"STRANGE SOUNDS WORLD WIDE"

When magma or fluids move through the crust, they can produce a seismic signal -- harmonic tremor. Unlike normal seismicity related to fault movement that creates punctuated seismicity -- a singular event that diminishes with time (and can then have aftershocks), the movement of magma or fluids can produce a constant, long-period tremor (see below). This tremor is also not like most tectonic seismicity in the sense that it is usually only measurable by seismic

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