Volcanic earthquakes can also result from stress changes in solid rock caused by the movement of magma. Earthquakes are produced when rock collapses into spaces created by the withdrawal of magma or by the injection of magma into the surrounding rock. A 5.1 magnitude earthquake occurred during the Mount St Helens eruption of 1980, triggering a massive landslide on the north face of the volcano.
EXAM LINK (HL)
Earthquakes (30 marks) Explain, with reference to examples that you have studied, how the theory of plate tectonics helps to explain the distribution of earthquakes around the world.
Seismologists use an instrument called a seismograph to detect and record earthquake activity (Fig. 3.3). Seismographs measure the intensity of seismic waves which can shake and displace the land on the earth’s crust both horizontally (sideways) and vertically (up and down). They generate a graph called a seismogram.
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Rotating drum
Marker Weight Spring Weight Marker
Rotating drum
Vertical earth motion
Base anchored onto bedrock and moves Fig. 3.3 Seismographs record the vertical and horizontal movement of the earth's crust. 31 earth motion Horizontal Cable A-Z
Seismologists: Scientists who study the causes and effects of earthquakes.
