Professor Araya Akito visited College of Earth Sciences and gave a talk titled "Broadband geophysical observation using a laser interferometer" in 704 in teaching building on Mar. 1st, 2012.
A laser interferometer is widely used in physics, engineering, astronomy, metrology, and so on, for precise measurements. It is useful also in geophysics because it provides precise standard of length which can be used for measurements of crustal deformation. A couple of its geophysical application, a laser strainmeter and a compact absolute gravimeter, will be presented. The laser strainmeter is in operation at Kamioka mine located 1000-m underground, and measures long-term strain changes as well as seismic motion of the ground. We have observed several coseismic strain steps with the resolution of ~10^{-10} in strain, and they can be used for determining seismic moment geodetically even for deep or ocean earthquakes. An absolute gravimeter is used for determining gravity acceleration which gives information on ground density distribution and movement of underground mass. We have been developing a compact absolute gravimeter for the purpose of volcanic observation detecting motion of magma. Current performance of the instrument and its observation before and after the Tohoku earthquake are introduced.
