The Rossi–Forel scale was one of the first seismic scales to reflect earthquake intensities. Developed by Michele Stefano Conte de Rossi of Italy and François-Alphonse Forel of Switzerland in the late 19th century, it was used for about two decades until the introduction of the Mercalli intensity scale in 1902.
The Rossi–Forel scale and/or its modifications is still in use in some countries, such as the Philippines.
The 1873 version of the Rossi–Forel scale had 10 intensity levels:
- I. Microseismic tremor. Recorded by a single seismograph or by seismographs of the same model, but not by several seismographs of different kinds. The shock felt by an experienced observer.
- II. Extremely feeble tremor. Recorded by several seismographs of different kinds. Felt by a small number of persons at rest.
- III. Feeble tremor. Felt by several persons at rest. Strong enough for the direction or duration to be appreciable.
- IV. Slight tremor. Felt by persons in motion. Disturbance of movable objects, doors, windows, cracking of ceilings.
- V. Moderate tremor. Felt generally by everyone. Disturbance of furniture, ringing of some bells.
- VI. Strong tremor. General awakening of those asleep. General ringing of bells. Oscillation of chandeliers, stopping of clocks, visible agitation of trees and shrubs. Some startled persons leaving their dwellings.
- VII. Very strong tremor. Overthrow of movable objects, fall of plaster, ringing of church bells. General panic. Moderate to heavy damage buildings.
- VIII. Damaging tremor. Fall of chimneys. Cracks in the walls of buildings.
- IX. Devastating tremor. Partial or total destruction of buildings.
- X. Extremely high intensity tremor. Great disaster, ruins, disturbance of the strata, fissures in the ground, rock falls from mountains.
- Tiedemann, Herbert (1992). Earthquakes and Volcanic Eruptions. A Handbook on Risk Assessment. Zurich: Swiss Reinsurance Company.