A scar across a nation
The Sagaing Fault is a massive, 1,400-kilometer-long right-lateral strike-slip fault that runs the length of Myanmar. It marks the boundary between the Indian Plate and the Sunda Plate, taking up about half of their relative motion. This geological feature connects the Andaman Sea spreading center in the south with the Himalayan continental collision zone to the north. Modern GPS measurements show the two sides of the fault are slipping past each other at a rate of approximately 18 to 20 millimeters per year. This constant, slow movement builds up strain that is released in periodic earthquakes. The fault passes directly through some of Myanmar's most populated areas, including the cities of Sagaing, Mandalay, and the nation's capital, Naypyidaw.
The fault's geomorphology is visible on the landscape. It creates linear valleys, fault scarps, and offset stream channels. In some locations, streams have been displaced laterally by as much as 2.4 kilometers over time. The total displacement along the fault since its inception is estimated to be between 360 and 400 kilometers. The fault is not a single, simple line but has several segments. For instance, the Naypyidaw segment consists of two parallel fault traces running for about 70 kilometers directly beneath the capital city.
A history of violent ruptures
The Sagaing Fault has a long history of producing large and destructive earthquakes. Between 1929 and 1931, a series of major events ruptured more than half the fault's length. On May 5, 1930, a magnitude 7.3 earthquake struck near Bago (formerly Pegu), causing widespread destruction and killing over 500 people. This event caused at least 3 meters of surface offset. Just months later, on December 4, 1930, another magnitude 7.3 earthquake occurred further north near Pyu.
Other seismic events mark the fault's recent history. In 1946, a powerful earthquake doublet with magnitudes of 7.3 and 7.7 struck north of Mandalay. A magnitude 7.1 earthquake hit near Mandalay in 1956, killing at least 40 people. More recently, a magnitude 6.8 earthquake in 2012 north of Mandalay caused significant damage and at least 26 fatalities. The 1839 Ava earthquake is another major historical event linked to the fault, which caused immense damage to the then-royal capital of Inwa. Geologists identify sections of the fault that have not ruptured in a long time as seismic gaps, which may be accumulating strain for a future large earthquake.