BANGKOK: Earthquakes in Surat Thani are caused by two active fault lines that are still moving—Ranong Fault and Klong Marui Fault.
The Ranong Fault is the longest (270 km), while the Klong Marui Fault (150 km) cuts directly through Surat Thani province.
The tremors are a result of the release of accumulated stress from the movement of large tectonic plates, confirming that both faults are still active.
Recent earthquakes in Surat Thani have caught many by surprise. The southern region, often associated with beautiful beaches and world-class tourist destinations, has raised questions about why the land there is shaking. The explanation lies not on the surface, but deep beneath the Earth's crust, within the geological structure known as “active fault lines.”
The Geo-Informatics and Space Technology Development Agency (GISTDA) explains that, from a geographical standpoint, Thailand’s southern region is not just a peninsula with seas on both sides. It also has a central spine made up of granite mountains running north–south, serving as the "backbone" of the peninsula.
However, this structure is not entirely stable, as there are major cracks running in the northeast–southwest (NE–SW) direction, the result of tectonic plate movements over millions of years.
These cracks are at the heart of the recent seismic activity, particularly two major fault lines: Ranong Fault and Klong Marui Fault.
Ranong Fault: The “big brother” of the peninsula
The Ranong Fault is the largest and longest fault in the region, stretching about 270km. It starts from the Andaman Sea in Ranong province, crossing through Prachuap Khiri Khan, Chumphon, and extending to Phang Nga. This fault acts as a split, dividing layers of rock from different eras. Even small movements in this fault can create widespread tremors in surrounding areas.
Klong Marui Fault: The route south to Phuket
Parallel to the Ranong Fault, the Klong Marui Fault runs approximately 150km. This fault cuts through the heart of Surat Thani, reaching down to Krabi, Phang Nga, and continuing to Phuket.
The name “Klong Marui” comes from a canal in Thap Put district, Phang Nga, where the fault line is visible through erosion. This shows how clearly geology influences the formation of rivers and valleys.
Why does Surat Thani tremble?
Academics explain that this earthquake is a sign that the two fault lines are still “active.” The tremors didn’t result from direct plate collisions in southern Thailand, but from the stress accumulated due to the movement of tectonic plates on a global scale, such as the collision between the Indian Plate and the Eurasian Plate.
This energy is transmitted through layers of rock to the fault lines. Once the accumulated energy exceeds a threshold, it is released through strike-slip faulting, creating tremors that can be felt on the surface.
What is the magnitude of the threat?
Generally, most of Thailand's faults generate small to moderate earthquakes, which are not as intense as those in the “Ring of Fire” like Japan or Indonesia.
However, the increasing frequency of these events over the past few years serves as a warning for heightened vigilance and preparedness.
Currently, building designs in many areas of southern Thailand have started considering earthquake resistance standards more seriously.
This event serves as a reminder that the landscapes we see today — whether mountains, rivers, or coastlines — were formed by subterranean forces that are still at work.
Understanding the Ranong and Klong Marui faults is not something distant, but rather a crucial part of learning how to live in harmony with nature, on land that may appear calm but is actually alive beneath our feet. - The Nation/ANN
