Minerals and Geoscience Department explains quakes in Segamat

KUALA LUMPUR: A minor earthquake measuring 4.1 on the Richter scale struck Segamat, Johor, on August 24, followed by five subsequent tremors, including one this morning, raising concerns among residents in the district and surrounding areas.

The Minerals and Geoscience Department has confirmed that these tremors are caused by the reactivation of the Mersing Fault.

What is a fault line?

A fault is a crack in the Earth’s crust caused by the movement of rock blocks due to subduction zones. When energy is released suddenly along these cracks, it results in an earthquake.

In Malaysia, several fault lines have been identified, including the Mersing Fault, Bok Bak Fault, Bukit Tinggi Fault, Kuala Pilah Fault, Kuala Lumpur Fault, and Terengganu Fault.

The energy released by these faults can vary, resulting in horizontal, reverse, or normal fault movements.

The Reactivation of the Mersing Fault

Minerals and Geoscience Department director-general Datuk Zamri Ramli told Buletin TV3 that the recent earthquake in Segamat occurred when the 50km-long Mersing Fault released energy due to friction.

He clarified that these tremors were caused by the movement of the Earth’s crustal plates within the same tectonic plate, not due to an external subduction zone.

“When this release of energy occurs, we observe that the energy pattern is declining, signalling that it is moving toward stability. It’s uncertain whether it will store energy again,” he said.

Zamri said calling this an active fault would be inaccurate, describing the phenomenon as a “reactivation.” According to him, the energy release pattern is weakening.

Fault Movement in Malaysia

Zamri further explained that faults in Malaysia typically move between four to 10cm annually, driven by pressure on either side of the fault.

Studies conducted by geologists, in collaboration with international experts, have found that no fault in Peninsular Malaysia has the capacity to generate earthquakes of magnitude 5.0 or higher.

Most tremors recorded in the region have been below magnitude 5.

“Based on our research with experts, the worst-case scenario would be a 5.5 magnitude quake. Scientifically, this fault system cannot generate stronger quakes. We are located on the stable Sunda Plate, and while we do experience pressure from both sides of the fault, this is not the case in Sabah, where earthquakes as strong as magnitude 6.0 have been recorded. In the worst-case scenario, we expect a 6.5 magnitude quake in Sabah,” he explained.

On-the-ground monitoring

Following the tremors, Zamri said their Johor branch, together with the Malaysian Meteorological Department (MetMalaysia), is conducting monitoring around the affected area.

“I was informed of hairline cracks and such, but not all of Segamat is affected. We need to examine the underlying rock composition, whether it is peat or soft soil.

“If it is soft soil, tremors will amplify, or if buildings are not built according to specifications, they will be affected.

“In 2020, we had already discussed and enforced the use of Bio-Seismic codes in building construction, and the Public Works Department has fully implemented this,” he said.

© New Straits Times Press (M) Bhd

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