An Analysis of Mechanical Constraints when Using Superconducting Gravimeters for Far-Field Pre-Seismic Anomaly Detection

Abstract

Pre-seismic gravity anomalies from records obtained at a 1 Hz sampling rate from superconducting gravimeters (SG) around East Asia are analyzed. A comparison of gravity anomalies to the source parameters of associated earthquakes shows that the detection of pre-seismic gravity anomalies is constrained by several mechanical conditions of the seismic fault plane. The constraints of the far-field pre-seismic gravity amplitude perturbation were examined and the critical spatial relationship between the SG station and the epicenter precursory signal for detection was determined. The results show that: (1) the preseismic amplitude perturbation of gravity is inversely proportional to distance; (2) the transfer path from the epicenter to the SG station that crosses a tectonic boundary has a relatively low pre-seismic gravity anomaly amplitude; (3) the pre-seismic gravity perturbation amplitude is also affected by the attitude between the location of an SG station and the strike of the ruptured fault plane. The removal of typhoon effects and the selection of SG stations within a certain intersection angle to the strike of the fault plane are essential for obtaining reliable pre-seismic gravity anomaly results.

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

“…9f). Since only 17 sites are used in this study and these stations are not evenly distributed in space, it is hard to find a dominant direction that might have significant influence on the amplitude as suggested by Lan et al (2011). Nevertheless, the amplitude dependence on the epicentral distance is much more valid and not vulnerable to be affected by either a smaller local earthquake or complex of large scale tectonic loading Kennett et al 2011;Tajima et al 2013).…”

“…During the perturbation the amplitude of the gravity time series increases prior to the earthquake and gradually decreases after the earthquake (Lan et al 2011;Shen et al 2011). Such phenomena have been detected with SG data during several large earthquakes such as the 2004 M w 9.3 Sumatra earthquake (Wang et al 2007), the 2008 M w 7.9 Wenchuan earthquake ) and some smaller ones (Lan et al 2011). Before the M w 9.0 Tohoku-oki earthquake, similar anomalies appeared in 5-day (March 6 -11, 2011) recordings in SGs (Zhang et al 2013) and gPhone gravimeters (Wei et al 2011).…”

“…Thus, the gravity fluctuation due to longdistance earthquakes with magnitudes larger than 6 would be more carefully focused when the pre-seismic perturbation signals are extracted as many researchers have realized (Lan et al 2011;Shen et al 2011;Zhang et al 2013). …”

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

“…Ketika sebuah batuan mengalami stress maupun strain terjadi peningkatan nilai anomali gaya berat dan mencapai amplitudo maksimum ketika gempa bumi terjadi. Anomali gaya berat terjadi penurunan setelah terjadinya gempa bumi hingga kembali ke posisi stabilnya (Lan et al 2011).…”

ANOMALI SINYAL SEBELUM GEMPABUMI YANG TERDETEKSI OLEH REKAMAN SUPERCONDUCTING GRAVIMETER DAN SEISMOMETER (LHZ) (STUDI KASUS: GEMPABUMI DI INDONESIA MW > 6)

“…Berdasarkan penelitian sebelumnya Superconducting Gravimeter (SG) mampu merekam kejadian gempabumi lebih dulu dibanding seismometer, dikarenakan SG merupakan alat yang mengukur perubahan nilai gayaberat yang memiliki tingkat sensitivitas yang tinggi, keakuratannya mencapai 1 nGal [2]. Akibat sensitivitas yang cukup tinggi, SG mampu merekam dinamika aktivitas kebumian dengan baik, seperti dinamika resonansi pada mantel bumi [5], efek hidrologi [7], Pasang surut bumi [1], hingga kejadian seismik baik yang mikroseismik maupun yang macroseismik [4], [6].…”