Study on the thermal anomaly due to active faulting

为了更好地了解地震断层的热产生和传递，我们测量了1995年神户地震(兵库县南部地震)期间激活的日本旭岛断裂的锆石裂变径迹(FT)长度数据。使用Ogura 500m钻孔和日本地质调查局(GSJ)钻孔从深部白垩纪花岗岩中采集样品，并在钻探地点附近的露头采集样品。野岛断裂面的钻探深度为389.4米(沿岩心视深度)，GSJ约为625米。小仓样品在距断层面60m处和露头部位的锆石FT长度的平均值为~10~(-11)μm，呈单峰分布，呈正偏态分布，未显示FT长度明显减小的迹象。相反，来自断层附近的深部地震的平均值明显减少，平均为7-8μm，分布在6-7μm附近出现峰值，偏度较大。GSJ样品也有类似的趋势，但在6-7μm附近的峰较不占优势。结合其他地质约束，这些结果可以用最近断层周围的热异常来最好地解释，这可归因于断层运动的摩擦加热和/或通过地壳深部流体的热传递。

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.