Insights into Earthquake Propagation Processes from the Chelungpu Fault Drilling, Project, Taiwan

Utah State University, Logan UT

Investigators

Abstract

0098108 Evans In September 1999 a large earthquake occurred on the Chelungpu fault in Taiwan. The fault forms the boundary between the highlands of central Taiwan and the coastal plain along the western side of the island. The earthquake resulted in 2400 fatalities, ~$11 billion in damage, and the development of spectacular fault scarps along an 85Km long surface rupture. The Chelengpu rupture illustrates one of the outstanding questions in earthquake rupture dynamics and the related issues of earthquake hazard analysis - how does seismic energy radiate to the ground surface, and what are the near surface conditions that lead to the distribution of slip and ground motion associated with large earthquakes? The Japanese geophysical community, with funding from the Japanese Ministry of Science and Technology (JAMSTEC), plans to address this and related questions by drilling two 300-m holes through the tip of the fault at two sites. These cored holes will examine the character of the fault zone and attempt to address questions regarding the nature of slip propagation in the near surface region. These cored holes provide a unique opportunity to extend our understanding of fault zone structure beyond that typically examined in paleoseismological investigations into a region where very little is known about the structure and composition of the fault zone and its relationship to the radiation or dispersal of seismic energy. This Small Grant for Exploratory Research (SGER) award will allow the Principal Investigator to take advantage of this rare opportunity to investigate the near surface tip zone of a large, recently rupture fault by providing funds for the full suite of borehole geophysical logs and to provide two on-site structural geologists to collaborate on the initial core logging and borehole geophysical logging of the two holes. They will analyze the borehole data, and integrate detailed surface rupture trace maps, bedrock exposure mapping, and shallow seismic reflection data in collaboration with Japanese and Taiwanese geologists, to provide a detailed description of the fault zone, including fault composition and structure, fluid characteristics, location and nature of the high-slip zones. Samples will be collected for further testing and analysis. Drilling will begin in November 2000 and last for approximately two months, thus the time urgency of this SGER request. This work, through international collaboration and integrated methodologies, will provide a detailed view of the processes and structure of a major seismogenic fault in the upper km of the earth, and yield significant new insights into the processes by which seismic energy reaches the earth's surface during large earthquakes. ***