The great Kamchatka earthquake of magnitude 8.8 on July 29 was not only devastating in its impact on life, infrastructure and geology, but also an important addition to one of the most derided sciences – that of seismic predictions. For decades, scientists around the world have been chasing a compelling question: Can we predict earthquakes in time to save lives?

Most seismic practitioners have given up on this science. Yet, a few persevere, driven by Kamchatka-like events and the logic that if there were 50 early warnings before a great earthquake then there has to be an undiscovered science to explain it. That science dwells upon a host of parameters generated by each shock. Great earthquakes naturally become the subject of intense scientific, engineering and policy-level investigations due to the scale of their impact and the complexity of processes involved. These events offer valuable insights into not only the dynamics of earthquake generation and propagation but also the vulnerabilities within our built environment and governance systems. 

Various expert communities – scientific, engineering and policy – approach such events from their respective lenses to better understand, respond to and prepare for future occurrences. The scientific community focuses on understanding the physical processes underlying the earthquake. This includes analysing the rupture propagation, the time-history data, and studying how subsurface geological materials influenced the behaviour of seismic waves. Scientists also explore how the tsunami was triggered, the sequencing of wave propagation, and whether the foreshocks observed could have been used for forecasting the main event. 

While the strongest-ever recorded event on the Pacific Ring of Fire was an M9.5 in Valdivia (Chile) in 1960, the current shock was the strongest in 15 years – since the Tohoku shock (M9.1, 2011) which swamped Japan’s Fukushima prefecture and nuclear plant with a devastating tsunami. This earthquake occurred in the Kuril-Kamchatka subduction zone where the Pacific tectonic plate is subducting under the North American plate at a tectonically alarming speed of 9 cm per year. This compares unfavourably with the more sedate Indian plate subducting north-eastward at the rate of 5 cm per year. The Ring of Fire, which hosts over 90% of the world’s earthquakes, links multiple subduction zones and fault boundaries encircling the Pacific Ocean. 

In the ten-day period (July 20-30) this plate experienced 125 shocks, with 50 preceding the M8.8 shock on July 29, and 74 in quick succession. All such pre- and post-shocks were M5.0 to 7.4. The earthquake was preceded by two notable foreshocks: an M7.4 on July 20 and an M7.1 in August 2024. Both occurred in close proximity to the epicentre of the mainshock, suggesting a possible preparatory phase leading up to the rupture. Following the mainshock, the aftershock sequence remains active, indicating ongoing crustal adjustment in the region. 

Historically, the largest recorded event in this segment was the M9.0 earthquake in 1952. Given the convergence rate of approximately 9 cm per year, it is estimated that around 6.5 meters of tectonic strain had accumulated along the fault over the past 73 years. This accumulated strain has now been partially released, not only through the mainshock but also via large-magnitude foreshocks. The occurrence of large foreshocks prior to great earthquakes is not uncommon but is not consistent across all major events. While it would have been easy to expect a larger foreshock, the location, magnitude and shaking remain near-impossible to predict.

The successful prediction of the 1975 Haicheng earthquake in China had given hope to this science, when a sequence of intense foreshocks occurred days before the M7.3 main shock. Though debated as to whether it was a scientific prediction or fortunate coincidence, authorities had issued a rare two-day early warning based on foreshocks, leading to a mass evacuation, significantly reducing casualties. In this golden anniversary year of the Haicheng prediction, it is important to revisit our understanding of foreshocks, earthquake nucleation and precursory signals.

The M8.8 shock involved a sudden thrust movement that resulted in extensive energy release, triggering intense ground shaking and a tsunami. Preliminary estimates by USGS indicate that this particular reverse-faulting event involved a rupture area of nearly 390 by 140 km. The combination of this extensive fault area with an average slip displacement ranging from 5-15 meters results also offers crucial data for a complex equation that needs resolution.

Such megathrust earthquakes also generate significant vertical displacement of the seafloor, often triggering tsunamis that can travel across ocean basins. The M8.8 had a shallow focal depth of about 20 km. The reverse faulting mechanism aligns perfectly well with this focal depth, offering another parameter for study.

Yet another parameter generated by such events is the severity of felt-shaking, as recorded by the Modified Mercalli Intensity Scale of I to XII. This M8.8 caused an MMI of up to VIII in nearby coastal towns. The accompanying tsunami waves, which flooded Severo-Kurilsk – a study of the parameters so generated could also add to the much-awaited prediction science, which could save countless losses to human, animal and plant life and livelihoods.

This event is a stark reminder to the Indian Himalayan region as well. While not situated on the Pacific Rim, India’s tectonic setting of subducting under the Eurasian plate represents a continent-continent collision zone where compressional forces induce major thrust faulting and crustal deformation, making northern India, Nepal and adjoining areas highly susceptible to both shallow and deep earthquakes.

Another region of concern is the Andaman and Nicobar Islands, located along the seismically active boundary where the Indian plate subducts beneath the Burma microplate. This convergence zone is prone to frequent earthquakes and tsunami-generating events. 

India has experienced several great earthquakes in its history, which, although fewer in number than those in the Pacific region, have caused significant damage due to population density, poor construction practices and limited disaster preparedness. For India, this event underscores a parallel urgency to enhance earthquake preparedness in the geologically active Himalayan region and vulnerable coastal zones like the Andaman and Nicobar Islands. 

Ranu Chauhan is a senior consultant, Earthquake Risk Mitigation, NDMA.

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