Abstract
AbstractThe instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and three short‐period seismic sensors is installed on the surface on Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. One ubiquitous artifact in the raw data is an abundance of transient one‐sided pulses often accompanied by high‐frequency spikes. These pulses, which we term “glitches”, can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to SEIS‐internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of either the instrument or the ground. In this study, we focus on the analysis of the glitch+spike phenomenon and present how these signals can be automatically detected and removed from SEIS's raw data. As glitches affect many standard seismological analysis methods such as receiver functions, spectral decomposition and source inversions, we anticipate that studies of the Martian seismicity as well as studies of Mars' internal structure should benefit from deglitched seismic data.
Highlights
InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) landed successfully on Mars on 26 November 2018 (Sol 0, a sol is a Martian day with around 24 hr 40 min)
We have developed a physical model for the generation of glitches and their associated high‐frequency spikes that occur simultaneously with the glitch onsets
We used this model to develop different algorithms for the glitch detection that are all able to identify most of the high amplitude glitches for both the very broadband (VBB) and SP seismometers
Summary
InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) landed successfully on Mars on 26 November 2018 (Sol 0, a sol is a Martian day with around 24 hr 40 min). It is this frequency dependence of the seismometers' self‐noise that determines their names as established for the InSight project (Lognonné et al, 2019), even though the naming convention does not follow terrestrial standards (e.g., Ahern et al, 2012) Due to their different noise floors, the VBB is the main instrument to detect distant marsquakes, while the SP is used to cover the frequency range of ∼5–50 Hz for more detailed analysis of regional events and lander‐induced signals. On Earth, data influenced by such disturbances are often discarded especially when coinciding with earthquake phase arrivals (e.g., Zahradnik & Plesinger, 2005) This obviously represents no valid option for the seismic data returned from Mars, the correct treatment of the glitches is of upmost importance for the scientific analyses. It extends Supplement V of Lognonné et al (2020)
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