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Twenty thousand aftershocks of a very small (M2) earthquake and their relation to the mainshock rupture and geological structures

Makoto Naoi, Masao Nakatani, Yasuo Yabe, Grzegorz Kwiatek, Toshihiro Igarashi and Katrin Plenkers
Twenty thousand aftershocks of a very small (M2) earthquake and their relation to the mainshock rupture and geological structures
Bulletin of the Seismological Society of America (October 2011) 101 (5): 2399-2407

Abstract

We have determined the locations of more than 20,000 aftershocks (as small as moment magnitude M (sub w) -4.4 or even smaller) following an M 2 event in a South African gold mine, using manually picked arrival times. Spatial clustering into five groups was clearly discerned. A majority of the aftershocks formed a planar cluster ( approximately 4 m in apparent thickness, approximately 100 X 80 m in areal extent). This cluster is thought to delineate the rupture area of the mainshock because its orientation and spatial extent were consistent with the nodal plane of the centroid moment tensor (CMT) solution and with the corner frequency of the mainshock, respectively. The cluster's attitude suggests that the mainshock was a Mohr-Coulomb failure (or formation of a shear rupture surface in intact rock at an angle that obeys the Coulomb failure criterion) that took place in a vertical compression stress field that is indicated by borehole breakout patterns. The aftershock distribution also shows that the mainshock rupture was largely confined to the interior of a 25-m-thick vertical dike, although there are indications of interactions taking place between the rupture and the dike's material boundary with the host rock.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 101
Serial Issue: 5
Title: Twenty thousand aftershocks of a very small (M2) earthquake and their relation to the mainshock rupture and geological structures
Affiliation: University of Tokyo, Earthquake Research Institute, Tokyo, Japan
Pages: 2399-2407
Published: 201110
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 22
Accession Number: 2011-103250
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
S35°00'00" - S22°00'00", E16°00'00" - E33°00'00"
Secondary Affiliation: Tohoku University, USA, United StatesGFZ German Research Centre for Geosciences, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201152
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