The thermal response of the martian subsurface due to solar forcing
lacks direct measurements. The InSight mission provides the best
opportunity to detect the thermal behavior of the subsurface since it
was equipped with both air temperature sensors and a subsurface heat
flow probe. Here, we model heat conduction under the InSight landing
site based on the measured subsurface thermal parameters and air
temperature records, which provide insights into heat flow in the
martian subsurface. Daily temperature variation over 1 K occurs only
within 25 cm under the ground surface. The highest absolute rate of
temperature change appears around sol 440, which coincides closely with
the season of the dominant number of marsquakes observed around sunset.
Thermal-mechanical finite-element method simulations indicate that more
potential afternoon marsquakes might exist but be covered by the wind
noise. Our results indicate that most high-frequency and low-magnitude
marsquakes are likely thermal in origin.