QUESTION:
Are there, or have there ever been Marsquakes?

ANSWER from Mary Urquhart on November 7, 1997:
A very good question! Yes, there almost certainly have been Martian
earthquakes or as some would say "marsquakes".  All of the evidence is
indirect, but strong.  Many features on Mars are of tectonic orgin.  A
tectonic origin simply means movement of the crust (surface layer) of Mars
has occured.  That movement would have produced an earthquake or earthquakes
just like people in California feel when there is movement in the Earth's
crust due pressure along the San Andreas fault.

Are there "marsquakes" today?  We don't know.  We don't have any of the
special instruments (called seismometers) used to study movement in the
crust of the Earth (or another planetary object) on Mars.  We know the Moon
has tiny "moonquakes" because the spacecraft we sent there had seismometers. 
Movements in the crust of a planet (even the Earth) usually are hard to
detect unless there is an instrument that can sense the movement. 
Earthquakes happen everyday in many places all over the Earth, but are too
small to even feel.  Even the major Earthquakes on the Earth cause so little
movement of the Earth's crust that we usually wouldn't see any changes with
an orbiting camera.  These tiny changes build up over a long period of time
to make big changes that can shape the face of a planet.

Many scientists (including me) would like to have seismometers on Mars. 
Maybe someday we will.

Mary