Scientists define an earthquake which happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Smaller earthquakes that follow in the same place as the larger earthquake, called aftershocks, may occur for weeks, months, and even years after the main shock.
The earth has four major layers: inner core, outer core, mantle, and crust. The crust, and the top of the mantle make up a thin skin on the surface of our planet, made up of many pieces like a puzzle covering the surface of the earth.
But these puzzle pieces, called tectonic plates, keep slowly moving around, sliding past one another, and bumping into each other. The edges of the tectonic plates, called plate boundaries, are made up of many faults; most of the earthquakes around the world occur on these faults.
Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. When the plate has moved far enough, the edges ‘unstick’ on one of the faults, causing an earthquake.
Energy radiates from the fault outward in all directions in the form of seismic waves, like ripples on a pond, which can be recorded by instruments called seismographs.
There are two types of earthquakes: tectonic and volcanic. Tectonic earthquakes are produced by sudden movement along faults and plate boundaries. While earthquakes induced by rising lava or magma (beneath active volcanoes) is called volcanic earthquakes.
Scientists have tried many different ways of predicting earthquakes, but none have been successful. On any particular fault, scientists know there will be another earthquake sometime in the future, but they have no way of telling when it will happen.
Recently, a 6.8 magnitude earthquake hit Morocco killing more than 2,900 people (and counting) and injuring thousands. The epicenter of the quake was around 70 kms. southwest of Marrakech, high in the Atlas Mountains, meaning the worst-affected areas are in central Morocco.
At present, our Philippine Institute of Volcanology & Seismology (PhIVolcS) operates 108 seismic monitoring stations all over the Philippines (as of December 2020). These stations are equipped with seismometers that detect and record earthquakes. Data are sent to the PhiVolcs Data Receiving Center to determine earthquake parameters such as magnitude, depth of focus, and epicenter.
PhiVolcs predicts that a 7.2 magnitude earthquake resulting from the movement of the West Valley Fault is expected — which will have a devastating impact in Metro Manila.
Scientists predict it has a recurrence interval of 400 to 500 years. The last major earthquake originating from the fault was recorded in the year 1658, or 365 years ago.
Are you ready for the big one? Pwera buyag!
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