Strong M6.6 earthquake hits Halmahera, Indonesia at intermediate depth

A strong earthquake registered by the BMKG as M6.6 hit Halmahera, Indonesia at 02:48 UTC (09:48 LT) on November 22, 2023. The agency is reporting a depth of 109 km (67.7 miles). USGS and EMSC are reporting M6.0 at a depth of 119 km (73.9 miles).

The epicenter was located 93.6 km (58.1 miles) W of Tobelo (population 34 150), and 107.4 km (66.7 miles) NNW of Ternate (population 205 001), North Maluku, Indonesia.

This region is known for producing strong and destructive earthquakes.

Based on the location, depth of the epicenter of the earthquake, and source mechanism data from BMKG and USGS of the United States, this earthquake was caused by double subduction activity of the Talaud Mayu Ridge or can be called an intraslab earthquake with the type of mechanism being a horizontal fault.

BMKG analysis of this earthquake and preliminary reports show this earthquake had resulted in the death of a worker who was working on the tower (on Jalan Mononutu, Stadium Village, Ternate Tengah, Ternate City, North Maluku), crushed by iron. 

According to BMKG data, earthquake shocks were felt in the cities of Manado, Minahasa, North Minahasa, Southeast Minahasa, Tomohon, Ternate, North Halmahera and West Halmahera on the MMI III-IV intensity scale.

This earthquake does not have the potential to cause a tsunami even though the epicenter of the earthquake is located in the sea, because the energy is not strong enough to cause deformation of the seabed which can trigger a tsunami, BMKG said.

It is not expected to have the potential to cause collateral hazards in the form of ground cracks, land subsidence, ground movement, and liquefaction.

According to the USGS’ PAGER, 1 088 000 people are estimated to have felt light shaking. However, keep in mind USGS is reporting a significantly lower magnitude than Indonesian BMKG.

The USGS issued a Green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Overall, the population in this region resides in structures that are vulnerable to earthquake shaking, though resistant structures exist. The predominant vulnerable building types are unreinforced brick with concrete floor and precast concrete frame with wall construction.

BMKG said aftershocks are expected and advised the public to remain calm and follow directions and information from the local BPBD, remain calm, remain alert to subsequent earthquakes and do not be provoked by irresponsible rumors regarding earthquakes and tsunamis.

Regional seismicity

Featured image credit: TW/SAM, Google