• DOI:10.1126/science.1222119
• Corpus ID: 33508855

Isotropic Events Observed with a Borehole Array in the Chelungpu Fault Zone, Taiwan

@article{Ma2012IsotropicEO,
  title={Isotropic Events Observed with a Borehole Array in the Chelungpu Fault Zone, Taiwan},
  author={Kuo-Fong Ma and Yen-Yu Lin and Shiann-Jong Lee and James J. Mori and Emily E. Brodsky},
  journal={Science},
  year={2012},
  volume={337},
  pages={459 - 463}
}

• K. Ma, Yen-Yu Lin, +2 authors E. Brodsky
• Published 27 July 2012
• Geology
• Science

Cracking Up Hydraulic fracturing by fluids at high pressure results in damage or breakage along cracks in deep rocks, a process that in some cases causes earthquakes. This process can occur naturally when the hydrologic setting is just right, or can be induced by human activity when fluids are pumped at high pressure into deep aquifers. By studying the fault along which the 1999 magnitude 7.6 Chi-Chi earthquake occurred in Taiwan, where there are currently low tectonic stresses following the large earthquake, Ma et al. (p. 459) observed an unusual type of earthquake-like event that they attribute to natural hydraulic fracturing. High-pressure fluids induce fracturing along preexisting cracks near the site of a recent earthquake. Shear failure is the dominant mode of earthquake-causing rock failure along faults. High fluid pressure can also potentially induce rock failure by opening cavities and cracks, but an active example of this process has not been directly observed in a fault zone. Using borehole array data collected along the low-stress Chelungpu fault zone, Taiwan, we observed several small seismic events (I-type events) in a fluid-rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7.6 Chi-Chi earthquake. Modeling of the events suggests an isotropic, nonshear source mechanism likely associated with natural hydraulic fractures. These seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing.