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Reading a Marsquake Seismogram: A Case Study of S1222a

Description: 

Detailed analysis and interpretation of seismic waveforms has yielded countless discoveries about earthquake source mechanisms and the Earth’s interior. Commonly, this seismogram “reading” is facilitated by comparisons with predictions from geologically-motivated proposed structures and by constraints on ray parameters provided by seismic arrays. Additionally, polarization attributes of individual seismic phases can also aid in seismogram interpretation. While the analysis of waveforms of impacts and marsquakes recorded by the InSight mission have yielded new insights into the internal structure and seismo-tectonic activity of the red planet, several factors have conspired to stymie detailed interpretation of the waveforms. First, the existence of only a single seismic station on Mars makes receiver array methods impossible. Second, prior geological constraints on subsurface layering are far weaker than on Earth. Third, strong scattering produces extended codas that are more challenging to interpret. Finally, contamination by wind noise and both sustained and transient signals presents pitfalls for seismogram analysis.

Here, we primarily focus on S1222a, the largest marsquake that occurred during the InSight mission, which was recorded with by far the highest signal-to-noise levels, mitigating the fourth challenge identified above. We first constrain the event’s source spectrum in order to estimate its stress drop and spectral fall-off. By leveraging frequency-dependent polarization analysis and synthetic waveforms computed for sub-surface structures constrained by prior converted wave and surface wave dispersion analyses, we then carry out detailed seismogram interpretation to associate individual arrivals with specific paths through the subsurface. We discuss the implications of these analyses for inferences of subsurface structure, for the source characteristics of S1222a, and place the event's source characteristics and aftershock productivity in the context of other marsquakes.

Session: Exploring Planetary Interiors and Seismology: Observations, Models, Experiments and Future Missions - I

Type: Oral

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Vedran

Student Presenter: No

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