Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes
Rock stress measurements in Iceland show maximum horizontal compression perpendicular to the trend of Reykjanes Ridge crest and of its extension, the active volcanic zone of Iceland. Fault-plane solutions of dormant stage earthquakes are consistent with the measured stress orientations, but strike—s...
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1981
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fthighwire:oai:open-archive.highwire.org:gji:65/3/627 2023-05-15T16:48:22+02:00 Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes Keith, M. L. 1981-06-01 00:00:00.0 text/html http://gji.oxfordjournals.org/cgi/content/short/65/3/627 https://doi.org/10.1111/j.1365-246X.1981.tb04876.x en eng Oxford University Press http://gji.oxfordjournals.org/cgi/content/short/65/3/627 http://dx.doi.org/10.1111/j.1365-246X.1981.tb04876.x Copyright (C) 1981, Oxford University Press Articles TEXT 1981 fthighwire https://doi.org/10.1111/j.1365-246X.1981.tb04876.x 2012-11-23T22:14:40Z Rock stress measurements in Iceland show maximum horizontal compression perpendicular to the trend of Reykjanes Ridge crest and of its extension, the active volcanic zone of Iceland. Fault-plane solutions of dormant stage earthquakes are consistent with the measured stress orientations, but strike—slip earthquakes associated with volcanic surges and some earthquake swarms in active geothermal areas exhibit apparent reversals of mechanism and are here defined as ‘stress-discordant’ in the sense that they yield deduced stress orientations 90° from the regional stress field as determined by hydrofracturing and strain relief methods. It is proposed, supported by comparison with the pore-pressure induced Denver earthquakes, that the ‘stress-discordant’ volcanic earthquakes are triggered by increased pore pressure and probably involve stick-slip motion similar to that reported for some laboratory tests of the pore pressure effect, characterized by gradual onset and sudden stopping of each slip episode. The question is raised as to whether stress-discordant earthquakes are dominated by a stopping phase or terminal shock with consequent reversal of the deduced shear couple. A possible stopping mechanism is suggested: the dilatant stiffening of fault gouge during shear. It is proposed that direct measurements of stress orientation be made by hydrofracturing tests at other places along the mid-ocean ridge crest and on the margins of the Red Sea and East African rifts. The Icelandic stress data indicate the need for sceptical re-examination of some fundamentals of plate tectonics theory. Text Iceland HighWire Press (Stanford University) Reykjanes ENVELOPE(-22.250,-22.250,65.467,65.467) Geophysical Journal International 65 3 627 644 |
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HighWire Press (Stanford University) |
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English |
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Articles |
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Articles Keith, M. L. Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
topic_facet |
Articles |
description |
Rock stress measurements in Iceland show maximum horizontal compression perpendicular to the trend of Reykjanes Ridge crest and of its extension, the active volcanic zone of Iceland. Fault-plane solutions of dormant stage earthquakes are consistent with the measured stress orientations, but strike—slip earthquakes associated with volcanic surges and some earthquake swarms in active geothermal areas exhibit apparent reversals of mechanism and are here defined as ‘stress-discordant’ in the sense that they yield deduced stress orientations 90° from the regional stress field as determined by hydrofracturing and strain relief methods. It is proposed, supported by comparison with the pore-pressure induced Denver earthquakes, that the ‘stress-discordant’ volcanic earthquakes are triggered by increased pore pressure and probably involve stick-slip motion similar to that reported for some laboratory tests of the pore pressure effect, characterized by gradual onset and sudden stopping of each slip episode. The question is raised as to whether stress-discordant earthquakes are dominated by a stopping phase or terminal shock with consequent reversal of the deduced shear couple. A possible stopping mechanism is suggested: the dilatant stiffening of fault gouge during shear. It is proposed that direct measurements of stress orientation be made by hydrofracturing tests at other places along the mid-ocean ridge crest and on the margins of the Red Sea and East African rifts. The Icelandic stress data indicate the need for sceptical re-examination of some fundamentals of plate tectonics theory. |
format |
Text |
author |
Keith, M. L. |
author_facet |
Keith, M. L. |
author_sort |
Keith, M. L. |
title |
Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
title_short |
Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
title_full |
Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
title_fullStr |
Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
title_full_unstemmed |
Regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
title_sort |
regional mid-ocean stress and a proposed focal mechanism of 'stress-discordant' earthquakes |
publisher |
Oxford University Press |
publishDate |
1981 |
url |
http://gji.oxfordjournals.org/cgi/content/short/65/3/627 https://doi.org/10.1111/j.1365-246X.1981.tb04876.x |
long_lat |
ENVELOPE(-22.250,-22.250,65.467,65.467) |
geographic |
Reykjanes |
geographic_facet |
Reykjanes |
genre |
Iceland |
genre_facet |
Iceland |
op_relation |
http://gji.oxfordjournals.org/cgi/content/short/65/3/627 http://dx.doi.org/10.1111/j.1365-246X.1981.tb04876.x |
op_rights |
Copyright (C) 1981, Oxford University Press |
op_doi |
https://doi.org/10.1111/j.1365-246X.1981.tb04876.x |
container_title |
Geophysical Journal International |
container_volume |
65 |
container_issue |
3 |
container_start_page |
627 |
op_container_end_page |
644 |
_version_ |
1766038472411316224 |