Earthquakes are unpredictable because there is no way of knowing when they will happen or how intense they will be.
An earthquake happens when two sections on the earth suddenly slip past each other. The slip occurs because of a crack or break in the earth. This is called the fault plane. Directly below the fault plane is the epicenter. Below that is the hypocenter, which is where the earthquake originates.
Earthquakes are typically associated with a shaking of the ground, either mild or severe. Some may have foreshocks, which are smaller shakes that happen before the main one. The largest earthquake is referred to as the main shock. Aftershocks are smaller quakes in the same spot and always happen following the main shock. These small quakes may continue for several weeks up to several years after the main shock.
The earth is made up of four main layers. These are the inner core, outer core, mantle and crust. Of these, the crust is the top-most layer. This layer is not made of a single piece, however. The crust is broken into several parts that are sitting together like pieces in a puzzle. The pieces of the earth’s crust are called tectonic plates. These plates have rough, cracked edges known as plate boundaries.
As the tectonic plates move about, they slide past and bump into each other. The rough plate boundaries may get caught on one another and get stuck. Since the ground’s forces keep moving the plates, eventually the tectonic plates will break and slide at a crack, or fault, in the plate boundary. This sliding is what causes an earthquake.
Natural energy is the force that moves the plates. Even though the plate boundaries are stuck together, the rest of the tectonic plate continues to move. The energy that would normally go into moving the entire plate is stored. Finally, the force of the moving plate overpowers the friction of the stuck edges. All the stored energy releases and radiates from the breaking point in all directions. These ripples of energy, called seismic waves, shake the ground as they pass through it. The waves reach the surface and shake the ground, causing an earthquake.
Some earthquakes are small and are barely felt on the surface. Others are severe and cause extensive damage. The size of the earthquake is measured using seismograms. These instruments consist of a needle that vibrates up and down as the shaking occurs. The intensity of the shakes is recorded as vertical lines on a graph. Short, small lines indicate relatively small earthquakes, while long, big lines mean a larger earthquakes.
The size of the fault and the amount of the slip of the plate play a direct role in how intense the earthquake is. The size of the fault can be estimated by looking at the horizontal length of the recorded lines. The amount of slip is seen in the vertical height of the lines. The overall size of the quake is assigned a magnitude, which is a relative number scale for indicating the scope of the quake.
Seismograms are also used to determine the epicenter of a quake. They measure the two different seismic waves that an earthquake has. The first wave, called the P wave, travels fast and is felt first. The second wave, called the S wave, is slower and felt last. The waves will be felt closer together nearer the epicenter. This tells scientists how far away from a seismogram station that the quake happened. They are then able to determine the radius. By comparing notes at different seismogram stations, they can tell the direction from which the readings came. The point where the radiuses overlap is the epicenter.
Scientists are able to determine where fault lines lie by looking at satellite pictures. However, it is unlikely that anyone will ever be able to determine when the fault will give way and cause an earthquake. In addition, it is impossible to tell whether a shake is a foreshock or the main shock. This makes recognizing warning signs of a high-magnitude a earthquake extremely difficult. Earthquakes are unpredictable because there is no way of knowing when they will happen or how intense they will be.
An earthquake is just one of many natural disasters that we should be aware of and prepare for. Other natural disasters include flood, tornado, wildfire, volcano, hurricane, avalanche, lightning and tsunami.
