in the city collapsed, wholly or partially, infrastructure was severely damaged, and essential services such as electric power, water supply, and communications were entirely knocked out. This area of maximum damage – the meizoseismal area – was approximately long and from 3.5 to 5.5 km wide, centered roughly along the railway. The area of intensity X shaking – where only new, one-story brick buildings were merely "damaged or slightly damaged", the rest being severely damaged or worse – was 36 km long and 15 km across. In this "high intensity" zone (intensity X and XI, within the red contour on the map) 20 highway bridges and five railway bridges cross the Douhe River in Tangshan; only six survived with only minor damage. Intensity IX and VIII zone Shaking of intensity IX (or greater) occurred in a zone roughly long and (about 1800 km2, inner orange contour on the map), and also around the aftershocks at Luanxian and Ninghe. In this zone most buildings classified as Class III (well-built buildings of wood, masonry, or reinforced concrete) survived, but many Class II buildings (typically old wood-frame buildings lacking a well-built frame, and quite common outside of the cities) were destroyed, while a majority of Class I buildings (built of adobe or stone) were destroyed. Further out (to the outer orange contour), and around the city of Tianjin and a few isolated patches, intensity VIII shaking mostly affected Class I buildings (more than half destroyed), bridges, and tall brick chimneys. Railway track was also subject to bending or displacement, depending on soil conditions. Intensity VII zone The zone of intensity VII shaking – inside the dark brown contour – marks the extent of moderate damage, where many Class I structures (of weak design or construction) were damaged but only "few"—between 10% and 30%—were destroyed, and only a "few" Class two buildings damaged. This ellipsoid zone extended about 75 km north and south of Tangshan and 120 km east and west, from about 25 km short of Beijing to short of Qinhuangdao City (which had anomalously higher shaking), and from the Sea of Bohai in the south and southwest to just north of Zunhua. The north–south shortening of this zone is attributed to buttressing by the bedrock of the Yanshin mountains. Significant damage occurred beyond this in the VI zone, but (like in Beijing) affected less than 10% of the buildings, or occurred in