Seismicity and stresses in the eastern part of the Amazon craton: implications for the intraplate stress field in South America

SUMMARY Despite generally low seismicity typical of intraplate regions, magnitudes larger than 6 have occurred in the Amazon craton. The installation of permanent stations of the Brazilian Seismic Network in the Amazon around 2014, the Vale 5-station network in the Carajás mineral province in 2019 and a 30-station temporary deployment (October 2021–March 2024) significantly improved earthquake detectability in the eastern part of the Amazon craton. A review of the seismotectonic characteristics of the oldest, Eastern part of the Amazon craton is presented here. Seismicity is not uniform, and areas of higher seismicity are identified, such as in the northern part of the Tapajós-Parima province and along the eastern border of the craton. No clear correlation with the main trends of faults was observed. Contrary to Central and Eastern Brazil, seismicity is not directly correlated with lithospheric thin spots in the Amazon craton but tends to occur in the flanks of thick keels (‘craton edge’ effect). A possible influence of free-air gravity anomalies was noted suggesting that flexural stresses contribute to control seismicity. Five new focal mechanisms are presented for the eastern edge of the Amazon craton, indicating a stress field with NW-SE compression and NE-SW extension. An updated map of the stress field for mid-plate South America shows that the maximum horizontal stresses vary from E-W in SE Brazil, NW-SE in central Brazil and SW-NE in the north. This pattern can potentially be explained by upper mantle flow, provided more detailed convection models are used.