Terrestrial single-station analog for constraining the Martian core and deep interior: Implications for InSight

We used a terrestrial single-station seismometer to quantify the uncertainty of InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) data for determining Martian core size. To mimic Martian seismicity, we formed a catalog using 917 terrestrial earthquakes, from which we randomly selected events. We stacked ScS amplitudes on modeled arrival times and searched for where ScS produced coherent seismic amplitudes. A core detection was defined by a coherent peak with small offset between predicted and user-selected arrival times. Iterating the detection algorithm with varying signal-to-noise (SNR) ranges and quantity of events determined the selection frequency of each model and quantified core depth uncertainty. Increasing the quantity of events reduced core depth uncertainty while increasing the recovery rate, while increasing event SNR had little effect. Including ScS2 multiples increased the recovery rate and reduced core depth uncertainty when we used low quantities of events. The most-frequent core depths varied by back azimuth, suggesting our method is sensitive to the presence of mantle heterogeneities. When we added 1° in source distance errors, core depth uncertainty increased by up to 11 km and recovery rates decreased by <5%. Altering epicentral distances by 25% added ~35 km of uncertainty and reduced recovery rates to <50% in some cases. From these experiments, we estimate that if InSight can detect five events with high location precision (<10% epicentral distance errors), that there is at least an 88% chance of core depth recovery using ScS alone with uncertainty in core depth approaching 18 km and decreasing as more events are located. Plain language summary: We used a seismometer on Earth to study how well the NASA mission, InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) could detect the Martian core. We created a catalog of earthquakes from which we randomly selected events to mimic the seismic events (marsquakes) InSight is expected to detect. Several models of Earth's interior were tested to see which best predicted the arrival of seismic waves reflecting off the core. We found utilizing more events allowed us to determine the core size better than using a limited number of events. Using an additional seismic phase also helped us recover a more accurate core depth if there were not a lot of events. We were also able to find variations in the mantle by using events within certain location ranges. Since the InSight team may not be able to locate marsquakes as accurately as we locate earthquakes, we changed the location of the earthquakes. When changes in location were small, we were still able to determine the size of the core. Larger changes in location prevented us from finding an accurate core depth. If InSight detects at least five events with high location accuracy, we will be able to determine the Martian core size.