Frictional Temperature and Alteration of Chelungpu Fault Zone in 1999 Chi-Chi Earthquake
Date Issued
2008
Date
2008
Author(s)
Huang, Lin
Abstract
Understanding energy changes during an earthquake is one of the most challenging problems confronting the earth science community. An earthquake releases accumulated elastic strain energy, which in turn is transformed into radiated energy, fractured energy and frictional heat. Among them frictional heat not only represents the largest share of energy but also the least known due to subsurface and surface weathering. The Chelungpu fault, which moved in the 1999 Chi-Chi earthquake, has provided us a good opportunity to shed light on the aforementioned questions via checking the reaction of clay minerals after frictional heating. In this study, starting material samples from the ChinShui Shale of TCDP, were each heated for 5 minutes in a furnace under different temperature conditions: 600°C, 700°C, 800°C, 900°C, 1000°C, and 1100°C, respectively. They were then analyzed by X-ray Powder Diffraction (XRD) and Scanning Electron Microscopy (SEM) to investigate mineral reactions and phase changes. Results of SEM observation indicated that grains of minerals did not change before 900°C. As soon as the heating temperature reached over 900°C, some melting phenomena began to be detected, with many vesicles were observed over 1000°C. The results of XRD show that the clay minerals began decomposing and melting at temperature over 900°C. revious studies have shown that, in the abnormal content of clay minerals, smectite was relatively richer in fault-zones than in host rocks. Melting has also been observed in fault-zones. Based on the results from Chen (2008), the concentrations of sodium and bicarbonate were higher in borehole water at depth 1,110m in TCDP- A hole and they might come from the Kueichulin Formation. Also, calcite veins were found around the Chelungpu fault zone (Yeh, 2007). We interpreted that the smectite could originate from glass alteration, which the glass was generated by frictional melting in seismic events. We designed a series of experiments to simulate the hydrothermal reactions in order to confirm that the rock in the Chelungpu fault zone was first heated to glass, and then reacted with liquids to precipitate smectite. The results show that smectite could be formed in both of the hydrothermal systems of sodium bicarbonate and sodium chloride. Results of ion concentration analysis of fluid product associated with sodium bicarbonate reaction experiment reveal that the sodium and potassium ions would reduce to precipitate zeolite and the sulfate ion would increase after hydrothermal reactions, which could be caused by the relatively high concentrations of those ions in pore fluid of fault gauge. The result of sodium chloride reaction experiment indicates that sodium, sulfate and chloride ion would increase, and it may be related to precipitating smectite. These results from heating and simulating experiments of TCDP materials may provide us information for estimates of frictional heat and processes in the 1999 Chi-Chi Taiwan earthquake.
Subjects
Chi-Chi earthquake
frictional temperature
smectite
alteration
Type
thesis
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