![]() Roman numerals I to XII are used to show the effects of the earthquake. Modified Mercalli scale The modified Mercalli scale used for these maps divides the intensity of the earthquake into twelve groups. The map has circles radiating out from the epicenter of the earthquake with Roman numerals showing the intensity of the earthquake in different areas. They file their reports with the earthquake center.Ĭlick for More Information and to Order Generation of an intensity mapĬreating an intensity map The earthquake center uses the information from these observers to create an intensity map. Engineers also examine structural damage to buildings and other man made structures. Questions reflect criteria for intensity Each of these questions are part of the criteria used to determine the intensity of the earthquake at their location. They are asked if they were awakened by the earthquake, if furniture moved, was there damage to chimneys or to walls in their home. Observations by people People fill out reports on what happened to them during an earthquake. Gathering information for a mercalli scale map You can tell on the map where the most destruction occurred and where the earthquake waves were not felt by people in the surrounding areas. The map shows eleven different intensities. Intensity maps show areas of destruction The 1904 San Francisco has an estimated 7.9 magnitude on the moment magnitude and had a maximum intensity of XI. The map above is based on people's observations and structural damage to the buildings during the 1904 San Francisco earthquake. The higher numbers on the scale are based on observed structural damage to buildings.ġ904 San Francisco historical earthquake Seismologists can determine the extent of damage of historical earthquakes based on the criteria now used for the Modified Mercalli scale. Observed damages caused by large earthquakes The lower divisions of the scale deals with how the earthquake was felt by people. The scale uses Roman Numerals for each division. The current name used for the scale is Modified Mercalli scale and contains 12 divisions. Modified Mercalli scale Over the years new versions of this scale have been adopted. It was adopted by the Italian's Department of Meteorology. The revised scale had 10 categories and he expanded his description of each category. He was an Italian volcanologist that used only six categories. ![]() The original Mercalli scale The first intensity scale was created in 1883 by Giuseppe Mercalli. ![]() Intensity map of 1906 San Francisco earthquake, USGS History of the Mercalli Scale ![]()
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