Annual reports detailing observatory activities have been prepared up till 1990. This report covers activity for the year 1991. Basic program in geomagnetism, ionospherics and seismology continued at the Mundaring Geophysical Observatory during the period. The main instruments were an Eschenhagen normal-run magnetograph, an IPS type 4B ionosonde, a Worldwide Standard Seismograph, and a Seismic Research Observatory.
Seismographs were operated at Ballidu, Coolgardie, Forrest, Kellerberrin, Kununurra, Marble Bar,Manton Dam (NT), Meekatharra, Morawa, Mundaring, Rocky Gully, Narrogin and Warburton.
The observatory operated nine accelerographs in the South-west seismic zone. Another 13 accelerographs in WA are operated by the Water Authority and Telecom. The earthquake list (ML>2) shows details of 217 Western Australian earthquakes during the year. Isoseismal maps were prepared for earthquakes that occurred near Kalgoorlie, Karratha, Albany,Shay Gap and Cranbrook.
A major project to determine varying responses of different sub-soil conditions to earthquake vibrations concluded in June.