%0 Journal Article
%@ 0094-8276
%A Naoi, Makoto
%A Ogasawara, Hiroshi
%A Takeuchi, Junichi
%A Yamamoto, Akihito
%A Shimoda, Naoyuki
%A Morishita, Ken
%A Ishii, Hiroshi
%A Nakao, Shigeru
%A van Aswegen, Gerrie
%A Mendecki, Aleksander J.
%A Lenegan, Patrick
%A Ebrahim-Trollope, Rookshana
%A Iio, Yoshihisa
%A Graduate School of Science and Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan,
%A Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan,
%A National Instrument Corporation, Tokyo, 105-0011, Japan,
%A Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan,
%A Graduate School of Science and Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan,
%A Graduate School of Science and Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan,
%A Tono Research Institute of Earthquake Science, Mizunami, 509-6132, Japan,
%A Faculty of Science, Kagoshima University, Kagoshima, 892-0871, Japan,
%A ISS International Ltd., Stellenbosch, 7600, South Africa,
%A ISS International Ltd., Stellenbosch, 7600, South Africa,
%A ISS International Ltd., Stellenbosch, 7600, South Africa,
%A Geohydroseis CC, Klerksdorp, 2571, South Africa,
%A Disaster Prevension Research Institute, Kyoto University, Uji, 611-0011, Japan,
%D 2006
%F epos:1385
%I Wiley
%J Geophysical Research Letters
%N 12
%T Small slow-strain steps and their forerunners observed in gold mine in South Africa
%U https://episodesplatform.eu/eprints/1385/
%V 33
%X The Research Group for Semi-controlled Earthquake-generation Experiments in South African deep gold mines (SeeSA) has continuously monitored strain changes with a resolution of 24 bit 25 Hz at the Bambanani mine near Welkom. An Ishii borehole strainmeter was installed at a depth of 2.4 km near the potential M ∼ 3 earthquake source area. Instantaneous strain steps of ∼10^−4 strains associated with two M2 events were observed within a length of seismic fault. These steps were followed by significant post-seismic creep-like drift, but not preceded by forerunners. Analysis of the continuous 25 Hz data reveals many smaller steps with much longer durations (100 ms ∼ 100 s) than seen in normal earthquakes (−1 < M < 2) with source durations of 1 ms∼50 ms. Some of the especially slow steps were preceded by accelerations in strain, the maximum being as large as one-third of the step.