two weeks after the August 5 earthquake that left at least 480 people dead in Indonesia, the region was hit by another earthquake of the same magnitude (6.9 on the Richter scale), and having the same epicentre (the holiday island of Lombok to the east of Bali).
Four significant quakes were recorded that day — the first, measuring 6.3 on the Richter scale, it was followed 12 hours later by another measuring 6.9, and subsequently by two more, of strength 5.9 and 5.3 on the Richter scale.
deed, a series of temblors have hit the Indonesian archipelago since July 29.
. Seismologists describe such a phenomenon as an “earthquake swarm”.
Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time.
They are differentiated from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence is obviously the main shock.
A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space.
The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the full sequence of events has happened
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock.
If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock.
While the April 2015 Nepal earthquake demonstrated the foreshocks-main shock (7.8)- aftershocks trend, the seismic activity in Indonesia fits the typology of the swarm
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