RECENT METEOROID IMPACTS ON MARS: SEISMIC SIGNAL PREDICTIONS

The detailed structure of the planetary interior places essential constraints on the formation, evolution, and dynamics of Mars. Impact events are a key source of seismic waves for interrogating internal structure; the future NASA Discovery Program lander InSight will be capable of detecting these events. InSight is instrumented to monitor thermal, seismic, and other geophysical parameters of Mars. Recent, fresh craters formed by ongoing impacts in dusty areas are detectable in high-resolution orbital images of the Martian surface. Seismically detecting and subsequently imaging impacts will provide an extremely accurate epicenter, and enable calibration of Martian seismic velocities and retrieval of internal structure.

We use detailed characterizations of new, dated impacts, including measurements of crater diameter, morphometry, and geospatial information for individual craters in impacts occurring as clusters, to investigate recent impact-produced seismic activity on Mars. Measured parameters are converted to seismic predictions for the impact source using a scaling law that relates crater diameter to the released seismic moment. This scaling law is dependent upon the target properties and the efficiency of conversion of impact to seismic energy. Therefore we use a range of target properties (bedrock vs. regolith), to bound the seismic moment for the observed crater distribution.

We model the expected seismic source(s) using a 3-D wave propagation code that predicts the ground motion due to the impact. For some discrete impact events, the bolide disintegrates, forming multiple craters of varying size; our code captures these more complex effects. The result is a seismic source function that can be used to evaluate the detectability of different types of impact events at various distances. Additionally, the resulting seismic amplitudes allow us to quantify the detectable distances for body and surface wave phases and also to implement techniques to recover Martian internal structure from a single 3-component seismometer.