Navigation satellites capture far-reaching effects of two powerful earthquakes

Two earthquakes with magnitudes of 7.8 and 7.5 hit southeastern Turkey on a single day in February 2023. Nearly 60 000 people died, and millions were affected by the damage to homes and other buildings. Such large earthquakes are unusual for the region. Even though eastern and south-central Turkey lie at the boundary between the Anatolian and Arabian tectonic plates, just a few large earthquakes have occurred there over the past century.

After analyzing the 2023 sequence of earthquakes, Semih Ergintav, of Boğaziçi University in Istanbul, and colleagues learned that it caused more far-reaching effects than previously thought. The researchers used Turkey’s global navigation satellite system (GNSS) to collect continuous ground-motion data across a large area. They found that contrary to existing crust-deformation models, the earthquakes in Turkey deformed the crust not only within the immediate vicinity of their origin but also much farther away.

The seismic activity and dynamics of the 2023 earthquakes have already been studied in detail by researchers using geodetic and seismic data collected at the fault zones. Those data, however, cannot capture whether the earthquakes generated far-field displacements, which is what Ergintav and colleagues were interested in. Turkey’s GNSS network is well suited for the task because it monitors ground motion continuously, and it is dense enough to measure differences between far-field and near-field displacements.

For the magnitude 7.8 earthquake, surface displacements of 8–10 mm were observed as far as 700 km from the fault zone. For that size earthquake and geological setting, models that simulate dislocation of Earth’s crust had predicted that the surface could be displaced by as much as 6–7 mm within about 400 km of the fault zone. The observations show that the 2023 earthquakes displaced the Anatolian plate by 10 mm relative to the neighboring Eurasian plate, which is about half the total offset that has been observed annually. The unexpectedly large, far-reaching displacements of the earthquakes suggest that hazard assessors may need to monitor for seismic activity farther from earthquake sources than models have predicted.

Ergintav and colleagues have yet to settle on what may have triggered the tectonic plates to move that much. The motion could be caused by long-term stresses from the nearby Hellenic arc subduction zone, which is pulling the Anatolian plate into the mantle. Because the lithospheric crust under the plate is relatively thin compared with crust in other locations, it is more extensionally strained and susceptible to far-field deformation. Says coauthor Özgün Konca, “We strongly believe that this phenomenon will be visible in other earthquakes in similar tectonic settings.” (S. Ergintav et al., Science 386, 328, 2024 .)