An Extremely Shallow Mw4.1 Thrust Earthquake in the Eastern Sichuan Basin (China) Likely Triggered by Unloading During Infrastructure Construction

Triggered or induced earthquakes have been widely reported as resulting from various human activities, yet seismicity triggered by small‐scale infrastructure construction is rare. Here, we report on an investigation of an extremely shallow M w 4.1 earthquake which occurred on 11 August 2016 in the Sichuan Basin (China), a region with historically low seismicity. Our seismic waveform analyses indicate an almost pure thrust focal mechanism at a centroid depth of ~1 km. Furthermore, 18 Sentinel‐1 synthetic aperture radar interferograms, stacked to obtain subcentimeter accuracy, reveal up to 3 cm line‐of‐sight deformation which overlaps with an automotive testing site constructed in 2014. Removal of 10 m of a surface rock layer during the construction may have produced an unloading effect and resulted in up to 0.11 MPa Coulomb stress changes on a blind fault, larger than the 0.01 MPa threshold typically invoked in studies of tectonic earthquakes. However, the delayed triggering still requires further investigation.