How Large Are Marsquakes? Revisiting Magnitude Scaling and Implications for Marsquakes and Meteoroid Impacts

Abstract

Reliable estimates of seismic source size on Mars are critical for interpreting tectonic activity and impact processes, constraining the planet's interior evolution, and informing the design of future Martian seismic experiments. However, because InSight observations are limited to a single station, magnitude estimates cannot rely on empirical averaging of site and path effects as on Earth, and instead depend on comparisons between observed and modeled waveform amplitudes. Consequently, inferred magnitudes are sensitive to assumptions about interior structure, attenuation, and source parametrization. Existing Marsquake Service (MQS) magnitude-scaling relations were calibrated using pre-InSight interior models and tectonic source assumptions, potentially biasing magnitude estimates. Here, we reanalyze spectral amplitudes using InSight seismic data and investigate how post-InSight interior models and source-dependent parametrization influence inferred moment magnitudes. Using waveform simulations for a suite of 1-D interior models, we quantify the effects of velocity structure, attenuation, three-dimensional heterogeneity, and source physics on long-period magnitude scaling. We introduce separate source representations and scaling relations for marsquakes and impacts. Across the tested post-InSight models, the shallow crustal structure beneath InSight primarily controls scaling. Recalibrated marsquake magnitudes are lower by approximately 0.5 $M_w$ on average relative to MQS magnitudes, with the reduction varying across plausible shallow structures. Applying impact-specific scaling brings seismic and crater-derived estimates into closer agreement, although differences remain for large distant impacts, and the recalibrated magnitudes enable tentative matching of seismic detections to cataloged Martian impact craters. These relations provide site-specific calibration for InSight observations and tighter constraints on Martian seismicity and impact processes.