Superconducting Gravimeters Detect Gravity Fluctuations Induced by Mw 5.7 Earthquake Along South Pacific Rise Few Hours Before the 2011 Mw 9.0 Tohoku-Oki Earthquake

Abstract

Gravity changes sometimes appear before a big earthquake. To determine the possible sources is important for recognizing the mechanism and further geodynamic studies. During the first two hours on March 11 before the M w 9.0 Tohoku-Oki earthquake, the non-tidal gravity time series of superconducting gravimeters worldwide showed low-frequency (< 0.10 Hz) fluctuations with amplitude of ~1 to 4 × 10 -8 ms -2 lasting ~10 -20 minutes. Through comparing global seismicity with the arrival times of seismic waves, we find that the fluctuations were induced by the M w 5.7 earthquake that occurred at 0:14:54.68 at (53.27°S, 118.18°W) along the eastern South Pacific Rise. Several body waves such as P, S are clearly recorded in the station with ~400 km distance to the hypocenter. The fluctuations are in response to the waves that propagate with a velocity of about 4 km s -1 . Their amplitudes are proportional to the inverse of the epicentral distances even though the fluctuations of European sites were overlapped with waves associated with a smaller, i.e., M w 2.6, event in Europe during this period. That is, the M w 5.7 earthquake induced remarkable gravity fluctuations over long distances at stations all over the world. As such, the foreshocks with larger magnitudes occurred before the M w 9.0 earthquake would have more significant influence on the gravity recordings and the seismic-wave induced component should be removed during the analysis of anomalies prior to a great earthquake in future studies.

Comparison of Rayleigh Wave Characteristics on Superconducting Gravimeter and Sesimometer LHZ Recordings

“…SG mampu merekam aktivitas kebumian lainnya, hingga kejadian seismik, baik yang mikroseismik maupun yang makroseismik (Lan et al 2011), (Shen at al. 2011), (Zhang, K and Ma 2014) dan respons yang diberikan alat gravimeter berkorelasi dengan hasil pencatatan saat terjadi gempa bumi (Niebauer et al 2011 (Baldi et al 1995), dinamika resonansi mantel bumi (Omerbashich 2007) efek hidrologi (Virtanen 2006) dan beberapa indikasi perubahan alam lainnya. Akan tetapi, untuk mendapatkan nilai gaya berat yang dipengaruhi oleh gempa bumi, hanya dilakukan koreksi pasang surutnya saja.…”