Observation of numerous aftershocks of an Mw 1.9 earthquake with an AE network installed in a deep gold mine in South Africa

JAGUARS

Research output: Contribution to journalLetterpeer-review

21 Citations (Scopus)

Abstract

This is the first report from the JAGUARS (JApanese-German Underground Acoustic Emission Research in South Africa) project, the overall aim of which is to observe ultra-small fracturing in a more or less natural environment. We installed a local (∼40-m span) network of eight acoustic emission (AE) sensors, which have the capability to observe up to 200 kHz at a depth of 3.3 km in a South African gold mine. Our specific objective was to monitor a 30-m thick dyke that remains as a dip pillar against active mining ∼90 m above our network. An Mw 1.9 earthquake whose hypocenter was ∼30 m above the network occurred in the dyke. Although the mineowned geophone (4.5 Hz) network detected only five earthquakes in the surrounding 200×200×150-m3 volume within the first 150 h following the main shock, our AE network detected more than 20,000 earthquakes in the same period. More than 13,000 of these formed a distinct planar cluster (∼100×80 m2) on which the main shock hypocenter lay, suggesting that this cluster delineates the main shock rupture plane. Most of the aftershocks were presumably very small, probably as low as M ∼ −4. The aftershock cluster dipped ∼60◦. This is consistent with normal faulting under a nearly vertical compression field, as indicated by nearly horizontal breakouts found in a borehole crossing the rupture plane.

Original languageEnglish
Pages (from-to)e49-e52
Journalearth, planets and space
Volume61
Issue number10
DOIs
Publication statusPublished - 2009 Oct

Keywords

  • Acoustic emission
  • Aftershocks
  • Deep South African gold mines
  • Main shock rupture plane
  • Mining-induced earthquake
  • Semi-controlled earthquake generation experiment

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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