The brown data points and curve show the observed number of marsquakes as a function of magnitude from Giardini et al.2. The orange envelope represents these data extrapolated to the entire planet, with the vertical spread of values representing the uncertainty in the completeness of observations for smaller, distant events. The pre-InSight estimate of Mars seismic activity (red) is from Golombek et al.32. Lunar seismicity (grey data points) is based on the analysis of shallow moonquake activity by Oberst39, with the grey envelope representing the unknown completeness. The global seismicity of the Earth (blue) is from the GlobalCMT catalogue47, and is dominated by plate boundaries. The terrestrial intraplate seismicity estimates separate tectonically deformed regions away from plate boundaries (turquoise) and stable continental interiors (green) (data from ref. 40). Terrestrial curves and the upper part of the lunar bar are scaled to the surface area of Mars. The diffuse red area in the upper left denotes numerous small, high-frequency (HF) events for which the exact distance, and therefore magnitude, is not yet understood2.