Earthquakes: “A real threat that lurks in our future”

Luis M. Rolón Luna

Recently we may have seen or heard the word earthquake by the media and witnessed its powerful capabilities here on the island and throughout the world. Places like Haiti, Japan, Chile, etc. have lived the devastating power and energy an earthquake possesses. A quake is a shock of the land that takes place due to the shock of the tectonic plates and to the liberation of energy in the course of an abrupt reorganization of materials of the terrestrial crust when surpassing the state of mechanical balance. Most important and frequent they take place when accumulated elastic potential energy in the gradual deformation of contiguous rocks is freed to the plane of an active fault, but also can happen by other causes, for example around volcanic processes, or slope movements.

How are trembles produced? They are vibrations of the land caused by an abrupt liberation of energy coming from the edges of tectonic plates. The tectonic plates hit to each other and produce liberation of energy as a result of the efforts that they were supporting. The point in which the earthquake in the surface is detected is the epicenter and the point where the earthquake takes place is the hypocenter. In the hypocenter, the waves disperse towards all directions. First that arrives are the waves P (primary), followed of waves S (secondary). They are different from others in the speed of propagation and in the possibility of crossing surfaces you eliminate, like the external nucleus. Primary P waves are those that are detected first in the seismograph. Also they are waves L, the superficial ones, these they are in surface and they are most destructive, they are also but the slow ones and they are those that cause the damages.

How do quakes affect a building? Most of the earthquakes are the result of a fast movement throughout the plane of faults in the terrestrial crust. This sudden movement of the fault publishes a great amount of energy that travels through the Earth as a seismic waveform.  The seismic waves travel great distances before losing most of their energy. At some time after their generation, these seismic waves will arrive at the Earth surface, and to put it in movement. When this movement of the ground happens under a building and if it is strong enough, the creation of movement commences, beginning with the construction of the foundation, and transfers the movement through rest of the building in a very complex form. When the content of frequency of the movement of the ground is centered around the natural frequency of the building, it is said that the building and the movement of the ground are in resonance with each other. The resonance tends to increase or to amplify the answer of the building. Due to this, the buildings suffer the greater damages by the movement of the ground to a frequency near or equal to their natural frequency.

This is why we must create a seismic conscience in Puerto Rico because we live in a highly active island where earthquakes of different magnitudes occur every day. I greatly recommend that we seek education in what to do before, during and after a quake. This way we can be prepared if the situation presents itself and possibly help others. You can also go to this website www.ciapr.org which is the cybernetic page of the School of Engineers and Surveyors to find orientation and the seismic plan for Puerto Rico. 

References:

1. es.wikipedia.org/wiki/Terremoto. Web. April 22, 2011.

2. http://www.angelfire.com/ri/chterymercalli/. Web. April 22, 2011.