https://www.scinexx.de/news/kosmos/hat-der-mars-doch-einen-festen-kern/
When the seismic waves from tremors pass through different materials, like surrounding rocks or water, they create subtle electromagnetic fields. Some scientists believe they may be able to find buried liquid water by studying seismic and magnetic readings to reconstruct the aftermath of Mars temblors. https://www.space.com/marsquakes-liquid-water-mars-insight-lander