Citizen seismology helps decipher the 2021 Haiti earthquake

5 pages, 4 figures, supplementary materials https://doi.org/10.1126/science.abn1045.-- Data and materials availability: All data and code used in this study are openly available. RADAR data can be obtained through ESA (Sentinel) or JAXA (Alos-2). Aftershock data can be obtained from https://ayiti.unice.fr/ayiti-seismes/ (7). The codes used to process or model the data are published and public (8). The catalog of high-precision earthquake relocated with the NLL-SSST-coherence procedure (SM4) is available as supplementary dataOn 14 August 2021, the moment magnitude (Mw) 7.2 Nippes earthquake in Haiti occurred within the same fault zone as its devastating 2010 Mw 7.0 predecessor, but struck the country when field access was limited by insecurity and conventional seismometers from the national network were inoperative. A network of citizen seismometers installed in 2019 provided near-field data critical to rapidly understand the mechanism of the mainshock and monitor its aftershock sequence. Their real-time data defined two aftershock clusters that coincide with two areas of coseismic slip derived from inversions of conventional seismological and geodetic data. Machine learning applied to data from the citizen seismometer closest to the mainshock allows us to forecast aftershocks as accurately as with the network-derived catalog. This shows the utility of citizen science contributing to our understanding of a major earthquakeThis work was supported by the Centre National de la Recherche Scientifique (CNRS) and the Institut de Recherche pour le Développement (IRD) through their “Natural Hazard” program (E.C., S.S., T.M., B.D., F.C., J.P.A., J.C., A.D., D.B., S.P.); the FEDER European Community program within the Interreg Caraïbes “PREST” project (E.C., S.S., D.B.); Institut Universitaire de France (E.C., R.J.); Université Côte d’Azur and the French Embassy in Haiti (S.P.); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 758210, Geo4D project to R.J. and grant no. 805256 to Z.D.); the French National Research Agency (project ANR-21-CE03-0010 “OSMOSE” to E.C. and ANR-15-IDEX-01 “UCAJEDI Investments in the Future” to Q.B.); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 949221 to Q.B.); and HPC resources of IDRIS (under allocations 2020-AD011012142, 2021-AP011012536, and 2021-A0101012314 to Q.B.With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe