Earthquake

This is an earthquake frequent time period in China. As the number that I have from internet, 57  earthquakes were determined in China from January 26th to February 26th . It is a horrible number that can make everyone in China feel uncomfortable.  . We can look backward in 2008 in China. There was an 8.0 magnitude earthquake happened in Wenchuan, China. Official figures stated that 69,197 were confirmed dead, including 68,636 in Sichuan province, and 374,176 injured, with 18,222 listed as missing. The earthquake left about 4.8 million people homeless, though the number could be as high as 11 million. From the number, we can easier to see that how does a big earthquake effect on human lives and properties. It can make homeless and hopeless for human; also it may generate a death for family members. Earthquake is a natural disaster that we cannot avoid. They happen randomly in any time and place. An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. When the earthquake is coming, there are two componentts in seismic waves, one is longitudinal, and one is horizontal. Intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the more damage to structures it causes.
I am studying in Civil Engineering department at NDSU. Otherwise, I am working in Structural Engineering field now. When we design a structure, we should do load calculation and load combination before we start design overall structure. Seismic load is one of the important factors in load calculation and load combination. In case we need to do seismic load in North Dakota area, we can simplified round it to 1% of the building dead load. But for the real design, we cannot do seismic load in this way.
Why is seismic load so important for a structural? In fact, there are only two loads that can affect horizontally. Seismic load is one that can affect the structure in the horizontal direction. It will totally change the structural arrangement if different seismic load applied. For the steel, if we have larger seismic load, we need to add braces on each side to support the structure will not fail to one direction. When we will design reinforced concrete structural, seismic load will involve the load calculation in specific section. Such as if we have a larger seismic load, the rebar in the sidewall will be replaced by a heavy one to ensure the wall can support more load.
As usual, the municipal building can afford 7.0 magnitude earthquake all over the world, although some of the countries have a higher or lower requirement, but all of the requirements are around 7.0 magnitude. How does the earthquake affect personal properties? When the magnitude of an earthquake is greater than 7.0, it is already out of the safety consideration of the designer. The building may fail by the large horizontal force due to the structure. As usual, the designer will apply larger load when they design the building structure for safety considerations. It means that the constructor will replace heavier member in columns, beams, and girders for safety factor. In case the structure crashes, it will destroy so many families no doubt. It is not only a disaster for a simple family, but also a nightmare for a country.
All the civil engineers should pay more attention in earthquake to protect our family and property. It is not good for ourselves, also good for everyone who lives in this planet.