Comodulation Analysis of Atmospheric Energy Injection into the Ground Motion at InSight Part 2: Environmental Sensitivity of SEIS and Quake Detection

NASA's InSight mission on Mars has deployed its Seismic Experiment for Interior Structure (SEIS) instrument, composed of the very broad band (VBB) and short period (SP) seismometers. SEIS is complemented by the Auxiliary Payload Sensor Suite (APSS) which records atmospheric variables, such as wind speed, wind direction, and pressure [1].

SEIS interacts with the Martian environment via complex, overlapping atmospheric effects which couple into the seismic signal. Detection and analysis of the seismic component requires separation from such aseismic signal sources. These nonlinear coupling dynamics are investigated using comodulation, a mechanism which quantifies the signal synchrony between seismic, wind and pressure energies (see Part 1, [2]). The atmospheric pressure and wind fluctuations are here shown to exhibit cross-frequency coupling across multiple bands sensed by SEIS. By working in the energy domain, we identify the origins of underlying processes in the seismic observations and provide an overall site sensitivity to environmental variables and their relationships.

We first quantify the environmental injections into potential seismic events via our comodulation approach, providing a degree of confidence in the seismic origin and independence from atmospheric coupling. Examination of this metric across all events determines the seismic event detectability threshold for the InSight landing site, with important implications for future missions. Second, we use our approach to retrieve the wind speed, direction, and pressure solely from the ground acceleration recorded by SEIS, and the wind speed from the pressure signal alone. Such a redundancy may preserve mission science return for different scenarios. Finally, we apply this method over different frequency bands to decouple and enhance the seismic signal enabling a search for previously undetected seismic events.

References:

[1] Lognonné, et al. SSR (2019).

[2] Stott, et al. this issue