Our Beautiful World
(It has taken quite a bit of time to get so far as to understand what the difference and meaning
of all the quakes, which are reported from different places, really mean.
It is hoped this page will help you to understand a little bit more.)
Seismic monitoring at HVO (Hawaiian Volcano Observatory) has helped to clarify the distinction between the two main classes of earthquakes, volcanic and tectonic. Although all earthquakes associated with active volcanoes are ultimately related to volcanic processes, volcanic earthquakes are directly associated with magma movement, while tectonic earthquakes occur in zones separated from the principal areas of magma movement. Tectonic earthquakes on Hawaii share characteristics with seismic events elsewhere that are not associated with volcanic systems, such as the earthquakes generated by the San Andreas fault zone in California.
During inflation the rocks surrounding the reservoir become stressed, and this stress is partly relieved by increasing numbers of earthquakes, too small to be felt, but easily recorded by seismometers.These earthquakes, called short-period or tectonic, are recorded as high-frequency features on a seismograph.
During deflation the stress is completely relieved. The short-period earthquakes stop, but their place is taken by low-frequency earthquakes, called long-period or volcanic, which reflect adjustments related to the exit of magma from the summit reservoir to feed the eruption.
The long-period earthquakes are related to harmonic tremor, the continuous seismic record of underground magma movement. Normally these kind only are registered by the seismometers, but at special violent eruptions, it may be felt as far as up to 8 kilometers from the center of the eruption.
Volcanic tremor, a type of continuous, rhythmic ground shaking different from the discrete sharp jolts characteristic of earthquakes. Such continuous ground vibrations, commonly associated with eruptions at volcanoes in Hawaii, Iceland, Japan, and elsewhere, are interpreted to reflect subsurface movement of fluids, either gas or magma.
VA = Deep volcanic tremors, VB = Shallow volcanic tremors
After sifting through a decade of information, McNutt
and Benoit noticed a pattern. Volcanoes often go
|Earthquakes and Seismicity, when you wish to understand more. USGS