The study finds that weaknesses in the Earth's ancient crust contribute to modern earthquakes in West Africa

New research delves into the mechanisms behind earthquakes in the interior and coast of West Africa. Credit: NASA Landsat 7, public domain

Although it was the site of active tectonics 140 million years ago, the West African coast today represents a passive margin, far from active tectonic plate boundaries and thought to be seismically quiet. So scientists don't fully understand why the region is experiencing an increasing number of earthquakes between magnitude 2 and 5. The lack of large-scale seismic stations throughout the region represents a major challenge.

In a study published in Geophysical Research Letters, Legree and his colleagues wanted to determine the type of slip (strike-slip, normal-slip, thrust-slip, or a combination) behind West African earthquakes, as well as the direction of stresses along the passive margin and inland. interior of the continent.

They examined records from 62 seismic stations between 1991 and 2021, and focused on 14 intraplate earthquakes that had high- to moderate-quality wave data.

Two of these earthquakes had sufficient waveforms that scientists were able to identify their focal mechanisms from seismograms. For the other 12, they used multi-mode body wave inversion, a technique well suited to sparse data sets that involve fitting recorded ground vibrations to the model.

They found that the continental margin undergoes a combination of thrust and slip deformation. The region may also be more affected by stresses transferred from oceanic crust to the passive margin and from tectonically active North Africa to the continental interior.

The researchers concluded that the changing stress patterns and slip motion occurring in West Africa result from a combination of tectonic stress transfers and local stress perturbations that cause reactivation of crustal weaknesses from ancient shear zones and failed fractures. They also point out that while anthropogenic disturbances may reactivate ancient structures, a cluster of earthquakes in Mauritania's mining region was likely caused by activity in iron ore mines.

The authors point out that their work provides the best available collection of average seismic data, but they hope that improved instrumentation and monitoring around earthquake clusters will expand the available data set.

More information: Jean-Joel Legree et al., Intra-plate stress field in West Africa, Geophysical Research Letters (2024). doi: 10.1029/2023GL107614

This story is republished with permission from Eos, hosted by the American Geophysical Union. Read the original story here.

Citation: Ancient Crustal Weaknesses Contribute to Modern Earthquakes in West Africa, Study Finds (2024, June 7) Retrieved June 8, 2024 from https://phys.org/news/2024-06-ancient-crustal-weaknesses-contribute -modern. programming language

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