Magnitude estimation of Paleo-moonquakes from boulder tracks in Finsen crater

Abstract

High-resolution images taken by the Lunar Reconnaissance Orbiter show the existence of many boulder tracks within the Finsen crater. Current research suggests that shallow moonquakes and meteorite impacts are likely to be the cause of boulder falls. Based on a simplified model, we simulate the rolling process of the boulder along the slope when the lunar surface shakes and provide the critical PGA (peak ground acceleration) required for the boulder to start rolling under different conditions. The results show that boulders may roll down slopes within one or more cycles under strong ground shaking. The critical PGA of seismic waves required for a boulder to conduct slope rolling is related to the size of the boulder, the slope at the initial location, the dominant period of the seismic wave, and the ratio of horizontal and vertical peak ground accelerations. Except for rolling against the slope, in some cases, boulders may jump and roll downhill. Using the high-resolution images taken by the LRO to determine how the boulders rolled downhill, we can then estimate the lower limit of the magnitude of moonquakes in the region under different conditions. Finally, we provide a preliminary estimation of the lower limit of the paleo-moonquakes magnitude in the Finsen Crater.