InSight is planned to deploy a seismometer to listen for seismic activity on Mars. Seismometers were deployed on the Moon by the Apollo astronauts. Several spent/discarded stages/modules (ascent modules, S-IVB stages) were used as impactors (deliberately crashed on the Moon) to study its internal structure by analyzing the resulting seismometer signals. Is there any plan to do likewise on Mars, or will InSight's seismic study be purely passive, listening only for natural events?
According to NASA's webpage on the SEIS instrument aboard InSight,
The seismometer waits patiently to sense the pulse, or seismic waves, from marsquakes, and thumps of meteorite impacts. A suite of wind, pressure, temperature, and magnetic field sensors help fine-tune the seismometer's measurements. This helps it sense surface vibrations generated by weather systems such as dust storms, or by turbulence in the atmosphere due to phenomena such as dust devils, which can also generate seismic waves.
Using the seismometer, scientists expect to detect 5 to 10 meteor impacts over the course of InSight’s mission.
A number of physical phenomena can create seismic waves, including marsquakes, meteorites striking the surface, landslides, or even the pressure of the wind on the surface. Weather phenomena, such as dust devils, can also generate seismic waves.
Notably, it does not mention crashing any spacecraft into the surface. Thus, it appears the plan is to examine natural phenomena, including the 5-10 meteor impacts expected (i.e. no "active pinging").
It wasn't part of the original mission plan, but hammering by the HP3 drill is being recorded by the seismometer to try to figure out the local soil substructure. Specifically, they're trying to figure out if the drill is running into a buried rock, a gravel layer, or is just wedged in its housing.
Nothing as dramatic as crashing a Saturn V upper stage, or even launching high-explosive charges from a mortar, though.