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 pre-seismic 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.
Highlights
A superconducting gravimeter (SG) is a spring-type gravimeter that is used for long-term gravity observation
The ES, BA, and MA data were obtained from the National Astronomical Observatory of Japan (NAOJ) and the Ocean Hemisphere Project Data Management Center (OHP DMC)
The pre-seismic gravity anomaly amplitude is not obviously associated with the moment magnitude of the earthquake, the pre-seismic gravity anomaly amplitude is inversely proportional to the straight line distance between the epicenter and an superconducting gravimeters (SG) station
Summary
A superconducting gravimeter (SG) is a spring-type gravimeter that is used for long-term gravity observation. The mechanical spring is replaced by a magnetically levitated superconducting sphere (Goodkind 1999). The voltage signals indicate the sphere’s displacement from its null position, which is proportional to the gravity. SGs are the most sensitive and stable instruments for gravity measurement (Iwano and Fukuda 2004). A 1 nanoGal sensitivity and a 1 Hz sampling rate make SGs very useful for detecting internal gravity waves inside the earth, and for determining the influence of environmental effects on gravity (Ikeda et al 2005). A series of co-seismic gravity perturbations were detected and analyzed using SGs to demonstrate their sensitivity, with results compared with those obtained by seismometers
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