%A Makoto Naoi
%A Hiroshi Ogasawara
%A Junichi Takeuchi
%A Akihito Yamamoto
%A Naoyuki Shimoda
%A Ken Morishita
%A Hiroshi Ishii
%A Shigeru Nakao
%A Gerrie van Aswegen
%A Aleksander J. Mendecki
%A Patrick Lenegan
%A Rookshana Ebrahim-Trollope
%A Yoshihisa Iio
%J Geophysical Research Letters
%T Small slow-strain steps and their forerunners observed in gold mine in South Africa
%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.
%N 12
%V 33
%D 2006
%R doi:10.1029/2006GL026507
%I Wiley
%L epos1385