Results from parallel observations of superconducting and absolute gravimeters and GPS at the Hsinchu station of Global Geodynamics Project, Taiwan

In this paper, the calibration factor of the superconducting gravimeter 057 (SG057) at the Lhasa station is accurately determined for the first time with a frequency-domain approach and the data recorded by the LaCoste Romberg Earth Tides No. 20 (LCR-ET20) gravimeter which is installed nearby SG057. The advantage of the frequency-domain approach is that it eliminates the influence of different gravimeter drifts on the determination of the calibration factor. The determined calibration factor of SG057 is (-77.7358 ± 0.0409) × 10 -8 m s -2 V -1 , and the relative accuracy is about 0.5‰. The newly determined calibration factor has been calculated with the Wuhan international tidal gravity reference values (ITGRVs) based on the data recorded by LCR-ET20 at the Wuhan station before it was installed at the Lhasa station. A high-precision synthesized gravity tide is achieved at the Lhasa station with accurate tidal parameters and theoretical tidal parameters for the long tidal waves from the Dehant-Defraigne-Wahr (DDW) earth tide model. The synthesized gravity tide can be used for tidal gravity corrections of future gravity measurements in the Tibetan area. The linear gravimeter drift of SG057 is estimated by gravity records without the effects of land uplift, atmosphere and polar motion yielding a rate of 6.8 × 10 -8 m s -2 yr -1 .

Section: The Gravimeter Drift Of Sg057mentioning

confidence: 99%

Determination of the Calibration Factor of Superconducting Gravimeter 057 at the Lhasa Station: A frequency-Domain Approach

Chen¹,

Sun²,

Xu³

et al. 2013

“…HCHG, co-located with Hsinchu SG (#T48; , is located in the Toukoshan Formation between alluvium and lateritic terrace deposits. HCHG is also near the Hsinchu Fault, which has been re-classified as an active fault of the second category (Chang et al 1998;Lin et al 2000;Hwang et al 2009 2010). Earlier gravity measurements at TAES and PKGG were used for inferring land subsidence in the two counties and the result indicated that gravity changes here could originate from a number of sources.…”

Section: The Geological Settings Around the Absolute Gravity Sitesmentioning

confidence: 99%

“…For all the AGTO sites, we measured gravity values every November, with the exceptions that the gravity measurements at AG3, AG4, and AG5 were collected in March 2008. Collecting gravity data in the same month of the year could potentially remove common-mode temporal gravity effects, particularly the hydrology gravity effect, which is largely seasonal effect in Taiwan (Van Dam and Wahr 1998;Boy and Hinder 2006;Hwang et al 2009). …”

Section: Gravity Uncertainties and Temporal Gravity Effectsmentioning

confidence: 99%

Absolute gravity change in Taiwan: Present result of geodynamic process investigation

Kao¹,

Hwang²,

Kim³

et al. 2017

Self Cite

Gravity values at 24 sites over 2004 -2016 measured with absolute gravimeters are used to study geodynamic processes in Taiwan. We model rain-induced gravity effects and other temporal effects of non-geodynamic origins to obtain residual gravity, which cannot be fully explained by GPS-derived vertical displacements. We explain the gravity changes associated with deposited debris, earthquake, volcanism and Moho deepening. Gravity changes of 53.37 and 23.38 μGal near Sinwulyu and Laonong Rivers are caused by typhoon Morakot, leading to estimated volumes of 6.0 × 10 5 and 3.6 × 10 5 m 3 in deposited debris. The observed co-seismic gravity change near the epicenter of the M 6.9 Pingtung earthquake (26 December 2006) is 3.12 ± 0.99 μGal, consistent with a dislocation-based gravity change at the μGal level, thereby supplying a gravity constraint on the modeled fault parameters. The AG record at the Tatun Volcano Group is the longest, but large temporal gravity effects here has led to a current gravity signal-to-noise ratio of less than one, which cannot convince a sinking magma chamber, but supply an error bound for gravity detections of long-term or transient magma movements. The gravity values at Ludao and Lanyu decline steadily at the rates of -2.20 and -0.50 μGal yr -1 , consistent with the expected magma states of the two extinct volcanoes. The gravity rates at an uplifting site in central Taiwan and three subsiding sites in eastern Taiwan are negative, and are potentially caused by Moho deepening at a rate of -3.34 cm yr -1 and a combined Moho deepening and plate subduction at the rates of -0.18, -2.03, and -1.34 cm yr -1 . Article history:Received 10

“…SG records obtained at a 1 Hz sampling rate were used in this study. The gravity residual values were obtained by removing the effects of body and ocean tides from the raw records, as suggested by Hwang et al (2009). These effects were removed using Tsoft (Van Camp et al 2005) and ETERNA (Wenzel 1996) software packages.…”

Section: Sg Stations and Datamentioning

confidence: 99%

“…A 1 nanoGal sensitivity and a 1 Hz sampling rate make SGs very useful for detecting internal gravity waves inside the earth, and thus 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 (Imanishi et al 2004;Hwang et al 2009;Kim et al 2009;Nawa et al 2009). The gravity signal of an SG is influenced by many natural events, including free oscillations of the Earth after a strong earthquake (Virtanen 1996;Park et al 2005;Arora et al 2008), seismic background noise (Virtanen 1998), the gravity effects of hydrological phenomena (Virtanen 2000(Virtanen , 2001, and variation in atmospheric mass (Virtanen and Mäkinen 2003;Virtanen 2004).…”

Section: Introductionmentioning

confidence: 99%

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

Lan¹,

Yu²,

Hwang³

et al. 2011

Self Cite

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.