Fault mirrors in seismically active fault zones: A fossil of small earthquakes at shallow depths

Li Wei Kuo*, Sheng Rong Song, John Suppe, En Chao Yeh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


Fault mirrors (FMs) are naturally polished and glossy fault slip surfaces that can record seismic deformation at shallow depths. They are important for investigating the processes controlling dynamic fault slip. We characterize FMs in borehole samples from the hanging wall damage zone of the active Hsiaotungshi reverse fault, Taiwan. Here we report the first documented occurrence of the combination of silica gel and melt patches coating FMs, with the silica gel resembling those observed on experimentally formed FMs that were cataclastically generated. In addition, the melt patches, which are unambiguous indicators of coseismic slip, suggest that the natural FMs were produced at seismic rates, presumably resulting from flash heating at asperities on the slip surfaces. Since flash heating is efficient at small slip, we propose that these natural FMs represent fossils of small earthquakes, formed in either coseismic faulting and folding or aftershock deformation in the active Taiwan fold-and-thrust belt.

Original languageEnglish
Pages (from-to)1950-1959
Number of pages10
JournalGeophysical Research Letters
Issue number5
Publication statusPublished - 2016 Mar 16


  • fault mirror
  • flash heating
  • fossil earthquakes
  • melt
  • silica gel

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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