Browsing by Author "Kao, R."

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Co-seismic Gravity Change of M-w 7.9 Wenchuan Earthquake and Pre-Seismic Gravity Anomaly Detection by Superconducting Gravimeter at Hsinchu, Taiwan, from April to June 2008
(2012)
Lan, S. C.
;
Yu, T. T.
;
Hwang, C.
;
Kao, R.
;
土木工程學系
Earthquakes are caused by crustal movement that releases a huge amount of energy and leads to deformation. The gravity near the epicenter is changed by the deformation of rock materials. Precursors may be detected during the period of seismogenic activity. On 12 May, 2008, a M-w 7.9 earthquake struck near Wenchuan in China. A co-seismic gravity offset of 10: 5 mu Gal and a pre-seismic gravity anomaly about 2 days before the main shock was found in gravity records of the superconducting gravimeter (SG) at Hsinchu, Taiwan. SG records from April to June 2008 were used in this study. During this period of time, 8 gravity anomaly events caused by earthquakes were found. Sonograms of time-frequency analysis show that the perturbations occurred in 1-2 major bands (0.1-0.15 Hz and 0.2-0.3 Hz). The results of canonical correlation analysis show a significant positive correlation between the duration of gravity perturbation before the main shock and the magnitude of the earthquake. This study suggest that SG is a promising instrument for the analysis of earthquake events.
Erosion effects assessed by repeated gravity measurements in southern Taiwan
(2013-01-01)
Mouyen, M.
;
Masson, F.
;
Hwang, C.
;
Cheng, C. -C.
;
Le Moigne, N.
We analyse temporal variations of gravity measured in southern Taiwan since November 2006 at 10 sites using absolute gravimeters and, since November 2008, at 70 sites using a relative gravimeter. We describe and apply methods to interpret the gravity changes in terms of local hydrological processes and vertical ground motions. The effect of land water is computed from local rainfall data and a model of rain accumulation and discharge in the ground. The effect of the vertical motions of the ground is estimated using time-series of permanent Global Positioning System (GPS) stations and the theoretical gravity to height ratio of -2 mu Gal cm(-1). Unexpectedly, Morakot typhoon (2009 August), the strongest typhoon in Taiwan in 50 yr, was responsible for the highest gravity changes. Morakot triggered numerous large landslides and debris flow deposits. Their thicknesses are estimated from the gravity changes (up to similar to 280 mu Gal) along with field observations and satellite images.