Seismology of Mars 

A few years a go WEGA had a lecture from a Bristol University lecturer on this subject. He was somewhat limited as the only seismometer on Mars was ON a lander which had a very effective suspension. He thought that you would need an earthquake marsquake above 8 on the Richter scale to be recorded! So a lot of his talk was about the next seismometer on Mars. 

And that seismometer is the subject of THIS ARTICLE by two researchers at Bristol. 

The seismometer has detected hundreds of quakes and the conclusion is that Mars has a much larger core than previously thought. Because it is larger it must have a larger proportion of lighter elements than Earths core. And such a composition would not have an inner solid core - and hence no magnetic field.

The crust of Mars has been estimated from the quakes as 24 to 72km thick and the lithosphere 400 to 600km.

Shear waves travel from a marsquake and reflect off the iron-nickel core. Chris Bickel/Science