Abstract: Earthquakes are usually assumed to result when the gradual stress buildup in a region eventually exceeds some initial local strength. There are observations which suggest that a number of mechanisms must have a significant role in stress redistribution in active earthquake regions. The stress build-up could be non-linear in time; there is evidence that this is so in the case of some major earthquakes. One mechanism that might explain non-linear strain buildup is a "slow" earthquake. This is similar to a normal earthquake except that the rupture and slip velocities are very low so that negligible energy is radiated in the normally observed seismic frequency band. The slow earthquakes studied here have been recorded by a network of Sacks-Evertson borehole strainmeters installed along the seismically active Pacific coast of Honshu (Japan). Larger slow events may have (slow) foreshocks and aftershocks in a manner similar to that for normal earthquakes. The aftershocks appear to have lower stress drops than the foreshocks. The static field changes associated with the Izu-Oshima earthquake (m = 7) of January 1978 were sufficiently large that they were clearly recorded by the nearest three strainmeters. Interpretation of the records indicate that this earthquake was in essence a normal quake followed by a slow event of similar moment. This interpretation is corroborated by reports of ground vibration and faulting on the Izu peninsula.
Publication Year: 1982
Publication Date: 1982-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 23
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