How do primary waves affect a building

There are four types of seismic waves. How will three identically engineered buildings react to an earthquake on different types of substrate? They usually cause very little damage. S waves, or secondary waves , come next since they travel more slowly than P waves. They travel in the same direction, but they shake the ground back and forth perpendicular to the direction the wave is traveling.

S waves are more dangerous than P waves because they have greater amplitude and produce vertical and horizontal motion of the ground surface. The slowest waves, surface waves, arrive last. They travel only along the surface of the Earth. At the Earth's surface, these waves cause the ground to shake and vibrate, sometimes violently. Geologists classify seismic waves into two broad categories: body and surface waves.

Body waves , which include P and S waves, travel through the Earth's interior. P waves resemble sound waves, which means they compress and expand material as they pass. S waves resemble water waves, which means they move material up and down. P waves travel through both solids and liquids, while S waves only travel through solids. After an earthquake strikes, P waves ripple through the planet first, followed by S waves. Then come the slower surface waves -- what geologists refer to as Love and Rayleigh waves.

Both kinds move the ground horizontally, but only Rayleigh waves move the ground vertically, too. Surface waves form long wave trains that travel great distances and cause most of the shaking -- and much of the damage -- associated with an earthquake.

If earthquakes only moved the ground vertically, buildings might suffer little damage because all structures are designed to withstand vertical forces -- those associated with gravity -- to some extent. But the rolling waves of an earthquake, especially Love waves, exert extreme horizontal forces on standing structures. These forces cause lateral accelerations , which scientists measure as G-forces.

A magnitude Such a sudden movement to the side almost as if someone violently shoved you creates enormous stresses for a building's structural elements, including beams, columns, walls and floors, as well as the connectors that hold these elements together. If those stresses are large enough, the building can collapse or suffer crippling damage.

Earthquakes As the lithospheric plates of the Earth continue their slow motions, stresses build up in the crust, especially near the plate boundaries. Those stresses compression, tension, shear build up in the crust until the stress exceeds the strength of the rock or the friction along a preexisting fault. Then, sudden slippage of rock along a fault occurs. The ground shakes as the stress energy is released and the rocks lurch to their new position in a matter of seconds.

Seismic waves travel outward from the portion of the fault that broke, like expanding ripples from a pebble dropped in still water. The whole fault doesn't move at one time; only the part of the fault around which the stress exceeded the strength. Seismologists can determine the point on a fault where the slippage began, the area length and depth of the fault that slipped, the amount of slippage or fault throw how far the crust moved , and the time it took for the slippage to occur.