The earthquakes occurred on several faults, in subduction zones, and outer rises, according to the Medan branch of the Meteorology, Climatology, and Geophysics Agency (BMKG),
"The active faults triggering the earthquake occurred in Seulimeum, Central Aceh, Batee C, Renun, and Toru," the agency's spokesperson, Eridawati, remarked.
A local fault in Samosir Island, North Sumatra, also contributed to the earthquake occurrences, she noted in a statement that ANTARA quoted here on Saturday.
The magnitudes of 44 of the 48 earthquakes that the agency recorded from May 28 to June 3, 2021, were above four, while those of four others were below four.
Referring to the epicenters of those earthquakes, 45 of them occurred on land, while three others occurred at sea, Eridawati stated.
Most of the earthquakes that occurred from May 28 to June 3, 2021, were classified as shallow earthquakes, the agency's researcher, Marzuki Sinambela, noted.
Earthquakes regularly rock various parts of Indonesia since the country lies on the Circum-Pacific Belt, also known as the Ring of Fire, where several tectonic plates meet and cause frequent volcanic and seismic activities.
Sumatra and various smaller islands off its coastal areas are vulnerable to earthquake.
On May 22, 2021, for instance, a 5.2-magnitude earthquake rattled Enggano Island in the Indonesian province of Bengkulu, but it did not trigger a tsunami.
The epicenter of the quake that struck at around 1:36 a.m. local time was located some 31 kilometers (km) away from the west of Enggano Island's waters, at a depth of 10 km.
Aceh Province, located at the northernmost tip of Sumatra Island, had also experienced the deadliest ever earthquake, followed by a tsunami on December 26, 2004.
The catastrophe that also affected certain coastal areas in countries, such as Thailand, Sri Lanka, and India, reportedly killed some 230 thousand people.
The latest deadly earthquake to have rattled Indonesia was in West Sulawesi Province on January 15, 2021.
The 6.2-magnitude earthquake, ensued by several aftershocks, jolted the districts of Mamuju and Majene, claiming more than 100 lives and destroying several buildings.
Related news: Magnitude-7.2 quake rattles West Nias, North Sumatra
Related news: BMKG identifies seven hotspots in North Sumatra
Related news: BMKG records 115 quakes in N Sumatra, Aceh in second week of May