Seismograms from the Moon

50 years ago, first people stepped onto the lunar surface. During the first visit, they installed seismograph stations among other research equipment. A few months later professor Vesanen, head of the Institute of Seismology of the University of Helsinki, received mail from the USA. It appeared to be a copy of the first seismograms from the Moon.

World-Wide Network of Seismograph Stations (WWSSN) was built in the 1960s. It consisted of more than 100 seismic stations around the world and it provided an unprecentended collection of high quality seismic data. Finland hosted two WWSSN stations, one in Kevo and another in Nurmijärvi. Kevo station is even today part of the successor of WWSSN, GSN (Global Seismic Network).

WWSSN was built and funded by the U.S. Department of Defence. American engineer Howard April arrived to Finland to install the stations. He did not need to go home alone, but was accompanied by future Mrs April, Terttu Aurela, who had been working at the Institute of Seismology as a librarian.  Personal contact between the Finnish Institute of Seismology and American people responsible for their seismic stations stayed alive even after WWSSN was ready, and thus also copies of the first seismograms from the Moon arrived to Finland soon after they were published.

Seismographs installed by the Apollo 11 crew operated only three weeks, but provided interesting first views to the seismic events in the Moon. More seismic stations were installed during the following moonflights and lunar seismic data was received until September 1977.  This dataset has been analysed in numerous projects, always anew when new analysis methods have been developed enabling better use of the existing data.  During one recent project, 28 moonquakes were relocated and the results were used to analyze the cause of the moonquakes (Nature Geoscience: Shallow seismic activity and young thrust faults on the Moon).  It seems like the cause of the quakes is cooling of the interior of the Moon and its shrinking in the process (NASA: Shrinking Moon May Be Generating Moonquakes). 

A good overview to the seismology on the Moon can be found from here: