Morocco earthquake source deeper than common for that region, did not break surface: Study

New Delhi: A study of the 2023 Morocco earthquake suggests that the shocks ruptured roughly 25 kilometers beneath the surface, deeper than what might be commonly expected in the region.

Researchers at the US Geological Survey (USGS) said that the seismic waves from this point did not reach the surface.

The source modelling showed a compact source for the earthquake with slip occurring between 15 and 35 kilometers deep, they said. Their rapid characterisation study is published in the journal The Seismic Record.

However, given that the earthquake occurred in a region with a thin history of recorded seismic activity, the team did not have a "great idea" of what was "common" of large earthquakes in the Atlas Mountains, according to USGS seismologist William Yeck and the study's corresponding author. The Atlas Mountains in northern Africa extend from southwestern Morocco to northern Tunisia.

The Al Haouz earthquake, named after the Moroccan province most impacted by the shaking, occurred on September 8 with violent tremors near its epicentre and very strong ones in the city of Marrakesh. Nearly 3,000 people were killed and over 5,500 reportedly injured, and there was widespread damage to structures, according to the researchers.

The team said their modelling showed that the earthquake at about 25 kilometers beneath the western Moroccan High Atlas Mountains was a "blind rupture", meaning it did not reach the surface. Depth of earthquake slip helps seismologists understand the seismic hazard in a particular region.

The deep rupture of the Al Haouz earthquake did not break the surface and few aftershocks (only five) were recorded, together making it difficult to confirm which faults were involved in the earthquake, according to Yeck.

"We have some sense of the (area's) large surface faults and some sense of how they dip and how they extend at depth, but their shape can change at depth, which makes it difficult to pin this to a fault on the surface," said Yeck.

Yeck further explained that a good picture of the aftershocks helps understand the faulting in the region and that in its absence, there can be some ambiguity about where the slip occurred.

For their analysis, the researchers relied on teleseismic data, or seismic wave data collected from stations globally. They combined it with InSAR satellite data, which captures changes in ground deformation, to create several models of the earthquake source.

The study illustrated the benefits of regional and national networks following international data exchange standards to share real-time data with the global seismic monitoring community, the researchers said.

This is helpful especially for earthquakes in remote regions with sparse seismic coverage, they said.