The breakthrough in the study, published earlier this summer in the journal Geophysical Research Letters, was made possible by the discovery of a new technique to find very small earthquakes — quakes as small as magnitudes 0 and 1, and some as small as magnitude negative 2.
Quakes can now have negative magnitudes because this new technique allows for observation of quakes so small they were previously thought to be undetectable. For the study, Trugman and Ross focused on 46 of the largest quakes in Southern California between and while excluding those that were aftershocks of other larger events.
They found that 33 of the 46 had a statistically significant jump in foreshocks compared with the normal rate of earthquakes for that area. They discovered a particularly lengthy foreshock sequence preceding the magnitude 5. There were foreshocks in the magnitude 0 and 1 range as early as 17 days ahead of the mainshock. The Easter Sunday magnitude 7. But that earthquake was preceded by a notable foreshock sequence. The scientists could not determine a specific pattern to the foreshocks that would lead to a magnitude 4 or greater quake. Sometimes, it would appear as a burst of quakes near what would become the mainshock epicenter days or hours later.
Other times, it would appear as a widespread increase in the earthquake rate in the general area before the mainshock. They also found that shallower mainshocks tended to have more foreshocks, as do areas with higher heat flow, such as around the Coso Volcanic Field in Inyo County and the Salton Sea, which are warmed by magma. The results help solve a long mystery that earthquake scientists had not been able to explain.
In lab experiments where scientists would simulate earthquakes with sensitive equipment, there would always be small earthquakes that came before the main quake. About Us. Brand Publishing. Times News Platforms. Real Estate.
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