The Wikipedia subsection Moonquake says:
Information about moonquakes comes from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15 and 16 functioned perfectly until they were switched off in 1977.
According to NASA, there are at least four different kinds of moonquakes:
- Deep moonquakes (~700 km below the surface, probably tidal in origin)
- Meteorite impact vibrations
- Thermal moonquakes (the frigid lunar crust expands when sunlight returns after the two-week lunar night)
- Shallow moonquakes (20 or 30 kilometers below the surface) The first three kinds of moonquakes mentioned above tend to be mild; however, shallow moonquakes can register up to 5.5 on the Richter scale. Between 1972 and 1977, 28 shallow moonquakes were observed. On Earth, quakes of magnitude 4.5 and above can cause damage to buildings and other rigid structures.
Question: Why were the "perfectly functioning" seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977?
See the question Any potential downside to throwing personal life support out the door on the Moon? for more about the Apollo lunar seismometers.
below: images from ALSEP, Apollo Lunar Surface Experiments Package, 20 November 1969 – 30 September 1977, by Hamish Lindsay, Click for full size.