The Omori scale is a seven-point scale of seismic intensity, created by Fusakichi Omori, that relates various phenomena to maximum ground acceleration. It is based on the behavior of typical Japanese structures and is still widely used in Japan. This description is from Building Structures in Earthquake Countries by Alfredo Montel (Lippincott, Philadelphia, 1912). Notice that its level I is equivalent to a Mercalli intensity of VI.
I. Maximum Acceleration = 300 mm per sec. per sec.The shock is rather strong, so much so that it generally induces people to escape from their houses into the open. The walls of badly constructed brick houses crack slightly and some parquet falls down; ordinary wooden houses are shaken in such a degree that they loudly creak; furniture is overturned; trees are visibly shaken; the water in ponds and pools gets turbid, owing to the disturbance of the mud; pendulum clocks stop; some very badly built factory chimneys are damaged.
II. Maximum Acceleration = 900 mm per sec. per sec.The walls in the wooden houses of Japan crack; old wooden houses get slightly out of plumb; the Japanese tombstones and the badly constructed stone lanterns are overturned; in a few cases the flow of the thermal and mineral springs is changed; ordinary factory chimneys are not damaged.
III. Maximum Acceleration = 1200 mm per sec. per sec.About one-fourth of the factory chimneys are damaged; badly constructed brick houses are partially or totally destroyed; some old wooden houses are destroyed; wooden bridges are slightly damaged; some tombstones and stone lanterns are overturned; Japanese sliding doors (covered with paper) are broken; the tiles of wooden houses are displaced; some fragments of rocks are detached from the sides of the mountains.
IV. Maximum Acceleration = 2000 mm per sec. per sec.All factory chimneys are ruined; the majority of the ordinary brick houses are partially or totally destroyed; some wooden houses are totally destroyed; the wooden sliding doors are mostly thrust out of their channels; crevices from 2 to 3 inches (5 to 7-1/2 cm) wide appear in low and soft grounds; here and there the embankments are slightly damaged; wooden bridges are partially destroyed; ordinarily constructed stone lanterns are overturned.
V. Maximum Acceleration = 2500 mm per sec. per sec.All ordinary brick houses are very seriously damaged; about 3 percent of the wooden houses are totally destroyed; some Buddhist temples are ruined; the embankments are badly damaged; the railways are slightly contorted; ordinary tombstones are overturned; brick walls are damaged; here and there, large fissures from 1 to 2 feet (30 to 60 cm) wide appear along the banks of the watercourses. The water of rivers and ditches is thrown on the banks; the contents of the wells are disturbed; landslides occur.
VI. Maximum Acceleration = 4000 mm per sec. per sec.The greater part of the Buddhist temples are ruined; from 50 to 80 percent of the wooden houses are totally destroyed; the embankments are almost destroyed; the roads through paddy fields are ruined and interrupted by fissures in such a degree that traffic by animals or vehicles is impeded; the railways are very much contorted; great iron bridges are destroyed; wooden bridges are partially or totally damaged; tombstones of solid construction are overturned; fissures some feet wide appear in the soil, and are sometimes accompanied by jets of water and sand; iron or terra cotta tanks embedded in the ground are mostly destroyed; all lowlying grounds are completely convulsed horizontally as well as vertically in such a degree that sometimes the trees and all the vegetation on them die off; numerous landslides take place.
VII. Maximum Acceleration = much more than 4000 mm per sec. per sec.All buildings are completely destroyed except a few wooden constructions; some doors or wooden houses are thrown over distances from 1 to 3 feet; enormous landslides with faults and shears of the ground occur.