Fault-Drilling Investigation of Earthquake Slip Behavior and Physicochemical Processes

Abstract

Several fault-drilling projects have been conducted with the common aim of seeking direct access to zones of active faulting and understanding the fundamental processes governing earthquakes and fault behavior, as well as the factors that control their natural variability. Here, we review recent scientific drilling projects related to the Nojima Fault which slipped during the 1995 Hyogo-ken Nanbu Earthquake, the Chelungpu Fault which slipped during the 1999 Taiwan Chi-Chi earthquake, the San Andreas Fault Observatory at Depth, and the Nankai Trough Seismo genic Zone Experiment. We also briefly introduce the ongoing drilling research by the Geophysical Observatory at the North Anatolian Fault Zone, the Deep Fault Drilling Project at the Alpine Fault, and the Japan Trench Fast Drilling Project. One of the main findings of fault-drilling research is a better understanding of the physicochemical processes of the primary slip zone during an earthquake, which is closely related to the mechanism of dynamic fault weakening. In the case of the Chelungpu fault, integrated research with borehole experiments, core sample analyses, and numerical simulations were performed, and the results indicate that thermal pressurization occurred during the 1999 earthquake, explain ing the peculiar seismic behavior during the earthquake. These fault-drilling projects relat ed to active faults certainly improve our knowledge and understanding of earthquakes. In addition, we discuss new technical problems related to handling core samples, identifying the latest slip zone, and overprinting by ancient earthquake events.

An Overview: Special Issue on ^|^ldquo;Current Status of On-land Scientific Drilling in Japan and Its Prospects^|^rdquo;

“…Several fault-drilling projects have been also conducted with the common aim of seeking direct access to zones of active faulting and understanding the fundamental processes governing earthquakes and fault behavior. Hirono et al (2013) review recent scientific drilling projects related to the Nojima Fault, which slipped during the 1995 Hyogo-ken Nanbu Earthquake, the Chelungpu Fault, which slipped during the 1999 Taiwan, Chi-Chi earthquake, the San Andreas Fault Observatory at Depth, and also briefly introduce ongoing drilling research. One of the main outcomes of fault-drilling research is a better understanding of the physicochemical processes of a primary slip zone during an earthquake, which is closely related to the mechanism of dynamic fault weakening.…”