Data reveals why last month’s earthquake was so devastating
The ground in Myanmar was split and dragged in different directions during the massive 7.7 magnitude earthquake that hit the Southeast Asian nation on March 28. The quake tore a rupture through the earth’s surface stretching for more than 285 miles (460 km), around twice the distance expected from a quake of this magnitude, according to scientists.
This reveals how much the surface moved in opposite directions during the quake, using data from the U.S. Geological Survey (USGS). The long surface rupture can be plotted along the contrasting sections of land, which shifted around 5 metres (16.4 feet) in different directions, according to the analysis.
The quake has killed more than 3,700 people, flattened communities and crippled infrastructure in the impoverished nation.
A month after the quake hit, nearly 200,000 people remain displaced and living outdoors, according to the International Federation of Red Cross and Red Crescent Societies (IFRC), even as parts of central Myanmar are jolted almost daily by aftershocks.
“Myanmar’s cyclone season starts within days, exposing coastal populations to strong winds and rains – leaving families to face the risks of floods and landslides,” IFRC said on Monday. “Conditions on the ground continue to be very challenging.”
The monsoon rains typically arrive in Myanmar by late May, possibly piling more misery on the displaced.
Supershear
The speed of the massive rupture may have also played a role in the devastation. Scientists believe this was a “supershear” earthquake, a rare event where the rupture in the ground moved faster than the seismic waves produced.
“Preliminary studies indicate that the rupture was supershear,” said Dr. Judith Hubbard, Professor at Cornell University and co-founder of Earthquake Insights.
Earthquakes begin at a specific point on a fault and spread rapidly along it, usually at speeds of a few miles (km) per second. In this instance, scientists observed that the rupture spread even faster than usual.
“When an earthquake occurs, it does not happen all at once,” said Hubbard. The rupture constantly creates waves of energy that spread like ripples in a pond. If the rupture moves faster than these waves, they can pile up and form a Mach wave, similar to the sonic booms from supersonic jets, she told Reuters.
Sub-shear rupture
Energy is released at various points along the rupture as it moves.
The supershear effect may have led to greater damage at greater distances than typical earthquakes, with significant structural failures observed as far away as Bangkok in neighbouring Thailand.
“Supershear ruptures generally result in longer than expected earthquakes, which means shaking occurs over a larger area compared to other earthquakes of the same magnitude,” said Steven Sobieszczyk, scientist at USGS.
Record rupture
“One of the things that stands out about this earthquake is its length,” said Hubbard, who believes it is the longest M7.7 earthquake rupture ever recorded.
Data from USGS indicates the rupture was about 174 miles (190 km) longer than that of the massive earthquake which struck Turkey and Syria in February, 2023, killing more than 55,000 people.
“This was an abnormally long earthquake,” said Sobieszczyk. He explained that the rupture length was approximately double what is typically expected for its magnitude.
The maps below show the size of the rupture relative to other well-known land masses. The crack is comparable to the length of Taiwan, South Korea, or Portugal.
Connecting the dots
For smaller earthquakes, a point on a map is sufficient to depict the epicentre, where the quake originates. However, large earthquakes, like the one in Myanmar, with ruptures extending hundreds of miles, impact areas far away from the epicentre.
The smaller towns situated along the rupture suffered some of the most severe shaking as it tore straight through some of these settlements, along with the capital, Naypyidaw, as if it were joining the dots on a map.
The rupture is visible in satellite imagery at some locations along the fault, such as the following location on the outskirts of Naypyidaw.
Across Myanmar, the quake damaged thousands of structures and crippled critical infrastructure, even bringing down parts of its purpose-built capital city Naypyidaw.
Nationwide, it damaged over 400 roads, 300 hospitals and clinics, 95 bridges, 2,500 schools and 55,000 houses, totaling about $1.9 billion USD worth of losses as per current estimates, according to the Association of Southeast Asian Nations – ASEAN Coordinating Centre for Humanitarian Assistance on Disaster Management.
The military regime is now working to rebuild some government buildings to withstand earthquakes of up to 8 magnitude, regime media reported last week.
More than 1,000 buildings were damaged in Mandalay alone, the city close to the epicentre, according to a damage assessment by the U.N. – United Nations Satellite Centre. About 900 other buildings were found to be possibly damaged.
Further south in the Thai capital, Bangkok, the quake killed at least 63 people, including 56 after an under-construction building collapsed. Thai authorities are still working to clear the debris at the site, where 38 people are still missing.
Despite Bangkok being 620 miles (1,000 km) from the epicentre, it is only 416 miles (670 km) from the southern end of the rupture, Sobieszczyk told Reuters. He also noted that the earthquake ruptured predominantly from north to south, channeling stronger shaking towards the city.
The impacts in Bangkok are still being studied, but several factors likely played a role, including Bangkok’s soft sediment which can amplify ground shaking, similar to Kathmandu and Mexico City, Sobieszczyk explained.
According to Hubbard, untangling these issues may take significant work by experts over the coming months to years, looking at the specific waveforms recorded by seismometers in the region.
“Unfortunately, records within Myanmar are very sparse, and south of Myanmar is the Andaman Sea, which also does not have seismometers,” said Hubbard. However, records from within Thailand should provide some insight, she added.
The Earth Observatory of Singapore, a research institute at the Nanyang Technological University, removed two-thirds of its seismic monitors in Myanmar last year because of “logistic difficulty related to the pandemic and the coup”, according to Dr. Shengji Wei, Principal Investigator at the observatory.
Wei explained that they missed the chance to collect strong motion data near the ruptured fault and to monitor seismic activity in the region, including numerous aftershocks.
