Study on the thermal anomaly due to active faulting

为了更好地理解地震断层的生热和沿着传递，我们测量了1995年日本淡路岛野岛断层在科比地震（兵库县南部地震）中的锆石裂变径迹（FT）长度数据。使用Ogura 500 m钻孔和日本地质调查局（GSJ）钻孔从白垩纪花岗岩中采集样品，以及在钻孔点附近的露头处采集样品。Ogura的Nojima断层面钻深为389.4 m（沿岩心视深度），GSJ的Nojima断层面钻深约为625 m。对于Ogura样品，距断层面>60 m处的锆石FT长度平均值为10-11 μm，呈单峰正偏态分布，没有显示FT长度明显减小的迹象。相反，断层附近深度的地震波平均值显著降低，在6-7 μ m附近有一个峰值，偏度相当负。GSJ样品也观察到类似的趋势，但6-7 μm附近的峰不占主导地位。结合其他地质制约因素，这些结果是最好的解释，最近的热异常断层，这是由于摩擦加热断层运动和/或热传递通过流体从地壳深部内部。

To better understand the heat generation and transfer along earthquake fault, we measured zircon fission-track (FT) length data from Nojima fault, Awaji-shima Island, Japan, which was activated during the 1995 Kobe earthquake (Hyogo-ken Nanbu earthquake). Samples were collected from Cretaceous granitic rocks at depths using the Ogura 500 m borehole and Geological Survey of Japan (GSJ) borehole, as well as at outcrops nearby the boring sites. The Nojima fault plane was drilled at 389.4 m depth (along-core apparent depth) for Ogura and at about 625 m for GSJ. For Ogura samples, FT lengths in zircons from localities>60 m away from the fault plane as well as those from outcrops are characterized by the mean values of 〜10-11 μm and unimodal distributions with positive skewness, showing no signs of appreciable reduction of FT length. In contrast, those from nearby the fault at depths show significantly reduced mean of 〜7-8 μm and distributions having a peak around 6-7 μm with rather negative skewness. A similar trend was observed for GSJ samples, in which the peak around 6-7 μm is less dominant however. In conjunction with other geological constraints, these results are best interpreted by the recent thermal anomaly around the fault, which is attributable to the frictional heating of fault motion and/or heat transfer via fluids from the deep interior of the crust.