Since 1900, 35 earthquakes worldwide have each killed at least 10,000 people. Of these, 26 were in the Alpine-Himalayan seismic belt – a broad “crumple zone” where the African, Arabian and Indian tectonic plates collide with Europe and Asia. Most of these deadly earthquakes were caused by the rupture of faults that had not previously been identified.
Tim Wright is Professor of Satellite Geodesy at the University of Leeds and Director of the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). His work has been at the forefront of developing the use of satellite radar for measuring tectonic and volcanic deformation.
Below is a lecture presented by Tim at the Geological Society talking about his work trying to understand the nature of seismic hazard within the Alpine-Himalayan region.
Earthquakes have not been releasing energy as fast as the energy has been building up along the Himalayan arc. Meaning that there could be a giant earthquake in the region placing millions at risk.
A new study of the 2000 km long Main Himalaya Thrust, the largest earthquake generating fault in the Himalaya, has revealed that large quakes could occur in any location along the Himalayan arc.
Unlike in subduction zones, where some patches of the fault are moving, or ‘creeping’ at a constant speed, in the Himalaya we don’t see any creeping patches. This means that the fault is fully ‘locked’, i.e. strain energy is building up most of the time. This energy is released suddenly during earthquakes. Because there are no creeping patches, there are no barriers to rupture, which means once an earthquake has started, it could rupture a very long way along the fault without anything to limit its size.
The study shows that the pattern of coupling, i.e. the degree of fault locking, has been stationary with time. From the coupling pattern, the rate of moment build-up can be found. This is how much energy is building up each year, and is also the amount that needs to be released in earthquakes if all the energy is released seismically.
Earthquakes have not been releasing energy as fast as the energy has been building up, so we may expect very large earthquakes in this region in the future. Studies of ancient earthquakes have shown that quakes approaching magnitude 9 have occurred previously in both the western and eastern halves of the Himalayas. It is not impossible that these giant earthquakes could occur again.
This has important implications for seismic hazard in the region. The population living in the Himalayas has increased dramatically in the past few decades, and most buildings are not resistant to large shaking caused by earthquakes. As we saw with the recent devastating April Gorkha-Nepal earthquake, the Himalayan countries prone to earthquakes are not yet prepared to meet all the challenges this natural hazards present.