KQED Inform. Save Article Save Article. Andrea Aust. Mar 21, Failed to save article Please try again. Love waves move back and forth horizontally. The damage caused by earthquakes is from ground shaking, ground rupture, landslides, tsunamis, and liquefaction. Earthquake damage from fires is the most important secondary effect. The Ridgecrest earthquakes that hit on July 4 and July 5 , with a magnitude 6.
The second quake with a magnitude 7. More than 6, homes lost power. The Ridgecrest earthquakes followed a year "quiet period" after the Northridge earthquake. Northridge, at a 6. The damaging shaking of major earthquakes can be felt hundreds of miles away. A house damaged in the San Simeon earthquake.
Ground shaking is the vibration of the ground during an earthquake. The shaking triggers other hazards such as liquefaction and landslides. Most earthquake damage results from the seismic waves passing beneath buildings, roads, and other structures.
The primary earthquake hazard is surface rupture. It can be caused by vertical or horizontal movement on either side of a ruptured fault. Ground displacement, which can affect large land areas, can produce severe damage to structures, roads, railways and pipelines. Earthquakes can trigger landslides and mudslides, especially in areas with water-soaked soils. S waves can travel through solid material but not through liquid or gas. Surface waves, in contrast to body waves can only move along the surface.
They arrive after the main P and S waves and are confined to the outer layers of the Earth. They cause the most surface destruction. Earthquake surface waves are divided into two different categories: Love and Rayleigh.
Love waves have a particle motion, which, like the S-wave, is transverse to the direction of propagation but with no vertical motion. Their side-to-side motion like a snake wriggling causes the ground to twist from side to side, that's why Love waves cause the most damage to structures. Rayleigh waves create a rolling, up and down motion with an elliptical and retrograde particle motion confined to the vertical plane in the direction of propagation. Surface waves are generally not generated by deep earthquakes.
Death and injuries from surface faulting are very unlikely, but casualties can occur indirectly through fault damage to structures. Surface faulting, in the case of a strike-slip fault, generally affects a long narrow zone whose total area is small compared with the total area affected by ground shaking. Nevertheless, the damage to structures located in the fault zone can be very high, especially where the land use is intensive. A variety of structures have been damaged by surface faulting, including houses, apartments, commercial buildings, nursing homes, railroads, highways, tunnels, bridges, canals, storm drains, water wells, and water, gas, and sewer lines.
Damage to these types of structures has ranged from minor to very severe. An example of severe damage occurred in when three railroad tunnels were so badly damaged by faulting that traffic on a major rail linking northern and southern California was stopped for 25 days despite an around-the-clock repair schedule. The displacements, lengths, and widths of surface fault ruptures show a wide range. Fault displacements in the United States have ranged from a fraction of an inch to more than 20 feet of differential movement.
As expected, the severity of potential damage increases as the size of the displacement increases. The lengths of the surface fault ruptures on land have ranged from less than 1 mile to more than miles.
Most fault displacement is confined to a narrow zone ranging from 6 to 1, feet in width, but separate subsidiary fault ruptures may occur 2 to 3 miles from the main fault. The area subject to disruption by surface faulting varies with the length and width of the rupture zone. Liquefaction is not a type of ground failure; it is a physical process that takes place during some earthquakes that may lead to ground failure. As a consequence of liquefaction, clay-free soil deposits, primarily sands and silts, temporarily lose strength and behave as viscous fluids rather than as solids.
Liquefaction takes place when seismic shear waves pass through a saturated granular soil layer, distort its granular structure, and cause some of the void spaces to collapse. Disruptions to the soil generated by these collapses cause transfer of the ground-shaking load from grain-to-grain contacts in the soil layer to the pore water.
This transfer of load increases pressure in the pore water, either causing drainage to occur or, if drainage is restricted, a sudden buildup of pore-water pressure.
When the pore-water pressure rises to about the pressure caused by the weight of the column of soil, the granular soil layer behaves like a fluid rather than like a solid for a short period. In this condition, deformations can occur easily. Liquefaction is restricted to certain geologic and hydrologic environments, mainly areas where sands and silts were deposited in the last 10, years and where ground water is within 30 feet of the surface.
Generally, the younger and looser the sediment and the higher the water table, the more susceptible a soil is to liquefaction. Liquefaction causes three types of ground failure: lateral spreads , flow failures, and loss of bearing strength.
In addition, liquefaction enhances ground settlement and sometimes generates sand boils fountains of water and sediment emanating from the pressurized liquefied zone. Sand boils can cause local flooding and the deposition or accumulation of silt. Lateral Spreads - Lateral spreads involve the lateral movement of large blocks of soil as a result of liquefaction in a subsurface layer.
Movement takes place in response to the ground shaking generated by an earthquake. Lateral spreads generally develop on gentle slopes, most commonly on those between 0.
Horizontal movements on lateral spreads commonly are as much as 10 to 15 feet, but, where slopes are particularly favorable and the duration of ground shaking is long, lateral movement may be as much as to feet. Lateral spreads usually break up internally, forming numerous fissures and scarps.
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