Focus vs Epicenter
Technically, an object becomes the center of attention when a person puts his focus on it. In this view, the center becomes the focus. The difference between the two, however, is not seen in this light in the field of seismology.
An earthquake’s focus is also called the hypocenter. It is in the hypocenters or foci that the waves of the earthquake originate. They are described in three different levels: Shallow (10-100 km. below), Intermediate (70-300 km.), and Deep (300 km or deeper). The rule of thumb is that the closer an area is to the epicenter, the stronger the shaking of ground is felt.
The epicenter of an earthquake, on the other hand, is the point in the ground located directly above the focus. It can be accounted for the movement or shaking of the ground that people usually feel during an earthquake. Simply put, the focus is where the “real” and actual earthquake occurs. It happens miles away from the crust layers and may be triggered by tectonic plates or volcanic eruptions. The epicenter, on the other hand, serves as the geographical point of reference in determining the relation of the area and the actual location of the earthquake’s occurrence.
The earthquake starts at the focus and travels up to the epicenter where the ground shaking is felt at its maximum. Thus, by locating the epicenter of the earthquake, seismologists can determine the origin of the earthquake both above and below the crust. Seismograms are utilized in locating the epicenter through the three seismic stations.
The scientists start with recording the time lapse between the detection of the first P-wave and the first S-wave. Doing so would allow for the recording of a time-distance graph that would point to the proximity of the epicenter from the seismic station. Once the epicenter has been located, the position of the focus can then be determined below the Earth’s crust. One can, therefore, say that one difference between the hypocenter and the epicenter is the way they are located. Epicenters are detected through seismographs, while foci are located after the epicenter has been found.
Movements in the focus and epicenter are also triggered by different factors. Plate tectonics or volcanic eruptions cause the shaking at the focus. It is where rocks break under stress (during volcanic eruptions) and where the plates move and shift position (during plate tectonics). Earthquakes occur at the focus when energy stored is suddenly released. In such cases, the waves transfer the released energy from the focus towards the surface of the Earth at the epicenter.
The focus, then, is the area where the released energy comes from, and the epicenter is defined as the area which is the direct receiver of the energy released. The waves travel through the fault that has ruptured.
In simpler terms, “epicenter” and “focus” are both determinants of the origin of the ground movements. The epicenter, nonetheless, is found at the crust while the focus is located way beneath the ground. It is because of the difference in location that seismologists find it easier to first locate the epicenter in order for them to detect the focus. In terms of determining the cause of the earthquake, however, seismologists start first with the study of the focus.
Summary:
1.An earthquake’s epicenter and focus are both determinants of the origin of the ground movements.
2.Epicenters are located on the surface of the Earth, while the focus is beneath the crust and located right below the epicenter.
3.In locating the origin of the earthquake, seismologists first locate the epicenter.
4.When seismologists aim to find the cause of the earthquake, they study the area around the focus.