Applications of Time‐Frequency Domain Polarization Filtering to InSight Seismic Data

Abstract The seismometer Seismic Experiment for Interior Structure (SEIS) onboard the InSight lander was used to continuously record the seismicity on Mars from February 2019 to December 2022. To maximize the information that can be extracted from the seismic data, it is critical to identify and to suppress undesired features (e.g., environmental noise, scattered waves, seismic imprint of lander vibrations) and non‐seismic noise (e.g., instrument related artifacts). We present an advanced polarization filtering workflow in the time‐frequency domain to suppress undesired features and to enhance the signal‐to‐noise ratio of the SEIS recordings. We estimate time‐frequency‐dependent polarization attributes such as the ellipticity, directionality of the particle motion, and the degree of polarization to identify and filter out undesired data parts. After filtering in the time‐frequency domain, the seismic data are transformed back to the time domain, yielding broadband waveform data that can be used for further seismological analysis. We illustrate the benefits of our filtering approach with three use cases. Firstly, we show how polarization filtered data can help to constrain the source mechanism of the sol 1,222 event, the largest marsquake detected so far. Using the proposed polarization filtering techniques, we are able to enhance the S‐wave arrival by suppressing interfering randomly polarized scattered waves to successfully infer on the moment tensor of this event. Secondly, we show that polarization filters can be used to suppress instrument‐related glitches and, thirdly, to remove the seismic imprint left by the vibrating lander (mechanical resonances of the lander).