KOCHI: The devastating earthquake that struck Morocco on September 8, killing close to 3,000 and injuring another 5,000, throws up some disturbing facts. While the high casualties in the 6.8 magnitude quake could be partially attributed to the traditional mudbrick houses common in the region, many experts point out that temblors were felt in an area not considered prone to major earthquakes. That the quake broke out at 11.11 pm local time added to the casualties as most people were home fast asleep or turning in for the night.
According to the United States Geological Survey (USGS), the earthquake’s epicentre was Al-Haouz province in the Atlas Mountains, southwest of the historic Moroccan city of Marrakesh. The Mediterranean region in general, including Morocco, is susceptible to earthquakes. However, the majority of quakes are concentrated in the northern part of the country where the African and European tectonic plates meet. The September 8 quake took place farther south in a region of low seismicity, which was hitherto considered safe. Experts consider an earthquake of close to 7 magnitude in the Atlas Mountains area to be a rare occurrence. With no seismic activity expected in the region, people were ill-prepared and the fragile buildings had no chance of withstanding the gigantic earthquake.
Shallow and dangerous
The USGS data show the Morocco earthquake occurred at a depth of 26 km. While temblors can occur anywhere between the Earth’s surface and 700 km deep, scientists divide earthquakes into three zones for analytical purposes. Tremors occurring within 70 km from the ground level are called shallow earthquakes, those between 70km and 300 km intermediate, and those in the 300-700 km range deep earthquakes.
Of these, the shallow ones are the most dangerous because the enormous energy released from the rupture is passed on to the surface almost in its entirety. In such cases, the affected area experiences violent shaking and buildings that are not designed and built to resist earthquakes collapse like a house of cards. In contrast, deeper earthquakes release their energy over a large area and, as a consequence, the effects are spread out thin.
Another shallow earthquake with far greater casualties and damage was the magnitude 7.8 earthquake that shook Turkiye and Syria on February 6, 2023. The quake occurred at a depth of just 18 km below the Earth’s surface. It was followed by another powerful tremor of magnitude 7.5 nine hours later. With the affected area spread across hundreds of kilometres, 43,000 people were killed in Turkiye and 5,500 in Syria, according to United Nations data. Experts are unanimous that the shallow nature of the tremor accentuated the damage.
Tectonic shifts
In the Morocco earthquake, the entire region shook violently and the vibrations were felt as far as away as Portugal’s capital Lisbon. This is because the quake was shallow and caused by what geologists term an ‘oblique-reverse faulting’, where tectonic plates collide with each other as well as move sideways, causing the Earth’s crust to rise up. Morocco sits on the African plate, also called the Nubian plate, which is known to be slowly moving in the northern direction towards the Eurasian plate. Geologists believe the ongoing collision of the African plate with the Eurasian plate caused the recent quake. According to Jesús Galindo-Zaldivar, professor of geodynamics at Universidad de Granada, the Atlas Mountain range is ‘actively rising’ and there has been a recent movement in the Earth beneath the area. “The stress along these fault lines can induce earthquakes as rocks abruptly shift to release accumulated stress, which is characteristic of a seismic fault,” he says.
Why do earthquakes occur?
The tectonic plates are always in motion, at a very slow pace. Tectonic plates are very large slabs of solid rock with their size ranging from a few hundred to thousands of kilometres. Sometimes they get stuck due to friction at the boundaries between the plates, causing tension to build up along the fault over time. At some point, the tension is released suddenly and the result is an earthquake. Tremors release massive amounts of energy in the form of waves that travel through the earth’s crust, causing the surface to shake.
For context, the Morocco earthquake was equivalent to detonating 30 nuclear bombs, similar to those dropped on Hiroshima in 1945, according to Bill McGuire, professor emeritus of geophysical and climate hazards at University College London.
Is India safe?
The subcontinent is sitting on the highly seismic Indian plate that has some major fault lines. India has a history of both large and small earthquakes. Among the large earthquakes is the 2001 Bhuj tremor which scored 7.6 in magnitude and killed over 20,000 people. The 1993 Latur earthquake was shallow one with the focus of the tremor being just 10 km deep. The Latur quake killed over 10,000 and had a magnitude of 6.4.
India is situated in a high seismic region and no part of the country is completely safe from earthquakes, according to experts. Based on historical seismic activity, the Bureau of Indian Standards has categorised the country into four seismic zones - zone 2, zone 3, zone 4, and zone 5. Of these, zone 5 is considered the most seismically active area while zone 2 is relatively safer from damage.
Data shows that earthquakes of small magnitude keep occurring in India but go unnoticed because of nil casualty or damage. According to data released by the National Center for Seismology, the nodal agency of the Government of India for monitoring of earthquake activity in the country, there were as many as 41 tremors in India and its neighbourhood region in August 2023 alone. Of these, 35 were smaller quakes of less than 3 magnitude and six were of magnitude 5 and above.
Himalayan fault lines
The Himalayan region is highly prone to earthquakes due to its location at the boundary of two tectonic plates—the Indian plate and Eurasian plate. The collision of the two plates began millions of years ago and the Himalayan mountains were created after the Indian plate was forced under the Eurasian plate.
The Himalayan region has experienced several large earthquakes in the past, including the 2015 Nepal earthquake, which had a magnitude of 7.8 and caused widespread destruction and loss of life. There have been numerous lower-intensity tremors in the region since then including the 2022 earthquake in Afghanistan that measured 6.2. The effects of the tremors in the Himalayan region are invariably felt across north India, including the national capital Delhi.
The alarming frequency with which these quakes are happening has geologists and seismologists sit up and contemplate the prospect of ‘the great Himalayan earthquake’ that is said to be waiting to happen any time with disastrous consequences in the subcontinent.
HOW TO REACT DURING A QUAKE
Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimise your movements to a few steps so that can reach a nearby safe place and stay indoors until the shaking has stopped
IF INDOORS
IF OUTDOORS
IF IN A MOVING VEHICLE
IF TRAPPED UNDER DEBRIS
Source: NDMA