Earthquake Monitoring with Gravity Meters: Case studies from the November 2006 and January 2007 Kuril Islands Earthquakes

Relative gravity meters are sensitive instruments capable of detecting small changes of the earth’s gravity field with a precision of a few parts per billion (10) over time scales of one second. They are often used to characterize earth-tides that vary with diurnal and semidiurnal periods. Recently, a superconducting gravity meter was successfully used to record low frequency gravest seismic modes ( 9) Sumatra-Andaman earthquake (Rosat et al., 2005; Ferreira et al., 2006). High frequency and high amplitude signals such as the S and P body waves and the Rayleigh and Love surface waves associated with earthquakes have traditionally been the purvey of seismometers. Seismometers are usually optimized to record seismic frequencies (0.1-10Hz) and are designed not to saturate during large amplitude signals. Gravity meters, on the other hand, are usually optimized to filter out seismic noise and often are too sensitive to faithfully record the high amplitude waves associated with the first arrival of an earthquake. Recently, these difficulties have been overcome with the introduction of a new type of gravity meter (gPhone) with both large dynamic range and high sensitivity.