THE HAZARD OF THE COUNTERFEIT E-1' SIGNAL IN QUARTZ TO THE ESR DATINGOF FAULT MOVEMENTS

We have previously found (Toyoda and Schwarcz, in press) that gamma-ra y irradiation of granitic quartz produces a distinct ESR signal which overlaps the E-1' centre signal; this signal is a removed by a heat tr eatment at 170 degrees C for 1 min. Here we report the presence of thi s 'counterfeit' signal in irradiated samples from fault gouge taken fr om the Hayward fault California. The contribution of the counterfeit E -1' signal to the total apparent E-1' centre intensity is significant and appears to account for most of the growth of the combined signal w ith irradiation. The intensity real' E-1' centre signal rises abruptly between irradiation doses of 300 and 1000 Gy, after removing the cont ribution of the counterfeit signal by heating. (C) 1997 Elsevier Scien ce Ltd.