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City of Santa Ana Emergency Operations Plan
<br />Part I Basic Plan
<br />Figure 42 Modified Mercalli Intensity (MMI) Scale (Richter, 1958)
<br />Value
<br />Description
<br />Not felt. Marginal and long period effects of large earthquakes.
<br />II
<br />Felt by persons at rest, on upper floors, or favorably placed.
<br />III
<br />Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be recognized
<br />as an earthquake.
<br />IV
<br />Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy weight striking the
<br />walls. Parked cars rock. Windows, dishes, doors rattle. Glasses clink. In the upper range of IV, wooden walls and
<br />frames creak.
<br />V
<br />Felt outdoors; direction estimated. Sleepers wakened. Liquids disturbed, some spilled. Small unstable objects
<br />displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, change rate.
<br />VI
<br />Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, dishes, glassware broken.
<br />Knickknacks, books, etc., off shelves. Pictures off walls. Furniture moved or overturned. Weak plaster and Masonry
<br />D cracked. Trees, bushes shaken visibly, or heard to rustle.
<br />VII
<br />Difficult to stand. Noticed by drivers of cars. Hanging objects quiver. Furniture broken. Damage to Masonry D,
<br />including cracks. Weak chimneys broken at roofline. Fall of plaster, loose bricks, stones, tiles, cornices (also unbraced
<br />parapets and architectural ornaments). Some cracks in Masonry C. Waves on ponds; water turbid with mud. Small
<br />slides and caving in along sand or gravel banks. Concrete irrigation ditches damaged.
<br />VIII
<br />Steering of cars affected. Damage to Masonry C; partial collapse. Some damage to Masonry B; none to Masonry A.
<br />Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks.
<br />Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Decayed piling broken off.
<br />Tree ranches broken. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes.
<br />IX
<br />General panic. Masonry D destroyed; Masonry C heavily damaged, sometimes with complete collapse; Masonry B
<br />seriously damaged. (General damage to foundations.) Frame structures, if not bolted, shifted off foundations. Frames
<br />racked. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluvial areas
<br />sand and mud ejected; earthquake fountains and sand craters form.
<br />X
<br />Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges
<br />destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers,
<br />lakes. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.
<br />XI
<br />Rails bent greatly. Underground pipelines completely out of service.
<br />XII
<br />Damage nearly total. Large rock masses displaced. Lines of sight and level distorted. Objects thrown into the air.
<br />Masonry
<br />Good workmanship, mortar, and design; reinforced, especially laterally, and bound together by using steel, concrete,
<br />A
<br />etc.; designed to resist lateral forces.
<br />Masonry
<br />Good workmanship and mortar; reinforced, but not designed in detail to resist lateral forces.
<br />B
<br />Masonry
<br />Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither reinforced nor
<br />C
<br />designed against horizontal forces.
<br />Masonry
<br />Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally.
<br />D
<br />Each of the major local fault systems is described briefly on the pages that follow, with Shakemaps depicting
<br />ground shaking patterns for eight scenarios potentially impacting Orange County, including:
<br />• M 7.8 Repeat of the 1857 Fort Tejon Earthquake on the San Andreas Fault
<br />• M 7.8 Event on the Southern San Andreas Fault "Shakeout Scenario'
<br />• M 6.9 Earthquake on the Newport -Inglewood Fault
<br />• M 6.8 Earthquake on the Elsinore Fault
<br />• M 6.8 Earthquake on the Whittier Fault
<br />• M 6.7 Earthquake on the Chino Hills Fault
<br />• M 6.6 Earthquake on the San Joaquin Hills Fault
<br />• M 7.1 Earthquake on the Puente Hills Fault
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