There is one magnitude for each earthquake. The size of the earthquake is called its magnitude. The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. A short wiggly line that doesn’t wiggle very much means a small earthquake, and a long wiggly line that wiggles a lot means a large earthquake. So how do they measure an earthquake? They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was (figure 5). The size of an earthquake depends on the size of the fault and the amount of slip on the fault, but that’s not something scientists can simply measure with a measuring tape since faults are many kilometers deep beneath the earth’s surface. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.Īn example of a seismic wave with the P wave and S wave labeled. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries.
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The earth has four major layers: the 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.īut this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock! What causes earthquakes and where do they happen?Ī simplified cartoon of the crust (brown), mantle (orange), and core (liquid in light gray, solid in dark gray) of the earth. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Mainshocks always have aftershocks that follow. The largest, main earthquake is called the mainshock. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. 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. The surface where they slip is called the fault or fault plane. A normal (dip-slip) fault is an inclined fracture where the rock mass above an inclined fault moves down (Public domain.)Īn earthquake is what happens when two blocks of the earth suddenly slip past one another.
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