapsed and damaged
  • Affected areas: Central Luzon and Cordillera region

4.) Luzon Earthquakes of July 1880

  • Date: July 14-25, 1880
  • Magnitude:  10 on Rossi-Forel scale
  • Epicenter: Luzon
  • Damages: Scores of churches and buildings were damages and destroyed
  • Affected areas: Manila, Laguna, Nueva Ecija, Pampanga, Cavite and Bulacan

5.) 1968 Casiguran Earthquake –268 deaths

  • Date: August 2, 1968
  • Magnitude: 7.3
  • Epicenter:  Casiguran, Aurora
  • Damages: Ruby Tower fell and several buildings were destroyed and damaged.
  • Affected areas: Manila, Aurora and Pampanga

6.) 2012 Visayas Earthquake – 81 deaths

  • Date:: February 6, 2012
  • Magnitude: 6.9 Mw
  • Epicenter: Negros Oriental
  • Damages: Bridges collapsed, buildings were damaged and roads were totally ruined
  • Affected areas: Negros Oriental and neighboring provinces
Tags : Geology
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