Unusually high stress drops associated with shallow moonquakes

Abstract

New estimates of stress drops and energy release associated with shallow moonquakes, believed to represent the only lunar seismic events of tectonic origin, have been made, taking into account (1) properties of source spectra, (2) radiation pattern of foci, (3) anelastic attenuation of seismic waves, (4) response of the seismometer, and (5) intense scattering of seismic signals. The results indicate that the three largest events show body wave magnitudes of mB > 5.5 and stress drops of Δσ > 100 MPa. The values for stress drops are high compared with those generally associated with most terrestrial events, but they are compatible with results predicted from thermoelastic models of the moon. Presence of high stresses in the lunar crust may indicate that at the beginning of its history the moon was originally molten not only in the outer surface region, but throughout its whole volume.