Which Apollo 11 surface instrument was used to measure moonquakes?

The Apollo 11 surface instrument used to measure moonquakes was the Passive Seismic Experiment Package.

The PSEP was part of Apollo 11’s Early Apollo Surface Experiments Package, or EASEP. Astronaut Buzz Aldrin deployed it near the lunar module Eagle at Tranquility Base on July 21, 1969. It was the first seismometer placed on another planetary body.

The package used several seismometers to detect ground motion, including horizontal and vertical movement. Its observations helped scientists distinguish natural lunar seismic events from vibrations caused by astronaut activity, equipment, thermal changes, and impacts.

A common mix-up is Apollo 11’s PSEP versus the Passive Seismic Experiments carried on later missions. Apollo 11’s unit was self-powered by solar cells and operated for about three weeks, while later seismic packages were part of larger ALSEP stations powered by radioisotope generators. The experiment detected signals consistent with shallow moonquakes, meteoroid impacts, and other lunar disturbances.