Groundshaking damage to buildings, Japan

So much of the damage done after the Tohoku quake resulted from the tsunami, but there was also damage of buildings due to the groundshaking in high areas that were not damaged by the tsunami. Some reports and images can be found at the Earthquake Engineering Research Institute web site.

A number of field reports on damage done in the epicentral area are given here.

A report by Shunzuke Otani on Building Damage in Sendai says:

"Miki Shoji Co, a commercial business company, reported building damage statistics by external observation along the Sendai main street; out of 175 buildings
          No damage: 95
          Some damage, but could be operational in short time: 66
          Severe damage, need some time before use: 14
          Collapse or tilting: 0
Sendai is the largest city in the affected area.  A church in Mito City, Ibaragi Prefecture, suffered severe damage in the tower. A automobile ramp to the roof parking area collapse and killed three persons in automobiles; the ramp is supported by steel columns and connected to the main structure of a super market building."  Images of these are shown below.

Sendai church damage

Sendai parking garage damage

Ground acceleration for the Tohoku quake

Tohoku, by the way, is Japanese for northeast, since that is the part of the island of Honshu where the earthquake occurred. It is also being referred to as the Sendai earthquake, Sendai being the largest big city nearby.

The primary hazard intrinsically associated with earthquakes is groundshaking. When the elastic energy stored in the crust is released by the earthquake and motion on the fault, the stored energy causes the ground to vibrate, or accelerate back and forth.  The figure below from the USGS shows the peak acceleration in the vicinity of the quake caused by the shaking earth.

The peak ground acceleration in the graph below was almost three times the Earth's gravitational acceleration (g).

By default, buildings are designed to withstand the vertical acceleration due to gravity, but not necessarily to withstand horizontal ground accelerations of the same magnitude. This is why earthquake-resistant buildings must be designed to deal with. Japan has done a good job with this, so the major damage in the quake was not caused by the groundshaking.

Acceleration due to seismic waves - Chile poster

One of the primary hazards intrinsically associated with an earthquake is groundshaking.  This is a vector, with both horizontal ad vertical components.  The second derivative of the displacement is the acceleration.   Buildings are made to withstand vertical acceleration - after all, that is what gravity is.  However, by default, buildings are not engineered to withstand horizontal accelerations, although lateral bracing can be used, and should be within seismic zones.

The figure below, from our USGS poster on the Chile quake, plots ground motion accelerations from the Chile quake, and shows a couple of very interesting features. Note that the maximum acceleration caused by the Chilean quake is around 4.8 m/s², which is half the acceleration of gravity (9.8 m/s²). That's pretty impressive. Also, note that the contours of equal acceleration run in a north-south direction, parallel to the plate boundary between the Nazca and South American plates.