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.
#Ocean waves pictures websites skin
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. The gravitational pull of the sun and moon also cause waves to form – these are known as tides.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.
#Ocean waves pictures websites series
Seismic activity can cause a series of long-wavelength waves known as a tsunami, due to the displacement of large amounts of water. Not all waves are caused by the wind though. Some research suggests that extreme waves are becoming more likely as a result of climate change, due to an increase in storms and melting of polar ice. The complex forces that give rise to them are now better understood, raising the possibility of rogue wave forecasts in the future. However, through better monitoring of the seas, we now know these freak waves are surprisingly common. These rogue waves were once thought to be fictional, or vanishingly rare. Occasionally waves merge to form one that is far higher than those surrounding it. But if it blew for 48 hours, the wave’s crest would increase to 10.5 metres, about twice the height of a double-decker bus. Wind blowing for an hour at a speed of 55.6 kilometres per hour over a stretch of water 1000km wide would generate waves with a significant wave height of 0.7 metres. Oceanographers measure wave height using a term called “significant wave height”, which is the average height of the largest 33 per cent of waves in that region of ocean at the time. The height of a wave is determined by the wind strength, the length of time it blows and its fetch – the distance it travels over the water. This causes the wave to stand up then pitch forward before eventually breaking. An analogy is a crowd of people doing a Mexican wave in a stadium: they stay in the same location, but the wave they create travels around the arena.Īs waves reach the shore, the shallow floor begins to run into their base, slowing their deeper parts. The rise and fall of water molecules creates a wave that moves in the direction of the wind. Waves occur when the force of the wind blows over surface water, transferring its energy and causing the water to move in a circular motion. They are mainly caused by winds, and, if unimpeded, can travel for thousands of kilometres. There are many types of waves flowing across the oceans, from small ripples to huge walls of water, 30 metres high peak-to-trough.
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