**7. Conclusion**

I described ESR techniques for detecting seismic frictional heat. We can detect the frictional heat using some FMR signals derived from ferrimagnetic minerals such as maghemite or magnetite produced by heating. To actually estimate the frictional heat from fault rocks, we must carry out high-resolution measurements of FMR signals necessary for determining the width of heat generation. I believe that the scanning ESR microscopic technique makes it possible. Since faults commonly move repeatedly, the frictional heat is also generated repeatedly. Therefore, we need to separate multiplex frictional heating events to accurately estimate the frictional heat energy. Moreover, we need to determine the formation depth of fault rocks used for ESR analyses because the frictional heat commonly increases with increasing the depth of the fault. The frictional heat energy per unit volume is more meaningful than that per unit area. For these purposes, it is important to select fault rock samples with a lot of information revealed by many previous studies, for example the Nojima fault rocks.

### **8. Acknowledgments**

I would like to thank Dr. Wonn Soh and Prof. Sheng-Rong Song for their permission to publish the ESR data on the TCDP Hole B cores in this chapter. This work was funded by Grant-in-Aid for Scientific Research (B) of the Ministry of Education, Science, Sports and Culture, Japan (No.20340139).

#### **9. References**

338 Earthquake Research and Analysis – Seismology, Seismotectonic and Earthquake Geology

the scanning ESR microscope is much lower than the ordinary ESR spectrometer. Since the resolution of the scanning ESR microscope depends on the detection sensitivity, at this stage

the limit of resolution is about 0.25 mm.

Fig. 23. A 1-D profile obtained from the Nojima pseudotachylyte.

I described ESR techniques for detecting seismic frictional heat. We can detect the frictional heat using some FMR signals derived from ferrimagnetic minerals such as maghemite or magnetite produced by heating. To actually estimate the frictional heat from fault rocks, we must carry out high-resolution measurements of FMR signals necessary for determining the width of heat generation. I believe that the scanning ESR microscopic technique makes it possible. Since faults commonly move repeatedly, the frictional heat is also generated repeatedly. Therefore, we need to separate multiplex frictional heating events to accurately estimate the frictional heat energy. Moreover, we need to determine the formation depth of fault rocks used for ESR analyses because the frictional heat commonly increases with increasing the depth of the fault. The frictional heat energy per unit volume is more meaningful than that per unit area. For these purposes, it is important to select fault rock samples with a lot of information revealed by many previous studies, for example the

**7. Conclusion** 

Nojima fault rocks.

