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According to the news hundreds of people have fled to higher ground in the feat that the tremor may trigger a tsunami. Chilean Navy officials have not issued a warning. Still citizens there are leary of any quake on or so close to shore. The quake occurred at 20:20:16 UTC time according to the official USGS notifier in the Araugania region some 370 miles Southwest of Santiago. The quake was at a relatively shallow depth of only 10.5 miles deep, but so far no significant damage or any injuries have been reported. According to the USGS’s shakemaps, the quake was of moderate felt intensity reaching out to about 100 km from the epicenter.
Originally posted by muzzy
DEPARTAMENTO DE GEOFISICA SERVICIO SISMOLOGICO UNIVERSIDAD DE CHILE has the epi centre offshore
Aftershocks are also interesting because they're fairly well behaved—meaning that they have a detectable pattern, unlike all other quakes. The definition that scientists use for an aftershock is any seismic event occurring within one rupture-zone length of a main shock and within the time it takes for seismicity to fall off to what it was before the main shock. This body of quakes fits three mathematical rules, more or less. The first is the Gutenberg-Richter relation, which says that as you go down one magnitude unit in size, aftershocks increase in number by about ten times. The second is called Bath's law, which says that the largest aftershock is, on average, 1.2 magnitude units smaller than the main shock. And finally, Omori's law states that aftershock frequency decreases by roughly the reciprocal of time after the main shock. These numbers differ a bit in different active regions depending on their geology, but they're close enough for government work as the saying goes.