Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data1. The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation, rupture processes and seismic efficiency. The 1999 magnitude-7.7 earthquake in Chi-Chi, Taiwan, produced large slip (8 to 10 metres) at or near the surface2, which is accessible to borehole drilling and provides a rare opportunity to sample a fault that had large slip in a recent earthquake. Here we present the retrieved cores from the Taiwan Chelungpu-fault Drilling Project and identify the main slip zone associated with the Chi-Chi earthquake. The surface fracture energy estimated from grain sizes in the gouge zone of the fault sample was directly compared to the seismic fracture energy determined from near-field seismic data3,4. From the comparison, the contribution of gouge surface energy to the earthquake breakdown work is quantified to be 6 per cent.
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We thank the working group of TCDP, including the drilling company FangYu and WonDa, the on-site assistants and more than 60 participating students from NCU and NTU, S. T. Huang at CPC for core storage and splitting, Y.-M. Chen of the NSRRC for taking TEM and TXM images, and K. S. Liang of the NSRRC. We also thank M. Zoback, S. Hickman, W. Ellsworth and H. Ito for discussion before and during drilling. We also thank H. Kanamori and E. Brodsky for discussions and a review of an early version of this paper. This project was supported by the NSC, Taiwan, and partially supported by the ICDP. Author Contributions K.-F.M., paper writing and project planning. H.T., core observation, data analysis and project planning. S.-R.S., petrographic and XRD analysis and project planning. C.-Y.W., J.-H.H., Y.-B.T., W.S., project planning. J.M., paper preparation. Y.-F.S., TEM and TXM taken at NSRRC and data analysis. E.-C.Y. and H.S., on-site geologists during coring. L.-W.K. and H.-Y.W., on-site assistants.
About this article
Lithological and structural characterization of the Longmen Shan fault belt from the 3rd hole of the Wenchuan Earthquake Fault Scientific Drilling project (WFSD-3)
International Journal of Earth Sciences (2016)