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Title: Oceanic intraplate earthquakes: Implications for local and regional intraplate stress

Abstract

Focal mechanisms of intraplate earthquakes provide the only means at present by which to characterize the long-wavelength tectonic stress field in oceanic lithosphere. Stress orientations inferred from focal mechanisms may not accurately reflect the state of stress in the epicentral area, however, or the measured stresses may be dominated by local rather than regional sources. To establish a data set with which to study these possibilities, a comprehensive catalog of 159 oceanic intraplate earthquakes has been complied for events since 1963 with m/sub b/ 4.7 or larger. Focal mechanisms are available for approximately one quarter of the events, and several new mechanisms are presented here. For a representative subset of this catalog (83 events), the bathymetry and tectonic history of the epicentral areas have been assembled, and the earthquakes have been rated according to their association with (1) a preexisting fault zone, which might decouple the P axis of the focal mechanism from the true orientation of maximum compressive stress, and (2) large bathymetric relief, which might be a source of large local stresses. Oceanic intraplate earthquakes are commonly found in association with zones of previous weakness (usually fracture zones), but they do not show any particular association with largemore » bathymetric features. In the central Indian Ocean there are enough focal mechanisms available to establish a well-defined NW-SE orientation for P axes and presumably for the direction of greatest compressive stress. The consistency of the P axes of these widely varying mechanisms in the presence of the Ninetyeast Ridge, a site of major intraplate deformation and large bathymetric relief, is remarkable. A possible explanation is that in the presence of a large number of preexisting faults with a range of orientations, slip occurs on those faults which have large resolved shear stresses from the regional stress field.« less

Authors:
;
Publication Date:
Research Org.:
Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
OSTI Identifier:
6925569
Resource Type:
Journal Article
Journal Name:
J. Geophys. Res.; (United States)
Additional Journal Information:
Journal Volume: 85:B10
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; PLATE TECTONICS; EARTHQUAKE FOCI; BATHYMETRY; GEOLOGIC FAULTS; OCEANIC CRUST; STRESSES; EARTH CRUST; GEOLOGIC STRUCTURES; TECTONICS; 580201* - Geophysics- Seismology & Tectonics- (1980-1989)

Citation Formats

Bergman, E A, and Solomon, S C. Oceanic intraplate earthquakes: Implications for local and regional intraplate stress. United States: N. p., 1980. Web. doi:10.1029/JB085iB10p05389.
Bergman, E A, & Solomon, S C. Oceanic intraplate earthquakes: Implications for local and regional intraplate stress. United States. https://doi.org/10.1029/JB085iB10p05389
Bergman, E A, and Solomon, S C. 1980. "Oceanic intraplate earthquakes: Implications for local and regional intraplate stress". United States. https://doi.org/10.1029/JB085iB10p05389.
@article{osti_6925569,
title = {Oceanic intraplate earthquakes: Implications for local and regional intraplate stress},
author = {Bergman, E A and Solomon, S C},
abstractNote = {Focal mechanisms of intraplate earthquakes provide the only means at present by which to characterize the long-wavelength tectonic stress field in oceanic lithosphere. Stress orientations inferred from focal mechanisms may not accurately reflect the state of stress in the epicentral area, however, or the measured stresses may be dominated by local rather than regional sources. To establish a data set with which to study these possibilities, a comprehensive catalog of 159 oceanic intraplate earthquakes has been complied for events since 1963 with m/sub b/ 4.7 or larger. Focal mechanisms are available for approximately one quarter of the events, and several new mechanisms are presented here. For a representative subset of this catalog (83 events), the bathymetry and tectonic history of the epicentral areas have been assembled, and the earthquakes have been rated according to their association with (1) a preexisting fault zone, which might decouple the P axis of the focal mechanism from the true orientation of maximum compressive stress, and (2) large bathymetric relief, which might be a source of large local stresses. Oceanic intraplate earthquakes are commonly found in association with zones of previous weakness (usually fracture zones), but they do not show any particular association with large bathymetric features. In the central Indian Ocean there are enough focal mechanisms available to establish a well-defined NW-SE orientation for P axes and presumably for the direction of greatest compressive stress. The consistency of the P axes of these widely varying mechanisms in the presence of the Ninetyeast Ridge, a site of major intraplate deformation and large bathymetric relief, is remarkable. A possible explanation is that in the presence of a large number of preexisting faults with a range of orientations, slip occurs on those faults which have large resolved shear stresses from the regional stress field.},
doi = {10.1029/JB085iB10p05389},
url = {https://www.osti.gov/biblio/6925569}, journal = {J. Geophys. Res.; (United States)},
number = ,
volume = 85:B10,
place = {United States},
year = {Fri Oct 10 00:00:00 EDT 1980},
month = {Fri Oct 10 00:00:00 EDT 1980}
}