<特別寄稿>Friction Level of Faults During Large Earthquakes

Temperature measurements were used to estimate the level of fault friction of large earthquakes. These observations were made in boreholes drilled into fault-zones following large earthquakes in Taiwan, China and Japan. From the temperatures, we are able to estimate the heat generated at the time of the earthquake and thus the level of friction on the fault. The results for all three earthquakes show that the coefficient of friction during the earthquake was 0.1 or less. This is much smaller than values for rock friction measured in the laboratory. The friction determined from rock mechanics experiments represents static friction values, while the temperature measurement values are the dynamic friction during large slip of earthquakes. So static friction of rocks is much higher than the dynamic friction during large earthquake slip.