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

Abstract

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

Short‐Time Geodetic Determination of Aquifer Storage Coefficient in Taiwan

“…Figure also shows typical uncertainties of absolute and relative gravimeter measurements. The uncertainties of 2 and 6 μgal in Figure are expanded uncertainties (at the 95% confidence level) for absolute and relative measurements (section ; Crossley et al, ; Kao et al, ). If we use 2 μgal as the lowest acceptable gravity change for S y determination, Figure suggests that pumping‐induced gravity changes can be detected by an AG only at Neicheng and Jushan (see Table for the actual horizontal distances between the gravimeter and pumping wells).…”

“…At the four test sites, the numbers of sets collected range from 52 to 266 in durations of 4–6 days (Table ). According to our laboratory tests at Hsinchu (Kao et al, ), a typical accuracy of a set gravity value from FG5 #231 can be 1 μgal. In principle, if the temperature variation, ground vibration, and dust are kept as small as possible in a gravity field work, this 1‐μgal accuracy can be achieved.…”

“…The Ministry of the Interior, Taiwan, supports a gravity laboratory that is equipped with two superconducting gravimeters and two AGs (Hwang et al, ). Since 2004, gravity changes in Taiwan have been continuously collected and were used to study land subsidence (Hwang et al, ), mountain building (Mouyen et al, ), volcanism (Mouyen et al, ), and other geodynamic processes (Kao et al, ). In addition, Lien et al () used gravity changes from the T48 superconducting gravimeter and groundwater changes at Hsinchu to assess a potentially active fault near the Hsinchu Science Park of Taiwan, which houses one of the world's three major semiconductor manufacturers (Waldrop, ).…”

Quantifying sediment mass redistribution from joint time-lapse gravimetry and photogrammetry surveys

“…The first reason for choosing this location is that time-lapse absolute gravity surveys have been done at AG06 since 2006, in the frame of the Absolute Gravity in the Taiwan Orogen (AGTO) project. This project permitted to identify, for the first time, sediment redistribution using time-lapse absolute gravimetry and shown that significant sediment transfers occurred around Paolai (Kao et al, 2017;Mouyen et al, 2013). Indeed, this site experiences vigorous sediment transfer processes powered by heavy rains brought by tropical cyclones (typhoons) and monsoonal events, especially in May to August (Chen and Chen, 2003).…”

HUST-GOGRA2018s: A new gravity field model derived from the combination of GRACE and GOCE data

“…It is significant for different disciplines, such as geophysics, geodesy and seismology, to construct global static gravity field models with high precision and spatial resolution, which are vital strategic data to understand structure of the Earth interior and solve the problems of resource and disaster (Kao et al 2017;Tanaka et al 2019). With the implementation of the Gravity Recovery and Climate Experiment (GRACE) on 17 March 2002 (Tapley et al 2004) and the Gravity field and steady-state Ocean Circulation Explorer (GOCE) on 17 March 2009 (Floberghagen et al 2011), various GRACE-only gravity field models including AIUB-GRACE03S (Jäggi et al 2012), GGM05S (Tapley et al 2013), ITG-Grace2010s (Mayer-Gürr et al 2010, ITSG-Grace2014s (Mayer-Gürr et al 2014, ITU-GRACE16 (Guo et al 2015), and Tongji-GRACE01S (Chen et al 2015), and independent GOCE models including GO_CONS_GCF_2_ DIR_R1, GO_CONS_GCF_2_TIM_R1 and GO_CONS_ GCF_2 _SPW_R1 (Pail et al 2011), have been developed in recent years.…”