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Related to Foreshocks: Seismic waves, Aftershocks
Mini-earthquakes that often precede the largest earthquake in a series
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Foreshocks are different from aftershocks, other sources said.
There were no foreshocks, and therefore no warning.
Undoubtedly, these events encouraged me to become a geophysicist and earthquake researcher--to seek to understand the fundamental physics of earthquakes and learn, for example, why foreshocks preceded the quake in Haicheng, but not in Tangshan.
Flurries of foreshocks also appear to have occurred prior to a number of other moderate-size earthquakes in our study region in the Pacific.
The closely spaced foreshocks were all magnitude 3 or weaker, and they occurred within the last 12 hours before the main shock, which registered magnitude 7.
It's been one of the big questions for us: whether there is anything that looks different about foreshocks," says Jones.
In studies of past foreshocks, seismologists have not succeeded in detecting any discriminating characteristic that could serve as the basis for identifying which jolt precedes a larger quake.
Of course, scientists cannot definitively label tremors as foreshocks until a larger quake follows, and by then it's too late to issue a warning.
She calls the earlier quakes "preshocks" to distinguish them from the foreshocks that can appear hours or weeks before a main shock.
Few aftershocks were recorded, but it was preceded by a foreshock of M 4.