Turning smartphones into earthquake sensors

The impact of an earthquake on people and property depends not only on the earthquake's characteristics like magnitude and depth, but also on local soil conditions, which contribute to the so-called “site effect”. Mapping the site effect at a high spatial resolution in an urban context is crucial for understanding which areas and buildings are at higher risk or under greater stress during subsequent seismic events.

A study published in Nature Communications by Prof. Dr Francesco Finazzi (University of Bergamo, Italy), Prof. Dr Fabrice Cotton (GFZ Helmholtz Centre for Geosciences, Germany) and Dr Rémy Bossu (European-Mediterranean Seismological Centre, France) reveals a breakthrough: citizens' smartphones can be used to create highly detailed site amplification maps. Thanks to their built-in accelerometers — the same sensors that enable interactive gaming — smartphones can detect earthquake vibrations. By combining thousands of these measurements from the Italian Campi Flegrei region with statistical modelling, the researchers show that it is possible to map how local geology amplifies shaking, achieving a level of detail far beyond what seismic stations alone can provide. This information provides critical input for seismic hazard assessment and supports earthquake emergency response.

New approach based on the Earthquake Network (EQN), a citizen science initiative

The novel approach builds on the Earthquake Network (EQN), a citizen science initiative launched in 2013 by Francesco Finazzi. EQN, which has involved so far more than 20 million citizens, is part of an ongoing global effort to use smartphones for real-time seismic monitoring and early warning. When an earthquake occurs, participating phones detect the shaking and send signals to a central server. Within seconds, alerts can be issued to users in surrounding areas, giving them precious time—sometimes more than half a minute—to seek safety before strong shaking arrives.

Although smartphones have been proven useful for seismic monitoring, the question of whether they could be used to map ground shaking remained pending. Smartphone accelerometers, in fact, measure motion differently from seismic instruments – as readings are influenced by building characteristics, device location, and placement. To exploit the correlation structure between smartphone and station records, the authors applied a spatial statistical model. The method averages out device- and building-specific effects, allowing the underlying amplification pattern to emerge. While individual smartphone records are noisy, the aggregation of thousands of measurements and their fusion with classical seismological data yields reliable high-resolution amplification maps.

First high-resolution amplification map of the test region Campi Flegrei, Italy

The Campi Flegrei region near Naples, Italy—home to about 500,000 people in a high-risk volcanic and seismic zone—provided the perfect testbed for the new approach. Between April and June 2024, the region experienced a period of increased seismic activity that put citizens and local administrators under pressure. 7,000–9,000 residents in the 130 km2 “red zone” actively contributed data through EQN, compared with just 29 traditional seismic stations in the same area (see Figure 1). Analysis of this data enabled the researchers to produce the first high-resolution amplification map of the “red zone” (Figure 2).

“The EQN smartphone network is of high density and covers areas of the red zone where no stations are installed. This allows the variability of the ground shaking to be captured at a higher spatial resolution over the entire red zone,” explains Francesco Finazzi, first author of the study.

The obtained amplification map shows that wave amplification due to the superficial layers varies from a factor between 0.25 and 0.5 in the eastern part of the zone—which is effectively equivalent to damping—to a factor between 2 and 3 in the south-west—which is effectively equivalent to amplification—, over a distance of only 10 km.

Crucial for emergency response teams

In the case of a new earthquake, the amplification maps, which are based on past smartphone data, and new event-specific smartphone acceleration measurements can be used to generate so called high-resolution “ShakeMaps” of this event—that are maps showing the intensity of shaking in different areas. These Shake Maps have become an essential tool for assessing the impact of a recent earthquake or for scenario studies of future events, and they are crucial for guiding rescue teams, estimating damage and organising emergency responses.

“With urban populations growing worldwide and the urgent need for high-resolution ShakeMaps, this study shows that combining citizens’ smartphone accelerometer data with seismic network observations enables the generation of site-specific, high-resolution ShakeMaps in densely populated urban areas. This improves the characterisation of ground motion in the built environment, where seismic risk is concentrated”, summarises co-author Prof. Dr Fabrice Cotton, Head of GFZ-Section 2.6 “Seismic Hazard and Risk Dynamics”.

Original publication:

Finazzi, F., Cotton, F. & Bossu, R. Citizens’ smartphones unravel earthquake shaking in urban areas. Nat Commun 16, 9527 (2025). https://doi.org/10.1038/s41467-025-64543-3